CN108155797B

CN108155797B - Electric vehicle, DC-DC converter thereof and control method of DC-DC converter

Info

Publication number: CN108155797B
Application number: CN201611102277.0A
Authority: CN
Inventors: 张妮; 王兴辉; 王超; 沈晓峰; 邬白贺
Original assignee: BYD Co Ltd
Current assignee: BYD Co Ltd
Priority date: 2016-12-02
Filing date: 2016-12-02
Publication date: 2020-03-31
Anticipated expiration: 2036-12-02
Also published as: CN108155797A

Abstract

The invention discloses an electric automobile, a DC-DC converter thereof and a control method of the DC-DC converter, wherein the DC-DC converter comprises an H bridge, the H bridge comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, and the control method comprises the following steps: in the whole life cycle of the DC-DC converter, a control mode of phase shift modulation and a control mode of lower tube modulation are alternately carried out, the H bridge is alternately controlled in a first mode or a second mode based on setting time Tx and Ty when the control mode of phase shift modulation is adopted, the H bridge is controlled in a third mode or a fourth mode based on total time TC and TD when the control mode of lower tube modulation is adopted, the H bridge is alternately controlled in the third mode or the fourth mode based on setting time Ti and Tm, and temperature balance control is carried out on the first to fourth switching tubes, so that the heating of the first to fourth switching tubes in the H bridge is relatively balanced, and the service life of the switching tubes in the H bridge is prolonged.

Description

Electric vehicle, DC-DC converter thereof and control method of DC-DC converter

Technical Field

The invention relates to the technical field of electric automobiles, in particular to a control method of a DC-DC converter, the DC-DC converter and an electric automobile.

Background

The DC-DC converter has been an important component in the field of power electronics, and along with the development of electric vehicle commercialization, the DC-DC converter has also become one of important parts of electric vehicles. The topology of the DC-DC converter is many, and in the medium and large power field, the full-bridge PWM converter is the most used topology.

The full-bridge PWM converter has many control modes, and the related art mostly adopts a phase-shift modulation control mode and a low-tube modulation control mode. However, when the phase shift modulation control mode is adopted, the leading arm is easy to realize soft switching, and the lagging arm is not easy to realize soft switching, so that the lagging arm is more serious in heat generation than the leading arm; when the control mode of the lower tube modulation is adopted, the upper tube is easy to realize soft switching, and the lower tube is not easy to realize soft switching, so that the lower tube generates heat more seriously than the upper tube.

Therefore, the above two control modes can cause the serious problem of heating of the switch tube, and the service life of the switch tube is influenced.

Disclosure of Invention

The present invention is directed to solving, at least to some extent, one of the technical problems in the art described above. Therefore, a first object of the present invention is to provide a method for controlling a DC-DC converter, which can relatively balance the heat generation of the first to fourth switching tubes in the H-bridge and improve the operating life of the switching tubes in the H-bridge.

A second object of the present invention is to provide a DC-DC converter. The third purpose of the invention is to provide an electric automobile.

In order to achieve the above object, an embodiment of an aspect of the present invention provides a control method of a DC-DC converter, where the DC-DC converter includes an H-bridge, and the H-bridge includes a first switching tube, a second switching tube, a third switching tube, and a fourth switching tube, where the first switching tube and the second switching tube form a first bridge arm, and the third switching tube and the fourth switching tube form a second bridge arm, and the control method includes the following steps: when the DC-DC converter works, acquiring a control mode of the DC-DC converter during last working, and selecting the control mode during the current working according to the control mode of the DC-DC converter during the last working, wherein the control mode of the DC-DC converter comprises a phase-shift modulation control mode and a lower tube modulation control mode; when the control mode during the work is selected to be the phase shift modulation control mode, acquiring setting time Tx for controlling the H bridge in a first mode and setting time Ty for controlling the H bridge in a second mode, and alternately controlling the H bridge according to the setting time Tx and the setting time Ty to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, wherein when the H bridge is controlled in the first mode, the first bridge arm is used as an advance bridge arm, and the second bridge arm is used as a delay bridge arm; when the H bridge is controlled in the second mode, the second bridge arm is used as an advanced bridge arm, and the first bridge arm is used as a delayed bridge arm; when the control mode in the current work is selected to be the control mode of the lower tube modulation, acquiring total time TC for controlling the H bridge in a third mode and total time TD for controlling the H bridge in a fourth mode, acquiring setting time Ti for controlling the H bridge in the third mode and setting time Tm for controlling the H bridge in the fourth mode in each work cycle in the work process of the DC-DC converter in the control mode of the lower tube modulation, selecting the mode of controlling the H bridge when the DC-DC converter is started by judging the relation between the total time TC and the total time TD, and alternately controlling the H bridge according to the setting time Ti and the setting time Tm to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, when the H bridge is controlled in the third mode, the first switching tube and the third switching tube are used as upper tubes, the second switching tube and the fourth switching tube are used as lower tubes, and the first switching tube to the fourth switching tube are controlled in a lower tube modulation control mode; and when the H bridge is controlled in the fourth mode, the first switching tube and the third switching tube are used as a lower tube, the second switching tube and the fourth switching tube are used as an upper tube, and the first switching tube to the fourth switching tube are controlled in a control mode of lower tube modulation.

According to the control method of the DC-DC converter, when the DC-DC converter works, the control mode of the DC-DC converter in the last working process is obtained, and the control mode in the current working process is selected according to the control mode of the DC-DC converter in the last working process, so that the control mode of phase shift modulation and the control mode of lower tube modulation in the whole life cycle of the DC-DC converter are alternately carried out. When the control mode in the current work is selected to be a phase shift modulation control mode, acquiring the setting time Tx for controlling the H bridge in a first mode and the setting time Ty for controlling the H bridge in a second mode, and then alternately controlling the H bridge according to the Tx and the Ty to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube; when the control mode during the current work is selected to be a down tube modulation control mode, the total time TC for controlling the H bridge in a third mode and the total time TD for controlling the H bridge in a fourth mode are obtained, the setting time Ti for controlling the H bridge in the third mode and the setting time Tm for controlling the H bridge in the fourth mode in each work cycle of the DC-DC converter in the work process of adopting the down tube modulation control mode are obtained, then the relation between the total time TC and the total time TD is judged, finally the mode for controlling the H bridge when the DC-DC converter is started is selected according to the relation between the total time TC and the total time TD, the H bridge is alternately controlled according to the Ti and the Tm in the work process of the DC-DC converter, so as to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, thereby in the whole life cycle, when the DC-DC converter works in a phase-shift modulation control mode, the H bridge is controlled alternately in a first mode and a second mode, when the DC-DC converter adopts a lower tube modulation control mode, the third mode or the fourth mode is selected to control the H bridge according to the recorded total time TC and the total time TD, and then the third mode and the fourth mode are adopted to control the H bridge alternately, so that the heat generation of each switching tube is relatively balanced, the service life of the switching tubes in the H bridge is prolonged under the condition of not increasing the cost, and the life cycle of the DC-DC converter can be prolonged.

In order to achieve the above object, according to another embodiment of the present invention, a DC-DC converter includes: the bridge comprises an H bridge and a bridge body, wherein the H bridge comprises a first switching tube, a second switching tube, a third switching tube and a fourth switching tube, the first switching tube and the second switching tube form a first bridge arm, and the third switching tube and the fourth switching tube form a second bridge arm; a control module, configured to obtain a control manner of a last operation of the DC-DC converter when the DC-DC converter operates, and select a control manner of the last operation of the DC-DC converter according to the control manner of the last operation of the DC-DC converter, where the control manner of the DC-DC converter includes a control manner of phase shift modulation and a control manner of down tube modulation, and when the control manner of the last operation is selected as the control manner of phase shift modulation, the control module obtains a setting time Tx for controlling the H-bridge in a first manner and a setting time Ty for controlling the H-bridge in a second manner, and alternately controls the H-bridge according to the setting time Tx and the setting time Ty to perform temperature equalization control on the first switching tube, the second switching tube, the third switching tube, and the fourth switching tube, when the H bridge is controlled in the first mode, the first bridge arm is used as a leading bridge arm, and the second bridge arm is used as a lagging bridge arm; when the H bridge is controlled in the second mode, the second bridge arm is used as an advanced bridge arm, and the first bridge arm is used as a delayed bridge arm; when the control mode during the current work is selected to be the control mode of the lower tube modulation, the control module acquires total time TC for controlling the H bridge in a third mode and total time TD for controlling the H bridge in a fourth mode, acquires set time Ti for controlling the H bridge in the third mode and set time Tm for controlling the H bridge in the fourth mode in each work cycle of the DC-DC converter in the work process of adopting the control mode of the lower tube modulation, selects a mode for controlling the H bridge when the DC-DC converter is started by judging the relation between the total time TC and the total time TD, alternately controls the H bridge according to the set time Ti and the set time Tm to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, when the H bridge is controlled in the third mode, the first switching tube and the third switching tube are used as upper tubes, the second switching tube and the fourth switching tube are used as lower tubes, and the first switching tube to the fourth switching tube are controlled in a lower tube modulation control mode; and when the H bridge is controlled in the fourth mode, the first switching tube and the third switching tube are used as a lower tube, the second switching tube and the fourth switching tube are used as an upper tube, and the first switching tube to the fourth switching tube are controlled in a control mode of lower tube modulation.

According to the DC-DC converter provided by the embodiment of the invention, when the DC-DC converter is started to work, the control mode of the DC-DC converter in the last working is obtained through the control module, and the control mode in the current working is selected according to the control mode of the DC-DC converter in the last working, so that the control mode of phase shift modulation and the control mode of lower tube modulation are alternately carried out in the whole life cycle of the DC-DC converter. When the control mode in the current work is selected to be a phase shift modulation control mode, acquiring the setting time Tx for controlling the H bridge in a first mode and the setting time Ty for controlling the H bridge in a second mode through a control module, and then alternately controlling the H bridge according to the Tx and the Ty to perform temperature equalization control on a first switch tube, a second switch tube, a third switch tube and a fourth switch tube; when the control mode during the current work is selected to be a down tube modulation control mode, the control module acquires the total time TC for controlling the H bridge in a third mode and the total time TD for controlling the H bridge in a fourth mode, acquires the setting time Ti for controlling the H bridge in the third mode and the setting time Tm for controlling the H bridge in the fourth mode in each work cycle in the work process of the DC-DC converter in the down tube modulation control mode, then judges the relation between the total time TC and the total time TD, finally selects a mode for controlling the H bridge when the DC-DC converter is started according to the relation between the total time TC and the total time TD, and alternately controls the H bridge according to the Ti and the Tm in the work process of the DC-DC converter so as to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, therefore, in the whole life cycle, the H bridge is controlled alternately through the first mode and the second mode when the control mode of phase shift modulation is adopted to work, the third mode or the fourth mode is selected to control the H bridge according to the recorded total time TC and the total time TD when the control mode of lower tube modulation is adopted, and then the third mode and the fourth mode are adopted to control the H bridge alternately, so that the heat generation of each switch tube is relatively balanced, the service life of the switch tubes in the H bridge is prolonged under the condition of not increasing the cost, and the life cycle can be prolonged.

In addition, the embodiment of the invention also provides an electric automobile which comprises the DC-DC converter.

The electric automobile of the embodiment of the invention can control the DC-DC converter to adopt the control mode of phase shift modulation and the control mode of lower tube modulation to be alternately carried out in the whole life cycle, when the control mode of phase shift modulation is adopted to work, the H bridge is controlled alternately through a first mode and a second mode, when the control mode of lower tube modulation is adopted, a third mode or a fourth mode is selected to control the H bridge according to the recorded total time TC and total time TD, then the H bridge is controlled alternately through the third mode and the fourth mode, the temperature balance control of a first switch tube, a second switch tube, a third switch tube and a fourth switch tube in the H bridge can be realized, and the heating of each switch tube is relatively balanced, under the condition of not increasing the cost, the service life of a switching tube in the H bridge is prolonged, so that the life cycle of the DC-DC converter is prolonged.

Drawings

FIG. 1 is a circuit schematic of a DC-DC converter according to one embodiment of the present invention;

fig. 2 is a flowchart of a control method of a DC-DC converter according to an embodiment of the present invention;

fig. 3A is a schematic diagram of driving waveforms of four switching tubes when an H-bridge is controlled by a first manner according to an embodiment of the present invention;

fig. 3B is a schematic diagram of driving waveforms of four switching tubes when an H-bridge is controlled by a second method according to an embodiment of the present invention;

fig. 4A is a schematic diagram of driving waveforms of four switching tubes when an H-bridge is controlled by a third method according to an embodiment of the present invention;

fig. 4B is a schematic diagram of driving waveforms of four switching tubes when an H-bridge is controlled by a fourth method according to an embodiment of the present invention;

FIG. 5 is a flow chart of a method of controlling a DC-DC converter according to an embodiment of the present invention;

fig. 6 is a block diagram schematically illustrating an electric vehicle according to an embodiment of the present invention.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

A control method of a DC-DC converter, and an electric vehicle having the DC-DC converter according to an embodiment of the present invention will be described with reference to the accompanying drawings.

As shown in fig. 1, the DC-DC converter according to an embodiment of the present invention includes an H-bridge, which may include a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, and a fourth switching tube Q4. The first switching tube Q1 and the second switching tube Q2 form a first bridge arm, the third switching tube Q3 and the fourth switching tube Q4 form a second bridge arm, a first node a is arranged between the first switching tube Q1 and the second switching tube Q2, and a second node B is arranged between the third switching tube Q3 and the fourth switching tube Q4.

As shown in fig. 1, the DC-DC converter further includes a transformer, a first inductor L1, a first capacitor C1, a second inductor L2, a second capacitor C2, a fifth switch Q5, and a sixth switch Q6, wherein one end of the first inductor L1 is connected to the first node a, the other end of the first inductor L1 is connected to one end of the first capacitor C1, the other end of the first capacitor C1 is connected to one end of a primary winding of the transformer, and the other end of the primary winding of the transformer is connected to the second node B. The secondary winding of the transformer is respectively connected with a fifth switching tube Q5 and a sixth switching tube Q6, and a second inductor L2 and a second capacitor C2 are connected at the output end of the DC-DC converter.

In an embodiment of the present invention, as shown in fig. 2, the control method of the DC-DC converter includes the following steps:

and S1, when the DC-DC converter works, acquiring the control mode of the DC-DC converter during the last working, and selecting the control mode during the current working according to the control mode of the DC-DC converter during the last working, wherein the control mode of the DC-DC converter comprises a phase-shift modulation control mode and a lower tube modulation control mode.

That is, each time the DC-DC converter starts to operate, the control mode adopted last time is read, and if the control mode adopted last time operation is the control mode of phase shift modulation, the control mode of lower tube modulation is adopted in the current operation of the DC-DC converter; if the control mode adopted by the last work is the control mode of the lower tube modulation, the DC-DC converter adopts the control mode of the phase shift modulation in the work. Thus, the control mode of the phase shift modulation and the control mode of the lower tube modulation are alternately performed in the whole life cycle of the DC-DC converter.

S2, when the control mode during the work is selected to be the phase shift modulation control mode, acquiring the setting time Tx for controlling the H bridge in the first mode and the setting time Ty for controlling the H bridge in the second mode, and alternately controlling the H bridge according to the setting time Tx and the setting time Ty so as to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube.

When the H bridge is controlled in the first mode, the first bridge arm is used as a leading bridge arm, and the second bridge arm is used as a lagging bridge arm; and when the H bridge is controlled in the second mode, taking the second bridge arm as a leading bridge arm and taking the first bridge arm as a lagging bridge arm.

According to an embodiment of the present invention, when the H-bridge is controlled in the first manner, the control signal output to the first switch Q1 is complementary to the control signal output to the second switch Q2, and the control signal output to the third switch Q3 is complementary to the control signal output to the fourth switch Q4, and the first switch Q1 is turned on one phase angle ahead of the fourth switch Q4, and the second switch Q2 is turned on one phase angle ahead of the third switch Q3.

Specifically, the driving waveform of the first switching tube Q1, the driving waveform of the second switching tube Q2, the driving waveform of the third switching tube Q3, the driving waveform of the fourth switching tube Q4 and the voltage U between the two legs of the H-bridge_ABThe waveform is shown in fig. 3A. As can be seen from fig. 3A, the control signals of Q1 and Q2 of the four switching tubes of the H-bridge are complementary, the control signals of Q3 and Q4 are complementary, the diagonal switching tube Q1 is turned on one phase angle before Q4, and Q2 is turned on one phase angle before Q3. And the output voltage is adjusted by adjusting the magnitude of the phase angle.

When the H-bridge is controlled in the second mode, the control signal output to the first switching tube Q1 is complementary to the control signal output to the second switching tube Q2, and the control signal output to the third switching tube Q3 is complementary to the control signal output to the fourth switching tube Q4, and the fourth switching tube Q4 is turned on one phase angle ahead of the first switching tube Q1, and the third switching tube Q3 is turned on one phase angle ahead of the second switching tube Q2.

Specifically, the driving waveform of the first switching tube Q1, the driving waveform of the second switching tube Q2, the driving waveform of the third switching tube Q3, the driving waveform of the fourth switching tube Q4 and the voltage U between the two legs of the H-bridge_ABThe waveform is shown in fig. 3B. It can be seen from fig. 4 that the control signals of Q1 and Q2 of the four switching tubes of the H-bridge are complementary, the control signals of Q3 and Q4 are complementary, the diagonal switching tube Q4 is turned on one phase angle before Q1, and Q3 is turned on one phase angle before Q2. Likewise, the output voltage is adjusted by adjusting the magnitude of the phase angle.

It should be noted that, in the operation process of the DC-DC converter using the phase shift modulation control method, if the H-bridge is controlled only by the first method a, it is difficult to realize soft switching, i.e., zero-voltage switching, as the switching tubes Q3 and Q4 in the hysteresis bridge arm, and therefore, the switching losses of the switching tubes Q3 and Q4 are large, which causes overheating.

Similarly, in the operation of the DC-DC converter using the phase shift modulation control method, if the H-bridge is controlled only by the second method B, it is difficult to realize soft switching, i.e., zero-voltage switching, of the switching tubes Q1 and Q2 in the hysteresis bridge arm, and therefore, the switching losses of the switching tubes Q1 and Q2 are large, which causes overheating.

Therefore, in an embodiment of the present invention, when the DC-DC converter operates in the phase-shift modulation control manner, Tx and Ty are set, then during the operation of the DC-DC converter in the phase-shift modulation control manner, the H-bridge may be controlled in the first manner a to operate the DC-DC converter until the time for controlling the H-bridge in the first manner a reaches Tx, the H-bridge may be controlled in the second manner B to operate the DC-DC converter until the time for controlling the H-bridge in the second manner B reaches Ty, so as to complete an operation cycle (i.e. one operation cycle time is Tx + Ty), and then the H-bridge may be controlled in the first manner a to operate the DC-DC converter until the time for controlling the H-bridge in the first manner a reaches Tx, and then, the H bridge is controlled by adopting a second mode B so that the DC-DC converter works until the time for controlling the H bridge by adopting the second mode B reaches Ty, … …, and the steps are repeated to realize the alternate control of the H bridge, so that the temperature balance control of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is realized. Of course, in the working process of the DC-DC converter by using the phase shift modulation control method, the second method B may also be used to control the H-bridge to operate the DC-DC converter first until the time for controlling the H-bridge by using the second method B reaches Ty, and the control is switched to the first method a to control the H-bridge to operate the DC-DC converter until the time for controlling the H-bridge by using the first method a reaches Tx, so as to complete a working cycle, and the operation is repeated according to the working cycle until the DC-DC converter stops operating this time.

That is, in one embodiment of the present invention, alternately controlling the H-bridge according to the set time Tx and the set time Ty includes: when the time for controlling the H bridge in the first mode reaches Tx, controlling the H bridge in the second mode until the time for controlling the H bridge in the second mode reaches Ty; or when the time for controlling the H bridge in the second mode reaches Ty, the H bridge is controlled in the first mode until the time for controlling the H bridge in the first mode reaches Tx.

It should be noted that, in the embodiment of the present invention, the DC-DC converter adopts a control method of phase shift modulation regardless of whether the H-bridge is controlled in the first manner or the H-bridge is controlled in the second manner. The first to fourth switching tubes are driven by 50% duty ratio, the driving voltages of the same bridge arm are complementary, the phase difference is 180 degrees, the phase difference between the leading bridge arm and the lagging bridge arm is a phase angle, and the output voltage is adjusted by adjusting the phase angle.

According to an embodiment of the present invention, the setting time Tx for controlling the H-bridge in the first manner is equal to the setting time Ty for controlling the H-bridge in the second manner, which ensures that the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4 generate heat in a relatively balanced manner when the H-bridge is controlled alternately in the first manner and the second manner.

Of course, it is understood that, in other embodiments of the present invention, the setting time Tx for controlling the H-bridge in the first manner and the setting time Ty for controlling the H-bridge in the second manner may not be equal.

In summary, when the DC-DC converter operates in the phase shift modulation control mode, the H-bridge is alternately controlled by selecting the first mode or the second mode based on the setting times Tx and Ty, and the relative balance of the heat generation amounts of the switching tubes Q1, Q2, Q3, and Q4 in the H-bridge can be realized in the phase shift modulation control mode of the DC-DC converter, so that no additional component is required, the cost is reduced, the service life of the DC-DC converter can be prolonged, and the failure rate is reduced.

And S3, when the control mode during the current work is selected to be a down tube modulation control mode, acquiring total time TC for controlling the H bridge in a third mode and total time TD for controlling the H bridge in a fourth mode, acquiring setting time Ti for controlling the H bridge in the third mode and setting time Tm for controlling the H bridge in the fourth mode in each work cycle in the work process of the DC-DC converter adopting the down tube modulation control mode, selecting the mode for controlling the H bridge when the DC-DC converter is started by judging the relation between the total time TC and the total time TD, and alternately controlling the H bridge according to the setting time Ti and the setting time Tm so as to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube.

When the H-bridge is controlled in the third mode, the first switching tube Q1 and the third switching tube Q3 are used as upper tubes, the second switching tube Q2 and the fourth switching tube Q4 are used as lower tubes, and the first switching tube to the fourth switching tube are controlled in a lower tube modulation control mode; when the H-bridge is controlled in the fourth mode, the first switching tube Q1 and the third switching tube Q3 are used as a lower tube, the second switching tube Q2 and the fourth switching tube Q4 are used as an upper tube, and the first switching tube to the fourth switching tube are controlled in a control mode of lower tube modulation.

According to an embodiment of the present invention, when the H-bridge is controlled in the third manner, the control signal output to the first switching transistor Q1 is complementary to the control signal output to the third switching transistor Q3 and has a fixed duty ratio, and the falling edges of the control signals output to the second switching transistor Q2 and the fourth switching transistor Q4 are PWM controlled.

Specifically, the driving waveform of the first switching tube Q1, the driving waveform of the second switching tube Q2, the driving waveform of the third switching tube Q3, the driving waveform of the fourth switching tube Q4 and the voltage U between the two legs of the H-bridge_ABThe waveform is shown in fig. 4A. As can be seen from fig. 4A, the control signals of Q1 and Q3 in the four switching tubes of the H-bridge are complementary and have a fixed 50% duty cycle, the falling edges of Q2 and Q4 are modulated according to the PWM rule, and the output voltage is adjusted by adjusting the falling edge of the driving voltage of the lower tube.

When the H-bridge is controlled in the fourth mode, the control signal output to the second switching transistor Q2 is complementary to the control signal output to the fourth switching transistor Q4, has a fixed duty ratio, and the falling edges of the control signals output to the first switching transistor Q1 and the third switching transistor Q3 are PWM controlled.

Specifically, the driving waveform of the first switching tube Q1, the driving waveform of the second switching tube Q2, the driving waveform of the third switching tube Q3, the driving waveform of the fourth switching tube Q4 and the voltage U between the two legs of the H-bridge_ABThe waveform is shown in fig. 4B. As can be seen from fig. 4B, the control signals of Q2 and Q4 in the four switching tubes of the H-bridge are complementary and have a fixed 50% duty cycle, the falling edges of Q1 and Q3 are modulated according to the PWM rule, and the output voltage is adjusted by adjusting the falling edge of the driving voltage of the lower tube.

It should be noted that, in the working process of the DC-DC converter using the control method of the down tube modulation, if the H-bridge is controlled only by the third method C, since only the primary side resonant inductor can be used in the resonant discharge stage, it is difficult to realize soft switching, i.e., zero voltage switching, for the switching tubes Q2 and Q4 of the down tube, so that the switching losses of the switching tubes Q2 and Q4 are large, which causes overheating.

Similarly, in the operation process of the DC-DC converter using the down tube modulation control method, if the H-bridge is controlled only by the fourth method D, since only the primary side resonant inductor can be utilized in the resonant discharge stage, the switching tubes Q1 and Q3 as the down tubes are difficult to realize soft switching, i.e., zero voltage switching, and thus the switching losses of the switching tubes Q1 and Q3 are large, which leads to overheating.

Therefore, in an embodiment of the present invention, when the DC-DC converter operates in the down tube modulation control mode and the H-bridge is controlled in the third mode C, the time for controlling the H-bridge in the third mode C is recorded, so that the total time TC for controlling the H-bridge in the third mode can be obtained and then stored; when the H bridge is controlled by the fourth mode D, the time for controlling the H bridge by the fourth mode D is recorded, so that the total time TD for controlling the H bridge by the fourth mode can be obtained and then stored. And then judging the relation between the total time TC and the total time TD when the DC-DC converter is started every time, and finally selecting a mode for controlling the H bridge when the DC-DC converter is started according to the relation between the total time TC and the total time TD.

Specifically, according to an embodiment of the present invention, when the manner of controlling the H-bridge at the time of starting the DC-DC converter is selected according to the relationship between the total time TC and the total time TD, when the total time TC is greater than the total time TD, the fourth manner is selected to control the H-bridge at the time of starting the DC-DC converter until the total time TC is equal to the total time TD; when the total time TC is smaller than the total time TD, selecting the third mode to control the H bridge when the DC-DC converter is started until the total time TC is equal to the total time TD; when the total time TC is equal to the total time TD, selecting the third mode or the fourth mode at the starting of the DC-DC converter to alternately control the H bridge according to Ti and Tm.

Wherein the alternately controlling the H bridge according to the set time Ti and the set time Tm comprises: when the time for controlling the H bridge by adopting the third mode reaches Ti, controlling the H bridge by adopting the fourth mode until the time for controlling the H bridge by adopting the fourth mode reaches Tm; or when the time for controlling the H bridge by adopting the fourth mode reaches Tm, controlling the H bridge by adopting the third mode until the time for controlling the H bridge by adopting the third mode reaches Ti.

That is, before the DC-DC converter operates in the down tube modulation control mode, the total time TC for controlling the H-bridge in the third way and the total time TD for controlling the H-bridge in the fourth way are obtained from the storage area, Ti and Tm are set, then the total time TC and the total time TD are judged, and it is determined whether to control the H-bridge in the third way or in the fourth way according to the judgment result, that is, the total time TC for controlling the H-bridge in the third way and the total time TD for controlling the H-bridge in the fourth way are obtained from the storage area, and the judgment on the relationship between the total time TC and the total time TD is to confirm the H-bridge control mode selected first when the DC-DC converter starts. For example, if the obtained TC is 20 minutes and TD is 18 minutes, the DC-DC converter selects the fourth method D to control the H-bridge to start up the DC-DC converter in the current operation, and switches to the third method C to control the H-bridge to operate the DC-DC converter after 2 minutes until the time for controlling the H-bridge by the third method C reaches Ti, then switches to the fourth method D to control the H-bridge to operate the DC-DC converter until the time for controlling the H-bridge by the fourth method D reaches Tm, so that one operation cycle is completed (i.e., one operation cycle time is Ti + Tm), then switches to the third method C to control the H-bridge to operate the DC-DC converter until the time for controlling the H-bridge by the third method C reaches Ti, and then, the H bridge is controlled by adopting a fourth mode D so that the DC-DC converter works until the time for controlling the H bridge by adopting the fourth mode D reaches Tm, … …, and the steps are repeated to realize the alternate control of the H bridge, so that the temperature balance control of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is realized. If the obtained TC is 18 minutes and TD is 20 minutes, the DC-DC converter firstly selects a third mode C to control the H bridge to start the DC-DC converter during the work, and switches to a fourth mode D to control the H bridge to work after 2 minutes until the time for controlling the H bridge by the fourth mode D reaches Tm, then switches to the third mode C to control the H bridge to work until the time for controlling the H bridge by the third mode C reaches Ti, thus completing a work cycle (i.e. one work cycle time is Ti + Tm), then switches to the fourth mode D to control the H bridge to work until the time for controlling the H bridge by the fourth mode D reaches Tm, and then, the H bridge is controlled by adopting a third mode C so that the DC-DC converter works until the time for controlling the H bridge by adopting the third mode C reaches Ti, … …, and the steps are repeated to realize the alternate control of the H bridge, so that the temperature balance control of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is realized.

Of course, when the obtained total time TC is equal to the total time TD, when the DC-DC converter is started, the H bridge may be directly controlled by the third method C to operate the DC-DC converter until the time for controlling the H bridge by the third method C reaches Ti, the H bridge is controlled by the fourth method D to operate the DC-DC converter until the time for controlling the H bridge by the fourth method D reaches Tm, so that one working cycle is completed (i.e., one working cycle time is Ti + Tm), the H bridge is controlled by the third method C to operate the DC-DC converter until the time for controlling the H bridge by the third method C reaches Ti, and then the H bridge is controlled by the fourth method D to operate the DC-DC converter, and (4) until the time for controlling the H bridge by adopting the fourth mode D reaches Tm and … …, repeating the steps to realize the alternate control of the H bridge, thereby realizing the temperature balance control of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube. Or when the obtained total time TC is equal to the total time TD, directly adopting the fourth mode D to control the H bridge to enable the DC-DC converter to work when the DC-DC converter is started, switching to the third mode C to control the H bridge to enable the DC-DC converter to work until the time for controlling the H bridge by adopting the fourth mode D reaches Tm, and repeating the working cycle until the DC-DC converter stops working until the time for controlling the H bridge by adopting the third mode C reaches Ti.

After the method is selected in each working cycle, the H-bridge is controlled according to a fixed method, that is, a third method or a fourth method, and the total time is recorded during the switching method, for example, when the H-bridge is controlled by the third method first, the total time recorded during the switching method for controlling the H-bridge in the third method is the total time for controlling the H-bridge in the third method, which is obtained from the storage area when the current operation of the DC-DC converter starts, plus the time for controlling the H-bridge in the third method, which is recorded during the current working cycle of the DC-DC converter.

In an embodiment of the present invention, the setting time Ti for controlling the H-bridge in the third manner may be equal to the setting time Tm for controlling the H-bridge in the fourth manner, so that it is ensured that the heat generation of the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 is relatively balanced when the H-bridge is controlled alternately in the third manner and the fourth manner.

Of course, it is understood that, in other embodiments of the present invention, the setting time Ti for controlling the H-bridge in the third manner and the setting time Tm for controlling the H-bridge in the fourth manner may not be equal.

In the embodiment of the present invention, the DC-DC converter adopts the control method of the down tube modulation regardless of whether the H-bridge is controlled in the third manner or the fourth manner. When the control mode of the lower tube modulation is adopted, the two switching tubes of the upper tube are alternately switched on according to the 50% duty ratio without dead time, and the regulation of the output voltage is realized by regulating the falling edges of the driving voltage of the two switching tubes of the lower tube.

In the control mode of the lower tube modulation, the two switching tubes of the upper tube are easy to realize soft switching, i.e. zero voltage switching, corresponding to the leading bridge arm in the control mode of the phase shift modulation, while the two switching tubes of the lower tube are corresponding to the lagging bridge arm in the control mode of the phase shift modulation, so that zero voltage switching is difficult to realize.

In the embodiment of the invention, when the DC-DC converter adopts a control mode of lower tube modulation in the whole life cycle, the first to fourth switching tubes can be alternately used as the upper tube and the lower tube, namely Q1, Q3, Q2 and Q4 are alternately used as the upper tube and the lower tube, so that the temperature stress is effectively and uniformly distributed in the four switching tubes of the H bridge, the heat generation of each switching tube is relatively balanced, the integral heat balance is realized, and the service life of the DC-DC converter is prolonged.

In summary, when the DC-DC converter operates in the down tube modulation control mode, the H-bridge is controlled by recording whether the DC-DC converter adopts the third mode or the fourth mode, recording the total time TC when the third mode is adopted and the total time TD when the fourth mode is adopted, and then determining the relationship between TC and TD, so as to select the H-bridge control mode when the DC-DC converter starts up, and then alternately controlling the H-bridge based on the set time Tm and the set time Ti, thereby achieving the relative balance of the heat generation amounts of the switching tubes Q1, Q2, Q3, and Q4 in the H-bridge in the control mode in which the DC-DC converter adopts the down tube modulation, without adding additional components, reducing the cost, increasing the working life of the DC-DC converter, and reducing the failure rate.

According to an embodiment of the present invention, the setting time Ti for controlling the H-bridge in the third manner may be equal to the setting time Tm for controlling the H-bridge in the fourth manner, which may ensure that the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 generate heat in relative balance when the H-bridge is controlled alternately in the third manner and the fourth manner.

In a preferred embodiment of the present invention, Tx may be equal to Ty, Ti may be equal to Tm, and Tx may also be equal to Ti at the same time.

Specifically, according to an embodiment of the present invention, as shown in fig. 5, the control method of the DC-DC converter includes the following steps:

s501, when the DC-DC converter starts to work, a control waveform needs to be output to control a switching tube in an H bridge.

S5011, reading a control mode adopted by the DC-DC converter in the last working.

S5011, determining whether the control mode of phase shift modulation was used last time. If yes, go to step S507; if not, step S502 is performed.

That is, if the control mode adopted in the last operation is the phase shift modulation control mode, the DC-DC converter will adopt the control mode of the lower tube modulation in the current operation; if the control mode adopted by the last work is not the phase-shift modulation control mode, the DC-DC converter adopts the phase-shift modulation control mode in the work.

S502, Tx and Ty are set.

S503, controlling the H bridge by adopting a first mode A to enable the DC-DC converter to work, judging whether the current work of the DC-DC converter is finished or not in the working process of the DC-DC converter, if so, finishing the process, and if not, returning to continue judging.

S504, whether the time for controlling the H bridge by the first mode A reaches Tx is judged. If yes, go to step S505; if not, return to step S503.

And S505, controlling the H bridge by adopting a second mode B to enable the DC-DC converter to work, judging whether the current work of the DC-DC converter is finished or not in the working process of the DC-DC converter, if so, finishing the process, and if not, returning to continue judging.

And S506, judging whether the time for controlling the H bridge by adopting the second mode B reaches Ty. If yes, returning to execute the step S503; if not, return to step S505.

And S507, reading the total time TC for controlling the H bridge in the third mode C and the total time TD for controlling the H bridge in the fourth mode D.

S508, setting Ti and Tm.

S509, judging whether TC is larger than TD. If yes, go to step S510; if not, step S511 is executed.

S510, the fourth mode D is selected to control the H-bridge until TC becomes TD, and then step S513 is executed.

And S511, judging whether TC is smaller than TD. If yes, go to step S512; if not, step S513 or S514 is performed.

S512, the third mode C is selected to control the H-bridge until TC becomes TD, and then step S514 is executed.

S513, the H bridge is controlled by adopting a third mode C to enable the DC-DC converter to work, whether the work is finished or not is judged in the working process, if yes, the process is finished, and if not, the process returns to the continuous judgment.

And S514, controlling the H bridge by adopting a fourth mode D to enable the DC-DC converter to work, judging whether the work is finished or not in the working process, if so, finishing the process, and if not, returning to continue judging.

And S515, judging whether the time for controlling the H bridge by adopting the third mode C reaches Ti. If yes, go to step S514; if not, return to step S513.

And S516, judging whether the time for controlling the H bridge by the fourth mode D reaches Tm or not. If yes, go back to step S513; if not, return to step S514.

Therefore, in the embodiment of the present invention, during the whole life cycle of the DC-DC converter, the control mode of phase shift modulation and the control mode of down tube modulation are alternately performed, and the H-bridge is alternately controlled in the first mode or the second mode based on the set times Tx and Ty when the control mode of phase shift modulation is used, and the H-bridge is alternately controlled in the third mode or the fourth mode based on the total time TC and the total time TD when the control mode of down tube modulation is used, so as to start the DC-DC converter, and then the H-bridge is alternately controlled based on the set time Tm and the set time Ti, so that during the whole life cycle, the H-bridge is alternately controlled in the first mode and the second mode when the DC-DC converter operates in the control mode of phase shift modulation, and the H-bridge is controlled in the third mode or the fourth mode according to the recorded total time TC and the total time TD when the control mode of down tube modulation is used, And then the H bridge is alternately controlled by adopting a third mode and a fourth mode, so that the heating of each switching tube is relatively balanced, and the service life of the DC-DC converter is greatly prolonged.

As shown in fig. 1, the DC-DC converter according to an embodiment of the present invention includes an H-bridge and a Control module 100, such as an MCU (Micro Control Unit). The H-bridge comprises a first switch tube Q1, a second switch tube Q2, a third switch tube Q3 and a fourth switch tube Q4, the first switch tube Q1 and the second switch tube Q2 form a first bridge arm, the third switch tube Q3 and the fourth switch tube Q4 form a second bridge arm, a first node A is arranged between the first switch tube Q1 and the second switch tube Q2, and a second node B is arranged between the third switch tube Q3 and the fourth switch tube Q4.

The control module 100 is configured to obtain a control mode of the DC-DC converter during the last operation when the DC-DC converter operates, and select a control mode of the DC-DC converter during the current operation according to the control mode of the DC-DC converter during the last operation, where the control mode of the DC-DC converter includes a phase shift modulation control mode and a lower tube modulation control mode.

When the control mode of the current operation is selected as the phase shift modulation control mode, the control module 100 obtains a setting time Tx for controlling the H-bridge in a first mode and a setting time Ty for controlling the H-bridge in a second mode, and alternately controls the H-bridge according to the setting time Tx and the setting time Ty to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, wherein when the H-bridge is controlled in the first mode, the first bridge arm is used as an advance bridge arm, and the second bridge arm is used as a retard bridge arm; and when the H bridge is controlled in the second mode, taking the second bridge arm as a leading bridge arm and taking the first bridge arm as a lagging bridge arm. When the control mode during the current operation is selected as the control mode of the lower tube modulation, the control module 100 obtains a total time TC for controlling the H-bridge in a third way and a total time TD for controlling the H-bridge in a fourth way, obtains a setting time Ti for controlling the H-bridge in the third way and a setting time Tm for controlling the H-bridge in the fourth way in each working cycle of the DC-DC converter in the operation process using the control mode of the lower tube modulation, selects a mode for controlling the H-bridge when the DC-DC converter is started by judging a relationship between the total time TC and the total time TD, and alternately controls the H-bridge according to the setting time Ti and the setting time Tm to perform temperature equalization control on the first switching tube, the second switching tube, the third switching tube, and the fourth switching tube, when the H bridge is controlled in the third mode, the first switching tube and the third switching tube are used as upper tubes, the second switching tube and the fourth switching tube are used as lower tubes, and the first switching tube to the fourth switching tube are controlled in a lower tube modulation control mode; and when the H bridge is controlled in the fourth mode, the first switching tube and the third switching tube are used as a lower tube, the second switching tube and the fourth switching tube are used as an upper tube, and the first switching tube to the fourth switching tube are controlled in a control mode of lower tube modulation.

According to an embodiment of the present invention, when the control module alternately controls the H-bridge according to a set time Tx and a set time Ty, wherein when the time for controlling the H-bridge in the first manner reaches Tx, the control module controls the H-bridge in the second manner until the time for controlling the H-bridge in the second manner reaches Ty; or when the time for controlling the H bridge in the second mode reaches Ty, the control module controls the H bridge in the first mode until the time for controlling the H bridge in the first mode reaches Tx.

That is to say, in the embodiment of the present invention, each time the DC-DC converter operates in the phase shift modulation control manner, the control module sets Tx and Ty, and then during the operation of the DC-DC converter in the phase shift modulation control manner, the control module may first control the H-bridge in the first manner a to operate the DC-DC converter until the time for controlling the H-bridge in the first manner a reaches Tx, and then control the H-bridge in the second manner B to operate the DC-DC converter until the time for controlling the H-bridge in the second manner B reaches Ty, so as to complete an operation cycle (i.e., one operation cycle time is Tx + Ty), and then control the H-bridge in the first manner a to operate the DC-DC converter until the time for controlling the H-bridge in the first manner a reaches Tx, and then, the H bridge is controlled by adopting a second mode B so that the DC-DC converter works until the time for controlling the H bridge by adopting the second mode B reaches Ty, … …, and the steps are repeated to realize the alternate control of the H bridge, so that the temperature balance control of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is realized. Of course, in the working process of the DC-DC converter in the phase shift modulation control mode, the control module may also first control the H-bridge in the second mode B to operate the DC-DC converter until the time for controlling the H-bridge in the second mode B reaches Ty, and switch to control the H-bridge in the first mode a to operate the DC-DC converter until the time for controlling the H-bridge in the first mode a reaches Tx, so as to complete a working cycle, and repeat the working cycle until the DC-DC converter stops working.

In a preferred embodiment of the present invention, the set time Tx for controlling the H-bridge in the first manner may be equal to the set time Ty for controlling the H-bridge in the second manner. This ensures that the first switch tube Q1, the second switch tube Q2, the third switch tube Q3 and the fourth switch tube Q4 generate heat in a relatively balanced manner when the H-bridge is controlled alternately in the first mode and the second mode.

According to an embodiment of the present invention, when the H-bridge is controlled in the first manner, the control signal output by the control module to the first switching tube is complementary to the control signal output by the second switching tube, and the control signal output by the control module to the third switching tube is complementary to the control signal output by the fourth switching tube, and the first switching tube is turned on with a phase angle ahead of the fourth switching tube, and the second switching tube is turned on with a phase angle ahead of the third switching tube.

When the H-bridge is controlled in the second mode, the control signal output by the control module to the first switching tube is complementary to the control signal output to the second switching tube, and the control signal output to the third switching tube is complementary to the control signal output to the fourth switching tube, and the fourth switching tube is turned on one phase angle ahead of the first switching tube, and the third switching tube is turned on one phase angle ahead of the second switching tube.

In one embodiment of the invention, in the process that the DC-DC converter works in a down tube modulation control mode, the control module controls the H bridge in a third mode C so as to record the time for controlling the H bridge in the third mode C when the DC-DC converter works, so that the total time TC for controlling the H bridge in the third mode can be obtained and then stored; and when the control module controls the H bridge by adopting the fourth mode D so that the DC-DC converter works, recording the time for controlling the H bridge by adopting the fourth mode D, thus obtaining the total time TD for controlling the H bridge by adopting the fourth mode and then storing the total time TD. Therefore, when the DC-DC converter needs to adopt a control mode of lower tube modulation to start, the control module judges the relation between the total time TC and the total time TD, and selects a mode of controlling the H bridge when the DC-DC converter starts according to the relation between the total time TC and the total time TD.

Specifically, according to an embodiment of the present invention, when the control module selects the manner of controlling the H-bridge at the time of starting the DC-DC converter according to the relationship between the total time TC and the total time TD, when the total time TC is greater than the total time TD, the control module selects the fourth manner to control the H-bridge at the time of starting the DC-DC converter until the total time TC is equal to the total time TD; when the total time TC is smaller than the total time TD, the control module selects the third mode to control the H bridge when the DC-DC converter is started until the total time TC is equal to the total time TD; when the total time TC is equal to the total time TD, the control module selects the third mode or the fourth mode to alternately control the H-bridge according to Ti and Tm when the DC-DC converter is started.

When the control module controls the H bridge alternately according to set time Ti and set time Tm, when the time for controlling the H bridge by adopting the third mode reaches Ti, the control module controls the H bridge by adopting the fourth mode until the time for controlling the H bridge by adopting the fourth mode reaches Tm; or when the time for controlling the H bridge by adopting the fourth mode reaches Tm, controlling the H bridge by adopting the third mode until the time for controlling the H bridge by adopting the third mode reaches Ti.

That is, before the DC-DC converter operates in the down tube modulation control mode, the control module obtains the total time TC for controlling the H-bridge in the third way and the total time TD for controlling the H-bridge in the fourth way from the storage area, sets Ti and Tm, determines whether to control the H-bridge in the third way or in the second control way according to the determination result, that is, obtains the total time TC for controlling the H-bridge in the third way and the total time TD for controlling the H-bridge in the fourth way from the storage area, and determines the relationship between the total time TC and the total time TD in order to confirm the H-bridge control mode selected first when the DC-DC converter starts. For example, if the obtained TC is 20 minutes and TD is 18 minutes, the DC-DC converter selects the fourth method D to control the H-bridge to start up the DC-DC converter in the current operation, and switches to the third method C to control the H-bridge to operate the DC-DC converter after 2 minutes until the time for controlling the H-bridge by the third method C reaches Ti, then switches to the fourth method D to control the H-bridge to operate the DC-DC converter until the time for controlling the H-bridge by the fourth method D reaches Tm, so that one operation cycle is completed (i.e., one operation cycle time is Ti + Tm), then switches to the third method C to control the H-bridge to operate the DC-DC converter until the time for controlling the H-bridge by the third method C reaches Ti, and then, the H bridge is controlled by adopting a fourth mode D so that the DC-DC converter works until the time for controlling the H bridge by adopting the fourth mode D reaches Tm, … …, and the steps are repeated to realize the alternate control of the H bridge, so that the temperature balance control of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is realized. If the obtained TC is 18 minutes and TD is 20 minutes, the DC-DC converter firstly selects a third mode C to control the H bridge to start the DC-DC converter during the work, and switches to a fourth mode D to control the H bridge to work after 2 minutes until the time for controlling the H bridge by the fourth mode D reaches Tm, then switches to the third mode C to control the H bridge to work until the time for controlling the H bridge by the third mode C reaches Ti, thus completing a work cycle (i.e. one work cycle time is Ti + Tm), then switches to the fourth mode D to control the H bridge to work until the time for controlling the H bridge by the fourth mode D reaches Tm, and then, the H bridge is controlled by adopting a third mode C so that the DC-DC converter works until the time for controlling the H bridge by adopting the third mode C reaches Ti, … …, and the steps are repeated to realize the alternate control of the H bridge, so that the temperature balance control of the first switch tube, the second switch tube, the third switch tube and the fourth switch tube is realized.

According to an embodiment of the present invention, when the H-bridge is controlled in the third manner, the control signal output by the control module to the first switching tube is complementary to the control signal output by the third switching tube and has a fixed duty ratio, and the control module performs PWM control on the falling edges of the control signals output to the second switching tube and the fourth switching tube.

And when the H bridge is controlled in the fourth mode, the control signal output to the second switching tube by the control module is complementary to the control signal output to the fourth switching tube and has a fixed duty ratio, and the control module performs PWM control on the falling edges of the control signals output to the first switching tube and the third switching tube.

In the embodiment of the present invention, as shown in fig. 1, the first switching Transistor Q1, the second switching Transistor Q2, the third switching Transistor Q3 and the fourth switching Transistor Q4 are all IGBTs (Insulated Gate Bipolar transistors), but in another embodiment of the present invention, the first switching Transistor Q1, the second switching Transistor Q2, the third switching Transistor Q3 and the fourth switching Transistor Q4 may be MOS transistors.

Preferably, according to an embodiment of the present invention, the setting time Ti for controlling the H-bridge in the third manner may be equal to the setting time Tm for controlling the H-bridge in the fourth manner, so that it is ensured that the heat generation of the first switching tube Q1, the second switching tube Q2, the third switching tube Q3 and the fourth switching tube Q4 is relatively balanced when the H-bridge is controlled alternately in the third manner and the fourth manner.

In addition, as shown in fig. 6, an embodiment of the present invention further provides an electric vehicle 10 including the above-described DC-DC converter 20.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the invention and to simplify the description, and are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and are therefore not to be considered limiting of the invention.

Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A control method of a DC-DC converter is characterized in that the DC-DC converter comprises an H bridge, the H bridge comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, wherein the first switch tube and the second switch tube form a first bridge arm, and the third switch tube and the fourth switch tube form a second bridge arm, and the control method comprises the following steps:

when the DC-DC converter works, acquiring a control mode of the DC-DC converter during last working, and selecting the control mode during the current working according to the control mode of the DC-DC converter during the last working, wherein the control mode of the DC-DC converter during the last working is different from the control mode during the current working, and comprises a control mode of phase shift modulation and a control mode of lower tube modulation;

when the control mode during the work is selected to be the phase shift modulation control mode, acquiring setting time Tx for controlling the H bridge in a first mode and setting time Ty for controlling the H bridge in a second mode, and alternately controlling the H bridge according to the setting time Tx and the setting time Ty to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, wherein when the H bridge is controlled in the first mode, the first bridge arm is used as an advance bridge arm, and the second bridge arm is used as a delay bridge arm; when the H bridge is controlled in the second mode, the second bridge arm is used as an advanced bridge arm, and the first bridge arm is used as a delayed bridge arm;

when the control mode in the current work is selected to be the control mode of the lower tube modulation, acquiring total time TC for controlling the H bridge in a third mode and total time TD for controlling the H bridge in a fourth mode, acquiring setting time Ti for controlling the H bridge in the third mode and setting time Tm for controlling the H bridge in the fourth mode in each work cycle in the work process of the DC-DC converter in the control mode of the lower tube modulation, selecting the mode of controlling the H bridge when the DC-DC converter is started by judging the relation between the total time TC and the total time TD, and alternately controlling the H bridge according to the setting time Ti and the setting time Tm to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, when the H bridge is controlled in the third mode, the first switching tube and the third switching tube are used as upper tubes, the second switching tube and the fourth switching tube are used as lower tubes, and the first switching tube to the fourth switching tube are controlled in a lower tube modulation control mode; and when the H bridge is controlled in the fourth mode, the first switching tube and the third switching tube are used as a lower tube, the second switching tube and the fourth switching tube are used as an upper tube, and the first switching tube to the fourth switching tube are controlled in a control mode of lower tube modulation.

2. The method according to claim 1, wherein the alternately controlling the H-bridge according to the set time Tx and the set time Ty comprises:

when the time for controlling the H bridge in the first mode reaches Tx, controlling the H bridge in the second mode until the time for controlling the H bridge in the second mode reaches Ty; or

And when the time for controlling the H bridge in the second mode reaches Ty, controlling the H bridge in the first mode until the time for controlling the H bridge in the first mode reaches Tx.

3. The control method of a DC-DC converter according to claim 1 or 2, wherein,

when the H bridge is controlled in the first mode, a control signal output to the first switching tube is complementary to a control signal output to the second switching tube, a control signal output to the third switching tube is complementary to a control signal output to the fourth switching tube, the first switching tube is switched on by advancing a phase angle than the fourth switching tube, and the second switching tube is switched on by advancing a phase angle than the third switching tube;

when the H bridge is controlled in the second mode, the control signal output to the first switch tube is complementary to the control signal output to the second switch tube, the control signal output to the third switch tube is complementary to the control signal output to the fourth switch tube, the fourth switch tube is switched on by advancing one phase angle than the first switch tube, and the third switch tube is switched on by advancing one phase angle than the second switch tube.

4. The method according to claim 1, wherein when the manner of controlling the H-bridge at the time of starting the DC-DC converter is selected according to the relationship between the total time TC and the total time TD, wherein,

when the total time TC is larger than the total time TD, selecting the fourth mode to control the H bridge when the DC-DC converter is started until the total time TC is equal to the total time TD;

when the total time TC is smaller than the total time TD, selecting the third mode to control the H bridge when the DC-DC converter is started until the total time TC is equal to the total time TD;

when the total time TC is equal to the total time TD, selecting the third mode or the fourth mode at the starting of the DC-DC converter to alternately control the H bridge according to Ti and Tm.

5. The control method of a DC-DC converter according to claim 1 or 4, wherein,

when the H bridge is controlled in the third mode, the control signal output to the first switching tube is complementary to the control signal output to the third switching tube and has a fixed duty ratio, and the falling edges of the control signals output to the second switching tube and the fourth switching tube are subjected to PWM control;

when the H bridge is controlled in the fourth mode, the control signal output to the second switching tube is complementary to the control signal output to the fourth switching tube and has a fixed duty ratio, and PWM control is performed on the falling edges of the control signals output to the first switching tube and the third switching tube.

6. The control method of a DC-DC converter according to claim 1 or 4, wherein the alternately controlling the H-bridge according to the set time Ti and the set time Tm includes:

when the time for controlling the H bridge by adopting the third mode reaches Ti, controlling the H bridge by adopting the fourth mode until the time for controlling the H bridge by adopting the fourth mode reaches Tm; or

And when the time for controlling the H bridge by adopting the fourth mode reaches Tm, controlling the H bridge by adopting the third mode until the time for controlling the H bridge by adopting the third mode reaches Ti.

7. The control method of a DC-DC converter according to any one of claims 1 to 2 and 4, wherein a set time Tx for controlling the H-bridge in the first manner is equal to a set time Ty for controlling the H-bridge in the second manner, and a set time Ti for controlling the H-bridge in the third manner is equal to a set time Tm for controlling the H-bridge in the fourth manner.

8. A DC-DC converter, comprising:

the bridge comprises an H bridge and a bridge body, wherein the H bridge comprises a first switching tube, a second switching tube, a third switching tube and a fourth switching tube, the first switching tube and the second switching tube form a first bridge arm, and the third switching tube and the fourth switching tube form a second bridge arm;

a control module, configured to obtain a control mode of the DC-DC converter during the last operation when the DC-DC converter operates, and select a control mode of the DC-DC converter during the last operation according to the control mode of the DC-DC converter during the last operation, where the control mode of the DC-DC converter during the last operation is different from the control mode of the DC-DC converter during the current operation, and the control mode of the DC-DC converter includes a phase shift modulation control mode and a lower tube modulation control mode, where,

when the control mode during the work is selected to be the phase shift modulation control mode, the control module acquires a setting time Tx for controlling the H bridge in a first mode and a setting time Ty for controlling the H bridge in a second mode, and alternately controls the H bridge according to the setting time Tx and the setting time Ty to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, wherein when the H bridge is controlled in the first mode, the first bridge arm is used as a leading bridge arm, and the second bridge arm is used as a lagging bridge arm; when the H bridge is controlled in the second mode, the second bridge arm is used as an advanced bridge arm, and the first bridge arm is used as a delayed bridge arm;

when the control mode during the current work is selected to be the control mode of the lower tube modulation, the control module acquires total time TC for controlling the H bridge in a third mode and total time TD for controlling the H bridge in a fourth mode, acquires set time Ti for controlling the H bridge in the third mode and set time Tm for controlling the H bridge in the fourth mode in each work cycle of the DC-DC converter in the work process of adopting the control mode of the lower tube modulation, selects a mode for controlling the H bridge when the DC-DC converter is started by judging the relation between the total time TC and the total time TD, alternately controls the H bridge according to the set time Ti and the set time Tm to perform temperature equalization control on the first switch tube, the second switch tube, the third switch tube and the fourth switch tube, when the H bridge is controlled in the third mode, the first switching tube and the third switching tube are used as upper tubes, the second switching tube and the fourth switching tube are used as lower tubes, and the first switching tube to the fourth switching tube are controlled in a lower tube modulation control mode; and when the H bridge is controlled in the fourth mode, the first switching tube and the third switching tube are used as a lower tube, the second switching tube and the fourth switching tube are used as an upper tube, and the first switching tube to the fourth switching tube are controlled in a control mode of lower tube modulation.

9. The DC-DC converter according to claim 8, wherein the control module alternately controls the H-bridge according to the set time Tx and the set time Ty, wherein,

when the time for controlling the H bridge in the first mode reaches Tx, the control module controls the H bridge in the second mode until the time for controlling the H bridge in the second mode reaches Ty; or

When the time for controlling the H bridge in the second mode reaches Ty, the control module controls the H bridge in the first mode until the time for controlling the H bridge in the first mode reaches Tx.

10. The DC-DC converter according to claim 8 or 9, wherein,

when the H bridge is controlled in the first mode, the control signal output to the first switching tube by the control module is complementary with the control signal output to the second switching tube, and the control signal output to the third switching tube is complementary with the control signal output to the fourth switching tube, and the first switching tube is turned on by a phase angle before the fourth switching tube, and the second switching tube is turned on by a phase angle before the third switching tube;

when the H bridge is controlled in the second mode, the control signal output to the first switch tube by the control module is complementary to the control signal output to the second switch tube, and the control signal output to the third switch tube is complementary to the control signal output to the fourth switch tube, and the fourth switch tube is switched on by advancing the first switch tube by a phase angle, and the third switch tube is switched on by advancing the second switch tube by a phase angle.

11. The DC-DC converter of claim 8, wherein the control module selects a manner of controlling the H-bridge at startup of the DC-DC converter based on a relationship between the total time TC and the total time TD, wherein,

when the total time TC is greater than the total time TD, the control module selects the fourth mode to control the H bridge when the DC-DC converter is started until the total time TC is equal to the total time TD;

when the total time TC is smaller than the total time TD, the control module selects the third mode to control the H bridge when the DC-DC converter is started until the total time TC is equal to the total time TD;

when the total time TC is equal to the total time TD, the control module selects the third mode or the fourth mode to alternately control the H-bridge according to Ti and Tm when the DC-DC converter is started.

12. The DC-DC converter according to claim 8 or 11, wherein,

when the H bridge is controlled in the third mode, the control signal output to the first switching tube by the control module is complementary with the control signal output to the third switching tube and has a fixed duty ratio, and the falling edges of the control signals output to the second switching tube and the fourth switching tube are subjected to PWM control;

when the H bridge is controlled in the fourth mode, the control signal output to the second switching tube by the control module is complementary with the control signal output to the fourth switching tube and has a fixed duty ratio, and PWM control is performed on the falling edges of the control signals output to the first switching tube and the third switching tube.

13. The DC-DC converter according to claim 8 or 11, wherein the control module alternately controls the H-bridge according to the set time Ti and the set time Tm, wherein,

when the time for controlling the H bridge by adopting the third mode reaches Ti, the control module controls the H bridge by adopting the fourth mode until the time for controlling the H bridge by adopting the fourth mode reaches Tm; or

And when the time for controlling the H bridge by adopting the fourth mode reaches Tm, the control module controls the H bridge by adopting the third mode until the time for controlling the H bridge by adopting the third mode reaches Ti.

14. The DC-DC converter according to any one of claims 8 to 9 and 11, wherein a set time Tx for controlling the H-bridge in the first manner is equal to a set time Ty for controlling the H-bridge in the second manner, and a set time Ti for controlling the H-bridge in the third manner is equal to a set time Tm for controlling the H-bridge in the fourth manner.

15. An electric vehicle comprising a DC-DC converter according to any one of claims 8 to 14.