CN117792094A - Input-parallel-output-parallel non-isolated converter circulating current suppression circuit and method - Google Patents
Input-parallel-output-parallel non-isolated converter circulating current suppression circuit and method Download PDFInfo
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Abstract
The invention discloses a circulating current suppression circuit and method for a non-isolated converter with input connected in parallel and output connected in parallel. The invention also discloses a circulating current inhibition method of the non-isolated converter, which comprises the following steps: sampling the positive output current of the buck converter module, feeding back the difference between the current equalizing error and the positive output current to the controller, superposing the compensation quantity of the output voltage reference value and the output voltage reference value, and obtaining duty ratio signals of a main switching tube and a negative MOS tube in the buck converter module through voltage-current double closed-loop control; and carrying out pulse width modulation on the two duty ratio signals, and outputting driving signals of the main switching tube, the negative MOS tube and the follow current switching tube. The method of the invention can block circulation current to the greatest extent in the switching period, and can not influence normal operation of the circuit, and the circulating current inhibition effect is good.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a circulating current suppression circuit of a non-isolated converter with parallel input and parallel output, and a circulating current suppression method of the non-isolated converter with parallel input and parallel output.
Background
The traditional alternating current UPS data center power supply architecture has the defects of low power supply efficiency, large output current harmonic wave and the like, so that the 240V high-voltage direct current power supply technology is cited to a data center power supply scene, and in a step-down DC/DC conversion link in a 240V high-voltage direct current power supply system, because the power of a single converter is limited, the converters are generally combined by adopting an Input Parallel Output (IPOP) topology, the topology can provide low-voltage and high-current output, and all modules are mutually independent and have high reliability. To further increase the efficiency and power density of the system, each module in parallel typically employs a non-isolated Power Electronic Transformer (PET) that does not include a high frequency transformer.
In an actual 240V dc-dc power supply system, there are numerous voltage step-down modules, and there are large differences in the lengths of cables connected to loads from different modules. And because the non-isolated high-frequency transformers do not carry out voltage isolation between the input side and the output side of each module, the positive electrode circuits of different modules are directly connected in parallel, and the negative electrode circuits are directly connected in parallel, the current born on the branch circuit with smaller equivalent resistance of the circuits is larger, so that complex circulating current exists in the system. When the current difference value born by the anode and the cathode in one module exceeds the differential protection limit value of the relay protection device of the module, the relay protection device is triggered to act, and the reliability of power supply is affected. In addition, due to the difference of equivalent resistances of equivalent circuits of all the modules, the problem that part of the modules bear excessive power, so that the modules are over-heated and even damaged is caused, and therefore current sharing control among the modules is needed in the IPOP topology.
Chinese patent (application number: 201811140188.4, publication number: CN109347325A, application day: 2018-09-28) discloses a double-switching-tube Buck converter topology capable of inhibiting circulating current, wherein a switching tube is added to the negative electrode of a Buck circuit, the sampling result of the current of the positive electrode and the negative electrode is fed back to a differential mode controller, and the turn-off time of the switching tube of the negative electrode is controlled, so that circulation current is blocked. The circulating current suppression strategy needs to sample the positive and negative current, and the conventional Buck circuit only needs one current sampling chip, so the control strategy increases the cost of current sampling. In addition, the control of the circulating current in the scheme depends on a complex circulating current controller, and the control difficulty is increased.
The research on the current sharing problem of the modules in the parallel system mainly comprises a voltage reduction method and an active current sharing method, and the modules do not need to be communicated with each other when the voltage reduction method is adopted for carrying out the current sharing of the modules, but the problems of voltage deviation between load voltage and a voltage reference value and lower precision exist. The active current sharing method needs to sample the output current of each module and input the current value to the centralized controller for current sharing operation, but the active current sharing method needs to be realized by means of communication.
Disclosure of Invention
The invention aims to provide a circulating current suppression circuit of a non-isolated converter with parallel input and parallel output, which can reduce circulating current caused by equivalent resistance difference of parallel system lines.
It is another object of the present invention to provide a method for circulating current suppression in a non-isolated converter with parallel input and parallel output.
The invention adopts the technical proposal that the circulating current suppression circuit of the non-isolated converter with parallel input and parallel output comprises an input direct-current voltageLoad resistance->And N parallel buck converter modules, each of which is respectively associated with the input DC voltage +.>Load resistance->And (5) connection.
Each buck converter module comprises an input side positive line equivalent resistorInput side negative electrode line equivalent resistance->Input side positive electrode line equivalent resistance +.>One end is connected with the input DC voltage +.>Positive connection of the input side negative line equivalent resistance +.>One end is connected with the input DC voltage +.>Is connected with the negative electrode of the input side positive electrode line equivalent resistance +>The other end is connected with a main switch tube->Drain electrode of main switch tube->The source electrode of the (C) is connected with the positive power inductor->One end, positive pole power inductance->The other end is connected with the equivalent resistance of the positive electrode circuit at the output side>One end of the input side negative electrode line equivalent resistance +.>The other end is connected with a negative MOS tube->Source electrode of MOS tube of negative electrode->Drain electrode of (C) is connected with negative power inductor->One end, negative pole power inductance->The other end is connected with the equivalent resistance of the negative electrode circuit of the output side>One end; output side negative electrode line equivalent resistance->The other end is connected with a load resistor->One end, output side positive electrode line equivalent resistance +.>The other end is connected with a load resistor->And the other end.
Main switch tubeSource electrode and anode power inductor of (2)>Is also connected with a freewheel switch tube>Is connected with the source electrode of the transistor; negative MOS tube->Drain electrode of (d) negative power inductor->Is also connected with a freewheel switch tube>Is connected to the drain of the transistor.
Positive pole power inductorOutput side positive electrode line equivalent resistance +.>Also with the output side filter capacitor->Is connected with the positive electrode of the battery; negative pole power inductance->Output side negative electrode line equivalent resistance->Also with the output side filter capacitor->Is connected to the negative electrode of the battery.
The invention adopts another technical scheme that the method for inhibiting the circulating current of the non-isolated converter with parallel input and parallel output is implemented according to the following steps:
step 1, sampling the positive output current of each buck converter module in a circulating current suppression circuit, carrying out average current sharing control, feeding back the difference between the current sharing error and the positive output current of each buck converter module to a PI controller, and obtaining the compensation quantity of the output voltage reference value of each buck converter module；
Step 2, compensating the output voltage reference valueMeasuring amountAnd output voltage reference->Superposing to obtain the output voltage reference value ++of each buck converter module after compensation>The main switching tube +/in each buck converter module is obtained through the voltage and current double closed loop control>Duty ratio signal and negative MOS tube->Duty cycle signal of (a);
step 3, pulse width modulation is carried out on the two duty ratio signals through a modulator, and a main switching tube is outputNegative electrode MOS tube->Freewheel switch tube->Is provided.
In step 2, the negative MOS tubeDuty cycle signal +.>Is +_ connected with the main switch tube>Duty cycle signal +.>Equal; the formula is shown as follows;
；
wherein,is the proportionality coefficient of the current inner loop, +.>Is the integral coefficient of the inner loop of the current, +.>Is the proportionality coefficient of the current outer loop, +.>Is the integral coefficient of the inner loop of the current,sfor integration link, ++>For the voltage on the output side filter capacitor,is the current on the positive power inductor of the buck converter module.
In step 3, the specific modulation process is: main switch tubeNegative electrode MOS tube->The same triangular carrier wave is adopted to control the main switch tube +.>Negative electrode MOS tube->PWM driving signal +.>And->Keep synchronous, keep the sameSwitching on and off; freewheel switch tube>Is +_ connected with the main switch tube>Is complementary to the drive signal of (a).
The beneficial effects of the invention are as follows:
1. according to the circulating current suppression method, the circulating current is eliminated by utilizing different switching modes through synchronous control of the negative electrode switching tube and the positive electrode switching tube, the positive electrode current and the negative electrode current do not need to be sampled at the same time, and the sampling cost is reduced;
2. according to the circulating current inhibition method, the negative electrode switch tube and the positive electrode switch tube adopt the same control signals, a complex circulating current controller is not required to be designed, and circulation of circulating current can be blocked to the greatest extent;
3. the invention realizes high-precision current sharing among the buck converter modules by an average current sharing method, avoids excessive heating of part of the modules, and can improve the power supply reliability of the system.
Drawings
FIG. 1 shows a main switching tube of a module 1 for circulating current flowing from the module 1 to the module 2A flow path diagram at the conduction stage;
FIG. 2 shows a main switching tube of a module 1 for circulating current flowing from the module 1 to the module 2A flow path diagram at the off-phase;
FIG. 3 shows the main switching tube of the module 2 for circulating current flowing from the module 2 to the module 1A flow path diagram at the conduction stage;
FIG. 4 shows the main switching tube of the module 2 for circulating current flowing from the module 2 to the module 1A flow path diagram at the off-phase;
FIG. 5 is a circulating currentDifference from the parasitic resistance of the line->A relationship graph;
FIG. 6 is a block diagram of a non-isolated converter circulating current suppression circuit with input parallel output in parallel according to the present invention;
FIG. 7 is a block diagram of a buck converter module in the input-parallel output-parallel non-isolated converter circulating current suppression circuit of the present invention;
FIG. 8 is a control diagram of the method for suppressing circulating current of the non-isolated converter with parallel input and parallel output of the present invention;
FIG. 9 shows a main switching tube in the circulating current suppressing circuit of the non-isolated converter of the present inventionNegative electrode MOS tube->Freewheel switch tube->A PWM modulation method flow chart of (a);
fig. 10 is a diagram of an operating mode in which the positive and negative switches Guan Jun of the buck converter module 1 and the buck converter module 2 are simultaneously turned on after the suppression method of the present invention is adopted;
FIG. 11 is a diagram of an operating mode in which the positive and negative switching tubes of the buck converter module 1 are turned off simultaneously and the positive and negative switching tubes of the buck converter module 2 are turned on simultaneously after the suppression method of the present invention is adopted;
FIG. 12 is a diagram of an operating mode in which the positive and negative switching tubes of the buck converter module 1 are simultaneously turned on and the positive and negative switching tubes of the buck converter module 2 are simultaneously turned off after the suppression method of the present invention is adopted;
fig. 13 is a diagram of an operating mode in which the positive and negative switches Guan Jun of the buck converter module 1 and the buck converter module 2 are turned off simultaneously after the suppression method of the present invention is adopted;
FIG. 14 is a graph of current waveforms of positive and negative lines on the output side of each buck converter module after closed-loop control of the voltage is employed in the IPOP synchronous buck circuit;
FIG. 15 is a graph of positive and negative line current waveforms at the output side of each buck converter module after the suppression method of the present invention is employed in an IPOP synchronous buck circuit;
FIG. 16 is a waveform diagram of the circulating current within each buck converter module after voltage closed loop control is employed in the IPOP synchronous buck circuit;
FIG. 17 is a graph of the internal circulating current of each buck converter module after the suppression method of the present invention is employed in an IPOP synchronous buck circuit;
FIG. 18 is a graph of current sharing errors of each buck converter module after voltage closed loop control is employed in an IPOP synchronous buck circuit;
FIG. 19 is a graph of current sharing errors of each buck converter module after the suppression method of the present invention is employed in an IPOP synchronous buck circuit;
fig. 20 is a graph of the circulating current waveforms within each buck converter module using a conventional circulating current control strategy.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
Example 1
The topology adopted by the invention is an IPOP synchronous voltage reduction circuit, taking two IPOP synchronous voltage reduction circuits as an example, a schematic diagram of a circulating current circulation path is given based on the on/off state of a main switching tube in the two circuits, and in figures 1-4,、/>for the main switching tubes of module 1 and module 2, < >>、/>For module 1 and mouldFreewheel MOS tube of block 2->、/>For the power inductances of module 1 and module 2, < >>、/>Filter capacitance for the output side of module 1 and module 2, < >>、/>Equivalent resistance of positive and negative circuit of input side of module 1 respectively,>、/>the equivalent resistances of the positive and negative circuit on the input side of the module 2,、/>equivalent resistance of positive and negative circuit of output side of module 1, respectively, ">、/>Equivalent resistance of positive and negative circuit on output side of module 2, respectively,>for the voltage on the filter capacitor on the output side of module 1, is->For the voltage on the filter capacitor at the output side of module 2, is->Output current for positive line of module 1, +.>Output current for the positive line of module 2, +.>Output current for the negative line of module 1, +.>Output current for the negative line of module 2, +.>For load current +.>Is the load resistance.
Circulating current inside the module 1Can be defined as the difference between the currents on the positive and negative lines as shown in equation (1):
（1）；
according toS 11 AndS 21 the conducting and closing states of the two main switching tubes obtain four circulating current flowing paths. When the main switching tube of the module 1S 11 When conducting, if there is circulation current flowing from the module 1 to the module 2, the circulation path is as shown in FIG. 1, when the main switch tubeS 11 When the power-off is performed, the circulation path of the circulation current is shown in fig. 2, and the circulation current leads to the relationship between the currents on the positive and negative output lines of the two modules as follows，/>. If there is a circulating current flowing from module 2 to module 1, the main switching tube of module 2S 21 When the switch is turned on, the flow path is as shown in FIG. 3, and when the main switch tubeS 21 When the switch is turned off, the circulation path of the circulation current is shown in fig. 4, and the circulation current leads to the relation of the respective output currents of the two modules to be +.>，/>. When the difference value of the current of the positive electrode line and the current of the negative electrode line exceed the limit value of the differential protection of the relay protection device, the protection is started, the Buck module is stopped, and the reliability of power supply is further affected.
Neglecting the influence of the equivalent resistance of the input side line, if the two synchronous voltage reduction circuits are controlled by adopting a voltage closed loop and the output voltage reference values are the same, the formula (2) can be deduced according to kirchhoff's voltage law and the relation of the output voltages of all the modules:
（2）；
wherein,，/>the output voltages of the two modules, respectively, are obtained according to equation (2), the circulating current inside each module in the system +.>Can be expressed as the difference between the positive and negative output currents as shown in formula (3):
（3）；
the expression of the circulating current can be generalized to multiple modesA scene with parallel modules can be usedTo measure the line equivalent resistance difference inside the module, < >>The expression of (2) is shown as the expression (4):
（4）；
it can be seen that the circulating current and the equivalent resistance of the circuit are differentLoad current->Proportional byThe expression of (2) shows that the circulating current is not only affected by the difference of the equivalent resistances of the internal circuits of the modules, but also caused by the difference of the equivalent resistances of the circuits of other modules>The denominator of the front and back terms in the expression differs, resulting in a circulating current inside the module. FIG. 5 shows the circulating current +.>The relation graph of the difference between the circulating current and the equivalent resistance of the line further verifies that the circulating current is in direct proportion to the difference between the equivalent resistance of the line and is consistent with the expression of the circulating current in the formula (3). Therefore, under the given condition of load current, the circuit equivalent resistance difference can have a great influence on the circulating current, but because the actual multi-module parallel connection scene is difficult to ensure that the circuit equivalent resistance or the circuit length are strictly equal, the circulating current problem is difficult to avoid in the traditional IPOP non-isolated DC/DC converter structure.
Example 2
The input parallel output parallel non-isolated converter circulating current suppression circuit of the invention, as shown in figure 6, comprises an input DC voltageLoad resistance->And N parallel buck converter modules, each of which is respectively associated with the input DC voltage +.>Load resistance->Connecting;
as shown in fig. 7, each buck converter module includes an input side positive line equivalent resistanceInput side negative electrode line equivalent resistance->Input side positive electrode line equivalent resistance +.>One end is connected with the input DC voltage +.>Positive connection of the input side negative line equivalent resistance +.>One end is connected with the input DC voltage +.>Is connected with the negative electrode of the input side positive electrode circuit equivalent resistorThe other end is connected with a main switch tube->Drain electrode of main switch tube->The source electrode of the (C) is connected with the positive power inductor->One end, positive pole power inductance->The other end is connected with the equivalent resistance of the positive electrode circuit at the output side>One end of the input side negative electrode line equivalent resistance +.>The other end is connected with a negative MOS tube->Source electrode of MOS tube of negative electrode->Drain electrode of (C) is connected with negative power inductor->One end, negative pole power inductance->The other end is connected with the equivalent resistance of the negative electrode circuit of the output side>One end; output side negative electrode line equivalent resistance->The other end is connected with a load resistor->One end, output side positive electrode line equivalent resistance +.>The other end is connected with a load resistor->The other end;
main switch tubeSource electrode and anode power inductor of (2)>Is also connected with a freewheel switch tube>Is connected with the source electrode of the transistor; negative MOS tube->Drain electrode of (d) negative power inductor->Is also connected with a freewheel switch tube>Is connected with the drain electrode of the transistor;
positive pole power inductorOutput side positive electrode line equivalent resistance +.>Also with the output side filter capacitor->Is connected with the positive electrode of the battery; negative pole power inductance->Output side negative electrode line equivalent resistance->Also with the output side filter capacitor->Is connected with the negative electrode of the battery;
wherein,k=1, 2 … N, N being a positive integer;
defining variables in the circuit, inputting DC voltageOutput side filter capacitor->Voltage on->The positive electrode line outputs current +.>The negative electrode line outputs current->. Setting the duty ratio of the switching tube of each buck converter module to be +.>The relationship between the input voltage and the output voltage is shown in the formula (5):
（5）；
the circulating current suppression circuit of the invention is mainly different from the traditional synchronous voltage reduction circuit in that a negative MOS tube for suppressing the circulating current is added at the negative electrode of the synchronous voltage reduction circuitSecondly, a power inductor is added at the cathode of the synchronous voltage reduction circuit>. The circulating current inhibition method provided by the invention mainly depends on periodically controlling the negative electrode MOS tube +.>Is turned off to block the circulating current at IPOPThe path flowing in the step-down circuit realizes the suppression of the circulating current. The main function of the negative power inductor is freewheeling and a negative MOS tube +.>The positive and negative current are forced to be equal when the switch is turned off, when +.>When the power inductor is conducted, the current of the positive electrode and the negative electrode flows through the power inductor, so that the current of the positive electrode and the negative electrode cannot be suddenly changed, and the direct current components of the current of the positive electrode and the negative electrode still keep equal. When device selection and loss calculation are carried out, the MOS tube of the negative electrode is +.>Is +_ connected with the main switch tube>Because of the structural symmetry, the voltage and current stresses born are also equal, so that the same type of switching tube device can be selected. The power inductances of the positive electrode and the negative electrode are also symmetrical in structure, the two inductances are jointly used as the power inductances of the synchronous voltage reduction circuit, and the value of the power inductances can be calculated according to the formula (6):
（6）；
wherein,for inputting DC voltage +.>For the output-side direct-current voltage,Dfor synchronizing the on-duty of the buck circuit, < >>For the switching period of the switch-on and switch-off period,rfor the power inductance current ripple coefficient, +.>To output current.
Example 3
The invention relates to a circulating current inhibition method of a non-isolated converter with parallel input and parallel output, which is shown in fig. 8, and is specifically implemented according to the following steps:
step 1, sampling the positive output current of each buck converter module in the circulating current suppression circuit, carrying out average current sharing control through averaging operation and PI operation, and carrying out the current sharing error as shown in a formula (7)And the positive output current of each buck converter module +.>Is fed back to the PI controller to obtain the compensation amount of the output voltage reference value of each buck converter module>The expression is shown as a formula (8):
（7）；
（8）；
wherein,for the average value of each buck converter module, < > for each buck converter module>For the proportionality coefficient of the current sharing control loop,the integral coefficient of the current sharing control loop;
step 2, compensating the output voltage reference valueAnd output voltage reference->Superposing to obtain the output voltage reference value ++of each buck converter module after compensation>As shown in the formula (9), the main switching tube in each buck converter module is obtained through voltage-current double closed-loop control>Duty cycle signal +.>. Because the positive and negative electrode switching tubes are completely synchronous, the negative electrode MOS tube is +.>Duty cycle signal +.>Is +_ connected with the main switch tube>Duty cycle signal +.>Equal; as shown in formula (10);
（9）；
（10）；
wherein,is the proportionality coefficient of the current inner loop, +.>Is the integral coefficient of the inner loop of the current, +.>Is the proportionality coefficient of the current outer loop, +.>Is the integral coefficient of the inner loop of the current, +.>For the voltage on the output-side filter capacitor, +.>Current on the positive power inductor for each buck converter module;sis an integral link;
step 3, duty ratio signalAnd->Pulse width modulation is performed through a modulator, and a main switching tube is output>Negative electrode MOS tube->Freewheel switch tube->Is provided.
The specific modulation process is shown in FIG. 9, the main switch tubeNegative electrode MOS tube->The modulated waves of the (a) are equal, the same triangular carrier wave is adopted to control the main switching tube +.>Negative electrode MOS tube->PWM driving signal +.>And->And keeping synchronous and same on-off. Freewheel switch tube>Is +_ connected with the main switch tube>Is complementary to the drive signal of (a).
MOS tube with main effect on negative electrode for inhibiting circulating currentIs +_ connected with the main switch tube>And the synchronous turn-off stage, in which the positive and negative circuits are disconnected from the input side at the same time, so that the circulation current flow path of the module to other modules cannot be formed, positive and negative current flows through the freewheeling switch tube, and the positive and negative current are forced to be equal. When the negative electrode MOS tube->Is +_ connected with the main switch tube>When the current source is conducted, the direct current components of the positive and negative current cannot be suddenly changed due to the follow current action of the positive and negative inductors, and the direct current components still remain equal. Therefore, the circulating current control method is equivalent to correcting the current of the positive electrode and the negative electrode in each switching period in the follow current stage, and the inductance of the positive electrode and the negative electrode is +.>And->The follow current effect of the power supply can realize the equality of the circulating current in the whole period. And circulating current control methodThe method turns off the negative electrode switch tube only at the follow current step, and the circulation of the circulating current is blocked to the greatest extent on the premise of not influencing the normal operation of the circuit.
Fig. 10-13 show four modes of operation of the synchronous buck circuits of two IPOPs using the suppression method of the present invention, where 0 is used to indicate that the positive and negative switching tubes are turned off simultaneously, and 1 is used to indicate that the positive and negative switching tubes are turned on simultaneously. The dashed lines show the current flow paths inside the two buck converter modules. Because the positive and negative electrode switching tubes are synchronously turned on and off, the two switching tubes are turned off simultaneously by 0, and the two switching tubes are turned on simultaneously by 1. In fig. 11, 12 and 13, the circuit of the buck converter module 1 is completely cut off from the circuit of the buck converter module 2, the internal positive and negative currents of the two buck converter modules are equal, in fig. 10, due to the positive and negative inductancesAnd->The positive and negative current can not be suddenly changed and still remain equal, namely the circulating current is thoroughly eliminated.
In order to verify the difference between the circulating current inhibition method provided by the invention and the circulating current control method in the prior published patent (application number: 201811140188.4, publication number: CN109347325A, publication date: 2019-02-15), the two methods are adopted in a simulation system to respectively compare the circulating current inhibition effects;
table 1 shows the electrical parameters of the simulated PET module, the power inductance in the buck circuit is the sum of the positive and negative power inductances in the PET module, i.e. 200uH, and the other parameters are consistent with those in Table 1. Table 2 shows the equivalent resistance parameters of the input-side output-side circuit in the simulation. Changing the value of the line equivalent resistance in the simulation simulates the situation that the actual line equivalent resistance length is different, and is used for verifying the effect of the proposed topology on suppressing the circulating current.
Table 1 simulation module electrical parameters
TABLE 2 simulation parameters of equivalent resistances of lines
Fig. 14 and 15 are graphs of the output current of the positive and negative poles of each buck converter module after voltage closed loop control and the suppression method of the present invention are respectively employed in the topologies of the parameters of table 1 and table 2. Fig. 14 shows the output current of each buck converter module after the voltage closed-loop control, and the difference between the positive and negative currents is larger when there is a difference in the equivalent resistances of the lines, which indicates that the phenomenon of circulating current in the buck converter module is obvious. FIG. 15 shows the output current of each buck converter module after the suppression method of the present invention, it can be seen that the waveforms of the positive and negative currents of the buck converter modules are substantially coincident after the circulating current and the current sharing control strategy are adopted, which indicates that the internal circulating current is eliminated; and the output current of each buck converter module is 125A after being stabilized, which proves that the current sharing effect of the current sharing strategy is good.
Fig. 16 and 17 are waveforms of internal circulating currents of each buck converter module after voltage closed loop control and the suppression method of the present invention are respectively employed in the topologies of the parameters of table 1 and table 2. FIG. 16 shows the circulating currents of each module after the closed-loop control of the voltage, and the internal circulating currents of the module can reach 25A under the condition of the equivalent resistance difference of the lines in Table 2. Fig. 17 shows the circulating currents of the buck converter modules after the suppression method of the present invention is adopted, and the circulating currents in the buck converter modules can be limited to within 0.1A in 0.2S, which illustrates that the circulating current suppression method is effective in suppressing the circulating currents due to the line equivalent resistance difference.
Fig. 18 and 19 show the current sharing errors between the buck converter modules after the voltage closed loop control and the suppression method of the present invention are used in the topologies of the parameters of table 1 and table 2, respectively. Fig. 17 shows the current sharing error between each module after the voltage closed-loop control, and the current sharing error of each module can reach 15A under the condition of the equivalent resistance difference of the circuit of table 2. By adopting the current sharing strategy of the invention, the current sharing error among the modules is limited to be within 2A, and the effectiveness of the proposed method in the current sharing aspect is verified.
FIG. 20 is the circulating current after the circulating current control strategy of the prior published patent (application number: 201811140188.4, publication number: CN109347325A, publication date: 2019-02-15) was employed in the topologies of Table 1 and Table 2 parameters. The circulating current inside each module was reduced to 3A under the line equivalent resistance difference conditions of table 2. Fig. 17 shows the circulating currents inside each buck converter module after the suppression method of the present invention, the amplitude of the circulating currents is reduced to within 0.1A. Simulation results show that the circulating current inhibition method provided by the invention has a good effect under the same circuit condition.
Claims (7)
1. The input parallel output parallel non-isolated converter circulating current suppression circuit is characterized by comprising an input direct-current voltageLoad resistance->And N parallel buck converter modules, each of which is respectively associated with the input DC voltage +.>Load resistance->And (5) connection.
2. The input parallel output parallel non-isolated converter circulating current suppression circuit of claim 1, wherein each of said buck converter modules includes an input side positive line equivalent resistanceInput side negative electrode line equivalent resistance->The input side positive electrode line equivalent resistance +.>One end is connected with the input DC voltage +.>The positive connection of the input side negative line equivalent resistance +.>One end is connected with the input DC voltage +.>Is connected with the negative electrode of the input side positive electrode line equivalent resistance +>The other end is connected with a main switch tube->Drain electrode of said main switching tube->The source electrode of the (C) is connected with the positive power inductor->One end of the positive power inductor +.>The other end is connected with the equivalent resistance of the positive electrode circuit at the output side>One end of the input side negative electrode line equivalent resistance +.>The other end is connected withConnect negative pole MOS pipe->The negative MOS tube is +.>Drain electrode of (C) is connected with negative power inductor->One end of the negative power inductor>The other end is connected with the equivalent resistance of the negative electrode circuit of the output side>One end; the equivalent resistance of the negative electrode circuit of the output side>The other end is connected with a load resistor->One end of the output side positive electrode line equivalent resistance +>The other end is connected with a load resistor->And the other end.
3. The input-parallel output-parallel non-isolated converter circulating current suppression circuit of claim 2, wherein the main switching tubeSource electrode and anode power inductor of (2)>Is also connected with a freewheel switch tube>Is connected with the source electrode of the transistor; the negative electrode MOS tube->Drain electrode of (d) negative power inductor->Is also connected with a freewheel switch tube>Is connected to the drain of the transistor.
4. The input-parallel output-parallel non-isolated converter circulating current suppression circuit of claim 3, wherein the positive power inductorOutput side positive electrode line equivalent resistance +.>Also with the output side filter capacitor->Is connected with the positive electrode of the battery; the negative power inductor->Output side negative electrode line equivalent resistance->Also with the output side filter capacitor->Is connected to the negative electrode of the battery.
5. The method for suppressing the circulating current of the non-isolated converter with parallel input and parallel output is characterized by comprising the following steps of:
step 1, sampling the positive output current of each buck converter module in a circulating current suppression circuit, carrying out average current sharing control, feeding back the difference between the current sharing error and the positive output current of each buck converter module to a PI controller, and obtaining the compensation quantity of the output voltage reference value of each buck converter module；
Step 2, compensating the output voltage reference valueAnd output voltage reference->Superposing to obtain the output voltage reference value ++of each buck converter module after compensation>The main switching tube +/in each buck converter module is obtained through the voltage and current double closed loop control>Duty ratio signal and negative MOS tube->Duty cycle signal of (a);
step 3, pulse width modulation is carried out on the two duty ratio signals through a modulator, and a main switching tube is outputNegative electrode MOS tube->Freewheel switch tube->Is provided.
6. The method for circulating current inhibition of input-parallel output-parallel non-isolated converter according to claim 5, wherein in step 2, a negative MOS tube is usedDuty cycle signal +.>Is +_ connected with the main switch tube>Duty cycle signal +.>Equal; the formula is shown as follows;
；
wherein,is the proportionality coefficient of the current inner loop, +.>Is the integral coefficient of the inner loop of the current, +.>Is the proportionality coefficient of the voltage outer ring, +.>Is the integral coefficient of the outer loop of the voltage,sfor integration link, ++>For the voltage on the output-side filter capacitor, +.>Is the current on the positive power inductor of the buck converter module.
7. The method for suppressing circulating current of non-isolated converter with parallel input and parallel output as recited in claim 5, wherein in said step 3, the specific modulation process is as follows: main switch tubeNegative electrode MOS tube->The same triangular carrier wave is adopted to control the main switch tube +.>Negative electrode MOS tube->PWM driving signal +.>And->Maintaining synchronization and keeping the same on and off; freewheel switch tube>Is +_ connected with the main switch tube>Is complementary to the drive signal of (a).
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