CN115912931A - Bidirectional buck-boost four-quadrant partial power converter and control method thereof - Google Patents
Bidirectional buck-boost four-quadrant partial power converter and control method thereof Download PDFInfo
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Abstract
The invention discloses a bidirectional buck-boost four-quadrant partial power converter and a control method thereof, wherein the bidirectional buck-boost four-quadrant partial power converter comprises a bipolar bidirectional DC/DC, a first positive terminal and a second positive terminal of the bidirectional DC/DC are respectively connected with the ground through a direct current bus, a first negative terminal of the bidirectional DC/DC is connected with the ground, and a second negative terminal of the bidirectional DC/DC is connected with the ground after passing through an energy storage battery; the voltage of the direct current bus is equal to the voltage of the energy storage battery plus the voltage of the bidirectional DC/DC second positive pole; when the voltage of the direct current bus is greater than the voltage of the energy storage battery, the voltage of the second positive pole of the bidirectional DC/DC is positive; and when the voltage of the direct current bus is less than the voltage of the energy storage battery, the voltage of the second positive pole terminal of the bidirectional DC/DC is negative voltage. The bidirectional DC/DC only processes a small part of the total power of the system, so that the system efficiency and the power density of the partial power converter are greatly improved.
Description
Technical Field
The invention belongs to the technical field of direct-current battery energy storage converters, and particularly relates to a bidirectional buck-boost four-quadrant partial power converter and a control method thereof.
Background
Renewable energy power generation has intermittence and instability, and a traditional alternating current system is hard to be competent, so that a direct current distribution and utilization system is vigorously developed, and meanwhile, a large number of battery energy storage devices are connected. The direct-current battery energy storage converter (bidirectional DC/DC) is used as a power electronic interface for connecting the battery and the direct-current bus, and plays important roles in adjusting voltage, controlling charging and discharging of the battery and realizing bidirectional transmission of electric energy.
The existing direct-current battery energy storage converter generally adopts a full-power structure, namely, all electric energy transmitted between a battery and a direct-current bus flows through the converter; few direct-current battery energy storage converters adopt a partial power structure, namely, the transmission of the whole power of the system can be realized by processing a part of the total power of the system through the bidirectional DC/DC in the converter.
For the traditional full-power structure, as the power grade of the battery energy storage device is improved, the power grade of a full-power direct-current battery energy storage converter serving as an electric energy conversion interface is also improved, so that the size is increased, the cost is improved, the efficiency is reduced, and the heat dissipation design is difficult; for a partial power structure, the partial power structure can overcome the defect of a full-power scheme, but the existing partial power direct-current battery energy storage converter can only realize the work of two quadrants of boosting battery charging, battery discharging and voltage reducing or boosting battery discharging and battery charging and voltage reducing, so that the superior performance of partial power cannot be fully exerted, namely partial power processed by DC/DC in the converter cannot reach the minimum value.
Disclosure of Invention
The invention aims to solve the technical problem that a bidirectional buck-boost four-quadrant partial power converter and a control method thereof are provided for overcoming the defects in the prior art, and the technical problem that partial power processed by bidirectional DC/DC in the partial power converter is larger due to the fact that the partial power direct-current battery energy storage converter can only run in double quadrants, namely battery charging boost, battery discharging buck or battery discharging boost and battery charging buck is solved.
The invention adopts the following technical scheme:
a bidirectional buck-boost four-quadrant partial power converter comprises a bipolar bidirectional DC/DC, wherein a first positive terminal and a second positive terminal of the bidirectional DC/DC are respectively connected with the ground through a direct current bus, a first negative terminal of the bidirectional DC/DC is connected with the ground, and a second negative terminal of the bidirectional DC/DC is connected with the ground after passing through an energy storage battery; the voltage of the direct current bus is equal to the voltage of the energy storage battery plus the voltage of the bidirectional DC/DC second positive pole; when the voltage of the direct current bus is greater than the voltage of the energy storage battery, the voltage of the second positive pole terminal of the bidirectional DC/DC is positive; and when the voltage of the direct current bus is less than the voltage of the energy storage battery, the voltage of the second positive pole terminal of the bidirectional DC/DC is negative voltage.
Specifically, the bidirectional DC/DC includes a front-stage bidirectional unipolar LLC resonant circuit, which is cascaded with a rear-stage bidirectional bipolar H-bridge circuit, and is used for pre-regulating voltage and implementing soft switching; the bidirectional bipolar H-bridge circuit is used for outputting positive voltage or negative voltage, compensating a voltage difference value between the energy storage battery and the direct current bus through secondary voltage regulation, and controlling charging and discharging of the energy storage battery.
Furthermore, the bidirectional unipolar LLC resonant circuit uses fixed frequency control, and the bidirectional bipolar H bridge circuit uses double closed loop PI control of an outer voltage loop and an inner voltage loop and an outer current loop.
Furthermore, the bidirectional unipolar LLC resonant circuit comprises an input filter capacitor C 1 Input filter capacitor C 1 One end of the output filter capacitor is connected with a direct current bus, and the other end of the output filter capacitor is connected with an output filter capacitor C through a primary side inverter circuit, a resonance circuit, an isolation transformer T and a secondary side rectifier circuit in sequence 2 One end of (1), an output filter capacitor C 2 The other end of the second-stage bidirectional bipolar H-bridge circuit is connected with a post-stage bidirectional bipolar H-bridge circuit.
Furthermore, the primary side inverter circuit comprises a switching tube S 1 And a switch tube S 2 And a switch tube S 3 And a switching tube S 4 Switching tube S 1 And a switching tube S 3 The drain electrode of the switch tube is connected with the positive electrode of the direct current bus and the switch tube S 2 And a switching tube S 4 The source electrode of the switch tube is connected with the cathode of the direct current bus and the switch tube S 1 Source electrode of (1) and switching tube S 2 Drain electrodes of the two-way capacitor are sequentially connected with a resonant capacitor C r And a resonant inductor L r The back part is divided into two paths, and one path is connected with the excitation inductance L of the transformer m One end of the switch tube S is connected with the primary side of the isolation transformer T, and the other end is connected with the switch tube S 3 Source electrode of (2) and switching tube S 4 Is connected with the excitation inductance L of the transformer m The other end of the primary winding and the primary side of the isolation transformer T; the secondary rectification circuit comprises a switching tube S 5 Switch tube S 6 Switch tube S 7 And a switching tube S 8 Switching tube S 5 And a switching tube S 7 Is connected with the output filter capacitor C 2 One end of (1), a switching tube S 6 And a switching tube S 8 Source electrode of the capacitor is connected with an output filter capacitor C 2 The other end of (2), a switch tube S 5 And a switching tube S 7 Source stage and switching tube S 6 And a switching tube S 8 Is connected to the secondary side of the isolation transformer T.
Still further, exciting inductance peak current I pk And dead time T dead The relationship is as follows:
resonant inductor L r And a resonance capacitor C r The relationship is as follows:
wherein, C oss Is the junction capacitance of the switching tube, V LLCin For LLC input voltage, f s Is the system switching frequency.
Furthermore, the bidirectional bipolar H-bridge circuit comprises an inverter circuit which is divided into two paths, wherein one path is respectively connected with the anode of the direct current bus and the filter capacitor C through the filter inductor L 3 One end of (1), a second path and a filter capacitor C 3 Are respectively connected with the other ends of the positive electrode of the energy storage battery.
Furthermore, the inverter circuit includes a switch tube S 9 Switch tube S 10 Switch tube S 11 And a switching tube S 12 Switching tube S 9 And a switching tube S 11 The drain electrode of the switching tube S is connected with one end of a preceding-stage bidirectional unipolar LLC resonant circuit 10 And a switching tube S 12 The drain electrode of the switching tube S is connected with the other end of the preceding-stage bidirectional unipolar LLC resonant circuit 9 Source electrode of (1) and switching tube S 10 The drain electrode of the switch tube S is connected with one end of a filter inductor L 11 Source electrode of (1) and switching tube S 12 The drain electrode of the energy storage battery is connected with the anode of the energy storage battery, and the cathode of the energy storage battery is connected with the cathode of the direct current bus in common.
Still further, the inductor current ripple Δ I L The relationship of (a) to (b) is as follows:
filter capacitor C 3 The relationship of (a) to (b) is as follows:
wherein, U Hin For H bridge input voltage, f s Is the system switching frequency.
According to another technical scheme, the control method of the bidirectional buck-boost four-quadrant partial power converter is characterized in that a bidirectional unipolar LLC resonant circuit always works at a resonant point by using a fixed frequency PWM control strategy, and output voltage is adjusted by changing the duty ratio of a switching tube or changing the turn ratio of an isolation transformer T during circuit parameter design;
the bidirectional bipolar H-bridge circuit is controlled by using a voltage and current double closed loop PI, an outer loop is a voltage loop, and an H-bridge filter capacitor C is controlled 3 Voltage tracking the difference between the direct current bus and the battery voltage; the inner ring is a current ring, the current of the H-bridge filter inductor L is controlled to track the charging and discharging current of the battery, and the output value is used as a modulation signal to carry out PWM control on the switch tube.
Compared with the prior art, the invention at least has the following beneficial effects:
according to the bidirectional buck-boost four-quadrant partial power converter, bidirectional DC/DC can output bipolar voltage, so that four-quadrant work is achieved, namely battery charging with battery voltage higher than direct-current bus voltage, battery discharging with battery voltage higher than direct-current bus voltage, battery charging with battery voltage lower than direct-current bus voltage, battery discharging with battery voltage lower than direct-current bus voltage, the ratio of partial power processed by the bidirectional DC/DC in partial power converter to the total power of a system can be remarkably reduced through the four-quadrant work of the converter, the efficiency and the power density are further improved, and battery charging and discharging are effectively controlled; the particular connection of the converters is such that the internal bidirectional DC/DC only handles a small fraction of the total power of the system, i.e. realizes a partial power. The internal bidirectional bipolar DC/DC can change the positive and negative of the output voltage, thereby compensating the voltage difference between the battery and the direct current bus in real time.
Furthermore, in the bidirectional DC/DC inside the converter, the preceding-stage bidirectional unipolar LLC resonant circuit not only meets the bidirectional flow demand of electric energy for charging and discharging batteries, but also solves the problem of low efficiency caused by overlarge voltage regulation ratio between the direct-current bus voltage and the differential voltage of the direct-current bus battery, plays a role in pre-regulating voltage, assists the rear-stage H bridge in accurately regulating voltage, and further improves the efficiency by using a soft switching technology; the rear-stage bidirectional bipolar H-bridge circuit not only meets the requirement of bidirectional flow of electric energy for charging and discharging the battery, but also has the function of compensating the voltage difference between the battery and the direct-current bus in real time, and outputs positive or negative voltage, namely voltage bipolarity, and simultaneously, because the current at the output end of the H-bridge is the same as the charging and discharging current of the battery, the charging and discharging of the battery are directly controlled.
Furthermore, in order to optimize the efficiency, the bidirectional unipolar LLC resonant circuit is controlled by fixed-frequency PWM (pulse-width modulation), so that the circuit always works at the optimal working point, and the optimal efficiency is realized while the soft switching is realized; in order to compensate the voltage difference between the battery and the direct current bus in real time and control the charging and discharging of the battery, the bidirectional bipolar H-bridge circuit uses double closed loop PI control of a voltage outer loop and a current inner loop.
Further, a filter capacitor C 1 The voltage regulation circuit is used for stabilizing voltage fluctuation of a direct current bus, reducing ripples, inputting a relatively stable voltage to the LLC and facilitating LLC voltage regulation; filter capacitor C 2 For stabilizing LLC output voltage fluctuation, reducing ripple, and connecting to H bridgeAnd a relatively stable voltage is input, so that the H-bridge voltage regulation is facilitated.
Furthermore, the front stage of DC/DC in the converter is a bidirectional unipolar LLC resonant circuit, the primary side of an isolation transformer T of the converter is an inverter circuit, and the direct-current voltage of a direct-current bus is inverted into alternating-current voltage so as to be transmitted to the rear stage through a T winding of the isolation transformer; the secondary side of the isolation transformer T is a rectification circuit which rectifies the alternating current voltage of the winding of the isolation transformer into direct current voltage, so that the direct current voltage passes through a filter capacitor C 2 And transmitting to a rear stage H bridge.
Furthermore, to realize zero voltage switching-on of LLC switching tube, excitation inductance peak current I pk Must be in the dead time T dead Junction capacitor C of internal yielding switch tube oss The switch tube which is completely discharged and is turned off simultaneously has the junction capacitance C oss And (6) charging. The LLC operates at the optimum operating point, i.e. the resonant frequency equals the switching frequency, and the resonant inductor-capacitor parameters can be determined.
Furthermore, in order to realize partial power, the H-bridge inverter circuit is divided into two paths, wherein one path is connected with the positive electrode of the direct current bus, so that most of power of the system is directly fed between the battery and the direct current bus; the other path is connected with the anode of the energy storage battery, and the purpose is to realize the bidirectional transmission of the rest small part of the power of the system through the internal DC/DC.
Furthermore, the purpose of the H-bridge inverter circuit is to change the voltage polarity, so that the voltage difference between the battery and the direct current bus is a positive value or a negative value, and the control of the charging and discharging of the battery is realized simultaneously.
Further, a filter inductor L and a filter capacitor C 3 The method is used for stabilizing the fluctuation of the output voltage of the H bridge, reducing ripples and better compensating the voltage difference between the direct current bus and the battery. According to the voltage-current relation of the inductor, an expression of the inductor current ripple can be obtained, when the output voltage of the H bridge is half of the input voltage, the inductor current ripple is maximum, and then the minimum value of the filter inductor L can be solved. Under PWM modulation, the output harmonic is higher harmonic of switching frequency or above, so the minimum value of cut-off frequency is 1/10 of the lowest output harmonic frequency (switching frequency), and the filter capacitor C is obtained 3 Is measured.
In order to optimize system efficiency, a bidirectional unipolar LLC resonant circuit uses a fixed-frequency PWM control strategy, the bidirectional unipolar LLC resonant circuit always works at an optimal working point, namely a resonant point, so that the optimal efficiency of an LLC can be realized, and output voltage adjustment is realized by changing the duty ratio of a switching tube or changing the turn ratio of an isolation transformer T. In order to better track the voltage difference between the battery and the direct current bus and control the charging and discharging of the battery, the bidirectional bipolar H-bridge circuit uses voltage and current double closed loop PI control, an outer ring is a voltage ring, namely, an H-bridge filter capacitor C is controlled 3 Tracking the voltage difference between the direct current bus and the battery by the voltage; the inner loop is a current loop, namely, the current of the H-bridge filter inductor L is controlled to track the charging and discharging current of the battery, and the output value of the inner loop is used as a modulation signal to carry out PWM control on the switching tube.
In summary, the present invention provides an improvement to the existing DC energy storage converter, and provides a bidirectional buck-boost four-quadrant power converter and a control method thereof, on one hand, the DC/DC in the converter only processes a small portion of the total power of the system, so as to effectively improve the power density, efficiency and cost of the converter; on the other hand, the internal bidirectional DC/DC is a bidirectional bipolar topology, four-quadrant work can be achieved, compared with the existing two-quadrant partial power converter, partial power processed by the internal DC/DC of the four-quadrant partial power converter is less, and the performance of the converter can be further improved. In control, four working modes corresponding to four quadrants can be realized, the efficiency is optimized, and the charging and discharging of the battery are effectively controlled.
The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.
Drawings
FIG. 1 is a partial power block diagram used in the present invention;
FIG. 2 is a block diagram of a bi-directional buck-boost four-quadrant power converter system;
FIG. 3 is a topology diagram of a main circuit of a bi-directional buck-boost four-quadrant partial power converter;
fig. 4 is a comparison graph of the ratio of the partial powers processed by the two-quadrant and four-quadrant partial power converters, wherein (a) is a boost mode, (b) is a buck mode, and (c) is a buck-boost mode.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "one side", "one end", "one side", and the like indicate orientations or positional relationships based on those shown in the drawings, merely for convenience of description and simplification of description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore, are not to be construed as limiting the present 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 one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.
In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
It will be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It is also to be understood that the terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in this specification and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
It should be further understood that the term "and/or" as used in this specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items and includes such combinations.
Various structural schematics according to the disclosed embodiments of the invention are shown in the drawings. The figures are not drawn to scale, wherein certain details are exaggerated and some details may be omitted for clarity of presentation. The shapes of various regions, layers and their relative sizes and positional relationships shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, according to actual needs.
Referring to fig. 1, the present invention provides a bidirectional buck-boost four-quadrant partial power converter, which includes a bidirectional DC/DC, a DC bus and an energy storage battery, wherein two positive terminals of the bidirectional DC/DC are respectively connected to ground via the DC bus, one negative terminal of the bidirectional DC/DC is connected to ground, and the other negative terminal of the bidirectional DC/DC is connected to ground via the energy storage battery.
In the invention, a partial power structure as shown in fig. 1 is selected, and besides the advantage of transmitting the whole system power can be realized by only processing a part of the total system power by the bidirectional DC/DC in the converter, the advantage is that the voltage of the direct current bus with small fluctuation relative to the battery voltage is clamped to the voltage of one end of the bidirectional DC/DC in the partial power converter, and the design of the control strategy is simpler.
The four-quadrant operation of the bidirectional buck-boost four-quadrant partial power converter requires that the internal bidirectional DC/DC must be bipolar, i.e., a positive voltage is input and then a positive or negative voltage is output. DC bus voltage V in FIG. 1 dc Equal to the battery voltage V bat Plus internal bidirectional DC/DC terminal voltage V 2 (ii) a When V is dc Greater than V bat When, V 2 A positive voltage is required; when V is dc Less than V bat When, V 2 Need to be a negative voltage.
Referring to fig. 2, the bidirectional DC/DC set in the bidirectional buck-boost four-quadrant power converter includes a front-stage bidirectional unipolar LLC resonant circuit and a rear-stage bidirectional bipolar H-bridge circuit, and the front-stage bidirectional unipolar LLC resonant circuit is cascaded with the rear-stage bidirectional bipolar H-bridge circuit.
The bidirectional unipolar LLC resonant circuit plays a role in pre-voltage regulation, soft switching is achieved to reduce loss, fixed frequency control is used in a control strategy, and the LLC can work at an optimal working point to optimize efficiency.
The bidirectional bipolar H-bridge circuit can output positive or negative voltage, secondarily regulate the voltage to compensate the voltage difference between the battery and the direct current bus, simultaneously control the charging and discharging of the battery, and use voltage outer loop inductive current inner loop double closed loop PI control on a control strategy.
Referring to fig. 3, a circuit topology of a bidirectional buck-boost four-quadrant partial power converter according to the present invention specifically includes a bidirectional unipolar LLC resonant circuit and a bidirectional bipolar H-bridge circuit.
The preceding-stage bidirectional unipolar LLC resonant circuit comprises an input filter capacitor C 1 Primary side inverter circuit, resonant circuit, isolation transformer T, secondary side rectifying circuit and output filter capacitor C 2 。
Input filter capacitor C 1 One end of the first connecting rod is connected with a direct current bus,the other end is connected with a primary side inverter circuit, a resonant circuit, an isolation transformer T, a secondary side rectifier circuit and an output filter capacitor C in sequence 2 One end of (1), an output filter capacitor C 2 The other end of the second-stage bidirectional bipolar H-bridge circuit is connected with a post-stage bidirectional bipolar H-bridge circuit.
The primary side inverter circuit comprises four switching tubes S 1 、S 2 、S 3 、S 4 Switching tube S 1 And S 3 The drain electrode of the switch tube is connected with the anode of the direct current bus and the switch tube S 2 And S 4 The source electrode of the switch tube is connected with the cathode of the direct current bus and the switch tube S 1 Source electrode of (1) and switching tube S 2 The drain electrode of the capacitor is connected with a resonant capacitor C in sequence r Resonant inductor L r And transformer excitation inductance L m One end of (2), a switching tube S 3 Source electrode of (1) and switching tube S 4 Is connected with the excitation inductance L of the transformer m And the other end of the same.
The resonant circuit comprises a resonant inductor L r Resonant capacitor C r And transformer exciting inductance L m Resonant capacitor C r One end of the switch tube S is connected with 1 Source electrode of (2) and switching tube S 2 The other end of the drain electrode passes through a resonant inductor L r Respectively connected with the excitation inductors L of the transformer m And the primary side of the isolation transformer T, the transformer excitation inductance L m The other end of the switch tube S is connected with a switch tube S 3 Source electrode of (1) and switching tube S 4 Of the substrate.
The secondary rectifying circuit comprises four switching tubes S 5 、S 6 、S 7 、S 8 Switching tube S 5 And S 7 The drain electrode of the switching tube S is connected with one end of a post-stage bidirectional bipolar H-bridge circuit 6 And S 8 The source electrode of the switching tube S is connected with the other end of the post-stage bidirectional bipolar H-bridge circuit 5 And S 7 Source stage and switching tube S 6 And S 8 Is connected to the secondary side of the isolation transformer T.
For the preceding stage bidirectional unipolar LLC resonant circuit, the transformer excitation inductance L is mainly considered m Resonant inductor L r Resonant capacitor C r The design of (3).
Transformer excitation inductance L m ：
To realize zero voltage switching-on of the switch tube, the peak current I of the exciting inductor pk The junction capacitance of the switch tube must be completely discharged in the dead time, and the cut-off switch tube simultaneously discharges the junction capacitance C oss Charging to the input voltage. LLC input voltage is V LLCin LLC output voltage is V LLCout System switching frequency of f s And the turns ratio of the transformer is n.
Excitation inductance peak current I to be satisfied pk And dead time T dead The relationship is as follows:
peak current I of exciting inductor pk Is calculated as follows:
obtaining the dead time T dead The constraint conditions of (1) are:
the transformer excitation inductance L can be obtained m Is measured.
Resonant inductor L r Resonant capacitor C r ：
Resonant frequency f of LLC r Comprises the following steps:
the LLC works at the optimum working point, making the switching frequency equal to the resonant frequency, obtaining:
further obtain the resonant inductance L r And a resonance capacitor C r The product of the two parameters can be obtained according to the actual element model selection.
The post-stage bidirectional bipolar H-bridge circuit comprises an inverter circuit, a filter inductor L and a filter capacitor C 3 。
The inverter circuit comprises four switching tubes S 9 、S 10 、S 11 、S 12 Switching tube S 9 And S 11 The drain electrode of the switching tube S is connected with one end of a preceding-stage bidirectional unipolar LLC resonant circuit 10 And S 12 The drain electrode of the switching tube S is connected with the other end of the preceding-stage bidirectional unipolar LLC resonant circuit 9 Source electrode of (2) and switching tube S 10 The drain electrode of the filter inductor L is connected with one end of a filter inductor L, the other end of the filter inductor L is divided into two paths, one path is connected with the anode of a direct current bus, and the other path passes through a filter capacitor C 3 Connected with the positive pole of the energy storage battery, and a switching tube S 11 Source electrode of (1) and switching tube S 12 The drain electrode of the energy storage battery is connected with the anode of the energy storage battery, and one end of the anode of the energy storage battery is connected with the ground.
For a post-stage bidirectional bipolar H bridge circuit, a filter inductor L and a filter capacitor C are mainly considered 3 The design of (3). The filter circuit parameters are calculated mainly from two aspects of current ripple and cut-off frequency.
And (3) filter inductance L:
for the current ripple, the value of the filter inductor under PWM modulation is generally determined by the maximum ripple of the inductor current, which is the maximum ripple Δ I of the inductor current Lmax For charging and discharging current I of battery bat 10% of (a), namely:
ΔI Lmax ＝10％×I bat
h bridge output voltage U Hout And an input voltage U Hin The ratio of the two is equivalent duty ratio D, which is specifically as follows:
obtaining an inductive current ripple wave Delta I according to the voltage-current relation of the inductor L Expression (c):
when U is turned Hout ＝0.5U Hin Time, inductor current ripple Δ I L Max, the expression is:
and obtaining the minimum value of the filter inductance.
Filter capacitor C 3 ：
Cut-off frequency f c The calculation formula of (2) is as follows:
under PWM modulation, the output harmonic is the switching frequency f s And higher harmonics above, so that the cut-off frequency f can be taken c Of the lowest output harmonic frequency (switching frequency)
Namely:
the minimum value of the filter capacitor can be obtained.
The invention discloses a control method of a bidirectional buck-boost four-quadrant power converter, which comprises the following steps of:
the bidirectional unipolar LLC resonant circuit uses a fixed-frequency PWM control strategy, the bidirectional unipolar LLC resonant circuit always works at an optimal working point, namely a resonant point, so that the optimal efficiency of the LLC can be realized, and the output voltage is adjusted by changing the duty ratio of a switching tube or changing the turn ratio of an isolation transformer T.
Bidirectional bipolar H-bridge circuitUsing voltage current double closed loop PI control, the outer loop being voltage loop, i.e. controlling H-bridge filter capacitor C 3 Tracking the voltage difference between the direct current bus and the battery by the voltage; the inner loop is a current loop, namely, the current of the H-bridge filter inductor L is controlled to track the charging and discharging current of the battery, and the output value of the inner loop is used as a modulation signal to carry out PWM control on the switching tube.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of the embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Taking the operating conditions of the partial power converter system in table 1 as an example, the four-quadrant operation of the partial power converter is realized. Recording DC bus voltage V at a certain steady state moment under four working modes dc Battery voltage V bat The ratio K of partial power processed by bidirectional DC/DC in the partial power converter to the total power of the system pr See table 2.
TABLE 1 partial Power converter operating conditions
TABLE 2 partial power converter four quadrant operating results
As can be seen from table 2, in the operating mode of charging the battery with the battery voltage greater than the DC bus voltage, when the battery voltage approaches the peak value, the total power of the system is the largest, and the operating condition is the worst, but the partial power processed by the bidirectional DC/DC in the partial power converter only accounts for 16.03% of the total power of the system.
The efficiency of partial power converters is calculated under the limit working conditions of highest battery voltage, battery charging and maximum system power, and meanwhile, a full power converter is designed under the same working conditions for efficiency comparison, and the result is shown in table 3.
TABLE 3 comparison of efficiency
As can be seen from table 3, the efficiency of bidirectional DC/DC inside the partial power converter is only 86.94%, but since it only processes 16.03% of the total power of the system, the efficiency of the partial power converter system is as high as 97.91%, while the efficiency of the full power converter under the same operating condition is only 94.11%, and the efficiency advantage of the partial power converter is significant.
Referring to fig. 4, the difference between the two-quadrant operation and the four-quadrant operation is compared to highlight the advantage of the four-quadrant operation. Assuming that the voltage regulation range is 30%, the four-quadrant partial power converter works in a buck-boost mode, and the bidirectional DC/DC in the four-quadrant partial power converter only processes 15% of the total power of the system at most; and the two-quadrant partial power converter works in a voltage boosting mode or a voltage reducing mode, and the internal bidirectional DC/DC of the two-quadrant partial power converter can process 30% of the total power of a system at most.
In summary, according to the bidirectional buck-boost four-quadrant power converter and the control method thereof, the DC/DC in the converter only processes a small part of the total power of the system, so that the power density, the efficiency and the cost of the converter are effectively improved; the internal bidirectional DC/DC is a bidirectional bipolar topology, four-quadrant work can be realized, compared with the existing two-quadrant partial power converter, partial power processed by the internal DC/DC of the four-quadrant partial power converter is less, and the performance of the converter can be further improved. In control, four working modes corresponding to four quadrants can be realized, efficiency is optimized simultaneously, and charging and discharging of the battery are effectively controlled.
The above-mentioned contents are only for illustrating the technical idea of the present invention, and the protection scope of the present invention is not limited thereby, and any modification made on the basis of the technical idea of the present invention falls within the protection scope of the claims of the present invention.
Claims (10)
1. A bidirectional buck-boost four-quadrant partial power converter is characterized by comprising a bipolar bidirectional DC/DC, wherein a first positive terminal and a second positive terminal of the bidirectional DC/DC are respectively connected with the ground through a direct current bus, a first negative terminal of the bidirectional DC/DC is connected with the ground, and a second negative terminal of the bidirectional DC/DC is connected with the ground after passing through an energy storage battery; the voltage of the direct current bus is equal to the voltage of the energy storage battery plus the voltage of the bidirectional DC/DC second positive pole; when the voltage of the direct current bus is greater than the voltage of the energy storage battery, the voltage of the second positive pole of the bidirectional DC/DC is positive; and when the voltage of the direct current bus is less than the voltage of the energy storage battery, the voltage of the second positive pole terminal of the bidirectional DC/DC is negative voltage.
2. The bi-directional buck-boost four-quadrant partial power converter according to claim 1, wherein the bi-directional DC/DC includes a front-stage bi-directional unipolar LLC resonant circuit, the front-stage bi-directional unipolar LLC resonant circuit is cascaded with a rear-stage bi-directional bipolar H-bridge circuit, and the bi-directional unipolar LLC resonant circuit is used for pre-regulating voltage and realizing soft switching; the bidirectional bipolar H-bridge circuit is used for outputting positive voltage or negative voltage, compensating a voltage difference value between the energy storage battery and the direct current bus through secondary voltage regulation, and controlling charging and discharging of the energy storage battery.
3. The bi-directional buck-boost four-quadrant partial power converter according to claim 2, wherein the bi-directional unipolar LLC resonant circuit uses fixed frequency control and the bi-directional bipolar H-bridge circuit uses dual closed loop PI control of an inductor current inner loop of a voltage outer loop.
4. The bi-directional buck-boost four-quadrant power converter of claim 2,the bidirectional unipolar LLC resonant circuit comprises an input filter capacitor C 1 Input filter capacitor C 1 One end of the output filter capacitor is connected with a direct current bus, and the other end of the output filter capacitor is connected with an output filter capacitor C through a primary side inverter circuit, a resonance circuit, an isolation transformer T and a secondary side rectifier circuit in sequence 2 One end of (1), an output filter capacitor C 2 The other end of the H bridge circuit is connected with a post-stage bidirectional bipolar H bridge circuit.
5. The bi-directional buck-boost four-quadrant power converter according to claim 4, wherein the primary side inverter circuit comprises a switching tube S 1 Switch tube S 2 Switch tube S 3 And a switching tube S 4 Switching tube S 1 And a switching tube S 3 The drain electrode of the switch tube is connected with the positive electrode of the direct current bus and the switch tube S 2 And a switching tube S 4 The source electrode of the switch tube is connected with the negative electrode of the direct current bus and the switch tube S 1 Source electrode of (1) and switching tube S 2 The drain electrode of the capacitor is connected with a resonant capacitor C in sequence r And a resonant inductor L r The back part is divided into two paths, and one path is connected with the excitation inductance L of the transformer m One end of the switching tube S is connected with the primary side of the isolation transformer T and the switching tube S 3 Source electrode of (2) and switching tube S 4 Is connected with the excitation inductance L of the transformer m The other end of the primary winding and the primary side of the isolation transformer T; the secondary rectification circuit comprises a switching tube S 5 Switch tube S 6 Switch tube S 7 And a switching tube S 8 Switching tube S 5 And a switching tube S 7 Is connected with the output filter capacitor C 2 One end of (1), a switching tube S 6 And a switching tube S 8 Source electrode of the capacitor is connected with an output filter capacitor C 2 The other end of (S), a switch tube 5 And a switching tube S 7 Source stage and switching tube S 6 And a switching tube S 8 Is connected to the secondary side of the isolation transformer T.
6. The bi-directional buck-boost four-quadrant power converter according to claim 5, wherein excitation inductor peak current I pk And dead time T dead The relationship is as follows:
resonant inductor L r And a resonance capacitor C r The relationship is as follows:
wherein, C oss Is the junction capacitance of the switching tube, V LLCin For LLC input voltage, f s Is the system switching frequency.
7. The bi-directional buck-boost four-quadrant power converter according to claim 2, wherein the bi-directional bipolar H-bridge circuit comprises an inverter circuit, the inverter circuit is divided into two paths, one path is connected to the positive electrode of the dc bus and the filter capacitor C through the filter inductor L, respectively 3 One end of (1), a second path and a filter capacitor C 3 The other ends of the two-way valve are respectively connected with the positive electrode of the energy storage battery.
8. The bi-directional buck-boost four-quadrant power converter according to claim 7, wherein the inverter circuit comprises a switch tube S 9 Switch tube S 10 Switch tube S 11 And a switching tube S 12 Switching tube S 9 And a switching tube S 11 The drain electrode of the switching tube S is connected with one end of a preceding-stage bidirectional unipolar LLC resonant circuit 10 And a switching tube S 12 The drain electrode of the switching tube S is connected with the other end of the preceding-stage bidirectional unipolar LLC resonant circuit 9 Source electrode of (1) and switching tube S 10 The drain electrode of the switch tube S is connected with one end of a filter inductor L 11 Source electrode of (1) and switching tube S 12 The drain electrode of the energy storage battery is connected with the anode of the energy storage battery, and the cathode of the energy storage battery is connected with the cathode of the direct current bus in common.
9. The bi-directional buck-boost four-quadrant power converter according to claim 8, wherein an inductor current ripple ai L The relationship of (a) to (b) is as follows:
filter capacitor C 3 The relationship of (a) to (b) is as follows:
wherein, U Hin For H bridge input voltage, f s Is the system switching frequency.
10. A control method of the bidirectional buck-boost four-quadrant power converter according to claim 1, wherein the bidirectional unipolar LLC resonant circuit always operates at a resonant point by using a fixed frequency PWM control strategy, and the output voltage is adjusted by changing the duty ratio of a switching tube or the turn ratio of an isolation transformer T during parameter design;
the bidirectional bipolar H-bridge circuit is controlled by using a voltage and current double closed loop PI, an outer loop is a voltage loop, and an H-bridge filter capacitor C is controlled 3 Voltage tracking a voltage difference between the DC bus and the battery; the inner ring is a current ring, the current of the H-bridge filter inductor L is controlled to track the charging and discharging current of the battery, and the output value is used as a modulation signal to carry out PWM control on the switch tube.
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