Control circuit and control method of bidirectional four-transistor Buck-Boost converter

Abstract

The control circuit and control method of a bidirectional four-tube Buck-Boost converter, the converter is composed of four switch tubes and a filter inductor, the two ends of the filter inductor are respectively connected to the midpoints of the bridge arms of the switch tubes Q1, Q2 and the midpoints of the bridge arms of Q3, Q4, Q1 and Q2 are complementary conductive, Q3 and Q4 are complementary conductive, and the converter can realize bidirectional flow of energy. In order to improve the working efficiency of the converter, the four switch tubes realize ZVS while minimizing the effective value of the current, and a quadrilateral current control method is adopted for the four-tube Buck-Boost converter. The present invention proposes a control circuit and a control method for realizing stable operation and smooth switching of the converter in constant voltage mode and constant current mode, realizing natural commutation and smooth transition of the inductor current, so that the inductor current can realize smooth commutation of the current within a single switching cycle, and at the same time, it can also ensure that after the commutation signal is triggered, the switch tube does not lose the realization conditions of the soft switch, thereby improving the operating efficiency and reliability of the converter.

Description

Technical Field

[0001] The invention belongs to the technical field of power converters, and in particular relates to a control circuit and a control method of a bidirectional four-tube Buck-Boost converter. Background Art

[0002] In order to alleviate the energy crisis and environmental pollution and achieve sustainable development of human society, renewable energy represented by solar energy and wind energy is gradually replacing traditional fossil energy. However, due to weather conditions, the electric energy generated by renewable energy power generation systems may fluctuate greatly. To solve this problem, energy storage devices such as batteries and supercapacitors can be introduced. The power flow between the energy storage device and the DC bus is controlled by a bidirectional DC-DC converter, so that the electric energy can flow smoothly to the load end and ensure the stability of the bus voltage. Bidirectional DC-DC converters can be divided into two categories: isolated and non-isolated according to different application requirements. The present invention mainly studies non-isolated bidirectional DC-DC converters. Since the terminal voltage of the energy storage device has a certain range of variation during the charging and discharging process, if the bus voltage is within its range of variation, the bidirectional converter can have a higher conversion efficiency within the voltage variation range of the energy storage device. To meet this design requirement, a bidirectional converter with a step-up and step-down function needs to be selected. The topology of the Four-Switch Buck-Boost (FSBB) converter has the advantages of positive output voltage and low voltage stress of the switch tube, and therefore has been widely used.

[0003] The working mode of the bidirectional converter has multiple working modes according to the changes in renewable energy generation and load demand: constant current charging, constant voltage charging, constant current power supply and bus constant voltage power supply. The renewable energy power generation system is greatly affected by the weather environment. In order to maintain the stability of the bus voltage, the bidirectional converter needs to frequently switch the working mode according to external conditions. Therefore, realizing the natural commutation and smooth transition of the inductor current in the bidirectional FSBB converter is conducive to improving the stability and reliability of the converter during operation. Finding a simple and feasible control method is an urgent problem to be solved by researchers in this field. Summary of the invention

[0004] The present invention fully considers the problem that the renewable energy power generation system is greatly affected by the weather environment and requires the bidirectional converter to work more frequently, and proposes a control circuit and control method for a bidirectional four-tube Buck-Boost converter. For the bidirectional converter used in the energy storage system, the natural commutation, smooth transition and mode switching of the inductor current in the bidirectional FSBB converter are effectively realized, the bus voltage can be maintained stable, and it is also beneficial to improve the stability and reliability of the converter during operation, so that the converter has better dynamic performance.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A control circuit of a bidirectional four-tube Buck-Boost converter, the converter comprising four switch tubes Q1, Q2, Q3, Q4 and a filter inductor L c , the filter inductor L c The two ends of the converter are connected to the midpoints of the bridge arms of the switch tubes Q1 and Q2 and the midpoints of the bridge arms of the switch tubes Q3 and Q4 respectively. The switch tubes Q1 and Q2 are complementary turned on, and the switch tubes Q3 and Q4 are complementary turned on. One end of the converter is the bus voltage V bus , one end is the battery voltage V bat , characterized in that the control circuit comprises:

[0007] A drive signal generating module A is used to generate drive signals for the switch tubes Q1 and Q2 when the converter is running in the forward direction, and to generate drive signals for the switch tubes Q3 and Q4 when the converter is running in the reverse direction;

[0008] A drive signal generating module B is used to generate drive signals for the switch tubes Q3 and Q4 when the converter is running in the forward direction, and to generate drive signals for the switch tubes Q1 and Q2 when the converter is running in the reverse direction;

[0009] A phase-shift duty cycle circuit generation module is used to generate a phase difference between the turn-on times of the switch tubes Q1 and Q3 when the converter is running in the forward direction and the reverse direction;

[0010] A natural commutation module, used to generate a commutation signal for controlling the converter to switch operating states;

[0011] The current flows to the smooth transition module, which is used to realize the filter inductance L after receiving the commutation signal from the natural commutation module. c The inductor current i Lc of smooth transition.

[0012] To optimize the above technical solutions, the specific measures taken also include:

[0013] Furthermore, the driving signal generating module A includes a current regulator, a voltage regulator, a comparator 1 and an RS trigger 1. The outputs of the current regulator and the voltage regulator are connected through diodes D1 and D2 respectively. The final output v r is the smaller of the two outputs;

[0014] When the converter is running in the forward direction, the input of the current regulator is the current sampling value flowing into the battery, the input of the voltage regulator is the battery voltage sampling value, and the voltage reference of the voltage regulator is the maximum battery voltage. batWhen the battery voltage is below the maximum, the voltage regulator maintains a positive saturation output, the current regulator works, the battery is charged with a constant current, the diode D1 is turned on, and D2 is turned off; when the battery voltage V bat When the maximum battery voltage is reached, the voltage regulator works to maintain the battery voltage V bat unchanged, the current regulator is saturated and outputs positively, diode D2 is turned on, and D1 is turned off; the final output v r With sawtooth wave v saw The output of RS trigger 1 and the clock signal CLK1 are sent to RS trigger 1, thereby obtaining the driving signals of Q1 and Q2;

[0015] When the converter runs in reverse, the input of the current regulator is the current sampling value flowing into the bus, the input of the voltage regulator is the bus voltage sampling value, and the voltage reference of the voltage regulator is the rated voltage. bus When the rated voltage is not reached, the voltage regulator will maintain a positive saturation output, the current regulator will work, and the battery will discharge. At this time, diode D1 is turned on and D2 is turned off. When the bus voltage V bus When the voltage is the same as the rated voltage, the voltage regulator works to maintain the bus voltage V bus unchanged, the current regulator is saturated and outputs positively, diode D2 is turned on, and D1 is turned off; the final output v r With sawtooth wave v saw The output of RS trigger 1 and clock signal CLK1 are sent to RS trigger 1, thereby obtaining the driving signals of Q3 and Q4.

[0016] Furthermore, the driving signal generating module B comprises a comparator 2 and an RS trigger 2, wherein the positive input terminal of the comparator 2 is the inductor current sampling value, and the negative input terminal is -I ZVS , -I ZVS To ensure the negative current reference required for soft switching of switch tubes Q1 and Q4, I ZVS To ensure that the negative current reference required for soft switching of the switch tubes Q2 and Q3 is achieved, the output v of comparator 2 is comp After performing an OR operation with the clock signal CLK1, the clock signal CLK2 generated by the phase shift duty cycle circuit generation module is sent to the RS trigger 2;

[0017] When the converter is running in the forward direction, the clock signal CLK2 is used to turn on the switch Q3; when the inductor current i Lc Down to -I ZVS When the output of comparator 2 is comp becomes high, resetting RS flip-flop 2, thereby turning off Q3 and turning on Q4;

[0018] When the converter is running in reverse, the clock signal CLK2 is used to turn on the switch Q1; when the inductor current iLc Rise to I ZVs When the output of comparator 2 is comp It becomes a high potential, resetting RS flip-flop 2, thereby turning off Q1 and turning on Q2.

[0019] Furthermore, the phase-shift duty cycle circuit generation module generates a phase difference between the turn-on times of the switch tubes Q1 and Q3 according to the phase-shift duty cycle between the two bridge arms:

[0020] When the converter is running in the forward direction, the approximate phase difference between the turn-on times of Q1 and Q3 is D θ_appr (V bat ,i bat )for:

[0021] D θ_appr (V bat ,i bat )=a1V bat +b1i bat +V c1

[0022] When the converter is working in reverse, the approximate phase difference D′ between the turn-on time of Q3 and Q1 is θappr (V bat ,i bus )for:

[0023] D′ θ_appr (V bat ,i bus )=a2V bat +b2i bus +V c2

[0024] In the formula, a1, b1, a2, b2 represent linear coefficients, V c1 and V c2 is a constant term;

[0025] According to the phase difference between the turn-on moments of the switch tubes Q1 and Q3, a clock signal CLK2 is generated and input into the drive signal generating module B.

[0026] Furthermore, the natural commutation module includes comparators 4, 5 and RS trigger 3, and the positive input terminal of comparator 4 is the lowest reference value V bus_L , the reverse input terminal is the bus voltage sampling value v bus_s , the positive input terminal of comparator 5 is the bus voltage sampling value v bus_s , the reverse input terminal is the highest reference value V bus_H ;

[0027] When the bus voltage V bus falls below V bus_LWhen the output of comparator 4 is high, the output of comparator 4 is ORed with the clock signal CLK1 to generate a signal v flip1 Input RS flip-flop 3, when the rising edge of clock signal CLK1 arrives, v flip1 Set high, RS trigger 3 is reset, the q1 signal output by RS trigger 3 is set low, the q2 signal is set high, the converter works in reverse, and the generated commutation signal q2 input current flows to the smooth transition module;

[0028] When the bus voltage V bus rises above V bus_H When the comparator 5 output is high, the output of the comparator 5 is ORed with the clock signal CLK1 to generate a signal v flip2 Input RS flip-flop 3, when the rising edge of clock signal CLK1 arrives, v flip2 Set high, RS trigger 3 is reset, the q1 signal output by RS trigger 3 is set high, the q2 signal is set low, the converter works forward, and the generated commutation signal q2 input current flows to the smooth transition module.

[0029] Furthermore, the current flow smooth transition module causes the commutation signal q2 generated by the natural commutation module to generate narrow pulse signals at both the rising and falling edges of the jump, and generates q after performing an OR operation on the two. 2_d The signal is used as a driving signal to turn on the transistor set at the reference of the current regulator; after the transistor is turned on, the reference value of the current regulator is pulled down to 0; after the narrow pulse signal disappears, the transistor is cut off, and the reference voltage of the current regulator gradually rises from 0; at q 2_d Under the action of the signal, the reference voltage of the current regulator is set to 0 at the moment of commutation, and then gradually rises, making the inductor current i Lc The reverse direction starts from zero and gradually increases.

[0030] The present invention also proposes a control method for a bidirectional four-tube Buck-Boost converter based on the control circuit as described above, characterized in that the control method comprises:

[0031] When the converter is working in the forward direction, the battery voltage V bat The current flowing into the battery i bat , the phase shift angle D between the phase difference of the switch tubes Q1 and Q3 at the time of opening is approximately calculated θ ;

[0032] When the converter works in reverse, the battery voltage V bat With the bus current i bus , the phase shift angle D′ between the phase difference of the switch tubes Q3 and Q1 at the time of their opening can be approximately calculated θ ;

[0033] When the converter is working in the forward direction, the inductor current i Lc and the negative current reference -I required to ensure soft switching of the switch tubes Q1 and Q4 zvs For comparison, when i Lc Linear decrease to -I zvs When the switch tube Q3 is turned off, the duty cycle of the switch tube Q3 is 1-D y2 ;

[0034] When the converter works in reverse, the negative inductor current -i Lc and the negative current reference I required to ensure soft switching of the switch tubes Q3 and Q2 zvs For comparison, when i Lc Linear rise to I zvs When the switch tube Q1 is turned off, the duty cycle of the switch tube Q1 is 1-D′ y2 .

[0035] Furthermore, the bus voltage V bus The minimum reference value and the maximum reference value, when the bus voltage V bus When the voltage is lower than the minimum reference value, the converter works in reverse and the battery supplies energy to the bus terminal, making the bus voltage V bus When the power generated by the power generation system is greater than the load demand, the bus voltage V bus rises, at which time the energy storage device stores excess energy; when the bus voltage V bus When the maximum reference value is higher, the converter works in the forward direction, the battery stores excess energy, and the bus voltage V bus Reduce to rated value.

[0036] The beneficial effects of the present invention are as follows: the present invention provides a control circuit and a control method for realizing natural commutation, smooth transition and mode switching of a bidirectional four-tube Buck-Boost converter, and determines the current flow direction and the working mode of the converter by detecting the bus voltage, thereby maintaining the stability of the bus voltage. At the same time, through the current loop reference soft start method, a smooth transition during current commutation is realized to avoid large current overshoot, thereby improving the reliability of the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the circuit structure diagram of the four-tube Buck-Boost converter.

[0038] Figure 2 V bus <V bat Take for example, the current waveform diagram when the load changes and the current switches.

[0039] Figure 3aThe circuit diagram of the module for generating the driving signals of Q1 and Q2 when the converter is running in the forward direction and the driving signals of Q3 and Q4 when the converter is running in the reverse direction.

[0040] Figure 3b The circuit diagram of the module for generating the drive signals of Q3 and Q4 when the converter is running in the forward direction and the drive signals of Q1 and Q2 when the converter is running in the reverse direction.

[0041] Figure 3c The circuit diagram of the phase-shift duty cycle circuit generation module.

[0042] Figure 3d This is the circuit diagram of the natural commutation module.

[0043] Figure 3e The circuit diagram of the current flow smooth transition module.

[0044] Figure 4a This is the simulation waveform diagram when the converter is working in the forward direction and the battery voltage is 75V.

[0045] Figure 4b This is the simulation waveform diagram when the converter is working in the forward direction and the battery voltage is 100V.

[0046] Figure 4c This is the simulation waveform diagram when the converter is working in the forward direction and the battery voltage is 125V.

[0047] Figure 5a This is the simulation waveform diagram when the converter works in reverse and the battery voltage is 75V.

[0048] Figure 5b This is the simulation waveform diagram when the converter works in reverse and the battery voltage is 100V.

[0049] Figure 5c This is the simulation waveform diagram when the converter works in reverse and the battery voltage is 125V.

[0050] Figure 6 It is a dynamic waveform diagram of the bidirectional converter switching from constant voltage charging of the battery to maximum current constant current discharge.

[0051] Figure 7 It is a dynamic waveform diagram of the bidirectional converter switching from maximum power constant current charging to maximum current constant current discharging of the battery. DETAILED DESCRIPTION

[0052] The present invention will now be described in further detail with reference to the accompanying drawings.

[0053] Figure 1The circuit structure diagram of the four-tube Buck-Boost converter is mainly composed of four switch tubes and a filter inductor. The switch tubes Q1 and Q2 are complementary turned on to form a bridge arm unit, and the switch tubes Q3 and Q4 are complementary turned on to form a bridge arm unit. The filter inductor L c They are connected to the midpoints of the two bridge arms to store and transfer energy. One end of the converter is the bus voltage V bus , one end is the battery voltage V bat The current flowing into the bus terminal is defined as i bus , the current flowing into the battery terminal is i bat .

[0054] In order to improve the working efficiency of the converter, it is hoped to achieve ZVS (zero voltage switching) of all switches while minimizing the effective value of the inductor current. Figure 2 V bus <V bat As an example, the working waveform of the FSBB converter under load change and current commutation is given. When the converter is working in the forward direction, the Q1 turn-on time is defined as the starting time of each switching cycle. When the inductor current linearly rises to -I ZVS When Q3 is turned off, Q4 can achieve ZVS and minimize the current ripple. s Trigger the commutation signal at all times, T s The driving signals of the two bridge arms will be interchanged for the switching cycle. Therefore, the starting time of each switching cycle is the turn-on time of Q3, and the phase shift duty ratio is the phase difference between the turn-on time of Q3 and Q1. After the commutation signal is triggered, when the inductor current rises linearly to I ZVS Q1 should be turned off immediately to ensure that Q2 achieves ZVS while minimizing current ripple.

[0055] The FSBB converter has three control variables when running in the forward direction, namely the duty cycle D of Q1. y1 , Q4 duty cycle D y2 , and the phase shift duty ratio D corresponding to the phase difference between the turn-on times of Q1 and Q3 θ ; When the converter runs in reverse, the driving signals of the two bridge arms are exchanged. At this time, there are still three control quantities: the duty cycle of Q3 is D′ y1 , the duty cycle of Q2 is D′ y2 , and the phase shift duty ratio corresponding to the phase difference between the turn-on time of Q3 and Q1 is D′ θ Among them, the duty cycle is used to control the switch action, and the phase shift duty cycle is used to control the phase difference at the opening moment. To achieve soft switching of the switch tubes Q1 and Q4, it is necessary to ensure that the inductor current is over-negative before the switch tube is turned on, discharge the junction capacitance of the switch tube to zero, and make its reverse parallel diode naturally turn on. The size of the negative current required to achieve is defined as -I ZVSTo achieve soft switching of the switch tubes Q2 and Q3, it is necessary to ensure that the inductor current is positive before the switch tube is turned on, discharge the junction capacitance of the switch tube to zero, and make its reverse parallel diode naturally turn on. The magnitude of the positive current required to achieve this is defined as I ZVS .

[0056] In one embodiment, the present invention proposes a control circuit for a bidirectional four-tube Buck-Boost converter, taking an analog control circuit as an example, the schematic diagram of the principle is shown in FIG. Figure 3a to Figure 3e As shown, it mainly includes five components: a module for generating drive signals of Q1 and Q2 when the converter is running in the forward direction and Q3 and Q4 when the converter is running in the reverse direction, a module for generating drive signals of Q3 and Q4 when the converter is running in the forward direction and Q1 and Q2 when the converter is running in the reverse direction, a phase-shift duty cycle circuit generating module, a natural commutation module, and a current flow smooth transition module.

[0057] Some parameters in the figure are as follows: bat_s is the current sampling value flowing into the battery; i bat_s is the current sampling value flowing into the bus terminal; i os for i bat_s and i bat_s The output value after the switch is selected by S1 (determined by the current flow direction); I o_ref is the reference value of the current regulator; q 2_d It is generated by the q2 signal through the current flow to the smooth transition module, jumps high when the commutation signal arrives, and is used for the current regulator reference soft start; v bat_s is the battery voltage sampling value; v bus_s is the bus voltage sampling value; v os v bat_s and v bus_s The output value after the switch is selected by S2 (determined by the current flow direction); V o_ref is the reference value of the voltage regulator; C ref is the capacitance of the discharge capacitor used for the soft start of the current regulator; i Lc_s is the inductor current sampling value.

[0058] 1. A module for generating drive signals of Q1 and Q2 when the converter is running in the forward direction and drive signals of Q3 and Q4 when the converter is running in the reverse direction (drive signal generating module A)

[0059] like Figure 3a As shown in the figure, when a battery is selected as an energy storage device, the battery voltage fluctuates accordingly with the different states of charge of the battery. When the converter is working in the forward direction, the battery is charged. The charging process is to first charge the battery to the maximum voltage with a constant current and then charge it with a constant voltage. The outputs of the current regulator and the voltage regulator are connected through diodes D1 and D2 respectively, and the final output v rThe voltage reference of the voltage regulator is the voltage sampling value corresponding to the maximum battery voltage. Therefore, when the battery voltage does not reach the maximum value, the voltage regulator will maintain a positive saturation output, the current regulator will work, and the battery will be charged with a constant current. At this time, the diode D1 is turned on and D2 is turned off. When the battery voltage reaches the maximum value, the voltage regulator works to maintain the voltage across the battery unchanged. At this time, the charging current i bat If the current regulator is less than the set value, the current regulator will output positive saturation, diode D2 will be turned on, and D1 will be turned off. r With sawtooth wave v saw is sent to comparator 1, and its output is sent to RS trigger 1, thereby obtaining the driving signals of Q1 and Q2. It should be noted that v saw Synchronized with the clock signal CLK1.

[0060] When the converter works in reverse, the working principle of module A is the same as that of forward work, that is, when the bus voltage does not reach the rated voltage, the converter works in constant current mode, the voltage regulator will maintain positive saturation output, the current regulator works, and the battery discharges. At this time, diode D1 is turned on and D2 is turned off; when the bus voltage is the same as the rated voltage, the converter works in constant voltage mode, the voltage regulator works, and the voltage at both ends of the bus remains unchanged. At this time, the charging current i bat If the current is less than the set value, the current regulator will output positive saturation, diode D2 will be turned on, and D1 will be turned off. Depending on the external environmental conditions, the working conditions of the bidirectional converter are also different.

[0061] 2. A module for generating drive signals of Q3 and Q4 when the converter is running in the forward direction and drive signals of Q1 and Q2 when the converter is running in the reverse direction (drive signal generating module B)

[0062] like Figure 3b As shown, when the converter is running in the forward direction, the clock signal CLK2 (its generation circuit is shown in the phase-shift duty cycle circuit generation module) is used to turn on Q3. Lc Down to -I ZVS When the output of comparator 2 is comp becomes high, resetting RS flip-flop 2, thereby turning off Q3 and turning on Q4. Lc Before Q2 turns off, it does not drop to -I ZVS , CLK1 and v are intentionally added here comp Perform "OR" to force Q3 to turn off to ensure that the switching timing of the converter remains unchanged.

[0063] When the converter is running in reverse, -i Lc with -I ZVS For comparison, CLK2 is used to turn on Q1. When the inductor current i Lc Rise to I ZVSWhen the output of comparator 2 is comp becomes high, resetting RS flip-flop 2, thereby turning off Q1 and turning on Q2. Lc Before Q4 turns off, it does not rise to I ZVS , CLK1 and v are intentionally added here comp Perform "OR" to force Q1 to turn off to ensure that the switching timing of the converter remains unchanged.

[0064] 3. Phase-shift duty cycle circuit generation module

[0065] After determining the duty cycle of each switch tube, it is also necessary to determine the phase shift duty cycle between the two bridge arms. When the bidirectional converter is working in the forward direction, the phase shift duty cycle D θ , that is, the theoretical calculated value of the phase difference between the turn-on moments of Q1 and Q3 is actually about the battery voltage V bat And the battery charging current i ba function; when the bidirectional converter works in reverse, the phase shift duty ratio D′ θ , that is, the theoretical calculated value of the phase difference between the turn-on time of Q3 and Q1 is actually about the battery voltage V bat And the charging current i flowing into the bus bus The surface of the phase shift duty cycle is approximated by a plane, thereby achieving the goal of simplified control. After simplification, the phase shift duty cycle is a linear combination of the voltage and current sampling values. When the converter is working in the forward direction, the phase difference between the turn-on moments of Q1 and Q3 is approximately:

[0066] D θ_appr (V bat ,i bat )=a1V bat +b1i bat +V c1

[0067] When the converter works in reverse, the phase difference between the turn-on time of Q3 and Q1 can be expressed as:

[0068] D′ θ_appr (V bat ,i bus )=a2V bat +b2i bus +V c2

[0069] In the formula, a1, b1, a2, b2 represent linear coefficients, V c1 and V c2 is a constant term. θ_appr (V bat ,i bat ) and D′ θ_appr (V bat,i bus ) respectively by Figure 3c The module shown is obtained by a proportional addition circuit when the converter works in forward and reverse directions.

[0070] 4. Natural commutation module

[0071] To maintain the stability of the bus voltage, when the electric energy generated by the renewable energy power generation system is greater than the load demand, the bus voltage will begin to rise, and the energy storage device will begin to store excess energy; when the electric energy generated by the power generation system is not enough to meet the load demand, the bus voltage will drop, and the energy storage device will release energy to supply energy to the load. Figure 3d When the output q1 of the RS trigger 3 is high, the switches S1 to S8 are connected to the upper signal, and the converter works forward; when q1 is low, the converter works reversely. The positive input terminal of the comparator 4 is the lowest reference value V bus_L , the reverse input terminal is the bus voltage sampling value; the positive input terminal of comparator 5 is the bus voltage sampling value, and the reverse input terminal is the highest reference value V bus_H When the bus voltage V bus falls below V bus_L When the comparator 4 outputs a high potential, it waits for the start of the next switching cycle, that is, when the rising edge of the CLK1 signal arrives, v flip1 Set high, the trigger is reset, the q1 signal is set low, the q2 signal is set high, and the converter works in reverse; when the bus voltage V bus rises above V bus_H When the comparator 5 outputs a high potential, the next switching cycle starts. flip2 Set high, the trigger is set, the q1 signal is set high, the q2 signal is set low, and the converter works forward.

[0072] 5. Current flows to smooth transition module

[0073] If the smooth commutation of the bidirectional converter can be achieved, the reliability of the converter during commutation can be improved. From the above analysis, it can be seen that when the converter switches from forward operation to reverse operation, q2 is set high; when the converter switches from reverse operation to forward operation, q2 is set low. Therefore, as long as the commutation condition is triggered, the q2 signal will jump. Figure 3e The logic circuit shown in the figure makes the q2 signal generate narrow pulse signals at both the rising and falling edges of the transition. 2_d The signal after the two are ORed together is used as a driver to turn on the transistor at the reference of the current regulator. After the transistor is turned on, the capacitor C ref Discharge, the reference value is pulled down to 0. After the narrow pulse signal disappears, the transistor is cut off, and the reference V i_ref Re-energize capacitor C ref Charging, the reference voltage gradually rises from 0.2_d Under the action of, the reference voltage of the current regulator is set to 0 at the moment of commutation, and then gradually rises, so that the inductor current reverses and gradually rises from zero, thereby achieving a smooth transition of the current and ensuring that the switch tube does not lose the soft switch before and after the commutation signal is triggered.

[0074] In another embodiment, the present invention proposes a control method for a bidirectional four-tube Buck-Boost converter, which is implemented based on the control circuit proposed above. In order to improve the working efficiency of the converter and enable the four switch tubes to achieve ZVS while minimizing the effective value of the current, the control method adopts a quadrilateral current control method for the four-tube Buck-Boost converter.

[0075] According to the current flow direction and working mode, the sampled battery voltage V bat , bus voltage V bus , the current flowing into the battery i bat and the bus current i bus , and compared with different reference values ​​in different working modes, the duty cycle D of Q1 in forward working is regulated by current regulator and voltage regulator. y1 Or the duty cycle D′ of Q3 when working in reverse y1 , thus achieving current stability and voltage stability. At the same time, the two regulators are connected through diodes to achieve switching from constant current mode to constant voltage mode.

[0076] When the converter is working in the forward direction, the battery voltage V bat The current flowing into the battery i bat , the phase shift angle D between the phase difference of the switch tubes Q1 and Q3 at the time of opening is approximately calculated θ ; When the converter works in reverse, the sampled battery voltage V bat With the bus current i bus , the phase shift angle D′ between the phase difference of the switch tubes Q3 and Q1 at the time of their opening can be approximately calculated θ .

[0077] The converter forward working sampling inductor current i Lc and the negative current reference -I required to ensure soft switching of the switch tubes Q1 and Q4 zvs For comparison, when i Lc Linear decrease to -I zvs When the switch tube Q3 is turned off, the duty cycle of the switch tube Q3 is 1-D y2 ;Converter reverse working sampling negative inductor current -i Lc and the negative current reference I required to ensure soft switching of the switch tubes Q3 and Q2 zvs For comparison, when i Lc Linear rise to I zvsWhen the switch tube Q1 is turned off, the duty cycle of the switch tube Q1 is obtained as 1-D′ y2 .

[0078] In order to achieve natural commutation, smooth transition and mode switching of the inductor current, the following specific measures need to be taken:

[0079] Natural commutation: To maintain the stability of the bus voltage, when the power generated by the renewable energy generation system is greater than the load demand, the bus voltage will begin to rise, and the energy storage device will begin to store excess energy; when the power generated by the power generation system is not enough to meet the load demand, the bus voltage will drop, and the energy storage device will release energy to supply energy to the load. To achieve the natural commutation of the inductive current, the lower and upper limits of the bus voltage need to be set. When the bus voltage is lower than the lower limit, the enable signal is high, the converter works in reverse, and the battery supplies energy to the bus end, causing the bus voltage to rise; when the power generated by the power generation system is greater than the load demand, the bus voltage rises, and the energy storage device stores excess energy. When the bus voltage is higher than the upper limit, the enable signal is low, the converter works in the forward direction, the battery stores excess energy, and the bus voltage drops to the rated value. This achieves the natural commutation of the inductive current.

[0080] Smooth transition: If smooth commutation of the bidirectional converter can be achieved, the reliability of the converter during commutation can be improved. Since there is a moment when the current is 0 during the commutation process, if no measures are taken, the regulator will output positive saturation, which will cause a reverse current overshoot in the inductor current. Therefore, the present invention adds a transistor at the reference of the current regulator, and uses the commutation enable signal to generate a pulse signal at the moment when the commutation condition is triggered to turn on the transistor, so that the reference value and the regulator output drop to 0. After maintaining for a very short period of time, the reference voltage gradually rises, so that the current starts to rise from zero at the commutation moment, thereby achieving a smooth transition of the inductor current and ensuring that the switch tube does not lose the soft switch before and after the commutation signal is triggered.

[0081] Mode switching: The outputs of the current regulator and the voltage regulator are connected through diodes, and the final output is the smaller value of the two. The voltage reference of the voltage regulator is the voltage sampling value corresponding to the rated voltage. When the voltage does not reach the rated value, the voltage regulator will maintain positive saturation output, the current regulator will work, and the converter will work in constant current mode. When the voltage reaches the set value, the voltage regulator will work, the converter will work in constant voltage mode, and the current regulator will output positive saturation. The bidirectional converter mode is switched to adapt to different external environment requirements.

[0082] In order to further illustrate the superiority of the control method proposed in the present invention, a simulation example of the present invention is given below.

[0083] According to the 1.25kW four-tube Buck-Boost converter parameters given in Table 1, a simulation circuit was built using Saber simulation software. Figure 4a-4c The simulation waveform of the four-tube Buck-Boost converter working in the forward direction at rated power is given, where: Figure 4a This is the simulation waveform diagram of the battery voltage at 75V full load; Figure 4b This is the simulation waveform diagram of the battery voltage at 100V under full load; Figure 4c This is a simulation waveform diagram under full load with a battery voltage of 125V. It can be seen that all switch tubes can achieve ZVS and the inductor current pulsation is small. Figure 5a to Figure 5c The simulation waveform of the four-tube Buck-Boost converter working in reverse at rated power is given, where: Figure 5a This is the simulation waveform diagram of the battery voltage at 75V full load; Figure 5b This is the simulation waveform diagram of the battery voltage at 100V under full load; Figure 5c This is a simulation waveform diagram under full load with a battery voltage of 125V. It can be seen that all switch tubes can achieve ZVS and the inductor current pulsation is small. Figure 6 The dynamic waveform of the bidirectional converter switching from constant voltage charging of the battery to maximum current constant current discharge. Figure 7 The figure is the dynamic waveform of the bidirectional converter switching from maximum power constant current charging to maximum current constant current discharging. It can be seen that based on this control method, the natural commutation of the converter is realized, and during the commutation process, the bidirectional converter meets the requirements of different working modes while the inductor current achieves a smooth transition, with a faster dynamic response speed.

[0084] Table 1 Main parameters of bidirectional converter

[0085] parameter Numeric parameter Numeric <![CDATA[Bus voltage V bus > 100V <![CDATA[Switching frequency f s > 1MHz <![CDATA[Battery voltage V bat > 75～125V <![CDATA[Inductance value L c > 0.8μH Maximum charge / discharge current 10A Maximum output power 1.25kW

[0086] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A control circuit of a bidirectional four-tube Buck-Boost converter, the converter comprising four switch tubes Q1, Q2, Q3, Q4 and a filter inductor L c , the filter inductor L c The two ends of the converter are connected to the midpoints of the bridge arms of the switch tubes Q1 and Q2 and the midpoints of the bridge arms of the switch tubes Q3 and Q4 respectively. The switch tubes Q1 and Q2 are complementary turned on, and the switch tubes Q3 and Q4 are complementary turned on. One end of the converter is the bus voltage V bus , one end is the battery voltage V bat , characterized in that, The control circuit comprises: A drive signal generating module A is used to generate drive signals for the switch tubes Q1 and Q2 when the converter is running in the forward direction, and to generate drive signals for the switch tubes Q3 and Q4 when the converter is running in the reverse direction; A drive signal generating module B is used to generate drive signals for the switch tubes Q3 and Q4 when the converter is running in the forward direction, and to generate drive signals for the switch tubes Q1 and Q2 when the converter is running in the reverse direction; A phase-shift duty cycle circuit generation module is used to generate a phase difference between the turn-on times of the switch tubes Q1 and Q3 when the converter is running in the forward direction and the reverse direction; A natural commutation module, used to generate a commutation signal for controlling the converter to switch operating states; The current flows to the smooth transition module, which is used to realize the filter inductance L after receiving the commutation signal from the natural commutation module. c The inductor current i Lc Smooth transition; The driving signal generating module A includes a current regulator, a voltage regulator, a comparator 1 and an RS trigger 1. The outputs of the current regulator and the voltage regulator are connected through diodes D1 and D2 respectively. The final output v r is the smaller of the two outputs; When the converter is running in the forward direction, the input of the current regulator is the current sampling value flowing into the battery, the input of the voltage regulator is the battery voltage sampling value, and the voltage reference of the voltage regulator is the maximum battery voltage. bat When the battery voltage is below the maximum, the voltage regulator maintains a positive saturation output, the current regulator works, the battery is charged with a constant current, the diode D1 is turned on, and D2 is turned off; when the battery voltage V bat When the maximum battery voltage is reached, the voltage regulator works to maintain the battery voltage V bat unchanged, the current regulator is saturated and outputs positively, diode D2 is turned on, and D1 is turned off; the final output v r With sawtooth wave v saw The output of RS trigger 1 and the clock signal CLK1 are sent to RS trigger 1, thereby obtaining the driving signals of Q1 and Q2; When the converter runs in reverse, the input of the current regulator is the current sampling value flowing into the bus, the input of the voltage regulator is the bus voltage sampling value, and the voltage reference of the voltage regulator is the rated voltage. bus When the rated voltage is not reached, the voltage regulator will maintain a positive saturation output, the current regulator will work, and the battery will discharge. At this time, diode D1 is turned on and D2 is turned off. When the bus voltage V bus When the voltage is the same as the rated voltage, the voltage regulator works to maintain the bus voltage V bus unchanged, the current regulator is saturated and outputs positively, diode D2 is turned on, and D1 is turned off; the final output v r With sawtooth wave v saw The output of RS trigger 1 and clock signal CLK1 are sent to RS trigger 1, thereby obtaining the driving signals of Q3 and Q4.

2. A control circuit for a bidirectional four-transistor Buck-Boost converter as claimed in claim 1, characterized in that: The driving signal generating module B includes a comparator 2 and an RS trigger 2. The positive input terminal of the comparator 2 is the inductor current sampling value, and the negative input terminal is -I ZVS , -I ZVS To ensure the negative current reference required for soft switching of switch tubes Q1 and Q4, I ZVS To ensure that the negative current reference required for soft switching of the switch tubes Q2 and Q3 is achieved, the output v of comparator 2 is comp After performing an OR operation with the clock signal CLK1, the clock signal CLK2 generated by the phase shift duty cycle circuit generation module is sent to the RS trigger 2; When the converter is running in the forward direction, the clock signal CLK2 is used to turn on the switch Q3; when the inductor current i Lc Drop to -I ZVS When the output of comparator 2 is comp becomes high, resetting RS flip-flop 2, thereby turning off Q3 and turning on Q4; When the converter is running in reverse, the clock signal CLK2 is used to turn on the switch Q1; when the inductor current i Lc Rise to I ZVS When the output of comparator 2 is comp It becomes a high potential, resetting RS flip-flop 2, thereby turning off Q1 and turning on Q2.

3. A control circuit for a bidirectional four-transistor Buck-Boost converter as claimed in claim 1, characterized in that: The phase shift duty cycle circuit generation module generates a phase difference between the turn-on times of the switch tubes Q1 and Q3 according to the phase shift duty cycle between the two bridge arms: When the converter is running in the forward direction, the approximate phase difference between the turn-on times of Q1 and Q3 is D θ_appr (V bat ,i bat )for: D θ_appr (V bat ,i bat )=a1V bat +b1i bat +V c1 When the converter is working in reverse, the approximate phase difference between the turn-on time of Q3 and Q1 is D' θ_appr (V bat ,i bus )for: D' θ_appr (IN bat ,and bus )=a2V bat +b2i bus +V c2 In the formula, a1, b1, a2, b2 represent linear coefficients, V c1 and V c2 is a constant term; According to the phase difference between the turn-on moments of the switch tubes Q1 and Q3, a clock signal CLK2 is generated and input into the drive signal generating module B.

4. A control circuit for a bidirectional four-transistor Buck-Boost converter as claimed in claim 1, characterized in that: The natural commutation module includes comparators 4, 5 and RS trigger 3. The positive input terminal of comparator 4 is the lowest reference value V bus_L , the reverse input terminal is the bus voltage sampling value v bus_s , the positive input terminal of comparator 5 is the bus voltage sampling value v bus_s , the reverse input terminal is the highest reference value V bus_H ; When the bus voltage V bus falls below V bus_L When the output of comparator 4 is high, the output of comparator 4 is ORed with the clock signal CLK1 to generate a signal v flip1 Input RS flip-flop 3, when the rising edge of clock signal CLK1 arrives, v flip1 Set high, RS trigger 3 is reset, the q1 signal output by RS trigger 3 is set low, the q2 signal is set high, the converter works in reverse, and the generated commutation signal q2 input current flows to the smooth transition module; When the bus voltage V bus rises above V bus_H When the comparator 5 output is high, the output of the comparator 5 is ORed with the clock signal CLK1 to generate a signal v flip2 Input RS flip-flop 3, when the rising edge of clock signal CLK1 arrives, v flip2 Set high, RS trigger 3 is reset, the q1 signal output by RS trigger 3 is set high, the q2 signal is set low, the converter works forward, and the generated commutation signal q2 input current flows to the smooth transition module.

5. A control circuit for a bidirectional four-transistor Buck-Boost converter as claimed in claim 1, characterized in that: The current flow smooth transition module makes the commutation signal q2 generated by the natural commutation module generate narrow pulse signals at both the rising and falling edges of the jump, and generates q after performing an OR operation on the two. 2_d The signal is used as a driving signal to turn on the transistor set at the reference of the current regulator; after the transistor is turned on, the reference value of the current regulator is pulled down to 0; after the narrow pulse signal disappears, the transistor is cut off, and the reference voltage of the current regulator gradually rises from 0; at q 2_d Under the action of the signal, the reference voltage of the current regulator is set to 0 at the moment of commutation, and then gradually rises, making the inductor current i Lc The reverse direction starts from zero and gradually increases.

6. A control method for a bidirectional four-transistor Buck-Boost converter based on the control circuit according to any one of claims 1 to 5, characterized in that: The control method comprises: When the converter is working in the forward direction, the battery voltage V bat The current flowing into the battery i bat , the phase shift angle D between the phase difference of the switch tubes Q1 and Q3 at the time of opening is approximately calculated θ ; When the converter works in reverse, the battery voltage V bat With the bus current i bus , the phase shift angle D' between the phase difference at the turn-on time of the switch tubes Q3 and Q1 is approximately calculated θ ; When the converter is working in the forward direction, the inductor current i is sampled. Lc and the negative current reference -I required to ensure soft switching of the switch tubes Q1 and Q4 zvs For comparison, when i Lc Linear decrease to -I zvs When the switch tube Q3 is turned off, the duty cycle of the switch tube Q3 is 1-D y2 ; When the converter works in reverse, the negative inductor current -i Lc and the negative current reference I required to ensure soft switching of the switch tubes Q3 and Q2 zvs For comparison, when i Lc Linear rise to I zvs When the switch tube Q1 is turned off, the duty cycle of the switch tube Q1 is 1-D' y2 .

7. The control method of the bidirectional four-transistor Buck-Boost converter according to claim 6, characterized in that: Set bus voltage V bus The lowest reference value and the highest reference value, when the bus voltage V bus When the voltage is lower than the minimum reference value, the converter works in reverse and the battery supplies energy to the bus terminal, making the bus voltage V bus When the power generated by the power generation system is greater than the load demand, the bus voltage V bus rises, at which time the energy storage device stores excess energy; when the bus voltage V bus When the maximum reference value is higher, the converter works in the forward direction, the battery stores excess energy, and the bus voltage V bus Reduce to rated value.

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