Control method of power conversion circuit, power conversion device and power supply system

Abstract

The present application provides a control method, a power conversion device and a power supply system for a power conversion circuit. The control method can obtain a target inner phase-shift duty cycle corresponding to the highest voltage matching degree according to the real-time DC voltage and the real-time AC voltage, obtain a reference outer phase-shift duty cycle according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the preset target AC power and the power transmission constraint, adjust the reference outer phase-shift duty cycle according to the real-time AC current and the preset target AC current to obtain the target outer phase-shift duty cycle, obtain the target switching frequency according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the reference outer phase-shift duty cycle, the target AC power and the switching frequency constraint, and control the power transmission of the power conversion circuit according to the target switching frequency, the target inner phase-shift duty cycle and the target outer phase-shift duty cycle. Through the method of the present application, the transmission efficiency of the power conversion circuit can be improved and the current stress can be reduced.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a control method for a power conversion circuit, a power conversion device, and a power supply system. Background Art

[0002] In the field of new energy, single-stage micro-inverters are increasingly used. At present, the control strategy of single-stage micro-inverters often adopts fixed-frequency control, which has the advantages of wide soft switching range and few control variables. However, micro-inverters under fixed-frequency control are prone to lose soft switching and generate power oscillations, resulting in reduced efficiency and device overcurrent stress. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present application provides a control method for a power conversion circuit, a power conversion device and a power supply system, which can realize variable frequency control of the power conversion circuit, effectively improve the transmission efficiency and reduce the current stress.

[0004] The first aspect of the present application provides a control method for a power conversion circuit. The power conversion circuit includes a DC side bridge circuit, a transformer, a resonant inductor and an AC side bridge circuit, wherein the first end of the DC side bridge circuit is connected to the primary side of the transformer, and the first end of the AC side bridge circuit is connected to the secondary side of the transformer through the resonant inductor; wherein the DC side bridge circuit includes a first bridge arm and a second bridge arm connected in parallel, and the AC side bridge circuit includes a third bridge arm and a fourth bridge arm connected in parallel, wherein the first bridge arm, the second bridge arm and the third bridge arm all include a switch tube, and the fourth bridge arm includes a resonant capacitor, and the resonant capacitor and the resonant inductor constitute a resonant circuit. The control method of the power conversion circuit includes: obtaining a real-time DC voltage on the second end of the DC side bridge circuit, a real-time AC voltage and a real-time AC current on the second end of the AC side bridge circuit; obtaining a target inner phase-shift duty cycle of the DC side bridge circuit corresponding to the highest voltage matching degree according to the real-time DC voltage and the real-time AC voltage; obtaining a reference outer phase-shift duty cycle according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, a preset target AC power and a preset power transmission constraint; wherein the power transmission constraint is used to indicate the AC power of the power conversion circuit and the outer phase-shift duty cycle, the inner phase-shift duty cycle, The constraint relationship between the DC voltage and the AC voltage; adjusting the reference external phase-shift duty cycle according to the real-time AC current and the preset target AC current to obtain the target external phase-shift duty cycle between the DC side bridge circuit and the AC side bridge circuit; obtaining the target switching frequency according to the real-time DC voltage, the real-time AC voltage, the target internal phase-shift duty cycle, the reference external phase-shift duty cycle, the target AC power and the preset switching frequency constraint condition; wherein the switching frequency constraint condition is used to constrain the size of the switching frequency of the power conversion circuit; controlling the power transmission of the power conversion circuit according to the target switching frequency, the target internal phase-shift duty cycle and the target external phase-shift duty cycle.

[0005] In one embodiment, the switching frequency constraint condition includes an upper frequency limit constraint condition and a lower frequency limit constraint condition. According to the real-time DC voltage, the real-time AC voltage, the target inner phase shift duty cycle, the reference outer phase shift duty cycle, the target AC power and the preset switching frequency constraint condition, the target switching frequency is obtained, including: according to the real-time DC voltage, the real-time AC voltage, the target inner phase shift duty cycle, the reference outer phase shift duty cycle, the target AC power and the upper frequency limit constraint condition, the upper frequency limit constraint condition is used to constrain the upper frequency limit of the switching frequency when the power conversion circuit transmits the target AC power; according to the real-time DC voltage, the real-time AC voltage, the target inner phase shift duty cycle, the target AC power and the lower frequency limit constraint condition, the lower frequency limit is determined; wherein the lower frequency limit constraint condition is used to constrain the lower frequency limit of the switching frequency when the power conversion circuit is soft switched; the target switching frequency is calculated according to the upper frequency limit and the lower frequency limit.

[0006] In one embodiment, the target switching frequency is calculated according to the upper limit of the switching frequency and the lower limit of the switching frequency, including: performing mean calculation on the upper limit of the switching frequency and the lower limit of the switching frequency to obtain the target switching frequency.

[0007] In one embodiment, the power transmission of the power conversion circuit is controlled according to the target switching frequency, the target inner phase-shift duty cycle and the target outer phase-shift duty cycle, including: according to the target switching frequency, the target inner phase-shift duty cycle and the target outer phase-shift duty cycle, the switch tubes of the DC side bridge circuit and the AC side bridge circuit are controlled to perform soft switching actions; wherein, when the switch tube in the DC side bridge circuit is turned on, the secondary current of the transformer is negative polarity; when the switch tube in the AC side bridge circuit is turned on, the secondary current of the transformer is positive polarity.

[0008] In one embodiment, according to the target switching frequency, the target inner phase-shift duty cycle and the target outer phase-shift duty cycle, the switch tubes of the DC side bridge circuit and the AC side bridge circuit are controlled to perform soft switching actions, including: controlling the phase difference between the first bridge arm and the second bridge arm in the DC side bridge circuit to be equal to the inner phase-shift angle corresponding to the target inner phase-shift duty cycle; controlling the phase difference between the voltage waveform on the first end of the DC side bridge circuit and the voltage waveform on the first end of the AC side bridge circuit to be equal to the outer phase-shift angle corresponding to the target outer phase-shift duty cycle; controlling the switch tubes in the DC side bridge circuit and the AC side bridge circuit to perform soft switching on and off actions at the target switching frequency.

[0009] In one embodiment, the first bridge arm includes a first switch tube and a second switch tube connected in series, the second bridge arm includes a third switch tube and a fourth switch tube connected in series, the third bridge arm includes a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube connected in series in sequence, wherein the fifth switch tube and the sixth switch tube are connected back to back, and the seventh switch tube and the eighth switch tube are connected back to back, and the fourth bridge arm includes a first resonant capacitor and a second resonant capacitor connected in series, and the first resonant capacitor, the second resonant capacitor and the resonant inductor constitute a resonant circuit. Furthermore, according to the target switching frequency, the target inner phase-shift duty cycle and the target outer phase-shift duty cycle, the process of controlling the switch tubes of the DC side bridge circuit and the AC side bridge circuit to perform soft switching action includes: controlling the first switch tube and the second switch tube to be complementary turned on, the third switch tube and the fourth switch tube to be complementary turned on, and the conduction phase difference between the first switch tube and the third switch tube is equal to the inner phase-shift angle corresponding to the target inner phase-shift duty cycle; when the real-time AC voltage is in the positive half cycle, controlling the fifth switch tube and the seventh switch tube to be complementary turned on, and the sixth switch tube and the eighth switch tube to be constantly turned on; when the real-time AC voltage is in the negative half cycle, controlling the fifth switch tube and the seventh switch tube to be constantly turned on, and the sixth switch tube and the eighth switch tube to be complementary turned on.

[0010] In one embodiment, a target inner phase-shift duty cycle of a DC side bridge circuit corresponding to a highest voltage match is obtained based on a real-time DC voltage and a real-time AC voltage, including: obtaining a voltage matching constraint; the voltage matching constraint is used to indicate that the voltage matching is determined by the inner phase-shift duty cycle, the DC voltage, the AC voltage and the turns ratio of the transformer; and the target inner phase-shift duty cycle corresponding to the highest voltage match is calculated based on the real-time DC voltage, the real-time AC voltage and the voltage matching constraint.

[0011] In one embodiment, a reference external phase-shift duty cycle is adjusted according to a real-time AC current and a preset target AC current to obtain a target external phase-shift duty cycle between a DC-side bridge circuit and an AC-side bridge circuit, including: calculating a current difference between a preset desired AC current and a real-time AC current; performing a deviation adjustment on the current difference to obtain a compensation amount of the external phase-shift duty cycle; and obtaining a target external phase-shift duty cycle according to the reference external phase-shift duty cycle and the compensation amount of the external phase-shift duty cycle.

[0012] The second aspect of the present application provides a power conversion device. The power conversion device includes a power conversion circuit and a controller, the power conversion circuit includes a DC side bridge circuit, a transformer, a resonant inductor and an AC side bridge circuit, the first end of the DC side bridge circuit is connected to the primary side of the transformer, and the first end of the AC side bridge circuit is connected to the secondary side of the transformer through the resonant inductor; wherein the DC side bridge circuit includes a first bridge arm and a second bridge arm connected in parallel, the AC side bridge circuit includes a third bridge arm and a fourth bridge arm connected in parallel, the first bridge arm, the second bridge arm and the third bridge arm all include a switch tube, the fourth bridge arm includes a resonant capacitor, and the resonant capacitor and the resonant inductor constitute a resonant circuit. The controller is connected to the power conversion circuit, and the controller is used to: obtain a target inner phase-shift duty cycle of the DC side bridge circuit corresponding to the highest voltage matching degree according to the real-time DC voltage on the second end of the DC side bridge circuit and the real-time AC voltage on the second end of the AC side bridge circuit; obtain a reference outer phase-shift duty cycle according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the preset target AC power and the preset power transmission constraint condition; wherein the power transmission constraint condition is used to indicate the constraint relationship between the AC power of the power conversion circuit and the outer phase-shift duty cycle, the inner phase-shift duty cycle, the DC voltage and the AC voltage. ; Adjust the reference outer phase-shift duty cycle according to the real-time AC current on the second end of the AC side bridge circuit and the preset target AC current to obtain the target outer phase-shift duty cycle between the DC side bridge circuit and the AC side bridge circuit; obtain the target switching frequency according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the reference outer phase-shift duty cycle, the target AC power and the preset switching frequency constraint; wherein the switching frequency constraint is used to constrain the size of the switching frequency of the power conversion circuit; control the power transmission of the power conversion circuit according to the target switching frequency, the target inner phase-shift duty cycle and the target outer phase-shift duty cycle.

[0013] In one embodiment, when the power conversion circuit is in different operating conditions, the target switching frequency is different; wherein the operating conditions of the power conversion circuit include light load conditions, half load conditions, and heavy load conditions.

[0014] In one embodiment, the controller is used to: control the switch tubes of the DC side bridge circuit and the AC side bridge circuit to perform soft switching actions according to the target switching frequency, the target internal phase-shift duty cycle and the target external phase-shift duty cycle; wherein, when the switch tube in the DC side bridge circuit is turned on, the secondary current of the transformer is negative polarity; when the switch tube in the AC side bridge circuit is turned on, the secondary current of the transformer is positive polarity.

[0015] The third aspect of the present application provides a power supply system. The power supply system includes: a DC power supply and the power conversion device described in the second aspect of the present application or any one of the embodiments of the second aspect, the DC power supply is connected to the second end of the DC side bridge circuit, the second end of the AC side bridge circuit is connected to the common coupling point, the DC power supply includes at least one of an energy storage device and a photovoltaic power generation device, and the common coupling point is used to connect at least one of a power grid and an AC load.

[0016] Compared with the prior art, this application has at least the following advantages:

[0017] The control method of the power conversion circuit of the present application combines extended-phase shift (EPS) modulation and variable frequency control, which can effectively reduce the current stress of the transformer and reduce the conduction loss of the power device. At the same time, the control method can effectively avoid the soft switching loss phenomenon, realize full-range soft switching, and can be applied to various working conditions. Therefore, the control method of the power conversion circuit of the present application, the power conversion device and the power supply system can improve the power transmission efficiency of the power conversion circuit under various working conditions.

[0018] The control method of the power conversion circuit of the present application constrains the target inner phase-shift duty cycle through the voltage matching constraint condition, constrains the target outer phase-shift duty cycle through the power transmission constraint condition, and constrains the target switching frequency through the switching frequency constraint condition (including the upper frequency limit constraint condition and the lower frequency limit constraint condition), so that the target inner phase-shift duty cycle, the target outer phase-shift duty cycle and the target switching frequency can ensure that the power conversion circuit achieves the effect of reducing the current stress, transmitting the target AC power and realizing soft switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of a power supply system provided in an embodiment of the present application.

[0020] Figure 2 It is a circuit diagram of a power conversion circuit provided in an embodiment of the present application.

[0021] Figure 3 yes Figure 2 The working waveform diagram of the power conversion circuit shown is when it is running forward and the real-time AC voltage is in the positive half cycle.

[0022] Figure 4 It is a flow chart of a control method of a power conversion circuit provided in an embodiment of the present application.

[0023] Figure 5 It is a control loop diagram of the control method of the power conversion circuit provided in an embodiment of the present application.

[0024] Figure 6 yes Figure 4A detailed flow chart of step S50 in the method.

[0025] Figure 7 Under the control of the method of the embodiment of the present application Figure 3 The simulation waveform of the power conversion circuit shown is under full load condition.

[0026] Figure 8 yes Figure 7 A partial enlarged view of part A in FIG.

[0027] Fig. 9 yes Figure 7 A partial enlarged view of part B in FIG.

[0028] Fig.10 Under the control of the method of the embodiment of the present application Figure 3 The simulation waveform diagram of the power conversion circuit shown is under light load condition.

[0029] Fig.11 yes Fig.10 A partial enlarged view of part C in FIG.

[0030] Fig.12 This is the simulation waveform of the non-resonant micro-inverter under the fixed frequency control scheme when it is in light load condition.

[0031] Fig.13 yes Fig.12 A partial enlarged view of part D in FIG.

[0032] Main component symbols

[0033] 100-power supply system, 10-DC power supply, 11-energy storage equipment, 12-photovoltaic power generation equipment, 20-power conversion equipment,

[0034] 21-power conversion circuit, 211-DC side bridge circuit, 2111-first bridge arm, 2112-second bridge arm, 212-transformer,

[0035] 13-resonant inductor, 214-AC side bridge circuit, 2141-third bridge arm, 2142-fourth bridge arm, 22-controller,

[0036] 30- point of common coupling, 40- grid, 50- AC load. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only embodiments of a part of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application. In the absence of conflict, the following different embodiments and features in the embodiments can be combined with each other.

[0038] In the field of new energy, single-stage micro inverters are increasingly widely used. At present, the control strategy of single-stage micro inverters often adopts fixed frequency control, which has the advantages of wide soft switching range and few control variables. However, under fixed frequency control, the soft switching range of micro inverters is narrow, which is prone to soft switching critical phenomenon. Therefore, once there is a parameter error, it is easy to cause soft switching loss and power oscillation, especially in light load conditions, only part of the soft switching within the power frequency cycle can be achieved, resulting in reduced efficiency and device overcurrent stress.

[0039] Therefore, the embodiments of the present application propose a control method for a power conversion circuit, a power conversion device, and a power supply system, which can improve the power transmission efficiency of the power conversion circuit and reduce the current stress of the devices in the power conversion circuit.

[0040] Specifically, see Figure 1 , shows a topological diagram of the power supply system 100 according to an embodiment of the present application.

[0041] like Figure 1 As shown, the power supply system 100 includes a DC power supply 10 and a power conversion device 20. For the convenience of description, the DC power supply 10 is an energy storage device 11 and a photovoltaic power generation device 12. At this time, the power supply system 100 can also be called a photovoltaic storage and charging system.

[0042] It should be understood that in other scenarios, only the photovoltaic power generation device 12 or the energy storage device 11 may be used as the DC power source 10, or other devices that can provide DC power may be used as the DC power source 10. In the scenario where only the photovoltaic power generation device 12 is used as the DC power source 10, the power supply system 100 may also be called a photovoltaic system, and in the scenario where only the energy storage device 11 is used as the DC power source 10, the power supply system 100 may also be called an energy storage system or a storage and charging system.

[0043] The power conversion device 20 is a single-stage micro inverter. The power conversion device 20 includes a power conversion circuit 21. One end of the power conversion circuit 21 is connected to the energy storage device 11 and the photovoltaic power generation device 12. The energy storage device 11 includes a rechargeable energy storage battery. The other end of the power conversion circuit 21 is connected to a common coupling point 30 (abbreviated as PCC). The common coupling point 30 can be used to connect the power grid 40 and the AC load 50.

[0044] In the embodiments of this application, please refer to Figure 2 The power conversion circuit 21 includes a DC side bridge circuit 211, a transformer 212, a resonant inductor 213 (corresponding to Figure 2 Lr in the figure) and the AC side bridge circuit 214, wherein the DC side bridge circuit 211 can adopt a full bridge structure or a half bridge structure, and the AC side bridge circuit 214 adopts a half bridge structure. Therefore, the power conversion circuit 21 can also be called a resonant dual active bridge (DAB) conversion circuit.

[0045] For the convenience of description, the present application embodiment is Figure 2 The DC side bridge circuit 211 shown is a full-bridge structure, and the AC side bridge circuit 214 is a half-bridge structure for exemplary description.

[0046] like Figure 2 As shown, the DC side bridge circuit 211 includes a first bridge arm 2111 and a second bridge arm 2112 connected in parallel, the first bridge arm 2111 includes a first switch tube Q1 and a second switch tube Q2 connected in series, and the second bridge arm 2112 includes a third switch tube Q3 and a fourth switch tube Q4 connected in series. The midpoint of the first bridge arm 2111 and the midpoint of the second bridge arm 2112 together constitute the first end of the DC side bridge circuit 211, and the first end of the DC side bridge circuit 211 is connected to the primary side of the transformer 212. The two ends of the first bridge arm 2111 and the two ends of the second bridge arm 2112 constitute the second end of the DC side bridge circuit 211. The second end of the DC side bridge circuit 211 can be connected to the capacitor Cdc, and can be used to connect the DC power supply 10 or the DC load.

[0047] The AC side bridge circuit 214 includes a third bridge arm 2141 and a fourth bridge arm 2142 connected in parallel, and the third bridge arm 2141 includes a fifth switch tube Q5, a sixth switch tube Q6, a seventh switch tube Q7 and an eighth switch tube Q8 connected in series in sequence, wherein the fifth switch tube Q5 and the sixth switch tube Q6 are connected back to back to form a bidirectional switch, and the seventh switch tube Q7 and the eighth switch tube Q8 are connected back to back to form another bidirectional switch. The fourth bridge arm 2142 includes a first resonant capacitor Cr1 and a second resonant capacitor Cr2 connected in series. The midpoint of the third bridge arm 2141 and the midpoint of the fourth bridge arm 2142 together constitute the first end of the AC side bridge circuit 214, and the first end of the AC side bridge circuit 214 is connected to the secondary side of the transformer 212. The resonant inductor Lr is connected between the midpoint of the third bridge arm 2141 and the secondary side of the transformer 212. The two ends of the third bridge arm 2141 and the two ends of the fourth bridge arm 2142 constitute the second end of the AC side bridge circuit 214. The second end of the AC side bridge circuit 214 can be used to connect to the common coupling point 30, thereby connecting to the AC power supply or the AC load 50. A filtering circuit can be provided between the second end of the AC side bridge circuit 214 and the common coupling point 30, for example Figure 2 The filter inductor Lf in.

[0048] Among them, the first switch tube Q1 to the eighth switch tube Q8 can use corresponding types of semiconductor switch devices according to actual needs. For the convenience of description, Figure 2 In the example, the first switch tube Q1 to the eighth switch tube Q8 are all MOSFETs.

[0049] The turns ratio between the secondary side and the primary side of the transformer 212 is n:1. In short, the turns ratio of the transformer 212 is n, n>1. The secondary leakage inductance of the transformer 212 can be used as the resonant inductor Lr. It should be understood that in some other embodiments, an independently set inductor element can also be used as the resonant inductor Lr, or an independently set inductor element and the secondary leakage inductance can be used as the resonant inductor Lr.

[0050] The resonant inductor Lr, the first resonant capacitor Cr1 and the second resonant capacitor Cr2 together form a resonant circuit. The equivalent impedance Xeq of the resonant circuit is equivalent to the sum of the capacitive reactance of the first resonant capacitor Cr1 and the second resonant capacitor Cr2 connected in series and the inductive reactance of the resonant inductor Lr. That is:

[0051]

[0052] in, is the angular frequency and fs is the switching frequency.

[0053] In the embodiment of the present application, both the DC load and the AC load can be light load, half load or heavy load. The load rate of half load is 50%, and the load rate of light load is less than the load rate of half load, that is, less than 50%. The load rate of heavy load is greater than the load rate of half load, that is, greater than 50%. When the load rate of heavy load reaches 100%, it can be called full load.

[0054] Based on such a design, when the power supply system 100 is working, the energy storage device 11 can be used as a DC power source 10, and the power conversion circuit 21 can transmit the power provided by the energy storage device 11 to the AC load 50 and / or the power grid 40. When the power conversion circuit 21 feeds power to the power grid 40, the power grid 40 can be regarded as an AC load 50. Conversely, the energy storage device 11 can also be used as a DC load, and the power grid 40 can be used as an AC power source. The power conversion circuit 21 can transmit the power provided by the power grid 40 to the energy storage device 11 to charge the energy storage device 11.

[0055] For the convenience of description, in the embodiment of the present application, the process of transmitting power from the DC side bridge circuit 211 to the AC side bridge circuit 214 is referred to as the forward operation process of the power conversion circuit 21, and the process of transmitting power from the AC side bridge circuit 214 to the DC side bridge circuit 211 is referred to as the reverse operation process of the power conversion circuit 21. In other embodiments, the forward and reverse directions may also be reversed, which is not specifically limited here.

[0056] In the above process, the DC side bridge circuit 211 constitutes a DC / AC conversion circuit, and the voltage generated at the second end of the DC side bridge circuit 211 is a DC voltage Vdc. The AC side bridge circuit 214 constitutes an AC / AC conversion circuit, and the voltage generated at the second end of the AC side bridge circuit 214 is an AC voltage Vac.

[0057] The transformer 212 plays an isolation and coupling role, and can transfer energy between the DC side bridge circuit 211 and the AC side bridge circuit 214 through a magnetic field. The resonant circuit can store and transmit energy.

[0058] The voltage generated on the primary side of the transformer 212 may be referred to as the primary voltage Vp. The primary voltage Vp is also the voltage generated on the first end of the DC side bridge circuit 211, or the voltage between the midpoint of the first bridge arm 2111 and the midpoint of the second bridge arm 2112 of the DC side bridge circuit 211 (for convenience of description, referred to as the bridge arm midpoint voltage of the DC side bridge circuit 211).

[0059] The current generated on the secondary side of the transformer 212 may be referred to as the secondary current is. The secondary current is is also the inductor current flowing through the resonant inductor Lr. The voltage generated on the secondary side of the transformer 212 may be referred to as the secondary voltage Vs. The secondary voltage Vs is the voltage on the first end of the AC side bridge circuit 214, or the voltage between the midpoint of the third bridge arm 2141 and the midpoint of the fourth bridge arm 2142 of the AC side bridge circuit 214 (for convenience of description, referred to as the bridge arm midpoint voltage of the AC side bridge circuit 214).

[0060] Furthermore, in the DC side bridge circuit 211, the first switch tube Q1 and the second switch tube Q2 are turned on at high frequency and complementarily, and the third switch tube Q3 and the fourth switch tube Q4 are turned on at high frequency and complementarily. The duty ratio of Q1-Q4 is in the range of (0, 0.5], and the specific size can be adjusted accordingly according to actual conditions.

[0061] There is a conduction phase difference, or conduction time difference, between the first switch tube Q1 and the third switch tube Q3. The conduction phase difference is also the phase difference between the first bridge arm 2111 and the second bridge arm 2112 of the DC side bridge circuit 211, and can therefore be referred to as the internal phase shift angle of the DC side bridge circuit 211. . . D1 is the internal phase shift angle The corresponding duty cycle, that is, the ratio of the conduction time difference between the first switch tube Q1 and the third switch tube Q3 to a switching period Ts, can be referred to as the inner shift phase ratio or the inner shift phase duty cycle. The switching period Ts is equal to the reciprocal of the switching frequency fs.

[0062] When Q1 and Q4 are turned on, it is the first working mode, and the DC side bridge circuit 211 generates a positive level (i.e., a high level) Vp. When Q2 and Q3 are turned on, it is the second working mode, and the DC side bridge circuit 211 generates a negative level (i.e., a low level) Vp. When Q1 and Q3 are turned on, or Q2 and Q4 are turned on, it is the freewheeling mode, and the DC side bridge circuit 211 generates a 0 level Vp. Correspondingly, Figure 3 As shown, the waveform of Vp has three level states.

[0063] Further, in the AC side bridge circuit 214, when the real-time AC voltage is in the positive half cycle, the fifth switch tube Q5 and the seventh switch tube Q7 are turned on with high frequency complementation, the sixth switch tube Q6 and the eighth switch tube Q8 are constantly turned on, at this time, the duty ratio of Q5 and Q7 is equal to 0.5 or close to 0.5, and the duty ratio of Q6 and Q8 is equal to 1. When the real-time AC voltage is in the negative half cycle, the sixth switch tube Q6 and the eighth switch tube Q8 are turned on with high frequency complementation, the fifth switch tube Q5 and the seventh switch tube Q7 are constantly turned on, at this time, the duty ratio of Q6 and Q8 is equal to 0.5 or close to 0.5, and the duty ratio of Q5 and Q7 is equal to 1.

[0064] There is a conduction phase difference, or a conduction time difference, between the fifth switch tube Q5 and the first switch tube Q1. The conduction phase difference can be called the external shift phase angle between the DC side bridge circuit 211 and the AC side bridge circuit 214. . D2 is the duty cycle corresponding to the external shift phase angle, that is, the ratio of the conduction time difference between the fifth switch tube Q5 and the first switch tube Q1 to a switching cycle Ts, which can be referred to as the external shift phase ratio or the external shift phase duty cycle.

[0065] Taking the AC voltage in the positive half cycle as an example, when Q5, Q6 and Q8 are turned on, the AC side bridge circuit 214 generates a positive level (i.e., a high level) Vs; when Q7, Q6 and Q8 are turned on, the AC side bridge circuit 214 generates a negative level (i.e., a low level) Vs. Correspondingly, Figure 3 As shown, the waveform of Vs has two level states.

[0066] There is a phase difference between the waveform of Vs and the waveform of Vp, and this phase difference is equal to the external phase angle It should be understood that the bridge arm midpoint voltages Vp and Vs can be decomposed into fundamental wave components and higher harmonic components. The fundamental wave is the main component. The fundamental wave of Vp and the fundamental wave of Vs are both sinusoidal waves, and there is a corresponding phase difference between the peak values ​​of the two, which is also equal to the external phase shift angle Among them, the outward phase angle The polarity of is associated with the operating direction of the power conversion circuit 21. For example, when the power conversion circuit 21 is running in the forward direction, Vp leads Vs, so the phase angle is shifted outward. When the power conversion circuit 21 runs in reverse, Vp lags behind Vs, so the external phase angle is negative.

[0067] Please continue reading Figure 1 The power conversion device 20 further includes a controller 22. The controller 22 may be a microcontroller unit (MCU), a digital signal processor (DSP) or other control elements or circuits. Figure 1 As shown, the controller 22 is connected to the power conversion circuit 21. Specifically, when the power conversion circuit 21 adopts Figure 2 In the circuit shown, the controller 22 is connected to the control ends of the switch tubes Q1 to Q8 in the DC side bridge circuit 211 and the AC side bridge circuit 214 .

[0068] The controller 22 can be used to execute the control method of the power conversion circuit provided in the embodiment of the present application. The control method combines extended-phase shift (EPS) modulation and variable frequency control to control the operation of the power conversion circuit 21 through three control degrees of freedom: inner phase shift duty cycle D1, outer phase shift duty cycle D2 and switching frequency fs.

[0069] Next, based on Figure 2 The structural topology of the power conversion circuit 21 shown in FIG. Figure 4 and Figure 5 The control method of the power conversion circuit in the embodiment of the present application is described in detail. Figure 4 A flow chart showing a control method of a power conversion circuit according to an embodiment of the present application is shown. Figure 5 A control loop diagram of a control method for a power conversion circuit according to an embodiment of the present application is shown. For simplified illustration, Figure 5 The input parameters of each constraint condition link only show some parameters that need to be detected or preset.

[0070] Please also read Figure 4 and Figure 5 , the control method of the embodiment of the present application includes:

[0071] Step S10, acquiring a real-time DC voltage on the second end of the DC-side bridge circuit, and a real-time AC voltage and a real-time AC current on the second end of the AC-side bridge circuit.

[0072] Among them, the controller 22 can perform voltage sampling on the second end of the DC side bridge circuit 211 through the voltage sampling circuit to obtain the real-time DC voltage Vdc, perform voltage sampling on the second end of the AC side bridge circuit 214 through the voltage sampling circuit to obtain the real-time AC voltage Vac, and perform current sampling on the second end of the AC side bridge circuit 214 through the current sampling circuit to obtain the real-time AC current iac.

[0073] Step S20: Obtain a target inner phase shift duty ratio corresponding to the highest voltage matching degree according to the real-time DC voltage and the real-time AC voltage.

[0074] Specifically, step S20 may include the following sub-steps:

[0075] Step S201, obtaining a voltage matching constraint condition. The voltage matching constraint condition is used to indicate that the voltage matching is determined by the inner phase shift duty cycle, the DC voltage, the AC voltage and the turns ratio of the transformer.

[0076] It can be understood that when the circuit 21 adopts the SPS single-phase shift modulation method, since the duty cycle of the switching tubes in the AC side bridge circuit 214 and the DC side bridge circuit 211 are fixed at 0.5, the voltage matching degree can be accurately described by directly using the ratio of the output voltage to the input voltage.

[0077] In the embodiment of the present application, Figure 2 The power conversion circuit 21 shown adopts the EPS extended phase-shift modulation method. In this case, the duty cycle of the switch tubes Q5~Q8 in the AC side bridge circuit 214 is stable in the positive and negative half cycles of the AC voltage, and the duty cycle of the switch tubes Q1~Q4 in the DC side bridge circuit 211 is variable. Therefore, it is more appropriate and accurate to use the ratio of the effective value of the output voltage to the effective value of the input voltage to describe the voltage matching degree K.

[0078] Taking the second end of the AC side bridge circuit 214 as an output end and the second end of the DC side bridge circuit 211 as an input end as an example, in step S201, the voltage matching constraint condition can be expressed as the ratio of the effective value of the AC voltage Vac on the second end of the AC side bridge circuit 214 to the effective value of the DC voltage Vdc on the second end of the DC side bridge circuit 211, that is:

[0079]

[0080] It can be seen from formula (3) that the voltage matching degree K is negatively correlated with the DC voltage Vdc, K is negatively correlated with the turns ratio of the transformer 212, K is negatively correlated with the internal phase shift duty cycle D1, and K is positively correlated with the absolute value of the AC voltage |Vac|.

[0081] When K=1, the voltage matching degree is the highest. At this time, it can be obtained from formula (3):

[0082]

[0083] It should be understood that the expression of the voltage matching constraint condition may be different according to different power conversion circuits 21, all within the protection scope of the embodiments of the present application.

[0084] Step S202: Calculate the target inner phase shift duty ratio corresponding to the highest voltage matching degree according to the real-time DC voltage, the real-time AC voltage and the voltage matching degree constraint condition.

[0085] Specifically, the turns ratio n of the transformer 212 is a known device parameter. The absolute value of the real-time DC voltage Vdc, the real-time AC voltage Vac and the turns ratio n of the transformer 212 can be substituted into the expression of the voltage matching constraint condition (for example, equation (4)) to calculate the target internal phase shift duty cycle D1.

[0086] It can be understood that when the voltage does not match, that is, when the voltage matching degree is low, the effective value of the AC voltage Vac is not equal to the effective value of the DC voltage Vdc, which will generate a large reflux power, increase the inductor current, that is, increase the current stress, and make it difficult to achieve soft switching. When the voltage matching degree K is the highest, since the effective value of the AC voltage Vac remains equal to the effective value of the DC voltage Vdc, the reflux power is the least. Therefore, once the AC voltage is reduced, the positive and negative level durations of the DC voltage Vdc are also reduced at the same time, and the 0 level duration of the DC voltage Vdc is correspondingly increased, which reduces the rise and fall time of the current, and the current stress is reduced accordingly. Therefore, the highest voltage matching degree can reduce current stress and facilitate soft switching.

[0087] Therefore, in step S20, by determining the target inner phase shift duty ratio corresponding to the highest voltage matching degree, it is helpful to reduce current stress and achieve soft switching.

[0088] Step S30, obtaining a reference outer phase-shift duty cycle according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the preset target AC power and the preset power transmission constraint condition, wherein the power transmission constraint condition is used to indicate the constraint relationship between the AC power of the power conversion circuit and the outer phase-shift duty cycle, the inner phase-shift duty cycle, the DC voltage and the AC voltage.

[0089] Among them, the target AC power The size of can be selected according to the needs of AC load or DC load, and is not specifically limited here.

[0090] In the embodiment of the present application, according to the fundamental wave analysis method, it can be obtained Figure 2 The power transfer expression of the power conversion circuit 21 shown is:

[0091]

[0092] Wherein, Pac is the AC power of the power conversion circuit 21, PN is the reference power, and |Vac| is the absolute value of the AC voltage. Formula (5) and Formula (6) are the power transmission constraints.

[0093] Therefore, in step S30, the real-time DC voltage Vdc, the absolute value of the real-time AC voltage |Vac|, the target internal phase shift duty cycle D1, and the target AC power Substituting the transformer turns ratio n and the equivalent impedance Xeq of the resonant circuit into the above equations (5) and (6), we can obtain , and then solve the reference external phase shift duty cycle D2'.

[0094] The equivalent impedance Xeq of the resonant circuit can be calculated according to the real-time switching frequency, the first resonant capacitor, the second resonant capacitor and the resonant inductor through the above equations (1) and (2). The first resonant capacitor, the second resonant capacitor and the resonant inductor are all known device parameters.

[0095] It should be understood that the expression of the power transmission constraint condition may be different according to different power conversion circuits 21, all within the protection scope of the embodiments of the present application.

[0096] Step S40: adjusting the reference outer phase-shift duty cycle according to the real-time AC current and the preset target AC current to obtain a target outer phase-shift duty cycle between the DC side bridge circuit and the AC side bridge circuit.

[0097] In the embodiment of the present application, a current loop can be established according to the real-time AC current and the preset target AC current to adjust the reference external phase shift duty cycle. Accordingly, the process of step S40 may include:

[0098] Step S401: Calculate the current difference between the preset expected AC current and the real-time AC current.

[0099] Specifically, the expected AC current can be determined based on the power required by the AC load or DC load and the real-time AC voltage. When the second end of the AC side bridge circuit 214 is connected to the grid through the common coupling point, the phase of the grid voltage can be obtained through the phase-locked loop, and the phase of the grid voltage can be used as the desired AC current The phase of the phase-locked loop includes but is not limited to a second-order generalized integrator phase-locked loop (SOGI-PLL). When the second end of the AC side bridge circuit 214 is connected to the AC load through a common coupling point and is not connected to the power grid, the phase of the rated working current of the load can be used as the expected AC current phase.

[0100] In step S401, the desired AC current The instantaneous value of the real-time AC current iac is subtracted from the instantaneous value of the real-time AC current iac to obtain the current difference .

[0101] Step S402: performing deviation adjustment on the current difference to obtain a compensation amount of the outer phase shift duty cycle.

[0102] The deviation adjustment method includes but is not limited to proportional resonant (PR) adjustment. PR adjustment can eliminate iac and The effect of steady-state error.

[0103] Step S403: Obtain a target outer phase-shift duty cycle according to a reference outer phase-shift duty cycle and a compensation amount of the outer phase-shift duty cycle.

[0104] The reference external phase-shift duty cycle is used as a feedforward quantity, and the compensation quantity of the external phase-shift duty cycle can compensate the feedforward quantity.

[0105] In step S403, the reference external phase-shift duty cycle D2' and the compensation amount ΔD2 of the external phase-shift duty cycle may be mathematically calculated to obtain the target external phase-shift duty cycle D2. Figure 5 As shown, the reference external phase-shift duty cycle D2' and the compensation amount ΔD2 of the external phase-shift duty cycle can be added to obtain the target external phase-shift duty cycle D2. That is, D2 = D2' + ΔD2.

[0106] Step S50, according to the real-time DC voltage, the real-time AC voltage, the target inner phase shift duty cycle, the reference outer phase shift duty cycle, the target AC power and the preset switching frequency constraint condition, the target switching frequency is obtained. The switching frequency constraint condition is related to the DC voltage, the AC voltage, the inner phase shift duty cycle, the outer phase shift duty cycle and the AC power, and the switching frequency constraint condition is used to constrain the switching frequency of the power conversion circuit.

[0107] Specifically, the real-time DC voltage Vdc, the real-time AC voltage Vac, the target inner phase shift duty cycle D1, the reference outer phase shift duty cycle D2' and the target AC power Substitute the switching frequency constraints to calculate the target switching frequency fs.

[0108] It can be understood that because the real-time DC voltage Vdc, the real-time AC voltage Vac, the target inner phase shift duty cycle D1, the reference outer phase shift duty cycle D2' and the target AC power are all variable, therefore, according to the real-time DC voltage Vdc, the real-time AC voltage Vac, the target inner phase shift duty cycle D1, the reference outer phase shift duty cycle D2', the target AC power The calculated target switching frequency fs is also variable and not a fixed value.

[0109] For example, under different working conditions, the real-time DC voltage Vdc, the real-time AC voltage Vac, the target inner phase shift duty cycle D1, the reference outer phase shift duty cycle D2' and the target AC power Therefore, when the power conversion circuit is in different working conditions, different target switching frequencies suitable for the corresponding working conditions can be calculated through step S50.

[0110] In the embodiment of the present application, the switching frequency constraint condition can be set according to the actual situation. For example, different switching frequency constraint condition expressions can be established according to different power conversion circuit topologies, different optimization objectives, etc.

[0111] For example, in one embodiment, the switching frequency constraint condition may be related to power transmission and soft switching optimization. The target switching frequency fs always satisfies the switching frequency constraint condition, that is, it is always within the boundary range of the switching frequency limited by the switching frequency constraint condition, so that the power conversion circuit 21 can complete the transmission of the target AC power and realize soft switching at the target switching frequency.

[0112] Specifically, the switching frequency constraint condition includes a lower frequency constraint condition and an upper frequency constraint condition. Among them, the lower frequency constraint condition is used to constrain the lower limit of the switching frequency when the power conversion circuit 21 is soft switched. The upper frequency constraint condition is used to constrain the upper limit of the switching frequency when the power conversion circuit 21 transmits the target AC power.

[0113] by Figure 2 Take the power conversion circuit 21 shown in FIG. 2 as an example. Before the switch tube of the DC side bridge circuit 211 or the AC side bridge circuit 214 is turned off, since the switch tube is already turned on, the voltage across the switch tube (i.e., the drain-source) is already 0 or nearly 0. Therefore, it can be considered that when the switch tube is turned off, it is a natural zero voltage turn-off. Therefore, the zero switching of the DC side bridge circuit 211 and the AC side bridge circuit 214 is mainly considered to be zero voltage turn-on.

[0114] For the DC side bridge circuit 211, before the switch tube of the DC side bridge circuit 211 is turned on, if the primary current can flow through the body diode of the switch tube (at this time, the secondary current is<0), the voltage across the switch tube will be clamped to 0 or nearly 0, so the switch tube can achieve zero voltage turn-on at the turn-on moment.

[0115] Therefore, the zero voltage switch (ZVS) condition of the switch tube of the DC side bridge circuit 211 can be: when the switch tube of the DC side bridge circuit 211 is turned on, the secondary current is<0. The corresponding expression can be as follows:

[0116]

[0117] For the AC side bridge circuit 214, before the switch tube of the AC side bridge circuit 214 is turned on, if the secondary current is>0, the secondary current can flow through the body diode of the switch tube, and the voltage across the switch tube is clamped to almost 0, so the switch tube can achieve zero voltage turn-on at the turn-on moment.

[0118] Therefore, the zero voltage switch (ZVS) condition of the switch tube of the AC side bridge circuit 214 can be: when the switch tube of the AC side bridge circuit 214 is turned on, the secondary current is (ie, the inductor current)>0. The corresponding expression can be as follows:

[0119]

[0120] According to equations (7) and (8), the frequency lower limit constraint condition shown in equation (9) can be obtained as follows:

[0121]

[0122] Among them, fsmin refers to the lower limit of the switching frequency; max( ) is the maximum value function; Leq0 and Leq1 are the intermediate variables in the fsmin solution process, which are expressed as follows:

[0123]

[0124] In addition, to ensure that the power conversion circuit 21 can reach the target AC power , combining equations (5), (6), and (1), and using the root-finding formula, we can get the angular frequency The constraint range of , and then according to formula (2), the upper frequency limit constraint condition shown in formula (11) can be obtained:

[0125]

[0126] Among them, fsmax refers to the upper limit of the switching frequency; Leq2 is the intermediate variable in the fsmax solution process, which is expressed as follows:

[0127]

[0128] Correspondingly, such as Figure 6 As shown, the process of step S50 may include the following sub-steps:

[0129] Step S501, determining the upper limit of the switching frequency according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the reference outer phase-shift duty cycle, the target AC power and the upper limit constraint of the frequency.

[0130] In step S501, the real-time DC voltage Vdc, the real-time AC voltage Vac, the target inner phase shift duty cycle D1, the reference outer phase shift duty cycle D2', the target AC power Substitute it into the expression of the upper frequency limit constraint to calculate the upper limit of the switching frequency fsmax.

[0131] Step S502: Determine the lower limit of the switching frequency according to the real-time DC voltage, the real-time AC voltage, the target internal phase shift duty cycle, the target AC power and the frequency lower limit constraint.

[0132] In step S502, the real-time DC voltage Vdc, the real-time AC voltage Vac, the target inner phase shift duty cycle D1, the reference outer phase shift duty cycle D2', the target AC power Substitute it into the expression of the frequency lower limit constraint to calculate the lower limit of the switching frequency fsmin.

[0133] Step S503: Calculate the target switching frequency according to the upper limit of the switching frequency and the lower limit of the switching frequency.

[0134] In step S503, a mathematical operation may be performed on fsmax and fsmin to obtain the target switching frequency fs, so as to ensure that the target switching frequency fs never exceeds the upper limit fsmax and the lower limit fsmin limited by the switching frequency constraint condition.

[0135] For example, in one embodiment, the upper limit of the switching frequency and the lower limit of the switching frequency may be averaged to obtain the target switching frequency fs, fs=0.5fsmax+0.5fsmin. Obviously, the target switching frequency fs is neither lower than fsmin defined by the frequency lower limit constraint nor higher than fsmax defined by the frequency upper limit constraint, so it is beneficial to ensure soft switching and power margin.

[0136] Step S60: Controlling power transmission of the power conversion circuit according to the target switching frequency, the target inner phase-shift duty cycle, and the target outer phase-shift duty cycle.

[0137] In step S60, the controller 22 may generate corresponding control signals according to the target switching frequency fs, the target inner phase shift duty cycle D1, and the target outer phase shift duty cycle D2, and send them to the control end of the switch tube in the power conversion circuit 21. Under the control of the control signals, the switch tubes of the DC side bridge circuit 211 and the AC side bridge circuit 214 perform soft switching actions, so that the power conversion circuit 21 generates corresponding voltage and current, and transmits corresponding power.

[0138] Specifically, the phase difference between the first bridge arm and the second bridge arm in the DC side bridge circuit 211 is equal to the internal phase shift angle corresponding to the target internal phase shift duty cycle D1. The phase difference between the voltage waveform on the first end of the DC side bridge circuit 211 and the voltage waveform on the first end of the AC side bridge circuit 214 is equal to the external phase shift angle corresponding to the target external phase shift duty cycle D2. The switch tubes of the DC side bridge circuit 211 and the AC side bridge circuit 214 perform soft switching on and off actions at the target switching frequency.

[0139] Further, the control signal of the first switch tube Q1 is represented by S1, the control signal of the second switch tube Q2 is represented by S2, the control signal of the third switch tube Q3 is represented by S3, and so on, ..., the control signal of the eighth switch tube Q1 is represented by S8. The control signal can be a pulse width modulation (PWM) control signal, a pulse frequency modulation (PFM) control signal, or a control signal combining PWM and PFM. Take the control signal as an example that the switch tube is turned on when the control signal is at a high level and the switch tube is turned off when the control signal is at a low level.

[0140] S1 and S2 are complementary, S3 and S4 are complementary, and the phase difference between S1 and S3 is equal to the target internal phase shift angle When the real-time AC voltage Vac is in the positive half cycle, S5 and S7 complement each other, and S6 and S8 maintain a high level. When the real-time AC voltage Vac is in the negative half cycle, S6 and S8 complement each other, and S5 and S7 maintain a high level. The phase difference between S5 and S1 is equal to the target external phase shift angle .

[0141] Therefore, if Figure 4 As shown, under the control of the control signals S1-S4, the first switch tube Q1 and the second switch tube Q2 are complementarily turned on, the third switch tube Q3 and the fourth switch tube Q4 are complementarily turned on, and the conduction phase difference between the first switch tube Q1 and the third switch tube Q3 is equal to the target inner phase shift angle .

[0142] Under the control of the control signals S5-S8, when the real-time AC voltage Vac is in the positive half cycle, the fifth switch tube Q5 and the seventh switch tube Q7 are controlled to be turned on complementarily, and the sixth switch tube Q6 and the eighth switch tube Q8 are constantly turned on; when the real-time AC voltage Vac is in the negative half cycle, the fifth switch tube Q5 and the seventh switch tube Q7 are controlled to be constantly turned on, and the sixth switch tube Q6 and the eighth switch tube Q8 are complementarily turned on; the conduction phase difference between the fifth switch tube Q5 and the first switch tube Q1 is equal to the target external phase shift angle .

[0143] Among them, when the target moves outward, the phase angle When the polarity is positive, the power conversion circuit 21 uses the second end of the primary bridge circuit 211 as the input end and the second end of the secondary bridge circuit 214 as the output end, and the power is transmitted from the primary bridge circuit 211 to the secondary bridge circuit 214. Accordingly, the waveform of the voltage Vp on the first end of the primary bridge circuit 211 is at the target external phase shift angle The waveform of the voltage Vs at the first end of the secondary bridge circuit 214 is ahead of the waveform of the voltage Vs at the first end of the secondary bridge circuit 214 , and the real-time AC power output at the second end of the secondary bridge circuit 214 is equal to the target AC power.

[0144] When the target outward phase angle When the polarity is negative, the power conversion circuit 21 uses the second end of the secondary bridge circuit 214 as the input end and the second end of the primary bridge circuit 211 as the output end, and the power is transmitted from the secondary bridge circuit 214 to the primary bridge circuit 211. Accordingly, the waveform of the voltage Vp on the first end of the primary bridge circuit 211 is at the target external phase shift angle The waveform of the voltage Vs at the first end of the secondary bridge circuit 214 lags behind that of the voltage Vs at the first end of the secondary bridge circuit 214 , and the real-time AC power input at the second end of the secondary bridge circuit 214 is equal to the target AC power.

[0145] Moreover, when the switch tube in the DC side bridge circuit 211 is turned on, the secondary current is is just negative (that is, is less than 0), so that the switch tube of the DC side bridge circuit 211 can be turned on at zero voltage. When the switch tube in the AC side bridge circuit 214 is turned on, the secondary current is is just positive (that is, is greater than 0), so that the switch tube of the AC side bridge circuit 214 can be turned on at zero voltage.

[0146] In addition, in order to verify the control effect of the control method of the embodiment of the present application, the embodiment of the present application also conducted a simulation experiment. Among them, the simulation parameters are shown in Figure 1. In addition, the expected AC current peak value of the power conversion circuit 21 is set to 3.21A, and the power conversion circuit 21 is in a grid-connected, full-load, forward operating condition.

[0147] Table 1

[0148]

[0149] Combine the following Figures 7 to 13 It should be understood that Figures 7 to 13 The data of the horizontal and vertical coordinates shown are only examples and do not constitute a special limitation on the embodiments of the present application. In addition, for the convenience of description, Figure 8 , Fig. 9 , Fig.11 and Fig.13 In the figure, the relatively advanced switch tube in the DC side bridge circuit 211 is referred to as the primary leading tube, the relatively lagging switch tube in the DC side bridge circuit 211 is referred to as the primary lagging tube, and the switch tube in the AC side bridge circuit 214 is referred to as the secondary tube.

[0150] See also Figures 7 to 9 , Figure 7 The controller 22 is shown to control the Figure 3The simulation waveform diagram of the power conversion circuit 21 is shown. Figure 8 Shows Figure 7 A partial enlarged view of part A in Fig. 9 Shows Figure 7 A partial enlarged view of part B in the figure, where part A corresponds to Figure 7 At the high phase of the waveform (approximately at the peak), part B corresponds to Figure 7 The low phase of the waveform (close to the trough).

[0151] from Figures 7 to 9 It can be seen that the waveforms of the real-time AC current iac, the primary voltage Vp, the secondary voltage Vs, and the secondary current is generated by the power conversion circuit 21 can all change regularly and periodically, wherein the primary voltage Vp leads the secondary voltage Vs, and the peak value of the real-time AC current iac can reach the expected AC current peak value. The transmission power can be calculated from the effective value of the real-time AC current iac and the effective value of the real-time AC voltage Vac (same as Vg) to be: , reaching the rated power. Moreover, the AC voltage iac has good sinusoidality and low distortion. This shows that under the grid-connected working condition, the method of the embodiment of the present application can control the power conversion circuit 21 to stably run forward, achieve full power output, and the output power quality is good.

[0152] Further, such as Figure 8 , Fig. 9 As shown by the first dotted vertical line in , when Vp changes from 0 level to positive level, the corresponding secondary current is is less than 0, indicating that at this time, the switch tube of the DC side bridge circuit 211 is switched from the freewheeling mode to the first working mode, and the primary leading tube Q1 / Q4 is soft switched. At the moment of completion of the on-off action, Q1 and Q4 are both turned on, and Q2 and Q3 are both turned off.

[0153] like Figure 8 , Fig. 9 As shown by the third dotted vertical line in , when Vp changes from negative level to 0 level, the corresponding secondary current is is less than 0, indicating that at this time, the switch tube of the DC side bridge circuit 211 is switched from the second working mode to the freewheeling mode, and the primary side lagging tube Q2 / Q3 is soft switched. At the moment of completion of the on-off action, Q1 and Q2 are both turned on, and Q3 and Q4 are both turned off.

[0154] like Figure 8 , Fig. 9 As shown by the second dotted vertical line in , when Vs changes level, the corresponding secondary current is is greater than 0, indicating that the secondary tubes Q5-Q8 of the AC side bridge circuit 214 perform soft switching. When the on-off action is completed, Q5, Q6, and Q8 are all turned on, and Q7 is turned off.

[0155] It can be seen that under the control of the method of the embodiment of the present application, the switch tube of the DC side bridge circuit 211 and the switch tube of the AC side bridge circuit 214 can both achieve soft switching, and Figure 7 and Figure 8 As shown, the maximum current of the secondary side of the transformer is 11.5A, indicating that the current stress is only 11.5A.

[0156] In addition, in order to verify the performance of the power conversion circuit 21 of the embodiment of the present application under light load conditions, the embodiment of the present application also conducts a comparative experiment on the control method of the embodiment of the present application (i.e., variable frequency control) and the existing fixed frequency control scheme. It should be understood that the circuit topology of the micro-inverter under the fixed frequency control scheme is the same as the circuit topology of the micro-inverter in the embodiment of the present application, but the two capacitors Cr1 and Cr2 of the fourth bridge arm in the fixed frequency control scheme do not participate in the resonance, that is, Cr1 and Cr2 do not form a resonant circuit together with the resonant inductor Lr, and the switching frequency is fixed, so the micro-inverter under the fixed frequency control scheme is a non-resonant micro-inverter.

[0157] In the comparative experiment, the target AC power was uniformly set to 100W, the switching frequency of the non-resonant micro-inverter used in the fixed-frequency control scheme was fixed to 100kHz, and other experimental conditions were the same.

[0158] See also Figures 10 to 13 , Fig.10 The simulation waveform diagram of the method of the embodiment of the present application is shown. Fig.11 Shows Fig.10 A partial enlarged view of part C in FIG. Fig.12 The simulation waveform of the fixed frequency control scheme is shown. Fig.13 Shows Fig.12 A partial enlarged view of part D in FIG.

[0159] from Fig.10 and Fig.11 It can be seen that under light load conditions, the primary leading tube action (corresponding to Fig.11 The first dotted vertical line in the figure) and the hysteresis tube action (corresponding to Fig.11 When is is less than 0, the primary leading and lagging transistors can be soft switched. Fig.11 ), is greater than 0, so the secondary tube can also be soft-switched. It can be seen that under light load conditions, the resonant power conversion circuit 21 of the embodiment of the present application can still achieve the original secondary soft switching by using the method of the embodiment of the present application (i.e., variable frequency control). In addition, if Fig.10 and Fig.11 As shown, the secondary current of the transformer is 2.6A, indicating that the current stress is 2.6A.

[0160] from Fig.12 and Fig.13 It can be seen that under light load conditions, the primary leading tube action (corresponding to Fig.13 The first dotted vertical line in the figure) and the hysteresis tube action (corresponding to Fig.13 When is is greater than 0, the primary leading and lagging tubes cannot achieve soft switching. It can be seen that the non-resonant micro inverter adopts a fixed frequency control scheme, which will lose the soft switching of the primary leading and lagging tubes, that is, lose part of the soft switching. Moreover, if Fig.12 and Fig.13 As shown, the secondary current of the transformer is 5A, which means that the current stress is as high as 5A, which is significantly larger than the 2.6A current stress corresponding to the variable frequency control.

[0161] In general, compared with the fixed frequency control scheme, the control method of the embodiment of the present application can reduce the transformer current stress of the micro inverter, effectively reduce the copper loss of the transformer and the conduction loss of the switch tube. At the same time, the control method of the embodiment of the present application can realize full-range soft switching, further reducing the turn-on loss of the switch tube. Fig.11 The Vs peak value is greater than Fig.13 It can also be seen from the Vs peak value that the power loss generated by the control method of the embodiment of the present application is small. Therefore, the control method of the embodiment of the present application can improve the power transmission efficiency of the micro inverter under various working conditions.

[0162] Therefore, in summary, the control method, power conversion device and power supply system of the power conversion circuit of the embodiment of the present application combine extended phase-shift modulation and frequency conversion control, which can effectively reduce the current stress of the transformer and reduce the conduction loss of the power device. At the same time, the control method can effectively avoid the soft switching loss phenomenon, realize full-range soft switching, and can be applied to various working conditions. Therefore, the control method, power conversion device and power supply system of the power conversion circuit of the embodiment of the present application can improve the power transmission efficiency of the power conversion circuit under various working conditions.

[0163] It can be understood that extended phase shift modulation involves two control degrees of freedom (inner phase shift duty cycle D1 and outer phase shift duty cycle D2). The high control degree of freedom is beneficial to the performance optimization and control effect of the power conversion circuit 21.

[0164] Different from the fixed switching frequency under fixed frequency control, the switching frequency under variable frequency control can be adjusted accordingly according to the actual situation, so as to avoid the critical phenomenon of soft switching. Therefore, the method of the embodiment of the present application can more easily ensure the full range soft switching of the power conversion circuit and avoid the generation of power oscillation, effectively improving the transmission efficiency and reducing the current stress.

[0165] Moreover, in the method of the embodiment of the present application, a voltage matching constraint is used to constrain the target inner phase-shift duty cycle D1, a power transmission constraint is used to constrain the target outer phase-shift duty cycle D2, and a switching frequency constraint (including an upper frequency limit constraint and a lower frequency limit constraint) is used to constrain the target switching frequency fs, so that the target inner phase-shift duty cycle D1, the target outer phase-shift duty cycle D2 and the target switching frequency fs can ensure that the power conversion circuit achieves current stress reduction, reaches the target AC power and realizes the effect of soft switching.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application and are not intended to limit it. Although the present application has been described in detail with reference to the preferred embodiments, a person of ordinary skill in the art should understand that the technical solution of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present application.

Claims

1. A control method for a power conversion circuit, characterized in that: The power conversion circuit includes a DC side bridge circuit, a transformer, a resonant inductor and an AC side bridge circuit, wherein the first end of the DC side bridge circuit is connected to the primary side of the transformer, and the first end of the AC side bridge circuit is connected to the secondary side of the transformer through the resonant inductor; wherein the DC side bridge circuit includes a first bridge arm and a second bridge arm connected in parallel, and the AC side bridge circuit includes a third bridge arm and a fourth bridge arm connected in parallel, wherein the first bridge arm, the second bridge arm and the third bridge arm all include a switch tube, and the fourth bridge arm includes a resonant capacitor, and the resonant capacitor and the resonant inductor constitute a resonant circuit; and the control method includes: Acquire a real-time DC voltage on the second end of the DC-side bridge circuit, and a real-time AC voltage and a real-time AC current on the second end of the AC-side bridge circuit; According to the real-time DC voltage and the real-time AC voltage, a target internal phase shift duty ratio of the DC side bridge circuit corresponding to the highest voltage matching degree is obtained; wherein the voltage matching degree refers to the ratio of the effective value of the output voltage of the power conversion circuit to the effective value of the input voltage, one of the real-time DC voltage and the real-time AC voltage is the output voltage, and the other of the real-time DC voltage and the AC voltage is the input voltage; A reference outer phase-shift duty cycle is obtained according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the preset target AC power and the preset power transmission constraint condition; wherein the power transmission constraint condition is used to indicate the constraint relationship between the AC power of the power conversion circuit and the outer phase-shift duty cycle, the inner phase-shift duty cycle, the DC voltage and the AC voltage; Adjusting the reference outer phase shift duty cycle according to the real-time AC current and the preset target AC current to obtain a target outer phase shift duty cycle between the DC side bridge circuit and the AC side bridge circuit; A target switching frequency is obtained according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the reference outer phase-shift duty cycle, the target AC power and a preset switching frequency constraint; wherein the switching frequency constraint is used to constrain the magnitude of the switching frequency of the power conversion circuit; Power transmission of the power conversion circuit is controlled according to the target switching frequency, the target inner phase-shifted duty cycle, and the target outer phase-shifted duty cycle.

2. The control method according to claim 1, characterized in that: The switching frequency constraint condition includes an upper frequency limit constraint condition and a lower frequency limit constraint condition; The step of obtaining a target switching frequency according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the reference outer phase-shift duty cycle, the target AC power and a preset switching frequency constraint condition includes: Determining an upper limit of a switching frequency according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the reference outer phase-shift duty cycle, the target AC power and the upper frequency limit constraint; wherein the upper frequency limit constraint is used to constrain an upper limit of a switching frequency when the power conversion circuit transmits the target AC power; Determining a lower limit of a switching frequency according to the real-time DC voltage, the real-time AC voltage, the target internal phase shift duty cycle, the target AC power and the frequency lower limit constraint; wherein the frequency lower limit constraint is used to constrain the lower limit of the switching frequency during soft switching of the power conversion circuit; The target switching frequency is calculated according to the upper limit of the switching frequency and the lower limit of the switching frequency.

3. The control method according to claim 2, characterized in that: The calculating the target switching frequency according to the upper limit of the switching frequency and the lower limit of the switching frequency includes: The upper limit of the switching frequency and the lower limit of the switching frequency are averaged to obtain the target switching frequency.

4. The control method according to any one of claims 1 to 3, characterized in that: The controlling the power transmission of the power conversion circuit according to the target switching frequency, the target inner phase-shift duty cycle and the target outer phase-shift duty cycle comprises: According to the target switching frequency, the target inner phase-shift duty cycle, and the target outer phase-shift duty cycle, the switch tubes of the DC side bridge circuit and the AC side bridge circuit are controlled to perform soft switching action; Wherein, when the switch tube in the DC side bridge circuit is turned on, the secondary current of the transformer is negative polarity; When the switch tube in the AC side bridge circuit is turned on, the secondary current of the transformer is positive.

5. The control method according to claim 4, characterized in that: The step of controlling the switch tubes of the DC side bridge circuit and the AC side bridge circuit to perform soft switching according to the target switching frequency, the target inner phase shift duty cycle, and the target outer phase shift duty cycle includes: Controlling the phase difference between the first bridge arm and the second bridge arm in the DC side bridge circuit to be equal to the inner phase shift angle corresponding to the target inner phase shift duty cycle; Controlling the phase difference between the voltage waveform on the first end of the DC side bridge circuit and the voltage waveform on the first end of the AC side bridge circuit to be equal to the external phase shift angle corresponding to the target external phase shift duty cycle; The switch tubes in the DC side bridge circuit and the AC side bridge circuit are controlled to perform soft switching on and off actions at the target switching frequency.

6. The control method according to claim 4, characterized in that: The first bridge arm includes a first switch tube and a second switch tube connected in series, the second bridge arm includes a third switch tube and a fourth switch tube connected in series, the third bridge arm includes a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube connected in series in sequence, wherein the fifth switch tube and the sixth switch tube are connected back to back, the seventh switch tube and the eighth switch tube are connected back to back, the fourth bridge arm includes a first resonant capacitor and a second resonant capacitor connected in series, and the first resonant capacitor, the second resonant capacitor and the resonant inductor constitute the resonant circuit; The process of controlling the switch tubes of the DC side bridge circuit and the AC side bridge circuit to perform soft switching according to the target switching frequency, the target inner phase shift duty cycle, and the target outer phase shift duty cycle includes: Controlling the first switch tube and the second switch tube to be complementary turned on, the third switch tube and the fourth switch tube to be complementary turned on, and the conduction phase difference between the first switch tube and the third switch tube is equal to the inner phase shift angle corresponding to the target inner phase shift duty cycle; When the real-time AC voltage is in a positive half cycle, the fifth switch tube and the seventh switch tube are controlled to be complementary turned on, and the sixth switch tube and the eighth switch tube are constantly turned on; When the real-time AC voltage is in a negative half cycle, the fifth switch tube and the seventh switch tube are controlled to be constantly turned on, and the sixth switch tube and the eighth switch tube are controlled to be complementarily turned on.

7. The control method according to claim 1, characterized in that: The step of obtaining a target inner phase shift duty ratio of the DC side bridge circuit corresponding to a highest voltage matching degree according to the real-time DC voltage and the real-time AC voltage includes: Obtaining a voltage matching constraint condition; the voltage matching constraint condition is used to indicate that the voltage matching is determined by the inner phase shift duty cycle, the DC voltage, the AC voltage and the turns ratio of the transformer; The target inner phase shift duty ratio corresponding to the highest voltage matching degree is calculated according to the real-time DC voltage, the real-time AC voltage and the voltage matching degree constraint condition.

8. The control method according to claim 1, characterized in that: The step of adjusting the reference external phase-shift duty cycle according to the real-time AC current and the preset target AC current to obtain a target external phase-shift duty cycle between the DC side bridge circuit and the AC side bridge circuit includes: Calculating a current difference between a preset expected alternating current and the real-time alternating current; Performing deviation adjustment on the current difference to obtain a compensation amount of the outer phase shift duty cycle; The target outer phase-shift duty cycle is obtained according to the reference outer phase-shift duty cycle and the compensation amount of the outer phase-shift duty cycle.

9. A power conversion device, characterized in that: The power conversion device includes a power conversion circuit and a controller, wherein the power conversion circuit includes a DC side bridge circuit, a transformer, a resonant inductor and an AC side bridge circuit, wherein a first end of the DC side bridge circuit is connected to a primary side of the transformer, and a first end of the AC side bridge circuit is connected to a secondary side of the transformer through the resonant inductor; wherein the DC side bridge circuit includes a first bridge arm and a second bridge arm connected in parallel, and the AC side bridge circuit includes a third bridge arm and a fourth bridge arm connected in parallel, wherein the first bridge arm, the second bridge arm and the third bridge arm all include a switch tube, and the fourth bridge arm includes a resonant capacitor, and the resonant capacitor and the resonant inductor constitute a resonant circuit; The controller is connected to the power conversion circuit, and the controller is used for: According to the real-time DC voltage on the second end of the DC side bridge circuit and the real-time AC voltage on the second end of the AC side bridge circuit, a target internal phase shift duty ratio of the DC side bridge circuit corresponding to the highest voltage matching degree is obtained; wherein the voltage matching degree refers to the ratio of the effective value of the output voltage of the power conversion circuit to the effective value of the input voltage, one of the real-time DC voltage and the real-time AC voltage is the output voltage, and the other of the real-time DC voltage and the AC voltage is the input voltage; A reference outer phase-shift duty cycle is obtained according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the preset target AC power and the preset power transmission constraint condition; wherein the power transmission constraint condition is used to indicate the constraint relationship between the AC power of the power conversion circuit and the outer phase-shift duty cycle, the inner phase-shift duty cycle, the DC voltage and the AC voltage; Adjusting the reference outer phase shift duty cycle according to the real-time AC current on the second end of the AC side bridge circuit and the preset target AC current to obtain a target outer phase shift duty cycle between the DC side bridge circuit and the AC side bridge circuit; A target switching frequency is obtained according to the real-time DC voltage, the real-time AC voltage, the target inner phase-shift duty cycle, the reference outer phase-shift duty cycle, the target AC power and a preset switching frequency constraint; wherein the switching frequency constraint is used to constrain the magnitude of the switching frequency of the power conversion circuit; Power transmission of the power conversion circuit is controlled according to the target switching frequency, the target inner phase-shifted duty cycle, and the target outer phase-shifted duty cycle.

10. The power conversion device according to claim 9, characterized in that When the power conversion circuit is in different operating conditions, the target switching frequency is different; wherein the operating conditions of the power conversion circuit include light load conditions, half load conditions and heavy load conditions.

11. The power conversion device according to claim 9, characterized in that The controller is used to: According to the target switching frequency, the target inner phase-shift duty cycle, and the target outer phase-shift duty cycle, the switch tubes of the DC side bridge circuit and the AC side bridge circuit are controlled to perform soft switching action; Wherein, when the switch tube in the DC side bridge circuit is turned on, the secondary current of the transformer is negative polarity; When the switch tube in the AC side bridge circuit is turned on, the secondary current of the transformer is positive.

12. A power supply system, characterized in that: The power supply system comprises: a DC power supply and a power conversion device as described in any one of claims 9 to 11, the DC power supply is connected to the second end of the DC side bridge circuit, the second end of the AC side bridge circuit is connected to a common coupling point, the DC power supply comprises at least one of an energy storage device and a photovoltaic power generation device, and the common coupling point is used to connect at least one of a power grid and an AC load.

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