Control method of bidirectional power converter, electronic device and storage medium

Abstract

The invention discloses a control method of a bidirectional power converter. The bidirectional power converter comprises a transformer, a first directional switch unit, a second directional switch unit, a third MOS tube, a fourth MOS tube, a first capacitor, a second capacitor, a third capacitor and a fourth capacitor. The control method comprises the following steps: in response to a determined energy flow direction, obtaining a given required power; a zero crossing point is obtained on the alternating current side through power grid phase locking, and gating signals of the first directional switch unit and the second directional switch unit are generated according to the voltage polarity; and acquiring a direct current bus voltage and an alternating current bus voltage, and judging a current conduction mode based on the number of turns of the transformer so as to determine the duty ratio of the third MOS tube and the fourth MOS tube according to the required power. On the basis of a single-machine converter half-bridge circuit structure, high power density and low complexity can be achieved, and modulation is easy to achieve while the energy flow direction is controlled.

Description

Technical Field

[0001] The present application relates to the field of circuit control technology, and in particular to a control method, an electronic device and a storage medium for a bidirectional power converter. Background Art

[0002] In recent years, as the popularity of smart grids and renewable energy is expanding and the efficiency and stability of power systems are gradually gaining attention, the demand for power conversion systems in new energy power systems for power supply and demand control and power quality improvement is increasing. Generally, the output and capacity of power conversion systems vary depending on the purpose of use. For example, after adding an energy storage system, the power conversion circuit also needs to realize a bidirectional conversion function.

[0003] In the process of conceiving and forming this application, the applicant has discovered at least the following problems: current power converter circuits are complex, most of which contain a large number of switches and gate drivers, and the control scheme is not easy to achieve stable power output quality and it is difficult to achieve high power density. Summary of the invention

[0004] The main purpose of the present application is to propose a control method for a bidirectional power converter, wherein the bidirectional power converter includes a transformer, a first directional switch unit, a second directional switch unit, a third MOS tube, a fourth MOS tube, a first capacitor, a second capacitor, a third capacitor and a fourth capacitor: The first end of the first directional switch unit is connected to the live end of the AC bus, the second end of the first directional switch unit is connected to the second end of the second directional switch unit and the first end of the AC side of the transformer, and the first end of the second directional switch unit is connected to the neutral end of the AC bus; The drain of the third MOS tube is connected to the positive terminal of the DC bus, and the source of the third MOS tube is connected to the first end of the fourth MOS tube and the negative terminal of the DC bus; The first end of the first capacitor is connected to the drain of the third MOS transistor, the second end of the first capacitor is connected to the second end of the second capacitor, the first end of the second capacitor is connected to the source of the fourth MOS transistor, and the second end of the DC side of the transformer is connected to the common end of the first capacitor and the second capacitor; The first end of the third capacitor is connected to the first end of the first directional switch unit, the second end of the third capacitor is connected to the second end of the fourth capacitor, the first end of the fourth capacitor is connected to the first end of the second directional switch unit, and the second end of the transformer AC side is connected to the common end of the first capacitor and the second capacitor; The first directional switch unit and the second directional switch unit are used for directional conduction under different half-cycle currents of the AC bus; The control method of the bidirectional power converter comprises: Responsive to determining the energy flow direction, obtaining a given required power; A zero-crossing point is obtained by phase locking of the power grid on the AC side to generate gate control signals of the first directional switch unit and the second directional switch unit according to the voltage polarity; A DC bus voltage and an AC bus voltage are obtained, and a current conduction mode is determined based on the number of turns of the transformer, so as to determine the duty ratios of the third MOS tube and the fourth MOS tube according to the required power.

[0005] Optionally, in response to determining the energy flow direction, the step of obtaining a given required power includes: Obtaining a primary voltage and a secondary voltage of the transformer, and determining an energy flow direction based on a phase relationship between the primary voltage and the secondary voltage; The required power is determined according to the input current or the load power.

[0006] Optionally, the first directional switch unit includes a first A MOS transistor, a second B MOS transistor, a first diode and a second diode; The drain of the first A MOS transistor is connected to the first end of the first directional switch unit, the source of the first A MOS transistor is connected to the anode of the first diode, and the cathode of the first diode is connected to the second end of the first directional switch unit; The drain of the second MOS tube is connected to the second end of the first directional switch unit, the source of the second MOS tube is connected to the anode of the second diode, and the cathode of the second diode is connected to the first end of the first directional switch unit; Or, the second directional switch unit includes a first B MOS tube, a second A MOS tube, a third diode and a fourth diode; The drain of the first B MOS tube is connected to the first end of the second directional switch unit, the source of the first B MOS tube is connected to the anode of the third diode, and the cathode of the third diode is connected to the second end of the second directional switch unit; The drain of the second A MOS transistor is connected to the second end of the second directional switch unit, the source of the second A MOS transistor is connected to the anode of the fourth diode, and the cathode of the fourth diode is connected to the first end of the second directional switch unit; Or, the first directional switch unit includes a first A MOS transistor and a second B MOS transistor, the drain of the first A MOS transistor is connected to the first end of the first directional switch unit, the source of the first A MOS transistor is connected to the source of the second B MOS transistor, and the drain of the second B MOS transistor is connected to the second end of the first directional switch unit; Alternatively, the second directional switching unit includes a second P-type MOS transistor and a first N-type MOS transistor. The source of the second P-type MOS transistor is connected to the first end of the second directional switching unit. The drain of the second P-type MOS transistor is connected to the drain of the first N-type MOS transistor. The source of the first N-type MOS transistor is connected to the second end of the second directional switching unit; The step of obtaining the zero-crossing point by grid phase-locking on the AC side to generate the gating signals of the first directional switching unit and the second directional switching unit according to the voltage polarity includes: During the positive half-cycle of the AC-side bus voltage, control the first P-type MOS transistor and the first N-type MOS transistor as complementary high-frequency switches with a 50% duty cycle respectively, and keep the second P-type MOS transistor and the second N-type MOS transistor always on; During the negative half-cycle of the AC-side bus voltage, control the second P-type MOS transistor and the second N-type MOS transistor as complementary high-frequency switches with a 50% duty cycle respectively, and keep the first P-type MOS transistor and the first N-type MOS transistor always on.

[0007] Optionally, the step of obtaining the DC bus voltage and the AC bus voltage, determining the current conduction mode based on the turns ratio of the transformer, and determining the duty cycles of the third MOS transistor and the fourth MOS transistor according to the required power further includes: Determine the mode switching boundary condition based on the target duty cycle in the current conduction mode based on the DC bus voltage and the AC bus voltage; When the target duty cycle reaches the mode switching boundary condition, operate at a constant frequency until the mode switching is completed.

[0008] Optionally, in the step of determining the mode switching boundary condition based on the target duty cycle in the current conduction mode based on the DC bus voltage and the AC bus voltage, use the duty cycle when the current of the fourth MOS transistor increases from 0 to the maximum current as the target duty cycle, and determine the target duty cycle according to the following expression:

[0009]

[0010] where d1 is the target duty cycle, and 0 < d1 < 1; T1 is the time when the current of the fourth MOS transistor increases from 0 to the maximum current, Ts is the working cycle, d2 is the duty cycle when the third MOS transistor decreases from the maximum current to 0, n is the turns ratio of the transformer, Vac is the AC bus voltage, and Vdc is the DC bus voltage.

[0011] Optionally, the transformer includes an exciting inductance; the step of operating at a constant frequency until the mode switching is completed when the target duty cycle reaches the mode switching boundary condition includes: The required current is determined based on the required power. When the target duty cycle is less than the mode switching boundary condition, the mode is switched to the discontinuous conduction mode. The target duty cycle is calculated according to the following expression:

[0012] Among them, Ls is the inductance of the excitation inductor, fs is the operating frequency, and IL is the required current.

[0013] Optionally, when the target duty cycle reaches the mode switching boundary condition, the step of operating at a constant frequency until the mode switching is completed includes: The required current is determined based on the required power. When the target duty cycle is greater than the mode switching boundary condition, the mode is switched to the continuous conduction mode, and the target duty cycle is calculated according to the following expression:

[0014] Among them, Ls is the inductance of the excitation inductor, fs is the operating frequency, and IL is the required current.

[0015] Optionally, the control method of the bidirectional power converter further includes: When operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit, and the third MOS transistor and the fourth MOS transistor operate in a zero voltage switching manner when turned on.

[0016] Optionally, when operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit and the third MOS tube operate in a zero current switching manner when turned off.

[0017] Optionally, when operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit, and the third MOS transistor and the fourth MOS transistor operate in a zero voltage switching manner when turned on.

[0018] The present application also provides an electronic device, the electronic device comprising a processor and a memory; The memory stores a computer program, and when the computer program is executed by the processor, the steps of the control method of the bidirectional power converter as described above are implemented.

[0019] The present application also provides a storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the control method of the bidirectional power converter as described above are implemented.

[0020] The control method, electronic device and storage medium of the bidirectional power converter provided in the present application are based on the bidirectional power converter circuit provided in the present application, and obtain a given required power by responding to determining the direction of energy flow; obtain a zero crossing point through grid phase locking on the AC side to generate a gating signal of the first directional switch unit and the second directional switch unit according to the voltage polarity; obtain the DC bus voltage and the AC bus voltage, and judge the current conduction mode based on the number of turns of the transformer to determine the duty cycle of the third MOS tube and the fourth MOS tube according to the required power; on the basis of the half-bridge circuit structure of a stand-alone converter, in conjunction with the control switching function, it is possible to achieve higher power density and lower complexity, and while controlling the direction of energy flow, an easily implementable modulation scheme can be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application. In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the description of the embodiments are briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor.

[0022] Figure 1 A schematic diagram of a bidirectional power converter circuit according to an embodiment of the present application is shown in FIG. Figure 1 .

[0023] Figure 2 A schematic diagram of a bidirectional power converter circuit according to an embodiment of the present application is shown in FIG. Figure 2 .

[0024] Figure 3 Schematic diagram of the connection between the first directional switch unit and the second directional switch unit according to an embodiment of the present application Figure 1 .

[0025] Figure 4 Schematic diagram of the connection between the first directional switch unit and the second directional switch unit according to an embodiment of the present application Figure 2 .

[0026] Figure 5 This is a flow chart of a control method of a bidirectional power converter according to an embodiment of the present application.

[0027] Figure 6 FIG. 1 is a timing diagram of a DC to AC conversion process according to an embodiment of the present application.

[0028] The realization of the purpose, functional features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. The above-mentioned drawings have shown clear embodiments of this application, which will be described in more detail later. These drawings and textual descriptions are not intended to limit the scope of the concept of this application in any way, but to illustrate the concept of this application to those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0029] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0030] Now, various embodiments of the present application will be described with reference to the accompanying drawings. In the following description, suffixes such as "module", "component" or "unit" used to represent elements are only used to facilitate the description of the present application and have no specific meaning.

[0031] First embodiment The present application first provides a bidirectional power converter. Figure 1 A schematic diagram of a bidirectional power converter circuit according to an embodiment of the present application is shown in FIG. Figure 1 .

[0032] like Figure 1 As shown, the bidirectional power converter includes a transformer T, a first directional switch unit K1, a second directional switch unit K2, a third MOS transistor S3, a fourth MOS transistor S4, a first capacitor Cp1, a second capacitor Cp2, a third capacitor Cs3 and a fourth capacitor Cs4.

[0033] A power converter is an electronic device that can convert a certain type of current into another type of current, including both DC power conversion and AC power conversion. For example, a bidirectional AC / DC converter, as a power electronic device that can achieve bidirectional conversion between AC and DC, has a working principle involving multiple key components and complex control strategies.

[0034] The first end of the first directional switch unit K1 is connected to the live end of the AC bus, the second end of the first directional switch unit K1 is connected to the second end of the second directional switch unit K2 and the first end of the AC side of the transformer T, and the first end of the second directional switch unit K2 is connected to the neutral end of the AC bus. The first directional switch unit K1 and the second directional switch unit K2 are used for directional conduction under different half-cycle currents of the AC bus.

[0035] A transformer is a device that uses the principle of electromagnetic induction to change AC voltage. Depending on the number of turns on the source side and the secondary side, the transformer can convert the AC waveform on one side into an AC waveform on the other side for output. Using a transformer can achieve functions such as voltage conversion, current conversion, impedance conversion, isolation, and voltage stabilization. Please refer to Figure 1 , the transformer uses magnetic integration technology to use leakage inductance as the energy storage inductor Ls. Using magnetic integration technology, the leakage inductance is formed by opening the air gap in the transformer core as the excitation inductor to transfer energy. The excitation inductance of the transformer is used to achieve zero voltage switching (ZVS) operation.

[0036] For example, the first directional switch can be turned on in the positive half cycle of the AC bus towards the AC source, and in the negative half cycle of the AC bus towards the transformer. The second directional switch can be turned on in the negative half cycle of the AC bus towards the AC source, and in the positive half cycle of the AC bus towards the transformer. Thus, the circuit control can flexibly control the direction of the current in different situations.

[0037] Please continue to refer to Figure 1 The first end of the third capacitor Cs3 is connected to the first end of the first directional switch unit K1, the second end of the third capacitor Cs3 is connected to the second end of the fourth capacitor Cs4, the first end of the fourth capacitor Cs4 is connected to the first end of the second directional switch unit K2, and the second end of the transformer T is connected to the common end of the first capacitor Cp1 and the second capacitor Cp2.

[0038] Exemplarily, the third capacitor and the fourth capacitor can store or release electricity in different oscillation cycles, thereby forming electromagnetic oscillation with the inductance component in the circuit. Exemplarily, due to the magnetic flux characteristics, there is leakage inductance in the transformer using magnetic integration technology, and the leakage inductance can act as an energy storage inductor. By directional conduction control of the first directional switch unit and the second directional switch unit under different half-cycle currents, a suitable AC waveform can be provided to the transformer during the AC-to-DC conversion process, or a suitable AC waveform can be output during the DC-to-AC conversion process.

[0039] The drain of the third MOS transistor S3 is connected to the positive terminal of the DC bus, and the source of the third MOS transistor S3 is connected to the first end of the fourth MOS transistor S4 and the negative terminal of the DC bus.

[0040] For example, MOSFET has three legs, generally divided into a gate, a source and a drain. By adding a control signal between the gate and the source, the conduction and cutoff between the drain and the source can be changed.

[0041] The first end of the first capacitor Cp1 is connected to the drain of the third MOS transistor S3, the second end of the first capacitor Cp1 is connected to the second end of the second capacitor Cp2, the first end of the second capacitor Cp2 is connected to the source of the fourth MOS transistor S4, and the second end of the DC side of the transformer T is connected to the common end of the first capacitor and the second capacitor Cp2.

[0042] Exemplarily, the first capacitor and the second capacitor can store or release energy in different oscillation cycles, thereby forming electromagnetic oscillation with the inductance component in the circuit. Exemplarily, in a transformer using magnetic integration technology, there is leakage inductance due to the magnetic flux characteristics, and the leakage inductance can act as an energy storage inductor. By turning on the third MOS tube and the fourth MOS tube at different half-cycle currents, a suitable DC voltage can be output during the AC-to-DC conversion process, or a suitable AC waveform can be generated for the transformer during the DC-to-AC conversion process.

[0043] Optionally, the third MOS transistor S3 and the fourth MOS transistor S4 are N-type transistors. Optionally, the third MOS transistor S3 and the fourth MOS transistor S4 have body diodes.

[0044] Exemplarily, the body diode of a MOS tube, also called a parasitic diode or a built-in diode, refers to a parasitic element present in a metal-oxide-semiconductor field effect transistor (MOSFET). It is formed by a PN junction between the substrate (B pole) and the drain (D pole) of the MOS tube. Since the source (S pole) and the substrate (B pole) are short-circuited, a body diode between the source and the drain is formed. In this embodiment, by electromagnetic oscillations of the primary and secondary sides of the transformer, the body diodes of the third MOS tube and the fourth MOS tube can be used to achieve zero voltage or zero current switching of the DC side circuit of the transformer, thereby effectively reducing circuit losses. Compared with the full-bridge structure, the two MOS tubes on the low-voltage side are omitted, and the control is less complex. Through the simple circuit structure of the single-stage converter half-bridge, not only the zero voltage switch ZVS is realized, but also the zero current switch ZCS is realized, which can improve the reliability of power conversion, and suppress heat generation with lower circuit losses, thereby improving the power density of the circuit.

[0045] Figure 2 A schematic diagram of a bidirectional power converter circuit according to an embodiment of the present application is shown in FIG. Figure 2 .

[0046] Please refer to Figure 2 Optionally, the bidirectional power converter circuit further includes a filter capacitor EC3, a positive electrode of the filter capacitor EC3 is connected to the positive terminal of the DC bus, and a negative electrode of the filter capacitor EC3 is connected to the negative terminal of the DC bus.

[0047] Filter capacitors have many functions in electronic circuits, mainly including filtering noise, stabilizing voltage and storing energy. Through its energy storage characteristics, filter capacitors can filter out AC components in the rectifier circuit, making the output DC voltage smoother and more stable. Specifically, when the rectifier voltage is higher than the capacitor voltage, the capacitor is charged; when the rectifier voltage is lower than the capacitor voltage, the capacitor is discharged. In this process, the output voltage remains basically stable. As an energy storage device, filter capacitors can provide a stable DC power supply when needed. In all circuits that need to convert AC power into DC power, setting up filter capacitors will make the working performance of the electronic circuit more stable, and also reduce the interference of alternating pulsating ripples on the electronic circuit.

[0048] Please continue to refer to Figure 2 Optionally, the bidirectional power conversion circuit also includes a first inductor Ldc, which is connected between the drain of the third MOS tube S3 and the positive electrode of the filter capacitor EC3, or the first inductor Ldc is connected between the source of the fourth MOS tube S4 and the negative electrode of the filter capacitor EC3.

[0049] Please continue to refer to Figure 2 Optionally, the bidirectional power conversion circuit further includes a second inductor Lac. The second inductor Lac is connected between the first end of the first directional switch unit K1 and the live end of the AC bus, or the second inductor Lac is connected between the first end of the second directional switch unit K2 and the neutral end of the AC bus.

[0050] Exemplarily, the first inductor and the second inductor cooperate with the capacitor to achieve an oscillation effect and a filtering effect. The inductor plays the role of energy storage in the circuit. When the switch tube is turned on, the inductor current rises linearly and the inductor stores energy. In the circuit at both ends of the transformer, the inductor effects mainly include filtering, oscillation and energy storage. The inductor not only affects the oscillation frequency, but can also be used to adjust circuit performance parameters, filter, isolate noise, etc., to improve the stability and reliability of the circuit. Through switch control, the inductor current can be switched between DCM (discontinuous conduction mode) and CCM (continuous conduction mode), where it can work in DCM mode at low power and in CCM mode at high power, which is easier to implement in algorithm control.

[0051] Figure 3 Schematic diagram of the connection between the first directional switch unit and the second directional switch unit according to an embodiment of the present application Figure 1 .

[0052] like Figure 3As shown, optionally, the first directional switch unit K1 includes a first A MOS transistor S1a and a second B MOS transistor S2a, the drain of the first A MOS transistor S1a is connected to the first end of the first directional switch unit K1, the source of the first A MOS transistor S1a is connected to the source of the second B MOS transistor S2b, and the drain of the second B MOS transistor S2b is connected to the second end of the first directional switch unit K1.

[0053] Optionally, the second directional switch unit K2 includes a second A MOS transistor S2a and a first B MOS transistor S1b, the source of the second A MOS transistor S2a is connected to the first end of the second directional switch unit K2, the drain of the second A MOS transistor S2a is connected to the drain of the first B MOS transistor S1b, and the source of the first B MOS transistor S1b is connected to the second end of the second directional switch unit K2.

[0054] Exemplarily, the first directional switch unit and the second directional switch unit are connected in reverse through two MOS tubes, and one MOS tube can be controlled to be in a normally open state through the control terminal. When the other MOS tube is controlled to be in a closed state, the unidirectional conduction characteristic of the body diode of the MOS tube can be used to realize zero voltage or zero current switching of the circuit, thereby further reducing circuit loss.

[0055] Figure 4 Schematic diagram of the connection between the first directional switch unit and the second directional switch unit according to an embodiment of the present application Figure 2 .

[0056] like Figure 4 As shown, optionally, the first directional switch unit K1 includes a first A MOS transistor S1a, a second B MOS transistor S2b, a first diode D1 and a second diode D2.

[0057] For example, a diode is an electronic device made of semiconductor materials (silicon, selenium, germanium, etc.) [1]. A diode has two electrodes, a positive electrode, also called an anode, and a negative electrode, also called a cathode. When a forward voltage is applied between the two electrodes of the diode, the diode is turned on, and when a reverse voltage is applied, the diode is turned off. The diode has unidirectional conductivity. When it is turned on, the current flows from the anode through the tube to the cathode. The conduction and cutoff of the diode are equivalent to the on and off of a switch.

[0058] Further, the drain of the first A MOS transistor S1a is connected to the first end of the first directional switch unit K1, the source of the first A MOS transistor S1a is connected to the anode of the first diode D1, and the cathode of the first diode D1 is connected to the second end of the first directional switch unit K1.

[0059] By connecting the diode and the MOS transistor in series, it is possible to ensure that the current can flow in one direction on the preset branch. For example, the series connection of the first A MOS transistor and the first diode can limit the current of the branch to flow from the AC bus toward the transformer.

[0060] Further, the drain of the second MOS transistor S2b is connected to the second end of the first directional switch unit K1, the source of the second MOS transistor S2b is connected to the anode of the second diode D2, and the cathode of the second diode D2 is connected to the first end of the first directional switch unit K1.

[0061] By connecting the diode and the MOS tube in series, it is possible to ensure that the current can flow in one direction on the preset branch. For example, the second MOS tube and the second diode are connected in series to limit the current of the branch to flow from the transformer to the AC bus.

[0062] Please continue to refer to Figure 4 Optionally, the second directional switch unit K2 includes a first B MOS transistor S1b, a second A MOS transistor S2a, a third diode D3 and a fourth diode D4.

[0063] The drain of the first B MOS transistor S1b is connected to the first end of the second directional switch unit K2, the source of the first B MOS transistor S1b is connected to the anode of the third diode D3, and the cathode of the third diode D3 is connected to the second end of the second directional switch unit K2.

[0064] The drain of the second A MOS transistor S2a is connected to the second end of the second directional switch unit K2, the source of the second A MOS transistor S2a is connected to the anode of the fourth diode D4, and the cathode of the fourth diode D4 is connected to the first end of the second directional switch unit K2.

[0065] By connecting a diode and a MOS tube in series, it is possible to ensure that the current can flow in one direction on a preset branch. Exemplarily, by connecting a first B MOS tube and a third diode in series, the current of the branch can be limited to flow from the AC bus toward the transformer. Exemplarily, by connecting a second A MOS tube and a fourth diode in series, the current of the branch can be limited to flow from the transformer toward the AC bus.

[0066] In this embodiment, a single-stage converter half-bridge DAB structure is used, in which both the AC side and the DC side are half-bridges and can be switched bidirectionally, to provide an AC / DC converter based on a half-bridge direct matrix, which also has the ability of single-stage power conversion and bidirectional power transmission. By using a half-bridge structure on both the AC and DC sides, compared with a converter using a full-bridge structure, the number of switches and gate drivers in this embodiment is smaller, making the circuit board structure simple, reducing the complexity of the AC / DC converter, and improving reliability and power density. The higher the power density, the higher the efficiency of heat dissipation or heat suppression, so ZCS (zero current switching) and ZVS (zero voltage switching) are particularly important.

[0067] This embodiment provides a modulation scheme without current sensor. In the full range of AC voltage and wide load range, the MOS tube switch involved can achieve ZCS and ZVS in the whole AC voltage range. The performance of the proposed AC / DC converter has been verified by a 2 kW prototype based on silicon carbide (SiC), achieving a high efficiency of 96.8% under rated conditions, a current THD of less than 4%, and a power density of 1.8kW / dm3.

[0068] Second embodiment On the basis of the first embodiment, the power converter circuit provided by the present application can operate at a constant switching frequency and can achieve soft switching in the entire operating range through a simple modulation scheme.

[0069] Figure 5 This is a flow chart of a control method of a bidirectional power converter according to an embodiment of the present application.

[0070] like Figure 5 As shown, the control method of the bidirectional power converter includes: S10: in response to determining the energy flow direction, obtaining a given required power; S20: obtaining a zero-crossing point by grid phase locking on the AC side to generate gate control signals of the first directional switch unit and the second directional switch unit according to voltage polarity; S30: Obtaining a DC bus voltage and an AC bus voltage, and judging a current conduction mode based on the number of turns of the transformer, so as to determine a duty cycle of the third MOS tube and the fourth MOS tube according to the required power.

[0071] For example, the energy direction is first determined, AC (alternating current) to DC (direct current) or DC to AC, and then the given required power is obtained. For example, DC to AC is generally determined by the input current to ensure that the incoming energy is inverted; while AC to DC can be determined by the load power. After the grid is phase-locked, the zero crossing point is obtained, and a control signal is generated according to the voltage polarity, thereby controlling the duty cycle of the DC side switch according to the corresponding conduction mode.

[0072] Optionally, the control method of the bidirectional power converter further includes: When operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit, and the third MOS transistor and the fourth MOS transistor operate in a zero voltage switching manner when turned on.

[0073] Optionally, when operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit and the third MOS tube operate in a zero current switching manner when turned off.

[0074] Optionally, when operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit, and the third MOS transistor and the fourth MOS transistor operate in a zero voltage switching manner when turned on.

[0075] In this embodiment, the switch gating signal on the AC side is determined by measuring the zero-crossing point on the AC side. According to the voltage ratio and the conduction mode requirement on the DC side, the duty cycle of the MOS tube is controlled on the DC side while the gating timing of the third MOS tube and the fourth MOS tube is taken into consideration. In the full range of the AC voltage and the wide load range, the MOS tube switches involved are made to achieve zero voltage switching and zero current switching in the entire AC voltage range, thereby improving the power conversion efficiency.

[0076] Optionally, in response to determining the energy flow direction, the step of obtaining a given required power includes: Obtaining a primary voltage and a secondary voltage of the transformer, and determining an energy flow direction based on a phase relationship between the primary voltage and the secondary voltage; The required power is determined according to the input current or the load power.

[0077] Figure 6 The following is a timing diagram of a DC to AC converter according to an embodiment of the present application, wherein (a) is a timing diagram of a discontinuous conduction mode (DCM), and (b) is a timing diagram of a continuous conduction mode (CCM).

[0078] For example, in the process of determining whether the energy direction is AC (alternating current) to DC (direct current) or DC to AC, the voltage curves of the AC side and the DC side of the transformer can be collected and determined according to the voltage phase relationship on both sides of the transformer. For example, in terms of the phase relationship, the side with the leading phase is the input side, which serves as the primary side of the transformer, and the side with the lagging phase is the output side, which serves as the secondary side of the transformer. Figure 6 In the embodiment shown, the DC side voltage phase leads, and the AC side voltage phase lags. Therefore, this embodiment is described in detail with the control logic of DC to AC.

[0079] Optionally, the step of obtaining a zero-crossing point by grid phase locking on the AC side to generate a gating signal of the first directional switch unit and the second directional switch unit according to the voltage polarity includes: In the positive half cycle of the AC side bus voltage, the first A MOS transistor and the first B MOS transistor are controlled to be complementary high-frequency switches with a duty cycle of 50%, and the second A MOS transistor and the second B MOS transistor are made normally open; In the negative half cycle of the AC side bus voltage, the second A MOS tube and the second B MOS tube are controlled to be complementary high-frequency switches with a duty cycle of 50%, and the first A MOS tube and the first B MOS tube are kept normally open.

[0080] Please continue to refer to Figure 6 And also refer to Figure 2 , Figure 3 and Figure 4 For example, in the positive half cycle of the AC, the first A MOS tube S1a and the first B MOS tube S1b each have a 50% duty cycle, which is set as a gate signal of a complementary high-frequency switch to control the second A MOS tube S1a and the second B MOS tube S1b to be normally open.

[0081] Please continue to refer to Figure 6 And also refer to Figure 2 , Figure 3 and Figure 4 For example, in the negative half cycle of the AC, the second A MOS tube S1a and the second B MOS tube S1b each have a 50% duty cycle, which is set as a gate signal of a complementary high-frequency switch to control the first A MOS tube S1a and the first B MOS tube S1b to be normally open.

[0082] By performing different controls under different half-cycle currents on the AC side, the first directional switch unit K1 and the second directional switch unit K2 are directionally conducted under different half-cycle currents on the AC side, thereby realizing DC to AC conversion and achieving zero voltage switching and zero current switching in the entire AC voltage range, thereby improving power conversion efficiency.

[0083] Optionally, the step of obtaining the DC bus voltage and the AC bus voltage, judging the current conduction mode based on the number of turns of the transformer, and determining the duty cycle of the third MOS tube and the fourth MOS tube according to the required power further includes: Determine a mode switching boundary condition based on a target duty cycle in a current conduction mode based on a DC bus voltage and an AC bus voltage; When the target duty cycle reaches the mode switching boundary condition, the system operates at a constant frequency until the mode switching is completed.

[0084] Exemplarily, during the switching process between the discontinuous conduction mode (DCM) and the continuous conduction mode (CCM), the switching needs to be performed according to the boundary conditions. Exemplarily, when converting from AC to DC, during the calculation of the switching boundary conditions between the discontinuous conduction mode (DCM) and the continuous conduction mode (CCM), when the fourth MOS transistor is turned on, the duty cycle during which the energy storage current increases from 0 to the maximum current can be a reference factor, and when the third MOS transistor is turned on, the duty cycle during which the energy storage current decreases from the maximum current to 0 can also be a reference factor.

[0085] Optionally, in the step of determining the mode switching boundary conditions based on the target duty cycle in the current conduction mode according to the DC bus voltage and the AC bus voltage, taking the duty cycle during which the current of the fourth MOS transistor increases from 0 to the maximum current as the target duty cycle, the target duty cycle is determined according to the following expression:

[0086]

[0087] where d1 is the target duty cycle, and 0 < d1 < 1; T1 is the time during which the current of the fourth MOS transistor increases from 0 to the maximum current, Ts is the working cycle, d2 is the duty cycle during which the third MOS transistor decreases from the maximum current to 0, n is the number of turns of the transformer, Vac is the AC bus voltage, and Vdc is the DC bus voltage.

[0088] Please also refer to Figure 2 , exemplarily, the circuit topology of this embodiment supports bidirectional energy flow, that is, inversion can be achieved. For example, DC input and AC output can achieve PFC, that is, the energy flow direction of AC input and DC output is determined by the boundary duty cycle db mentioned below, which affects the duty cycles of the third MOS transistor S3 and the fourth MOS transistor S4. Where b is the abbreviation of boundary, representing the boundary.

[0089] Exemplarily, the boundary conditions for the switching of the working mode (DCM, CCM) when converting from AC to DC are:

[0090] At this time, d1 is the duty cycle during which the energy storage current (inductor current) increases from 0 to the maximum current when the fourth MOS transistor S4 is turned on. t1 is the time, and the current t1 value can be obtained by looking up the table according to the current control frequency. d2 is the duty cycle during which the energy storage current (inductor current) decreases from the maximum current to 0 when the third MOS transistor S3 is turned on.

[0091] Optionally, the transformer includes an excitation inductor; and when the target duty cycle reaches the mode switching boundary condition, the step of operating at a constant frequency until the mode switching is completed includes: The required current is determined based on the required power. When the target duty cycle is less than the mode switching boundary condition, the mode is switched to the discontinuous conduction mode. The target duty cycle is calculated according to the following expression:

[0092] Among them, Ls is the inductance of the excitation inductor, fs is the operating frequency, and IL is the required current.

[0093] Exemplarily, when the target duty cycle d1 is less than the boundary duty cycle db, the control system operates in the discontinuous conduction mode.

[0094] Optionally, when the target duty cycle reaches the mode switching boundary condition, the step of operating at a constant frequency until the mode switching is completed includes: The required current is determined based on the required power. When the target duty cycle is greater than the mode switching boundary condition, the mode is switched to the continuous conduction mode, and the target duty cycle is calculated according to the following expression:

[0095] Among them, Ls is the inductance of the excitation inductor, fs is the operating frequency, and IL is the required current.

[0096] Exemplarily, when the target duty cycle d1 is greater than the boundary duty cycle db, the control system operates in the continuous conduction mode. According to the calculation formula of the target duty cycle d1, once the target duty cycle d1 is determined, the duty cycle d2 of the third MOS tube from the maximum current to 0 can also be determined. All the quantities in the above block diagram become known, and the control of the topology can be realized.

[0097] For example, a gap is left between the opening of the third MOS tube and the closing of the fourth MOS tube, which is called the dead time, to avoid the entire load being short-circuited when the third MOS tube is turned on and the fourth MOS tube is turned on at the same time. The working cycle Ts and the working frequency fs are determined according to the performance of the hardware controller, and the higher the better.

[0098] Please refer to Figure 6, for example, referring to the single phase shift control strategy of the DAB topology, when switching from DCM to CCM mode, at the critical point of switching, the proportion of t1 will gradually equal t2, and at a certain point, t1 of the third MOS tube S3 will be equal to t2, t1 is the on time, t2 is the off time, and the duty cycle is 0.5 respectively. From this point to the complete CCM mode, a constant frequency operation will be maintained to achieve constant frequency switching control. From this moment on, in the entire CCM mode, since there is a linear relationship between power and phase shift angle, the only variable is the phase shift angle between Vp and Vs. It can be seen from the above formula that in the DCM and CCM control process, it is only necessary to detect the zero crossing point, and there is no need to detect the current. This greatly simplifies the control difficulty and becomes very easy to control. There is no need to design complex algorithms to achieve the target state.

[0099] Please continue to refer to Figure 6 , depending on whether the secondary current drops to zero during Ts / 2, it can be divided into discontinuous conduction mode (DCM) or continuous conduction mode (CCM) Figure a shows the DCM mode, where the inductor current reaches 0 in advance within Ts / 2. b shows the CCM mode, the inductor current has not reached 0 at the end of Ts / 2 Please explain the control logic of zero current switching ZCS or zero voltage switching ZVS in this circuit.

[0100] For example, a MOS tube that can freewheel during operation can clamp the voltage across the diode through its own body diode. At this time, current can flow when the switch is turned on. According to P=IV, it can be seen that I is relatively large at this time, but V is only the voltage drop of the diode 0.7V (the default voltage is zero), which can greatly reduce the conduction loss of the diode, thus achieving ZVS and thus realizing ZVS logic.

[0101] Please also refer to Figure 2 and Figure 6 For example, ZCS refers to zero current shutdown, that is, in DCM mode, the transformer current can be reduced to 0, so the transformer current zero-crossing comparator can be designed through a comparator. Once it crosses zero, the target MOS can be turned off, and I in P=IV can be 0, which can greatly reduce the MOS shutdown loss. For the complementary S3 and S4, the third MOS tube S3 is turned off when the current is zero. After a dead time, the other fourth MOS tube S4 switch is just 0.7v to open and realize ZVS.

[0102] For example, the inductor current returns to 0 when the inductor is turned off in half a cycle, so the MOS on the AC side can achieve ZCS soft switching. For the complementary S1 and S2, one is turned off when the current is zero, and after a dead time, the other switch is turned on at 0.7V to achieve ZVS.

[0103] like Figure 6 As shown in Figure 2, the switching loss of S4 on the DC side is higher than that of S3 because S4 is turned off at high current, while S3 is zero current shutdown (ZCS). Figure 6 (a). This makes the control angle in DCM mode have two dimensions, one is the duty cycle of S3 and S4, and the other is the phase shift angle between the DC side and the AC side, that is, the delay time of controlling the wave of S3 and S4.

[0104] Please continue to refer to Figure 6 , CCM mode: At each MOS switch instant, the current iL is not zero. During continuous conduction mode (CCM) operation, all MOS switches achieve zero voltage switching (ZVS). In this case, the power can be adjusted by the phase shift angle. In other words, in DCM mode, ZVS can be achieved when other MOS except S4 are turned on and ZCS can be achieved when turned off, because the transformer current will reach 0. In CCM mode, all MOS can only achieve ZVS, but not ZCS, because the current at each instant is not 0.

[0105] In this implementation, by using magnetic integration technology, the leakage inductance formed by the air gap of the transformer core is used as the excitation inductance to transfer energy. The excitation inductance of the transformer is used to achieve zero voltage switching (ZVS) operation, and the load range is also very large. In terms of efficiency, this helps to reduce switching losses. In terms of control, the inductor DCM and CCM switching can be achieved to match different working conditions. In addition to simplification, the modulation scheme obtained by time domain analysis is also easy to implement.

[0106] The converter has the lowest number of switches and gate drivers, making the circuit board simpler. In addition, the proposed converter operates at a constant switching frequency and can achieve soft switching over the entire operating range through a simple modulation scheme. It is mainly used in solar micro grid-connected inverters and can achieve bidirectional energy flow. Only software-level modifications are required to control the direction of energy flow, which helps to simplify the hardware.

[0107] Third embodiment The present application also provides an electronic device, the electronic device comprising a processor and a memory; The memory stores a computer program, and when the computer program is executed by the processor, the steps of the control method of the bidirectional power converter as described above are implemented.

[0108] The present application also provides a storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the control method of the bidirectional power converter as described above are implemented.

[0109] The control method, electronic device and storage medium of the bidirectional power converter provided in the present application are based on the bidirectional power converter circuit provided in the present application, and obtain a given required power by responding to determining the direction of energy flow; obtain a zero crossing point through grid phase locking on the AC side to generate a gating signal of the first directional switch unit and the second directional switch unit according to the voltage polarity; obtain the DC bus voltage and the AC bus voltage, and judge the current conduction mode based on the number of turns of the transformer to determine the duty cycle of the third MOS tube and the fourth MOS tube according to the required power; on the basis of the half-bridge circuit structure of a stand-alone converter, in conjunction with the control switching function, it is possible to achieve higher power density and lower complexity, and while controlling the direction of energy flow, an easily implementable modulation scheme can be obtained.

[0110] It should be noted that in the present application, step codes such as S10, S20, etc. are used for the purpose of expressing the corresponding content more clearly and concisely, and do not constitute a substantial limitation on the sequence. When implementing the step, those skilled in the art may execute S20 first and then S10, etc., but these should all be within the scope of protection of the present application.

[0111] In the embodiments of the device and storage medium provided in the present application, all technical features of any of the above-mentioned method embodiments may be included, and the expanded and explained contents of the specification are basically the same as those of the above-mentioned method embodiments, and will not be repeated here.

[0112] The embodiment of the present application further provides a computer program product, which includes a computer program code. When the computer program code runs on a computer, the computer executes the methods in the above various possible implementation modes.

[0113] An embodiment of the present application also provides a chip, including a memory and a processor, the memory is used to store a computer program, and the processor is used to call and run the computer program from the memory, so that a device equipped with the chip executes the methods in various possible implementation modes as described above.

[0114] It is understood that the above scenarios are only examples and do not constitute a limitation on the application scenarios of the technical solutions provided in the embodiments of the present application. The technical solutions of the present application can also be applied to other scenarios. For example, it is known to those skilled in the art that with the evolution of device architecture and the emergence of new business scenarios, the technical solutions provided in the embodiments of the present application are also applicable to similar technical problems.

[0115] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0116] The steps in the method of the embodiment of the present application can be adjusted in order, combined and deleted according to actual needs.

[0117] The units in the device of the embodiment of the present application can be merged, divided and deleted according to actual needs.

[0118] In the present application, the same or similar terminology concepts, technical solutions and / or application scenario descriptions are generally described in detail only the first time they appear. When they appear again later, they are generally not repeated for the sake of brevity. When understanding the technical solutions and other contents of the present application, for the same or similar terminology concepts, technical solutions and / or application scenario descriptions that are not described in detail later, reference can be made to the previous related detailed descriptions.

[0119] In the present application, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0120] The various technical features of the technical solution of the present application can be arbitrarily combined. In order to make the description concise, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of the present application.

[0121] The above are only preferred embodiments of the present application, and the application scope of the present application is not limited thereto. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the application protection scope of the present application.

Claims

1. A control method for a bidirectional power converter, characterized in that: The bidirectional power converter comprises a transformer, a first directional switch unit, a second directional switch unit, a third MOS transistor, a fourth MOS transistor, a first capacitor, a second capacitor, a third capacitor and a fourth capacitor: The first end of the first directional switch unit is connected to the live end of the AC bus, the second end of the first directional switch unit is connected to the second end of the second directional switch unit and the first end of the AC side of the transformer, and the first end of the second directional switch unit is connected to the neutral end of the AC bus; The drain of the third MOS tube is connected to the positive terminal of the DC bus, and the source of the third MOS tube is connected to the first end of the fourth MOS tube and the negative terminal of the DC bus; The first end of the first capacitor is connected to the drain of the third MOS transistor, the second end of the first capacitor is connected to the second end of the second capacitor, the first end of the second capacitor is connected to the source of the fourth MOS transistor, and the second end of the DC side of the transformer is connected to the common end of the first capacitor and the second capacitor; The first end of the third capacitor is connected to the first end of the first directional switch unit, the second end of the third capacitor is connected to the second end of the fourth capacitor, the first end of the fourth capacitor is connected to the first end of the second directional switch unit, and the second end of the transformer AC side is connected to the common end of the first capacitor and the second capacitor; The first directional switch unit and the second directional switch unit are used for directional conduction under different half-cycle currents of the AC bus; The control method of the bidirectional power converter comprises: Responsive to determining the energy flow direction, obtaining a given required power; A zero-crossing point is obtained by phase locking of the power grid on the AC side to generate gate control signals of the first directional switch unit and the second directional switch unit according to the voltage polarity; A DC bus voltage and an AC bus voltage are obtained, and a current conduction mode is determined based on the number of turns of the transformer, so as to determine the duty ratios of the third MOS tube and the fourth MOS tube according to the required power.

2. The control method of a bidirectional power converter according to claim 1, characterized in that: The step of obtaining a given required power in response to determining the energy flow direction includes: Obtaining a primary voltage and a secondary voltage of the transformer, and determining an energy flow direction based on a phase relationship between the primary voltage and the secondary voltage; The required power is determined according to the input current or the load power.

3. The control method of a bidirectional power converter according to claim 2, characterized in that: The first directional switch unit includes a first A MOS tube, a second B MOS tube, a first diode and a second diode; The drain of the first A MOS transistor is connected to the first end of the first directional switch unit, the source of the first A MOS transistor is connected to the anode of the first diode, and the cathode of the first diode is connected to the second end of the first directional switch unit; The drain of the second MOS tube is connected to the second end of the first directional switch unit, the source of the second MOS tube is connected to the anode of the second diode, and the cathode of the second diode is connected to the first end of the first directional switch unit; Or, the second directional switch unit includes a first B MOS tube, a second A MOS tube, a third diode and a fourth diode; The drain of the first p - MOS transistor is connected to the first end of the second directional switch unit, the source of the first p - MOS transistor is connected to the anode of the third diode, and the cathode of the third diode is connected to the second end of the second directional switch unit; The drain of the second n - MOS transistor is connected to the second end of the second directional switch unit, the source of the second n - MOS transistor is connected to the anode of the fourth diode, and the cathode of the fourth diode is connected to the first end of the second directional switch unit; Alternatively, the first directional switch unit includes a first n - MOS transistor and a second p - MOS transistor. The drain of the first n - MOS transistor is connected to the first end of the first directional switch unit, the source of the first n - MOS transistor is connected to the source of the second p - MOS transistor, and the drain of the second p - MOS transistor is connected to the second end of the first directional switch unit; Alternatively, the second directional switch unit includes a second n - MOS transistor and a first p - MOS transistor. The source of the second n - MOS transistor is connected to the first end of the second directional switch unit, the drain of the second n - MOS transistor is connected to the drain of the first p - MOS transistor, and the source of the first p - MOS transistor is connected to the second end of the second directional switch unit; The step of obtaining the zero - crossing point by grid - side phase - locked loop on the AC side to generate the gating signals of the first directional switch unit and the second directional switch unit according to the voltage polarity includes: In the positive half - cycle of the AC - side bus voltage, control the first n - MOS transistor and the first p - MOS transistor as complementary high - frequency switches with a 50% duty cycle respectively, and keep the second n - MOS transistor and the second p - MOS transistor always on; In the negative half - cycle of the AC - side bus voltage, control the second n - MOS transistor and the second p - MOS transistor as complementary high - frequency switches with a 50% duty cycle respectively, and keep the first n - MOS transistor and the first p - MOS transistor always on.

4. A control method for a bidirectional power converter according to any one of claims 1 to 3, characterized in that: The step of obtaining the DC bus voltage and the AC bus voltage, judging the current conduction mode based on the turns ratio of the transformer, and determining the duty cycles of the third MOS transistor and the fourth MOS transistor according to the required power further includes: Determine the mode - switching boundary condition based on the target duty cycle in the current conduction mode according to the DC bus voltage and the AC bus voltage; When the target duty cycle reaches the mode - switching boundary condition, operate at a constant frequency until the mode - switching is completed.

5. The control method of a bidirectional power converter according to claim 4, characterized in that: In the step of determining the mode - switching boundary condition based on the target duty cycle in the current conduction mode according to the DC bus voltage and the AC bus voltage, take the duty cycle when the current of the fourth MOS transistor increases from 0 to the maximum current as the target duty cycle, and determine the target duty cycle according to the following expression: Where, d1 is the target duty cycle, and 0 < d1 < 1; T1 is the time when the current of the fourth MOS transistor increases from 0 to the maximum current, Ts is the working cycle, d2 is the duty cycle when the third MOS transistor decreases from the maximum current to 0, n is the turns ratio of the transformer, Vac is the AC bus voltage, and Vdc is the DC bus voltage.

6. The control method of a bidirectional power converter according to claim 5, characterized in that: The transformer includes an excitation inductor; and when the target duty cycle reaches the mode switching boundary condition, the step of operating at a constant frequency until the mode switching is completed includes: The required current is determined based on the required power. When the target duty cycle is less than the mode switching boundary condition, the mode is switched to the discontinuous conduction mode. The target duty cycle is calculated according to the following expression: Among them, Ls is the inductance of the excitation inductor, fs is the operating frequency, and IL is the required current.

7. The control method of a bidirectional power converter according to claim 6, characterized in that: The step of operating at a constant frequency until the mode switching is completed when the target duty cycle reaches the mode switching boundary condition comprises: The required current is determined based on the required power. When the target duty cycle is greater than the mode switching boundary condition, the mode is switched to the continuous conduction mode, and the target duty cycle is calculated according to the following expression: Among them, Ls is the inductance of the excitation inductor, fs is the operating frequency, and IL is the required current.

8. The control method of a bidirectional power converter according to claim 7, characterized in that: The control method of the bidirectional power converter further includes: When operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit, and the third MOS tube and the fourth MOS tube operate in a zero voltage switching mode when turned on; And / or, when operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit and the third MOS tube operate in a zero current switching mode when turned off; And / or, when operating in the discontinuous conduction mode, the switches of the first directional switch unit, the second directional switch unit, and the third MOS transistor and the fourth MOS transistor operate in a zero voltage switching manner when turned on.

9. An electronic device, characterized in that: The electronic device includes a processor and a memory; The memory stores a computer program, and when the computer program is executed by the processor, the steps of the control method of the bidirectional power converter according to any one of claims 1 to 8 are implemented.

10. A storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by the processor, the steps of the control method of the bidirectional power converter according to any one of claims 1 to 8 are implemented.

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