A control method and control system of a bidirectional series resonant converter

Abstract

The application provides a control method and a control system of a bidirectional series resonant converter, wherein the method comprises the following steps: obtaining a charging and discharging working condition corresponding to an electric energy transmission direction of the bidirectional series resonant converter; determining current electric energy parameter values corresponding to an input side and an output side of the bidirectional series resonant converter in the charging and discharging working condition; calculating a current gain of the bidirectional series resonant converter according to the current electric energy parameter values; determining a current phase shift angle through a target interval of the current gain and a target fitting function corresponding to the charging and discharging working condition, and the target fitting function is used for determining a current phase shift angle corresponding to a soft switch realized under the current gain; determining a switching working frequency of the bidirectional series resonant converter through a proportional integral controller according to the current electric energy parameter values of the output side and preset electric energy parameter values; and controlling the bidirectional series resonant converter according to the current phase shift angle and the switching working frequency.

Description

Technical Field

[0001] This application relates to the field of bidirectional series resonant converter topology control technology, and in particular to a control method and control system for a bidirectional series resonant converter. Background Technology

[0002] In existing technologies, the control strategy for bidirectional series resonant converters (DBSRCs) is either single-phase shift adjustment (adjusting the inter-bridge phase shift angle) or dual-phase shift adjustment (adjusting both the inter-bridge and intra-bridge phase shift angles). When only the inter-bridge phase shift angle is adjusted, soft switching (i.e., zero-voltage turn-on (ZVS) and zero-current turn-off (ZCS)) can only be achieved when the gain is less than 1, or when the gain is greater than 1 and the cosine of the phase shift angle is less than the reciprocal of the gain. This leads to increased circulating current losses due to the increased phase shift angle when the gain deviates from 1, affecting the efficiency of the switching transistors. Furthermore, when the bidirectional series resonant converter performs battery-to-bus charging and discharging circuitry, the reverse gain is always less than or equal to 1, making it impossible to achieve a wide output voltage range from the low-voltage battery to the high-voltage bus (i.e., it cannot achieve a normalized gain greater than 1). Consequently, the application scenarios for this system are limited. Summary of the Invention

[0003] In view of this, the purpose of this application is to provide at least one control method and control system for a bidirectional series resonant converter. This method determines the charging and discharging conditions corresponding to the power transmission direction of the bidirectional series resonant converter, and the current power parameter values ​​corresponding to the input and output sides of the converter under these conditions. The current gain is calculated using the current power parameter values ​​of the input and output sides. The current phase shift angle corresponding to the current gain is determined using the target range of the current gain and the target fitting function corresponding to the charging and discharging conditions. The switching frequency is determined by a proportional-integral controller based on the current power parameter value of the output side and a preset power parameter value. Thus, the bidirectional series resonant converter is controlled according to the switching frequency and the current phase shift angle. This solves the technical problems of small soft-switching range and low reverse gain in the prior art, achieving the technical effect of increasing the soft-switching range and increasing the reverse gain.

[0004] This application mainly includes the following aspects:

[0005] In a first aspect, embodiments of this application provide a control method for a bidirectional series resonant converter. The method includes: acquiring a charging / discharging condition corresponding to the power transmission direction on the bidirectional series resonant converter; determining the current power parameter values ​​corresponding to the input and output sides of the bidirectional series resonant converter under the charging / discharging condition; calculating the current gain of the bidirectional series resonant converter based on the current power parameter values; determining the current phase shift angle using a target interval of the current gain and a target fitting function corresponding to the charging / discharging condition, wherein the target fitting function is used to determine the current phase shift angle corresponding to soft switching under the current gain; determining the switching operating frequency of the bidirectional series resonant converter using a proportional-integral controller based on the current power parameter value corresponding to the output side and a preset power parameter value; and controlling the bidirectional series resonant converter according to the current phase shift angle and the switching operating frequency.

[0006] Optionally, the bidirectional series resonant converter includes a transformer, a first bridge circuit, a resonant cavity, and a second bridge circuit. The primary side of the transformer is connected to one end of the first bridge circuit, one end of the resonant cavity is connected to the secondary side of the transformer, and the other end of the resonant cavity is connected to one end of the second bridge circuit. The other end of the first bridge circuit serves as the battery side of the bidirectional series resonant converter, and the other end of the second bridge circuit serves as the bus side of the bidirectional series resonant converter. The input side of the bidirectional series resonant converter is either the battery side or the bus side, and the output side is the other of the battery side and the bus side. The switching operating frequency refers to the operating frequency of the control switches in the first bridge circuit and the second bridge circuit.

[0007] Optionally, the current power parameter value corresponding to the input side of the bidirectional series resonant converter includes the input side voltage value, and the current power parameter value corresponding to the output side of the bidirectional series resonant converter includes the output side voltage value. The current gain of the bidirectional series resonant converter is calculated as follows: based on the battery-side voltage value and the transformer turns ratio of the bidirectional series resonant converter, a target voltage value of the bidirectional series resonant converter is calculated, where the battery-side voltage value is one of the input side voltage value and the output side voltage value; the current gain is calculated according to the target voltage value and a preset voltage value, where the preset voltage value is the other of the input side voltage value and the output side voltage value.

[0008] Optionally, the current phase shift angle includes the inter-bridge phase shift angle or the intra-bridge phase shift angle of the bridge circuit connected to the output side of the bidirectional series resonant converter, wherein the target interval of the current gain includes the enhancement interval where the current gain is greater than 1 corresponding to the intra-bridge phase shift angle or the reduction interval where the current gain is less than 1 corresponding to the inter-bridge phase shift angle.

[0009] Optionally, the charging and discharging conditions include charging conditions or discharging conditions, wherein the target range and the target fitting function corresponding to the charging and discharging conditions are determined by the following methods: under the charging and discharging conditions limiting the bidirectional series resonant converter, the gain of the bidirectional series resonant converter is controlled to be within the target range by adjusting the power parameter values ​​on the input and output sides of the bidirectional series resonant converter; when the resonant current on the input side of the bidirectional series resonant converter is negative, the gain is controlled to reach a preset gain within the target range by adjusting the preset phase shift angle corresponding to the target range; based on the preset phase shift angle and its corresponding preset gain, the target fitting function corresponding to the target range and the charging and discharging conditions, used to describe the conversion relationship between gain and phase shift angle, is determined.

[0010] Optionally, the method further includes: determining whether the switching operating frequency is greater than a preset frequency threshold; when the switching operating frequency is greater than the preset frequency threshold, controlling the bidirectional series resonant converter to enter a light-load mode; and when the switching operating frequency is less than or equal to the preset frequency threshold, controlling the bidirectional series resonant converter according to the current phase shift angle and the switching operating frequency.

[0011] Optionally, the current power parameter values ​​corresponding to the output side of the bidirectional series resonant converter include the output voltage value, the output current value, and the output power value. The output power value is calculated using the output voltage value and the output current value. The switching operating frequency of the bidirectional series resonant converter is determined as follows: for each current power parameter value, the current power parameter value and its corresponding preset power parameter value are input to the proportional-integral controller to obtain the target operating frequency corresponding to the current power parameter value; the maximum value of the target operating frequency corresponding to at least one current power parameter value is taken as the switching operating frequency.

[0012] Secondly, embodiments of this application also provide a control system, the control system including a bidirectional series resonant converter and a processor, wherein the bidirectional series resonant converter includes a transformer, a first bridge circuit, a resonant cavity, and a second bridge circuit, wherein the primary side of the transformer is connected to one end of the first bridge circuit, one end of the resonant cavity is connected to the secondary side of the transformer, the other end of the resonant cavity is connected to one end of the second bridge circuit, the other end of the first bridge circuit serves as the battery side of the bidirectional series resonant converter, and the other end of the second bridge circuit serves as the bus side of the bidirectional series resonant converter, the processor being configured to execute the control method of the bidirectional series resonant converter as described in the first aspect or any possible embodiment of the first aspect.

[0013] Optionally, the first bridge circuit includes multiple first bridge circuits connected in parallel, the primary side of the transformer includes multiple primary windings, the secondary side of the transformer includes multiple secondary windings, and the multiple secondary windings are connected in series. In this case, one first bridge circuit is connected to one primary winding, and one primary winding corresponds to one secondary winding.

[0014] Optionally, the bridge circuit includes a first bridge arm and a second bridge arm, wherein each bridge arm includes a control switch connected in series and a junction capacitor connected in parallel across the control switch.

[0015] This application provides a control method and control system for a bidirectional series resonant converter. The method includes: acquiring the charging and discharging conditions corresponding to the power transmission direction on the bidirectional series resonant converter; determining the current power parameter values ​​corresponding to the input and output sides of the bidirectional series resonant converter under the charging and discharging conditions; calculating the current gain of the bidirectional series resonant converter based on the current power parameter values; determining the current phase shift angle by using the target interval of the current gain and the target fitting function corresponding to the charging and discharging conditions, wherein the target fitting function is used to determine the current phase shift angle corresponding to soft switching under the current gain; determining the switching operating frequency of the bidirectional series resonant converter by a proportional-integral controller based on the current power parameter value corresponding to the output side and a preset power parameter value; and controlling the bidirectional series resonant converter according to the current phase shift angle and the switching operating frequency.

[0016] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A circuit diagram of a bidirectional series resonant converter provided in an embodiment of this application is shown.

[0019] Figure 2 A circuit diagram of another bidirectional series resonant converter provided in an embodiment of this application is shown.

[0020] Figure 3 A flowchart of a control method for a bidirectional series resonant converter provided in an embodiment of this application is shown. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the drawings in this application are for illustrative and descriptive purposes only and are not intended to limit the scope of protection of this application. Furthermore, it should be understood that the schematic drawings are not drawn to scale. The flowcharts used in this application illustrate operations implemented according to some embodiments of this application. It should be understood that the operations in the flowcharts may not be implemented in sequence, and steps without logical contextual relationships may be reversed or implemented simultaneously. In addition, those skilled in the art, guided by the content of this application, may add one or more other operations to the flowcharts, or remove one or more operations from the flowcharts.

[0022] Furthermore, the described embodiments are merely some, not all, of the embodiments of this application. The components of the embodiments of this application described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0023] In existing technologies, traditional control strategies for DBSRCs include single-phase shift regulation and dual-phase shift regulation. Because only the phase shift angle can be controlled, the soft-switching range is limited and efficiency is low. For example, with single-phase shift control, soft switching of the transformer primary side can only be achieved when the gain M is less than 1, or when the gain M is greater than 1 and the cosine of the phase shift angle is less than the reciprocal of the gain. Furthermore, when the gain deviates from 1, the increased phase shift angle leads to significant circulating current losses, affecting the efficiency of the switching transistor. When DBSRCs are applied to the charging and discharging circuit from a low-voltage battery to a high-voltage bus, the calculation of the DBSRC gain M... Where Q is the quality factor, and F is the ratio of the operating frequency of the control switch in the DBSRC to the resonant frequency of the resonant cavity. To reduce the current stress on the resonant capacitor and resonant inductor in the resonant cavity, the resonant cavity is placed on the high-voltage side. Because the denominator in the above formula is always greater than or equal to 1, M is always less than or equal to 1 if and only if F = 1, that is, when the operating frequency equals the resonant frequency, M = 1. Therefore, the gain of the low-voltage battery to high-voltage bus under pure frequency conversion control is low, and it is not suitable for high-gain applications.

[0024] Based on this, this application provides a control method and control system for a bidirectional series resonant converter. By determining the charging and discharging conditions corresponding to the power transmission direction of the bidirectional series resonant converter, and the current power parameter values ​​corresponding to the input and output sides of the converter under these conditions, the current gain is calculated using the current power parameter values ​​of the input and output sides. The current phase shift angle corresponding to the current gain is determined by the target range of the current gain and the target fitting function corresponding to the charging and discharging conditions. The switching frequency is determined by a proportional-integral controller based on the current power parameter value of the output side and a preset power parameter value. Thus, the bidirectional series resonant converter is controlled according to the switching frequency and the current phase shift angle. This solves the technical problems of small soft-switching range and low reverse gain in the prior art, achieving the technical effect of increasing the soft-switching range and increasing the reverse gain, as detailed below:

[0025] Please see Figure 1 , Figure 1 This is a circuit diagram of a bidirectional series resonant converter provided in an embodiment of this application. Figure 1 As shown, the bidirectional series resonant converter provided in this application embodiment includes a transformer T, a first bridge circuit 101, a resonant cavity 102, and a second bridge circuit 103. The primary side of the transformer is connected to one end of the first bridge circuit, one end of the resonant cavity is connected to the secondary side of the transformer, and the other end of the resonant cavity is connected to one end of the second bridge circuit. The other end of the first bridge circuit serves as the battery side of the bidirectional series resonant converter, and the other end of the second bridge circuit serves as the bus side of the bidirectional series resonant converter.

[0026] In other words, the battery side of the bidirectional series resonant converter is used to connect the battery (BAT), and the bus side is used to connect the bus (BUS). The bus can be a DC bus or an AC bus used for grid connection to transmit the battery's electrical energy to the grid, or to charge the battery with electrical energy from the grid.

[0027] Please see Figure 2 , Figure 2 This is a circuit diagram of another bidirectional series resonant converter provided in an embodiment of this application. Figure 2 As shown, the first bridge circuit includes multiple first bridge circuits 101 connected in parallel. The primary side of the transformer includes multiple primary windings L1, and the secondary side of the transformer includes multiple secondary windings L2. The multiple secondary windings are connected in series. One first bridge circuit corresponds to one primary winding, and one primary winding corresponds to one secondary winding.

[0028] In other words, for each first bridge circuit, the other end of the first bridge circuit is led out to serve as the battery side of the bidirectional series resonant converter. For each primary winding, both ends of the primary winding are connected to one end of its corresponding first bridge circuit. Electromagnetic induction occurs between the primary winding and its corresponding secondary winding, and the primary winding is not connected to any other primary winding. Multiple secondary windings are connected in series, and these multiple series-connected secondary windings serve as the secondary side of the transformer, connected to one end of the second bridge circuit.

[0029] For example, the bridge circuit of this application is an H-bridge circuit. The bridge circuit includes a first bridge arm and a second bridge arm, which are connected in parallel. Each bridge arm includes a control switch connected in series and a junction capacitor connected in parallel across the control switch.

[0030] like Figure 1 and Figure 2As shown, the first bridge arm of the first bridge circuit includes a first control switch Q1 and a second control switch Q2 connected in series. A diode D1 and a junction capacitor C1 are connected in parallel to the first control switch, and a diode D2 and a junction capacitor C2 are connected in parallel to the second control switch. The second bridge arm of the first bridge circuit includes a third control switch Q3 and a fourth control switch Q4 connected in series. A diode D3 and a junction capacitor C3 are connected in parallel to the third control switch, and a diode D4 and a junction capacitor C4 are connected in parallel to the fourth control switch. The connection points of the first and second control switches, as well as the connection points of the third and fourth control switches, are led out as one end of the first bridge circuit. The connection point between the first and second bridge arms of the first bridge circuit is led out as the other end of the first bridge circuit. The connection points of the first and third control switches, as well as the connection points of the second and fourth control switches, are led out as the connection points between the first and second bridge arms of the first bridge circuit.

[0031] The first arm of the second bridge circuit includes a fifth control switch Q5 and a sixth control switch Q5 connected in series. A diode D5 and a junction capacitor C5 are connected in parallel to the fifth control switch, and a diode D6 and a junction capacitor C6 are connected in parallel to the sixth control switch. The second arm of the second bridge circuit includes a seventh control switch Q7 and an eighth control switch Q8 connected in series. A diode D7 and a junction capacitor C7 are connected in parallel to the seventh control switch, and a diode D8 and a junction capacitor C8 are connected in parallel to the eighth control switch. The connection points between the fifth and sixth control switches, and between the seventh and eighth control switches, are led out as one end of the second bridge circuit. The connection point between the first and second arms of the second bridge circuit is led out as the other end of the second bridge circuit. The connection points between the fifth and seventh control switches, and between the sixth and eighth control switches, are led out as the connection points between the first and second arms of the second bridge circuit.

[0032] The control switch can be selected from bipolar transistors, MOSFETs, or insulated gate bipolar transistors. The diode, as a freewheeling diode, can protect the control switch from breakdown and control the direction of current. The junction capacitance is used to protect the control switch from overvoltage and overcurrent to improve safety.

[0033] Please see Figure 3 , Figure 3 This is a flowchart illustrating a control method for a bidirectional series resonant converter provided in an embodiment of this application. Figure 3 As shown in the embodiments of this application, the control method for a bidirectional series resonant converter includes the following steps:

[0034] S101: Obtain the charging and discharging conditions corresponding to the power transmission direction on the bidirectional series resonant converter.

[0035] The input side of the bidirectional series resonant converter is one of the battery side and the bus side, and the output side of the bidirectional series resonant converter is the other of the battery side and the bus side.

[0036] In other words, the direction of power transmission on the bidirectional series resonant converter includes either the direction of power transmission from the battery side to the bus side or the direction of power transmission from the bus side to the battery side. The charging and discharging conditions include charging and discharging conditions for the battery. When the battery is charging, the direction of power transmission on the bidirectional series resonant converter is the direction of power transmission from the bus side to the battery side. The power grid connected to the bus side charges the battery. The input side of the bidirectional series resonant converter is the bus side, and the output side is the battery side. When the battery is discharging, the direction of power transmission on the bidirectional series resonant converter is the direction of power transmission from the battery side to the bus side. The battery connected to the battery side transmits power to the bus connected to the bus side. The input side of the bidirectional series resonant converter is the battery side, and the output side is the bus side.

[0037] S102: Determine the current electrical energy parameter values ​​corresponding to the input and output sides of the bidirectional series resonant converter under the charging and discharging conditions.

[0038] The current power parameter values ​​corresponding to the input side of the bidirectional series resonant converter include the input voltage value, and the current power parameter values ​​corresponding to the output side of the bidirectional series resonant converter include the output voltage value, the output current value, and the output power value. The output power value is calculated using the output voltage value and the output current value.

[0039] The input voltage and output voltage are used to calculate the current gain of the bidirectional series resonant converter, while the output voltage, output current, and output power are used to calculate the switching frequency.

[0040] In other words, the input voltage value of the bidirectional series resonant converter is collected, as well as the output voltage value and output current value of the bidirectional series resonant converter, and the output power value is obtained by calculating the product of the output voltage value and the output current value.

[0041] S103: Calculate the current gain of the bidirectional series resonant converter based on the current power parameter values.

[0042] The current gain of the bidirectional series resonant converter is calculated as follows: based on the battery-side voltage value and the transformer turns ratio of the bidirectional series resonant converter, the target voltage value of the bidirectional series resonant converter is calculated, where the battery-side voltage value is one of the input-side voltage value and the output-side voltage value; the current gain is calculated according to the target voltage value and a preset voltage value, where the preset voltage value is the other of the input-side voltage value and the output-side voltage value.

[0043] The target voltage value is the product of the battery-side voltage of the bidirectional series resonant converter and the transformer turns ratio. Furthermore, when the battery is charging, with the input side of the bidirectional series resonant converter being the bus side and the output side being the battery side, the output voltage is the battery-side voltage, and the ratio of the target voltage to the input voltage is used as the current gain. When the battery is discharging, with the input side of the bidirectional series resonant converter being the bus side and the output side being the bus side, the input voltage is the battery-side voltage, and the ratio of the output voltage to the target voltage is used as the current gain.

[0044] S104: Determine the current phase shift angle by using the target range where the current gain is located and the target fitting function corresponding to the charging and discharging conditions.

[0045] The target fitting function is used to determine the current phase shift angle corresponding to the soft switching achieved at the current gain. The current phase shift angle includes the inter-bridge phase shift angle or the intra-bridge phase shift angle of the bridge circuit connected to the output side of the bidirectional series resonant converter. The target interval of the current gain includes the enhancement interval where the current gain is greater than 1 corresponding to the intra-bridge phase shift angle or the reduction interval where the current gain is less than 1 corresponding to the inter-bridge phase shift angle.

[0046] Therefore, when the gain is determined to be equal to 1, no adjustment is required. Then, return to step S102 to redetermine the current power parameter values ​​corresponding to the input and output sides of the bidirectional series resonant converter under the charging and discharging conditions.

[0047] Specifically, the inter-bridge phase shift angle is the phase difference between the first and second bridge circuits, while the intra-bridge phase shift angle refers to the phase difference between the two arms of the bridge circuit connected to the output side. For example... Figure 2 As shown, the phase difference of each first bridge circuit is the same. If the output side is the battery side, the phase shift angle between bridges is the phase difference between the first bridge circuit and the second bridge circuit, and the phase shift angle within the bridge is the phase difference of the first bridge circuit.

[0048] The target fitting function corresponding to the target range and the charging / discharging condition is determined as follows: Under the limited charging / discharging condition of the bidirectional series resonant converter, the gain of the bidirectional series resonant converter is controlled to be within the target range by adjusting the power parameter values ​​on the input and output sides of the bidirectional series resonant converter; when the resonant current on the input side of the bidirectional series resonant converter is negative, the gain is controlled to reach a preset gain within the target range by adjusting the preset phase shift angle corresponding to the target range; based on the preset phase shift angle and its corresponding preset gain, the target fitting function corresponding to the target range and the charging / discharging condition is determined to describe the conversion relationship between gain and phase shift angle.

[0049] In the process of adjusting the phase shift angle within the bridge circuit on the output side, there may be situations where the control switches within the bridge arms are simultaneously closed. In this case, a short circuit will cause a voltage boost. Therefore, when the current gain is greater than 1 in the enhancement range, the target phase shift angle is the phase shift angle within the bridge, and the phase shift angle between the bridges is not adjusted. When the current gain is less than 1, a voltage reduction function is achieved, which is equivalent to LLC frequency conversion regulation mode. By adjusting the size of the phase shift angle between the bridges, the energy exchange between the primary and secondary sides can be changed, thereby achieving the purpose of voltage reduction. Therefore, when the current gain is less than 1 in the reduction range, the target phase shift angle is the phase shift angle between the bridges, and the phase shift angle within the bridges is not adjusted.

[0050] In other words, the battery is pre-charged using a bidirectional series resonant converter, and the target range of gain is limited by restricting the voltage values ​​at both ends of the battery connected to the battery side and the constant voltage device connected to the bus side.

[0051] For example, when the battery is charging, the gain of the bidirectional series resonant converter is limited to the enhancement range where it is always greater than 1 by adjusting the voltage values ​​at both ends of the battery and the voltage value of the constant voltage device connected to the bus side. The inter-bridge phase shift angle between the input and output sides is controlled to be always 0, and the resonant current on the input side is observed in real time to see if it is negative. When the resonant current on the input side is negative, the bridge phase shift angle of the bridge circuit connected to the output side is adjusted at 5° intervals according to the first-order adjustment frequency of 5kHz. After adjusting 5° to reach the preset bridge phase shift angle, the gain corresponding to each preset bridge phase shift angle is calculated by collecting the actual input and output voltages. This yields a reference table of each preset bridge phase shift angle and its corresponding gain. The least squares method is used to fit the reference table to obtain a fitting function in which the gain is the independent variable and the bridge phase shift angle is the dependent variable when the gain is greater than 1 under charging conditions.

[0052] When the battery is charging, the resonant current on the input side (i.e., the bus side) is negative. This means that the excitation current can discharge the junction capacitance of the switching transistor in the bridge circuit connected to the bus side in reverse, so that the switching transistor can be turned on at zero voltage the next time it is turned on, thus achieving soft switching.

[0053] For example, when the battery is in discharge mode, the gain of the bidirectional series resonant converter is limited to the enhancement range of always being greater than 1 by adjusting the voltage values ​​at both ends of the battery and the voltage value of the constant voltage device connected to the bus side. The inter-bridge phase shift angle of the input and output sides is controlled to be always 0, and the resonant current of the input side is observed in real time to see if it is negative. When the resonant current of the input side is negative, the bridge phase shift angle of the bridge circuit connected to the output side is adjusted at 5° intervals according to the first-order adjustment frequency of 5kHz. After adjusting 5° to reach the preset bridge phase shift angle, the gain corresponding to each preset bridge phase shift angle is calculated, thereby obtaining a reference table of each preset bridge phase shift angle and its corresponding gain. The least squares method is used to fit the reference table to obtain a fitting function in which the gain is the independent variable and the bridge phase shift angle is the dependent variable when the gain is greater than 1 under discharge mode.

[0054] When the battery is in discharge mode, the resonant current on the input side (i.e., the battery side) is negative. This means that the excitation current can discharge the junction capacitance of the switching transistor in the bridge circuit connected to the battery side in reverse, so that the switching transistor can be turned on at zero voltage the next time it is turned on, thus achieving soft switching.

[0055] For example, when the battery is charging, the gain of the bidirectional series resonant converter is limited to a reduction range where it is always less than 1 by adjusting the voltage values ​​at both ends of the battery and the voltage value of the constant voltage device connected to the bus side. This controls the phase shift angle within the bridge circuit on the output side to be always 0, and the resonant current on the input side is observed in real time to ensure it is negative. When the resonant current on the input side is negative, the inter-bridge phase shift angle is adjusted in 5° increments at a first-order adjustment frequency of 5kHz. After each 5° adjustment to a preset inter-bridge phase shift angle, the gain corresponding to each preset inter-bridge phase shift angle is calculated, thus obtaining a lookup table of each preset inter-bridge phase shift angle and its corresponding gain. Least squares fitting is then performed using this lookup table to obtain a fitting function where the gain is the independent variable and the inter-bridge phase shift angle is the dependent variable when the gain is less than 1 under charging conditions. Similarly, when the battery is discharging and the gain is less than 1, the gain corresponding to each inter-bridge phase shift angle is collected to obtain a fitting function where the gain is the independent variable and the inter-bridge phase shift angle is the dependent variable when the gain is less than 1 under discharging conditions.

[0056] In other words, when the phase shift angle of the control switch is adjusted to reach the preset phase shift angle, it is necessary to ensure that the resonant current on the input side is negative. This means that each preset phase shift angle can achieve a negative resonant current on the input side. A negative resonant current on the input side means that the junction capacitor connected in parallel on the control switch is discharged, thereby enabling the control switch to close or open without power loss.

[0057] When the current gain is less than 1, the bidirectional series resonant converter can be placed in a near-LLC mode. Since the transformer in the bidirectional series resonant converter has no air gap, its magnetizing inductance is very large. At this time, the ratio of the transformer's magnetizing inductance to the resonant inductance of the resonant cavity is large. Therefore, adjusting the switching frequency of the control switch to be lower than the resonant frequency of the resonant cavity can achieve voltage reduction. Furthermore, before the control switch is turned on, the magnetizing inductance generates a magnetizing current, which reduces the voltage across the junction capacitor connected in parallel across the control switch to zero. This allows the primary-side control switch to be in zero-voltage turn-on (ZVS) mode and the secondary-side control switch to be in zero-current turn-off (ZCS) mode, thus reducing switching losses.

[0058] When the gain is greater than 1, the bidirectional series resonant converter can be put into a boost-like mode. In this mode, by adjusting the phase shift angle within the bridge, a brief short circuit can be achieved on the secondary side, and the resonant inductor can be charged (e.g., ...). Figure 1 In this process, Q1 and Q4 on the primary side are turned on, while Q5 and Q7 on the secondary side are turned on simultaneously, or Q6 and Q8 are turned on simultaneously, to ensure a gain greater than 1. Furthermore, since the phase shift angle is adjusted only when the resonant current on the input side is negative during the determination of the fitting function, it can be determined that the corresponding resonant current is negative at each phase shift angle. A negative resonant current means that the junction capacitor connected in parallel on the control switch is discharged, enabling zero-voltage turn-on (ZVS) and zero-current turn-off (ZCS) of the control switch. This allows for soft switching even when the gain is greater than 1. Therefore, compared to existing technologies, soft switching can be achieved whether the gain is greater than 1 or less than 1.

[0059] Furthermore, based on the target range of the current gain and the charging / discharging conditions, the corresponding target fitting function can be determined. Substituting the current gain into the target fitting function yields the current phase shift angle corresponding to the current gain. Moreover, the current phase shift angle obtained at this point can achieve soft switching.

[0060] S105: Based on the current power parameter value and the preset power parameter value corresponding to the output side, the switching operating frequency of the bidirectional series resonant converter is determined by the proportional-integral controller.

[0061] The switching operating frequency refers to the operating frequency of the control switches in the first bridge circuit and the second bridge circuit.

[0062] The switching operating frequency of the bidirectional series resonant converter is determined as follows: for each current power parameter value, the current power parameter value and its corresponding preset power parameter value are input to the proportional-integral controller to obtain the target operating frequency corresponding to the current power parameter value; the maximum value of the target operating frequency corresponding to at least one current power parameter value is taken as the switching operating frequency.

[0063] In other words, the voltage difference between the output voltage value and the preset output voltage value is input to the proportional-integral controller to obtain the first target operating frequency mapped by the voltage difference; the current difference between the output current value and the preset output current value is input to the proportional-integral controller to obtain the second target operating frequency mapped by the current difference; and the power difference between the output power value and the preset output power value is input to the proportional-integral controller to obtain the third target operating frequency mapped by the power difference. Any one of the first, second, and third target operating frequencies can be used as the switching operating frequency to be adjusted, or the maximum value of at least two of the first, second, and third target operating frequencies can be used as the switching operating frequency to be adjusted.

[0064] For example, using the maximum value among the first target operating frequency, the second target operating frequency, and the third target operating frequency as the switching operating frequency of the bidirectional series resonant converter can provide a faster response speed, the output waveform can be closer to the desired waveform, and the power quality on the output side can be improved.

[0065] S106: Control the bidirectional series resonant converter according to the current phase shift angle and the switching operating frequency.

[0066] The method further includes: determining whether the switching operating frequency is greater than a preset frequency threshold; when the switching operating frequency is greater than the preset frequency threshold, controlling the bidirectional series resonant converter to enter a light-load mode; when the switching operating frequency is less than or equal to the preset frequency threshold, controlling the bidirectional series resonant converter according to the current phase shift angle and the switching operating frequency.

[0067] In other words, after determining the switching frequency of the bidirectional series resonant converter, it is necessary to compare the switching frequency with a preset frequency threshold. If the switching frequency is greater than the preset frequency threshold, it means that the operating frequency of the control switch cannot be increased further. Consequently, the bidirectional series resonant converter is controlled to enter a light-load mode (burst mode), where the control switch stops switching for several cycles before starting to operate again, which can effectively reduce switching losses and lower static power consumption. If the switching frequency is less than or equal to the preset frequency threshold, it means that the control switch can operate according to the switching frequency. Consequently, the phase shift angle of the bidirectional series resonant converter is adjusted according to the current phase shift angle corresponding to the current gain. At the same time, the operating frequency of the control switch of the bridge circuit of the bidirectional series resonant converter is adjusted according to the switching frequency, thereby achieving control of the bidirectional series resonant converter.

[0068] For example, after adjusting the current phase shift angle and the switching operating frequency, step S102 can be re-executed for cyclic control until the charging and discharging state is changed, at which point step S101 is re-executed.

[0069] Based on the same application concept, this application also provides a control system corresponding to the control method provided in the above embodiments. Since the principle of the control system in this application is similar to the control method in the above embodiments of this application, the implementation of the control system can refer to the implementation of the method, and the repeated parts will not be described again.

[0070] For example, the control system includes a bidirectional series resonant converter and a processor, wherein the processor is connected to the bidirectional series resonant converter and is used to control the current phase shift angle and switching operating frequency of the bidirectional series resonant converter. The processor is configured to execute the control method for the bidirectional series resonant converter as provided in the above embodiments.

[0071] Furthermore, the strategy of this application, based on multiple controls of the phase shift angle within the bridge, the phase shift angle between bridges, and the switching operating frequency, allows for separate control when the gain is greater than 1 and when the gain is less than 1. This ensures that soft switching can be achieved when the gain is greater than 1, improving system efficiency and reducing the difficulty of thermal design. Simultaneously, by fitting, the actual angle value of the phase shift angle corresponding to each gain is determined, improving the adjustment accuracy and avoiding increasing the complexity of the algorithm. Moreover, by adjusting the phase shift angle within the bridge to briefly short-circuit the control switch and resonant inductor on the secondary side to allow them to store and release energy, the normalized gain from the low-voltage battery to the high-voltage bus is greater than 1. Therefore, it can be compatible with DC / DC circuits (DC-DC converters) with a high gain variation range, solving the problem that the maximum reverse gain of LLC circuits is only 1.

[0072] Based on the same concept, embodiments of this application also provide a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of the control method provided in the above embodiments.

[0073] Specifically, the storage medium can be a general-purpose storage medium, such as a portable disk or hard disk. When the computer program on the storage medium is run, it can execute the above-mentioned control method. By determining the charging and discharging conditions corresponding to the power transmission direction of the bidirectional series resonant converter, and the current power parameter values ​​corresponding to the input and output sides of the bidirectional series resonant converter under these charging and discharging conditions, the current gain is calculated using the current power parameter values ​​of the input and output sides and the current power parameter values ​​of the output side. The current phase shift angle corresponding to the current gain is determined by the target interval of the current gain and the target fitting function corresponding to the charging and discharging conditions. The switching operating frequency is determined by the proportional-integral controller according to the current power parameter value of the output side and the preset power parameter value. Thus, the bidirectional series resonant converter is controlled according to the switching operating frequency and the current phase shift angle. This solves the technical problems of small soft-switching range and low reverse gain in the prior art, and achieves the technical effect of increasing the soft-switching range and increasing the reverse gain.

[0074] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems and devices described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. In the several embodiments provided in this application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of units is only a logical functional division; in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Another point is that the displayed or discussed mutual coupling or direct coupling or communication connection may be through some communication interfaces; the indirect coupling or communication connection of devices or units may be electrical, mechanical, or other forms.

[0075] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0076] In addition, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

[0077] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a processor-executable, non-volatile, computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0078] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A control method for a bidirectional series resonant converter, characterized in that, The method includes: Obtain the charging and discharging conditions corresponding to the direction of power transmission on the bidirectional series resonant converter; Determine the current electrical energy parameter values ​​corresponding to the input and output sides of the bidirectional series resonant converter under the charging and discharging conditions; Based on the current power parameter values, calculate the current gain of the bidirectional series resonant converter; The current phase shift angle is determined by the target range where the current gain is located and the target fitting function corresponding to the charging and discharging condition. The target fitting function is used to determine the current phase shift angle corresponding to the soft switching achieved under the current gain. Based on the current power parameter value and the preset power parameter value corresponding to the output side, the switching operating frequency of the bidirectional series resonant converter is determined by the proportional-integral controller. The bidirectional series resonant converter is controlled according to the current phase shift angle and the switching operating frequency.

2. The method according to claim 1, characterized in that, The bidirectional series resonant converter includes a transformer, a first bridge circuit, a resonant cavity, and a second bridge circuit. The primary side of the transformer is connected to one end of the first bridge circuit, one end of the resonant cavity is connected to the secondary side of the transformer, and the other end of the resonant cavity is connected to one end of the second bridge circuit. The other end of the first bridge circuit serves as the battery side of the bidirectional series resonant converter, and the other end of the second bridge circuit serves as the bus side of the bidirectional series resonant converter. Wherein, the input side of the bidirectional series resonant converter is one of the battery side and the bus side, the output side of the bidirectional series resonant converter is the other of the battery side and the bus side, and the switching operating frequency refers to the operating frequency of the control switch in the first bridge circuit and the second bridge circuit.

3. The method according to claim 1 or 2, characterized in that, The current power parameter values ​​corresponding to the input side of the bidirectional series resonant converter include the input voltage value, and the current power parameter values ​​corresponding to the output side of the bidirectional series resonant converter include the output voltage value. The current gain of the bidirectional series resonant converter is calculated in the following manner: Based on the battery-side voltage value and transformer turns ratio of the bidirectional series resonant converter, the target voltage value of the bidirectional series resonant converter is calculated, wherein the battery-side voltage value is one of the input-side voltage value and the output-side voltage value; The current gain is calculated based on the target voltage value and the preset voltage value, wherein the preset voltage value is the other of the input voltage value and the output voltage value.

4. The method according to claim 1, characterized in that, The current phase shift angle includes the inter-bridge phase shift angle or the intra-bridge phase shift angle of the bridge circuit connected to the output side of the bidirectional series resonant converter. The target interval of the current gain includes the enhancement interval where the current gain is greater than 1 corresponding to the phase shift angle within the bridge, or the reduction interval where the current gain is less than 1 corresponding to the phase shift angle between bridges.

5. The method according to claim 4, characterized in that, The charging and discharging conditions include charging conditions or discharging conditions. The target fitting function corresponding to the target range and the charge / discharge condition is determined in the following way: Under the limited charging and discharging conditions of the bidirectional series resonant converter, the gain of the bidirectional series resonant converter can be controlled to be within the target range by adjusting the power parameter values ​​on the input and output sides of the bidirectional series resonant converter. When the resonant current on the input side of the bidirectional series resonant converter is negative, the gain is controlled to reach the preset gain within the target range by adjusting the preset phase shift angle corresponding to the target range. Based on the preset phase shift angle and its corresponding preset gain, the target fitting function for describing the conversion relationship between gain and phase shift angle is determined for the target range and the charging / discharging condition.

6. The method according to claim 1, characterized in that, The method further includes: Determine whether the operating frequency of the switch is greater than a preset frequency threshold; When the switching operating frequency is greater than a preset frequency threshold, the bidirectional series resonant converter is controlled to enter a light-load mode. When the switching operating frequency is less than or equal to a preset frequency threshold, the bidirectional series resonant converter is controlled according to the current phase shift angle and the switching operating frequency.

7. The method according to claim 1, characterized in that, The current power parameters corresponding to the output side of the bidirectional series resonant converter include the output voltage, output current, and output power. The output power is calculated from the output voltage and output current. The switching frequency of the bidirectional series resonant converter is determined by the following method: For each current power parameter value, the current power parameter value and its corresponding preset power parameter value are input to the proportional-integral controller to obtain the target operating frequency corresponding to the current power parameter value; The maximum value of the target operating frequency corresponding to at least one current power parameter value shall be used as the switching operating frequency.

8. A control system, characterized in that, The control system includes a bidirectional series resonant converter and a processor. The bidirectional series resonant converter includes a transformer, a first bridge circuit, a resonant cavity, and a second bridge circuit. The primary side of the transformer is connected to one end of the first bridge circuit, one end of the resonant cavity is connected to the secondary side of the transformer, and the other end of the resonant cavity is connected to one end of the second bridge circuit. The other end of the first bridge circuit serves as the battery side of the bidirectional series resonant converter, and the other end of the second bridge circuit serves as the bus side of the bidirectional series resonant converter. The processor is configured to execute the control method for the bidirectional series resonant converter as described in any one of claims 1 to 7.

9. The system according to claim 8, characterized in that, The first bridge circuit includes multiple first bridge circuits connected in parallel. The primary side of the transformer includes multiple primary windings, and the secondary side of the transformer includes multiple secondary windings connected in series. In this circuit, one primary winding is connected to one primary winding, and one primary winding corresponds to one secondary winding.

10. The system according to claim 8 or 9, characterized in that, A bridge circuit includes a first bridge arm and a second bridge arm. Each bridge arm includes a control switch connected in series and a junction capacitor connected in parallel across the control switch.

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