Inverter

Abstract

An inverter. In a primary bridge arm of the inverter, a first end of a first switching tube and a first end of a third switching tube are connected to a positive output end of a direct-current power source, a second end of the first switching tube is connected to a negative output end of the direct-current power source by means of a second switching tube, a second end of the third switching tube is connected to the negative output end of the direct-current power source, and a connection end between the first switching tube and the second switching tube and a connection end between the third switching tube and the fourth switching tube are respectively connected to two ends of a primary winding of a transformer unit. A controller controls the turn-on interval between the turn-on of the first switching tube and the turn-on of the third switching tube to be a first phase angle, and the phase difference between a first alternating-current voltage across the primary winding and a second alternating-current voltage across a secondary winding to be a second phase angle. The controller adjusts the first phase angle, the second phase angle and a switching frequency according to different control modes to control an output power until an output current is a set current value, different polarity changes of the first and second alternating-current voltages correspond to different control modes, and in different control modes, the relationships between the output power and the three control variables are different.

Description

Inverter

[0001] This application claims priority to Chinese Patent Application No. 202410493998.7, filed with the China National Intellectual Property Administration on April 23, 2024, entitled "Inverter", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electronic power, and more particularly to an inverter. Background Technology

[0003] Microinverters, as module-level control inverters, are used to directly connect to individual photovoltaic (PV) modules and can independently achieve maximum power point tracking (MPPT) control. The application of microinverters improves the power generation efficiency of PV systems under conditions such as PV module power mismatch and shading, while also offering advantages such as safety, high reliability, and module-level monitoring. With the continuous development and improvement of microinverter technology, its application scope can gradually expand from PV systems to residential energy storage systems, indicating huge market potential. Currently, microinverters with a DC bus-less single-stage microinverter topology are the mainstream in the market, and their control strategies can be divided into two main categories: open-loop control and closed-loop control. Open-loop control, based on the different control variables, can be further divided into three categories: single-phase shift, extended phase shift, and frequency conversion phase shift control. However, open-loop control strategies have inherent problems such as parameter sensitivity and low control accuracy, which are unavoidable in open-loop control strategies. Closed-loop control strategies have emerged to address this issue, and they can also be divided into three categories based on the different control variables: single-phase shift, extended phase shift, and single-mode frequency conversion phase shift control. However, existing closed-loop control strategies do not make full use of control variables, and the modulation mode of micro-inverters is singular, resulting in low overall control efficiency and low accuracy of current output control. Summary of the Invention

[0004] This application provides an inverter that can make fuller use of control variables, improve the flexibility of inverter control and the overall control efficiency of the inverter, and has high output current control accuracy.

[0005] In a first aspect, this application provides an inverter comprising a primary side bridge arm, a secondary side bridge arm, a transformer unit, and a controller. The primary side bridge arm includes a first switch, a second switch, a third switch, and a fourth switch. The first terminals of the first and third switches are connected to the positive output terminal of a DC power supply. The second terminal of the first switch is connected to the negative output terminal of the DC power supply via a second switch. The second terminal of the third switch is connected to the negative output terminal of the DC power supply via a fourth switch. The connection terminals of the first and second switches, and the connection terminals of the third and fourth switches, are respectively connected to the first and second terminals of the primary winding of the transformer unit. The secondary winding of the transformer unit is connected to the secondary side bridge arm. The controller is used to control the first and second switches to conduct alternately, and the third and fourth switches to conduct alternately, in one control cycle. The interval between the conduction of the first and third switches is a first phase angle, and the phase difference between the first AC voltage across the primary winding and the second AC voltage across the secondary winding is a second phase angle. The controller is also used to adjust the first phase angle, the second phase angle, and the switching frequency of each switch according to the first control mode, the second control mode, or the third control mode based on the polarity changes of the first AC voltage and the second AC voltage, so that the output power of the inverter changes until the output current of the inverter is a set current value. Different polarity changes of the first AC voltage and the second AC voltage correspond to different control modes, and the relationship between the output power of the inverter and the three variables of the first phase angle, the second phase angle, and the switching frequency is different under different control modes.

[0006] In this application, the controller switches between a first control mode, a second control mode, or a third control mode based on the polarity changes of the first AC voltage and the second AC voltage. In each mode, it adjusts the first phase angle, the second phase angle, and the switching frequency of each switching transistor, causing the inverter's output power to vary until the inverter's output current reaches a set value. Here, different polarity changes of the first and second AC voltages correspond to different control modes, and the relationship between the output power and the three variables—the first phase angle, the second phase angle, and the switching frequency—is different in each control mode. During the controller's modulation of the inverter circuit, the controller aims to achieve a set output current value while simultaneously adjusting the three variables: the first phase angle, the second phase angle, and the switching frequency. This results in high utilization of control variables. Furthermore, switching between different control modes based on the polarity changes of the first and second AC voltages improves the flexibility of inverter control, enhances the overall control efficiency of the inverter, and achieves high output current control accuracy.

[0007] In one possible implementation, the controller is configured to adjust the first phase angle, the second phase angle, and the switching frequency according to a first control mode while the second AC voltage remains positive during a period when the first AC voltage is negative, thereby changing the output power of the inverter. In the first control mode, the output power of the inverter satisfies:

[0008] Where D1 and D2 are the first phase angle and the second phase angle, respectively, f s V is the switching frequency. in V is the input voltage of the inverter. g Where is the output voltage of the inverter, n is the transformation ratio of the transformer unit, and L is the voltage of the inverter. r This refers to the leakage inductance value between the primary and secondary windings of the transformer unit. Here, the controller aims to control the output current to reach a set current value, while simultaneously adjusting three variables: the first phase angle, the second phase angle, and the switching frequency. This results in high utilization of control variables, and the controller switches between different control modes based on the polarity changes of the first and second AC voltages, improving the flexibility of inverter control, enhancing the overall control efficiency of the inverter, and achieving high accuracy in output current control.

[0009] In one possible implementation, the controller is configured to adjust the first phase angle, the second phase angle, and the switching frequency according to a second control mode during a period when the first AC voltage is negative and the second AC voltage switches between positive and negative voltages, thereby changing the output power of the inverter. In the second control mode, the output power of the inverter satisfies:

[0010] Where D1 and D2 are the first phase angle and the second phase angle, respectively, f s V is the switching frequency. in V is the input voltage of the inverter. g Where is the output voltage of the inverter, n is the transformation ratio of the transformer unit, and L is the voltage of the inverter. r This refers to the leakage inductance value between the primary and secondary windings of the transformer unit. Here, the controller aims to control the output current to reach a set current value, while simultaneously adjusting three variables: the first phase angle, the second phase angle, and the switching frequency. This results in high utilization of control variables, and the controller switches between different control modes based on the polarity changes of the first and second AC voltages, improving the flexibility of inverter control, enhancing the overall control efficiency of the inverter, and achieving high accuracy in output current control.

[0011] In one possible implementation, the controller is configured to adjust the first phase angle, the second phase angle, and the switching frequency according to a third control mode while the second AC voltage remains negative during a period when the first AC voltage is negative, thereby varying the inverter's output power. In the third control mode, the inverter's output power satisfies:

[0012] where, D1 and D2 are the first phase angle and the second phase angle respectively, f s is the switching frequency, V in is the input voltage of the inverter, V g is the output voltage of the inverter, n is the voltage transformation ratio of the voltage transformation unit, L r is the leakage inductance value between the primary winding and the secondary winding of the voltage transformation unit. Here, the controller aims to control the output current to reach the set current value, and at the same time adjusts three variables, namely the first phase angle, the second phase angle and the switching frequency. The utilization degree of the control variables is high, and different control modes are switched based on the polarity changes of the first AC voltage and the second AC voltage, which improves the flexibility of the inverter control, enhances the overall control efficiency of the inverter, and has high output current control accuracy.

[0013] In a possible implementation manner, the controller is configured to, during the period when the first AC voltage is a negative voltage and the second AC voltage remains a positive voltage, and when -180° < D1 ≤ 180° and (1 - D1) / 2 < |D2| ≤ 180° are satisfied, adjust the first phase angle, the second phase angle and the switching frequency according to the first control mode. Here, based on the fact that the first AC voltage and the second AC voltage meet the polarity requirements, the controller further uses the values of the first phase angle and the second phase angle as the determination conditions for different control modes, which improves the discrimination between different control modes, reduces the misjudgment of the control mode by the controller, and further improves the output current control accuracy.

[0014] In a possible implementation manner, the controller is configured to, during the period when the first AC voltage is a negative voltage and the second AC voltage switches between a positive voltage and a negative voltage, and when -...

[0015] In a possible implementation, the controller is configured to adjust the first phase angle, the second phase angle, and the switching frequency according to a third control mode when the second AC voltage remains negative during a period when the first AC voltage is negative, and -180° < D1 ≤ 180° and 0 < |D2| ≤ D1 / 2 are satisfied. Here, based on the fact that the first AC voltage and the second AC voltage meet the polarity requirements, the controller further uses the values of the first phase angle and the second phase angle as the determination conditions for different control modes, improving the discrimination between different control modes, reducing the misjudgment of the control mode by the controller, and further improving the output current control accuracy.

[0016] In a possible implementation, the controller is configured to obtain at least one set of variable combinations, each variable combination including three variable values of different first phase angles, second phase angles, and switching frequencies, and the output current of the inverter corresponding to each variable combination is a set current value. The controller is further configured to use the variable combination corresponding to the minimum resonance current value in the at least one set of variable combinations as the target variable combination, and adjust the first phase angle, the second phase angle, and the switching frequency based on the target variable combination. The resonance current value is the magnitude of the current between the connection end of the first secondary half-bridge arm and the second secondary half-bridge arm and the first end of the secondary winding of the transformer unit. Here, based on the fact that the output current of the inverter is controlled to be a set current value, the controller adds an optimization goal of minimizing the resonance cavity current of the inverter, that is, controlling the current between the connection end of the first secondary half-bridge arm and the second secondary half-bridge arm and the first end of the secondary winding of the transformer unit in the inverter to be the smallest, thereby reducing the loss of the switching tubes in the inverter.

[0017] In a possible implementation, the controller is configured to increase or decrease the switching frequency based on the output current of the inverter and the set current value, where the amplitude of the switching frequency adjusted by the controller is positively correlated with the absolute value of the difference between the output current of the inverter and the set current value. Here, in the feed-forward control link, the controller aims to control the output current to reach the set current value, and at the same time adjusts the three variables of the first phase angle, the second phase angle, and the switching frequency. In addition, the controller simultaneously performs a current control link, generating a switching frequency adjustment value based on the set current value and the current output of the current inverter, and then adding the switching frequency generated by the feed-forward link and the switching frequency adjustment value generated by the current control link to output the final switching frequency. By combining the output results of the feed-forward control link and the current control link, the output current control accuracy can be further improved.

[0018] In one possible implementation, the controller increases or decreases the second phase angle based on the inverter's output current and a set current value. The magnitude of the controller's adjustment of the second phase angle is positively correlated with the absolute value of the difference between the inverter's output current and the set current value. Here, in the feedforward control loop, the controller aims to control the output current to reach the set current value, while simultaneously adjusting three variables: the first phase angle, the second phase angle, and the switching frequency. Furthermore, the controller simultaneously performs a current control loop, generating a second phase angle adjustment value based on the set current value and the current inverter output current. The final second phase angle is output by adding the second phase angle generated by the feedforward loop and the second phase angle adjustment value generated by the current control loop. By combining the output results of the feedforward control loop and the current control loop, the output current control accuracy can be further improved.

[0019] In one possible implementation, the inverter includes a first capacitor and a second capacitor, and a secondary bridge arm is connected in parallel with the first and second capacitors connected in series. The secondary bridge arm includes a first secondary half-bridge arm and a second secondary half-bridge arm connected in series. The connection terminals of the first secondary half-bridge arm and the second secondary half-bridge arm, as well as the connection terminals of the first and second capacitors, are respectively connected to the first and second terminals of the secondary winding of the transformer unit. The first secondary half-bridge arm and the second secondary half-bridge arm include at least one switching transistor.

[0020] In one possible implementation, the first secondary half-bridge arm includes a fifth and a sixth switch connected in series, and the second secondary half-bridge arm includes a seventh and an eighth switch connected in series. The connection terminals of the sixth and seventh switches are connected to the first terminal of the secondary winding of the transformer unit. The controller is configured to, when the inverter's output voltage is positive, keep the sixth and eighth switches on while alternating the conduction of the fifth and seventh switches; and when the inverter's output voltage is negative, keep the fifth and seventh switches on while alternating the conduction of the sixth and eighth switches. Attached Figure Description

[0021] Figure 1 is a schematic diagram of the application scenario of the power supply system provided in this application;

[0022] Figure 2 is a structural schematic diagram of the inverter provided in this application;

[0023] Figure 3 is a timing diagram of a switching transistor control provided in this application;

[0024] Figure 4 is another switching transistor control timing diagram provided in this application;

[0025] Figure 5 is a voltage waveform diagram provided in this application;

[0026] Figure 6 is another voltage waveform diagram provided in this application;

[0027] Figure 7 is another voltage waveform diagram provided in this application;

[0028] Figure 8 is a schematic diagram of current control provided in this application. Detailed Implementation

[0029] Referring to Figure 1, Figure 1 is a schematic diagram of an application scenario for the power supply system provided in this application. The power supply system provided in this application may include a DC power supply and an inverter. The DC power supply may be a photovoltaic module, and the output terminal of the photovoltaic module can be connected to the input terminal of the inverter. The output terminal of the inverter is connected in parallel to the load. Here, the inverter includes an inverter circuit, which can convert the DC power provided by the photovoltaic module into AC power to supply the load. When the inverter is connected to the grid, the load can be the AC power grid; when the inverter is off-grid, the load can be AC ​​electrical equipment.

[0030] In the inverter shown in Figure 1, the inverter circuit can be a single-stage micro-inverter topology without a DC bus. The control strategies for this inverter can include open-loop control and closed-loop control. Open-loop control, based on the number of controllable variables, can be further divided into single-phase shift, extended phase shift, and frequency conversion phase shift control. However, the inherent problems of open-loop control—parameter sensitivity and low control accuracy—are unavoidable in this type of control strategy. Closed-loop control strategies have emerged to address this, and they can also be divided into single-phase shift, extended phase shift, and single-mode frequency conversion phase shift control based on the different controllable variables. Among these, single-phase shift and extended phase shift, due to the limited number of controllable variables, are difficult to implement for efficient micro-inverter control. Although single-mode inverter phase-shift control makes full use of the three control variables of this type of topology, namely inner phase shift, outer phase shift and frequency, this method only works in a single modulation mode within the power frequency cycle. This method limits the range of values ​​of control variables (such as inner phase shift angle, outer phase shift angle, etc.) to a certain extent, and the overall control efficiency of the inverter does not reach the optimal level, and the accuracy of output current control is low.

[0031] The inverter provided in this application includes an inverter circuit comprising a primary-side bridge arm, a secondary-side bridge arm, a transformer unit, a first capacitor, a second capacitor, and a controller. Specifically, the primary-side bridge arm can be a full-bridge inverter, comprising a first switch, a second switch, a third switch, and a fourth switch. The first terminal of the first switch and the first terminal of the third switch are connected to the positive output terminal of the DC power supply. The second terminal of the first switch is connected to the negative output terminal of the DC power supply via a second switch. The second terminal of the third switch is also connected to the negative output terminal of the DC power supply via a fourth switch. The connection terminals of the first and second switches, and the connection terminals of the third and fourth switches, are respectively connected to the first and second terminals of the primary winding of the transformer unit. The secondary bridge arm is connected in parallel with the first and second capacitors, which are connected in series. The secondary bridge arm includes a first secondary half-bridge arm and a second secondary half-bridge arm connected in series. The connection terminals of the first and second secondary half-bridge arms, and the connection terminals of the first and second capacitors, are respectively connected to the first and second terminals of the secondary winding of the transformer unit. Each of the first and second secondary half-bridge arms includes at least one switching transistor. In one control cycle, the controller controls the first and second switching transistors to conduct alternately, and the third and fourth switching transistors to conduct alternately. The interval between the conduction of the first and third switching transistors is a first phase angle; in other words, the phase difference between the signal waveforms of the control signals corresponding to the first and third switching transistors generated by the controller is a first phase angle. The phase difference between the first AC voltage across the primary winding and the second AC voltage across the secondary winding is a second phase angle. Furthermore, the controller switches between a first control mode, a second control mode, or a third control mode based on the polarity changes of the first AC voltage and the second AC voltage. In each mode, it adjusts the first phase angle, the second phase angle, and the switching frequency of each switching transistor, causing the inverter's output power to vary until the inverter's output current reaches the set current value. Here, different polarity changes of the first and second AC voltages correspond to different control modes, and the relationship between the output power and the three variables—the first phase angle, the second phase angle, and the switching frequency—is different in each control mode. During the controller's modulation of the inverter circuit, the controller aims to achieve a set current value for the output current while simultaneously adjusting the three variables: the first phase angle, the second phase angle, and the switching frequency. This results in high utilization of control variables, and the switching between different control modes based on the polarity changes of the first and second AC voltages improves the flexibility of inverter control, enhances the overall control efficiency of the inverter, and achieves high output current control accuracy.

[0032] The inverter provided in this application will be illustrated below with reference to Figures 2 to 8. In some feasible implementations, the inverter includes a primary side bridge arm, a secondary side bridge arm, a transformer unit, a first capacitor, a second capacitor, and a controller. The primary side bridge arm includes a first switch, a second switch, a third switch, and a fourth switch. Please refer to Figure 2, which is a structural schematic diagram of the inverter provided in this application. As shown in Figure 2, the primary side bridge arm of the inverter includes a first switch, a second switch, a third switch, and a fourth switch, which can be referred to as switch S1, switch S2, switch S3, and switch S4, respectively, for ease of description. The first terminals of switching transistors S1 and S3 are connected to the positive output terminal of the DC power supply. The second terminal of switching transistor S1 is connected to the negative output terminal of the DC power supply through switching transistor S2, and the second terminal of switching transistor S3 is connected to the negative output terminal of the DC power supply through switching transistor S4. The connection terminals of switching transistors S1 and S2, and the connection terminals of switching transistors S3 and S4, are respectively connected to the first and second terminals of the primary winding of the transformer unit. The secondary bridge arm includes a first secondary half-bridge arm and a second secondary half-bridge arm connected in series, and both the first and second secondary half-bridge arms include at least one switching transistor. Taking an example where both the first and second secondary half-bridge arms include two switching transistors, please refer to Figure 2 again. The secondary bridge arm is connected in parallel with the first capacitor Cs1 and the second capacitor Cs2 connected in series. The first secondary half-bridge arm includes a fifth and a sixth switching transistor connected in series, namely switching transistors S5 and S6. The second secondary half-bridge arm includes a seventh and an eighth switching transistor connected in series, namely switching transistors S7 and S8. The connection terminals of switching transistors S6 and S7, and the connection terminals of the first capacitor Cs1 and the second capacitor Cs2, are respectively connected to the first and second terminals of the secondary winding of the transformer unit. In one control cycle, the controller controls switching transistors S1 and S2 to conduct alternately, and switching transistors S3 and S4 to conduct alternately, with the interval between the conduction of switching transistors S1 and S3 being the first phase angle. The phase difference between the first AC voltage across the primary winding and the second AC voltage across the secondary winding is the second phase angle. Furthermore, when the inverter's output voltage is positive, the controller controls switching transistors S6 and S8 to remain on, and switching transistors S5 and S7 to conduct alternately. When the inverter's output voltage is negative, the controller controls switching transistors S5 and S7 to remain on, and switching transistors S6 and S8 to conduct alternately. Please also refer to Figure 3, which is a timing diagram of a switching transistor control provided in this application. As shown in Figure 3, Figure 3 includes the signal waveforms of eight drive control signals corresponding to switching transistors S1 to S8 generated by the controller. It can be understood that when the drive control signal is low, the corresponding switching transistor is turned off, and when the drive control signal is high, the corresponding switching transistor is turned on.The duration of one control cycle is Ts. During one control cycle, the controller controls switches S1 and S2 to conduct alternately, and switches S3 and S4 to conduct alternately. When the inverter's output voltage is positive, the controller keeps switches S6 and S8 on, and switches S5 and S7 conduct alternately. Please also refer to Figure 4, which is another timing diagram for switch control provided in this application. As shown in Figure 4, Figure 4 includes the signal waveforms of eight drive control signals corresponding to switches S1 to S8 generated by the controller. It can be understood that when the drive control signal is low, the corresponding switch is off; when the drive control signal is high, the corresponding switch is on. The duration of one control cycle is Ts. During one control cycle, the controller controls switches S1 and S2 to conduct alternately, and switches S3 and S4 to conduct alternately. When the inverter's output voltage is negative, the controller controls switches S6 and S8 to conduct alternately, while switches S5 and S7 remain on. In the control timing diagram shown in Figure 3 or Figure 4, the interval between the conduction of switch S1 and switch S3 is D1; ​​in other words, the phase difference between the drive control signal corresponding to switch S1 and the drive control signal corresponding to switch S3 is D1. The interval D1 between the conduction of switch S1 and switch S3 is considered the first phase angle. Furthermore, Figures 3 and 4 also include the voltage waveforms corresponding to the first AC voltage Vab across the primary winding and the second AC voltage Vcd across the secondary winding of the transformer unit. The voltage value of the first AC voltage Vab periodically changes to a positive voltage value, a negative voltage value, or zero, while the voltage value of the second AC voltage Vcd periodically changes to a positive voltage value or a negative voltage value. The phase difference between the first AC voltage Vab and the second AC voltage Vcd is D2, and D2 is considered the second phase angle. The controller switches between a first control mode, a second control mode, or a third control mode based on the polarity changes of the first AC voltage Vab and the second AC voltage Vcd. In each mode, it adjusts the first phase angle D1, the second phase angle D2, and the switching frequency of each switching transistor to change the inverter's output power until the inverter's output current reaches the set current value. The value of the aforementioned switching frequency can be equal to the reciprocal of the control cycle duration Ts. The controller aims to control the output current to reach the set current value, while simultaneously adjusting three variables: the first phase angle, the second phase angle, and the switching frequency. This results in high utilization of control variables. Furthermore, switching between different control modes based on the polarity changes of the first and second AC voltages improves the flexibility of inverter control, enhances the overall control efficiency of the inverter, and provides high accuracy in output current control.

[0033] In some feasible implementations, the different polarity changes of the first AC voltage and the second AC voltage correspond to different control modes, and the relationship between the output power and the three variables of the first phase angle, the second phase angle, and the switching frequency differs under different control modes. When the first AC voltage is negative and the second AC voltage remains positive, the controller adjusts the first phase angle, the second phase angle, and the switching frequency according to the first control mode, causing the inverter's output power to change. Please refer to Figure 5, which is a voltage waveform diagram provided in this application. As shown in Figure 5, Figure 5 includes the voltage waveforms corresponding to the first AC voltage Vab across the primary winding and the second AC voltage Vcd across the secondary winding of the transformer unit. When the first AC voltage Vab is negative and the second AC voltage Vcd remains positive, the controller adjusts the first phase angle, the second phase angle, and the switching frequency according to the first control mode, causing the inverter's output power to change. Specifically, under the first control mode, the inverter's output power satisfies:

[0034] Where D1 and D2 are the first phase angle and the second phase angle, respectively, f s V is the switching frequency. in V is the input voltage of the inverter. g Where is the output voltage of the inverter, n is the transformation ratio of the transformer unit, and L is the voltage of the inverter. r This refers to the leakage inductance value between the primary and secondary windings of the transformer unit. During the controller's modulation of the inverter circuit, the controller aims to achieve a set output current value while simultaneously adjusting three variables: the first phase angle, the second phase angle, and the switching frequency. This results in high utilization of control variables. Furthermore, by switching between different control modes based on the polarity changes of the first and second AC voltages, the controller improves the flexibility of inverter control, enhances the overall control efficiency of the inverter, and achieves high output current control accuracy.

[0035] In some feasible implementations, the different polarity changes of the first AC voltage and the second AC voltage correspond to different control modes, and the relationship between the output power and the three variables of the first phase angle, the second phase angle, and the switching frequency differs under different control modes. When the first AC voltage is negative and the second AC voltage switches between positive and negative voltages, the controller adjusts the first phase angle, the second phase angle, and the switching frequency according to the second control mode, causing the inverter's output power to change. Please also refer to Figure 6, which is another voltage waveform diagram provided in this application. As shown in Figure 6, Figure 6 includes the voltage waveforms corresponding to the first AC voltage Vab across the primary winding and the second AC voltage Vcd across the secondary winding of the transformer unit. When the first AC voltage Vab is negative and the second AC voltage Vcd switches between positive and negative voltages, the controller adjusts the first phase angle, the second phase angle, and the switching frequency according to the second control mode, causing the inverter's output power to change. Specifically, under the second control mode, the inverter's output power satisfies:

[0036] Where D1 and D2 are the first phase angle and the second phase angle, respectively, f s V is the switching frequency. in V is the input voltage of the inverter. g Where is the output voltage of the inverter, n is the transformation ratio of the transformer unit, and L is the voltage of the inverter. r This refers to the leakage inductance value between the primary and secondary windings of the transformer unit. During the controller's modulation of the inverter circuit, the controller aims to achieve a set output current value while simultaneously adjusting three variables: the first phase angle, the second phase angle, and the switching frequency. This results in high utilization of control variables. Furthermore, by switching between different control modes based on the polarity changes of the first and second AC voltages, the controller improves the flexibility of inverter control, enhances the overall control efficiency of the inverter, and achieves high output current control accuracy.

[0037] In some feasible embodiments, different polarity changes of the above-mentioned first AC voltage and second AC voltage correspond to different control modes, and under different control modes, the relationship between the output power and three variables, namely the first phase angle, the second phase angle, and the switching frequency, is different. During the period when the first AC voltage is a negative voltage, the second AC voltage remains a negative voltage, and the controller adjusts the first phase angle, the second phase angle, and the switching frequency according to the third control mode, so that the output power of the inverter changes. Please also refer to FIG. 7. FIG. 7 is another voltage waveform diagram provided by the present application. As shown in FIG. 7, FIG. 7 includes the voltage waveforms corresponding to the first AC voltage Vab across the primary winding of the transformer unit and the second AC voltage Vcd across the secondary winding. When the first AC voltage Vab is a negative voltage, the second AC voltage Vcd remains a negative voltage, and the controller adjusts the first phase angle, the second phase angle, and the switching frequency according to the third control mode, so that the output power of the inverter changes. Specifically, in the third control mode, the output power of the inverter satisfies:

[0038] where D1 and D2 are the first phase angle and the second phase angle respectively, and f s is the switching frequency, V in is the input voltage of the inverter, V g is the output voltage of the inverter, n is the voltage transformation ratio of the transformer unit, and L r is the leakage inductance value between the primary winding and the secondary winding of the transformer unit. During the modulation process of the controller for the inverter circuit, the controller takes controlling the output current to reach the set current value as the control target, and at the same time adjusts the three variables of the first phase angle, the second phase angle, and the switching frequency. The utilization degree of the control variables is high, and different control modes are switched based on the polarity changes of the first AC voltage and the second AC voltage, which improves the flexibility of the inverter control, enhances the overall control efficiency of the inverter, and has high output current control accuracy.

[0039] In some feasible embodiments, when the second AC voltage remains a positive voltage during the period when the first AC voltage is a negative voltage, and -180° < D1 ≤ 180° and (1 - D1) / 2 < |D2| ≤ 180° are satisfied, the controller adjusts the first phase angle, the second phase angle, and the switching frequency according to the first control mode. Here, on the basis that the first AC voltage and the second AC voltage meet the polarity requirements, the controller further uses the values of the first phase angle and the second phase angle as the determination conditions for different control modes, which improves the discrimination between different control modes, reduces the misjudgment of the control mode by the controller, and further improves the output current control accuracy.

[0040] In some feasible embodiments, during the period when the first AC voltage is a negative voltage, when the second AC voltage switches between a positive voltage and a negative voltage, and -180° < D1 ≤ 180° and D1 / 2 < |D2| ≤ (1 - D1) / 2 are satisfied, the first phase angle, the second phase angle, and the switching frequency are adjusted according to the second control mode. Here, based on the fact that the first AC voltage and the second AC voltage meet the polarity requirements, the controller further uses the values of the first phase angle and the second phase angle as the determination conditions for different control modes, improving the discrimination between different control modes, reducing the misjudgment of the control mode by the controller, and further improving the output current control accuracy.

[0041] In some feasible embodiments, during the period when the first AC voltage is a negative voltage, when the second AC voltage remains a negative voltage, and -180° < D1 ≤ 180° and 0 < |D2| ≤ D1 / 2 are satisfied, the first phase angle, the second phase angle, and the switching frequency are adjusted according to the third control mode. Here, based on the fact that the first AC voltage and the second AC voltage meet the polarity requirements, the controller further uses the values of the first phase angle and the second phase angle as the determination conditions for different control modes, improving the discrimination between different control modes, reducing the misjudgment of the control mode by the controller, and further improving the output current control accuracy. [[ID=—4]]

[0042] In some feasible embodiments, the controller obtains at least one set of variable combinations, each variable combination including three variable values of different first phase angles, second phase angles, and switching frequencies, and the output current of the inverter corresponding to each variable combination is a set current value. The controller is also used to take the variable combination corresponding to the minimum resonant current value in at least one set of variable combinations as the target variable combination, and adjust the first phase angle, the second phase angle, and the switching frequency based on the target variable combination. The resonant current value is the magnitude of the current between the connection end of the first secondary half-bridge arm and the second secondary half-bridge arm and the first end of the secondary winding of the transformer unit. Specifically, the controller adjusts the first phase angle, the second phase angle, and the switching frequencies of each switching tube in each mode, so that the output power of the inverter changes until the ratio of the output power of the inverter to the output voltage of the inverter at the current moment is the set current value. Further, the controller can obtain multiple sets of variable combinations, each variable combination including three variable values of different first phase angles, second phase angles, and switching frequencies, and the ratio of the output power of the inverter corresponding to each variable combination to the output voltage of the inverter at the current moment is the set current value. For example, there are variable combinations (D 11 , D 21 , f s1 ), (D 12 , D 22 , f s2 ), and (D 13 , D 23 , f s3The ratio of the inverter's output power to its current output voltage for each of the above variable combinations is a set current value, and the resonant current value differs for each variable combination. The resonant current is the current between the connection terminals of the first and second secondary half-bridge arms in the inverter and the first terminal of the secondary winding of the transformer unit. If the variable combination with the smallest corresponding resonant current value is (D... 11 D 21 ,f s1 ), then (D) 11 D 21 ,f s1 As the target variable combination, the controller adjusts the first phase angle, the second phase angle, and the switching frequency to D respectively. 11 D 21 and f s1 Here, the controller, while maintaining the inverter's output current at a set value, incorporates an optimization objective of minimizing the inverter's resonant cavity current. Specifically, it minimizes the current between the connection points of the first and second secondary half-bridge arms and the first terminal of the secondary winding of the transformer unit, thereby reducing the losses of the switching transistors in the inverter. Understandably, the controller also incorporates other control objectives beyond simply maintaining the inverter's output current at the set value, such as minimizing the overall switching transistor losses of the inverter. Optionally, the controller can obtain the optimal control variables in real-time based on the current inverter output voltage, i.e., acquire one or more combinations of variables for the current inverter output voltage. Furthermore, the controller can also calculate one or more combinations of variables corresponding to each output voltage offline. In a specific implementation, the inverter's output voltage at all times within the power frequency cycle (e.g., within 20ms) can be obtained first. For any given moment's output voltage, the controller adjusts the first phase angle, the second phase angle, and the switching frequency of each transistor in various modes to change the inverter's output power until the ratio of the inverter's output power to the acquired output voltage equals a set current value, thus obtaining the variable combination corresponding to the output voltage at any given moment. During modulation, the controller adjusts the first phase angle, the second phase angle, and the switching frequency of each transistor based on the offline calculated variable combination using a lookup table and linear interpolation.

[0043] In some feasible implementations, the controller can increase or decrease the switching frequency based on the inverter's output current and a set current value, wherein the magnitude of the controller adjusting the switching frequency is positively correlated with the absolute value of the difference between the inverter's output current and the set current value. Optionally, the controller can also increase or decrease the second phase angle based on the inverter's output current and the set current value, wherein the magnitude of the controller adjusting the second phase angle is positively correlated with the absolute value of the difference between the inverter's output current and the set current value. Specifically, referring again to Figure 2, the controller controls the output current to reach the set current value I.ref To achieve the control objective (or, other control objectives may be added simultaneously), the control is applied to the first phase angle D1, the second phase angle D2, and the switching frequency f. s Three variables are adjusted. The controller's control process can include current control, feedforward control, and control quantity synthesis. In the feedforward control, the controller aims to achieve a set current value (I) in the output current. ref The controller switches between a first control mode, a second control mode, and a third control mode (for example, switching can be based on the polarity change of the first AC voltage Vab and the second AC voltage Vcd). The relationship between the output power and the three variables—the first phase angle, the second phase angle, and the switching frequency—is different in each control mode. The controller adjusts the first phase angle D1, the second phase angle D2, and the switching frequency f of each switching transistor in each mode. s The target variable combination (D′1,D′2,f) output by the feedforward control loop is obtained. s The controller can generate a second phase angle adjustment value ΔD′2 or a switching frequency adjustment value Δf′ through the current control loop. s The controller can generate the switching frequency adjustment value Δf′ through the current control loop. s For example, please refer to Figure 8, which is a schematic diagram of current control provided in this application. As shown in Figure 8, current control may include quasi-PR controller control and linearization circuit. The controller can set the current value I. ref With the current inverter output current I g Input a quasi-PR controller, where the transfer function of the quasi-PR controller is:

[0044] Among them, K p K is the proportionality coefficient. r Let w be the resonance coefficient. c w0 is the cutoff frequency, and w0 is the resonant frequency. The output PR of the quasi-PR controller... oUT As input to the linearization stage, the switching frequency adjustment value Δf′ is obtained. s It can be represented as:

[0045] Current inverter output current I g With the set current value I ref The larger the absolute value of the difference, the larger the output PR of the quasi-PR controller. oUT The smaller the absolute value, the smaller the switching frequency adjustment value Δf′. s The smaller the absolute value, in other words, the more the controller adjusts the switching frequency amplitude and the inverter's output current I. g and set current value I refThe absolute value of the difference is positively correlated. During the period when the inverter output voltage is positive, the aforementioned output current I... g The small-signal model expression relative to frequency is as follows: ΔI g =HΔf s

[0046] During the period when the inverter output voltage is negative, the output current I g The small-signal model expression relative to frequency is as follows: ΔI g =-HΔf s

[0047] Here, taking the positive half-cycle of the grid voltage as an example, the output current I is obtained according to the fundamental frequency approximation method. g expression:

[0048] And the above X L f r Z r a p The expressions for θ and θ are as follows: a p =90D1 θ=180D2-ap

[0049] Among them, C r For the resonant capacitor. Please refer to Figure 2 again. The controller obtains the target variable combination (D′1, D′2, f) from the feedforward control loop output. s The switching frequency adjustment value Δf′ generated by the current control loop. s In the control input synthesis stage, the first phase angle D′1 and the second phase angle D′2 generated by the feedforward control are directly output as the first phase angle D1 and the second phase angle D2 in the synthesis stage. The switching frequency f′ generated by the feedforward stage is... s The switching frequency adjustment value Δf′ generated by the current control loop s The summation outputs the final switching frequency f. s Here, in the feedforward control loop, the controller aims to achieve a set output current value while simultaneously adjusting three variables: the first phase angle, the second phase angle, and the switching frequency. Additionally, the controller performs a current control loop, generating either a second phase angle adjustment value or a switching frequency adjustment value based on the set current value and the current inverter output current. The final switching frequency is then output by adding the switching frequency adjustment value generated by the feedforward loop and the current control loop, or by adding the second phase angle adjustment value generated by the feedforward loop and the current control loop. By combining the outputs of the feedforward and current control loops, the output current control accuracy can be further improved.

Claims

1. An inverter, characterized in that, The inverter includes a primary side bridge arm, a secondary side bridge arm, a transformer unit, and a controller. The primary side bridge arm includes a first switch, a second switch, a third switch, and a fourth switch. The first ends of the first switch and the third switch are used to connect to the positive output terminal of the DC power supply. The second end of the first switch is connected to the negative output terminal of the DC power supply through the second switch. The second end of the third switch is connected to the negative output terminal of the DC power supply through the fourth switch. The connection ends of the first switch and the second switch, and the connection ends of the third switch and the fourth switch are respectively connected to the first end and the second end of the primary winding of the transformer unit. The secondary winding of the transformer unit is connected to the secondary side bridge arm; The controller is configured to control the first switch and the second switch to conduct alternately, and the third switch and the fourth switch to conduct alternately. The interval between the conduction of the first switch and the conduction of the third switch is a first phase angle, and the phase difference between the first AC voltage across the primary winding and the second AC voltage across the secondary winding is a second phase angle; The controller is further configured to adjust the first phase angle, the second phase angle, and the switching frequency of each switch according to a first control mode, a second control mode, or a third control mode based on the polarity changes of the first AC voltage and the second AC voltage, so that the output power of the inverter changes until the output current of the inverter reaches a set current value; Wherein, different polarity changes of the first AC voltage and the second AC voltage correspond to different control modes, and in different control modes, the relationship between the output power of the inverter and the three variables of the first phase angle, the second phase angle, and the switching frequency is different.

2. The inverter according to claim 1, characterized in that, The controller is configured to, when the first AC voltage is a negative voltage and the second AC voltage remains a positive voltage, adjust the first phase angle, the second phase angle, and the switching frequency according to the first control mode, so that the output power of the inverter changes; In the first control mode, the output power of the inverter satisfies: Where D1 and D2 are the first phase angle and the second phase angle, respectively, f s V is the switching frequency. in V is the input voltage of the inverter. g Let n be the output voltage of the inverter, n be the transformation ratio of the transformer unit, and L be the voltage of the inverter. r The leakage inductance value is the value between the primary winding and the secondary winding of the transformer unit.

3. The inverter according to claim 1, characterized in that, The controller is configured to, when the first AC voltage is a negative voltage and the second AC voltage switches between positive and negative voltages, adjust the first phase angle, the second phase angle, and the switching frequency according to the second control mode, so that the output power of the inverter changes; In the second control mode, the output power of the inverter satisfies: Where D1 and D2 are the first phase angle and the second phase angle, respectively, f s V is the switching frequency. in V is the input voltage of the inverter. g Let n be the output voltage of the inverter, n be the transformation ratio of the transformer unit, and L be the voltage of the inverter. r The leakage inductance value is the value between the primary winding and the secondary winding of the transformer unit.

4. The inverter according to claim 1, characterized in that, The controller is configured to, when the first AC voltage is a negative voltage and the second AC voltage remains a negative voltage, adjust the first phase angle, the second phase angle, and the switching frequency according to the third control mode, so that the output power of the inverter changes; In the third control mode, the output power of the inverter satisfies: Where D1 and D2 are the first phase angle and the second phase angle, respectively, f s V is the switching frequency. in V is the input voltage of the inverter. g Let n be the output voltage of the inverter, n be the transformation ratio of the transformer unit, and L be the voltage of the inverter. r The leakage inductance value is the value between the primary winding and the secondary winding of the transformer unit.

5. The inverter according to claim 2, characterized in that, The controller is configured to, when the first AC voltage is a negative voltage and the second AC voltage remains a positive voltage, and -180° < D1 ≤ 180° and (1 - D1) / 2 < |D2| ≤ 180° are satisfied, adjust the first phase angle, the second phase angle, and the switching frequency according to the first control mode.

6. The inverter according to claim 3, characterized in that, The controller is configured to, when the second AC voltage switches between a positive voltage and a negative voltage during a period when the first AC voltage is a negative voltage, and -180° < D1 ≤ 180° and D1 / 2 < |D2| ≤ (1 - D1) / 2 are satisfied, adjust the first phase angle, the second phase angle, and the switching frequency according to the second control mode.

7. The inverter according to claim 4, characterized in that, The controller is configured to, when the second AC voltage remains a negative voltage during a period when the first AC voltage is a negative voltage, and -180° < D1 ≤ 180° and 0 < |D2| ≤ D1 / 2 are satisfied, adjust the first phase angle, the second phase angle, and the switching frequency according to the third control mode.

8. The inverter according to any one of claims 1-7, characterized in that, The controller is configured to obtain at least one set of variable combinations, each of the variable combinations including three variable values of different first phase angles, second phase angles, and switching frequencies, and the output current of the inverter corresponding to each of the variable combinations being the set current value. The controller is further configured to use, as a target variable combination, the variable combination corresponding to the minimum resonance current value among at least one set of the variable combinations, and adjust the first phase angle, the second phase angle, and the switching frequency based on the target variable combination, where the resonance current value is the magnitude of the current between the connection end of the first secondary half-bridge arm and the second secondary half-bridge arm and the first end of the secondary winding of the voltage transformation unit.

9. The inverter according to any one of claims 1-8, characterized in that, The controller is configured to increase or decrease the switching frequency based on the output current of the inverter and the set current value, where the magnitude of the switching frequency adjusted by the controller is positively correlated with the absolute value of the difference between the output current of the inverter and the set current value.

10. The inverter according to any one of claims 1-8, characterized in that, The controller is configured to increase or decrease the second phase angle based on the output current of the inverter and the set current value, where the magnitude of the second phase angle adjusted by the controller is positively correlated with the absolute value of the difference between the output current of the inverter and the set current value.

11. The inverter according to any one of claims 1-10, characterized in that, The inverter includes a first capacitor and a second capacitor, the secondary bridge arm is connected in parallel with the serially connected first capacitor and second capacitor, the secondary bridge arm includes a serially connected first secondary half-bridge arm and a second secondary half-bridge arm, the connection end of the first secondary half-bridge arm and the second secondary half-bridge arm, and the connection end of the first capacitor and the second capacitor are respectively connected to the first end and the second end of the secondary winding of the voltage transformation unit, and the first secondary half-bridge arm and the second secondary half-bridge arm include at least one switching tube.

12. The inverter according to claim 11, characterized in that, The first secondary half-bridge arm includes a serially connected fifth switching tube and a sixth switching tube, the second secondary half-bridge arm includes a serially connected seventh switching tube and an eighth switching tube, and the connection end of the sixth switching tube and the seventh switching tube is connected to the first end of the secondary winding of the voltage transformation unit. The controller is configured to, when the output voltage of the inverter is positive, control the sixth and eighth switches to remain on, and the fifth and seventh switches to alternately conduct; and when the output voltage of the inverter is negative, control the fifth and seventh switches to remain on, and the sixth and eighth switches to alternately conduct.

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