Inverter

Abstract

The embodiment of the invention provides an inverter, a first end of a first switch tube and a first end of a third switch tube in a primary side bridge arm in the inverter are connected with a positive electrode output end of a direct current power supply, a second end of the first switch tube is connected with the direct current power supply through a second switch tube, and a second end of the third switch tube is connected with the direct current power supply through a fourth switch tube. The connecting ends of the first switching tube and the second switching tube and the connecting ends of the third switching tube and the fourth switching tube are connected with the two ends of a primary winding of the voltage transformation unit respectively. The controller controls the conduction interval between the first switch tube and the third switch tube to be a first phase angle, and the alternating voltage phase difference between the two ends of the primary winding and the two ends of the secondary winding to be a second phase angle. The controller adjusts the first phase angle, the second phase angle and the switching frequency according to different control modes so as to control the output power until the output current 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 relations between the output power and the three control variables in the different control modes are different.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, and particularly relates to an inverter. BACKGROUND

[0002] As a component-level control inverter, the micro-inverter is used for direct connection with a single photovoltaic component, and can independently realize maximum power point tracking control. The application of the micro-inverter improves the power generation efficiency of the photovoltaic power generation system under the conditions of photovoltaic component power mismatch, shadow and the like, and simultaneously has the advantages of safety, high reliability and realization of component-level monitoring. With the continuous development and improvement of the micro-inverter technology, the application range of the micro-inverter can be gradually expanded from the photovoltaic system to the household energy storage system, and the market development potential is huge. At present, the micro-inverter with a single-stage micro-inverter topology without a direct-current bus is the mainstream in the market, and the control strategy thereof can be divided into two categories: open-loop control and closed-loop control. Among them, the open-loop control can be divided into three categories: single phase-shift, extended phase-shift and variable frequency phase-shift control according to different control variables. However, the open-loop control strategy has inherent problems such as parameter sensitivity and low control precision, which cannot be avoided in the open-loop control strategy. The closed-loop control strategy emerges as the times require, and can also be divided into three categories: single phase-shift, extended phase-shift and single-mode variable frequency phase-shift control according to different control variables. However, the existing closed-loop control strategy does not fully utilize the control variables, and the modulation mode of the micro-inverter is single, resulting in low overall control efficiency of the micro-inverter and low precision of current output control. SUMMARY

[0003] The embodiment of the present application provides an inverter, which can more fully utilize the control variables, improve the flexibility of inverter control and the overall control efficiency of the inverter, and has high output current control precision.

[0004] In a first aspect, the 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 comprising a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, a first end of the first switch tube and a first end of the third switch tube being used for connecting a positive output end of a DC power supply, a second end of the first switch tube being connected to a negative output end of the DC power supply through the second switch tube, a second end of the third switch tube being connected to the negative output end of the DC power supply through the fourth switch tube, a connection end of the first switch tube and the second switch tube and a connection end of the third switch tube and the fourth switch tube being connected to a first end and a second end of a primary winding of the transformer unit respectively, and a secondary winding of the transformer unit being connected to the secondary side bridge arm. The controller is configured to control the first switch tube and the second switch tube to be turned on alternately and the third switch tube and the fourth switch tube to be turned on alternately in a control period, and the interval of the first switch tube being turned on and the third switch tube being turned on is a first phase angle, and the phase difference between a first alternating voltage across the primary winding and a second alternating 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 tube based on the polarity change of the first alternating voltage and the second alternating voltage according to a first control mode, a second control mode or a third control mode, 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 alternating voltage and the second alternating 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 in different control modes.

[0005] In the application, the controller switches among the first control mode, the second control mode and the third control mode based on the polarity change of the first alternating voltage and the second alternating voltage, and adjusts the first phase angle, the second phase angle and the switching frequency of each switch tube in each mode, so that the output power of the inverter changes until the output current of the inverter reaches the set current value. Here, different polarity changes of the first alternating voltage and the second alternating 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 is different in different control modes. In the modulation process of the controller to the inverter circuit, the controller takes the control of the output current reaching the set current value as the control target, and adjusts the three variables of the first phase angle, the second phase angle and the switching frequency at the same time, so that the control variables have high utilization, and the different control modes are switched based on the polarity change of the first alternating voltage and the second alternating voltage, which improves the flexibility of the inverter control, improves the overall control efficiency of the inverter, and improves the control accuracy of the output current.

[0006] 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 first control mode to change the output power of the inverter when the second AC voltage remains positive during the first AC voltage being negative. In the first control mode, the output power of the inverter satisfies:

[0007]

[0008] 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 transformer unit, L r is the leakage inductance between the primary winding and the secondary winding of the transformer unit. Here, the controller takes controlling the output current to reach a set current value as a control target, and adjusts the first phase angle, the second phase angle and the switching frequency, which has high utilization of control variables. Different control modes are switched based on the polarity change of the first AC voltage and the second AC voltage, which improves the flexibility of inverter control, improves the overall control efficiency of the inverter, and has high output current control precision.

[0009] 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 second control mode to change the output power of the inverter when the second AC voltage switches between positive and negative during the first AC voltage being negative. In the second control mode, the output power of the inverter satisfies:

[0010]

[0011] 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 transformer unit, L r is the leakage inductance between the primary winding and the secondary winding of the transformer unit. Here, the controller takes controlling the output current to reach a set current value as a control target, and adjusts the first phase angle, the second phase angle and the switching frequency, which has high utilization of control variables. Different control modes are switched based on the polarity change of the first AC voltage and the second AC voltage, which improves the flexibility of inverter control, improves the overall control efficiency of the inverter, and has high output current control precision.

[0012] In a possible implementation, the controller is configured to, during the period when the first AC voltage is a negative voltage, keep the second AC voltage as a negative voltage, and adjust the first phase angle, the second phase angle and the switching frequency according to a third control mode, so that the output power of the inverter changes. In the third control mode, the output power of the inverter satisfies:

[0013]

[0014] 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 transformer unit, L r is the leakage inductance between the primary winding and the secondary winding of the transformer unit. Here, the controller takes the control target of controlling the output current to reach the set current value, and adjusts the three variables of the first phase angle, the second phase angle and the switching frequency, the control variables have high utilization degree, and different control modes are switched based on the polarity change of the first AC voltage and the second AC voltage, which improves the flexibility of inverter control, improves the overall control efficiency of the inverter, and has high output current control precision.

[0015] In a possible implementation, the controller is configured to, during the period when the first AC voltage is a negative voltage, keep the second AC voltage as 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 a first control mode. Here, the controller further takes the values of the first phase angle and the second phase angle as the judgment conditions of different control modes on the basis of the polarity requirements of the first AC voltage and the second AC voltage, which improves the discrimination between different control modes, reduces the misjudgment of the controller on the control mode, and further improves the output current control precision.

[0016] In a possible implementation, the controller is configured to, during the period when the first AC voltage is a negative voltage, switch the second AC voltage between a positive voltage and a negative voltage, and when -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 a second control mode. Here, the controller further takes the values of the first phase angle and the second phase angle as the judgment conditions of different control modes on the basis of the polarity requirements of the first AC voltage and the second AC voltage, which improves the discrimination between different control modes, reduces the misjudgment of the controller on the control mode, and further improves the output current control precision.

[0017] In a possible implementation, the controller is configured to adjust the first phase angle, the second phase angle and the switching frequency according to the third control mode when the first alternating voltage is a negative voltage, the second alternating voltage remains a negative voltage, and -180° < D1 ≤ 180° and 0 < |D2| ≤ D1 / 2 are satisfied. Here, the controller further takes the values of the first phase angle and the second phase angle as the judgment condition of different control modes on the basis of the polarity requirement of the first alternating voltage and the second alternating voltage, improves the distinction between different control modes, reduces the misjudgment of the controller on the control mode, and further improves the output current control precision.

[0018] In a possible implementation, the controller is configured to obtain at least one variable combination, each variable combination including different values of the first phase angle, the second phase angle and the switching frequency, and the output current of the inverter corresponding to each variable combination being the set current value. The controller is further configured to take the variable combination corresponding to the minimum resonant current value in the at least one variable combination as a 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 being the current between the connection end of the first secondary-side half-bridge arm and the second secondary-side half-bridge arm and the first end of the secondary-side winding of the transformer unit. Here, the controller adds the optimization target of minimizing the resonant cavity current of the inverter on the basis of controlling the output current of the inverter to be the set current value, that is, controlling the current between the connection end of the first secondary-side half-bridge arm and the second secondary-side half-bridge arm in the inverter and the first end of the secondary-side winding of the transformer unit to be minimum, thereby reducing the loss of the switching tube in the inverter.

[0019] 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 controller positively correlates the amplitude of the switching frequency adjusted by the controller with the absolute value of the difference between the output current of the inverter and the set current value. Here, the controller takes the control target of controlling the output current to be the set current value in the feedforward control link, and simultaneously adjusts the first phase angle, the second phase angle and the switching frequency. In addition, the controller simultaneously performs the current control link, generates the switching frequency adjustment value based on the set current value and the current output by the inverter, and outputs the final switching frequency by adding the switching frequency generated by the feedforward link and the switching frequency adjustment value generated by the current control link. By combining the output results of the feedforward control link and the current control link, the output current control precision can be further improved.

[0020] In a possible implementation, 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, and the controller is configured to positively correlate the amplitude of the second phase angle with the absolute value of the difference between the output current of the inverter and the set current value. Here, the controller takes the control target of controlling the output current to reach the set current value in the feedforward control link, and adjusts the first phase angle, the second phase angle, and the switching frequency. In addition, the controller simultaneously performs the current control link to generate a second phase angle adjustment value based on the set current value and the current output current of the inverter, so as to add the second phase angle generated by the feedforward link and the second phase angle adjustment value generated by the current control link to output the final second phase angle. By combining the output results of the feedforward control link and the current control link, the output current control accuracy can be further improved.

[0021] In a possible implementation, the inverter includes a first capacitor and a second capacitor, the secondary side bridge arm is connected in parallel with the first capacitor and the second capacitor in series, the secondary side bridge arm includes a first secondary side half-bridge arm and a second secondary side half-bridge arm in series, the connection end of the first secondary side half-bridge arm and the second secondary side 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 side winding of the transformer unit, and the first secondary side half-bridge arm and the second secondary side half-bridge arm include at least one switch tube.

[0022] In a possible implementation, the first secondary side half-bridge arm includes a fifth switch tube and a sixth switch tube in series, the second secondary side half-bridge arm includes a seventh switch tube and an eighth switch tube in series, and the connection end of the sixth switch tube and the seventh switch tube is connected to the first end of the secondary side winding of the transformer unit. The controller is configured to control the sixth switch tube and the eighth switch tube to remain conductive, and the fifth switch tube and the seventh switch tube to alternately conduct when the output voltage of the inverter is a positive voltage, and control the fifth switch tube and the seventh switch tube to remain conductive, and the sixth switch tube and the eighth switch tube to alternately conduct when the output voltage of the inverter is a negative voltage. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 FIG. 1 is a schematic diagram of an application scenario of a power supply system provided by the present application;

[0024] Figure 2 FIG. 2 is a structural schematic diagram of an inverter provided by the present application;

[0025] Figure 3 FIG. 3 is a switch tube control timing diagram provided by the present application;

[0026] Figure 4 FIG. 4 is another switch tube control timing diagram provided by the present application;

[0027] Figure 5 FIG. 5 is a voltage waveform diagram provided by the present application;

[0028] Figure 6 is another voltage waveform diagram provided by this application;

[0029] Figure 7 is another voltage waveform diagram provided by this application;

[0030] Figure 8 This is a current control schematic diagram provided by this application. DETAILED DESCRIPTION

[0031] See also Figure 1 , Figure 1 : is a schematic diagram of an application scenario of the power supply system provided in the present application. The power supply system provided in the present application may include a DC power supply and an inverter. Among them, the DC power supply may be a photovoltaic module, the output end of the photovoltaic module may be connected to the input end of the inverter, and the output end of the inverter is connected in parallel to the load. Here, the above-mentioned inverter includes an inverter circuit, and the inverter can invert the DC power provided by the photovoltaic module through the inverter circuit, thereby outputting the AC power obtained after the inversion conversion to power the load. Here, when the above-mentioned inverter is connected to the grid, the load may be an AC power grid, and when the above-mentioned inverter is off-grid, the load may be an AC power device.

[0032] exist Figure 1 In the inverter shown, the inverter circuit can be a single-stage micro-inverter topology without a DC bus. The inverter's control strategy can include open-loop control and closed-loop control. Open-loop control can be categorized into three types based on the number of control variables: single-phase shift, extended phase shift, and variable frequency phase shift. However, the inherent problems of open-loop control, namely parameter sensitivity and low control accuracy, are unavoidable in this type of control strategy. Consequently, closed-loop control strategies have emerged, which can also be categorized into single-phase shift, extended phase shift, and single-mode variable frequency phase shift based on the control variables. Single-phase shift and extended phase shift have difficulty achieving efficient micro-inverter control due to the limited number of controllable variables. While single-mode variable frequency phase shift control fully utilizes the three control variables of this topology—inner phase shift, outer phase shift, and frequency—it operates only in a single modulation mode within the power frequency cycle. This limits the range of control variables (such as the inner and outer phase shift angles), resulting in suboptimal overall inverter control efficiency and low output current control accuracy.

[0033] The inverter provided in the application comprises 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, which comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube. The first end of the first switch tube and the first end of the third switch tube are used for connecting the positive output end of a direct current power supply, the second end of the first switch tube is connected to the negative output end of the direct current power supply through the second switch tube, the second end of the third switch tube is connected to the negative output end of the direct current power supply through the fourth switch tube, and the connection end of the first switch tube and the second switch tube and the connection end of the third switch tube and the fourth switch tube are respectively connected to the first end and the second end of the primary winding of the transformer unit. The secondary side bridge arm is connected in parallel with the first capacitor and the second capacitor in series, the secondary side bridge arm comprises a first secondary side half bridge arm and a second secondary side half bridge arm in series, the connection end of the first secondary side half bridge arm and the second secondary side 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 transformer unit, and the first secondary side half bridge arm and the second secondary side half bridge arm comprise at least one switch tube. The controller controls the first switch tube and the second switch tube to be turned on alternately and the third switch tube and the fourth switch tube to be turned on alternately in a control period, and the interval of the turning on of the first switch tube and the turning on of the third switch tube is a first phase angle, in other words, the phase difference of the signal waveforms of the control signals corresponding to the first switch tube and the third switch tube generated by the controller is the first phase angle. The phase difference between the first alternating current voltage at the two ends of the primary winding and the second alternating current voltage at the two ends of the secondary winding is a second phase angle. Further, the controller switches among a first control mode, a second control mode or a third control mode based on the polarity change of the first alternating current voltage and the second alternating current voltage, and adjusts the first phase angle, the second phase angle and the switching frequency of each switch tube in each mode, so that the output power of the inverter changes until the output current of the inverter reaches a set current value. Here, the different polarity changes of the first alternating current voltage and the second alternating current 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 is different in different control modes. In the modulation process of the controller to the inverter circuit, the controller takes the control of the output current to reach the set current value as the control target, and adjusts the three variables of the first phase angle, the second phase angle and the switching frequency at the same time, the control variables have high utilization degree, and different control modes are switched based on the polarity change of the first alternating current voltage and the second alternating current voltage, which improves the flexibility of the inverter control, improves the overall control efficiency of the inverter, and has high output current control precision.

[0034] The application will be described in detail below in combination with Figures 2 to 8The inverter provided by the embodiment of the present application is exemplarily described. In some possible implementation, the inverter comprises a primary bridge arm, a secondary bridge arm, a transformer unit, a first capacitor, a second capacitor and a controller. The primary bridge arm comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube. Please refer to Figure 2 , Figure 2 for the structure diagram of the inverter provided by the present application. As shown in Figure 2 , the primary bridge arm of the inverter comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, which can be respectively represented as switch tube S1, switch tube S2, switch tube S3 and switch tube S4 for convenience of description. The first end of the switch tube S1 and the first end of the switch tube S3 are used for connecting the positive output end of the direct current power supply, the second end of the switch tube S1 is connected to the negative output end of the direct current power supply through the switch tube S2, the second end of the switch tube S3 is connected to the negative output end of the direct current power supply through the switch tube S4, and the connection end of the switch tube S1 and the switch tube S2 and the connection end of the switch tube S3 and the switch tube S4 are respectively connected to the first end and the second end of the primary winding of the transformer unit. The secondary bridge arm comprises a first secondary half-bridge arm and a second secondary half-bridge arm connected in series, and the first secondary half-bridge arm and the second secondary half-bridge arm comprise at least one switch tube. Taking the case that the first secondary half-bridge arm and the second secondary half-bridge arm each comprise two switch tubes as an example, please refer to Figure 2 , 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 comprises a fifth switch tube and a sixth switch tube connected in series, i.e. switch tube S5 and switch tube S6. The second secondary half-bridge arm comprises a seventh switch tube and an eighth switch tube connected in series, i.e. switch tube S7 and switch tube S8. The connection end of the switch tube S6 and the switch tube S7 and the connection end of the first capacitor Cs1 and the second capacitor Cs2 are respectively connected to the first end and the second end of the secondary winding of the transformer unit. In a control period, the controller controls the switch tube S1 and the switch tube S2 to be alternately turned on, and the switch tube S3 and the switch tube S4 to be alternately turned on, and the interval of the above-mentioned switch tube S1 being turned on and the switch tube S3 being turned on is a first phase angle, and the phase difference between the first alternating current voltage at the two ends of the primary winding and the second alternating current voltage at the two ends of the secondary winding is a second phase angle. In addition, when the output voltage of the inverter is a positive voltage, the controller controls the switch tube S6 and the switch tube S8 to be kept turned on, and the switch tube S5 and the switch tube S7 to be alternately turned on, and when the output voltage of the inverter is a negative voltage, the controller controls the switch tube S5 and the switch tube S7 to be kept turned on, and the switch tube S6 and the switch tube S8 to be alternately turned on. Please refer to Figure 3 , Figure 3 for the switch tube control timing diagram provided by the present application. As shown in Figure 3 , Figure 3The signal waveforms of the eight drive control signals corresponding to the eight switching tubes S1-S8 generated by the controller are shown in the figure. It can be understood that when the drive control signal is low, the corresponding switching tube is turned off, and when the drive control signal is high, the corresponding switching tube is turned on. The duration of one control cycle is Ts, and the controller controls the switching tube S1 and the switching tube S2 to be turned on alternately, and the switching tube S3 and the switching tube S4 to be turned on alternately in one control cycle. When the output voltage of the inverter is positive, the controller controls the switching tube S6 and the switching tube S8 to be turned on, and the switching tube S5 and the switching tube S7 to be turned on alternately. Please see Figure 4 , Figure 4 Another switching tube control timing diagram provided by the present application is shown in Figure 4 , Figure 4 The signal waveforms of the eight drive control signals corresponding to the eight switching tubes S1-S8 generated by the controller are shown in the figure. It can be understood that when the drive control signal is low, the corresponding switching tube is turned off, and when the drive control signal is high, the corresponding switching tube is turned on. The duration of one control cycle is Ts, and the controller controls the switching tube S1 and the switching tube S2 to be turned on alternately, and the switching tube S3 and the switching tube S4 to be turned on alternately in one control cycle. When the output voltage of the inverter is positive, the controller controls the switching tube S6 and the switching tube S8 to be turned on, and the switching tube S5 and the switching tube S7 to be turned on alternately. Please see Figure 3 or Figure 4 In the control timing diagram shown in the above Figure 3 and Figure 4The inverter also includes 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. The voltage value of the first AC voltage Vab periodically varies between positive, negative, or zero values, and the voltage value of the second AC voltage Vcd periodically varies between positive and negative values. The phase difference between the first AC voltage Vab and the second AC voltage Vcd is D2, with D2 serving as a 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, the controller adjusts the first phase angle D1, the second phase angle D2, and the switching frequency of each switch to adjust the output power of the inverter until the output current of the inverter reaches a set current value. The switching frequency may be equal to the inverse of the control cycle duration Ts. The controller controls 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 control variable utilization 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.

[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 under different control modes, the relationship between the output power and the three variables of the first phase angle, the second phase angle, and the switching frequency is different. 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, so that the output power of the inverter changes. Please also refer to Figure 5 , Figure 5 This is a voltage waveform diagram provided by this application, such as Figure 5 As shown, Figure 5 The controller adjusts 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. Specifically, in the first control mode, the output power of the inverter satisfies:

[0036]

[0037] 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 transformation ratio of the transformer unit, L rThe leakage inductance between the primary winding and the secondary winding of the transformer unit. In the modulation process of the inverter circuit by the controller, the controller takes the control of the output current reaching the set current value as the control target, and adjusts the first phase angle, the second phase angle and the switching frequency, the control variable utilization degree is high, and different control modes are switched based on the polarity change of the first alternating voltage and the second alternating voltage, which improves the flexibility of the inverter control, improves the overall control efficiency of the inverter, and the output current control precision is high.

[0038] In some possible embodiments, the different polarity changes of the first alternating voltage and the second alternating voltage correspond to different control modes, and in different control modes, the relationship between the output power and the first phase angle, the second phase angle and the switching frequency is different. During the period when the first alternating voltage is a negative voltage, when the second alternating voltage is switched between a positive voltage and a negative voltage, the controller adjusts 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. Please see Figure 6 , Figure 6 is another voltage waveform provided by the present application, as shown in Figure 6 , Figure 6 The first alternating voltage Vab across the primary winding of the transformer unit and the second alternating voltage Vcd across the secondary winding correspond to the voltage waveform, and during the period when the first alternating voltage Vab is a negative voltage, the second alternating voltage Vcd is switched between a positive voltage and a negative voltage. Then the controller adjusts 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. Specifically, in the second control mode, the output power of the inverter satisfies:

[0039]

[0040] Wherein, D1 and D2 are the first phase angle and the second phase angle, 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 transformer ratio of the transformer unit, L r The leakage inductance between the primary winding and the secondary winding of the transformer unit. In the modulation process of the inverter circuit by the controller, the controller takes the control of the output current reaching the set current value as the control target, and adjusts the first phase angle, the second phase angle and the switching frequency, the control variable utilization degree is high, and different control modes are switched based on the polarity change of the first alternating voltage and the second alternating voltage, which improves the flexibility of the inverter control, improves the overall control efficiency of the inverter, and the output current control precision is high.

[0041] In some possible implementation manners, the different polarity changes of the first alternating voltage and the second alternating voltage correspond to different control modes, and the output power has different relationships with the first phase angle, the second phase angle and the switching frequency in different control modes. During the period when the first alternating voltage is a negative voltage, the second alternating 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 refer to Figure 7 , Figure 7 is another voltage waveform provided in the application, as shown in Figure 7 , Figure 7 The first alternating voltage Vab across the primary winding of the transformer unit and the second alternating voltage Vcd across the secondary winding correspond to the voltage waveform, and during the period when the first alternating voltage Vab is a negative voltage, the second alternating voltage Vcd remains a negative voltage, then 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:

[0042]

[0043] wherein 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 transformer unit, and L r is the leakage inductance between the primary winding and the secondary winding of the transformer unit. During the modulation of the controller to the inverter circuit, the controller takes the control of the output current to reach the set current value as the control target, and adjusts the first phase angle, the second phase angle and the switching frequency at the same time, so that the control variables have high utilization degree, and different control modes are switched based on the polarity changes of the first alternating voltage and the second alternating voltage, which improves the flexibility of the inverter control, improves the overall control efficiency of the inverter, and has high output current control precision.

[0044] In some possible implementation manners, during the period when the first alternating voltage is a negative voltage and the second alternating voltage remains a positive voltage, and when -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, the controller further takes the values of the first phase angle and the second phase angle as the judgment conditions of different control modes on the basis of the polarity requirements of the first alternating voltage and the second alternating voltage, which improves the distinguishability between different control modes, reduces the misjudgment of the controller to the control mode, and further improves the output current control precision.

[0045] In some possible implementation, during the period when the first AC voltage is a negative voltage, the second AC voltage is switched between a positive voltage and a negative voltage, and the following conditions are met: -180°<D1≤180°, and D1 / 2<|D2|≤(1-D1) / 2, the first phase angle, the second phase angle and the switching frequency are adjusted according to the second control mode. Here, the controller further takes the values of the first phase angle and the second phase angle as the judgment condition of different control modes on the basis of the polarity requirement of the first AC voltage and the second AC voltage, improves the distinction between different control modes, reduces the misjudgment of the controller on the control mode, and further improves the output current control precision.

[0046] In some possible implementation, during the period when the first AC voltage is a negative voltage, the second AC voltage is kept as a negative voltage, and the following conditions are met: -180°<D1≤180°, and 0<|D2|≤D1 / 2, the first phase angle, the second phase angle and the switching frequency are adjusted according to the third control mode. Here, the controller further takes the values of the first phase angle and the second phase angle as the judgment condition of different control modes on the basis of the polarity requirement of the first AC voltage and the second AC voltage, improves the distinction between different control modes, reduces the misjudgment of the controller on the control mode, and further improves the output current control precision.

[0047] In some possible implementation, the controller obtains at least one set of variable combinations, each variable combination including three variable values of different first phase angle, second phase angle and switching frequency, and the output current of the inverter corresponding to each variable combination is a set current value. The controller is further configured to take the variable combination corresponding to the minimum resonant current value in the at least one set of variable combinations as a 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 being the current between the connection end of the first secondary-side half-bridge arm and the second secondary-side 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 frequency of each switch 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 a plurality of sets of variable combinations, each variable combination including three variable values of different first phase angle, second phase angle and switching frequency, 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 s3), the ratio of the output power of the inverter corresponding to the variable combination to the output voltage of the inverter at the current time is the set current value, and the resonant current values under each variable combination are different, and the resonant current is the current between the connection end of the first secondary-side half-bridge arm and the second secondary-side half-bridge arm in the inverter and the first end of the secondary-side winding of the transformer unit. If the variable combination corresponding to the minimum resonant current value in the variable combination is (D 11 ,D 21 ,f s1 ), then (D 11 ,D 21 ,f s1 ) is taken as the target variable combination, and the controller adjusts the first phase angle, the second phase angle and the switching frequency value to D 11 , D 21 and f s1 , respectively. Here, the controller adds the optimization goal of minimizing the resonant cavity current of the inverter on the basis of controlling the output current of the inverter to be the set current value, that is, the current between the connection end of the first secondary-side half-bridge arm and the second secondary-side half-bridge arm in the inverter and the first end of the secondary-side winding of the transformer unit is minimized, thereby reducing the loss of the switching tube in the inverter. It can be understood that the controller also adds other control goals, such as the control goal of minimizing the overall switching tube loss of the inverter, on the basis of controlling the output current of the inverter to be the set current value. Optionally, the controller can obtain the optimal control variable based on the current output voltage of the inverter in real time, that is, one or more variable combinations of the current output voltage of the inverter are obtained. In addition, the controller can also calculate one or more variable combinations corresponding to each output voltage offline. In a specific implementation, the output voltage of the inverter at all times within a power frequency period (for example, within 20 ms) can be obtained first. For the output voltage at any time, the controller adjusts the first phase angle, the second phase angle and the switching frequency 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 obtained output voltage is the set current value, thereby obtaining the variable combination corresponding to the output voltage at the above any time. During the modulation process, the controller adjusts the first phase angle, the second phase angle and the switching frequency of each switching tube based on the variable combination calculated offline by means of table lookup and linear interpolation.

[0048] In some possible implementations, the controller can increase or decrease the switching frequency based on the output current of the inverter and the set current value, wherein 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. Optionally, the controller can also increase or decrease the second phase angle based on the output current of the inverter and the set current value, wherein the amplitude 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. For details, please refer to Figure 2, the controller takes the output current reaching the set current value I ref as the control target (or, other control targets can also be added at the same time), and adjusts the first phase angle D1, the second phase angle D2 and the switching frequency f s at the same time. The control process of the controller can include a current control link, a feedforward control and control quantity synthesis. In the feedforward control link, the controller takes the output current reaching the set current value I ref switches between the first control mode, the second control mode or the third control mode (for example, the control mode switching can be based on the polarity change of the first alternating voltage Vab and the second alternating voltage Vcd), and the relationship between the output power and the three variables of the first phase angle, the second phase angle and the switching frequency is different in different control modes. The controller adjusts the first phase angle D1, the second phase angle D2 and the switching frequency f s of each switching tube in each mode to obtain the target variable combination (D′1, D′2, f′ s ) output by the feedforward control link. The controller can generate the second phase angle adjustment value ΔD′2 or the switching frequency adjustment value Δf′ s through the current control link. The controller can generate the switching frequency adjustment value Δf′ s For example, please refer to Figure 8 , Figure 8 is the current control schematic diagram provided by the application, as shown in Figure 8 , the current control can include a quasi-PR controller control and a linearization link. The controller can input the set current value I ref and the current inverter output current I g into the quasi-PR controller, wherein the transfer function of the quasi-PR controller is:

[0049]

[0050] , K p is the proportional coefficient, K r is the resonance coefficient, w c is the cut-off frequency, and w0 is the resonance frequency. The output PR OUT of the quasi-PR controller is input into the linearization link, so as to obtain the switching frequency adjustment value Δf′ s , which can be represented as:

[0051]

[0052] The greater the absolute value of the difference between the current inverter output current I g and the set current value I ref , the smaller the absolute value of the output PR OUT of the quasi-PR controller, and the switching frequency adjustment value Δf′s In other words, the controller adjusts the amplitude of the switching frequency and the output current I g and set current value I ref The absolute value of the difference is positively correlated. When the inverter output voltage is positive, the output current I g The small signal model expression with respect to frequency is as follows:

[0053] ΔI g =HΔf s

[0054]

[0055]

[0056] When the inverter output voltage is negative, the output current I g The small signal model expression with respect to frequency is as follows:

[0057] ΔI g =-HΔf s

[0058]

[0059]

[0060] Here, taking the positive half cycle of the grid voltage as an example, the output current I is obtained according to the fundamental wave approximation method. g expression:

[0061]

[0062] And the above X L , f r , Z r , a p The expressions of and θ are:

[0063]

[0064]

[0065]

[0066] a p =90D1

[0067] θ=180D2-a p

[0068] Among them, C r is the resonant capacitor. Please participate again Figure 2, the controller obtains the target variable combination (D′1, D′2, f′ s ) and the switching frequency adjustment value Δf′ generated by the current control link s In the control quantity synthesis link, 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 link, and the switching frequency f′ generated by the feedforward link s The switching frequency adjustment value Δf′ generated by the current control link s After adding, the final switching frequency f is output s . Here, the controller controls the output current to reach the set current value as the control target in the feedforward control link, and adjusts the three variables of the first phase angle, the second phase angle and the switching frequency at the same time. In addition, the controller simultaneously performs the current control link, and generates a second phase angle adjustment value or a switching frequency adjustment value based on the set current value and the current inverter output current, thereby adding the switching frequency generated by the feedforward link and the switching frequency adjustment value generated by the current control link to output the final switching frequency, or adding the second phase angle generated by the feedforward link and the second phase angle adjustment value generated by the current control link to output the final second phase angle. By combining the output results of the feedforward control link and the current control link, the output current control accuracy can be further improved.

Claims

1. An inverter, characterized by, The inverter comprises a primary side bridge arm, a secondary side bridge arm, a transformer unit and a controller, the primary side bridge arm comprises a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, the first end of the first switch tube and the first end of the third switch tube are used for connecting the positive output end of a direct current power supply, the second end of the first switch tube is connected with the negative output end of the direct current power supply through the second switch tube, the second end of the third switch tube is connected with the negative output end of the direct current power supply through the fourth switch tube, the connection end of the first switch tube and the second switch tube and the connection end of the third switch tube and the fourth switch tube are connected with the first end and the second end of the primary side winding of the transformer unit respectively, and the secondary side winding of the transformer unit is connected with the secondary side bridge arm; The controller is used for controlling the first switch tube and the second switch tube to be alternately turned on, and the third switch tube and the fourth switch tube to be alternately turned on, and the interval of the first switch tube being turned on and the third switch tube being turned on is a first phase angle, and the phase difference between the first alternating current voltage at the two ends of the primary side winding and the second alternating current voltage at the two ends of the secondary side winding is a second phase angle; The controller is further used for adjusting the first phase angle, the second phase angle and the switching frequency of each switch tube according to a first control mode, a second control mode or a third control mode based on the polarity change of the first alternating current voltage and the second alternating current voltage, so that the output power of the inverter changes until the output current of the inverter is a set current value; Wherein, different polarity changes of the first alternating current voltage and the second alternating current 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.

2. The inverter of claim 1, wherein, The controller is used for adjusting the first phase angle, the second phase angle and the switching frequency according to the first control mode when the first alternating current voltage is a negative voltage and the second alternating current voltage remains a positive voltage, so that the output power of the inverter changes; Wherein, under the first control mode, the output power of the inverter satisfies: wherein D1 and D2 are the first and second phase angles, 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 transformation ratio of the transformer unit, L r is the leakage inductance between the primary winding and the secondary winding of the transformer unit.

3. The inverter of claim 1, wherein, The controller is used for adjusting the first phase angle, the second phase angle and the switching frequency according to the second control mode when the first alternating current voltage is a negative voltage and the second alternating current voltage switches between a positive voltage and a negative voltage, so that the output power of the inverter changes; Wherein, under the second control mode, the output power of the inverter satisfies: wherein 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 transformation ratio of the transformer unit, L r is the leakage inductance between the primary winding and the secondary winding of the transformer unit.

4. The inverter of claim 1, wherein, The controller is used for adjusting the first phase angle, the second phase angle and the switching frequency according to the third control mode when the first alternating current voltage is a negative voltage and the second alternating current voltage remains a negative voltage, so that the output power of the inverter changes; Wherein, under the third control mode, the output power of the inverter satisfies: wherein 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 transformation ratio of the transformer unit, L r is the leakage inductance between the primary winding and the secondary winding of the transformer unit.

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

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

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

8. The inverter according to any one of claims 1 to 7, characterized by, The controller is configured to obtain at least one variable combination, each variable combination comprising different values of the first phase angle, the second phase angle and the switching frequency, and each variable combination corresponding to an output current of the inverter being the set current value. The controller is further configured to select, as a target variable combination, a variable combination corresponding to a minimum resonant current value among at least one 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 being a current between the connection end of the first secondary-side half-bridge arm and the second secondary-side half-bridge arm and the first end of the secondary-side winding of the transformer unit.

9. The inverter according to any one of claims 1 to 8, characterized by, The controller is configured to increase or decrease the switching frequency based on the output current of the inverter and the set current value, wherein the controller adjusts the amplitude of the switching frequency positively in relation to 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 to 8, characterized by, 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, wherein the controller adjusts the amplitude of the second phase angle positively in relation to 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 to 10, characterized by The inverter comprises a first capacitor and a second capacitor, the secondary-side bridge arm is connected in parallel with the first capacitor and the second capacitor in series, the secondary-side bridge arm comprises a first secondary-side half-bridge arm and a second secondary-side half-bridge arm in series, the connection end of the first secondary-side half-bridge arm and the second secondary-side half-bridge arm, the connection end of the first capacitor and the second capacitor are connected to the first end and the second end of the secondary-side winding of the transformer unit respectively, and the first secondary-side half-bridge arm and the second secondary-side half-bridge arm comprise at least one switch tube.

12. The inverter of claim 11, wherein, The first secondary-side half-bridge arm comprises a fifth switch tube and a sixth switch tube in series, the second secondary-side half-bridge arm comprises a seventh switch tube and an eighth switch tube in series, and the connection end of the sixth switch tube and the seventh switch tube is connected to the first end of the secondary-side winding of the transformer unit. The controller is configured to control the sixth switch tube and the eighth switch tube to be kept conductive when the output voltage of the inverter is a positive voltage, and control the fifth switch tube and the seventh switch tube to be alternately conductive; and control the fifth switch tube and the seventh switch tube to be kept conductive when the output voltage of the inverter is a negative voltage, and control the sixth switch tube and the eighth switch tube to be alternately conductive.

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