CN-115498906-B - Photovoltaic inverter and control method thereof

CN115498906BCN 115498906 BCN115498906 BCN 115498906BCN-115498906-B

Abstract

The application provides a photovoltaic inverter and a control method thereof, wherein the photovoltaic inverter is suitable for a power supply system, the photovoltaic inverter comprises a conversion circuit, a collection circuit and a controller, the collection circuit is used for obtaining positive direct current bus voltage and negative direct current bus voltage of the conversion circuit, the controller is used for generating even harmonic voltage adjusting signals based on phases of the positive direct current bus voltage and the negative direct current bus voltage of the conversion circuit and output voltage of the photovoltaic inverter, generating driving control signals based on the even harmonic voltage adjusting signals and controlling switching tubes in the conversion circuit to be switched on or off so as to control the conversion circuit to output target voltage and reduce difference value of the positive direct current bus voltage and the negative direct current bus voltage of the conversion circuit. The application can adjust the on or off of the switching tube in the conversion circuit, improve the voltage stability of the midpoint of the conversion circuit, has simple structure, simple and convenient method and strong applicability.

Inventors

LI WENCHAO
DONG MINGXUAN
XIN KAI

Assignees

华为数字能源技术有限公司

Dates

Publication Date: 20260505
Application Date: 20220916

Claims (11)

1. The photovoltaic inverter is used for a power supply system and is characterized by comprising a conversion circuit, a collection circuit and a controller; The input end of the conversion circuit is used for being connected with a power supply through a positive direct current bus and a negative direct current bus, and the output end of the conversion circuit is used for being connected with a load; The acquisition circuit is used for acquiring positive direct current bus voltage of the conversion circuit and negative direct current bus voltage of the conversion circuit; the controller is used for generating even harmonic amplitude signals based on the positive direct current bus voltage and the negative direct current bus voltage, generating a plurality of even harmonic phase signals with different phases based on the phases corresponding to the inductive load, the capacitive load and/or the resistive load of the photovoltaic inverter, generating a plurality of even harmonic voltage regulating signals based on the even harmonic amplitude signals and the even harmonic phase signals with different phases, superposing the even harmonic voltage regulating signals according to weights to obtain even harmonic voltage regulating signals, generating a driving control signal based on the even harmonic voltage regulating signals, and controlling a switch tube in the conversion circuit to be turned on or off so as to control the conversion circuit to output a target voltage and reduce the difference value between the positive direct current bus voltage and the negative direct current bus voltage.
2. The photovoltaic inverter of claim 1, wherein the conversion circuit comprises two groups of capacitors and at least one switch bridge arm, one switch bridge arm comprises a plurality of switch tubes, the two groups of capacitors are connected in series and then are connected in parallel with the at least one switch bridge arm between a positive direct current bus and a negative direct current bus of the conversion circuit, a series connection point of the two groups of capacitors is a midpoint of the conversion circuit, and an input end of the acquisition circuit is connected with the positive direct current bus, the negative direct current bus and the midpoint of the conversion circuit; the acquisition circuit is used for acquiring the positive direct current bus voltage and the negative direct current bus voltage of the conversion circuit based on the potential of the positive direct current bus, the potential of the negative direct current bus and the potential of the midpoint of the conversion circuit.
3. The photovoltaic inverter of claim 1 or 2, wherein the controller comprises a signal generation unit, a voltage control unit and a drive control unit, the signal generation unit being connected to the acquisition circuit and the voltage control unit, the voltage control unit being connected to the conversion circuit through the drive control unit; The signal generation unit is used for generating even harmonic amplitude signals based on the positive direct current bus voltage and the negative direct current bus voltage, generating a plurality of even harmonic phase signals with different phases based on the phases corresponding to the inductive load, the capacitive load and/or the resistive load of the photovoltaic inverter, generating a plurality of even harmonic voltage regulating signals based on the even harmonic amplitude signals and the even harmonic phase signals with different phases, and superposing the even harmonic voltage regulating signals according to weights to obtain even harmonic voltage regulating signals; the voltage control unit is used for generating a voltage command signal of the conversion circuit based on the even harmonic voltage regulation signal; The driving control unit is used for generating the driving control signal based on the voltage command signal of the conversion circuit and controlling the on or off of a switching tube in the conversion circuit based on the driving control signal.
4. The photovoltaic inverter of claim 3 wherein the voltage control unit is further configured to obtain fundamental wave commands of an external central control system; The voltage control unit is also used for superposing the fundamental wave instruction and the even harmonic voltage regulation signal to obtain a voltage instruction signal of the conversion circuit.
5. The photovoltaic inverter of claim 4 wherein the controller further comprises a voltage feedback unit connecting the harvesting circuit and the voltage control unit; The voltage feedback unit is used for acquiring the output voltage of the photovoltaic inverter through the acquisition circuit and taking the output voltage of the photovoltaic inverter as a voltage feedback signal; the voltage control unit is further used for generating a primary voltage command signal based on the voltage feedback signal and a voltage command signal of the conversion circuit; the drive control unit is further configured to generate the drive control signal based on the primary voltage command signal.
6. The photovoltaic inverter of claim 5 wherein the controller further comprises a current control unit and a current feedback unit, the current control unit connecting the voltage control unit and the drive control unit, the current feedback unit connecting the harvesting circuit and the current control unit; The current feedback unit is used for acquiring the output current of the photovoltaic inverter through the acquisition circuit and taking the output current of the photovoltaic inverter as a current feedback signal; The current control unit is used for generating a secondary voltage command signal based on the primary voltage command signal output by the voltage control unit and the current feedback signal; the drive control unit is further configured to generate the drive control signal based on the secondary voltage command signal.
7. The photovoltaic inverter of claim 6 wherein the drive control unit is further connected to the signal generation unit; The drive control unit is further configured to acquire the even harmonic voltage adjustment signal of the signal generation unit, and generate the drive control signal based on the even harmonic voltage adjustment signal and the secondary voltage command signal.
8. A photovoltaic inverter control method for a photovoltaic inverter, the photovoltaic inverter comprising a conversion circuit and positive and negative direct current buses, one ends of the positive and negative direct current buses being connected with the conversion circuit, and the other ends of the positive and negative direct current buses being used for being connected with a power supply, the method comprising the steps of: detecting a positive DC bus voltage of the conversion circuit and a negative DC bus voltage of the conversion circuit; Generating even harmonic amplitude signals based on the positive direct current bus voltage and the negative direct current bus voltage, generating a plurality of even harmonic phase signals with different phases based on the inductive load, the capacitive load and/or the resistive load of the photovoltaic inverter, generating a plurality of even harmonic voltage regulating signals based on the even harmonic amplitude signals and the even harmonic phase signals with different phases, superposing the even harmonic voltage regulating signals according to weights to obtain even harmonic voltage regulating signals, generating a driving control signal based on the even harmonic voltage regulating signals, and controlling a switching tube in the conversion circuit to be turned on or off so as to control the conversion circuit to output a target voltage and reduce the difference value between the positive direct current bus voltage and the negative direct current bus voltage of the conversion circuit.
9. The control method according to claim 8, wherein the conversion circuit includes two sets of capacitors and at least one switch bridge arm, one of the switch bridge arms includes a plurality of switch transistors, the two sets of capacitors are connected in series and then connected in parallel with the at least one switch bridge arm between a positive dc bus and a negative dc bus of the conversion circuit, a series connection point of the two sets of capacitors is a midpoint of the conversion circuit, and the detecting the positive dc bus voltage of the conversion circuit and the negative dc bus voltage of the conversion circuit includes: the positive dc bus voltage and the negative dc bus voltage of the conversion circuit are detected based on the potential of the positive dc bus, the potential of the negative dc bus, and the potential of the midpoint of the conversion circuit.
10. The control method according to claim 8 or 9, characterized in that the generating a drive control signal based on the even harmonic voltage adjustment signal includes: generating a voltage command signal for the conversion circuit based on the even harmonic voltage regulation signal; the drive control signal is generated based on a voltage command signal of the conversion circuit.
11. The control method according to claim 10, characterized in that the generating the voltage command signal of the conversion circuit based on the even harmonic voltage adjustment signal includes: detecting a fundamental wave instruction of an external central control system; And superposing the fundamental wave instruction and the even harmonic voltage regulation signal to obtain a voltage instruction signal of the conversion circuit.

Description

Photovoltaic inverter and control method thereof Technical Field The application relates to the technical field of power electronics, in particular to a photovoltaic inverter and a control method thereof. Background In the field of power electronics, a conversion circuit in an inverter converts dc power from a power source into ac power to be supplied to a load. Among them, the conversion circuit (for example, neutral point clamped (Neutral Point Clamped, NPC) inverter circuit) has been widely used because of its high safety, high efficiency, less loss, and less harmonic. Referring to fig. 1, fig. 1 is a schematic structural diagram of two NPC inverter circuits provided in the present application. As shown in part (a) of fig. 1 and part (b) of fig. 1, the NPC inverter circuit (i.e., the conversion circuit) includes two capacitors connected in series and three switching legs, the series point of the two capacitors being the midpoint of the conversion circuit, each switching leg including four switching transistors and two clamping diodes. In an ideal case, the amount of charge flowing into and out of the midpoint of the conversion circuit is the same during one supply cycle of the conversion circuit, i.e. the voltages of the two series capacitors of the conversion circuit are equal. However, in practical applications, since the operating states of the switching tubes in the switching bridge arm of the conversion circuit are generally asymmetric (for example, the switching tube types are different, the losses are different, the loads are asymmetric, or the switching dead zone is affected), the amounts of charges flowing into and out of the midpoint of the conversion circuit are not the same in one power supply period, that is, the amounts of charges (or discharges) of the two capacitors connected in series in the conversion circuit are not equal, resulting in unequal voltages of the two capacitors connected in series in the conversion circuit (that is, the positive dc bus voltage and the negative dc bus voltage of the conversion circuit are not equal, or the midpoint voltage of the conversion circuit is not balanced), which may distort the output voltage (or the output current) of the conversion circuit and even damage the power elements in the system. The inventor of the application finds that the method for adjusting the midpoint voltage based on the calculation of the direct current bus voltage difference value is complex, has complex calculation process, high cost and complex control in the research and practice process, and the method for injecting the zero sequence voltage balance midpoint voltage into the modulated wave has more limits on the algorithm and the load type of the modulated wave of the conversion circuit, for example, when discontinuous pulse width modulation (Discontinuous Pulse Width Modulation, DPWM) wave is carried out, the space of the modulated wave for injecting the zero sequence is limited, thus leading to poor adaptability, poor adjustment capability and poor control effect of the method for modulating the midpoint voltage. Disclosure of Invention The application provides a photovoltaic inverter and a control method thereof, which can improve the voltage stability of the midpoint of a conversion circuit by adjusting the on-off time of a switching tube in the conversion circuit, and has the advantages of simple structure, simple and convenient control method and strong applicability. In a first aspect, the present application provides a photovoltaic inverter adapted for use in a power supply system, the photovoltaic inverter comprising a conversion circuit, a harvesting circuit, and a controller. Here, the input terminal of the conversion circuit may be connected to a power source through a positive dc bus and a negative dc bus, and the output terminal of the conversion circuit may be used to connect to a load. The acquisition circuit can acquire the positive DC bus voltage of the conversion circuit and the negative DC bus voltage of the conversion circuit. The controller may generate an even harmonic voltage adjustment signal based on a phase of a positive dc bus voltage of the conversion circuit, a negative dc bus voltage of the conversion circuit, and an output voltage of the photovoltaic inverter, and generate a drive control signal based on the even harmonic voltage adjustment signal, to control switching transistors in the conversion circuit to turn on or off, to control the conversion circuit to output a target voltage and to reduce a difference between the positive dc bus voltage and the negative dc bus voltage of the conversion circuit. In the application, the power supply can be connected with the conversion circuit through the positive direct current bus and the negative direct current bus, and the conversion circuit can convert direct current electric energy provided by the power supply into alternating current electric energy to be provided for a load. In the power sup