Photovoltaic power generation system and control method

Abstract

The present application provides a solar power generation system and a control method thereof, in which a negative output terminal of a master DC / DC converter (101) is connected to an N line, a negative input terminal of a master DC / AC converter (201) is connected to an N line, a negative input terminal of a slave DC / DC converter (102) is connected to a negative output terminal of the master DC / DC converter (101), a positive input terminal of the slave DC / DC converter (102) is connected to a positive output terminal of the master DC / DC converter (101), a positive output terminal of the slave DC / DC converter (102) is connected to an N line, and a negative output terminal of the slave DC / DC converter (102) is connected to a slave The master DC / AC converter (201) has a negative output terminal connected to the negative output terminal of the slave DC / AC converter (202) and a positive output terminal connected to the N line, the master DC / AC converter (201) transmits a current command value and an input voltage of the master DC / AC converter (201) to the slave DC / AC converter (202), and the slave DC / AC converter (202) controls an output current based on the input voltage of the slave DC / AC converter (202), the current command value, and the input voltage of the master DC / AC converter (202) so that the current of the N line becomes smaller than a preset current, thereby reducing power consumption.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to a Chinese patent application bearing application number 202111308573.7, filed with the State Intellectual Property Office of the People's Republic of China on November 5, 2021, and entitled "Solar Power Generation System and Control Method," the entire contents of which are incorporated herein by reference. [Technical field] The present application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic power generation system and a control method. [Background technology]

[0002] At present, photovoltaic power generation is attracting more and more attention, and the voltage level is getting higher and higher. Photovoltaic power generation is a system in which a photovoltaic array outputs DC power, which is converted to AC power through an inverter, and then the system is turned on-grid or supplied to a load.

[0003] The DC busbar in the conventional photovoltaic power generation system includes a DC positive busbar and a DC negative busbar, that is, the positive input terminal of the inverter is connected to the DC positive busbar, and the negative input terminal of the inverter is connected to the DC negative busbar. The voltage between the DC positive busbar and the DC negative busbar is the input voltage of the inverter. The voltage level of the entire photovoltaic power generation system is the maximum voltage between the DC positive busbar voltage and the DC negative busbar voltage, and the safety standard is also designed according to this voltage level.

[0004] In order to meet the standards of safety standards, the input voltage of the inverter, i.e., the DC side voltage, must not exceed the requirements of the safety standards, otherwise it will cause damage to personnel and devices. In particular, for the power devices inside the inverter, each power device has a corresponding withstand voltage requirement, and if the withstand voltage is exceeded, it will be destroyed and damaged. As the voltage level of the photovoltaic power generation system increases, the withstand voltage of the power devices becomes a new challenge, and the selection of the type of power devices becomes more and more difficult.

[0005] Currently, there is a photovoltaic power generation system with three DC busbars, including two inverters, the input terminal of the first inverter is connected to the DC positive busbar and the N line, and the input terminal of the second inverter is connected to the N line and the DC negative busbar. In this way, the voltage level can be improved, but the safety standard requirements for the inverters do not change. However, in order to reduce the loss of the N line, it is necessary to control the current of the N line as small as possible or to zero. Summary of the Invention [Problem to be solved by the invention]

[0006] In order to solve the above technical problems, the present application provides a photovoltaic power generation system and a control method capable of controlling the current flowing through the N line to be extremely small and reducing power consumption. [Means for solving the problem]

[0007] To achieve the above objectives, the technical solutions provided in the embodiments of the present application are as follows: The present application provides a solar power generation system, including a master DC / DC converter, a slave DC / DC converter, a master DC / AC converter, and a slave DC / AC converter, The input end of the master DC / DC converter is used to connect to the photovoltaic power generation array, the positive output end of the master DC / DC converter is connected to the positive input end of the master DC / AC converter, the negative output end of the master DC / DC converter is connected to the N line, and the negative input end of the master DC / AC converter is connected to the N line; The negative input terminal of the slave DC / DC converter is connected to the negative output terminal of the master DC / DC converter, the positive input terminal of the slave DC / DC converter is connected to the positive output terminal of the master DC / DC converter, the positive output terminal of the slave DC / DC converter is connected to the N line, and the negative output terminal of the slave DC / DC converter is connected to the negative Enter The positive terminal of the slave DC / AC converter is connected to the Enter The power end is connected to the N line. The master DC / AC converter is used to send the current command value and the input voltage of the master DC / AC converter to the slave DC / AC converter. The slave DC / AC converter is used to control the output current so that the current of the N line is smaller than a preset current, based on the input voltage of the slave DC / AC converter, a current command value, and the input voltage of the master DC / AC converter.

[0008] Preferably, the slave DC / AC converter is used to control the output current so that the output current is proportional to both the input voltage and the current command value of the slave DC / AC converter and inversely proportional to the input voltage of the master DC / AC converter, specifically so that the current of the N line is smaller than a preset current.

[0009] Preferably, the slave DC / AC converter is specifically used to control the output current to U2*I1 / U1, where U2 is the input voltage of the slave DC / AC converter, U1 is the input voltage of the master DC / AC converter, and I1 is the current command value.

[0010] Preferably, when the master DC / AC converter is not limiting its output power, the input voltage of the master DC / AC converter is a preset value.

[0011] Preferably, when the master DC / AC converter limits its output power, the master DC / AC converter collects the input voltage of the master DC / AC converter and transmits the collected input voltage of the master DC / AC converter to the slave DC / AC converter, or the slave DC / AC converter directly collects the input voltage of the master DC / AC converter.

[0012] Preferably, when the solar power generation system does not limit power and the slave DC / AC converter detects a communication abnormality with the master DC / AC converter, the slave DC / AC converter obtains a current command value based on the input voltage of the master DC / AC converter, the current of the N line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and is used to control the output current of the slave DC / AC converter based on the current command value so that the current of the N line is smaller than a preset current.

[0013] Preferably, when the solar power generation system is limiting power and the slave DC / AC converter is not receiving the input voltage of the master DC / AC converter transmitted from the master DC / AC converter, the slave DC / AC converter obtains a current command value based on the input voltage of the master DC / AC converter, the current of the N line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and is used to control the output current of the slave DC / AC converter based on the current command value so that the current of the N line is smaller than a preset current.

[0014] Preferably, when low voltage ride-through or high voltage ride-through occurs in the solar power generation system, the master DC / AC converter is used to control the master DC / AC converter to output a first reactive power and to control the slave DC / AC converter to output a second reactive power.

[0015] The present application further provides a control method for a solar power generation system, the solar power generation system including a master DC / DC converter, a slave DC / DC converter, a master DC / AC converter, and a slave DC / AC converter, an input end of the master DC / DC converter is used for connecting to a solar power generation array, a positive output end of the master DC / DC converter is connected to a positive input end of the master DC / AC converter, a negative output end of the master DC / DC converter is connected to an N line, a negative input end of the master DC / AC converter is connected to an N line, a positive input end of the slave DC / DC converter is connected to a negative output end of the master DC / DC converter, a negative input end of the slave DC / DC converter is connected to a positive output end of the master DC / DC converter, a positive output end of the slave DC / DC converter is connected to an N line, and a negative output end of the slave DC / DC converter is connected to a negative output end of the slave DC / AC converter. Enter The positive terminal of the slave DC / AC converter is connected to the Enter The output end is connected to the N line, and the method includes controlling the master DC / AC converter to transmit a current command value and an input voltage of the master DC / AC converter to the slave DC / AC converter, and controlling the slave DC / AC converter to control an output current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that the current of the N line is smaller than a preset current.

[0016] Preferably, the control of the output current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter is specifically This includes controlling the output current to be proportional to both the input voltage and the current command value of the slave DC / AC converter and inversely proportional to the input voltage of the master DC / AC converter so that the current of the N line is smaller than a preset current.

[0017] Preferably, the method further includes controlling the input voltage of the master DC / AC converter to a preset value when the master DC / AC converter is not limiting its output power.

[0018] Preferably, the method further includes collecting an input voltage of the master DC / AC converter by the master DC / AC converter when the master DC / AC converter limits the output power, and transmitting the collected input voltage of the master DC / AC converter to the slave DC / AC converter.

[0019] Preferably, when the photovoltaic power generation system is not limiting power and the slave DC / AC converter does not receive the input voltage of the master DC / AC converter transmitted from the master DC / AC converter, the output current is controlled based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that the current of the N line is smaller than the preset current, specifically, The method includes a step of obtaining a current command value based on an input voltage of the master DC / AC converter, a current of the N line, an input voltage of the slave DC / AC converter, and an output power of the slave DC / AC converter, and using the current command value to control the output current of the slave DC / AC converter so that the current of the N line is smaller than a preset current.

[0020] Preferably, when the photovoltaic power generation system is limiting power and the slave DC / AC converter does not receive the input voltage of the master DC / AC converter transmitted from the master DC / AC converter, the output current is controlled based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that the current of the N line is smaller than the preset current, specifically, This includes obtaining a current command value based on the input voltage of the master DC / AC converter, the current of the N line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and controlling the output current of the slave DC / AC converter based on the current command value so that the current of the N line is smaller than a preset current.

[0021] As can be seen from the above technical solutions, the present application has the following beneficial effects: In order to reduce or eliminate the current on the N line, the output power of the DC / AC converter and the output power of the slave DC / AC converter must be equal, and the output power of the slave DC / AC converter follows the output power of the master DC / AC converter. If power consumption is ignored, the output power of the master DC / AC converter is equal to the input power, the output power of the slave DC / AC converter is equal to the input power, and the input power of the master DC / AC converter is equal to the input power of the slave DC / AC converter, so that the current on the N line can be controlled to be smaller than the preset current by controlling the output power of the master DC / AC converter to be equal to the output power of the slave DC / AC converter. Specifically, the master DC / AC converter transmits a current command value and an input voltage of the master DC / AC converter to the slave DC / AC converter, and the slave DC / AC converter controls the output current so that the current on the N line is smaller than the preset current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter, and the smaller the current on the N line, the smaller the power consumption on the N line becomes. For example, if the current on the N line is at a minimum, it can be controlled to zero. [Brief description of the drawings]

[0022] In order to more clearly describe the technical solutions in the embodiments of the present application or the prior art, the drawings that need to be used in the description of the embodiments or the prior art are briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings based on these drawings without making creative efforts. [Figure 1] FIG. 1 is a schematic diagram of a solar power generation system provided by an embodiment of the present application. [Diagram 2] FIG. 2 is a schematic diagram of another solar power generation system provided by an embodiment of the present application. [Diagram 3] 1 is a flowchart of a control method for a solar power generation system provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In order to facilitate a better understanding of the technical solutions provided by the embodiments of the present application, before introducing the methods provided by the embodiments of the present application, application scenarios of the technical solutions in the embodiments of the present application will be introduced. [System implementation example]

[0024] Please refer to FIG. 1, which is a schematic diagram of a photovoltaic power generation system provided according to an embodiment of the present application.

[0025] The solar power generation system provided in this embodiment includes two direct current / direct current (DC / DC, Direct Current) converters and two inverters, the two inverters including a first inverter and a second inverter, and each inverter includes one direct current / alternating current (DC / AC, Altering Current) converter.

[0026] The two DC / DC converters include a master DC / DC converter 100 and a slave DC / DC converter 102 , and the two DC / AC converters include a master DC / AC converter 201 and a slave DC / AC converter 202 .

[0027] The two DC / DC converters can be integrated and arranged in a combiner box 1000. The input end of the combiner box 1000 is connected to a solar power generation array. In the embodiment of the present application, there is no limitation on whether the solar power generation system includes a combiner box, and the solar power generation system may not include a combiner box, and the two DC / DC converters may exist independently.

[0028] The photovoltaic power generation system is different from the conventional photovoltaic power generation system in that it includes three buses, a DC positive bus BUS+, a DC negative bus BUS-, and an N-line, whereas the conventional photovoltaic power generation system includes only two buses, BUS+ and BUS-. The advantage of the photovoltaic power generation system provided by the present application including three buses is that it can double the voltage level, but does not increase the withstand voltage of each device in the converter, that is, the devices in the photovoltaic power generation system with two buses, such as IGBTs, can continue to be used. For example, the voltage of BUS+ is positive 1500V, the voltage of BUS- is negative 1500V, and the voltage level of the entire photovoltaic power generation system is 3000V.

[0029] As shown in FIG. 1, the input terminal of the master DC / DC converter 101 is used to connect to a photovoltaic power array, i.e., the positive input terminal of the master DC / DC converter 101 is used to connect to the positive pole PV+ of the photovoltaic power array, and the negative input terminal of the master DC / DC converter 101 is used to connect to the negative pole PV- of the photovoltaic power array.

[0030] In the embodiments of the present application, the number of master DC / DC converters 101 is not particularly limited, and FIG. 1 merely roughly illustrates the connection relationship between the master DC / DC converter 101 and the solar power generation array. The solar power generation system provided in the embodiments of the present application may include multiple master DC / DC converters 101, and the input terminal of each master DC / DC converter 101 may be connected to a corresponding solar power generation array, and the output terminals of the multiple master DC / DC converters 101 may be connected in parallel.

[0031] The positive output terminal of the master DC / DC converter 101 is connected to the positive input terminal of the master DC / AC converter 201, the negative output terminal of the master DC / DC converter 101 is connected to the N line, and the negative input terminal of the master DC / AC converter 201 is connected to the N line; The negative input terminal of the slave DC / DC converter 102 is connected to the negative output terminal of the master DC / DC converter 101, the positive input terminal of the slave DC / DC converter 102 is connected to the positive output terminal of the master DC / DC converter 101, the positive output terminal of the slave DC / DC converter 102 is connected to the N line, and the negative output terminal of the slave DC / DC converter 102 is connected to the negative Enter The positive terminal of the slave DC / AC converter 202 is connected to the positive terminal of the slave DC / AC converter 202. Enter The output end of the slave DC / DC converter 102 is connected to the N line. Similarly, in the embodiment of the present application, the number of slave DC / DC converters 102 is not particularly limited, and may be one or more. In the case of multiple DC / DC converters 102, the output ends of the multiple DC / DC converters 102 are also connected in parallel.

[0032] Since the photovoltaic power generation system includes an N-wire, in order to make the N-wire relatively thin, the current of the N-wire is controlled to be as small as possible, that is, the current of the N-wire needs to be smaller than the preset current, and the preset current can be set according to actual needs, for example, the current of the N-wire is controlled to 0, that is, no current flows through the N-wire, and the power consumption at this time is the lowest. However, in reality, various errors generally exist, and the preset current may be a relatively small current greater than 0. The smaller current of the N-wire not only allows the use of a relatively thin cable, but also reduces power consumption.

[0033] The embodiments of the present application provide a technical solution for controlling the current on the N line to 0. First, the output power of the slave DC / DC converter 102 needs to be half of the output power of the master DC / DC converter 101. As can be seen from FIG. 1, the input power of the slave DC / AC converter 202 is the output power of the slave DC / DC converter 102. When the input power of the master DC / AC converter 201 and the input power of the slave DC / AC converter 202 are equal, the current on the N line is 0. In addition, the sum of the input powers of the two inverters comes from the output power of the master DC / DC converter 101. Therefore, if the power consumption is ignored, the output power of the master DC / DC converter 101 is twice the input power of the slave DC / AC converter 202. In addition, the input power of the DC / AC converter 202 is equal to the output power of the slave DC / DC converter 102, so the output power of the slave DC / DC converter 102 is half the output power of the master DC / DC converter 101.

[0034] In the embodiments of the present application, the circuit topology of the DC / DC converters in the master DC / DC converter 101 and the slave DC / DC converter 102 is not limited, for example, in order to improve the electric energy conversion efficiency of the combiner box, the slave DC / DC converter 102 can adopt a quasi-resonant soft-switched converter.

[0035] Since the inverter needs to quickly perform maximum power point tracking (MPPT) and fast response under temporary operating conditions, high requirements are put forward for the control response speed and reliability of the slave DC / DC converter 102. The present application simplifies the power control of the slave DC / DC converter 102 in the combiner box, and uses a post-stage inverter to control the voltage difference between the input voltage and the output voltage of the slave DC / DC converter 102 to realize high-speed control of the power of the slave DC / DC converter 102, while the control of the slave DC / DC converter 102 adopts a fixed frequency and fixed duty cycle method to minimize the control complexity of the solar power generation system. At the same time, it can be realized that the current flowing through the neutral line (N line) is smaller than the preset current or very small, and the wire diameter of the neutral line can be reduced, that is, made very thin, thereby reducing the construction cost of the entire solar power plant.

[0036] In order to reduce the control complexity, the present application realizes the overall control by the master DC / AC converter 201, and realizes the current of N line to be 0. The specific operating principle will be introduced in detail below in combination with the drawings.

[0037] Both the master DC / AC converter 201 and the slave DC / AC converter 202 are provided with controllers, and during specific operation, the controller of the master DC / AC converter 201 and the controller of the slave DC / AC converter 202 interact with each other to realize control of the slave DC / AC converter 202 by the master DC / AC converter 201. It should be understood that in order to realize that the current of the N line is smaller than the preset current, the output power of the master DC / AC converter 201 and the output power of the slave DC / AC converter 202 must be equal, and when the master DC / AC converter 201 realizes control, the output power of the slave DC / AC converter 202 is made to track the output power of the master DC / AC converter 201. If power consumption is ignored, the output power of the master DC / AC converter 201 is equal to the input power, and the output power of the slave DC / AC converter 202 is equal to the input power; in other words, when the output power of the master DC / AC converter 201 is equal to the output power of the slave DC / AC converter 202, the input power of the master DC / AC converter 201 is equal to the input power of the slave DC / AC converter 202; therefore, by controlling the output power of the master DC / AC converter 201 to be equal to the output power of the slave DC / AC converter 202, the current of the N line can be controlled to be smaller than the preset current.

[0038] The master DC / AC converter 201 is used to send a current command value I1 and an input voltage U1 of the master DC / AC converter 201 to the slave DC / AC converter 202, and at this time, it is in a normal operation mode, that is, the solar power generation system does not perform power output limiting, and at this time, in order to perform MPPT, U1 is a preset value, and I1 is a value obtained based on U1.

[0039] The slave DC / AC converter 202 is used to control the output current I2 of the slave DC / AC converter 202 based on the current command value I1, the input voltage U2 of the slave DC / AC converter 202, and the input voltage U1 of the master DC / AC converter 201 so that the current of the N line is smaller than the preset current.

[0040] U2 is the actual input voltage of the slave DC / AC converter 202, which can be obtained by sampling.

[0041] The following is a specific implementation example. Specifically, the slave DC / AC converter 202 is used to control the output current to be proportional to both the input voltage U2 and the current command value I1 of the slave DC / AC converter 202 and inversely proportional to the input voltage U1 of the master DC / AC converter 201, so that the current of the N line is smaller than the preset current.

[0042] The slave DC / AC converter 202 is specifically used to control its own output current to U2*I1 / U1, where U2 is the input voltage of the slave DC / AC converter, U1 is the input voltage of the master DC / AC converter 201, and I1 is the current command value.

[0043] The following will specifically introduce the principle of the current of the N line becoming 0 when the output current of the slave DC / AC converter 202 is U2*I1 / U1.

[0044] Information interaction is performed between the master DC / AC converter 201 and the slave DC / AC converter 202. When the master DC / AC converter 201 does not limit the power, its output power is P1, its input voltage is controlled to U1, and a current command value I1 is sent to the slave DC / AC converter 202. The slave DC / AC converter 202 receives the current command value I1 of the master DC / AC converter 201 and controls its output current to be equal to I1. At this time, the input voltage of the slave DC / AC converter 202 is in an uncontrolled state. For example, the voltage value is U2, and U2 < U1. At this time, the master DC / DC converter 101 controls its input voltage to V1, and V1 is the voltage corresponding to the maximum power point of the photovoltaic array. At this time, a small current (the magnitude of which is

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[0045] The following introduces the derivation process of the above formula.

[0046] The current flowing through BUS+ is

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[0047] The current in the N line is set to 0, i.e.

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[0048] Above we introduced the control method for the N-line current when the solar power generation system is not limiting power, but below we will introduce a control method that ensures that the N-line current is 0 when the solar power generation system is limiting power output. Below we will continue by using an example where the master DC / AC converter in the solar power generation system controls the operation of a slave DC / AC converter. The difference between when the photovoltaic power generation system is power-limited and when it is not power-limited is that when the power is limited, the inverter cannot output according to the power that is tracked at the maximum power, but needs to output according to the power command sent from the photovoltaic power station, that is, the output power needs to be below the power limit value, and at this time, the input voltage of the master DC / AC converter is not a preset value, that is, the master DC / AC converter does not control its own input voltage, for example, when the power is limited, the output power of the master DC / AC converter is P2. To distinguish from the parameters when the power is not limited, when the power is limited, the input voltage of the master DC / AC converter is U3. The current command value sent by the master DC / AC converter to the slave DC / AC converter is I2, and the slave DC / AC converter receives the current command value of the master DC / AC converter and controls its output current to I2, and at this time the input voltage of the slave DC / AC converter is in an uncontrolled state, and U4 indicates the input voltage of the slave DC / AC converter, and U4 is smaller than U3. At this time, the master DC / DC converter controls its output voltage to V2, which is not equal to the voltage V1 corresponding to the maximum power point of the photovoltaic array, and the current of the N line is

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[0049] The above describes how the master DC / AC converter controls the slave DC / AC converter. However, during actual operation, there is a possibility that an abnormality may occur in the communication between the two. Therefore, below we will introduce the control method for special operating conditions, that is, when an abnormality occurs in the communication between the master DC / AC converter and slave DC / AC converter, or when communication is not possible.

[0050] Since a communication failure, i.e., a communication abnormality, has occurred between the master DC / AC converter and the slave DC / AC converter, the master DC / AC converter cannot transmit a current command value and its own input voltage to the slave DC / AC converter, i.e., the slave DC / AC converter cannot receive the current command value and the input voltage of the master DC / AC converter transmitted from the master DC / AC converter. Therefore, the slave DC / AC converter can only obtain the input voltage and current command value of the master DC / AC converter, and can collect, for example, the input voltage of the master DC / AC converter. In addition, the slave DC / AC converter cannot receive the current of the N line, i.e., IN The slave DC / AC converter can also collect its own input voltage, that is, the slave DC / AC converter can realize control of its own output current based on its own input voltage, the input voltage of the master DC / AC converter, and the current of the N line, that is, can obtain a current command value. That is, when the photovoltaic power generation system is not limiting the power, when the slave DC / AC converter detects an abnormality in communication with the master DC / AC converter, for example, when the input voltage of the master DC / AC converter transmitted from the master DC / AC converter is not received, the slave DC / AC converter obtains a current command value based on the input voltage of the master DC / AC converter, the current of the N line, and the input voltage of the slave DC / AC converter, and controls the current I of the N line based on the current command value. N The output current of the slave DC / AC converter is controlled so that is smaller than the preset current. In order to distinguish from the case where the communication between the master DC / AC converter and the slave DC / AC converter is normal, each parameter will be denoted differently from the parameters in the above embodiment. When the master DC / AC converter is not limiting the power, it controls the input voltage to U5, and the slave DC / AC converter controls the current I N The input voltage U5 of the master DC / AC converter can be collected, the output power of the slave DC / AC converter itself is P3, and the input voltage of the slave DC / AC converter is U6, and U6 is smaller than U5. At the same time, the slave DC / AC converter is I N Based on this, the power control command

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[0051] Next, the slave DC / AC converters are N We will introduce the procedure for obtaining the power control command based on the above. Since it is necessary for the slave DC / AC converter to follow the power of the master DC / AC converter, we will first introduce the procedure for obtaining the power of the master DC / AC converter, and it is sufficient that the power of the slave DC / AC converter and the power of the master DC / AC converter are equal.

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[0052] From the above three formulas,

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[0053] Above we introduced the control method when there is an abnormality in communication between the master DC / AC converter and the slave DC / AC converter and there is no power limit. Next we will introduce the control method when there is an abnormality in communication between the master DC / AC converter and the slave DC / AC converter and there is a power limit.

[0054] When the communication between the two inverters is abnormal, the control method of the slave DC / AC converter does not change and the current I N It should be understood that the input voltage U7 of the master DC / AC converter is collected, and the input voltage U8 of the master DC / AC converter is collected.

[0055] When the master DC / AC converter performs power limitation, for example, it limits the output power to P2 and its input voltage is U7, and the slave DC / AC converter limits the current I N The output power of the slave DC / AC converter is P4, its input voltage is U8, and U7 is smaller than U8. At the same time, the slave DC / AC converter collects the current I N Based on the output power control command

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[0056] Next, we will introduce another special situation of the photovoltaic power generation system. When low-voltage ride-through occurs in the power grid or high-voltage ride-through occurs, the inverter needs to output reactive power because the power grid needs to compensate for reactive power. For example, the master DC / AC converter outputs the first reactive power Q1, and the slave DC / AC converter outputs the second reactive power Q2. The output of reactive power does not affect the magnitude of the current on the N line, so the two inverters can arbitrarily assign the magnitude of reactive power, and Q1 may or may not be equal to Q2. For example, one inverter can bear all the reactive power, and the required reactive current magnitude can be obtained according to the reactive power that needs to be borne. One possible implementation is that the master DC / AC converter outputs reactive power, and the slave DC / AC converter does not need to output reactive power. When performing reactive compensation, the master DC / AC converter can arbitrarily assign the magnitude of reactive current that the slave DC / AC converter needs to bear.

[0057] In addition, the reactive power control by the two inverters can be applied to other operation scenarios and is not limited to the voltage ride-through scenario described above. Based on the solar power generation system provided by the above embodiments, the present application further provides a control method for a solar power generation system, which will be described in detail below in conjunction with the drawings. [Method Example]

[0058] Please refer to FIG. 3, which is a flow chart of a control method for a solar power generation system provided by an embodiment of the present application.

[0059] The control method for a photovoltaic power generation system provided by this embodiment is applied to a photovoltaic power generation system, and the photovoltaic power generation system includes a master DC / DC converter, a slave DC / DC converter, a master DC / AC converter, and a slave DC / AC converter, an input terminal of the master DC / DC converter is used to connect to a photovoltaic power generation array, a positive output terminal of the master DC / DC converter is connected to a positive input terminal of the master DC / AC converter, a negative output terminal of the master DC / DC converter is connected to an N line, a negative input terminal of the master DC / AC converter is connected to an N line, a negative input terminal of the slave DC / DC converter is connected to a negative output terminal of the master DC / DC converter, a positive input terminal of the slave DC / DC converter is connected to a positive output terminal of the master DC / DC converter, a positive output terminal of the slave DC / DC converter is connected to an N line, and a negative output terminal of the slave DC / DC converter is connected to a negative output terminal of the slave DC / AC converter. Enter The positive terminal of the slave DC / AC converter is connected to the Enter The power end is connected to the N line. The method includes the following steps. S301: The master DC / AC converter controls to transmit a current command value and an input voltage of the master DC / AC converter to the slave DC / AC converter. S302: The slave DC / AC converter controls the output current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that the current of the N line is smaller than the preset current.

[0060] Both the master DC / AC converter 201 and the slave DC / AC converter 202 are provided with controllers, and during specific operation, the controller of the master DC / AC converter 201 and the controller of the slave DC / AC converter 202 interact with each other to realize control of the slave DC / AC converter 202 by the master DC / AC converter 201, and in order to realize that the current of the N line is smaller than the preset current, the output power of the master DC / AC converter 201 and the output power of the slave DC / AC converter 202 need to be equal, and when the master DC / AC converter 201 realizes control, the output power of the slave DC / AC converter 202 can be made to track the output power of the master DC / AC converter 201. If power consumption is ignored, the output power of the master DC / AC converter 201 is equal to the input power, and the output power of the slave DC / AC converter 202 is equal to the input power; in other words, when the output power of the master DC / AC converter 201 is equal to the output power of the slave DC / AC converter 202, the input power of the master DC / AC converter 201 is equal to the input power of the slave DC / AC converter 202; therefore, by controlling the output power of the master DC / AC converter 201 to be equal to the output power of the slave DC / AC converter 202, the current of the N line can be controlled to 0.

[0061] In order to realize that the current of the N line is smaller than the preset current, the output power of the master DC / AC converter and the output power of the slave DC / AC converter must be equal, and the output power of the slave DC / AC converter tracks the output power of the master DC / AC converter. Specifically, the master DC / AC converter transmits a current command value and an input voltage of the master DC / AC converter to the slave DC / AC converter, and the slave DC / AC converter controls the output current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that the current of the N line is smaller than the preset current, and when the current of the N line is smaller than the preset current, the power consumption of the N line can be reduced.

[0062] In a specific embodiment, the control of the output current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter is specifically as follows: This includes controlling the output current to be proportional to both the input voltage and the current command value of the slave DC / AC converter and inversely proportional to the input voltage of the master DC / AC converter so that the current of the N line is smaller than a preset current.

[0063] Moreover, if the master DC / AC converter does not limit its output power, the method provided by this embodiment further includes controlling the input voltage of the master DC / AC converter to a preset value.

[0064] When the master DC / AC converter limits its output power, the method provided by this embodiment further includes collecting an input voltage of the master DC / AC converter by the master DC / AC converter and transmitting the collected input voltage of the master DC / AC converter to the slave DC / AC converter.

[0065] Specifically, when the photovoltaic power generation system does not limit the power and the slave DC / AC converter does not receive the input voltage of the master DC / AC converter transmitted from the master DC / AC converter, the output current is controlled based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that the current of the N line is smaller than the preset current. A current command value is obtained based on the input voltage of the master DC / AC converter, the current of the N line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and is used to control the output current of the slave DC / AC converter based on the current command value so that the current of the N line is smaller than a preset current.

[0066] Specifically, when the photovoltaic power generation system is limiting power and the slave DC / AC converter does not receive the input voltage of the master DC / AC converter transmitted from the master DC / AC converter, the output current is controlled so that the current of the N line is smaller than the preset current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter. The method includes obtaining a current command value based on the input voltage of the master DC / AC converter, the current of the N line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and controlling the output current of the slave DC / AC converter based on the current command value so that the current of the N line is smaller than a preset current.

[0067] It should be noted that, as used herein, the terms "comprising," "including," or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a procedure, method, product, or device that includes a set of elements includes not only those elements, but also other elements not expressly listed or that are inherent to such procedure, method, product, or device. In the absence of further limitations, an element defined by the phrase "including one" does not exclude the presence of other identical elements in the procedure, method, product, or device that includes said element.

[0068] The above description of the disclosed embodiments will enable those skilled in the art to realize or use various modifications of these embodiments according to the present application, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Thus, the present application is not limited to these embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A solar power generation system, comprising: A master DC / DC converter, a slave DC / DC converter, a master DC / AC converter, and a slave DC / AC converter, The input end of the master DC / DC converter is used to connect to a photovoltaic power generation array, the positive output end of the master DC / DC converter is connected to the positive input end of the master DC / AC converter, the negative output end of the master DC / DC converter is connected to an N line, and the negative input end of the master DC / AC converter is connected to the N line; a negative input terminal of the slave DC / DC converter is connected to a negative output terminal of the master DC / DC converter, a positive input terminal of the slave DC / DC converter is connected to a positive output terminal of the master DC / DC converter, a positive output terminal of the slave DC / DC converter is connected to the N line, a negative output terminal of the slave DC / DC converter is connected to a negative input terminal of the slave DC / AC converter, and a positive input terminal of the slave DC / AC converter is connected to the N line; The master DC / AC converter is used to transmit a current command value and an input voltage of the master DC / AC converter to a slave DC / AC converter; the slave DC / AC converter is used to control an output current based on an input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that a current of the N line becomes zero; Specifically, the slave DC / AC converter is used to control an output current in proportion to both the input voltage of the slave DC / AC converter and the current command value, and inversely proportional to the input voltage of the master DC / AC converter, so that the current of the N line becomes zero. A solar power generation system comprising:

2. The slave DC / AC converter is specifically used to control the output current to U2*I1 / U1, where U2 is the input voltage of the slave DC / AC converter, U1 is the input voltage of the master DC / AC converter, and I1 is the current command value.

2. The solar power generation system according to claim 1 .

3. When the master DC / AC converter is not limiting its output power, the input voltage of the master DC / AC converter is a preset value.

3. The solar power generation system according to claim 1 or 2.

4. When the master DC / AC converter limits its output power, the master DC / AC converter collects an input voltage of the master DC / AC converter and sends the collected input voltage of the master DC / AC converter to the slave DC / AC converter, or the slave DC / AC converter directly collects the input voltage of the master DC / AC converter.

3. The solar power generation system according to claim 1 or 2.

5. When the solar power generation system does not limit power and the slave DC / AC converter detects a communication abnormality with the master DC / AC converter, the slave DC / AC converter obtains a current command value based on the input voltage of the master DC / AC converter, the current of the N line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and is used to control the output current of the slave DC / AC converter based on the current command value so that the current of the N line becomes zero.

3. The solar power generation system according to claim 1 or 2.

6. When the solar power generation system is limiting power and the slave DC / AC converter does not receive the input voltage of the master DC / AC converter transmitted from the master DC / AC converter, the slave DC / AC converter obtains a current command value based on the input voltage of the master DC / AC converter, the current of the N-line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and is used to control the output current of the slave DC / AC converter based on the current command value so that the current of the N-line becomes zero.

3. The solar power generation system according to claim 1 or 2.

7. When a low voltage ride-through or a high voltage ride-through occurs in the solar power generation system, the master DC / AC converter is used to control the master DC / AC converter to output a first reactive power and to control the slave DC / AC converter to output a second reactive power.

3. The solar power generation system according to claim 1 or 2.

8. A method for controlling a solar power generation system, comprising: The photovoltaic power generation system includes a master DC / DC converter, a slave DC / DC converter, a master DC / AC converter, and a slave DC / AC converter, an input terminal of the master DC / DC converter is used for connecting to a photovoltaic power generation array, a positive output terminal of the master DC / DC converter is connected to a positive input terminal of the master DC / AC converter, a negative output terminal of the master DC / DC converter is connected to an N line, a negative input terminal of the master DC / AC converter is connected to the N line, a positive input terminal of the slave DC / DC converter is connected to a negative output terminal of the master DC / DC converter, a negative input terminal of the slave DC / DC converter is connected to a positive output terminal of the master DC / DC converter, a positive output terminal of the slave DC / DC converter is connected to the N line, a negative output terminal of the slave DC / DC converter is connected to a negative input terminal of the slave DC / AC converter, and a positive input terminal of the slave DC / AC converter is connected to the N line; Controlling the master DC / AC converter to transmit a current command value and an input voltage of the master DC / AC converter to the slave DC / AC converter; controlling the slave DC / AC converter to control an output current based on an input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter so that the current of the N line becomes zero; Specifically, controlling the output current based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter is controlling an output current to be proportional to both the input voltage of the slave DC / AC converter and the current command value, and inversely proportional to the input voltage of the master DC / AC converter, so that the current of the N line becomes zero; The method according to claim 1, further comprising:

9. controlling an input voltage of the master DC / AC converter to a preset value when the master DC / AC converter is not limiting its output power; The method of claim 8 further comprising:

10. When the master DC / AC converter is limiting the output power, collecting an input voltage of the master DC / AC converter by the master DC / AC converter, and transmitting the collected input voltage of the master DC / AC converter to the slave DC / AC converter; The method of claim 8 further comprising:

11. When the solar power generation system is not limiting power and the slave DC / AC converter does not receive the input voltage of the master DC / AC converter transmitted from the master DC / AC converter, Specifically, the control of the output current so that the current of the N line becomes zero based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter is as follows: a current command value is obtained based on an input voltage of the master DC / AC converter, a current of the N line, an input voltage of the slave DC / AC converter, and an output power of the slave DC / AC converter, and the current command value is used to control an output current of the slave DC / AC converter so that the current of the N line becomes zero based on the current command value; The method according to any one of claims 8 to 10, comprising:

12. the solar power generation system is limiting power and the slave DC / AC converter is not receiving the input voltage of the master DC / AC converter transmitted from the master DC / AC converter; Specifically, the control of the output current so that the current of the N line becomes zero based on the input voltage of the slave DC / AC converter, the current command value, and the input voltage of the master DC / AC converter is as follows: obtaining a current command value based on the input voltage of the master DC / AC converter, the current of the N line, the input voltage of the slave DC / AC converter, and the output power of the slave DC / AC converter, and controlling the output current of the slave DC / AC converter based on the current command value so that the current of the N line becomes zero; The method according to any one of claims 8 to 10, comprising:

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