Photovoltaic inverter start-stop control method and system

Abstract

The invention discloses a start-stop control method and system for a photovoltaic inverter. The method comprises the following steps: acquiring an input voltage Uin of the photovoltaic inverter; the input voltage Uin of the photovoltaic inverter is compared with a first preset voltage threshold value Uth1; when the input voltage Uin is not less than a first preset voltage threshold value Uth1, starting a load of the photovoltaic inverter and carrying out progressive loading; obtaining the input voltage Uin of the photovoltaic inverter again, and comparing the input voltage Uin of the photovoltaic inverter with a second preset voltage threshold value Uth2; when the input voltage Uin of the photovoltaic inverter is greater than a second preset voltage threshold Uth2, turning off a fan or a fixed load of the photovoltaic inverter, and starting the photovoltaic inverter for grid connection; wherein Uth1gt; uth1, Uth2. According to the invention, minimum-frequency weak light start-stop control can be realized, the start success rate is improved, and the generating capacity is improved.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of photovoltaic inverters, and in particular to a photovoltaic inverter start-stop control method and system. Background Art

[0002] Existing photovoltaic inverters usually use AC contactors or relays (hereinafter referred to as grid-connected switches) to achieve separation control from the power grid. These devices are mechanical action switches with limited service life, generally ranging from thousands to tens of thousands of times. In order to ensure the service life of the inverter for more than 10 years, the photovoltaic inverter must minimize the number of grid-connected switch actions and control them to one switch action each morning and evening.

[0003] In the morning, due to weak sunlight, the open-circuit voltage of the photovoltaic panels is high, but the actual output power is low. The inverter detects and judges the input voltage value as the grid-connected operation condition. After the inverter is started, due to the loss of fans, semiconductor devices, etc., the voltage of the photovoltaic panels is pulled down, the inverter enters the shutdown state, and the inverter and the grid-connected switch are repeatedly started and stopped. Frequent starting and stopping of the grid-connected switch will reduce the life of the device. At the same time, other components inside the inverter, such as cooling fans, semiconductor power devices, capacitors, etc., will also affect their long-term life and reliability.

[0004] Due to the above problems, before grid-connected operation, it is necessary to determine whether the output power of the solar panel is sufficient to support the inverter's own losses and leave a certain margin before pulling in the grid-connected switch. The conventional methods are as follows: The first is to connect a fixed load to the input side of the photovoltaic inverter. The load may use a starting resistor, power device, or inverter switch loss. When the output power of the solar panel is sufficient to support the energy consumption of the load, stabilize the input voltage, cut off the load, and pull in the grid switch. This circuit usually requires additional resistors, relays and other devices, which are more expensive, and the built-in relays also have a limited lifespan.

[0005] The second method is to form a hysteresis loop between the starting voltage and the shutdown voltage of the photovoltaic grid-connected inverter, including auxiliary judgment through time. The minimum starting voltage of the photovoltaic grid-connected inverter and the shutdown voltage during operation form a hysteresis loop to avoid frequent switching on and off. The essence of this method is to increase the startup voltage point to ensure that the solar panel has sufficient power output before starting. Although the hardware circuit is removed, it is at the expense of delayed startup time and loss of power generation. At the same time, the size of this hysteresis loop will be related to the type of solar panel and the configured power level, so the scope of use of this method is limited.

[0006] The third method is to provide auxiliary power to the inverter by connecting to the input voltage of the photovoltaic panel and the AC voltage on the grid side, so as to avoid insufficient input power and passive power failure of the control circuit, thereby controlling the start and stop time and frequency of the inverter, but the essence is to consume the grid-side power. Summary of the invention

[0007] In view of the technical problems existing in the prior art, the present invention provides a photovoltaic inverter start-stop control method and system for avoiding repeated start-stop of the photovoltaic inverter under weak light conditions.

[0008] In order to solve the above technical problems, the technical solution proposed by the present invention is: A photovoltaic inverter start-stop control method comprises the following steps: Obtaining an input voltage Uin of the photovoltaic inverter; Comparing the input voltage Uin of the photovoltaic inverter with a first preset voltage threshold Uth1; when the input voltage Uin is not less than the first preset voltage threshold Uth1, starting the load of the photovoltaic inverter; The input voltage Uin of the photovoltaic inverter is obtained again, and the input voltage Uin of the photovoltaic inverter is compared with the second preset voltage threshold Uth2; when the input voltage Uin of the photovoltaic inverter is greater than the second preset voltage threshold Uth2, the wind turbine and fixed load of the photovoltaic inverter are turned off, and the photovoltaic inverter is started and connected to the grid; wherein Uth1>Uth2.

[0009] Preferably, when starting the load of the photovoltaic inverter, the load is loaded by gradually increasing the load.

[0010] Preferably, the load is gradually increased by controlling the number and rotation speed of fans of the photovoltaic inverter; or the load is loaded by increasing a fixed load.

[0011] Preferably, when the load is gradually increased, when Uin is greater than Uth2, all loads are loaded until they are completely loaded.

[0012] Preferably, when the load is gradually increased, when Uin is less than Uth2, each load is turned off.

[0013] Preferably, when the input voltage Uin is not less than a first preset voltage threshold Uth1, the load of the photovoltaic inverter is started after a delay of a preset time t.

[0014] Preferably, when starting the load of the photovoltaic inverter, the target load is directly loaded.

[0015] The present invention also discloses a photovoltaic inverter start-stop control system, comprising: A voltage acquisition module, used to acquire an input voltage Uin of the photovoltaic inverter; A first comparison module, used for comparing the input voltage Uin of the photovoltaic inverter with a first preset voltage threshold Uth1; when the input voltage Uin is not less than the first preset voltage threshold Uth1, starting the load of the photovoltaic inverter and progressively loading; The second comparison module is used to obtain the input voltage Uin of the photovoltaic inverter again, and compare the input voltage Uin of the photovoltaic inverter with the second preset voltage threshold Uth2; when the input voltage Uin of the photovoltaic inverter is greater than the second preset voltage threshold Uth2, the wind turbine or fixed load of the photovoltaic inverter is turned off, and the photovoltaic inverter is started and connected to the grid; wherein Uth1>Uth2.

[0016] Preferably, the voltage acquisition module is a voltage sensor.

[0017] Preferably, the first comparison module and the second comparison module are both control units.

[0018] Compared with the prior art, the advantages of the present invention are: The present invention gradually loads power by utilizing the inverter's own fan and other loads, and at the same time combines the photovoltaic panel output power and voltage curve to judge the photovoltaic panel output power capacity, thereby avoiding the problem of repeated weak light start and stop of the photovoltaic inverter; realizes startup logic control by loading internal fan and other loads and detection circuits, avoids adding new circuits and devices, and has low cost; at the same time, by setting two voltage comparison points, increases power output capacity evaluation, and combines the startup delay time to achieve appropriate startup condition judgment, realize the minimum frequency of weak light start and stop control, improve startup success rate, and increase power generation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The topological structure diagram of the photovoltaic inverter of the present invention in a specific application.

[0020] Figure 2 It is a flow chart of a photovoltaic inverter startup control method in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0022] The specific application topology of photovoltaic inverters is as follows: Figure 1As shown, the input of the photovoltaic inverter is connected to the PV battery assembly, and the output is connected to the grid. The photovoltaic inverter includes an energy storage filter capacitor, a power conversion unit, a grid-connected switch, an auxiliary power supply, a control circuit, a fan or a fixed load; the PV battery assembly, the energy storage filter capacitor, the power conversion unit and the grid-connected switch are connected in sequence; the control circuit is respectively connected to the power conversion unit, the grid-connected switch, the fan or a fixed load; the auxiliary power supply is used to power the control circuit, the fan or a fixed load; and the auxiliary power supply is provided with electric energy by the energy storage filter capacitor.

[0023] like Figure 2 As shown, the photovoltaic inverter startup control method according to the embodiment of the present invention comprises the following steps: S1. As the light intensity increases, the voltage of the PV cell assembly begins to rise. After the auxiliary power input of the photovoltaic inverter is powered on, the control circuit is powered on and the input voltage is detected (the power-on of the control circuit here is not considered as the start of the inverter; the control power start and stop caused by the loss of the control circuit is not included in the inverter start and stop range); S2. When the input voltage Uin is greater than or equal to Uth1 (here Uth1 can be any value within the rated operating voltage range of the inverter, usually close to the minimum input voltage value), go to step S3; if Uin is less than Uth1, continue to perform cyclic detection; S3, set a suitable delay time. This delay time can be simply a fixed time; it can also be set according to the input voltage, time period of the day, application scenario, etc. For example, the higher the input voltage, the shorter the delay time; the delay time becomes longer in the morning and evening time periods, and the delay time is short in the noon time period; application scenarios such as long delay time on cloudy days and short delay time on sunny days; long delay time in areas with low light intensity and short delay time in areas with high light intensity. After waiting for the delay time, go to step S4; S4, gradually load and start the fan (or fixed load). The fan power is related to the speed. By controlling the speed or the number of fans started, the output load or fixed load can be gradually increased. Here, the corresponding fan (or fixed load) corresponds to the load that is converted from the power supply output by the DC battery panel side; after loading the load, enter step S5; S5. Detect the input voltage Uin to determine whether it is greater than or equal to Uth2 (Uth2 is less than Uth1, but higher than the inverter's minimum input operating voltage); if Uin is less than Uth2, shut down the fan (or fixed load) and return to step S2; if Uin is not less than Uth2, proceed to step S6; S6, determine whether the preset load has been fully loaded. The load size can refer to the minimum power loss value required for the inverter to start up; if the loading is not completed, loop to step S4 to continue to increase the load; if the loading is completed, go to step S7; S7, cancel the load. The fan or fixed load is turned off, or part of the fan load is retained according to the heat dissipation demand, and then enter step S8.

[0024] S8, the inverter starts up and connects to the grid, completing the start-up and grid-connection control.

[0025] In the above steps, the delay time link can be cancelled or changed to a fixed delay. The progressive loading of the load can also be changed to direct loading of the target load. In addition, the selection of Uth1 and Uth2 can also be adjusted as setting parameters according to the scene or conditions.

[0026] The present invention gradually loads power by utilizing the inverter's own fan and other loads, and at the same time combines the photovoltaic panel output power and voltage curve to judge the photovoltaic panel output power capacity, thereby avoiding the problem of repeated weak light start and stop of the photovoltaic inverter; realizes startup logic control by loading internal fan and other loads and detection circuits, avoids adding new circuits and devices, and has low cost; at the same time, by setting two voltage comparison points, increases power output capacity evaluation, and combines the startup delay time to achieve appropriate startup condition judgment, realize the minimum frequency of weak light start and stop control, improve startup success rate, and increase power generation.

[0027] The present invention also discloses a photovoltaic inverter start-stop control system, which is used to execute the control method as described above, and the control system includes: A voltage acquisition module, used to acquire an input voltage Uin of the photovoltaic inverter; A first comparison module, used for comparing the input voltage Uin of the photovoltaic inverter with a first preset voltage threshold Uth1; when the input voltage Uin is not less than the first preset voltage threshold Uth1, starting the load of the photovoltaic inverter and progressively loading; The second comparison module is used to obtain the input voltage Uin of the photovoltaic inverter again, and compare the input voltage Uin of the photovoltaic inverter with the second preset voltage threshold Uth2; when the input voltage Uin of the photovoltaic inverter is greater than the second preset voltage threshold Uth2, the wind turbine or fixed load of the photovoltaic inverter is turned off, and the photovoltaic inverter is started and connected to the grid; wherein Uth1>Uth2.

[0028] The voltage acquisition module is a voltage sensor; the first comparison module and the second comparison module are both control units. The control system of the present invention is used to execute the control method described above, and also has the advantages described above.

[0029] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A photovoltaic inverter start-stop control method, characterized in that: Includes steps: Obtaining an input voltage Uin of the photovoltaic inverter; Compare the input voltage Uin of the photovoltaic inverter with a first preset voltage threshold Uth1; when the input voltage Uin is not less than the first preset voltage threshold Uth1, start the load of the photovoltaic inverter and progressively load it; Acquire the input voltage Uin of the photovoltaic inverter again, and compare the input voltage Uin of the photovoltaic inverter with a second preset voltage threshold Uth2; When the input voltage Uin of the photovoltaic inverter is greater than the second preset voltage threshold Uth2, the wind turbine or fixed load of the photovoltaic inverter is turned off, and the photovoltaic inverter is started and connected to the grid; Among them, Uth1>Uth2.

2. The photovoltaic inverter start-stop control method according to claim 1, characterized in that: When starting the load of the photovoltaic inverter, the load is loaded by gradually increasing the load.

3. The photovoltaic inverter start-stop control method according to claim 2, characterized in that: The load can be gradually increased by controlling the number and speed of fans in the photovoltaic inverter; or the load can be loaded by increasing the fixed load.

4. The photovoltaic inverter start-stop control method according to claim 2 or 3, characterized in that: When the load is gradually increased, when Uin is greater than Uth2, all loads are loaded.

5. The photovoltaic inverter start-stop control method according to claim 4, characterized in that: When the load is gradually increased, when Uin is less than Uth2, each load is turned off.

6. The photovoltaic inverter start-stop control method according to claim 1, 2 or 3, characterized in that: When the input voltage Uin is not less than the first preset voltage threshold Uth1, the load of the photovoltaic inverter is started after a delay of a preset time t.

7. The photovoltaic inverter start-stop control method according to claim 1, characterized in that: When starting the load of the PV inverter, the target load is directly loaded.

8. A photovoltaic inverter start-stop control system, characterized in that: include: A voltage acquisition module, used to acquire an input voltage Uin of the photovoltaic inverter; A first comparison module, used for comparing the input voltage Uin of the photovoltaic inverter with a first preset voltage threshold Uth1; when the input voltage Uin is not less than the first preset voltage threshold Uth1, starting the load of the photovoltaic inverter and progressively loading; A second comparison module, used for obtaining the input voltage Uin of the photovoltaic inverter again, and comparing the input voltage Uin of the photovoltaic inverter with a second preset voltage threshold Uth2; When the input voltage Uin of the photovoltaic inverter is greater than the second preset voltage threshold Uth2, the wind turbine or fixed load of the photovoltaic inverter is turned off, and the photovoltaic inverter is started and connected to the grid; Among them, Uth1>Uth2.

9. The photovoltaic inverter start-stop control system according to claim 8, characterized in that: The voltage acquisition module is a voltage sensor.

10. The photovoltaic inverter start-stop control system according to claim 8 or 9, characterized in that: The first comparison module and the second comparison module are both control units.

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