An off-grid three-phase inverter, photovoltaic system and power limiting control method

Abstract

This application discloses an off-grid three-phase inverter, a photovoltaic system, and a power curtailment control method. The off-grid three-phase inverter is characterized by comprising: a three-phase inverter circuit and a controller; the three-phase inverter circuit is used to convert the input DC power into three-phase AC power output; each phase of the three-phase AC power is used to supply power to the corresponding load; the controller is used to determine whether the load power of the first phase is greater than the load capacity of the first phase, wherein the first phase is any one of the three phases; if so, the output voltage of the first phase is reduced to reduce the load power of the first phase. Since the load power of each phase depends on the power consumption of the load, the overload of each phase is determined based on the load power. When an overload occurs, the voltage of the corresponding overloaded phase is reduced. After the voltage of the overloaded phase is reduced, the load power of that phase is reduced, the entire three-phase inverter circuit operates normally, and each phase load continues to work, improving the operating efficiency of the residential inverter.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, specifically to an off-grid three-phase inverter, a photovoltaic system, and a power curtailment control method. Background Technology

[0002] With the gradual promotion of photovoltaic power generation, it is now being used in residential applications. For example, residential three-phase inverters do not need to be connected to the grid and can supply power to household loads such as lights, water heaters, air conditioners, and refrigerators offline. In this case, the three output ports L1N, L2N, and L3N of the three-phase inverter can be connected to three sets of single-phase loads respectively. When the three-phase inverter is operating offline with load, if a single-phase overload occurs (such as the AC power exceeding the inverter's carrying capacity, or the AC load power exceeding the DC input power), the following methods are generally adopted: reducing the three-phase voltage or directly disconnecting the overloaded phase. Although the two methods described above allow the inverter to continue operating, they do not effectively utilize electrical energy. Summary of the Invention

[0003] In view of this, embodiments of this application provide an off-grid three-phase inverter, a photovoltaic system, and a power curtailment control method, which can effectively utilize electrical energy when the load is overloaded, enabling the inverter to operate normally.

[0004] This application provides an off-grid three-phase inverter, including: a three-phase inverter circuit and a controller;

[0005] A three-phase inverter circuit is used to convert the input DC power into a three-phase AC power output; each phase of the three-phase AC power is used to power the corresponding load.

[0006] The controller is used to determine whether the load power of the first phase is greater than the load capacity of the first phase, where the first phase is any one of the three phases; if so, the output voltage of the first phase is reduced to reduce the load power of the first phase.

[0007] Preferably, it further includes: a sampling circuit;

[0008] The sampling circuit is used to sample the output voltage and output current of each phase of the three-phase inverter circuit.

[0009] The controller is also used to obtain the load power of each phase based on the output voltage and output current of each phase.

[0010] Preferably, the controller is also used to obtain the load power of the first phase based on the input voltage Uin, input current Iin and inverter conversion efficiency a of the three-phase inverter circuit.

[0011] Preferably, the controller is specifically used to communicate with the DC power supply to obtain the output current of the DC power supply as the input current of the three-phase inverter circuit;

[0012] The controller is specifically used to obtain the input power of the three-phase inverter circuit based on the input voltage Uin, the input current Iin, and the inverter conversion efficiency a; and to obtain the load power of the first phase based on the input power of the three-phase inverter circuit and the rated power of the first phase.

[0013] Preferably, the controller is further configured to stop the output of the first phase when the output current of the first phase exceeds a preset current value after the output voltage of the first phase decreases.

[0014] This application also provides a photovoltaic system, including the inverter described above, and further including: a photovoltaic array;

[0015] The inverter's input is connected to the photovoltaic array.

[0016] This application also provides a power limiting control method for an off-grid three-phase inverter. The three-phase inverter includes a three-phase inverter circuit and a controller. The three-phase inverter circuit is used to convert the DC power input to a three-phase AC power output. Each phase of the three-phase AC power is used to supply power to the corresponding load.

[0017] The method includes:

[0018] Determine whether the load power of the first phase is greater than the load capacity of the first phase; where the first phase can be any one of the three phases.

[0019] If so, reduce the output voltage of the first phase to reduce the load power of the first phase.

[0020] Preferably, it further includes: obtaining the load power of the first phase based on the output voltage and output current of the first phase.

[0021] Preferably, it further includes:

[0022] The load power of the first phase is obtained from the input voltage Uin, input current Iin, and inverter conversion efficiency a of the three-phase inverter circuit.

[0023] Preferably, the load power of the first phase is obtained based on the input voltage Uin, input current Iin, and inverter conversion efficiency a of the three-phase inverter circuit, specifically including:

[0024] The input power of the three-phase inverter circuit is obtained from the input voltage Uin, the input current Iin, and the inverter conversion efficiency a.

[0025] The load power of the first phase is obtained based on the input power of the three-phase inverter circuit and the rated power of the first phase.

[0026] Preferably, the method further includes: after the output voltage of the first phase decreases, if the output current of the first phase is greater than a preset current value, stopping the output of the first phase.

[0027] Therefore, the technical solution provided in this application has at least the following beneficial effects:

[0028] The system determines whether the load power of the first phase exceeds the load capacity of the first phase, where the first phase can be any one of the three phases. If so, the output voltage of the first phase is reduced to decrease its load power. Since the load power of each phase depends on the load's power consumption, it's necessary to determine if each phase is overloaded based on the load power. When an overload occurs, the system doesn't abruptly stop the power supply to that phase, nor does it simply reduce the voltage of all three phases uniformly. Instead, it reduces the voltage of the phase corresponding to the overload. Once the voltage of the overloaded phase is reduced, the load power of that phase can be decreased, allowing the entire three-phase inverter circuit to operate normally while all phases continue to operate. This technical solution can precisely control the output voltage of each phase, thereby rationalizing and maximizing the utilization of output power and improving the efficiency of residential inverters. Attached Figure Description

[0029] Figure 1 A schematic diagram of an off-grid three-phase inverter provided in an embodiment of this application;

[0030] Figure 2 A schematic diagram of load voltage fluctuation provided in an embodiment of this application;

[0031] Figure 3 A schematic diagram of a photovoltaic system provided in an embodiment of this application;

[0032] Figure 4 A flowchart illustrating a power limiting control method for an off-grid three-phase inverter provided in this application embodiment. Detailed Implementation

[0033] To enable those skilled in the art to better understand the technical solutions provided in this application, specific application scenarios will be introduced below.

[0034] The off-grid three-phase inverter provided in this application embodiment can be applied to household photovoltaic power generation, i.e., household photovoltaic power generation system, including photovoltaic array and off-grid three-phase inverter. The three-phase inverter operates off-grid and includes three-phase output. Each phase output is used to power a group of loads, such as powering lights, refrigerators, washing machines or water heaters.

[0035] When a three-phase inverter is running off-grid under load, if a single-phase overload occurs, the following two methods will not be effective in utilizing electrical energy.

[0036] The first method involves reducing the inverter's output voltage to decrease load power or triggering the inverter's off-grid protection, causing it to shut down. If each inverter is connected to 80% load, and L3N is connected to 110% load: if the voltages of L1N, L2N, and L3N are all reduced to approximately 0.9 times their original value, although L3N can operate normally, the energy utilization rates of L1N and L2N will both decrease by 8%.

[0037] The second method is to directly disconnect the output of a phase when it is overloaded. If L1N and L2N are connected to 80% load and L3N is connected to 110% load, directly disconnecting the output of L3N will ensure that L1N and L2N can carry the load, but due to the disconnection of L3N, the overall load utilization rate will also decrease by 1 / 3.

[0038] See Figure 1 The figure is a schematic diagram of an off-grid three-phase inverter provided in an embodiment of this application.

[0039] The off-grid three-phase inverter provided in this embodiment includes: a three-phase inverter circuit 100 and a controller (not shown in the figure);

[0040] A three-phase inverter circuit 100 is used to convert the input DC power into a three-phase AC power output; each phase of the three-phase AC power is used to power the corresponding load; such as Figure 1 As shown, in this embodiment, a filter circuit 200 is connected to the output terminal of the three-phase inverter circuit 100. For example, the filter circuit may include inductors and capacitors. The specific connection method is not specifically limited in this application.

[0041] The three output terminals of the filter circuit 200 are connected to three sets of loads L1N, L2N and L3N respectively.

[0042] The controller is used to determine whether the load power of the first phase is greater than the load power of the corresponding phase of the three-phase inverter circuit, where the first phase is any one of the three phases; if so, the output voltage of the first phase is reduced to reduce the load power of the first phase.

[0043] In practical applications, the operating states and parameters of each phase load are different, resulting in differences in load power among the three phases. Therefore, it is necessary to determine the difference between the load power and the carrying power of each phase. It should be understood that the three-phase carrying power of the three-phase inverter circuit is the same, and it is only necessary to compare the actual load power and the carrying power of the three-phase inverter circuit.

[0044] It should be noted that each phase load can be one electrical device or multiple electrical devices, and this application embodiment does not make specific limitations.

[0045] The load power of each phase can be obtained based on the voltage and current of each phase. For example, the inverter may include a sampling circuit for sampling the output voltage and output current of each phase of the three-phase inverter circuit.

[0046] The controller is also used to obtain the load power of each phase based on the output voltage and output current of each phase, that is, the product of the output voltage and output current of each phase is used to obtain the load power.

[0047] Since the load power of each phase depends on the power consumption of the load, it is necessary to determine whether each phase is overloaded based on the load power. When an overload occurs, the power supply to that phase is not stopped abruptly, nor is the voltage of all three phases simply reduced uniformly. Instead, the voltage of the corresponding overloaded phase is reduced. After the voltage of the overloaded phase is reduced, the load power of that phase can be reduced so that the entire three-phase inverter circuit can operate normally, and each phase load can continue to work. This maximizes the utilization of the output power of the three-phase inverter circuit and maximizes efficiency.

[0048] In practical applications, household appliances operate over a wide voltage range, such as AC voltage between 180V and 230V, and do not necessarily need to be maintained at 220V. Examples include household lights or water heaters. Therefore, the technical solution provided in this application reduces the voltage of the overload phase, allowing the load to continue operating without completely cutting off the power supply and stopping the load. This maximizes the utilization of electrical energy and improves power supply efficiency.

[0049] See Figure 2 This figure is a schematic diagram of load voltage fluctuation provided in an embodiment of this application.

[0050] For example, if an overload occurs at time t1, the control voltage U decreases. As U decreases, the current decreases, and consequently, the power decreases. After startup, the load no longer requires high power to start, so the power decreases again. At this point, the control voltage can be restored, meaning the control voltage can return to normal at time t2. The timing of t2 depends on the magnitude of the power or the magnitude of the current; the voltage can be restored by detecting the load's current or power.

[0051] The following describes the method for obtaining the load power of each phase in the inverter provided in the embodiments of this application.

[0052] It should be understood that the three phases have the same load capacity. Since the inverter's input power comes from a DC power source, such as a photovoltaic array, the output power depends on the amount of DC power that the photovoltaic array can provide. If the DC power is small, the inverter's output power will not be able to meet the load's needs.

[0053] The embodiments of this application do not specifically limit the specific form in which the inverter obtains input power. For example, the inverter can obtain input power by detecting input voltage and input current. The input power multiplied by the inverter's conversion efficiency 'a' is the inverter's output power. The output power divided by 3 is the output power of each phase of the three-phase inverter circuit, that is, the load power of each phase.

[0054] Because the inverter communicates with the photovoltaic array, the photovoltaic array can transmit current and voltage to the inverter via communication. Since the inverter's input is connected to the photovoltaic array, the voltage and current of the photovoltaic array become the inverter's input voltage and input current. It should be understood that the inverter can also detect the input voltage and input current, but this is not specifically limited here.

[0055] The following describes only one possible implementation: the controller is also used to obtain the load power of the first phase based on the input voltage Uin, input current Iin, and inverter conversion efficiency a of the three-phase inverter circuit. Specifically, it is used to communicate with the DC power supply to obtain the output current of the DC power supply as the input current of the three-phase inverter circuit.

[0056] The controller is specifically used to obtain the input power of the three-phase inverter circuit based on the input voltage Uin, the input current Iin, and the inverter conversion efficiency a; and to obtain the load power of the first phase based on the input power of the three-phase inverter circuit and the rated power of the first phase.

[0057] The controller is specifically used to obtain the load power Pd of the first phase according to the following formula;

[0058] Pd = min(Pin / 3, Pn);

[0059] Where Pin is the input power of the three-phase inverter circuit; Pin = Uin * Iin * a;

[0060] Pn is the known rated power of the first phase.

[0061] Since each phase has the same Pn and Pin, the load power of the three phases is the same.

[0062] The inverter provided in this application fully considers the input power and conversion efficiency of the inverter, accurately obtains the load power of each phase, compares the load power of each phase with the load power of each phase, and only reduces the voltage of that phase when the load power is greater than the load power. Therefore, the output voltage of each phase can be precisely controlled, thereby rationalizing and maximizing the use of output power and improving the working efficiency of the residential inverter.

[0063] In addition, the inverter provided in this application embodiment also has a protection function. The controller is further used to stop the output of the first phase when the output voltage of the first phase decreases and the output current of the first phase is greater than a preset current value. That is, when the output voltage of the first phase of the inverter decreases but the output current of the first phase is still large, it indicates that a short circuit fault has occurred and short circuit protection is required. Therefore, the output of that phase is stopped to prevent the load from burning out.

[0064] System Implementation Examples

[0065] Based on the off-grid three-phase inverter provided in the above embodiments, this application also provides a photovoltaic system, which will be described in detail below with reference to the accompanying drawings.

[0066] See Figure 3 The figure is a schematic diagram of a photovoltaic system provided in an embodiment of this application.

[0067] The photovoltaic system provided in this embodiment includes an inverter and a photovoltaic array (PV).

[0068] The input terminal of inverter 1000 is connected to the photovoltaic array PV.

[0069] The inverter 1000 includes a three-phase inverter circuit 100 and a filter circuit 200. For details, please refer to the inverter described in the above embodiments, which will not be repeated here.

[0070] The photovoltaic system provided in this application embodiment can be applied to homes, i.e., residential photovoltaic power generation scenarios. Each of the three-phase outputs of the inverter is connected to an independent load, allowing for individual determination of whether the load on each phase is overloaded. When overloaded, the voltage of that phase is reduced, thereby reducing the load power of that phase. This allows all three phases of the inverter to continue operating without stopping the output of any one phase, and the overloaded phase does not affect the normal output of other phases. Therefore, it maximizes the utilization of electrical energy, improves the inverter's operating efficiency, and ultimately improves the power generation efficiency of the entire photovoltaic system.

[0071] Method Implementation Examples

[0072] Based on the off-grid three-phase inverter and photovoltaic system provided in the above embodiments, this application also provides a power limiting control method for an off-grid three-phase inverter, which will be described in detail below with reference to the accompanying drawings.

[0073] See Figure 4 The figure is a flowchart of a power limiting control method for an off-grid three-phase inverter provided in an embodiment of this application.

[0074] This embodiment provides a power limiting control method for an off-grid three-phase inverter. The three-phase inverter includes a three-phase inverter circuit and a controller. The three-phase inverter circuit is used to convert the DC power input to a three-phase AC power output. Each phase of the three-phase AC power is used to supply power to the corresponding load.

[0075] The method includes:

[0076] S401: Determine whether the load power of the first phase is greater than the load capacity of the first phase; where the first phase is any one of the three phases; if so, execute S402.

[0077] S402: Reduce the output voltage of the first phase to reduce the load power of the first phase.

[0078] The following describes the method for obtaining the load power of each phase in the inverter provided in the embodiments of this application.

[0079] It should be understood that the three phases have the same load capacity. Since the inverter's input power comes from a DC power source, such as a photovoltaic array, the output power depends on the amount of DC power that the photovoltaic array can provide. If the DC power is small, the inverter's output power will not be able to meet the load's needs.

[0080] The embodiments of this application do not specifically limit the specific form in which the inverter obtains input power. For example, the inverter can obtain input power by detecting input voltage and input current. The input power multiplied by the inverter's conversion efficiency 'a' is the inverter's output power. The output power divided by 3 is the output power of each phase of the three-phase inverter circuit, that is, the load power of each phase.

[0081] Because the inverter communicates with the photovoltaic array, the photovoltaic array can transmit current and voltage to the inverter via communication. Since the inverter's input is connected to the photovoltaic array, the voltage and current of the photovoltaic array become the inverter's input voltage and input current. It should be understood that the inverter can also detect the input voltage and input current, but this is not specifically limited here.

[0082] The following describes only one possible implementation method, which also includes: obtaining the load power of the first phase based on the input voltage Uin, input current Iin, and inverter conversion efficiency a of the three-phase inverter circuit. Specifically, it is used to communicate with the DC power supply to obtain the output current of the DC power supply as the input current of the three-phase inverter circuit;

[0083] The load power of the first phase is obtained based on the input voltage Uin, input current Iin, and inverter conversion efficiency a of the three-phase inverter circuit. Specifically, this includes: obtaining the input power of the three-phase inverter circuit based on the input voltage Uin, input current Iin, and inverter conversion efficiency a; and obtaining the load power of the first phase based on the input power of the three-phase inverter circuit and the rated power of the first phase. Specifically, this is used to obtain the load power Pd of the first phase according to the following formula;

[0084] Pd = min(Pin / 3, Pn);

[0085] Where Pin is the input power of the three-phase inverter circuit; Pin = Uin * Iin * a;

[0086] Pn is the known rated power of the first phase.

[0087] Since each phase has the same Pn and Pin, the load power of the three phases is the same.

[0088] The control method provided in this application fully considers the input power and conversion efficiency of the inverter, accurately obtains the load power of each phase, compares the load power of each phase with the load power of each phase, and only reduces the voltage of that phase when the load power is greater than the load power. Therefore, the output voltage of each phase can be precisely controlled, thereby rationalizing and maximizing the use of output power and improving the working efficiency of the residential inverter.

[0089] In addition, the control method provided in this application embodiment also has a protection function. The controller is further used to stop the output of the first phase when the output voltage of the first phase decreases and the output current of the first phase is greater than a preset current value. That is, if the output voltage of the first phase decreases but the output current of the first phase is still large, it indicates that a short circuit fault has occurred and short circuit protection is required. Therefore, the output of the first phase is stopped to prevent the load from burning out.

[0090] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An off-grid three-phase inverter, characterized in that, include: A three-phase inverter circuit and a controller; the input terminal of the three-phase inverter circuit is connected to a photovoltaic array; The three-phase inverter circuit is used to convert the input DC power into three-phase AC power output; each phase of the three-phase AC power is used to supply power to the corresponding load. The controller is configured to obtain the load power of the first phase based on the input voltage, input current, and inverter conversion efficiency of the three-phase inverter circuit, wherein the load power of the three phases is the same; determine whether the load power of the first phase is greater than the load power of the first phase, wherein the first phase is any one of the three phases; if so, reduce the output voltage of the first phase to reduce the load power of the first phase, so that the entire three-phase inverter circuit can operate normally, each phase load can continue to work, and the output power of the three-phase inverter circuit can be maximized.

2. The inverter according to claim 1, characterized in that, Also includes: Sampling circuit; The sampling circuit is used to sample the output voltage and output current of each phase of the three-phase inverter circuit; The controller is also configured to obtain the load power of each phase based on the output voltage and output current of each phase.

3. The inverter according to claim 1, characterized in that, The controller is specifically used to communicate with the DC power supply to obtain the output current of the DC power supply as the input current of the three-phase inverter circuit; The controller is specifically used to obtain the input power of the three-phase inverter circuit based on the input voltage Uin, the input current Iin, and the inverter conversion efficiency a; and to obtain the load power of the first phase based on the input power of the three-phase inverter circuit and the rated power of the first phase.

4. The inverter according to any one of claims 1-3, characterized in that, The controller is further configured to stop the output of the first phase when the output current of the first phase exceeds a preset current value after the output voltage of the first phase decreases.

5. A photovoltaic system characterized by, The inverter, comprising any one of claims 1-4, further comprises: a photovoltaic array; The input terminal of the inverter is connected to the photovoltaic array.

6. A method of power limiting control of an off-grid three-phase inverter, characterized by, The three-phase inverter includes a three-phase inverter circuit and a controller; the input terminal of the three-phase inverter circuit is connected to a photovoltaic array; the three-phase inverter circuit is used to convert the DC power at the input terminal into three-phase AC power output; each phase of the three-phase AC power is used to supply power to the corresponding load; The method includes: The load power of the first phase is obtained based on the input voltage, input current and inverter conversion efficiency of the three-phase inverter circuit; it is then determined whether the load power of the first phase is greater than the load power of the first phase; wherein, the first phase is any one of the three phases; If so, reduce the output voltage of the first phase to reduce the load power of the first phase, so that the entire three-phase inverter circuit can operate normally, and the loads of each phase can continue to work, maximizing the utilization of the output power of the three-phase inverter circuit.

7. The control method according to claim 6, characterized by Also includes: The load power of the first phase is obtained based on the output voltage and output current of the first phase.

8. The control method according to claim 6, characterized by The load power of the first phase is obtained based on the input voltage Uin, input current Iin, and inverter conversion efficiency a of the three-phase inverter circuit, specifically including: The input power of the three-phase inverter circuit is obtained based on the input voltage Uin, the input current Iin, and the inverter conversion efficiency a. The load power of the first phase is obtained based on the input power of the three-phase inverter circuit and the rated power of the first phase.

9. The control method according to any one of claims 6 to 8, characterized in that, Also includes: When the output voltage of the first phase decreases, the output current of the first phase exceeds a preset current value, and the output of the first phase stops.

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