Grid-connected control method and system thereof, storage medium

Abstract

This application provides a grid-connected control method and system, and a storage medium, including: determining the total inverter input voltage based on the inverter input voltages at the input terminals of all inverter circuits; determining a reference voltage compensation value based on the preset maximum effective value of the grid voltage, the inverter impedance, the preset maximum duty cycle value of the inverter circuit's switching transistors, and the effective value of the grid-connected current at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle, where the inverter impedance is the sum of the equivalent impedances of all inverter circuits; determining the inverter reference voltage for the output terminal of each inverter circuit used to connect to the grid based on the reference voltage compensation value and the maximum effective value; and obtaining the target duty cycle value of the drive signal for the switching transistors of each inverter circuit based on the inverter reference voltage and the loop control process. Considering factors such as the maximum duty cycle constraint of the switching transistors and the inverter impedance voltage drop circuit, the inverter reference voltage is dynamically set to determine the target duty cycle of the switching transistors, improving the stability and reliability of the grid-connected control.

Description

Technical Field

[0001] This application relates to the field of energy storage system technology, and in particular to a grid-connected control method and system, and a storage medium. Background Technology

[0002] In existing cascaded photovoltaic grid-connected systems, the inverter's output reference voltage is typically set only based on the grid voltage. This means that in the grid-connected loop control, the reference voltage at the inverter's grid-connected port is set to a fixed value, without considering the impact of other hardware circuits on the grid connection process. This can easily lead to a situation where the inverter's DC-side input voltage cannot exceed its grid-connected output voltage. Consequently, the grid-connected port of the photovoltaic grid-connected system cannot meet the grid voltage requirements, and may even cause a short circuit in the bus capacitor, thus reducing the stability of the photovoltaic grid-connected system. Summary of the Invention

[0003] This application provides a grid-connected control method and system, as well as a storage medium. By comprehensively considering factors such as the maximum duty cycle constraint of the switching transistor and the voltage drop of the inverter impedance, the inverter reference voltage and the target duty cycle of the switching transistor of each inverter circuit are dynamically adjusted to improve the stability and reliability of the grid-connected control.

[0004] In a first aspect, embodiments of this application provide a grid-connected control method applied to an energy storage system. The energy storage system includes at least two photovoltaic grid-connected inverters connected in series. Each photovoltaic grid-connected inverter includes a photovoltaic panel and an inverter circuit whose input terminal is connected to the photovoltaic panel. The method includes: determining the total inverter input voltage based on the inverter input voltages at the input terminals of all the inverter circuits; determining a reference voltage compensation value based on a preset maximum effective value of the grid voltage, the inverter impedance, a preset maximum duty cycle value of the switching transistors of the inverter circuits, and the effective value of the grid-connected current at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle, wherein the inverter impedance is the sum of the equivalent impedances of all the inverter circuits; determining the inverter reference voltage for the output terminal of each inverter circuit used to connect to the grid based on the reference voltage compensation value and the maximum effective value; and obtaining the target duty cycle value of the drive signal of the switching transistors of each inverter circuit based on the inverter reference voltage and the loop control process.

[0005] In one or more embodiments, a reference voltage compensation value is determined based on a preset maximum effective value of the grid voltage, the inverter impedance, a preset maximum duty cycle value of the switching transistor in the inverter circuit, and the effective value of the grid-connected current at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle. This includes: determining a duty cycle difference based on a standard duty cycle and the preset maximum duty cycle value, wherein the standard duty cycle is 1; determining a first voltage value based on the duty cycle difference and the maximum effective value; determining a second voltage value based on the inverter impedance and the effective value of the grid-connected current; and determining a reference voltage compensation value based on the sum of the first voltage value and the second voltage value.

[0006] In one or more embodiments, determining the inverter reference voltage for the output terminal of each inverter circuit used for connecting to the grid, based on the reference voltage compensation value and the maximum effective value, includes: determining a total reference voltage value based on the maximum effective value and the reference voltage compensation value; and determining the inverter reference voltage for each inverter circuit based on the total reference voltage value, the total number of inverter circuits in the energy storage system, and a preset influence factor.

[0007] In one or more embodiments, determining the inverter reference voltage for each inverter circuit based on the total reference voltage value, the total number of inverter circuits in the energy storage system, and a preset influence factor includes: determining a branch reference voltage based on the ratio of the total reference voltage value to the total number of inverter circuits; determining the inverter reference voltage for each inverter circuit based on the sum of the branch reference voltage and the voltage deviation, wherein the voltage deviation is the product of the branch reference voltage and the preset influence factor; wherein the preset influence factor is a value greater than 0 and less than 1.

[0008] In one or more embodiments, determining the total reference voltage value based on the maximum effective value and the reference voltage compensation value includes: the total reference voltage value V_Ref1 is calculated as follows: V_Ref1=GridVoltRms× +V comp ; Wherein, GridVoltRms is the maximum valid value, V comp This is the reference voltage compensation value.

[0009] In one or more embodiments, obtaining the target duty cycle value of the drive signal of the switching transistor of each inverter circuit based on the inverter reference voltage and the loop control process includes: performing voltage outer loop control based on the inverter reference voltage of each inverter circuit and the inverter input voltage at the input terminal of that inverter circuit to obtain the reference current value at the output terminal of that inverter circuit; performing voltage outer loop control based on the total reference voltage value and the total inverter input voltage to obtain a reference current correction value; and obtaining the target duty cycle value based on the reference current correction value and the reference current value at the output terminal of each inverter circuit.

[0010] In one or more embodiments, obtaining the target duty cycle value based on the reference current correction value and the reference current value at the output terminal of each inverter circuit includes: obtaining the maximum value among all reference current values ​​of N inverter circuits, where N is the total number of inverter circuits; determining a target reference current value based on the reference current correction value and the maximum value; and performing current inner-loop control based on the target reference current value and the grid-connected current sampling value at the grid-connected port of the energy storage system to obtain the target duty cycle value, wherein the grid-connected current sampling value at the grid-connected port of the energy storage system is equal to the current value at the output terminal of any inverter circuit.

[0011] In one or more embodiments, determining the total inverter input voltage based on the inverter input voltage at the input terminals of all the inverter circuits includes: the total inverter input voltage being the sum of the inverter input voltages at the input terminals of all the inverter circuits.

[0012] Secondly, embodiments of this application provide a grid-connected control system, which includes an energy storage system and a processor connected to the energy storage system; the energy storage system includes at least two photovoltaic grid-connected inverters connected in series, each photovoltaic grid-connected inverter including a photovoltaic panel, an MPPT module, a bus capacitor, an inverter circuit, and a filter network connected in sequence; each filter network includes an inductor and a filter capacitor, the two ends of a first series branch formed by the inductor and the filter capacitor connected in series are connected to the port of the inverter circuit for connecting to the power grid, all the filter capacitors of all photovoltaic grid-connected inverters are connected in series to form a second series branch, and the two ends of the second series branch are respectively connected to the neutral wire terminal and the live wire terminal of the power grid; the processor is used to execute the steps of the grid-connected control method as described in any embodiment of the first aspect.

[0013] Thirdly, embodiments of this application provide a computer storage medium storing instructions or programs that, when executed by at least one processor, cause the at least one processor to perform the method described in any of the first aspects above.

[0014] Fourthly, embodiments of this application also provide a computer program product, the computer program product including a computer program stored on a computer-readable storage medium, the computer program including program instructions, which, when executed by a computer, cause the computer to perform the method described in the first aspect above.

[0015] The beneficial effects of this application are as follows: This application provides a grid-connected control method and system, and a storage medium. The method includes: determining the total inverter input voltage based on the inverter input voltages at the input terminals of all inverter circuits; determining a reference voltage compensation value based on a preset maximum effective value of the grid voltage, the inverter impedance, a preset maximum duty cycle value of the switching transistors of the inverter circuits, and the effective value of the grid-connected current at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle, wherein the inverter impedance is the sum of the equivalent impedances of all inverter circuits; determining the inverter reference voltage for the output terminal of each inverter circuit used to connect to the grid based on the reference voltage compensation value and the maximum effective value; and obtaining the target duty cycle value of the drive signal of the switching transistors of each inverter circuit based on the inverter reference voltage and the loop control process. In practical applications, this grid-connected control method considers factors such as the maximum duty cycle constraint of the switching transistors and the voltage drop of the inverter impedance circuit when determining the inverter reference voltage for each inverter circuit. This allows the inverter reference voltage to be dynamically adjusted according to the situation, which can more accurately reflect the actual output voltage requirements for driving the grid-connected current. In this way, the target duty cycle of the switching transistors that matches the current operating state of the system can be obtained, which helps to improve the stability and reliability of grid-connected control. Attached Figure Description

[0016] One or more embodiments are illustrated by way of example with reference to the accompanying drawings, which are not intended to limit the embodiments, and elements having the same reference numerals in the drawings are designated as similar elements.

[0017] Figure 1 This is a schematic diagram of the structure of an energy storage system provided in an embodiment of this application; Figure 2 This is a flowchart of a grid-connected control method provided in an embodiment of this application; Figure 3 This is a schematic diagram of a control loop for calculating a preset influence factor provided in an embodiment of this application; Figure 4 This is a schematic diagram of a control loop for calculating a reference current value provided in an embodiment of this application; Figure 5 This is a schematic diagram of a control loop for calculating a reference current correction value, provided in an embodiment of this application. Figure 6 This is a schematic diagram of a control loop for calculating the target duty cycle value provided in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] Furthermore, the technical features involved in the various embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0020] It should be noted that the steps shown in the flowcharts in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowcharts, in some cases the steps shown or described may be performed in a different order than that shown here. It should also be noted that when an element is described as "connected" to another element, it can be directly connected to the other element, or there may be one or more intervening elements between them.

[0021] To facilitate understanding of the methods provided in the embodiments of this application, the grid-connected control system provided in the embodiments of this application will first be described in detail.

[0022] The grid-connected control system provided in this application includes an energy storage system and a processor connected to the energy storage system. Please refer to... Figure 1 , Figure 1 A schematic diagram of an energy storage system according to this application is shown. The energy storage system includes at least two photovoltaic grid-connected inverters connected in series. Each photovoltaic grid-connected inverter includes a photovoltaic panel, an MPPT module, a bus capacitor, an inverter circuit, and a filter network connected in sequence. Each filter network includes an inductor and a filter capacitor. The inductor and filter capacitor are connected in series to form a first series branch, and the two ends of the first series branch are connected to a port of the inverter circuit for connecting to the power grid. All the filter capacitors of all the photovoltaic grid-connected inverters are connected in series to form a second series branch, and the two ends of the second series branch are respectively connected to the neutral wire terminal GRID_N and the live wire terminal GRID_L of the power grid.

[0023] Specifically, when an energy storage system includes N grid-connected photovoltaic inverters (N is the total number of grid-connected photovoltaic inverters, and N is an integer greater than or equal to 2), then the energy storage system contains N grid-connected photovoltaic inverters connected in series, N inductors, N filter capacitors, and N bus capacitors.

[0024] In an energy storage system, N photovoltaic (PV) panels are designated as 111, 112, ..., 11N. A photovoltaic panel is a photovoltaic module that uses the photovoltaic effect to convert solar energy into direct current (DC) electricity. Its output voltage and output power dynamically change with factors such as light intensity and ambient temperature, and it is the basic energy input unit of the energy storage system.

[0025] In the energy storage system, the N MPPT modules are designated as 121, 122, ..., 12N. The MPPT module, or Maximum Power Point Tracking module, is used to track the maximum power point of the corresponding connected photovoltaic panel in real time based on its output voltage and current. By adjusting the operating state of its internal switching transistors, it ensures that the photovoltaic panel continuously operates at its maximum power output under the current conditions, thereby improving the energy utilization rate of each photovoltaic panel.

[0026] In the energy storage system, N inverter circuits are designated as 131, 132, ..., 13N. An inverter circuit is a circuit unit that converts the DC power output from a corresponding connected MPPT module into AC power. Each inverter circuit includes multiple power switching transistors, and its specific structure can be referenced from existing technologies and is not limited here. In the energy storage system, the DC-side input terminals of the N inverter circuits are INVin1, INVin2, ..., INVinN, and the AC-side output terminals are INVout1, INVout2, ..., INVoutN. The DC-side input terminals of the inverter circuits are connected to the output terminals of the MPPT modules, receiving the DC bus voltage as input. By controlling the on / off state of the internal switching transistors, the inverter circuits convert the DC-side voltage into an AC output voltage that meets the grid requirements, and then output it to the subsequent filter network via the AC-side output terminals of the inverter circuits to feed power to the grid.

[0027] The power grid is an external AC power network for power exchange between the grid-connected control system and the grid. In this embodiment, the power grid can be mains power, with two access ports: a live wire terminal (GRID_L) and a neutral wire terminal (GRID_N). Its rated voltage and frequency conform to the power standards of the region. The output terminals (i.e., the output terminals of the inverter circuits) of the N series-connected photovoltaic grid-connected inverters are connected to the live wire terminal (GRID_L) and the neutral wire terminal (GRID_N) of the power grid after passing through various filter networks, thus feeding the AC power generated by photovoltaic power generation into the grid.

[0028] An N-channel series-connected photovoltaic grid-connected inverter refers to an inverter circuit whose output terminals are connected end-to-end in a series cascade structure. Since the AC output voltages of each inverter circuit are superimposed sequentially, the total AC voltage required for grid connection is shared by the output voltages of all inverter circuits. Therefore, each inverter circuit only needs to output a lower AC voltage to meet the overall grid connection requirements, reducing the voltage stress on a single inverter circuit and helping to improve the system's reliability and flexibility.

[0029] In the energy storage system, there are N inductors, L1, L2, ..., LN, and N filter capacitors, C1, C2, ..., CN. Each inductor and each filter capacitor forms a filter network. Each filter network filters the AC voltage output from the inverter circuit, suppresses high-frequency switching harmonics, and improves the quality of the grid-connected current waveform.

[0030] In an energy storage system, N bus capacitors, designated Cbus1, Cbus2, ..., CbusN, are connected in the same photovoltaic grid-connected inverter. Each bus capacitor connects the output of the MPPT module to the input of the inverter circuit. The bus capacitors are used to stabilize the DC bus voltage, smooth power fluctuations between the MPPT module output and the inverter circuit input, and ensure the stability of the DC side voltage of the inverter circuit.

[0031] This application adopts a photovoltaic grid-connected inverter architecture with at least two series connections. Each photovoltaic grid-connected inverter can connect to one photovoltaic panel. The maximum power point tracking control of the connected photovoltaic panel is performed independently by each MPPT module, which helps to reduce the mutual constraints between panels in the traditional multi-panel series scheme, so that the power generation capacity of each photovoltaic panel can be fully utilized, thereby improving the overall photovoltaic power generation efficiency and user benefits to a certain extent.

[0032] The processor is connected to the energy storage system. In this embodiment, the processor is used to execute the steps of the grid-connected control method described in any embodiment of this application. The processor is used to provide computing and control capabilities to support the grid-connected control system in executing corresponding business logic, such as supporting the grid-connected control system in executing the methods provided in the embodiments of this application, or executing the steps in any possible implementation of the methods provided in the embodiments of this application. Those skilled in the art will understand that the processor can be a general-purpose processor, including a central processing unit (CPU), a network processor (NP), etc.; it can also be a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, or discrete hardware components.

[0033] In photovoltaic (PV) power generation systems, traditional string PV grid-connected inverters require multiple PV panels to be connected in series to meet the DC input voltage requirements for grid-connected control. For example, the PV input voltage often needs to be greater than 100V, which requires connecting three or more PV panels in series. However, connecting multiple panels in series cannot fully utilize the power generation capacity of a single panel, reducing PV power generation efficiency and affecting user income. In the grid-connected control system provided in this application, the inverter circuit is connected in series for output. Each PV grid-connected inverter is allowed to connect at least one PV panel. A PV panel refers to a single PV module used as an independent power generation unit, with an independent DC output port. The DC power output from the PV panel is processed by the MPPT module for maximum power point tracking before being output to the inverter circuit for DC-AC conversion. This enables independent control and independent power generation for each PV panel, reducing the mutual constraints between panels in traditional PV panel series output schemes and improving PV power generation efficiency. Furthermore, in practical applications, during the determination of the inverter reference voltage for each inverter circuit, the processor considers factors such as the maximum duty cycle constraint of the switching transistors and the inverter impedance voltage drop circuit to participate in the determination process of the inverter reference voltage for each inverter circuit. This allows the inverter reference voltage to be dynamically adjusted according to the adaptation situation, which can more accurately reflect the actual output voltage requirements required to drive the grid-connected current. In this way, the target duty cycle of the switching transistors that matches the current operating state of the system can be obtained, which helps to improve the stability and reliability of grid-connected control.

[0034] As can be understood from the above, the implementing entity of any method provided in the embodiments of this application can be any suitable type of device with certain computing and control capabilities, such as the processor described above. In some feasible implementations, any method provided in the embodiments of this application can be implemented by the processor executing computer program instructions stored in the memory. The memory, as a non-transitory computer-readable storage medium, can be used to store non-transitory software programs, non-transitory computer-executable programs, instructions, and modules, such as the programs, instructions, and modules corresponding to the methods in the embodiments of this application. In some embodiments, the memory may include a program storage area and a data storage area. The program storage area may store the operating system, at least one application program required for a function, and the data storage area may store data created according to the processor's use. The processor executes various functional applications and data processing by running the non-transitory software programs, instructions, and modules stored in the memory to implement the methods provided in the embodiments of this application, or to execute the steps in any possible implementation of the methods provided in the embodiments of this application. In some embodiments of this application, the memory may include high-speed random access memory, and may also include non-transitory memory. For example, at least one disk storage device, flash memory device, or other non-transitory solid-state storage device. In some embodiments, the memory may further include memory remotely configured relative to the processor, which is connected to the processor via a communication network. It is understood that examples of such communication networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0035] The following will describe in detail the grid-connected control method provided in this application embodiment, using the exemplary application and implementation of the processor provided in the embodiments of this application. This method is applied to the above-mentioned energy storage system. Specifically, the executing entity of this method is the processor in the grid-connected control system. (Refer to reference...) Figure 1 and Figure 2 The grid connection control method includes, but is not limited to, the following steps S100 to S400.

[0036] Step S100: Determine the total inverter input voltage based on the inverter input voltages at the input terminals of all inverter circuits.

[0037] See Figure 1 The inverter input voltages are Vinv in1 Vinv in2 Vinv inNInverter input voltage refers to the DC voltage at the input terminal of the inverter circuit, i.e., the voltage across the bus capacitor. Since the MPPT module of each photovoltaic grid-connected inverter independently performs maximum power point tracking control on the connected photovoltaic panels, the operating point voltage of different photovoltaic panels may differ. Therefore, the inverter input voltage (Vinv) of each inverter circuit is... in1 Vinv in2 Vinv inN The values ​​may not be the same, therefore it is necessary to adjust the input voltages of each inverter (Vinv, etc.). in1 Vinv in2 Vinv inN The data is collected separately. Specifically, voltage acquisition circuits can be set at the input terminals of each inverter circuit (INVin1, INVin2, ..., INVinN) or across the bus capacitors (Cbus1, Cbus2, ..., CbusN). The processor obtains the inverter input voltage (VinV) of each inverter circuit through each voltage acquisition circuit. in1 Vinv in2 Vinv inN ).

[0038] The total inverter input voltage (SumBUS) refers to the total inverter input voltage (VinV) of all inverter circuits in an N-channel series-connected photovoltaic grid-connected inverter. in1 Vinv in2 Vinv inN The sum of these values ​​represents the total voltage capacity that the entire grid-connected control system can provide under the current operating conditions.

[0039] The processor collects the inverter input voltage (Vinv) at the input terminals of each of the N inverter circuits. in1 Vinv in2 Vinv inN ), and for all inverter input voltages (respectively Vinv) in1 Vinv in2 Vinv inNThe total inverter input voltage, SumBUS, is calculated. In a grid-connected control system, the AC output voltage of each inverter circuit is obtained by modulating its inverter input voltage with switching transistors. With N inverter circuits connected in series, the upper limit of the voltage output from the AC side of the grid-connected control system is determined by the total inverter input voltage, SumBUS. Therefore, the subsequent setting of the inverter reference voltage, V_Ref, must be constrained by the total inverter input voltage, SumBUS, to ensure that the inverter circuit does not exceed the voltage range supported by the DC side during modulation. This reduces the risk of overmodulation caused by an excessively high inverter reference voltage, V_Ref, leading to the switching transistor duty cycle exceeding the feasible region, and also reduces grid current waveform distortion and even system instability.

[0040] Specifically, the inverter input total voltage SumBUS can be calculated using the following formula: ; in, Let be the inverter input voltage at the input terminal of the y-th inverter circuit.

[0041] In this embodiment, the total inverter input voltage SumBUS is calculated using a summation method. The computational structure is simple and clear, and the processor can quickly complete the calculation based on the real-time acquired inverter input voltages in each control cycle. This results in a low computational burden and facilitates efficient implementation on an embedded control platform.

[0042] Step S200: Based on the preset maximum effective value of the grid voltage, the inverter impedance, the preset maximum duty cycle value of the switching transistor of the inverter circuit, and the effective value of the grid-connected current at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle, determine the reference voltage compensation value. The inverter impedance is the sum of the equivalent impedances of all inverter circuits.

[0043] The preset maximum effective value of the grid voltage, GridVoltRms, refers to the maximum preset value of the effective AC voltage of the grid connected to the grid during the actual operation of the grid-connected control system. The grid voltage may vary within a certain range due to differences in regional power supply standards or grid fluctuations. Using the maximum expected value of the grid voltage as the design benchmark helps to ensure that the grid-connected control system can still operate stably when the grid voltage is high, reducing the risk of insufficient inverter modulation margin due to high grid voltage.

[0044] Inverter impedance R refers to the sum of the equivalent impedances of all inverter circuits in the entire grid-connected control system. Equivalent impedance is the impedance parameter obtained by summing the equivalent resistive parameters corresponding to various voltage drop causes during the grid-connected output process of the inverter circuit. It is used to quantitatively characterize the comprehensive resistive characteristics of the inverter circuit output. The aforementioned voltage drops include the on-state voltage drop of the power switches in the inverter circuit, the resistive voltage drop of the cables, etc. By summing the equivalent resistive parameters corresponding to various voltage drops and characterizing them in a unified equivalent impedance form, the comprehensive resistive voltage drop of the inverter circuit can be quantitatively described.

[0045] The preset maximum duty cycle value, Max_Duty, refers to the upper limit of the duty cycle allowed for the power switching transistors in the inverter circuit during operation according to the Pulse Width Modulation (PWM) signal. This upper limit is determined by the system hardware characteristics and modulation strategy. The duty cycle reflects the proportion of the switching transistor's on-time within a switching cycle, and its upper limit constraint determines the maximum AC voltage amplitude that the inverter circuit can output under a given DC bus voltage condition. The preset maximum duty cycle value, Max_Duty, is used as a constraint to determine the reference voltage compensation value V. comp This can reduce the risk of output voltage waveform distortion and grid current quality degradation caused by overmodulation due to excessively high inverter reference voltage V_Ref setting, which leads to the corresponding duty cycle exceeding the preset maximum duty cycle value Max_Duty.

[0046] RMS value of grid-connected current I RMS RMS current refers to the root mean square value of the grid-connected current output at the grid-connected port of the photovoltaic grid-connected inverter within one power frequency cycle, reflecting the current level fed into the grid by the grid-connected control system under the current operating state. RMS grid-connected current I RMS The acquisition method is as follows: The grid-connected current is sampled at preset current sampling points to obtain the grid-connected current sample value (instantaneous current value) I1. Then, the root mean square value is calculated for the sampling sequence within a complete power frequency cycle, thus obtaining the effective value I of the grid-connected current for the current power frequency cycle. RMS The processor measures the effective value of the grid-connected current I in units of the power frequency cycle. RMS Periodic updates are performed. Since the output terminals of each inverter circuit in the grid-connected control system are connected in series, the current at the output terminals of each inverter circuit is equal. Therefore, sampling the current at the output terminal of any inverter circuit can yield the instantaneous current value. In one specific implementation, see [reference needed]. Figure 1 A current sampling circuit can be configured at the output terminal INVout1 of the inverter circuit 131. The processor obtains the grid-connected current sampling value (instantaneous current value) I1 through this current sampling circuit, and calculates the effective value I of the grid-connected current in the current power frequency cycle based on it. RMS .

[0047] The preset maximum effective value of the grid voltage GridVoltRms, inverter impedance R, and preset maximum duty cycle value Max_Duty of the switching transistor can be configured by technicians according to actual engineering needs during the system initialization phase and pre-stored in memory for the processor to call during operation; alternatively, they can be set by the user through the human-machine interface during the system deployment phase. The effective value of the grid-connected current I within the current power frequency cycle... RMS The processor dynamically calculates and obtains the current based on the real-time collected grid-connected current data within each power frequency cycle. The processor acquires the preset maximum effective value of the grid voltage (GridVoltRms), the inverter impedance (R), the preset maximum duty cycle value (Max_Duty) of the switching transistor, and the effective value of the grid-connected current (I). RMS The reference voltage compensation value V is determined according to the preset calculation rules. comp Reference voltage compensation value V comp It refers to the voltage correction introduced to compensate for the voltage drop caused by the inverter impedance R and the upper limit constraint of the duty cycle of the switching transistor when determining the inverter reference voltage V_Ref.

[0048] Step S300: Based on the reference voltage compensation value and the maximum effective value, determine the inverter reference voltage for the output terminal of each inverter circuit used to connect to the power grid.

[0049] The inverter reference voltage V_Ref refers to the target output voltage value set by the processor for the output terminal of each inverter circuit. The processor will then adjust the reference voltage compensation value V_Ref. comp The inverter reference voltage V_Ref at the AC output of each inverter circuit is calculated by combining it with the maximum effective value of the grid voltage, GridVoltRms. A reference voltage compensation value V is then introduced. comp The inverter reference voltage V_Ref is calculated by introducing a reference voltage compensation value V_Ref, compared to the existing technology that only sets the maximum effective value of the grid voltage GridVoltRms as the inverter reference voltage V_Ref. comp By comprehensively correcting the inverter reference voltage V_Ref, taking into account factors such as the maximum duty cycle constraint of the switching transistor and the voltage drop across the inverter impedance R, the inverter reference voltage V_Ref is calculated. This helps the inverter reference voltage V_Ref to be closer to the actual operating requirements of the system, thereby reducing the risk of overmodulation caused by insufficient voltage margin and improving the stability and reliability of grid-connected control to a certain extent.

[0050] Step S400: Based on the inverter reference voltage and loop control process, obtain the target duty cycle value of the drive signal of the switching transistor of each inverter circuit.

[0051] The target duty cycle is the ratio of the on-time of the power switch in each inverter circuit to the switching cycle in each switching cycle, calculated by the processor through the loop control process by integrating the inverter reference voltage V_Ref of each inverter circuit and real-time feedback information. Its magnitude affects the AC output voltage amplitude of the inverter circuit in the current switching cycle.

[0052] The loop control process refers to the closed-loop adjustment process in which the processor uses the inverter reference voltage V_Ref as the control target, iteratively calculates according to a preset control algorithm (such as proportional-integral control), and outputs the duty cycle of the switch drive signal.

[0053] Specifically, the processor uses the inverter reference voltage V_Ref as the control benchmark, and combines it with the output voltage and other information of each inverter circuit collected in real time. Through the loop control process, it calculates the target duty cycle value of the switching transistor drive signal of each inverter circuit, and outputs it to each inverter circuit, so that the corresponding switching transistor performs switching action according to the target duty cycle value, thereby realizing grid-connected control.

[0054] In existing cascaded photovoltaic grid-connected systems, the grid voltage is typically used as the basis for setting the inverter reference voltage V_Ref, without fully considering the voltage drop caused by the system's equivalent impedance and the upper limit constraint of the switching transistor's duty cycle. When the grid voltage fluctuates or the system output current is large, if the inverter reference voltage V_Ref is set too low, the inverter circuit will face the problem of insufficient modulation margin, which will lead to overmodulation, resulting in distortion of the grid-connected current waveform or even system instability and grid disconnection.

[0055] In practical applications, the grid-connected control method provided in this application dynamically sets the reference voltage compensation value V by considering factors such as the maximum duty cycle constraint of the switching transistors and the voltage drop of the inverter impedance R circuit during the determination of the inverter reference voltage for each inverter circuit. comp Furthermore, the inverter reference voltage V_Ref is modified to dynamically adjust according to the situation, making its setting closer to the actual operating requirements of the system. This provides a more reasonable control benchmark for subsequent loop control, helps reduce the risk of overmodulation, and improves the quality of the grid-connected current waveform. In addition, by setting the inverter reference voltage V_Ref with the total inverter input voltage SumBUS as the upper limit constraint, and generating the target duty cycle value for each switch accordingly, each inverter circuit can maintain a relatively stable DC bus voltage while working collaboratively. This helps improve the overall stability and reliability of the grid-connected control system under complex operating conditions.

[0056] In some embodiments, the maximum effective value of the grid voltage GridVoltRms, the inverter impedance R, the maximum effective duty cycle value Max_Duty of the inverter circuit's switching transistors, and the effective value of the grid-connected current I at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle are used as the basis. RMS Determine the reference voltage compensation value V comp This includes, but is not limited to, the following steps S210 to S240.

[0057] Step S210: Determine the duty cycle difference based on the standard duty cycle and the preset maximum duty cycle value Max_Duty. The standard duty cycle is 1.

[0058] The standard duty cycle refers to the theoretical upper limit of the duty cycle of a switching transistor under ideal modulation conditions, that is, the duty cycle value corresponding to the transistor being fully turned on throughout a complete switching cycle, which is 1. In practical engineering applications, due to the limitations of the switching characteristics of the transistor itself, the dead time setting, and system reliability requirements, the actual duty cycle of the transistor cannot reach the theoretical upper limit. Therefore, a preset maximum duty cycle value Max_Duty needs to be set as the allowable upper limit of the duty cycle to ensure the safe and stable operation of the system.

[0059] The duty cycle difference is the difference between the standard duty cycle and the preset maximum duty cycle value, Max_Duty. It is calculated by subtracting the preset maximum duty cycle value, Max_Duty, from the standard duty cycle. This difference quantitatively reflects the degree of modulation capability loss in the grid-connected control system caused by duty cycle constraints, characterizing the output voltage capability loss of the inverter circuit under actual modulation conditions compared to the ideal situation. A larger duty cycle difference indicates a greater deviation between the actual usable modulation range and the ideal state, a more significant loss of output voltage capability due to duty cycle constraints, and a correspondingly larger amount of voltage compensation required.

[0060] In some embodiments, a first voltage value is determined based on the duty cycle difference and the maximum effective value GridVoltRms, including calculating the first voltage value using the following formula: V1=(1-Max_Duty)×(GridVoltRms× ); Where V1 is the first voltage value, (1-Max_Duty) is the duty cycle difference, and GridVoltRms is the maximum effective value.

[0061] This embodiment compares the duty cycle difference (1-Max_Duty) with the peak grid voltage (GridVoltRms×). The product of the voltage and voltage values ​​is used to quantitatively calculate the output voltage loss of the inverter circuit caused by the duty cycle constraint of the switching transistor, i.e., the first voltage value V1. This provides a clear mathematical relationship to quantitatively characterize the modulation voltage loss introduced by the upper limit constraint of the switching transistor's duty cycle. Compared with the existing technology that relies on engineering experience for fixed voltage margin compensation, the calculation method in this embodiment can accurately reflect the actual correspondence between the duty cycle constraint, the peak grid voltage, and the first voltage value. This provides a reliable quantitative basis for the reasonable setting of the subsequent inverter reference voltage V_Ref, effectively reducing the risk of overmodulation caused by insufficient compensation estimation, which in turn leads to grid current waveform distortion and even system instability. Moreover, the calculation of the first voltage value V1 can be directly related to the actual grid voltage standard. When the system is applied to power networks in different regions and with different rated voltages, the processor can automatically calculate the corresponding first voltage value based on the preset local grid voltage maximum effective value GridVoltRms, without having to modify the compensation logic for different grid standards. This helps to improve the universality and applicability of the grid-connected control method to different application scenarios. Furthermore, this embodiment employs a multiplication operation to construct the calculation formula for the first voltage value, resulting in a simple operational structure and minimal computational resource consumption by the processor. Within each power frequency cycle, the processor can quickly complete the calculation of the first voltage value based on pre-stored fixed parameters, helping to reduce the real-time computational burden on the control algorithm.

[0062] Step S220: Determine the first voltage value based on the duty cycle difference and the maximum effective value GridVoltRms.

[0063] The first voltage value quantifies the amount of additional voltage compensation required between the inverter reference voltage V_Ref and the grid voltage due to the upper limit constraint of the switching transistor's duty cycle. Since the preset maximum duty cycle value Max_Duty is less than the standard duty cycle of 1, if the inverter reference voltage V_Ref is still set to the grid voltage, the actual maximum peak voltage output by the inverter circuit will be lower than the peak grid voltage, failing to meet the grid connection voltage requirements. Therefore, the inverter reference voltage V_Ref needs to be additionally compensated with a first voltage value based on the grid voltage to compensate for the modulation voltage loss caused by the duty cycle constraint. This additional compensation first voltage value can be calculated using the duty cycle difference and the maximum effective value GridVoltRms.

[0064] In some embodiments, the inverter impedance R and the effective value of the grid-connected current I are used as the basis. RMS The second voltage value is determined by calculating it using the following formula: V2=R×(I RMS × ); Where V2 is the second voltage value, R is the inverter impedance R, and I RMS The effective value of the grid-connected current I RMS.

[0065] When calculating the second voltage value, I is used in the formula. RMS × The effective value of the grid-connected current I RMS The peak value of the grid-connected current is converted into the corresponding peak value and multiplied by the inverter impedance R. The comprehensive resistive voltage drop generated by the equivalent impedance of the system under the current grid-connected current is quantitatively calculated, which is the second voltage value V2. The inverter reference voltage V_Ref needs to be compensated for this value on the basis of the corresponding reference to ensure that the inverter circuit can output an effective voltage that meets the requirements to the grid side.

[0066] It is worth noting that the resistive voltage drop increases with the increase of the grid-connected current. Under operating conditions with a large grid-connected current, if the voltage drop caused by the inverter impedance R is not compensated, the effective voltage actually applied to the grid side by the inverter circuit will be lower than the set value, affecting the stable control of the grid-connected current. Therefore, in each power frequency cycle, the processor dynamically calculates the effective value of the grid-connected current I based on the inverter impedance R pre-stored in memory and the current power frequency cycle's effective value. RMS The second voltage value V2 under the current operating state is calculated in real time according to the above formula and then transmitted to the reference voltage compensation value V. comp In subsequent calculations, it is used to comprehensively determine the inverter reference voltage V_Ref.

[0067] This embodiment calculates the second voltage value V2 using the above formula. Compared to existing technologies that ignore resistive voltage drop or rely on fixed empirical values ​​for compensation, this embodiment is based on the inverter impedance R and the effective value of the grid current I. RMS A direct voltage drop calculation model is established to reflect the actual resistive voltage drop of the system under different currents, providing reliable quantitative support for the reasonable setting of the inverter reference voltage V_Ref. This helps ensure that the inverter circuit can output an effective voltage to the grid side that meets the requirements under various operating conditions, reducing the risk of grid-connected current waveform distortion or even system instability caused by insufficient resistive voltage drop compensation. Furthermore, the formula incorporates the dynamically updated effective value I of the grid-connected current within the power frequency cycle. RMS As a calculation parameter, the second voltage value V2 can be adaptively adjusted according to changes in the actual operating current of the system. Under operating conditions with a large grid-connected current, the system resistive voltage drop increases accordingly, and the processor can adjust the voltage based on the effective value I of the grid-connected current in the current cycle. RMSThe system automatically calculates a larger second voltage value, thus reserving more sufficient resistive voltage drop compensation in the inverter reference voltage V_Ref. When the grid-connected current is small, the second voltage value decreases accordingly, avoiding unnecessary waste of voltage margin due to excessive compensation setting. This compensation mechanism, which dynamically changes with operating conditions, helps to achieve reasonable setting of the inverter reference voltage V_Ref under a wide range of current conditions, balancing grid-connected control stability and operational economy to a certain extent. Moreover, this embodiment uses a simple multiplication operation to construct the calculation formula for the second voltage value, which has low requirements for processor computing resources. Within each power frequency cycle, the processor can calculate the second voltage value based on the pre-stored inverter impedance R and the real-time updated effective value of the grid-connected current I. RMS The ability to quickly calculate the second voltage value helps reduce the overall real-time calculation burden of the grid-connected control algorithm.

[0068] Step S230: Determine the second voltage value based on the inverter impedance and the effective value of the grid current.

[0069] The second voltage value is used to quantify the combined resistive voltage drop generated by the system's equivalent impedance during grid-connected output of the inverter circuit. In actual grid-connected operation, when the output current of the inverter circuit flows through each equivalent impedance, a certain resistive voltage drop will be generated. This voltage drop increases with the increase of the grid-connected current, causing the effective voltage that the inverter circuit can actually apply to the grid side to be lower than its output voltage. Based on the inverter impedance R and the effective value of the grid-connected current I... RMS Calculations can be performed to obtain the comprehensive resistive voltage drop caused by the equivalent impedance under the current operating condition, i.e., the second voltage value. This second voltage value is then incorporated into the reference voltage compensation value V. comp The calculation helps to reserve sufficient resistive voltage drop margin in the setting of inverter reference voltage V_Ref, thereby ensuring that the inverter circuit can output the required effective voltage to the grid side under different load current conditions.

[0070] Step S240: Determine the reference voltage compensation value V based on the sum of the first voltage value and the second voltage value. comp .

[0071] In this embodiment, the reference voltage compensation value V comp The reference voltage compensation value V is obtained by adding the first voltage value and the second voltage value, taking into account both the voltage drop caused by the duty cycle constraint and the resistive voltage drop generated by the inverter impedance R. The first voltage value reflects the voltage margin required by the system under the condition of limited modulation capability, and the second voltage value reflects the amount of voltage compensation required by the system due to the resistive voltage drop under the current grid current. comp It can comprehensively characterize the total amount of additional voltage compensation required by the inverter circuit under actual operating conditions compared to the ideal situation, and provide a quantitative basis for the reasonable setting of the inverter reference voltage V_Ref.

[0072] In this embodiment, the voltage drop generated by the duty cycle constraint and the inverter impedance R is analyzed and quantified, and used to calculate the reference voltage compensation value V. comp Compared to setting a fixed compensation amount based solely on experience, this embodiment uses a reference voltage compensation value V. comp It can dynamically adjust according to the actual operating conditions, so that the setting of the inverter reference voltage V_Ref can accurately reflect the actual grid connection requirements of the system under different operating conditions, reducing the risk of overmodulation caused by insufficient compensation setting, and also helping to avoid unnecessary waste of voltage margin caused by excessive compensation setting. To a certain extent, it takes into account both the stability of grid connection control and the economy of actual operation.

[0073] In some embodiments, for step S300, based on the reference voltage compensation value V comp And the maximum effective value GridVoltRms, determine the inverter reference voltage V_Ref for the output terminal of each inverter circuit used to connect to the power grid, including but not limited to the following steps S310 to S320.

[0074] Step S310: Determine the total reference voltage value based on the maximum effective value and the reference voltage compensation value.

[0075] The total reference voltage value V_Ref1 refers to the minimum lower limit voltage that the sum of the output voltages of all inverter circuits in the entire grid-connected control system needs to reach under the current operating conditions.

[0076] Specifically, the processor calculates the total reference voltage value V_Ref1 using the following formula: V_Ref1=GridVoltRms× +V comp ; Where GridVoltRms is the maximum valid value, V comp V_Ref1 is the reference voltage compensation value, and V_Ref1 is the total reference voltage value.

[0077] In the above calculation, the peak value corresponding to the maximum effective value of the grid voltage, GridVoltRms (GridVoltRms × ... Using this as a benchmark helps the grid-connected control system maintain a relatively sufficient output capacity to a certain extent when the grid voltage experiences upper limit fluctuations; and when the grid voltage peak is superimposed with the reference voltage compensation value V compThe total reference voltage value V_Ref1 is calculated by combining the voltage loss caused by the duty cycle constraint and the resistive voltage drop generated by the inverter impedance R. This allows the total reference voltage value V_Ref1 to be closer to the total AC output voltage target required for the actual grid connection of the system, providing a more reliable calculation basis for the reasonable allocation of the reference voltage V_Ref of each inverter in the future.

[0078] Step S320: Determine the inverter reference voltage for each inverter circuit based on the total reference voltage value, the total number of inverter circuits in the energy storage system, and the preset influence factor.

[0079] The total number N refers to the total number of inverter circuits operating in series in the energy storage system. Since the AC output terminals of each inverter circuit are connected in series sequentially, the total output voltage of the grid-connected control system is shared by the combined output voltages of all inverter circuits. Therefore, under ideal uniform distribution, the ideal target output voltage that each inverter circuit should share is the total reference voltage value V_Ref1 divided by the total number of inverter circuits N, i.e., V_Ref1 / N. However, in the actual operation of the grid-connected control system, due to factors such as differences in panel configuration, uneven light intensity distribution, and temperature conditions among the photovoltaic panels, the inverter input voltage (Vinv) of each inverter circuit varies. in1 Vinv in2 Vinv inN Numerical differences may exist; furthermore, the dynamic response characteristics during subsequent current loop control may also affect the inverter input voltage (Vinv) of one or more inverter circuits. in1 Vinv in2 Vinv inN It is difficult to track and achieve the ideal target output voltage V_Ref1 / N in a timely manner, which cannot meet the grid-connected power supply requirements.

[0080] To address the aforementioned issues, this embodiment utilizes a preset influence factor x to correct the inverter reference voltage V_Ref of each inverter circuit, reserving a certain voltage margin for each inverter circuit. Here, the preset influence factor x is used to characterize the inverter input voltage of each inverter circuit (Vinv...). in1 Vinv in2 Vinv inN This is a dynamic correction coefficient for the deviation between the inverter input voltage (SumBUS) and the ideal target output voltage. Introducing a preset influence factor x helps reduce the risk of insufficient output capability of individual inverter circuits affecting the overall grid-connected power supply performance of the system; the preset influence factor is a value greater than 0 and less than 1. Specifically, the preset influence factor x can be dynamically generated based on the real-time deviation between the total inverter input voltage (SumBUS) and the total reference voltage value (V_Ref1). See [link to relevant documentation]. Figure 3As shown, the difference between the total inverter input voltage SumBUS and the total reference voltage V_Ref1 is calculated. The difference is then limited by the first limiter 211, and the result is input to the first PI controller 212 for calculation. The second limiter 213 then limits the output of the first PI controller 212 to obtain the preset influence factor x. The first limiting process prevents the difference from being too large, which could lead to saturation or overshoot in the subsequent regulator. The proportional-integral control characteristic of the PI controller is used to dynamically compensate for the voltage deviation and eliminate steady-state error. The second limiting process can constrain the reference current value within a reasonable range, avoiding the impact of an excessively large current setpoint on the safe operation of the inverter circuit.

[0081] Specifically, based on the total reference voltage value, the total number of inverter circuits in the energy storage system, and a preset influence factor, the inverter reference voltage of each inverter circuit is determined, including but not limited to the following steps S321 to S322.

[0082] Step S321: Determine the branch reference voltage based on the ratio of the total reference voltage value to the total number of items.

[0083] Specifically, the branch reference voltage V_Ref bra =V_Ref1 / N; Where V_Ref1 is the total reference voltage value, and N is the total number of inverter circuits in the energy storage system.

[0084] Step S322: Based on the sum of the branch reference voltage and the voltage deviation, determine the inverter reference voltage of each inverter circuit. The voltage deviation is the product of the branch reference voltage and the preset influence factor.

[0085] Specifically, the inverter reference voltage V_Ref is calculated as follows: V_Ref = (V_Ref1 / N) × (1 + x); Where V_Ref is the inverter reference voltage, V_Ref1 is the total reference voltage value, N is the total number of inverter circuits, and x is the preset influence factor.

[0086] Taking a specific embodiment as an example, when the maximum effective value GridVoltRms is 230V, the total number of inverter circuits N is 3, the preset influence factor x is 30%, and the effective value of the grid-connected current I... RMS When the inverter is rated at 3A, the inverter impedance R is 0.12Ω, and the preset maximum duty cycle Max_Duty is 0.9, combined with... V_Ref1=GridVoltRms× +V comp , V comp =V1+V2=(1 Max_Duty) × (GridVoltRms) )+R×(I RMS × ), The inverter reference voltage V_Ref for each inverter circuit is calculated to be approximately 155.24V.

[0087] Based on the above calculation process, the processor dynamically determines the inverter reference voltage V_Ref of each inverter circuit in each control cycle. Furthermore, this embodiment introduces a preset influence factor x to correct the inverter reference voltage V_Ref of each inverter circuit based on a uniform distribution of the total reference voltage value V_Ref1. This provides a certain voltage output margin for each inverter circuit, helping to address the differences in inverter input voltage (Vinv) caused by variations in the output of different photovoltaic panels. in1 Vinv in2 Vinv inN Inconsistency, and the inverter input voltage (Vinv) during the dynamic response of the current loop. in1 Vinv in2 Vinv inN In cases of temporary low voltage levels, the system mitigates the risk of the overall grid-connected power supply performance being affected by the limited output capacity of individual inverter circuits, thereby improving the overall stability and reliability of the grid-connected control system under complex operating conditions. Furthermore, the preset influence factor x is dynamically generated based on the real-time operating status of the system, rather than using a fixed empirical preset value. This allows the inverter reference voltage V_Ref to adaptively adjust with changes in system operating conditions, further enhancing the reliability of grid-connected control.

[0088] In some embodiments, for step S400, based on the inverter reference voltage and loop control process, the target duty cycle value of the drive signal of the switching transistor of each inverter circuit is obtained, including but not limited to the following steps S410 to S430.

[0089] Step S410: Based on the inverter reference voltage of each inverter circuit and the inverter input voltage at the input terminal of that inverter circuit, perform voltage outer loop control to obtain the reference current value at the output terminal of that inverter circuit.

[0090] Outer-loop voltage control refers to a closed-loop regulation process that uses the inverter reference voltage V_Ref as the target and the inverter input voltage as the feedback quantity. By comparing the inverter input voltage with the inverter reference voltage V_Ref and adjusting the deviation between them, a reference current value is output to drive the inner-loop control. This ensures that the output voltage of each inverter circuit's output terminals (INVout1, INVout2, ..., INVoutN) converges towards the inverter reference voltage V_Ref, achieving steady-state tracking control of the output voltage.

[0091] Specifically, see Figure 4 For the y-th inverter circuit, the inverter input voltage Vinv of the y-th inverter circuit is... iny The difference between the voltage and the inverter reference voltage V_Ref is calculated. After the difference is limited by the third limiter 221, the limiting result is input to the second PI controller 222 for calculation. Then, the output result of the second PI controller 222 is limited by the fourth limiter 223 to finally obtain the reference current value I_OBJ at the output of the y-th inverter circuit. y 1≤y≤N, where y is an integer. The first limiting process prevents excessive difference from causing saturation or overshoot in the subsequent regulator. The proportional-integral control characteristic of the PI controller is used to dynamically compensate for the voltage deviation and eliminate steady-state error. The second limiting process can constrain the reference current value within a reasonable range, avoiding the impact of excessive current setpoint on the safe operation of the inverter circuit.

[0092] Step S420: Based on the total reference voltage value and the total inverter input voltage, perform voltage outer loop control to obtain the reference current correction value.

[0093] Reference current correction value I_OBJ cor It refers to the value obtained by the control loop during the grid-connected control process, based on the real-time deviation between the total inverter input voltage SumBUS and the total reference voltage value V_Ref1, used to compensate and correct the reference current value of each inverter circuit.

[0094] Specifically, see Figure 5 The difference between the total inverter input voltage SumBUS and the total reference voltage V_Ref1 is calculated. This difference is then limited by the fifth limiter 231, and the limiting result is input to the third PI controller 232 for calculation. Finally, the output result of the third PI controller 232 is limited by the sixth limiter 233 to obtain the reference current correction value I_OBJ for the entire grid-connected control system. cor The first limiting process prevents excessive voltage difference from causing saturation or overshoot in subsequent regulators. The proportional-integral control characteristic of the PI controller is used to dynamically compensate for voltage deviation and eliminate steady-state error. The second limiting process can constrain the reference current value within a reasonable range, avoiding the impact of excessive current setpoint on the safe operation of the inverter circuit.

[0095] It is particularly important to note that, in order to feed power to the grid, the total DC voltage on the input side of the inverter circuit must be higher than the peak voltage of the grid to meet the basic voltage requirements for grid-connected discharge. Based on this, in this embodiment, when limiting the output of the third PI controller 232, the upper limit of the output of the third PI controller 232 is set to 0, i.e., the reference current correction value I_OBJ. corOnly negative or zero values ​​are used to suppress excessive current output from the system to the grid, reducing the pull-down effect on the inverter input DC total voltage and allowing the inverter input total voltage SumBUS to rise to the voltage level required for grid-connected power supply. Reference current correction value I_OBJ cor The larger the absolute value, the more significant the suppression effect on grid-connected current, and the more conducive it is to the rapid recovery of the total DC voltage on the inverter input side.

[0096] Step S430: Obtain the target duty cycle value based on the reference current correction value and the reference current value at the output of each inverter circuit.

[0097] After obtaining the reference current correction value I_OBJ cor Then, based on each reference current value and the reference current correction value I_OBJ cor The processor calculates the target duty cycle value of the switching transistor drive signal for each inverter circuit. Based on the target duty cycle value, the processor generates the corresponding PWM signal and outputs it to the drive terminal of the switching transistor in each inverter circuit, thereby adjusting the actual output voltage and actual output current of each inverter circuit to converge towards the target value. At this point, the control algorithm call is complete. The above control process will be re-executed in the next control cycle to achieve continuous closed-loop regulation of the system's grid-connected discharge process.

[0098] The processor generates a corresponding PWM signal based on the target duty cycle value, controls the switching transistors of the inverter circuit to switch according to the target duty cycle, thereby adjusting the actual output voltage of each inverter circuit to converge towards the target value.

[0099] In this embodiment, the grid-connected control system is based on a voltage outer-loop control architecture, performing independent voltage closed-loop regulation on each inverter circuit. The voltage outer loop targets the inverter reference voltage V_Ref, and dynamically outputs the reference current value for each inverter circuit by performing PI regulation on the inverter input voltage, which helps to achieve steady-state tracking of the output voltage of each circuit. Furthermore, the reference current correction value I_OBJ... cor Based on the real-time dynamic generation of the deviation between the inverter input total voltage SumBUS and the total reference voltage value V_Ref1, the DC voltage on the inverter input side is guaranteed to be higher than the grid peak voltage, which meets the requirements for power supply to the grid and reduces the risk of limited output of individual inverter circuits due to low inverter input voltage.

[0100] In some embodiments, for step S430, a target duty cycle value is obtained based on the reference current correction value and the reference current value at the output of each inverter circuit, including but not limited to steps S431 to S433.

[0101] Step S431: Obtain the maximum value among all reference current values ​​of the N-channel inverter circuit, where N is the total number of inverter circuits.

[0102] Since the N-channel inverter circuits use a series-parallel grid-connected configuration, the output current of each channel is equal. A unified grid-connected current target value must cover the voltage regulation requirements of all channels. Using the minimum or average value among the N reference currents as a reference would cause some inverter circuits to fail to maintain their inverter input voltage near the inverter reference voltage V_Ref due to a low reference current, thus affecting the grid-connected output capability of that inverter circuit. Therefore, this embodiment uses the maximum value I_OBJ among the N reference currents. max This serves as a unified reference benchmark to ensure that even the inverter circuits with the highest demand under current operating conditions can receive sufficient current drive.

[0103] Specifically, the processor obtains the reference current values ​​of each of the N inverter circuits from step S410, and takes the maximum value I_OBJ from them. max .Right now: I_OBJ max =max(I_OBJ1, I_OBJ2,…,I_OBJ y , ..., I_OBJ N ); Among them, I_OBJ max I_OBJy is the maximum value, I_OBJy is the reference current value of the y-th inverter circuit, and max() represents the operation of taking the maximum value of the sequence within the parentheses.

[0104] Step S432: Determine the target value of the reference current based on the reference current correction value and the maximum value.

[0105] The reference current target value I_OBJ refers to the final target current value I_OBJ used to drive the subsequent current inner loop control. Specifically, the reference current correction value I_OBJ... cor With the maximum value I_OBJ max Adding them together, we get the target reference current value I_OBJ, that is: I_OBJ=I_OBJ cor +I_OBJ max .

[0106] Step S433: Based on the target reference current value and the grid-connected current sampling value of the grid-connected port of the energy storage system, perform current inner loop control to obtain the target duty cycle value, wherein the grid-connected current sampling value of the grid-connected port of the energy storage system is equal to the current value at the output terminal of any inverter circuit.

[0107] Current inner-loop control refers to a closed-loop regulation process that uses the target reference current value I_OBJ as the objective and the sampled grid current value I1 as the feedback quantity. By comparing the sampled grid current value I1 with the target reference current value I_OBJ, performing proportional-integral calculations on the deviation, and finally outputting the target duty cycle value of the drive signals of the switching transistors of each inverter circuit, the actual grid current output by the system converges towards the target value.

[0108] Since the outputs of the N inverter circuits are connected in series, the current flowing through the outputs of each inverter circuit is equal. Therefore, sampling the current at the output of any one inverter circuit will yield the same result as the grid-connected current at the grid-connected port. In one specific implementation, see [reference needed]. Figure 1 Since the photovoltaic grid-connected inverters are connected in series, the currents at the output terminals INVout1, INVout2, ..., INVoutN of each inverter circuit are all equal. A current sampling circuit can be configured at the output terminal INVout1 of inverter circuit 131, and the processor obtains the grid-connected current sampling value (instantaneous current value) I1 through this current sampling circuit.

[0109] Specifically, see Figure 6 The processor calculates the difference between the target reference current value I_OBJ and the sampled grid current value I1. This difference is then processed by the fourth PI controller 242 to obtain the target duty cycle value 'duty'. Based on the target duty cycle value 'duty', the processor generates a corresponding PWM drive signal and outputs this signal to the respective switching transistor drive terminals of the N inverter circuits. Each inverter circuit uses the duty cycle obtained in the above manner to control its internal switching transistors to switch according to the target duty cycle, thereby coordinating the AC output voltage of each inverter circuit and achieving grid-connected discharge control.

[0110] In this embodiment, the maximum value I_OBJ is taken from the N reference current values. max As a factor in determining the reference current target value I_OBJ, this ensures that the unified grid-connected current target can cover the adjustment requirements of the inverter circuit with the highest demand among all circuits under the current operating conditions. This prevents the inverter input voltage of some inverter circuits from dropping due to a low reference current, and ensures that all inverter circuits can maintain stable operation of the inverter input voltage near the inverter reference voltage V_Ref. Furthermore, this embodiment employs a dual closed-loop control architecture with an outer voltage loop and an inner current loop. While ensuring the stability of the DC voltage on the inverter input side, this improves the tracking accuracy and dynamic response capability of the grid-connected current, reducing the risk of system instability and grid disconnection due to the accumulation of voltage or current deviations.

[0111] As another aspect of the embodiments of this application, the embodiments of this application also provide a computer-readable storage medium storing computer-executable instructions for causing an electronic device to perform the methods provided in the embodiments of this application.

[0112] In some embodiments, the storage medium may be a memory such as FRAM, ROM, PROM, EPROM, EEPROM, flash memory, magnetic surface memory, optical disk, or CD-ROM; or it may be a variety of devices including one or any combination of the above-mentioned memories.

[0113] In some embodiments, executable instructions may take the form of a program, software, software module, script, or code, written in any form of programming language (including compiled or interpreted languages, or declarative or procedural languages), and may be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0114] As an example, executable instructions may, but do not necessarily, correspond to files in the file system. They may be stored as part of a file that holds other programs or data, for example, in one or more scripts in a Hyper Text Markup Language (HTML) document, in a single file dedicated to the program in question, or in multiple collaborative files (e.g., a file that stores one or more modules, subroutines, or code sections).

[0115] As an example, executable instructions can be deployed to execute on a single computing device (including devices such as smart terminals and servers), or on multiple computing devices located in one location, or on multiple computing devices distributed across multiple locations and interconnected via a communication network.

[0116] As another aspect of the embodiments of this application, the embodiments of this application also provide a computer program product, the computer program product including a computer program stored on a computer-readable storage medium, the computer program including program instructions, which, when executed by a computer, cause the computer to perform the method as described in the foregoing embodiments.

[0117] It should be noted that the device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0118] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a general-purpose hardware platform, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the related technology, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions for at least one computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of this application as described above, which are not provided in detail for the sake of brevity; although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A grid-connected control method applied to an energy storage system, characterized in that, The energy storage system includes at least two photovoltaic grid-connected inverters connected in series. Each photovoltaic grid-connected inverter includes a photovoltaic panel and an inverter circuit with its input terminal connected to the photovoltaic panel. The method includes: The total inverter input voltage is determined based on the inverter input voltage at the input terminals of all the inverter circuits. Based on the preset maximum effective value of the grid voltage, the inverter impedance, the preset maximum duty cycle value of the switching transistor of the inverter circuit, and the effective value of the grid-connected current at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle, a reference voltage compensation value is determined, and the inverter impedance is the sum of the equivalent impedances of all the inverter circuits. Based on the reference voltage compensation value and the maximum effective value, the inverter reference voltage for the output terminal of each inverter circuit used for connecting to the power grid is determined; Based on the inverter reference voltage and loop control process, the target duty cycle value of the drive signal of the switching transistor of each inverter circuit is obtained.

2. The control method according to claim 1, characterized in that, Based on the preset maximum effective value of the grid voltage, the inverter impedance, the preset maximum duty cycle value of the switching transistors in the inverter circuit, and the effective value of the grid-connected current at the grid-connected port of the photovoltaic grid-connected inverter within the power frequency cycle, a reference voltage compensation value is determined, including: The duty cycle difference is determined based on the standard duty cycle and the preset maximum duty cycle value, wherein the standard duty cycle is 1; The first voltage value is determined based on the duty cycle difference and the maximum effective value; The second voltage value is determined based on the inverter impedance and the effective value of the grid-connected current; A reference voltage compensation value is determined based on the sum of the first voltage value and the second voltage value.

3. The control method according to claim 1, characterized in that, Based on the reference voltage compensation value and the maximum effective value, the inverter reference voltage for the output terminal of each inverter circuit used for connecting to the power grid is determined, including: The total reference voltage value is determined based on the maximum effective value and the reference voltage compensation value; Based on the total reference voltage value, the total number of inverter circuits in the energy storage system, and a preset influence factor, the inverter reference voltage of each inverter circuit is determined.

4. The control method according to claim 3, characterized in that, Based on the total reference voltage value, the total number of inverter circuits in the energy storage system, and a preset influence factor, the inverter reference voltage for each inverter circuit is determined, including: The branch reference voltage is determined based on the ratio of the total reference voltage value to the total number of items. Based on the sum of the branch reference voltage and the voltage deviation, the inverter reference voltage of each inverter circuit is determined, wherein the voltage deviation is the product of the branch reference voltage and the preset influence factor. The preset influence factor is a value greater than 0 and less than 1.

5. The control method according to claim 3, characterized in that, Based on the maximum effective value and the reference voltage compensation value, the total reference voltage value is determined, including: The total reference voltage value V_Ref1 is calculated as follows: V_Ref1=GridVoltRms× +V comp ; Wherein, GridVoltRms is the maximum valid value, V comp This is the reference voltage compensation value.

6. The control method according to claim 1, characterized in that, Based on the inverter reference voltage and loop control process, the target duty cycle value of the drive signal for the switching transistor of each inverter circuit is obtained, including: Based on the inverter reference voltage of each inverter circuit and the inverter input voltage at the input terminal of that inverter circuit, voltage outer loop control is performed to obtain the reference current value at the output terminal of that inverter circuit. Based on the total reference voltage value and the total inverter input voltage, voltage outer loop control is performed to obtain the reference current correction value; The target duty cycle value is obtained based on the reference current correction value and the reference current value at the output terminal of each inverter circuit.

7. The control method according to claim 6, characterized in that, Based on the reference current correction value and the reference current value at the output terminal of each inverter circuit, the target duty cycle value is obtained, including: Obtain the maximum value among all reference current values ​​of the N-channel inverter circuit, where N is the total number of inverter circuits; Based on the reference current correction value and the maximum value, determine the reference current target value; Based on the target reference current value and the grid-connected current sampling value of the grid-connected port of the energy storage system, current inner loop control is performed to obtain the target duty cycle value, wherein the grid-connected current sampling value of the grid-connected port of the energy storage system is equal to the current value at the output terminal of any of the inverter circuits.

8. The control method according to claim 1, characterized in that, Based on the inverter input voltages at the input terminals of all the aforementioned inverter circuits, the total inverter input voltage is determined, including: The total inverter input voltage is the sum of the inverter input voltages at the input terminals of all the inverter circuits.

9. A grid-connected control system, characterized in that, Includes an energy storage system and a processor connected to the energy storage system; An energy storage system includes at least two photovoltaic grid-connected inverters connected in series, each of which includes a photovoltaic panel, an MPPT module, a bus capacitor, an inverter circuit, and a filter network connected in sequence. Each of the filter networks includes an inductor and a filter capacitor. The two ends of a first series branch formed by the inductor and the filter capacitor are connected to the port of the inverter circuit for connecting to the power grid. All the filter capacitors of all photovoltaic grid-connected inverters are connected in series to form a second series branch, and the two ends of the second series branch are respectively connected to the neutral wire terminal and the live wire terminal of the power grid. The processor is used to perform the steps of the grid connection control method as described in any one of claims 1 to 8.

10. A computer storage medium, characterized in that, The computer storage medium stores instructions or programs that, when executed by at least one processor, cause the at least one processor to perform the steps of the grid-connected control method as described in any one of claims 1 to 8.

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