Optimized control method of inverter output waveform, inverter and storage medium

Abstract

The application relates to the technical field of micro-grid, and discloses an optimization control method of an inverter output waveform, an inverter and a storage medium, wherein the method comprises the following steps: constructing a switching cycle average model of a single-phase off-grid inverter and an output waveform optimization function, and determining a calculation model of a modulation wave compensation signal based on the output waveform optimization function and the switching cycle average model; obtaining an input signal for controlling the inverter output waveform, performing double-loop control on the inverter based on the input signal, and outputting an original modulation wave signal; calculating the modulation wave compensation signal based on the input signal, an inductance current reference value generated in the double-loop control and the calculation model of the modulation wave compensation signal; and superimposing the original modulation wave signal and the modulation wave compensation signal to obtain an optimized modulation wave signal. According to the method, the modulation wave signal is compensated and optimized, and the purpose of optimizing the output voltage waveform quality when the single-phase off-grid inverter is loaded with a nonlinear load is achieved.

Description

Technical Field

[0001] This application relates to the field of microgrid technology, and in particular to an optimized control method for inverter output waveform, an inverter, and a storage medium. Background Technology

[0002] Single-phase off-grid inverters are widely used in the field of microgrid technology, such as Figure 1 As shown, a typical single-phase off-grid inverter consists of four full-bridge switches and a filter circuit. Currently, the commonly used control scheme for single-phase off-grid inverters is a dual-closed-loop control strategy with an outer loop for output voltage and an inner loop for inductor current. However, under the dual-closed-loop control framework, when the single-phase off-grid inverter is loaded with a nonlinear load, the harmonic components in the output current will adversely affect the waveform quality of the inverter's output voltage, resulting in a poor Total Harmonic Distortion (THD) index for the inverter's output voltage. Summary of the Invention

[0003] The embodiments of this application aim to provide an optimized control method for inverter output waveform, an inverter, and a storage medium, to solve the technical problem of large THD of output voltage when a single-phase off-grid inverter is driven by a nonlinear load in the prior art.

[0004] To address the aforementioned technical problems, this application provides the following technical solutions:

[0005] According to a first aspect of this application, an optimized control method for the output waveform of an inverter is provided, the method being applied to a single-phase off-grid inverter, comprising:

[0006] Based on Kirchhoff's laws and the switching cycle averaging method, an inverter switching cycle averaging model is established.

[0007] Construct an output waveform optimization function based on the inverter's dual closed-loop control strategy;

[0008] Based on the output waveform optimization function and the switching period averaging model, the calculation model of the modulation wave compensation signal is determined.

[0009] The system acquires an input signal that controls the output waveform of the inverter, and performs dual closed-loop control on the inverter based on the input signal to output the original modulated wave signal.

[0010] The modulation wave compensation signal is calculated based on the input signal, the inductor current reference value generated in the dual closed-loop control, and the calculation model of the modulation wave compensation signal.

[0011] The original modulated wave signal is superimposed with the modulated wave compensation signal to obtain the optimized modulated wave signal.

[0012] Optionally, establishing the switching cycle averaging model of the inverter based on Kirchhoff's laws and the switching cycle averaging method includes:

[0013] Based on Kirchhoff's laws, the mathematical model of the inverter is obtained;

[0014] The inverter arm output voltage in the mathematical model is replaced with the average value of the inverter arm output voltage during the switching cycle to obtain the average switching cycle model of the inverter. The average switching cycle value is obtained according to the switching cycle averaging method.

[0015] Optionally, the switching cycle averaging model is:

[0016]

[0017] in, This is the inductance value of the filter inductor. This is the capacitance value of the filter capacitor. For inductor current, For output voltage, For output current, This is the average value of the switching cycle.

[0018] Optionally, the formula for calculating the average value of the switching cycle is:

[0019]

[0020] in, It is a modulated wave signal. The amplitude of the triangular carrier wave. This is the DC input voltage.

[0021] Optionally, the output waveform optimization function is:

[0022]

[0023] in, For output voltage, For output voltage reference, For inductor current, This serves as a reference for the inductor current.

[0024] Optionally, the calculation model for determining the modulation wave compensation signal based on the output waveform optimization function and the switching period averaging model includes:

[0025] Minimize the output waveform optimization function to obtain the first relationship between the inductor current and the output voltage sensitivity.

[0026] Based on the switching cycle averaging model, the second relationship between the inductor current and the output voltage sensitivity is obtained;

[0027] Based on the first and second relational expressions, the calculation model for the modulated wave compensation signal is determined.

[0028] Optionally, the calculation model for the modulated wave compensation signal is as follows:

[0029]

[0030] in, For modulated wave compensation signal, The amplitude of the triangular carrier wave. DC input voltage For output current, This is the inductance value of the filter inductor. This is the capacitance value of the filter capacitor.

[0031] According to a second aspect of this application, a single-phase off-grid inverter is provided, the single-phase off-grid inverter including a controller, the controller including: at least one processor and a memory communicatively connected to the at least one processor, the memory storing instructions executable by the at least one processor, the instructions being executed by the at least one processor to enable the at least one processor to perform the method described in any of the above.

[0032] Optionally, the single-phase off-grid inverter further includes a DC voltage input source and a first switching transistor. Second switching transistor Third switching transistor Fourth switching transistor Filter inductor and filter capacitor .

[0033] According to a third aspect of this application, a computer-readable storage medium is provided, the computer-readable storage medium storing a computer program, which, when executed by a processor, performs the steps of any of the methods described above.

[0034] The beneficial effects of this application's embodiments are as follows: Unlike existing technologies, this application provides an optimized control method for inverter output waveform. First, it constructs an average switching cycle model and an output waveform optimization function for a single-phase off-grid inverter. Based on the output waveform optimization function and the average switching cycle model, it determines a calculation model for the modulation wave compensation signal. It then acquires the input signal for controlling the inverter's output waveform and performs dual-loop control on the inverter based on the input signal, outputting the original modulation wave signal. Finally, it calculates the modulation wave compensation signal based on the input signal, the inductor current reference value generated in the dual-loop control, and the calculation model of the modulation wave compensation signal. Finally, it superimposes the original modulation wave signal and the modulation wave compensation signal to obtain the optimized modulation wave signal. This method, by optimizing the modulation wave signal and comparing the optimized modulation wave with a triangular carrier wave to generate a drive signal, achieves the goal of optimizing the output voltage waveform quality when a single-phase off-grid inverter is carrying a nonlinear load. Attached Figure Description

[0035] One or more embodiments are illustrated by way of example with reference numerals in the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements with the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0036] Figure 1 This is a schematic diagram of the structure of a single-phase off-grid inverter provided in an embodiment of this application;

[0037] Figure 2 This is a schematic diagram of the controller provided in an embodiment of this application;

[0038] Figure 3 This is a flowchart of an optimized control method for inverter output waveform provided in an embodiment of this application;

[0039] Figure 4 This is a schematic diagram of key waveforms within one switching cycle of a single-phase off-grid inverter provided in an embodiment of this application;

[0040] Figure 5 This is a schematic diagram of the original dual-closed-loop control strategy provided in the embodiments of this application;

[0041] Figure 6 This is a schematic diagram of the optimized control strategy provided in the embodiments of this application;

[0042] Figure 7 This is a waveform diagram of the output voltage when using the original dual closed-loop control strategy to drive a nonlinear load, as provided in the embodiments of this application.

[0043] Figure 8This is a waveform diagram of the output voltage when the optimized control strategy of this application is used to drive a nonlinear load, as provided in the embodiments of this application. Detailed Implementation

[0044] 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.

[0045] 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.

[0046] It should be noted that the steps shown in the flowchart 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 flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0047] Please see Figure 1 , Figure 1 This is a schematic diagram of the structure of a single-phase off-grid inverter provided in an embodiment of this application. For example... Figure 1 As shown, the single-phase off-grid inverter includes an inverter circuit 10 and a controller 20. The inverter circuit 10 includes a DC voltage input source and a first switching transistor. Second switching transistor Third switching transistor Fourth switching transistor Filter inductor and filter capacitor Furthermore, this single-phase off-grid inverter carries a nonlinear load Z, and the inverter arm output voltage is expressed as follows: .

[0048] The controller 20 is connected to the switching transistors in the inverter circuit 10. The connection is based on the built-in control program that controls the switching transistor. The controller 20 can be turned on and off. In some embodiments, the controller 20 may be a microcontroller unit (MCU) or a digital signal processing (DSP) controller, etc.

[0049] In some embodiments, the single-phase off-grid inverter may further include a DC voltage sampling unit, an output voltage sampling unit, an output current sampling unit, and an inductor current sampling unit. The DC voltage sampling unit is located on both sides of the DC voltage input source and is used to acquire the DC input voltage in real time. The output voltage sampling unit is located on both sides of the nonlinear load Z to collect the output voltage in real time. The output current sampling unit is located on the inflow side of the nonlinear load Z and is used to acquire the output current in real time. The inductor current sampling unit is located on the filter inductor. The inflow side is used to collect the filter inductor current in real time. .

[0050] Please refer to Figure 2 , Figure 2 An exemplary structure of controller 20 is shown. For example... Figure 2 As shown, the controller 20 includes at least one processor 21 and a memory 22. The memory 22 can be built into the controller 20 or external to the controller 20. The memory 22 can also be a remotely configured memory connected to the controller 20 via a network.

[0051] Memory 22, as a non-volatile computer-readable storage medium, can be used to store non-volatile software programs, non-volatile computer-executable programs, and modules. Memory 22 may include a program storage area and a data storage area, wherein the program storage area may store the operating system and application programs required for at least one function; the data storage area may store data created based on the use of the terminal, etc. Furthermore, memory 22 may include high-speed random access memory and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other non-volatile solid-state storage device. In some embodiments, memory 22 may optionally include memory remotely located relative to processor 21, and these remote memories can be connected to the terminal via a network. Examples of such networks include, but are not limited to, the Internet, corporate intranets, local area networks, mobile communication networks, and combinations thereof.

[0052] The processor 21 performs various functions of the terminal and processes data by running or executing software programs and / or modules stored in the memory 22 and calling data stored in the memory 22, thereby performing overall monitoring of the terminal, such as implementing the inverter output waveform optimization control method described in any embodiment of this application.

[0053] Processor 21 can be one or more. Figure 2The example provided is a processor 21. Processor 21 and memory 22 can be connected via a bus or other means. Processor 21 may include a central processing unit (CPU), a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a controller, a field-programmable gate array (FPGA) device, etc. Processor 21 can also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors combined with a DSP core, or any other such configuration.

[0054] Please refer to Figure 3 , Figure 3 This is a flowchart illustrating an optimized control method for the output waveform of an inverter according to an embodiment of this application. This method is applied to a single-phase off-grid inverter. The single-phase off-grid inverter may include an inverter circuit and a controller, etc. In some embodiments, the single-phase off-grid inverter can... Figure 1 The implementation of the structure is described in detail in the above embodiments and will not be repeated here.

[0055] like Figure 3 As shown, the optimized control method for the inverter output waveform includes:

[0056] Step S301: Based on Kirchhoff's laws and the switching cycle averaging method, establish the inverter's switching cycle averaging model.

[0057] According to Kirchhoff's Current Law: the total current flowing into a node is equal to the total current flowing out of that node, therefore:

[0058] (1)

[0059] According to Kirchhoff's voltage law: In any closed loop, the algebraic sum of the voltages across all components is equal to zero, therefore:

[0060] (2)

[0061] in, This is the inductance value of the filter inductor. This is the capacitance value of the filter capacitor. For inductor current, For output voltage, For output current, This is the output voltage of the inverter bridge arm.

[0062] therefore, Figure 1 The mathematical model of the inverter shown can be expressed as:

[0063] (3)

[0064] Since the triangular wave carrier frequency is much higher than the modulation wave frequency, the average value of the inverter bridge arm output voltage during the switching period can be used. To approximate the output voltage of the inverter bridge arm .therefore, Figure 1 The average switching cycle model of the inverter shown can be expressed as:

[0065] (4)

[0066] Please refer to Figure 4 , Figure 4 This is a schematic diagram of key waveforms within one switching cycle of a single-phase off-grid inverter. Among them, It is a modulated wave signal. The amplitude of the triangular carrier wave. This is the DC input voltage. The inverter bridge arm output voltage is calculated using the switching cycle averaging method. Average switching cycle The calculation formula is:

[0067] (5)

[0068] Step S302: Construct an output waveform optimization function based on the inverter's dual closed-loop control strategy.

[0069] The inverter's dual closed-loop control strategy includes an outer voltage loop control and an inner current loop control. Its control objective is to achieve a stable output voltage in the outer voltage loop control. Track the output voltage reference value as closely as possible In the inner current loop control, the inductor current is reduced. Track the inductor current reference value as closely as possible. Based on this dual-closed-loop control strategy, the following output waveform optimization function is constructed. :

[0070] (6)

[0071] Step S303: Based on the output waveform optimization function and the switching period averaging model, the calculation model of the modulation wave compensation signal is determined.

[0072] Based on the optimization control objective, the minimum value of equation (6) is taken. According to the method for finding the extremum of higher-order functions, let equation (6) be applied to the target variable. Since the derivative is zero, the inductor current can be obtained. For output voltage Sensitivity (i.e.) The first relation that must be satisfied:

[0073] (7)

[0074] Furthermore, based on the switching cycle averaging model of equation (4), the inductor current can be obtained. For output voltage The second relationship that sensitivity satisfies:

[0075] (8)

[0076] When the average value of the switching cycle satisfies equation (8), then the compensation term for the average value of the switching cycle should also satisfy equation (8). The average value of the switching cycle in equation (8)... Replace with average value compensation term for switching cycle Substituting into equation (7), we can obtain the average value compensation term for the switching cycle. The calculation formula is:

[0077] (9)

[0078] Similarly, the average switching cycle in equation (5) Replace with average value compensation term for switching cycle and modulated waves Replace with modulated wave compensation signal The equation still holds true, that is:

[0079] (10)

[0080] Substituting equation (10) into equation (9), we obtain the calculation model for the modulated wave compensation signal:

[0081] (11)

[0082] Step S304: Obtain the input signal for controlling the output waveform of the inverter, and perform dual closed-loop control on the inverter based on the input signal to output the original modulated wave signal.

[0083] In one embodiment, the input signal may include output voltage sample value, output current sample value, inductor current sample value, output voltage reference value, DC input voltage value, and triangular carrier amplitude, etc.

[0084] The inverter's dual closed-loop control strategy includes voltage outer loop control and current inner loop control. The voltage outer loop control process is as follows: the voltage outer loop control is performed based on the output voltage sample value and the output voltage reference value, and the inductor current reference value is output. The current inner loop control process is as follows: the current inner loop control is performed based on the inductor current sample value and the inductor current reference value, and the original modulated wave signal is output.

[0085] Please refer to Figure 5 , Figure 5 This is a schematic diagram of the original dual-closed-loop control strategy provided in the embodiments of this application. For example... Figure 5As shown, the output voltage reference value With output voltage sampling value The difference is then fed into the outer voltage loop controller. Generate inductor current reference value Inductor current reference value Then compared with the inductor current sampling value The difference is then fed into the inner current loop controller. The original modulated wave signal is obtained. The original modulated wave signal The signal is fed into a PWM (Pulse Width Modulation) modulator for modulation. Figure 5 The approximation is (proportional adjustment) to obtain the inverter bridge arm output voltage ( Figure 5 The average value of the switching period is approximated. Inverter bridge arm output voltage and output voltage sampling value. The voltage of the filter inductor is obtained by subtraction. Filter inductor voltage With filter inductor reactance Divide to obtain the sampled value of the inductor current. Inductor current sampling value With output current sampling value The difference is used to obtain the capacitor current. Capacitor current With capacitor reactance Multiply to obtain the output voltage. .

[0086] Step S305: Calculate the modulation compensation signal based on the input signal, the inductor current reference value generated in the dual closed-loop control, and the modulation compensation signal calculation model.

[0087] According to the calculation model of the modulated wave compensation signal, the modulated wave compensation signal can be calculated based on the triangular wave amplitude, DC input voltage sample value, output voltage sample value, filter inductor inductance value, filter capacitor capacitance value, inductor current sample value, output current sample value, output voltage reference value, and inductor current reference value. Among these, except for the inductor current reference value, which is generated by the voltage outer loop controller, all other signals can be obtained in advance.

[0088] Step S306: The original modulated wave signal is superimposed with the modulated wave compensation signal to obtain the optimized modulated wave signal.

[0089] Please refer to Figure 6 , Figure 6 This is a schematic diagram illustrating the optimized control strategy provided in an embodiment of this application. Figure 5Compared to the original dual-closed-loop control strategy, the optimized control strategy in this application uses a different inductor current reference value. With inductor current sampling value Differential input current inner loop controller Obtain the original modulated wave signal Then, the original modulated wave signal The modulation wave compensation signal calculated in step S305 The signals are superimposed to obtain the optimized modulated wave signal. Then the optimized modulation signal The optimized modulated wave signal is sent to the PWM modulator for modulation. A driving signal is generated by comparing the signal with a triangular carrier wave, and the optimized output voltage is finally obtained.

[0090] Please refer to Figure 7 and Figure 8 , Figure 7 This is a waveform diagram of the output voltage when using the original dual closed-loop control strategy to drive a nonlinear load, as provided in an embodiment of this application. Figure 8 This is a schematic diagram of the output voltage waveform when a nonlinear load is driven using the optimized control strategy of this application, as provided in an embodiment of this application. (Comparison) Figure 7 and Figure 8 It can be seen that the waveform quality of the output voltage when using the optimized control strategy of this application to drive a nonlinear load is significantly better than that when using the original dual closed-loop control strategy to drive a nonlinear load, thus reducing the THD index of the output voltage.

[0091] The inverter output waveform optimization control method provided in this application first constructs a switching cycle averaging model and an output waveform optimization function for a single-phase off-grid inverter. Based on the output waveform optimization function and the switching cycle averaging model, a calculation model for the modulation wave compensation signal is determined. The input signal for controlling the inverter output waveform is acquired, and dual closed-loop control is performed on the inverter based on the input signal to output the original modulation wave signal. The modulation wave compensation signal is then calculated based on the input signal, the inductor current reference value generated in the dual closed-loop control, and the calculation model of the modulation wave compensation signal. Finally, the original modulation wave signal and the modulation wave compensation signal are superimposed to obtain the optimized modulation wave signal. This method, by compensating and optimizing the modulation wave signal and comparing the optimized modulation wave with a triangular carrier wave to generate a drive signal, achieves the goal of optimizing the output voltage waveform quality of a single-phase off-grid inverter when carrying a nonlinear load.

[0092] This application also provides a non-volatile computer-readable storage medium storing computer-executable instructions that are executed by one or more processors, for example, executing the instructions described above. Figure 3The method and steps.

[0093] 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 method for optimizing control of an inverter output waveform, characterized by, The method is applied to a single-phase off-grid inverter, and the method comprises: According to the Kirchhoff's law and the switching period average method, a switching period average model of the inverter is established; According to a double closed-loop control strategy of the inverter, an output waveform optimization function is constructed; Based on the output waveform optimization function and the switching period average model, a calculation model of a modulation wave compensation signal is determined; An input signal for controlling the output waveform of the inverter is acquired, and a double closed-loop control is performed on the inverter based on the input signal to output an original modulation wave signal; Based on the input signal, an inductance current reference value generated in the double closed-loop control and the calculation model of the modulation wave compensation signal, a modulation wave compensation signal is calculated; The original modulation wave signal is superimposed with the modulation wave compensation signal to obtain an optimized modulation wave signal.

2. The method of claim 1, wherein, The switching period average model of the inverter is established according to the Kirchhoff's law and the switching period average method, which comprises: According to the Kirchhoff's law, a mathematical model of the inverter is obtained; The output voltage of the inverter bridge arm in the mathematical model is replaced by a switching period average value of the output voltage of the inverter bridge arm to obtain the switching period average model of the inverter, and the switching period average value is obtained according to the switching period average method.

3. The method of claim 2, wherein, The switching period average model is: wherein, is the inductance value of the filter inductor, is the capacitance value of the filter capacitor, is the inductor current, is the output voltage, is the output current, is the average value of the switching period.

4. The method of claim 3, wherein, The calculation formula of the switching period average value is: wherein is the modulation wave signal, is the triangular carrier amplitude, is the direct input voltage.

5. The method according to any one of claims 1 to 4, characterized in that, The output waveform optimization function is: wherein, is an output voltage, is an output voltage reference value, is an inductor current, is an inductor current reference value.

6. The method of claim 5, wherein, Based on the output waveform optimization function and the switching period average model, the calculation model of the modulation wave compensation signal is determined, which comprises: The output waveform optimization function is minimized to obtain a first relationship formula in which the inductance current satisfies the sensitivity of the output voltage; According to the switching period average model, a second relationship formula in which the inductance current satisfies the sensitivity of the output voltage is obtained; Based on the first relationship formula and the second relationship formula, the calculation model of the modulation wave compensation signal is determined.

7. The method of claim 6, wherein, The calculation model of the modulation wave compensation signal is: wherein is the modulation wave compensation signal, is the triangular carrier amplitude, is the DC input voltage, is the output current, is the inductance of the filter inductor, is the capacitance of the filter capacitor.

8. A single phase off-grid inverter characterized in that, The single-phase off-grid inverter comprises a controller, and the controller comprises at least one processor and a memory in communication connection with the at least one processor, the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to execute the method in any one of claims 1 to 7.

9. The single-phase off-grid inverter of claim 8, wherein, The single-phase off-grid inverter further comprises a direct-current voltage input source, a first switch tube , a second switch tube , a third switch tube , a fourth switch tube , a filter inductor and a filter capacitor.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program, and when the computer program is executed by a processor, the processor executes the steps of the method in any one of claims 1 to 7.

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