Method for compensating inductive current reference value, inverter and storage medium

Abstract

The invention relates to the technical field of microgrids, in particular to a method for compensating an inductive current reference value, an inverter and a storage medium. The method comprises the following steps: establishing a state equation of an inverter circuit; according to the state equation, determining an inductive current reference value compensation model and constructing a disturbance observer for estimating unknown disturbance quantity; obtaining an output voltage reference value, an inductive current sampling value and an output voltage sampling value, and executing voltage outer loop control on the inverter to obtain an original inductive current reference value; inputting the inductive current sampling value and the output voltage sampling value into a disturbance observer to obtain an estimated value of an unknown disturbance quantity; and based on the original inductive current reference value, the estimated value of the unknown disturbance quantity and the inductive current reference value compensation model, obtaining a compensated inductive current reference value. According to the method provided by the invention, the inductive current reference value is compensated, and the purpose of optimizing the waveform quality of the output voltage when the single-phase off-grid inverter is loaded with the nonlinear load is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro-grid, and particularly relates to a method for compensating an inductance current reference value, an inverter and a storage medium. BACKGROUND

[0002] Single-phase off-grid inverters are widely used in the technical field of micro-grid, such as Figure 1 As shown in the figure, a common single-phase off-grid inverter is composed of four full-bridge switching tubes and a filter circuit. At present, a common control scheme for the single-phase off-grid inverter is a double-loop control strategy of an output voltage outer loop and an inductance current inner loop. However, under the double-loop control framework, when the single-phase off-grid inverter is loaded with a nonlinear load, the harmonic components in the output current will have an adverse effect on the waveform quality of the output voltage of the inverter, resulting in a poor total harmonic distortion (THD) index of the output voltage of the inverter. SUMMARY

[0003] Embodiments of the present application aim to provide a method for compensating an inductance current reference value, an inverter and a storage medium, and solve the technical problem of a large THD of the output voltage of the single-phase off-grid inverter when loaded with a nonlinear load in the prior art.

[0004] To solve the above technical problem, embodiments of the present application provide the following technical solutions: According to a first aspect of the present application, a method for compensating an inductance current reference value is provided, the method is applied to a single-phase off-grid inverter, and includes the following steps: establishing a state equation of an inverter circuit according to Kirchhoff's law; determining an inductance current reference value compensation model containing an unknown disturbance quantity according to the state equation of the inverter circuit; constructing a disturbance observer for estimating the unknown disturbance quantity according to the state equation of the inverter circuit; obtaining an output voltage reference value, an inductance current sample value and an output voltage sample value, performing voltage outer loop control on the inverter based on the output voltage sample value and the output voltage reference value, and obtaining an original inductance current reference value; inputting the inductance current sample value and the output voltage sample value into the disturbance observer to obtain an estimated value of the unknown disturbance quantity; obtaining a compensated inductance current reference value based on the original inductance current reference value, the estimated value of the unknown disturbance quantity and the inductance current reference value compensation model.

[0005] Optionally, the state equation of the inverter circuit is as follows:

[0006] wherein, is a capacitance value of the filter capacitor, is an inductor current, is a capacitor current, is an output current, is an output voltage.

[0007] Optionally, the inductor current reference value compensation model is:

[0008] wherein, is a compensated inductor current reference value, is an original inductor current reference value output by a voltage outer loop controller, is an estimated value of an unknown disturbance.

[0009] Optionally, the unknown disturbance is a load current.

[0010] Optionally, the obtaining of the compensated inductor current reference value based on the original inductor current reference value, the estimated value of the unknown disturbance and the inductor current reference value compensation model comprises: superimposing the original inductor current reference value and the estimated value of the unknown disturbance to obtain the compensated inductor current reference value.

[0011] Optionally, the disturbance observer is:

[0012] wherein, is an estimated value of an output voltage, is an inductor current sample value, is an estimated value of an unknown disturbance, and is an observer coefficient.

[0013] Optionally, the obtaining of the estimated value of the unknown disturbance based on the inductor current sample value, the output voltage sample value and the disturbance observer comprises: discretizing the disturbance observer to obtain a discretized disturbance observer, wherein, is a control period:

[0014] initializing the estimated value of the output voltage and the estimated value of the unknown disturbance in the discretized disturbance observer; inputting the inductor current sample value and the output voltage sample value into the discretized disturbance observer to obtain the estimated value of the unknown disturbance in a current control period.

[0015] According to a second aspect of the present application, a single-phase off-grid inverter is provided, the single-phase off-grid inverter comprising a controller, the controller comprising 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 of any one of the preceding aspects.

[0016] Optionally, 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.

[0017] According to a third aspect of the present application, a computer-readable storage medium is provided, the computer-readable storage medium storing a computer program, when the computer program is executed by a processor, the processor performs the steps of the method of any one of the preceding aspects.

[0018] The beneficial effects of the embodiments of the present application are that, unlike the prior art, the embodiments of the present application provide a method for compensating an inductor current reference value, first, a state equation of an inverter circuit is established, and based on the state equation of the inverter circuit, an inductor current reference value compensation model containing an unknown disturbance quantity is determined and a disturbance observer for estimating the unknown disturbance quantity is constructed; second, an output voltage reference value, an inductor current sample value and an output voltage sample value are obtained, voltage outer loop control of the inverter is performed based on the output voltage sample value and the output voltage reference value to obtain an original inductor current reference value, the inductor current sample value and the output voltage sample value are input into the disturbance observer to obtain an estimated value of the unknown disturbance quantity; finally, based on the original inductor current reference value, the estimated value of the unknown disturbance quantity and the inductor current reference value compensation model, a compensated inductor current reference value is obtained. The method of the present application, after the disturbance observer estimates the disturbance quantity, compensates the inductor current reference value based on the estimated value of the disturbance quantity, and sends the compensated inductor current reference value as the final inductor current reference value into a current control inner loop to generate a modulation wave, so as to achieve the purpose of suppressing the disturbance of the load current on the output voltage and optimizing the output voltage waveform quality when the inverter is loaded with a nonlinear load. BRIEF DESCRIPTION OF DRAWINGS

[0019] One or more embodiments are illustrated by way of example in the figures that form a part of this patent document, these example are not intended to limit the embodiments, elements having the same reference numbers in the figures indicate like elements unless otherwise expressly stated, the figures in the drawings do not constitute a proportional limitation.

[0020] Figure 1 is a structural schematic diagram of a single-phase off-grid inverter provided by the embodiments of the present application; Figure 2is a structural schematic diagram of a controller provided by an embodiment of the present application; Figure 3 is a flow chart of a method for compensating an inductor current reference value provided by an embodiment of the present application; Figure 4 is a schematic diagram of a conventional double closed-loop control strategy provided by an embodiment of the present application; Figure 5 is a schematic diagram of an inductor current reference value compensation control strategy provided by an embodiment of the present application; Figure 6 is a control effect comparison diagram of the conventional double closed-loop control strategy and the inductor current reference value compensation control strategy provided by an embodiment of the present application. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0022] In addition, the technical features involved in each of the embodiments of the present application described below can be combined with each other as long as there is no conflict.

[0023] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a group of computer executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described herein can be executed in an order different from that shown herein.

[0024] Please refer to Figure 1 , Figure 1 is a structural schematic diagram of a single-phase off-grid inverter provided by an embodiment of the present application. As shown in Figure 1 , the single-phase off-grid inverter includes an inverter circuit 10 and a controller 20. Wherein, the inverter circuit 10 includes 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 . In addition, the single-phase off-grid inverter carries a nonlinear load Z, and the inverter bridge arm output voltage is represented as .

[0025] The controller 20 is respectively connected with the switch tubes Connect, control the switch tube based on the built-in control program In some embodiments, the controller 20 can employ a microcontroller unit (MCU) or a digital signal processing (DSP) controller, etc.

[0026] In some embodiments, the single-phase off-grid inverter can further include an output voltage sampling unit and an inductor current sampling unit. The output voltage sampling unit is arranged on both sides of the non-linear load Z, and is used to collect the output voltage in real time; the inductor current sampling unit is arranged on the inflow side of the filter inductor , and is used to collect the filter inductor current in real time.

[0027] Please refer to Figure 2 , Figure 2 for an exemplary structure of the controller 20. As shown in Figure 2 , the controller 20 includes at least one processor 21 and a memory 22, wherein the memory 22 can be built-in in the controller 20, or can be external to the controller 20, and the memory 22 can also be a remotely arranged memory connected to the controller 20 through a network.

[0028] The memory 22 is a non-volatile computer readable storage medium, which can be used to store non-volatile software programs, non-volatile computer executable programs and modules. The memory 22 can include a program storage area and a data storage area, wherein the program storage area can store an operating system and application programs required by at least one function; the data storage area can store data created according to the use of the terminal, etc. In addition, the memory 22 can include a high-speed random access memory, and can also include a non-volatile memory, such as at least one magnetic disk storage device, a flash memory device, or other non-volatile solid-state storage device. In some embodiments, the memory 22 can optionally include a memory arranged remotely relative to the processor 21, and these remote memories can be connected to the terminal through a network. Examples of the above network include but are not limited to the Internet, an intranet, a local area network, a mobile communication network, and a combination thereof.

[0029] The processor 21 executes 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, so as to perform overall monitoring of the terminal, such as implementing the method for compensating the inductor current reference value according to any embodiment of the present application.

[0030] The processor 21 can be one or more, Figure 2The processor 21 and the memory 22 can be connected by a bus or other means. The processor 21 can 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, or the like. The processor 21 can also be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0031] Please refer to Figure 3 , Figure 3 is a flowchart of a method for compensating an inductor current reference value provided by the embodiments of the present application. The method is applied to a single-phase off-grid inverter. The single-phase off-grid inverter can include an inverter circuit and a controller, etc. In some embodiments, the single-phase off-grid inverter can be implemented by the structure of Figure 1 , and the specific implementation process has been described in detail in the above embodiments, which will not be described here.

[0032] As shown in Figure 3 , the method for compensating the inductor current reference value includes: Step S301, according to the Kirchhoff's law, a state equation of the inverter circuit is established.

[0033] According to the Kirchhoff's current law: the total current flowing into a node is equal to the total current flowing out of the node, then: (1) wherein, is a capacitance value of a filter capacitor, is an inductor current, is a capacitor current, is an output current, is an output voltage.

[0034] Step S302, according to the state equation of the inverter circuit, an inductor current reference value compensation model containing unknown disturbance quantity is determined.

[0035] The original inductor current reference value output by the voltage outer loop controller is essentially to provide the capacitor current to maintain the sinusoidal output voltage . However, when the load current contains harmonic components, in order to maintain the stability of the output voltage, the inductor current must be able to compensate for the change of the load current , that is, the inductor current needs to be able to perfectly support the capacitor current and the load current Therefore, according to formula (1), the ideal inductance current reference value should be: (2) wherein, is the original inductance current reference value output by the voltage outer loop controller, used for maintaining the stability of the sinusoidal output voltage , is the compensation current (i.e. the load current) required to cope with the load current disturbance. In order to reduce the hardware cost, a current sensor is usually not added at the load end, and the load current cannot be measured in real time, therefore, the present application introduces a disturbance observer to estimate the load current, and superimposes the estimated load current on the output of the voltage outer loop controller for feedforward compensation. At this time, the inductance current reference value compensation model containing the unknown disturbance quantity is: (3) wherein, is the compensated inductance current reference value, is the original inductance current reference value output by the voltage outer loop controller, is the estimated value of the unknown disturbance quantity.

[0036] As can be seen from the inductance current reference value compensation model, the compensated inductance current reference value contains two parts: one part is the capacitor current component output by the voltage outer loop for maintaining the output voltage, and the other part is the feedforward load current estimate value . In this way, the inductance current can directly provide the load current , thereby suppressing the disturbance of the output voltage variation caused by the load current .

[0037] Step S303, according to the state equation of the inverter circuit, a disturbance observer for estimating the unknown disturbance quantity is constructed.

[0038] According to formula (1), the state equation of the inverter circuit can be rewritten as follows: (4) For the unknown disturbance quantity in formula (4), a disturbance observer is constructed as follows to estimate it: (5) wherein, is the estimated value of the output voltage, is the inductance current sampling value, is the estimated value of the unknown disturbance quantity, and are the observer coefficients.

[0039] Step S304, the output voltage reference value, the inductor current sampling value and the output voltage sampling value are obtained, the voltage outer loop control is performed on the inverter based on the output voltage sampling value and the output voltage reference value, and the original inductor current reference value is obtained.

[0040] The double closed loop control strategy of the single-phase off-grid inverter includes voltage outer loop control and current inner loop control, and the control target is to make the output voltage track the output voltage reference value as much as possible , and make the inductor current track the inductor current reference value as much as possible . Specifically, the execution process of the conventional double closed loop control strategy is as follows: the voltage outer loop control is performed based on the output voltage sampling value and the output voltage reference value, and the inductor current reference value is output; and the current inner loop control is performed based on the inductor current sampling value and the inductor current reference value, and the modulation wave signal is output.

[0041] Please refer to Figure 4 , which is a schematic diagram of the conventional double closed loop control strategy applied to the single-phase off-grid inverter provided by the embodiment of the present application. As Figure 4 shown, the output voltage reference value is subtracted from the output voltage sampling value and then sent to the voltage outer loop controller , so as to generate the inductor current reference value . The inductor current reference value is subtracted from the inductor current sampling value and then sent to the current inner loop controller , so as to obtain the modulation wave signal. The modulation wave signal is sent to the PWM (Pulse Width Modulation) modulator for modulation Figure 4 , which is approximately proportional to , wherein is the triangular carrier amplitude, is the DC input voltage), so as to obtain the inverter bridge arm output voltage . The inverter bridge arm output voltage is subtracted from the output voltage sampling value , so as to obtain the filter inductor voltage . The filter inductor voltage is divided by the filter inductor reactance , so as to obtain the inductor current sampling value . The inductor current sampling value is subtracted from the output current , so as to obtain the capacitor current . The capacitor current is divided by the capacitor capacitance Multiplying, the output voltage is obtained .

[0042] In step S305, the inductor current sample value and the output voltage sample value are input to the disturbance observer to obtain an estimated value of the unknown disturbance.

[0043] Specifically, the disturbance observer of formula (5) is discretized to obtain the following discretized disturbance observer: (6) Wherein, is a control period.

[0044] Further, in the discretized disturbance observer, the estimated value of the output voltage and the estimated value of the unknown disturbance are initialized, and the inductor current sample value and the output voltage sample value are input to the discretized disturbance observer for recursive calculation to obtain the estimated value of the unknown disturbance in the current control period. Specifically, in the discretized disturbance observer, 0 time And 0 time Are initialized, and then the inductor current sample value And the output voltage sample value At the first time are obtained, the inductor current sample value And the output voltage sample value At the first time are input to the disturbance observer of formula (6), and the estimated value of the output voltage at the first time And the estimated value of the unknown disturbance at the first time are obtained. Recursive calculation in this way can obtain the estimated value of the output voltage and the estimated value of the unknown disturbance in each control period.

[0045] In step S306, based on the original inductor current reference value, the estimated value of the unknown disturbance, and the inductor current reference value compensation model, the compensated inductor current reference value is obtained.

[0046] Based on the estimated value of the unknown disturbance in the current control period obtained in step S305, and based on the original inductor current reference value, the estimated value of the unknown disturbance, and the inductor current reference value compensation model of formula (3), the compensated inductor current reference value is obtained. In an embodiment, the unknown disturbance is the load current, and the compensated inductor current reference value is obtained by superimposing the original inductor current reference value and the estimated value of the unknown disturbance.

[0047] Please refer to Figure 5 , Figure 5 is a schematic diagram of the inductor current reference value compensation control strategy provided by the embodiment of the application. Compared with the conventional double closed-loop control strategy of Figure 4 In the inductor current reference value compensation control strategy of the application, the output voltage reference value the output voltage sampling value after the difference is sent to the voltage outer loop controller to generate an original inductance current reference value; the inductance current sampling value and the output voltage sampling value are sent to a disturbance observer to output an estimated value of an unknown disturbance ; the original inductance current reference value and the estimated value of the unknown disturbance are superimposed to obtain a compensated inductance current reference value ; and the compensated inductance current reference value is sent to a current inner loop controller to obtain a modulation wave signal, thereby achieving the purpose of suppressing the disturbance of the load current on the output voltage and optimizing the waveform quality of the output voltage when the inverter is loaded with a nonlinear load.

[0048] Please refer to Figure 6 , Figure 6 is a control effect comparison chart provided by the embodiment of the application, which compares the control effect of the conventional double closed loop control strategy and the inductance current reference value compensation control strategy. Figure 6 As can be seen from the chart, the waveform quality of the output voltage when the inverter is loaded with a nonlinear load by using the inductance current reference value compensation control strategy of the application is obviously superior to the waveform quality of the output voltage when the inverter is loaded with a nonlinear load by using the conventional double closed loop control strategy, and the THD index of the output voltage is reduced.

[0049] The method for compensating the inductance current reference value provided by the embodiment of the application first establishes a state equation of an inverter circuit, and determines an inductance current reference value compensation model containing an unknown disturbance and constructs a disturbance observer for estimating the unknown disturbance based on the state equation of the inverter circuit; then, an output voltage reference value, an inductance current sampling value and an output voltage sampling value are obtained, voltage outer loop control is performed on the inverter based on the output voltage sampling value and the output voltage reference value to obtain an original inductance current reference value, and the inductance current sampling value and the output voltage sampling value are input to the disturbance observer to obtain an estimated value of the unknown disturbance; finally, a compensated inductance current reference value is obtained based on the original inductance current reference value, the estimated value of the unknown disturbance and the inductance current reference value compensation model. The method of the application estimates the disturbance by using the disturbance observer, compensates the inductance current reference value based on the estimated value of the disturbance, and inputs the compensated inductance current reference value as the final inductance current reference value to a current control inner loop to generate a modulation wave, thereby achieving the purpose of suppressing the disturbance of the load current on the output voltage and optimizing the waveform quality of the output voltage when the inverter is loaded with a nonlinear load.

[0050] The embodiments of the present application further provide a non-volatile computer readable storage medium storing computer executable instructions, which are executed by one or more processors to perform the method steps described above. Figure 3

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the same; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in a corresponding order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for simplicity; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features therein can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.​

Claims

1. A method of compensating an inductor current reference value, characterized by, The method is applied to a single-phase off-grid inverter, and comprises the following steps: According to Kirchhoff's law, a state equation of an inverter circuit is established; According to the state equation of the inverter circuit, an inductance current reference value compensation model containing an unknown disturbance quantity is determined; According to the state equation of the inverter circuit, a disturbance observer for estimating the unknown disturbance quantity is constructed; An output voltage reference value, an inductance current sample value and an output voltage sample value are obtained, voltage outer loop control is performed on the inverter based on the output voltage sample value and the output voltage reference value, and an original inductance current reference value is obtained; The inductance current sample value and the output voltage sample value are input into the disturbance observer, and an estimated value of the unknown disturbance quantity is obtained; Based on the original inductance current reference value, the estimated value of the unknown disturbance quantity and the inductance current reference value compensation model, a compensated inductance current reference value is obtained.

2. The method of claim 1, wherein, The state equation of the inverter circuit is: wherein, is a capacitance value of the filter capacitor, is an inductive current, is a capacitive current, is an output current, is an output voltage.

3. The method of claim 1, wherein, The inductance current reference value compensation model is: wherein, is the compensated inductor current reference value, is the original inductor current reference value output by the voltage outer loop controller, is the estimated value of the unknown disturbance.

4. The method of claim 1, wherein, The unknown disturbance quantity is a load current.

5. The method of claim 4, wherein, The compensation of the inductance current reference value based on the original inductance current reference value, the estimated value of the unknown disturbance quantity and the inductance current reference value compensation model comprises: The original inductance current reference value and the estimated value of the unknown disturbance quantity are superimposed to obtain a compensated inductance current reference value.

6. The method according to any one of claims 1 to 5, characterized in that, The disturbance observer is: wherein, is an estimate of the output voltage, is an inductor current sample value, is an estimate of the unknown disturbance quantity, and is an observer coefficient, is a filter capacitance value, is an output voltage.

7. The method of claim 6, wherein, The estimation of the unknown disturbance quantity based on the inductance current sample value, the output voltage sample value and the disturbance observer comprises: The disturbance observer is discretized to obtain a discretized disturbance observer as follows, where Control period: The estimated value of the output voltage and the estimated value of the unknown disturbance quantity are initialized in the discretized disturbance observer; The inductance current sample value and the output voltage sample value are input into the discretized disturbance observer to obtain an estimated value of the unknown disturbance quantity in a current control period.

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 connected with the at least one processor in communication, 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 inductance and a filter capacitance.

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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