Inverter and method for controlling inverter

Abstract

The invention provides an inverter and an inverter control method, a circuit is connected with a power grid, and the circuit comprises an inverter circuit which comprises a switching device; the filter circuit comprises an LC filter circuit, and an inductor of the LC filter circuit is connected with the inverter circuit; the feedback controller is electrically connected with the filter circuit, the feedback controller is used for superposing the obtained fundamental component of the capacitive current with the inductive current to generate a feedback current, the capacitive current is the current of a capacitor in the LC filter circuit, and the inductive current is the current of an inductor in the LC filter circuit; and the pulse generator is electrically connected with the feedback controller and the inverter circuit and is used for generating a pulse signal according to the grid-connected instruction current of the inverter and the received feedback current, the pulse signal is used for controlling a switching device of the inverter circuit so as to generate the output current of the inverter circuit, and the grid-connected instruction current is determined by the target output power of the inverter.

Description

Technical Field

[0001] The present application relates to the field of inverters, and in particular to an inverter and a control method for the inverter. Background Art

[0002] The grid-connected system, also known as the grid-connected power generation system, is an electric power system that connects the power generation system to the power grid. At present, in the grid-connected system, the grid-connected inverter is the core device that connects the power generation system to the power grid, which is crucial to the stable operation of the power system. However, in the process of grid connection, the stability of the grid-connected system may be affected due to factors such as the volatility of the power generation system or the nonlinear characteristics of electronic equipment. The relevant technology proposes that a filter circuit can be set at the output end of the inverter circuit in the inverter, which can effectively filter out high-order harmonics, thereby improving the stability of the grid-connected system.

[0003] In order to improve the stability of the grid-connected system, the grid-connected current can be monitored by the control system to determine whether it is stable. In the related art, the control system can use the inductor current in the filter circuit as the feedback quantity for closed-loop control. However, since the filter circuit also includes a capacitor, the branch where the capacitor is located will introduce a reactive current, which will lead to the generation of reactive power, thereby reducing the unity power factor of the grid-connected system and affecting the stability of the grid-connected system.

[0004] In response to this problem, the relevant technology proposes that the capacitor current can be superimposed on the feedback of the inductor current in the control system to achieve compensation for reactive power, so as to avoid the problem of power factor reduction caused by superimposing the capacitor current as feedback. However, in actual circuit design, the existing method of obtaining capacitor current has the following problems: the use of a new current sensor in the circuit to obtain the capacitor current will lead to an increase in the cost of the grid-connected system; the capacitor current is obtained by differentiating the grid-connected point voltage, which will more easily bring high-frequency interference to the grid-connected system, thereby affecting the stability of the grid-connected system. Therefore, how to better ensure the stability of the grid-connected system needs to be solved urgently. Summary of the invention

[0005] In view of this, embodiments of the present application are directed to providing an inverter and a method for controlling the inverter.

[0006] In a first aspect, an inverter is provided, which is electrically connected to a power grid, and includes: an inverter circuit, which includes a switching device; a filter circuit, which includes an LC filter circuit, and the inductor in the LC filter circuit is electrically connected to the inverter circuit; a feedback controller, which is electrically connected to the filter circuit, and is used to superimpose the fundamental component of the acquired capacitor current with the inductor current to generate a feedback current, wherein the capacitor current is the current of the capacitor in the LC filter circuit, and the inductor current is the current of the inductor in the LC filter circuit; a pulse generator, which is electrically connected to the feedback controller and the filter circuit, and is used to generate a pulse signal according to the grid-connected command current of the inverter and the received feedback current, and the pulse signal is used to control the switching device of the inverter circuit to generate an output current of the inverter circuit, wherein the grid-connected command current is determined by the target output power of the inverter.

[0007] According to the first aspect, the point where the inverter is electrically connected to the grid is the grid connection point, and the fundamental component of the capacitor current is determined by the fundamental component of the grid connection point voltage, wherein the fundamental component of the grid connection point voltage is determined by the grid connection point voltage value and the phase angle of the grid connection point voltage corresponding to the grid connection point voltage value.

[0008] According to the first aspect, or any implementation of the first aspect above, the inverter also includes: a phase-locked loop, the phase-locked loop is electrically connected to the feedback controller and the grid-connected point voltage sensor, the grid-connected point voltage sensor is used to sample the grid-connected point voltage, the phase-locked loop is used to obtain sampling data of the grid-connected point voltage sensor, and is used to obtain the phase angle of the grid-connected point voltage based on the sampling data.

[0009] According to the first aspect, or any implementation of the first aspect above, the inverter further includes: a differential circuit, the differential circuit is electrically connected to the feedback controller, and the differential circuit is used to differentiate the fundamental component of the grid-connected point voltage to obtain the fundamental component of the capacitor current.

[0010] According to the first aspect, or any implementation of the first aspect above, the inverter further includes: a divider, the divider is electrically connected to the feedback controller, and the divider is used to perform a division operation of the fundamental component of the grid-connected point voltage and the impedance of the capacitor.

[0011] In a second aspect, the present application provides a control method for an inverter, wherein the inverter is electrically connected to a power grid, the inverter circuit includes a switching device, the inverter includes a filtering circuit, a feedback controller, a pulse generator and a switching device, the filtering circuit includes an LC filtering circuit, the inductor in the LC filtering circuit is electrically connected to the inverter circuit, the feedback controller is electrically connected to the filtering circuit, the pulse generator is electrically connected to the feedback controller and the filtering circuit, and the control method includes: obtaining a fundamental component of a capacitor current and an inductor current, superimposing the fundamental component of the capacitor current and the inductor current through a feedback controller to generate a feedback current; obtaining a grid-connected command current of the inverter, wherein the grid-connected command current is determined by a target output power of the inverter; obtaining the grid-connected command current of the inverter and the feedback current through a pulse generator to generate a pulse signal; controlling the switching device of the inverter circuit through the pulse signal to generate an output current of the inverter circuit, wherein the capacitor current is the current of the capacitor in the LC filtering circuit, and the inductor current is the current of the inductor in the LC filtering circuit.

[0012] According to the second aspect, the point where the inverter is electrically connected to the grid is the grid connection point, and the fundamental component of the capacitor current is determined by the fundamental component of the grid connection point voltage, wherein the fundamental component of the grid connection point voltage is determined by the grid connection point voltage value and the phase angle of the grid connection point voltage corresponding to the grid connection point voltage value.

[0013] According to the second aspect, or any implementation of the second aspect above, the inverter also includes a phase-locked loop, the phase-locked loop is electrically connected to the feedback controller and the grid-connected point voltage sensor, the grid-connected point voltage sensor is used to sample the grid-connected point voltage, and the control method also includes: obtaining sampling data of the grid-connected point voltage sensor through the phase-locked loop, and obtaining the phase angle of the grid-connected point voltage according to the sampling data.

[0014] According to the second aspect, or any implementation of the second aspect above, the inverter also includes a differential circuit, the differential circuit is electrically connected to the feedback controller, and the control method also includes: differentiating the fundamental component of the grid-connected point voltage through the differential circuit to obtain the fundamental component of the capacitor current.

[0015] According to the second aspect, or any implementation of the second aspect above, the inverter also includes a divider, the divider is electrically connected to the feedback controller, and the control method also includes: performing a division operation of the fundamental component of the grid-connected point voltage and the impedance of the capacitor by the divider.

[0016] In a third aspect, the present application provides a computer-readable storage medium, which is used for a program code executed by a computer, and the program code includes a control method for executing the inverter of the second aspect.

[0017] In a fourth aspect, an embodiment of the present application provides a computer program, which includes commands for executing the inverter control method of the second aspect.

[0018] The inverter proposed in the embodiment of the present application controls the output current of the inverter circuit by superimposing the fundamental components of the inductor current and the capacitor current as feedback, thereby reducing the reactive power in the grid-connected system, avoiding the impact on the power factor of the grid-connected system, and improving the stability of the grid-connected system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a LCL type three-phase grid-connected inverter topology diagram proposed in the related technology.

[0020] Figure 2 It is a LCL type single-phase grid-connected inverter topology diagram proposed in the related technology.

[0021] Figure 3 This is a circuit current phase diagram provided in an embodiment of the present application.

[0022] Figure 4 This is another circuit current phase diagram provided in an embodiment of the present application.

[0023] Figure 5 A schematic diagram of the structure of an inverter provided in an embodiment of the present application.

[0024] Figure 6 A schematic diagram of the structure of another inverter provided in an embodiment of the present application.

[0025] Figure 7 A flowchart of an inverter control system provided in an embodiment of the present application.

[0026] Figure 8 A schematic flow chart of a method for controlling an inverter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field based on the present application belong to the scope of protection of the present application.

[0028] The term "and / or" in this article is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

[0029] The terms "first" and "second" in the description and claims of the embodiments of the present application are used to distinguish different objects rather than to describe a specific order of objects. For example, a first target object and a second target object are used to distinguish different target objects rather than to describe a specific order of target objects.

[0030] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0031] It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] The grid-connected system, also known as the grid-connected power generation system, is a power system that connects the power generation system to the power grid. At present, in the grid-connected system, the grid-connected inverter is the core device that connects the power generation system to the power grid, which is crucial to the stable operation of the power system. The grid-connected inverter can be understood as a special inverter. In addition to converting DC power into AC power, the AC power output of the grid-connected inverter can be synchronized with the frequency and phase of the power grid, thereby achieving connection with the power grid.

[0033] However, in the process of grid connection, the stability of the grid-connected system may be affected due to factors such as the volatility of the power generation system or the nonlinear characteristics of electronic equipment. For example, the grid-connected inverter will generate a large number of harmonics during operation, which will affect the stability of the grid-connected system and may even cause accidents in the power system. Therefore, in order to improve the stability of the grid-connected system, the relevant technology proposes to set a filter circuit at the output end of the inverter circuit in the inverter, such as an LCL type or LC type filter circuit, which can effectively filter out high-order harmonics, thereby improving the stability of the grid-connected system. Taking a single-phase or three-phase grid-connected inverter with an LCL type or LC type filter circuit as an example, Figure 1 This is the topology diagram of the LCL type three-phase grid-connected inverter. Figure 2 This is the topology diagram of the LCL type single-phase grid-connected inverter. Figure 1 and Figure 2 In the circuit topology diagram, the filtering parameter design method of large inductance and small capacitance can be adopted.

[0034] In order to improve the stability of the grid-connected system, the grid-connected current can be monitored by the control system to determine whether it is stable. When the control system finds that the grid-connected current fluctuates, the output of the inverter, such as the current output, can be controlled to ensure the stability of the grid-connected current. In the related art, the control system can use the inductor current in the filter circuit as a feedback quantity for closed-loop control. Compared with the method of directly controlling the grid-side current, the system that controls the inductor current has better stability. Taking the inverter with an LCL or LC filter circuit as an example, the control method of the inductor current in the filter circuit can be used to improve the system stability.

[0035] In the grid-connected system, the power factor (PF) can be used to measure whether the grid-connected system effectively utilizes electric energy. It can also be understood that the grid-connected system can judge the utilization rate of the power equipment and the quality of electric energy in the grid-connected system through the power factor. The power factor can be expressed as the ratio of active power to apparent power in the circuit. Active power is the actual power consumed, that is, the actual power used for work, and apparent power is the total power provided by the power supply. The higher the power factor, the higher the utilization rate of the power equipment and the better the quality of the electric energy. At the same time, the concept of reactive power is also proposed in the power factor. When the reactive power is too large, the power factor will decrease. This is because the power factor is the ratio of active power to apparent power, and the apparent power is composed of active power and reactive power. The unity power factor can be understood as the grid-connected current and voltage are completely in phase, and there is no exchange of reactive power, thereby improving the overall efficiency and stability of the system. Therefore, in the grid-connected system, by reducing the reactive power to approach the unity power factor, the grid-connected system can be operated efficiently and stably. In the related art, reactive power is related to reactive current or reactive voltage. For example, when the reactive current in the grid-connected system is larger, the reactive power in the system is also larger, which will cause the power factor to decrease.

[0036] In the above control system, although the inductor current in the filter circuit can be used as feedback quantity for closed-loop control to improve the stability of the grid-connected system. Figure 2 For example, due to the presence of capacitor C in the filter circuit, the branch where the capacitor C is located will introduce a reactive current I C , the reactive current I C The inductor current I of the inverter circuit L and grid current I G There is a certain phase difference. Figure 3 As shown, when the inductor current of the inverter filter circuit is the control object and the control target is the unity power factor, the inductor current I L and voltage U g are in phase. Due to the existence of the capacitor branch, the reactive current I C, resulting in the grid-side voltage U g and grid-side current I G There is a phase difference, which reduces the power factor of the grid-connected system. Therefore, in the grid-connected system that controls the inductor current, the grid current I G and voltage U g It is difficult to operate at unity power factor, and the larger the filter capacitor C, the larger the reactive current introduced, and the greater the impact on the power factor of the grid-side voltage and current.

[0037] In response to the above problems, the related technology proposes that the capacitor current can be superimposed on the feedback of the inductor current to achieve compensation for reactive power, so as to avoid the problem of power factor reduction caused by superimposing the capacitor current as feedback. Figure 4 As an example, the capacitor current and the inductor current in the above filter circuit can be superimposed, and the inverter grid-side current I can be obtained according to Kirchhoff's principle. G The control system can indirectly control the grid current by directly controlling the inductor current and capacitor current, so that the power factor of the grid-connected current and voltage is closer to the command value, thereby ensuring the efficient and stable operation of the grid-connected system. In the related technology, two methods are usually used to obtain the capacitor current. Method 1 is to add a current sensor to the capacitor circuit to sample and obtain the capacitor current; Method 2 is to differentiate the grid-connected point voltage, and the capacitor current formula can be used to obtain the capacitor current. The capacitor current is calculated and then superimposed on the inductor current feedback for compensation. In a grid-connected system, the grid connection point may refer to the connection point between the power equipment in the grid-connected system and the grid. The grid connection point voltage is an important indicator to measure the power state of the connection point.

[0038] However, in actual circuit design, the above two methods of obtaining capacitor current will have the following problems. The implementation of method one requires adding a current sensor to the circuit, which will increase the cost of the grid-connected system; while the implementation of method two will more easily bring high-frequency interference to the grid-connected system. When the grid impedance is large, that is, under weak grid conditions, the capacitor current obtained by these two methods will fluctuate in the grid connection point voltage and the capacitor current. For example, when the grid impedance is large, the grid connection point voltage can be Where U nrms is the effective value of the n-th voltage, n For the corresponding voltage phase angle, n = 1, 2, 3..., according to the capacitor current formula The value of I can be obtained. When the capacitor current and the inductor current are superimposed as feedback components, it can be seen from the above that the capacitor current includes multiple high-order harmonics, which leads to the introduction of multiple high-order harmonics in the feedback current, making the control system unstable and affecting the stability of the grid-connected system. Therefore, how to better ensure the stability of the grid-connected system needs to be solved urgently.

[0039] The present application proposes an inverter to solve the above problems. Figure 5 , the embodiments of the present application are described.

[0040] Figure 5 A schematic diagram of the structure of an inverter 500 provided in an embodiment of the present application. Figure 5 The inverter 500 in the embodiment can be electrically connected to the power generation system and the power grid.

[0041] like Figure 5 As shown, the inverter 500 includes an inverter circuit 510 , a filter circuit 520 , a feedback controller 530 , and a pulse generator 540 .

[0042] In the embodiment of the present application, the inverter circuit 510 can be electrically connected to the filter circuit 520, the feedback controller 530 can be electrically connected to the filter circuit and the pulse generator, and the pulse generator can also be electrically connected to the filter circuit 520.

[0043] In some embodiments, the inverter 500 may be a grid-connected inverter, which may be used to convert the direct current generated by the renewable energy power generation system into alternating current, and to connect the alternating current to the power grid. For example, the grid-connected inverter may connect a plurality of parallel photovoltaic strings to the input of the grid-connected inverter. For another example, the grid-connected inverter may connect a wind power generation system to the input of the grid-connected inverter.

[0044] In some embodiments, the inverter circuit 510 may include a switch device. Optionally, the inverter circuit 510 may realize an inverter function by controlling the on and off of the switch device.

[0045] In some embodiments, the filter circuit 520 may include an LC filter circuit. Alternatively, the filter circuit 520 may also include an LCL filter circuit. In some embodiments, the inductor in the LC filter circuit may be electrically connected to the inverter circuit 510.

[0046] Exemplarily, when the filter circuit 520 includes an LC filter circuit, the inverter 500 may be an LC type single-phase inverter. Alternatively, the inverter 500 may be an LC type three-phase inverter. Exemplarily, when the filter circuit 520 includes an LCL filter circuit, the inverter 500 may be an LCL type single-phase inverter, such as Figure 2 Optionally, the inverter 500 may be a three-phase inverter of LCL type, such as Figure 1 shown.

[0047] In some embodiments, the feedback controller 530 can obtain the inductor current in the filter circuit 520 and the fundamental component of the capacitor current in the filter circuit 520. After obtaining, the feedback controller 530 can superimpose the fundamental components of the inductor current and the capacitor current to generate a feedback current and output it.

[0048] Optionally, when the filter circuit 520 includes an LC filter circuit, the inductor current may be the current of the inductor in the LC filter circuit, and the capacitor current may be the current of the capacitor in the LC filter circuit. Exemplarily, the inductor current may be the current of the inductor in the LC filter circuit electrically connected to the inverter circuit 510.

[0049] In some embodiments, the inductor current in the filter circuit 520 refers to the current flowing through the inductor electrically connected to the filter circuit 520 , and the feedback controller 530 can obtain the inductor current from the filter circuit 520 .

[0050] In some embodiments, the capacitor current in the filter circuit 520 refers to the current flowing through the capacitor. Exemplarily, when the grid impedance is large under a weak grid, the voltage and current output by the inverter circuit 510 may contain high-frequency switching harmonics. When these harmonic components pass through the filter circuit 520, some of the harmonic components will be filtered and absorbed by the filter circuit 520, resulting in the capacitor current in the filter circuit 520 including not only the fundamental component, but also the harmonic component. The fundamental component of the capacitor current can be understood as the lowest frequency sine wave component in the current on the capacitor in the AC circuit, and the frequency of the fundamental component can be the same as the frequency of the grid-connected point voltage. Since only the fundamental frequency needs to be considered when calculating the power factor, in order to avoid the harmonic component in the capacitor current from affecting the power factor, the feedback controller 530 can superimpose the fundamental component of the capacitor current obtained with the inductor current obtained, generate feedback current to compensate for reactive power, so as to achieve the reduction of reactive power in the grid-connected system, avoid the influence on the power factor of the grid-connected system, and improve the stability of the grid-connected system.

[0051] In some embodiments, the point where the inverter in the grid-connected system is electrically connected to the grid can be called a grid-connected point, and the fundamental component of the capacitor current can be determined by the fundamental component of the grid-connected point voltage. Optionally, in the grid-connected system, the fundamental component of the grid-connected voltage is differentiated to obtain the fundamental component of the capacitor current in the filter circuit 520. The fundamental component of the capacitor current is used as part of the feedback current to enter the closed-loop control, which can avoid the influence of the reactive current generated by the capacitor current on the power factor.

[0052] In some embodiments, the fundamental component of the grid connection point voltage can be determined by the grid connection point voltage value and the phase angle of the grid connection point voltage corresponding to the grid connection point voltage value. Exemplarily, the fundamental component is a sine wave, and its characteristics can be described by two parameters: amplitude and phase angle. Optionally, the amplitude of the grid connection point voltage can be used as the amplitude of the fundamental component sine wave, and the phase angle corresponding to the grid connection point voltage can be used as the phase angle of the fundamental component sine wave. A sine wave can be uniquely determined by the amplitude and phase angle, for example, Among them, U PCC Can be the voltage value of the fundamental component, U 1rms is the amplitude of the fundamental component, is the phase angle corresponding to the grid connection point voltage value.

[0053] For example, under weak grid conditions, when the grid impedance is large, the grid connection point voltage will fluctuate or oscillate. Since only the fundamental component of the capacitor current is introduced into the feedback current, even under weak grid conditions, the feedback current is not affected by the grid connection point voltage fluctuation. Therefore, the fundamental component of the capacitor current determined by the fundamental component of the grid connection point voltage can avoid the problem of system instability caused by grid connection point voltage oscillation under weak grid conditions, thereby improving the stability of the grid-connected system.

[0054] In some embodiments, the pulse generator 540 may obtain a grid-connected command current of the inverter 500. Optionally, the grid-connected command current is determined by a target output power of the inverter.

[0055] In some embodiments, in a grid-connected system, in order to achieve specific control objectives, such as maintaining voltage stability, adjusting power factor, etc., the grid-connected system can generate a reference value or target value of the grid-connected current based on real-time monitoring data and control strategies. This reference value or target value of the grid-connected current can be called a grid-connected command current. It can also be understood that the grid-connected command current is the current that the inverter should generate in the grid-connected system.

[0056] In some embodiments, the grid-connected command current includes not only the current value but also the phase value. That is, the grid-connected command current includes the current magnitude and phase that the inverter should output. Optionally, if the target is unity power factor, the grid-connected command current should be in phase with the grid-connected point voltage, and the phase can be the phase angle value of the grid-connected point voltage.

[0057] In some embodiments, the pulse generator 540 can receive the feedback current output by the feedback controller 530, and generate a pulse signal according to the grid-connected command current and the feedback current. Optionally, the pulse generator 540 can also be a sinusoidal pulse width modulation (SPWM) controller. Optionally, the pulse generator 540 can also be a pulse width modulation (PWM) controller.

[0058] In some embodiments, a proportional-integral controller (PI) may be provided before the pulse generator 540. The grid-connected command current and the feedback current may first enter the PI controller, which may be adjusted according to the error between the grid-connected command current and the feedback current, and output a control signal, which may be input into the pulse generator to finally generate a pulse signal.

[0059] In some embodiments, the pulse signal generated by the pulse generator 540 can control the switching device of the inverter circuit to generate an output current of the inverter circuit.

[0060] In the embodiment of the present application, during the grid connection process, the feedback controller 530 can obtain the fundamental wave components of the inductor current and the capacitor current of the filter circuit 520 to generate a feedback current. Based on the power requirement set by the grid-connected system, it can also be understood that according to the power requirement of the inverter 500, the grid-connected command current can be obtained. The pulse generator 540 can generate a pulse signal according to the grid-connected command current and the feedback signal, and the pulse signal can drive or control the switching device of the inverter circuit 510 to output the output current of the inverter circuit 510. It can be understood that in the embodiment of the present application, the output current of the inverter circuit 510 can track the grid-connected command current. When the output current of the inverter circuit 510 obtained after adding the fundamental wave component of the capacitor current to the feedback current, when passing through the filter circuit 520, the output current of the inverter circuit 510 will be divided by a part of the path where the capacitor is located, and the remaining current is the grid-connected current, which is close to the grid-connected command current.

[0061] Below Figure 5 Take the example to illustrate the embodiments of the present application. Figure 5 In the example, the output current of the inverter circuit 510 is the current I of L1. L The grid-connected current of the inverter 500 can also be considered as the output current of the filter circuit 520, that is, the current I of L2 G The output current I of the inverter circuit 510 is L In a grid-connected system that does not use capacitor current as compensation, the output current IL When passing through the filter circuit 520, a portion of the current will be divided by the capacitor C in the filter circuit 520, resulting in the grid current I G The current and the grid-connected command current are inconsistent, resulting in an increase in reactive power, which in turn causes the power factor of the grid-connected system to decrease. Therefore, the fundamental component of the inductor current can be used together with the inductor current as the feedback current I L +I C , and controls the switching device of the inverter circuit 510 through the pulse generator 540 to generate a new output current of the inverter circuit 510, that is, the current I L '. It can be understood that the current I L ′ contains the fundamental component of the capacitor current. When the current I L 'When passing through the filter circuit 520, the capacitor path can transfer the current I L ′ contains the fundamental component I of the capacitor current C ′, to compensate for the reactive power caused by the capacitor, and the other part I G ′ is the grid-connected command current of the grid-connected system.

[0062] Therefore, the inverter proposed in the embodiment of the present application can control the output current of the inverter circuit by superimposing the fundamental components of the inductor current and the capacitor current as feedback, thereby reducing the reactive power in the grid-connected system, avoiding the impact on the power factor of the grid-connected system, and improving the stability of the grid-connected system.

[0063] In some embodiments, the inverter in the embodiment of the present application further includes a phase-locked loop, which can be electrically connected to the feedback controller and the grid-connected point voltage sensor, such as Figure 6 For example, the grid connection point voltage sensor can be used to sample the grid connection point voltage.

[0064] In some embodiments, the phase-locked loop can obtain sampling data through a grid-connected point voltage sensor, and obtain the phase angle of the grid-connected point voltage based on the sampling data. Exemplarily, the power grid may include a grid-connected point voltage sensor to monitor and sample the grid-connected point voltage, and the grid-connected point voltage sensor may send its sampling data to the phase-locked loop. After receiving the sampling data, the phase-locked loop can process the sampling data to extract the phase information of the grid-connected point voltage, and finally, through the negative feedback mechanism inside the phase-locked loop, the phase-locked loop can output the phase angle of the grid-connected point voltage. Exemplarily, the phase angle of the grid-connected point voltage can be obtained according to the phase-locked loop.

[0065] The phase-locked loop can accurately track the phase and frequency changes of the grid-connected point voltage, and can maintain high accuracy and stability even when the grid fluctuates or is disturbed. The phase-locked loop also has a faster dynamic response capability, which can improve the reliability of the grid-connected system. At the same time, the phase-locked loop can effectively suppress noise and interference through the control algorithm, improve the signal-to-noise ratio of the signal, and thus obtain more accurate phase angle information.

[0066] In some embodiments, the inverter in the embodiment of the present application may further include a differential circuit, which may be electrically connected to the feedback controller, such as Figure 6 The differential circuit shown in FIG. The differential circuit can be used to differentiate the fundamental component of the grid-connected point voltage, so as to obtain the fundamental component of the capacitor current. For example, when the fundamental component of the grid-connected point voltage is According to the capacitor current formula Passing the fundamental component of the grid-connected voltage through the differential circuit, we can get In this formula, C is the capacitance value, U is rms is the effective value of voltage, is the corresponding voltage phase angle.

[0067] In some embodiments, the differential circuit may include a capacitor and a resistor to implement differential operation on the input signal. Exemplarily, the differential circuit may be implemented by a capacitor connected in parallel with a resistor.

[0068] In the embodiment of the present application, the fundamental component of the grid connection point voltage is differentiated by a differential circuit to obtain the fundamental component of the capacitor current. Compared with the software algorithm in digital signal processing, the differential circuit can be used to perform differential calculations on the input signal in real time, and a faster control response can be achieved. Optionally, a filtering function can also be included in the differential circuit, so that high-frequency noise can be effectively suppressed and the accuracy of the differential result can be improved. Under weak grid conditions, the grid impedance is large, which easily causes the grid connection point voltage to oscillate. By differentiating the fundamental component of the grid connection point voltage, the influence of these oscillations can be avoided, and the stability of the system under weak grid conditions can be improved.

[0069] In some embodiments, the inverter in the embodiment of the present application may further include a divider, which may be electrically connected to the feedback controller, such as Figure 6 The divider shown in FIG. 1 can be used to perform a division operation between the fundamental component of the grid-connected point voltage and the capacitor impedance. For example, in an AC circuit, the fundamental component of the grid-connected point voltage can be The impedance modulus of the capacitor is R C In AC, the calculation of capacitor current needs to take into account the phase difference of capacitor current leading the voltage by 90 degrees. First, the impedance Z of the capacitorC is a complex number. When the impedance modulus of the capacitor is R C When the phase can be -90 degrees (or radians), so Z C = -j·R C , through the divider, the capacitor current can be obtained because so Also because Therefore, the capacitor current

[0070] Optionally, the impedance of the capacitor can be determined by the capacitance value C and the signal frequency. For example, the capacitance value C has been determined in the circuit design stage and can be obtained from the circuit diagram or the original specification book. Taking the filter circuit of a single-phase LCL inverter as an example, the signal frequency can be the fundamental frequency of the grid-connected point voltage. Optionally, the fundamental frequency of the grid-connected point voltage can be obtained by a phase-locked loop.

[0071] In some embodiments, a field-programmable gate array (FPGA) in the circuit can be reused as a divider to calculate the capacitor current I C The value of .

[0072] In the embodiment of the present application, the fundamental component of the grid connection point voltage is divided by the impedance of the capacitor by a divider to obtain the fundamental component of the capacitor current. It can accurately reflect the changes in capacitor current and improve the control accuracy of the control system. Directly calculating the fundamental component of the grid-connected point voltage can avoid the interference of high-order harmonic components and reduce the unstable factors in the control system, thereby improving the stability of the grid-connected system.

[0073] Combine the following Figure 6 and Figure 7 , the embodiments of the present application are described in detail. Figure 6 In the figure, L1, L2 and C form the grid-side filter inductor, L GRID is the grid impedance. For example, when the grid is strong, L GRID Close to 0; when in weak grid conditions, L GRID Cannot be ignored. Figure 7 for Figure 6 Flow chart of the inverter control system.

[0074] In some embodiments, I_ Dref is the current value that the inverter expects to generate. The phase angle of the grid-connected point voltage is obtained through the phase-locked loop and can be compared with I_ Dref Multiply them to generate the inverter grid-connected command current I_ref , grid-connected command current I_ ref It can be a sine wave, I L is the current of inductor L1, I C is the current of capacitor C. The grid voltage feedforward is U_ grid .

[0075] In some embodiments, when a single-phase inverter filter circuit is used, Figure 7 The control system shown controls the output current of the inverter. Optionally, when a filter circuit of a three-phase inverter is used, each of the three phases corresponds to a Figure 7 The control system shown.

[0076] In some embodiments, the feedback controller outputs the feedback current I L +I C .

[0077] In some embodiments, a PI controller may be provided before the pulse generator. The grid-connected command current and the feedback current may first enter the PI controller, which may be adjusted according to the error between the grid-connected command current and the feedback current, and output a control signal, which may be input into the pulse generator to ultimately generate a pulse signal to control the switching device of the inverter circuit, and ultimately generate the required current waveform.

[0078] In some embodiments, the control signal output by the PI controller can be combined with the grid voltage feedforward before the pulse generator, and the grid voltage feedforward can compensate for the change of the grid voltage, so that the control system can respond to the fluctuation of the grid voltage more quickly. This helps to reduce the error in the dynamic process, improve the dynamic response speed of the system, and improve the performance and stability of the control system.

[0079] Figure 7 The working process of the inverter control system shown is as follows:

[0080] Step 1: Get the current value I_ that the inverter expects to generate Dref , and obtain the phase angle of the grid connection point voltage according to the phase-locked loop Generate grid-connected command current I_ ref .

[0081] Step 2: According to the effective value of the grid voltage U rms And the phase angle of the grid connection point voltage obtained by the phase-locked loop Calculate the fundamental component of the grid connection point voltage

[0082] Step 3: According to the capacitor current formula Get the fundamental component of the capacitor current.

[0083] Step 4: Use the feedback controller to control the capacitor current I C Superimposed on the inductor current I L , generating feedback current I C +I L , and obtain the current feedback value of the control system.

[0084] Step 5: PI controller can be used according to the grid-connected command current I_ ref and feedback current I C +I L The error adjustment output signal.

[0085] Step 6: The output signal obtained in the fifth step can be used to compensate for the grid-connected point voltage feedforward and enter the pulse generator to obtain a pulse signal.

[0086] Step 7: The final output pulse signal can drive the switching device of the inverter circuit and control the output current of the inverter circuit.

[0087] In some embodiments, the third step in the above steps can be replaced by the following method:

[0088] According to the grid connection point voltage obtained in the second step, the fundamental component of the capacitor current can be obtained by dividing it with the capacitor impedance.

[0089] The inverter proposed in the embodiment of the present application can control the output current of the inverter by superimposing the fundamental components of the inductor current and the capacitor current as feedback, thereby reducing the reactive power in the grid-connected system, avoiding the impact on the power factor of the grid-connected system, and improving the stability of the grid-connected system. At the same time, the fundamental component of the capacitor current is determined by the fundamental component of the grid-connected point voltage, which can avoid the problem of instability of the control system caused by the interference caused by the capacitor current oscillation caused by the grid-connected point voltage oscillation under the condition of weak power grid.

[0090] The circuit embodiments of the present application are described in detail above. Based on the above content, the present application also proposes a control method for an inverter. Figure 8 The method embodiment of the present application is described in detail. It should be understood that the description of the above circuit embodiment corresponds to the description of the method embodiment, so the parts not described in detail can refer to the above circuit embodiment.

[0091] Figure 8 It is a flow chart of a control method of an inverter provided in an embodiment of the present application. Figure 8The inverter in the control method shown is electrically connected to the power grid, the inverter circuit includes a switching device, the inverter includes a filter circuit, a feedback controller, a pulse generator and a switching device, the filter circuit includes an LC filter circuit, the inductor in the LC filter circuit is electrically connected to the inverter circuit, the feedback controller is electrically connected to the filter circuit, and the pulse generator is electrically connected to the feedback controller and the filter circuit.

[0092] Figure 8 Includes steps S810 to S840.

[0093] Step S810, obtaining the fundamental component of the capacitor current and the inductor current, and superimposing the fundamental component of the capacitor current and the inductor current through a feedback controller to generate a feedback current.

[0094] Step S820, obtaining a grid-connected command current of the inverter, where the grid-connected command current is determined by the target output power of the inverter.

[0095] Step S830: Obtain the grid-connected command current and feedback current of the inverter through a pulse generator to generate a pulse signal.

[0096] Step S840: Control the switch device of the inverter circuit by the pulse signal to generate the output current of the inverter circuit.

[0097] Optionally, the capacitor current is the current of the capacitor in the LC filter circuit, and the inductor current is the current of the inductor in the LC filter circuit.

[0098] In some embodiments, the point where the inverter is electrically connected to the grid is the grid connection point, and the fundamental component of the capacitor current is determined by the fundamental component of the grid connection point voltage, wherein the fundamental component of the grid connection point voltage is determined by the grid connection point voltage value and the phase angle of the grid connection point voltage corresponding to the grid connection point voltage value.

[0099] In some embodiments, the inverter also includes a phase-locked loop, which is electrically connected to the feedback controller and the grid-connected point voltage sensor, and the grid-connected point voltage sensor is used to sample the grid-connected point voltage. The control method also includes: obtaining sampling data of the grid-connected point voltage sensor through the phase-locked loop, and obtaining the phase angle of the grid-connected point voltage based on the sampling data.

[0100] In some embodiments, the inverter further includes a differential circuit, which is electrically connected to the feedback controller, and the control method further includes: differentiating the fundamental component of the grid-connected point voltage through the differential circuit to obtain the fundamental component of the capacitor current.

[0101] In some embodiments, the inverter further includes a divider, the divider is electrically connected to the feedback controller, and the control method further includes: performing a division operation of the fundamental component of the grid-connected point voltage and the impedance of the capacitor by the divider.

[0102] In addition, an embodiment of the present application further proposes a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a computer, the operations in the inverter control method provided in the above embodiment are implemented. The specific steps are not repeated here.

[0103] The embodiment of the present application further provides a computer program, which includes commands for executing the inverter control method provided by the above embodiment.

[0104] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity / operation / object from another entity / operation / object, and do not necessarily require or imply any such actual relationship or order between these entities / operations / objects; the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or system including the element.

[0105] As for the device embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment. The device embodiment described above is only schematic, and the units described as separate components may or may not be physically separated. Some or all of the modules can be selected according to actual needs to achieve the purpose of the present application scheme. Those of ordinary skill in the art can understand and implement it without paying creative work.

[0106] The serial numbers of the above-mentioned embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0107] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present application is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes a number of instructions for a terminal device (which can be a mobile phone, computer, server, TV, or network device, etc.) to execute the methods described in each embodiment of the present application.

[0108] The above are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An inverter, characterized in that: The inverter is electrically connected to a power grid, and the inverter comprises: An inverter circuit, wherein the inverter circuit includes a switching device; A filter circuit, the filter circuit comprising an LC filter circuit, an inductor in the LC filter circuit being electrically connected to the inverter circuit; A feedback controller, the feedback controller is electrically connected to the filter circuit, and the feedback controller is used to superimpose the fundamental component of the obtained capacitor current with the inductor current to generate a feedback current, the capacitor current is the current of the capacitor in the LC filter circuit, and the inductor current is the current of the inductor in the LC filter circuit; A pulse generator, the pulse generator is electrically connected to the feedback controller and the filter circuit, and is used to generate a pulse signal according to the grid-connected command current of the inverter and the received feedback current, wherein the pulse signal is used to control the switching device of the inverter circuit to generate the output current of the inverter circuit, wherein the grid-connected command current is determined by the target output power of the inverter.

2. The inverter according to claim 1, characterized in that: The point where the inverter is electrically connected to the power grid is a grid connection point, and the fundamental component of the capacitor current is determined by the fundamental component of the grid connection point voltage, wherein the fundamental component of the grid connection point voltage is determined by the grid connection point voltage value and the phase angle of the grid connection point voltage corresponding to the grid connection point voltage value.

3. The inverter according to claim 2, characterized in that: The inverter further comprises: A phase-locked loop, wherein the phase-locked loop is electrically connected to the feedback controller and the grid-connected point voltage sensor, the grid-connected point voltage sensor is used to sample the grid-connected point voltage, the phase-locked loop is used to obtain sampling data of the grid-connected point voltage sensor, and is used to obtain the phase angle of the grid-connected point voltage based on the sampling data.

4. The inverter according to claim 2, characterized in that: The inverter further comprises: A differential circuit is electrically connected to the feedback controller, and is used to differentiate the fundamental component of the grid-connected point voltage to obtain the fundamental component of the capacitor current.

5. The inverter according to claim 2, characterized in that: The inverter further comprises: A divider is electrically connected to the feedback controller, and is used to perform a division operation between the fundamental component of the grid connection point voltage and the impedance of the capacitor.

6. A control method for an inverter, characterized in that: The inverter is electrically connected to a power grid, the inverter circuit includes a switch device, the inverter includes a filter circuit, a feedback controller, a pulse generator and a switch device, the filter circuit includes an LC filter circuit, the inductor in the LC filter circuit is electrically connected to the inverter circuit, the feedback controller is electrically connected to the filter circuit, the pulse generator is electrically connected to the feedback controller and the filter circuit, and the control method includes: Acquire the fundamental component of the capacitor current and the inductor current, and superimpose the fundamental component of the capacitor current and the inductor current through a feedback controller to generate a feedback current; Acquiring a grid-connected command current of the inverter, wherein the grid-connected command current is determined by a target output power of the inverter; Obtaining the grid-connected command current of the inverter and the feedback current through a pulse generator to generate a pulse signal; Controlling the switching device of the inverter circuit by a pulse signal to generate an output current of the inverter circuit, The capacitor current is the current of the capacitor in the LC filter circuit, and the inductor current is the current of the inductor in the LC filter circuit.

7. The control method according to claim 6, characterized in that: The point where the inverter is electrically connected to the power grid is a grid connection point, and the fundamental component of the capacitor current is determined by the fundamental component of the grid connection point voltage, wherein the fundamental component of the grid connection point voltage is determined by the grid connection point voltage value and the phase angle of the grid connection point voltage corresponding to the grid connection point voltage value.

8. The control method according to claim 6, characterized in that: The inverter further includes a phase-locked loop, the phase-locked loop is electrically connected to the feedback controller and a grid-connected point voltage sensor, the grid-connected point voltage sensor is used to sample the grid-connected point voltage, and the control method further includes: The sampling data of the grid-connected point voltage sensor is acquired through the phase-locked loop, and the phase angle of the grid-connected point voltage is acquired according to the sampling data.

9. The control method according to claim 6, characterized in that: The inverter further includes a differential circuit, and the differential circuit is electrically connected to the feedback controller. The control method further includes: The fundamental component of the grid connection point voltage is differentiated by the differential circuit to obtain the fundamental component of the capacitor current.

10. The control method according to claim 6, characterized in that: The inverter further includes a divider, and the divider is electrically connected to the feedback controller. The control method further includes: The divider performs a division operation of the fundamental wave component of the grid connection point voltage and the impedance of the capacitor.

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