Inverter and line impedance detection method thereof

Abstract

The invention provides an inverter and a line impedance detection method of the inverter. Calculating a current direct-current component, a voltage direct-current component, a power grid direct-current component, a current alternating-current component, a voltage alternating-current component and a power grid alternating-current component according to a real-time output current, a real-time output voltage and a power grid voltage which are acquired in a power frequency period at a preset sampling frequency; and updating the line impedance according to the current direct current component, the voltage direct current component, the power grid direct current component, the current alternating current component, the voltage alternating current component and the power grid alternating current component. On the basis, dynamic and accurate identification of the line impedance of the inverter can be realized, a disturbance signal does not need to be actively injected into the inverter, and the control on the inverter is simple. Moreover, the inverter needs to control the output of the inverter by detecting the real-time output voltage, the real-time output current and the power grid voltage, so that a circuit for detecting the line impedance does not need to be additionally arranged in the inverter, and the cost of the inverter can be reduced.

Description

Technical Field

[0001] The present application belongs to the technical field of inverters, and in particular relates to an inverter and a line impedance detection method thereof. Background Art

[0002] When the line impedance from the photovoltaic grid-connected inverter to the grid changes, the controlled model of the grid-connected inverter control system will change, affecting the control performance of the grid-connected inverter, and adversely affecting the power quality of the grid-connected inverter and the stable operation of the system. Therefore, accurate identification of the impedance of the grid-connected inverter output line is crucial for accurate control of the inverter and stable operation of the grid. Summary of the invention

[0003] An embodiment of the present application provides an inverter and a line impedance detection method thereof, wherein the output end of the inverter is used to connect to a power grid, and the line impedance detection method comprises: when the inverter is powered on, collecting the real-time output current and real-time output voltage of the inverter and the power grid voltage within the power frequency cycle at a preset sampling frequency; obtaining a current DC component, a voltage DC component, a power grid DC component, and a current AC component, a voltage AC component, and a power grid AC component according to the real-time output current, the real-time output voltage, and the power grid voltage; and updating the line impedance between the inverter and the power grid according to the current DC component, the voltage DC component, the power grid DC component, the current AC component, the voltage AC component, and the power grid AC component in a sampling order.

[0004] In the embodiment of the present application, when the inverter is powered on, the real-time output current, real-time output voltage and grid voltage collected within the power frequency cycle are used to calculate the current DC component, voltage DC component, grid DC component and current AC component, voltage AC component and grid AC component, and then the line impedance is updated according to the current DC component, voltage DC component, grid DC component and current AC component, voltage AC component and grid AC component. Based on this, dynamic and accurate identification of the line impedance of the inverter can be achieved, and there is no need to actively inject a disturbance signal into the inverter, and the control of the inverter is simple. Moreover, the inverter itself needs to control the output of the inverter by detecting its real-time output voltage, real-time output current and grid voltage, so there is no need to add an additional circuit for detecting line impedance in the inverter, which can reduce the cost of the inverter.

[0005] In one possible implementation, a current DC component, a voltage DC component, a grid DC component, and a current AC component, a voltage AC component, and a grid AC component are obtained based on the real-time output current, the real-time output voltage, and the grid voltage, including: obtaining the current DC component based on the average value of all real-time output currents obtained within the power frequency cycle; obtaining the voltage DC component based on the average value of all real-time output voltages obtained within the power frequency cycle; obtaining the grid DC component based on the average value of all grid voltages obtained within the power frequency cycle; obtaining the current AC component based on the difference between the sampled real-time output current and the current DC component; obtaining the voltage AC component based on the difference between the sampled real-time output voltage and the voltage DC component; and obtaining the grid AC component based on the difference between the sampled grid voltage and the grid DC component.

[0006] In a possible implementation, the line impedance between the inverter and the grid is updated in a sampling order according to the current DC component, the voltage DC component, the grid DC component, and the current AC component, the voltage AC component, and the grid AC component, including: obtaining a DC deviation value according to the difference between the voltage DC component and the grid DC component; obtaining an AC deviation value according to the difference between the voltage AC component and the grid AC component at the current sampling moment; obtaining a resistance value according to the DC deviation value and the current DC component; obtaining a reactance value at the current sampling moment according to the AC deviation value and the current AC component at the current sampling moment; and updating the line impedance according to the sum of the resistance value and the reactance value.

[0007] In a possible implementation, the inverter is further used to: update the line impedance according to the sum of the resistance value and the reactance value, including: obtaining the impedance detection value at the current sampling moment according to the sum of the resistance value and the reactance value; and updating the line impedance according to the impedance detection value.

[0008] In a possible implementation, the line impedance detection method further includes: when the difference between the impedance detection value and the line impedance is not within a preset range, updating the impedance detection value to the line impedance of the inverter.

[0009] In a possible implementation, the line impedance detection method further includes: when the difference between the impedance detection value and the line impedance is within a preset range, stopping updating the line impedance.

[0010] In one possible implementation, during the first power frequency cycle when the inverter is initially powered on, the real-time output current and real-time output voltage of the inverter and the grid voltage are collected at a sampling frequency during the first power frequency cycle; based on the real-time output current, real-time output voltage and grid voltage collected during the first power frequency cycle, the DC component of the current, the DC component of the voltage and the DC component of the grid of the inverter during the first power frequency cycle are obtained; and the initial line impedance of the inverter is calculated based on the DC component of the current, the DC component of the voltage and the DC component of the grid during the first power frequency cycle.

[0011] In one possible implementation, the output end of the inverter includes at least two phase lines, each phase line is connected to at least two terminals of the power grid; the real-time output current includes the phase line current of each phase line; the real-time output voltage includes the phase line voltage of each phase line; the power grid voltage includes the terminal voltage of each terminal; and the line impedance includes the line impedance of each phase line.

[0012] In a second aspect, the present application provides an inverter, comprising: an inverter circuit, wherein an output end of the inverter circuit is used to connect to a power grid; and The control circuit is used for: when the inverter circuit is powered on, collecting the real-time output current and real-time output voltage of the inverter circuit and the grid voltage within the power frequency cycle at a preset sampling frequency; obtaining the current DC component, voltage DC component, grid DC component, current AC component, voltage AC component and grid AC component according to the real-time output current, real-time output voltage and grid voltage; updating the line impedance between the inverter circuit and the grid according to the current DC component, voltage DC component, grid DC component, current AC component, voltage AC component and grid AC component in the sampling order.

[0013] In one possible implementation, the control circuit includes: a sampling unit, the sampling unit is used to collect real-time output current, real-time output voltage and grid voltage within the power frequency cycle at a preset sampling frequency; and a control unit, connected to the sampling unit, the control unit is used to receive the real-time output current, real-time output voltage and grid voltage, and calculate the current DC component, voltage DC component, grid DC component and current AC component, voltage AC component and grid AC component according to the real-time output current, real-time output voltage and grid voltage, and update the line impedance according to the current DC component, voltage DC component, grid DC component and current AC component, voltage AC component and grid AC component.

[0014] In a possible implementation, the inverter circuit includes a bus capacitor unit, a positive and negative DC bus, a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm; the bus capacitor unit is connected between the positive and negative DC bus, and the bus capacitor unit includes two bus capacitors connected in series; the first bridge arm is connected between the positive and negative DC bus, and the first bridge arm includes a first switch tube and a second switch tube connected in series; the midpoint between the first switch tube and the second switch tube is connected to the first terminal of the power grid through a first phase line; the second bridge arm is connected between the midpoint of the first bridge arm and the midpoints of the two bus capacitors; The third bridge arm is connected between the positive and negative DC busbars, and the third bridge arm includes a third switch tube and a fourth switch tube connected in series; the midpoint between the third switch tube and the fourth switch tube is connected to the second terminal of the power grid through the second phase line; the fourth bridge arm is connected between the midpoint of the third bridge arm and the midpoints of the two bus capacitors; the fifth bridge arm is connected between the positive and negative DC busbars, and the fifth bridge arm includes a fifth switch tube and a sixth switch tube connected in series; the midpoint between the fifth switch tube and the sixth switch tube is connected to the third terminal of the power grid through the third phase line; the sixth bridge arm is connected between the midpoint of the first bridge arm and the midpoints of the two bus capacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a module schematic diagram of the inverter provided in an embodiment of the present application.

[0016] Figure 2 It is a module schematic diagram of an inverter provided in another embodiment of the present application.

[0017] Figure 3 It is a schematic diagram of the circuit structure of the inverter provided in an embodiment of the present application.

[0018] Figure 4 It is a flow chart of a line impedance detection method provided in an embodiment of the present application.

[0019] Figure 5 yes Figure 4 Detailed flowchart of step S200.

[0020] Figure 6 yes Figure 4 Detailed flowchart of step S300.

[0021] Figure 7 yes Figure 6 Detailed flowchart of step S350.

[0022] Figure 8 It is a partial flow chart of the line impedance detection method provided in an embodiment of the present application.

[0023] Fig. 9 It is a flow chart of a line impedance detection method provided in a specific example of the present application. DETAILED DESCRIPTION

[0024] It should be noted that the terms "first" and "second" in the specification, claims and drawings of the present application are used to distinguish similar objects, rather than to describe a specific order or sequence. In the specification, claims and drawings of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, the term "multiple" in the specification, claims and drawings of the present application refers to two or more than two.

[0025] It is understandable that the connection relationship described in the present application refers to direct or indirect connection. For example, A is connected to B or A is electrically connected to B, which can be either A and B are directly connected or A and B are indirectly connected through one or more other electrical components, for example, A and C are directly connected, and C and B are directly connected, so that A and B are connected through C.

[0026] It should also be noted that the method disclosed in the embodiments of the present application or the method shown in the flowchart includes one or more steps for implementing the method. Without departing from the scope of the claims, the execution order of multiple steps can be interchangeable with each other, and some of the steps can also be deleted.

[0027] Some embodiments will be described below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0028] See also Figure 1 , Figure 1 A module schematic diagram of the inverter 10 provided in an embodiment of the present application is shown.

[0029] like Figure 1 As shown, the inverter 10 includes an inverter circuit 100 and a control circuit 200. The output end of the inverter circuit 100 is used to connect to the power grid 20, and the control circuit 200 is used to control the inverter circuit 100 to work so that the inverter circuit 100 is integrated into the power grid 20.

[0030] It can be understood that the DC input port of the inverter 10 can be connected to the photovoltaic module 30. The inverter 10 can also be provided with a grid-connected output port and an off-grid output port, and the output end of the inverter circuit 100 is respectively connected to the grid-connected output port and the off-grid output port, the grid-connected output port is used to connect the grid 20, and the off-grid output port is used to connect the load 40. The inverter 10 can also be provided with a battery connection port, and the battery connection port is used to connect the energy storage battery 50. The input end of the inverter circuit 100 is respectively connected to the DC input port and the battery connection port, and the output end of the inverter circuit 100 is respectively connected to the grid-connected output port and the off-grid output port, so that the photovoltaic module 30 and the energy storage battery 50 can output electric energy to the off-grid output port through the inverter circuit 100 to supply power to the load 40. When the grid 20 is connected to the grid-connected output port, that is, when the inverter 10 is in the grid-connected state, the grid 20 can also supply power to the load 40 through the grid-connected output port. Of course, the grid 20 can also charge the energy storage battery 50 through the grid-connected output port and then through the inverter circuit 100. At this time, the inverter 10 is a photovoltaic energy storage inverter. Of course, the inverter 10 of the embodiment of the present application is not limited to a photovoltaic energy storage inverter.

[0031] In the embodiment of the present application, the inverter circuit 100 may be a bidirectional inverter circuit, a T-type three-level inverter circuit, or the like.

[0032] When the inverter circuit 100 is powered on, the control circuit 200 can collect the real-time output current and real-time output voltage of the inverter circuit and the grid voltage within the power frequency cycle at a preset sampling frequency. The control circuit 200 then calculates the current DC component, voltage DC component, grid DC component, and current AC component, voltage AC component, and grid AC component at each sampling moment based on the sampled real-time output current, real-time output voltage, and grid voltage, and updates the line impedance between the inverter circuit 100 and the grid 20 in the sampling order based on the current DC component, voltage DC component, grid DC component, and current AC component, voltage AC component, and grid AC component at each sampling moment.

[0033] In this way, the control circuit 200 can calculate the current DC component, voltage DC component, grid DC component and the current AC component, voltage AC component and grid AC component at each sampling moment through the real-time output current, real-time output voltage and grid voltage sampled in the power frequency cycle, and then update the line impedance according to the current DC component, voltage DC component, grid DC component and current AC component, voltage AC component and grid AC component. Based on this, dynamic and accurate identification of the line impedance of the inverter circuit 100 can be achieved, and there is no need to actively inject a disturbance signal into the inverter circuit 100, and the control of the inverter circuit 100 is simple. Moreover, the control circuit 200 itself needs to detect its real-time output voltage, real-time output current and grid voltage to control the output of the inverter circuit 100, so there is no need to add an additional circuit for detecting the line impedance in the inverter 10, which can reduce the cost of the inverter 10. It should be noted that the power frequency can represent the rated frequency used by the power generation, transmission, transformation and distribution equipment of the power system and industrial and civil electrical equipment, and the unit is Hertz (HZ). Under the standard power frequency of 50Hz, each power frequency cycle is 20 milliseconds (ms). When the grid 20 is connected to the grid-connected output port of the inverter 10, the inverter 10 needs to be synchronized with the grid 20, so the power frequency cycle of the inverter 10 is the power frequency cycle of the grid 20. The sampling order refers to the order of sampling moments.

[0034] It can be understood that the preset sampling frequency needs to be greater than the power frequency, and correspondingly, the sampling period is less than the power frequency period. For example, when the power frequency is 50 Hz and the power frequency period is 20 milliseconds (ms), the sampling frequency can be set to 50 kHz, and the sampling period is 20 microseconds (us), that is, within one power frequency period, the control circuit 200 samples the real-time output current, real-time output voltage and grid voltage of the inverter circuit 100 at 1000 sampling moments. In the embodiment of the present application, the sampling frequency can be consistent with the frequency of the control signal of the switch tube in the inverter 10 by the control circuit 200. Of course, the embodiment of the present application does not limit the specific value of the sampling frequency, and can be set according to actual application requirements.

[0035] Furthermore, if Figure 2As shown, the control circuit 200 may include a sampling unit 210 and a control unit 220. The sampling unit 210 is used to collect real-time output current, real-time output voltage and grid voltage within the power frequency cycle at a preset sampling frequency. The control unit 220 is connected to the sampling unit 210, and the control unit 220 is used to receive the real-time output current, real-time output voltage and grid voltage collected by the sampling unit 210, and calculate the current DC component, voltage DC component, grid DC component and current AC component, voltage AC component and grid AC component according to the real-time output current, real-time output voltage and grid voltage, and update the line impedance according to the current DC component, voltage DC component, grid DC component and current AC component, voltage AC component and grid AC component.

[0036] The control unit 220 may include a central processing unit (CPU), other general-purpose processors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA) or other programmable logic devices, discrete gates or transistor logic devices, etc.

[0037] It is understandable that Figure 3 As shown, the sampling unit 210 may include a current sampling unit 211, a first voltage sampling unit 212, and a second voltage sampling unit 213. The current sampling unit 211 is connected to the output end of the inverter circuit 100, and the current sampling unit 211 is used to collect the real-time output current of the inverter circuit 100. The first voltage sampling unit 212 is connected to the output end of the inverter circuit 100, and the first voltage sampling unit 212 is used to collect the real-time output voltage of the inverter circuit 100. The second voltage sampling unit 213 is connected to the power grid 20, and the second voltage sampling unit 213 is used to collect the power grid voltage.

[0038] The current sampling unit 211 may be implemented by any one of a sampling resistor, a Hall element or a current transformer to collect the real-time output current of the inverter circuit 100. The first voltage sampling unit 212 and the second voltage sampling unit 213 may be implemented by any one of voltage divider resistor sampling, differential sampling, isolation sampling, etc. to collect the real-time output voltage and grid voltage of the inverter circuit 100 respectively.

[0039] Specifically, Figure 3As shown, the inverter circuit 100 may be a three-phase T-type three-level inverter circuit, wherein the inverter circuit 100 includes a bus capacitor unit, a positive and negative DC bus (BUS+, BUS-), a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm.

[0040] The bus capacitor unit is connected between the positive and negative DC buses (BUS+, BUS-), and the bus capacitor unit includes two bus capacitors connected in series. Figure 3 In the figure, two bus capacitors are described as bus capacitor Ci1 and bus capacitor Ci2. One end of bus capacitor Ci1 is connected to the positive DC bus BUS+, the other end of bus capacitor Ci1 is connected to one end of bus capacitor Ci2, and the other end of bus capacitor Ci2 is connected to the negative DC bus BUS-. The midpoint O of the two bus capacitors is the connection point between the two bus capacitors, and the potential of this point is the reference zero potential. The positive and negative DC bus (BUS+, BUS-) are used to connect the photovoltaic component 30 or the energy storage battery 50 to transmit the DC power provided by the photovoltaic component 30 or the energy storage battery 50 to the bus capacitor Ci1 and the bus capacitor Ci2, and store energy through the bus capacitor Ci1 and the bus capacitor Ci2. When the DC input port of the inverter 10 is connected to the photovoltaic component 30, the voltage at the input end of the inverter circuit 100 is the photovoltaic voltage V PV The bus capacitor Ci1 and the bus capacitor Ci2 divide the input voltage of the inverter circuit 100 into three levels, which are V PV / 2, 0, - V PV / 2.

[0041] The first bridge arm is connected between the positive and negative DC busbars (BUS+, BUS-), and the first bridge arm includes a first switch tube Q1 and a second switch tube Q2 connected in series. The midpoint between the first switch tube Q1 and the second switch tube Q2 is connected to the first terminal (not marked in the figure) of the power grid 20 through the first phase line A. Specifically, the first end of the first switch tube Q1 is connected to the positive DC busbar BUS+, the second end of the first switch tube Q1 is connected to the first end of the second switch tube Q2 (that is, the midpoint of the first bridge arm), and the second end of the second switch tube Q2 is connected to the negative DC busbar BUS-.

[0042] The second bridge arm is connected between the midpoint of the first bridge arm and the midpoints of the two bus capacitors.

[0043] The third bridge arm is connected between the positive and negative DC busbars (BUS+, BUS-), and the third bridge arm includes a third switch tube Q3 and a fourth switch tube Q4 connected in series. The midpoint between the third switch tube Q3 and the fourth switch tube Q4 is connected to the second terminal (not marked in the figure) of the power grid 20 through the second phase line B. Specifically, the first end of the third switch tube Q3 is connected to the positive DC busbar BUS+, the second end of the third switch tube Q3 is connected to the first end of the fourth switch tube Q4 (that is, the midpoint of the third bridge arm), and the second end of the fourth switch tube Q4 is connected to the negative DC busbar BUS-.

[0044] The fourth bridge arm is connected between the midpoint of the third bridge arm and the midpoints of the two bus capacitors.

[0045] The fifth bridge arm is connected between the positive and negative DC busbars (BUS+, BUS-), and the fifth bridge arm includes a fifth switch tube Q5 and a sixth switch tube Q6 connected in series. The midpoint between the fifth switch tube Q5 and the sixth switch tube Q6 is connected to the third terminal (not marked in the figure) of the power grid 20 through the third phase line C. Specifically, the first end of the fifth switch tube Q5 is connected to the positive DC busbar BUS+, the second end of the fifth switch tube Q5 is connected to the first end of the sixth switch tube Q6 (that is, the midpoint of the fifth bridge arm), and the second end of the sixth switch tube Q6 is connected to the negative DC busbar BUS-.

[0046] The sixth bridge arm is connected between the midpoint of the fifth bridge arm and the midpoints of the two bus capacitors.

[0047] The second bridge arm includes a seventh switch tube Q7 and an eighth switch tube Q8 connected in reverse series, a first end of the seventh switch tube Q7 is connected to a first end of the eighth switch tube Q8, a second end of the seventh switch tube Q7 is connected to a midpoint of two bus capacitors, and a second end of the eighth switch tube Q8 is connected to the midpoint of the first bridge arm.

[0048] The fourth bridge arm includes a ninth switch tube Q9 and a tenth switch tube Q10 connected in reverse series, a first end of the ninth switch tube Q9 is connected to a first end of the tenth switch tube Q10, a second end of the ninth switch tube Q9 is connected to a midpoint of two bus capacitors, and a second end of the tenth switch tube Q10 is connected to the midpoint of the third bridge arm.

[0049] The sixth bridge arm includes an eleventh switch tube Q11 and a twelfth switch tube Q12 connected in reverse series, a first end of the eleventh switch tube Q11 is connected to a first end of the twelfth switch tube Q12, a second end of the eleventh switch tube Q11 is connected to a midpoint of two bus capacitors, and a second end of the twelfth switch tube Q12 is connected to the midpoint of the fifth bridge arm.

[0050] The midpoint of the first bridge arm is connected to the first terminal of the grid 20 through the first phase line A, the midpoint of the third bridge arm is connected to the second terminal of the grid 20 through the second phase line B, and the midpoint of the fifth bridge arm is connected to the third terminal of the grid 20 through the third phase line C.

[0051] The control unit 220 can be connected to the control end of the switch tube of each bridge arm respectively, and send a control signal to each switch tube, so that each switch tube can be turned on or off under the drive of the control signal. The control signal is a pulse width modulation (PWM) signal.

[0052] In this way, when the inverter circuit 100 is inverting, the photovoltaic module 30 or the energy storage battery 50 can input direct current through the positive and negative DC bus bars, and convert it into three-phase alternating current through the on and off of the switching tubes on the first bridge arm, the second bridge arm, the third bridge arm, the fourth bridge arm, the fifth bridge arm and the sixth bridge arm, and output it to the first phase line A, the second phase line B and the third phase line C respectively.

[0053] It can be understood that the present application does not specifically limit each switch tube, and each switch tube may include but is not limited to a triode, a silicon controlled rectifier (Silicon Controlled Rectifier, SCR), a metal oxide semiconductor field effect transistor (Metal Oxide Semiconductor Field Effect Transistor, MOSFET), an insulated gate bipolar transistor (Insulated Gate Bipolar Transistor, IGBT) or a gallium nitride high electron mobility transistor (GaN High Electron Mobility Transistor, GaN HEMT), or at least one of a triode, SCR, MOSFET, IGBT, and GaN HEMT connected in parallel with a reverse-connected diode. For example, when the switch tube is a triode, the base of the triode is the control terminal, the collector is the first terminal, and the emitter is the second terminal.

[0054] Correspondingly, the real-time output current of the inverter circuit 100 includes the phase line current on each phase line, and the current sampling unit 211 can be connected to the first phase line A, the second phase line B and the third phase line C respectively to detect the phase line current of the first phase line A, the second phase line B and the third phase line C respectively. The real-time output voltage of the inverter circuit 100 includes the phase line voltage of the connection node between the output end of the inverter circuit 100 and each phase line, that is, the voltage of the midpoint of the first bridge arm, the third bridge arm and the fifth bridge arm. The first voltage sampling unit 212 is connected to the midpoint of the first bridge arm, the third bridge arm and the fifth bridge arm respectively to detect the phase line voltage of the midpoint of the three bridge arms. The grid voltage includes the terminal voltages of the three terminals connected to the three phase lines, and the second voltage sampling unit 213 is connected to the three terminals of the grid 20 respectively to detect the terminal voltage of each terminal. The line impedance of the inverter circuit 100 includes the line impedance of the three phase lines. Among them, Figure 3The three phase lines in the A , L B , L C ) and line resistance (R A , R B , R C ) represents the line impedance of the three phase lines.

[0055] The inverter 10 and the line impedance detection method thereof provided by the embodiment of the present invention will be described in detail below through specific embodiments.

[0056] See also Figure 4 , which shows a schematic flow chart of a line impedance detection method provided by an embodiment of the present invention, and the line impedance detection method is applied to the inverter 10. In at least one implementation manner, the line impedance detection method can be executed by the control circuit 200 described above.

[0057] like Figure 4 As shown, the line impedance detection method includes: S100: When the inverter is powered on, the real-time output current and real-time output voltage of the inverter and the grid voltage are collected within the power frequency cycle at a preset sampling frequency.

[0058] The inverter 10 is powered on and running, which means that the grid-connected output port of the inverter 10 is connected to the grid 20 and the control circuit 200 sends a control signal of turning on and off each switch in the inverter circuit 100 .

[0059] S200, obtaining a current DC component, a voltage DC component, a grid DC component, a current AC component, a voltage AC component, and a grid AC component according to the real-time output current, the real-time output voltage, and the grid voltage.

[0060] Among them, since the DC component of the signal is the average value of the signal, the DC component of the current can be determined according to the average value of the real-time output current obtained by sampling, the DC component of the voltage can be determined according to the average value of the real-time output voltage obtained by sampling, and the DC component of the power grid can be determined according to the average value of the power grid voltage obtained by sampling. The AC component of the current can be determined according to the difference between the real-time output current corresponding to the sampling moment and the DC component of the current, and the AC component of the voltage can be determined according to the difference between the real-time output voltage corresponding to the sampling moment and the DC component of the voltage. The AC component of the power grid can be determined according to the difference between the power grid voltage corresponding to the sampling moment and the DC component of the power grid.

[0061] S300, updating the line impedance between the inverter and the grid according to the current DC component, the voltage DC component, the grid DC component, the current AC component, the voltage AC component, and the grid AC component in a sampling order.

[0062] According to the sampling time sequence, the line impedance is updated in turn according to the current DC component, the voltage DC component, the grid DC component, the current AC component, the voltage AC component, and the grid AC component. In this way, the line impedance between the inverter 10 and the grid 20 is dynamically detected, and when the line impedance between the inverter 10 and the grid 20 changes, a timely response can be made.

[0063] For example, at the initial sampling time of a power frequency cycle, the control circuit 200 determines the line impedance according to the current DC component, the voltage DC component, the grid DC component, and the current AC component, the voltage AC component, and the grid AC component at the initial sampling time. Then, the control circuit 200 determines the line impedance at the second sampling time according to the current DC component, the voltage DC component, the grid DC component, and the current AC component, the voltage AC component, and the grid AC component at the second sampling time, and updates the line impedance to the line impedance at the second sampling time, and so on, to achieve dynamic identification of the line impedance. It can be understood that in a power frequency cycle, the current DC component, the voltage DC component, and the grid DC component used by the control circuit 200 are calculated based on the average value of the real-time output current, the average value of the real-time output voltage, and the average value of the grid voltage sampled in the previous power frequency cycle.

[0064] In the embodiment of the present application, the line impedance detection method applied to the inverter 10 can be executed by the control circuit 200 in the inverter 10, specifically, by the control unit 220. For example, by the microcontroller unit 220 (MCU), digital signal processor (DSP) or energy management system (EMS) in the inverter 10. Among them, the control circuit 200 may include multiple controllers or control chips, such as a DSP chip and a RAM (Random Access Memory) chip, etc.

[0065] It can be understood that, in the embodiment of the present application, the control circuit 200 in the inverter 10 can repeatedly execute steps S100 to S300 during the entire operation process to realize the identification of line impedance in the dynamic process.

[0066] Of course, the control circuit 200 in the inverter 10 may also repeat steps S100 to S300 until the identified line impedance is stable, and then the identification of the line impedance is terminated. At this time, the control circuit 200 may start to execute steps S100 to S300 when the inverter 10 is powered on, and after one or more power frequency cycles, the identified line impedance is stable, and the execution of steps S100 to S300 is terminated. In some specific examples, after the control circuit 200 ends the identification of the line impedance, it may also execute steps S100 to S300 again after a certain interval to re-identify the line impedance, so as to prevent the control circuit 200 from failing to timely identify the change in line impedance after the execution of steps S100 to S300, thereby affecting the quality of the power output by the inverter circuit 100.

[0067] See also Figure 5 , Figure 5 Shows Figure 4 Detailed flowchart of step S200 in FIG.

[0068] like Figure 5 As shown, in some embodiments, step S200 may include: S210 , obtaining a DC component of the current according to an average value of all real-time output currents obtained within a power frequency cycle.

[0069] The control circuit 200 can add up all the real-time output currents collected in one power frequency cycle and then divide it by the number of samples to obtain the average value of the real-time output current, that is, the DC component of the current. For example, when the sampling frequency is 50 kHz, the number of samples is 1000, and all the real-time output currents are I1, I2, I3, ..., I 1000 , then the DC component of the current is: Of course, when the output end of the inverter circuit 100 is connected to multiple phase lines, the average value of the real-time output current of each phase line is calculated respectively to obtain the DC component of the current of each phase line.

[0070] S220 , obtaining a voltage DC component according to an average value of all real-time output voltages obtained within a power frequency cycle.

[0071] The control circuit 200 can add up all the real-time output voltages collected in one power frequency cycle and then divide it by the number of samples to obtain the average value of the real-time output voltage, that is, the DC component of the voltage. For example, when the sampling frequency is 50 kHz, the number of samples is 1000, and all the real-time output voltages are U1, U2, U3, ..., U 1000 , then the DC component of the current is: Of course, when the output end of the inverter circuit 100 is connected to multiple phase lines, the average value of the real-time output voltage corresponding to each phase line is calculated respectively to obtain the DC component of the voltage of each phase line.

[0072] S230 , obtaining a grid DC component according to an average value of all grid voltages obtained within a power frequency cycle.

[0073] The control circuit 200 can add up all the grid voltages collected in one power frequency cycle and then divide it by the number of samples to obtain the average value of the grid voltage, that is, the DC component of the voltage. For example, when the sampling frequency is 50 kHz, the number of samples is 1000, and the sampled grid voltages are E1, E2, E3, ..., E 1000 , then the DC component of the power grid is: Of course, when the output end of the inverter circuit 100 is connected to multiple phase lines, the average value of the grid voltage corresponding to each phase line is calculated respectively to obtain the grid DC component corresponding to each phase line.

[0074] S240 , obtaining an AC component of the current according to a difference between the sampled real-time output current and the DC component of the current.

[0075] The control circuit 200 can subtract the DC component of the real-time output current at the current sampling moment from the DC component of the current to obtain the AC component of the current at the current sampling moment. For example, the AC component of the current at the initial sampling moment is The AC component of the current at the second sampling moment is The AC component of the current at the tth sampling moment is . By analogy, the AC component of the current at each sampling moment can be obtained. Of course, the control circuit 200 can also calculate the AC component of the current at the current sampling moment before updating the line impedance each time. In this way, if the control circuit 200 ends the identification of the line impedance after the line impedance is stable, the control circuit 200 will no longer continue to calculate the AC component of the current at the next sampling moment. When the output end of the inverter circuit 100 is connected to multiple phase lines, the difference between the real-time output current and the DC component of the current corresponding to each phase line is calculated respectively to obtain the AC component of the current of each phase line.

[0076] S250 , obtaining an AC component of the voltage according to the difference between the sampled real-time output voltage and the DC component of the voltage.

[0077] The control circuit 200 can subtract the DC component of the voltage from the real-time output voltage at the current sampling moment to obtain the AC component of the voltage at the current sampling moment. For example, the AC component of the voltage at the initial sampling moment is The voltage AC component at the second sampling moment is The AC component of the current at the tth sampling moment is . By analogy, the voltage AC component at each sampling moment can be obtained. Of course, the control circuit 200 can also calculate the voltage AC component at the current sampling moment before updating the line impedance each time. In this way, if the control circuit 200 ends the identification of the line impedance after the line impedance is stable, the control circuit 200 will no longer continue to calculate the voltage AC component at the next sampling moment, which can reduce the calculation amount of the control circuit 200. When the output end of the inverter circuit 100 is connected to multiple phase lines, the difference between the real-time output voltage and the voltage DC component corresponding to each phase line is calculated respectively to obtain the voltage AC component of each phase line.

[0078] S260: Obtain an AC component of the grid according to a difference between the sampled grid voltage and the DC component of the grid.

[0079] The control circuit 200 can subtract the DC component of the grid voltage at the current sampling time from the grid voltage to obtain the AC component of the grid at the current sampling time. For example, the AC component of the grid at the initial sampling time is The AC component of the power grid at the second sampling moment is The AC component of the current at the tth sampling moment is . By analogy, the AC component of the power grid at each sampling moment can be obtained. Of course, the control circuit 200 can also calculate the AC component of the power grid at the current sampling moment before updating the line impedance each time. In this way, if the control circuit 200 ends the identification of the line impedance after the line impedance is stable, the control circuit 200 will no longer continue to calculate the AC component of the power grid at the next sampling moment. When the output end of the inverter circuit 100 is connected to multiple phase lines, the difference between the power grid voltage and the DC component of the power grid corresponding to each phase line is calculated respectively to obtain the AC component of the power grid of each phase line.

[0080] In some embodiments, the control circuit 200 can also calculate the current DC component, the voltage DC component and the grid DC component respectively according to the real-time output current, the real-time output voltage and the grid voltage sampled in the previous power frequency cycle. In the current power frequency cycle, the control circuit 200 subtracts the current DC component calculated according to the real-time output current of the previous power frequency cycle from the real-time output current sampled at the current sampling moment of the current power frequency cycle to obtain the current AC component of the current sampling moment. The control circuit 200 subtracts the voltage DC component calculated according to the real-time output voltage of the previous power frequency cycle from the real-time output voltage sampled at the current sampling moment of the current power frequency cycle to obtain the voltage AC component at the current sampling moment. The control circuit 200 subtracts the grid DC component calculated according to the grid voltage of the previous power frequency cycle from the grid voltage sampled at the current sampling moment of the current power frequency cycle to obtain the grid AC component at the current sampling moment.

[0081] See also Figure 6 , Figure 6 Shows Figure 4Detailed flowchart of step S300 in FIG.

[0082] like Figure 6 As shown, in some embodiments, step S300 may include: S310, obtaining a DC deviation value according to a difference between a DC component of the voltage and a DC component of the power grid.

[0083] The control circuit 200 can subtract the DC component of the voltage from the DC component of the grid to obtain a DC deviation value. Specifically, the DC deviation value is .

[0084] S320: Obtain an AC deviation value according to the difference between the voltage AC component and the grid AC component at the current sampling moment.

[0085] The control circuit 200 can obtain an AC deviation value by subtracting the AC component of the grid from the AC component of the voltage at the current sampling moment. Specifically, the AC deviation value is . Wherein, t is the sampling time, for example, when the current sampling time is the second sampling time, t=2.

[0086] S330, obtaining a resistance value according to the DC deviation value and the DC component of the current.

[0087] It can be understood that there is a parasitic resistance (R A , R B , R C )、parasitic inductance(L A , L B , L C ) and parasitic capacitance (not shown). The line impedance includes the resistance value of the parasitic resistor and the reactance values ​​of the parasitic inductance and parasitic capacitance. In a linear system, according to Ohm's law, the control circuit 200 can divide the DC deviation value by the DC component of the current to obtain the resistance value. Specifically, the resistance value is Among them, Figure 3 For example, R is the line resistance on the phase line (R A , R B , R C ) resistance value.

[0088] S340: Obtain the reactance value at the current sampling moment according to the AC deviation value and the AC component of the current at the current sampling moment.

[0089] The control circuit 200 can divide the AC deviation value at the current sampling moment by the AC component of the current to obtain the reactance value. Specifically, the reactance value is Among them, Figure 3 For example, jωL is the sum of the inductive reactance of the line inductance and the capacitive reactance of the line capacitance (not shown), that is, the reactance value.

[0090] S350: Update the line impedance according to the sum of the resistance value and the reactance value.

[0091] The control circuit 200 can update the line impedance according to the calculated sum of the resistance value and the reactance value. Specifically, the updated line impedance is .

[0092] See also Figure 7 , Figure 7 Shows Figure 6 Detailed flowchart of step S350 in FIG.

[0093] like Figure 7 As shown, in some embodiments, step S350 may include: S351. Obtain the impedance detection value at the current sampling moment according to the sum of the resistance value and the reactance value.

[0094] The control circuit 200 adds the resistance value and the reactance value at the current sampling moment to obtain the impedance detection value at the current sampling moment. Specifically, the impedance detection value at the current sampling moment is .

[0095] S352: Update the line impedance according to the impedance detection value.

[0096] When the difference between the impedance detection value and the line impedance is not within the preset range, the impedance detection value is updated to the line impedance of the inverter 10 .

[0097] When the difference between the impedance detection value and the line impedance is within a preset range, the line impedance is stopped from being updated.

[0098] In the embodiment of the present application, the control circuit 200 can subtract the line impedance from the impedance detection value to obtain a difference. Specifically, the difference is .when When in the preset range, . And when When it is within the preset range, the line impedance stops updating and remains at Z.

[0099] It can be understood that when the difference between the impedance detection value and the line impedance is within the preset range, it means that the line impedance at the two sampling moments before and after is basically stable. Among them, the preset range can be a single value, for example, the preset range is zero. When the difference is within the preset range, it means that the impedance detection value and the line impedance are equal, that is, the line impedance is stable. Of course, since the control circuit 200 will have a certain error in sampling the output current, output voltage and grid voltage of the inverter circuit 100, the preset range can also be set according to the error, for example, it can be set to (-100mΩ, 100mΩ), and this application does not limit this.

[0100] It is understandable that since the DC component of the current, the DC component of the voltage and the DC component of the grid need to be calculated based on the average value of the real-time output current, the average value of the real-time output voltage and the average value of the grid voltage sampled within a power frequency cycle, the control circuit 200 cannot update the line impedance in real time during the first power frequency cycle when the inverter 10 is initially powered on. For this purpose, please refer to Figure 8 , the line impedance detection method may further include: S101 . In a first power frequency cycle when the inverter is initially powered on, real-time output current and real-time output voltage of the inverter and grid voltage are collected at a preset sampling frequency in the first power frequency cycle.

[0101] S102, obtaining a current DC component, a voltage DC component, and a grid DC component of the inverter in the first power frequency cycle according to the real-time output current, the real-time output voltage, and the grid voltage collected in the first power frequency cycle.

[0102] At the last sampling moment of the first power frequency cycle, the control circuit 200 calculates the DC component of current, DC component of voltage and grid component in the first power frequency cycle based on the collected average values ​​of all real-time output currents, all real-time output voltages and all grid values.

[0103] S103, calculating the initial line impedance of the inverter according to the DC component of the current, the DC component of the voltage, and the DC component of the power grid in the first power frequency cycle.

[0104] The control circuit 200 calculates the initial line impedance of the inverter 10 according to the current DC component, the voltage DC component and the grid DC component in the first power frequency cycle. Furthermore, in steps S100 to S300, the control circuit 200 updates the initial line impedance with the impedance detection value calculated at the first sampling moment in the second power frequency cycle, that is, the impedance detection value at the first sampling moment in the second power frequency cycle is used as the line impedance.

[0105] In the embodiment of the present application, the initial line impedance may only include the resistance value calculated based on the current DC component, voltage DC component and grid DC component in the first power frequency cycle. Of course, in addition to the resistance value, the initial line impedance may also include the reactance value calculated based on the current AC component obtained by subtracting the current DC component from the real-time output current at the last sampling moment of the first power frequency cycle, the voltage DC component obtained by subtracting the voltage DC component from the real-time output voltage, and the grid AC component obtained by subtracting the grid DC component from the grid voltage.

[0106] It can be understood that at each sampling moment of the second power frequency cycle, the control circuit 200 calculates the resistance value based on the current DC component, voltage DC component and grid DC component of the first power frequency cycle, and the reactance value is calculated based on the current AC component obtained by subtracting the current DC component from the real-time output current, the voltage AC component obtained by subtracting the voltage DC component from the real-time output voltage, and the grid AC component obtained by subtracting the grid DC component from the grid voltage.

[0107] The following Figure 3 The three-phase T-type three-level inverter circuit shown is taken as an example to illustrate the line impedance detection method of the embodiment of the present application.

[0108] See also Fig. 9 , Fig. 9 Shown is applied to Figure 3 The schematic diagram of the line impedance detection method is shown in FIG. Fig. 9 As shown, the line impedance detection method includes: S810, collect I A ,I B ,I C , U A , U B , U C 、E A 、E B and E C .

[0109] Among them, I A is the first phase line current, I B is the second phase line current, I C is the third phase line current, U A is the first phase line voltage, U B is the second phase line voltage, U C is the third phase line voltage, E A is the first terminal voltage, E B is the second terminal voltage, E C is the third terminal voltage.

[0110] The first phase line current, the second phase line current, and the third phase line current are respectively the output currents of the three phase lines (A, B, C) at the output end of the inverter circuit 100. The first phase line voltage, the second phase line voltage, and the third phase line voltage are respectively the output voltages of the midpoints of the first bridge arm, the third bridge arm, and the fifth bridge arm of the inverter circuit 100. The first terminal voltage, the second terminal voltage, and the third terminal voltage are respectively the voltages of the terminals of the power grid 20 connected to the three phase lines.

[0111] Specifically, Figure 3As shown, the three phase lines are the first phase line A, the second phase line B and the third phase line C. Correspondingly, the first phase line current sampled by the control circuit 200 in one power frequency cycle is I A1 ,I A2 ,I A3 ,…,I An , the second phase line current is I B1 ,I B2 ,I B3 ,…,I Bn , the third phase line current is I C1 ,I C2 ,I C3 ,…,I Cn The first phase line voltage is U A1 , U A2 , U A3 , …, U An , the second phase line voltage is U B1 , U B2 , U B3 , …, U Bn , the third phase line voltage is U C1 , U C2 , U C3 , …, U Cn The first terminal voltage is E A1 、E A2 、E A3 ,…,E An , the second terminal voltage is E B1 、E B2 、E B3 ,…,E Bn , the third terminal voltage is E C1 、E C2 、E C3 ,…,E Cn Wherein, n is the number of samples taken by the control circuit 200 in one power frequency cycle.

[0112] S820, respectively, according to the I collected during the power frequency cycle A The average value of I B The average value and I C The average value of I ADC ,I BDC and I CDC ; According to the U collected during the power frequency cycle A The average value of U B The average value and U C The average value of U ADC , U BDC and U CDC ; According to the E collected during the power frequency cycleA The average value of E B The average value and E C The average value of E ADC 、E BDC and E CDC .

[0113] Among them, I ADC is the first current DC component of the first phase line A, I BDC is the second current DC component of the second phase line B, I CDC is the third current DC component of the third phase line C. ADC is the first voltage DC component of the output voltage of the first bridge arm, U BDC is the second voltage DC component of the output voltage of the second bridge arm, U CDC E is the third voltage DC component of the output voltage of the third bridge arm. ADC is the first grid DC component of the voltage at the first terminal, E BDC is the second grid DC component of the voltage at the second terminal, E CDC A third grid DC component of the voltage at the third terminal.

[0114] Specifically, the first current DC component is , the second current DC component is , the third current DC component is .

[0115] The first voltage DC component is , the second voltage DC component is , the third voltage DC component is .

[0116] The DC component of the first grid is , the DC component of the second power grid is , the DC component of the third grid is .

[0117] S830, respectively according to the I of the current sampling time At and I ADC The difference, I Bt and I BDC The difference and I Ct and I CDC The difference is I AACt ,I BACt and I CACt ; According to the U at the current sampling time A and U ADC The difference, U B and U BDC The difference and U C and U CDC The difference is UAACt , U BACt and U CACt ; According to the E at the current sampling time A and E ADC The difference, E B and E BDC The difference and E C and E CDC The difference is E AACt 、E BACt and E CACt .

[0118] Among them, I AACt is the first current AC component, I BACt is the second current AC component, I CACt is the third current AC component. AACt is the first voltage AC component, U BACt is the second voltage AC component, U CACt is the third voltage AC component. AACt is the first grid AC component, E BACt is the AC component of the second power grid, E CACt is the AC component of the third power grid.

[0119] Specifically, the first current AC component is , the second current AC component is , the third current AC component is . Where t is the current sampling time.

[0120] The first voltage AC component is , the second voltage AC component is , the third voltage AC component is .

[0121] The first grid AC component is , the AC component of the second power grid is , the AC component of the third power grid is .

[0122] S840, respectively according to U ADC and E ADC The difference, U BDC and E BDC The difference and U CDC and E CDC The difference is V 1A 、V 1B and V 1C ; According to U AACt and E AACt The difference, U BACt and E BACt The difference and U CACtand E CACt The difference is V 2A 、V 2B and V 2C .

[0123] Among them, V 1A is the first DC deviation value, V 1B is the second DC deviation value, V 1C is the third DC deviation value. 2A is the first AC deviation value, V 2B is the second AC deviation value, V 2C is the third AC deviation value.

[0124] Specifically, the first DC offset value is The second DC offset value is The third DC deviation value is .

[0125] The first AC deviation value is The second AC deviation value is The third AC deviation value is .

[0126] S850, V 1A Divide by I ADC Get R A , V 1B Divide by I BDC Get R B , V 1C Divide by I CDC Get R C , V 2A Divide by I AACt Get jωL At , V 2B Divide by I BACt Get jωL Bt , V 2C Divide by I CACt Get jωL Ct .

[0127] Among them, R A is the first resistance value, R B is the second resistance value, R C is the third resistance value. At is the first reactance value, jωL Bt is the second reactance value, jωL Ct is the third reactance value.

[0128] The first resistance value is the resistance value of the line resistance on the first phase line A, the second resistance value is the resistance value of the line resistance on the second phase line B, and the third resistance value is the resistance value of the line resistance on the third phase line C. The first reactance value is the sum of the inductive reactance of the line inductance on the first phase line A and the capacitive reactance of the line capacitance, the second reactance value is the sum of the inductive reactance of the line inductance on the second phase line B and the capacitive reactance of the line capacitance, and the third reactance value is the sum of the inductive reactance of the line inductance on the third phase line C and the capacitive reactance of the line capacitance.

[0129] Specifically, the first resistance value is The second resistor value is The third resistor value is .

[0130] The first reactance is , the second reactance value is , the third reactance value is . Where t is the current sampling time.

[0131] S860, according to R A With jωL At The sum of the two is Z At , according to R B With jωL Bt The sum of the two is Z Bt , according to R C With jωL Ct The sum of the two is Z Ct .

[0132] Among them, Z At is the first impedance detection value, Z Bt is the second impedance detection value, Z Ct is the third impedance detection value.

[0133] The first impedance detection value is the line impedance of the first phase line A at the current sampling moment, the second impedance detection value is the line impedance of the second phase line B at the current sampling moment, and the third impedance detection value is the line impedance of the third phase line C at the current sampling moment.

[0134] Specifically, the first impedance detection value is The second impedance detection value is , the third impedance detection value is .

[0135] S870, determine Z respectively At and Z A The difference between , Z Bt and Z B The difference between and Z Ct and Z C The difference between Are they all equal to zero?

[0136] Among them, Z A is the first line impedance of the first phase line A, Z B is the second line impedance of the second phase line B, Z C is the third line impedance of the third phase line C.

[0137] It can be understood that the control circuit 200 needs to respectively calculate the difference between the first impedance detection value and the first line impedance, the difference between the second impedance detection value and the second line impedance, and the difference between the third impedance detection value and the third line impedance, and then compare each difference with zero.

[0138] The difference between the first impedance detection value and the first line impedance is The difference between the second impedance detection value and the second line impedance is , the difference between the third impedance detection value and the third line impedance is .

[0139] S880, when When both are equal to zero, output the current Z A , Z B , Z C .

[0140] S890, when When there is a value not equal to zero in Z A =Z At , Z B =Z Bt , Z C =Z Ct .

[0141] It can be understood that after step S890, the process returns to step S830 to start calculating the line impedance at the next sampling moment. When the line impedance iterated by the control circuit 200 in one power frequency cycle is unstable (that is, when the impedance detection values ​​at every two adjacent sampling moments in the entire power frequency cycle are not equal), steps S810-S890 are re-executed to continue iterating the line impedance in the next power frequency cycle until the line impedance is stable.

[0142] Therefore, by sampling the three-phase output current, three-phase output voltage and three-phase grid voltage of the three-phase T-type three-level inverter circuit, and obtaining the three-phase line impedance of the conductive network 20 of the inverter circuit 100 according to the sampled output current, output voltage and grid voltage, and then iterating the line impedance at each sampling moment in turn according to the sampling sequence, a stable line impedance is obtained, and accurate identification of the line impedance in the dynamic process is achieved, without actively injecting a disturbance signal into the inverter circuit 100, the control is simple and cost-saving can be achieved.

[0143] Of course, the inverter circuit 100 in the inverter 10 of the embodiment of the present application is not limited to a three-phase T-type three-level inverter circuit, but can also be a bidirectional inverter circuit, a two-phase inverter circuit, other three-phase inverter circuits, and the like.

[0144] 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 them. In the actual application process, the entire content of the technical solutions described in any embodiment of the present application can be implemented, or some content can be added, or some content can be deleted, or some content can be changed / replaced. Although the present application is described in detail with reference to the preferred embodiments, it should be understood by those of ordinary skill in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A method for detecting line impedance of an inverter, wherein the output end of the inverter is used to connect to a power grid, characterized in that: The line impedance detection method comprises: When the inverter is powered on, the real-time output current and real-time output voltage of the inverter and the grid voltage are collected within the power frequency cycle at a preset sampling frequency; According to the real-time output current, the real-time output voltage and the grid voltage, a current DC component, a voltage DC component, a grid DC component, a current AC component, a voltage AC component and a grid AC component are obtained; The line impedance between the inverter and the grid is updated in a sampling order according to the current DC component, the voltage DC component, the grid DC component, and the current AC component, the voltage AC component, and the grid AC component.

2. The line impedance detection method according to claim 1, characterized in that: The step of obtaining a current DC component, a voltage DC component, a grid DC component, a current AC component, a voltage AC component, and a grid AC component according to the real-time output current, the real-time output voltage, and the grid voltage includes: Obtaining the current DC component according to an average value of all the real-time output currents obtained within the power frequency cycle; Obtaining the voltage DC component according to an average value of all the real-time output voltages obtained within the power frequency cycle; Obtaining the grid DC component according to an average value of all grid voltages obtained within the power frequency cycle; Obtaining the current AC component according to the difference between the sampled real-time output current and the current DC component; Obtaining the voltage AC component according to the difference between the sampled real-time output voltage and the voltage DC component; The grid AC component is obtained according to the difference between the sampled grid voltage and the grid DC component.

3. The line impedance detection method according to claim 1 or 2, characterized in that: The updating of the line impedance between the inverter and the grid according to the current DC component, the voltage DC component, the grid DC component, the current AC component, the voltage AC component, and the grid AC component in a sampling order includes: Obtaining a DC deviation value according to a difference between the voltage DC component and the grid DC component; Obtaining an AC deviation value according to the difference between the voltage AC component and the power grid AC component at the current sampling moment; Obtaining a resistance value according to the DC deviation value and the DC component of the current; Obtaining a reactance value at the current sampling moment according to the AC deviation value and the current AC component at the current sampling moment; The line impedance is updated according to the sum of the resistance value and the reactance value.

4. The line impedance detection method according to claim 3, characterized in that: The updating of the line impedance according to the sum of the resistance value and the reactance value comprises: Obtaining an impedance detection value at a current sampling moment according to the sum of the resistance value and the reactance value; The line impedance is updated according to the impedance detection value.

5. The line impedance detection method according to claim 4, characterized in that: Also includes: When the difference between the impedance detection value and the line impedance is not within a preset range, the impedance detection value is updated to the line impedance of the inverter.

6. The line impedance detection method according to claim 5, characterized in that: Also includes: When the difference between the impedance detection value and the line impedance is within a preset range, the line impedance is stopped from being updated.

7. The line impedance detection method according to claim 1, characterized in that: Also includes: In a first power frequency cycle when the inverter is initially powered on, the real-time output current and real-time output voltage of the inverter and the grid voltage are collected at the sampling frequency in the first power frequency cycle; According to the real-time output current, the real-time output voltage and the grid voltage collected in the first power frequency cycle, a current DC component, a voltage DC component and a grid DC component of the inverter in the first power frequency cycle are obtained; The initial line impedance of the inverter is calculated according to the current DC component, the voltage DC component and the grid DC component in the first power frequency cycle.

8. The line impedance detection method according to any one of claims 1 to 7, characterized in that: The output end of the inverter comprises at least two phase lines, each of which is connected to at least two terminals of the power grid; The real-time output current includes the phase line current of each phase line; the real-time output voltage includes the phase line voltage of the connection node between the output end of the inverter and each phase line; the grid voltage includes the terminal voltage of each terminal; and the line impedance includes the line impedance of each phase line.

9. An inverter, characterized in that: include: An inverter circuit, wherein an output end of the inverter circuit is used to connect to a power grid; as well as A control circuit, the control circuit being used for: When the inverter circuit is powered on, the real-time output current and real-time output voltage of the inverter circuit and the grid voltage are collected within the power frequency cycle at a preset sampling frequency; According to the real-time output current, the real-time output voltage and the grid voltage, a current DC component, a voltage DC component, a grid DC component, a current AC component, a voltage AC component and a grid AC component are obtained; The line impedance between the inverter circuit and the grid is updated in a sampling order according to the current DC component, the voltage DC component, the grid DC component, and the current AC component, the voltage AC component, and the grid AC component.

10. The inverter according to claim 9, characterized in that: The control circuit comprises: A sampling unit, the sampling unit is used to collect the real-time output current, the real-time output voltage and the grid voltage within the power frequency cycle at the preset sampling frequency; and A control unit is connected to the sampling unit, and is used to receive the real-time output current, the real-time output voltage and the grid voltage, and calculate the current DC component, the voltage DC component, the grid DC component, the current AC component, the voltage AC component and the grid AC component according to the real-time output current, the real-time output voltage and the grid voltage, and update the line impedance according to the current DC component, the voltage DC component, the grid DC component, the current AC component, the voltage AC component and the grid AC component.

11. The inverter according to claim 9 or 10, characterized in that: The inverter circuit includes a bus capacitor unit, a positive and negative DC bus, a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm; The bus capacitor unit is connected between the positive and negative DC bus bars, and the bus capacitor unit includes two bus capacitors connected in series; The first bridge arm is connected between the positive and negative DC busbars, and the first bridge arm includes a first switch tube and a second switch tube connected in series; a midpoint between the first switch tube and the second switch tube is connected to a first terminal of the power grid through a first phase line; The second bridge arm is connected between the midpoint of the first bridge arm and the midpoints of the two bus capacitors; The third bridge arm is connected between the positive and negative DC busbars, and the third bridge arm includes a third switch tube and a fourth switch tube connected in series; the midpoint between the third switch tube and the fourth switch tube is connected to the second terminal of the power grid through a second phase line; The fourth bridge arm is connected between the midpoint of the third bridge arm and the midpoints of the two bus capacitors; The fifth bridge arm is connected between the positive and negative DC busbars, and the fifth bridge arm includes a fifth switch tube and a sixth switch tube connected in series; a midpoint between the fifth switch tube and the sixth switch tube is connected to a third terminal of the power grid through a third phase line; The sixth bridge arm is connected between the midpoint of the fifth bridge arm and the midpoints of the two bus capacitors.

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