Inverter and line impedance detection method thereof

Abstract

The present application provides an inverter and a line impedance detection method thereof. When the inverter is powered on and running, the real-time output current, real-time output voltage and grid voltage collected within the power frequency cycle at a preset sampling frequency 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 the line impedance is updated 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. 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.

Description

Technical Field

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

[0002] When the line impedance from a photovoltaic grid-connected inverter to the grid changes, it will change the controlled model of the grid-connected inverter control system, affect the control performance of the grid-connected inverter, and have an adverse impact on the power quality of the grid-connected inverter and the stable operation of the system. Therefore, accurately identifying the impedance of the output line of the grid-connected inverter is crucial for the accurate control of the inverter and the stable operation of the grid. Summary of the Invention

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

[0004] In an embodiment of this application, the DC component of the current, DC component of the voltage, DC component of the grid, as well as the AC component of the current, AC component of the voltage, and AC component of the grid are calculated based on the real-time output current, real-time output voltage, and grid voltage collected within the power frequency period at a preset sampling frequency when the inverter is powered on and running. Furthermore, the line impedance is updated according to the DC component of the current, DC component of the voltage, DC component of the grid, as well as the AC component of the current, AC component of the voltage, and AC component of the grid. 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, which simplifies the control of the inverter. 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. Therefore, there is no need to additionally add a circuit for detecting the line impedance in the inverter, which can reduce the cost of the inverter.

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

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

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

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

[0012] In a second aspect, the present application provides an inverter, including: an inverter circuit, the output terminal of the inverter circuit is used to connect to the power grid; and

[0013] a control circuit, the control circuit is used to: when the inverter circuit is powered on and operating, collect the real-time output current and real-time output voltage of the inverter circuit and the grid voltage within the power frequency period at a preset sampling frequency; obtain the DC component of the current, the DC component of the voltage, the DC component of the grid, as well as the AC component of the current, the AC component of the voltage, and the AC component of the grid according to the real-time output current, the real-time output voltage, and the grid voltage; and update the line impedance between the inverter circuit and the power grid in sequence according to the DC component of the current, the DC component of the voltage, the DC component of the grid, as well as the AC component of the current, the AC component of the voltage, and the AC component of the grid in the sampling order.

[0014] In a possible implementation, the control circuit includes: a sampling unit, the sampling unit is used to collect the real-time output current and real-time output voltage and the grid voltage within the power frequency period 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 and real-time output voltage and the grid voltage, calculate the DC component of the current, the DC component of the voltage, the DC component of the grid, as well as the AC component of the current, the AC component of the voltage, and the AC component of the grid according to the real-time output current, the real-time output voltage, and the grid voltage, and update the line impedance according to the DC component of the current, the DC component of the voltage, the DC component of the grid, as well as the AC component of the current, the AC component of the voltage, and the AC component of the grid.

[0015] In a possible implementation, the inverter circuit includes a bus capacitor unit, positive and negative DC buses, a first arm, a second arm, a third arm, a fourth arm, a fifth arm, and a sixth arm; the bus capacitor unit is connected between the positive and negative DC buses, and the bus capacitor unit includes two bus capacitors connected in series; the first arm is connected between the positive and negative DC buses, and the first arm includes a first switch and a second switch connected in series; the midpoint between the first switch and the second switch is connected to the first terminal of the power grid through a first phase line; the second arm is connected between the midpoint of the first arm and the midpoint of the two bus capacitors; the third arm is connected between the positive and negative DC buses, and the third arm includes a third switch and a fourth switch connected in series; the midpoint between the third switch and the fourth switch is connected to the second terminal of the power grid through a second phase line; the fourth arm is connected between the midpoint of the third arm and the midpoint of the two bus capacitors; the fifth arm is connected between the positive and negative DC buses, and the fifth arm includes a fifth switch and a sixth switch connected in series; the midpoint between the fifth switch and the sixth switch is connected to the third terminal of the power grid through a third phase line; the sixth arm is connected between the midpoint of the first arm and the midpoint of the two bus capacitors. Description of the Drawings

[0016] Figure 1 is a schematic diagram of the modules of the inverter provided by an embodiment of the present application.

[0017] Figure 2 is a schematic diagram of the modules of the inverter provided by another embodiment of the present application.

[0018] Figure 3 is a schematic diagram of the circuit structure of the inverter provided by an embodiment of the present application.

[0019] Figure 4 is a schematic flowchart of the line impedance detection method provided by an embodiment of the present application.

[0020] Figure 5 is Figure 4 a refined flowchart of step S200 in

[0021] Figure 6 is Figure 4 a refined flowchart of step S300 in

[0022] Figure 7 is Figure 6 a refined flowchart of step S350 in

[0023] Figure 8 is a partial flowchart of the line impedance detection method provided by an embodiment of the present application.

[0024] Figure 9 is a flowchart of the line impedance detection method provided by a specific example of the present application. Detailed implementation manners

[0025] It should be noted that in the description of the present application, the terms "first" and "second" in the specification, claims and drawings 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 may mean A or B. For example, A and / or B may mean: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the term "multiple sets" in the specification, claims and drawings of the present application means two or more than two sets.

[0026] It can be understood 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 may be either A is directly connected to B or A and B are indirectly connected through one or more other electrical components. For example, A may be directly connected to C and C may be directly connected to B, so that A and B are connected through C.

[0027] In addition, it should be noted that the methods disclosed in the embodiments of the present application, or the methods shown in the flowcharts, include one or more steps for implementing the methods. Without departing from the scope of the claims, the execution order of multiple steps can be interchanged with each other, and some steps can also be deleted.

[0028] Some embodiments will be described below in conjunction with the drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0029] Please refer to Figure 1 , Figure 1 which shows a schematic diagram of the modules of the inverter 10 provided by the embodiment of the present application.

[0030] As Figure 1 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 operation of the inverter circuit 100 so that the inverter circuit 100 is connected to the power grid 20.

[0031] 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. 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 to the power grid 20, and the off-grid output port is used to connect to the load 40. The inverter 10 can also be provided with a battery connection port, and the battery connection port is used to connect to 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. Thus, 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 power grid 20 is connected to the grid-connected output port, that is, when the inverter 10 is in the grid-connected state, the power grid 20 can also supply power to the load 40 through the grid-connected output port. Of course, the power 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 in the embodiment of the present application is not limited to the photovoltaic energy storage inverter.

[0032] In the embodiment of the present application, the inverter circuit 100 can be a bidirectional inverter circuit, a T-type three-level inverter circuit, etc.

[0033] Among them, when the inverter circuit 100 is powered on and running, 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 period at a preset sampling frequency. The control circuit 200 then calculates the DC component of the current, the DC component of the voltage, the DC component of the grid, and the AC component of the current, the AC component of the voltage, and the AC component of the grid at each sampling moment according to the sampled real-time output current, real-time output voltage, and grid voltage, and sequentially updates the line impedance between the inverter circuit 100 and the power grid 20 according to the DC component of the current, the DC component of the voltage, the DC component of the grid, and the AC component of the current, the AC component of the voltage, and the AC component of the grid at each sampling moment in the sampling order.

[0034] Thus, the control circuit 200 can calculate the DC components of current, voltage, and grid voltage, as well as the AC components of current, voltage, and grid voltage at each sampling moment by sampling the real-time output current, real-time output voltage, and grid voltage within the power frequency cycle. Furthermore, the line impedance can be updated based on the DC components of current, voltage, and grid voltage, and the AC components of current, voltage, and grid voltage. 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, making the control of the inverter circuit 100 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. Therefore, there is no need to additionally add a circuit for detecting the line impedance in the inverter 10, which can reduce the cost of the inverter 10.

[0035] It should be noted that the power frequency can represent the rated frequency adopted by power generation, transmission, transformation, and distribution equipment in the power system, as well as industrial and civil electrical equipment, with the unit of hertz (HZ). Under the standard power frequency of 50 Hz, each power frequency cycle is 20 milliseconds (ms). When the power grid 20 is connected to the grid-connected output port of the inverter 10, the inverter 10 needs to be synchronized with the power grid 20. Therefore, the power frequency cycle of the inverter 10 is the same as that of the power grid 20. The sampling order refers to the order of sampling moments.

[0036] It can be understood that the preset sampling frequency needs to be greater than the power frequency. Correspondingly, the sampling period is less than the power frequency cycle. For example, when the power frequency is 50 Hz and the power frequency cycle 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 cycle, 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 embodiments of the present application, the sampling frequency can be the same as the frequency of the control signal of the switching tubes in the inverter 10 by the control circuit 200. Of course, the specific value of the sampling frequency in the embodiments of the present application is not limited and can be set according to actual application requirements.

[0037] Furthermore, as Figure 2As shown, the control circuit 200 may include a sampling unit 210 and a control unit 220. The sampling unit 210 is configured to collect the real-time output current, the real-time output voltage, and the grid voltage within the power frequency cycle at a preset sampling frequency. The control unit 220 is connected to the sampling unit 210. The control unit 220 is configured to receive the real-time output current, the real-time output voltage, and the grid voltage collected by the sampling unit 210, calculate the DC components of the current, the voltage, and the grid, as well as the AC components of the current, the voltage, and the grid, and update the line impedance according to the DC components of the current, the voltage, and the grid, and the AC components of the current, the voltage, and the grid.

[0038] 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 gate or transistor logic devices, etc.

[0039] It can be understood that, as Figure 3 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. Among them, the current sampling unit 211 is connected to the output terminal of the inverter circuit 100, and the current sampling unit 211 is configured to collect the real-time output current of the inverter circuit 100. The first voltage sampling unit 212 is connected to the output terminal of the inverter circuit 100, and the first voltage sampling unit 212 is configured 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 configured to collect the grid voltage.

[0040] Among them, the current sampling unit 211 can 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 can be implemented by any one of voltage division resistor sampling, differential sampling, isolation sampling, etc. to collect the real-time output voltage of the inverter circuit 100 and the grid voltage respectively.

[0041] Specifically, as Figure 3As shown, the inverter circuit 100 can be a three-phase T-type three-level inverter circuit. The inverter circuit 100 includes a bus capacitor unit, positive and negative DC buses (BUS+, BUS-), a first arm, a second arm, a third arm, a fourth arm, a fifth arm, and a sixth arm.

[0042] The bus capacitor unit is connected between the positive and negative DC buses (BUS+, BUS-), and the bus capacitor unit includes two series-connected bus capacitors. Figure 3 In the description, the two bus capacitors are respectively the bus capacitor Ci1 and the bus capacitor Ci2. One end of the bus capacitor Ci1 is connected to the positive DC bus BUS+, the other end of the bus capacitor Ci1 is connected to one end of the bus capacitor Ci2, and the other end of the 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 buses (BUS+, BUS-) are used to connect the photovoltaic module 30 or the energy storage battery 50 to transmit the DC power provided by the photovoltaic module 30 or the energy storage battery 50 to the bus capacitors Ci1 and Ci2 and store energy through the bus capacitors Ci1 and Ci2. When the DC input port of the inverter 10 is connected to the photovoltaic module 30, the voltage at the input end of the inverter circuit 100 is the photovoltaic voltage V PV , and the bus capacitors Ci1 and Ci2 divide the input voltage of the inverter circuit 100 into three levels, which are V PV / 2, 0, -V PV / 2.

[0043] The first arm is connected between the positive and negative DC buses (BUS+, BUS-), and the first arm includes a series-connected first switch tube Q1 and a second switch tube Q2. 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 bus BUS+, the second end of the first switch tube Q1 is connected to the first end of the second switch tube Q2 (i.e., the midpoint of the first arm), and the second end of the second switch tube Q2 is connected to the negative DC bus BUS-.

[0044] The second arm is connected between the midpoint of the first arm and the midpoint of the two bus capacitors.

[0045] The third bridge arm is connected between the positive and negative DC buses (BUS+ and BUS-), and the third bridge arm includes a series connection of a third switching transistor Q3 and a fourth switching transistor Q4. The midpoint between the third switching transistor Q3 and the fourth switching transistor 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 switching transistor Q3 is connected to the positive DC bus BUS+, the second end of the third switching transistor Q3 is connected to the first end of the fourth switching transistor Q4 (which is the midpoint of the third bridge arm), and the second end of the fourth switching transistor Q4 is connected to the negative DC bus BUS-.

[0046] The fourth bridge arm is connected between the midpoint of the third bridge arm and the midpoint of the two bus capacitors.

[0047] The fifth bridge arm is connected between the positive and negative DC buses (BUS+ and BUS-), and the fifth bridge arm includes a series connection of a fifth switching transistor Q5 and a sixth switching transistor Q6. The midpoint between the fifth switching transistor Q5 and the sixth switching transistor 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 switching transistor Q5 is connected to the positive DC bus BUS+, the second end of the fifth switching transistor Q5 is connected to the first end of the sixth switching transistor Q6 (which is the midpoint of the fifth bridge arm), and the second end of the sixth switching transistor Q6 is connected to the negative DC bus BUS-.

[0048] The sixth bridge arm is connected between the midpoint of the fifth bridge arm and the midpoint of the two bus capacitors.

[0049] The second bridge arm includes a reverse series connection of a seventh switching transistor Q7 and an eighth switching transistor Q8. The first end of the seventh switching transistor Q7 is connected to the first end of the eighth switching transistor Q8. The second end of the seventh switching transistor Q7 is connected to the midpoint of the two bus capacitors, and the second end of the eighth switching transistor Q8 is connected to the midpoint of the first bridge arm.

[0050] The fourth bridge arm includes a reverse series connection of a ninth switching transistor Q9 and a tenth switching transistor Q10. The first end of the ninth switching transistor Q9 is connected to the first end of the tenth switching transistor Q10. The second end of the ninth switching transistor Q9 is connected to the midpoint of the two bus capacitors, and the second end of the tenth switching transistor Q10 is connected to the midpoint of the third bridge arm.

[0051] The sixth bridge arm includes a reverse series connection of an eleventh switching transistor Q11 and a twelfth switching transistor Q12. The first end of the eleventh switching transistor Q11 is connected to the first end of the twelfth switching transistor Q12. The second end of the eleventh switching transistor Q11 is connected to the midpoint of the two bus capacitors, and the second end of the twelfth switching transistor Q12 is connected to the midpoint of the fifth bridge arm.

[0052] The midpoint of the first bridge arm is connected to the first terminal of the power grid 20 through the first phase line A, the midpoint of the third bridge arm is connected to the second terminal of the power grid 20 through the second phase line B, and the midpoint of the fifth bridge arm is connected to the third terminal of the power grid 20 through the third phase line C.

[0053] The control unit 220 can be respectively connected to the control terminals of the switching tubes of each bridge arm and send control signals to each switching tube, so that each switching tube can be turned on or off under the drive of the control signal. Among them, the control signal is a Pulse Width Modulation (PWM) signal.

[0054] In this way, when the inverter circuit 100 performs inversion, the photovoltaic module 30 or the energy storage battery 50 can input direct current through the positive and negative DC buses, and be converted into three-phase alternating current through the on-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 be respectively output to the first phase line A, the second phase line B and the third phase line C.

[0055] It can be understood that the present application does not make specific limitations on each switching tube, and each switching tube can include but is not limited to a triode, a Silicon Controlled Rectifier (SCR), a Metal Oxide Semiconductor Field Effect Transistor (MOSFET), an Insulated Gate Bipolar Transistor (IGBT), or a Gallium Nitride High Electron Mobility Transistor (GaN HEMT), or is formed by at least one of a triode, an SCR, a MOSFET, an IGBT, a GaN HEMT in parallel with a reversely connected diode. For example, when the switching 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.

[0056] Correspondingly, the real-time output current of the inverter circuit 100 includes the phase line current on each phase line. The current sampling unit 211 can be respectively connected to the first phase line A, the second phase line B and the third phase line C to respectively detect the phase line current of the first phase line A, the second phase line B and the third phase line C. The real-time output voltage of the inverter circuit 100 includes the phase line voltage of the connection node between the output terminal of the inverter circuit 100 and each phase line, that is, the voltage at the midpoints of the first bridge arm, the third bridge arm and the fifth bridge arm. The first voltage sampling unit 212 is respectively connected to the midpoints of the first bridge arm, the third bridge arm and the fifth bridge arm to detect the phase line voltage at the midpoints of the three bridge arms. The grid voltage includes the terminal voltage of the three terminals connected to the three phase lines. The second voltage sampling unit 213 is respectively connected to the three terminals of the power grid 20 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 3On each of the three phase lines, the line inductance (L A 、L B 、L C )and the line resistance (R A 、R B 、R C )represent the line impedance of the three phase lines.

[0057] The following will detail the inverter 10 and its line impedance detection method provided by the embodiments of the present invention through specific embodiments.

[0058] Please refer to Figure 4 , which shows a schematic flowchart of the line impedance detection method provided by an embodiment of the present invention. This line impedance detection method is applied to the inverter 10. In at least one implementation, the line impedance detection method can be executed by the above control circuit 200.

[0059] As Figure 4 shown, the line impedance detection method includes:

[0060] S100. When the inverter is powered on and running, collect the real-time output current, real-time output voltage, and grid voltage of the inverter within the power frequency period at a preset sampling frequency.

[0061] The inverter 10 being powered on and running means that the grid connection output port of the inverter 10 is connected to the grid 20 and the control circuit 200 sends control signals for turning on and off to each switching tube in the inverter circuit 100.

[0062] S200. According to the real-time output current, real-time output voltage, and grid voltage, obtain the DC component of the current, DC component of the voltage, DC component of the grid, as well as the AC component of the current, AC component of the voltage, and AC component of the grid.

[0063] Among them, since the DC component of a 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 grid can be determined according to the average value of the 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, 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, and the AC component of the grid can be determined according to the difference between the grid voltage corresponding to the sampling moment and the DC component of the grid.

[0064] S300. Update the line impedance between the inverter and the grid in sequence according to the DC component of the current, DC component of the voltage, DC component of the grid, as well as the AC component of the current, AC component of the voltage, and AC component of the grid in the sampling order.

[0065] According to the sequence of sampling times, the line impedance is updated successively based on the DC component of the current, the DC component of the voltage, the DC component of the power grid, as well as the AC component of the current, the AC component of the voltage, and the AC component of the power grid. Thus, dynamic detection of the line impedance between the inverter 10 and the power grid 20 is achieved. When the line impedance between the inverter 10 and the power grid 20 changes, it can respond in a timely manner.

[0066] For example, at the initial sampling moment of a power frequency cycle, the control circuit 200 determines the line impedance based on the DC component of the current, the DC component of the voltage, the DC component of the power grid, as well as the AC component of the current, the AC component of the voltage, and the AC component of the power grid at the initial sampling moment. Then, the control circuit 200 determines the line impedance at the second sampling moment based on the DC component of the current, the DC component of the voltage, the DC component of the power grid, as well as the AC component of the current, the AC component of the voltage, and the AC component of the power grid at the second sampling moment, and updates the line impedance to the line impedance at the second sampling moment, and so on, to achieve dynamic identification of the line impedance. It can be understood that in a power frequency cycle, the DC component of the current, the DC component of the voltage, and the DC component of the power grid 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 power grid voltage sampled in the previous power frequency cycle.

[0067] 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, it is executed by the control unit 220. For example, it is executed by the microcontroller unit 220 (MCU), digital signal processor (DSP), or energy management system (EMS), etc. in the inverter 10. Among them, the control circuit 200 may include multiple controllers or control chips, such as including a DSP chip and a RAM (Random Access Memory) chip, etc.

[0068] 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 achieve identification of the line impedance in the dynamic process.

[0069] Of course, the control circuit 200 in the inverter 10 can also repeatedly execute steps S100 to S300 until the identified line impedance is stable, and then the identification of the line impedance ends. At this time, the control circuit 200 can start to execute steps S100 to S300 when the inverter 10 starts to power on and run. After one or more power frequency cycles, the identified line impedance is stable, and the execution of steps S100 to S300 ends. In some specific examples, after the control circuit 200 ends the identification of the line impedance, it can also execute steps S100 to S300 again after a certain time interval to re-identify the line impedance, so as to prevent the power quality of the electrical energy output by the inverter circuit 100 from being affected because the control circuit 200 cannot timely identify the change of the line impedance after the execution of steps S100 to S300 ends.

[0070] Please refer to Figure 5 , Figure 5 which shows Figure 4 the refined flowchart of step S200 in

[0071] As Figure 5 shown, in some embodiments, step S200 may include:

[0072] S210. Obtain the DC component of the current according to the average value of all real-time output currents obtained within the power frequency cycle.

[0073] The control circuit 200 can add all the real-time output currents collected within one power frequency cycle and then divide by the number of samples to obtain the average value of the real-time output currents, that is, the DC component of the current. For example, when the sampling frequency is 50 kHz and the number of samples is 1000, and all the real-time output currents are I 1 , I 2 , I 3 , …, I 1000 , then the DC component of the current is: . Of course, when there are multiple phase lines connected to the output end of the inverter circuit 100, the average value of the real-time output currents of each phase line is calculated respectively to obtain the DC component of the current of each phase line.

[0074] S220. Obtain the DC component of the voltage according to the average value of all real-time output voltages obtained within the power frequency cycle.

[0075] The control circuit 200 can add all the real-time output voltages collected within one power frequency cycle and then divide by the number of samples to obtain the average value of the real-time output voltages, that is, the DC component of the voltage. For example, when the sampling frequency is 50 kHz and the number of samples is 1000, and all the real-time output voltages are U 1 , U 2 , U 3 , …, U1000 , the DC component of the current is: . Of course, when multiple phase lines are connected to the output end of the inverter circuit 100, 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.

[0076] S230. Obtain the grid DC component according to the average value of all grid voltages obtained within the power frequency period.

[0077] The control circuit 200 can add all the grid voltages collected within one power frequency period and then divide by the number of samples to obtain the average value of the grid voltages, that is, the DC component of the voltage. For example, when the sampling frequency is 50 kHz and the number of samples is 1000, and the sampled grid voltages are E 1 , E 2 , E 3 , …, E 1000 , then the grid DC component is: . Of course, when multiple phase lines are connected to the output end of the inverter circuit 100, the average value of the grid voltages corresponding to each phase line is calculated respectively to obtain the grid DC component corresponding to each phase line.

[0078] S240. Obtain the AC component of the current according to the difference between the sampled real-time output current and the DC component of the current.

[0079] The control circuit 200 can subtract the DC component of the current from the real-time output current at the current sampling moment 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 t-th sampling moment is . And so on, 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 each update of the line impedance. 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 multiple phase lines are connected to the output end of the inverter circuit 100, 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.

[0080] S250. Obtain the AC component of the voltage according to the difference between the sampled real-time output voltage and the DC component of the voltage.

[0081] 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 AC component of the voltage at the second sampling moment is The AC component of the current at the t-th sampling moment is And so on, the AC component of the voltage at each sampling moment can be obtained. Of course, the control circuit 200 can also calculate the AC component of the voltage at the current sampling moment before each update of the line impedance. 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 voltage 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 with multiple phase lines, the difference between the real-time output voltage corresponding to each phase line and the DC component of the voltage is calculated respectively to obtain the AC component of the voltage of each phase line.

[0082] S260. Obtain the grid AC component according to the difference between the sampled grid voltage and the grid DC component.

[0083] The control circuit 200 can subtract the grid DC component from the grid voltage at the current sampling moment to obtain the grid AC component at the current sampling moment. For example, the grid AC component at the initial sampling moment is The grid AC component at the second sampling moment is The AC component of the current at the t-th sampling moment is And so on, the grid AC component at each sampling moment can be obtained. Of course, the control circuit 200 can also calculate the grid AC component at the current sampling moment before each update of the line impedance. 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 grid AC component at the next sampling moment. When the output end of the inverter circuit 100 is connected with multiple phase lines, the difference between the grid voltage corresponding to each phase line and the grid DC component is calculated respectively to obtain the grid AC component of each phase line.

[0084] In some embodiments, the control circuit 200 can also calculate the DC component of the current, the DC component of the voltage and the DC component of the grid 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 DC component of the current calculated according to the real-time output current in the previous power frequency cycle from the real-time output current sampled at the current sampling moment in the current power frequency cycle to obtain the AC component of the current at the current sampling moment. The control circuit 200 subtracts the DC component of the voltage calculated according to the real-time output voltage in the previous power frequency cycle from the real-time output voltage sampled at the current sampling moment in the current power frequency cycle to obtain the AC component of the voltage at the current sampling moment. The control circuit 200 subtracts the DC component of the grid calculated according to the grid voltage in the previous power frequency cycle from the grid voltage sampled at the current sampling moment in the current power frequency cycle to obtain the AC component of the grid at the current sampling moment.

[0085] Please refer to Figure 6 , Figure 6 which shows Figure 4 a refined flowchart of step S300 in

[0086] As Figure 6 shown, in some embodiments, step S300 may include:

[0087] S310. Obtain a DC deviation value based on the difference between the DC component of the voltage and the DC component of the power grid.

[0088] The control circuit 200 may subtract the DC component of the power grid from the DC component of the voltage to obtain a DC deviation value. Specifically, the DC deviation value is .

[0089] S320. Obtain an AC deviation value based on the difference between the AC component of the voltage at the current sampling moment and the AC component of the power grid.

[0090] The control circuit 200 may subtract the AC component of the power grid from the AC component of the voltage at the current sampling moment to obtain an AC deviation value. Specifically, the AC deviation value is . Where t is the sampling moment. For example, when the current sampling moment is the second sampling moment, t = 2.

[0091] S330. Obtain a resistance value based on the DC deviation value and the DC component of the current.

[0092] It can be understood that there are parasitic resistances (R A , R B , R C ), parasitic inductances (L A , L B , L C ) and parasitic capacitances (not shown in the figure) in the line between the output terminal of the inverter circuit 100 and the power grid 20. The line impedance includes the resistance value of the parasitic resistance and the reactance values of the parasitic inductance and the parasitic capacitance. In a linear system, according to Ohm's law, the control circuit 200 may divide the DC deviation value by the DC component of the current to obtain a resistance value. Specifically, the resistance value is . Where, taking Figure 3 as an example, R is the resistance value of the line resistance (R A , R B , R C ) on the phase line.

[0093] S340. Obtain the reactance value at the current sampling moment based on the AC deviation value at the current sampling moment and the AC component of the current.

[0094] The control circuit 200 may divide the AC deviation value at the current sampling moment by the AC component of the current to obtain a reactance value. Specifically, the reactance value is Among them, taking Figure 3 as an example, jωL is the sum of the inductive reactance of the line inductance and the capacitive reactance of the line capacitance (not shown in the figure), that is, the reactance value.

[0095] S350. Update the line impedance according to the sum of the resistance value and the reactance value.

[0096] The control circuit 200 can update the line impedance according to the sum of the calculated resistance value and reactance value. Specifically, the updated line impedance is .

[0097] Please refer to Figure 7 , Figure 7 which shows Figure 6 the detailed flowchart of step S350 in

[0098] As Figure 7 shown, in some embodiments, step S350 may include:

[0099] S351. Obtain the impedance detection value at the current sampling moment according to the sum of the resistance value and the reactance value.

[0100] 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 .

[0101] S352. Update the line impedance according to the impedance detection value.

[0102] Among them, when the difference between the impedance detection value and the line impedance is not within the preset range, update the impedance detection value to the line impedance of the inverter 10.

[0103] And when the difference between the impedance detection value and the line impedance is within the preset range, stop updating the line impedance.

[0104] In the embodiment of the present application, the control circuit 200 can subtract the line impedance from the impedance detection value to obtain the difference. Specifically, the difference is . When is within the preset range, . And when is within the preset range, then stop updating the line impedance, and the line impedance remains Z.

[0105] It can be understood that when the difference between the impedance detection value and the line impedance is within a preset range, it indicates that the line impedance between two adjacent sampling moments is basically stable. Herein, 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 is equal to the line impedance, that is, the line impedance is stable. Of course, since there are certain errors in the sampling of the output current, output voltage, and grid voltage of the inverter circuit 100 by the control circuit 200, the preset range can also be set according to the error. For example, it can be set to (-100 mΩ, 100 mΩ), and the present application does not limit this.

[0106] It can be understood that since the DC components of the current, voltage, and grid need to be calculated based on the average values of the real-time output current, real-time output voltage, and grid voltage sampled within one power frequency period, within the first power frequency period when the inverter 10 is initially powered on, the control circuit 200 cannot update the line impedance in real time. For this reason, please refer to Figure 8 , the line impedance detection method may further include:

[0107] S101. During the first power frequency period when the inverter is initially powered on, collect the real-time output current, real-time output voltage, and grid voltage of the inverter within the first power frequency period at a preset sampling frequency.

[0108] S102. According to the real-time output current, real-time output voltage, and grid voltage collected during the first power frequency period, obtain the DC components of the current, voltage, and grid of the inverter within the first power frequency period.

[0109] At the last sampling moment of the first power frequency period, the control circuit 200 calculates the DC components of the current, voltage, and grid within the first power frequency period according to the average values of all the collected real-time output currents, all the collected real-time output voltages, and all the grids.

[0110] S103. Calculate the initial line impedance of the inverter according to the DC components of the current, voltage, and grid within the first power frequency period.

[0111] The control circuit 200 calculates the initial line impedance of the inverter 10 according to the DC components of the current, voltage, and grid within the first power frequency period. Furthermore, in steps S100 to S300, at the first sampling moment of the second power frequency period, the control circuit 200 updates the initial line impedance with the impedance detection value calculated at the first sampling moment, that is, the impedance detection value at the first sampling moment of the second power frequency period is used as the line impedance.

[0112] In the embodiments of the present application, the initial line impedance may only include the resistance value calculated according to the DC components of the current, voltage, and power grid 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 according to the AC component of the current obtained by subtracting the DC component of the current from the real-time output current at the last sampling moment of the first power frequency cycle, the AC component of the voltage obtained by subtracting the DC component of the voltage from the real-time output voltage, and the AC component of the power grid voltage obtained by subtracting the DC component of the power grid from the power grid voltage.

[0113] It can be understood that in each sampling moment of the second power frequency cycle, the control circuit 200 calculates the resistance value according to the DC components of the current, voltage, and power grid in the first power frequency cycle, while the reactance value is calculated according to the AC component of the current obtained by subtracting the DC component of the current from the real-time output current, the AC component of the voltage obtained by subtracting the DC component of the voltage from the real-time output voltage, and the AC component of the power grid voltage obtained by subtracting the DC component of the power grid from the power grid voltage.

[0114] The following takes Figure 3 the shown three-phase T-type three-level inverter circuit as an example to illustrate the line impedance detection method of the embodiments of the present application.

[0115] Please refer to Figure 9 , Figure 9 which shows the schematic flowchart of the line impedance detection method applied to Figure 3 . As Figure 9 shown, the line impedance detection method includes:

[0116] S810. Collect I A , I B , I C , U A , U B , U C , E A , E B and E C respectively within the power frequency cycle at a preset sampling frequency.

[0117] Among them, I A is the current of the first phase line, I B is the current of the second phase line, I C is the current of the third phase line, U A is the voltage of the first phase line, U B is the voltage of the second phase line, U C is the voltage of the third phase line, E A is the voltage of the first terminal, E B is the voltage of the second terminal, E C is the voltage of the third terminal.

[0118] The first phase line current, the second phase line current, and the third phase line current are the output currents of the three phase lines (A, B, and C) at the output end of the inverter circuit 100, respectively. The first phase line voltage, the second phase line voltage, and the third phase line voltage are the output voltages at the midpoints of the first bridge arm, the third bridge arm, and the fifth bridge arm of the inverter circuit 100, respectively. The first terminal voltage, the second terminal voltage, and the third terminal voltage are the voltages of the terminals where the power grid 20 is connected to the three phase lines, respectively.

[0119] Specifically, as Figure 3 shown, the three phase lines are the first phase line A, the second phase line B, and the third phase line C, respectively. Correspondingly, the first phase line currents sampled by the control circuit 200 within one power frequency cycle are I A1 , I A2 , I A3 , …, I An , the second phase line currents are I B1 , I B2 , I B3 , …, I Bn , and the third phase line currents are I C1 , I C2 , I C3 , …, I Cn . The first phase line voltages are U A1 , U A2 , U A3 , …, U An , the second phase line voltages are U B1 , U B2 , U B3 , …, U Bn , and the third phase line voltages are U C1 , U C2 , U C3 , …, U Cn . The first terminal voltages are E A1 , E A2 , E A3 , …, E An , the second terminal voltages are E B1 , E B2 , E B3 , …, E Bn , and the third terminal voltages are E C1 , E C2 , E C3 , …, E Cn . Among them, n is the number of samples taken by the control circuit 200 within one power frequency cycle.

[0120] S820. Respectively, according to the averages of I A , I B , and I CThe average value of obtains I ADC , I BDC and I CDC ; According to the average value of U A collected within the power frequency period, the average value of U B and the average value of U C obtain U ADC , U BDC and U CDC ; According to the average value of E A collected within the power frequency period, the average value of E B and the average value of E C obtain E ADC , E BDC and E CDC .

[0121] Among them, I ADC is the first DC component of the current of the first phase line A, I BDC is the second DC component of the current of the second phase line B, I CDC is the third DC component of the current of the third phase line C. U ADC is the first DC component of the output voltage of the first bridge arm, U BDC is the second DC component of the output voltage of the second bridge arm, U CDC is the third DC component of the output voltage of the third bridge arm. E ADC is the first grid DC component of the voltage of the first terminal, E BDC is the second grid DC component of the voltage of the second terminal, E CDC is the third grid DC component of the voltage of the third terminal.

[0122] Specifically, the first DC component of the current is , the second DC component of the current is , and the third DC component of the current is .

[0123] The first DC component of the voltage is , the second DC component of the voltage is , and the third DC component of the voltage is .

[0124] The first grid DC component is , the second grid DC component is , and the third grid DC component is .

[0125] S830, respectively according to the difference between I At and I ADC at the current sampling moment, the difference between I Bt and I BDC and ICt and I CDC The difference between them gives I AACt , I BACt and I CACt ; respectively, according to the difference between U A and U ADC , the difference between U B and U BDC , and the difference between U C and U CDC the difference gives U AACt , U BACt and U CACt ; respectively, according to the difference between E A and E ADC , the difference between E B and E BDC , and the difference between E C and E CDC the difference gives E AACt , E BACt and E CACt .

[0126] 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. U AACt is the first voltage AC component, U BACt is the second voltage AC component, U CACt is the third voltage AC component. E AACt is the first grid AC component, E BACt is the second grid AC component, E CACt is the third grid AC component.

[0127] Specifically, the first current AC component is , the second current AC component is , and the third current AC component is . Where t is the current sampling time.

[0128] The first voltage AC component is , the second voltage AC component is , and the third voltage AC component is .

[0129] The first grid AC component is , the second grid AC component is , and the third grid AC component is .

[0130] S840, respectively, according to the difference between U ADC and E ADC the difference, the difference between UBDC and E BDC the difference between and U CDC and E CDC the difference between and to obtain V 1A 、V 1B and V 1C ; respectively according to U AACt and E AACt the difference between, U BACt and E BACt the difference between and to obtain V CACt and E CACt the difference between and to obtain V 2A 、V 2B and V 2C .

[0131] 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. V 2A is the first AC deviation value, V 2B is the second AC deviation value, V 2C is the third AC deviation value.

[0132] Specifically, the first DC deviation value is . The second DC deviation value is . The third DC deviation value is .

[0133] The first AC deviation value is . The second AC deviation value is . The third AC deviation value is .

[0134] S850, divide V 1A by I ADC to obtain R A , V 1B divide by I BDC to obtain R B , V 1C divide by I CDC to obtain R C , V 2A divide by I AACt to obtain jωL At , V 2B divide by I BACt to obtain jωL Bt , V 2C divide by I CACt to obtain jωL Ct .

[0135] Among them, R A is the first resistance value, R Bis the second resistance value, R C is the third resistance value. jωL At is the first reactance value, jωL Bt is the second reactance value, jωL Ct is the third reactance value.

[0136] 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 and the capacitive reactance of the line capacitance on the first phase line A, the second reactance value is the sum of the inductive reactance of the line inductance and the capacitive reactance of the line capacitance on the second phase line B, and the third reactance value is the sum of the inductive reactance of the line inductance and the capacitive reactance of the line capacitance on the third phase line C.

[0137] Specifically, the first resistance value is and the second resistance value is and the third resistance value is .

[0138] The first reactance value is and the second reactance value is and the third reactance value is . Where t is the current sampling time.

[0139] S860. Obtain Z A from the sum of R At and jωL At , obtain Z B from the sum of R Bt and jωL Bt , obtain Z C from the sum of R Ct and jωL Ct .

[0140] 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.

[0141] The first impedance detection value is the line impedance of the first phase line A at the current sampling time, the second impedance detection value is the line impedance of the second phase line B at the current sampling time, and the third impedance detection value is the line impedance of the third phase line C at the current sampling time.

[0142] Specifically, the first impedance detection value is and the second impedance detection value is and the third impedance detection value is .

[0143] S870. Determine Z Atand Z A The difference between and Z Bt and Z B The difference between and Z Ct and Z C The difference between are all equal to zero

[0144] where 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

[0145] It can be understood that the control circuit 200 needs to 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 respectively, and then compare each difference with zero

[0146] 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 , and the difference between the third impedance detection value and the third line impedance is .

[0147] S880. When are all equal to zero, output the current Z A , Z B , Z C .

[0148] S890. When there is a value not equal to zero among them, Z A = Z At , Z B = Z Bt , Z C = Z Ct .

[0149] It can be understood that after step S890, return to step S830 to start calculating the line impedance at the next sampling moment. When the line impedances iterated by the control circuit 200 within one power frequency cycle are all unstable (that is, the impedance detection values at every two adjacent sampling moments within the entire power frequency cycle are not equal), then re - execute steps S810 - S890 to continue iterating the line impedance in the next power frequency cycle until the line impedance is stable

[0150] Thus, 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 conduction network 20 of the inverter circuit 100 based on the sampled output current, output voltage, and grid voltage, and then iterating the line impedance at each sampling moment in sequence according to the sampling order, a stable line impedance is obtained, realizing accurate identification of the line impedance in the dynamic process without the need to actively inject a disturbance signal into the inverter circuit 100, with simple control and cost savings.

[0151] 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, and can also be a bidirectional inverter circuit, a two-phase inverter circuit, other three-phase inverter circuits, and the like.

[0152] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and are not restrictive. In the actual application process, all the content of the technical solutions described in any embodiment of the present application can be implemented, or part of the content can be added, or part of the content can be deleted, or part of the content can be changed / replaced. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced 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; 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.

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, 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.

4. The line impedance detection method according to claim 3, 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.

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 within a preset range, the line impedance is stopped from being updated.

6. 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.

7. The line impedance detection method according to any one of claims 1 to 6, 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.

8. 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; 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 between the inverter circuit and the power grid is updated according to the sum of the resistance value and the reactance value.

9. The inverter according to claim 8, 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.

10. The inverter according to claim 8 or 9, 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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