Filter capacitor discharging method, inverter and grid-connected starting method thereof
By performing filter capacitor voltage balance before the inverter is connected to the grid, the problem of excessive current at the moment when the inverter is connected to the grid is solved, ensuring the long-term operation and smooth operation of the inverter.
Patent Information
- Application Number
- CN202510384098.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-28
- Publication Date
- 2025-06-24
AI Technical Summary
During the inverter grid-connected startup process, the unequal voltage of the filter capacitor causes the inverter to generate a large current instantly, affecting the long-term operation and smooth operation of the inverter.
By controlling the switching states of the upper and lower tubes of the inverter, the voltage of the filter capacitor on the AC side is equal, and the voltage balance is performed by using the filter capacitor discharge method before starting the grid.
Before the inverter is connected to the grid, the voltage of the filter capacitor is almost equal, avoiding the damage to the inverter by the large current at the moment of grid-connected start, which is conducive to the long-term operation and smooth operation of the inverter.
Smart Images
Figure CN120200255A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of grid-connected inverter control, and relates to a method for discharging a filter capacitor, an inverter and a grid-connected starting method thereof. Background Art
[0002] Such as Figure 1 For the three-phase two-level inverter shown, during the grid-connected starting process of the inverter, first, the input PWM waveform controls the six switching tubes Q1-Q6 to conduct alternately, so that the phases and amplitudes of the inverter-side voltage and the grid-side voltage are the same, and then the contactors S1, S2, and S3 are closed to complete the grid connection. However, in general grid-connected control schemes, the influence brought by the residual voltage in the filter capacitors C1, C2, and C3 is not considered; when the voltages of the filter capacitors are not equal, non-zero vectors will be generated, causing a large current to be generated at the moment of wave generation by the inverter. As Figure 2 shown, it is the current change situation of the filter capacitor C3 branch at the moment of wave generation by the inverter. Generating a large current at the moment of wave generation by the inverter is not conducive to the long-term operation and stable operation of the inverter. Summary of the Invention
[0003] The technical solution of the present invention is used to solve the problem of how to reduce the current at the moment of grid-connected starting of the inverter.
[0004] The present invention solves the above technical problems through the following technical solutions:
[0005] The present invention provides a method for discharging a filter capacitor, which controls the upper tubes of the inverter to be in the switching state at the same time and controls the lower tubes of the inverter to be in the off state at the same time, or controls the lower tubes of the inverter to be in the switching state at the same time and controls the upper tubes of the inverter to be in the off state at the same time, so that the voltages of the AC-side filter capacitors are equal.
[0006] Preferably, the inverter adopts an LC filter or an LCL filter.
[0007] Preferably, the inverter is a two-level, three-level, four-level or five-level inverter.
[0008] Preferably, the inverter is a single-phase or three-phase inverter.
[0009] The present invention also provides a grid-connected starting method for an inverter, specifically: first, use the above method for discharging a filter capacitor to discharge the AC-side filter capacitor to make the voltages of the AC-side filter capacitors equal, then perform PWM open-loop wave generation to make the phases and amplitudes of the inverter-side voltage and the grid-side voltage the same, and finally close the AC-side contactor to complete the grid-connected starting.
[0010] The present invention also provides an inverter, which uses the above method for discharging a filter capacitor to discharge the AC-side filter capacitor.
[0011] The present invention also provides an electronic device, including a memory and a processor. The memory is used to store a program that supports the processor to execute the above-mentioned filtering capacitor discharging method, and the processor is configured to execute the program stored in the memory.
[0012] The present invention also provides a storage medium, on which a computer program is stored. When the computer program is run by a processor, it executes the steps of the above-mentioned filtering capacitor discharging method.
[0013] The present invention also provides an electronic device, including a memory and a processor. The memory is used to store a program that supports the processor to execute the above-mentioned inverter grid-connection starting method, and the processor is configured to execute the program stored in the memory.
[0014] The present invention also provides a storage medium, on which a computer program is stored. When the computer program is run by a processor, it executes the steps of the above-mentioned inverter grid-connection starting method.
[0015] The beneficial effects of the present invention are as follows:
[0016] The technical solution of the present invention controls the upper switches of the inverter to be in the switching state at the same time and controls the lower switches of the inverter to be in the off state at the same time, or controls the lower switches of the inverter to be in the switching state at the same time and controls the upper switches of the inverter to be in the off state at the same time, so that the voltages of the filtering capacitors are close to equal and reach a balanced state before the inverter grid-connection starts, avoiding the damage to the inverter caused by a large current generated at the moment of the inverter grid-connection starting, which is beneficial to the long-term operation and stable operation of the inverter. Description of the Drawings
[0017] Figure 1 is the topological structure diagram of a three-phase two-level grid-connected inverter;
[0018] Figure 2 is the diagram of the current change situation of the filtering capacitor C3 branch at the moment of wave generation of the inverter;
[0019] Figure 3 is the periodic PWM waveform diagram of the control switch tube;
[0020] Figure 4 is the equivalent circuit diagram of the t1 period in a period of the periodic PWM waveform of the three-phase two-level grid-connected inverter at Figure 3 ;
[0021] Figure 5 is the voltage waveform diagram of the filtering capacitor after adopting the method of the present invention;
[0022] Figure 6 is the diagram of the current change situation of the filtering capacitor C3 branch at the moment of wave generation of the inverter after adopting the method of the present invention. Detailed implementation manners
[0023] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are only a part rather than all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present invention.
[0024] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings of the specification and specific embodiments:
[0025] Embodiment 1
[0026] As Figure 1 shown, the content of a method for discharging the AC-side filtering capacitors of a three-phase two-level inverter in this embodiment is as follows: Before the three-phase two-level inverter is connected to the grid and starts up, control the three lower switches Q4, Q5, and Q6 to be simultaneously in a switching state with a certain duty cycle or an intermittent duty cycle (sending waves for a certain time and not sending waves for a certain time), and control the three upper switches Q1, Q2, and Q3 to be simultaneously in the off state.
[0027] As Figure 3 shown, to control the periodic PWM waveforms of the three lower switches Q4, Q5, and Q6, the given duty cycle in the figure is 0.05, and the actual range may be between 0 and 1. The high level is for turning on the switching tube, and the low level is for turning off the switching tube. The switching tubes Q4, Q5, and Q6 use the same duty cycle and have the same phase.
[0028] As Figure 3 shown in a one-period PWM waveform of, the high-level time is t1 and the low-level time is t2; in the t1 time period, the three lower switches Q4, Q5, and Q6 are all turned on, and the three upper switches Q1, Q2, and Q3 are all turned off. The circuit on the inverter side of the three-phase two-level inverter is equivalently as Figure 4 , the right sides of the inductors L4, L5, and L6 are equivalent to being short-circuited. When the voltages on the three filtering capacitors C1, C2, and C3 are not equal, the current charges and discharges through the resistors R1, R2, R3 and the inductors L4, L5, and L6 until the voltages on the three filtering capacitors C1, C2, and C3 are equal. In the t2 time period, the three lower switches Q4, Q5, and Q6 are all turned off, and the three filtering capacitors C1, C2, and C3 are in an open-circuit state. There is no current flowing in the circuit, and the capacitor voltages on the three filtering capacitors C1, C2, and C3 remain unchanged.
[0029] Verification by simulation experiment
[0030] Set simulation parameters: the capacitance value of filtering capacitor C1 is 33 uF and the initial voltage is 100 V; the capacitance value of filtering capacitor C2 is 33 uF and the initial voltage is 0 V; the capacitance value of filtering capacitor C3 is 33 uF and the initial voltage is 600 V.
[0031] Control the three lower switches Q4, Q5, and Q6 to be in the switching state with a certain duty cycle simultaneously, and control the three upper switches Q1, Q2, and Q3 to be in the off state simultaneously. After generating the waveform for a period of time, as Figure 5 shown, it can be observed that the voltages of filtering capacitors C1, C2, and C3 are close to equal.
[0032] At this time, then normally start the three-phase two-level inverter to be connected to the grid, and the current change situation of the filtering capacitor C3 branch is as Figure 6 shown. Compared with Figure 2 , it can be observed that the current magnitude of the C3 branch is significantly reduced at this time, and the inverter can start smoothly at this time.
[0033] Embodiment 2
[0034] The content of a method for discharging the AC-side filtering capacitors of a three-phase two-level inverter in this embodiment is: before the three-phase two-level inverter is connected to the grid and starts, control the three lower switches Q4, Q5, and Q6 to be in the off state simultaneously, and control the three upper switches Q1, Q2, and Q3 to be in the switching state with a certain duty cycle simultaneously.
[0035] As Figure 3 shown, it is the periodic PWM waveforms for controlling the three upper switches Q1, Q2, and Q3. The given duty cycle in the figure is 0.05, and the actual range may be between 0 and 1. The high level turns on the switching tube, and the low level turns off the switching tube. The switching tubes Q1, Q2, and Q3 use the same duty cycle and the same phase.
[0036] As Figure 3 in a period of PWM waveform, the high-level time is t1 and the low-level time is t2; in the t1 time period, the three upper switches Q1, Q2, and Q3 are all turned on, and the three lower switches Q4, Q5, and Q6 are all turned off. The circuit on the inverter side of the three-phase two-level inverter is equivalent to Figure 4 . The right sides of the inductors L4, L5, and L6 are equivalent to being short-circuited. When the voltages on the three filtering capacitors C1, C2, and C3 are not equal, the current charges and discharges through the resistors R1, R2, R3 and the inductors L4, L5, and L6 until the voltages on the three filtering capacitors C1, C2, and C3 are equal. In the t2 time period, the three upper switches Q1, Q2, and Q3 are all turned off, and the three filtering capacitors C1, C2, and C3 are in the open-circuit state. There is no current flowing in the circuit, and the capacitor voltages on the three filtering capacitors C1, C2, and C3 remain unchanged.
[0037] Embodiment 3
[0038] This embodiment provides an inverter that adopts the filtering capacitor discharging method of Embodiment 1 and Embodiment 2. The inverter is a single-phase or three-phase two-level, three-level, four-level or five-level inverter that adopts an LC filter or an LCL filter, such as: single-phase two-level inverter, three-phase two-level inverter, single-phase T-type three-level inverter, three-phase T-type three-level inverter, single-phase NPC-type three-level inverter, three-phase NPC-type three-level inverter.
[0039] Embodiment 4
[0040] This embodiment provides an inverter grid connection startup method. In this inverter grid connection startup method, first, the filtering capacitor discharging method of Embodiment 1 or Embodiment 2 is adopted to discharge the AC-side filtering capacitor to make the voltages of the AC-side filtering capacitors equal, and then PWM open-loop wave generation is performed to make the phase and amplitude of the inverter-side voltage the same as those of the grid-side voltage. Finally, the AC-side contactor is closed to complete the grid connection startup.
[0041] Embodiment 5
[0042] An electronic device includes a memory and a processor. The memory is used to store a program that supports the processor to execute the inverter AC-side filtering capacitor discharging method in Embodiment 1 or the inverter grid connection startup method in Embodiment 4, and the processor is configured to execute the program stored in the memory.
[0043] Embodiment 6
[0044] A storage medium stores a computer program. When the computer program is run by a processor, it executes the steps of the inverter AC-side filtering capacitor discharging method in Embodiment 1 or the inverter grid connection startup method in Embodiment 4.
[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.
Claims
1. A filter capacitor discharge method, characterized in that: The upper tubes of the inverter are controlled to be in a switching state at the same time and the lower tubes of the inverter are controlled to be in a shut-off state at the same time, or the lower tubes of the inverter are controlled to be in a switching state at the same time and the upper tubes of the inverter are controlled to be in a shut-off state at the same time, so that the voltages of the AC side filter capacitors are equal.
2. The filter capacitor discharge method according to claim 1, characterized in that: The inverter adopts an LC filter or an LCL filter.
3. The filter capacitor discharge method according to claim 1, characterized in that: The inverter is a two-level, three-level, four-level or five-level inverter.
4. The filter capacitor discharge method according to claim 3, characterized in that: The inverter is a single-phase or three-phase inverter.
5. A method for starting an inverter in grid connection, characterized in that: First, the filter capacitor discharge method described in any one of claims 1 to 4 is used to discharge the AC side filter capacitor to make the voltage of the AC side filter capacitor equal, and then PWM open-loop wave generation is performed to make the phase and amplitude of the inverter side voltage and the grid side voltage the same, and finally the AC side contactor is attracted to complete the grid-connected startup.
6. An inverter, characterized in that: The filter capacitor discharge method according to any one of claims 1 to 4 is used to discharge the AC side filter capacitor.
7. An electronic device, comprising a memory and a processor, characterized in that: The memory is used to store a program that supports a processor to execute the filter capacitor discharge method according to any one of claims 1 to 4, and the processor is configured to execute the program stored in the memory.
8. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the filter capacitor discharge method according to any one of claims 1 to 4 are executed.
9. An electronic device, comprising a memory and a processor, characterized in that: The memory is used to store a program that supports the processor to execute the inverter grid-connected startup method according to claim 5, and the processor is configured to execute the program stored in the memory.
10. A storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, the steps of the inverter grid-connected startup method described in claim 5 are executed.