WO2021073097A1 - 一种接地检测方法及其应用设备 - Google Patents

一种接地检测方法及其应用设备 Download PDF

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Publication number
WO2021073097A1
WO2021073097A1 PCT/CN2020/092061 CN2020092061W WO2021073097A1 WO 2021073097 A1 WO2021073097 A1 WO 2021073097A1 CN 2020092061 W CN2020092061 W CN 2020092061W WO 2021073097 A1 WO2021073097 A1 WO 2021073097A1
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Prior art keywords
grid
pwm
grounding
voltage
connected inverter
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PCT/CN2020/092061
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English (en)
French (fr)
Inventor
陈鹏
伍永富
徐清清
Original Assignee
阳光电源股份有限公司
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Application filed by 阳光电源股份有限公司 filed Critical 阳光电源股份有限公司
Priority to AU2020366408A priority Critical patent/AU2020366408A1/en
Priority to EP20877380.4A priority patent/EP3992651A4/en
Priority to JP2021573506A priority patent/JP7223884B2/ja
Publication of WO2021073097A1 publication Critical patent/WO2021073097A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/52—Testing for short-circuits, leakage current or ground faults
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
    • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
    • G01R27/16—Measuring impedance of element or network through which a current is passing from another source, e.g. cable, power line
    • G01R27/18—Measuring resistance to earth, i.e. line to ground

Definitions

  • the present invention relates to the field of power electronics technology, in particular to a grounding detection method and its application equipment.
  • the grid-connected inverter realizes a reliable connection between its own grounding point and an external grounding point, it needs to ensure that its leakage current does not exceed the safety current of the human body. If the leakage current is large, it needs to be connected to the grid.
  • the device has at least 2 grounding points to ensure reliable grounding.
  • the present invention provides a grounding detection method and its application equipment to realize automatic detection of the grounding condition of the grid-connected inverter.
  • the first aspect of the present application provides a grounding detection method, which is applied to a controller in a PWM-controlled grid-connected inverter in a low-voltage power grid system.
  • the grounding detection method includes:
  • the PWM-controlled grid-connected inverter If the PWM-controlled grid-connected inverter satisfies the grounding detection condition, control the grounded power source in the PWM-controlled grid-connected inverter to a preset position in the PWM-controlled grid-connected inverter and the ground A preset current or a preset voltage is applied between; the preset position is one pole of the DC bus or the output end of the AC-side coupling circuit;
  • judging whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit to the ground changes includes:
  • the grounding detection condition includes: receiving a grounding detection instruction, and/or reaching a preset detection time.
  • the grounding detection condition further includes:
  • the PWM control type grid-connected inverter is in a grid-connected state.
  • the grounding detection condition further includes:
  • the PWM control type grid-connected inverter is in a standby or grid-connected state.
  • the second aspect of the present application provides a controller for executing the grounding detection method provided in the first aspect of the present application.
  • the controller is connected to an output terminal of a grounding detection switch button outside the device where it is located, and receives a grounding detection instruction output by the grounding detection switch button.
  • a timing module is provided inside the controller for notifying the controller to perform grounding detection after the current time reaches a preset detection time.
  • the third aspect of the present application provides a PWM controlled grid-connected inverter suitable for low-voltage power grid systems, including: a main circuit, a grounded power supply, a detection module, an AC-side coupling circuit, and the controller provided in the second aspect of the present application; wherein :
  • the DC side of the main circuit is used to receive or output DC power
  • the AC side of the main circuit is used to output or receive AC power
  • the AC side of the AC coupling circuit is connected to the AC side of the main circuit
  • the negative pole of the grounded power supply is connected to the internal grounding point of the PWM-controlled grid-connected inverter; the positive pole of the grounded power supply is connected to a preset position in the PWM-controlled grid-connected inverter;
  • the preset position is a pole of the DC bus in the main circuit, or the output terminal of the AC coupling circuit;
  • the command output terminal of the controller is connected to the control terminal of the grounded power supply; the receiving terminal of the controller is connected to the output terminal of the detection module to receive one pole of the DC bus detected by the detection module Or the voltage between the output terminal of the AC-side coupling circuit and the ground.
  • the grounding power supply includes: a controllable DC voltage source and a current-limiting resistor; where:
  • the positive pole of the controllable DC voltage source is connected to the positive pole of the grounding power source, and the negative pole of the controllable DC voltage source is connected to the negative pole of the grounding power source;
  • the current-limiting resistor is arranged between the positive electrode of the controllable DC voltage source and the positive electrode of the grounding power source;
  • the current-limiting resistor is arranged between the negative electrode of the controllable DC voltage source and the negative electrode of the grounding power source;
  • the control terminal of the controllable DC voltage source serves as the control terminal of the grounding power supply.
  • the grounded power supply includes: a controllable direct current source; where:
  • the positive pole of the controllable direct current source is used as the positive pole of the grounding power source
  • the negative electrode of the controllable DC voltage source is used as the negative electrode of the grounding power supply
  • the control terminal of the controllable direct current source serves as the control terminal of the grounding power supply.
  • the AC-side coupling circuit is a rectifier
  • the output terminal of the AC-side coupling circuit is the DC side positive or the DC side negative of the rectifier
  • the AC side of the rectifier is connected to the AC side of the main circuit ;
  • the AC-side coupling circuit is a Y-type circuit composed of impedance, the output end of the AC-side coupling circuit is the virtual N point of the Y-type circuit, and the other three ends of the Y-type circuit are connected to the main circuit.
  • the AC side is connected.
  • the main circuit includes: an inverter circuit, or, an inverter circuit and a plurality of boost circuits connected in parallel to the DC bus on the high voltage side.
  • the fourth aspect of the present application provides a low-voltage power grid system, including a transformer, at least one DC power supply, and the PWM controlled grid-connected inverter provided in the third aspect of the present application; wherein:
  • the DC side of the PWM-controlled grid-connected inverter is connected to the DC power supply;
  • the AC side of the PWM controlled grid-connected inverter is connected to the grid through the transformer;
  • the midpoint of the transformer is grounded.
  • this application provides a grounding detection method and its application equipment, wherein the grounding detection method provided by this application is applied to a controller in a PWM controlled grid-connected inverter in a low-voltage power grid system.
  • the controller of the PWM-controlled grid-connected inverter of the present application first controls the PWM-controlled grid-connected inverter when the PWM-controlled grid-connected inverter meets the grounding detection condition
  • the neutral grounding power supply applies a preset current or a preset voltage between a preset position in the PWM control type grid-connected inverter and the ground, wherein the preset position is a pole of the DC bus or the output terminal of the AC-side coupling circuit; After that, by judging whether the voltage between one pole of the DC bus or the output end of the AC-side coupling circuit and the ground has changed, it can be judged whether the PWM control type grid-connected inverter is well grounded, and then the grid-connected inverter is realized.
  • the automatic detection of the grounding condition of the generator solves the problem of artificial dependence in the prior art.
  • FIG. 1 is a schematic flowchart of a grounding detection method provided by an embodiment of this application.
  • FIGS. 2 and 3 are schematic diagrams of two structures of the PWM control grid-connected inverter provided by the embodiments of the application;
  • FIG. 4 is a schematic structural diagram of a rectifier provided by an embodiment of the application.
  • FIG. 5 is a schematic structural diagram of a Y-type circuit provided by an embodiment of the application.
  • Fig. 6a is a schematic structural diagram of a TN-C system provided by an embodiment of this application.
  • FIG. 6b is a schematic structural diagram of a TN-C-S system provided by an embodiment of this application.
  • Fig. 6c is a schematic structural diagram of a TN-S system provided by an embodiment of the application.
  • Figure 6d is a schematic structural diagram of a TT system provided by an embodiment of the application.
  • the terms “include”, “include” or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes no Other elements clearly listed, or also include elements inherent to this process, method, article, or equipment. If there are no more restrictions, the element defined by the sentence “including a" does not exclude the existence of other identical elements in the process, method, article, or equipment that includes the element.
  • an embodiment of the present application provides a grounding detection method, which is applied to a controller in a PWM-controlled grid-connected inverter in a low-voltage power grid system.
  • FIGs 2 and 3 the specific structure of the PWM controlled grid-connected inverter is shown in Figures 2 and 3, including: a main circuit 10, a grounded power supply 20, a detection module 30, a controller 40, and an AC-side coupling circuit 50 (not shown in Figure 2 show).
  • the DC side of the main circuit 10 is used for receiving or outputting DC power
  • the AC side of the main circuit 10 is used for outputting or receiving AC power.
  • the AC side of the AC side coupling circuit 50 is connected to the AC side of the main circuit 10.
  • the positive pole of the grounded power source 20 is connected to a preset position in the PWM control type grid-connected inverter; wherein, the preset position is: one pole of the DC bus (shown in Figure 2 with the negative pole as an example), or, the AC side
  • the output terminal of the coupling circuit (the port on the left side of the AC side coupling circuit 50 in FIG. 3); the negative electrode of the grounding power supply 20 is connected to the internal grounding point of the PWM control type grid-connected inverter.
  • the command output terminal of the controller 40 is connected to the control terminal of the grounded power supply 20; the receiving terminal of the controller 40 is connected to the output terminal of the detection module 30, and receives one pole of the DC bus or the AC side coupling circuit 50 detected by the detection module 30 The voltage between the output terminal and the ground.
  • Fig. 1 the specific process of the grounding detection method is shown in Fig. 1, and includes the following steps:
  • the grounding detection condition of the PWM-controlled grid-connected inverter is: receiving a grounding detection instruction, and/or reaching a preset detection time.
  • the grounding detection command is generated by the staff after pressing the grounding detection button when the PWM control type grid-connected inverter needs to be grounded. It should be noted that after pressing the grounding detection button once, only A grounding detection command can be generated once; and the preset detection time can be at least one preset time point, or at least one preset time point with periodicity, which is not specifically limited here, depending on the specific situation However, they are all within the scope of protection of this application.
  • the PWM control grid-connected inverter can be grounded only when the grounding detection instruction is received and/or when the preset time is reached; if the PWM-controlled grid-connected inverter meets the grounding detection If the condition is met, step S200 is executed. If the PWM-controlled grid-connected inverter does not meet the grounding detection condition, then the PWM-controlled grid-connected inverter will not be grounded.
  • the grounding detection condition when the preset position is one pole of the DC bus, the grounding detection condition also includes: the PWM-controlled grid-connected inverter is in a grid-connected state.
  • the grid-connected state of the PWM-controlled grid-connected inverter refers to the position of the PWM-controlled grid-connected inverter when all the switches in the main circuit 10 of the PWM-controlled grid-connected inverter are closed. status.
  • the preset position is one pole of the DC bus
  • the controller 40 of the PWM-controlled grid-connected inverter receives the grounding detection Command
  • the PWM-controlled grid-connected inverter meets the grounding detection conditions; or, if the PWM-controlled grid-connected inverter is in the grid-connected state and the current time reaches the preset detection time, the PWM-controlled grid-connected inverter The inverter meets the grounding detection conditions.
  • the grounding detection condition when the preset position is the output terminal of the AC-side coupling circuit 50, the grounding detection condition also includes: the PWM-controlled grid-connected inverter is in a standby state, or a grid-connected state.
  • the standby state of the PWM-controlled grid-connected inverter refers to: when all the switches in the main circuit 10 of the PWM-controlled grid-connected inverter are turned off, the PWM-controlled grid-connected inverter is located status. It can be seen that the standby state is the state before grid connection.
  • the preset position is the output terminal of the AC-side coupling circuit 50, if the PWM-controlled grid-connected inverter is in the standby state or grid-connected state, and the control of the PWM-controlled grid-connected inverter If the inverter 40 receives the grounding detection instruction, the PWM-controlled grid-connected inverter meets the grounding detection conditions; or, if the PWM-controlled grid-connected inverter is in the standby state or grid-connected state, and the current time reaches the preset detection Time, the PWM-controlled grid-connected inverter meets the grounding detection conditions.
  • the preset current is a preset input current
  • the preset voltage is a preset input voltage
  • the preset position in FIG. 2 is the negative pole of the DC bus, and the case where the positive pole of the DC bus is the preset position is not shown; the preset position in FIG. 3 is the output terminal of the AC-side coupling circuit 50.
  • the AC side coupling circuit 50 may be the rectifier shown in FIG. 4, or a Y-shaped circuit composed of impedance shown in FIG.
  • the AC side coupling circuit 50 when the AC side coupling circuit 50 is a rectifier, the AC side of the rectifier and the AC side of the main circuit 10
  • the output terminal of the AC-side coupling circuit 50 refers to the DC-side positive or DC-side negative of the rectifier;
  • the AC-side coupling circuit 50 when the AC-side coupling circuit 50 is a Y-shaped circuit composed of impedance, the other three ends of the Y-shaped circuit are connected to the main circuit 10
  • the AC side is connected, and the output terminal of the AC side coupling circuit 50 refers to the virtual N point of the Y-shaped circuit.
  • S300 Determine whether the voltage between one pole of the DC bus or the output end of the AC-side coupling circuit to the ground has changed.
  • step S400 If the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit 50 and the ground changes, it means that the applied preset current or preset voltage cannot be completely directed to the ground, and step S400 is executed. If the voltage between one pole of the DC bus or the output terminal of the AC side coupling circuit 50 to the ground does not change, it means that the applied preset current or preset voltage is completely directed to the ground, and step S500 is performed.
  • the preset position is one pole of the DC bus or the output terminal of the AC-side coupling circuit 50, it can be determined whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit 50 and the ground is Change to determine whether the PWM control type grid-connected inverter is badly grounded.
  • the specific implementation for judging whether the voltage between the negative electrode of the DC bus bar and the ground has changed is: judging whether the voltage between the negative electrode of the DC bus bar and the ground is gradually decreasing and approaching zero potential; and judging
  • the specific implementation of whether the voltage between the positive pole of the DC bus bar and the ground changes is: judging whether the voltage between the positive pole of the DC bus bar and the ground gradually increases and approaches the DC bus voltage; at this time, if the negative pole of the DC bus bar is The voltage between the ground gradually decreases and approaches zero potential, or the voltage between the positive pole of the DC bus and the ground gradually increases and approaches the DC bus voltage, then step S400 is performed; at this time, if the negative pole of the DC bus is The voltage between the ground remains unchanged, or the voltage between the positive pole of the DC bus and the ground remains unchanged, then step S500 is executed.
  • the specific implementation for judging whether the voltage between the output terminal of the AC-side coupling circuit 50 and the ground has changed is: judging whether the virtual N point of the Y-shaped circuit is between the virtual point and the ground. Whether the voltage gradually rises and approaches the preset value, at this time, if the voltage between the virtual point N of the Y-type circuit and the ground gradually rises and approaches the preset value, step S400 is executed; at this time, if the Y-type circuit The voltage between the virtual point N of the circuit and the ground remains unchanged, and step S500 is executed.
  • the preset value refers to a specific value of the preset current or preset voltage applied by the controller 40 to control the grounding power source 20.
  • the controller 40 can detect the voltage conversion between one pole of the DC bus and the ground to achieve grounding detection, or it can detect AC
  • the side coupling circuit 50 converts the voltage between the ground to realize grounding detection.
  • the grounded power supply 20 can be controlled to apply a preset current or a preset voltage to the output end of the AC-side coupling circuit 50 before grid connection, and the DC bus is in the main circuit 10 Under the reverse conversion action of the inverter circuit, it realizes its own soft start and establishes a normal DC bus voltage.
  • the preset position is the output terminal of the AC-side coupling circuit 50
  • it is determined whether the PWM control type grid-connected inverter is badly grounded by judging whether the voltage between the output terminal of the AC-side coupling circuit 50 and the ground changes. Therefore, related operations on the main circuit 10 of the inverter circuit can be avoided, and the detection steps can be simplified.
  • step S100 in this embodiment can be executed according to its own cycle, and step S200, step S300, step S400, and step S500 are executed according to the above logic trigger, that is, only after step S100 is executed, Step S200, step S300, step S400 and step S500 will be executed accordingly; moreover, as a whole, in the whole detection process, every other cycle, it is judged whether to ground the PWM control type grid-connected inverter. Detection, when the period takes a minimum value, it can be continuously judged whether to perform grounding detection on the PWM-controlled grid-connected inverter, so that the PWM-controlled grid-connected inverter can be grounded in time.
  • step S100, step S200, step S300, step S400, and step S500 can also be executed according to the above logic cycle trigger, that is, when the whole detection process completes step S400 or step S500, return to trigger execution step S100, so that step S100, Step S200, step S300, step S400, and step S500 form a loop; when the loop is formed, it can continuously determine whether the PWM control type grid-connected inverter is grounded or not, so that the PWM control type parallel inverter can be detected in time.
  • the grid inverter performs grounding detection; however, it should be noted that when the controller 40 is turned on, the entire detection process starts.
  • the controller 40 of the PWM-controlled grid-connected inverter first controls the grounding in the PWM-controlled grid-connected inverter when the PWM-controlled grid-connected inverter meets the grounding detection conditions.
  • the power supply 20 applies a preset current or a preset voltage between a preset position in the PWM-controlled grid-connected inverter and the ground, where the preset position is a pole of the DC bus or the output terminal of the AC-side coupling circuit 50; After that, by judging whether the voltage between one pole of the DC bus or the output terminal of the AC-side coupling circuit 50 and the ground has changed, it can be judged whether the PWM control type grid-connected inverter is well grounded, thereby realizing the inverse of the grid-connected inverter.
  • the automatic detection of the grounding condition of the transformer solves the problem of artificial dependence in the prior art.
  • the grounding detection method provided in this embodiment only needs to apply a predetermined current or a predetermined voltage between the predetermined position of the PWM-controlled grid-connected inverter and the ground before and after the grounding power supply 20 applies a predetermined current or a predetermined voltage. If the voltage between the output terminal of the AC-side coupling circuit 50 and the ground is changed, it can be judged whether the PWM control type grid-connected inverter is well grounded, so that the grounding detection method provided by this embodiment is simple, Convenient and reliable.
  • Another embodiment of the present application provides a controller for executing the grounding detection method shown in FIG. 1.
  • the controller is connected to the output terminal of the grounding detection switch button outside the device where it is located, and receives the grounding detection command output by the grounding detection switch button.
  • the condition for the grounding detection switch button to generate the grounding detection instruction is: when the PWM control type grid-connected inverter needs to be grounded, the worker presses the grounding detection switch button.
  • a timing module is provided inside the controller, and the timing module is used to notify the controller to perform grounding detection after the current time reaches the preset detection time.
  • FIG. 2 Another embodiment of the present application provides a PWM controlled grid-connected inverter suitable for low-voltage power grid systems.
  • the specific structure is shown in Figures 2 and 3, including: a main circuit 10, a grounded power supply 20, and a detection module 30 , AC side coupling circuit 50 (not shown in FIG. 2) and the controller 40 provided in the previous embodiment.
  • the DC side of the main circuit 10 is used to receive or output DC power
  • the AC side of the main circuit 10 is used to output or receive AC power.
  • the AC side of the AC side coupling circuit 50 is connected to the AC side of the main circuit 10.
  • the negative pole of the grounding power source 20 is connected to the internal grounding point of the PWM-controlled grid-connected inverter; the positive pole of the grounding power source 20 is connected to the preset position in the PWM-controlled grid-connected inverter.
  • the command output terminal of the controller 40 is connected to the control terminal of the grounded power source 20; the receiving terminal of the controller 40 is connected to the output terminal of the detection module 30, and receives one pole of the DC bus detected by the detection module 30, that is, the positive or negative pole of the DC bus.
  • the negative pole (as shown in FIG. 2), or the voltage between the output terminal of the AC side coupling circuit 50 (as shown in FIG. 3) and the ground.
  • the preset position is one pole of the DC bus.
  • Figure 2 shows the negative pole of the DC bus as an example.
  • the controller 40 receives
  • the voltage received by the terminal through the detection module 30 can be the voltage between the negative pole of the DC bus and the ground, or the voltage between the positive pole of the DC bus and the ground. There is no specific limitation here, and it depends on the specific situation. All are within the protection scope of this application.
  • the receiving end of the controller 40 receives the voltage detected by the detection module 30, which can be a pole of the DC bus.
  • the voltage between the ground can also be the voltage between the output terminal of the AC-side coupling circuit 50 and the ground (as shown in FIG. 3), which is not specifically limited here, and can be changed according to specific circumstances. Are all within the scope of protection of this application.
  • the AC side coupling circuit 50 is used to implement the grounding detection function.
  • the preset position can also be a pole of the DC bus.
  • the receiving end of the controller 40 receives the voltage detected by the detection module 30, which is the AC side coupling circuit 50. The voltage between the output terminal and the earth.
  • the AC-side coupling circuit 50 may be a rectifier.
  • the specific structure of the rectifier is shown in FIG. 4, including: a capacitor C and three rectifying branches 60; the rectifying branch 60 is composed of two diodes D in series.
  • the positive poles of the three rectifying branches 60 are connected to one end of the capacitor C, and the connection point is used as the positive pole of the rectifier DC side; the positive poles of the three rectifying branches 60 are connected to the other end of the capacitor C, and the connection point is used as the negative pole of the rectifier DC side.
  • the output end of the AC-side coupling circuit 50 refers to the positive or negative pole of the DC side; the intermediate connection points of the three rectifying branches 60 are used as the AC side of the rectifier, which are connected to the connection points of each phase of the AC side of the main circuit 10 respectively.
  • the AC-side coupling circuit 50 may also be a Y-type circuit composed of impedances.
  • the specific structure of the Y-type circuit is shown in FIG. 5, including: a first impedance Z1, a second impedance Z2, and a third impedance Z3.
  • one end of the first impedance Z1, one end of the second impedance Z2, and one end of the third impedance Z3 are all connected, and the connection point is used as the virtual point N of the Y-type circuit; the output end of the AC-side coupling circuit 50 refers to the Y-type circuit Virtual point N; the other end of the first impedance Z1, the other end of the second impedance Z2, and the other end of the third impedance Z3 are all connected to the AC side of the main circuit 10.
  • first impedance Z1, the second impedance Z2, and the third impedance Z3 can all be pure resistance, pure capacitance, or pure inductance, or all of them can be a combination of at least any two of resistance, capacitance, and inductance. There is no specific limitation, and combinations can be made according to specific circumstances, and all are within the protection scope of this application.
  • the controller 40 For the grounding detection method executed by the controller 40, refer to the above-mentioned embodiment, which will not be repeated here. It is worth noting that for the PWM controlled grid-connected inverter shown in FIG. 2 and the preset position is one pole of the DC bus and the detection module 30 detects the voltage between the output terminal of the AC side coupling circuit 50 and the ground , The controller 40 can only perform grounding detection after grid connection; while the PWM control type grid-connected inverter shown in FIG. 3, and the preset position is the output terminal of the AC-side coupling circuit 50, and the detection module 30 detects the DC bus When the voltage is between the negative pole of the power and the ground, the controller 40 can not only perform grounding detection after grid connection, but also perform grounding detection before grid connection.
  • the structure of the AC-side coupling circuit 50 is as shown in FIG. 5, and the predetermined position where the grounding power source 20 in the PWM-controlled grid-connected inverter applies a preset voltage or a preset current is the AC-side coupling circuit
  • the voltage detected by the detection module 30 is the voltage between the output terminal of the AC-side coupling circuit 50 and the ground, so it can not only perform grounding detection before grid connection, but also avoid damage to the main circuit 10 Perform related operations.
  • FIG. 2 Another embodiment of the present application provides a specific implementation of the grounded power supply 20.
  • the specific structure is shown in FIG. 2 or FIG. 3, and includes: a controllable DC voltage source 21 and a current-limiting resistor R.
  • the positive pole of the controllable DC voltage source 21 is connected to the positive pole of the grounding power source 20; the negative pole of the controllable DC voltage source 21 is connected to the negative pole of the grounding power source 20, and the control terminal of the controllable DC voltage source 21 is used as the control terminal of the grounding power source 20;
  • the current resistance R is arranged between the positive electrode of the controllable DC voltage source 21 and the positive electrode of the grounding power source 20, or the current limiting resistor R is arranged between the negative electrode of the controllable DC voltage source 21 and the negative electrode of the grounding power source 20.
  • the current-limiting resistor R can effectively limit the output capability of the controllable DC voltage source 21 to avoid electric shocks to workers.
  • the grounded power source 20 may also include a controllable direct current source; wherein, the positive electrode of the controllable direct current source serves as the positive electrode of the grounded power source 20, and the controllable direct current source The negative pole of the current source serves as the negative pole of the grounded power supply 20, and the control terminal of the controllable DC current source serves as the control terminal of the grounded power supply 20. It should be noted that the two implementations of the grounding power supply 20 may be determined according to specific conditions, and both are within the protection scope of the present application.
  • This embodiment also provides two implementations of the main circuit 10, the first specific implementation includes: an inverter circuit 11; the second implementation includes: an inverter circuit 11 and multiple boosters connected in parallel with the high-voltage side of the DC bus Circuit 12 (as shown in Fig. 2 and Fig. 3); it should be noted that the two implementation manners may be determined according to specific circumstances, and both are within the protection scope of the present application.
  • controller 40 provided in this embodiment borrows the existing circuit inside the PWM-controlled grid-connected inverter in the low-voltage power grid system without adding new circuits or external tools.
  • the grounding detection of the PWM-controlled grid-connected inverter reduces its own cost, which is convenient for market promotion and competition.
  • FIGS. 6a-6d Another embodiment of the present application provides a low-voltage power grid system, the specific structure of which is shown in FIGS. 6a-6d, including: a transformer (a part of the transformer is shown as a black square in FIGS. 6a-6d), and at least one DC The power supply 80 and the PWM control type grid-connected inverter 90 shown in FIG. 2 or FIG. 3.
  • the DC side of the PWM-controlled grid-connected inverter 90 is connected to a DC power supply 80; the AC side of the PWM-controlled grid-connected inverter 90 is connected to the grid through a transformer; the midpoint of the transformer is grounded.
  • the DC power supply 80 can be a photovoltaic string, an energy storage system, or a photovoltaic string and an energy storage system.
  • a photovoltaic string an energy storage system
  • a photovoltaic string and an energy storage system There is no specific limitation here, and it depends on the specific circumstances, all of which are protected in this application. Within range.
  • the PE line of the PWM control grid-connected inverter 90 is connected to the PEN line of the transformer, and the PEN line of the transformer is connected to the neutral point of the transformer, the PWM control type grid-connected with the above-mentioned connection method is adopted
  • the inverter 90 and the transformer form a TN-C system (as shown in Fig. 6a).
  • the PE wire of the PWM controlled grid-connected inverter 90 is connected to the PE wire of the transformer, the PE wire of the transformer is connected to the N wire of the transformer, and the connection point of the PE wire of the transformer and the N wire of the transformer is connected to the transformer If the center points of the two are connected, the PWM-controlled grid-connected inverter 90 and the transformer in the above-mentioned connection mode form a TN-CS system (as shown in Fig. 6b).
  • the PWM of the above-mentioned connection mode is adopted.
  • the controlled grid-connected inverter 90 and the transformer form a TN-S system (as shown in Figure 6c).
  • the PWM-controlled grid-connected inverter 90 and the neutral point of the transformer are connected by the above-mentioned connection method.
  • the transformer forms the TT system (as shown in Figure 6d).
  • connection forms of the PWM-controlled grid-connected inverter 90 and the transformer may be determined according to specific conditions, and are not specifically limited here, and they are all within the protection scope of the present application.

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Abstract

提供一种接地检测方法及其应用设备，该接地检测方法应用于低压电网系统中的PWM控制型并网逆变器内的控制器，其在PWM控制型并网逆变器满足接地检测条件的情况下，先控制PWM控制型并网逆变器中接地电源向该预设位置与大地之间施加预设电流或预设电压（S200），其中，预设位置为PWM控制型并网逆变器中直流母线的一极或交流侧耦合电路的输出端；之后，通过判断直流母线的一极或交流侧耦合电路的输出端对大地之间的电压是否发生变化（S300），来判断该PWM控制型并网逆变器是否接地良好，进而实现了对于并网逆变器接地情况的自动检测，解决了现有技术中存在人工依赖性的问题。

Description

一种接地检测方法及其应用设备
本申请要求于2019年10月16日提交中国专利局、申请号为201910983849.8、发明名称为“一种接地检测方法及其应用设备”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及电力电子技术领域，特别是涉及一种接地检测方法及其应用设备。
背景技术
目前，根据安规要求，并网逆变器在自身接地点与外部接地点实现可靠连接时，需要保证自身工作时的漏电电流不超过人体安全电流，如果漏电流较大，需要并网逆变器有至少2个接地点，以保障可靠接地。
但是，在并网施工过程中，可能因为人为疏忽，导致接地点漏接、接地线断裂或者接地点悬空等并网逆变器接地不良的情况发生，从而使得工作人员在接触并网逆变器的机壳时，存在被电击的风险。另外，在并网逆变器长期运行后，也可能因底线阻抗增大而导致自身接地不良，若没有及时发现，则工作人员在接触并网逆变器的机壳时，也存在被电击的风险。
为了避免在接触并网逆变器机壳时被电击的情况发生，现有技术中，工作人员通常会利用测试设备对现场的并网逆变器进行接地阻抗测试，但是这种检测方法存在人工依赖性。
发明内容
有鉴于此，本发明提供一种接地检测方法及其应用设备，以实现对于并网逆变器接地情况的自动检测。
为实现上述目的，本发明实施例提供如下技术方案：
本申请第一方面提供一种接地检测方法，应用于低压电网系统中PWM控制型并网逆变器内的控制器，所述接地检测方法，包括：
判断所述PWM控制型并网逆变器是否满足接地检测条件；
若所述PWM控制型并网逆变器满足所述接地检测条件，则控制所述PWM控制型并网逆变器中接地电源向所述PWM控制型并网逆变器中预设位置与大地之间施加预设电流或预设电压；所述预设位置为直流母线的一极或交 流侧耦合电路的输出端；
判断所述直流母线的一极或所述交流侧耦合电路的输出端对大地之间的电压是否发生变化；
若所述电压发生变化，则判定所述PWM控制型并网逆变器接地不良；
若所述电压未发生变化，则判定所述PWM控制型并网逆变器接地良好。
可选的，判断所述直流母线的一极或所述交流侧耦合电路的输出端对大地之间的电压是否发生变化，包括：
判断所述直流母线的负极对大地之间的电压是否逐渐降低并趋近于零电位；
或者，
判断所述直流母线的正极对大地之间的电压是否逐渐升高并趋近于所述直流母线电压；
或者，
判断所述交流侧耦合电路的输出端对大地之间的电压是否逐渐升高并趋近于预设值。
可选的，所述接地检测条件包括：接收到接地检测指令，和/或，达到预设检测时间。
可选的，若所述预设位置为直流母线的一极，则所述接地检测条件，还包括：
所述PWM控制型并网逆变器处于并网状态。
可选的，若所述预设位置为交流侧耦合电路的输出端，则所述接地检测条件，还包括：
所述PWM控制型并网逆变器处于待机或并网状态。
本申请第二方面提供一种控制器，用于执行本申请第一方面提供的接地检测方法。
可选的，所述控制器与所在设备外部的接地检测开关按钮的输出端相连，接收所述接地检测开关按钮输出的接地检测指令。
可选的，所述控制器内部设置有计时模块，用于在当前时间达到预设检测时间后，通知所述控制器进行接地检测。
本申请第三方面提供一种PWM控制型并网逆变器，适用于低压电网系统，包括：主电路、接地电源、检测模块、交流侧耦合电路以及本申请第二方面提供的控制器；其中：
所述主电路的直流侧用于接收或输出直流电能，所述主电路的交流侧用于输出或接收交流电能；
所述交流耦合电路的交流侧与所述主电路的交流侧相连；
所述接地电源的负极与所述PWM控制型并网逆变器的内部接地点相连；所述接地电源的正极与所述PWM控制型并网逆变器中的预设位置相连；
所述预设位置为所述主电路中直流母线的一极，或者，所述交流耦合电路的输出端；
所述控制器的指令输出端与所述接地电源的控制端相连；所述控制器的接收端与所述检测模块的输出端相连、接收所述检测模块检测到的所述直流母线的一极或所述交流侧耦合电路的输出端对大地之间的电压。
可选的，所述接地电源，包括：可控直流电压源和限流电阻；其中：
所述可控直流电压源的正极连接所述接地电源的正极，所述可控直流电压源的负极连接所述接地电源的负极；
所述限流电阻设置于所述可控直流电压源的正极与所述接地电源的正极之间；
或者，
所述限流电阻设置于所述可控直流电压源的负极与所述接地电源的负极之间；
所述可控直流电压源的控制端作为所述接地电源的控制端。
可选的，所述接地电源，包括：可控直流电流源；其中：
所述可控直流电流源的正极作为所述接地电源的正极；
所述可控直流电压源的负极作为所述接地电源的负极；
所述可控直流电流源的控制端作为所述接地电源的控制端。
可选的，所述交流侧耦合电路为整流器，所述交流侧耦合电路的输出端为所述整流器的直流侧正极或者直流侧负极，所述整流器的交流侧与所述主电路的交流侧相连；
或者，
所述交流侧耦合电路为由阻抗构成的Y型电路，所述交流侧耦合电路的输出端为所述Y型电路的虚拟N点，所述Y型电路的另外三端与所述主电路的交流侧相连。
可选的，所述主电路包括：逆变电路，或者，逆变电路及高压侧并联于直流母线的多个升压电路。
本申请第四方面提供一种低压电网系统，包括变压器、至少一个直流电源和本申请第三方面提供的PWM控制型并网逆变器；其中：
所述PWM控制型并网逆变器的直流侧与所述直流电源相连；
所述PWM控制型并网逆变器的交流侧通过所述变压器连接电网；
所述变压器的中点接地。
由上述技术方案可知，本申请提供了一种接地检测方法及其应用设备，其中，本申请提供的接地检测方法应用于低压电网系统中的PWM控制型并网逆变器内的控制器。与现有技术相比，本申请该PWM控制型并网逆变器的控制器在该PWM控制型并网逆变器满足接地检测条件的情况下，先控制该PWM控制型并网逆变器中接地电源向该PWM控制型并网逆变器中预设位置与大地之间施加预设电流或预设电压，其中，预设位置为直流母线的一极或交流侧耦合电路的输出端；之后，通过判断直流母线的一极或交流侧耦合电路的输出端对大地之间的电压是否发生变化，来判断该PWM控制型并网逆变器是否接地良好，进而实现了对于并网逆变器接地情况的自动检测，解决了现有技术中存在人工依赖性的问题。
附图说明
图1为本申请实施例提供的一种接地检测方法的流程示意图；
图2和图3为本申请实施例提供的PWM控制型并网逆变器的两种结构示意图；
图4为本申请实施例提供的整流器的结构示意图；
图5为本申请实施例提供的Y型电路的结构示意图；
图6a为本申请实施例提供的TN-C系统的结构示意图；
图6b为本申请实施例提供的TN-C-S系统的结构示意图；
图6c为本申请实施例提供的TN-S系统的结构示意图；
图6d为本申请实施例提供的TT系统的结构示意图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
在本申请中，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法、物品或者设备不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法、物品或者设备所固有的要素。在没有更多限制的情况下，由语句“包括一个……”限定的要素，并不排除在包括所述要素的过程、方法、物品或者设备中还存在另外的相同要素。
为了实现对于并网逆变器接地情况的自动检测，本申请实施例提供一种接地检测方法，应用于低压电网系统中PWM控制型并网逆变器内的控制器。
其中，该PWM控制型并网逆变器的具体结构如图2和图3所示，包括：主电路10、接地电源20、检测模块30控制器40以及交流侧耦合电路50(图2中未示出)。
主电路10的直流侧用于接收或输出直流电能，主电路10的交流侧用于输出或接收交流电能。交流侧耦合电路50的交流侧与主电路10的交流侧相连。
接地电源20的正极与该PWM控制型并网逆变器中的预设位置相连；其中，该预设位置为：直流母线的一极(图2以负极为例进行展示)，或，交流侧耦合电路的输出端(图3中交流侧耦合电路50左侧的端口)；接地电源20的负极与该PWM控制型并网逆变器的内部接地点相连。
控制器40的指令输出端与接地电源20的控制端相连；控制器40的接收端与检测模块30的输出端相连、接收检测模块30检测到的直流母线的一极或交流侧耦合电路50的输出端对大地之间的电压。
具体的，该接地检测方法的具体流程如图1所示，包括如下步骤：
S100、判断该PWM控制型并网逆变器是否满足接地检测条件。
其中，该PWM控制型并网逆变器的接地检测条件为：接收到接地检测指令，和/或，达到预设检测时间。在实际应用中，接地检测指令是工作人员在需要对该PWM控制型并网逆变器进行接地检测时按动接地检测按钮后产生的，需要说明的是，按动一次接地检测按钮后，只能产生一次接地检测指令；而预设检测时间可以是预先设定的至少一个时间点，也可以是预先设定的具有周期性的至少一个时间点，此处不做具体限定，可视具体情况而定，均在本申请的保护范围内。
在实际应用中，只有接到接地检测指令，和/或，达到预设时间时，才能对该PWM控制型并网逆变器进行接地检测；若该PWM控制型并网逆变器满足接地检测条件，则执行步骤S200，若该PWM控制型并网逆变器未满足接地检测条件，则不对该PWM控制型并网逆变器进行接地检测。
在实际应用中，当预设位置为直流母线的一极时，其接地检测条件还包括：该PWM控制型并网逆变器处于并网状态。
其中，该PWM控制型并网逆变器的并网状态是指：该PWM控制型并网逆变器主电路10中的各个开关全部闭合时，该PWM控制型并网逆变器所处的状态。
需要说明的是，当预设位置为直流母线的一极时，若该PWM控制型并网逆变器处于并网状态，并且该PWM控制型并网逆变器的控制器40接收到接地检测指令，则该PWM控制型并网逆变器满足接地检测条件；或者，若该PWM控制型并网逆变器处于并网状态，并且当前时间达到预设检测时间，则该PWM控制型并网逆变器满足接地检测条件。
在实际应用中，当预设位置为交流侧耦合电路50的输出端时，接地检测条件，还包括：该PWM控制型并网逆变器处于待机状态，或者，并网状态。
其中，该PWM控制型并网逆变器的待机状态是指：该PWM控制型并网逆变器主电路10中的各个开关全部断开时，该PWM控制型并网逆变器所处的状态。由此可知，处于待机状态即是处于并网前状态。
需要说明的是，当预设位置为交流侧耦合电路50的输出端时，若该PWM控制型并网逆变器处于待机状态或并网状态，并且该PWM控制型并网逆变器的控制器40接收到接地检测指令，则该PWM控制型并网逆变器满足接地检 测条件；或者，若该PWM控制型并网逆变器处于待机状态或并网状态，并且当前时间达到预设检测时间，则该PWM控制型并网逆变器满足接地检测条件。
S200、控制PWM控制型并网逆变器中接地电源向PWM控制型并网逆变器中预设位置与大地之间施加预设电流或预设电压。
其中，预设电流是预先设定的输入电流，预设电压是预先设定的输入电压；在实际应用中，预设电流或预设电压需要根据实际情况进行合理选取。
图2中的预设位置为直流母线的负极，以直流母线的正极为预设位置的情况未进行图示；图3中的预设位置为交流侧耦合电路50的输出端，实际应用中，交流侧耦合电路50可以是图4所示的整流器，也可以是图5所示由阻抗构成的Y型电路；当交流侧耦合电路50为整流器时，整流器的交流侧与主电路10的交流侧相连，交流侧耦合电路50的输出端是指整流器的直流侧正极或者直流侧负极；当交流侧耦合电路50为由阻抗构成的Y型电路时，Y型电路的另外三端与主电路10的交流侧相连，交流侧耦合电路50的输出端是指Y型电路的虚拟N点。
S300、判断直流母线的一极或交流侧耦合电路的输出端对大地之间的电压是否发生变化。
在实际应用中，若直流母线的一极或交流侧耦合电路50的输出端对大地之间的电压发生变化，则说明施加的预设电流或预设电压不能完全被导向地面，则执行步骤S400；若直流母线的一极或交流侧耦合电路50的输出端对大地之间的电压未发生变化，则说明施加的预设电流或预设电压完全被导向地面，则执行步骤S500。
具体而言，无论预设位置是直流母线的一极，还是交流侧耦合电路50的输出端，均可以通过判断直流母线的一极或交流侧耦合电路50的输出端对大地之间的电压是否发生变化来判断该PWM控制型并网逆变器是否接地不良。并且，在实际应用中，判断直流母线的负极对大地之间的电压是否发生变化的具体实施方式为：判断直流母线的负极对大地之间的电压是否逐渐降低并趋近于零电位；而判断直流母线的正极对大地之间的电压是否发生变化的具体实施方式为：判断直流母线的正极对大地之间的电压是否逐渐升高并趋近于直流母线电压；此时若直流母线的负极对大地之间的电压逐渐降低并趋近于零电位，或者， 直流母线的正极对大地之间的电压逐渐升高并趋近于直流母线电压，则执行步骤S400；此时若直流母线的负极对大地之间的电压保持不变，或者，直流母线的正极对大地之间的电压保持不变，则执行步骤S500。
当交流侧耦合电路50具体为Y型电路时，判断交流侧耦合电路50的输出端对大地之间的电压是否发生变化的具体实施方式为：判断Y型电路的虚拟N点对大地之间的电压是否逐渐升高并趋近于预设值，此时若Y型电路的虚拟N点对大地之间的电压逐渐升高并趋近于预设值，则执行步骤S400；此时若Y型电路的虚拟N点对大地之间的电压保持不变，则执行步骤S500。该预设值是指控制器40控制接地电源20施加的预设电流或预设电压的具体值。
需要说明的是，若该预设位置为直流母线的一极，则在并网后控制器40可以通过检测直流母线的一极对大地之间的电压变换来实现接地检测，也可以通过检测交流侧耦合电路50对大地之间的电压变换来实现接地检测。当预设位置为交流侧耦合电路50的输出端时，可以在并网前控制接地电源20向交流侧耦合电路50的输出端施加预设电流或预设电压，则直流母线在主电路10中逆变电路的反向变换作用下，实现自身的软启动、建立正常的直流母线电压，因此，向交流侧耦合电路50的输出端施加预设电流或预设电压后，若该PWM控制型并网逆变器出现接地故障，则不仅可以在交流侧耦合电路50的输出端检测到电压变化，还可以在直流母线的一极测量到电压变化。
并且，当预设位置是交流侧耦合电路50的输出端时，通过判断交流侧耦合电路50的输出端对大地之间的电压是否发生变化来判断该PWM控制型并网逆变器是否接地不良，可以避免对逆变电路的主电路10进行的相关操作，简化检测步骤。
S400、判定该PWM控制型并网逆变器接地不良。
S500、判定该PWM控制型并网逆变器接地良好。
需要说明的是，本实施例中的步骤S100可以是按照自身的周期执行的，而步骤S200、步骤S300、步骤S400以及步骤S500是按照上述逻辑触发执行的，即只有当步骤S100执行完成后，步骤S200、步骤S300、步骤S400以及步骤S500才会相应执行；而且，从整体上看，在整个检测过程中，每隔一个周期，就判断一次是否对该PWM控制型并网逆变器进行接地检测，当周期取 极小值时，就可以连续判断是否对该PWM控制型并网逆变器进行接地检测，从而可以及时对该PWM控制型并网逆变器进行接地检测。
或者，步骤S100、步骤S200、步骤S300、步骤S400以及步骤S500也可以是按照上述逻辑循环触发执行的，即当整个检测过程完成步骤S400或步骤S500后，返回触发执行步骤S100，使步骤S100、步骤S200、步骤S300、步骤S400以及步骤S500形成一个循环；当循环形成后，可以实现连续判断是否对该PWM控制型并网逆变器进行接地检测的目的，从而可以及时对该PWM控制型并网逆变器进行接地检测；不过需要注意的是，当控制器40开启后，整个检测过程即开始进行。
由上述技术方案可知，该PWM控制型并网逆变器的控制器40在该PWM控制型并网逆变器满足接地检测条件的情况下，先控制该PWM控制型并网逆变器中接地电源20向该PWM控制型并网逆变器中预设位置与大地之间施加预设电流或预设电压，其中，预设位置为直流母线的一极或交流侧耦合电路50的输出端；之后，通过判断直流母线的一极或交流侧耦合电路50的输出端对大地之间的电压是否发生变化，来判断该PWM控制型并网逆变器是否接地良好，进而实现了对于并网逆变器接地情况的自动检测，解决了现有技术中存在人工依赖性的问题。
值得说明的是，本实施例提供的接地检测方法只需要根据在接地电源20向该PWM控制型并网逆变器中预设位置与大地之间施加预设电流或预设电压前后，直流母线的一极或交流侧耦合电路50的输出端对大地之间的电压是否发生变化，便可以判断该PWM控制型并网逆变器是否接地良好，从而使得本实施例提供的接地检测方法简单、方便并且可靠。
本申请另一实施例，提供一种控制器，该控制器用于执行图1所示的接地检测方法。
在实际应用中，控制器与所在设备外部的接地检测开关按钮的输出端相连，接收接地检测开关按钮输出的接地检测指令。需要说明的是，该接地检测开关按钮产生接地检测指令的条件为：当需要对该PWM控制型并网逆变器进行接地检测时，工作人员按动该接地检测开关按钮。
另外，在实际应用中，该控制器内部设置有计时模块，该计时模块用于在当前时间达到预设检测时间后，通知控制器进行接地检测。
本申请另一实施例，提供一种PWM控制型并网逆变器，适用于低压电网系统，其具体结构如图2和图3所示，包括：主电路10、接地电源20、检测模块30、交流侧耦合电路50(图2中未示出)以及上一实施例提供的控制器40。
其中，主电路10的直流侧用于接收或输出直流电能，主电路10的交流侧用于输出或接收交流电能。交流侧耦合电路50的交流侧与主电路10的交流侧相连。
接地电源20的负极与该PWM控制型并网逆变器的内部接地点相连；接地电源20的正极与该PWM控制型并网逆变器中的预设位置相连。
控制器40的指令输出端与接地电源20的控制端相连；控制器40的接收端与检测模块30的输出端相连、接收检测模块30检测到的直流母线的一极，即直流母线的正极或负极(如图2所示)，或者，交流侧耦合电路50的输出端(如图3所示)对大地之间的电压。
需要说明的是，若不采用交流侧耦合电路50实现接地检测功能，则该预设位置为直流母线的一极，图2以直流母线的负极为例进行展示，此时，控制器40的接收端通过检测模块30接收到的电压可以是直流母线的负极对大地之间的电压，也可以是直流母线的正极对大地之间的电压，此处不做具体限定，可视具体情况而定，均在本申请的保护范围内。
若采用交流侧耦合电路50实现接地检测功能，则该预设位置为交流侧耦合电路50的输出端时，控制器40的接收端接收检测模块30检测到的电压，可以为直流母线的一极对大地之间的电压(未进行图示)，也可以为交流侧耦合电路50的输出端对大地之间的电压(如图3所示)，此处不做具体限定，可视具体情况而定，均在本申请的保护范围内。另外，采用交流侧耦合电路50实现接地检测功能，该预设位置也可以为直流母线的一极，此时，控制器40的接收端接收检测模块30检测到的电压，为交流侧耦合电路50的输出端对大地之间的电压。
在实际应用中，交流侧耦合电路50可以为整流器，整流器的具体结构如 图4所示，包括：电容C和三个整流支路60；整流支路60由两个二极管D顺次串联构成。
其中，三个整流支路60的正极和电容C的一端均相连，连接点作为整流器直流侧正极；三个整流支路60的正极和电容C的另一端均相连，连接点作为整流器直流侧负极；交流侧耦合电路50的输出端是指其直流侧的正极或负极；三个整流支路60的中间连接点作为整流器交流侧，分别与主电路10交流侧各相连接点相连。
在实际应用中，交流侧耦合电路50还可以为由阻抗构成的Y型电路，Y型电路的具体结构如图5所示，包括：第一阻抗Z1、第二阻抗Z2和第三阻抗Z3。
其中，第一阻抗Z1的一端、第二阻抗Z2的一端以及第三阻抗Z3的一端均相连，连接点作为Y型电路的虚拟N点；交流侧耦合电路50的输出端是指Y型电路的虚拟N点；第一阻抗Z1的另一端、第二阻抗Z2的另一端以及第三阻抗Z3的另一端均与主电路10的交流侧相连。
需要说明的是，第一阻抗Z1、第二阻抗Z2以及第三阻抗Z3均可以是纯电阻、纯电容或纯电感、也均可以是电阻、电容以及电感中至少任意两种的组合，此处不做具体限定，可视具体情况进行组合，均在本申请的保护范围内。
该控制器40所执行的接地检测方法参见上述实施例即可，此处不再一一赘述。值得说明的是，对于图2所示的PWM控制型并网逆变器，以及预设位置为直流母线的一极而检测模块30检测交流侧耦合电路50的输出端对大地之间的电压时，其控制器40只能在并网后进行接地检测；而图3所示的PWM控制型并网逆变器，以及预设位置为交流侧耦合电路50的输出端而检测模块30检测直流母线的负极对大地之间的电压时，其控制器40不仅能在并网后进行接地检测，还能够在并网前进行接地检测。特别的，若交流侧耦合电路50的结构如图5所示，且该PWM控制型并网逆变器中的接地电源20施加预设电压或预设电流的预设位置，是交流侧耦合电路50的输出端，同时，其检测模块30检测到的电压是交流侧耦合电路50的输出端对大地之间的电压，则其不仅可以在并网前进行接地检测，还可以避免对主电路10进行相关操作。
本申请另一实施例提供接地电源20的一种具体实施方式，其具体结构如图 2或图3所示，包括：可控直流电压源21和限流电阻R。
其中，可控直流电压源21的正极连接接地电源20的正极；可控直流电压源21的负极连接接地电源20的负极，可控直流电压源21的控制端作为接地电源20的控制端；限流电阻R设置于可控直流电压源21的正极与接地电源20的正极之间，或者，限流电阻R设置于可控直流电压源21的负极与接地电源20的负极之间。
需要说明的是，限流电阻R可以有效限制可控直流电压源21的输出能力，避免发生工作人员被电击。
上述仅示出接地电源20的一种优选实施方式，在实际应用中，接地电源20还可以包括可控直流电流源；其中，可控直流电流源的正极作为接地电源20的正极，可控直流电流源的负极作为接地电源20的负极，可控直流电流源的控制端作为接地电源20的控制端。需要说明的是，接地电源20的两种实施方式可视具体情况而定，均在本申请的保护范围内。
本实施例还提供主电路10的两种实施方式，第一种具体实施方式包括：逆变电路11；第二种实施方式包括：逆变电路11及高压侧并联于直流母线的多个升压电路12(如图2和图3所示)；需要说明的是，两种实施方式可视具体情况而定，均在本申请的保护范围内。
需要说明的是，本实施例提供的控制器40通过借用低压电网系统中的PWM控制型并网逆变器内部的已有电路，而无需增加新的电路，也无需借助外部工具，就可以实现对该PWM控制型并网逆变器的接地检测，使得自身的成本降低，便于市场推广和竞争。
本申请另一实施例，提供一种低压电网系统，其具体结构如图6a-图6d所示，包括：变压器(变压器的一部分如图6a-图6d中的黑色方块所示)、至少一个直流电源80、以及图2或图3所示的PWM控制型并网逆变器90。
该PWM控制型并网逆变器90的直流侧与直流电源80相连；PWM控制型并网逆变器90的交流侧通过变压器连接电网；变压器的中点接地。
可选的，直流电源80可以为光伏组串，也可以为储能系统，还可以为光伏组串和储能系统，此处不做具体限定，可视具体情况而定，均在本申请保护范 围内。
在实际应用中，若PWM控制型并网逆变器90的PE线与变压器的PEN线相连，且变压器的PEN线与变压器的中性点相连，则采用上述连接方式的该PWM控制型并网逆变器90和变压器，构成TN-C系统(如图6a所示)。
在实际应用中，若该PWM控制型并网逆变器90的PE线与变压器的PE线相连、变压器的PE线与变压器的N线相连、变压器的PE线与变压器的N线连接点与变压器的中心点相连，则采用上述连接方式的该PWM控制型并网逆变器90和变压器，构成TN-C-S系统(如图6b所示)。
在实际应用中，若该PWM控制型并网逆变器90的PE线与变压器的PE线相连，且变压器的N线、PE线均与变压器的中心点相连，则采用上述连接方式的该PWM控制型并网逆变器90和变压器，构成TN-S系统(如图6c所示)。
在实际应用中，若该PWM控制型并网逆变器90的PE线接地，变压器的N线与变压器的中性点相连，则采用上述连接方式的该PWM控制型并网逆变器90和变压器，构成TT系统(如图6d所示)。
上述四种该PWM控制型并网逆变器90与变压器的连接形式，可视具体情况而定，此处不做具体限定，均在本申请的保护范围内。
本说明书中的各个实施例均采用递进的方式描述，各个实施例之间相同相似的部分互相参见即可，每个实施例重点说明的都是与其他实施例的不同之处。尤其，对于系统或系统实施例而言，由于其基本相似于方法实施例，所以描述得比较简单，相关之处参见方法实施例的部分说明即可。以上所描述的系统及系统实施例仅仅是示意性的，其中所述作为分离部件说明的单元可以是或者也可以不是物理上分开的，作为单元显示的部件可以是或者也可以不是物理单元，即可以位于一个地方，或者也可以分布到多个网络单元上。可以根据实际的需要选择其中的部分或者全部模块来实现本实施例方案的目的。本领域普通技术人员在不付出创造性劳动的情况下，即可以理解并实施。
专业人员还可以进一步意识到，结合本文中所公开的实施例描述的各示例的单元及算法步骤，能够以电子硬件、计算机软件或者二者的结合来实现，为了清楚地说明硬件和软件的可互换性，在上述说明中已经按照功能一般性地描述了各示例的组成及步骤。这些功能究竟以硬件还是软件方式来执行，取决于 技术方案的特定应用和设计约束条件。专业技术人员可以对每个特定的应用来使用不同方法来实现所描述的功能，但是这种实现不应认为超出本发明的范围。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本发明。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下，在其它实施例中实现。因此，本发明将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (14)

  1. 一种接地检测方法，其特征在于，应用于低压电网系统中PWM控制型并网逆变器内的控制器，所述接地检测方法，包括：
    判断所述PWM控制型并网逆变器是否满足接地检测条件；
    若所述PWM控制型并网逆变器满足所述接地检测条件，则控制所述PWM控制型并网逆变器中接地电源向所述PWM控制型并网逆变器中预设位置与大地之间施加预设电流或预设电压；所述预设位置为直流母线的一极或交流侧耦合电路的输出端；
    判断所述直流母线的一极或所述交流侧耦合电路的输出端对大地之间的电压是否发生变化；
    若所述电压发生变化，则判定所述PWM控制型并网逆变器接地不良；
    若所述电压未发生变化，则判定所述PWM控制型并网逆变器接地良好。
  2. 根据权利要求1所述的接地检测方法，其特征在于，判断所述直流母线的一极或所述交流侧耦合电路的输出端对大地之间的电压是否发生变化，包括：
    判断所述直流母线的负极对大地之间的电压是否逐渐降低并趋近于零电位；
    或者，判断所述直流母线的正极对大地之间的电压是否逐渐升高并趋近于所述直流母线电压；
    又或者，判断所述交流侧耦合电路的输出端对大地之间的电压是否逐渐升高并趋近于预设值。
  3. 根据权利要求1所述的接地检测方法，其特征在于，所述接地检测条件包括：接收到接地检测指令，和/或，达到预设检测时间。
  4. 根据权利要求3所述的接地检测方法，其特征在于，若所述预设位置为直流母线的一极，则所述接地检测条件，还包括：
    所述PWM控制型并网逆变器处于并网状态。
  5. 根据权利要求3所述的接地检测方法，其特征在于，若所述预设位置为交流侧耦合电路的输出端，则所述接地检测条件，还包括：
    所述PWM控制型并网逆变器处于待机或并网状态。
  6. 一种控制器，其特征在于，用于执行权利要求1-5任一项所述的接地检测方法。
  7. 根据权利要求6所述的控制器，其特征在于，所述控制器与所在设备外部的接地检测开关按钮的输出端相连，接收所述接地检测开关按钮输出的接地检测指令。
  8. 根据权利要求6所述的控制器，其特征在于，所述控制器内部设置有计时模块，用于在当前时间达到预设检测时间后，通知所述控制器进行接地检测。
  9. 一种PWM控制型并网逆变器，其特征在于，适用于低压电网系统，包括：主电路、接地电源、检测模块、交流侧耦合电路以及如权利要求6-8任一项所述的控制器；其中：
    所述主电路的直流侧用于接收或输出直流电能，所述主电路的交流侧用于输出或接收交流电能；
    所述交流耦合电路的交流侧与所述主电路的交流侧相连；
    所述接地电源的负极与所述PWM控制型并网逆变器的内部接地点相连；所述接地电源的正极与所述PWM控制型并网逆变器中的预设位置相连；
    所述预设位置为所述主电路中直流母线的一极，或者，所述交流耦合电路的输出端；
    所述控制器的指令输出端与所述接地电源的控制端相连；所述控制器的接收端与所述检测模块的输出端相连、接收所述检测模块检测到的所述直流母线的一极或所述交流侧耦合电路的输出端对大地之间的电压。
  10. 根据权利要求9所述的PWM控制型并网逆变器，其特征在于，所述接地电源，包括：可控直流电压源和限流电阻；其中：
    所述可控直流电压源的正极连接所述接地电源的正极，所述可控直流电压源的负极连接所述接地电源的负极；
    所述限流电阻设置于所述可控直流电压源的正极与所述接地电源的正极之间，或者，设置于所述可控直流电压源的负极与所述接地电源的负极之间；
    所述可控直流电压源的控制端作为所述接地电源的控制端。
  11. 根据权利要求9所述的PWM控制型并网逆变器，其特征在于，所述接地电源，包括：可控直流电流源；其中：
    所述可控直流电流源的正极作为所述接地电源的正极；
    所述可控直流电压源的负极作为所述接地电源的负极；
    所述可控直流电流源的控制端作为所述接地电源的控制端。
  12. 根据权利要求9所述的PWM控制型并网逆变器，其特征在于，所述交流侧耦合电路为整流器，所述交流侧耦合电路的输出端为所述整流器的直流侧正极或者直流侧负极，所述整流器的交流侧与所述主电路的交流侧相连；
    或者，
    所述交流侧耦合电路为由阻抗构成的Y型电路，所述交流侧耦合电路的输出端为所述Y型电路的虚拟N点，所述Y型电路的另外三端与所述主电路的交流侧相连。
  13. 根据权利要求9所述的PWM控制型并网逆变器，其特征在于，所述主电路包括：逆变电路，或者，逆变电路及高压侧并联于直流母线的多个升压电路。
  14. 一种低压电网系统，其特征在于，包括变压器、至少一个直流电源和权利要求9-13任一项所述的PWM控制型并网逆变器；其中：
    所述PWM控制型并网逆变器的直流侧与所述直流电源相连；
    所述PWM控制型并网逆变器的交流侧通过所述变压器连接电网；
    所述变压器的中点接地。
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