Inverter ac side ground impedance detection circuit and photovoltaic system applying same

Abstract

The utility model provides a kind of inverter ac side impedance to ground detection circuit and the photovoltaic system of application thereof belong to power electronics technical field, including three-phase cable, clamping module, impedance to ground detection module, voltage sampling module to ground and controller, clamping module is connected in the output end of inverter;Impedance to ground detection module includes detection resistance R2, detection resistance R1, controlled switch Q1, detection resistance R2 is connected in series between the output end of clamping module and protective earth PE;Detection resistance R1 and controlled switch Q1 are connected in series, and parallel with detection resistance R2;Voltage sampling module to ground is connected between three-phase cable and protective earth PE, for sampling the voltage of three-phase cable to ground;Controller is connected with voltage sampling module to ground signal, and for controlling the on-off of controlled switch Q1.The utility model circuit structure is simple, not only reduce manufacturing cost and volume, also improve the reliability and stability of system, more easily integrated into existing inverter system.

Description

Technical Field

[0001] This utility model relates to the field of power electronics technology, and in particular to an inverter AC side impedance to ground detection circuit and a photovoltaic system using the same. Background Technology

[0002] In photovoltaic power generation systems, the inverter, as the core power conversion device connecting the photovoltaic array and the power grid, has insulation safety performance that directly affects the reliable operation of the entire system and personal safety. Among these parameters, the AC side insulation resistance to ground is a key parameter for assessing the system's insulation status.

[0003] However, existing methods for testing insulation to ground mainly rely on specific testing instruments or external sensors.

[0004] This results in a complex system structure, high costs, and difficulty in maintaining stable adaptability under complex operating conditions. In actual operating environments, it suffers from limited detection conditions, poor environmental adaptability, and high detection costs. Utility Model Content

[0005] To address the aforementioned issues, this invention provides an inverter AC side impedance to ground detection circuit and a photovoltaic system using it. Through a simple circuit design, it not only reduces manufacturing costs and size but also improves system reliability and stability, making it easier to integrate into existing inverter systems.

[0006] The objective of this utility model is achieved through the following technical solution: On one hand, embodiments of this utility model provide an inverter AC side impedance to ground detection circuit, including: Three-phase cable, connected to the output terminal of the inverter; A clamping module, whose input is connected to the three-phase cable, is used to construct a unidirectional conduction path from its output to the three-phase cable; The impedance to ground detection module includes a detection resistor R2, a detection resistor R1, and a controlled switch Q1; one end of the detection resistor R2 is connected to the output terminal of the clamping module, and the other end is connected to the protective ground PE; the detection resistor R1 and the controlled switch Q1 are connected in series and then in parallel with the detection resistor R2. A ground voltage sampling module is connected between the three-phase cable and the protective ground PE to sample the voltage of the three-phase cable to ground. The controller is connected to the ground voltage sampling module and controls the on / off state of the controlled switch Q1.

[0007] Furthermore, the controller is configured to: The controlled switch Q1 is controlled to be in the off state, so that the equivalent resistance of the ground impedance detection module is the detection resistance R2, and the first voltage value Vrid_PE1 is obtained based on the ground voltage sampling module; The controlled switch Q1 is controlled to be in the on state, so that the equivalent resistance of the ground impedance detection module is the parallel resistance of the detection resistor R1 and the detection resistor R2, and the second voltage value Vrid_PE2 is obtained based on the ground voltage sampling module. The ground insulation impedance Rg of the three-phase cable is calculated based on the first voltage value Vrid_PE1, the second voltage value Vrid_PE2, the resistance value of the detection resistor R1, and the resistance value of the detection resistor R2.

[0008] Furthermore, it also includes a controlled switch K2, which is used to realize the connection and disconnection between the ground impedance detection module and the three-phase cable.

[0009] Furthermore, the clamping module includes a diode D1 and an autotransformer T. One end of the autotransformer T is connected to one phase of the three-phase cable, and the other end is connected to the negative terminal of the diode D1. The positive terminal of the diode D1 is the output terminal of the clamping module.

[0010] Furthermore, the clamping module includes three parallel branches, each branch corresponding to one phase cable, and each branch includes a diode; The negative terminals of diodes D2, D3, and D4 in the three branches are respectively connected to one phase of the three-phase cable, and their positive terminals are connected together to form the output terminal of the clamping module.

[0011] Furthermore, the clamping module includes three parallel branches, each branch corresponding to one phase cable, and each branch includes a resistor and a diode. One end of resistors R3, R4, and R5 in the three branches is respectively connected to one phase of the three-phase cable; The negative terminals of diodes D5, D6, and D7 in the three branches are respectively connected to the other ends of the corresponding resistors R3, R4, and R5, and their positive terminals are connected together to form the output terminal of the clamping module.

[0012] Furthermore, the clamping module includes a diode D8 and three parallel branches, each branch corresponding to one phase cable, and each branch includes a resistor; One end of resistors R6, R7, and R8 in the three branches is connected to one phase of the three-phase cable, and the other end is connected together and connected to the negative terminal of diode D8; the positive terminal of diode D8 is the output terminal of the clamping module.

[0013] Furthermore, the impedance to ground detection circuit also includes a current sensor, which is connected in series between the output terminal of the clamping module and the detection resistor R2.

[0014] Furthermore, the ground impedance detection circuit also includes a filtering sampling module for acquiring the voltage signal between each phase cable and the protective ground (PE); the controller is connected to the filtering sampling module and configured to determine the fault phase and the impedance range of the fault phase based on the voltage signal.

[0015] On the other hand, embodiments of this utility model also provide a photovoltaic system, including: at least one photovoltaic module, at least one inverter, a transformer, and a detection circuit for AC side impedance to ground of the inverter. Each inverter's DC input terminal is electrically connected to at least one of the photovoltaic modules, and its three-phase AC output terminal is connected to the three-phase cable of the impedance-to-ground detection circuit, the three-phase cable being connected to the power grid via the transformer.

[0016] Compared with the prior art, the beneficial effects of this utility model are as follows: By introducing a clamping module and a ground impedance detection module in a coordinated design, this utility model constructs a directional conduction path from the ground impedance detection module to the three-phase cable, achieving efficient detection function with simple hardware. This not only effectively reduces the manufacturing cost and physical volume of the system, but also significantly improves the reliability and long-term operational stability of the circuit due to the simplification of the structure. In addition, the clamping module can adjust the ground potential of the photovoltaic system to a negative or positive potential, thereby effectively suppressing the potential induced decay (PID) effect and reducing the safety risks caused by abnormal potential rise, realizing the integration of protection and detection functions. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the circuit structure of a photovoltaic system provided in an embodiment of this application; Figure 2 This is a structural block diagram of an inverter AC side impedance to ground detection circuit provided in an embodiment of this application; Figure 3 This is a circuit diagram of an inverter AC side impedance to ground detection circuit provided in Embodiment 1 of this application; Figure 4 This is a circuit diagram of an inverter AC side impedance to ground detection circuit provided in Embodiment 2 of this application; Figure 5 This is a circuit diagram of an inverter AC side impedance to ground detection circuit provided in Embodiment 3 of this application; Figure 6 This is a circuit diagram of an inverter AC side impedance to ground detection circuit provided in Embodiment 4 of this application. Detailed Implementation

[0018] The technical solution of this utility model will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0019] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances. Furthermore, the technical features involved in the different embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0021] Combination Figure 1 The diagram illustrates a photovoltaic system where multiple photovoltaic arrays are DC-connected to corresponding inverters. Each inverter converts the DC output from the photovoltaic array into three-phase AC power (outputting U, V, and W phases). The three-phase AC outputs of the inverters are connected in parallel and connected to subsequent three-phase cables (L1, L2, and L3 phases). The three-phase cables (L1, L2, and L3 phases) are connected to the public power grid via a transformer, ultimately integrating the photovoltaic power into the grid.

[0022] Combination Figures 2 to 6As shown, this utility model's inverter AC side ground impedance detection circuit is used to detect the insulation impedance Rg of three-phase cables to ground. The circuit mainly consists of a clamping module, a ground impedance detection module, a ground voltage sampling module, and a controller. The clamping module includes one or more diodes, whose output terminals are connected to the three-phase cables. On the one hand, by actively clamping the photovoltaic system's ground potential to a negative or positive potential, it effectively suppresses the potential-induced degradation (PID) effect and reduces safety risks; on the other hand, by utilizing the unidirectional conduction characteristic of the diodes, a directional conduction path is constructed from the ground impedance detection module to the three-phase cables, which can stabilize the common-mode voltage during the detection process and avoid reverse current interference with detection accuracy. There are various embodiments of the specific circuit implementation of the clamping module, which will be described in detail below and will not be elaborated upon here. The ground impedance detection module provides a variable equivalent impedance for detection by switching the resistance values ​​of the connected circuit. This includes detection resistors R2 and R1, and a controlled switch Q1. One end of detection resistor R2 is connected to the input of the clamping module, and the other end is connected to protective earth (PE). Detection resistor R1 and controlled switch Q1 are connected in series, and then in parallel with detection resistor R2. When controlled switch Q1 is open, the equivalent resistance of the ground impedance detection module is the detection resistor R2; when controlled switch Q1 is on, the equivalent resistance of the ground impedance detection module is the parallel resistance of detection resistors R1 and R2. The ground voltage sampling module is connected between the three-phase cable and the protective earth (PE). It is responsible for real-time acquisition of the voltage signal between the three-phase cable and the protective earth (PE) and outputting the sampled data to the controller, providing input parameters for insulation impedance calculation. As the core of the circuit's control and calculation, the controller establishes a connection with the ground voltage sampling module to receive voltage sampling values ​​in real time. On the other hand, it outputs control signals to control the on / off state of the controlled switch Q1. Based on the on / off state of the controlled switch Q1, circuit equations are established for the two detection states, and the insulation impedance Rg of the three-phase cable to ground is solved simultaneously.

[0023] The process and calculation principle of ground impedance detection: The detection process involves the controller periodically switching the on / off state of the controlled switch Q1.

[0024] First state: Controlled switch Q1 is open When the controlled switch Q1 is in the open state, the circuit of the ground impedance detection module consists only of the detection resistor R2. At this time, the circuit forms a closed clamping circuit of protective ground PE → detection resistor R2 → clamping module → three-phase cable → insulation impedance Rg → protective ground PE.

[0025] After the circuit reaches steady state, the ground voltage sampling module collects the voltage signal between the three-phase cable and the protective ground PE. The controller obtains the first voltage value Vrid_PE1 based on this voltage signal, and the first equation can be obtained according to Ohm's law:

[0026] Second state: Controlled switch Q1 is turned on. When the controlled switch Q1 is in the on state, the circuit of the ground impedance detection module is a parallel circuit of detection resistor R2 and detection resistor R1. At this time, a closed clamping circuit is formed: protective ground PE → detection resistor R2 / / R1 → clamping module → three-phase cable → insulation impedance Rg → protective ground PE.

[0027] After the circuit reaches steady state, the ground voltage sampling module collects the voltage signal between the three-phase cable and the protective ground. The controller obtains the second voltage value Vrid_PE2 based on this voltage signal. According to Ohm's law, the second equation can be derived:

[0028] Where Vf1 and Vf2 are the forward voltage drops across the diodes in the clamping module under the two states. Since the diodes conduct in a single phase, their forward voltage drop remains essentially constant in steady state; that is, the forward voltage drop Vf1 in the first state is equal to the forward voltage drop Vf2 in the second state. Based on the above two sets of equations, combined with the known resistance values ​​of the sensing resistors R1 and R2, and the first voltage value Vrid_PE1 and the second voltage value Vrid_PE2 obtained by the controller, the insulation resistance to ground Rg can be solved by solving the simultaneous equations. It should be noted that if the clamping module includes a current-limiting resistor, its resistance value is also included as a known quantity in the equation calculation.

[0029] Specifically, since Vf1=Vf2, subtracting the two equations can eliminate the conduction voltage drop interference. Substituting the detection resistors R1 and R2, the insulation impedance Rg of the three-phase cable to ground can be accurately calculated.

[0030]

[0031] In summary, this utility model, by periodically controlling the on / off state of the controlled switch Q1, can achieve uninterrupted detection of the insulation impedance to ground without affecting the normal operation of the inverter, ensuring that abnormal circuit insulation can be identified in a timely manner, and significantly improving the safety and maintainability of the system.

[0032] Furthermore, the clamping module of this utility model can be implemented using various circuit structures, and the specific implementation methods are as follows.

[0033] Example 1: Combination Figure 3 As shown, the clamping module in this embodiment includes a diode D1 and an autotransformer T. One end of the autotransformer T is connected to one phase of the three-phase cable, and the other end is connected to the negative terminal of the diode D1. The positive terminal of the diode D1 is the output terminal of the clamping module.

[0034] Example 2: Combination Figure 4 As shown, the clamping module in this embodiment includes three parallel branches, each branch corresponding to one phase cable, and each branch includes a diode; The negative terminals of diodes D2, D3, and D4 in the three branches are independently connected to phases L1, L2, and L3 of the three-phase cable, respectively, while their positive terminals are connected together to form the output terminal of the clamping module and connected to one end of the detection resistor R2.

[0035] Example 3: Combination Figure 5 As shown, the clamping module in this embodiment includes three parallel branches, each branch corresponding to one phase cable, and each branch includes a resistor and a diode. One end of resistors R3, R4, and R5 in the three branches is connected to one phase of the three-phase cable, respectively. The negative terminals of diodes D5, D6, and D7 in the three branches are respectively connected to the other ends of the corresponding resistors R3, R4, and R5, and their positive terminals are connected together to form the output terminal of the clamping module, which is then connected to one end of the detection resistor R2.

[0036] Example 4: Combination Figure 6 As shown, the clamping module in this embodiment includes a diode D8 and three parallel branches, each branch corresponding to one phase cable, and each branch includes a resistor; One end of resistors R6, R7, and R8 in the three branches is connected to one phase of the three-phase cable, and the other end is connected together and connected to the negative terminal of diode D8; the positive terminal of diode D8 is connected to one end of the detection resistor R2.

[0037] The above embodiments demonstrate multiple feasible implementations of the clamping module, achieving directional conduction from the detection circuit to the three-phase cable through different component combinations, thus meeting the circuit design requirements of different application scenarios.

[0038] Furthermore, the inverter AC side impedance to ground detection circuit of this utility model also includes a controlled switch K2. One end of the controlled switch K2 is connected to the detection resistor R2, and the other end is connected to the output terminal of the clamping module. By setting the controlled switch K2, the start and stop of the detection circuit can be controlled as needed.

[0039] Furthermore, the inverter AC side ground impedance detection circuit of this utility model also includes a current sensor HALL1. The current sensor HALL1 is connected in series between the output terminal of the clamping module and the detection resistor R2, and is used to monitor the current in the ground impedance detection circuit in real time. The current sensor is also signal-connected to the controller, which is configured to continuously monitor the current value. When the current value exceeds a preset threshold, a fault protection program is immediately executed to prevent components such as the detection resistor R2 and detection resistor R1 from being damaged due to overload, thereby significantly improving the reliability and service life of the detection circuit.

[0040] Furthermore, the inverter AC side ground impedance detection circuit of this invention also includes a filter sampling module for collecting the voltage between each phase of the three-phase cable and the protective ground. The controller is connected to the filter sampling module and configured to determine the faulty phase and its impedance range based on the sampled values. Through the filter sampling circuit, the ground impedance detection circuit of this invention can accurately identify the specific faulty phase when an abnormal ground insulation impedance is detected, significantly improving the system's maintenance efficiency and safety.

[0041] In summary, this invention, through the collaborative design of a clamping module and a ground impedance detection module, constructs a directional conduction path from the ground impedance detection module to the three-phase cable. It achieves efficient detection functionality with simple hardware, effectively reducing system manufacturing costs and physical size, and significantly improving circuit reliability and long-term operational stability due to structural simplification. Furthermore, the clamping module can adjust the photovoltaic system's ground potential to a negative or positive potential, effectively suppressing the potential-induced degradation (PID) effect and reducing safety risks caused by abnormal potential rise, thus integrating protection and detection functions. Finally, this invention adopts a modular design, providing high deployment flexibility. It can be used as a standalone device or seamlessly integrated into an inverter.

[0042] It should be emphasized that the above are merely preferred embodiments of the present utility model and are not intended to limit the present utility model in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model shall still fall within the scope of the technical solution of the present utility model.

Claims

1. A circuit for detecting the AC side impedance to ground of an inverter, characterized in that, include: Three-phase cable, connected to the output terminal of the inverter; A clamping module, whose input is connected to the three-phase cable, is used to construct a unidirectional conduction path from its output to the three-phase cable; The impedance to ground detection module includes a detection resistor (R2), a detection resistor (R1), and a controlled switch (Q1); one end of the detection resistor (R2) is connected to the output terminal of the clamping module, and the other end is connected to the protective ground (PE); the detection resistor (R1) and the controlled switch (Q1) are connected in series and then in parallel with the detection resistor (R2); A ground voltage sampling module is connected between the three-phase cable and the protective ground (PE) to sample the voltage of the three-phase cable to ground. The controller is connected to the ground voltage sampling module and controls the on / off state of the controlled switch (Q1).

2. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, The controller is configured to: The controlled switch (Q1) is controlled to be in the off state, so that the equivalent resistance of the ground impedance detection module is the detection resistance (R2), and the first voltage value (Vrid_PE1) is obtained based on the ground voltage sampling module. The controlled switch (Q1) is controlled to be in the on state, so that the equivalent resistance of the ground impedance detection module is the parallel resistance of the detection resistor (R1) and the detection resistor (R2), and the second voltage value (Vrid_PE2) is obtained based on the ground voltage sampling module. Based on the first voltage value (Vrid_PE1), the second voltage value (Vrid_PE2), the resistance value of the detection resistor (R1), and the resistance value of the detection resistor (R2), calculate the ground insulation impedance (Rg) of the three-phase cable.

3. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, It also includes a controlled switch (K2), which is used to switch the ground impedance detection module on and off with the three-phase cable.

4. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, The clamping module includes a diode (D1) and an autotransformer (T). One end of the autotransformer (T) is connected to one phase of the three-phase cable, and the other end is connected to the negative terminal of the diode (D1). The positive terminal of the diode (D1) is the output terminal of the clamping module.

5. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, The clamping module includes three parallel branches, each branch corresponding to one phase cable, and each branch includes a diode; The negative terminals of the diodes (D2, D3, D4) in the three branches are respectively connected to one phase of the three-phase cable, and their positive terminals are connected together to form the output terminal of the clamping module.

6. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, The clamping module includes three parallel branches, each branch corresponding to one phase cable, and each branch includes a resistor and a diode. One end of each of the resistors (R3, R4, R5) in the three branches is connected to one phase of the three-phase cable; The negative terminals of the diodes (D5, D6, D7) in the three branches are respectively connected to the other end of the corresponding resistors (R3, R4, R5), and their positive terminals are connected together to form the output terminal of the clamping module.

7. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, The clamping module includes a diode (D8) and three parallel branches, each branch corresponding to one phase cable, and each branch includes a resistor; One end of each of the resistors (R6, R7, R8) in the three branches is connected to one phase of the three-phase cable, and the other end is connected together and connected to the negative terminal of the diode (D8); the positive terminal of the diode (D8) is the output terminal of the clamping module.

8. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, It also includes a current sensor, which is connected in series between the output of the clamping module and the detection resistor (R2).

9. The inverter AC side impedance to ground detection circuit according to claim 1, characterized in that, It also includes a filtering sampling module for acquiring the voltage signal between each phase cable and the protective earth (PE); the controller is connected to the filtering sampling module and is configured to determine the fault phase and the impedance range of the fault phase based on the voltage signal.

10. A photovoltaic system, characterized in that, include: At least one photovoltaic module, at least one inverter, a transformer, and an inverter AC side to ground impedance detection circuit as described in any one of claims 1-9; Each inverter's DC input terminal is electrically connected to at least one of the photovoltaic modules, and its three-phase AC output terminal is connected to the three-phase cable of the impedance-to-ground detection circuit, the three-phase cable being connected to the power grid via the transformer.

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