Fault detection method and system for grid-connected switch

Abstract

The application discloses a grid-connected switch fault detection method and system. The fault detection system comprises a grid-connected switch connected between a power grid and an inverter; a current sampling device for detecting a grid current; and a controller configured to determine whether the grid-connected switch has a closing failure fault or an opening failure fault according to a relationship between a control signal, the grid current and a preset current threshold, wherein the control signal is used for controlling the grid-connected switch to open or close. The grid-connected switch fault detection method and system provided by the application can determine whether the grid-connected switch has a closing failure fault or an opening failure fault according to the relationship between the control signal of the grid-connected switch, the grid current and the preset current threshold, and the detection is accurate, does not require a switch state contact feedback device and has a low cost.

Description

Technical Field

[0001] This application relates to the field of grid connection technology, and in particular to a fault detection method and system for grid-connected switches. Background Technology

[0002] In grid-connected systems, such as photovoltaic power generation systems, photovoltaic inverters are needed to convert the direct current output from solar panels into alternating current, which is then fed into the power grid via an AC grid-connection switch.

[0003] Due to factors such as components and application environments, AC grid-connected switches have a certain failure rate. In existing fault detection technologies, high-power photovoltaic inverters generally use contactors as AC grid-connected switches. These contactors typically have built-in switch status contact feedback devices, which, combined with software drive commands, can determine whether the contactor has malfunctioned. However, as mechanical devices, the signals generated by these feedback devices are unreliable in practical engineering applications, frequently resulting in false feedback. Furthermore, string photovoltaic inverters use relays as AC grid-connected switches. Since relays themselves lack contact feedback devices, there is no effective hardware means to determine whether the relay has malfunctioned. Summary of the Invention

[0004] This application provides a fault detection method and system for grid-connected switches to achieve fault detection of grid-connected switches.

[0005] One aspect of this application provides a fault detection system for a grid-connected switch, the fault detection system comprising:

[0006] A grid-connected switch that connects the power grid and the inverter;

[0007] A current sampling device used to detect the current in the power grid;

[0008] The controller is configured to determine whether the grid-connected switch has experienced a closing failure or a disconnection failure based on a control signal, the relationship between the grid current and a preset current threshold; wherein the control signal is used to control the grid-connected switch to open or close.

[0009] Another aspect of this application provides a fault detection method for a grid-connected switch, the fault detection method comprising:

[0010] Acquire control signals and grid current; wherein, the control signals are used to control the grid-connected switch to open or close;

[0011] Based on the relationship between the control signal, the grid current, and the preset current threshold, it is determined whether the grid-connected switch has experienced a closing failure or an opening failure.

[0012] The fault detection method and system for grid-connected switches provided in this application can determine whether the grid-connected switch has experienced a closing failure or opening failure based on the relationship between the control signal of the grid-connected switch, the grid current and the preset current threshold; the detection is accurate, no switch status contact feedback device is required, and the cost is low. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of a fault detection system for a grid-connected switch provided in an embodiment of this application;

[0014] Figure 2 A schematic diagram of a fault detection method for a grid-connected switch provided in an embodiment of this application.

[0015] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0016] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer and more understandable, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit the scope of this application.

[0017] In the description of this application, it should be understood that the terms "center," "upper," "lower," "front," "rear," "left," and "right," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this application 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 on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0018] like Figure 1 As shown, one embodiment of this application provides a fault detection system for a grid-connected switch, including a grid-connected switch K connected between the grid and an inverter, a capacitor C and an inductor L connected between the grid-connected switch K and the inverter, a current sampling device for detecting grid current, a first voltage sampling device for detecting grid voltage, and a second voltage sampling device for detecting the voltage across the capacitor.

[0019] The capacitor C and the inductor L constitute a filter component to filter the AC output of the inverter.

[0020] In the preferred embodiment, capacitor C is connected in a delta configuration, and each phase (phases A, B, and C) is connected to at least one inductor; each phase (phases A, B, and C) is connected to at least one grid-connected switch.

[0021] The fault detection system further comprises a controller, the current sampling device, the first voltage sampling device and the second voltage sampling device are connected with the controller, and the controller can further output a control signal for controlling the grid-connected switch K to be opened or closed.

[0022] In an example, the controller is configured to determine whether the grid-connected switch K has a closing failure or an opening failure according to a relationship between the control signal, the grid current detected by the current sampling device and a preset current threshold.

[0023] Specifically, if the control signal is a first signal for controlling the grid-connected switch K to be closed, and the grid current does not exceed a first preset current threshold within a first preset time, it is determined that the grid-connected switch K has a closing failure.

[0024] If the control signal is a second signal for controlling the grid-connected switch K to be opened, and the grid current does not fall below a second preset current threshold within a second preset time, it is determined that the grid-connected switch K has an opening failure.

[0025] The first signal and the second signal can be high or low.

[0026] The grid current includes one of a grid current effective value, a grid current modulus value and a grid current instantaneous value.

[0027] The first preset time is greater than a time for the grid-connected switch to be successfully closed, for example, a duration from when the grid-connected switch K receives the first signal to when it is closed, which can be a maximum duration or an average duration; and the second preset time is greater than a time for the grid-connected switch to be successfully opened, for example, a duration from when the grid-connected switch K receives the second signal to when it is opened, which can be a maximum duration or an average duration.

[0028] The first preset current threshold and the second preset current threshold can be determined in the following manner:

[0029] Taking a rated current of the capacitor C or a grid rated current as a first reference value, taking a first percentage of the first reference value as the first preset current threshold, and taking a second percentage of the first reference value as the second preset current threshold. The first percentage and the second percentage can be empirical values or test values.

[0030] In an example, the controller is further configured to determine whether the grid-connected switch K has an abnormal opening failure during closing or an abnormal closing failure during opening according to a relationship between the grid voltage, the voltage across the capacitor C and a preset voltage threshold during closing or opening of the grid-connected switch K.

[0031] Specifically, if the difference between the grid voltage and the voltage across the capacitor C is greater than a first preset voltage threshold, and the duration that the difference is greater than the first preset voltage threshold reaches a third preset time, it is determined that the grid-connected switch K has an abnormal opening failure during closing.

[0032] If the difference between the grid voltage and the voltage across the capacitor C is less than a second preset voltage threshold, and the duration that the difference is less than the second preset voltage threshold reaches a fourth preset time, it is determined that the grid-connected switch K has an abnormal closing failure during opening.

[0033] The difference between the grid voltage and the voltage across the capacitor C includes one of:

[0034] The difference between the effective value of the grid voltage and the effective value of the voltage across the capacitor C;

[0035] The difference between the modulus value of the grid voltage and the modulus value of the voltage across the capacitor C;

[0036] The difference between the instantaneous value of the grid voltage and the instantaneous value of the voltage across the capacitor C.

[0037] The first preset voltage threshold and the second preset voltage threshold can be determined by the following method:

[0038] Taking the grid rated voltage as a second reference value, taking a third percentage of the second reference value as the first preset voltage threshold, and taking a fourth percentage of the second reference value as the second preset voltage threshold. The third percentage and the fourth percentage can be empirical values or test values. The third preset time and the fourth preset time can also be empirical values or test values.

[0039] Embodiment one

[0040] Suppose the inverter is a distributed inverter (achieves multi-path MPPT optimization function through prepositioning multiple MPPT controllers, and adopts centralized inversion after convergence), the rated power is 1.25 MW, the rated voltage is 520 vAC, the rated frequency is 50 Hz, the capacitor C is 400 uF, the grid-connected switch K is a contactor, the failure mode is a contactor closing failure, the first preset time is 200 ms, and the first preset current threshold is (capacitor rated current * 40%), that is, 113 A * 40%, about 45 A.

[0041] Before the contactor closing control signal is sent, the grid current is 0. After the closing control signal is sent, within the first preset time 200 ms, the modulus value of the grid current has never exceeded the first preset current threshold 45 A, so it is detected that the contactor has a closing failure.

[0042] Example 2

[0043] Assume the inverter is a single-phase string inverter (which directly converts the DC power generated by the solar panel into AC power, then boosts and connects it to the grid), its rated voltage is 220V AC, the grid connection switch is a relay, the fault mode is an abnormal closing fault that occurs during the relay's open period, the fourth preset time is 500ms, and the second preset voltage threshold is the grid rated voltage * 5%, i.e., 11V.

[0044] After the relay successfully disconnects, the residual DC voltage on the capacitor has been completely discharged, the capacitor voltage is 0V, and the mains voltage is 220Vac. At this time, due to a relay malfunction causing abnormal closure, the absolute value of the difference between the instantaneous value of the capacitor voltage and the instantaneous value of the mains voltage is less than the second preset voltage threshold of 11V, and the duration reaches the fourth preset time of 500ms. Therefore, an abnormal closure fault of the relay during the disconnection period is detected.

[0045] like Figure 2 As shown, another embodiment of this application provides a fault detection method for a grid-connected switch, and the fault detection system can refer to the foregoing content. The fault detection method includes:

[0046] Step S11: Acquire control signals and grid current;

[0047] Step S12: Based on the control signal, the relationship between the grid current and the preset current threshold, determine whether the grid-connected switch K has experienced a closing failure or an opening failure.

[0048] In one example, if the control signal is a first signal that controls the grid-connected switch K to close, and the grid current does not exceed a first preset current threshold within a first preset time, then it is determined that the grid-connected switch K has failed to close.

[0049] If the control signal is a second signal that controls the grid-connected switch K to disconnect, and the grid current does not fall below the second preset current threshold within a second preset time, then it is determined that the grid-connected switch K has failed to disconnect.

[0050] The grid current includes one of the following: the effective value of the grid current, the modulus of the grid current, and the instantaneous value of the grid current.

[0051] The first preset time is greater than the time when the grid-connected switch successfully closes. For example, the duration from when the grid-connected switch K receives the first signal to when it closes can be the maximum duration or the average duration. The second preset time is greater than the time when the grid-connected switch successfully opens. For example, the duration from when the grid-connected switch K receives the second signal to when it opens can be the maximum duration or the average duration.

[0052] The first preset current threshold and the second preset current threshold can be determined in the following manner:

[0053] Taking the rated current of the capacitor C or the rated current of the power grid as a first reference value, taking a first percentage of the first reference value as the first preset current threshold, and taking a second percentage of the first reference value as the second preset current threshold. The first percentage and the second percentage can be empirical values or test values.

[0054] In another example, if the difference between the power grid voltage and the voltage across the capacitor C is greater than a first preset voltage threshold, and the duration that the difference is greater than the first preset voltage threshold reaches a third preset time, it is determined that the grid-connected switch K has an abnormal opening fault during closing;

[0055] If the difference between the power grid voltage and the voltage across the capacitor C is less than a second preset voltage threshold, and the duration that the difference is less than the second preset voltage threshold reaches a fourth preset time, it is determined that the grid-connected switch K has an abnormal closing fault during opening.

[0056] The difference between the power grid voltage and the voltage across the capacitor C includes one of the following:

[0057] The difference between the effective value of the power grid voltage and the effective value of the voltage across the capacitor C;

[0058] The difference between the modulus of the power grid voltage and the modulus of the voltage across the capacitor C;

[0059] The difference between the instantaneous value of the power grid voltage and the instantaneous value of the voltage across the capacitor C.

[0060] The first preset voltage threshold and the second preset voltage threshold can be determined in the following manner:

[0061] Taking the rated voltage of the power grid as a second reference value, taking a third percentage of the second reference value as the first preset voltage threshold, and taking a fourth percentage of the second reference value as the second preset voltage threshold. The third percentage and the fourth percentage can be empirical values or test values. The third preset time and the fourth preset time can also be empirical values or test values.

[0062] The preferred embodiments of the present application are described above with reference to the accompanying drawings, and are not intended to limit the scope of the present application. Any modifications, equivalent replacements and improvements made by those skilled in the art without departing from the scope and essence of the present application shall be within the scope of the present application.

Claims

1. A fault detection system for a grid-connected switch, characterized in that, The fault detection system includes: A grid-connected switch that connects the power grid and the inverter; A current sampling device used to detect the current in the power grid; The controller is configured to determine whether the grid-connected switch has experienced a closing failure fault or an opening failure fault based on a control signal, the relationship between the grid current and a preset current threshold; wherein the control signal is used to control the grid-connected switch to open or close. The fault detection system also includes a capacitor connected between the grid-connected switch and the inverter, a first voltage sampling device for detecting the grid voltage, and a second voltage sampling device for detecting the voltage across the capacitor. The controller is further configured to determine, based on the relationship between the grid voltage, the voltage across the capacitor, and a preset voltage threshold, whether an abnormal disconnection fault occurs during the closing or disconnection period of the grid-connected switch. The controller is configured to: If the difference between the grid voltage and the voltage across the capacitor is greater than a first preset voltage threshold, and the duration of the difference being greater than the first preset voltage threshold reaches a third preset time, then it is determined that the grid-connected switch has experienced an abnormal disconnection fault during the closing period. If the difference between the grid voltage and the voltage across the capacitor is less than a second preset voltage threshold, and the duration of this difference being less than the second preset voltage threshold reaches a fourth preset time, then it is determined that the grid-connected switch has experienced an abnormal closing fault during the disconnection period.

2. The fault detection system according to claim 1, characterized in that, The controller is configured to: If the control signal is a first signal that controls the grid-connected switch to close, and the grid current does not exceed a first preset current threshold within a first preset time, then it is determined that the grid-connected switch has failed to close. If the control signal is a second signal that controls the grid-connected switch to disconnect, and the grid current does not fall below the second preset current threshold within a second preset time, then it is determined that the grid-connected switch has failed to disconnect.

3. The fault detection system according to claim 2, characterized in that, The first preset time is longer than the time it takes for the grid-connected switch to successfully close; the second preset time is longer than the time it takes for the grid-connected switch to successfully open.

4. The fault detection system according to claim 2, characterized in that, Using the rated current of the capacitor or the rated current of the power grid as the first reference value, a first percentage of the first reference value is taken as the first preset current threshold, and a second percentage of the first reference value is taken as the second preset current threshold.

5. The fault detection system according to claim 2, characterized in that, The grid current includes one of the following: the effective value of the grid current, the modulus of the grid current, and the instantaneous value of the grid current.

6. The fault detection system according to claim 1, characterized in that, Using the grid rated voltage as the second reference value, a third percentage of the second reference value is taken as the first preset voltage threshold, and a fourth percentage of the second reference value is taken as the second preset voltage threshold.

7. The fault detection system according to claim 1, characterized in that, The difference between the grid voltage and the voltage across the capacitor includes one of the following: The difference between the effective value of the grid voltage and the effective value of the voltage across the capacitor; The difference between the magnitude of the grid voltage and the magnitude of the voltage across the capacitor; The difference between the instantaneous value of the grid voltage and the instantaneous value of the voltage across the capacitor.

8. A fault detection method for a grid-connected switch, characterized in that, The fault detection method includes: Acquire control signals and grid current; wherein, the control signals are used to control the grid-connected switch to open or close; Based on the relationship between the control signal, the grid current, and the preset current threshold, determine whether the grid-connected switch has experienced a closing failure or an opening failure. The fault detection method further includes: During the closing or opening of the grid-connected switch, based on the relationship between the grid voltage, the voltage across the capacitor, and a preset voltage threshold, it is determined whether the grid-connected switch experiences an abnormal disconnection fault during the closing period or an abnormal closing fault during the opening period. If the difference between the grid voltage and the voltage across the capacitor is greater than a first preset voltage threshold, and the duration of the difference being greater than the first preset voltage threshold reaches a third preset time, then it is determined that the grid-connected switch has experienced an abnormal disconnection fault during the closing period. If the difference between the grid voltage and the voltage across the capacitor is less than a second preset voltage threshold, and the duration of this difference being less than the second preset voltage threshold reaches a fourth preset time, then it is determined that the grid-connected switch has experienced an abnormal closing fault during the disconnection period.

Images