Grid-side voltage measurement abnormality determination device, flexible DC system and control method

Abstract

The present invention discloses a grid-side voltage measurement anomaly determination device, a flexible direct current (DC) system, and a control method. The grid-side voltage measurement anomaly determination device includes: an electrical quantity acquisition module that acquires electrical quantity signals from the flexible DC system and sends digital signals obtained after digital-to-analog conversion of the electrical quantity signals to an algorithm control module. The electrical quantity signals include: grid-side voltage, grid-side current, valve-side current, DC voltage, and grid-side voltage at a second measuring point. The algorithm control module receives the digital signals and performs a determination operation on the grid-side voltage. When the grid-side voltage value is abnormal, the grid-side voltage is replaced with the grid-side voltage at the second measuring point to perform dq conversion and phase-locked loop control of the grid-side voltage, thereby meeting the requirements of inner-loop current closed-loop control. After quickly determining that the grid-side voltage is abnormal, a grid-side voltage anomaly identification signal is issued, the grid-side voltage is quickly switched to the grid-side voltage at the second measuring point, and the switching of the grid-side voltage measurement anomaly determination device is initiated, thereby ensuring normal and stable operation of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current system detection, and in particular to a grid-side voltage measurement abnormality determination device, a flexible direct current system and a control method. Background Art

[0002] The voltage source converter-high voltage direct current (VSC-HVDC) system based on voltage source converters has the following advantages: no need for reactive power compensation, no commutation failure problem, can power passive systems, can independently adjust active power and reactive power, has low harmonic levels, and is suitable for building multi-terminal DC systems. With the rapid development of clean energy generation technologies represented by wind power generation and solar power generation, VSC-HVDC has been widely used as a new transmission technology in current practical projects.

[0003] In domestic engineering applications, VSC-HVDC systems typically adopt a dual closed-loop control strategy of "outer loop power + inner loop current". The grid-side voltage is used for the voltage feedforward required for flexible DC phase-locked loop operation and inner loop current closed control. Grid-side voltage anomalies directly determine the performance of the VSC-HVDC system's phase-locked link and inner loop closed-loop control links. Therefore, the identification and control methods of grid-side voltage measurement anomalies are extremely important.

[0004] like Figure 1 As shown, the grid side voltage u sa ,u sb ,u sc Acquisition abnormalities directly affect the output results of the phase-locked loop and inner current closed-loop control, resulting in abnormal calculations of the voltage reference values of each bridge arm sub-module of the converter, and the flexible DC system may eventually be forced to shut down. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a grid-side voltage measurement abnormality judgment device, a flexible DC system and a control method. After quickly judging that the grid-side voltage is abnormal, a grid-side voltage abnormality identification signal is given, the grid-side voltage is quickly switched to the grid-side voltage of a second measuring point, and the algorithm control module switching is started at the same time, thereby ensuring the normal and stable operation of the flexible DC system and improving the stability and reliability of the flexible DC system.

[0006] To solve the above technical problems, a first aspect of an embodiment of the present invention provides a grid-side voltage measurement abnormality determination device, comprising: an electrical quantity acquisition module and an algorithm control module;

[0007] The electrical quantity acquisition module acquires electrical quantity signals of the flexible DC system and sends digital signals obtained by digital-to-analog conversion of the electrical quantity signals to the algorithm control module, wherein the electrical quantity signals include: grid-side voltage, grid-side current, grid-side voltage, DC voltage, and converter current;

[0008] The algorithm control module receives the digital signal, performs a judgment operation on the grid-side voltage, and replaces the grid-side voltage with the grid-side voltage of the second measuring point when the grid-side voltage value is abnormal, so as to perform dq transformation and phase-locked loop control of the grid-side voltage, thereby meeting the inner current closed-loop control requirements.

[0009] Furthermore, the electrical quantity acquisition module includes:

[0010] a dielectric acquisition unit for acquiring the grid-side voltage, grid-side current, and valve-side current of the flexible DC system;

[0011] an optical medium acquisition unit for acquiring the DC voltage of the flexible DC system and the network-side voltage of the second measuring point;

[0012] A digital-to-analog conversion unit receives the electrical quantity signals collected by the dielectric acquisition unit and the optical medium acquisition unit respectively, converts the electrical quantity signals into digital signals, and sends the digital signals to the algorithm control module.

[0013] Furthermore, the algorithm control module includes: an electrical quantity calculation unit communicating via a backplane bus, a grid-side voltage measurement abnormality determination unit, an outer power closed-loop control unit, and an inner current closed-loop control unit;

[0014] The electrical quantity calculation unit receives the digital signal and performs per-unit calculation on it, calculates the voltage amplitude and grid frequency based on the grid-side voltage, calculates the active power and reactive power based on the grid-side voltage and the grid-side current, and sends them to the grid-side voltage measurement abnormality judgment unit, the outer loop power closed-loop control unit, and the inner loop current closed-loop control unit, and simultaneously completes phase-locked loop control, and calculates the DC voltage based on the positive and negative DC voltages;

[0015] The grid-side voltage measurement abnormality determination unit performs a judgment operation on the grid-side voltage, and when the value of the grid-side voltage is abnormal, sends an abnormal identification signal to the inner-loop current closed-loop control module and the algorithm control device switching module;

[0016] The outer power closed-loop control unit obtains the inner current closed-loop control reference value required by the inner current closed-loop control unit after selecting the active power category and the reactive power category;

[0017] After receiving the abnormal identification signal, the inner current closed-loop control unit replaces the grid-side voltage with the grid-side voltage of the second measuring point to perform dq conversion and phase-locked loop control of the grid-side voltage, thereby meeting the inner current closed-loop control requirements.

[0018] Furthermore, the grid-side voltage measurement abnormality judgment unit obtains and judges, based on the grid-side voltage amplitude, whether the calculated value of the sudden change of the grid-side voltage amplitude, the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point, and the grid-side voltage measurement abnormality judgment enable state meet a first preset condition; if the first preset condition is met, the grid-side voltage measurement is judged to be abnormal and an abnormal identification signal is generated; if not, the grid-side voltage measurement is judged to be normal.

[0019] Furthermore, the algorithm control module also includes:

[0020] The algorithm control device switching unit is communicatively connected with the corresponding algorithm control device switching unit in the other flexible DC system grid-side voltage measurement abnormality determination device to transmit the abnormality identification signal.

[0021] Accordingly, a second aspect of an embodiment of the present invention provides a method for controlling a grid-side voltage measurement abnormality determination device, which is used to control any of the above-mentioned grid-side voltage measurement abnormality determination devices, including the following steps:

[0022] Obtain the grid-side voltage amplitude of the flexible DC system;

[0023] According to the grid-side voltage amplitude, obtaining a calculated value of a sudden change in the grid-side voltage amplitude and an absolute value of a difference between the grid-side voltage amplitude and the grid-side voltage amplitude at a second measuring point;

[0024] Determining whether the calculated value of the mutation amount, the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point, and the grid-side voltage measurement abnormality determination enable state meet a first preset condition;

[0025] If yes, it is determined that the grid-side voltage measurement is abnormal, and an abnormality identification signal is generated;

[0026] If not, it is determined that the grid-side voltage measurement is normal.

[0027] Furthermore, obtaining the calculated value of the sudden change amount of the grid-side voltage amplitude includes:

[0028] Calculate the mutation amount of the grid-side voltage amplitude, wherein the mutation amount calculation value is the maximum value of the first difference and the second difference;

[0029] The first difference is the absolute value of the difference between the grid-side voltage amplitude in the current cycle and the grid-side voltage amplitude in the previous cycle, and the second difference is the absolute value of the difference between the grid-side voltage amplitude in the current cycle and the grid-side voltage amplitudes in the previous two cycles.

[0030] Furthermore, after determining that the grid-side voltage measurement is abnormal and generating an abnormality identification signal, the method further includes:

[0031] Determining whether the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point and the grid-side voltage measurement abnormality determination enable state meet a second preset condition;

[0032] If yes, it is determined that the grid-side voltage amplitude has returned to normal, and the abnormal identification signal is reset;

[0033] If not, it is determined that the grid-side voltage amplitude is still abnormal, and the abnormal identification signal is maintained.

[0034] Accordingly, a third aspect of an embodiment of the present invention provides a flexible DC system, comprising any of the above-mentioned mutually switchable main grid-side voltage measurement abnormality determination device and hot standby grid-side voltage measurement abnormality determination device;

[0035] The main grid-side voltage measurement abnormality judgment device obtains an abnormal identification signal and sends the abnormal identification signal to the hot standby grid-side voltage measurement abnormality judgment device, the hot standby grid-side voltage measurement abnormality judgment device switches to the main state, and at the same time switches the main grid-side voltage measurement abnormality judgment device to the hot standby state.

[0036] Accordingly, a fourth aspect of an embodiment of the present invention provides a flexible DC system control method for controlling the flexible DC system, comprising the following steps:

[0037] When the abnormality identification device for measuring the main grid-side voltage in the flexible DC system generates an abnormality identification signal, the grid-side voltage is replaced with the grid-side voltage of the second measuring point;

[0038] Determining whether the communication between the active grid-side voltage measurement abnormality determination device and the hot standby grid-side voltage measurement abnormality determination device is normal;

[0039] If so, the main grid-side voltage measurement abnormality determination device and the hot standby grid-side voltage measurement abnormality determination device are switched, and the grid-side voltage in the hot standby grid-side voltage measurement abnormality determination device is used as the voltage feedforward amount required for the inner current closed-loop control, and normal operation is continued;

[0040] If not, the operating state of the main grid side voltage measurement abnormality determination device is maintained, and the grid side voltage of the second measuring point is used as the voltage feedforward amount required for the inner loop current closed-loop control, and normal operation is continued.

[0041] The above technical solutions of the embodiments of the present invention have the following beneficial technical effects:

[0042] After quickly judging that the grid-side voltage is abnormal, a grid-side voltage abnormality identification signal is given, the grid-side voltage is quickly switched to the grid-side voltage of the second measuring point, and the algorithm control module switching is started at the same time to ensure the normal and stable operation of the flexible DC system, thereby improving the stability and reliability of the flexible DC system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of the logic structure of the dual closed-loop control strategy of the flexible DC system;

[0044] Figure 2 This is a schematic diagram showing the principle of a device for determining abnormal grid-side voltage measurement provided by an embodiment of the present invention;

[0045] Figure 3 This is a structural block diagram of a grid-side voltage control variable switching algorithm provided by an embodiment of the present invention;

[0046] Figure 4 This is a structural block diagram of a grid-side voltage measurement abnormality discrimination algorithm provided by an embodiment of the present invention;

[0047] Figure 5 This is a structural block diagram of a grid-side voltage mutation detection algorithm provided by an embodiment of the present invention;

[0048] Figure 6 This is a logic diagram of a control method for a grid-side voltage measurement abnormality determination device provided by an embodiment of the present invention;

[0049] Figure 7 It is a logic diagram of the flexible DC system control method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0051] Figure 2 It is a schematic diagram of the principle of the grid-side voltage measurement abnormality judgment device provided by an embodiment of the present invention.

[0052] Figure 3This is a structural block diagram of a grid-side voltage control variable switching algorithm provided by an embodiment of the present invention.

[0053] Please refer to Figure 2 and Figure 3 A first aspect of an embodiment of the present invention provides a grid-side voltage measurement abnormality determination device, comprising: an electrical quantity acquisition module and an algorithm control module. The electrical quantity acquisition module acquires electrical quantity signals from a flexible DC system and sends digital signals obtained by digital-to-analog conversion of the electrical quantity signals to the algorithm control module, wherein the electrical quantity signals include: grid-side voltage, grid-side current, grid-side voltage, DC voltage, and converter current. The algorithm control module receives the digital signals, performs a determination operation on the grid-side voltage, and when the grid-side voltage value is abnormal, replaces the grid-side voltage with the grid-side voltage at a second measuring point to perform dq conversion and phase-locked loop control of the grid-side voltage, thereby meeting the closed-loop control requirements of the inner current.

[0054] The above-mentioned grid-side voltage measurement abnormality judgment device quickly determines that the grid-side voltage is abnormal, gives a grid-side voltage abnormality identification signal, quickly switches the grid-side voltage to the grid-side voltage of the second measuring point, and simultaneously starts the algorithm control module switching to ensure the normal and stable operation of the flexible DC system, thereby improving the stability and reliability of the flexible DC system.

[0055] Optionally, two identical sets of grid-side voltage measurement abnormality determination devices operate simultaneously, namely a main grid-side voltage measurement abnormality determination device and a hot standby grid-side voltage measurement abnormality determination device.

[0056] The electrical quantity acquisition module primarily performs functions such as electrical quantity signal acquisition and analog-to-digital conversion, and transmits the converted digital signals to the algorithm control module via optical fiber. Specifically, the electrical quantity acquisition module comprises a dielectric acquisition unit, an optical acquisition unit, and a digital-to-analog conversion unit. The dielectric acquisition unit collects the grid-side voltage, grid-side current, and valve-side current of the flexible DC system; the optical acquisition unit collects the DC voltage of the flexible DC system and the grid-side voltage at the second measuring point; and the digital-to-analog conversion unit receives the electrical quantity signals collected by the dielectric acquisition unit and the optical acquisition unit, converts them into digital signals, and transmits them to the algorithm control module.

[0057] The electrical quantity acquisition module has both dielectric and optical acquisition ports. The dielectric port collects grid-side voltage, grid-side current, and valve-side current, while the optical port collects DC voltage and the grid-side voltage at the second measuring point. The electrical quantity acquisition module has both dielectric and optical acquisition ports, enabling simultaneous acquisition and analog-to-digital conversion of electrical quantities across different acquisition media.

[0058] The algorithm control module primarily performs functions such as electrical quantity calculation, grid-side voltage measurement anomaly detection, outer power closed-loop control, inner current closed-loop control, and algorithm control device switching. Communication with external interfaces utilizes optical fiber. Specifically, the algorithm control module includes an electrical quantity calculation unit (which communicates via the backplane bus), a grid-side voltage measurement anomaly detection unit, an outer power closed-loop control unit, and an inner current closed-loop control unit.

[0059] The electrical quantity calculation unit receives the digital signal and performs normalized calculation on it, and calculates the voltage amplitude U according to the grid side voltage. ac The system calculates active power P and reactive power Q from the grid-side voltage and current, and the grid-side frequency F. It then sends the electrical quantity signal via the PCIe backplane bus to the grid-side voltage measurement anomaly determination unit, the outer power closed-loop control unit, and the inner current closed-loop control unit. It simultaneously performs phase-locked loop control and calculates the DC voltage from the positive and negative DC voltages. Upon receiving a grid-side voltage measurement anomaly indicator signal, it quickly switches the grid-side voltage to the grid-side voltage at the second measurement point, completing phase-locked calculations and other functions.

[0060] The grid-side voltage measurement anomaly determination unit performs a calculation on the grid-side voltage. If the grid-side voltage value is abnormal, it sends an abnormality indication signal to the inner current closed-loop control module and the algorithm control device switching module. This unit communicates with another system's grid-side voltage measurement anomaly determination unit using optical fiber, exchanging grid-side voltage amplitude signals between the two devices.

[0061] After the outer power closed-loop control unit is selected by the active power class and the reactive power class, it obtains the inner current closed-loop control reference value i required by the inner current closed-loop control unit. dref and i qref .

[0062] The inner loop current closed loop control unit obtains the d-axis component and q-axis component of the grid side voltage through dq transformation; obtains the d-axis component and q-axis component of the valve side current through dq transformation; after receiving the abnormal identification signal, the grid side voltage u sa ,u sb ,u sc Replaced with the grid-side voltage u of the second measuring point sa_2nd ,u sb_2nd ,u sc_2nd , in order to perform dq conversion and phase-locked loop control of the grid-side voltage, thereby meeting the requirements of inner current closed-loop control.

[0063] Figure 4 This is a structural block diagram of a grid-side voltage measurement abnormality discrimination algorithm provided by an embodiment of the present invention.

[0064] Figure 5 This is a structural block diagram of a grid-side voltage mutation detection algorithm provided by an embodiment of the present invention.

[0065] For further information, please refer to Figure 4 and Figure 5 The grid-side voltage measurement abnormality judgment unit obtains and judges, based on the grid-side voltage amplitude, a calculated value of the sudden change amount of the grid-side voltage amplitude, an absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the second measuring point, an absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the hot standby flexible DC system, and a grid-side voltage measurement abnormality judgment enabling state whether they meet a first preset condition. If the first preset condition is met, it is determined that the grid-side voltage measurement is abnormal and an abnormality identification signal is generated; if not, it is determined that the grid-side voltage measurement is normal.

[0066] The first precondition is that the following four conditions are met simultaneously:

[0067] 1) The calculated value of the sudden change of the grid-side voltage amplitude is greater than △1;

[0068] 2) The absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point is greater than △2;

[0069] 3) The absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the hot standby flexible DC system is greater than △2;

[0070] 4) The grid-side voltage measurement abnormality judgment enabling state is put into operation.

[0071] Specifically, △1, △2, and △3 are per-unit values based on the grid-side voltage. △1 is usually 0.05 pu, △2 is usually 0.18 pu, and △3 is usually 0.12 pu.

[0072] The grid-side voltage amplitude mutation detection algorithm determines whether there is a mutation by comparing the absolute value of the difference between the current voltage amplitude and the amplitude of the previous cycle, and the absolute value of the difference between the current voltage amplitude and the amplitude of the previous two cycles with △1 in the first preset condition.

[0073] Furthermore, the algorithm control module further includes an algorithm control device switching unit that is communicatively connected with corresponding algorithm control device switching units in other flexible DC system grid-side voltage measurement abnormality determination devices to transmit abnormality identification signals.

[0074] The algorithm control device switching unit communicates with the algorithm control device switching unit of another device using optical fiber to achieve device switching. When the grid-side voltage measurement anomaly identification device in the primary state receives a grid-side voltage measurement anomaly identification signal, it switches to another device if the other device is in hot standby mode. If the other device is not in hot standby mode, the system does not switch, and the primary device continues to operate.

[0075] Figure 6It is a logic diagram of a control method of a grid-side voltage measurement abnormality determination device provided by an embodiment of the present invention.

[0076] Accordingly, please refer to Figure 6 A second aspect of an embodiment of the present invention provides a method for controlling a grid-side voltage measurement abnormality determination device, which is used to control any of the above-mentioned grid-side voltage measurement abnormality determination devices, including the following steps:

[0077] S110: Obtain a grid-side voltage amplitude of the flexible DC system.

[0078] S120 , based on the grid-side voltage amplitude, obtaining a calculated value of a sudden change in the grid-side voltage amplitude, an absolute value of a difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point, and an absolute value of a difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the hot standby flexible DC system.

[0079] S130 , determining whether the calculated value of the sudden change amount, the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the second measuring point, the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the hot standby flexible DC system, and the grid-side voltage measurement abnormality determination enablement state meet a first preset condition.

[0080] The first precondition is that the following four conditions are met simultaneously:

[0081] 1) The calculated value of the sudden change of the grid-side voltage amplitude is greater than △1;

[0082] 2) The absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point is greater than △2;

[0083] 3) The absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the hot standby flexible DC system is greater than △2;

[0084] 4) The grid-side voltage measurement abnormality judgment enabling state is put into operation.

[0085] S140: If yes, it is determined that the grid-side voltage measurement is abnormal, and an abnormality identification signal is generated.

[0086] S150: If not, it is determined that the grid-side voltage measurement is normal.

[0087] Furthermore, in step S130, a calculated value of a sudden change in the grid-side voltage amplitude is obtained, specifically:

[0088] The grid-side voltage amplitude is subjected to a sudden change calculation, and the calculated sudden change value is the maximum of the first difference and the second difference. The first difference is the absolute value of the difference between the grid-side voltage amplitude of the current cycle and the grid-side voltage amplitude of the previous cycle, and the second difference is the absolute value of the difference between the grid-side voltage amplitude of the current cycle and the grid-side voltage amplitude of the previous two cycles.

[0089] Furthermore, in step S150, after determining that the grid-side voltage measurement is abnormal and generating an abnormality identification signal, the method further includes:

[0090] S161 , determining whether the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point, the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the hot standby flexible DC system, and the grid-side voltage measurement abnormality determination enablement state meet a second preset condition.

[0091] The second preset condition is to meet any of the following conditions:

[0092] 1) The absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point is less than △3;

[0093] 2) The absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude of the hot standby flexible DC system is less than △3;

[0094] 3) The grid-side voltage measurement abnormality judgment enabling state is exited.

[0095] S162: If yes, it is determined that the grid-side voltage amplitude has returned to normal, and the abnormal identification signal is reset.

[0096] S163: If not, it is determined that the grid-side voltage amplitude is still abnormal, and the abnormal identification signal is maintained.

[0097] Accordingly, a third aspect of an embodiment of the present invention provides a flexible DC system, comprising any of the above-mentioned switchable main grid-side voltage measurement abnormality determination device and hot standby grid-side voltage measurement abnormality determination device.

[0098] The main grid side voltage measurement abnormality judgment device obtains the abnormal identification signal and sends the abnormal identification signal to the hot standby grid side voltage measurement abnormality judgment device, the hot standby grid side voltage measurement abnormality judgment device switches to the main state, and at the same time switches the main grid side voltage measurement abnormality judgment device to the hot standby state.

[0099] The grid-side voltage measurement anomaly detection device is dual-configured. When both devices are operating normally, one is in primary mode and the other in hot standby mode. When the other device is not in hot standby mode, the two devices cannot switch, and the primary device operates independently.

[0100] In addition, when the flexible DC system includes a main grid-side voltage measurement abnormality judgment device and a hot standby grid-side voltage measurement abnormality judgment device that can be switched with each other, the judgment criterion of the first preset condition further includes: whether the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude in another device is greater than △2 in the first preset condition; similarly, the judgment criterion of the second preset condition further includes: whether the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude in another device is less than △3 in the second preset condition.

[0101] Figure 7 It is a logic diagram of the flexible DC system control method provided by an embodiment of the present invention.

[0102] Accordingly, please refer to Figure 7 A fourth aspect of an embodiment of the present invention provides a flexible DC system control method for controlling the flexible DC system, comprising the following steps:

[0103] S210 , when the main grid-side voltage measurement abnormality determination device in the flexible DC system generates an abnormality identification signal, the grid-side voltage is replaced with the grid-side voltage of the second measuring point.

[0104] S220 , determining whether the communication between the active grid-side voltage measurement abnormality determination device and the hot standby grid-side voltage measurement abnormality determination device is normal.

[0105] S230, if yes, then switch the main grid-side voltage measurement abnormality judgment device and the hot standby grid-side voltage measurement abnormality judgment device, and then use the grid-side voltage in the hot standby grid-side voltage measurement abnormality judgment device as the voltage feedforward required for the inner loop current closed-loop control, and continue normal operation.

[0106] S240: If not, the operation state of the main grid side voltage measurement abnormality determination device is maintained, and the grid side voltage of the second measuring point is used as the voltage feedforward amount required for the inner loop current closed-loop control, and normal operation is continued.

[0107] The embodiment of the present invention aims to protect a grid-side voltage measurement abnormality judgment device, a flexible DC system and a control method. The grid-side voltage measurement abnormality judgment device includes: an electrical quantity acquisition module to obtain the electrical quantity signal of the flexible DC system, and sends the digital signal obtained after the electrical quantity signal is converted from digital to analog to the algorithm control module. The electrical quantity signal includes: grid-side voltage, grid-side current, valve-side current, DC voltage and second-measurement-point grid-side voltage; the algorithm control module receives the digital signal, performs judgment operation on the grid-side voltage, and replaces the grid-side voltage with the second-measurement-point grid-side voltage when the grid-side voltage value is abnormal, and at the same time starts the switching of the grid-side voltage measurement abnormality judgment device to perform dq transformation and phase-locked loop control of the grid-side voltage, thereby meeting the inner-loop current closed-loop control requirements. The above technical solution has the following effects:

[0108] After quickly judging that the grid-side voltage is abnormal, a grid-side voltage abnormality identification signal is given, the grid-side voltage is quickly switched to the grid-side voltage of the second measuring point, and the grid-side voltage measurement abnormality judgment device is started to switch, thereby ensuring the normal and stable operation of the flexible DC system and improving the stability and reliability of the flexible DC system.

[0109] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A device for determining abnormality in grid-side voltage measurement, characterized in that: include: Electrical quantity acquisition module and algorithm control module; The electrical quantity acquisition module acquires electrical quantity signals of the flexible DC system and sends digital signals obtained by digital-to-analog conversion of the electrical quantity signals to the algorithm control module, wherein the electrical quantity signals include: grid-side voltage, grid-side current, valve-side current, DC voltage, and grid-side voltage of the second measuring point; The algorithm control module receives the digital signal, performs a judgment operation on the grid-side voltage, and replaces the grid-side voltage with the grid-side voltage of the second measuring point when the grid-side voltage value is abnormal, so as to perform dq conversion and phase-locked loop control of the grid-side voltage, thereby meeting the inner current closed-loop control requirements; The algorithm control module includes: an electrical quantity calculation unit communicating via a backplane bus, a grid-side voltage measurement abnormality determination unit, an outer power closed-loop control unit, and an inner current closed-loop control unit; The electrical quantity calculation unit receives the digital signal and performs per-unit calculation on it, calculates the voltage amplitude and grid frequency based on the grid-side voltage, calculates the active power and reactive power based on the grid-side voltage and the grid-side current, and sends them to the grid-side voltage measurement abnormality judgment unit, the outer loop power closed-loop control unit, and the inner loop current closed-loop control unit, and simultaneously completes phase-locked loop control, and calculates the DC voltage based on the positive and negative DC voltages; The grid-side voltage measurement abnormality determination unit performs a judgment operation on the grid-side voltage, and when the value of the grid-side voltage is abnormal, sends an abnormal identification signal to the inner-loop current closed-loop control module and the algorithm control device switching module; The outer power closed-loop control unit obtains the inner current closed-loop control reference value required by the inner current closed-loop control unit after selecting the active power category and the reactive power category; After receiving the abnormal identification signal, the inner current closed-loop control unit replaces the grid-side voltage with the grid-side voltage of the second measuring point to perform dq conversion and phase-locked loop control of the grid-side voltage, thereby meeting the inner current closed-loop control requirements.

2. The grid-side voltage measurement abnormality determination device according to claim 1, characterized in that: The electrical quantity acquisition module includes: a dielectric acquisition unit for collecting the grid-side voltage, grid-side current, and valve-side current of the flexible DC system; an optical medium acquisition unit for acquiring the DC voltage of the flexible DC system and the network-side voltage of the second measuring point; A digital-to-analog conversion unit receives the electrical quantity signals collected by the dielectric acquisition unit and the optical medium acquisition unit respectively, converts the electrical quantity signals into digital signals, and sends the digital signals to the algorithm control module.

3. The grid-side voltage measurement abnormality determination device according to claim 1, characterized in that: The grid-side voltage measurement abnormality determination unit obtains and determines, based on the grid-side voltage amplitude, whether a calculated value of a sudden change in the grid-side voltage amplitude, an absolute value of a difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point, and a grid-side voltage measurement abnormality determination enable state meet a first preset condition; if the first preset condition is met, the grid-side voltage measurement is determined to be abnormal and an abnormality identification signal is generated; if not, the grid-side voltage measurement is determined to be normal.

4. The grid-side voltage measurement abnormality determination device according to claim 1, characterized in that: The algorithm control module also includes: The algorithm control device switching unit is communicatively connected with the corresponding algorithm control device switching unit in the other flexible DC system grid-side voltage measurement abnormality determination device to transmit the abnormality identification signal.

5. A control method for a grid-side voltage measurement abnormality determination device, characterized in that: The device for determining abnormal grid-side voltage measurement according to any one of claims 1 to 4 comprises the following steps: Obtain the grid-side voltage amplitude of the flexible DC system; According to the grid-side voltage amplitude, obtaining a calculated value of a sudden change in the grid-side voltage amplitude and an absolute value of a difference between the grid-side voltage amplitude and the grid-side voltage amplitude at a second measuring point; Determining whether the calculated value of the mutation amount, the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point, and the grid-side voltage measurement abnormality determination enable state meet a first preset condition; If yes, it is determined that the grid-side voltage measurement is abnormal, and an abnormality identification signal is generated; If not, it is determined that the grid-side voltage measurement is normal.

6. The control method of the grid-side voltage measurement abnormality determination device according to claim 5, characterized in that: The obtaining of the calculated value of the sudden change amount of the grid-side voltage amplitude includes: Calculate the mutation amount of the grid-side voltage amplitude, wherein the mutation amount calculation value is the maximum value of the first difference and the second difference; The first difference is the absolute value of the difference between the grid-side voltage amplitude in the current cycle and the grid-side voltage amplitude in the previous cycle, and the second difference is the absolute value of the difference between the grid-side voltage amplitude in the current cycle and the grid-side voltage amplitudes in the previous two cycles.

7. The control method of the grid-side voltage measurement abnormality determination device according to claim 5, characterized in that: After determining that the grid-side voltage measurement is abnormal and generating an abnormality identification signal, the method further includes: Determining whether the absolute value of the difference between the grid-side voltage amplitude and the grid-side voltage amplitude at the second measuring point and the grid-side voltage measurement abnormality determination enable state meet a second preset condition; If yes, it is determined that the grid-side voltage amplitude has returned to normal, and the abnormal identification signal is reset; If not, it is determined that the grid-side voltage amplitude is still abnormal, and the abnormal identification signal is maintained.

8. A flexible DC system, characterized in that: It includes a grid-side voltage measurement abnormality determination device in a main state and a grid-side voltage measurement abnormality determination device in a hot standby state, wherein the grid-side voltage measurement abnormality determination device is the grid-side voltage measurement abnormality determination device according to any one of claims 1 to 4; The grid-side voltage measurement abnormality discrimination device in the master state obtains an abnormal identification signal and sends the abnormal identification signal to the grid-side voltage measurement abnormality discrimination device in the hot standby state, switches the grid-side voltage measurement abnormality discrimination device in the hot standby state to the master state, and at the same time switches the grid-side voltage measurement abnormality discrimination device in the master state to the hot standby state.

9. A flexible DC system control method, characterized in that: It is used to control the flexible DC system according to claim 8, comprising the following steps: When the abnormality identification device for measuring the main grid-side voltage in the flexible DC system generates an abnormality identification signal, the grid-side voltage is replaced with the grid-side voltage of the second measuring point; Determining whether the communication between the active grid-side voltage measurement abnormality determination device and the hot standby grid-side voltage measurement abnormality determination device is normal; If so, the main grid-side voltage measurement abnormality determination device and the hot standby grid-side voltage measurement abnormality determination device are switched, and the grid-side voltage in the hot standby grid-side voltage measurement abnormality determination device is used as the voltage feedforward amount required for the inner current closed-loop control, and normal operation is continued; If not, the operating state of the main grid side voltage measurement abnormality determination device is maintained, and the grid side voltage of the second measuring point is used as the voltage feedforward amount required for the inner loop current closed-loop control, and normal operation is continued.

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