Impedance characteristic measurement method, circuit, device and system of flexible direct current power transmission grid

Abstract

This invention provides a method, circuit, device, and system for measuring the impedance characteristics of a flexible DC transmission network. The method specifically includes: generating current source amplitude information based on the power information of the grid connection point of the flexible DC transmission network under test; generating current source phase information based on the power information and the voltage phasor information of the grid connection point; and inputting the current source amplitude information and the current source phase information as current source power measurement signals to the flexible DC transmission network under test. This invention uses the magnitude and phase angle of the three-phase voltage at the grid connection point of the current source as input, and calculates the amplitude and phase angle of the current source current phasor based on the relationship between active and reactive power and voltage and current phasors. This eliminates the frequency deviation between the MMC-HVDC and the host computer, achieving phase synchronization between the host and slave computers while avoiding the influence of control loop response on the accuracy of MMC-HVDC impedance measurement.

Description

Technical Field

[0001] This invention relates to the field of power distribution network measurement, and specifically to a method, circuit, device, and system for measuring the impedance characteristics of a flexible DC transmission network. Background Technology

[0002] Modular multi-level converter based HVDC (MMC-HVDC) is capable of providing voltage and frequency support to weak power grids / passive systems, and is gradually becoming a new method for transmitting power from weak power grids / offshore wind power. However, some wind farms have experienced broadband oscillations when transmitting power via MMC-HVDC. Currently, impedance scanning is commonly used in engineering to obtain the impedance characteristics of the MMC-HVDC itself and the renewable energy units, and frequency domain analysis is used to reveal the mechanism of broadband oscillations in the transmission system.

[0003] When operating in islanded mode, the MMC-HVDC employs constant voltage / frequency control. Connected renewable energy units supply power to the MMC-HVDC system according to given active and reactive power commands via phase-locked loop (PLL) and current loop control. To obtain the impedance characteristics of the MMC-HVDC under various operating conditions in islanded mode, the renewable energy units need to be connected to the MMC-HVDC system to establish a steady-state operating point for a specific condition (given active and reactive power output). Then, harmonic current disturbances are injected into the system, and voltage disturbances are measured to obtain the impedance characteristics. For example... Figure 1 The diagram shows the primary circuit structure for impedance scanning in islanded mode of an MMC-HVDC system. CCS1 and CCS2 are both controlled current sources, used to establish specific operating conditions and inject sweep current, respectively. Existing sweep methods employ pre-calculated fixed amplitude and phase control of CCS1 to provide stable power output to the MMC-HVDC system. Disturbance currents of different frequencies are then injected into the system sequentially through CCS2. The voltage and current at the grid connection point are measured, and the MMC-HVDC impedance characteristics are obtained through post-processing.

[0004] Typical current-source power sources include phase-locked loop (PLL) and power control components. Directly using them as a CCS1 (Continuous Switching Center) will react to external disturbances, affecting the accuracy of MMC-HVDC impedance measurements. Therefore, an open-loop current source is needed to establish the steady-state operating point of the islanded system. This method works without significant problems in single-machine simulation systems, but in MMC-HVDC hardware-in-loop (HIL) simulation systems, multiple lower-level hardware devices are involved. The lack of clock synchronization between these devices and the inherent differences in their internal crystal oscillator frequencies cause a continuous widening of the phase difference between the MMC-HVDC voltage and the open-loop current source, resulting in a shift in the steady-state operating point and affecting the accuracy of impedance characteristic measurements.

[0005] To address the aforementioned issues, if the phase offset rate is limited, it can be corrected manually; alternatively, hardware modifications can be made by adding clock synchronization signals between simulation devices to achieve phase synchronization. However, both methods have certain limitations. The former is only applicable when the crystal oscillator frequencies of the simulation devices differ only slightly, and it is cumbersome and inefficient; the latter requires adding extra hardware circuitry and modifying the existing simulation system, increasing hardware costs. Therefore, current technologies have numerous drawbacks and shortcomings. Summary of the Invention

[0006] To address the problems of insufficient accuracy, cumbersome operation, complex circuitry, and high hardware cost in current impedance characteristic measurements, this invention provides the following technical solution:

[0007] In a first aspect, embodiments of the present invention provide a method for measuring the impedance characteristics of a flexible DC transmission network, comprising:

[0008] In response to a current source power disturbance termination signal, current source amplitude information is generated based on the power information of the grid connection point of the flexible DC transmission grid under test.

[0009] In response to the current source power disturbance termination signal, current source phase information is generated based on the power information and the voltage phasor information of the grid connection point;

[0010] The current source amplitude information and the current source phase information are used as current source power measurement signals and input to the flexible DC transmission network under test to measure the impedance characteristics of the flexible DC transmission network.

[0011] In a preferred embodiment, the power information includes active power data and reactive power data; the voltage phasor information at the grid connection point includes the phase angle data of the voltage phasor.

[0012] The process of generating current source amplitude information based on the power information of the grid connection point of the flexible DC transmission network under test includes:

[0013] The ratio of active power data to reactive power data at the grid connection point is calculated using the four-quadrant arctangent function to obtain the arctangent result of the active power data and reactive power data.

[0014] The current source amplitude information is generated based on the phase angle data of the voltage phasor and the arctangent result.

[0015] In a preferred embodiment, it further includes:

[0016] The arctangent result is input into a memory so that the memory latches the currently received arctangent result in response to the current source power disturbance end signal; wherein the memory continuously outputs the currently received arctangent result until the next adjacent current source power disturbance signal is received.

[0017] In a preferred embodiment, the power information includes active power data and reactive power data; the voltage phasor information at the grid connection point includes: phase angle data and amplitude data of the voltage phasor; generating current source phase information based on the power information and the voltage phasor information at the grid connection point includes:

[0018] The ratio of active power data to reactive power data at the grid connection point is calculated using the four-quadrant arctangent function to obtain the arctangent result of the active power data and reactive power data.

[0019] Current source phase information is generated based on the arctangent result.

[0020] In a preferred embodiment, generating current source phase information based on the arctangent result includes:

[0021] The cosine function is calculated on the arctangent result to generate the cosine result;

[0022] The cosine result and the magnitude data of the voltage phasor are multiplied together to obtain the multiplication result;

[0023] Calculate the ratio of the active power at the grid connection point to the multiplication result to generate current source phase information.

[0024] In a preferred embodiment, the power information includes active power data and reactive power data; before generating current source amplitude information based on the power information of the grid connection point of the flexible DC transmission network under test, the impedance characteristic measurement method further includes:

[0025] By comparing the reference active power data of the grid connection point with the active power data of the grid connection point, the open-loop control error data corresponding to the active power is eliminated.

[0026] By comparing the reference reactive power data of the grid connection point with the reactive power data of the grid connection point, the open-loop control error data corresponding to the reactive power is eliminated.

[0027] Secondly, embodiments of the present invention provide an impedance characteristic measurement circuit for a flexible DC transmission network, comprising:

[0028] The current source amplitude information generation module generates current source amplitude information in response to a current source power disturbance termination signal, based on the power information of the grid connection point of the flexible DC transmission grid under test.

[0029] The current source phase information generation module generates current source phase information in response to the current source power disturbance termination signal, based on the power information and the voltage phasor information of the grid connection point.

[0030] The current source power measurement module inputs the current source amplitude information and the current source phase information as current source power measurement signals to the flexible DC transmission network under test in order to measure the impedance characteristics of the flexible DC transmission network.

[0031] In a preferred embodiment, the power information includes active power data and reactive power data;

[0032] The current source amplitude information generation module includes:

[0033] The power information input line for the grid connection point is used to input the power information of the grid connection point;

[0034] The four-quadrant arctangent function calculator calculates the ratio of active power data to reactive power data at the grid connection point using the four-quadrant arctangent function, and obtains the arctangent result of the active power data and reactive power data.

[0035] The amplitude calculation unit, in response to the current source power disturbance termination signal, generates the current source amplitude information based on the phase angle data of the voltage phasor and the arctangent result.

[0036] In a preferred embodiment, it further includes:

[0037] The memory latches the currently received arctangent result in response to the current source power disturbance end signal; wherein the memory continuously outputs the currently received arctangent result until the next adjacent current source power disturbance signal is received; wherein the arctangent result received by the amplitude calculation unit at any time comes from either the memory or the four-quadrant arctangent function calculator.

[0038] In a preferred embodiment, the amplitude calculation unit includes:

[0039] A single-pole double-throw switch includes a moving terminal, a first stationary terminal, and a second stationary terminal. The first stationary terminal is coupled to the output terminal of the four-quadrant arctangent function calculator, and the second stationary terminal is coupled to the output terminal of the memory. In the initial state, the moving terminal is coupled to the second stationary terminal, and in response to the current source power disturbance end signal, it is switched to the first stationary terminal.

[0040] An amplitude calculator, coupled to the moving end, receives the arctangent result at any given time from either the memory or the four-quadrant arctangent function calculator.

[0041] In a preferred embodiment, the current source phase information generation module includes:

[0042] A cosine calculator, coupled to the moving end, performs cosine function calculation on the arctangent result to generate a cosine result;

[0043] The multiplier takes the cosine result and the magnitude data of the voltage phasor as input and outputs the multiplication result.

[0044] The divider takes the active power at the grid connection point and the multiplication result as input, and outputs the ratio of the active power at the grid connection point to the multiplication result, wherein the ratio of the active power at the grid connection point to the multiplication result is current source phase information.

[0045] In a preferred embodiment, it further includes:

[0046] The first open-loop control circuit compares the reference active power data at the grid connection point with the active power data at the grid connection point, and eliminates the open-loop control error data corresponding to the active power.

[0047] The second open-loop control circuit compares the reference reactive power data of the grid connection point with the reactive power data of the grid connection point, and eliminates the open-loop control error data corresponding to the reactive power.

[0048] Thirdly, embodiments of the present invention provide an impedance characteristic measurement device for a flexible DC transmission network, comprising:

[0049] The impedance characteristic measurement circuit for the flexible DC transmission network described above.

[0050] Fourthly, embodiments of the present invention provide an impedance characteristic measurement system for a flexible DC transmission network, comprising an impedance characteristic measurement device for a flexible DC transmission network as described above, a disturbance signal input circuit, and a flexible DC transmission network under test; the disturbance signal input circuit is used to generate a disturbance signal, and the impedance characteristic measurement device and the disturbance signal input circuit are connected in parallel to one end of the flexible DC transmission network.

[0051] As can be seen from the above technical solution, the present invention provides a method, circuit, device and system for measuring the impedance characteristics of a flexible DC transmission network. The present invention takes the magnitude and phase angle of the three-phase voltage at the grid connection point of the current source as input, and calculates the magnitude and phase angle of the current source current phasor based on the relationship between active and reactive power and voltage and current phasors. This eliminates the frequency deviation between the MMC-HVDC and the host computer, realizes phase synchronization between the host and slave computers, and avoids the influence of the control loop response on the accuracy of the MMC-HVDC impedance measurement. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of the structure of the MMC-HVDC impedance scanning circuit in the prior art of this invention.

[0054] Figure 2 This is a flowchart illustrating the impedance characteristic measurement method of a flexible DC transmission network in an embodiment of the present invention.

[0055] Figure 3 This is an embodiment of the present invention. Figure 2 The detailed flowchart of step S1 is shown below.

[0056] Figure 4 This is an embodiment of the present invention. Figure 2 The detailed flowchart of step S2 is shown below.

[0057] Figure 5 This is an embodiment of the present invention. Figure 4 The detailed flowchart of step S22 is shown below.

[0058] Figure 6 This is a schematic diagram of the error calculation method in the impedance characteristic measurement method of the flexible DC transmission network in this embodiment of the invention.

[0059] Figure 7 This is a schematic flowchart of the impedance characteristic measurement circuit of the flexible DC transmission network in an embodiment of the present invention.

[0060] Figure 8 This is a schematic diagram of harmonic injection and trigger signals at each stage in an embodiment of the present invention.

[0061] Figure 9 This is a schematic diagram of the power offset phenomenon during HIL impedance scanning in an embodiment of the present invention.

[0062] Figure 10 This is a schematic diagram illustrating the power offset situation using a latching and state switching strategy in an embodiment of the present invention.

[0063] Figure 11 This is a schematic diagram of the impedance characteristic measurement circuit of the flexible DC transmission network in an embodiment of the present invention.

[0064] Figure 12 This is an embodiment of the present invention. Figure 11 A schematic diagram of the current source amplitude information generation module. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0066] This invention first provides a method for measuring the impedance characteristics of a flexible DC transmission network, such as... Figure 2 As shown, it includes:

[0067] S1: In response to a current source power disturbance termination signal, generate current source amplitude information based on the power information of the grid connection point of the flexible DC transmission grid under test;

[0068] S2: In response to the current source power disturbance termination signal, generate current source phase information based on the power information and the voltage phasor information of the grid connection point;

[0069] S3: Input the current source amplitude information and the current source phase information as current source power measurement signals to the flexible DC transmission network under test to measure the impedance characteristics of the flexible DC transmission network.

[0070] As can be seen from the above description, the impedance characteristic measurement method for flexible DC transmission networks provided by the embodiments of the present invention takes the magnitude and phase angle of the three-phase voltage at the grid connection point of the current source as input, and calculates the magnitude and phase angle of the current source current phasor based on the relationship between active and reactive power and voltage and current phasors. This eliminates the frequency deviation between the MMC-HVDC and the host computer, realizes phase synchronization between the host and slave computers, and avoids the influence of the control loop response on the accuracy of the MMC-HVDC impedance measurement.

[0071] The embodiments of the present invention will be described in detail below. In the present invention, the current source power disturbance signal is obtained through, as follows: Figure 1The MMC-HVDC impedance scanning circuit shown uses CCS2 input. Under the feedback of the disturbance signal input by CCS2, the CCS1 circuit generates current source amplitude information based on the power information of the grid connection point of the flexible DC transmission network under test. Specifically, the flexible DC transmission network under test is... Figure 1 The impedance characteristics of the MMC-HVDC are measured using CCS1.

[0072] Existing technologies generate pre-calculated fixed amplitude and phase using CCS1. The difference with this invention is that the amplitude and phase generated by this invention are not fixed, and it does not use the methods of existing technologies. This invention generates current source amplitude information based on the power information of the grid connection point of the flexible DC transmission network under test, and generates current source phase information based on the power information and the voltage phasor information of the grid connection point.

[0073] Specifically, the power information mentioned in this invention includes active power data and reactive power data; the voltage phasor information of the grid connection point includes the phase angle data of the voltage phasor.

[0074] Those skilled in the art will understand that active power refers to the actual alternating current energy generated or consumed per unit time; it is the average power over a period. Reactive power, on the other hand, refers to the energy absorbed from the power source by the electric or magnetic field in an AC circuit with reactance during a portion of a period, and released during another portion. The average power is zero over the entire period, but energy is continuously exchanged between the power source and reactive components (capacitors, inductors). The maximum value of this exchange rate is called "reactive power."

[0075] It can be understood that for the AC circuit of the present invention, reactive power is equal to the sum of the products of the effective voltage value, the effective current value, and the power factor of each of the three phases; active power is equal to the product of the effective voltage value, the effective current value, and the sine of the phase angle between voltage and current.

[0076] Specifically, such as Figure 3 As shown, step S1 specifically includes:

[0077] S11: Calculate the ratio of active power data to reactive power data at the grid connection point using the four-quadrant arctangent function to obtain the arctangent result of the active power data and reactive power data.

[0078] Specifically, atan2 (active power, reactive power data) can be understood as follows: the four-quadrant arctangent function calculation can be implemented by an MCU or PID logic circuit. Furthermore, any device with certain processing capabilities can be used to perform the four-quadrant arctangent function of this invention, but this invention is not limited to these.

[0079] S12: Generate the current source amplitude information based on the phase angle data of the voltage phasor and the arctangent result.

[0080] Specifically, the phase angle data of the voltage phasor can be obtained by sampling the voltage at the grid connection point and then performing a Clarke transform to calculate the amplitude and phase of the voltage phasor.

[0081] Furthermore, the measurement method in this embodiment of the invention also includes:

[0082] S4: Input the arctangent result into a memory, so that the memory latches the currently received arctangent result in response to the current source power disturbance end signal; wherein the memory continuously outputs the currently received arctangent result until the next adjacent current source power disturbance signal is received.

[0083] In this embodiment, the memory can latch the signal in response to the disturbance signal. In some embodiments, the disturbance signal is as follows: Figure 8 As shown, the injection of disturbance signals in CCS2 can generally be divided into the following stages: disturbance injection stage, data recording stage, and calming stage. After the disturbance is injected, the system needs to stabilize; therefore, the data recording stage overlaps somewhat with the disturbance stage. For example... Figure 8 I abc The system is configured to inject a disturbance signal into CCS2; Disturbance is the disturbance injection flag; Record is the data recording flag; and Stable is the system reset flag. After the disturbance signal, the system resets to a high level. The memory can latch upon receiving this high level and continuously output the currently received arctangent result until the next adjacent current source power disturbance signal is received.

[0084] In a specific embodiment, the purpose of the memory is to continuously output the previous arctangent result, thereby achieving the purpose of continuous measurement.

[0085] In a preferred embodiment, such as Figure 4 As shown, step S2 specifically includes:

[0086] S21: Calculate the ratio of active power data to reactive power data at the grid connection point using the four-quadrant arctangent function to obtain the arctangent results of the active power data and reactive power data.

[0087] The arctangent function calculation in this step is shown above. Specifically, it is atan2 (active power, reactive power data). It can be understood that the four-quadrant arctangent function calculation can be implemented by MCU or PID logic circuit. Furthermore, any device with certain processing capabilities can be used to perform the four-quadrant arctangent function of this invention. This invention is not limited to these.

[0088] S22: Generate current source phase information based on the arctangent result.

[0089] In some embodiments, such as Figure 5 As shown, this step specifically includes:

[0090] S221: Calculate the cosine function on the arctangent result to generate a cosine result.

[0091] The cosine function can be calculated immediately using an MCU or PID logic circuit. Furthermore, any device with a certain processing capability can be used to perform the cosine function calculation of this invention, but this invention is not limited thereto.

[0092] The calculation of the cosine function is the same as the calculation of the y = cosx function, that is, the cosine result = cos(arctangent result).

[0093] S222: Multiply the cosine result and the magnitude data of the voltage phasor to obtain the multiplication result.

[0094] In this step, the amplitude data of the voltage phasor is the aforementioned Vmag, which is obtained by performing Clarke transformation on the grid-connected voltage.

[0095] Similar to the arctangent function calculation and cosine calculation described above, the multiplication calculation of this invention can also be implemented by an MCU or PID circuit, which will not be elaborated here.

[0096] S223: Calculate the ratio of the active power at the grid connection point to the multiplication result, and generate current source phase information.

[0097] In this step, the phase information of the current source of the present invention is obtained by division calculation.

[0098] Specifically, the calculation method is as follows:

[0099] First, the following relationship exists from the three-phase power calculation formula, where V mag I mag Let θ be the voltage and current vectors, θ be the power factor angle, and P and Q be the active and reactive power, respectively. Here, P and Q represent P0 and P1, respectively. ref -P meas With Q ref -Q meas The value calculated by the PI module

[0100] P = V mag I mag cos(θ) (1)

[0101] Q = V mag I mag sin(θ) (2)

[0102]

[0103] Assuming the grid voltage vector V (including voltage amplitude V) is known mag Given the phase θ0 and the active power P and reactive power Q to be injected into the system, the process of determining the current vector (including amplitude and phase) of the injected system is as follows:

[0104] The phase between the current and the grid voltage can be obtained using the atan2 function:

[0105] θ=atan2(X,Y)=atan2(P,Q) (4)

[0106] Then, use formula (1) to calculate the injection current amplitude:

[0107]

[0108] Then I phase =θ0+θ is the phase angle driving the CCS1 current source, I mag This is the amplitude of the current source driving CCS1.

[0109] Furthermore, in a preferred embodiment, such as Figure 6 As shown, the present invention also includes:

[0110] S01: Compare the reference active power data of the grid connection point with the active power data of the grid connection point, and eliminate the open-loop control error data corresponding to the active power.

[0111] S02: Compare the reference reactive power data of the grid connection point with the reactive power data of the grid connection point, and eliminate the open-loop control error data corresponding to the reactive power.

[0112] The measurement error of the present invention can be further reduced by using the above-mentioned open-loop control error data. Specifically, the open-loop control error can be eliminated by using a PI controller.

[0113] As can be seen from the above technical solution, the impedance characteristic measurement method of the flexible DC transmission network provided by the present invention takes the magnitude and phase angle of the three-phase voltage at the grid connection point of the current source as input, and calculates the magnitude and phase angle of the current source current phasor based on the relationship between active and reactive power and voltage and current phasors. This eliminates the frequency deviation between the MMC-HVDC and the host computer, realizes phase synchronization between the host and slave computers, and avoids the influence of the control loop response on the accuracy of the MMC-HVDC impedance measurement.

[0114] The present invention further provides a circuit for implementing the above measurement method, please refer to... Figure 11 As shown, the measurement circuit of the present invention includes:

[0115] The current source amplitude information generation module 1 generates current source amplitude information in response to a current source power disturbance termination signal, based on the power information of the grid connection point of the flexible DC transmission grid under test.

[0116] The current source phase information generation module 2, in response to the current source power disturbance end signal, generates current source phase information based on the power information and the voltage phasor information of the grid connection point;

[0117] The current source power measurement module 3 inputs the current source amplitude information and the current source phase information as current source power measurement signals to the flexible DC transmission network under test in order to measure the impedance characteristics of the flexible DC transmission network.

[0118] This invention provides an impedance characteristic measurement circuit for a flexible DC transmission network. It takes the magnitude and phase angle of the three-phase voltage at the grid connection point of the current source as input, and calculates the magnitude and phase angle of the current source phasor based on the relationship between active and reactive power and voltage and current phasors. This eliminates the frequency deviation between the MMC-HVDC and the host computer, achieves phase synchronization between the host and slave computers, and avoids the influence of the control loop response on the accuracy of the MMC-HVDC impedance measurement.

[0119] The following is combined Figures 7 to 10 The measurement circuit of the present invention will be described in detail.

[0120] In this invention, the current source power disturbance signal is obtained through, as follows: Figure 1 The MMC-HVDC impedance scanning circuit shown uses CCS2 input. Under the feedback of the disturbance signal input by CCS2, the CCS1 circuit generates current source amplitude information based on the power information of the grid connection point of the flexible DC transmission network under test. Specifically, the flexible DC transmission network under test is... Figure 1 The impedance characteristics of the MMC-HVDC are measured using CCS1.

[0121] As can be understood from the above embodiments, the power information includes active power data and reactive power data. Meanwhile, the phase angle data of the voltage phasor can be obtained by sampling the voltage at the grid connection point and calculating the amplitude and phase of the voltage phasor after Clarke transformation.

[0122] like Figure 12 As shown, the current source amplitude information generation module includes:

[0123] The power information input line 21 of the grid connection point is used to input the power information of the grid connection point (in the figure, Pref is the reference active power, Pmeas is the measured active power, Qref is the reference reactive power, and Qmeas is the measured reactive power).

[0124] The four-quadrant arctangent function calculator 22 calculates the ratio of active power data to reactive power data at the grid connection point using the four-quadrant arctangent function to obtain the arctangent result of the active power data and reactive power data.

[0125] The amplitude calculation unit 23, in response to the current source power disturbance termination signal, generates the current source amplitude information based on the phase angle data of the voltage phasor and the arctangent result.

[0126] Specifically, the four-quadrant arctangent function, also known as atan2 (active power, reactive power data), can be understood as a four-quadrant arctangent function calculator that can be an MCU or a PID logic circuit. Furthermore, any device with a certain processing capability can be used as the four-quadrant arctangent function calculator of this invention, but this invention is not limited to these.

[0127] Please continue to combine Figure 7 The measurement circuit of the present invention further includes:

[0128] The memory 24 latches the currently received arctangent result in response to the current source power disturbance end signal; wherein the memory continuously outputs the currently received arctangent result until the next adjacent current source power disturbance signal is received; wherein the arctangent result received by the amplitude calculation unit at any time comes from either the memory or the four-quadrant arctangent function calculator.

[0129] Furthermore, in this embodiment, please continue to combine Figure 7 The amplitude calculation unit includes:

[0130] The single-pole double-throw switch 25 includes a moving terminal (the right terminal in the figure), a first stationary terminal (the upper left terminal in the figure), and a second stationary terminal (the lower left terminal in the figure). The first stationary terminal is coupled to the output terminal of the four-quadrant arctangent function calculator 23, and the second stationary terminal is coupled to the output terminal of the memory 24. In the initial state, the moving terminal is coupled to the second stationary terminal, and in response to the current source power disturbance end signal, it is switched to the first stationary terminal.

[0131] Amplitude calculator 26, coupled to the moving end, receives the arctangent result at any given time from either the memory or the four-quadrant arctangent function calculator.

[0132] In addition, the current source phase information generation module includes:

[0133] Cosine calculator 27, coupled to the moving end, performs cosine function calculation on the arctangent result to generate a cosine result;

[0134] Multiplier 28 takes the cosine result and the magnitude data of the voltage phasor as input, and outputs the multiplication result;

[0135] Divider 29 takes the active power at the grid connection point and the multiplication result as input, and outputs the ratio of the active power at the grid connection point to the multiplication result, wherein the ratio of the active power at the grid connection point to the multiplication result is current source phase information.

[0136] Specifically, the phase information of the current source of this invention can be obtained through division.

[0137] Specifically, the calculation method is as follows:

[0138] First, the following relationship exists from the three-phase power calculation formula, where V mag I mag Let θ be the voltage and current vectors, θ be the power factor angle, and P and Q be the active and reactive power, respectively. Here, P and Q represent P0 and P1, respectively. ref -P meas With Q ref -Q meas The value calculated by the PI module

[0139] P = V mag I mag cos(θ) (1)

[0140] Q = V mag I mag sin(θ) (2)

[0141]

[0142] Assuming the grid voltage vector V (including voltage amplitude V) is known mag Given the phase θ0 and the active power P and reactive power Q to be injected into the system, the process of determining the current vector (including amplitude and phase) of the injected system is as follows:

[0143] The phase between the current and the grid voltage can be obtained using the atan2 function:

[0144] θ=atan2(X,Y)=atan2(P,Q) (4)

[0145] Then, use formula (1) to calculate the injection current amplitude:

[0146]

[0147] Then I phase =θ0+θ is the phase angle driving the CCS1 current source, I mag This is the amplitude of the current source driving CCS1.

[0148] It is understood that the multipliers and dividers mentioned above can be calculated using MCU or PID logic circuits, and will not be elaborated further in this invention.

[0149] Furthermore, the measurement circuit of the present invention also includes:

[0150] The first open-loop control circuit (PI controller 22 located at the top in the figure) compares the reference active power data of the grid connection point with the active power data of the grid connection point, and eliminates the open-loop control error data corresponding to the active power.

[0151] The second open-loop control circuit (PI controller 22 located at the bottom in the figure) compares the reference reactive power data of the grid connection point with the reactive power data of the grid connection point, and eliminates the open-loop control error data corresponding to the reactive power.

[0152] By utilizing the aforementioned open-loop control error data, this invention can further reduce the measurement error. It is understood that both the first and second open-loop control circuits can be PI controllers.

[0153] Initially, the single-pole double-throw switch 25 is connected to the memory 24 and the cosine calculator 27. After receiving the disturbance signal end signal, the single-pole double-throw switch switches to the atant2 calculator 23 for amplitude calculation. Similarly, the single-pole double-throw switch 31 performs cosine, multiplication, and division calculations on the arctangent result, which is then latched in the memory 30 and continuously output. The memory 30 unlocks the latch in response to the disturbance end signal, and the single-pole double-throw switch 31 switches between the output of the memory 30 and the result of the divider. The single-pole double-throw switch 31 then outputs the current source phase information in response to the disturbance end signal.

[0154] The circuit operation process of the present invention will be described in detail below.

[0155] Please combine Figure 7 As shown, the present invention first samples the grid connection point voltage to obtain v. abc Then, after Clarke transformation, the magnitude and phase angle of the voltage phasor are calculated, i.e., V. mag and V phase .

[0156] Then the active power P measured at the grid connection point meas and reactive power Q measThe power information is input into the circuit via the grid connection point's input line. After error elimination using the reference active and reactive power by the PI control circuit of the aforementioned circuit, the data is input to the atant2 calculator. The memory responds to the system calming flag signal after the disturbance signal ends. When the disturbance signal ends, latch_trig is the storage module drive signal, valid on the rising edge. When an input rising edge is detected, the Mem module stores the input at that moment and continuously outputs it until the next latch_trig rising edge is detected. sync is the single-pole double-throw switch drive signal, level-driven; when sync = 0, the lower terminal is connected; when sync = 1, the upper terminal is connected. sync can be used to switch the input arctangent result, followed by cosine, multiplication, and division calculations to obtain the current source phase information.

[0157] Generally, the injection of disturbance signals in CCS2 can be divided into the following stages: disturbance injection stage, data recording stage, and calming stage. After the disturbance is injected, the system needs to stabilize; therefore, the data recording stage overlaps somewhat with the disturbance stage. For example... Figure 8 As shown, I abc The disturbance signal to be injected into CCS2; Disturbance is the disturbance injection flag; Record is the data recording flag; Stable is the system calming flag, and the memory and single-pole double-throw switch respond to the high level of the stable signal.

[0158] Here, the stable trig is used as the input to both the latch_trig and sync signals. After the disturbance injection ends, the sync port detects a high level on the stable trig and connects its upper terminal. The current source is in a controlled state. After the smoothing process ends, the latch_trig detects a falling edge on the stable trig and latches the amplitude and phase of the current source in the controlled state. The sync input port goes low, and the sync terminal is connected, using the latched amplitude and phase to perform open-loop control of CCS1.

[0159] Generally, in an MMC-HVDC in-loop simulation system, there is a frequency deviation between the MMC-HVDC and the host computer. Without closed-loop control, the active and reactive power will change due to the phase shift of the CCS1 injected current. Figure 9 The diagram shows a frequency sweep process without the method of this invention. It can be seen that both active and reactive power shift significantly over time. Figure 10 This shows the effect after applying this method. As you can see, the offset only occurs within each frequency point and does not accumulate.

[0160] Based on the same inventive concept, the present invention further provides an impedance characteristic measuring device for a flexible DC transmission network, including the aforementioned impedance characteristic measuring circuit for a flexible DC transmission network.

[0161] In some embodiments, the measuring device of the present invention may further include a housing in which the aforementioned impedance characteristic measuring circuit of the flexible DC transmission network is built.

[0162] As can be seen from the above technical solution, the impedance characteristic measurement device for a flexible DC transmission network provided by the present invention takes the magnitude and phase angle of the three-phase voltage at the grid connection point of the current source as input, and calculates the magnitude and phase angle of the current source current phasor based on the relationship between active and reactive power and voltage and current phasors. This eliminates the frequency deviation between the MMC-HVDC and the host computer, realizes phase synchronization between the host and slave computers, and avoids the influence of the control loop response on the accuracy of the MMC-HVDC impedance measurement.

[0163] Furthermore, the present invention provides an impedance characteristic measurement system for a flexible DC transmission network, comprising the aforementioned impedance characteristic measurement device for a flexible DC transmission network, a disturbance signal input circuit, and a flexible DC transmission network under test; the disturbance signal input circuit is used to generate a disturbance signal, and the impedance characteristic measurement device and the disturbance signal input circuit are connected in parallel to one end of the flexible DC transmission network.

[0164] In this embodiment, as Figure 1 As shown, the impedance characteristic measurement device for the flexible DC transmission network is CCS1, the disturbance signal input circuit is CCS2, and the flexible DC transmission network under test is the MMC-HVDC module.

[0165] As can be seen from the above technical solution, the impedance characteristic measurement system of the flexible DC transmission network provided by the present invention takes the magnitude and phase angle of the three-phase voltage at the grid connection point of the current source as input, and calculates the magnitude and phase angle of the current source current phasor based on the relationship between active and reactive power and voltage and current phasors. This eliminates the frequency deviation between the MMC-HVDC and the host computer, realizes phase synchronization between the host and slave computers, and avoids the influence of the control loop response on the accuracy of the MMC-HVDC impedance measurement.

[0166] Specific embodiments have been used to illustrate the principles and implementation methods of this invention. The descriptions of the embodiments above are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method of impedance characteristic measurement of a flexible HVDC power transmission grid, characterized by, The method comprises the following steps: in response to a current source power disturbance end signal, generating current source amplitude information according to power information of a grid-connected point of a flexible direct current power transmission grid to be tested; wherein the current source is used to inject a sweep frequency current; in response to the current source power disturbance end signal, generating current source phase information according to the power information and voltage phasor information of the grid-connected point; inputting the current source amplitude information and the current source phase information as current source power measurement signals to the flexible direct current power transmission grid to be tested, so as to measure impedance characteristics of the flexible direct current power transmission grid and eliminate frequency deviation between the MMC-HVDC and the upper computer; wherein the power information comprises active power data and reactive power data; before generating the current source amplitude information according to the power information of the grid-connected point of the flexible direct current power transmission grid to be tested, the impedance characteristic measurement method further comprises the following steps: comparing reference active power data of the grid-connected point with the active power data of the grid-connected point to eliminate open-loop control error data corresponding to the active power; comparing reference reactive power data of the grid-connected point with the reactive power data of the grid-connected point to eliminate open-loop control error data corresponding to the reactive power.

2. The method of impedance characteristic measurement of a flexible HVDC power transmission grid according to claim 1, characterized in that, The power information comprises active power data and reactive power data; and the voltage phasor information of the grid-connected point comprises amplitude data of the voltage phasor; The step of generating the current source amplitude information according to the power information of the grid-connected point of the flexible direct current power transmission grid to be tested comprises the following steps: performing four-quadrant arctangent function calculation on a ratio of the active power data to the reactive power data of the grid-connected point to obtain arctangent results of the active power data and the reactive power data; generating the current source amplitude information according to the amplitude data of the voltage phasor and the arctangent results.

3. The method of impedance characteristic measurement of a flexible HVDC power transmission grid according to claim 2, characterized in that, The method further comprises the following steps: inputting the arctangent results into a storage device, so that the storage device latches the currently received arctangent results in response to the current source power disturbance end signal; wherein the storage device continuously outputs the currently received arctangent results until the next adjacent current source power disturbance signal is received.

4. The method of impedance characteristic measurement of a flexible HVDC power grid according to claim 1, characterized in that, The power information comprises active power data and reactive power data; the voltage phasor information of the grid-connected point comprises phase angle data and amplitude data of the voltage phasor; and the step of generating the current source phase information according to the power information and the voltage phasor information of the grid-connected point comprises the following steps: performing four-quadrant arctangent function calculation on a ratio of the active power data to the reactive power data of the grid-connected point to obtain arctangent results of the active power data and the reactive power data; generating the current source phase information according to the phase angle data of the voltage phasor and the arctangent results.

5. The method of impedance characteristic measurement of a flexible HVDC power grid according to claim 4, characterized in that, The step of generating the current source amplitude information according to the arctangent results comprises the following steps: performing cosine function calculation on the arctangent results to generate cosine results; performing multiplication calculation on the cosine results and the amplitude data of the voltage phasor to obtain multiplication results; calculating a ratio of the active power of the grid-connected point to the multiplication results to generate the current source amplitude information.

6. An impedance characteristic measurement circuit of a flexible HVDC power transmission grid, characterized by The method comprises the following steps: The current source amplitude information generation module generates current source amplitude information according to power information of a grid-connected point of the flexible direct current power transmission grid in response to a current source power disturbance end signal; wherein the current source is used to inject a sweep frequency current; The current source phase information generation module generates current source phase information according to the power information and voltage phasor information of the grid-connected point in response to the current source power disturbance end signal; The current source power measurement module inputs the current source amplitude information and the current source phase information as current source power measurement signals into the flexible direct current power transmission grid to measure impedance characteristics of the flexible direct current power transmission grid, and eliminate frequency deviation between the MMC-HVDC and the upper computer; The impedance characteristic measurement circuit of the flexible direct current power transmission grid further comprises: The first open-loop control circuit compares reference active power data of the grid-connected point with active power data of the grid-connected point to eliminate open-loop control error data corresponding to the active power; The second open-loop control circuit compares reference reactive power data of the grid-connected point with reactive power data of the grid-connected point to eliminate open-loop control error data corresponding to the reactive power.

7. The impedance characteristic measurement circuit of a flexible HVDC power grid according to claim 6, characterized in that, The power information comprises active power data and reactive power data; The current source amplitude information generation module comprises: A power information input line of the grid-connected point is used to input power information of the grid-connected point; A four-quadrant arctangent function calculator performs four-quadrant arctangent function calculation on a ratio of the active power data to the reactive power data of the grid-connected point to obtain an arctangent result of the active power data to the reactive power data; An amplitude calculation unit generates the current source amplitude information according to amplitude data of the voltage phasor and the arctangent result in response to the current source power disturbance end signal.

8. The impedance characteristic measurement circuit of a flexible HVDC power grid according to claim 7, characterized in that, Further comprising: A memory latches the currently received arctangent result in response to the current source power disturbance end signal; wherein the memory continuously outputs the currently received arctangent result until an adjacent next current source power disturbance signal is received; wherein the arctangent result received by the amplitude calculation unit at any time is from one of the memory and the four-quadrant arctangent function calculator.

9. The impedance characteristic measurement circuit of a flexible HVDC power grid according to claim 8, characterized in that, The amplitude calculation unit comprises: A single-pole double-throw switch comprises a moving terminal, a first stationary terminal and a second stationary terminal, the first stationary terminal is coupled to an output terminal of the four-quadrant arctangent function calculator, the second stationary terminal is coupled to an output terminal of the memory, the moving terminal is coupled to the second stationary terminal in an initial state, and is switched to be coupled to the first stationary terminal in response to the current source power disturbance end signal; An amplitude calculator is coupled to the moving terminal, and thus receives the arctangent result from one of the memory and the four-quadrant arctangent function calculator at any time.

10. The impedance characteristic measurement circuit of a flexible HVDC power grid according to claim 9, characterized in that, The current source amplitude information generation module comprises: A cosine calculator is coupled to the moving terminal, performs cosine function calculation on the arctangent result to generate a cosine result; A multiplier inputs the cosine result and amplitude data of the voltage phasor, and outputs a multiplication result; A divider, inputting the grid-connected point active power and the multiplication result, outputting a ratio of the grid-connected point active power and the multiplication result, wherein the ratio of the grid-connected point active power and the multiplication result is the current source amplitude information.

11. Impedance characteristic measuring device for a flexible HVDC power transmission grid, characterized by Comprising: Impedance characteristic measurement circuit of flexible direct current power transmission grid according to any one of claims 6-10.

12. A system for measuring impedance characteristics of a flexible HVDC power transmission grid, characterized by Impedance characteristic measurement device of flexible direct current power transmission grid according to claim 11, a disturbance signal input circuit for generating a disturbance signal, and a flexible direct current power transmission grid to be measured, wherein the impedance characteristic measurement device and the disturbance signal input circuit are connected in parallel at one end of the flexible direct current power transmission grid.

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