Broadband high-voltage direct-current side impedance characteristic measuring device and control method thereof

Abstract

The invention discloses a broadband high-voltage direct-current side impedance characteristic measuring device and a control method thereof. A direct-current voltage control module is used for generating a direct-current voltage instruction value; the harmonic current control module is used for generating a harmonic voltage instruction value; the starting control module is used for charging the half-bridge MMC module group and the full-bridge MMC module group in sequence by taking the sum of the direct-current voltage instruction value and the harmonic voltage instruction value as an output voltage instruction value, and enabling the output voltage of the half-bridge MMC module group to reach the output voltage instruction value after charging is completed; the valve-level modulation control module is used for generating modulation waves of the full-bridge MMC module group according to the harmonic voltage instruction value, so that the full-bridge MMC module group outputs harmonic current; after the harmonic current is injected into the tested equipment, harmonic voltages of the tested equipment at different frequencies are obtained, and the impedance characteristic of the broadband high-voltage direct current side is determined by using the harmonic current and the harmonic voltages. The harmonic control precision is improved, the cost is saved, the equipment structure is simplified, and the method is suitable for impedance measurement in a high-voltage direct-current scene.

Description

Technical Field

[0001] The present invention belongs to the technical field of impedance characteristic measurement of high - medium voltage DC micro - grid. Specifically, it relates to a new topology and control method for a wide - band DC - side impedance characteristic measurement device. Background Art

[0002] The access level of new energy in the power grid is gradually increasing, and the coupling effect between power electronic devices and the power grid is becoming increasingly serious, interfering with the action accuracy of the original relay protection devices and leading to frequent accidents of grid - connected oscillation. The impedance analysis method is an effective stability analysis method. In the scenario of equipment grid - connection, it is difficult to model the impedance model of the large - scale power grid or the grid - connected operating equipment, and it can only be obtained through an impedance measurement device.

[0003] In the prior art, for a wide - band harmonic impedance measurement device based on a cascaded H - bridge converter, the three - phase AC system obtains the static DC operating point in the DQ coordinate system through Park transformation, and the converter control system also realizes control through the control of DQ - axis components. Therefore, the obtained impedance is also the impedance in the DQ coordinate system. In the application scenario of high - medium voltage DC micro - grid, there is no DQ axis in the DC system; the terminal voltage of the impedance device in the three - phase AC system is a three - phase sinusoidal voltage, and its instantaneous value changes rapidly with time; while the terminal voltage of the DC system is a DC voltage with a relatively small instantaneous value fluctuation, and there is no need to repeatedly switch high - voltage multiple capacitors. Therefore, in order to inject harmonic current into the DC voltage, a topology structure matching is required. A converter with a cascaded H - bridge structure of N sub - modules has a total positive level number of N, and each level voltage is Udc / N, where Udc is the DC voltage. To avoid affecting the DC static operating point of the device under test, the DC impedance measurement device requires that the amplitude Urm of the harmonic voltage injected into the device under test is significantly less than Udc. Considering the module cost and limiting the number of modules, the amplitude Urm of the harmonic voltage is also significantly less than the voltage Udc / N of a single sub - module. It can only have one sub - module for generating harmonic voltage, and the small duty cycle results in poor harmonic output accuracy. The DC side of the H - bridge of the impedance measurement device is a capacitor. In the coordinate system of the DQ axis of the three - phase AC system, by controlling the amplitude and angle of the D - axis voltage and current, the control of the external active power output is realized, and indirectly the control of the capacitor voltage is realized. For the application scenario of DC impedance measurement, the voltage - current control method in the DQ - axis coordinate system will not be applicable. Therefore, it is necessary to re - design the matching capacitor charge - discharge algorithm and voltage - sharing control algorithm. For the impedance device in the three - phase AC system, in order to make the output voltage distortion of the device smaller, a three - phase six - bridge - arm multi - level structure is often used, which uses a large number of MMC sub - modules. This not only significantly increases the cost of the equipment, but also makes the equipment bulky, and requires the use of cranes and containers for installation, and its installation and maintenance are relatively complex. Summary of the Invention

[0004] To solve the deficiencies existing in the prior art, the present invention provides a broadband high-voltage DC side impedance characteristic measurement device and its control method, which can improve the harmonic control accuracy, save costs, simplify the device structure, be applicable to impedance measurement in high-voltage DC scenarios, and improve the system stability at the same time.

[0005] The present invention adopts the following technical solutions.

[0006] The present invention proposes a broadband high-voltage DC side impedance characteristic measurement device, including a multilevel module group and a control system.

[0007] The multilevel module group includes: a series-connected half-bridge MMC module group and a full-bridge MMC module group; the control system includes: a startup control module, a DC voltage control module, a harmonic current control module, and a valve-level modulation control module.

[0008] The DC voltage control module is used to generate the DC voltage command value of the measurement device; the harmonic current control module is used to generate the harmonic voltage command value of the measurement device; the startup control module is used to use the sum of the DC voltage command value and the harmonic voltage command value as the output voltage command value, and charge the half-bridge MMC module group and the full-bridge MMC module group in sequence. After the charging is completed, the output voltage of the half-bridge MMC module group reaches the output voltage command value; the valve-level modulation control module is used to generate the modulation wave of the full-bridge MMC module group according to the harmonic voltage command value when the output voltage of the half-bridge MMC module group reaches the output voltage command value, so that the full-bridge MMC module group outputs harmonic current.

[0009] After the harmonic current is injected into the device under test, the harmonic voltage of the device under test at different frequencies is obtained, and the broadband high-voltage DC side impedance characteristic is determined by using the harmonic current and the harmonic voltage.

[0010] The half-bridge MMC module group includes N H cascaded half-bridge MMC modules with the same circuit structure. Each half-bridge MMC module includes 2 switching devices with anti-parallel diodes and a DC capacitor. The full-bridge MMC module group includes N L cascaded full-bridge MMC modules with the same circuit structure. Each full-bridge MMC module includes 4 switching devices with anti-parallel diodes and a DC capacitor.

[0011] The measurement device further includes: a main switch, a startup resistor, a charging short-circuit switch, and a filter inductor.

[0012] One end of the main switch is connected to one end of the starting resistor and one end of the charging short - circuit switch. The other end of the starting resistor and the other end of the charging short - circuit switch are connected to one end of the filter inductor. The other end of the filter inductor is connected to one end of the half - bridge MMC module group. The other end of the half - bridge MMC module group is connected to one end of the full - bridge MMC module group. The other end of the main switch is connected to the positive pole of the DC side. The other end of the full - bridge MMC module group is connected to the negative pole of the DC side.

[0013] The working process of the starting control module includes:

[0014] 1). Uncontrolled rectification charging stage of the half - bridge MMC module group; in this stage, the main switch is closed and the charging short - circuit switch is open. The lower arms of each half - bridge MMC module are conducting to charge the DC capacitors in each half - bridge MMC module. At the same time, the upper arms of each full - bridge MMC module are conducting to short - circuit the DC capacitors in each full - bridge MMC module; when the capacitor voltage of the half - bridge MMC module group reaches the output voltage command value U out , it enters the uncontrolled rectification charging stage of the full - bridge MMC module group; among them, the capacitor voltage of the half - bridge MMC module group is the sum of the capacitor voltages in all half - bridge MMC modules;

[0015] 2). Uncontrolled rectification charging stage of the full - bridge MMC module group; in this stage, the main switch is closed and the charging short - circuit switch is open. The upper and lower arms of each full - bridge MMC module are conducting to charge the DC capacitors in each full - bridge MMC module. At the same time, the upper and lower arms of N H - 1 half - bridge MMC modules in the half - bridge MMC module group are both open - circuited, so that the capacitor voltage of the full - bridge MMC module group is the capacitor voltage of a single half - bridge MMC module, which is U out / N H , so the capacitor voltage of a single full - bridge MMC module is U out / (N H ×N L ); when the capacitor voltage of the full - bridge MMC module group reaches 0.95 times of U out / N H , the charging short - circuit switch is closed;

[0016] Among them, the capacitor voltage of the full - bridge MMC module group is the sum of the capacitor voltages in all full - bridge MMC modules;

[0017] 3). After a delay after closing the charging short - circuit switch, when the charging current is less than 0.1 A, the half - bridge MMC module group is put into operation and the full - bridge MMC module group is withdrawn. At this time, the half - bridge MMC module group continuously outputs a DC voltage that meets the output voltage command value.

[0018] The DC voltage control module adopts a constant DC voltage control strategy, including: according to the target output voltage U of the measuring device dc_ref and the total port voltage Udc_sum For the error between them, PI control is adopted to determine the DC voltage command value of the measuring device

[0019] The harmonic current control module adopts an open-loop control structure to generate the harmonic voltage command value U r , satisfying the following relational expression:

[0020] U r = I r ×jω r L

[0021] In the formula, I r is the harmonic current value, ω r is the harmonic frequency, and L is the filter inductor.

[0022] The valve-level modulation control module adopts the carrier stacking modulation method to generate the modulation waves of each full-bridge MMC module, including:

[0023] Determine the number of full-bridge MMC modules put into operation according to the ratio of the voltage amplitude in the harmonic voltage command value to the capacitor voltage of a single full-bridge MMC module;

[0024] Generate triangular carriers with the same frequency and phase stacking for each put-in full-bridge MMC module; and generate a sine modulation wave according to the voltage amplitude and frequency in the harmonic voltage command value;

[0025] When the voltage value of the sine modulation wave is greater than the voltage value of the triangular carrier, control the upper bridge arm of the full-bridge MMC module corresponding to the triangular carrier to conduct; when the voltage value of the sine modulation wave is less than the voltage value of the triangular carrier, control the lower bridge arm of the full-bridge MMC module corresponding to the triangular carrier to conduct.

[0026] The present invention also proposes a control method for a wide-band high-voltage DC side impedance characteristic measuring device, including:

[0027] Obtain the difference between the target output voltage and the total port voltage of the measuring device, and adopt a constant DC voltage control strategy to obtain the DC voltage command value of the measuring device;

[0028] Obtain the target harmonic current and frequency of the measuring device, and adopt an open-loop control strategy to obtain the harmonic voltage command value of the measuring device;

[0029] Use the sum of the DC voltage command value and the harmonic voltage command value as the output voltage command value, and charge the half-bridge MMC module group and the full-bridge MMC module group in sequence. After the charging is completed, make the output voltage of the half-bridge MMC module group reach the output voltage command value;

[0030] When the output voltage of the half-bridge MMC module group reaches the output voltage command value, a modulation wave of the full-bridge MMC module group is generated according to the harmonic voltage command value, so that the full-bridge MMC module group outputs harmonic current;

[0031] After the harmonic current is injected into the device under test, the harmonic voltages at different frequencies of the device under test are obtained, and the broadband high-voltage DC side impedance characteristics are determined by using the harmonic current and the harmonic voltage.

[0032] Harmonic voltage command value U r , satisfies the following relationship:

[0033] U r = I r ×jω r L

[0034] In the formula, I r is the harmonic current value, ω r is the harmonic frequency, and L is the filter inductor.

[0035] Taking the sum of the DC voltage command value and the harmonic voltage command value as the output voltage command value, charging the half-bridge MMC module group and the full-bridge MMC module group in sequence. After the charging is completed, the output voltage of the half-bridge MMC module group reaches the output voltage command value, including:

[0036] 1), the uncontrolled rectification charging stage of the half-bridge MMC module group; in this stage, the main switch is closed and the charging short-circuit switch is opened. The lower arms of each half-bridge MMC module are turned on to charge the DC capacitors in each half-bridge MMC module. At the same time, the upper arms of each full-bridge MMC module are turned on to short-circuit the DC capacitors in each full-bridge MMC module; when the capacitor voltage of the half-bridge MMC module group reaches the output voltage command value U out , enter the uncontrolled rectification charging stage of the full-bridge MMC module group; among them, the capacitor voltage of the half-bridge MMC module group is the sum of the capacitor voltages in all half-bridge MMC modules;

[0037] 2), the uncontrolled rectification charging stage of the full-bridge MMC module group; in this stage, the main switch is closed and the charging short-circuit switch is opened. The upper and lower arms of each full-bridge MMC module are turned on to charge the DC capacitors in each full-bridge MMC module. At the same time, the upper and lower arms of N H -1 half-bridge MMC modules in the half-bridge MMC module group are both opened, so that the capacitor voltage of the full-bridge MMC module group is the capacitor voltage of a single half-bridge MMC module, which is U out / N H , therefore, the capacitor voltage of a single full-bridge MMC module is U out / (N H ×N L ); when the capacitor voltage of the full-bridge MMC module group reaches 0.95 times of Uout / N H When it is / N, close the charging short - circuit switch;

[0038] Among them, the capacitor voltage of the full - bridge MMC module group is the sum of the capacitor voltages in all full - bridge MMC modules;

[0039] 3) After closing the charging short - circuit switch and after a delay, when the charging current is less than 0.1 A, put into the half - bridge MMC module group and withdraw from the full - bridge MMC module group. At this time, the half - bridge MMC module group continuously outputs a DC voltage that meets the output voltage command value.

[0040] According to the harmonic voltage command value, use the carrier stacking modulation method to generate the modulation wave of the full - bridge MMC module group, including:

[0041] 1) Determine the number of full - bridge MMC modules put in according to the ratio of the harmonic voltage command value to the capacitor voltage of a single full - bridge MMC module;

[0042] 2) Generate triangular carrier waves with the same frequency and phase stacking for each put - in full - bridge MMC module; and generate a sine modulation wave according to the voltage amplitude and frequency in the harmonic voltage command value;

[0043] 3) When the voltage value of the sine modulation wave is greater than the voltage value of the triangular carrier wave, control the upper bridge arm of the full - bridge MMC module corresponding to the triangular carrier wave to conduct; when the voltage value of the sine modulation wave is less than the voltage value of the triangular carrier wave, control the lower bridge arm of the full - bridge MMC module corresponding to the triangular carrier wave to conduct.

[0044] The present invention is also a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to operate according to the instructions to execute the steps of the method.

[0045] The present invention is also a computer - readable storage medium, on which a computer program is stored, and when the program is executed by the processor, the steps of the method are implemented.

[0046] The beneficial effects of the present invention are as follows. Compared with the prior art, it at least includes that the broadband high-voltage DC-side impedance characteristic measurement device proposed by the present invention optimizes the main circuit topology. By adopting the series combination of a half-bridge MMC module group and a full-bridge MMC module group, the number of full-bridge MMC modules is reduced, thereby reducing the equipment cost. Moreover, on the one hand, when the optimized main circuit topology outputs harmonic voltage, the voltage of a single capacitor decreases, and the harmonic control accuracy is higher. On the other hand, the DC voltage control strategy realizes the feed-forward control of the port voltage through a PI controller, can quickly respond and stabilize the DC voltage, and improves the harmonic control accuracy. The harmonic current control link adopts an open-loop control structure, generates a real-time sinusoidal perturbation current according to the command frequency and command amplitude, and calculates the voltage to be output through an inductor, further improving the harmonic control accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is the topological principle structure diagram of the broadband high-voltage DC-side impedance characteristic measurement device proposed by the present invention;

[0048] Figure 2 is the fixed DC voltage control strategy block diagram adopted by the DC voltage control module in the broadband high-voltage DC-side impedance characteristic measurement device proposed by the present invention;

[0049] Figure 3 is the modulation process waveform diagram of the triangular carrier wave and the sinusoidal modulation wave generated by the valve-level modulation control module in the broadband high-voltage DC-side impedance characteristic measurement device proposed by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0051] The present invention proposes a broadband high-voltage DC-side impedance characteristic measurement device, as Figure 1 shown, including: main switch K1, starting resistor R, charging short-circuit switch K2, filtering inductor L, multi-level module group; wherein, the multi-level module group includes a series-connected half-bridge MMC module group and a full-bridge MMC module group, and the half-bridge MMC module group includes N H cascaded half-bridge MMC modules SM-H1, SM-H2,..., SM-Hn, and the full-bridge MMC module group includes N LCascaded full-bridge MMC modules SM-L1, SM-L2, ……, SM-Ln; One end of the main switch K1 is connected to one end of the starting resistor R and one end of the charging short-circuit switch K2. The other end of the starting resistor R and the other end of the charging short-circuit switch K2 are connected to one end of the filter inductor L. The other end of the filter inductor L is connected to one end of the half-bridge MMC module group. The other end of the half-bridge MMC module group is connected to one end of the full-bridge MMC module group. The other end of the main switch K1 is connected to the positive pole A of the DC side. The other end of the full-bridge MMC module group is connected to the negative pole B of the DC side. The input voltage is U AB .

[0052] Among them, N H half-bridge MMC modules have the same circuit structure, including 2 switching devices S1 and S2 with anti-parallel diodes, and DC capacitor C H ; N L full-bridge MMC modules have the same circuit structure, including 4 switching devices S1, S2, S3, S4 with anti-parallel diodes, and DC capacitor C L ;

[0053] When using the full-bridge MMC module to control the output voltage, when the capacitor voltage is E, through switch modulation control, the output voltage of the full-bridge MMC module port can be E, 0, -E. Among them, the -E level is mainly used to generate the negative voltage in the sinusoidal voltage. In the DC application scenario, the -E level is actually meaningless. Therefore, the present invention proposes to use a half-bridge MMC module group to generate the high-voltage DC bus voltage. After the half-bridge MMC module group generates the DC bus voltage, in order to make the equipment further generate a disturbance current with a specific frequency, the present invention also proposes to use an H-type full-bridge MMC module group and make it output a voltage with a specific frequency through modulation control technology. Based on the above idea, the present invention proposes to optimize the main circuit topology, adopt the series combination of the half-bridge MMC module group and the full-bridge MMC module group, reduce the number of full-bridge MMC modules, and thus reduce the equipment cost.

[0054] In the optimized main circuit topology, although the multilevel module group includes a series-connected half-bridge MMC module group and a full-bridge MMC module group, the control strategies of the half-bridge MMC module group and the full-bridge MMC module group need to be unified and coordinated. Therefore, the broadband high-voltage DC side impedance characteristic measuring device further includes a control system, and the control system includes a start control module, a DC voltage control module, a harmonic current control module, and a valve-level modulation control module;

[0055] Specifically, from disconnecting the device under test to the normal operation of the measuring device, first, the start control of the measuring device needs to be carried out to prepare for the subsequent output of the disturbance current. The start control module is used to charge the half-bridge MMC module group and the full-bridge MMC module group in sequence. After the charging is completed, the half-bridge MMC module group outputs the DC voltage Udc ; The working process of the startup control of the measuring device includes:

[0056] 1), the uncontrolled rectification charging stage of the half-bridge MMC module group;

[0057] In this stage, the main switch is closed and the charging short-circuit switch is opened. The lower arms of each half-bridge MMC module are turned on (switch device S2 is closed) to charge the DC capacitors in each half-bridge MMC module. At the same time, the upper arms of each full-bridge MMC module are turned on (switch devices S1 and S3 are closed) to short-circuit the DC capacitors in each full-bridge MMC module; when the capacitor voltage of the half-bridge MMC module group reaches the output voltage command value U out , it enters the uncontrolled rectification charging stage of the full-bridge MMC module group;

[0058] Among them, the capacitor voltage of the half-bridge MMC module group is the sum of the capacitor voltages in all half-bridge MMC modules;

[0059] 2), the uncontrolled rectification charging stage of the full-bridge MMC module group;

[0060] In this stage, the main switch is closed and the charging short-circuit switch is opened. The upper and lower arms of each full-bridge MMC module are both turned on (switch devices S1 and S4 are closed) to charge the DC capacitors in each full-bridge MMC module. At the same time, the upper and lower arms of N H -1 half-bridge MMC modules in the half-bridge MMC module group are both turned off (switch devices S1 and S2 are opened), so that the capacitor voltage of the full-bridge MMC module group is the capacitor voltage U of a single half-bridge MMC module out / N H , therefore, the capacitor voltage of a single full-bridge MMC module is U out / (N H ×N L ); when the capacitor voltage of the full-bridge MMC module group reaches 0.95 times of U out / N H , the charging short-circuit switch is closed;

[0061] Among them, the capacitor voltage of the full-bridge MMC module group is the sum of the capacitor voltages in all full-bridge MMC modules;

[0062] 3), after a delay after closing the charging short-circuit switch, when the charging current is less than 0.1 A, the half-bridge MMC module group is put into operation and the full-bridge MMC module group is exited. At this time, the half-bridge MMC module group continuously outputs a DC voltage that meets the requirements and is ready for harmonic injection control.

[0063] Specifically, in order to maintain the stability of the DC voltage output by the measurement device, the DC voltage control of the measurement device needs to be performed. The DC voltage control module is used to generate a DC voltage command value by adopting a fixed DC voltage control strategy; the fixed DC voltage control strategy is as Figure 2 shown. According to the error between the target output voltage U dc_ref of the measurement device and the total port voltage U dc_sum , PI control is adopted to determine the DC voltage command value

[0064] In the present invention, the DC voltage control strategy realizes the feedforward control of the total port voltage of the measurement device through a PI controller, can quickly respond and stabilize the DC voltage, and improves the harmonic control accuracy.

[0065] Specifically, when a harmonic current is injected into the device under test, the measured total port voltage of the device under test also contains the frequency component of the harmonic injection. Therefore, the harmonic current control of the measurement device needs to be performed. Considering that after the harmonic current is injected, the response characteristics of the device under test are unknown and may generate a large voltage response, and the closed-loop control may lead to the instability of the control strategy; the harmonic current control target of the measurement device is to inject a harmonic current so as to measure and obtain the harmonic voltage output of the device under test, and the impedance characteristics at the harmonic frequency point are obtained through calculation. Therefore, it is not necessary to limit that the actual injected current must be a fixed command value. Therefore, the harmonic current control module adopts an open-loop control structure and is used to generate a harmonic voltage command value U r , satisfying the following relational expression:

[0066] U r = I r ×jω r L

[0067] In the formula, I r is the harmonic current value, ω r is the harmonic frequency, and L is the filter inductor.

[0068] The harmonic current control link proposed by the present invention adopts an open-loop control structure, generates a real-time sinusoidal disturbance current according to the target frequency and target amplitude, and calculates the voltage to be output through the inductor, further improving the harmonic control accuracy.

[0069] When the start control module charges the half-bridge MMC module group and the full-bridge MMC module group, the sum of the DC voltage command value and the equivalent harmonic voltage command value is used as the output voltage command value, satisfying the following relational expression:

[0070]

[0071] The valve-level modulation control module is used to generate the modulation wave of the full-bridge MMC module group according to the harmonic voltage command value when the output voltage of the half-bridge MMC module group reaches the output voltage command value, so that the full-bridge MMC module group outputs harmonic current;

[0072] In the embodiment, a valve-level modulation control strategy is designed to implement the specific on-off signals of the IGBTs in the MMC module; the valve-level modulation control is used to generate the switching modulation pulses of each full-bridge MMC module according to the terminal voltage of the full-bridge MMC module group.

[0073] Specifically, in the uncontrolled rectification charging stage of the full-bridge MMC module group, the capacitor voltage of the full-bridge MMC module group is U, and the capacitor voltage of a single half-bridge MMC module is out / N H , so N H half-bridge MMC modules continuously output to meet the output requirements of the DC voltage part. In order to make the N L full-bridge MMC modules output specific harmonic disturbance current, the valve-level modulation control module uses the carrier stacking modulation method to generate the modulation wave of each full-bridge MMC module, including:

[0074] 1), Determine the number of full-bridge MMC modules put into operation according to the ratio of the harmonic voltage command value to the capacitor voltage of a single full-bridge MMC module;

[0075] 2), Generate triangular carriers with the same frequency and phase stacking for each full-bridge MMC module put into operation; and generate a sine modulation wave according to the voltage amplitude and frequency in the harmonic voltage command value;

[0076] 3), When the voltage value of the sine modulation wave is greater than the voltage value of the triangular carrier, control the upper bridge arm of the full-bridge MMC module corresponding to the triangular carrier to conduct; when the voltage value of the sine modulation wave is less than the voltage value of the triangular carrier, control the lower bridge arm of the full-bridge MMC module corresponding to the triangular carrier to conduct.

[0077] In the embodiment of the present invention, the voltage amplitude in the harmonic voltage command value is used to determine the number of full-bridge MMC modules put into operation to ensure the voltage balance of each full-bridge MMC module; assuming that the number of low-voltage module groups is 4, the modulation process of the generated triangular carrier and sine modulation wave is as Figure 3 shown, v ris a sine modulation wave, and v1, v2, v3, and v4 are the triangular carrier waves of the four full-bridge MMC modules respectively. When the amplitude of the modulation wave is positive, when the modulation wave is above the carrier wave, S1 and S4 of the corresponding SM-L are closed, and S2 and S4 are open. When the amplitude of the modulation wave is negative, when the modulation wave is below the carrier wave, S1 and S4 of the corresponding SM-L are closed, and S2 and S4 are open. From this, the switching on and off relationships of each switch of each full-bridge MMC module can be obtained, and then the modulation voltage vr is equivalently output across the entire full-bridge MMC module.

[0078] When the main circuit topology structure proposed by the present invention outputs harmonic current, due to the reduction of the capacitor voltage of a single full-bridge MMC module, the harmonic control accuracy is higher.

[0079] The present invention also proposes a control method for a wide-band high-voltage DC side impedance characteristic measurement device, including:

[0080] Obtain the difference between the target output voltage and the total port voltage of the measurement device, and adopt a constant DC voltage control strategy to obtain the DC voltage command value of the measurement device;

[0081] Obtain the target harmonic current and frequency of the measurement device, and adopt an open-loop control strategy to obtain the harmonic voltage command value of the measurement device;

[0082] Use the sum of the DC voltage command value and the harmonic voltage command value as the output voltage command value, and charge the half-bridge MMC module group and the full-bridge MMC module group in sequence. After charging is completed, make the output voltage of the half-bridge MMC module group reach the output voltage command value;

[0083] When the output voltage of the half-bridge MMC module group reaches the output voltage command value, generate the modulation wave of the full-bridge MMC module group according to the harmonic voltage command value, so that the full-bridge MMC module group outputs harmonic current;

[0084] After the harmonic current is injected into the device under test, obtain the harmonic voltage of the device under test at different frequencies, and use the harmonic current and the harmonic voltage to determine the wide-band high-voltage DC side impedance characteristic.

[0085] In the scenario of device grid connection, it is difficult to model and obtain the impedance model of the large power grid or the impedance model of the device already in grid-connected operation, and it can only be obtained through an impedance measurement device. The impedance measurement device proposed by the present invention inputs a harmonic disturbance current to the device under test, and then observes the output of the disturbance response voltage at the corresponding frequency of the device under test, and constructs the input-output relationship as the impedance characteristic measurement result at different frequencies.

[0086] Through the improvement of the topology design, the present invention reduces the volume of the device, improves the working efficiency of the impedance measurement experiment. The device structure is relatively simplified, and the installation and maintenance are more convenient, reducing the maintenance cost of the device. In terms of adapting to high-voltage DC scenarios, the main circuit topology and control algorithm of the present invention are designed specifically for high-voltage DC scenarios, can adapt to the operating characteristics of DC systems, and meet the requirements of high-voltage DC impedance measurement. The impedance measurement device of the present invention can effectively reduce the harmonic error of impedance measurement, contribute to the accurate acquisition of impedance, and improve the measurement accuracy. In summary, the present invention has significant advantages in multiple aspects, providing a more efficient, accurate, and economical solution for high-voltage DC impedance measurement.

[0087] The present disclosure may be a system, method, and / or computer program product. The computer program product may include a computer-readable storage medium having thereon computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0088] The computer-readable storage medium may be a tangible device that can retain and store instructions for use by an instruction execution device. The computer-readable storage medium may be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disc (DVD), a memory stick, a floppy disk, a mechanically encoded device such as a punch card or raised structures in grooves having instructions stored thereon, and any suitable combination of the foregoing. The computer-readable storage medium as used herein is not construed as an instantaneous signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., an optical pulse through an optical fiber cable), or an electrical signal transmitted through a wire.

[0089] The computer-readable program instructions described herein may be downloaded from a computer-readable storage medium to various computing / processing devices, or downloaded to an external computer or external storage device through a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network may include copper transmission cables, optical fiber transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions for storage in the computer-readable storage medium in each computing / processing device.

[0090] Computer program instructions for performing the operations of the present disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine - related instructions, microcode, firmware instructions, state - setting data, or source code or object code written in any combination of one or more programming languages, including object - oriented programming languages such as Smalltalk, C++, etc., and conventional procedural programming languages such as the "C" language or similar programming languages. The computer - readable program instructions may be executed entirely on the user's computer, partially on the user's computer, executed as a stand - alone software package, partially on the user's computer and partially on a remote computer, or entirely on the remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., through the Internet using an Internet service provider). In some embodiments, by using the state information of the computer - readable program instructions to customize an electronic circuit, such as a programmable logic circuit, a field - programmable gate array (FPGA), or a programmable logic array (PLA), the electronic circuit can execute the computer - readable program instructions to implement various aspects of the present disclosure.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or make equivalent replacements. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A wide - band high - voltage DC - side impedance characteristic measuring device, comprising a multilevel module group and a control system, characterized in that, The multilevel module group includes: a series - connected half - bridge MMC module group and a full - bridge MMC module group; The control system includes: a start - up control module, a DC voltage control module, a harmonic current control module, and a valve - level modulation control module; The DC voltage control module is used to generate a DC voltage command value of the measuring device; The harmonic current control module is used to generate a harmonic voltage command value of the measuring device; The start - up control module is used to use the sum of the DC voltage command value and the harmonic voltage command value as the output voltage command value, and charge the half - bridge MMC module group and the full - bridge MMC module group in sequence. After charging is completed, the output voltage of the half - bridge MMC module group reaches the output voltage command value; The valve - level modulation control module is used to generate a modulation wave of the full - bridge MMC module group according to the harmonic voltage command value when the output voltage of the half - bridge MMC module group reaches the output voltage command value, so that the full - bridge MMC module group outputs harmonic current; After the harmonic current is injected into the device under test, the harmonic voltage of the device under test at different frequencies is obtained, and the wide - band high - voltage DC - side impedance characteristic is determined by using the harmonic current and the harmonic voltage.

2. The wide - band high - voltage DC - side impedance characteristic measuring device according to claim 1, characterized in that, The half-bridge MMC module group includes N H cascaded half-bridge MMC modules with the same circuit structure. Each half-bridge MMC module includes two switching devices with anti-parallel diodes and a DC capacitor. The full-bridge MMC module group includes N L cascaded full-bridge MMC modules with the same circuit structure. Each full-bridge MMC module includes four switching devices with anti-parallel diodes and a DC capacitor; The measuring device further includes: a main switch, a start - up resistor, a charging short - circuit switch, and a filter inductor; One end of the main switch is connected to one end of the start - up resistor and one end of the charging short - circuit switch. The other end of the start - up resistor and the other end of the charging short - circuit switch are connected to one end of the filter inductor. The other end of the filter inductor is connected to one end of the half - bridge MMC module group. The other end of the half - bridge MMC module group is connected to one end of the full - bridge MMC module group. The other end of the main switch is connected to the positive pole of the DC side, and the other end of the full - bridge MMC module group is connected to the negative pole of the DC side.

3. The wide - band high - voltage DC - side impedance characteristic measuring device according to claim 2, characterized in that, The working process of the start - up control module includes: 1), Uncontrolled rectifier charging stage of the half-bridge MMC module group; in this stage, the main switch is closed and the charging short-circuit switch is open. The lower arms of each half-bridge MMC module are conducting to charge the DC capacitors in each half-bridge MMC module. At the same time, the upper arms of each full-bridge MMC module are conducting to short-circuit the DC capacitors in each full-bridge MMC module; when the capacitor voltage of the half-bridge MMC module group reaches the output voltage command value U out When it reaches this value, it enters the uncontrolled rectifier charging stage of the full-bridge MMC module group; among them, the capacitor voltage of the half-bridge MMC module group is the sum of the capacitor voltages in all half-bridge MMC modules; 2) Uncontrolled rectification charging stage of the full-bridge MMC module group; in this stage, the main switch is closed and the charging short-circuit switch is open. The upper and lower arms of each full-bridge MMC module are both turned on to charge the DC capacitors in each full-bridge MMC module. At the same time, the upper and lower arms of N H -1 half-bridge MMC modules are both turned off, so that the capacitor voltage of the full-bridge MMC module group is the capacitor voltage of a single half-bridge MMC module, which is U out / N H . Therefore, the capacitor voltage of a single full-bridge MMC module is U out / (N H ×N L ); when the capacitor voltage of the full-bridge MMC module group reaches 0.95 times of U out / N H , close the charging short-circuit switch; Among them, the capacitor voltage of the full - bridge MMC module group is the sum of the capacitor voltages in all full - bridge MMC modules; 3), after the charging short - circuit switch is closed and after a delay, when the charging current is less than 0.1A, the half - bridge MMC module group is put into operation and the full - bridge MMC module group is withdrawn. At this time, the half - bridge MMC module group continuously outputs a DC voltage that meets the output voltage command value.

4. The wide - band high - voltage DC - side impedance characteristic measuring device according to claim 3, characterized in that, The DC voltage control module adopts a constant DC voltage control strategy, including: according to the error between the target output voltage U of the measuring device dc_ref and the total port voltage U dc_sum , PI control is adopted to determine the DC voltage command value of the measuring device 5. The wide - band high - voltage DC - side impedance characteristic measuring device according to claim 3, characterized in that, The harmonic current control module adopts an open-loop control structure and is used to generate a harmonic voltage command value U r , satisfying the following relation: U r = I r × jω r L Where, I r is the harmonic current value, ω r is the harmonic frequency, and L is the filtering inductance.

6. The wide - band high - voltage DC - side impedance characteristic measuring device according to claim 3, characterized in that, The valve - level modulation control module uses a carrier - stacking modulation method to generate the modulation waves of each full - bridge MMC module, including: Determining the number of full - bridge MMC modules put into operation according to the ratio of the voltage amplitude in the harmonic voltage command value to the capacitor voltage of a single full - bridge MMC module; Generating triangular carrier waves with the same frequency and phase - stacked for each full - bridge MMC module put into operation; and generating a sine modulation wave according to the voltage amplitude and frequency in the harmonic voltage command value. When the voltage value of the sine modulation wave is greater than the voltage value of the triangular carrier wave, control the upper bridge arm of the full-bridge MMC module corresponding to the triangular carrier wave to conduct; when the voltage value of the sine modulation wave is less than the voltage value of the triangular carrier wave, control the lower bridge arm of the full-bridge MMC module corresponding to the triangular carrier wave to conduct.

7. A control method for a broadband high-voltage DC side impedance characteristic measurement device, applicable to the measurement device according to any one of claims 1 to 6, characterized in that, Including: Obtain the difference between the target output voltage and the total port voltage of the measuring device, and adopt a constant DC voltage control strategy to obtain the DC voltage command value of the measuring device; Obtain the target harmonic current and frequency of the measuring device, and adopt an open-loop control strategy to obtain the harmonic voltage command value of the measuring device; Use the sum of the DC voltage command value and the harmonic voltage command value as the output voltage command value, and charge the half-bridge MMC module group and the full-bridge MMC module group in sequence. After charging is completed, make the output voltage of the half-bridge MMC module group reach the output voltage command value; When the output voltage of the half-bridge MMC module group reaches the output voltage command value, generate a modulation wave for the full-bridge MMC module group according to the harmonic voltage command value, so that the full-bridge MMC module group outputs harmonic current; After the harmonic current is injected into the device under test, obtain the harmonic voltage of the device under test at different frequencies, and use the harmonic current and harmonic voltage to determine the broadband high-voltage DC side impedance characteristics.

8. The control method of the broadband high-voltage DC side impedance characteristic measuring device according to claim 7, characterized in that Harmonic voltage command value U r , satisfies the following relational expression: U r = I r × jω r L Where, I r is the harmonic current value, ω r is the harmonic frequency, and L is the filtering inductance.

9. The control method of the broadband high-voltage DC side impedance characteristic measuring device according to claim 7, characterized in that Use the sum of the DC voltage command value and the harmonic voltage command value as the output voltage command value, and charge the half-bridge MMC module group and the full-bridge MMC module group in sequence. After charging is completed, make the output voltage of the half-bridge MMC module group reach the output voltage command value, including: 1), uncontrolled rectifier charging stage of the half-bridge MMC module group; in this stage, the main switch is closed and the charging short-circuit switch is opened. The lower arms of each half-bridge MMC module are turned on to charge the DC capacitors in each half-bridge MMC module. At the same time, the upper arms of each full-bridge MMC module are turned on to short-circuit the DC capacitors in each full-bridge MMC module; when the capacitor voltage of the half-bridge MMC module group reaches the output voltage command value U out When it reaches, it enters the uncontrolled rectifier charging stage of the full-bridge MMC module group; among them, the capacitor voltage of the half-bridge MMC module group is the sum of the capacitor voltages in all half-bridge MMC modules; 2) Uncontrolled rectifier charging stage of the full-bridge MMC module group; in this stage, the main switch is closed and the charging short-circuit switch is open. The upper and lower arms of each full-bridge MMC module are both conducting to charge the DC capacitors in each full-bridge MMC module. At the same time, the upper and lower arms of N H -1 half-bridge MMC modules in the half-bridge MMC module group are both open, so that the capacitor voltage of the full-bridge MMC module group is the capacitor voltage of a single half-bridge MMC module, which is U out / N H . Therefore, the capacitor voltage of a single full-bridge MMC module is U out / (N H ×N L ); when the capacitor voltage of the full-bridge MMC module group reaches 0.95 times of U out / N H , close the charging short-circuit switch; Among them, the capacitor voltage of the full-bridge MMC module group is the sum of the capacitor voltages in all full-bridge MMC modules; 3), after closing the charging short-circuit switch and after a delay, when the charging current is less than 0.1 A, put into the half-bridge MMC module group and withdraw the full-bridge MMC module group. At this time, the half-bridge MMC module group continuously outputs a DC voltage that meets the output voltage command value.

10. The control method of the broadband high-voltage DC side impedance characteristic measuring device according to claim 7, characterized in that According to the harmonic voltage command value, adopt a carrier stacking modulation method to generate a modulation wave for the full-bridge MMC module group, including: 1), determine the number of full-bridge MMC modules put into operation according to the ratio of the harmonic voltage command value to the capacitor voltage of a single full-bridge MMC module; 2), generate triangular carrier waves with the same frequency and phase stacking for each full-bridge MMC module put into operation; and generate a sine modulation wave according to the voltage amplitude and frequency in the harmonic voltage command value; 3), when the voltage value of the sine modulation wave is greater than the voltage value of the triangular carrier wave, control the upper bridge arm of the full-bridge MMC module corresponding to the triangular carrier wave to conduct; when the voltage value of the sine modulation wave is less than the voltage value of the triangular carrier wave, control the lower bridge arm of the full-bridge MMC module corresponding to the triangular carrier wave to conduct.

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