High-voltage system broadband impedance measurement device and voltage stabilizing method of sub-module thereof

Abstract

This invention discloses a broadband impedance measurement device for high-voltage systems and a voltage regulation method for its sub-modules. Each sub-module of the device consists of a cascaded H-bridge and a floating DC / DC converter connected in series on the DC side. One end of the cascaded H-bridge is connected to the current of each phase of the high-voltage system, and the AC side of the cascaded H-bridges in each sub-module is cascaded. The other end of the cascaded H-bridge is connected to the floating DC / DC converter. One end of the floating DC / DC converter is connected to the cascaded H-bridge, and the other end is floating. The device of this invention controls the energy balance on the bus capacitor of the cascaded H-bridge connected to the DC / DC converter in real time, so that the DC bus voltage remains stable when implementing current injection functions at different frequencies, thereby improving the impedance measurement effect. Through three-phase active and reactive power control, the energy loss on the floating side of the high-frequency DC / DC converter is compensated, a certain voltage range is maintained, and the voltage regulation and balance control effect between phases within the sub-module is improved.

Description

Technical Field

[0001] This invention relates to a wideband impedance measurement device and its sub-module voltage regulation method, particularly a wideband impedance measurement device and its sub-module voltage regulation method for high-voltage systems. Background Technology

[0002] Currently, the main method for analyzing the stability of grid-connected new energy power generation systems is impedance analysis. However, direct modeling can lead to inaccurate or difficult-to-model models, especially with large systems. Therefore, external impedance measurement is often used. This involves treating the new energy generator unit or the entire local power grid as a "black box," injecting a certain proportion of disturbance signal from the outside, obtaining the impedance characteristics of the entire unit or system, and then combining these impedance characteristics to determine the stability of the entire system or to implement measures to change or improve impedance matching characteristics.

[0003] Harmonic current injection, as one method, is equivalent to injecting disturbance current in parallel onto a new energy system. It is characterized by its ease of implementation and minimal impact on the power grid and the grid-connected inverter of the new energy source under test. However, current injection requires the disturbance source to generate a controllable disturbance injection signal for impedance measurement. But current disturbance sources based on conventional inverter topologies generate significant coupling components when injecting non-power frequency components. The self-coupling component and the coupling component of the system under test are superimposed, causing significant interference to the system impedance analysis.

[0004] High-voltage impedance measurement systems are often composed of numerous sub-modules connected in series or cascaded. Due to the separation of multiple sub-modules, the capacitance of a single sub-module is smaller than that of a conventional low-voltage inverter, which makes the impact of frequency coupling more severe. The voltage equalization effect of the sub-modules is also worse, resulting in more coupling components with uncontrollable amplitude and phase in the non-power frequency components of the system output. In severe cases, this can even affect the system's functionality and stable operation.

[0005] To address the aforementioned issues, some technical research has been conducted both domestically and internationally. For example, in existing technologies, each sub-power module unit of the impedance measurement device consists of a three-phase uncontrolled rectifier converter, a high-frequency isolated DC / DC converter, and a single-phase H-bridge DC / AC converter; the DC-side capacitor of each single-phase H-bridge DC / AC converter is powered by the preceding high-frequency DC / DC converter. This approach uses external power supply, requiring the design of additional high-voltage energy extraction circuits, including custom high-voltage multi-tap transformers and numerous rectifier circuits. This not only increases the total system cost and size but also makes the circuit topology more complex, correspondingly increasing the probability of system failure.

[0006] Existing technologies also include schemes using direct cascaded H-bridges, where the DC bus voltage of the H-bridges is directly controlled and stabilized by the three-phase system. Under this control method, when the impedance measuring device injects non-power frequency current into the power frequency system, it causes fluctuations in the DC bus voltage. These fluctuations further degrade the quality of the injected current during impedance measurement, which in turn affects the DC bus voltage fluctuations, complicating the situation and severely impacting the impedance measurement results at the current frequency. This impact is greater the closer the frequency is to the power frequency, and less so at higher frequencies. Summary of the Invention

[0007] Purpose of the invention: The purpose of this invention is to provide a wideband impedance measurement device for high-voltage systems and its sub-module voltage regulation method that avoids frequency coupling and external power supply and maintains voltage stability.

[0008] Technical solution: Each sub-module of the high-voltage system broadband impedance measurement device of the present invention is composed of a cascaded H-bridge and a floating DC / DC converter connected in series on the DC side; one end of the cascaded H-bridge is connected to the current of each phase of the high-voltage system, and the AC side of the cascaded H-bridge of each sub-module is cascaded, and the other end of the cascaded H-bridge is connected to the floating DC / DC converter; one end of the floating DC / DC converter is connected to the cascaded H-bridge, and the other end is floating.

[0009] Furthermore, the floating DC / DC converter is equipped with DC bus capacitors at both ends.

[0010] Furthermore, the suspended DC / DC converter is a duty cycle-adjustable topology or a phase-shift control topology.

[0011] The voltage stabilization method of the sub-module of the high-voltage system broadband impedance measurement device of the present invention comprises each sub-module of the device consisting of a cascaded H-bridge and a floating DC / DC converter connected in series on the DC side; one end of the floating DC / DC converter is connected to the cascaded H-bridge, and the other end is suspended; the floating DC / DC converter absorbs or outputs energy from the suspended side to stabilize the DC bus voltage of the cascaded H-bridge; the cascaded H-bridge controls the DC bus voltage and capacitor voltage of the suspended end of the floating DC / DC converter to stabilize according to the phase-to-phase voltage equalization control strategy.

[0012] Furthermore, the floating DC / DC converter is equipped with DC bus capacitors at both ends.

[0013] Furthermore, the suspended DC / DC converter is a duty cycle-adjustable topology or a phase-shift control topology.

[0014] Furthermore, the average value of the DC bus voltage at the floating DC / DC terminal of each sub-module is calculated based on the DC bus voltage at the floating DC / DC terminal of each sub-module. The difference between the average value of the DC bus voltage at the floating DC / DC terminal and the DC bus voltage at the floating DC / DC terminal of each sub-module is calculated using PI to obtain the fine-tuning variable used for phase-to-phase voltage equalization control within the whole machine.

[0015] Furthermore, a target value for voltage control on the cascaded H-bridge side is set, and the difference between the measured voltage value on the cascaded H-bridge side and the target voltage control value on the cascaded H-bridge side is calculated using PI to obtain the duty cycle or phase shift angle of the switching transistor in the floating DC / DC circuit, which is used to control the DC bus voltage stability of the cascaded H-bridge.

[0016] Set the target value for the DC component control of the DC bus voltage at the floating terminal of the DC / DC converter, collect the measured value of the DC bus voltage at the floating terminal of the DC / DC converter, and perform PI calculation on the difference between the average value of the measured DC bus voltage and the target value for the DC component control of the DC bus voltage to obtain the overall active power control variable, which is used to generate the d-axis reference for the inner loop control of the whole machine current.

[0017] The broadband impedance measurement method based on the device described in this invention connects the device to a high-voltage system and uses a parallel perturbation current injection method to measure the broadband impedance characteristics.

[0018] The computer-readable storage medium of the present invention stores a computer program, which, when executed by a processor, implements the broadband impedance measurement method.

[0019] Beneficial effects: Compared with the prior art, the advantages of the present invention are: (1) It adopts a self-powered method, which eliminates the high-voltage power extraction circuit, simplifies the circuit topology, and reduces the probability of failure; (2) It avoids the more complex coupling problem caused by the AC component of the DC bus voltage, avoids the influence of the wideband impedance measurement device itself on the system under test, and makes the injected wideband current in a precise and controllable state in terms of amplitude, phase and frequency, which is beneficial to the continuous frequency sweep and impedance analysis of the wideband impedance measurement device. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the topology of the high-voltage system broadband impedance measurement device of the present invention.

[0021] Figure 2 These are two duty cycle adjustable suspended DC / DC topologies in Embodiment 1 of the present invention.

[0022] Figure 3 This is the topology of the broadband impedance measurement device submodule formed by using a buck circuit in Embodiment 1 of the present invention.

[0023] Figure 4 This is a block diagram of voltage stabilization control on the cascaded H-bridge side in an embodiment of the present invention.

[0024] Figure 5 This is a block diagram of the voltage stabilization control of the floating DC / DC converter in an embodiment of the present invention.

[0025] Figure 6 These are three phase-shift control type suspended DC / DC topologies in Embodiment 2 of the present invention.

[0026] Figure 7 This is the topology of the broadband impedance measurement device submodule formed by using a half-bridge dual active bridge circuit in Embodiment 2 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0028] Example 1

[0029] like Figure 1 As shown, each sub-module of the high-voltage system broadband impedance measurement device consists of a cascaded H-bridge and a floating DC / DC converter connected in series on the DC side. The AC sides of the H-bridges in the sub-modules are cascaded together to share the AC side voltage of the high-voltage impedance measurement device. The floating DC / DC converter in the sub-module has one end connected to the DC side of the H-bridge, and the other end in a floating potential state. The floating DC / DC converter includes isolated and non-isolated DC-DC converter circuits. A DC bus capacitor of a certain size is configured at both ends of the DC / DC circuit, with one end connected to the cascaded H-bridge and the other end floating.

[0030] The method for impedance measurement using the device described in this invention is as follows: The device is connected to a high-voltage system. A current disturbance signal of a specific frequency, ranging from several Hz to several kHz, is injected at the grid connection point. The injected disturbance current will shunt to the source and load ends of the grid connection point, with the shunt magnitude varying depending on the impedance of the source and load ends. During the disturbance current injection, a certain voltage disturbance will also occur at the grid connection point. The disturbance voltage and the disturbance current at the source and load ends are measured, and the impedance characteristics of the source and load ends at that frequency point are calculated. Then, by scanning the entire frequency range using this method, a wide-range impedance characteristic of the source and load ends can be obtained.

[0031] In this embodiment, the suspended DC / DC converter adopts a duty cycle adjustable topology, for example... Figure 2 (a) and Figure 2 The diagram in (b) shows a DC / DC topology with adjustable duty cycle. Figure 2 Taking the buck circuit topology shown in (a) as an example, where C H Let U be the capacitor on the side where the Buck circuit connects to the cascaded H-bridge. The voltage value of the Nth module is denoted as U.CHN C L Let U be the capacitor on the floating side of the Buck circuit. The voltage of the Nth module is denoted as U. CLN The entire module topology is as follows Figure 3 As shown.

[0032] Regarding the submodule voltage regulation control strategy, for the voltage on the H-bridge side of the Buck circuit cascaded, such as Figure 4 As shown, set the target voltage control value on the cascaded H-bridge side, for example, set U. Cset1 =1000V, collect the measured voltage values ​​on the cascaded H-bridge side of each submodule in the three-phase topology, and perform PI calculation on the difference between each measured voltage value and the voltage control target value to obtain... Figure 3 Duty cycle d of S1 N The duty cycle of S2 is complementary to that of S1. For each Buck circuit, it is only necessary to maintain the stability of the voltage on the cascaded H-bridge side.

[0033] For the floating side voltage of a Buck circuit, such as Figure 5 As shown, the target control value for the DC component of the floating terminal voltage of the Buck circuit is set, for example, U. Cset2 =1000V, collect the measured value of the floating terminal voltage of the Buck circuit in each submodule of the three-phase topology, calculate the average value of all measured voltage values, and perform PI calculation on the difference between each measured average value and the target value to obtain the overall active power control variable I. d This is used to generate the d-axis reference for the inner loop control of the overall machine current. Since the above control targets the average value of all floating-side voltages, for the floating voltage of each submodule, the difference between the average value and the floating-side voltage of the submodule is calculated using PI to obtain a fine-tuning variable ΔN, which is used for phase-to-phase voltage equalization control within the overall machine.

[0034] Example 2

[0035] In this embodiment, each sub-module of the broadband impedance measurement device consists of a cascaded H-bridge and a floating DC / DC converter connected in series on the DC side. The impedance measurement method is the same as in Embodiment 1.

[0036] In this embodiment, the floating DC / DC converter adopts a phase-shift control topology, for example... Figure 6 The schematic diagrams of the phase-shift control topology shown in (a), (b), and (c) are as follows. Figure 6 Taking the half-bridge dual active bridge circuit topology shown in Figure (a) as an example, where C H1 C is the upper capacitor on the side where the half-bridge dual active bridge circuit connects to the cascaded H-bridge. H2 The lower capacitor on the side connecting the half-bridge dual active bridge circuit and the cascaded H-bridge is denoted as U. The sum of the voltages of the upper and lower capacitors of the Nth module is denoted as U. CHN C L1C is the upper capacitor on the floating side of the half-bridge dual active bridge circuit. L2 For the lower capacitor on the floating side of the half-bridge dual active bridge circuit, the sum of the upper and lower capacitor voltages of the Nth module is denoted as U. CLN The voltage of the Nth module is denoted as U. CLN The entire module topology is as follows Figure 7 As shown.

[0037] Regarding the submodule voltage regulation control strategy, for the cascaded H-bridge voltage of a half-bridge dual active bridge circuit, such as... Figure 4 As shown, set the target voltage control value on the cascaded H-bridge side, for example, set U. Cset1 =1000V, collect the measured voltage values ​​on the cascaded H-bridge side of each submodule in the three-phase topology, and perform PI calculation on the difference between each measured voltage value and the voltage control target value to obtain... Figure 4 Phase shift angle between S1 and Q1 The duty cycles of S1 and Q1 are maintained at 50%, the duty cycle of S2 is complementary to that of S1, and the duty cycle of Q2 is complementary to that of Q1. For each half-bridge dual active bridge circuit, it is only necessary to maintain the stability of the voltage on the cascaded H-bridge side.

[0038] For the floating-side voltage of a half-bridge dual active bridge circuit, such as Figure 5 As shown, the target value for controlling the DC component of the DC bus voltage at the floating terminal of the half-bridge dual active bridge circuit is set, for example, U. Cset2 =1000V, collect the measured values ​​of the DC bus voltage at the floating end of the half-bridge dual active bridge circuit in each submodule of the three-phase topology, calculate the average value of all voltages, and perform PI calculation on the difference between each measured average value and the target value to obtain the overall active power control variable I. d This is used to generate the d-axis reference for the inner loop control of the overall machine current. Since the above control targets the average value of all floating-side voltages, for the floating voltage of each submodule, the difference between the average value and the floating-side voltage of the submodule is calculated using PI to obtain a fine-tuning variable ΔN, which is used for phase-to-phase voltage equalization control within the overall machine.

[0039] The computer-readable storage medium of the present invention stores a computer program, which, when executed by a processor, implements the broadband impedance measurement method.

[0040] The computer-readable storage medium may include RAM, ROM, EEPROM, CD-ROM or other optical disc storage devices, magnetic disk storage devices or other magnetic storage devices, flash memory, or any other media that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer.

[0041] The processor is used to execute a computer program stored in memory to implement the various steps in the methods described in the above embodiments.

Claims

1. A voltage regulation method for a submodule of a broadband impedance measurement device for a high-voltage system, characterized in that, Each sub-module of the device consists of a cascaded H-bridge and a floating DC / DC converter connected in series on the DC side; one end of the floating DC / DC converter is connected to the cascaded H-bridge, and the other end is suspended; the floating DC / DC converter absorbs or outputs energy from the suspended side to stabilize the DC bus voltage of the cascaded H-bridge; the cascaded H-bridge controls the DC bus voltage and capacitor voltage at the suspended end of the floating DC / DC converter to stabilize according to the phase-to-phase voltage equalization control strategy. The average value of the DC bus voltage at the floating DC / DC terminal of each sub-module is calculated. The difference between the average value of the DC bus voltage at the floating DC / DC terminal and the DC bus voltage at the floating DC / DC terminal of each sub-module is calculated using PI to obtain the fine-tuning variable used for phase-to-phase voltage equalization control of the whole machine. Set the target value for voltage control on the cascaded H-bridge side, collect the measured voltage value on the cascaded H-bridge side and perform PI calculation on the difference between the measured voltage value on the cascaded H-bridge side and the target voltage control value on the cascaded H-bridge side to obtain the duty cycle or phase shift angle of the switching transistor in the floating DC / DC circuit, which is used to control the DC bus voltage stability of the cascaded H-bridge. Set the target value for the DC component control of the DC bus voltage at the floating terminal of the DC / DC converter, collect the measured value of the DC bus voltage at the floating terminal of the DC / DC converter, and perform PI calculation on the difference between the average value of the measured DC bus voltage and the target value for the DC component control of the DC bus voltage to obtain the overall active power control variable, which is used to generate the d-axis reference for the inner loop control of the whole machine current.

2. The voltage regulation method for a submodule of the broadband impedance measurement device for high-voltage systems according to claim 1, characterized in that, The floating DC / DC converter is equipped with DC bus capacitors at both ends.

3. The voltage regulation method for a submodule of the broadband impedance measurement device for high-voltage systems according to claim 1, characterized in that, The suspended DC / DC converter is a duty cycle-adjustable topology or a phase-shift control topology.

4. The voltage regulation method for a submodule of the broadband impedance measurement device for high-voltage systems according to claim 1, characterized in that, One end of the cascaded H-bridge is connected to the current of each phase of the high-voltage system, and the AC side of the cascaded H-bridge of each sub-module is cascaded. The other end of the cascaded H-bridge is connected to the floating DC / DC converter.

5. A broadband impedance measurement method for a broadband impedance measurement device for a high-voltage system, characterized in that, The sub-modules of the device are regulated and controlled by the sub-module voltage regulation method described in claim 1. The device is connected to a high-voltage system and the broadband impedance characteristics are measured by the parallel disturbance current injection method.

6. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by the processor, it implements the wideband impedance measurement method according to claim 5.

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