A resonant shunt impedance measuring device and its control system

Abstract

The present invention discloses a resonant shunt impedance measurement device and its control system. The resonant shunt impedance measurement device comprises an LC series resonant branch, a capacitor-coupled series impedance measurement device (SIMD), and a bypass switch. The LC series resonant branch, the SIMD, and the bypass switch are connected in parallel. The LC series resonant branch flows through the steady-state current of most of the system to be measured without affecting the injection of the disturbance voltage. The control of the resonant shunt impedance measurement device consists of three parts: signal processing, reference generation, and PR-based dual closed-loop control. This control can achieve the control objectives of controllable disturbance voltage output amplitude and minimizing the fundamental current flowing through the SIMD. The present invention can achieve the goal of almost no fundamental current flowing through the SIMD across the entire frequency band, increase the switching frequency of the impedance measurement device, and reduce the size, cost, and loss of the impedance measurement device.

Description

Technical Field

[0001] The present invention belongs to the technical field of impedance measurement, and in particular relates to a resonant shunt impedance measurement device and a control system thereof. Background Art

[0002] Against the backdrop of “carbon peak” and “carbon neutrality”, the development and utilization of new energy sources have been further accelerated. However, the interaction between power electronic equipment and the power grid often causes broadband oscillation accidents. Impedance analysis is an important tool for analyzing this broadband oscillation phenomenon. The input / output impedance of the system can be obtained through mathematical modeling and actual measurement. However, when the internal parameters of the system are uncertain and the system topology has time-varying characteristics, the accuracy of the impedance model obtained by the modeling method is reduced, and impedance measurement has become a research hotspot. At present, research on impedance measurement at home and abroad is mainly focused on low-power occasions with medium and low voltages. With the increasing scale of new energy sites, high-power impedance measurement devices are in urgent need of development, and it is very necessary to study the control algorithm of high-power impedance measurement devices.

[0003] Impedance measurement is categorized into two main types: passive and active. Passive measurement calculates the impedance of the system under test by extracting its own background harmonics. Active measurement injects a specific disturbance into the system under test through a disturbance injection circuit and extracts the disturbance voltage and current response to calculate the impedance. Active measurement offers controllable disturbances and high measurement accuracy, making it the mainstream measurement method. Based on the nature of the injected disturbance signal, active measurement methods are further divided into series voltage injection and parallel current injection. According to the parallel current divider law, the parallel current injection method is applicable when the grid impedance is significantly greater than the equivalent impedance of the renewable energy source under test. According to the series voltage divider law, the series voltage injection method is applicable when the grid impedance is significantly less than the equivalent impedance of the renewable energy source under test. Because the equivalent impedance of renewable energy power generation devices is significantly greater than the AC grid impedance, the series voltage injection method is studied here.

[0004] There are two main coupling methods for voltage disturbance injection: transformer-coupled injection and capacitor-coupled injection. Regardless of the coupling method, the fundamental frequency current flowing through the system under test will flow through the impedance measurement device, increasing the size, cost, and losses of the impedance measurement device. Therefore, it is necessary to reduce the fundamental frequency current flowing through the impedance measurement device. Summary of the Invention

[0005] In view of the characteristics of the impedance measurement device using the series voltage injection method in which the fundamental current flows, the present application provides a resonant shunt impedance measurement device and its control system, which ensures high impedance measurement accuracy without interfering with the stable operation of the system to be measured, significantly reduces the fundamental current flowing through the impedance measurement device, and reduces the volume, cost and loss of the impedance measurement device.

[0006] A resonant shunt impedance measuring device includes a parallel-connected LC series resonant branch, a series impedance measuring device based on capacitor coupling, and a bypass switch; the LC series resonant branch includes a resistor R2, a capacitor C2, and an inductor L2 connected in series; the resonant frequency of the LC series resonant branch is equal to the fundamental frequency of the power grid.

[0007] A control system for a resonant shunt impedance measurement device includes a signal processing module, a reference generation module, and a dual closed-loop control module based on PR control;

[0008] The signal processing module includes a notch filter and a Clark transform; when the fundamental current flows through the LC series resonant branch, the voltage u at both ends of the series impedance measuring device is c The fundamental frequency component on the voltage is filtered out with a notch filter and then Clark transformation is performed to ensure that there is no fundamental frequency component in the harmonic current reference generated by the voltage outer loop;

[0009] The fundamental current reference of the reference generation module is set to 0; the harmonic voltage reference is set to 1% to 10% of the voltage level of the system to be measured;

[0010] The dual closed-loop control module based on PR control includes an outer-loop harmonic voltage control module and an inner-loop fundamental current and harmonic current control module; the outer-loop harmonic voltage control module is used to generate a harmonic current reference value for inner-loop current control, which is added to the fundamental current reference value as a reference signal for the inner current loop; the inner-loop fundamental current and harmonic current control module includes two parallel-connected PR controllers that control the fundamental current and harmonic current respectively.

[0011] Furthermore, the transfer function of the notch filter is:

[0012]

[0013] Where ξ1 and ξ2 are notch coefficients, ω0 is the fundamental angular frequency, and s is the Laplace operator.

[0014] Furthermore, the transfer functions of the harmonic PR controller and the fundamental PR controller in the dual closed-loop control module are:

[0015]

[0016]

[0017] Among them, ω h is the harmonic angular frequency; K P and K R are the proportional parameter and the resonance parameter respectively.

[0018] The beneficial effects of the present invention are:

[0019] (1) The present invention adopts a resonant shunt topology and its control system, which can effectively reduce the fundamental current flowing through the series impedance measurement device (SIMD);

[0020] (2) The present invention adopts a resonant shunt topology and its control system so that the peak current passing through the SIMD is much lower than the rated current of the system under test, so the switching frequency can be increased to inject high-frequency voltage disturbances.

[0021] (3) The present invention adopts a resonant shunt topology and its control scheme to ensure the stable operation of the impedance measurement device in the full frequency band and ensure high-precision measurement results. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic structural diagram of the resonant shunt impedance measurement device provided in an embodiment of the present application.

[0023] Figure 2 This is a signal processing block diagram provided in an embodiment of the present application.

[0024] Figure 3 A reference generation block diagram is provided for an embodiment of the present application.

[0025] Figure 4 This is a block diagram of a dual closed-loop control system based on PR control provided in an embodiment of the present application. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] In a first aspect, an embodiment of the present application discloses a resonant shunt impedance measurement device, comprising an LC series resonant branch, a series impedance measurement device (SIMD) based on capacitor coupling, and a bypass switch; the LC series resonant branch, a traditional series voltage injection device based on capacitor coupling, and the bypass switch are connected in parallel; the LC series resonant branch flows through most of the steady-state current of the system to be measured and does not affect the injection of the disturbance voltage.

[0028] The resonant frequency of the LC series resonant branch is shown in formula (1).

[0029]

[0030] Among them, L2 and C2 are the inductance and capacitance of the resonant branch respectively, and ω0 is the resonant angular frequency.

[0031] The LC series resonant branch is designed to achieve the goal of flowing as much fundamental current as possible, and the resonant frequency is equal to the fundamental frequency of the power grid;

[0032] The LC series resonant branch shunt principle is as follows: for the fundamental frequency loop, the impedance of the LC resonant branch is the resistance R2 of the branch. When it is much smaller than the impedance of the SIMD, most of the fundamental frequency current flows through the resonant branch, and the SIMD is short-circuited by the resonant branch. For the disturbance voltage frequency loop, the impedance of the LC resonant branch is very large and can be regarded as an open circuit. Therefore, this branch will not affect the harmonic injection function of the impedance measurement device.

[0033] like Figure 1 As shown, this embodiment provides a resonant shunt impedance measurement device, including an LC series resonant branch, a traditional series voltage injection device based on capacitor coupling, and a bypass switch; the LC series resonant branch, the traditional series voltage injection device based on capacitor coupling, and the bypass switch are connected in parallel; the LC series resonant branch flows through most of the steady-state current of the system to be measured and does not affect the injection of the disturbance voltage.

[0034] In a second aspect, an embodiment of the present application discloses a control system based on the above-mentioned measuring device, including a signal processing module, a reference generation module and a dual closed-loop control module based on PR control.

[0035] The signal processing module includes a notch filter and Clark transformation. When the fundamental current flows through the LC resonant branch, the resistor R2 causes the voltage u across the two ends of the series impedance measuring device to c The voltage outer loop is used to generate the harmonic current reference, so the signal processing module is used to measure the voltage u across the series impedance device. c The fundamental frequency component on is filtered out by a notch filter to ensure that there is no fundamental frequency component in the harmonic current reference generated by the voltage outer loop. The notch filter transfer function is shown in Equation (2);

[0036]

[0037] Among them, ξ1 and ξ2 are notch coefficients, and ω0 is the fundamental angular frequency.

[0038] like Figure 2 As shown, the signal processing module in the H-bridge inverter control provided by this embodiment. The voltage u across SIMD is c After the fundamental frequency component is filtered out by the notch filter, Clark transformation is performed to ensure that there is no fundamental frequency component in the harmonic current reference generated by the voltage outer loop.

[0039] The reference value of the reference generation module is shown in formula (3). In order to minimize the fundamental current flowing through the SIMD, the fundamental current reference value is set to 0; the harmonic voltage reference is set to 1% to 10% of the voltage level of the system to be tested.

[0040] i bdref =i bqref =u qref =0,u dref =U hm (3)

[0041] Among them, U hm is the harmonic voltage amplitude to be injected.

[0042] like Figure 3 As shown in FIG, a reference generation block diagram in the H-bridge inverter control provided by this embodiment is shown, wherein the fundamental current reference is set to 0, and the harmonic voltage reference is set to 1% to 10% of the voltage level of the system to be measured.

[0043] The dual closed-loop control module based on PR control includes an outer loop harmonic voltage control and an inner loop fundamental current and harmonic current control. The outer loop voltage PR control is used to generate a harmonic current reference value for the inner loop current control, which is added to the fundamental current reference value as the reference signal for the inner current loop. The inner current loop consists of two PR controllers connected in parallel to control the fundamental current and harmonic current respectively. The transfer functions of the harmonic PR controller and the fundamental PR controller are shown in (4)(5).

[0044]

[0045]

[0046] Among them, ω h is the harmonic angular frequency, K P and K R are the proportional parameter and the resonance parameter respectively.

[0047] like Figure 4 The figure shows a block diagram of a PR-based dual closed-loop control system for an H-bridge inverter control system according to this embodiment. The outer-loop voltage PR control generates a harmonic current reference value for the inner-loop current control. This reference value is added to the fundamental current reference value and serves as the reference signal for the inner current loop. The inner current loop consists of two parallel PR controllers that control the fundamental current and harmonic current, respectively.

[0048] The technical solution of the present application can achieve the goal of almost no fundamental current flowing through the impedance measuring device in the entire frequency band, increase the switching frequency of the impedance measuring device, and reduce the volume, cost and loss of the impedance measuring device.

Claims

1. A control system for a resonant shunt impedance measurement device, characterized in that: The resonant shunt impedance measuring device includes an LC series resonant branch connected in parallel, a series impedance measuring device based on capacitor coupling, and a bypass switch; the LC series resonant branch includes a resistor R2, a capacitor C2, and an inductor L2 connected in series; the resonant frequency of the LC series resonant branch is equal to the fundamental frequency of the power grid; The control system includes a signal processing module, a reference generation module and a double closed-loop control module based on PR control; The signal processing module includes a notch filter and a Clark transform; when the fundamental current flows through the LC series resonant branch, the voltage u at both ends of the series impedance measuring device is c The fundamental frequency component on the voltage is filtered out with a notch filter and then Clark transformation is performed to ensure that there is no fundamental frequency component in the harmonic current reference generated by the voltage outer loop; The fundamental current reference of the reference generation module is set to 0; the harmonic voltage reference is set to 1% to 10% of the voltage level of the system to be measured; The dual closed-loop control module based on PR control includes an outer-loop harmonic voltage control module and an inner-loop fundamental current and harmonic current control module; the outer-loop harmonic voltage control module is used to generate a harmonic current reference value for inner-loop current control, which is added to the fundamental current reference value as a reference signal for the inner current loop; the inner-loop fundamental current and harmonic current control module includes two parallel-connected PR controllers that control the fundamental current and harmonic current respectively.

2. The control system according to claim 1, characterized in that: The transfer function of the notch filter is: Where ξ1 and ξ2 are notch coefficients, ω0 is the fundamental angular frequency, and s is the Laplace operator.

3. The control system according to claim 1, characterized in that: The transfer functions of the harmonic PR controller and the fundamental PR controller in the dual closed-loop control module are: Among them, ω h is the harmonic angular frequency; K P and K R are the proportional parameter and the resonance parameter respectively.

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