A high-low frequency composite modulation current mode disturbance power supply

Abstract

This invention belongs to the field of power system technology, specifically relating to a high-low frequency composite modulation current-source disturbance power supply. In this invention, the AC power output from the equivalent power grid system is transformed and then input to the system under test (SUT) and a fully controlled rectifier. The fully controlled rectifier converts the transformed AC power into DC power, which is then input to the fully controlled inverter. The fully controlled inverter converts the DC power into low-frequency and high-frequency signals, which are then input to a T-type notch filter. The T-type notch filter includes a parallel low-pass filter and a high-pass filter, used to synthesize and modulate the low-frequency and high-frequency signals into a mid-frequency signal, generating a disturbance current that is transmitted to the SUT. This invention generates a high-low frequency combined disturbance signal through composite disturbance, which can be directly used in the analysis and testing of system impedance, effectively improving frequency sweep efficiency compared to traditional single-frequency methods.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, specifically relating to a current-type disturbance power supply with high and low frequency composite modulation. Background Technology

[0002] As more and more nonlinear power electronic devices are connected to power systems, the traditional method of directly obtaining the power system impedance through modeling is becoming increasingly difficult to analyze. Therefore, the current method for obtaining power system stability is through impedance scanning, which involves injecting small signals into the power grid and collecting feedback to calculate the power grid impedance under disturbances at different frequencies. The disturbance frequencies range from low to high, requiring more accurate disturbance sources with better performance.

[0003] There are two traditional types of disturbance sources: one is to input a disturbance voltage in series into the system, measure the output current, and calculate the system impedance; the other is to input a disturbance current in parallel into the system, measure the output voltage, and calculate the system impedance. The traditional frequency sweep method for obtaining impedance is characterized by the fact that only a single frequency disturbance can be injected at any given time. Since a large number of frequencies actually need to be swept during a frequency sweep, the duration of the disturbance is longer, resulting in a longer sweep time. The longer the disturbance duration, the more harmonics of different frequencies accumulate in the power grid, posing potential risks and affecting the results of sweeps at other frequencies. Furthermore, voltage-type disturbance sources are limited by the current limitations of the device itself, significantly restricting the capacity of the device under test. Typically, the capacity of the system under test must be less than the power capacity of the disturbance source for it to be used normally. Summary of the Invention

[0004] The purpose of this invention is to provide a current-type disturbance power supply with high and low frequency composite modulation.

[0005] A high-low frequency composite modulation current-source disturbance power supply includes a power grid equivalent system, a transformer, a fully controlled rectifier, a fully controlled inverter, and a T-type notch filter. The AC power output from the power grid equivalent system is input to the system under test and the fully controlled rectifier after passing through the transformer. The fully controlled rectifier converts the transformed AC power into DC power, which is then input to the fully controlled inverter. The fully controlled inverter converts the DC power into low-frequency and high-frequency signals, which are then input to the T-type notch filter. The T-type notch filter includes a parallel low-pass filter and a high-pass filter, used to synthesize and modulate the low-frequency and high-frequency signals into a mid-frequency signal, generating a disturbance current that is transmitted to the system under test.

[0006] Furthermore, the single-phase topology of the low-pass filter in the T-type notch filter includes a first resistor R1, a second resistor R2, and a third capacitor C3; one end of the first resistor R1 is connected to the voltage input terminal U. iOne end is connected to the second resistor R2 and the other end is connected to one end of the third capacitor C3, respectively. The other end of the second resistor R2 is connected to the voltage output terminal U. o Connect the other end of the third capacitor C3 to ground.

[0007] Furthermore, the low-pass filter and its edge cutoff frequency in the T-type notch filter are expressed as follows:

[0008]

[0009] Furthermore, the single-phase topology of the high-pass filter in the T-type notch filter includes a third resistor R3, a first capacitor C1, and a second capacitor C2; one end of the first capacitor C1 is connected to the voltage input terminal U. i One end is connected to the third resistor R3, and the other end is connected to one end of the second capacitor C2. The other end of the second capacitor C2 is connected to the voltage output terminal U. o Connect the other end of the third resistor R3 to ground.

[0010] Furthermore, the high-pass filter and its edge cutoff frequency in the T-type notch filter are expressed as follows:

[0011]

[0012] Furthermore, the first resistor R1, the second resistor R2, the third resistor R3, the first capacitor C1, the second capacitor C2, and the third capacitor C3 satisfy the following relationship:

[0013]

[0014] Where m is the asymmetry coefficient, 0 < m < 1.

[0015] Furthermore, the voltage equation expression for the disturbance current transmitted from the T-type notch filter to the system under test is as follows:

[0016]

[0017] Where ω0 is the center frequency of the disturbance current, which is related to the asymmetry coefficient m, the first resistor R1, and the first capacitor C1; Q0 is the quality factor, which is only related to the asymmetry coefficient m.

[0018] Furthermore, the center frequency ω0 of the disturbance current is specifically:

[0019]

[0020] Furthermore, the quality factor Q0 is specifically:

[0021]

[0022] The beneficial effects of this invention are as follows:

[0023] This invention generates a combined high- and low-frequency disturbance signal through composite perturbation. This signal can be directly used in system impedance analysis and testing, effectively improving frequency sweep efficiency compared to traditional single-frequency methods. This invention employs a T-type notch filter, which is not commonly used in filtering systems, providing effective high- and low-frequency gain for the hybrid modulation method. Different dynamic gain methods are used to control and compensate the system at different frequencies. This invention utilizes a T-type notch filter and a corresponding gain control strategy in the power electronic device; the simultaneous use of both ensures a stable disturbance signal output to the power grid. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a high- and low-frequency composite modulated current-source disturbance power supply system.

[0025] Figure 2 This is a schematic diagram of the single-phase topology of a T-type notch filter.

[0026] Figure 3 This is a schematic diagram of the frequency gain characteristics of a T-type notch filter.

[0027] Figure 4 This is a schematic diagram of the gain characteristics of the control parameters of a T-type notch filter. Detailed Implementation

[0028] The present invention will now be further described with reference to the accompanying drawings.

[0029] Frequency sweep disturbance sources require a long sweep time within a complete sweep cycle. The longer the disturbance is injected into the system, the greater its impact, significantly affecting impedance analysis results and characteristics. Traditional disturbance sources use low-pass or band-pass filters, which affect the output characteristics of the disturbance. To improve upon the problems of traditional disturbance sources, the following three methods can typically be used to improve the device:

[0030] 1. Change the filter type in the system topology.

[0031] 2. Change the modulation wave generation method

[0032] 3. Use different control gains in different frequency bands.

[0033] This invention makes improvements to the above three points to varying degrees in order to improve the efficiency of the disturbance source.

[0034] This invention utilizes a T-type notch filter to alter the gain of impedance at different frequencies. By mixing and modulating the high-frequency and low-frequency impedances, the disturbance modulation wave is transformed from a traditional single-frequency modulation to a mixed-modulation frequency. By changing the gain of the control parameters at the system control level at different frequencies, low-gain control is used at high and low frequencies, while high-gain control is used in the mid-frequency range.

[0035] The basic system structure of the disturbance source is as follows: Figure 1 As shown, the system includes a power grid equivalent system, a transformer, a fully controlled rectifier, a fully controlled inverter, and a T-type notch filter. The AC power output from the power grid equivalent system is fed into the system under test and the fully controlled rectifier after passing through the transformer. The fully controlled rectifier converts the transformed AC power into DC power, which is then fed into the fully controlled inverter. The fully controlled inverter converts the DC power into low-frequency and high-frequency signals, which are then fed into the T-type notch filter. The T-type notch filter includes a parallel low-pass filter and a high-pass filter, which are used to synthesize and modulate the low-frequency and high-frequency signals into a mid-frequency signal, generating a disturbance current that is transmitted to the system under test.

[0036] Traditional filters are first-order low-pass filters or LCL filters. These filters are characterized by strong attenuation of high-frequency signals. This invention modifies their structure into a T-type notch filter, as shown in the attached figure. Figure 2 As shown, the single-phase topology of the low-pass filter in the T-type notch filter includes a first resistor R1, a second resistor R2, and a third capacitor C3; one end of the first resistor R1 is connected to the voltage input terminal U. i One end is connected to the second resistor R2 and the other end is connected to one end of the third capacitor C3, respectively. The other end of the second resistor R2 is connected to the voltage output terminal U. o The other end of the third capacitor C3 is grounded; the single-phase topology of the high-pass filter in the T-type notch filter includes a third resistor R3, a first capacitor C1, and a second capacitor C2; one end of the first capacitor C1 is connected to the voltage input terminal U. i One end is connected to the third resistor R3, and the other end is connected to one end of the second capacitor C2. The other end of the second capacitor C2 is connected to the voltage output terminal U. o Connect the other end of the third resistor R3 to ground.

[0037] The voltage equation for a T-type filter is expressed as:

[0038]

[0039] in:

[0040] m1 = R3(C1 + C2)

[0041] m2=R3(R1+R2)C1C2

[0042] m3=R1R2R3C1C2C3

[0043] n1 = R3(C1+C2) + R2C2 + R1(C1+C3)

[0044] n2=R3[R1C3(C1+C2)+(R2+R1)C1C2]+R1R2C2C3

[0045] n3=R1R2R3C1C2C3

[0046] The parameters in the filter network are determined according to the following rules:

[0047]

[0048] Where m is the asymmetry coefficient, further simplification yields:

[0049]

[0050] In the formula:

[0051]

[0052] From the above formula, the center frequency ω0 depends on the asymmetry coefficient m and the values ​​of R1 and C1 in the circuit, while the quality factor Q0 is only related to m. When m = 1, C1 = C2 = C, C3 = 2C, R1 = R2 = R, R3 = R / 2, which is a symmetrical RC double-T stopband filter. When m ≠ 1, the double-T network is an asymmetric bandstop filter, and when m > 1, Q0 > 1 / 4.

[0053] Substituting s = jω into F(s), we can simplify to obtain:

[0054]

[0055] After modifying the filter structure, due to the attenuation characteristics in the mid-frequency band, the gain at certain frequencies will exceed the controllable range at the control strategy level. Therefore, the attenuation cannot be too large, so the control asymmetry coefficient m < 1. The relationship between system filtering and frequency is shown in the appendix. Figure 3 As shown.

[0056] The low-pass filter and its edge cutoff frequency can be expressed as:

[0057]

[0058] The high-pass filter and its edge cutoff frequency can be expressed as:

[0059]

[0060] The relationship between the frequency and gain of the filter is as follows: Figure 3As shown.

[0061] The control gain has been changed from a single gain with constant parameters to a gain characteristic that needs to change with the disturbance frequency. In the mid-frequency range, the gain characteristic is as follows: Figure 4 The output characteristics and gain must satisfy the following relationship:

[0062] 1 = H(s) filter G(s)

[0063] Figure 4 and Figure 3 The gain products between the gain curves are complementary, ultimately stabilizing the output of the disturbance source. Figure 4 There are two strategies for determining the gain characteristics of the filter: the lookup table method and the gain compensation method. The lookup table method involves setting the corresponding gain parameters for each frequency during the design phase, and then directly calling the parameters from the gain strategy table when a specific frequency is scanned. The gain compensation method, after determining the amplitude and phase frequency output characteristics of the filter, and ensuring a constant external gain, directly subtracts the filter's attenuation gain from the constant value to obtain the control gain characteristic curve, and then directly writes the corresponding gain characteristic into the control system parameters. Traditional disturbance strategies generate frequencies from low frequency → mid frequency → high frequency; the method used in this invention is low frequency + high frequency → mid frequency.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A high- and low-frequency composite modulated current-source disturbance power supply, characterized in that: The system includes a power grid equivalent system, a transformer, a fully controlled rectifier, a fully controlled inverter, and a T-type notch filter. The AC power output from the power grid equivalent system is passed through the transformer and then input to the system under test and the fully controlled rectifier. The fully controlled rectifier converts the transformed AC power into DC power, which is then input to the fully controlled inverter. The fully controlled inverter converts the DC power into low-frequency and high-frequency signals, which are then input to the T-type notch filter. The T-type notch filter includes a parallel low-pass filter and a high-pass filter, used to synthesize and modulate the low-frequency and high-frequency signals into a mid-frequency signal, generating a disturbance current that is transmitted to the system under test. The single-phase topology of the low-pass filter in the T-type notch filter includes a first resistor R1, a second resistor R2, and a third capacitor C3; one end of the first resistor R1 is connected to the voltage input terminal U. i One end is connected to the second resistor R2 and the other end is connected to one end of the third capacitor C3, respectively. The other end of the second resistor R2 is connected to the voltage output terminal U. o Connect the other end of the third capacitor C3 to ground; The single-phase topology of the high-pass filter in the T-type notch filter includes a third resistor R3, a first capacitor C1, and a second capacitor C2; one end of the first capacitor C1 is connected to the voltage input terminal U. i One end is connected to the third resistor R3, and the other end is connected to one end of the second capacitor C2. The other end of the second capacitor C2 is connected to the voltage output terminal U. o Connect the other end of the third resistor R3 to ground; The first resistor R1, the second resistor R2, the third resistor R3, the first capacitor C1, the second capacitor C2, and the third capacitor C3 satisfy the following relationship: Where m is the asymmetry coefficient, 0 < m < 1.

2. The high- and low-frequency composite modulation current-source disturbance power supply according to claim 1, characterized in that: The low-pass filter and its edge cutoff frequency in the T-type notch filter are expressed as follows:

3. The high- and low-frequency composite modulation current-source disturbance power supply according to claim 1, characterized in that: The high-pass filter and its edge cutoff frequency in the T-type notch filter are expressed as follows:

4. The high- and low-frequency composite modulation current-source disturbance power supply according to claim 1, characterized in that: The voltage equation for the disturbance current transmitted from the T-type notch filter to the system under test is expressed as follows: Where ω0 is the center frequency of the disturbance current, which is related to the asymmetry coefficient m, the first resistor R1, and the first capacitor C1; Q0 is the quality factor, which is only related to the asymmetry coefficient m.

5. A high- and low-frequency composite modulation current-source disturbance power supply according to claim 4, characterized in that: The center frequency ω0 of the disturbance current is specifically:

6. A high- and low-frequency composite modulation current-source disturbance power supply according to claim 4, characterized in that: The quality factor Q0 is specifically:

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