High and low frequency composite modulation current type disturbance power supply

Abstract

The invention belongs to the technical field of power systems, and particularly relates to a high and low frequency composite modulation current type disturbance power supply. An alternating current power supply output by a power grid equivalent system passes through a transformer and then is respectively input to a system to be tested and a full-control rectifier; the full-control rectifier converts the alternating-current power supply after voltage transformation into direct-current power supply and inputs the direct-current power supply to the full-control inverter; the full-control inverter converts a direct-current power supply into a low-frequency-band signal and a high-frequency-band signal and inputs the low-frequency-band signal and the high-frequency-band signal into the T-shaped notch The T-type notch filter comprises a low-pass filter and a high-pass filter which are connected in parallel, and is used for synthesizing and modulating the low-frequency-band signal and the high-frequency-band signal into a middle-frequency-band signal, generating disturbance current and transmitting the disturbance current to a system to be tested. The high-low frequency combined disturbance signal is generated in a composite disturbance mode, the signal can be directly used in analysis and test of system impedance, and compared with a traditional single frequency, the frequency sweeping efficiency can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power systems, and in particular relates to a current-type disturbance power supply with high- and low-frequency composite modulation. Background Art

[0002] As more and more nonlinear power electronic devices are connected to the power system, the traditional method of directly obtaining the impedance of the power system through modeling is becoming increasingly difficult to analyze. Therefore, the current method of obtaining the stability of the power system is through impedance scanning, that is, injecting a small signal into the power grid and collecting feedback to calculate the impedance of the power grid under different frequency disturbances. The disturbance frequency ranges from low to high, and a more precise disturbance and a better performance disturbance source are required.

[0003] There are two traditional disturbance sources. One is to input disturbance voltage into the system in series, measure output current, and calculate and process to obtain system impedance; the other is to input disturbance current into the system in parallel, measure output voltage, and calculate and process to obtain system impedance. The characteristic of the traditional method of obtaining impedance by frequency sweeping is that only a single frequency disturbance can be injected at the same time. Since there are many frequencies that actually need to be swept in the frequency sweeping, the continuous disturbance time is longer, and the frequency sweeping time is longer. The longer the disturbance lasts, the more harmonics of different frequencies will be accumulated in the power grid, which will have potential risks and affect the results of other frequency sweeping. At the same time, the voltage-type disturbance source is limited by the current limitation of the machine's own devices, which has a great limitation on the capacity of the device to be tested. Usually, the system capacity to be tested can only be used normally if it is less than the power capacity of the disturbance source. Summary of the invention

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

[0005] A high-low frequency composite modulated current type disturbance power supply comprises 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 by the power grid equivalent system passes through the transformer and is respectively input to a system to be tested and the fully controlled rectifier; the fully controlled rectifier converts the transformed AC power into a DC power supply and inputs it into the fully controlled inverter; the fully controlled inverter converts the DC power into a low-frequency band signal and a high-frequency band signal and inputs them into the T-type notch filter; the T-type notch filter comprises a low-pass filter and a high-pass filter connected in parallel, and is used for synthesizing and modulating the low-frequency band signal and the high-frequency band signal into a medium-frequency band signal, generating a disturbance current and transmitting it to the system to be tested.

[0006] Furthermore, the single-phase topology structure of the low-pass filter in the T-type notch filter includes a first resistor R 1 , the second resistor R 2 And the third capacitor C 3 The first resistor R 1 One end of the voltage input terminal Ui The other end is connected to the second resistor R 2 And the third capacitor C 3 One end of the second resistor R 2 The other end is connected to the voltage output terminal U o Connect the third capacitor C 3 The other end is grounded.

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

[0008]

[0009] Furthermore, the single-phase topology structure of the high-pass filter in the T-type notch filter includes a third resistor R 3 , the first capacitor C 1 and the second capacitor C 2 ; The first capacitor C 1 One end of the voltage input terminal U i The other end is connected to the third resistor R 3 and the second capacitor C 2 One end of the second capacitor C 2 The other end is connected to the voltage output terminal U o Connect the third resistor R 3 The other end is grounded.

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

[0011]

[0012] Furthermore, the first resistor R 1 , the second resistor R 2 , the third resistor R 3 , the first capacitor C 1 , the second capacitor C 2 And the third capacitor C 3 The following relationship is satisfied:

[0013]

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

[0015] Furthermore, the voltage equation expression of the disturbance current transmitted by the T-type notch filter to the system to be measured is:

[0016]

[0017] Among them, ω 0is the center frequency of the disturbance current, and the asymmetry coefficient m, the first resistor R 1 and the first capacitor C 1 Related: Q 0 is the quality factor, which is only related to the asymmetry coefficient m.

[0018] Furthermore, the center frequency ω of the disturbance current 0 Specifically:

[0019]

[0020] Furthermore, the quality factor Q 0 Specifically:

[0021]

[0022] The beneficial effects of the present invention are:

[0023] The present invention generates a high- and low-frequency combined disturbance signal by means of a composite disturbance. The signal can be directly used in the analysis and testing of the system impedance, and can effectively improve the frequency scanning efficiency compared to the traditional single frequency. The present invention adopts a T-type notch filter that is not commonly used in the filtering system, provides effective gain of high frequency and low frequency for the mixed modulation method, and uses different dynamic gain methods to control and compensate the system at different frequencies. In the present invention, a T-type notch filter and a corresponding gain control strategy are used in the power electronic device. The simultaneous use of the two can smoothly output a stable disturbance signal to the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a system schematic diagram of a current-type disturbance power supply with high and low frequency composite modulation.

[0025] Figure 2 Schematic diagram of the single-phase topology structure of the T-type notch filter.

[0026] Figure 3 Schematic diagram of the frequency gain characteristics of the T-type notch filter.

[0027] Figure 4 Schematic diagram of the control parameter gain characteristics of the T-type notch filter. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] The sweeping time required for the swept disturbance power supply is relatively long within a complete sweeping cycle. The longer the disturbance is injected into the system, the greater the impact on the system, which will have a significant impact on the impedance analysis results and characteristics. Traditional disturbance sources use low-pass or band-pass filters, which will affect the output characteristics of the disturbance. In order to improve the problems of traditional disturbance sources, the following three methods can usually be used to improve the device:

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

[0031] 2. Change the modulation wave generation method

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

[0033] The present invention improves the above three points to varying degrees to achieve improved disturbance source efficiency.

[0034] The present invention changes the gain of impedances of different frequencies through a T-type notch filter; by mixed modulation of high-frequency and low-frequency impedances, the disturbance modulation wave is changed from a traditional single frequency to a mixed modulation frequency. By changing the control parameter gain of the system control level at different frequencies, low gain control is used at high and low frequencies, and high gain control is used at the mid-frequency band.

[0035] The basic system structure of the disturbance source is as follows: Figure 1 As shown, it 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 by the power grid equivalent system passes through the transformer and is respectively input to the system to be tested and the fully-controlled rectifier; the fully-controlled rectifier converts the transformed AC power into a DC power and inputs it to the fully-controlled inverter; the fully-controlled inverter converts the DC power into a low-frequency band signal and a high-frequency band signal and inputs them into the T-type notch filter; the T-type notch filter includes a low-pass filter and a high-pass filter connected in parallel, which are used to synthesize and modulate the low-frequency band signal and the high-frequency band signal into a medium-frequency band signal, and generate a disturbance current to transmit to the system to be tested.

[0036] The conventional filter is a first-order low-pass filter or an LCL filter, which has the characteristic of having a strong attenuation effect on high-frequency signals. The present invention modifies its structure into a T-type notch filter, as shown in the attached figure. Figure 2 As shown, the single-phase topology structure of the low-pass filter in the T-type notch filter includes a first resistor R 1 , the second resistor R 2 And the third capacitor C 3 The first resistor R 1 One end of the voltage input terminal U i The other end is connected to the second resistor R 2 And the third capacitor C 3 One end of the second resistor R2 The other end is connected to the voltage output terminal U o Connect the third capacitor C 3 The other end is grounded; the single-phase topology structure of the high-pass filter in the T-type notch filter includes a third resistor R 3 , the first capacitor C 1 and the second capacitor C 2 ; The first capacitor C 1 One end of the voltage input terminal U i The other end is connected to the third resistor R 3 and the second capacitor C 2 One end of the second capacitor C 2 The other end is connected to the voltage output terminal U o Connect the third resistor R 3 The other end is grounded.

[0037] The voltage equation of the T-type filter is expressed as:

[0038]

[0039] in:

[0040] m 1 =R 3 (C 1 +C 2 )

[0041] m 2 =R 3 (R 1 +R 2 )C 1 C 2

[0042] m 3 =R 1 R 2 R 3 C 1 C 2 C 3

[0043] n 1 =R 3 (C 1 +C 2 )+R 2 C 2 +R 1 (C 1 +C 3 )

[0044] n 2 =R 3 [R 1 C 3 (C 1+C 2 )+(R 2 +R 1 )C 1 C 2 ]+R 1 R 2 C 2 C 3

[0045] n 3 =R 1 R 2 R 3 C 1 C 2 C 3

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

[0047]

[0048] Among them, m is the asymmetric coefficient, and further arrangement can be obtained:

[0049]

[0050] Where:

[0051]

[0052] According to the above formula, the center frequency ω 0 Depends on the asymmetry coefficient m and R in the circuit 1 and C 1 value, and the quality factor Q 0 It is only related to m. When m=1, C 1 =C 2 =C, C 3 =2C, R 1 =R 2 =R, R 3 =R / 2, this is a symmetrical RC double-T stopband filter. When m≠1, the double-T network is an asymmetrical band-stop filter. When m>1, Q 0 >1 / 4.

[0053] Substituting s=jω into F(s), we can get:

[0054]

[0055] After changing the filter structure, due to the attenuation characteristics of the mid-frequency band, the gain at a specific frequency will exceed the controllable range at the control strategy level, so the attenuation cannot be too large, so the control asymmetry coefficient m is controlled to be less than 1. The relationship between system filtering and frequency is shown in the attached figure. Figure 3 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 filter gain and frequency is as follows: Figure 3 shown.

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

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

[0063] Figure 4 and Figure 3 The gain products between the gain curves complement each other, and finally the output of the disturbance source is stable. Figure 4 There are two methods for the gain characteristic strategy, namely the table lookup method and the gain compensation method. The table lookup method is to set the corresponding gain parameters for the gains of each frequency in the design stage, and directly call the parameters in the gain strategy table when scanning to a specific frequency. The gain compensation method is to directly use the constant value to subtract the attenuation gain of the filter to obtain the control gain characteristic curve after determining the amplitude-frequency and phase-frequency output characteristics of the filter, and after the external gain shows a constant characteristic, and directly write the corresponding gain characteristics into the control system parameters. The traditional disturbance strategy generates frequency from low frequency → medium frequency → high frequency, and the method used in the present invention is low frequency + high frequency → medium frequency.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high-low frequency composite modulated current-type disturbance power supply, characterized in that: It 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 by the power grid equivalent system passes through the transformer and is respectively input into the system to be tested and the fully-controlled rectifier; the fully-controlled rectifier converts the transformed AC power into a DC power and inputs it into the fully-controlled inverter; the fully-controlled inverter converts the DC power into a low-frequency band signal and a high-frequency band signal and inputs them into the T-type notch filter; the T-type notch filter includes a low-pass filter and a high-pass filter connected in parallel, which are used to synthesize and modulate the low-frequency band signal and the high-frequency band signal into a medium-frequency band signal, and generate a disturbance current to transmit to the system to be tested.

2. The high-low frequency composite modulated current-type disturbance power supply according to claim 1, characterized in that: The single-phase topology structure 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 The other end is connected to the second resistor R2 and one end of the third capacitor C3 respectively, and 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.

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

4. The high-low frequency composite modulated current-type disturbance power supply according to claim 2, characterized in that: The single-phase topology structure 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 The other end is connected to the third resistor R3 and one end of the second capacitor C2 respectively, and the other end of the second capacitor C2 is connected to the voltage output terminal U o The other end of the third resistor R3 is grounded.

5. The high-low frequency composite modulated current-type disturbance power supply according to claim 4, characterized in that: The T-type notch filter high pass filter and its edge cutoff frequency are expressed as:

6. The high-low frequency composite modulated current-type disturbance power supply according to claim 4, characterized in that: 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: Wherein, m is the asymmetry coefficient, 0<m<1.

7. The high-low frequency composite modulated current-type disturbance power supply according to claim 6, characterized in that: The voltage equation expression of the disturbance current transmitted to the system under test by the T-type notch filter is: Wherein, 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.

8. The high-low frequency composite modulated current-type disturbance power supply according to claim 7, characterized in that: The central frequency ω0 of the disturbance current is specifically:

9. The high-low frequency composite modulated current-type disturbance power supply according to claim 8, characterized in that: The quality factor Q0 is specifically:

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