Mechanism Analysis and Suppression Strategy of Continuous High-Frequency Oscillation in MMC-HVDC System
Abstract
:1. Introduction
2. Continuous High-Frequency Oscillation of Back-to-Back MMC-HVDC System
3. High-Frequency Impedance Model of MMC Considering Time Delay
3.1. High-Frequency Small Signal Model of Main Circuit in MMC
3.2. Small Signal Model of MMC Control System Considering Time Delay
3.2.1. System Delay Modeling
3.2.2. Power Outer Loop Modeling
3.2.3. Current Inner Loop Modeling
3.3. High-Frequency Simplified Impedance Modeling of MMC
3.4. Impedance Model Verification
4. Mechanism Analysis of Continuous High-Frequency Oscillation
4.1. Analysis of High-Frequency Oscillation Mechanism of Back-to-Back MMC-HVDC
4.2. Mechanism Analysis of Continuous High-Frequency Oscillation Based on Impedance Matching
- (1)
- The impedance amplitude of MMC-HVDC is consistent with that of the AC system;
- (2)
- The impedance phase angle difference between the MMC-HVDC and AC system is greater than 180°.
5. High-Frequency Oscillation Suppression Strategy Based on Nonlinear Low Pass Filter
5.1. Operation Principle of Nonlinear Low-Pass Filter
5.2. Parameter Design of Nonlinear Low-Pass Filter
- (1)
- Determination of center frequency and cut-off frequency of the low-pass filter. After the low-pass filter is put into operation, it is still necessary to ensure the flow of the voltage components of fundamental frequency and nearby frequencies, that is, the passband of the low-pass filter is required to contain the fundamental frequency 50 Hz, and the low-pass filter can also block high-frequency oscillation, so the center frequency can be set at 50 Hz, and then the cut-off frequency can be determined according to the selection result of the cut-off frequency screening module ωn.
- (2)
- Initial value of damping coefficient ξ0 of the low-pass filter. The cut-off frequency and center frequency f0 of the low-pass filter jointly define the adjustment range of the low-pass filter. The initial value of the damping coefficient can be calculated according to the cut-off frequency and center frequency of the filter.
- (3)
- Final value of damping coefficient ξn. When the center frequency is given, the greater the damping coefficient, the greater the adjustment degree of the low pass filter to the amplitude and phase characteristics of the impedance, and the larger the corresponding influence range. Therefore, on the basis of the initial value of the damping coefficient, further adjust the damping coefficient according to the requirements of the stability margin of the system and the dynamic adjustment ability of the control link to obtain the final value of the damping coefficient.
5.3. Effect of Nonlinear Low-Pass Filter on Impedance Characteristics of MMC
5.3.1. Analysis of MMC Impedance after Adding Nonlinear Low-Pass Filter
5.3.2. Performance Comparison of Different Filters Added to the Feedforward Link
- (1)
- Band-stop filter:
- (2)
- Band-pass filter:
6. Time Domain Simulation Verification
7. Conclusions
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
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Parameter | Value |
---|---|
Rated power/MW | 1250 |
dc Voltage/kv | 800 |
ac Voltage/ks | 525 |
Number of SMs | 216 |
SM capacitance/mF | 18 |
Arm inductance/mH | 75 |
PI controller of current loop | Kp = 1.5, Ki = 12.5 |
PI controller of power loop | Kp = 3.5, Ki = 25 |
PI controller of circulating current | Kp = 0.35, Kr = 55 |
PI controller of PLL | Kp = 59.8, Ki = 10 |
Strategies | Negative Damping Band | Control Complexity |
---|---|---|
Low-pass filter | 500–700 Hz | Low |
Band-pass filter | 500–650 Hz | Low |
Band-stop filter | 550–630 Hz | Low |
Nonlinear low-pass filter | / | Low |
Notch filter [19] | / | Medium |
Active damping controller based on virtual flux linkage [22] | / | High |
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Wang, H.; Zhou, N.; Huang, P.; Duan, X.; Huang, R. Mechanism Analysis and Suppression Strategy of Continuous High-Frequency Oscillation in MMC-HVDC System. Electronics 2022, 11, 3555. https://doi.org/10.3390/electronics11213555
Wang H, Zhou N, Huang P, Duan X, Huang R. Mechanism Analysis and Suppression Strategy of Continuous High-Frequency Oscillation in MMC-HVDC System. Electronics. 2022; 11(21):3555. https://doi.org/10.3390/electronics11213555
Chicago/Turabian StyleWang, Hongbin, Niancheng Zhou, Peng Huang, Xiuchao Duan, and Ruiling Huang. 2022. "Mechanism Analysis and Suppression Strategy of Continuous High-Frequency Oscillation in MMC-HVDC System" Electronics 11, no. 21: 3555. https://doi.org/10.3390/electronics11213555
APA StyleWang, H., Zhou, N., Huang, P., Duan, X., & Huang, R. (2022). Mechanism Analysis and Suppression Strategy of Continuous High-Frequency Oscillation in MMC-HVDC System. Electronics, 11(21), 3555. https://doi.org/10.3390/electronics11213555