On-line uninterrupted power supply (UPS) is used to guarantee stable power supply in case of grid faults. It is widely applied in industry, commerce, medical and transportation. In many application scenarios, several on-line UPSs are required to work in parallel due to high load demand. However, high-frequency resonance might occur in the output current of paralleled UPSs. This paper provides impedance model analysis of the resonance and proposes a mitigation method based on digital notch filter. Through this method, the resonance can be mitigated significantly, and voltage dynamic performance is not deteriorated. The effectiveness of the proposed method is verified through experimental tests.
The rank deficiency of conventional model reference adaptive system(MRAS)multi-parameter identification method leads to the parameter identification error.To address this problem,an MRAS multi-parameter identification method based on permanent magnet synchronous motor(PMSM)current incremental state equation is proposed.Taking advantage of the fact that the motor electrical time constant is much smaller than the mechanical time constant,the current incremental state equation is constructed and used as the adjustable model of MRAS.Thus,the resistance and inductance parameter accurate identification can be realized in the case of the flux parameter is completely unknown,and the identification error caused by the rank deficiency issue is avoided.The proposed method does not need to in-ject additional excitation signal.Finally,experimental validation demonstrates that the proposed method can accurately identify motor parameters.
A novel voltage-frequency response control strategy for MMC-HVDC systems is introduced,leveraging ener-gy storage to enhance grid-side voltage regulation and system stability.By integrating a coupling coefficient between voltage and frequency deviations,this approach incorporates grid frequency variations during oscillations into the con-trol loop of the grid-side converter.This modulation of the MMC-HVDC impedance not only suppresses oscillations but also supports frequency inertia,enhancing the overall system resilience.The efficacy of this strategy in mitigating wide-frequency oscillations is demonstrated using the Typhoon HIL 404 experimental platform.
The turn-off capability of integrated gate commutated thyristor(IGCT)is highly dependent on the commu-tation capability of its gate drive unit.In order to improve its commutation capability,limiting stray inductance is the key.The main factors affecting the stray inductance in the turn-off circuit are analyzed,and a method to suppress and reduce the stray inductance of the circuit is proposed.By using this method,the total stray inductance of the turn-off circuit is reduced from 13.6 nH to 4.7 nH,and finally reaches 3.5 nH,so that the peak and rise rate of gate current reach-6 120 A and-5 720 A/μs,respectively,which meets the requirements of the turn-off ability of the drive cir-cuit of 4 500 V/4 000 A IGCT.The stray inductance of the surrounding turn-off circuit is divided and measured in de-tail,and the inductance distribution of each part is analyzed.The results have important reference value for the design of IGCT drive circuit board with higher current capacity.
When the inverter is carrying an unbalanced load, the output voltage imbalance of the traditional VSG control strategy is too large. A virtual synchronous generator (VSG)-based adaptive negative sequence control method is suggested for a three-phase unbalanced load. First, the inverter's mathematical model is developed to examine the reasons behind the excessive output voltage imbalance. Second, the negative sequence VSG regulates the phase angle of the negative sequence voltage and suppresses the negative sequence component of the output voltage through adaptive negative sequence control, while the positive sequence VSG regulates the amplitude and phase angle of the positive sequence voltage to achieve the power control of the load.
