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Weiyao Wang,Ke Ma,Yunxiao Yang,Xu Cai 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
The modular multilevel converter (MMC) is one of the most promising converter topologies for medium/high voltage energy conversion. This paper focuses on the balancing method of the submodule capacitor voltages for MMC based on Carrier-Phase-Shift Pulse Width Modulation (CPS-PWM). Firstly, the unbalance mechanism of the submodule capacitor voltages is theoretically revealed. Then the capacitor voltage disturbances are extracted by sampling over a non-synchronized switching period. Based on the characteristics of the extracted disturbances in nonsynchronized switching period, a method for capacitor voltage balancing is thereby proposed which is efficient for various working conditions and easy to realize. Finally, the effect of the proposed method is verified by comprehensive simulation in PLECS.
Thermal Performance of Modular Multilevel Converters in HVDC Applications under Offset PWM
Harith R. Wickramasinghe,Weiyao Wang,Ke Ma,Georgios Konstantinou 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
The total number of submodules (SMs) in a modular multilevel converter (MMC) can be utilized by considering an offset in the arm currents in order always operate at the maximum duty cycle. This article presents the thermal performance of an MMC for an HVDC application when considering its operation under offset PWM. It is demonstrated that the reduction of the total energy in the SM capacitors and the improved performance under faults with lower overall losses but with a variation in the distribution of losses among the devices within an SM. Simulation results based on detailed thermal models as well as experimental cases with thermal behavior demonstrate the impact of offset PWM in an MMC for HVDC applications.
Yunxiao Yang,Ke Ma,Weiyao Wang 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Modular Multilevel Converter (MMC) has been widely used in medium/high voltage direct current transmission, motor drive, and renewable energy power generation, etc. The reliability requirements of MMC system which is composed of sub-modules(SM) as building blocks, are getting crucial. However, the testing for reliability of SMs in a full MMC system is time consuming and costly. In this paper, a mission profile emulator for SMs in MMC system is therefore focused, by using this mission profile emulator, the SMs can be tested individually without building a full MMC system. Simulation results show that the mission profiles of the SM under test is well agrees with the SM in a complete MMC system.
Damping of Inter-Area Low Frequency Oscillation Using an Adaptive Wide-Area Damping Controller
Wei Yao,L. Jiang,Jiakun Fang,Jinyu Wen,Shaorong Wang 대한전기학회 2014 Journal of Electrical Engineering & Technology Vol.9 No.1
This paper presents an adaptive wide-area damping controller (WADC) based on generalized predictive control (GPC) and model identification for damping the inter-area low frequency oscillations in large-scale inter-connected power system. A recursive least-squares algorithm (RLSA) with a varying forgetting factor is applied to identify online the reduced-order linearlized model which contains dominant inter-area low frequency oscillations. Based on this linearlized model, the generalized predictive control scheme considering control output constraints is employed to obtain the optimal control signal in each sampling interval. Case studies are undertaken on a two-area fourmachine power system and the New England 10-machine 39-bus power system, respectively. Simulation results show that the proposed adaptive WADC not only can damp the inter-area oscillations effectively under a wide range of operation conditions and different disturbances, but also has better robustness against to the time delay existing in the remote signals. The comparison studies with the conventional lead-lag WADC are also provided.
Wei Yao,Jiakun Fang,Ping Zhao,Shilin Liu,Jinyu Wen,Shaorong Wang 대한전기학회 2013 Journal of Electrical Engineering & Technology Vol.8 No.2
In this paper, a nonlinear adaptive damping controller based on radial basis function neural network (RBFNN), which can infinitely approximate to nonlinear system, is proposed for thyristor controlled series capacitor (TCSC). The proposed TCSC adaptive damping controller can not only have the characteristics of the conventional PID, but adjust the parameters of PID controller online using identified Jacobian information from RBFNN. Hence, it has strong adaptability to the variation of the system operating condition. The effectiveness of the proposed controller is tested on a two-machine five-bus power system and a four-machine two-area power system under different operating conditions in comparison with the lead-lag damping controller tuned by evolutionary algorithm (EA). Simulation results show that the proposed damping controller achieves good robust performance for damping the low frequency oscillations under different operating conditions and is superior to the lead-lag damping controller tuned by EA.