The program is to develop advanced power electronic converter technologies to increase efficiency, power density and reliability for emerging applicaitons such as renewable energy systems, EV chargers and powertrains, Wireless power transfer etc.
A new technology “Active Virtual Ground” has been proposed and verified by experimental results. Transformerless grid-connected converters (VSI and PFC) associated with Active Virtual Ground (AVG) topology are proposed to mitigate the High Frequency Common Mode voltage and reduce the High Frequency Differiential Mode current ripple concurrently. Two bidirectional blocking semiconductors and a capacitor form the AVG circuit which is connecting to the line terminal, the neutral terminal and a terminal of the input DC link. It provides the following advantages, 1) providing unipolar switching to reduce the inductances of output filter, 2) utilizing fast commutation cells, a MOSFET and an individual fast reverse recovery diode, e.g. SiC Schottky diode, to reduce switching losses of semiconductors, 3) suppressing leakage current to satisfy the industrial standards, 4) The output filter is a LCL filter but without additional grid side inductor. 5) As only high-frequency current components pass through the AVG circuit, additional conduction losses are minimized. The proposed topology is successfully demonstrated in a 1.5kW grid-connected converter prototype with a advanced digital controller. Experimental results show that the proposed system with AVG can effectively attenuate both HF CM and DM current ripples to the grid. The theoretical prediction and experimental results are in good agreement.
Suggested Reading - K. Siu, C. Ho, and R. Li, “A Four-Quadrant Single-Phase Grid-Connected Converter with only Two High Frequency Switches”, IEEE Trans. on Industrial Electronics, vol. 67, no. 3, pp. 1899-1909, Mar. 2020. (PDF)
A new solar inverter topology namely “Manitoba Inverter” have been proposed and its patent has been filed. It is a transformerless single-phase single-stage buck-boost grid-connected VSI circuit to transform DC voltage to AC voltage. The main advantages of the proposed topology are 1) wide input range with a single power stage, 2) sinusoidal continuous grid current and without additional grid inductor requirement, 3) low CM voltage with transformerless design, and 4) only one switch under HF operation in each half line cycle. An 800W, 120V laboratory prototype has been implemented and is used to demonstrate the performance of the proposed topology.
Suggested Reading - C. Ho, and K. Siu, “Manitoba Inverter – Single Phase Single-Stage Buck-Boost VSI Topology”, IEEE Trans. on Power Electronics, vol. 34, no. 4, pp. 3445 - 3456, Apr. 2019. (PDF)
A fast MPPT control scheme based on a boost type DC-DC converter to maximize energy generation from PV panels is proposed, especially panels on a moving object. In the control scheme, dp/dv slope of PV power curve is used to track MPP and boundary controller is utilized for fast modulating PV output voltage. This innovative combination of control loops provides a rapid response, in microsecond range instead of millisecond range for conventional MPPT algorithms, during irradiation transient and a stable operation during steady state. A laboratory prototype has been implemented and is used to verify the performance of the proposed controller with real PV panels.
Suggested Reading - Y. Zhou, C. Ho, and K. Siu, “A Fast MPPT Control Technique using Boundary Controller for PV Applications”, IEEE Journal of Photovoltaics, vol. 9, no. 3, pp. 849-857, May 2019. (PDF)
