Power Electronics Control
Power electronics technology plays a significant role in distributed power systems and other power conversion applications. Power electronics allow solar energy to be used by converting the direct current (DC) energy produced by solar panels into alternating current (AC) used in the commercial electrical grid. Wind energy also needs to be converted and must be fed into a grid at a constant frequency despite changing wind conditions. Other forms of alternative power such as thermal, hydro and nuclear also take advantage of the benefits of power electronics to deliver power effectively. The use of this technology can increase productivity and decrease the cost for the manufacturer and the consumer. Without power electronics, this energy cannot be harnessed and delivered efficiently.
Our recent works include:
- Universal fractional-order repetitive control (RC) scheme
Linear phase lead compensation, as a practical and efficient design method, prominently improves RC performance on convergence speed, tracking accuracy, and system stability. However, conventional linear phase lead confronts accuracy problems during several practical applications. To improve phase
lead resolution and provide a comprehensive solution for fractional-order RC, a universal fractional-order design of linear phase lead compensation RC is
developed in which both RC delay period N and phase lead step are fractional.
- Virtual variable sampling (VVS) based repetitive control scheme
When the ratio of reference signal period to the fixed sampling period is not an integer (e.g., 60 Hz reference signal with a 10 kHz sampling
frequency, or grid-connected converter under grid frequency fluctuation, etc.), the performance of RC will be significantly degraded. To solve this
problem efficiently, our team developed a virtual variable sampling RC scheme, which can adapt to the fractional or changing ratio. The VVS method creates a virtual unit delay to approximate one variable sampling delay and offers a universal way for all types of delay based digital controllers and filters
with fixed sampling rate to be robust to frequency variations and fluctuations.
- VVS-based selective harmonic repetitive control scheme
Selective harmonic RC schemes, nk±m-order harmonic RC and DFT-based RC, are more efficient and provides more stability than conventional RC. However, the selective harmonic RCs are sensitive to frequency fluctuation since even very small frequency fluctuation leads to a severe magnitude decrease. To address the problem, the VVS method is applied to the selective harmonic RC schemes. Moreover, a selective odd-order harmonic DFT filter is developed to deal with the dominant odd order harmonic. Because it halves the number of sampling delays in the DFT filter, the system transient response gets nearly 50% improvement.
- Applications to PWM power controller applications
Our team applied the developed RC schemes to PWM DC/AC converters. To test the robustness and frequency adaptation, they are used on single-phase DC/AC converter, three-phase DC/AC converter, single-phase AC/DC converter, and grid-connected power converter.
Industrial Systems