Miao-miao Cheng

Semiconductor Power Converterless Voltage Sag Compensator and UPS Using a Flywheel Induction Motor and an Engine Generator

Flywheel energy storage systems are focused as uninterruptible power supplies (UPS) from the viewpoint of environmental friendliness and high durability performance. Using a low-speed, heavy, simple flywheel, and a low-cost squirrel-cage induction motor/generator, this paper proposes two applications as follows; 1) 11-kW voltage sag compensator using a capacitor self-excited induction generator without semiconductor converters; 2) UPS composed of the flywheel system and an engine generator. From some experimental results, an ideal voltage sag compensator and UPS are realized by the low-technology flywheel system.

Control and design principle of SVC-MERS — A new reactive power compensator with line frequency switching and small capacitor —

This paper describes about control and design principles for SVC-MERS, a new reactive power compensator using MERS (magnetic energy recovery switch). Low capacitance of dc capacitor and reduced loss and electromagnetic noise due to line frequency switching are advantages of this system. The capacitor voltage waveform generated by SVC-MERS changes according to operating points because of the small capacitor. Operation mode is separated into three types by its waveform. This paper suggests control method for each mode. By using all waveform modes, SVC-MERS obtains wide variation of reactive power generation. Then characteristics of each mode are described and evaluated to discuss the design principle including available operation range. Finally, results of experiments to confirm the concept including control and design principles are shown.

A novel method for improving the overload capability of stand-alone power generating systems based on a flywheel induction motor

Flywheel energy storage systems are good power stabilizers for stand-alone power systems, especially for highly fluctuating load or inrush power demand. In this investigation, a simple setup of a flywheel induction motor device is proposed which is composed of a flywheel and an induction motor directly connected in parallel to the inverter-controlled load. Also, a novel control method to improve the overload capability of the stand-alone power systems is presented by applying frequency control to the load side inverter. Compared to the conventional flywheel energy storage system, the proposed system has the following advantages: 1) simple configuration due to less number of inverters in the proposed system; 2) not only an improved overload capability of the stand-alone power system, but also a decreased capacity of the load-side inverter; 3) simple control and low cost. Although the changes of the flywheelpsilas speed would lead to frequency variations, a survey reveals that a small frequency variation is permitted for quite a lot of industrial machines. The requirement for the frequency variation can be satisfied by a proper capacity design of the flywheel induction motor. A design method to meet the utilitypsilas demand is introduced in this paper. Some experiments are conducted to verify the proposed system and the frequency control method. The experimental results show that the proposed system is easy and practical as an overload improvement method.

Voltage control of induction generator powered distributed system using a new reactive power compensator SVC-MERS

Distributed power system has attracted great interest in terms of renewable energy use and new generation technology. Induction generator is one of the most widely used energy conversion means due to its low cost, robustness and simple control. This paper proposes a distributed system which is powered by squirrel cage induction generators (SCIG). Different from the synchronous generator, SCIG has to get exciting current from outer device at normal operation. Furthermore, voltage instability problem exists at the load change when it is excited with fixed capacitor bank. In order to solve this problem, this paper proposes a new technology named Static VAR Compensation Magnetic Energy Recovery Switch (SVC-MERS) for the induction generators. The SVC-MERS aims to stabilize the generator voltage by providing continues variable reactive power. The operation principle is further developed in order to get a broader operating range. It is confirmed by simulation results. Then, voltage control of induction generator is experimented and the SVC-MERS is proved to stabilize the generator voltage with quick response. Compared to the STATCOM, the SVC-MERS has advantage in line frequency switching and small dc-capacitor.

Cache power for stand-alone power systems: Flywheel-based AC power solution

Stand-alone power systems (SPS) are attracting more and more interest with the global movement toward the distributed generation. Due to their disconnection to the power grid, they are suffering from poor load following capability under load variations. In order to solve this problem, this paper provides an AC power solution based on flywheel energy storage. The proposed flywheel system is characterized of the following two aspects: 1) AC generation, therefore no power converter is needed; 2) automatic power compensation responding to the frequency/voltage change of the power supply. These characteristics make the proposed flywheel system suitable for stabilizing the stand-alone power system against the load variations. Some simulation and experimental results are given to prove the validity and effectiveness of the proposed solution.