Kazuhiro Usuki

Feasible series compensation applications using Magnetic Energy Recovery Switch (MERS)

Different series compensation applications by using the magnetic energy recovery switch are reviewed. The magnetic energy recovery switch is a variable series compensation device characterized by simple configuration and control as well as a large operating range. Three different applications areas are introduced; load control, generator power capability improvements and series compensation in transmission systems. Load control application seems promising for cases where control of the frequency is not a necessity, such as for fluorescent lamps. By using MERS in series with permanent magnet generators can the output power capability of the generator be increased. At the high power end, MERS is discussed for use as a series compensator in transmission systems, where the power flow can be controlled and increased. In summary, the paper suggests a wider use of series compensation in electrical systems.

Improved Performance of Induction Motor Using Magnetic Energy Recovery Switch

This paper discusses applications of a magnetic energy recovery switch (MERS) to induction motor drive. The MERS is a series compensation device, which can control voltage and input power factor. Characteristics and operation principles of voltage control and power factor correction by MERS are described. Some applications of the MERS to induction motor drive are investigated. Series capacitor compensation may cause some unstable situation. Electrical oscillations caused by the self-excitation with series capacitor are discussed. Experimental results show the MERS also can cause the same problems since the MERS works as a series capacitor. A 5.5 kW experimental system was developed. Damping control by terminal voltage feedback is investigated. Experimental results show that damping control is effective for improving stability of the induction motor drive with MERS. Starting and steady state characteristics are evaluated experimentally.

A new automatic voltage regulator of self-excited induction generator using SVC magnetic energy recovery switch (MERS)

In this paper, a new voltage regulator applied to self-excited induction generator using SVC magnetic energy recovery switch (MERS) is proposed. Reactive compensation is required to maintain rated voltage when operating in load varying conditions or variable speeds. The proposed system consists of a bidirectional current switch, dc capacitor and inductor as a filter and operates as a variable reactive compensator. Two types of experiments were conducted to perform voltage control in load varying conditions at constant and variable speed. The proposed system has the following advantages: i) simple and fast control, where only two voltage sensors are required, PI controller for feedback operation gives fast response, ii) low switching losses can be achieved using zero voltage switching and low switching frequency, iii) low harmonic distortion; optimal selection of capacitor and inductor will lead to low distortion. The proposed system is proved to have good performance when being applied as a voltage regulation to induction generator. Further more, rating reduction of SVC MERS of about 60% can be achieved by connecting fixed capacitor in parallel to induction generator terminal.

Control design and experimental verification of a series compensated 50 kW permanent magnet wind power generator

The increase in converter rating when going to permanent magnet generators for wind power turbines motivates the search for low loss and compact power electronic solutions. Previous investigations show that by using a combination of a diode bridge rectifier and an active series compensation device, the losses can be reduced. This paper investigates the control issues of this concept further. By applying appropriate control modes, the size of the dc-dc chopper can be reduced with 50 percent. A control method when using an active series compensator called magnetic energy recover switch is demonstrated. Small scale experiments verify the control concepts without the use of rotary encoder. Simulations show that maximum power point tracking can be achieved with simple control. Potential for implementing active drive train damping is also indicated.

Variable frequency induction heating using magnetic energy recovery switch (MERS)

This paper proposes a power converter for induction heating which can control the output frequency. This power converter is using a configuration named MERS (magnetic energy recovery switch). A 90 kVA 150-1000 Hz controllable frequency power supply for steel strip induction heating was developed. The power supply used optimally designed IGBTs for the MERS configuration. Loss reduction due to soft-switching and use of the IGBTs makes induction heating possible to operate with variable frequency. Demonstration using the proposed power supply confirms advantages of variable frequency operation.

Loss and Rating Considerations of a Wind Energy Conversion System with Reactive Compensation by Magnetic Energy Recovery Switch (MERS)

Summary Electrical conversion system for permanent magnet wind generators is challenging due to the large rating of power semiconductor devices needed and the associated costs and losses. This motivates the search for new configurations improving these relationships. Additionally, due to the large inductance present in the generator (synchronous reactance), voltage drops results with resistive load and the generator output power is limited. Traditionally, a conventional active rectifier is used, with a 3-level type illustrated in Fig. 1a. The main challenges with this solution are the costs and also increased losses resulting from high speed switching and filter operation. A solution utilizing an active series compensation device combined with a diode bridge is investigated in this paper as shown in Fig. 1b. The series compensator supplies only reactive power with a resulting good generator utilization. This also means that the VA capability of the active semiconductor part can be reduced compared to an active rectifier since the active rectifier also needs to supply the full active power. The use of an active series compensator called Magnetic Energy Recovery Switch (MERS) is studied. MERS is a simple configuration with low switching losses and simple control acting as a variable capacitor. Due to the special characteristics of this configuration, a new IGBT with low on-state voltage has been developed. The performance of the configuration has been confirmed with experiments on a 50 kW multi-pole permanent magnet generator. Numerical investigations on large scale system indicate potential for loss reductions and power semiconductor rating reduction compared to using an active rectifier solution.