Jan Arild Wiik

Characteristics of the Magnetic Energy Recovery Switch (MERS) as a Series FACTS Controller

Developing active series compensation in transmission systems is challenging due to the large currents and voltage capabilities required. The main purpose of this paper is to show that the magnetic energy recovery switch (MERS) can be an attractive new series compensator by applying appropriate control. The MERS is similar to a single-phase full bridge, meaning that compared to the gate-commutated series capacitor, it has twice the number of active switches. However, advantages, such as the double voltage-current operating range, eliminating the need for reverse blocking switches, zero current turn-on, and a lower current conduction period of each switch can make the MERS an attractive alternative. The basic characteristics of the MERS have been found to be similar to a series connection of a voltage source and a capacitor in steady state. With this dual characteristic, a control method has been developed where the minimization of the harmonics in the series-injected voltage and stable operation during large setpoint changes have been achieved. The resulting subharmonic characteristic also indicates a low risk of subsynchronous resonance. Experimental results verify the proposed configuration and control.

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 AC Current Switch Called MERS with Low On-State Voltage IGBTs (1.54 V) for Renewable Energy and Power Saving Applications

Emergence of new power electronics configurations have historically been one of the important drivers for improvement of the IGBT technology. Development of new IGBTs is said to be a trade-off between saturation voltage, short-circuit capability and switching losses. With the common applications requiring high switching frequency and short-circuit capability, the saturation voltage performance has not been fully optimized. This paper describes a new configuration called the Magnetic Energy Recovery Switch (MERS). It is characterized by using simple control and low switching frequency, where saturation voltage is the main contributor to losses. The semiconductor requirements of this configuration have led to the development of a new low on-state voltage IGBT. Application in the area of wind power conversion shows potential for efficiency improvements. Additionally, due to the soft-switching nature of the MERS application, series connection of the new IGBTs in variable frequency induction heating application is shown to be easy without voltage sharing problems.

Series Connected Power Flow Control using Magnetic Energy Recovery Switch (MERS)

A new series connected power flow controller, called the magnetic energy recovery switch, has been investigated. It is characterized by four active switches and a dc-capacitor in each phase. The device is capable of injecting up to rated voltage within the current rating. It behaves similar to a controllable voltage source and a variable capacitor connected in series. A control algorithm has been developed in order to facilitate power flow control with these combined characteristics. Experimental results suggest the MERS to be a promising new power flow controller.

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 of series compensated induction motor using magnetic energy recovery switch

This paper proposes a induction motor drive using magnetic energy recovery switch (MERS). The MERS is a series compensation device and it can control the load voltage and input power factor. Stability problem because of self-excitation was found. However, this could be solved with voltage feedback control. Small scale experiments and field test results are reported.

Feasibility Study on Current Source Power Conversion for Superconducting Magnets Using Series Compensated Thyristor Converters

Thyristor converters are used as power conditioning systems for superconducting coils. The objective of this work is to discuss the series compensation of thyristor converters using variable series capacitors. Traditional thyristor converters operate with lagging power factor requiring large reactive compensation efforts. Similarly, the series capacitor can control the coil voltage through a unity power factor thyristor converter with a resulting leading power factor seen from the grid. Therefore, by combining the two, both leading and lagging reactive power control, and also the active power control of the superconducting coils can be achieved. In order to demonstrate the feasibility of the series compensation of the thyristor converter, a prototype converter using a gate-commuted series capacitor (GCSC) is developed. From the experimental results using a superconducting coil, the authors demonstrated the leading current control capability of the series compensated thyristor converter, and verified the leading, lagging, and unity power factor control capability based on thyristor converter systems. This feature leads to a potential reduction in reactive power compensation need of 50 percent of the conventional thyristor converter system.

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.

Series compensation of thyristor converters for superconducting magnets

Thyristor converters are used as power conditioning systems for superconducting coils. The objective of this work is to discuss the series compensation of thyristor converters using variable series capacitors. Traditional thyristor converters can control the coil voltage by changing the firing angle and then also the lagging power factor on the ac side. Similarly, the series capacitor can control the coil voltage through a unity power factor thyristor converter (α=0) with a resulting leading power factor seen from the grid. Therefore, by combining the two, both leading and lagging reactive power control, and also the active power control of the superconducting coils can be achieved. In fact, when neglecting commutation angles, the combined system reduces the total installed reactive power compensation need with 50% compared to a pure traditional system. In order to demonstrate the feasibility of the series compensation of the thyristor converter, a prototype converter using a gate-commuted series capacitor (GCSC) is developed. From the experimental results using a superconducting coil, the authors verified the leading current control capability of the series compensated thyristor converter, and also demonstrated the reactive power compensation of the combined thyristor converter system.