Takanori Isobe

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

Electrical conversion system for permanent magnet wind generators is challenging due to the large rating of power electronics devices needed and the associated costs. 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. A solution utilizing an active series compensation device called magnetic energy recovery switch (MERS) for cancelling the voltage drop across the synchronous reactance is investigated. MERS is a simple configuration with low switching losses. Due to the special characteristics of the configuration, a new IGBT with low on-state voltage has been applied. 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 rating reduction compared to using a conventional active rectifier solution.

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.

Offshore-Wind-Farm Configuration Using Diode Rectifier With MERS in Current Link Topology

This paper proposes a novel current link topology with a diode rectifier and magnetic energy recovery switch (MERS) using a current source inverter for offshore-wind-farm application. Despite the use of a diode rectifier, the proposed topology is capable of regulating individual turbine torque partially. Because offshore wind condition is more stable and has less turbulence intensity (typically 0.08) than that of onshore wind, the individual full-range controllability realized typically by pulse-controlled converters is not necessary. Instead of them, the proposed scheme, a diode rectifier with MERS, has only partial controllability of the individual generator torque which is estimated to be sufficient to achieve the maximum power point tracking operation for offshore-wind-farm application. The proposed topology is aiming to be applicable for offshore wind farms where maintenance reduction is conclusively a critical issue because of the inaccessibility. In this paper, experimental results represent the effectiveness of the topology. Moreover, a new control strategy for offshore wind farms with the proposed topology is also proposed.

Voltage Rating Reduction of Magnet Power Supplies Using a Magnetic Energy Recovery Switch

A new concept of magnet power supplies that can reduce voltage ratings of the power supplies is proposed. Circuit diagram and operation principles of magnetic energy recovery switch (MERS) are described. MERS consists of a capacitor and four semi-conductor devices such as MOSFETs and IGBTs. It is connected in series to a power supply and a coil. MERS is a switch module and it has no power supply in itself. Because MERS generates a voltage required for the inductance of the coil, the power supply only has to supply a voltage required for the resistance of the coil. Therefore, using MERS can reduce voltage rating and capacity of the power supply. Two types of power supply using MERS and voltage rating reduction are discussed. Comparatively small power supplies for high-repetition pulsed magnets and alternating magnetic field coils can be designed. Some experiments were carried out and confirmed that MERS can reduce voltage ratings of power supplies

A soft-switching active rectifier using a concept of magnetic energy recovery switch

Converters using active switches can improve harmonic components of input current and power factor. Moreover, these converters contribute to the footprint downsizing. However, increase of switching losses and EMI due to high frequency switching is one challenge of these types of converters. This paper proposes a new active rectifier circuit topology, which can reduce the switching losses and EMI with soft-switching. Design principles were described. Experimental results confirmed that the proposed circuit has high efficiency with high power factor and low current harmonics. Additionally, the results show that there is a trade-off between loss and harmonics performance.

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.

Soft-Switching Single-Phase Grid-Connecting Converter Using DCM Operation and a Turn-Off Snubber Capacitor

This paper proposes a new single-phase dc/ac converter topology with soft-switching operation. The proposed converter achieves soft-switching by using DCM (discontinuous current mode) operation and a common turn-off snubber capacitor connected to the dc terminals of a full-bridge configuration. One additional semiconductor switch is used to disconnect the snubber capacitor from the dc side, and allows the snubber capacitor to be discharged. The DCM operation realizes zero-current turn-on and the snubber capacitor achieves zero-voltage turn-off. The proposed converter can be applied to a grid-connected converter for domestic renewable energy and energy storage, including Photovoltaic and battery energy storage devices. This paper describes operation principles, control and modulation techniques as a grid-connecting converter. Experimental verification including loss analysis with a 1-kW pilot device is provided.