Tatsuhito Saito

Frequency domain based power controller of energy storage device for a hybrid traction system in a DC-electrified railway

In the DC-electrified railway system that is fed by diode rectifiers at a substation, the substation cannot transmit DC electric power to an AC-grid. Hence, the electric power regenerated by a train should be consumed by other trains. Therefore, a regenerative brake cannot be used when other trains do not consume the electric power. In order to use the regenerative brake independent of the state of other trains, using energy storage device (ESD) for DC-electrified railway systems is examined in recent years. This paper deals with feeding line and electric double layer capacitor (EDLC) hybrid train system. This research aims at establishment of the design method of controlling electric EDLC power for using a regenerative brake for any conditions. In this paper, to smooth the power from the feeding line, the control method of EDLC power based on the frequency band of the motor power is proposed, and it is verified by the numerical simulation.

A study on a method to design energy capacity of wayside energy storage devices in DC-electrified railway systems

In this paper, a method to design energy capacity of wayside energy storage devices (ESDs) is proposed, considering the energy-saving effect and the cost performance of ESDs. Then, the designing method is verified by the numerical simulations. It is also revealed that the train operating diagram does not affect the proposed method to design energy capacity of ESDs.

A study on energy management controller of EDLC for batteries and capacitors hybrid electric vehicles

There are still technical issues with batteries for electric vehicles(EVs), such as less driving distance, and their short life. Then, there is an idea providing a more highly efficient and longer life energy storage system by hybridizing batteries and EDLCs (Electric Double Layer Capacitors). The purpose of choosing EDLCs is to cut the peak power of the battery. However, EDLC cannot be utilized without managing the energy properly since the energy capacity of EDLC is low. For this reason, a control system has been proposed to keep the energy of EDLC within the limits. This paper describes a design criteria of the proposed controller and experimentally validates that the control system is effective.

A realization of high-performance motion control systems by applying multi-level converters

In the field of motion control systems, voltage ripple, harmonics, and electromagnetic interferences (EMI) in an output of converters negatively affect the control performance. However, so far, there has been practically few works that explicitly consider the power converters in motion control systems. Currently, general 2-level converters are widely used. However, it is concerned that the 2-level converter becomes one of the obstacles to realize high-performance control because the output voltage has high harmonics and EMI. Those possibly degrade the position or force control performance. As the solution to this problem, linear amplifiers may be useful because they outputs continuous voltage without pulsed waveform. However, low efficiency of the linear amplifiers becomes critical issue as the power converter. In this paper, performance improvement of the motion control systems by applying multilevel converters is investigated as a solution to realize both high control performance and high efficiency at a higher level. From the results of some experiments, it is seen that current waveform is distorted in the case of using the 2-level converter due to the output voltage ripple of the converter. In addition, the operation of disturbance observer (DOB) causes current ripple with lower frequency. On the other hand, it is confirmed that 9-level converter reduces the ripples of the current effectively. Moreover, EMI which is major concern in high-performance control system such as extremely small motor applications for high-precision control, can be improved by using the multi-level converter even without any filters.

Loss compensation by disturbance observer on energy management controller for hybrid traction circuit

This paper deals with a frequency domain based energy management controller for energy storage devices (ESD). This paper presents a disturbance observer that estimates and compensates the loss of the ESD to keep stored energy of the ESD in an appropriate range. The authors use a disturbance observer to estimate the loss because it is difficult to make a model of the loss of the ESD. Simulation results show the loss observer is able to keep stored energy of the ESD near the reference. As the result, it is able to use smaller capacity of the ESD by avoiding over-discharge.

DC-reactor-less hybrid DC-DC converter with a core composed of four legs

Efficiency improvement and cost reduction are important requirements for the design of DC-DC converters. Zero voltage switching is one good solution for increasing efficiency, and an active clamp circuit is useful for implementing it effectively. A cost reduction could be achieved by devising a new transformer that functions not only as a conventional transformer but also as a DC reactor that reduces the switching device peak current. The magnetic core of the new transformer is composed of four legs. A novel hybrid DC-DC converter in which forward and fly-back converters are combined by using the transformer was developed. However, no design methodology for such a transformer has yet been established. Therefore, the modeling of the excitation circuit of the transformer is required. This paper proposes a novel method that simulates the operations of the DC-DC converter and estimates the magnetic flux distribution in the new transformer. The magnetic circuit of the transformer is transformed into its equivalent electric circuit with two ideal transformers. The performance of the DC-DC converter was examined by circuit simulations including the magnetic circuit of the transformer. Circuit simulation results agree fairly well with experimental ones.