Shoji Iida’s research while affiliated with Tokyo Denki University and other places

We propose a novel inverter that can be operated either as a Current Source Inverter (CSI) or as a Voltage Source Inverter (VSI) by changing only the control signals. It is proper to apply it to the interconnecting system with renewal energy, such as photovoltaic cells or wind generation systems, to a grid. This inverter is usually operated as the CSI connected to the grid. Even if the energy source has a lower voltage than the grid, the energy can be supplied to the grid through the proposed inverter. The power factor can be briefly maintained at almost unity. When power supply from the grid is interrupted, the proposed circuit should be operated as the VSI in the stand-alone operation mode. In this way, the circuit can maintain a constant output voltage to the loads. In this paper, the proposed circuit configuration and the control schemes for both the CSI and the VSI are described. Further, the circuit characteristics for both are discussed experimentally.

We propose an electric energy storage system with batteries by a current source inverter. It is interconnected to the single-phase three-wire distribution system. In order to reduce the dc reactor capacity and change the discharging and the charging operations by signals, a set of DC-DC converters is added between the inverter and the batteries. In this paper, the proposed circuit configuration, the control scheme and the operating method are described, and then the discharging and the charging characteristics are discussed experimentally.

Photovoltaic (PV) modules under different solar irradiances have generally the distinct maximum power points. In this paper, a circuit topology for obtaining the respective maximum powers from the above PV modules is investigated. Simplified double cascade boost choppers are proposed and a control scheme to derive the respective maximum output powers from individual PV modules is discussed. Furthermore, the Maximum Power Point Tracking controls on the starting operation, on the solar irradiance change and on the load fluctuation are confirmed by several experiments.

In this paper, a double connected three-phase hybrid rectifier employing thyristors and self-turn-off devices without input transformers is proposed. Two three-phase bridge rectifiers with auxiliary circuit injecting harmonic currents are connected in parallel. This system can be performed as the conventional 24-step rectifier on the optimum conditions. In this paper, circuit performances of the proposed method are discussed by graphical analysis, and optimum parameters are derived. Then, effects on harmonics reduction can be clarified by simulations.

We have already proposed a power factor correction converter, composed of two half-bridge structures, connected to the single-phase three-wire distribution system. In this paper, by applying the above converter, we propose an AC-DC converter with several power compensator functions, as current balancer, static var generator and active filter, for the distribution system. As a result, even if every kind of loads are connected to the distribution system, the source currents can be balanced, their power factors can be maintained almost the unity and harmonic currents can be decreased effectively by the proposed converter, while itself outputs the DC power

In this paper, we propose several control schemes for the three-phase current source inverter interconnecting the dispersed dc source to the utility. They have in common the control patterns with overlapping signals partially into two switching devices in the same polarity arms. The first is the basic scheme. The next is one by improving the basic. The third is the modified scheme for the second. The optimum control scheme combined with the second and the third is proposed finally. Several experimental discussions are presented.

A novel current source inverter system interconnected to the single-phase grid is proposed. It has the same construction as the conventional three-phase current source inverter that is interconnected to the single-phase three-wire distribution system. Though the proposed circuit has no output transformer, it can be equivalently performed as the single-phase double cascade inverter by diverting the pole transformer in the utility system. By controlling the appropriate scheme, the output currents can be obtained as the five-level waveforms and their distortions can be decreased sufficiently. It is applied to the interactive electric energy storage system with batteries and the basic discharging characteristics are discussed experimentally. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(2): 50–61, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10380

The single-phase three-wire distribution system is employed extensively in Japan and the several countries. It has two voltage sources, which are in phase and have the same effective values. Numerous loads are connected to this distribution system. System line currents from two sources tend to be out of balance, because consumers make use of these loads at random. If many working loads lean to a one-sided source, the power interruption will occur by the operation of circuit breakers. For preventing the above trouble, we propose a novel Current Balancer. It consists of two half-bridge converters composed of an ac reactor and two bidirectional switching devices in common with a neutral line and two dc capacitors. In this paper, it is made clear that the proposed system can equalize both source currents even if the load currents are unbalanced. Moreover, we discuss the several characteristics in steady state and transient state by simulations and experiments.