Gunji Kimura

A novel high-performance utility-interactive photovoltaic inverter system

This paper presents a novel photovoltaic inverter that cannot only synchronize a sinusoidal AC output current with a utility line voltage, but also control the power generation of each photovoltaic module in an array. The proposed inverter system is composed of a half-bridge inverter at the utility interface and a novel generation control circuit which compensates for reductions in the output power of the system that are attributable to variations in the generation conditions of respective photovoltaic modules. The generation control circuit allows each photovoltaic module to operate independently at peak capacity, simply by detecting the output power of the system. Furthermore, the generation control circuit attenuates low-frequency ripple voltage, which is caused by the half-bridge inverter, across the photovoltaic modules. Consequently, the output power of the system is increased due to the increase in average power generated by the photovoltaic modules. The effectiveness of the proposed inverter system is confirmed experimentally and by means of simulation.

Megahertz operation of voltage-fed inverter for HID lamps using distributed constant line

A novel type of solid-state ballast, which operates on the MHz-range frequency, is presented in this paper. A circuit composed of a voltage-fed half-bridge inverter, a distributed constant line, and a parallel LC resonant circuit have been developed for this purpose. The HID (high intensity discharge) lamp is connected to the output terminal of the inverter through the distributed constant line. Here, since the length of the line is adjusted to 1/4 of the propagation wavelength /spl lambda/, the output voltage of the voltage-fed inverter can be converted to a current source in the load side. From experimental results, it was found that the ballast can supply not only high voltage but also constant current for starting the discharge of an HID lamp. Experimental results from a prototype system are used to verify the theoretical procedure.

Unity-power-factor PWM rectifier with DC ripple compensation

This paper presents a new topology of PWM rectifier which can achieve unity-power-factor on the AC supply side and ripple-reduction on the DC output side. The main circuit of this rectifier is accomplished by adding only a pair of switches to a conventional PWM rectifier. And it does not need the large DC capacitor or passive L-C resonant circuit. These additional switches and PWM rectifier are controlled not only to make a unity power factor but also to reduce the ripple current. The effectiveness of this circuit is confirmed by the experiments and analysis. This rectifier is useful for UPS and DC power supply, especially in case that the batteries are connected to the DC line.<<ETX>>

A novel utility interactive photovoltaic inverter with generation control circuit

This paper describes a novel utility interactive photovoltaic inverter. Since photovoltaic modules in photovoltaic power generation systems in urban areas are installed on roofs, shadows created by neighboring homes, utility poles, and trees may sometimes cover some part of the photovoltaic modules. In this case, power generated from each photovoltaic module becomes unbalanced and its total generation power is greatly decreased, especially when the photovoltaic modules are connected in series. These problems cannot be solved in conventional systems. We developed a novel utility interactive inverter with generation control circuit. In this proposed inverter system, each of these photovoltaic modules is individually operated at its corresponding maximum power point. By using this inverter, the efficiency of the photovoltaic system can be improved.

A high-frequency electronic ballast for HID lamps based on a /spl lambda//4-long distributed constant line

A novel type of solid-state ballast, which operates in the megahertz-range frequency, is presented in this paper. A circuit composed of a voltage-source half-bridge inverter, a distributed constant line and a parallel LC resonant circuit has been developed for this purpose. The high-intensity discharge (HID) lamp is connected to the output terminal of the inverter through the distributed constant line. Here, since the length of the line is adjusted to 1/4 of the propagation wavelength /spl lambda/ (/spl lambda//4 condition), the output voltage of the voltage-source inverter can be converted to a current source on the load side. Therefore, the ballast can supply not only high voltage to the HID lamp for initiating discharge, but also stable current to it during discharge condition. The modification of the proposed circuit is also proposed in order to expand the operating frequency without increasing the undesirable harmonic current. The experimental results from a prototype system verify the theoretical procedure.

Auxiliary resonant commutated pole inverter using two internal voltage-points of DC source

This paper presents a new auxiliary resonant commutated pole inverter that has series-connected batteries as the DC source. This inverter has two main switches and two auxiliary switches, and of all these devices achieve soft switching. The resonant operations are employed only during the commutating intervals; therefore, pulsewidth modulation (PWM) can be applied to the circuit. This circuit has the feature of using two internal voltage points of the DC source. Consequently, the circuit has the advantages of stability, simplicity in control, and high efficiency. The principle of the circuit operation and the experimental results are described in this paper.

Five-stepped PWM inverter used in photovoltaic systems

A PWM (pulse-width-modulated) inverter that has five-stepped output-voltage levels is introduced. In this inverter, the waveform of the output voltage has a smaller harmonic content than that of a conventional PWM inverter. A novel PWM technique is analyzed. The PWM pulses included in the waveform of the output voltage are formed using a criterion based on the calculation that each area of voltage pulses is equal to the integrated value of each time shared area of a reference sinusoidal waveform. This PWM technique for the five-stepped PWM inverter is superior to the conventional PWM technique, and the experimental results coincided with the calculation obtained using the fast Fourier transform. In addition, the relations between the number of PWM pulses and the harmonic contents of the output voltage are described. >

A novel high performance utility interactive photovoltaic inverter system

This paper presents a novel photovoltaic inverter system that can achieve not only a sinusoidal AC output current synchronized with the utility line voltage but also a generation power control on each of the photovoltaic modules connected in series. The proposed inverter system is composed of a half bridge inverter and novel generation control circuit that can compensate for the reduction in output power caused by the shadow covering the photovoltaic modules. The proposed generation control circuit can make the operation point on each of the photovoltaic modules correspond to the maximum power point individually, and the generation power control on each of the photovoltaic modules is executed only by detecting the total output power of the photovoltaic system. Furthermore, the low frequency ripple voltages on the series-connected DC bus capacitors caused by the utility interactive inverter operation are reduced owing to the effect of the generation control circuit. Hence, the average value of photovoltaic generation power is much increased. The effectiveness of the proposed system is confirmed experimentally and through simulation results.

New control method of resonant DC-DC converter in small scaled photovoltaic system

The authors describe a control method for a resonant DC-DC converter in a small-scale photovoltaic system linked up with storage batteries. The converter is suitable for tracking control of storage battery charging. The control method and experimental results are presented. Optimum operation was achieved by the application of the improved control circuit presented. With this circuit, it is possible to implement tracking control for various intensities of solar radiation.<<ETX>>

New type of ballast for HID lamps using series resonant circuit

A new type of solid state ballast, which can provide the high-frequency power to high intensity discharge (HID) lamps without an acoustic resonance, is presented. A ballast is needed to lighten the HID images, and is expected to be small and stably operating. The ballast equipment is composed of an inverter circuit, having variable switching frequency, a series resonant circuit, and a starting capacitor of the HID lamps. The operating characteristics of the ballast circuit are presented. The proposed circuit is useful for the HID lamps due to the small size and the low switching losses.<<ETX>>