In recent years, interest in natural energy has grown in response to increased concern for the environment. Many kinds of inverter circuits and their control schemes for photovoltaic (PV) power generation systems have been studied. A conventional system employs a PV array in which many PV modules are connected in series to obtain sufficient dc input voltage for generating ac utility line voltage from an inverter circuit. However, the total power generated from the PV array is sometimes decreased remarkably when only a few modules are partially covered by shadows, thereby decreasing inherent current generation, and preventing the generation current from attaining its maximum value on the array. To overcome this drawback, an ac module strategy has been proposed. In this system, a low-power dc-ac utility interactive inverter is individually mounted on each PV module and operates so as to generate the maximum power from its corresponding PV module. Especially in the case of a single-phase utility interactive inverter, an electrolytic capacitor of large capacitance has been connected on the dc input bus in order to decouple the power pulsation caused by single-phase power generation to the utility line. However, especially during the summer season, the ac module inverters have to operate under a very high atmospheric temperature, and hence the lifetime of the inverter is shortened, because the electrolytic capacitor has a drastically shortened life when used in a high-temperature environment. Of course, we may be able to use film capacitors instead of the electrolytic capacitors if we can pay for the extreme large volume of the inverter. However, this is not a realistic solution for ac module systems. This paper proposes a novel flyback-type utility interactive inverter circuit topology suitable for ac module systems when its lifetime under high atmospheric temperature is taken into account. A most distinctive feature of the proposed system is that the decoupling of power pulsation is executed by an additional circuit that enables employment of film capacitors with small capacitance not only for the dc input line but also for the decoupling circuit, and hence the additional circuit is expected to extend the lifetime of the inverter. The proposed inverter circuit also enables realization of small volume, lightweight, and stable ac current injection into the utility line. A control method suitable for the proposed inverter is also proposed. The effectiveness of the proposed inverter is verified thorough P-SIM simulation and experiments on a 100-W prototype

This paper deals with a curious phenomenon referred to as the "whack-a-mole" that may occur in a long-distance distribution feeder having many capacitors for power-factor correction. The idea of whack-a-mole is that installation of an active or passive filter on the feeder makes voltage harmonics increase on some buses, whereas it makes voltage harmonics decrease on other buses, especially at the point of installation. The distributed-parameter representation is applied to a simplified feeder, thus making it possible to perform analysis of the whack-a-mole. As a result, this analysis yields such a basic way as to avoid the whack-a-mole. Moreover, both theory and experiment clarify that installation of the active filter acting as a harmonic terminator on the end bus of the feeder can damp out harmonic propagation throughout the feeder without causing any whack-a-mole.

A general-purpose clocked gate driver integrated circuit (IC) to generate an arbitrary gate waveform is proposed to provide a universal platform for fine-grained gate waveform optimization handling various power transistors. The fabricated IC with a 0.18 μm Bipolar-CMOS-DMOS process has 63 P-type MOS (PMOS) and 63 N-type MOS (NMOS) driver transistors on a chip whose activation patterns are controlled by 6-bit digital signals and 40 ns time step control. In the 500 V switching measurements with a manual gate waveform optimization, the proposed gate driver reduces the I_C overshoot by 25% and 41%, and the energy loss by 38% and 55% for Si-insulated-gate bipolar transistor and SiC-MOSFET, respectively, which demonstrate the feasibility of driving various power devices with the same driver. An automatic optimization by simulated annealing algorithm is introduced to fully utilize the benefit of the gate driver, and the further reduction of I_C overshoot by 26% and the energy loss by 18% are achieved over the manual optimization.

This paper addresses a transformerless shunt hybrid filter integrated into a three-phase diode rectifier. The hybrid filter consists of a three-phase passive filter tuned to the seventh-harmonic frequency, and a small-rated active filter based on a three-phase voltage-source pulsewidth modulation converter. The validity of the system design is confirmed by experimental results obtained from a 400-V, 15-kW laboratory system. The experimental results show that the active filter plays an essential role in reducing supply harmonic currents. The total harmonic distortion of the supply current gets less than 5%. Moreover, the hybrid filter provides satisfactory transient performance as a result of having achieved an optimal design of circuit and control parameters including the dc capacitor voltage and feedback gains of the active filter, along with the cutoff frequency of high-pass filters for harmonic extraction.

The requirements for peripheral circuits of power converters are becoming more restrictive due to enhancement of Si-based power devices and due to practical use of SiC device. In the design of modern high-speed switching converters, the stray inductances and capacitances both in the device package and in the gate drive circuit in addition to those in the main circuit of the power converter must be considered. In these situations, the gate driving technique represents the key technology for enhancement of high-speed switching ability of power devices, as there are design limitations to reduce the stray inductances and capacitances. So far, several active gate control methods have been proposed. Most conventional active gate drivers are configured using analog circuits such as transistors and diodes. Thus, it is difficult to reconfigure their control parameters to fit the stray inductances and capacitances after the implementation of power converter and gate circuits. As a solution to these problems, the authors have proposed a programmable gate driver IC, which is a digitally controlled circuit. This gate driver IC can control the gate current at 63 separate levels, operated by programmable fully digital 12-bit and clock signals. In this paper, an active gate current control based on the load current in a half-bridge inverter with two programmable gate driver ICs is demonstrated. It is verified that the proposed active gate control can effectively improve the trade-off relationship between the surge voltage and switching loss of the PWM half-bridge inverter circuit.