Development of a solar power conditioner using diode-clamped linear amplifiers without any ac inductor nor EMI filter

2007 Fiscal Year Final Research Report Summary

• Project/Area Number: 18560271
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 電力工学・電気機器工学
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: FUJITA Hideaki Tokyo Institute of Technology, Graduate School of Engineering, Associate Professor (40238580)
• Project Period (FY): 2006 – 2007
• Keywords: Linear Amplifier / Inverters / Diode-Clamping Circuit / Solar Power Generation / Conversion Efficiency

Research Abstract

The aim of this project is to develop a solar-power conditioner without using any ac inductor or EMI filter by using diode-clamped linear amplifiers as the main power circuit The diode-clamped linear amplifier consists of series-connected MOSFETs, the source terminal of which is damped by dc-voltage levels. This configuration is similar to diode-clamped multi-level inverters. A general-used diode-clamped multi-level inverter uses only n-channel devices in general. On the other hand, the diode-clamped linear amplifier, however, uses complimentary power MOSFETs, p-channel and n-channel devices, as the power devices. The diode-damped linear amplifier makes it possible to provide a sinusoidal output voltage to the ac loads without any ac inductors or filter, just like a conventional linear amplifier. One of the series-connected MOSFETs acts in an active-state of the operating region. The other MOSFETs work in on-states or off-states, resulting in a great reduction of the power loss caused by the operation in the active -state.
This project has developed a new current control method and current control circuit for the diode-clamped linear amplifier at first. Principle and performance have been verified by experiments using twelve-series diode-clamped linear amplifier. As a result, the developed circuit showed an accurate current control performance and a low current ripple under both normal load condition and a short-circuit condition. Next, the developed circuit has been implemented into a single-phase 200-V 2-kW prototype of an ac utility-interfaced solar power conditioner using two twelve-series diode-clamped linear amplifiers and a dc-voltage balancer. The experimental verified a current total harmonic distortion as low as 2% and power conversion efficiency as high as 90%. Moreover, a three-phase prototype also examined and demonstrated 93% conversion efficiency.