The ever increasing need for affordable and clean energy is driving the wind and solar industry towards reducing the cost of energy (CoE) continuously. This translates into the quest to increase the power density of power converters. Danfoss Silicon Power GmbH and SBE, Inc. are jointly working on a technology project to create an extremely compact power stack. This project in Aalborg University (Denmark) has shown that it is possible to build a 1MW super compact power stack. This Power stack weighs less than 45 kg and is only 66 L in volume and has Danfoss ShowerPower® cooling system for thermal management of the power module and SBE Power Ring Film Capacitor™. In the project, the flow of the coolant was set to 45 L/min, and the temperature of the outlet was controlled to 60 degrees C.
The capacitance of the SBE Power Ring Film Capacitorâ„¢ bank was 2.4 mF. The DC-link voltage was controlled to 1070V, output voltages were controlled at 650 V (line-to-line) modulated with continuous space vector pulse width modulation and switching at 2.5 kHz. The test results at unity power factor when operating in the inverting mode (power flow from dc to ac) were evaluated. Unity power factor operation in the inverting mode is the worst test case for the IGBTs. However, the temperature was well below 150 degrees C (maximum junction temperature). The RMS current at this operating point was 1080A, resulting in an output power of over 1 MW.
The SBE Power Ring Film Capacitor integrated with an optimized bus structure and ShowerPower cooling technology helps in increasing the power density. The project aims to lower the equivalent series inductance (ESL) in the dc-link and the equivalent series resistance (ESR) of the dc-link bus. This enhances the efficiency and the maximum allowable switched voltage at the same time maintaining a safe operating temperature of capacitors. ShowerPower helps in improving power density in two ways. Firstly, being direct liquid cooling technology it is more effective than air or indirect liquid cooling and secondly it is light weight and compact.
Project status will be presented at the PCIM 2015 conference and a demonstrator unit will be exhibited in the technology section of the Danfoss booth, Hall 9, Booth 327 at the same event in Nuremberg. Reference -“Converter Power Density Increase using Low Inductive Integrated DC-Link Capacitor/Busâ€; Ionut Trintis, Toke Franke, Bjørn Rannestad, Stig Munk-Nielsen; PCIM, Europe 2015.
