Integration of Multiple Modularized Distributed Energy Resource Devices Into AC Grid of Buildings: Issue of Active Power Circulation

Near-future green and intelligent buildings will likely have multiple and modularized distributed energy resource devices incorporated into their power distributed networks, e.g., modularized uninterruptible power supply (MUPS), to provide energy storage or modularized solar photovoltaic systems to provide renewable energy. However, the issue of unwanted active power circulation among parallel MUPS modules may cause dc bus overvoltage problems under no-load condition, leading to protective system activation and affecting normal system operation. Causes of the overvoltage are first investigated with detailed analysis of multiple parallel MUPS modules in this paper. The investigation is started with two parallel modules and is then extended to multiple modules. A novel method based on shifting carrier wave frequency is proposed to suppress the dc bus overvoltage. Experimental results show that the proposed solution is effective without any negative impact on the normal operation of a MUPS network.