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TC3 - Alternative microsource interface topologies

Power quality becomes an issue when DG is connected to the network since most of them are interfaced to the network via power electronic inverters. These introduce harmonics to the system and degrade the quality of power delivered to customers. Managing these harmonics is an important task. In this task ABB will deal with the following items:

• Investigation and comparison of different converter topologies for microsources (e.g. conventional PWM converter with low frequency transformer, alternative converter topologies with medium frequency transformer or transfomerless topologies for the interface to LV and MV grids).
• Optimization of converters, filters, control and damping schemes.
• Investigation and evaluation of converter control and modulation strategies for different distributed resources during grid and islanding operation. For example: Operation of microgrid connected to the main grid: frequency is constant and voltage set by the grid. Island operation of microgrid with only one microsource: the frequency and voltage are not set by the grid. The converter must control both. Changes in converter and/or filter topology might be needed. Island operation of microgrid with multiple microsources: Probably one of the converters has to take care of the voltage and frequency control. The others might be current-controlled. A load sharing function must be designed and implemented so the operating points for all converters are uniquely defined and instabilities are avoided).
• Development of universal and modular power electronic interface concepts for various power and voltage levels as well as different renewable energy sources.

IT-Power will study the applicability of its 120kW Ride-Through Inverter (RTI). The RTI provides the ability to condition the grid supply through the Inverter providing regulation of voltage and frequency and protecting the load distribution from brownouts, surge conditions and interruptions.