Engines & Power Electronics : Utility & microgrid

Engines & Power Electronics Portfolios


Power Conditioning Architecture for Wind Turbine

UW-Madison researchers have developed a viable solution that allows DFIG wind turbines connected to the grid to ride through a voltage sag. The turbines need converters, such as a DC/AC inverter, to change the power generated into a form that is compatible with the utility grid. In a conventional DFIG wind turbine, the grid-side converter is connected in parallel with the stator windings of the generator. This approach has the converter connected in series instead. The DC voltage bus of the converter is fed from the induction generator rotor windings through a second, machine-side converter. Connecting the grid-side converter in series allows continuous control of shaft torque and power delivered to the grid even during grid faults, enabling inherent voltage sag ride-through capability.

Autonomous Control of Inverter-Based Storage in Dynamic Distribution Systems

UW-Madison researchers have developed methods for effectively and autonomously controlling energy storage devices in a system that includes other DER units. Specialized power electronics control charge/discharge of an energy storage device (like a battery or flywheel) using locally available information. Electronic sensors analyze variables, such as power flow, operating frequency of a power inverter and level of charge in the storage device, to control the frequency of the output power of the inverter, and thus the rate of charge or discharge. The controls use power vs. frequency droop to track power demand when the DER is isolated from the utility grid and voltage vs. reactive power droop to ensure stability between DER components.

These methods work with other DER units to increase reliability, bring down costs and provide precise control over energy storage. They also reduce custom engineering, promote plug-and-play concepts and ensure stable operation of a DER system that includes energy storage devices. 

Non-Inverter-Based Distributed Energy Resource for Use in a Dynamic Distribution System

UW-Madison researchers have developed a method for effective autonomous control of non-inverter based generation in a system that includes other classes of DER units. The method relies on controllers that use local information to regulate rotation of the shaft of the microsource generator. The controller calculates an operating frequency for the generator based on a comparison between a power set point and a measured power flow. A requested speed for the shaft of the generator (prime mover) is calculated by combining a maximum frequency change, a minimum frequency change and the calculated operating frequency. The system then uses this information to calculate a shaft speed adjustment and implements the change by regulating a fuel command for the prime mover. This keeps the AC output voltage at a desired frequency, eliminating the need for a front-end inverter to couple the DC front end and the remaining AC components.

Interface Switch for Distributed Energy Resources

UW-Madison researchers have developed an improved interface switch that seamlessly and automatically connects and disconnects a DER microgrid from a utility grid. The interface switch disconnects the DER from the utility grid for protection and power quality events, allowing the cluster of loads and DER to continue to operate as an island. During island conditions, the frequency of the DER microgrid differs from that of the utility. When the conditions that created the islanding are gone, the interface switch exploits this frequency difference to rapidly and seamlessly reconnect the microgrid to the utility.

Control of Small, Distributed Energy Resources

UW-Madison researchers have developed a microsource controller that ensures stable operation of a large number of distributed energy resource generators. This cluster of microsources and loads allows for efficient connection to a power system of small, low cost and reliable distributed generators such as microturbines, fuel cells and photovoltaic cells. The system can include a microsource composed of a prime mover, a DC interface and a voltage source inverter; a means for controlling real and reactive power coupled to the microsource; and a means for regulating voltage through droop control to the microsource. Power electronics provide the control and flexibility to ensure stable operation for large numbers of distributed generators.