A new sensorless method for switched reluctance motor drives

This paper describes a new method for indirect sensing of the rotor position in switched reluctance motors (SRMs) using pulse width modulation voltage control. The detection method uses the change of the derivative of the phase current to detect the position where a rotor pole and stator pole start to overlap, giving one position update per energy conversion. As no a priori knowledge of motor parameters is required (except for the numbers of stator and rotor poles), the method is applicable to most SRM topologies in a wide power and speed range and for several inverter topologies. The method allows modest closed-loop dynamic performance. To start up the motor, a feedforward stepping method is used which assures robust startup (even under load) from standstill to a predefined speed at which closed-loop sensorless operation can be applied. Experimental results demonstrate the robust functionality of the method with just one current sensor in the inverter, even with excitation overlap, and the sensorless operation improves with speed. The method is comparable to the back-EMF position estimation for brushless DC motors in principle, performance and cost. A detailed operation and implementation of this scheme is shown, together with steady-state and dynamic transient test results

Online variation of wind turbine controller parameter for mitigation of SSR in DFIG based wind farms

The aim of this paper is to investigate the risk for Subsynchronous Resonance (SSR) conditions in Doubly Fed Induction Generator (DFIG) based wind farms connected to series-compensated transmission lines. The well-known IEEE First Benchmark Model for SSR studies is adopted and the impact of the turbine controller parameters on the risk for unstable conditions is analyzed. In particular, it is shown through frequency domain studies that a reduction of the closed-loop bandwidth of the current controller that regulates the rotor current effectively reduces the risk for SSR. Simulation results are presented to validate the theoretical findings

Fault-tolerant operation of single-phase SR generators

This paper studies fault-tolerant operation of multipole single-phase switched reluctance generators (SRGs), in particular, an 8/8-pole switched reluctance machine. The multipole single-phase SRG system is advantageous for reduced cost and higher efficiency compared to polyphase equivalents. However, using the classical phase-leg topology, a phase fault may prevent generating operation completely, since redundancy in the number of phases does not exist like polyphase systems. A new power converter topology which connects two coil banks in parallel is proposed for higher fault tolerance with minimum additional cost. Faulty coils can be disconnected with the proposed converter and the SRG can continue generating operation after coil faults with reduced output power. Output power per coil current under faults is studied. Open- and short-circuit coils are studied through linear analysis, finite-element analysis and static torque measurement. Generated currents under faults with the proposed converter are measured. The capability of the system to disconnect faulty coils dynamically is also shown

Online variation of wind turbine controller parameter for mitigation of SSR in DFIG based wind farms

The aim of this paper is to investigate the risk for Subsynchronous Resonance (SSR) conditions in Doubly Fed Induction Generator (DFIG) based wind farms connected to series-compensated transmission lines. The well-known IEEE First Benchmark Model for SSR studies is adopted and the impact of the turbine controller parameters on the risk for unstable conditions is analyzed. In particular, it is shown through frequency domain studies that a reduction of the closed-loop bandwidth of the current controller that regulates the rotor current effectively reduces the risk for SSR. Simulation results are presented to validate the theoretical findings