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This paper describes the start-up and integration of a doubly fed induction generator (DFIG)-based wind farm into the ac network through a voltage source converter-based (VSC) HVDC transmission system. A control strategy based on the closed-loop control of rotor current is proposed during DFIG cut-in process. In normal operation, an additional feedback signal is introduce to the control system of...
During grid faults, grid codes required wind turbine (WT) to provide dynamic reactive support within tens of ms as well as maintain grid connection continuously, namely low voltage ride through (LVRT). But owing to the limited DC bus voltage, the rotor side convertor in doubly fed induction generator (DFIG) cannot actually output sufficient voltage to provide reactive support until the rotor-side...
This paper proposes a novel direct torque control (DTC) scheme to reduce the torque and stator flux ripples for permanent-magnet synchronous motor (PMSM) drives using a relatively low sampling frequency. Unlike the conventional DTC in which the voltage vectors are determined by hysteresis controllers, the proposed DTC uses nonlinear saturation comparators and a duty ratio modulation scheme for switch...
Special switching sequences involving division of active state time are used in space-vector-based generation of pulse width modulation (PWM) waveforms. This paper proposes a hybrid PWM technique which is a combination of the conventional and special switching sequences. The proposed hybrid PWM technique reduces the peak-to-peak torque ripple at high speeds of an induction motor drive. Supporting...
Maximum torque per ampere (MTPA) control scheme for internal permanent magnet (IPM) machine is presented in this paper. Proposed control scheme was developed based on measurement of only DC link quantities eliminating the necessity of 3-phase current feedback. The scheme employs an online search algorithm with initial condition computed from a-priory system information. Hybridization of search based...
This paper presents an improved direct torque control (DTC) method for permanent magnet synchronous motors. The proposed DTC method generates the diver signal with SVPWM for the fixed switching frequency and low torque ripple relative to conventional hysteresis controllers. Different with the popular SVM-DTC, the proposed method obtains amplitude and angle of reference voltage vector directly by the...
This paper presents a simple algorithm for estimation of the rotor position. The injected high frequency voltage is a sinusoidal voltage and is injected into the stator of a motor. An interior permanent magnet synchronous motor (IPMSM) has spatial saliency because d-axis inductance and q-axis inductance are different from each other. The injected high frequency voltage is influenced by saliency. Therefore,...
In recent years, sensorless techniques based on HF carrier injection have become very popular as they are capable to estimate rotor position in a wide speed range. They can provide precise control over interior PMSMs without the accompanying need for a position sensor. However, in surface-mounted PMSMs, the estimation of rotor position is only reliable at light loads due to the very small saliency...
In a motor control, a voltage saturation is a serious problem as a motor speed increases. To solve the problem, various field weakening methods were studied for a long time. The field weakening methods with PI current controllers are normally used, however the voltage angle control without PI current controllers is receiving attention because of its simple implementation. In this work, the field weakening...
New grid codes demand the wind turbine systems to ride through recurring grid faults. In this paper, the performance of the Doubly Fed Induction Generator wind turbine system under recurring grid faults is analyzed. The stator natural flux produced by the voltage recovery after the first grid fault may be superposed on the stator natural flux produced by the second grid fault, and it may result in...
With the stator directly connected to the grid, doubly-fed induction generator is very sensitive to gird disturbance. However, wind turbines are required to stay connected to the grid for a given time duration during grid fault, according to the low voltage ride-through requirement. The key point of the low voltage ride-through solution is to depress high rotor current during grid fault. This paper...
This paper presents operation and control of a Squirrel Cage Induction Generator (SCIG) to generate power from an oscillating point absorber based wave energy conversion (WEC) system. The oscillating point absorber buoy is assumed to be connected with the SCIG through a rack and pinion gear arrangement, thus converting the linear motion of the buoy to rotary motion of the generator. Proper gear ratio...
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