Karim Hassan Youssef

A new method for voltage and frequency control of stand-alone self-excited induction generator using PWM converter with variable DC link voltage

Three-phase self-excited induction generators (SEIG) play an important rule in renewable energy sources such as wind and hydraulic energy. Their main disadvantage is poor voltage and frequency regulation under varying load and speed. This paper introduces a new and simple method for voltage and frequency control of three-phase unregulated speed induction generators in the islanding mode. The method uses a constant voltage constant frequency (CVCF) PWM converter without regulating the DC capacitor voltage. The capacitor voltage is left changing with the loading conditions and the AC side voltage is regulated by controlling the modulation index. This eliminates the need of an auxiliary switch in the DC side which reduces the cost and also reduces the high frequency current components flowing in the DC capacitor and that increases its life time. The proposed technique is tested under step changes in load and prime mover speed. The proposed technique gives the same response as the old technique but without the use of DC side switch.

Adaptive fuzzy APSO based inverse tracking-controller with an application to DC motors

This paper introduces the use of the adaptive particle swarm optimization (APSO) for adapting the weights of fuzzy neural networks (FNN) on line. The fuzzy neural network is used for identification of the dynamics of a DC motor with nonlinear load torque. Then the motor speed is controlled using an inverse controller to follow a required speed trajectory. The parameters of the DC motor are assumed unknown as well as the nonlinear load torque characteristics. In the first stage a nonlinear fuzzy neural network (FNN) is used to approximate the motor control voltage as a function of the motor speed samples. In the second stage, the above mentioned approximator is used to calculate the control signal (the motor voltage) as a function of the speed samples and the required reference trajectory. Unlike the conventional back-propagation technique, the adaptation of the weights of the FNN approximator is done on-line using adaptive particle swarm optimization (APSO). The APSO is based on the least squares error minimization with random initial condition and without any off-line pre-training. Simulation results are presented to prove the effectiveness of the proposed control technique in achieving the tracking performance.

A New Method for Online Sensitivity-Based Distributed Voltage Control and Short Circuit Analysis of Unbalanced Distribution Feeders

Reactive power support through shunt capacitors and distributed generation is used in conjunction with step voltage regulators (SVRs) for voltage control of distribution feeders. Distribution management system is responsible for coordination among distributed reactive power sources, such as capacitors, photovoltaic and wind power generators, and SVRs. In this paper, a novel method for calculating voltage sensitivity to active, reactive power injection, and SVR taps in unbalanced distribution feeders is developed. The method is based on ABCD parameters of network components which are used in forward/backward sweep of power-flow solution. The method can deal with network unbalance, network shunt admittances, single-phase sections, and ungrounded sections. The initial sensitivities are calculated in one power-flow forward sweep through a recursive way, and the online updating of sensitivities is very easy and straightforward so the method is suitable for online voltage control. A novel sensitivity-based online optimization method is developed for online coordinated voltage control with no prior information about the load. The same ABCD parameters are used for developing a novel method for calculating short circuit currents in unbalanced distribution feeders. The method can also handle unbalance, shunt elements, and single phase sections, and is applicable to all fault types. The developed method for voltage control and short circuit calculation are tested on the IEEE comprehensive test feeder and the results prove the effectiveness of the proposed algorithms.

A New Method for Voltage and Frequency Control of Stand-alone Self-excited Induction Generator Using Pulse Width Modulation Converter with Variable DC-link Voltage

Abstract Three-phase self-excited induction generators play an important role in renewable energy sources such as wind and hydraulic energy. Their main disadvantage is poor voltage and frequency regulation under varying load and speed. This article introduces a new and simple method for voltage and frequency control of three-phase unregulated speed induction generators in the islanding mode. The method uses a constant voltage constant frequency pulse width modulation converter without regulating the DC capacitor voltage. The capacitor voltage is left changing with the loading conditions, and the AC side voltage is regulated by controlling the modulation index or the normalized d-axis reference voltage for space vector modulation. This eliminates the need for an auxiliary switch in the DC side, reducing the cost and high-frequency current components flowing in the DC capacitor and increasing its lifetime. Simulation results are given for comparing between the conventional and the proposed techniques when applied to a 6-kW generator. The proposed technique is tested under step changes in load and prime mover speed, and it gives the same response as the old technique but without the use of DC side switch. Experimental implementation of the proposed technique is tested on a 1-hp generator, and both simulation and experimental results are given to validate the proposed technique.

Power Quality Constrained Optimal Management of Unbalanced Smart Microgrids During Scheduled Multiple Transitions Between Grid-Connected and Islanded Modes

In this paper, a novel power quality (PQ) constrained optimization framework for smart microgrids with nonlinear loads is proposed for scheduled multiple transitions between grid-connected and islanded modes. Loads, generation, and energy storage are optimally scheduled to maximize the overall microgrid profit, from selling energy to grid, while satisfying network and PQ constraints. Cost of power interruption to loads, steady-state frequency deviation during islanding, and power sharing among generators are considered. PQ and network constraints of three-phase unbalanced distribution microgrid are given in convex forms. Comprehensive simulation results are given for validating the proposed algorithm and effect of limiting total harmonic distortion on microgrid economics is investigated.

Effect of harmonics on distance relay in short and medium transmission lines

The continuous increasing in the number and the power ratings of the non-linear loads are the main sources of harmonics that affect the performance of all electrical elements. This harmonics either current or voltage harmonics have a serious effect on the quality of electricity power supply and all network elements like protection elements especially distance relays. In this paper, the effect of harmonics on distance relay is presented through a comparative study between the distance relay performance in the short and the medium models of the cable under different levels of harmonics including many components of current and voltage. This study is presented using Matlab to describe the distance relay, harmonics (current source), transmission line, fault simulation as a single line to ground fault SLG and the impedance type distance characteristic are chosen to be as the protection scheme.