Ahmed A. El-Sattar

An Adaptive Droop Control Scheme for DC Microgrids Integrating Sliding Mode Voltage and Current Controlled Boost Converters

One of the most widely used techniques for controlling the dc microgrid is the droop control method. The associated problems of the droop-based systems, such as the current sharing errors and the voltage deviation are solved using current sharing loops and secondary control loop, respectively. This paper presents an adaptive droop scheme for dc microgrids to overcome the non-linearity of the system. The droop resistance is adjusted using the adaptive PI controller to eliminate the current sharing error of each unit in the microgrid. In addition, another adaptive PI controller is dedicated for the secondary loop to regulate the dc bus voltage of the microgrid by shifting the droop lines. In the proposed scheme, only the current and voltage at the dc bus of the microgrid need to transmit through low-bandwidth communication channels to individual units. Moreover, the sliding mode control, which is distinguished by robustness and fast dynamic response, is utilized to manipulate the output voltage and the input current of each converter, instantaneously. The dynamic performance of the proposed adaptive droop scheme is evaluated using the PSCAD/EMTDC simulation package.

Sensorless Field Oriented Control based on improved MRAS speed observer for Permanent Magnet Synchronous Motor drive

Sensorless speed control of Permanent Magnet Synchronous Motor (PMSM) is still in development to eliminate the existing drawbacks such as speed ripples, torque ripples and slow response. This paper proposes Field Oriented Control (FOC) based on improved Model Reference Adaptive System (MRAS) to control the motor speed and minimize both the speed and torque ripples for the PMSM. The improved MRAS strategy is used for speed estimation. A regulator is added to the proposed MRAS to reduce the torque and speed ripples. Feed forward signal from reference speed has used with the PMSM dynamic equations to enhance the overall performance of the system. Cascaded Multi-Level Inverter (MLI), with special switching strategy and different DC sources, is used as PMSM drive. The switching and design of the cascaded MLI are based on getting more voltage levels with less number of components. The system is simulated using Matlab / Simulink package. The proposed controller success in minimizing the speed and torque ripples and provide faster system response. The simulation results of the proposed control system prove the capability of the controller for enhancing the performance of the system in both steady and dynamic states.

A Simple Control Scheme for the High Performance Z-Source Inverter

Abstract In the past decade, the Z-source inverter (ZSI) is successfully developed for many applications. This paper proposes a simple integrated control scheme for the high performance ZSI. A proportional-integral PI controller is used to regulate the voltage of the Z-network capacitor. Moreover, the peak value of the DC-link voltage is controlled by limiting the shoot-through duty ratio. Furthermore, the instantaneous voltage control technique is utilized to retain the sinusoidal shape of the output voltage. A feed-forward signal of the AC voltage is employed to smooth the output voltage. To generate the PWM signals for the ZSI switches, the simple boost control method is utilized which coordinates the operation of different controllers. Extensive digital simulations are conducted to evaluate the dynamic behavior of the proposed control scheme. Moreover, an experimental setup is built to verify the performance of the proposed control scheme for the high performance ZSI.

Direct torque control and direct power control with multilevel converters for variable speed wind turbines

This paper presents WECS (wind energy conversion system) installed with BTB (back-to-back) medium voltage diode clamped five-level converter and SCIG (Squirrel-Cage-Induction-Generator) for a large capacity wind turbine (5MW). The DTC (direct torque control) has been used for the machine side diode clamped five-level converter. The use of DTC with the MLC (multilevel converter) gives a better performance of SCIG (flux, torque, current and speed) to improve the energy efficiency of a variable speed WECS. Utility-grid side diode clamped five-level converter uses the DPC (direct power control) technique. This technique is used to improve the performance of the delivered power flowing from the dc-link to the electric utility-grid (decrease ripples of the DC-link voltage, decrease THD (total-harmonic-distortion) and improve the power factor of the injected power to the utility-grid). The proposed system simulation is done using Matlab/SimulinkSimscape Power Systems to compare this system and the classical two-level converter.