Mohamed I. Daoud

Parameter Identification of Five-Phase Induction Machines With Single Layer Windings

Despite the increased interest in multiphase induction machines for safety-critical applications, machine parameter identification for the different sequence planes is still a challenging research point. In most available literature, the effect of nonfundamental sequence planes is overlooked due to the assumption of sinusoidal winding distribution and healthy operation. However, in a single layer or concentric winding layout with an odd number of phases, the effect of flux produced by nonfundamental sequence planes cannot be ignored for the open-phase case. This paper proposes a simple offline method to estimate the parameters of a five-phase induction machine corresponding to different sequence planes. The proposed technique can estimate the stator leakage inductance as well as the magnetizing inductance of both fundamental and third sequences by applying a quasi-square voltage to the stator winding while the machine is running at no-load. Consequently, the rotor circuit parameters of the fundamental sequence plane can be simply obtained by deducting the stator impedance from the blocked rotor machine impedance. For the third sequence plane, an approximate relation to estimate these parameters based on the measured fundamental sequence rotor parameters is also given. An experimental 1.5 Hp prototype machine is used to verify the proposed technique.

DC bus control of an advanced flywheel energy storage kinetic traction system for electrified railway industry

The evolution of public transportation exhibits high potential nowadays due to the consistent demand of clean transportation with low pollution rates. Therefore electrified railway systems become viable with their environmentally friendly properties. This study aims to improve the efficiency of DC power supplied railways via employing energy storage technology to maximize the overall energy efficiency. A flywheel energy storage system has been applied to store the regenerated energy during braking instead of dissipating it in the form of heat; then this stored energy can be used to compensate system disturbances and imbalance periods. A 75 kW/90 kJ squirrel cage induction machine based flywheel energy storage system is dedicated with a 600 VDC electric railway system to control the energy between the traction motor and the DC bus. The proposed control strategy is simulated using MATLAB/Simulink and simulation results have been shown. An experimentally FESS is built to support the study by experimental results.

A Flywheel Energy Storage System for Fault Ride Through Support of Grid-Connected VSC HVDC-Based Offshore Wind Farms

Voltage source converter (VSC)-based high voltage DC (HVDC) transmission is considered the future of offshore power transmission. This paper aims at providing a reliable VSC-HVDC transmission system architecture between offshore wind farms and onshore grids. In this paper, a large-capacity, low-speed flywheel energy storage system (FESS) based on a squirrel cage induction machine is applied in parallel with the VSC-HVDC at the grid side converter. The FESS is dedicated for surge power (due to power flow imbalance during fault) absorption instead of being dissipated in the form of resistive losses. Since the duration of these surges is relatively small, it has been shown that the flywheel can effectively mitigate this problem. In addition to the fault ride-through support during fault conditions, the FESS is employed for power leveling functionality during normal operation. The performance parameters of the proposed approach are investigated via both simulation and experimental results. A 132-kV, 100-MW HVDC system is simulated using MATLAB/Simulink during normal and fault conditions. The proposed architecture is substantiated experimentally through a scaled down test rig with a 2-kW FESS.

Ride-through capability enhancement of VSC-HVDC based wind farms using low speed flywheel energy storage system

Reliable balancing of active power generated via wind farms is vital for power system stability and for maintaining system frequency deviations within acceptable limits. This paper presents a backup power balancing technique for the energy-fed voltage source converter high voltage DC transmission systems during different AC side faults based on flywheel energy storage systems. The proposed technique aims to prevent the DC link voltage rise during faults which reduces the voltage and current stresses on the switching devices. An induction machine (IM) based flywheel energy storage system is connected in parallel with the onshore side converter; therefore, the trapped energy in the DC link during AC faults can be stored in the flywheel. During normal conditions, the flywheel storage system is normally used for power leveling. A simulation case study for the proposed system using a 100MW HVDC system is presented, while experimental validation is carried out using a 2.2kW prototype flywheel IM storage system.

Investigation of sensorless capacitor voltage balancing technique for modular multilevel converters

Modular Multilevel converters (MMC) have become one of the most promising topologies for DC-AC conversion in recent years. Capacitor voltage balancing is a vital issue for proper operation of the MMC. Generally, conventional sensor-based balancing techniques require a significant amount of measurements, 2m(N-1) voltage sensors and 2m current sensors are required for a N-level m-phase converter. In this paper, a sensorless voltage balancing technique (self-balancing) is proposed for the MMC. The proposed technique eliminates all measurement boards used for monitoring capacitor voltages and arm currents, which in turn reduces system complexity and cost. Simulation and experimental results support and validate the proposed concept.

Maximum power transfer of PV-fed inverter-based distributed generation with improved voltage regulation using flywheel energy storage systems

One of the main issues accompanied with the high penetration of PV distributed generation (DG) systems in low voltage (LV) networks is the overvoltage challenge. The amount of injected power to the grid is directly related to the voltage at the point of common coupling (PCC), which necessitates limiting the amount of injected power to the grid to conservative values compared to the available capacity from the PV panels particularly at light loading. In order to mitigate the tradeoff between injecting the maximum amount of electrical power and voltage rise phenomena, many control schemes were suggested in order to optimize the operation of PV DG energy sources as well as maintaining safe voltage levels. Unlike these conventional methods, this paper proposes a combined PV inverter-based distributed generation and flywheel energy storage system to ensure improved voltage regulation as well as making use of the maximum available power from the PV source at any instant, decoupling its relation with the terminal voltage. The concluded assumptions were simulated through Matlab/Simulink and verified experimentally.

A dual three-phase induction machine based flywheel storage system driven by modular multilevel converters for fault ride through in HVDC systems

One of the main challenges of voltage source converter based high voltage direct current (VSC-HVDC) transmission systems is the AC faults at the grid side. This work introduces the integration of multiphase induction machine (IM) based flywheel energy storage systems (FESS) with VSC-HVDC systems for AC side fault ride through purposes employing modular multilevel converters (MMC). MMCs have become suitable candidates for medium/high power energy conversion systems due to the capability of simply extending the levels of the converter while retaining high levels of reliability. In order to enhance the storage system reliability, a dual three phase IM is used to drive the FESS due to its fault tolerance capability. In this paper, the performance of the FESS is investigated under the operation of a dual three phase IM being driven by two three-phase MMCs. To step-down the DC-link voltage of the HVDC system to a proper voltage level for IMs, the DC-link voltage is divided into two series connected capacitor, and each capacitor voltage is fed as an input DC voltage for each three- phase MMC. The control strategies of the MMCs and the IM are presented, in addition to the IM mathematical model. Simulation case studies are performed using MATLAB/Simulink to validate the proposed system.

An asymmetrical six phase induction machine for flywheel energy storage drive systems

Energy storage systems have become an essential part of power utilities due to their capability of providing high level of power quality and stability. Flywheel energy storage systems (FESSs) are now employed with numerous grid and renewable energy applications due to their operational merits. Some of these applications are related to fault ride-through and critical load support. Therefore, the reliability of the FESS should be ensured. The main concern of the FESS drive system reliability is the applied machine type and the required power converter. In this paper, an asymmetrical six phase machine is proposed to drive a low-speed FESS in order to enhance the overall reliability and improve system fault tolerance capability. Different simulation case studies during healthy and faulty conditions are presented using MATLAB/Simulink. The proposed FESS is built experimentally to investigate system performance during both cases.

A hybrid boost modular multilevel converter-based bipolar high voltage pulse generator

Conventional Modular Multilevel Converter (MMC) with Half-Bridge Sub-Modules (HB-SMs) can be used effectively as a solid-state high-voltage pulse generator to chop a high-voltage dc input into a bipolar pulsed output voltage without employing neither high-voltage semiconductor switches nor series-connected switches. Nonetheless, its boosting capability is constrained. In this paper, a hybrid boost MMC-based bipolar high-voltage pulse generator is proposed where each arm contains a combination of Full-Bridge SMs (FB-SMs) and HB-SMs. The HB-SMs and FB-SMs have the same rated voltage. The proposed approach is able to generate bipolar pulses, and operates with a wide range of boosting capability. Detailed illustration of the proposed configuration and its operational concept are presented. Simulation models for the proposed approach are built, for different FB-SMs to HB-SMs ratios, using Matlab/Simulink platform. Experimental results for a scaled-down prototype are presented to validate the concept.