Ahmed M. Massoud

An Improved Performance Direct-Drive Permanent Magnet Wind Generator Using a Novel Single-Layer Winding Layout

Direct-drive permanent magnet (PM) generators have become a strong contender in medium and large rating wind energy conversion systems as they not only provide higher efficiency and annual energy production, but also reduce the operational and maintenance cost. PM generators with nonoverlap single-layer windings provide a cost-effective design variation that eases manufacturing, reduces torque ripples, enhances voltage quality, and provides fault tolerant capability. The performance of such machines depends mainly on the proper selection of the pole and slot numbers, which results in negligible coupling between phases. The preferred slots per phase per pole (SPP) ratios eliminate the effect of low order harmonics in the stator magnetomotive force (MMF), and thereby the vibration and stray loss are reduced. This paper proposes a new three-phase winding configuration based on the 20 slots/18 poles five-phase PM machine. The proposed design is compared with the well-known 24 slots/20 poles three-phase PM machine. The comparison shows that the proposed generator offers reduced torque ripples, improved output voltage quality, and less core loss for the same machine volume.

Low Space Harmonics Cancelation in Double-Layer Fractional Slot Winding Using Dual Multiphase Winding

One of the main drawbacks of nonoverlapped coils in fractional slot concentrated winding permanent magnet (PM) machines are the high eddy current losses in both rotor core and permanent magnets induced by the asynchronous harmonics of the armature reaction field. It has been shown in the literature that the reduction of low space harmonics can effectively reduce the rotor eddy current losses. This paper shows that employing a combined star-delta winding to a three-phase PM machine with fractional slot windings and with a number of slots equal to 12, or its multiples, yields a complete cancellation to the fundamental magneto-motive force (MMF) component, which significantly reduces the induced rotor eddy current. Besides, it offers a slight increase in machine torque density. A case study on the well-known 12-slot/10-pole PM machine is conducted to explore the proposed approach. With the same concept, the general n-phase PM machine occupying 4n slots and with a dual n-phase winding is then proposed. This configuration offers a complete cancelation of all harmonics below the torque producing MMF component. Hence, the induced eddy currents in both rotor core and magnets are significantly reduced. The winding connection and the required number of turns for both winding groups are also given. The concept is applied to a 20-slot/18-pole stator with a dual five-phase winding, where the stator winding is connected as a combined star/pentagon connection. The proposed concept is assessed through a simulation study based on 2-D finite element analysis.

An Improved Fault-Tolerant Five-Phase Induction Machine Using a Combined Star/Pentagon Single Layer Stator Winding Connection

One of the main merits offered by multiphase machines is their high fault-tolerant capability. Literature has demonstrated that the performance of multiphase induction machines under fault conditions is affected by the employed stator winding connection. In open-loop controlled five-phase machines, the star connection is favorable under healthy conditions while the pentagon connection is favorable and yields a lower derating factor under the open phase condition. In this paper, a new combined star/pentagon single layer winding layout that combines the advantages of both star and pentagon connections is proposed for a five-phase induction machine. Although the proposed winding is intrinsically an asymmetrical ten-phase machine, the proposed connection allows for only five-phase terminals. Moreover, the proposed winding not only yields better flux distribution compared to a conventional single layer winding, but also provides a complete cancellation of the third-order harmonic flux component caused by the induced third sequence currents due to the saturation effect and/or under unbalanced operation. Hence, the machine losses are decreased, which improves the overall machine efficiency. For the healthy case, the machine is similar to a conventional star connected five-phase machine. However, with one phase open, the proposed connection results in a lower derating factor compared to conventional connections for both open-loop and optimal current control techniques. A 1-kW prototype machine is used for experimental verification.

A high voltage pulse-generator based on DC-to-DC converters and capacitor-diode voltage multipliers for water treatment applications

Pulsed electric field (PEF) can be used effectively in water treatment applications by passing infected water through two electrodes excited from a high voltage pulsed power supply which guarantees killing the harmful germs. In this paper, a new high-voltage pulse-generator with closed loop control of its output voltage is presented for treating water via underwater pulsed streamer corona discharge. The proposed generator is fed from a low AC voltage source (utility mains 220 V, 50 Hz) which makes it suitable for domestic applications. The proposed topology provides transformer-less operation which reduces the system size and enhances the overall efficiency. The proposed topology is based on capacitor-diode voltage multiplier (CDVM) circuits in conjunction with DC-DC converters (Boost and Buck-Boost converters). The simulation and experimental results elucidate the proposed configuration.

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.

A modified capacitor voltage control algorithm for suppressing the effect of measurement noise on grid-connected Z-source inverters controllers

Inverters are considered the orbit of research objectives for safe and reliable grid interface. Amongst the conventional inverters known as suitable candidates for gird connection in the last two decades, Z-source inverter (ZSI) emerged with buck/boost voltage capabilities compared to the counterpart voltage source inverter (VSI) and current source inverter (CSI). Therefore, ZSI introduces the merit of single stage grid interfacing of DG especially with renewable energy sources. Proper control of key parameters in single stage grid interface is essential. In the ZSI operation, the capacitor voltage is the most vital key parameter which can be controlled throughout the boosting factor. In this paper, the conventional capacitor voltage control is modified to enhance the performance of grid-connected ZSI and increase its immunity against the measurement noise. The proposed modification is verified throughout simulation. Furthermore, the experimental results obtained from a grid-connected ZSI prototype substantiate the proposed improvement.

Energy in smart grid: Strategies and technologies for efficiency enhancement

Incorporating advanced software and hardware technologies, to create a two way electricity and information flow, is forming the concept of the smart grid (SG). In an SG the energy delivery and control not only autonomous but also efficient. Hence, intelligently-planned SG which aims to consume energy wisely will be able to gain benefits for both power grid and end-users. Thus, the end-user continuity of electricity is assured even if a power grid failure occurs. In this paper, the concept of SG energy efficiency is explored. The applied strategies and technologies for energy efficiency improvement are introduced. Also, the impact of using plug in electric vehicles (PEV), and the employment of energy storage and combined-heat-and-power (CHP) are surveyed. Moreover, the role of using power electronics and energy management in energy efficiency are discussed.

Non-linear sliding-mode control of three-phase buck-boost inverter

The development of static power converters capable of transforming DC energy obtained from alternative sources into AC has become one of the main challenges in renewable energy systems. In this context, the buck-boost inverter is advantageous for being capable of providing an AC output voltage higher or lower than the input DC voltage in a single power conversion stage. In this paper, a controller based on the non-linear sliding mode theory is proposed for a three-phase buck-boost inverter to track a desired AC reference voltage. Unlike conventional linear sliding mode controllers that depend on the errors of the state variables, the control law used here depends only on the input and output voltages of the converter without the need to the inductor current measurement, which reduces the system complexity and cost. The proposed controller can not only track the desired reference quickly and accurately, but also achieve a high immunity to external perturbations, such as input voltage and output load disturbances. Several simulation studies are presented in order to investigate the performance of the proposed controller.

An adaptive PR controller for inverter-based distribution generation with active damped LCL filter

The fact distribution generation (DG) importance is growing rapidly in the recent years where the coupling between DG sources and the grid is done through inverters where exporting low distorted currents and high quality output power that copes with IEEE standards are main concerns. This paper demonstrates the regulation of the inverter current using proportional resonant (PR) controller that adapts to the grid voltage frequency to ensure reliable operation. Also to improve the quality of the output, an LCL passive filter is used as well as a demonstration of an alternative easier approach to achieve virtual damping of the resonance effect of the filter and construct an inner control loop improving robustness and stability simultaneously. The proposed concept has been simulated using Matlab Simulink for a 4KW IBDG.

A reduced switch-count single-phase SEPIC-based inverter

Recently, reduced switch-count converters have garnered exceptional attention in power electronic systems due to the diversified advantages such as low cost, low weight and volume, and high reliability offered by them. In this paper, a novel design of single-phase inverters with a reduced number of switching devices is proposed based on the single-ended primary-inductance converter (SEPIC). The proposed inverter topology achieves DC to AC conversion using only two switches, and generates a pure sinusoidal AC output voltage without a need for an additional output filter. The reduction in the number of the switching devices contributes to the reduction of the complexity and size of the DC-AC conversion system. The proposed inverter utilizes the DC-link voltage entirely, where the output voltage could be extended up to the full value of the DC input voltage. The integral sliding-mode control is used with the proposed topology to optimize its dynamics, and to ensure robustness of the system during different operating conditions. Operation, analysis, simulations, and experimental results for the proposed inverter topology are included in this paper.