Design of drives for inverter-assisted induction generators

pre-printThis paper investigates the control of power generation using two-phase squirrel-cage induction machines, where the load is connected to one stator winding and the load voltage is controlled through the other winding. The concept can be applied to three-phase machines as well. A state-space model of the machine is used to identify suitable operating regions. Then, two types of control algorithms are proposed: The first type regulates the frequency and the magnitude of the generated voltage and is suitable for stand-alone operation. The second type also regulates the phase of the voltages, enabling grid synchronization. Experimental results are presented for each of the control algorithms. The closed loop systems are found able to track the desired reference and to reject disturbances caused by significant changes in load and speed

Hybrid photovoltaic-thermoelectric generator powered synchronous reluctance motor for pumping applications

The interest in photovoltaic (PV) pumping systems has increased, particularly in rural areas where there is no grid supply available. However, both the performance and the cost of the whole system are still an obstacle for a wide spread of this technology. In this article, a hybrid photovoltaic (PV)-thermoelectric generator (TEG) is investigated for pumping applications. The electric drivetrain comprises a synchronous reluctance motor and an inverter. A control strategy for the drivetrain is employed to execute two main tasks: 1) driving the motor properly to achieve a maximum torque per Ampere condition and 2) maximizing the output power of the PV system at different weather conditions. This means that the conventional DC-DC converter is not used in the proposed system. Moreover, batteries, which are characterized by short life expectancy and high replacement cost, are also not used. It is found that the motor output power and the pump flow rate are increased by about 9.5% and 12% respectively when the hybrid PV-TEG array is used compared to only using PV array. Accordingly, the performance, cost and complexity of the system are improved. Measurements on an experimental laboratory setup are constructed to validate the theoretical results of this work

Master of Science

thesisThis thesis investigates the problem of producing power using a single-phase induction machine. Single-phase induction motors are typically nonsymmetric two-phase motors, also called split-phase motors, with a main winding and an auxiliary winding. We consider the control of power delivered by the main winding through the auxiliary winding. A state-space model of an asymmetric split-phase generator has been developed. This model is used to characterize and identify a 1/3 hp induction machine. The parameters are used to predict suitable operating regions for the generator. It is found that there exists a viable operating region in a band just above the synchronous speed of the motor. Four control algorithms are presented. The first is a simple open-loop algorithm for a sinusoidal reference signal. The second is a controller based on the inverse-G adaptive algorithm. The third is an algorithm featuring an adaptive estimate of the system frequency response. Finally, a PI control method is considered for situations where the phase of the generated voltage does not need to be controlled. Simulated and experimental results are presented for each of the control algorithms. The closed-loop algorithms were able to track a desired reference. These algorithms were also able to reject a disturbance caused by a 20 percent increase in speed

Study of Novel Power Electronic Converters for Small Scale Wind Energy Conversion Systems

This chapter proposes a study of novel power electronic converters for small scale wind energy conversion systems. In this chapter major topologies of power electronic converters that used in wind energy converter systems have been analysed. Various topologies of DC/AC single stage converters such as high boost Z-source inverters (ZSI) have been investigated. New proposed schemes for inverters such as multilevel and Z-source inverters have been studied in this proposed chapter. Multilevel converters are categorized into three major groups according to their topologies which are diode clamped multilevel converters (DCM), cascade multilevel converters (CMC) with multiple isolated dc voltage sources and flying capacitor based multilevel converters (FCMC). Z-source inverters are divided to ZSI, qZSI and trans-ZSI types. Trans-ZSI is mostly used for high step-up single stage conversions

A New Islanding Detection Method Based On Wavelet-transform and ANN for Inverter Assisted Distributed Generator

Nowadays islanding has become a big issue with the increasing use of distributed generators in power system. In order to effectively detect islanding after DG disconnects from main source, author first studied two passive islanding methods in this thesis: THD&VU method and wavelet-transform method. Compared with other passive methods, each of them has small non-detection zone, but both of them are based on the threshold limit, which is very hard to set. What’s more, when these two methods were applied to practical signals distorted with noise, they performed worse than anticipated. Thus, a new composite intelligent based method is presented in this thesis to solve the drawbacks above. The proposed method first uses wavelet-transform to detect the occurrence of events (including islanding and non-islanding) due to its sensitivity of sudden change. Then this approach utilizes artificial neural network (ANN) to classify islanding and non-islanding events. In this process, three features based on THD&VU are extracted as the input of ANN classifier. The performance of proposed method was tested on two typical distribution networks. The obtained results of two cases indicated the developed method can effectively detect islanding with low misclassification

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Comparison between unipolar and bipolar single phase grid-connected inverters for PV applications

An inverter is essential for the interfacing of photovoltaic panels with the AC network. There are many possible inverter topologies and inverter switching schemes and each one will have its own relative advantages and disadvantages. Efficiency and output current distortion are two important factors governing the choice of inverter system. In this paper, it is argued that current controlled inverters offer significant advantages from the point of view of minimisation of current distortion. Two inverter switching strategies are explored in detail. These are the unipolar current controlled inverter and the bipolar current controlled inverter. With respect to low frequency distortion, previously published works provide theoretical arguments in favour of bipolar switching. On the other hand it has also been argued that the unipolar switched inverter offers reduced switching losses and generates less EMI. On efficiency grounds, it appears that the unipolar switched inverter has an advantage. However, experimental results presented in this paper show that the level of low frequency current distortion in the unipolar switched inverter is such that it can only comply with Australian Standard 4777.2 above a minimum output current. On the other hand it is shown that at the same current levels bipolar switching results in reduced low frequency harmonics

Vector Control Of Wind Driven Self Excited Induction Generator Connected To Grid Using Twenty Four Pulse AC-DC Converter Employing Pulse Doubling Technique

This paper deals with multipulse AC-DC converters for improving the power quality in vector-controlled wind driven self excited induction generator at the point of common coupling. These multipulse AC-DC converters are realized using a reduced rating autotransformer. Moreover, DC ripple reinjection is used to double the rectification pulses resulting in an effective harmonic mitigation. The proposed AC-DC converter is able to eliminate up to 21st harmonics in the supply current. The effect of load variation on Vector Controlled Self Excited Induction Generator(VCSEIG) is also studied to demonstrate the effectiveness of the proposed AC-DC converter. A set of power quality indices on input AC mains and on the DC bus for a VCSEIG fed from different AC-DC converters .The complete electromechanical system is modeled and simulated in MATLAB using Simulink and simpower system block set. The simulated results are presented and compared for regulating voltage and frequency of SEIG driven by wind turbine. Keywords: Autotransformer, Multipulse AC DC converter, DC ripple reinjection, Pulse doubling, VCSEIG