Performance analysis of a three-phase induction generator connectedto a single-phase power system

This paper analyzes the performance of a three-phase induction generator which is connected to a single-phase power system. Significant improvement in machine performance can be obtained by using a single static phase-converter, provided that the machine is driven in the reverse direction. If two phase-converters, are employed, perfect phase balance can be obtained at any desired value of slip. The theoretical analysis is validated by experiments on a 2-kW test machine     

A brushless, exciterless, single-phase, sinusoidal wave synchronousmachine having an auxiliary stator winding

Analytical and experimental studies of a brushless, exciterless, single-phase, sinusoidal-wave synchronous machine operating as a generator or a motor, derived from a three-phase machine, are reported. One phase armature winding of the three-phase machine is used as an auxiliary stator winding of the single-phase machine and is used to supply the exciting power for the other two-phase armature windings acting as the load winding of the single-phase machine. A 1.5 kW, 200 V, 60 Hz, four-pole synchronous machine was used the experiments. It is shown that the waveforms of the armature terminal voltage and the load current are nearly sinusoidal. The advantages of the single-phase machine as a portable generator or small-load motor are discussed     

Capacitors Required for Maximum Power of a Self-Excited Single-Phase Induction Generator Using a Three-Phase Machine

This paper aims to determine the optimal capacitors required for maximum output power of a single-phase self-excited induction generator (SEIG), using a three-phase machine feeding inductive as well as capacitive loads. The generator consists of a three-phase star-connected induction machine with three capacitors and a single-phase load. The algorithm, which gives directly the values of the optimal capacitors for the maximum power output and the maximum power available, has been developed using the steady-state model of the SEIG and sequential unconstrained minimization technique (SUMT). The variations of the maximum power output with power factor (pf) of loads (both inductive and capacitive) and speed of the SEIG have been presented. The voltage regulation of the generator is small due to the effect of the two series capacitors. Experimental results have shown the effectiveness and accuracy of the developed algorithm.     

Single-phase operation of a three-phase induction generator using a novel line current injection method

By using two capacitances and a current injection transformer, a three-phase induction generator can operate with good phase balance and line power factor while delivering power to a single-phase power grid. This paper presents a systematic analysis on this novel induction generator configuration. The solution of the system's inspection equations using the method of symmetrical components enables the steady-state generator performance at any speed to be computed. The conditions for achieving perfect phase balance are deduced from the phasor diagram. It is shown that the capacitances that result in perfect phase balance depend on the generator admittance, power factor angle, as well as the turns-ratio of the current injection transformer. Where possible, the computed results are verified by experiments conducted on a 2-kW induction machine. An experimental investigation on the system waveforms and harmonics is also carried out.     

Steady-state analysis and performance of a stand-alone three-phaseinduction generator with asymmetrically connected load impedances andexcitation capacitances

This paper presents a steady-state performance analysis of a stand-alone three-phase induction generator self-excited with unbalanced capacitances and supplying unbalanced loads. Using the method of symmetrical components, the complex three-phase generator-load system is reduced to a simple equivalent passive circuit. A function minimization technique is employed to solve this equivalent circuit in order to determine the excitation frequency and magnetizing reactance. The proposed method enables practically all cases of unbalanced operation of the self-excited induction generator to be analyzed. Emphasis is next focused on single-phase loads and a special phase-balancing scheme, namely the modified Steinmetz connection (MSC), is investigated. It is shown that perfect phase balance of the SEIG can be obtained with an appropriate combination of excitation capacitances and loads. The theoretical analysis is validated by experiments on a 2.2 kW induction machine     

并网中小型风电系统最大功率跟踪控制

针对目前中小型风力发电系统发电效率低,提出了一种新型拓扑结构,即机侧采用三相PWM整流器,网侧采用单相PWM逆变器。在对永磁同步发电机数学模型和风力机最佳输出功率进行分析的基础上,采用转子磁链定向控制技术,实现对发电机输出的有功功率的控制,进而实现对风力发电机最大功率的跟踪控制;同时,在单相系统中引入"虚拟电路",使网侧单相变流电路参数可以转化到旋转坐标系下,实现无静差控制。通过仿真试验验证了控制策略的可行性。     

Capacitance requirements of a three-phase induction generatorself-excited with a single capacitance and supplying a single-phase load

This paper presents a practical method for computing the minimum capacitance required to initiate voltage build-up in a three-phase induction generator self-excited with a single capacitance and supplying a single-phase load. Attention is focused on the Steinmetz connection which gives superior performance over the plain single-phasing mode of operation. From a consideration of the input impedance of the induction generator and the self-excitation conditions, two nonlinear equations are obtained. Solution of one equation using the Secant method enables the excitation frequency to be determined, and the minimum excitation capacitance can be calculated from the second equation. This solution technique is subsequently employed in an iterative procedure for computing the capacitance required to maintain the terminal voltage at a preset value when the generator is supplying load. Experimental results obtained on a 2-kW induction machine are presented to verify the theoretical analysis where possible     

A novel single-phase self-regulated self-excited inductiongenerator using a three-phase machine

This paper presents a steady-state analysis of a novel single-phase self-regulated self-excited induction generator which employs a three-phase machine. Performance equations are derived using the method of symmetrical components, while the pattern search method of Hooke and Jeeves is used for the determination of the machine variables. The advantages of the generator include simple circuit configuration, small voltage regulation, good phase balance, and large power output. With an appropriate choice of the series and shunt capacitances, a nearly balanced operating condition can be obtained for a certain load. The theoretical analysis is validated by experiments performed on a small induction machine     

A novel excitation scheme for a stand-alone three-phase induction generator supplying single-phase loads

This paper presents the operating principle and steady-state analysis of a novel excitation scheme for a stand-alone three-phase induction generator that supplies single-phase loads. The phase windings and excitation capacitances are arranged in the form of the Smith connection and the excitation scheme is referred to as the SMSEIG. In addition to providing the reactive power for self-excitation, the capacitances also act as phase balancers. With this novel excitation scheme, isolated single-phase loads can be supplied with good phase balance in the induction machine, resulting in high efficiency, large power output, and quiet machine operation. Performance analysis is based on the method of symmetrical components, from which the input impedance of the generator can be determined. Numerical solution of a simplified equivalent circuit for the machine variables, namely the excitation frequency and magnetizing reactance, enables the generator performance to be evaluated for any load and speed. With the aid of a phasor diagram, the conditions for achieving perfect phase balance are deduced and a method to compute the capacitances required is developed. Experimental investigations on a 2.2-kW induction machine confirm the feasibility of the SMSEIG.     

Performance analysis of a three-phase induction generatorself-excited with a single capacitance

This paper presents a unified method of analysis for a three-phase induction generator self-excited with a single capacitance and supplying a single-phase load. Symmetrical components analysis is used to establish the input impedance of the generator, while the pattern search method of Hooke and Jeeves enables the per-unit frequency and magnetizing reactance of the machine to be determined, a crucial step in computing the generator performance. Best machine performance is obtained using the Steinmetz connection, with the excitation capacitance connected across the lagging phase. Experiments carried out using a 2.2 kW induction machine confirm the accuracy of the theoretical analysis and the solution method     

A six-phase synchronous generator for stand-alone renewable energy generation: Experimental analysis

This paper presents the steady-state behavior of a SPSG (six-phase synchronous generator) configured to operate as a stand-alone electric energy source in conjunction with a hydro power plant. A purely experimental treatment is provided with the emphasis placed on operating regimes that illustrate the advantages of using SPSG. In particular, it is shown that the generator can supply two separate three-phase loads which represent an additional advantage. Last but not least, outputs of the two three-phase windings can be used to supply a single three-phase load through an interconnecting six-phase to three-phase transformer, in which case failure of one three-phase winding does not lead to the system shutdown and the load can be still supplied from the remaining healthy winding. Experimental results include loading transients with independent three-phase resistive load at each of the two three-phase winding sets, and measured steady-state characteristics for various configurations and operating conditions.     

双向单相有功电能表和三相无功电能表的检定

介绍双向单相有功电能表和三相无功电能表检定时应注意的事项，提出减小双向单相有功电能表正、反向计量误差变化的办法，指出现在有的电能表检定装置，检定双向三相无功电能表时存在的不足及其解决办法。     

Performance evaluation of series compensated self-excited six-phase induction generator for stand-alone renewable energy generation

This paper presents the steady-state behavior of a series compensated (short-shunt) self-excited six-phase induction generator (SPSEIG) configured to operate as stand-alone electric energy source in conjunction with a hydro power plant. A purely experimental treatment is provided with the emphasis placed on operating regimes that illustrate the advantages of using SPSEIG. In particular, it is shown that the SPSEIG can operate with a single three-phase capacitor bank, so that the loss of excitation or fault at one winding does not lead to the system shutdown. The generator can also supply two separate three-phase loads, which represent an additional advantage. Experimental results include loading transients with independent three-phase resistive and resistive–inductive load at each of the two three-phase winding sets, and measured steady-state characteristics for various load and/or capacitor bank configurations. Practical results for long-shunt configuration are also given for comparative performance evaluation of series compensated SPSEIG.     

Minimum airgap flux linkage requirement for self-excitation instand-alone induction generators

A minimum airgap flux linkage is required for the self-excitation and stable operation of an isolated induction generator feeding an impedance load. With the aid of bifurcation theory, it is shown that the minimum airgap flux linkage requirement is the value at which the derivative of the magnetizing inductance with respect to the airgap flux linkage is zero. This minimum airgap flux linkage determines the minimum or maximum load impedance and minimum excitation capacitance requirements. This result is demonstrated using single-phase and three-phase induction generators     

Voltage and Frequency Controller for a Three-Phase Four-Wire Autonomous Wind Energy Conversion System

This paper deals with control of voltage and frequency of an autonomous wind energy conversion system (AWECS) based on capacitor-excited asynchronous generator and feeding three-phase four-wire loads. The proposed controller consists of three single-phase insulated gate bipolar junction transistor (IGBT)-based voltage source converters (VSCs) and a battery at dc link. These three single-phase VSCs are connected to each phase of the generator through three single-phase transformers. The proposed controller is having bidirectional flow capability of active and reactive powers by which it controls the system voltage and frequency with variation of consumer loads and the speed of the wind. VSCs along with transformer function as a voltage regulator, a harmonic eliminator, a load balancer, and a neutral current compensator while the battery is used to control the active power flow which, in turn, maintains the constant system frequency. The complete electromechanical system is modeled and simulated in the MATLAB using the Simulink and the power system blockset (PSB) toolboxes. The simulated results are presented to demonstrate the capability of the proposed controller as a voltage and frequency regulator, harmonic eliminator, load balancer, and neutral current compensator for different electrical (varying consumer loads) and mechanical (varying wind speed) dynamic conditions in an autonomous wind energy conversion system.     

基于交替单相PWM控制的三相光伏并网系统

提出了可用于多支路型三相光伏并网逆变器的交替单相PWM控制方法。该控制方法在一个工频周期内,逆变器有6种开关模式,每种开关模式中只须对三相中的一相桥臂进行PWM控制,从而有效降低了功率管开关损耗,在多支路光伏并网结构提高能量转换效率的基础上,进一步提高系统效率。采用电流滞环PWM跟踪控制,能够简单实现逆变正弦电流输出,跟踪性能好,并网功率因数为1,系统稳定性好,电流总谐波畸变率(THD)较低,可满足并网要求。通过Matlab仿真验证了该控制方法的正确性和有效性。     

Accurate power sharing among multi-DG resources in a microgrid

In this paper, a sliding mode (SM)-based direct active and reactive power control for the distributed generations (DGs) in microgrid is presented. The grid-connected microgrid contains two three-phase DGs that are photovoltaic (PV) units, and three single-phase DGs consisting of fuel cell (FC), PV, and battery. In the proposed strategy, controlling of the active and reactive powers is carried out for the single-phase and three-phase DGs without any phase angle tracking of the network voltage or synchronization transformations. The proposed robust control strategy improves power sharing and regulates power components injected by the DGs, and it is tested under balanced and unbalanced loads.     

Steady-state analysis of a three-phase induction motor with theSmith connection

This letter presents a steady-state analysis of the single-phase operation of a three-phase induction motor with the Smith connection. The motor performance, such as the phase voltages, phase currents, and torque, can be obtained quantitatively. The theoretical analysis is verified by experiments performed on a small induction machine     

Analysis and design of a two-speed single-phase induction motor with 2 and 18 pole special windings

The motor presented employs multiple independent windings for operation with two very different pole numbers. The 18-pole field is produced with a symmetrical three-phase winding connected in a Steinmetz arrangement to a single-phase supply. A unified analysis method has been developed and used to demonstrate the equivalence of a Steinmetz delta or star connection with a main and auxiliary winding of a single-phase motor. The method has been experimentally validated and also included are some specific motor design considerations.     

Modeling and analysis of six-phase synchronous generator for stand-alone renewable energy generation

This paper presents a mathematical model of six-phase synchronous generator (SPSG) for analysis of its transient and dynamic behavior for stand-alone renewable energy generation in conjunction with a hydro power plant. In the analytical model, effect of common mutual leakage reactance between the two three-phase winding sets, and the mutual leakage coupling between d- and q-axis of the two stator windings have been considered. Paper also discusses the applicability of SPSG for supplying two individual loads by presenting the results of analytical and experimental study of transient and steady-state behavior under various operating conditions. It is shown that it can be used to supply two independent three-phase loads. While the interaction between the two windings is inevitable and variation of load at one winding set changes the operating conditions at the other winding, the situation is still satisfactory for a wide range of rural resistive loads.