Six-phase Induction Generator Research Articles

Nonlinear Optimal Control for Six-Phase Induction Generator-Based Renewable Energy Systems

The article aims at optimizing six-phase induction generator-based renewable energy systems (6-phase IGs or dual star induction generators) through a novel nonlinear optimal control method. Six-phase induction generators appear to be advantageous compared to three-phase synchronous or asynchronous power generators, in terms of fault tolerance and improved power generation rates. The dynamic model of the six-phase induction generator is first written in a nonlinear and multivariable state-space form. It is proven that this model is differentially flat. The 6-phase IG is approximately linearized around a temporary operating point recomputed at each sampling interval to design the optimal controller. The linearization is based on first-order Taylor series expansion and the Jacobian matrices of the state-space model of the 6-phase IG. A stabilizing optimal (H-infinity) feedback controller is designed for the linearized state-space description of the six-phase IG. The feedback gains of the controller are computed by solving an algebraic Riccati equation at each iteration of the control method. Lyapunov analysis is used to demonstrate global stability for the control loop. The H-infinity Kalman Filter is also used as a robust state estimator, which allows for implementing sensorless control for 6-phase IG-based renewable energy systems. The nonlinear optimal control method achieves fast and accurate tracking of setpoints by the state variables of the 6-phase IG, under moderate variations of the control inputs.

Efficiency of a Six-Phase Induction Generator Employing a Static Excitation Controller to Generate AC Power for Wind Energy

The most widely applied six phase induction generator (SPIG) leads to insufficient frequency regulation ability of power system. A six phase induction generator (SPIG) Combined with appropriate capacitors and a motor, it produces an induction generator that is self-excited. The advantage of this generator, which has recently caught the interest of various experts, particularly in the field of wind energy, combines the advantages of multiphase devices. This study aims to offer a technique for regulating the voltage of a wind-powered SPIG. The methodology suggests two different compensation setups for (V-f) control, involving two switching capacitors. Different setups’ performance constraints, controls, and features will be closely scrutinized and contrasted. The performance limits of the suggested system will be contrasted. to those of variable speed and variable capacity systems after being modelled and simulated. The results show that using the optimal capacitances for each configuration improves voltage and frequency regulation significantly. The preferable option, however, is short-shunt compensation since it regulates the output voltage and frequency with the fewest capacitances and the least amount of necessary duty fluctuation.

Optimal Sliding Mode Control of a Symmetrical Six-Phase Induction Generator for Wind Turbines

In this article, a sliding mode control (SMC) is applied to regulate the delivered power of a symmetrical six-phase induction generator. For this, the SMC strategy associated to the field-oriented control strategy is used in order to adjust the inner current loops of a squirrel cage six-phase induction generator (SC6PIG). In this way, the control algorithm switches between positive and negative feedback according to the position of the operating point in the phase plane. This technique guarantees the robustness of the SC6PIG in case of the loss of one to three stator phases or machine converter legs. The switching line slope and the initial operating point have been set so that the system starts with a negative feedback, then it continuously switches back and forth to positive feedback in order to maintain the desired trajectory of the system. The simulation and experimental results demonstrate the effectiveness and the robustness of this technique since the delivered power of the SC6PIG presents the same dynamics in healthy or faulty modes with one to two phase losses.

Multi-variable Optimization Formulation for Maximum Power Transmission Capability of a Standalone Six-phase Induction Generator

This paper presents an optimization based scheme to derive the maxi-mum power transmission capability of a self-excited six-phase inductiongenerator (SPIG). For execution of this proposed scheme, an easy andstraight forward method has been developed here for figuring out themaximum amount of power which can be transmitted by SPIG consid-ering different functional conditions. An optimization based problem isformulated with the help of multi-variable constraint, for finding out themaximum power transmission capability of SPIG. The total impedance ofSPIG, calculated from its equivalent circuit, is considered as the objec-tive function. Fmincon optimization toolbox of MATLAB has been usedto solve this numerical based problem. The critical power and the max-imum power transmission capability have been investigated for varia-tions of capacitor, load power factor and speed. The power transmis-sion capability of SPIG directly depends on the factors like machineparameters, rotor speed, power factor of the load and the capacitance value of self-excitation. From the analysis of the simulated results, it isfound that the performance of SPIG is satisfactory for various operatingconditions.

Fault Tolerant Variable Structure Control Of Six-phase Induction Generator For Wind Turbines

In this paper, a fault-tolerant control of a symmetrical six-phase induction generator based on a variable structure strategy is experimentally tested and compared with a classical proportional-integral controller. For this, we use a linear feedback sliding mode controller with switched feedback gains in such a way to control the inner current loops of this machine. One main drawback of the classical three-phase induction generator is that it is no longer possible to generate electrical power if only one phase is lost on the stator side. To overcome this issue, we will use a squirrel cage six-phase induction machine that can still operate when at least three phases remain on the stator side. This article proposes to use a variable structure control in order to cope with unbalanced currents and also maintain the generation of power when a loss of the stator's phases occurs. The proposed controller shows its robustness and good regulation performance in healthy and faulty modes. The simulation and experimental tests were carried out with a 24 kW induction machine that represents 1/100 of the electrical power of a real wind turbine.

Modeling and stability analysis of three- and six-phase asymmetrical grid-connected induction generator

This paper presents the development of linearized model of asymmetrical six-phase grid-connected induction generator (GCIG) for small-signal stability. The developed linearized model has been used to obtain the eigenvalue to evaluate generator stability with respect to parameter variation of the machine in comparison with its three-phase counterpart. During the analysis, suitability of six-phase induction generator for higher output power has been accessed. Instability tendency during low electrical output power can be avoided through closed loop operation of the machine. Hence, the indirect field-oriented control scheme for asymmetrical six-phase GCIG has been proposed for stable operation with higher reliability. The key analytical results have been demonstrated with its experimental validation.

Fault-Tolerant Control of a Low-Speed Six-Phase Induction Generator for Wind Turbines

In this paper, a fault-tolerant control scheme for a low-speed squirrel cage six-phase induction generator (SC6PIG) connected to a full-scale back-to-back converter structure is proposed and tested on an experimental 24-kW wind turbine test bed that represents a 1/100 of the electrical power of a grid-connected real wind turbine multiphase generator (2.5 MW). The aim of this paper is to define a suitable control algorithm that allows the electrical generation despite the loss of one to three phases on the generator or converter sides. Furthermore, the pole number of the generator is increased to simplify or eliminate the gearbox in such a way as to reduce mechanical sensitivity. Indeed, by multiplying the phase and pole numbers, the robustness against mechanical and electrical faults is improved compared to that of a classic three-phase generator associated with a gearbox. Simulation and experimental tests carried out on a 24kW-230V-24-pole SC6PIG in healthy and faulty mode (one phase missing) assess the feasibility and capacity of the proposed strategy.

Modeling and experimental analysis of grid-connected six-phase induction generator for variable speed wind energy conversion system

In this paper, an advanced control for grid-connected asymmetrical six-phase induction generator (ASIG) in variable speed wind energy conversion system (WECS) is proposed. It involves a detailed model of ASIG, a six-phase converter for machine side control, and a three-level converter for grid side control. ASIG consists of two three-phase sets spatially space shifted by thirty electrical degrees. This configuration offers higher power in the same machine frame, more reliability, and robustness when compared to the conventional three-phase induction generator (TPIG). Back to back connected voltage source converters (VSCs) are utilized for interfacing ASIG with the grid. Efficient control strategies are applied to generator side and grid side converters. Two machine side converters connected in parallel are operated with an advanced rotor field oriented control (RFOC) for maximum power point tracking (MPPT). RFOC is achieved by involving six PI controllers. It mainly focuses on removal of unbalanced currents between two sets of three-phase windings. Three-level grid side converter is controlled for maintaining DC link voltage, and to regulate the flow of reactive power between grid and generator. Experimental investigation of the proposed method is performed with 1.5-hp, six-pole, six-phase induction generator reconfigured from an existing three-phase induction machine. Generated power is supplied to the grid at unity power factor. Validating results indicating power flow, grid voltage and grid current are also exhibited. Paper also presents a comparative analysis of ASIG with conventional TPIG.

Performance evaluation of multiphase induction generator in stand‐alone and grid‐connected wind energy conversion system

This study presents a detailed performance analysis of multi-phase (six-phase) induction generator in conjunction with different types of wind energy conversion systems (WECS). It targets to emphasise the advantages of considering an asymmetrical six-phase induction generator (ASIG) in stand-alone, grid-connected fixed speed and grid-connected variable speed operation. Various aspects such as efficiency, reliability and productivity are considered while performing the analysis. In stand-alone mode, reliability and efficiency of the self-excited ASIG are ascertained by disconnecting one of the two three-phase sets connected to a resistive load. In grid-connected fixed speed mode, two different scenarios are implemented to pursue the applicability of ASIG. In the first scenario, only one three-phase winding set is connected to the grid and another set is connected to a local resistive load. In the second scenario, both three-phase windings are connected to the grid via Y− Δ /Y three-winding transformer. Variable speed operation in grid-connected mode is accomplished by employing back-to-back pulse-width modulation converters between the generator and grid. In this configuration, ASIG is operated with indirect field oriented control to obtain maximum aerodynamic efficiency. Transmission of active and reactive power is monitored with vector-oriented control. Experimental results of considered scenarios are presented to verify the viability of ASIG in various configurations of WECS.

Performance Characteristics of Six-Phase Induction Generator for Renewable Power Generation

<p>This paper presents the performance behavior of a multi-phase induction generator operating in six-phase mode. An experimental analysis has been done to determine operating characteristics of the six-phase machine to illustrate the advantageous features of the machine as compared to its three phase counterpart. The machine is configured to operate as a standalone power source in conjunction with a DC prime mover. The multi-phase machine can operate with one three phase capacitor bank which does not lead to complete shutdown of the system during fault conditions across one of its two sets of its stator windings. In the analysis the machine is connected to different capacitor configuration and the influence of these connections on the machine performance during no load and load have been implemented. Experimental results include voltage build up of the machine with different excitation capacitors at both sets of stator windings with changing speed during no load condition, resistive load condition and resistive inductive load condition with simple shunt and short shunt configuration.</p>

Assessment of excitation capacitance for a multiphase isolated self-excited induction generator for power generation

Self-excited induction generators are used in remote places for electrical power generation from both conventional as well as non-conventional sources. An induction generator can operate as a capacitor-excited machine, provided the machine is driven beyond synchronous speed and a suitable capacitor is connected across its terminals. In this paper, a technique has been proposed to estimate the values of excitation capacitances to maintain desired terminal voltages in a multiphase induction generator. A mathematical model using nodal admittance technique of a six-phase induction generator has been analysed. Genetic algorithm technique is applied here to obtain the unknown parameters and the capacitance requirements to obtain desired terminal voltages under various operating conditions.

Assessment of excitation capacitance for a multiphase isolated self-excited induction generator for power generation

Self-excited induction generators are used in remote places for electrical power generation from both conventional as well as non-conventional sources. An induction generator can operate as a capacitor-excited machine, provided the machine is driven beyond synchronous speed and a suitable capacitor is connected across its terminals. In this paper, a technique has been proposed to estimate the values of excitation capacitances to maintain desired terminal voltages in a multiphase induction generator. A mathematical model using nodal admittance technique of a six-phase induction generator has been analysed. Genetic algorithm technique is applied here to obtain the unknown parameters and the capacitance requirements to obtain desired terminal voltages under various operating conditions.

On-line switched control of a six-phase induction generator in faulted mode

The operation of multiphase machines in open-phase fault conditions is always associated with undesirable ripples in torque and power, even in steady state conditions. In the literature, several methods have been proposed to reduce these oscillations considering a fixed-fault situation without taking into account the transient behavior during the modification. In this way, this paper deals with the design and implementation of a multi-control system for all possible open-phase situations of a symmetrical squirrel cage six-phase induction generator (SC6PIG) up to three opened phases in such a way to extract a qualified electrical power. For this, a general model of the SC6PIG in healthy and open-phase fault situations is employed to design the multi-control system. The control systems are re-arranged regarding the situation of the generator in different open-phase fault conditions to provide the output power as close as in healthy mode. A simple detection system is associated to define the state of the generator (number and type of opened phases in faulty operation) and to switch to the appropriate control system. Furthermore, in order to minimize the transient problems during the switching process between the different control systems, an on-line initial condition setting is imposed to the control systems during the motion. An experimental set up including a SC6PIG driven by a permanent magnet dc motor has been built to prove the capacities of the proposed on-line switched control system in different cases such as healthy, one opened phase and two opened phases situations with smooth switching.

Estimation of Excitation Capacitance Requirement of an Isolated Multi-phase Induction Generator for Power Generation

<table width="593" border="1" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top" width="387"><p>Self Excited induction generators are used in remote places for electrical power generation from both conventional as well as non-conventional sources. An Induction generator can operate as a capacitor excited machine provided the machine is driven beyond synchronous speed and a suitable capacitor is connected across its terminals. In this paper a technique has been proposed to estimate the values of excitation capacitances to maintain desired terminal voltages in a multi-phase induction generator. A mathematical model using nodal admittance technique of a six-phase induction generator has been analyzed. Genetic algorithm technique is applied here to obtain the unknown parameters and the capacitance requirements to obtain desired terminal voltages under various operating conditions.</p></td></tr></tbody></table>

A Novel Strategy for Sensorless Control Modification of a Six-phase Induction Generator in Faulted Mode

Due to the limited operations of three-phase machines in open-phase fault conditions, the multiphase induction generators are now introduced in high-performance power generation systems. In the case of six-phase induction generators, the operation with opened phases is associated with torque and consequently power oscillations even in steady state conditions. Previous works have reported different methods to reduce these oscillations but they only deal with sensored control issues. Therefore, this paper deals with on-line modification of a sensorless control system applied to a squirrel cage six-phase induction generator (SC6PIG) when one to three phases of the machine are lost. Designing ten different off-line Luenberger speed observers as well as ten control systems corresponding to the different possible fault types and switching between them as a function of a detection system is proposed in this paper. Furthermore, on-line imposing of the nonzero initial conditions induces a smooth switching between the observers as well as the controllers with minimum associated transient at switching instants. The proposed strategy is tested on a wind turbine simulator driven by a permanent magnet dc motor. The experimental results in healthy and faulty modes assess the validity of the proposed strategy.

Stability assessment of isolated six-phase induction generator feeding static loads

This paper presents the stability analysis of a six-phase self-excited induction generator (SP-SEIG) based on the eigenvalue stability criteria for its linearized model. This demonstrates the small signal stability behavior during steady-state operating conditions. The eigenvalue approach also establishes an opportunity to correlate eigenvalues with machine parameters. The investigation in this paper reveals that the eigenvalues are dependent upon the machine parameters, and the most critical parameter is the variation in magnetizing inductance (Lm) . The eigenvalues are varied in accordance with the machine variables and give focus to the stabilization of the SP-SEIG. A particular voltage build-up phenomenon is also experimentally verified to validate the proposed analytical approach in this paper.

Speed-sensorless control strategy for multi-phase induction generator in wind energy conversion systems

Renewable energy sources, especially wind energy conversion systems (WECS), exhibit constant growth. Increase in power and installed capacity led to advances in WECS topologies. Multi-phase approach presents a new development direction, with several key advantages over three-phase systems. Paired with a sensorless control strategy, multi-phase machines are expected to take primacy over standard solutions. This paper presents speed sensorless vector control of an asymmetrical six-phase induction generator based on a model reference adaptive system (MRAS). Suggested topology and developed control algorithm show that sensorless control can yield appropriate dynamic characteristics for the use in WECS with increase in reliability and robustness.

Wind-driven stand-alone six-phase self-excited induction generator transients under different loading conditions

This paper present the transient performance of an isolated six-phase self-excited induction generator (SPSEIG) driven by a fixed-pitch wind turbine. The approach is based on a wind-turbine model, SPSEIG model and detailed transient behaviour of an SPSEIG for stand-alone power generation, when subjected to sudden switching of balanced/unbalanced R, RL and RLC load for both three-phase winding sets. The computer model has been developed in an arbitrary reference frame. In the d–q axis model, the effects of common mutual leakage inductance between the two three-phase winding sets have been included. The simulation results show a good performance from the system under different loading conditions. 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.

Improved Performance of Wind-driven Isolated Induction Generators by Six-phase Operation

paper describes a new, generalized and efficient steady- state model for the performance analysis of isolated six-phase induction generators. The mathematical model is formed directly from the equivalent circuit of six-phase induction generator by nodal admittance method. The proposed model is very simple which completely avoids lengthy derivations of non linear equations. The model results in matrix form so that inclusion or elimination of any equivalent circuit elements can be easily achieved. Also, this model is flexible to find any combination of unknown quantities of the equivalent circuit. The matrix equation is solved by genetic algorithm to determine the steady-state performance of isolated six-phase induction generator (ISPIG). To validate the improvement of performance by six-phase operation, the experimental and theoretical results were compared with three-phase operation. In addition, the winding diagram of the six-phase / three- phase induction generator which is used as a prototype model for the experimental study is also presented. Keywords-phase induction generator, Steady-state analysis, Genetic

Steady-State Modeling and Analysis of Grid-Connected Six-Phase Induction Generator for Renewable Energy Generation

This article presents the steady-state modeling and analysis of a grid-connected six-phase induction generator for renewable energy generation powered by hydro turbine. The basis of the analysis is nodal admittance method as applied to the equivalent circuit, and used to analyze the behavior of the machine for the operating mode such as (i) when only one three-phase winding set is connected to grid, (ii) when one three-phase winding set is connected to grid and other three-phase winding set is subjected to load, and (iii) when both the three-phase winding sets are connected to grid through an interconnecting Y-/Y six-phase to three-phase transformer. Nodal admittance based matrix equations are easier to modify in order to account for mutual leakage coupling between two three-phase winding sets, core loss component, and make the analysis very easy, fast and accurate. Through analytical and practical studies, it is shown that machine can feed direct, reliable, and low cost power to grid without interface network. The analytical results are found to be in good agreement with experimental results.