Synchronous Reluctance Generator Research Articles

Electromagnetic torque analysis of wind-driven SRG with ferrite magnet

The present paper analyses the effect of placing the ferrite magnet into the rotor air barrier of synchronous reluctance generators (SRG) on its electromagnetic performance. The paper uses a difference of average electromagnetic torque and ripple torque as a measure of the performance index. Here, in the analysis, a magnetic material is placed in the middle of each air barrier, and its size is symmetrically increased on both sides to increase the percentage of the volume of the magnetic material. The effect of an increase in the volume of the magnetic material on its performance is presented. Moreover, the variation in electromagnetic features such as the d- and q-axes inductance and flux linkage are also explored and compared for different volumes and ferrite material. In the present work, finite element analysis is used to get the electromagnetic performance. The paper also includes hardware validation on the fabricated prototype of SRG (without ferrite magnet), but SRG with a ferrite magnet only includes the results with FEA simulation.

Robust Control Strategies for SyRG-PV and Wind-Based Islanded Microgrid

The nonlinearity in the consumption does not maintain steady voltage or frequency; therefore, in this article, a circular limited cycle oscillator frequency locked loop with prefilter (CLO-FLL-WPF) based control for voltage source converter control is used to achieve voltage and frequency regulation in an islanded microgrid (MG). This control is implemented to compensate local load reactive power, harmonic currents, and load unbalance. Besides, the active power of local loads is shared among the multiple energy sources. The CLO-FLL-WPF control technique performance is validated experimentally and through simulations by comparing it with the existing control algorithm in a MG. This MG is a combination of the solar photovoltaic array, pico-hydro turbine-driven synchronous reluctance generator, permanent magnet brushless dc generator based wind energy conversion, and battery storage. In traditional battery control, a proportional-integral control approach is used, which can cause a stability problem. Thereby, in this article, the bidirectional dc–dc converter control method is used, which provides improved stability and makes the controller design straightforward. Test results validate the effectiveness of the control algorithm under different dynamic and steady-state conditions.

SyRG-PV-BES-Based Standalone Microgrid Using Approximate Multipliers Based Adaptive Control Algorithm

This article deals with the adaptive control algorithm to maximize the distributed generations (DGs) in islanded microgrid. The approximate multiplier least mean square (AMLMS) control scheme is used for the extraction of fundamental load component with reduced steady state error and faster convergence to provide better performance than conventional LMS control. This control focuses on reduction of complexity of LMS by adding multipliers in the finite impulse response filter and updating the coefficients. The AMLMS control algorithm for a voltage source converter is also effective in compensating harmonics for power quality improvement of islanded microgrid system while feeding nonlinear load. In an islanded microgrid at ac side, a synchronous reluctance generator based pico-hydropower generator is used because it is economical than other conventional generators. At dc side, a photovoltaic array and a bidirectional dc–dc converter (BDC) are used. The BDC with a storage battery maintains the optimal power flow to provide the power equilibrium between load and sources through dc-link voltage regulation. The BDC also mitigates the second order harmonic from the battery charging and discharging current. Test and simulation results validate the effectiveness of AMLMS control under steady and dynamic conditions of solar insolation change and load unbalance.

A High-Speed Microturbine PMa-SynRG Emulation Using Power Hardware-in-the-Loop for Wind Energy Conversion Systems

In this paper, a high-speed microturbine (MT) permanent magnet assisted synchronous reluctance generator (PMa-SynRG) real-time emulation based on linear impedance regulator (LIR) using power hardware-in-the-loop (PHIL) for wind energy generation tests is presented. The LIR is designed without any feedback control loop for reshaping the $s$ -domain performances of the current filter along with the converter inside the PMa-SynRG emulated system. The PHIL platform not only provides a method for eliminating the high cost of using real renewable energy hardware but also it enables the developers to create new, rapid, and reliable controllers for renewable energy testing. This platform can be used in investigating the performance of energy system under various conditions even if the generator prototype is not yet developed or unavailable. PMa-SynRG mathematical model is emulated in the real-time using PHIL platform while the output voltage of the proposed emulator imitates the generated voltage through the simulated model. In addition, a voltage source converter is employed as a voltage amplifier for imitating the PMa-SynRG performance when supplying nonlinear/linear loads. In this paper, the proportional-integral resonant (PIR) controller is utilized at the voltage control loop for tracking the distorted output reference signal voltage. In order to investigate the performance of the proposed PMa-SynRG emulator, it has been simulated and compared with MATLAB/SIMULINK environment.

Low-Voltage Ride-Through of a Synchronous Generator-Based Variable Speed Grid-Interfaced Wind Energy Conversion System

Wind energy conversion systems (WECSs) based on synchronous generators devoid of rotor windings, such as permanent magnet synchronous generators and synchronous reluctance generators, have become popular due to their maintenance-free operation. As per grid codes, WECSs ought to stay connected, at least for a short while, to ensure reliability and stability, even if there is a fault in the grid. There are various techniques proposed in the literature, for implementing low-voltage ride-through (LVRT). This article explores a few methods for achieving LVRT for a synchronous machine-based WECS connected to the grid through a back-to-back connected full-rated converter. The machine-side converter is controlled by field-oriented control methodology to drive the generator at an optimum speed to harvest maximum power from the wind turbine. The grid-side converter makes use of the grid-voltage-oriented control algorithm to achieve decoupled control of real and reactive powers. The LVRT capability of the system is attained using four different control techniques, namely modulation index (MI) control, deloading, crow-bar protection, and interchanging the roles of the two converters to arrest the rise in dc-link voltage. These methods have been simulated in Simulink/MATLAB environment, and the results obtained show that these techniques work very effectively for realizing LVRT in a synchronous machine-based WECS. Finally, experimental results are presented to demonstrate the successful working of the maximum power point tracking algorithm and LVRT capability on a laboratory prototype; a comparison of LVRT techniques is presented to enable the users to make an informed choice.

Sensorless SynRG Based Variable Speed Wind Generator and Single-Stage Solar PV Array Integrated Grid System With Maximum Power Extraction Capability

This article presents a grid-integrated hybrid renewable energy sources based system comprising a solar photovoltaic (PV) array and a wind energy conversion system (WECS). The WECS uses a position-sensorless synchronous reluctance generator (SynRG) for the electric power generation from the wind turbine (WT), wherein, a sensorless field-oriented control (FOC) is made use of for the maximum power extraction (MPE). A second-order flux estimation (SFE) method along with frequency-locked loop (FLL) is utilized for the accurate flux estimation from the SynRG stator voltages and currents. A set of back-to-back connected three-phase two leg voltage source converter (VSC) topology is selected for the grid integration of WECS. This system has a common dc link where the solar PV array and the machine-side VSC (MSC) of the wind generator, are directly connected. The power output from the solar PV array and WECS, is shared between the grid and the local loads. The maximum power generation from SynRG in the WECS, is achieved by operating the SynRG at the speed estimated by the MPE algorithm. The maximum power is drawn from the solar PV array by adjusting the dc-link voltage, which is decided by the algorithm. For the proper power control and power quality improvement, the grid-side converter (GSC) is adequately controlled by implementing an observer-based control technique. The real-time validation of the system, is carried out using a developed laboratory prototype.

Robust 3IMPL Control Algorithm for Power Management of SyRG/PV/BES-Based Distributed Islanded Microgrid

In an islanded ac microgrid, a comprehensive algorithm of a three-phase, improved-magnitude, phase-locked-loop (3IMPL) control algorithm is developed in this paper to provide dc offset removal, steady-state error removal, and fast dynamic response. In addition, the control of the voltage-source converter (VSC) using the 3IMPL algorithm provides voltage and frequency control and elimination of harmonics of nonlinear loads. In the proposed microgrid, a solar photovoltaic (PV) array is connected to the dc link through a boost converter, and an incremental conductance technique is used for extraction of maximum power from a PV array. Due to intermittency of the PV array, a synchronous reluctance generator is used for pico-hydro generation because it is economical, ecologically sustainable, and extremely reliable and requires less maintenance. Moreover, a microgrid suffers from problems of variation in generation and continuous load fluctuations; therefore, for power balancing between the source and the load, a storage battery is connected across the dc link of the VSC through a bidirectional dc-dc converter. Test results on a prototype have verified the control strategy and are able to improve the power quality of the system at varying solar insolation and unbalance in the load.

Performance Analysis of Single-Phase Electrical Machine for Military Applications

A permanent magnet assisted synchronous reluctance generator (PMA-SynRG) and an induction generator (IG) were compared for portable generator applications. PMA-SynRG with two rotor configurations, namely rotors with ferrite magnet and NdFeB, were designed. Furthermore, a design strategy for both PMA-SynRG and IG is presented with their geometrical dimensions. The machine was designed and results were analyzed using finite element analysis. Results such as flux density, open circuit and full load voltages, torque in generating mode, weight comparison and detailed cost analysis were investigated. In addition, thermal analysis for various ambient conditions (−40 °C, +30 °C, +65 °C) was evaluated for both PMA-SynRG and IG. Furthermore, acoustic versus frequency plot and acoustic pressure level were investigated for both the generators. Finally, the results confirmed that the machine with a higher power-to-weight ratio was the right choice for military applications.

Position Sensor-Less Synchronous Reluctance Generator Based Grid-Tied Wind Energy Conversion System With Adaptive Observer Control

A new wind energy conversion system (WECS), with a position sensor-less synchronous reluctance generator (SynRG), integrated to the grid is proposed in this paper. Simple, brushless, compact structure of SynRG along with a full-scale converter makes it suitable for wind power applications. SynRG offers a fast dynamic response due to the absence of permanent magnets and windings in the rotor thus eliminating rotor losses completely. The torque pulsation from wind turbine (WT) are prevented from being transmitted to the grid by making use of a back-to-back (BTB) connected full-scale converters. The WECS and the grid are sharing a common DC-link through their respective voltage source converters (VSCs). The VSC connected to the machine side provides the required reactive power to the SynRG and operates it at a speed decided by the maximum power point (MPP) algorithm. A rotor position/speed sensor-less field-oriented control is implemented for controlling the SynRG. A fast, accurate, and oscillation-less adaptive observer based algorithm is introduced for the grid integration of WECS. MATLAB®/Simulink platform is used for the modeling and simulation of the system and a laboratory prototype is used for its experimental validation.

Electromagnetic and mechanical stress analysis of wind-driven synchronous reluctance generator

The investigation explores the mechanical stress and electromagnetic performance for a wind-driven synchronous reluctance generator (SRG). The change in the mechanical stress due to the presence of centripetal force, wind speed, and rotor speed are evaluated for different thickness of tangential and radial ribs. Moreover, the variation in the electromagnetic feature such as the q- and d-axes flux, reactance ratio, inductance, torque and torque ripple are discussed for different thickness of tangential and radial ribs. Increasing both tangential and radial ribs thickness has an effect on the electromagnetic performance, but it is observed that effect is significantly more with the variation of tangential rib thickness. Similarly, the mechanical stress analysis for rotor design has been explored in this paper. It is observed that high concentration of peak stress on the rotor ribs, which limits the range of rotor speed.

Synchronous reluctance generator with ferrite magnets for wind turbine

Synchronous reluctance generators with ferrite magnets in the rotor (PMSynRG) are a good alternative to synchronous generators (SG) with rare-earth magnets. The comparison between a SG with rare-earth magnets and a PMSynRG with ferrite magnets of the same diameter, stack length, power and speed is given in the paper. Twice as less magnets are required for the PMSynRG with ferrite magnets than for the SG with rare-earth magnets. The cost of the ferrite magnets is 4.4 times less than of the rare earth magnets. Also, the PMSynRG with ferrite magnets has much higher efficiency than the SG. The half-integer slot number per pole and phase is chosen to achieve rather low torque ripple without skewing the rotor.

The Loss of Self-Excitation Capability in Stand-Alone Synchronous Reluctance Generators

This paper analyzes the capability of synchronous reluctance generators (SynRGs) to achieve successful self-excitation when operating in stand-alone systems. To initiate the self-excitation process, the machine steel core has to retain sufficient residual flux during the generator startup. This residual flux depends on the magnetic properties of the machine core as well as the previous machine operating condition. A hysteresis model is developed to simulate the flux linkage–current characteristics of the SynRG for different operating conditions. The model then calculates the machine residual flux linkage after each operation, which indicates the machine capability for self-excitation during the next startup. The simulation results show that the rotor steel core of the synchronous reluctance machine (SynRM) can be demagnetized when the generator is subjected to a short-circuit condition or when the generator shaft is subjected to abrupt deceleration. These simulation results are also validated by experimental measurements on a 5 hp SynRM.

Effects of Design Parameters on Performance of Brushless Electrically Excited Synchronous Reluctance Generator

Permanent magnet synchronous generators, doubly fed induction generators, and traditional electrically excited synchronous generators are widely used for wind power applications, especially large offshore installations. In order to eliminate brushes and slip rings for improved reliability and maintenance-free operation, as well as to avoid costly permanent magnets, a novel brushless electrically excited synchronous reluctance generator having many outstanding advantages has been proposed in this paper. The fundamental operating principles, finite-element analysis design studies, and performance optimization aspects have been thoroughly investigated by simulations and experimentally under different loading conditions. The effects of different pole combinations and rotor dimensions on the magnetic coupling capacity of this machine have been specifically addressed and fully verified by offline testing of the 6/2 pole and 8/4 pole prototypes with magnetic barrier reluctance rotor and a new hybrid cage rotor offering superior performance.

Self-Excitation Criteria of the Synchronous Reluctance Generator in Stand-Alone Mode of Operation

The self-excited synchronous reluctance generator (SynRG) represents an alternative to supply electric power to remote communities. It is robust, simple, and less expensive compared with other types of brushless generators. However, for reliable operation in stand-alone mode, the self-excitation of the machine must be assured, which demands that certain starting conditions are met. It is observed through experiments that the existence of a minimum residual flux in the core, though necessary, is not sufficient to trigger self-excitation. The start-up acceleration also plays an important role since it may create transients in the q- axis flux linkage that can lead to demagnetization of the core and consequent failure in the terminal voltage build-up. This paper studies the effects of these starting conditions on the self-excitation phenomenon and presents criteria in terms of minimum residual flux and maximum start-up acceleration to trigger self-excitation without the risk of core demagnetization. The criteria to ensure the self-excitation for synchronous reluctance machines is developed using the dq -model of the machine and the energetic model. The developed concept is also applicable to other SynRGs operating in stand-alone mode.

Investigation of Self-Excited Synchronous Reluctance Generators

In this paper, an analytical model in the $dq$ reference frame is developed to recognize the steady state of the self-excited reluctance generator considering no-load and resistive load conditions. A fast method to estimate the minimum capacitance requirement is proposed. Experiments have been carried out to verify the analytical results. After that, attention is paid to the capability of self-excitation in the reluctance generator with different residual magnetisms in the rotor. Different levels of residual rotor magnetism are achieved by different magnetizing dc currents. An indicative value of phase current is defined to determine the self-excitation and the required minimum residual rotor magnetism for self-excitation in the reluctance generator connected with different capacitances is discussed. At last, the capability of self-excitation in the reluctance generator by connecting charged capacitors is investigated.

A New Control Algorithm for Power Quality Improvement in a Stand-alone Synchronous Reluctance Generator with Energy Storage

This article presents an adaptive control algorithm for power quality enhancement of a synchronous reluctance generator based stand-alone generator system with a battery energy storage system by employing the compensation capabilities of a voltage source converter. The proposed synchronous reluctance generator system is implemented using a 3.75-kW synchronous reluctance generator, a voltage source converter with a battery support, and a digital signal processor. The control algorithm is used for estimation of reference currents keeping in view the limited rating of the voltage source converter. A modified leaky least mean square algorithm using a variable-step–variable-weight factor is proposed for the control. The variable-step–variable-weight least mean square algorithm decomposes the load currents, extracts its real positive-sequence component to track the unit vectors by varying the rate of convergence of the algorithm, and accordingly tunes the weights, thus enabling selective compensation. The proposed control algorithm offers satisfactory harmonics mitigation, compensation of reactive power demand, and load balancing of a stand-alone synchronous reluctance generator system under linear/non-linear and dynamic loads.

Performance of synchronous reluctance generator for DG set based standalone supply system

This paper presents the performance of a SyRG (Synchronous Reluctance Generator) for DG (Diesel Engine Driven Generator) set based standalone generating system. A STATCOM (Static Compensator) is used for its voltage control, harmonics reduction and load balancing on a SyRG based DG set. The proposed system consists of a diesel engine driven specially designed SyRG with a rating of 3-phase, 3.7kW, 50Hz, 4-pole, 230V line voltage SyRG, an excitation capacitor bank of 6.25kVAr and a STATCOM of 5kVA. The modified PBT (Power Balance Theory) based control algorithm is used to estimate the reference source currents for control of STATCOM. A DSP (dSPACE) is used to implement this control algorithm of STATCOM. The performance of the proposed system is studied using STATCOM which improves the performance by exchanging the reactive power with the system. The source of reactive power is a capacitor bank and VSC (Voltage Source Converter) with a DC link capacitor used as STATCOM. The gating signals of VSC of the STATCOM are generated using PBT based control algorithm. The energy stored in the DC link is exchanged with the system to eliminate harmonics, voltage regulation and load balancing. The performance of the SyRG based standalone DG system is observed under a linear load of 3.19kW with power factor of 0.8 and a nonlinear load of 2.99kW under both balanced and unbalanced conditions. The proposed system has maintained fixed terminal voltage at 220V, voltage and current harmonics within 5% under highly nonlinear load and balanced source currents under highly unbalanced load currents.

Dynamic characteristics of an isolated self-excited synchronous reluctance generator driven by a wind turbine

This paper studies the dynamic characteristics of an isolated three-phase self-excited synchronous reluctance generator (SESRG) driven by a variable-speed wind turbine under different operating conditions. Self-excitation is achieved via capacitors connected across the generator terminals. A detailed mathematical modeling of the proposed self-excited wind generation system is presented. The proposed analysis is based on the dynamic qd-axis model of the SESRG. Magnetic saturation is taken into account and is assumed to be confined to the direct axis and is accounted for as a variable direct-axis magnetizing reactance. Effect of wind-speed variation, excitation-capacitance variation, and loading-conditions variation on the generated output voltage and frequency are presented and discussed. The presented results show the effectiveness of the proposed wind-generation system. A close agreement between experimental and simulated results has been observed, which supports the validity of the proposed analysis.

Power Quality Improvement in Isolated Distributed Power Generating System Using DSTATCOM

This paper presents the control of a synchronous reluctance generator (SyRG) driven by a biogas/biomass diesel engine as a prime mover in a distributed power generating system. This generator is used as a source to feed linear and nonlinear loads. A three-leg voltage source converter (VSC)-based distribution static compensator (DSTATCOM) is implemented using an adaptive neural network-based control algorithm for harmonic suppression, load balancing, and voltage regulation in a three-phase SyRG system with a battery energy storage system. This control algorithm is used for extraction of active and reactive power components of distorted load currents. These components of load currents are used for estimation of reference source currents to generate the gating pulses of VSC used as DSTATCOM. The performance of DSTATCOM is observed satisfactory for this type of power generating system under balanced and unbalanced loads.

Development of the equipment for gearless gas-turbine power plants

There has been a new trend in construction of gas-turbine power plants with power output of hundreds and thousands of kilowatts. An expensive gearbox and a bulky generator with a rotational speed of 1500–3000 rpm are excluded from the power plant. A gas-turbine engine rotates the generator directly without the gearbox. The rotational speeds of the gas turbine and the generator are equal. The generator produces a high-frequency voltage, which is converted into the 50-Hz voltage via a semiconductor converter. This solution simplifies the structure of the power plant, enhances its reliability, and decreases costs. Currently, in such power plants, permanent-magnet generators are used that are sensitive to overcurrents and overheating and require expensive rare-earth magnets. The problem of ensuring mechanical strength of the permanent-magnet rotor at high rotational speeds is also essential. We propose to use synchronous reluctance generators that are free of the above drawbacks. The generators are controlled by frequency converters according to a special algorithm. The results of testing a model of the system with a synchronous reluctance generator are presented in the article. Variants of electrical equipment of the power plant based on synchronous reluctance generators are considered. The possibility of creating high-speed, up to 30000 rpm, synchronous reluctance generators for the gas-turbine power plants is shown.