AC Machines Research Articles

AC Loss Measurements in a Hybrid REBCO/BSCCO Coil Assembly

Wire cost and ac loss are paramount issues for the future uptake of high-temperature superconductor (HTS) ac machines. In particular, new approaches which reduce the total manufacturing cost of HTS coils are critical to the future commercial uptake of HTS technology. Here, we present the results of ac loss measurements of a hybrid HTS coil assembly comprising end windings (EWs) wound with BSCCO wire and a central winding (CW) wound with REBCO wire. As a cost mitigation measure, we have chosen to use REBCO wire which possesses a relatively low self-field $I_{{\rm{c}}}$ at 77 K, equating to approximately half that of the BSCCO wire. Transport ac loss measurements were made on the total coil assembly at both 77 K and 65 K, using a recently developed lock-in amplifier approach. We show the ac losses in the assembly at these temperatures scale with the overall transport critical current threshold of the hybrid coil assembly. The results are then compared with a reference coil assembly having similar geometrical dimensions, and in which both the EWs and CW were wound with identical BSCCO wire. Surprisingly, we observe that the ac loss of the hybrid coil is lower than that of the BSCCO coil, despite the CW of the hybrid coil employing wire a lower overall average $I_{{\rm{c}}}$ . We attribute this effect to the lower ac loss of coated conductor REBCO wire under parallel field, which is the dominant field orientation in the CW region. Based on this observation, we conclude that the hybrid assembly design is a good design strategy for HTS coil assemblies, enabling both wire cost and ac loss to be balanced.

Simulation and Performance of AC Drives Using SVPWM Technique

Drives are mainly categorized into constant-speed and variable-speed drives. AC machines have been used in constant-speed applications, where as DC machines were preferred for variable speed drives. Due to the advancement in power semiconductor devices and microprocessors, AC machines are widely used in variable speed drives. This paper focuses on the simulation and performance evaluation for an ac drive system with Induction motor and PMSM Motor. The focus was based on the simulation of the power circuits using MATLAB/SIMULINK software. The performance of inverter was studied by SVPWM technique. Space Vector Pulse Width Modulation (SVPWM) is a digital technique, which increases the output voltage capability and increases DC bus utilization voltage. The performance of an ac drive system was simulated and evaluated for variable speed operation from no load to rated speed under constant torque operation. The advantages and disadvantages of Induction motor and PMSM are analyzed and presented in this paper.

Backstepping control of a separately excited DC motor

In the last decades, researches on speed control of electric motors have been very important in industrial systems. On the other hand, the development of power electronics and semiconductor technologies has expanded the scope of the AC and DC machines. However, the separately excited DC motor is widely used in the field of variable speed applications due to its simplicity to control. In this paper, we present the control of a separately excited DC motor using an analogue PI controller, a backstepping method and an adaptive backstepping control techniques. Simulations are performed in MATLAB Simulink software, and improved results of adaptive backstepping controller have been obtained overall system performance compared to conventional PI and backstepping.

Simultaneous Identification and Adaptive Torque Control of Permanent Magnet Synchronous Machines

This paper presents an experimentally verified, Lyapunov-based adaptive control design for permanent magnet synchronous ac machines, which exploits overactuation to achieve parameter identification and torque regulation objectives simultaneously. This is achieved by regulating the states of the system (i.e., the stator currents) to the output error-zeroing manifold, along which they are varied to provide excitation for parameter identification. The proposed control law utilizes a combination of adaptively tuned feedforward and feedback decoupling terms, in addition to proportional feedback, to achieve reference current tracking in the presence of parameter uncertainty. A switching-sigma modification to the adaptive update law is used to ensure robust stability of the closed-loop adaptive system, and excitation for parameter estimation is introduced via the direct-axis current reference input. The resulting controller achieves the simultaneous identification and control objective while providing consistent transient response characteristics with zero steady-state error over a wide range of operating points.

Algorithms for Determining the Parameters of Static Converters

Qualitative needs, ever higher, automatic control systems, correlated with the development of power electronics, microprocessors, programming techniques, development of unconventional energy production, resulting in bringing to the fore the three-phase power converters. Using asynchronous motor, the simplest and robust electric car, often can not meet the quality conditions of the machine working. AC machines can not achieve a wide range of speeds and a hub can not cover 250-300% overload.Widespread use in electric drive systems that we obtained semiconductor electronic control methods with techniques for high efficiency and precision control very good. Static converters have become easy to use and virtually through them obtain any desired mechanical characteristic for any type of electric machine.

Evaluation of the energy characteristics of an asynchronous inverter-fed induction motor at different approximations of the magnetization curve

Results of research on the effect of magnetization-curve approximation of the electrotechnical steel and excitation frequency of an asynchronous inverter-fed induction motor (IFIM) on its energy performance with extremal control algorithms based on energy-saving criteria are presented in this article. An IFIM is a variant of a double-fed motor with static frequency converters in the stator and rotor circuits. Its application in a variable-speed drive meets to the greatest extent the main requirements for an ac machine in terms of speed regulation and providing high energy performance. It is shown that application of piecewise linear approximation by three sections and the spline function provides improved values of energy performance relative to the simple approximation by two linear sections due to becoming close to a real magnetization curve. It provides, under otherwise equal values of electromagnetic torque, a higher flux linkage with decrease in magnetization current. Control of the excitation frequency of the asynchronous inverter-fed induction motor has a significant influence on the steel losses of the machine. In the region of low loads, they are particularly important relative to the active losses in the motor windings.

Determination of the inductance of a synchronous reactive machine for sensorless control

The problem of eliminating rotor-position sensors in ac drives has been the focus of intense research for over two decades. Among the expected benefits of the solution to this problem are reduction of drive cost and size, as well as increased reliability. The methods developed for this purpose are usually called “methods of sensorless control.” It has been shown that sensorless-control methods for ac machines provide high efficiency at medium and high speeds. However, these methods are less efficient at lower speeds and control of the position at low and near-zero speeds is not possible. To overcome this limitation, methods of sensorless control based on the tracking the position of rotor asymmetries have been proposed. These methods measure the response of a machine to the high-frequency component of the excitation signal. One of the most attractive aspects of this method is the absence of limitations when operating at very low or near-zero speeds, which allows one to control the rotor position. This paper presents the results of theoretical and experimental studies of the method for determining inductances Ld and Lq in a synchronous reluctance machine (SynRM) using the injection of a high-frequency component into the stator voltage. This paper discusses the principles of this method and its application to the mathematical model of the SynRM and the M3AL 90LDA 4 engine produced by ABB Co. Determination of these parameters is necessary for the implementation of sensorless-motor-control systems.

Experimentally Calibrated Thermal Stator Modeling of AC Machines for Short-Duty Transient Operation

This paper presents an approach to the thermal design of an ac machine where the application requires low-duty transient operation. To provide accurate temperature predictions, the design process has been informed with experimental data from tests on a stator-winding sector (motorette). These have been shown to be a time and cost-effective means of calibrating the thermal model of a full machine assembly, prior to manufacture of the final design. Such an approach is usually adopted in design analysis of machines with a concentrated winding topology. Here, the motorette testing has been extended to a machine with a distributed winding. Several alternate slot liner and impregnating materials have been evaluated to maximize the heat transfer from the winding body into the machine periphery, and a total of nine stator section samples have been manufactured and tested. The performance tradeoffs between the various combinations are discussed in detail alongside their ability to satisfy the design requirements. Based upon these experimental results, the most promising designs have been selected for transient duty analysis against the design specification. A lumped parameter thermal model has been used for this purpose and calibrated using the data from the subassembly testing. Experimental results on the full machine assembly are presented, showing good correlation with the motorette calibrated thermal model.

High performance nonlinear controller design for AC and DC machines: partial feedback linearization approach

This paper presents the design of a partial feedback linearization controller for speed control of DC and AC machines. The design of the controller is presented based on the nonlinear modeling of the plant. The model of the plant is obtained from differential dynamic equations. A stability analysis is presented to guarantee the stability of the proposed design. To validate the effectiveness of the controller, DC and AC machines systems are simulated. The performance of proposed controller is investigated with respect to different amount of load torque. Simulation studies show that the proposed controller provides the accuracy and high performance for both AC and DC machines.

Adaptive Decoupling of Nonideal Machine and Sensor Properties for Extraction of Fine Details When Using the Motor Drive as a Diagnostic Sensor

This paper presents methods to enhance the quality of spatial information that can be extracted when using the motor drive as a diagnostic sensor. When using the state-of-the-art motor drive-based techniques for extracting spatial information related to the state of wear in a gear train driven by an ac machine, position sensor-induced periodic position measurement errors and machine-induced spatial harmonic torque ripple can degrade the quality and the detail of the information that can be extracted. In this work, this degradation of information is displayed experimentally, and it is demonstrated that the quality of the spatial information extracted can be significantly improved through implementation of existing model reference adaptive system (MRAS)-based nonideal sensor property decoupling techniques and newly developed MRAS-based spatial harmonic torque ripple decoupling techniques. Furthermore, it is identified and demonstrated in this work that by removing the gear mesh harmonic component from the gear wear information extracted using the state-of-the-art techniques, and then calculating the spatial rate of change of this new information, a new signal is generated that strongly correlates to local gear tooth defects in a gear train driven by an ac machine.

Using computer for measurement and visualization of rotating magnetic field in AC machines

AbstractThis paper presents a new way of implementing a computer as a teaching tool in the teaching module “Rotating Magnetic Field in AC machines.” Software for simulation, measurement, and visualization of the rotating magnetic field using three‐axis hall sensor was created in the form of remote experiment. After students’ evaluation, it was found that remote experiments ensure better achievement of students regarding this particular topic, while also contributing to better quality of teaching rotating magnetic fields in the subject of electrical machines.

Online Broadband Insulation Spectroscopy of Induction Machines Using Signal Injection

The breakdown of the stator insulation is one of the main causes of failure in medium- and high-voltage ac machines. Even though there are several techniques available to detect the failure of the ground-wall insulation and the turn insulation, there are only few online techniques to detect the deterioration of the insulation prior to its breakdown. Established methods, like the partial discharge analysis or the capacitance and dissipation factor test that can be applied to monitor the insulation health online, are limited to assessing the condition of the ground-wall insulation. An attempt has been made to evaluate a different technique that might be used to monitor the ground-wall insulation, as well as the turn insulation condition, which is based on the broadband impedance spectroscopy of the motor. Insulation aging will change the resistance and capacitance of the ground-wall insulation, as well as the turn insulation. These changes in the insulation parameters are reflected in changes of the phase-to-ground impedance of the motor. This can be used to monitor the condition of the insulation. To exploit the relationship between the phase-to-ground impedance and the insulation parameters, for a given temperature, a signal injection-based technique is proposed to measure the impedance of stator insulation on an operating machine and trend the response over time. The basic concept for the signal injection is introduced and measurements on different machine classes (480 and 4160 V) are presented to show the feasibility of the method.

Performance Characterization of Random Pulse Width Modulation Algorithms in Industrial and Commercial Adjustable-Speed Drives

One of the problems of the pulse-width-modulation (PWM)-controlled ac machines is the acoustic noise that could become unacceptable when used in sensitive environments. Random PWM (RPWM) in industrial and commercial adjustable-speed drives (ASD) results in the partial transfer of power from the discrete spectrum (narrowband noise) of the output voltage to the continuous spectrum (wideband noise), with advantageous effects on reducing the acoustic noise in the motor drive system. In this paper, the theoretical power spectrum analysis as the basis for RPWM is presented. Five state-of-the-art RPWM strategies, their voltage, current, and acoustic noise spectra characteristics are quantitatively evaluated. The PWM schemes and theoretical analysis are validated through a 2.2-kW 380-V 50-Hz ASD induction machine experimental setup. The results provide valuable data for practicing engineering community to choose the best option in real-world applications.

Starter-Generator Design and Dynamic Processes Simulation for HEVs

Hybrid vehicle is characterized by the unification of the two functional systems, namely, the generating electricity system in the vehicle’s electrical system and the starter system of the internal combustion engine (ICE). The development of power electronics, as well as the growth of power consumed by vehicles, allow us to combine a starter system and power supply in one power unit - the starter-generator. It is the combination of the AC machine (ACM) and the power electronic converter. AC outs of the electronic power converter connected to the ACM stator. DC outs of this converter connected to the battery and (or) capacitive energy storage (CES). The ACM starts the ICE in the motor mode. In electric vehicles, the starter-generator allows recuperating electric energy and acts as a part of braking system. The article is devoted to the design of the induction starter-generator for the Russian automobile “LADA”. The result of dynamic processes simulation is given.

ANALYTICAL CALCULATIONS OF ELECTROMAGNETIC QUANTITIES FOR SLOTTED BRUSHLESS MACHINES WITH SURFACE-INSET MAGNETS

In this paper, two-dimensional (2-D) analytical magnetic field calculations are used to compute crucial quantities of Brushless permanent-magnet (PM) machines with surface-inset PMs. The analytical magnetic field distribution is based on the subdomain technique in which the slotting and tooth-tip effects have been considered. It includes both different magnetization patterns (e.g., radial, parallel and Halbach) and different spatial distribution of winding (e.g., concentrated and distributed with one or more layers). The saturation effect of the magnetic circuit is neglected. In this investigation, the phase and line induced back electromotive force (EMF) waveforms, electromagnetic/cogging/reluctance torques, self-/mutual-inductances and unbalanced magnetic forces (UMFs) have been analytically calculated. The analytical expressions can be used for Brushless machines having surface-inset PMs with any radius-independent magnetization pattern. In this study, two slotted Brushless PM machines with surface-inset PMs have been selected to evaluate the efficacy of the analytical expressions by comparing the results with those obtained by the finite-element method (FEM). One of the case studies is a 9-slots/8-poles Brushless DC (BLDC) machine with radially magnetized PMs, non-overlapping all teeth wound winding and six-step rectangular armature current waveforms. The other is a 15-slots/4-poles Brushless AC (BLAC) machine with Halbach magnetization PMs, double-layer overlapping winding and sinusoidal armature current waveforms.

Comparative study of low-pass filter and phase-locked loop type speed filters for sensorless control of AC drives

High quality speed information is one of the key issues in machine sensorless drives, which often requires proper filtering of the estimated speed. This paper comparatively studies typical low-pass filters (LPF) and phase-locked loop (PLL) type filters with respect to ramp speed reference tracking and steady-state performances, as well as the achievement of adaptive cutoff frequency control. An improved LPF-based filter structure with no ramping and steady-state errors caused by filter parameter quantization effects is proposed, which is suitable for applying LPF for sensorless drives of AC machines, especially when fixed-point digital signal processor is selected e.g. in mass production. Furthermore, the potential of adopting PLL for speed filtering is explored. It is demonstrated that PLL type filters can well maintain the advantages offered by the improved LPF. Moreover, it is found that the PLL type filters exhibit almost linear relationship between the cutoff frequency of the PLL filter and its proportional-integral (PI) gains, which can ease the realization of speed filters with adaptive cutoff frequency for improving the speed transient performance. The proposed filters are verified experimentally. The PLL type filter with adaptive cutoff frequency can provide satisfactory performances under various operating conditions and is therefore recommended.

A New Approach to Enhance the Torque Handling Capacity of a PMBLDC Motor Drive

Permanent Magnet Brushless DC (PMBLDC) Motors are trapezoidal shaped back EMF permanent magnet AC machine with high power density. Since the motor has a trapezoidal field pattern rather than sinusoidal it is desirable to study the motor behavior under different current fed conditions to analyze the developed electromagnetic torque. In this paper three different trapezoidal, square and sinusoidal current fed field oriented vector controlled PMBLDC motor drives are presented. The novel approach of this paper is that, the torque handling capacity of a PMBLDC motor can be increased up to its rated torque by only changing the pattern of reference current of a field oriented vector controlled PMBLDC motor drive. Adaptive PI controller based on motor speed error is also proposed in the paper to have a simplified drive system. When square and sinusoidal reference current fed vector controlled drives are used, the maximum torque handling capacity of a specified PMBLDC motor is 1.60 Nm and 1.55 Nm respectively. Only by using trapezoidal reference current fed drive, the maximum torque handling capacity of that specified motor can be increased to 2.0 Nm. The performance of these three different current drives are also compared on the basis of their torque pulsation. The dynamic performance of the vector controlled trapezoidal current fed drive is found outstanding than the square and sinusoidal current fed drives considering response time, load torque handling capacity, variable speed condition, settling time of the system.

Study of Energy Indicators and Features of Propulsion System Main Components of Electric Vehicle Using Mathematical Simulation

Objectives: To calculate the energy performance of the Electric Propulsion System (EPS) using the mathematical simulation and analysis of the obtained characteristics, taking into account the use of various types of electric motors. Method/ Statistical Analysis: The method of model-oriented programming was used to study the necessary parameters,by which the two mathematical models in Matrix Laboratory (Matlab) / Simulink were built. It allowed the calculations in a short time and a detailed analysis of the results. While building up the mathematical models of electric motors, the vector control was implemented, as based on the method of vector representation in variables of states in a space (Field oriented control). Findings: In addition to mathematical description of the motors, the article represented the mathematical model of the inverter on IGBT transistors required for commutation of the traction motor, lithium-ion battery as well as all major components required for proper system operation. This article discusses two of the most often used type of contactless AC machines - asynchronous motor with squirrel-cage rotor (Induction motor) and a synchronous motor with permanentmagnet excitation (Permanent Magnet Synchronous Motor). Because of mathematical simulation, the assessment of the energy parameters of two systems was carried out. Analysis of the obtained results allowed the identification of characteristic points in driving cycle, defining the minimum requirements for mechanical, electrical and power parameters of the electric propulsion of the electric vehicle on condition of implementation of the cycles reviewed. Because of the traction and energy calculation, the consumption values of electric energy for the electric power source were obtained,including the amount of energy regeneration. Application/improvement: These methods of mathematical models are universal and can be applied to various types of transport, from electric vehicles to electric trucks and electric buses.

Strategy for Predictive Modeling of the Common-Mode Impedance of the Stator Coils in AC Machines

This paper presents a methodology for the predictive modeling of common-mode (CM) impedance of the stator windings of AC three-phase machines taking into consideration all the parasitic inductive and capacitive phenomena. An electrical model with lumped parameters ( RLC ) is generated, based on a physical approach of the machine, which is implantable in a SPICE-type software. The prediction results are in satisfactory agreement with the measurements ones on a large frequency bandwidth [10 kHz to 100 MHz]: The low-frequency capacitance is predicted with better than 5% accuracy, while the peaks and dips in the CM impedance plot are very well predicted beyond 5 MHz.

Design and Analysis of an Electronic-Geared Magnetless Machine for Electric Vehicles

This paper proposes a new electronic-geared (EG) magnetless machine for electric vehicles. The proposed EG machine can offer the multitooth bipolar-flux (MTBF) operation for the low-gear (high-torque low-speed) situation, and the single-tooth unipolar-flux (STUF) operation for the high-gear (low-torque high-speed) situation. In particular, the balance-position winding arrangement is proposed to enable the machine having balanced flux linkages. Consequently, the proposed machine operates as the brushless ac machine for MTBF operation, leading to offer smoother torque at the low-gear situation. Meanwhile, it operates as the brushless dc machine for STUF operation, leading to produce better torque density at the high-gear situation. Various performances of the proposed EG machine are analyzed, with emphasis on the validity of electronic gearing. The experimental prototype is also built for verification.