Performance analysis of variable speed multiphase induction motor with pole phase modulation

In the recent days, for the traction and electric vehicle (EV) applications, multiphase machines with pole phase modulation (PPM) technique have been proposed. The smoother operation during pole changeovers as well as steady‐state operations is a significant constraint while adopting the PPM‐based multiphase induction motor (PPMIM) drives for EV and traction applications. So, in this paper, the PPMIM dynamic model and associated vector control are proposed for attaining a smoother operation of the machine. The machine modelling equations and transformation matrices are implemented in an arbitrary reference frame by considering the different pole phase combinations. Based on the modelling equations, the indirect field‐oriented control (IFOC) is proposed for PPMIM drives by reflecting the associated changes in parameters for different pole phase modes. In the IFOC, for regulating the d ‐axis and q‐ axis current components, single PI control loops have been implemented for all pole‐phase combinations. The proposed IFOC scheme is robust and applicable for adopting any type of pulse width modulation. The experimental, as well as simulation results, are given to illustrate the potentiality of the proposed dynamic model and IFOC. The PPMIM machine performance during the steady state as well as pole changeovers in different pole phase modes are analyzed and associated. Simulation and experimental results are presented.

Purpose – The purpose of this paper is to present the distribution of the magnetic field and additional losses analysis of the induction motors (IM) with opened and closed rotor slots. Design/methodology/approach – In the field-circuit approach the distribution and changes of magnetic flux density in the motor are computed using a time-stepping finite element method. The additional losses in each element are evaluated at different frequencies. Findings – An approximate analytical formulation is derived for rapid losses computation confirmed by the results of field-circuit method. For high-voltage motors due to the size ratios of the core and relatively deep stator and rotor slots major role in causing loss of higher harmonics play a fundamental slot harmonics. Higher harmonics order bigger than 100 cause only small part of total higher harmonics core losses. Closed rotor slots construction influenced significantly on no-load losses mainly due to reduction of losses at slot upper part. For nominal load condition that influence is not so strong according to the saturation of slot tips by rotor leakage flux. Nevertheless, core losses at load are several times higher as at no-load. Research limitations/implications – In future research authors will take into account motors feed from PWM inverter, working in the frequency range up to 400 Hz. Practical implications – The results of investigation will be used in more detailed design of IMs especially for motors with closed rotor slots. Originality/value – The methods presented in the paper was not used before. Also results of additional losses in the motor core calculation, especially according motors with closed slots at no load and load conditions are new.

Axial-flux-modulated motors (AFMMs) with two pole-slot combinations are presented and analyzed quantitatively. They all have new topology structures, and their design rules differ from those of the traditional machine. The concentrated stator windings are designed to reduce the end length and copper losses; therefore, the efficiency of the motors can be improved. Special iron segments in the air-gap are used to modulate the magnetic field. The two proposed AFMMs have 36 stator slots and 30 stator slots, respectively, and the pole-slot combinations are 6 poles for 36 slots and 4 poles for 30 slots. This paper focuses on the comparative performance analysis of the two proposed AFMMs by using the 3D time-stepping finite element method. The flux linkage, air-gap flux density, electromotive force waveforms, output torque, core losses, and efficiency of the two proposed AFMMs have been investigated.

In this paper, comparisons are made on various parameters of electromagnetic fields like air gap flux density (radial), flux distribution, phase currents, speed and torque of a healthy and stator inter-turn fault induction motor (IM). Using FEM (Finite Element Method), the inter-turn short circuit fault analysis of PWM (Pulse Width Modulated) inverter fed 3 phase IM is analyzed. The inter-turn fault is the initial stage of a short circuit in the stator winding and it progresses to a phase to phase fault or phase to ground fault if left undetected. When the IM is directly fed from the mains, the inter-turn fault can be identified using a popular technique known as MCSA (Motor Current Signature Analysis). But this method fails when the IM is fed from a PWM inverter due to rich noise content observed in the current spectrum due to high frequency inverter switching making it difficult to detect the fault. The electromagnetic field analysis of PWM inverter fed 3 phase IM with 12.5% and 25% stator winding inter-turn fault is carried out on a 7.5kW IM using ANSYS Maxwell FEA (Finite Element Analysis) tool. The spatial FFT spectrum of air gap flux density (radial) indicates the presence of stator winding inter-turn fault with rich noise content compared to healthy motor.

This paper investigates a nonsinusoidal power supply technique for a multiphase motor with a concentrated full-pitch winding. The technique focuses on how to select harmonics, how to determine the harmonics ratio, and the effects on the air-gap and yoke flux densities. Generally, the third-harmonic current is utilized for the air-gap flux density optimization in a five-phase motor. However, the method has a negative effect on the yoke flux density, and the yoke iron width should be increased. Alternatively, this problem can be solved by providing more control freedom degrees of the motor with a phase number greater than five. A nine-phase motor is employed to achieve the air-gap and yoke flux density distribution optimization simultaneously. Moreover, the performance of both motors is compared in the sinusoidal and nonsinusoidal power supply modes. The analysis of the torque density and the efficiency demonstrates that a nonsinusoidal power supply is more suitable for a heavy-load operation. Theoretically obtained results are verified by experiments.

Based on studying the transform theory of the multiphase system and the rotor field oriented control (RFOC) of multiphase induction motor (IM), the mathematical modulation of RFOC used in multiphase IM with closed-loops of harmonic currents is modeled. It can be used to solve the problems of harmonic currents in the conventional vector control of multiphase IM. The fundamental current and each of harmonic currents can be controlled independently for decoupling. The harmonic currents can be restrained effectively. In the paper, a nine-phase IM is proposed to verify the hypothesis. Experimental results confirm the theoretical analysis well. The paper further achieves the technology of electronic pole changing (EPC) under RFOC of multiphase IM. It is feasible for multiphase IMto realize pole-changing without cutting off the power and the EPC proposed could effectively extend the operational range of constant power in multiphase IM.

This paper introduces a new high-strength undiffused brushless machine that transfers the stationary excitation magnetomotive force to the rotor without any brushes. For a conventional permanent magnet (PM) machine, the air gap flux density cannot be enhanced effectively but can be weakened. In the new machine, both the stationary excitation coil and the PM in the rotor produce an enhanced air gap flux. The PM in the rotor prevents magnetic flux diffusion between the poles and guides the reluctance flux path. The pole flux density in the air gap can be much higher than what the PM alone can produce. A high-strength machine is thus obtained. The air gap flux density can be weakened through the stationary excitation winding. This type of machine is particularly suitable for electric and hybrid-electric vehicle applications. Patents of this new technology are either granted or pending.

A nonlinear model is proposed representing air-gap magnetic flux density distribution in a synchronous machine with magnetic saturation in the pole tips. In order to explain the effect of magnetic saturation in a synchronous machine, the authors have measured air-gap flux in a specially designed synchronous machine, and recently proposed a model for the air-gap flux density distribution, concentrating on magnetic saturation in the field pole iron cores. In this paper, we propose an adaptation of our model for calculating air-gap flux, specifically addressing the magnetic saturation in the pole tips. By regarding the saturation as a consumer of m. m. f. similar to a virtual winding, we construct a magnetic circuit which represents the flow of magnetic flux inside the synchronous machine, and derive expressions which represent air-gap flux density distribution. Close agreement is obtained between the theoretically calculated results, and the results measured using search coils placed at the teeth of the armature.

Locating rotor broken bars in induction motors using finite element method

Hybrid excited flux switching machines (HEFSM) are appropriate candidates for hybrid electric vehicles (HEV) application owing to their high torque/power density, robust rotor structure as well as flux weakening capability by DC excitation windings. However they exhibit relatively high cogging torque due to their high air-gap flux density and their doubly salient structure which is a major problem of employing HEFSM in HEVs application; hence the cogging torque reduction is a required approach in HEFSM design. Due to the relatively simple rotor structure of HEFSM in comparison with stator structure, optimal rotor design techniques are much more preferable to reduce the cogging torque and torque ripple of flux switching machine. In this paper, the rotor step skewing method is employed to reduce cogging torque and torque ripple of 6/13 HEFSM. In order to evaluate the effectiveness of the employed method finite element analysis is employed.

This paper introduces multiphase induction motor drives system under sensorless conditions, which is simulated and analyzed by utilizing its multiple control freedoms in the mode of high frequency signal injection. In this method, because nine phase induction motor have four orthogonal d-q planes compared to traditional three phase induction motor, so high harmonic plane can be used for other applications, for example, extracting rotor position based on high frequency injection signal technique. In the multiphase induction motor, inductance value is smaller in the high harmonic plane contrast to fundamental plane, in other words, it can get larger current signal amplitude under the same voltage amplitude, reducing the difficulty of the position signal extraction. changing rotor slot numbers will affect the air-gap length distribution, and it can be concluded that there is a saliency in the d 7 -q 7 plane through modulation of rotor slots. The module is simulated in the environment of simulink and ansoft.

In recent years, AC induction motors have replaced DC motor. The most important reason for this is that DC motors have a mechanical brush and commutator system that is subject to wear and tear over time. While DC motor drivers need a lot of maintenance due to this system, induction motors do not require almost any maintenance since this system is not available. In recent years, technological advances in the field of multiphase induction motors have led to a significant evolution. A lot of research has been done around the world and a lot of new and interesting developments have been reported to the literature. This paper provides information about six-phase induction. In addition, what kind of advantages the concept of multiphase provides and how this structure is formed contains information about them. The six-phase induction motor will be simulated through the MATLAB/SIMULINK package program and compare with three phase induction motor. Both motors were run in simulation using the same parameters. At the end of the simulation, current, moment and speed graphs of the six-phase induction motor and three-phase induction motor will be drawn according to time. The study also included equations used during modeling and equivalent circuits belonging to a six-phase induction motor. It has been graphically shown that a six-phase induction motor is more advantageous than a three-phase motor. For example, in six-phase induction motors, the transition time to a continuous state is shorter. In addition, while the frequency of torque vibration increases, its amplitude decreases, the current value of each phase decreases, the stator copper losses are less than the three-phase induction motor. In motors, usually the power needed is divided by the number of phases. So the more phases there are, the greater the power carrying capacity. Today, multi-phase induction motor drives are used in special applications such as electric vehicles, space technology, aerospace applications, as moving power on ships, electric trains, which require high reliability and power.

In this paper, the torque tracking problem of the induction motor for hybrid electric vehicle (HEV) applications is addressed. Because the standard field oriented control (FOC) provides poor performance under rotor resistance uncertainty, a new robust controller-observer combination is designed in this paper in order to improve the overall performance. Our controller is based on a new PI-based extension of the FOC controller while our flux observer is based on the sliding mode technique. Simulation results show robustness with respect to rotor resistance uncertainty. A new optimal flux reference is derived to minimize the consumption of electrical energy, rather than the commonly used standard flux reference that maximizes motor torque. This choice is justified by the use of our controller in HEV applications. Simulation results show a significant reduction (35%) in energy losses.

This study focuses on the core losses in the stator region of high-speed permanent magnet synchronous motors, magnetic field characteristics in the load region, and variations in iron losses caused by changes in these areas. A two-pole 120 kW high-speed permanent magnet synchronous motor is used as the object of study, and a two-dimensional transient electromagnetic field-variable load circuit combined calculation model is established. Based on electromagnetic field theory, the electromagnetic field of the high-speed permanent magnet synchronous motor under multi-load conditions is calculated using the time-stepping finite element method. The magnetic field distribution of the high-speed permanent magnet synchronous motor under a multi-load condition is obtained, and the variations in iron core losses in different parts of the motor under multi-load conditions are further analyzed. The calculation results show that most of the stator iron core losses are dissipated in the stator yoke. The stator yoke iron loss under the no-load condition exceeds 70% of the total stator iron core loss. The stator yoke iron loss under rated operation conditions exceeds 50% of the total stator iron core loss. The stator loss under rated load operation conditions is higher than that under no-load operation. These observations are sufficient to demonstrate that the running status of high-speed motors is closely related to the stator iron losses, which have significance in determining the reasonable yoke structure of high-speed and high-power motors and the cooling methods of motor stators.

Permanent magnet synchronous motors (PMSM) generate high-frequency electromagnetic vibration and noise when powered by inverters, and the cause is high-frequency electromagnetic exciting force (EMEF). In this paper, the frequencies and orders of EMEF are analyzed. The expression of EMEF acted on the stator inner surface is derived and the frequencies and orders of main components of vibration are listed. The high-frequency vibration experiments are conducted on a surface mounted 8-pole and 12-slot PMSM. The high-frequency vibrations near switch frequency and its multiples are main components of vibrations of motors when powered by inverters, and experiments are conducted to study the influence of switch frequency on the vibration acceleration. The impacts of periodic frequency PWM and random frequency PWM on the vibration acceleration and peak value of its frequency spectrum are studied by experiments. Introduction The vibration of motors is one of the most important performance indicators. The noise generated by vibration will pollute our working and living environment. A severe vibration can even destruct the machine structure. There are higher requirements for vibration in special applications. While the application of inverter improves the dynamic performance of the motor, it causes high frequency vibration and noise. Many researchers have done a lot of work about the vibration and noise of motors. The frequency of noise of inverter-fed induction machine is calculated[1,2]. The influence of inverters on the vibration of axial flux PM motors is studied by finite element method(FEM) and experiments. The impacts of random PWM and harmonic injection is studied[4-6]. The effect of pulse frequency modulation(PFM) in reducing noise of induction motor is studied[7]. When powered by inverters, the stator current has a lot of time harmonics which increases the complexity of air gap flux. The air gap flux determines the magnitude and frequency of electromagnetic exciting force (EMEF) acted on the inner surface of stator. In this paper, the flux distribution is derived by magnetic circuit method firstly. Then, the expression of radial of EMEF is obtained by Maxwell’s stress tensor. The frequency, order and sources of the main EMEF are listed. The high-frequency vibration experiments are conducted on a surface mounted 8-pole and 12-slot PMSM. The high-frequency vibrations near switch frequency and its multiples are main components of vibrations of motors when powered by inverters, and experiments are conducted to study the influence of switch frequency on the vibration acceleration. The impacts of periodic frequency PWM and random frequency PWM on the vibration acceleration and peak value of its frequency spectrum are compared by experiments. Calculation of EMEF in PMSM The vibration of stator of PMSM is mainly determined by radial EMEF acted on the inner surface of the stator. Neglecting the effect of magnetostriction and assuming 0 Fe μ μ  , the EMEF acted on the inner surface can be expressed as[8]: 2nd International Conference on Electrical, Computer Engineering and Electronics (ICECEE 2015) © 2015. The authors Published by Atlantis Press 1580 2 0 1 2 n n o F B μ = (1) where 0n B is the radial air gap flux density in the inner surface of stator. So the air gap flux distribution need to be obtained before calculating the EMEF. Neglecting the core magnetic reluctance, the air gap flux distribution can be expressed as ( ) ( ) ( ) , , , b t f t t θ θ λ θ = ⋅ (2) where θ is the mechanical angle, ( ) , f t θ is the air gap magneto-motive force(MMF) and ( ) , t λ θ is the air gap permeance. In a surface mounted PMSM (SPMSM), the air gap permeance does not change with time. It can be approximately expressed as ( ) 0 l θ λ λ = Λ +∑ (3) where 0 Λ is the constant part and l λ is the space periodic part caused by slots. l λ can be expressed as ( ) ( ) ( ) 0 ( 1) sin 1 cos cos ( 1) l l k l k k lZ lZ k l k k δ