Torque Pulsations Research Articles

Enhanced Second-Order Sliding Mode Control Technique for a Five-Phase Induction Motor

Recently, several research papers have addressed multiphase induction motor (IM) drives, owing to their several benefits compared to the three-phase motors, including increasing the torque pulsations frequency and reducing the rotor harmonic current losses. Thus, designing a robust controller to ensure the proper operation of such motors became a challenge. The present study reports the design of an effective second-order sliding mode control (SO-SMC) approach for a five-phase IM drive. The proposed control approach finds its strongest justification for the problem of using a law of nonlinear control robust to the system uncertainties of the model without affecting the system’s simplicity. The formulation of the proposed SO-SMC approach is a prescribed process to ensure the stability and proper dynamics of the five-phase IM. A detailed stability analysis is also presented for this purpose. To validate the effectiveness of the proposed controller, the five-phase IM drive is tested under different dynamic situations, including load changes and system uncertainties. The presented numerical results prove the ability of the designed SO-SMC to handle high system nonlinearities and maintain high robustness against uncertainties.

Full-order adaptive observer for interior permanent-magnet synchronous motor based on novel fast super-twisting algorithm

To improve the accuracy of speed estimation strategy over a wide speed range in the sensorless speed control system of an interior permanent – magnet synchronous motor (IPMSM), a full-order adaptive observer based on a novel fast super-twisting algorithm (NFSTA-AO) is proposed. The conventional model reference adaptive system (MRAS) takes the linear compensation matrix of the unit matrix, which can only achieve speed discrimination within a certain speed range. Therefore, in this paper, a new linear compensation matrix is first derived using Popov’s super stability theory, and then, a new tachograph – adaptive law is obtained. A feedback correction link is also added to the adjustable model to improve the convergence speed of the error between the reference and adjustable model outputs. To further improve the accuracy of the tachograph estimation strategy, a novel fast super-twisting algorithm (NFSTA) convergence law is introduced in place of the adaptive law in the full-order adaptive observer, combining the advantages of both algorithms. The NFSTA added the inverse hyperbolic sine function based on system state variables to the integral term of the fast super-twisting algorithm (FSTA) to effectively suppress the torque pulsation of the system. A soft switching function is also designed to replace the symbolic switching function in order to reduce the system jitter caused by the sliding mode variable structure control. The simulation experiments show that the system using the NFSTA-AO estimation strategy is more resistant to disturbances and robust; additionally, it has better dynamic following than the conventional MRAS in the presence of added load disturbances and sudden speed changes.

A Fault-Tolerant 24-Sided Voltage Space Vector Structure for Open-End Winding Induction Motor Drive

This article proposes a method of generating 24-sided polygonal voltage space vector structure composed of 24 real active vectors and a zero vector. Each active vector is a real vector in contrast to switched average vectors in literature. Generation of real 24-sided vectors minimizes switching losses and improves quality of phase voltage compared to switched averaged vectors technique. An important feature of the presented scheme is elimination of lower order harmonics up to 19th order from motor phase voltage throughout the modulation range that gives reduction in torque pulsation and near sinusoidal phase current. The proposed scheme extends the linear modulation range till 99.42 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> . Open-end winding induction motor is fed with primary and secondary inverters from either ends. Primary and secondary inverters are implemented by cascading two-level inverters. DC sources for both the inverters are realized using a simple star-delta transformer combination. The proposed concepts are verified with laboratory prototype and the respective results during the steady-state, transient, and fault scenario are presented. The supporting loss analysis and harmonic performance of the proposed drive is performed with existing topologies.

A Novel Method to Reduce Low-Frequency Output Current Ripple of PWM Inverters

The output current of PWM inverters may contain low-frequency harmonics due to nonidealities, such as fluctuating dc voltage and dead-time. Low-frequency harmonics are detrimental to the inverter's current controller performance as well as its operation. They increase losses, cause synchronization problems in a grid-connected inverter, and cause torque pulsations in motors. Reducing low-frequency harmonics through conventional means require a big and expensive filter. In this article, a method to reduce low-frequency current harmonics is proposed. This method uses a virtual impedance, which is a controller block that mimics the behavior of a real impedance. Because it is virtual, it does not have physical drawbacks to the system, such as volume, weight, and losses. It can be designed only to affect the disturbance signals and to assume characteristics unlike a real impedance. It can also be added as a plug-in block to an already existing controller, saving a significant amount of design effort. Simulation and experimental results show a decrease of current THD to almost 1/3 of the original THD when no virtual impedance is used, demonstrating the effectiveness of the proposed method.

A New Spoke PM Motor with ECC ASPs to Reduce Flux Density Harmonics

This paper proposes new eccentric (ECC) auxiliary salient poles (ASPs) applied in spoke permanent-magnet (PM) motors. These ECC ASPs optimize flux density harmonics and further reduce torque pulsation. Then, the optimization procedure is proposed to reveal the relationship between the ECC method and ASP, and optimization steps are reduced. Firstly, the design of the ECC ASPs is based on the stairs, which are equivalent to sinusoidal flux density. Second, the expressions of offset length for maximum air gap, pole arc angle, and thickness ratio are revealed. Through theoretical analysis and the finite element method (FEM), the proposed ECC ASPs can generate low torque pulsation and improve sound and vibration features.

Speed Control of Switched Reluctance Motor Based on Regulation Region of Switching Angle

This paper studies the speed control strategy of a switched reluctance motor based on angle-position control (APC). The switched reluctance motor has three control parameters: turn-on angle, turn-off angle and voltage PWM duty cycle. This paper studies the function of the three parameters and designs the control algorithms of the parameters, respectively, which can reduce the coupling degree, simplify the control process, and realize the optimal control of the switched reluctance motor. By studying the nonlinear characteristics of the switched reluctance motor, the optimal current waveform in the effective working range of the inductor is obtained, and then a control strategy of the turn-on angle is designed to realize the ideal winding current waveform. According to the torque characteristics of the motor, taking the coincidence of the freewheeling zero point and the position angle at the end of the maximum inductance interval as the control target, a control strategy for the turn-off angle that makes full use of the effective inductance working interval is proposed, which improves the efficiency of the system. For the nonlinear and time-variant switched reluctance motor running process, a data-driven model-free adaptive control algorithm is introduced, and a switched reluctance motor speed control algorithm based on voltage PWM duty cycle is designed. The main contribution of this paper is to propose a control strategy that is generally applicable to switched reluctance motors, which does not depend on the precise mathematical model of the motor. The control algorithms are designed separately for the three control parameters according to the characteristics of the motor, which reduces the degree of coupling among them. A switched reluctance motor drive system based on angle-position control is designed. This strategy is especially suitable for driving the load with sudden large torque pulsation.

Study of torque pulsation control of switched reluctance motor by auto-disturbance rejection control

The switched reluctance motor drives the rotor based on the principle of minimum reluctance, which is structurally simpler, but the doubly salient structure of the stator and rotor leads to severe torque pulsation. This paper briefly introduces the switched reluctance motor and the auto-disturbance rejection controller for suppressing the torque pulsation of the switched reluctance motor. Then, the auto-disturbance rejection controller was simulated in the MATLAB software, and it was compared with the direct torque control strategy. The results showed that the switched reluctance motor installed with the self-reluctance controller reached the set rotational speed faster, with a smoother torque change; when the set speed changed abruptly, it was adjusted to the new rotational speed faster, with a smooth and stable torque change; when the load torque changed abruptly, it was adjusted to the new torque smoother and faster, and the adjustment to the rotational speed was also faster.

Six-Step Operation of a Symmetric Dual Three-Phase PMSM With Minimal Circulating Currents for Extended Speed Range in Electric Vehicles

Automotive applications demand high efficiency, good reliability, and a wide operating speed range within limited dc bus voltage constraints. In this article, a zero degree displacement dual three-phase permanent magnet synchronous machines (PMSM) is derived from an original three-phase PMSM to enhance the power rating as well as the operating speed range. The proposed topology can be used as an alternative to the conventional configuration of three-phase PMSM with a bidirectional dc–dc converter for electric vehicles. Even though the commonly used dual three-phase PMSM with split-phase winding eliminates the sixth harmonic torque pulsation, a large circulating current is generated during six-step operation, which results in additional stator copper loss. In this article, six-step operation of the symmetric dual three-phase PMSM with zero degree winding displacement is proposed to achieve maximum inverter utilization. Both harmonic circulating current and torque pulsation were observed to be within satisfactory levels using this configuration. A changeover algorithm is also proposed to enable a smooth transition between closed-loop current vector control during low and medium speed operation to open-loop six-step voltage angle control for high speed operation. The performance of the proposed method is experimentally validated on a 3-kW dual three-phase PMSM drive.

Comparative Study of BLDC Motor Drives with Different Approaches: FCS-Model Predictive Control and Hysteresis Current Control

The control techniques of the brushless DC (BLDC) motor have gained a large amount of interest in recent years, with their use being implemented in order to achieve a high-performance drive, including quick transient response and high-quality waveforms at the steady state. This paper provides a comparative study between three control schemes of BLDC motors: the direct power control scheme using a finite control set model predictive control (FCS-MPC) approach, the stator current controlled scheme using an FCS-MPC approach, and the stator current controlled scheme using ON–OFF hysteresis current controllers. The three systems were studied and investigated under the same operating conditions. The comparative study included investigating the performance of the BLDC drive in both steady state and transient operations. Qualitative and quantitative analyses were performed on the results obtained with each control scheme. The obtained results demonstrate the validity and effectiveness of the three investigated schemes in controlling the motor speed to the desired value under sudden load changes and achieving satisfactory quick transient responses. However, the results indicate the superiority of the direct power control scheme using an FCS-MPC approach over the others in terms of its minimum torque ripple, lowest torque and speed pulsations, minimum active and reactive power ripples, and high-quality waveforms of the stator currents drawn by the motor with minimum THD.

Investigation of Sinusoidal Shaped Rotor to Reduce Torque Ripple in Axial Flux Permanent Magnet Machine

Cogging torque is one of the main reasons for torque pulsation in AFPM machines that arises due to the force of attraction between stator slots and rotor poles thus adversely affecting the smoothness of output torque. In this paper a rotor shape for the axial flux internal rotor (AFIR) PM machine is proposed for cogging torque reduction and smoothing the output torque. In this research, the reduction in cogging torque is accomplished in two stages. In the first stage, a sinusoidal magnet shape is proposed having less cogging torque as compared to conventional and arced shaped magnet. In the second stage, the magnet overhang technique is used in the optimization process of the machine to further improve the performance characteristics. The optimization process comprises of a selection of variables, Latin hypercube sampling (LHS), model approximation by kriging method, and Genetic Algorithm (GA) to get optimum values of variables. Output results of proposed and optimized models are also compared to demonstrate that the optimized model has reduced torque ripples and improved average output torque. Models are simulated using 3D finite element analysis (FEA) for comparative analysis.

Analytical Minimization of Interior Permanent Magnet Machine Torque Pulsations by Design of Sculpted Rotor

A new and efficient analytical optimization methodology for the design of rotor features is developed and used in interior permanent magnet motors (IPM). The analytical methodology is based on an extended winding function theory to include the IPM rotor’s primary and secondary reluctance paths and the non-homogeneous airgap of the rotor sculpt features. The shape and placement of the rotor features, derived from the analytical-based optimization process, show the improvement in torque average and torque ripple of the IPM machine at a fraction of computational effort. The analytical optimization results are validated with finite element analysis via an exhaustive search.

Effects of high-order space harmonics on the operation of five-phase induction machines under unbalance

The paper addresses the effects of high-order space harmonics on the steady-state performance of five-phase induction machines operating under unbalance. We show that the airgap harmonic fields with orders higher than three, although usually disregarded, can produce a significant increase in the torque pulsation and in the Joule losses. We propose a model based on symmetric components which is used to demonstrate that the field produced by each rotor harmonic current is related to two stator sequence currents. Further, the proposed model allows determining additional losses and harmonic torques produced by airgap harmonic fields with orders higher than three, which up to now have not been addressed elsewhere. As a case study, we applied the model to two five-phase induction machines with different designs and assessed the influence of high space harmonics under operation at steady state with one open phase in the stator. The model has been validated by comparing analytical results with results obtained through finite element analysis. Finally, the model validation was also based on experimental results obtained from tests with two prototypes under many different conditions.

Performance analysis of single-phase interior permanent magnet synchronous motor

Single-phase permanent magnet synchronous motor has been tipped as an alternative to single-phase induction motor due to its high efficiency and torque density. Consequently, a proper performance analysis of the motor is required to cope with the stator imbalance in order to prevent pulsation in the torque performance. This paper presented the dynamic and steady-state analysis of a single-phase interior permanent magnet synchronous motor. In this analysis, a proper combination of direct-quadrature (d-q) reference frame, and symmetrical component analyses were used. The symmetrical components analysis was used to obtain the steady state performance while the dynamic performance was obtained from d-q analysis. The symmetrical components cope with the imbalance and hence the resulting torque pulsation which may results in heating of the motor. The results obtained agreed with the theoretical analysis and yielded a unique steady state equivalent circuit and phasor diagram. The models of the motor were simulated using MATLAB/Simulink. A prototype of the motor was developed and experimentation was carried out to validate the dynamic performance.

ОСОБЕННОСТИ СИНТЕЗА СИНХРОННЫХ РЕАКТИВНЫХ И ИНДУКТОРНЫХ ЭЛЕКТРИЧЕСКИХ МАШИН

The problem of finding the best dimensions for the elements of magnetic systems of synchronous reluc-tance and inductor electric machines in an extended range of changes in load torque and power is considered. An algorithm for solving the problem is also proposed, involving the division of the elements of the magnetic system into two groups. The first group affects the magnitude of the torque pulsations, while the second does not affect this indicator. Such parti-tioning accelerates the process of convergence of the result. A method of sequential non-linear programming is proposed for resolving the problem. It has good convergence with minimal search time. Synthesis of finite element models of a syn-chronous reluctance machine with salient pole and anisotropic types of rotors, switched reluctance machine (SRD), ma-chine with field switching (FSDC), Vernier reluctance and double field Vernier reluctance machines was performed. It was shown that the proportion of winding copper relative to steel in the active part of the machines increases relative to conventional machines when operating in the nominal mode. On the contrary, this feature was manifested to a lesser extent when working in the zone of overloads in terms of torque. Electromagnetic loads increase with increasing power, equivalent to operating a machine of lower power in overload mode. It was shown that the sensi-tivity to the size of the air gap in Vernier reluctance machines is the highest in the class under study. Thus, with increasing power, the specific torque will increase significantly. On the contrary, the lowest sensitivity to the air gap value in ma-chines with one-sided gearing and distributed winding on the stator allows these machines to be made with a larger gap without compromising the specific torque.

A critical review of contemporary issues related to DFIG

The DFIG is a type of induction machine which has been serving extensively in the WEC system. Many researchers have worked on the DFIG and its integration to the grid system, proposed control schemes and designs for the DFIG. However, there have not been a comprehensive critical review on the contemporary issues related to the DFIG. This paper presents a critical review of the contemporary issues related to DFIG. The research findings of this paper are the issues related to the DFIG ranging from the unbalanced voltage dip which results to an induction of very large torque pulsations and DC ripples in the rotor circuit; the preferences and relativities on which control strategy is best for the DFIG considering the FOC and the DTC control schemes, and down to the LVRT issues. The contemporary issues relating to the DFIG operation and their effects on the DFIG operation are also discussed.

Comparative Study of 3-Bladed and Sсissors Tail Rotors Aerodynamics in Axial Flow

The paper is focused on the numerical study of the aerodynamic characteristics of 3-bladed and scissors tail rotors used on Mi-8/17 series helicopters. The hovering and axial flow modes, including the Vortex Ring State (VRS) area are considered. The free wake model developed by authors is used in the research. The study has been performed for two approaches: with a fixed blade pitch angle and with a fixed time-average thrust value. The dependences of the rotor thrust and torque coefficients vs. axial flow velocity and vs. number of revolutions of a rotor have been obtained. The vortex wake shapes and flow images via streamlines have been analyzed. The comparative analysis of the results has been performed. Scissors rotor demonstrates better aerodynamic characteristics in comparison with 3-bladed rotor. Among them: increased hovering efficiency, lower level of thrust and torque pulsations in the VRS modes, smaller power consumption while constant thrust. The authors came to the conclusion about the greater efficiency of the aerodynamic design of scissors tail rotor compared to 3-bladed rotor both in hover and in the VRS modes area.

Advanced Power Conversion System for Motor Drive in Electrified Vehicles.

This paper presents a power conversion system for six-switch BLDC motor drive and fourswitch BLDC motor drive. Brushless DC (BLDC) motor drive have the advantage of high efficiency, high power density and low maintenance. These advantages make BLDC motor drive be widely used in industrial applications. In addition, the four-switch inverter will reduce the cost of the system with less switches. However, the problem of torque pulsation of four- switch BLDC motor drive is an intrinsic problem. To reduce torque pulsation, a novel DC/DC converter whose name is multi-purpose bi-directional DC/DC converter will be proposed in the thesis. This DC/DC converter with diode-assisted network will help improve boost ratio for the input of the BLDC motor drive. For the control system, PI controllers are used to control DC/DC converter and hysteresis control is employed for BLDC motor drive. Though there are other advanced methods for control, the PI controllers and hysteresis control can reduce the complexity of the whole system. Both six-switch and four-switch BLDC motor drives with the proposed system are simulated in PSIM software and the results are compared and discussed.

Analysis of Cylinder Block Torque Characteristics of Dual-Drive Axial Piston Motor

A mathematical model of the cylinder block moment of a dual-drive axial piston motor considering the dynamic pressure in the piston chamber is developed. The influence of the number of plugs, staggering angle, inlet pressure and swashplate inclination on the individual moments applied to the cylinder block was analyzed. The results show: when the number of pistons in the inner and external emissions is the same, the cylinder block is subjected to a periodic pulsation of each moment and odd-numbered pistons have a higher frequency of torque fluctuations than even-numbered pistons. With increasing intersection angle, the pulsation rate of the torque around the x and y axes tends to increase and then decrease but the output torque varies in the opposite direction; The inlet pressure can increase the torque pulsation rate of the cylinder block in equal proportion. When the inclination angle of the inner and external swashplate is not the same, the reasonable selection of different inner and external swashplate inclination angles can make the overturning torque generated by the inner and external emissions offset and increase, so that the overturning torque of the cylinder block is reduced.

A numerical investigation on the influence of savonius blade helicity on the performance characteristics of hybrid cross-flow hydrokinetic turbine

One of the major drawbacks of having a hybrid cross-flow hydrokinetic turbine (HKT) is the alternative nature (positive and negative) of instantaneous torque generation by blades over one cycle of revolution, which will reduce the power coefficient and raise the pulsation level of instantaneous torque. Under the present study, the physical configuration of the proposed hybrid cross-flow HKT is altered by replacing the conventional Savonius HKT blade with a helical Savonius HKT blade. The numerical simulations have been carried out for five different hybrid HKT configurations with different Savonius blade helicity values as 0°, 45°, 90°, 135°, and 180° for the considered range of in-stream velocity from 0.5 m/s to 2.0 m/s. Based on the numerical study, the maximum power coefficient of hybrid cross-flow HKT having Savonius blade helicity of 45° was obtained as 0.208 corresponding to a TSR value of 0.9 and in-stream water velocity of 0.5 m/s. It is improved by 4.5%, in comparison to the maximum power coefficient obtained from the hybrid cross-flow HKT having conventional Savonius blade under the same flow conditions. The torque pulsation level for different configurations of hybrid HKT has also been analyzed in this study. The maximum reduction in TPF was observed as 31.54% for a hybrid cross-flow HKT model with a Savonius blade helicity of 180°. Further, it is observed that the negative magnitude of instantaneous torque generated by hybrid cross-flow HKT having Savonius blade helicity of 135° and 180°, completely nullified and positive instantaneous torque is achieved for all the values of rotor angle over one cycle of revolution. The transient nature of flow across turbine blades has also been visualized through velocity and pressure contours.

Torque Pulsation Reduction During Magnetization in Variable Flux Machines

This paper proposes two methods to minimize the pulsating torque during magnetization in a variable flux - permanent magnet synchronous machine (VF-PMSM). The VF-PMSM is demagnetized and remagnetized by injecting a current pulse to achieve the high speed and high torque requirements. During demagnetization and remagnetization, a d – axis current pulse is injected to change the magnetization state (MS). These MS changing current pulses will change the magnet flux linkage based on the amplitude of the pulse. However, the injected d – axis current abruptly changes the magnet torque as well as reluctance torque and results in a pulsating torque. Since the remagnetization current is much higher than the machine rated current, the pulsating torque is more severe during the remagnetization process. Thus, it is preferred to magnetize the magnet at zero speed and unloaded conditions. To solve this problem, a q – axis current reference during the remagnetization is determined by two different methods: voltage limit method and load torque method. The derived q – axis current reduces the torque pulsation during the remagnetization. The effectiveness of the proposed scheme is experimentally verified on a manufactured VF-PMSM prototype.