Stator Current Harmonics Research Articles

Design of adaptive speed controllers for matrix‐converter‐based interior permanent magnet synchronous motor drive systems

AbstractInterior permanent magnet synchronous motors (IPMSMs) which are driven by matrix converters have many advantages, including one‐stage power conversion, high efficiency, bidirectional power transfer, near unity input power factor, and low input current harmonics. However, the virtual DC‐link voltages of matrix‐converters vary from 0.866 to and the current commutations of matrix‐converters create serious three‐phase stator harmonic currents as well. Moreover, matrix‐converter‐based IPMSM drive systems, in general, have very large external loads, which require advanced control methods. To solve these problems, two adaptive controllers, including a model reference adaptive controller and a self‐tuning controller, are investigated in this article for matrix‐converter PMSM drive systems. From the experimental results, the proposed two adaptive speed controllers provide excellent dynamic responses, which are superior to PI speed controllers, including faster transient responses, better tracking abilities, and greater robustness. As a result, this proposed matrix‐converter‐based IPMSM drive system is very suitable in industrial applications.

An Improved Current-Source-Converter-Based Series-Connected Wind Energy Conversion System

The passive rectifier-based current source converter (CSC) used in the series-connected wind energy conversion system features low cost, high reliability, and simple control, but suffers highly distorted generator stator currents. A new CSC-based wind energy conversion system composed of a multi-phase generator, a passive rectifier, a modular medium-frequency transformer-based converter, and a CSC, is proposed. In addition, two versions of the proposed converter are developed for low- and medium-voltage turbine systems respectively. The operation principle is presented, controls are developed, and simulations and experiments are conducted. Both converters offer excellent generator stator current harmonics performance, while also retaining the advantages of existing CSC-based converters.

Power quality improvement of wind turbines using doubly-fed induction machines.

A novel approach to modelling doubly-fed induction machines facing (distorted) ac power networks is presented. It takes place in the frequency-domain and is based on frequency coupling matrices using tensor algebra. Benefits of this comprehensible and fast modelling approach are demonstrated by establishing a feed-forward control signal that reduces stator current harmonics and torque ripple thereby improving the network compatibility and reducing the stress on the mechanical drive train. Dynamic simulations using PSCAD/EMTDC and MATLAB/Simulink are presented demonstrating the effectiveness of the proposed modelling approach and the feed-forward compensation scheme.

Stator and Rotor Current Harmonics in Doubly Fed Machines with Cycloconverter in Rotor Circuit

The stator and rotor currents of a doubly fed machine (DFM) with a 12-pulse cycloconverter in the rotor circuit for different operating states are analyzed. It is shown that the stator as well as the rotor currents contain harmonic spectra dependent on the machine operating state, especially on the mutual relation of fundamental component frequencies of both the currents.

Fast Calculation of Electromagnetic Vibration of Surface-Mounted PMSM Considering Teeth Saturation and Tangential Electromagnetic Force

In view of the shortcomings of the existing calculation methods of electromagnetic forces, this paper proposes an analytical method (AM) combining the magnetomotive force (MMF)-permeance method and the improved subdomain method. The amplitude of each force density component considering stator teeth saturation and current harmonics is calculated, and the specific order and frequency components in the radial and tangential electromagnetic force densities are analyzed and sorted out. In modal analysis, the stator core and the casing are regarded as cylindrical shells with axial ribs, the natural frequencies of the stator are obtained based on the energy method, and the accuracy is well verified by the modal test. Finally, the frequency response functions of low-order modes of the stator only related to the stator structure parameters are determined, and the vibration accelerations under different working conditions are obtained based on the linear superposition principle by only updating the electromagnetic forces. Compared with the multi-physical coupling finite element analysis, the total calculation time of the proposed AM is reduced by more than 92%, which facilitates the fast prediction and effective reduction of electromagnetic vibrations in the motor design stage.

Methodology for Electromagnetic Optimization of a Partially Superconducting 1.4 MW Electric Machine for Electrified Aircraft Propulsion

Large transport aircraft with electrified propulsion systems require MW-class electric machines that have higher efficiency and power-to-weight ratio than existing machines. Superconducting machines are being evaluated as potential solutions. This paper presents a method to optimize the electromagnetic design of a partially superconducting machine in terms of these metrics and the approximate fuel burn of the aircraft. The optimization is based on 2D electromagnetic finite element simulations, a prediction of the superconducting coils' critical current, and geometry relations that design the superconducting coils based on dependent variables while constraining the total cost of superconductor and ensuring adequate space for structure. The design process is completed by (1) a 3D electromagnetic finite element simulation to improve the prediction of torque and assess magnetic flux leakage, (2) refinement of the superconductor width for each individual racetrack coil, and (3) evaluating inverter-produced stator current harmonics on eddy current losses in the rotor.

Near-Complete Suppression of Harmonic Currents in SPMSMs Caused by Back EMF and Dead Time

This paper introduces a novel algorithm forsuppression of phase current harmonics in three-phase sinusoidal surface mounted permanent magnet synchronous machines (SPMSMs) caused by non-ideal back-emf waveform and dead-time effects. Proposed feedback acquisition chain obtains an exact information on all the relevant harmonics within each period of the fundamental. Design of the harmonic current controller based on the internal model control principle is given. The paper outlines the relevant details of implementation and the results of verification performed by both computer simulations and experimentally, using a laboratory prototype machine. Experimental results, obtained in presence of non-sinusoidal back-emf and with erroneous dead-time compensation, prove the ability of the proposed solution to remove the stator current harmonics quickly, in just two fundamental periods, and thus eliminate torque ripple.

Optimal control method of induction motor torque ripple based on harmonic component

AbstractThe torque ripple of an induction motor has strong harmonic interference, which causes stator current distortion. Stability control is always a difficult problem in this field. An optimal control method for the torque ripple of induction motors based on harmonic components is proposed. To address the instability and significant energy loss caused by torque ripple in induction motors, an optimization control method for torque ripple in induction motors based on harmonic components is studied and designed. On the basis of the induction motor model, according to the characteristics and generation principle of torque ripple, combined with controllable and uncontrollable parts of harmonic torque, the stator current harmonics are used to suppress torque harmonics and minimize torque ripple. For the purpose of to cancel the harmonic component of the output voltage, achieve digital output voltage filtering, reduce the harmonic component of the stator current, and achieve optimal control of the torque ripple of the induction motor, the resonant digital filter is simultaneously deployed at the controller's output. The test results showed that the maximum torque ripple value was 2 Nm and the minimum torque ripple value was 0.1 Nm, which can restrain the distortion of stator current to the greatest extent and reduce the harmonic content of torque. In summary, the optimization control method proposed in the study can effectively suppress harmonic interference, which has important practical implications for future harmonic research.

Indirect Vector Control for Five-Phase Asynchronous Generator Using Three Level Rectifier in Wind Energy Systems

Five-phase induction generators in variable-speed wind energy systems are a focus of this study, and a unique method of regulating them utilizing indirect vector control is proposed in wind energy systems. Grid-side regulation is handled by a two-level converter, whereas machine-side control is handled by a five-phase three-level converter. There are five electrically distinct phases in ASG, and each one is 720 apart. More power can be generated in the same machine frame with this configuration than with a normal three-phase induction generator, and the system is also more stable and sturdier. In order to connect ASIG to the grid, voltage source converters (VSCs) must be employed. A mathematical analysis of the suggested control system is performed, and simulation results are generated in the MATLAB/ SIMULINK software package to account for the various ramps in wind speed. The simulation findings reveal a decrease in low harmonic distortion in injected grid currents, leading to a reduction in of harmonics in stator harmonic currents results in increase in the overall efficiency of the asynchronous generator.

Cascade-Free Modulated Predictive Direct Speed Control of PMSM Drives

Conventional predictive control for permanent magnet synchronous motors (PMSMs) contains dual speed and current loops, and has a complex structure and multiple parameters to be tuned. Conventional predictive direct speed control (PDSC) exhibits an unsatisfactory steady-state performance. To tackle these issues, this paper presents a cascade-free modulated PDSC (MPDSC) scheme for PMSM drives. First, a speed predictive model is built, where a second-order sliding mode observer is employed to quickly and robustly estimate the load torque. Then, a dual objective cost function with speed and stator current tracking is designed, which improves the system’s steady-state performance. Furthermore, the analytical solution of the constrained optimal voltage vector is derived and it is synthesized by space vector modulation, resulting in a fixed switching frequency. Experimental results show that the proposed MPDSC has stronger robustness, and lower torque ripples and stator current harmonics compared to conventional PDSC.

A Novel space vector modulated DTC scheme of induction motor drive with a single PI controller for electric vehicles

Facilitating instantaneous torque and smooth speed of Electric vehicle (EV) largely relies on modulation scheme employed and type of controller used for motor drive system. The DTC-SVM (Space Vector Modulation) approach with two PI controllers has an excellent steady state and transient response. However, there is still a need to reduce stator current and torque ripples in induction motor for application in Electric vehicle. This paper presents a new approach to minimize stator current harmonics, torque ripple of an induction motor drive with appropriate gain value for torque PI controller. Good performance of the induction motor drive is achieved using a single PI controller. Both flux and torque are controlled effectively with less torque ripple. In this study, torque and current ripples are obtained at full, one-half and one-fourth of the rated speeds at rated torque value. This work analyzes the transient operation of the drive for unit step change in command torque at various rotor speeds. Space Vector Pulse Width Modulation (SVPWM) of the drive at constant switching frequency is presented. Modeling and Simulation is performed in the stationary reference frame theory. The performance is observed during steady state and transient operations. The settling time of torque responses and stator currents are obtained during transient conditions. Torque ripples are obtained during steady state. A comparison with DTC-SVM with two PI controllers for the same Torque commands is well understood. Total Harmonic Distortion (THD) in the motor input current at different reference fluxes are tabulated for classical, two PI controllers and a single PI controller. The proposed DTC-SVM scheme with single PI controller is found to be robust with good steady state and transient characteristics with less settling time and is validated with flux vector trajectories.

Research on hybrid controller utilizing proportional and repetitive control scheme for Permanent Magnet Servo System

Due to the existence of high amount stator current harmonics caused by the inverter nonlinearity, the operation performance of Permanent Magnet Servo System (PMSS) used Proportional–Integral (PI) controller will be affected. To suppress the current harmonics in the PMSS, a hybrid controller utilizing proportional and repetitive control scheme for the current loop is proposed. Firstly, the phase-frequency characteristic and the magnitude–frequency characteristic for the hybrid controller bode diagrams are analysed. To improve the open-loop gain in the frequency band of high-proportion harmonics and compensate the phase lag, the hybrid controller parameter setting method is also studied. Furthermore, the stability and the anti-interference ability of the PMSS used hybrid controller are analysed through Lyapunov theory. Finally, the PMSS model is established through Matlab/Simulink software, and the operation performances of the PMSS utilizing different current loop controllers are studied. The simulation results show that the proposed hybrid controller can suppress the current harmonics and the output torque ripple effectively.

Virtual voltage vector based predictive current control of speed sensorless induction motor drives

Nowadays, predictive current control (PCC) strategy has been recognized as a promising option for the control of electric drives for their control flexibility, fast dynamic response and weighting factorless structure of objective function. However, such kinds of conventional control strategies make drives to suffer from the ingress of significant harmonics in stator current, increasing further the steady state flux ripple followed by a noticeable torque ripple. To ameliorate these aforementioned shortcomings of conventional scheme, the present work employs the concept of virtual voltage vector (V3) in PCC strategy. The mathematical steps of the proposed V3PCC make the scheme more frontward in delay compensation, and also less parameter sensitive than the conventional one. As a baseline for the performance analysis, the present V3PCC is compared with a weighting factorless V3 based predictive flux control (PFC) scheme in induction motor (IM) drive. A speed adaptive flux observer is considered for the speed estimation purpose in both the control schemes. The performance of both the sensorless schemes for IM drive are analysed in MATLAB/Simulink, and also experimentally verified in a 2.2 kW IM drive test bench.

Adaptive data-driven fault-tolerant control strategy for optimal power extraction in presence of broken rotor bars in wind turbine

Broken rotor bars of a Squirrel Cage Induction Generator (SCIG) impact significantly the quality and quantity of produced electrical energy from Wind Energy Conversion Systems (WECS) because: (1) they change the characteristics of SCIG entailing the invalidity of the designed Maximum Power Point Trucking (MPPT) control and pitch angle control, (2) they increase mechanical and thermal stresses, as well as the harmonic content in stator currents. Therefore, this paper proposes an efficient fault tolerant control strategy in order to mitigate the aforementioned consequences. This strategy is based on a hybrid (mechanic-electric) fault tolerant control (FTC) allowing obtaining optimal power extraction in presence of broken rotor bars. A failure (one or two broken bars) is detected in early stage based on the use of a data-driven (machine learning) approach. The latter uses a discriminative feature space (frequency and magnitude of stator harmonic currents) in order to represent and separate the normal operation mode from faulty modes (broken bars). Simulations using MATLAB demonstrated a nominal current in healthy rotor bars in wind turbine operation zone-3 and new optimal power extraction despite one or two broken bars.

Suppression of Beat Phenomenon for Electrolytic Capacitorless Motor Drives Accounting for Sampling Delay of DC-Link Voltage

Beat phenomenon is an important issue for the practical application of electrolytic capacitorless motor drives. In this study, the characteristics of stator current harmonics caused by the voltage sampling delay are analyzed. Further, the beat phenomenon generated from the interaction between the harmonics and the fundamental currents is investigated, and the envelope feature of the stator current is derived mathematically. For the purpose of suppressing the beat phenomenon, a voltage reconstruction strategy is proposed to reduce the influence of dc-link voltage sampling delay at the six times of grid frequency. By utilizing the reconstructed dc-link voltage for calculation of PWM duty ratio, the beat phenomenon can be attenuated significantly. The proposed method can be integrated into motor control system easily. Experimental results show the effectiveness of the proposed strategy in a prototype of electrolytic capacitorless permanent magnet synchronous motor drive.

Modified Brain Emotional Controller-Based Ripple Minimization for SVM-DTC of Sensorless Induction Motor Drive

This paper presents the Modified Brain Emotional Controller (MBEC) technique for the minimization of torque and flux ripples of sensorless Induction Motor (IM) drive. In low-speed operation, IM is very sensitive due to variations in torque and flux ripples. These variations inert low order harmonics in stator currents that adversely affect the performance of the IM drive. The drive’s performance can be improved by integrating a controller that not only minimizes harmonic presence but also increases the drive’s performance. In this paper a biological inspired intelligent speed controller namely, MBEC is proposed to obtain improved performance from the drive. The input to the MBEC is an error of the reference speed and the actual speed of the motor that is estimated using the Model Reference Adaptive System (MRAS). SVM based topology is used to develop the inverter and IM is operated in sensorless DTC technique. Stability analysis of MBEC based IM drive is presented in this paper to hold the effectiveness. The proposed control configuration is tested with different operating conditions and obtained results are verified through real-time experimentation using Opal-RT OP5600. The performance of the proposed control algorithm is compared with the BEC and PI techniques to hold the effectiveness in terms of low flux ripples and torque ripples in different operating conditions.

A Generalized, Fast and Robust Open-Circuit Fault Diagnosis Technique for Star-connected Symmetrical Multiphase Drives

Multiphase drives with fault-tolerant capability are favored in high-reliability applications. In most fault-tolerant multiphase drives, the fault types and locations must be known prior to the fault-tolerant control. Therefore, fault diagnosis is an indispensable procedure. This paper proposes a generalized method to detect and identify the open-circuit faults (including open-switch and open-phase faults) in star-connected symmetrical multiphase drives with different phase numbers. The selected fault diagnosis signals are calculated solely from simple arithmetical operations of measured phase currents, resulting in easy real-time implementation. As fault detection signals are derived from the physical constraint imposed by the neutral point, the proposed method is naturally robust and not sensitive to operating points, machine transients and harmonics in stator currents. Therefore, a relatively small fault detection threshold can be used and fast detection can also be achieved. After the fault has been detected, the fault type is further identified according to the polarity of the integration of phase currents. Experimental results on nine-phase and five-phase induction machine drives verify the generality, fast diagnosis speed and robustness of the proposed method.

Design and Implementation of Periodic Control for a Matrix Converter-Based Interior Permanent Magnet Synchronous Motor Drive System

The matrix converter-based IPMSM drive has 360 Hz virtual DC-bus voltage variations which produce severe stator harmonic currents. To solve this problem, a speed-loop classical periodic controller and two current-loop periodic controllers, including a classical periodic controller and a selective harmonic controller, are proposed in this paper. By using the proposed methods, the harmonic currents are obviously reduced and the speed responses of the IPMSM are clearly improved. A detailed analysis is discussed. A digital signal processor, type SH7237, manufactured by Renesas Electronics Corporation is used for the control algorithms. Experimental results show that those proposed periodic controllers reduce up to nearly 32% of the total harmonic distortion at the stator currents, and also apparently improve the transient, tracking, and repetitive load disturbance speed responses.

Air‐gap flux‐oriented vector control of dual stator induction generator used in wind energy conversion system with novel 13‐zone time optimized space vector‐based hybrid bus clamping PWM

This work presents a novel speed sensor less air-gap flux-oriented vector control of dual stator induction generator (DSIG) used for grid connected, variable speed wind energy generation system. The DSIG consists of two stator windings electrically separated by an angle of 30° with dissimilar pole numbers, which are in the ratio of 1:3. This arrangement offers reduced magnetic core saturation and less harmonics in stator currents, which results into reduced stator winding losses. Moreover, presence of two stator windings makes DSIG suitable to be used in high power application. In conventional rotor-flux-oriented control, the rotor flux is oriented along the d-axis of the rotor winding. But the rotor flux is not easily accessible. Air-gap flux-oriented vector control (AGFOVC) is advantageous as compared to conventional vector control because the air-gap flux is easily accessible and does not require any special arrangement for the measurement of variables. Moreover incorporation of this novel speed sensor less air-gap flux-oriented vector control also eliminates the use of speed encoder as the rotor speed is estimated from the machine terminal variables. Elimination of speed encoder not only reduces the cost of the overall system but also nullifies the error due to mismeasurement of speed and enhances control flexibility and robustness. As a result of which robustness of the system increases. Here, two separate converters are used for the two stator windings of the machine. And the converter switching's are being performed by space vector-based novel dwell time optimized 13-zone hybrid PWM. This special PWM results in better harmonic performance, reduced torque pulsation, and minimal switching loss. The simulation of the overall system is performed in MATLAB environment and the simulated results are validated experimentally using dSPACE controller board DS1104. Close proximity in simulated and experimental waveforms justifies the effectiveness of the proposed work.

An Enhanced Half-Quasi-Z-Source Inverter for Wind Energy Conversion System with D-PMSG

To solve the problem of the traditional quasi-Z-source inverters with low voltage gain, an enhanced half-quasi-Z-source inverter (E-HQZSI) is proposed and applied to direct-drive permanent-magnet wind power generation systems in this paper. The expression of the boosting factor is deduced, which shows that E-HQZSI has higher voltage gain compared with the QZSI and HQZSI. However, the higher voltage gain of the E-HQZSI will lead to the large distortion of the generator stator current necessarily. In this paper, a periodic shoot-through duty ratio control scheme is proposed to reduce the stator current harmonics for E-HQZSI. According to the change rule of the single-phase stator current, the shoot-through duty ratio is compromised to make that the three-phase stator currents are as close as possible to the sine wave. Finally, the correctness of the theoretical analysis is verified by simulation and experiment.