Stator Current Harmonics Research Articles

Optimization and control of water pumping PV systems using fuzzy logic controller

The aim of this work is to search for better control and optimization of a photovoltaic (PV) water pumping system (PWPS) using the induction motor. A proposed method based on Fuzzy Logic Control (FLC) is introduced and investigated to improve the conventional Direct Torque Control (DTC). Variable step size Perturb and observe (P&O) is used to extract the maximum possible power from the PV panel. The validation of the control strategy is ensured by reducing the high torque, stator flux ripples and current harmonics in induction machine and increasing pumped water flow. Simulation results of the DTC based on FLC are compared with those of the conventional DTC using MATLAB/SIMULINK. The comparison results show the effectiveness of the FLC controller in terms of torque and flux ripples reduction, and daily pumped water.

Novel Predictive Stator Flux Control Techniques for PMSM Drives

In this paper, a predictive stator flux control (PSFC) algorithm for permanent magnet synchronous motor (PMSM) drives is proposed, which can eliminate the influence of flux linkage parameter perturbation and rotor position error. First, the sensitivity of conventional predictive current control (PCC) to the flux linkage parameter and rotor position is analyzed. Then, the novel composite discrete time sliding mode observer (SMO) based on stator flux state is designed, which can estimate the flux linkage parameter perturbation, rotor position error, and load torque simultaneously. Finally, a novel PSFC method is developed, which can enhance the robustness of PCC against flux linkage parameter perturbation and rotor position error by using composite discrete time SMO. Simulation and experimental results indicate that the proposed PSFC can achieve low stator current harmonics, low torque ripple, and excellent steady-state performance under the flux linkage parameter perturbation and rotor position error.

Dual Three-Phase PMSM Torque Modeling and Maximum Torque per Peak Current Control Through Optimized Harmonic Current Injection

Vector space decomposition (VSD) model is widely used for dual three-phase permanent magnet synchronous machine (dual-PMSM) control, in which two direct-quadrature (DQ) frames, DQ1 and DQ2, are introduced to facilitate the controller design. Existing studies show that harmonic current injection in DQ2 frame can increase the output torque for a given peak phase current, which is referred as maximum torque per peak current (MTPPC) control. However, the injected harmonic current will induce a small dc torque and the harmonic torque. This paper first proposes a comprehensive torque model considering the harmonics in PM flux linkages, inductances and stator currents to investigate the induced torque components, which are neglected in existing approaches. These torque components are then considered in the harmonic current design to improve the MTPPC control performance. The harmonic current design results in a multiobjective optimization problem, and genetic algorithm (GA) is employed to optimize the harmonic current to maximize the output torque with minimal torque harmonic. Compared with existing approaches, the proposed approach is applicable to both surface-mounted and interior dual-PMSMs. Experimental investigations on a laboratory interior dual-PMSM show that the output torque of the test motor can be increased by more than ten percent with a negligible increase in torque ripple.

Encoder-less field-oriented control of permanent magnet synchronous motor by using a full order adaptive state observer

This paper proposes a full order adaptive state observer, for the field-oriented control of a permanent magnet synchronous motor (PMSM), without using a speed sensor. The observer is designed in the estimated field-synchronous coordinate system. The rotor speed is treated as an unknown parameter. The adaptive law for speed is derived by using Lyapunov's stability theorem. Since control algorithms and models are processed in micro computers, the proposed observer has been discretised by Euler's method. To make the observer dynamically faster than the motor dynamics, observer poles are fixed proportionally to those of the motor by using pole placement technique. The simplifying assumptions used to discretise the observer, along with the stator current harmonics, introduce ripples in the estimated rotor speed. To mitigate this effect, various counter-measures are explored. The validity of proposed scheme is verified through MATLAB Simulink.

A Simplified Model Predictive Control for a Dual Three-Phase PMSM With Reduced Harmonic Currents

The conventional model predictive control for dual three-phase motors only evaluates the largest voltage vectors to alleviate the computation burden, but at the costs of large current harmonics and torque ripple. This paper presents a simplified model predictive torque control (MPTC) for an asymmetrical dual three-phase permanent magnet synchronous motor (PMSM), which can significantly improve the machine performances. First, the 36 active voltage vectors in the outer three layers are considered with the proposed control method. In order to suppress the stator harmonic currents, the voltage vectors are preselected based on a switching table according to the flux position and torque deviation in the $\alpha \hbox{-} \beta, \text{x--}y$ subspace. Simultaneously, the number of prediction voltage vectors can also be reduced, thus effectively decreasing the computation time. In particular, with the proposed MPTC method, the harmonic currents can be effectively suppressed. Furthermore, the computational burden can be considerably alleviated. In the meantime, the merits of the conventional MPTC such as fast dynamic response and intuitive implementation are preserved. Finally, both simulation and experimental results are performed to verify the validation of the proposed MPTC methodology when comparing with the conventional MPTC for the dual three-phase PMSMs.

Combined parameters selection of a proportional integral plus resonant controller for harmonics compensation in a wind energy conversion system

This paper introduces the use of the Naslin polynomial technique in order to tune a proportional integral resonant (PIR) controller for the rotor-side converter of a grid-connected wind energy conversion system (WECS), which is based on a back-to-back converter and a doubly fed induction generator (DFIG). The objective of the proportional integral part of the PIR controller is to control the active and reactive power of the rotor-side converter, while the resonant part of the PIR controller deals with the stator current harmonics of the generator due to grid voltage distortions. Most papers that use PIR controllers for WECS often carry out the separated tuning of the PI part and then the tuning of the resonant part without any guide. In this paper, the tuning of the PIR controller as a single controller is proposed taking into account the mathematical base of the Naslin polynomial technique. The case of study is a WECS based on a 50 HP DFIG, and the considered grid voltage harmonics are the fifth and seventh. Simulations were implemented to evaluate the compensation of the current harmonics with the selected PIR controller values.

Stator Harmonic Currents Suppression for DFIG Based on Feed-Forward Regulator Under Distorted Grid Voltage

This paper presents a stator harmonic currents suppression method for doubly fed induction generators (DFIGs) under distorted grid voltage. In the proposed control strategy, the feed-forward regulator instead of the resonant regulator is employed to eliminate the negative impacts on the stator current caused by the distorted grid voltage. The leading phase compensator is applied to compensate the system delay when the sampling frequency is low. This approach can provide both the good dynamic response and strong rejection ability against the stator harmonic voltages. Based on the stator current model of DFIG, the feed-forward regulator is designed in detail. The comparison between the resonant controllers and the feed-forward regulator is also made on the basis of Bode diagram. Then, the robustness against the frequency variations and the parameter deviations is analyzed. Finally, the simulation and experimental results are presented to validate the effectiveness of the proposed control strategy.

A Novel Vector Control of Five-phase PMSM Based on Harmonic Current Closed Loop

Multi-phase electric machines such as five-phase permanent magnet synchronous motor (PMSM) play an important role in the ships electrical propulsion because of the advantages of high performance and high reliability. The decoupled mathematic models of five-phase PMSM in dq coordinate frame are established, and the reason caused to high stator harmonic current in the multi-phase motor is analyzed based on the mathematic models. To suppress the harmonic current, a novel vector control (VC) method based on SVPWM and harmonic current closed loop control is proposed. Based on the proposed algorithm, a five-phase PMSM vector control system is established with MATLAB, the performance is simulated and analyzed. The results show that, the stator harmonic current is much little than that of the traditional control method.

Minimization of Torque Ripple in the DFIG-DC System Via Predictive Delay Compensation

Torque ripple caused by stator current and flux harmonics is one of the main issues in the doubly fed induction generator (DFIG)-dc system, which inherently has to operate with distorted waveforms produced by the diode commutation. This paper proposes a torque-ripple mitigation strategy based on a predictive estimation of the reciprocal of flux linkage. The predictive estimation compensates for the intrinsic delay in the actuation of the torque-ripple rejection signal through the rotor current control loops. Unlike other approaches relying on complex current regulators with selective harmonic tracking, this strategy is based on well-established proportional-integral (PI) controllers for the rotor currents. PI current controllers can then still have bandwidth values typical of usual DFIG systems. Simulations and experiments on a test-rig show that the compensation strategy achieves a strong torque ripple reduction and is very robust against stator frequency variations.

Switching Frequency Dynamic Control for DFIG Wind Turbine Performance Improvement Around Synchronous Speed

In a doubly-fed induction generator (DFIG) wind turbine (WT), large thermal and mechanical oscillations occur around synchronous speed due to the nearly zero-frequency current circulating between rotor windings and rotor-side converter (RSC). A switching frequency dynamic control technique is proposed in this paper to overcome the problem. The basic idea is to dynamically reduce the switching frequency during operation so that both the switching losses and dead-time effect of RSC can be reduced around synchronous speed. According to the characteristic that high-frequency pulse width modulation (PWM) harmonics in DFIG decrease significantly with rotor slip, there would be a new space for switching frequency reduction especially around synchronous speed. The reduced of switching frequency is actually determined by a tradeoff between the increase of both the stator current PWM harmonics and speed PWM ripples and the decrease of insulated-gate bipolar transistor temperature. Compared with the conventional technique with constant switching frequency, the new technique can effectively improve the system performance around synchronous speed including not only better thermal behavior and efficiency of RSC but also smaller current total harmonics and speed total ripples in generator. To clarify the method, first, the effects of switching frequency reduction on a DFIG WT system are investigated. Second, the criteria, control scheme, and procedure of the method are presented. Finally, experimental and simulation studies were carried out, and the results validate its feasibility and effectiveness.

Genetic Algorithm-Based Current Optimization for Torque Ripple Reduction of Interior PMSMs

This paper investigates the torque ripple modeling and minimization for interior permanent magnet synchronous machines (PMSMs). At first, a novel torque ripple model is proposed in which the torque ripples resulted from the spatial harmonics of permanent magnet flux linkage, time harmonics of stator currents and the cogging torque are included. Based on the torque ripple model, a genetic algorithm (GA)-based harmonic current optimization approach is proposed for torque ripple minimization. In this approach, GA is applied to optimize both the magnitude and phase angle of the stator harmonic currents to minimize the peak-to-peak torque ripple, minimize the sum of squares of the harmonic currents, and maximize the average torque component produced by the injected harmonic currents. The results demonstrate that the magnitude of the harmonic current can be significantly reduced by optimizing the phase angles of these harmonic currents. This leads to further suppression of the torque ripple when compared with that of a case where phase angles are not considered in the optimization. Also, an increase of the average torque is achieved when the optimum harmonic currents are injected. The proposed model and approach are evaluated through both numerical and experimental investigations on a laboratory interior PMSM.

Stability and performance of current harmonic controllers for multiphase PMSMs

Multiphase electric machines can provide significant benefits over conventional three-phase machines. A drawback to multiphase machines is that they are known to have problems with stator current harmonics. The harmonics can be eliminated by various current harmonic control methods. However, there appears to be no clear agreement on the most suitable method for multiphase machines. This paper aims to compare different current harmonic controllers in terms of stability and performance under model uncertainty. A detailed theoretical analysis of the harmonic controllers is given by taking a modern multi-input multi-output approach based on a structured singular value analysis. Further, the performance of the harmonic controllers is studied with experimental results from a dual three-phase permanent magnet synchronous machine. The analysis and results of this paper show how to design robust high-performance current harmonic controllers for multiphase machines.

Partial Current Harmonic Compensation in Dual Three-Phase PMSMs Considering the Limited Available Voltage

Multiphase electric machines are known to have problems with stator current harmonics. The harmonics can be eliminated by various current harmonic compensation methods. However, using the active harmonic compensation can increase the required output voltage of the inverter supplying the machine. Because the maximum voltage is limited, complete elimination of the current harmonics may not always be possible. For such cases, this paper introduces a strategy for a partial compensation of the current harmonics. The aim of the proposed strategy is to provide a maximum reduction in the magnitude of the harmonics when the available voltage is limited. The strategy is verified by experimental results.

Saturation influence of the induction motor magnetic system on the current spectrum powered by a pulsed voltage source

A model for the study of the fundamental and higher stator current harmonics with a certain magnetic system saturation of the induction motor from form of power supply was proposed. The influence of induction motor magnetization curve non-linearity of the stator current form, powered by the three-phase bridge inverter was analyzed. The method of accounting non-linearity of the magnetization curve in the stator current spectrum analysis was proposed. A result of current spectra for different states of the induction motor was shows. Ref. 11, pic. 3

A comprehensive review of LVRT capability and sliding mode control of grid-connected wind-turbine-driven doubly fed induction generator

In this paper, a comprehensive review of several strategies applied to improve the Low Voltage Ride-Through (LVRT) capability is presented for grid-connected wind-turbine-driven Doubly Fed Induction Generator (DFIG). Usually, themost proposed LVRT solutions in the literature based on: hardware solutions, which increase the system costs and software solutions, which increase the control system complexity. Therefore, the main objective of this study is to take into account grid requirements over LVRT performance under grid fault conditions using software solution based on Higher Order-Sliding Mode Control (HOSMC). Effectively, this control strategy is proposed to overcome the chattering problem and the injected stator current harmonics into the grid of the classical First Order Sliding Mode (FOSMC). Furthermore, the resultant HOSMC methodology is relatively simple; where, the online computational cost and time are considerably reduced. The LVRT capacity and effectiveness of the proposed control method, compared to the conventional FOSMC, are validated by time-domain simulation studies under Matlab on a 1.5MW wind-turbine-driven DFIG.

Stator Current Harmonic Reduction in a Novel Half Quasi-Z-Source Wind Power Generation System

The generator stator current gets distorted with unacceptable levels of total harmonic distortion (THD) because impedance-source wind power generation systems use three-phase diode rectifiers. The stator current harmonics will cause increasing losses and torque ripple, which reduce the efficiency and stability of the system. This paper proposes a novel half quasi-Z-source inverter (H-qZSI) for grid-connected wind power generation systems, which can reduce the generator stator current harmonics a great deal. When H-qZSI operates in the shoot-through zero state, the derivative of the generator stator current is only determined by the instantaneous value of the generator stator voltage, so the nonlinear relationship between generator stator current and stator voltage is improved compared with the traditional impedance-source inverter. Theoretically, it is indicated that the stator current harmonics can be reduced effectively by means of the proposed H-qZSI. Finally, simulation and experimental results are given to verify the theoretical analysis.

Inverse-Based Current Harmonic Controller for Multiphase PMSMs

Multiphase electric machines can provide significant advantages over conventional three-phase machines. Unfortunately, multiphase machines also have a notable disadvantage that even a small voltage excitation of certain frequency components can cause large stator current harmonics. This paper presents an inverse-based current harmonic controller to eliminate the current harmonics. A detailed theoretical analysis of the proposed harmonic controller is given including a comprehensive set of analytical design principles. The robustness of the method is studied with a multi-input multi-output approach based on a structured singular value and H∞ norm analyses. In addition to the theoretical work, the performance of the harmonic controller is investigated with experimental results from a dual three-phase permanent magnet synchronous machine (PMSM). The analysis and results of this paper show that the inverse-based current harmonic controller provides a robust and high-performance method to eliminate the current harmonics in multiphase PMSMs.

Dynamic Performance Evaluation of a Nine-Phase Flux-Switching Permanent-Magnet Motor Drive With Model Predictive Control

Multiphase flux-switching permanent-magnet (FSPM) motor drives are nowadays considered for various applications due to numerous advantages when compared with their three-phase counterparts. In principle, stator-flux-oriented control of a nine-phase flux-switching permanent-magnet (FSPM) (9P-FSPM) motor can be realized theoretically by using four pairs of synchronous current controllers in conjunction with eight conventional proportional-integrals (PIs), for alleviation of the coupling effects and unwanted low-order stator current harmonics. In practice, however, drive performance will deteriorate if the PI-based current controller is not well tuned for optimum response to every dynamic scenario due to nonlinearity. In order to enhance dynamic performance of the drive system, a fully-decoupled model predictive control algorithm with fixed switching frequency is developed for the 9P-FSPM motor. The main contribution is comprehensive and detailed description of precise modeling of the 9P-FSPM motor and the controller design process. Also, some practical hints are given for implementation, such as the elimination of low-order harmonic currents and the selection of active voltage vector in the nine-phase drive system. Both simulation and experimental results are presented to validate the effectiveness of the developed current controller and the high dynamic performance of the 9P-FSPM motor drive.

Influence of Inverter Modulation Strategy on Electric Drive Efficiency and Perceived Sound Quality

This paper presents an evaluation of different modulation techniques and different levels of switching frequency randomization for a rear axle electrical drive unit used in automotive applications. Inverter and machine losses, and perceived sound quality of high-frequency acoustic noise are investigated by finite element calculations, experimental testing, and subjective noise assessment. Additionally, stator current harmonics, airgap flux density harmonics, and force density harmonics are compared for space vector modulation (SVM) and discontinuous pulsewidth modulation through finite element modeling. The main conclusion is that, primarily in the field weakening region, significant energy savings can be achieved (up to 17% decrease in total inverter losses with a switching frequency of 10 kHz). This is obtained without deterioration of perceived sound quality by the use of discontinuous pulsewidth modulation with switching frequency randomization. Furthermore, randomization of the switching frequency does not improve the perceived sound quality of the acoustic noise when using SVM. However, for discontinuous pulsewidth modulation, improvements in perceived sound quality when randomizing the switching frequency are observed, primarily below base speed.

Braking mode simulation of induction motor of variable-frequency drive using stator current harmonics **

The work objective is to study electrodynamic processes in the frequency-controlled drive (FCD) by the mathematical modeling method, in particular, in the two-current mode of the dynamic braking considering the 5th and 7th current harmonics of the induction motor (IM) stator. The features of forming IM stator current low frequencies (0.2-15 Hz) by the autonomous voltage inverter (AVI) followed by the additional electricity loss in the FCD, and the appearance of torque ripple on the IM shaft causing jerkiness of the actuating mechanism (AM) of the production machine (PM) executive device (ED) in the low speed zone and complicating their locating in the prearranged position, are given. It is hard to implement the FCD scheduled deceleration without trajectory correction at the friction forces ambiguity in the ED AM mobility links and availability of the torque ripple on the IM shaft. To solve this problem, the authors offer, first, to use a spatial-vector pulse-width modulation (SV PWM) with m-fold submodulation of the carrier frequency (CF) and without submodulation in the IM braking mode. Secondly, it is reasonable to apply (momentarily in a low speed area) the principle of linearization by oscillation to reduce the K friction coefficient to a decreased value in the ED AM mobility links by the IM rotor microvibration due to the 5th and 7th harmonics of the stator current. Thus, the work on modeling FCD (in Matlab + Simulink software package) allows more accurately define the impact of the 5th and 7th harmonics of the IM stator current on the capability of the software implementation of the two-current mode of the FCD dynamic braking while reducing the total energy loss in the ED AM low-speed motion area. In addition, the applicability of the proposed solutions of the electric drives of mechatronic and robotic multipurpose systems with higher requirements for positioning in the basic AM - AVI circuits is confirmed.