Stator Current Control Research Articles

Stator Current Harmonic Control With Resonant Controller for Doubly Fed Induction Generator

Voltage harmonics in the grid can introduce stator current harmonics in a doubly fed induction generator (DFIG) wind turbine system, which may potentially impact the generated power quality. Therefore, wind turbine current controllers need to be designed to eliminate the impact of grid voltage harmonics, especially low-order harmonics. This paper proposes a stator current harmonic suppression method using a sixth-order resonant controller to eliminate negative sequence fifth- and positive sequence seventh-order current harmonics. A stator current harmonic control loop is added to the conventional rotor current control loop for harmonic suppression. The overall control scheme is implemented in dq frame. Based on a mathematical model of the DFIG control system, the effects on system stability using the resonant controller, an analysis of the steady-state error, and the dynamic performance, are discussed in this paper. Taking these effects into account, the parameters of the resonant controller can be designed and effectively damp the influence from the grid voltage harmonics. As a result, the impacts of the negative sequence fifth- and positive sequence seventh-order voltage harmonics on the stator current as well as the electromagnetic torque are effectively removed. Simulations and experiments are presented to validate the theoretical analysis.

Input Power Factor Compensation for High-Power CSC Fed PMSM Drive Using d -Axis Stator Current Control

In this paper, an input power factor compensation method is proposed for a high-power pulse-width-modulated current-source-converter (CSC)-fed permanent magnet synchronous motor (PMSM) drive system. The proposed method is based on controlling the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis stator current component in the field-oriented control (FOC) scheme of the drive system. The CSC-fed PMSM drive system and its FOC scheme are first introduced. Then, the relationships between the machine side, dc-link, and the line side are investigated. Based on the analysis, a new <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis stator current control scheme that can ensure unity input power factor for the operating speed range is proposed. The main feature of the proposed scheme is to compensate the line-side power factor without the need for modulation index control in either the rectifier or the inverter. Therefore, offline Selective Harmonic Elimination (SHE) modulation schemes can be implemented on both line- and machine-side converters to minimize the total harmonic distortion. This results in reduced switching frequency and reduced switching losses. Simulation results for a 2.44 MW medium-voltage system and experimental results from a low-voltage 6.5 kW IPM motor drive are provided to verify the effectiveness of the proposed compensation method.

Study on Grid-Connected Converter for Permanent Magnet Direct-Driven Wind Power System

According to characteristics of unidirectional flow of energy in permanent magnet wind power system, the paper proposes a two-quadrant three-level converter topology. Combined with method of the optimum tip speed ratio for tracking the maximum wind energy, the generator-side converter uses the double closed-loop control, speed outer loop and stator current inner loop control, whose control objective is to track the given generator speed. Grid-side converter uses the direct power control strategy based on virtual flux-linkage orientation. On the basis of MATLAB simulation platform, the permanent magnet wind power system simulation model was established. The simulation results show that the grid- and generator-side converter can operate with unity power factor, furthermore, verifies that the proposed converter structure is feasible.

Ensuring of static stability of a synchronous motor with permanent magnets by choosing optimal phase voltage

It is shown that, by choosing a sufficient gain of a stator current control circuit, it is possible to make steady-state modes with optimal efficiencies statically stable at any admissible load moments, while the modes optimal over cosφ will be statically stable only at moments smaller than the boundary one. The equations for the amplitude of the output signal of the current control circuit providing for the optimal steadystate mode are derived for the specified moment of load.

Current Controller for Low-Frequency Signal Injection and Rotor Flux Position Tracking at Low Speeds

Rotor flux spatial position can be tracked in an ac machine even at low or zero stator frequency if a low-frequency harmonic current signal is injected into its stator. The harmonic current injection is source of the rotor speed perturbations which induce voltage oscillations in the stator winding at the injected frequency. By analyzing the stator winding voltage response, it is possible to detect the rotor flux position regardless of the stator frequency. This paper presents a stator current controller that is suitable for imposing rotating or pulsating harmonic current injection and a method for tracking the rotor flux position in either induction machines (IMs) or permanent-magnet synchronous machines (PMSMs). The controller contains, in addition to the standard fundamental-frequency-based synchronous reference frame (SRF) current controller, two sets of harmonic current integral controllers placed in respective harmonic SRFs. Such an extended current controller simultaneously performs two important tasks: controlled harmonic current injection with zero steady-state error and separation of particular spectral components in the stator voltage (spectral/sequence decomposition) which contain the rotor flux position information. The theoretical analysis presented, based on perturbation theory and averaging techniques, gives general expressions which link the rotor flux position error in IM and PMSM to the harmonic current controller outputs. Two special cases with the rotational and pulsating harmonic current injections are considered in more detail. The validity of the theoretical analysis and the feasibility of the sensorless rotor flux position detection are experimentally verified.

Research and Simulation of PMSM based on Coordination Control Technology

This paper proposed an improved stator current control algorithm of Permanent Magnet Synchronous Motor (PMSM) for efficiency optimization. According to the formula of maximum input power of PMSM, relational expression between d, q axis current is established. Appling multiple input and multiple output system coordinated control theory to current control system; the improved stator current control algorithm is given. The simulation results have proven that the algorithm proposed in this paper can maximization output power in the case of minimum coordination deviation.

Predictive relay-vector stator current control in induction electric drive with matrix direct frequency converter

Predictive relay-vector stator current control is proposed for an induction electric drive with a matrix direct frequency converter. Electromagnetic and electromechanical characteristics of the electric drive were studied in static and dynamic operation modes using the simulation method.

Three-Phase Induction Motor Stator Current Optimization

This research presents two mathematical –based optimal control systems for induction motor drives leading to stator current optimization and energy saving. The first is a classical optimal control system, which uses information on torque of the motor to generate the appropriate voltage amplitude that minimizes the induction motor stator current. The second is a genetic algorithmbased optimal control system, which uses information on torque of the motor to generate the appropriate minimum stator current according to fitness function. The constant f V optimal stator current controller models have been configured and built depending on a set of experimental data using MATLAB computer program, the models were validated by simulation using a typical induction motor drive model implemented with MATLAB/Simulink toolbox. The aim of this research is the industrial machineries performance improvement by analyzing and designing the induction motor optimal stator current controller, this will minimize the stator current under different loading conditions. Depending on the motor shaft mechanical load torque in order to minimize the stator current, the controller will supply stator of motor with proper voltage and frequency using appropriate control algorithm for industrial machinery. General Terms Algorithms, Performance, Experimentation

Bearing Fault Detection via Stator Current Noise Cancellation and Statistical Control

This paper proposes a new approach to detect <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">situ</i> bearing faults via stator current monitoring. For <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">situ</i> bearing faults, the characteristic bearing fault frequencies may not exist, particularly at an early stage. In addition, the bearing fault signatures are usually subtle compared to the dominant components in the sampled stator current. Therefore, in this paper, a noise cancellation technique is used to suppress those dominant components that are not related to a potential bearing fault. The remaining components, i.e., the noise-cancelled stator current, are then closely related to the health condition of the bearing. Furthermore, it is observed that under the presence of a bearing fault, the noise-cancelled stator current displays a significant amount of degrees of uncontrolled variation in its magnitude. The uncontrolled variation is detected by observing the samples falling outside the three-sigma limits on Shewhart's control charts. Therefore, it is possible to detect <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">situ</i> bearing faults by detecting the variation in magnitude of the noise-cancelled stator current, as verified by online experiments performed in this paper.

A New Power-Factor-Based Vector Control Method for Sensorless Drive of Permanent-Magnet Synchronous Motors -Simplification and Conversion to Voltage Reference Frame-

As a simple vector control method for sensorless drives of permanent-magnet synchronous motors, the so-called “Power-Factor-Based (PFB) Vector Control Method” has been proposed. The conventional PFB method directly estimates the phase of the quasi-optimal stator current through a control of the power factor phase, instead of the estimation of the rotor phase. The stator current is controlled in the current reference frame whose secondary axis phase is the same as the stator current phase. This paper proposes a new PEB method where the stator current is controlled in the voltage reference frame whose secondary axis phase is the same as the voltage phase rather than the current phase. It is shown that the similar quasi-optimal stator current control can be attained through the current control with appropriate current commands taking the power factor phase into account. This paper also shows a practical method for generating the current commands and a practical guideline for the design parameters of the new PFB method.

Predictive Stator Current Control for Medium Voltage Drives With LC Filters

The switching frequency of power semiconductor devices in high-power medium voltage drives is limited due to high switching losses. These drives often comprise an <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> output filter. The filter introduces a resonant circuit that may be excited, for instance, by fast control transients. One option to avoid such oscillations is to apply damping control methods, which on the other hand usually require switching frequencies well above the filter resonance. This paper presents a predictive stator current controller that avoids the excitation of the filter resonance, realizes active damping and enables fast current control while maintaining low switching frequency. Feasibility and good dynamic performance of the proposed control method is demonstrated by simulation results of a 2.4 kV induction motor drive and by experimental results obtained from a 55 kW prototype ac drive.

Bearing Fault Detection Via Stator Current Noise Cancellation and Statistical Control

This paper proposes a new approach to detect in situ bearing faults via stator current monitoring. For in situ bearing faults, the characteristic bearing fault frequencies may not exist, particularly at an early stage. In addition, the bearing fault signatures are usually subtle compared to the dominant components in the sampled stator current. Therefore, in this paper, a noise cancellation technique is used to suppress those dominant components that are not related to a potential bearing fault. The remaining components, i.e., the noise-cancelled stator current, are then closely related to the health condition of the bearing. Furthermore, it is observed that under the presence of a bearing fault, the noise-cancelled stator current displays a significant amount of degrees of uncontrolled variation in its magnitude. The uncontrolled variation is detected by observing the samples falling outside the three-sigma limits on Shewhart's control charts. Therefore, it is possible to detect in situ bearing faults by detecting the variation in magnitude of the noise-cancelled stator current, as verified by online experiments performed in this paper.

Two simple and novel SISO controllers for induction motors based on adaptive passivity

The design of two single-input single-output (SISO) controllers for induction motors based on adaptive passivity is presented in this paper. The two controllers work together with a field orientation block. Because of the adaptive nature of the proposed controllers, the knowledge of the set motor–load parameters is not needed and robustness under variations of such parameters is guaranteed. Simple proportional controllers for the torque, rotor flux and stator current control loops are used, due to the control simplification given by the use of feedback passive equivalence. A new principle called the “Torque–Flux Control Principle” is also stated in this article, which considerably simplifies the controller design, diminishing the control efforts and avoiding also rotor flux estimation.

PMSMセンサレス駆動のための力率位相形ベクトル制御法

This paper proposes a new simple vector control method for sensorless drive of permanent-magnet synchronous motors (PMSMs). The proposed method takes an approach to estimate directly phase of the quasi-optimal stator current through control of the power factor phase instead of estimation of rotor phase. It is established based on new analysis of motor characteristics and has the following attractive features: 1) it can be applied to both of salient and non-salient pole PMSMs; 2) stator current control quasi-minimizing copper and/or iron loss is directly performed; 3) it is insensitive to motor parameter variation, and does not requires motor parameters with precision; 4) it is simple. Simple and practical rules for selecting design parameters of the method are clearly given based on the analysis. Effectiveness of the analysis and usefulness of the proposed method are verified through experiments.

Torque ripple reduction in exterior-rotor permanent magnet synchronous motor

The paper presents torque ripple reduction in permanent magnet synchronous motor with exterior-rotor. The influence of the magnet pole arc width and the influence of the supply current waveform on the torque ripple are considered in the analysis. The results of the analysis are obtained by the finite element method simulation and are verified experimentally as well. The reduction of total torque ripple at nominal load conditions less than 2% is achieved by proper motor magnet pole arc design and by applying the optimal stator current waveform control.

Feedback-Linearizing Control of IPM Motors Considering Magnetic Saturation Effect

This paper describes feedback-linearizing control of interior permanent magnet (IPM) motors which operate in magnetic saturation. First, we propose a current tracking controller for direct control of stator currents. Then, we explicitly characterize all torque controllers that can make the motor torque of an IPM motor exactly linear with respect to torque command even if magnetic saturation occurs. In particular, our torque controller contains a free function that can be used to achieve other control objectives as well as linear dynamic characteristics. Finally, the free function is chosen so optimal as to maximize power efficiency. The practical use of our control method is demonstrated through various simulation and experimental results.

Advanced Current Regulated PWM Inverter with Simplified Load Model

In the article, a new stator current controller for voltage source inverter is presented. The proposed controller is based on back-emf calculation and applied to induction motors. The controller sensitivity to load parameters is discussed. The proposed controller is based on the model of inverter load with inductance and back-emf. Load resistance is neglected assuming that switching period is small enough that the average voltage drop across the resistance may be included in the back-emf. Constant switching frequency is used in the proposed system. The controller is realized in simulation and experimentally using fixed-point digital signal processor (DSP) and programmable field programmable gate arrays (FPGA).

A digital current control technique for voltage-fed induction motor drives

Precise control of stator current is essential to high performance field orientationcontrolled induction motor drives. Any current error degrades the performance ofthe drive in the same way as incorrect tuning of field orientation. Previous researchhas shown that accurate current control can be achieved with intelligent butcomplex control algorithms. This paper presents a new current control schemewhich can achieve high accuracy and fast dynamic response but which is verysimple for microprocessor implementation. The scheme was derived using thediscrete state space modelling of the induction motor. The control law does notrequire knowledge of rotor flux and was independent of the field orientation controltuning. Good static and dynamic performances were obtained in both thesimulation and experimental verifications. The results also show that the leakageinductance model error might cause a current ripple. However, this parameter canbe tuned to its correct value easily by inspecting the current response.

Control of induction motors: an adaptive passivity MIMO perspective

AbstractThe design of two multiple‐input multiple‐output (MIMO) controllers for induction motors, based on adaptive passivity, is presented in this paper. The controller design method is based on concepts of equivalence passivity via adaptive feedback, previously developed by the authors. Robustness under variations of the motor‐load parameters is guaranteed and the knowledge of such a parameters is not needed in the design. Simple proportional controllers for the torque, rotor flux and stator current control loops are used, due to the control simplification introduced by the use of feedback passive equivalence. A principle called ‘Torque‐Flux Control Principle’ is used in this article introducing a considerable simplification in the resultant controller. Because of the employment of this principle, the control efforts are diminished and rotor flux estimation (or measurement) is avoided. Copyright © 2003 John Wiley &amp; Sons, Ltd.

A deadbeat current controller for field oriented induction motor drives

Accurate stator current control is essential in high performance field orientation-controlled induction motor drives. Any current error degrades the drive's performance in the same way as an incorrectly tuned field orientation. This paper presents an efficient current control scheme that can achieve high accuracy and a fast dynamic response. This scheme uses voltage decoupling and deadbeat control loops. The decoupling controller provides the voltage needed to oppose the motor's back EMF. The deadbeat controller reduces the current error as fast as possible and stabilizes the system. The control law does not require knowledge of the rotor flux and is independent of the field orientation control tuning. Good static and dynamic performances were obtained in both the simulation and experimental verifications. Because the motor leakage inductance and resistance information were required for this control method, the influence of the estimation errors for these parameters was also investigated. The results show that the leakage inductance model error might cause a current ripple. However, this parameter can be tuned to its correct value easily by inspecting the current response.