Stator Current Control Research Articles

Tuning of modern speed drives using IFOC: A case study for a five-phase induction machine

Electric machines have existed since the beginning of the 19th century. Although variable-speed drive technology has evolved considerably during the last years, the indirect field-oriented control technique has been in use as a standard control method since the 1960s, using an outer speed loop and an inner current loop. This paper deals with the non-trivial problem of tuning the outer speed controller of modern variable-speed drives, where experimental results are provided to show the need for new tuning methods. The influence of non-modeled effects on the performance of the drive is illustrated considering the dynamical effect of the mechanical speed sensing procedure using optical devices. This effect has not been generally considered. However, it is shown that it has a notable effect on tuning for high performance drives. This is especially true when considering some figures of merits of relevance for drives, such as the torque ripple. A Pareto analysis is proposed to reveal trade-offs between typical figures of merit to establish new tuning methods. To focus our contribution, a five-phase induction drive is considered as the case study, using a finite-state model predictive controller for the stator current control and PI regulators for the outer speed control loop.

Coordinated Control of Transient Voltage Support in Doubly Fed Induction Generators

The large-scale integration of wind power significantly alters the voltage dynamic characteristics of power systems. Wind turbines have a weak ability to withstand grid disturbances and have difficulty in providing effective reactive power support during transient periods. The sensitivity of wind turbines to the grid voltage significantly increases the probability of large-scale, cascading off-grid events. This paper proposes a coordinated control strategy to enhance the transient reactive power support capability of doubly fed wind farms. The additional stator current demagnetization control reduces the risk of a crowbar protection action after a fault and ensures that the unit power is controllable. Based on the voltage–reactive power coupling relationship, each unit can produce reactive power according to the voltage–reactive power sensitivity matrix during the transient period. After the reactive power output of the unit reaches the limit, transient active and reactive combined control is further adopted to reduce the active power output of the unit to a certain extent and improve the reactive power support capability. Finally, two cases are built in the PSCAD to verify the effectiveness of the proposed control strategy. The results show that the proposed control strategy can enable the wind farm to output more reactive power to the grid during the transient period, effectively supporting the system voltage during the transient process and avoiding further deterioration of the fault.

Speed Measurement Delay and its Influence on IFOC Tuning

The Indirect Field-Oriented Control technique has been in use since the 1960s, with some innovations added to the basic original setting. Although variable-speed drive technology has evolved considerably, basic assumptions remain in place. This paper deals with the problem of sensing the mechanical speed using optical devices. This aspect has not been considered in previous works. To focus the contribution, finite-state model predictive control is used in this paper for stator current control. The outer (speed) loop considers PI control as is usually the case. The experimental results presented here show the need for new tuning methods.

Multi-Phase Stator Current Tracking with Gradual Penalization of Commutations

Energy efficiency in drives is an important issue. In converter-supplied variable-speed drives, switching losses can amount to a significant portion of all losses. This has been considered in Predictive Stator Current Control (PSCC), considering commutations at the power converter. However, in multi-phase drives, the computational burden limits the application of said techniques. Recent fast predictive algorithms have enabled shorter application times with enhanced tracking results. However, the switching frequency becomes larger with diminishing sampling periods. This paper presents a method that retains the fast computation of recent methods while reducing the switching frequency. The proposal revolves around a modification of the cost function to penalize commutations in a nonlinear way. For this task, a novel, gradual penalization is introduced. The method is experimentally applied to a five-phase induction motor. Experimental results show a significant reduction in switching frequency without compromising other control objectives. This results in an enhanced PSCC with a small sampling period and reduced switching losses.

Evolutionary Gaps Stator Current Control of Multiphase Drives Balancing Harmonic Content

Evolutionary Gaps Stator Current Control of Multiphase Drives Balancing Harmonic Content

SPEED CONTROL OF PERMANENT MAGNET SYNCHRONOUS MOTOR IN SLIDING MODE

The paper examines a series of speed control algorithms for a synchronous permanent magnet motor in sliding mode, providing asymptotic stability of the first, second, and third order. In the sliding mode, the control system exhibits properties that are unattainable with classical continuous control algorithms. The control algorithms are developed based on the inverse dynamics method combined with the minimization of local instantaneous energy functionals. The key idea of the method lies in the reversibility of the direct Lyapunov method for stability analysis. The closed-loop control system has a predefined Lyapunov function, represented by the instantaneous energy. Notably, the control algorithms do not require knowledge of the object's parameters or differentiation operations, which facilitates their practical implementation. The regulator parameters consist solely of coefficients used to specify the desired duration and shape of current and motor speed transient processes. The vector speed control system comprises two controllers for the stator current components and the motor speed controller. All regulators operate in sliding mode. The output signals of the stator current component controllers and speed vary discontinuously from maximum to minimum values. Simulation results demonstrate the effectiveness and high-quality performance of the control algorithms. To determine the control performance indicators for the three synthesized speed controllers, the motor startup trajectory is formed from characteristic segments of constant, linearly increasing, and parabolic signals. The speed control algorithm with a first-order asymptote ensures zero tracking error only for a constant reference signal. With a linearly increasing reference signal, the steady-state relative tracking error is 2,5 %, while for a parabolic reference signal, the error varies between zero and 2,5 %. The second-order asymptotic speed control algorithm ensures zero steady-state tracking error for constant and linearly increasing reference signals, and for a parabolic reference signal, the steady-state relative tracking error is 0,125 %. The third-order asymptotic speed control algorithm ensures zero steady-state tracking error for constant, linearly increasing, and parabolic reference signals, with a maximum dynamic relative tracking error of 0,05 %.

50 YEARS FIELD ORIENTED CONTROL OF THREE-PHASE AC DRIVES IN THE PRACTICE - THE STATE OF THE ART

From DC motors (DCM) we know, it is possible to independently control the two currents of the flux and torque generating. Because the two DCM circuits are completely isolated, we obtain simple adjustment algorithms that require little computing time on the microprocessor. For this reason, DCM has been at the forefront of the application of digital controls in drive control systems in the early years, especially in high-performance systems. On the contrary, the three-phase AC motor (ACM) has a complex structure due to the winding system and three-phase power supply, and has caused significant difficulties in the mathematical description of the above decoupling characteristics. The purpose of the field-oriented control (FOC) is therefore to create a tool that allows the decoupling control of the flux and torque-producing current components from the three-phase AC currents flowing in the coil. The FOC drive system is a system based on the principle of decoupling the above power components thanks to the stator current feedback control (the innermost circuit of the drive system). The FOC-type control method belongs to the class of vector control methods for electrical machines. On the occasion of the 50th anniversary of FOC, this paper aims to provide an overview of the development status of FOC in industrial practice. The content presented deals mainly with 3-phase induction motors.

Study and Evaluation a New Predictive Control Method for Speed and Stator Current Control of Induction Motor

It is clear that modern industries rely heavily on electric motors, especially induction motors. These motors convert electrical energy into mechanical energy. The distinction in the performance of the induction motor lies in that it is powerful when exposed to various operational and environmental variables, and it is also inexpensive. However, there are many traditional disadvantages that appear during the operation of the induction motor in its non-linear mechanical properties in addition to the difficulty in regulating the speed of the motor. In this paper , we present a new control method for controlling the stator current and speed of induction motor based on current control with speed control technique. The present model is based on conventional predictive controller development with a structure which is similar to rotor control and the direct torque control .It has double loops and both loops will use the prediction power. The inner loop controls the stator current based on Finite Control Set - Model Predictive Control (FCS-MPC) and the outer loop controls the speed to maximize the dynamic response of the loop. The MATLAB software has been used to implement the controller circuit. The obtained simulation results indicates that the presented control method has comparable performance to conventional controllers with some reduction in the overshoot and fast response interval.

Stabilization of LC-Filtered PMSM Drives With Modulated Predictive Stator Current Control

Stabilization of LC-Filtered PMSM Drives With Modulated Predictive Stator Current Control

Enhanced Control of Back-to-Back Converters in Wind Energy Conversion Systems Using Two-Degree-of-Freedom (2DOF) PI Controllers

The performance of a full-scale wind energy conversion system is dependent on the control system of the back-to-back power electronics converter. Different controllers have been proposed in the literature, many of which are variations of a generalized two-degrees-of-freedom (2DOF) PI controller. This paper presents a design method for the parameters of a 2DOF PI controller for the stator current, generator speed, grid current, and DC bus voltage control. The controller can be designed using a general independent zero and pole placement method. The proposed and conventional methods are analyzed based on their ability to track references, reject disturbances, and their sensitivity to noise. A tuning approach is proposed to enhance the controller’s bandwidth without sacrificing noise sensitivity or disturbance rejection capability. The conventional methods are shown to be special versions of the proposed design. Simulation results demonstrate the effectiveness of the proposed design.

Моделирование динамических режимов работы электроприводов с системой векторного управления синхронным двигателем

Purpose: The purpose of the work is a comparative assessment of dynamic processes in electric drives with a vector control system for permanent magnets synchronous motors and various methods of stator voltage modulation. To achieve this purpose, a mathematical description of a synchronous motor in a rotating dq coordinate system is given, and a mathematical model of a vector control system is developed. The model of the vector control system takes into account the decoupling of stator current control loops and proposes two options for generating a current reference along the d-axis, ensuring the efficiency of energy conversion processes at rotation speeds below the nominal value, depending on the design of the motor rotor. Algorithms for scalar pulse-width and space-vector modulation of motor stator voltage for a frequency converter with a two-level autonomous voltage inverter are presented. Methods: When developing mathematical models and algorithms, methods from the theory of electric drive and the theory of automatic control have been used. The developed mathematical models and algorithms are implemented in the Matlab Simulink software package. Results: The results of modeling dynamic processes in electric drives (mechanical characteristics, stator currents, stator current total harmonic distortion) are presented, which have shown the performance of the developed models and algorithms. Practical significance: The choice of modulation type does not affect the mechanical characteristics of the electric drive, but does affect the harmonic composition of the stator current. The greatest effect from the use of space-vector modulation algorithms is manifested at reduced values of the frequency of the stator current and partial load torque on the rotor shaft.

Generalized Data-Driven Model-Free Predictive Control for Electrical Drive Systems

The performance of model predictive control has a strong correlation to the precision of the physical parameters of the plant, and these parameters are hard to determine since they are continuously changing during the operation process. To fully eliminate the influence of the physical parameters and enhance robustness, a model-free predictive control is proposed in this article to suit the electrical drive systems. The plant model is designed as several discrete-time transfer functions used to decouple the input and output signals and to describe their relationships, and the coefficients of these functions are online designed based on the recursive least square algorithm. An observer is designed to obtain accurately sampled current components considering the delays. The proposed method is applied to a permanent magnet synchronous motor speed control system as the stator current controller, and the simulation and experimental results show the advantages of the improved dynamics, stator current quality, and robustness compared with the conventional model-free predictive current control strategy.

Adaptive control of DFIG-based wind turbines for fault ride-through and reactive power support based on stator current transient component

The fault ride-through performance is improved through the control of the transient components of the stator current. The reactive power provided by the DFIG within the margin of the converter can significantly enhance the grid-connected safety of the DFIG. Firstly, the reasons for the fault overcurrent of the DFIG’s rotor are analyzed. Secondly, according to the operating conditions of the wind turbine, the reactive power support limit of the DFIG-based wind turbines based on the stator current transient component control is analyzed, and an adaptive reactive power support control suitable for fault ride-through is proposed to maximize its support potential for grid-connected voltage. Finally, the DFIG can not only suppress the rotor overcurrent through the transient component of the stator current but also have a reactive power support capability that is superior to the grid-connected standard.

MAXIMUM POWER EXTRACTION USING TWISTING SLIDING MODE CONTROLLER FOR WIND ENERGY SYSTEMS

This paper presents a systematic control scheme for a wind energy conversion system with variable speed and describes a permanent magnet synchronous generator PMSG with five phases. The machine employs back-to-back converters, while the grid-side converters are used. Stator current and mechanical rotation speed control are employed to accomplish maximum power point tracking operation on the machine side converter at wind speed below the rated speed. The pitch of the angle is used to limit the extracted wind energy when the wind surpasses the specified wind. The grid current control loop regulates both active and reactive power injection at the unity power factor for the grid side converter. The five-phase PMSG rotor speed is controlled by the twisting sliding mode controller in order to maintain the reference speed in various wind speeds. Performance comparisons between the twisting sliding mode controller, conventional proportional integral controller, and integral sliding mode controller show that the twisting sliding mode controller is superior to the other controllers in steady state error. According to this study, the overall efficiency is increased to 94% when using the TSMC controller rather than the ISMC and PI controllers, which are currently at 92.45% and 88.12% respectively. MATLAB/Simulink simulation results are used to verify the effectiveness of the suggested control technique.

Deadbeat Power Distribution Control of Single-Stage Multiport Inverter-Fed PMSM Drive for Hybrid Electric Vehicles

Single-stage multiport inverter (SSMI)-fed motor drives are promising solutions for multisource hybrid electric vehicles (HEVs) since the dc-dc converter is removed and all the active power is delivered within a single power conversion stage. However, this topology presents inherent coupled issues in controller design because power distribution should be achieved simultaneously in addition to stator current control. To address this issue, an equivalent two-level model is proposed to achieve decoupled control of the SSMI, where stator current control is achieved by regulating the active vectors, and power distribution is achieved by regulating the zero vectors. A deadbeat power distribution scheme is developed under the equivalent two-level model. The proposed scheme provides these advantageous features: fewer computational burdens without complicated sector selection and dwell time calculation under the unevenly distributed voltage vector diagram, fewer adjusted parameters, and fast dynamic response. Moreover, the power distribution capability of the SSMI with the proposed scheme is also analytically revealed. A series of experimental results demonstrate the excellent performance of the proposed deadbeat power distribution control scheme.

Predictive Stator Current Control of a Five-Phase Motor Using a Hybrid Control Set

Finite state model predictive control (FSMPC) of multiphase drives can use an extra number of inverter configurations compared with the three-phase case. This, however, requires more computing power for the optimization phase. The application time of each selected voltage vector (VV) is then increased, which can result in higher harmonic content. Reducing the allowed VVs can speed up the computations, thus ameliorating the current tracking/regulation in different orthogonal subspaces. However, the flexibility offered by the reduced set of VVs is less than that of the full set. Furthermore, a lower sampling time can result in an increase in the switching frequency, especially for some speed-load combinations. This article proposes the use of a hybrid scheme where the set of allowed VVs is not fixed but rather selected on-line according to the actual speed and torque producing stator current which are computed by the outer loop. A five-phase induction machine (IM) is used as a test bed for the proposal, showing improved results with respect to the nonhybrid case.

Enhanced Reaching-Law-Based Discrete-Time Terminal Sliding Mode Current Control of a Six-Phase Induction Motor

This paper develops an inner stator current controller based on an enhanced reaching-law-based discrete-time terminal sliding mode. The problem of tracking stator currents with high accuracy while ensuring the robustness of a six-phase induction motor in the presence of uncertain electrical parameters and unmeasurable states is tackled. The unknown dynamics are approximated by using a time delay estimation method. Then, an enhanced power-reaching law is used to make each stage of the convergence faster. A stability analysis and the system controller’s finite-time convergence are demonstrated in detail. Practical work was conducted on an asymmetrical six-phase induction machine to illustrate the developed discrete approach’s robustness and effectiveness.

Discrete-Time Complex-Vector Model Based Closed-Loop Current Controller for CSC-Fed PMAC Machine Systems With Low Carrier Ratios

Pulsewidth modulated (PWM) current-source converters (CSCs) have been attractive for high-power adjustable-speed machine systems with low carrier ratios. However, the high-order nonlinear model of CSC-fed machine systems, the distinct digital delay from the low carrier ratios, and the cross-coupling caused by coordinate transformation bring great challenges to design of high-performance stator current controller for such kind of machine systems. Firstly, this article derives the discrete-time complex-vector model for the CSC-fed permanent-magnet ac (PMAC) machine system with low carrier ratios considering the distinct digital delay and cross-coupling effect mentioned above. On that basis, the stator current controller is proposed with the modified controller parameters and the compensation technique to improve both dynamic performance and stability of the CSC-fed PMAC machine systems with low carrier ratios. The theoretical analysis and controller design process have been presented in detail to provide a guide for the model derivation and controller design. The experiments on a laboratory prototype are conducted to verify the effectiveness of the developed modeling and controller.

Improved Sliding Mode Traction Control Combined Sliding Mode Disturbance Observer Strategy for High-Speed Maglev Train

To improve the robustness and dynamic tracking performance of the stator current control for the long stator linear synchronous motor (LSLSM) used in high-speed maglev train traction system, a composite current control strategy combining a sliding mode current controller (SMCC) and a sliding mode disturbance observer (SMDO) is proposed in this article. First, the LSLSM mathematical model in double feed mode is optimized. Then, an SMCC is designed based on the model. An improved stability criterion is proposed and the SMCC switching gain is obtained quantitatively to meet the current following speed required for the stator changeover process. As disturbance factors, parameter perturbation of the LSLSM and the stator changeover will bring about transient current fluctuations and chattering. Therefore, an SMDO is designed to estimate the disturbances and perform feed-forward compensation for the SMCC, thereby improving the robustness and suppressing the current chattering. Finally, the hardware-in-the-loop experiments verify the effectiveness of this strategy and compare it with the traditional current control strategy.

Control for induction motor drives using predictive model stator currents and speeds control

<span>This paper is presented for designing a new controller using the predictive model current and speed control method for the asynchronous motor. This control method is based on traditional predictive controller development to have a cascade structure similar to the rotor flux control (field-oriented control) and direct torque control (DTC). Therefore, this control method will have two control loops. Both inner and outer loop controllers use predictive power. The outer ring is speed control, while the internal circle is stator current control. The inner loop is based on the finite control set – model predictive control (FCS-MPC), while the outer ring to take full advantage of the high dynamic response of the inner circle uses the deadbeat MPC. MATLAB simulation results show that this control method has performance equivalent to traditional controllers while minimizing overshoot and having fast, on-demand response times.</span>