Shafiq Ahmed Odhano

Maximum Efficiency per Torque Direct Flux Vector Control of Induction Motor Drives

In this paper, a loss-minimizing strategy is proposed for induction motor drives to ensure maximum efficiency operation for a given torque demand. The proposed strategy directly regulates the machine stator flux, according to the desired torque, using an optimal stator flux reference. Therefore, the proposed strategy is suitable for motor control schemes that are based on direct flux regulation, such as direct torque control or direct flux vector control. The maximum efficiency per torque (MEPT) stator flux map is computed offline using the traditional no-load and short-circuit test data. An iron loss model based on the stator flux and frequency is also proposed for the calibration of the machine loss model and also for online monitoring of the iron losses during motor operation. The proposed MEPT strategy has been validated on a 2.2-kW induction machine, and the motor efficiency has been measured for different speed values and variable load conditions. The experimental results confirm the effectiveness of the proposed solution.

Self-commissioning of Interior Permanent Magnet Synchronous Motor Drives With High-Frequency Current Injection

In this paper, a simple and robust method for parameter estimation at rotor standstill is presented for interior permanent magnet (IPM) synchronous machines. The estimated parameters are the stator resistance through dc test, the dq inductances using high-frequency injection, and the permanent magnet flux by means of a closed-loop speed control maintaining rotor stationary. The proposed method does not require either locking the rotor or additional/special power supplies. The validity of the suggested method has been verified by implementation on two IPM motor prototypes. Finally, the estimated parameters have been compared against results obtained through finite-element simulations and with machine magnetic characterization, separately performed, to validate the methods effectiveness. Saturation and cross-saturation effects are taken care of through amplitude modulation and cross-axis current application, respectively.

Identification of the Magnetic Model of Permanent-Magnet Synchronous Machines Using DC-Biased Low-Frequency AC Signal Injection

This paper proposes a simple procedure for accurate identification of the magnetic model of permanent-magnet synchronous machines through inverter supply. The proposed method accounts for the magnetic saturation and the cross-saturation effects. The identification methods reported in the literature may require a servomotor to drive the motor under test at controlled constant speed or the motor itself must accelerate and decelerate. The technique proposed here can be applied at standstill with or without rotor locking and uses a dc+ac injection strategy to identify the machine inductances to construct its magnetic model. The direct current sets the operating point, whereas the superimposed ac component estimates the inductance at that particular point. Small ac signal is injected to ensure local linearity of the magnetic characteristic. Saturation effects are automatically accounted for by the dc bias level, and cross-saturation effects are quantified through maintaining a constant current along the cross-axis. The magnetic model thus obtained can be used for optimal control of the machine and for accurate torque estimation in vector-controlled drives.

Unified direct-flux vector control of induction motor drives with maximum torque per ampere operation

This paper deals with the Maximum Torque per Ampere (MTPA) operation of induction motor drives using Unified Direct Flux Vector Control (UDFVC). The UDFVC has been introduced in the past as a unified direct flux and vector control approach for both synchronous and asynchronous AC motor drives. The control is implemented in stator flux coordinates with the stator flux being directly controlled by the ds-axis voltage component, while the machine torque is controlled through qs-axis current component regulation using the qs-axis voltage component. The stator flux amplitude is generated using only the torque demand as the input of an MTPA profile that is particular for the AC machine being controlled, without the need of other complex LUTs and motor mapping. In this way, the optimal machine exploitation is reduced to a proper stator flux reference computation that can be done offline using the data from the standard no-load and short-circuit tests. The effectiveness of the proposed solution is verified through intensive experimental tests conducted with a 2.2 kW induction machine. The steady-state MTPA operation, the drive efficiency performance and the transient drive performance are presented.

Finite control set and modulated model predictive flux and current control for induction motor drives

The paper presents a new implementation of direct flux and current vector control of an induction motor drive using the techniques of model predictive control. The advantages offered by predictive control are used to enhance the dynamics of direct flux vector control. To minimize the problems of variable switching frequency inherent to finite control set predictive control, an alternative approach using pulse width modulation is studied for command execution as occurs in the so-called modulated model predictive control. A comparison between finite control set and modulated model predictive control is presented and the results are also compared with the control implementation through traditional proportional-integral regulators to highlight the advantages and drawbacks of predictive control based strategies. Apart from a greater harmonic content in stator currents, the predictive control can offers control dynamics comparable with proportional-integral control while maintaining immunity against machine parameter variations and excluding the need for controller tuning.

Unified direct-flux vector control of induction motor self-commissioning drive with analysis of parameter detuning effects

This paper analyses the detuning effects of machine electrical parameters on the performance of unified direct flux vector control (UDFVC) of induction motor drives. Drive self-commissioning is discussed as a way to estimate parameters for better control performance and accurate torque estimation. The potential of the unification of direct flux and current vector control has been recognized for both synchronous and asynchronous AC motor drives in the literature. This control operates in (ds, qs) stator flux coordinates with the stator flux being directly controlled by the ds axis voltage vector component. Machine torque is controlled using a current controller in qs-axis. Results for the effects of parameter mismatch on control performance are given. In this work, the detuning problem is overcome by drive self-commissioning which estimates machine parameters at start up through special tests at standstill.

Design of a repetitive controller as a feed-forward disturbance observer

From the structure point of view, a repetitive controller (RC) is considerably similar to a disturbance observer. By adding a correction term to the traditional RC and considering the disturbances as states, the repetitive controller can be designed in the same way as a disturbance observer. This paper presents therefore a new simple way of tuning a repetitive controller. Simulations show that, when compared with the traditional RC, the proposed RC configuration can achieve greater stability margin. As opposed to the traditional plug-in RC, the new RC structure studied in this paper is also shown to be robust against variations in the inner loop delays if it is used in a cascaded configuration. The immunity to plant parameter variations is another added benefit of the proposed controller.

Self-commissioning of interior permanent magnet synchronous motor drives with high-frequency current injection

The knowledge of electrical and mechanical parameters of high-performance electromechanical drive systems is of paramount importance for designing high-performance controllers and/or developing accurate simulation models. By high-performance control is meant least torque (position) ripple for torque (position) control. Machine parameters are typically load and temperature dependent. This makes their estimation a challenging task. In this paper, a simple and robust method for parameter estimation at rotor standstill is presented. The estimated parameters are stator resistance through dc test, dq inductances using high-frequency injection and permanent magnet flux by means of a closed-loop speed control maintaining rotor stationary. The proposed method does not require either locking the rotor or additional/special power supplies. The validity of the suggested method has been verified by implementation on Interior Permanent Magnet Synchronous Motors (IPMSMs). Finally, the estimated parameters have been compared against results obtained through finite element simulations and with machine magnetic characterization, separately performed, to validate the methods effectiveness. Saturation and cross-saturation effects are taken care of through amplitude modulation and cross-axis current application, respectively.

Modulated model predictive control with optimized overmodulation

Finite-set model-predictive control (FS-MPC) has many advantages, such as a fast dynamic response and an intuitive implementation. For these reasons, it has been thoroughly researched during the last decade. However, the waveform produced by FS-MPC has a switching component whose spread spectrum remains a major disadvantage of the strategy. This paper discusses a modulated model-predictive control that guarantees a spectrum switching frequency in the linear modulation range and extends its optimized response to the overmodulation region. Due to the equivalent high gain of the predictive control and to the limit on the voltage actuation of the power converter, it is expected that the actuation voltage will enter the overmodulation region during the large reference changes or in response to load impacts. An optimized overmodulation strategy that converges toward the FS-MPC ’s response for large tracking errors is proposed for this situation. This technique seamlessly combines PWM’s good steady-state switching performance with FS-MPC ’s high dynamic response during large transients. The constant switching frequency is achieved by incorporating modulation of the predicted current vectors in the model-predictive control of the currents in a similar fashion as the conventional space-vector pulsewidth modulation is used to synthesize an arbitrary voltage reference. Experimental results showing the proposed strategy’s good steady-state switching performance, its FS-MPC -like transient response, and the seamless transition between modes of operation are presented for a permanent magnet synchronous machine drive.

Model predictive direct flux vector control of multi three-phase induction motor drives

A model predictive control scheme for multiphase induction machines, configured as multi three-phase structures, is proposed in this paper. The predictive algorithm uses a Direct Flux Vector Control scheme based on a multi three-phase approach, where each three-phase winding set is independently controlled. In this way, the fault tolerant behavior of the drive system is improved. The proposed solution has been tested with a multi-modular power converter feeding a six-phase asymmetrical induction machine (10kW, 6000 rpm). Complete details about the predictive control scheme and adopted flux observer are included. The experimental validation in both generation and motoring mode is reported, including post open-winding fault operations. The experimental results demonstrate the feasibility of the proposed drive solution.