Iordanis Kioskeridis

Loss minimization in induction motor adjustable-speed drives

A loss model controller (LMC) for determining the optimal air-gap flux that minimizes the losses in scalar controlled induction motor drives is presented. The suggested LMC is simple, and its implementation does not affect significantly the cost and the complexity of the drive. Although the conception of the suggested LMC is based on the loss model of the induction motor, it is shown that its realization does not require knowledge of the loss model.

Loss minimization in scalar-controlled induction motor drives with search controllers

Loss minimization in scalar-controlled induction motor drives (IMD) with search controllers (SC) is investigated. The problems arising when the input power is used as the controlled variable are described. It is proved that better results are achieved if the stator current is used as the controlled variable.

Optimal efficiency control of switched reluctance generators

This paper investigates the problem of optimal control for accomplishing maximum energy conversion in switched reluctance generators. A controller that determines the optimal turn-on and turn-off angles in the mode of single-pulse operation is proposed. The structure of the controller and its implementation are simple, since the knowledge of the magnetization curves is not required. The suggested generator drive operates in a wide speed range and provides constant dc-link voltage at a desired value, with maximum energy efficiency. Simulation and experimental results are presented to validate the effectiveness and the resulting improvements of the proposed control scheme.

Optimizing performance in current-controlled switched reluctance generators

The problem of choosing the firing angles for accomplishing optimal performance in current-controlled switched reluctance generators (SRGs) is examined. The optimal performance is reached with the correct balance between the criteria of high efficiency and low torque ripple. The concept of the method is based on the optimal control of turn-on and turn-off angles according to electrical load requirements and depending on rotor speed and dc-link voltage. A simple controller is proposed that on-line determines the optimal firing angles. The suggested controller does not affect the complexity of the drive and the knowledge of the magnetization curves is not required for its implementation. Simulation and experimental results are presented to validate the resulting improvements of the proposed control scheme.

Gain-Scheduling Regulator for High-Performance Position Control of Switched Reluctance Motor Drives

The problem of high-precision position control in switched reluctance motor (SRM) drives is investigated in this paper. Advanced proportional-integral and proportional-differential controllers for speed and position controls, respectively, are adopted. A gain-scheduling technique is adopted in the speed controller design for providing high dynamic performance and precise position control. In order to improve the set-point tracking, a low-pass filter is included in the position controller. The proposed four-quadrant control scheme is based on the average torque control method. The turn-on and turn-off angles are online determined through simple formulas so as to reduce the torque ripple at an acceptable level over a wide speed range. This is important since the position precision is highly influenced from the motor torque ripple. Experimental results of the SRM dynamic response are presented to verify the theoretical considerations and to demonstrate the effectiveness of the proposed control scheme.

Optimization of single-phase induction Motors-part I: maximum energy efficiency control

This work investigates the problem of efficiency optimization in capacitor-run single-phase induction motors. The double-revolving-field concept is employed in the theoretical analysis and a relation between the main and auxiliary stator currents is derived that accomplishes optimal efficiency under constant torque operation. A triac-based drive with an optimal efficiency voltage controller is proposed. The controller is easily implemented since an experimental procedure is used for adjusting its parameters. Moreover, the proposed control scheme satisfies all of the prerequisites of simplicity, reliability, and cost-effectiveness that are imposed by the utilization of a single-phase motor. Several experimental results are presented to validate the effectiveness of the proposed efficiency optimization control method.

High-Efficiency Control for a Wind Energy Conversion System With Induction Generator

In this paper, an improved efficiency control scheme for wind energy conversion systems (WECSs) with squirrel cage induction generators is proposed. Thus, the power harvesting from the WECS is increased and additionally expansion of the exploitable wind speed region toward the lower speed range is accomplished. The generator is connected to the power grid by means of two space-vector-controlled back-to-back converters. A minimum ohmic loss (MOL) controller is introduced in order to minimize the generator resistive loss that is accomplished by adjusting the d-axis stator current according to torque conditions. The implementation of the proposed controller is easy and cost effective because neither additional control signals nor the knowledge of the generator loss model is required. The effectiveness of MOL controller and its successful cooperation with two types of maximum power point tracking (MPPT) controllers, which are employed to maximize the wind turbine output power, are experimentally verified. The MPPT controller is implemented by using an adaptive search control and a fuzzy-logic-based control technique, since both are independent of wind turbine characteristics and widely used. Selective experimental results are presented to demonstrate the resulting improvements of the suggested control scheme.

Optimal Efficiency Control Strategy in Wind Energy Conversion System With Induction Generator

This paper presents an optimal efficiency control strategy for wind energy conversion systems (WECSs) with squirrel cage induction generators (SCIGs). The developed control scheme provides an optimal efficiency of the induction generator and maximum power extraction from the wind turbine. Thus, maximum power harvesting from the whole WECS is achieved and additionally expansion of the exploitable wind speed region toward the lower speed range is accomplished. A minimum electric loss (MEL) controller is introduced to minimize the generator electric loss and a maximum power point tracking (MPPT) controller is used to maximize the wind turbine output power. Common input to the two optimal controllers is only the generator speed, while the measurement of the wind speed is not required. The controllers determine the optimal d- and q-axis stator current components of the SCIG through optimal conditions and, therefore, fast dynamic response of the WECS is accomplished. An experimental procedure is proposed to determine the MEL and MPPT controller parameters. Therefore, neither the knowledge of SCIG loss model, nor the characteristic curves of the wind turbine are required. The effectiveness and the operational improvements of the suggested optimal control scheme have been verified experimentally.

Maximum efficiency in single-pulse controlled switched reluctance motor drives

The problem of choosing the firing angles for accomplishing maximum efficiency in single-pulse controlled switched reluctance motor drives is investigated. The suggested method is based on the optimal control of flux-linkage, through the firing angles, according to load torque requirements and depending on rotor speed. A controller that determines online the optimal turn-on and turn-off angles is proposed. The suggested controller does not affect the complexity of the drive and it is easily implemented, since knowledge of magnetization curves is not required. Moreover, it provides smooth transition between optimal single-pulse and pulse width modulation (PWM) current control modes and thus, optimal performance of the switched reluctance motor drive is attained over the entire speed range. Simulation and experimental results are presented to validate the resulting improvements of the proposed control scheme.

Thermal and slip effects on rotor time constant in vector controlled induction motor drives

In this paper, the fast variation of rotor resistance due to winding temperature is shown. Thus, the rotor time constant in the vector controlled induction motor drives, in contrary to common belief, changes fast via temperature. Moreover, it depends on the motor slip. The slip dependency of rotor time constant is due to motor loss that is usually ignored. The iron and stray loss is introduced in the induction machine dynamic and static models and a new expression of the rotor time constant is derived, that contains the motor slip. Thus, the rotor time constant rapidly varies at load torque changes. A novel slip frequency calculation procedure is proposed that ensures the accurate and fast estimation of the valid machine rotor time constant. The above aspects have been verified by extensive simulation and experimental tests in a wide speed-torque range.