Djordje Stojic

Improved Stator Flux Estimator for Speed Sensorless Induction Motor Drives

In this paper, an improved induction motor (IM) stator flux estimation method is proposed, based on a novel integrator scheme with a closed-loop dc offset compensation algorithm. When compared with the existing stator flux estimators, the proposed solution represents an improved programmable low-pass filter. Namely, by introducing a novel closed-loop dc offset compensation structure, two major drawbacks of existing stator flux estimators are overcome; their stability and accuracy at low frequencies, and the estimator response time over the whole frequency range, introducing an estimation algorithm much simpler than existing solutions. The performance of the novel stator flux estimator is tested by means of simulation runs and experimental tests, with the proposed algorithm used for the estimation of the stator flux, rotor flux, and rotor speed in a direct field-oriented controlled IM control algorithm. The simulations and experimental results show that the proposed estimator enables accurate and stable operation under all operating conditions, including the critical low stator frequency range.

A new induction motor drive based on the flux vector acceleration method

A novel control strategy for the induction motor drive, based on the field acceleration method, is presented. The torque is controlled through variations of the stator flux angular velocity. The stator flux is controlled by using a feedforward control scheme, with the stator flux reference vector adjusted so as to obtain the fixed rotor flux amplitude. The applied controller assures a fast torque response, low torque ripple in the steady state, and drive operation with a constant switching frequency. The algorithm includes the improved stator and rotor flux estimation that guarantees the stable drive operation in all operating conditions, even at low speeds. The experimental tests verify the performance of the proposed algorithm, proving that good behavior of the drive is achieved in the transient and steady-state operating conditions.

Sensorless Induction Motor Drive Based on Flux Acceleration Torque Control

A novel structure for sensorless induction motor drive is proposed based on flux vector acceleration torque control. The proposed structure combines direct torque control with speed estimation based on slip frequency evaluation. A stable drive operation is enabled in a wide range of operating speeds, including at standstill

Stationary Frame Induction Motor Feed Forward Current Controller With Back EMF Compensation

In this paper, a novel induction motor (IM) stator current controller is proposed based on the stationary frame feed forward controlling structure. The proposed regulator represents an improved variant of the existing stationary and rotational frame IM stator current regulators based on the back EMF compensation. The paper novelty consists of the stationary frame controlling structure based on two feed forward actions that enable asymptotic reference tracking. Namely, the novel stationary frame regulator includes a proportional integral (PI) regulation term combined with a stator resistance voltage drop and back EMF feed forward compensations, with the back EMF compensation based on the stator flux value estimated by means of a programmable low-pass filter. The feedback term is based on a PI controller, with the corresponding parameter tuning procedure outlined in the paper. The simulation runs are included in the paper in order to examine the regulator performance in relation to the factors critical to the IM stator current regulation: variable IM model parameter values, transport delay introduced in the control loop, variable stator frequency, and rotor speed values. Also, the experimental tests are presented and carried out on an experimental setup for different operating conditions typical for an IM drive.

Voltage Controller for a Synchronous Generator with Exciter

In this paper, the excitation controller for a synchronous generator (SG) with an exciter is presented, based on novel stabilization feedback actions comprising the SG rotor current and rotor voltage measurements. The novel stabilizing feedback actions are used to compensate the dynamic lag introduced by the exciter machine, and to improve the overall excitation systems dynamic performance without employing differential control actions. Namely, by avoiding differential control actions, an improved level of performance can be achieved without compromising the control systems sensitivity in relation to the measurement noise. Also, compared with the existing solutions based on a different set of stabilizing feedback signals, the controlling structure proposed in this paper enables a more stable and faster dynamic response, which is illustrated in the paper by means of the system frequency response analysis. The performance of the proposed solution is verified through the set of simulation and experimental ...

Novel proportional-integral-resonant current controller for three phase PWM converters

In this paper a novel current control algorithm for a pulsewidth modulation (PWM) voltage-source converters is proposed, based on the reduced order generalized integrator (ROGI). Namely, existing ROGI based algorithms include proportional (P) and resonant (R) control action, while the integral (I) action was not, so far, combined with ROGI. Furthermore, since proportional-integral-resonant (PIR) controllers are employed in control of various three-phase PWM converters, in this paper the P-ROGI controller is combined with an integral control action in order to enable its use in the same field of application as PIR. Consequently, the novel PI-ROGI control algorithm is presented in the paper, and implemented in AC current control of a three phase PWM rectifier. The novel controller performance is verified by means of simulation.

Control of rotary exciter with series and separetly excitation windings excitation system of generator a2 at power plant “Kostolac A”

In this paper, the excitation control with rotary exciter of generator A2 in Thermal Power Plant “Kostolac A” is presented. Excitation system under consideration consists of a main exciter, an auxiliary exciter and power semiconductor rectifiers. The main exciter is a synchronous-reluctance generator with windingless toothed rotor. That excitation system is specific due to the fact that the main exciter has three excitation windings and three phase output a.c. windings, all located at stator. Series excitation is serially connected with rotor winding of the synchronous generator, while other two separate excitations are realized by independent windings, each of them generating the flux pointing in opposite direction. In the main three phase a.c. windings the 500 Hz frequency currents are induced. Auxiliary exciter is a 400 Hz permanent-magnet synchronous generator. It supplies separate excitation windings of the main exciter by means of thyristor rectifier bridges. The main aim of the control algorithm is to accomplish the magnetomotive force balance of all three excitation windings in order to regulate generator terminal voltage. In addition to the main outer voltage control loop, the inner local stabilizing current loop is added in order to achieve the satisfactory transient performance of the regulation. Control algorithm sets the values of the firing angle of the thyristors in two three-phase rectifier bridges, in order to produce corresponding excitation currents of separate excitation windings.

Modernization, reconstruction and development of excitation systems for synchronous generators

This paper presents the previous results of work and development of excitation systems with digital automatic voltage regulators regarding their design, development, manufacturing and commissioning. A special attention was paid to the characteristics of excitation system voltage regulator.