Ioan Iov Incze

Vector control schemes for Tandem-converter fed induction motor drives

The tandem converter is an arrangement of two inverters connected in parallel: a high-power pulse-amplitude modulated current-source inverter and a low-power pulse-width modulated voltage-source inverter. In comparison with an equivalent single voltage-source inverter, this structure offers several advantages, significant reduction of switching losses in particular. Results of experiments with a tandem inverter, and those of computer simulations of induction motor drives with that converter, are presented. Three vector control schemes for such drives were investigated: a) rotor-flux orientation with a voltage-controlled tandem converter, b) rotor-flux orientation with a current-controlled tandem converter, and c) stator-flux orientation with a voltage-controlled tandem converter. Performance characteristics of the described control schemes are discussed.

Comparative analysis of PWM techniques: Simulation and DSP implementation

The paper presents an overview of the pulse width modulation (PWM) techniques for a feed-forward voltage source inverter. Classical and optimized modulation methods are treated regarding the ease of implementation, harmonic spectra, maximum modulation index and switching losses. Classical PWM procedures like naturally sampled with saw-tooth or symmetrical triangle-carrier-wave, regular sampled and space vector modulation (SVM) or optimized methods like third harmonic reference injection and flat-top discontinuous SVM are simulated using MATLAB-Simulink® development package. An eZdsp development board was used to implement various PWM strategies on a fixed point DSP and compare their performances.

An improved speed identification method using incremental encoder in electric drives

The paper presents a variable sampling time method for speed identification using generated pulses from an incremental encoder. The most common procedures for speed identification are: in low speed range the period-measurement-and in high speed range the frequency-measurement-based method. Considering the error that occurs in the classical frequency method for speed calculation, the proposed procedure eliminates that error by increasing the sampling period with the necessarily amount of time in order to synchronize the sampling period with the generated encoder pulses. There are presented simulation results obtained with Matlab/Simulink® structures.

Vector control of the synchronous motor operating at unity power factor

The paper deals with n resultant stator-field-oriented vector control of a voltage-source-inverter-fed synchronous motor with variable excitation, controlled speed, and controlled flux, operating at unity power factor. These instructions give you basic guidelines for preparing camera-ready papers for conference proceedings. Simulation (using Matlab/Simulink environment) and implementations (on an experimental rig based on a dSPACE DS1104 controller card) were carried out.

Dual field orientation for vector controlled cage induction motors

The presented vector control structure combines the advantages of two types of field-oriented procedure. It is proposed for the short-circuited induction motor supplied from a voltage-source inverter (VSI) with voltage-feedforward (carrier-wave or space-vector) PWM. The speed and flux controllers generate directly the rotor-field-oriented components of the stator-current. The computation of the stator-voltage control variables of the inverter is made in the simplest manner in the stator-field oriented coordinate frame. As a consequence the control structure became motor parameter independent. There are presented simulation results and implementation possibilities.

Voltage-Hertz Control of the Synchronous Machine with Variable Excitation

In spite of the development of the vector control methods for the AC machines, the scalar control also finds his place in various industrial applications. Generally, the scalar control is used in reduced speed-range applications where is no need for exceptional dynamic behaviour. In order to achieve the highest torque per ampere ratio, the flux amplitude has to be maintained at his rated value. This can be achieved by adjusting in a proper way the US amplitude and the fS frequency of the stator-voltage. The working frequency is determined by the parameters of the application, so the constant flux operation can be maintained by adjusting the supply voltage amplitude. The first control method, which assures loss-less operation for the motor is the so-called constant voltage-Hertz operation. The only control variable is the stator-voltage frequency, while the voltage is computed based on the simplified steady-state equivalent circuit of the stator. Nevertheless, the main drawback of the constant volt/Hertz procedure consists on the effects of the voltage which can cause problems at low speed operation. These voltage drops at low frequencies has the same order of magnitude with the computed voltage, which makes the method inadequate at low speed. This can be eliminated by adopting different techniques, for the voltage drop compensation. The paper deals with current-feedback-based voltage-drop computation procedures for a salient-pole synchronous motor, with variable excitation. In addition to the known current-feedback compensation method, in this case also the excitation voltage is controlled, is order to improve the dynamic behaviour of the system

Incremental Encoder in Electrical Drives: Modeling and Simulation

Incremental encoders are electro-mechanical devices used as position sensors in electrical drives. They provide electrical pulses when their shaft is rotating. The number of pulses is proportional to the angular position of the shaft. The paper focuses on the modeling and simulation of an incremental encoder, and associated units serving for direction identification and position computing. Matlab-Simulink® structure was realized and tested. The proposed structure identifies the direction of the rotation in an angular interval equal to a quarter of the angular step of encoder graduation. The incremental encoder was integrated into the simulation structure of an induction motor based drive control system in order to provide the position of the motor shaft. Experimental results are also presented.

Flat-Top space-vector modulation implemented on a fixed-point DSP

The paper presents the method and implementation steps for space-vector (space-phasor) pulse width modulation, on a fixed-point digital signal processor using MATLABs Simulink® and the eZdsp development board. Besides the implementation of the simple suboptimal method, there are implemented 4 different Flat-Top (discontinuous) procedures. The simulation results show the improvements brought by the Flat-Top techniques: less commutations, even inside a sampling period, the ability to choose a Flat-Top method in correlation with the character of the inverters load in order to reduce furthermore the commutation losses. Also, the design of these Flat-Top techniques is improved by computing the position of the reference phasor without any trigonometric function, by using p.u. values for the on-times of basic vectors and by using the DC link voltage value, which can be compensated in case of the voltage ripples.

Flux identification for vector control of the synchronous motor drives

The paper deals with the identification of the orientation flux for a vector controlled salient-pole synchronous motor drive. There are presented two methods. According to the first method the stator flux is obtained by integration of the stator-voltage equations. A low-pass-filter-based closed-loop integration algorithm is discussed. The second method is based on the current model of the machine, with and without considering the damping currents. Both procedures were simulated and used in implemented stator-flux computation. Experimental results are presented, too.

Voltage-Hertz Strategy for Synchronous Motor with Controlled Exciting Field

The classical constant volt/hertz = ct. scalar control procedure applied to the induction motors historically was the first method which ensured loss-less operation. It is an indirect flux control method, which maintains the stator flux constant at its rated value. This can be achieved by adjusting in a proper way the stator-voltage amplitude according to the imposed stator-frequency. The method is applied with success for the induction and also for the synchronous motor drives. In case of the excited synchronous motors there is possible to increase the drive performances by controlling the excitation, too. It introduces an additional degree of freedom from the control point of view that offers one more possibility for flux or power factor control. In this paper there is presented a simple procedure, which ensures an improved dynamic behaviour of the synchronous motor. It consists of the exciting field control which is correlated with the volt-hertz control procedure, in order to maintain the simplicity of the control structure. Simulation and implementation results are also presented for validation.