Ajit K. Chattopadhyay

Observer-based stator-flux-oriented vector control of cycloconverter-fed synchronous motor drive

A six-pulse noncirculating-current cycloconverter-fed synchronous motor with stator-flux-oriented vector control for high-power and low-speed applications is discussed here. Vector control is achieved by stator flux estimation through a novel closed-loop reduced-order observer exhibiting stable speed regulation. Variable displacement factor operation is incorporated to keep both the system current continuous and the system utilization optimum. A simple method is used in designing the controller for armature current regulation with good performance. A generalized digital simulation of the drive system is made, and the simulation results are validated by a low-cost laboratory implementation of the drive with a 386DX PC-based system with 80387 floating point support.

Analysis of parallel-operated self excited induction generators

The paper presents an iterative solution for the problems related to steady state performance of self-excited induction generators operating in parallel. The analysis is based on voltage and current balance equations derived from an inverse-model for the steady state equivalent circuit of induction machines. The nonlinearity in the magnetization characteristics has been taken into account by piecewise linearisation. The proposed method is general and can be applied for analysis of any number of parallel connected machines. Theoretical predictions and experimental results are presented to study different performance characteristics of the system.

Excitation requirements for stand alone three-phase induction generator

Self excitation in induction machines depends on appropriate combination of speed, load and excitation capacitance. This paper presents direct methods derived from loop and nodal analyses to find different criteria for maintaining self-excitation. Unlike available techniques, the inverse-model for the steady state equivalent circuit has been used. This is found to be of much assistance in the analysis. Besides determination of speed-limits for fixed terminal parameters, and capacitance requirement under varying speed and load, a method to test the possibility of self-excitation for known speed, load and terminal capacitance has also been presented.

Performance of an SCR-inverter-based commutatorless series motor with load commutation and unaided start-up capability

The paper examines the starting and variable speed performance of an SCR-based commutatorless series motor (CLSM) with special emphasis on the commutating process for the operation of a self-controlled synchronous machine in the load-commutated mode, unassisted by extra components or special techniques even at very low speeds including starting. A dynamic simulation of the drive, in which the field winding of the synchronous machine is located in the DC link has been presented, the results of which are validated by comparison with those of an experimental prototype. The influence of the damper windings on the commutation process and in the suppression of the voltage spikes so generated, and in reducing overlap times have also been studied. A phasor diagram based steady state analysis predicts the parameters of suitable machines for such an operation. The inherent series characteristics of this drive, its high power factor and self-starting capability will find applications in large power traction drives, flywheel energy storage systems, centrifugal pumps etc.

Digital Computer Simulation of an Adjustable-Speed Induction Motor Drive with a Cycloconverter-Type Thyristor-Commutator in the Rotor

This paper deals with a digital computer-simulation study of a complex drive-system which incorporates a thyristor cycloconverter-type frequency-converter in the rotor circuit of a slip-ring induction motor for speed variation in the subsynchronous as well as the supersynchronous region by secondary voltage control The action of the frequency converter is analogous to that of a normal commutator in the stator-fed ac commutator motor while the circuit behavior is similar to that of a cycloconverter. A rotor-position detector is used to switch the thyristor configuration in a sequential manner to generate an output voltage having a predominant slip-frequency component. Simulation involves solution of a set of generalized performance equations of an ideal induction machine in an appropriate reference frame under the control conditions imposed by the thyristor-commutator which is simulated using simple logical and limiting statements. Differential equations are solved by the well-known Runge-Kutta numerical integration method. Initial simulation results assuming thyristors as ideal switches and neglecting source impedances show very similar characteristics to the case when a pure sine-wave slip-frequency voltage is injected to the rotor. Rigorous simulation results include the physical thyristor behavior, effect of source impedances, overlap, and logical control of the circulating currents that may occur. Simulation results are presented together with the experimental performance of the drive.

Analysis of parallel-operated self-excited induction generators

The paper presents an iterative solution for the problems related to steady state performance of self-excited induction generators operating in parallel. The analysis is based on voltage and current balance equations derived from an inverse-/spl Gamma/ model for steady state equivalent circuit of induction machines. The nonlinearity in the magnetization characteristics has been taken into account by piece-wise linearisation. The proposed method is general and can be applied for analysis of any number of parallel connected machines. Theoretical predictions and experimental results are presented to study different performance characteristics of the system.

An Adjustable-Speed Induction Motor Drive with a Cycloconverter-Type Thyristor-Commutator in the Rotor

This paper deals with an analog computer simulation study of a complex drive system by making simplifying assumptions. The system incorporates a thyristor cycloconverter-type frequency-converter in the rotor circuit of a slip-ring induction motor for speed variation in subsynchronous as well as supersynchronous region by secondary voltage control. The action of the frequency converter is analogous to that of a normal commutator in a stator-fed ac commutator motor while the circuit behavior is similar to that of a cyclo-converter. A rotor position detector is used to switch the thyristor configuration in a sequential manner to generate an output voltage having a predominant slip-frequency component. Simulation involves solution of a set of generalized performance equations of an ideal induction machine in an appropriate reference frame under the control conditions imposed by the thyristor-commutator which is simulated using the parallel logic facilities of a modern analog computer. To simplify the simulation to study the system behavior, the thyristor units are represented by D/A switches available in the computer and the effects of source impedances are neglected. Results show very similar characteristics to the case when a pure sine-wave slip-frequency voltage is injected into the rotor as in the case of an ac commutator motr.

Performance of parallel-operated self-excited induction generators with the variation of machine parameters

A stand alone system consisting of induction generators connected in parallel, has been considered in this paper. Detailed investigation of such system is carried out to find the influence of machine parameters on system performance. The inverse-/spl Gamma/ model of the per-phase steady state equivalent circuit has been used for the analysis. The nonlinearity imposed by the magnetization characteristics of the machines, calls for iterative technique for the solutions of equations derived from the inverse-/spl Gamma/ model. From the investigation it has been found that rotor resistance being the most sensitive parameter, needs careful selection/design. Influences of other parameter variations have also been presented.

An inverter-fed self-controlled commutatorless series motor with the field winding in the DC link

This paper examines the basic operation of a self-controlled synchronous motor driven by a three-phase MOSFET inverter with the field winding located in the DC link, yielding inherent series characteristics like a DC series motor. A new approach to the analytical and experimental study of the drive with the switches conducting for both 120/spl deg/ and 180/spl deg/ is presented, and typical results, both simulation and experimental, are shown and the performance characteristics compared. The effect of shifting the rotor position sensor is studied for both cases, as well as for four-quadrant operation. It is observed that the resulting drive system is simple, able to operate with reduced torque ripples and voltage spikes, and the characteristics of the drive are well suited for traction/transit propulsion applications and battery/flywheel energy storage systems.

Observer based stator flux oriented vector control of cycloconverter-fed synchronous motor drive

A 6-pulse noncirculating current cycloconverter-fed synchronous motor with stator flux oriented vector control for high power and low speed applications is discussed here. Vector control is achieved by stator flux estimation through a novel closed loop reduced order observer robust to speed variation. Variable displacement factor operation is incorporated to keep both the system current continuous and system utilisation optimum. A simple method is used for armature current regulation with good performance. A generalized digital simulation of the drive system is made and the simulation results are validated by a practical implementation of the drive with a 386DX-387 based system.