Shashank Wekhande

High-resolution absolute position Vernier shaft encoder suitable for high-performance PMSM servo drives

Permanent magnet synchronous motor (PMSM) drives are suitable for high-performance servo applications, as in robotics. This, however, requires an accurate position feedback, which is not possible with the existing absolute position encoders, unless one is prepared to compromise on the size of the encoder. This paper proposes a new encoding scheme based on the simple Vernier principle. The proposed scheme improves the resolution of the encoder within limited disk diameter. An improved encoder based on the same principle is also presented with minor modifications to improve the resolution. Computer simulations and experimental work have shown that a suitable modification of the Vernier concept can result in an encoder that is superior to the existing ones. Details of this work are presented.

A new variable speed constant voltage controller for self-excited induction generator

Abstract A new variable speed, constant voltage controller for self-excited induction generator (SEIG) is presented in this paper. The proposed PWM controller regulates the induction generator (IG) terminal voltage against varying rotor speed and changing load conditions. This scheme does not require any real time computations and information regarding rotor speed for calculating the excitation current, thereby minimizing the electronic hardware and the cost of the controller. A simple, over-current protection is incorporated to protect the inverter switches. Computer simulation and experimental results show satisfactory operation of an induction generator with the proposed control scheme.

A low cost inverter drive for 2-phase induction motor

Emerging high volume low power variable speed AC motor drives have the stringent requirements of low cost and compactness. Most low power, low performance applications use two phase induction motors. Operation of the inverter for a two phase induction motor is investigated in this paper employing a square fed delta modulation scheme. The objective of the work is to provide a cost effective inverter which can induce a change from constant speed to variable speed operation in the low power range.

Wind driven self-excited induction generator with simple de-coupled excitation control

An induction generator is a good option for low power stand-alone, nonconventional energy generation. Induction generators require low maintenance costs and are cheaper but require an external excitation controller. A recently proposed PWM controller, whose principle was demonstrated in an earlier work for resistive and reactive loads, has been satisfactorily employed for harmonic and unbalanced three phase loads. The closed loop, IGBT based controller, which does not require any mechanical position/speed sensors, has been used to regulate the three-phase AC output voltage of a self-excited induction generator with varying rotor speed, transient load conditions and unbalanced as well as reactive loads. Since no online computations are required, it turns out to be a low cost, simple controller. Computer simulation and experiments show good results.

Comparison of high frequency signal injection techniques for rotor position estimation at low speed to standstill of PMSM

Rotor position information is necessary to control PMSM (Permanent Magnet Synchronous Motors). Extracting rotor position information using physical position sensor presents several disadvantages, including increased size, reduced reliability, and additional cost of the whole system. To overcome these drawbacks, there has been considerable interest in sensor less control techniques. Sensor less control of PMSMs can be broadly classified as, fundamental model based methods and machine saliency based methods. Techniques that rely on the fundamental model have the advantages of simplicity and straightforwardness. However these techniques fail to extract rotor position information from low speed to standstill. In the last two decades, a number of high frequency signal injection techniques have been proposed and developed for PMSM rotor position estimation at standstill and low speed without position sensor. These techniques can be classified into continuous signal injection techniques, transient signal injection techniques and high frequency signal embed on to PWM. This paper gives an overview of various approaches to rotor position estimation from low speed to standstill using HFSI techniques. Finally comparison between different rotor position extraction schemes is presented based on hardware complexity, torque ripple, speed range and cost of current measurement system.

A simple wind driven self-excited induction generator with regulated output voltage

Induction generators are widely used in nonconventional power generation. Self-excited, squirrel cage induction generators are ideally suited for remote, stand-alone applications due to their robust construction. A new closed loop IGBT based PWM controller is proposed for a self-excited induction generator. The proposed controller regulates the excitation current of the induction generator to regulate the generated three phase voltage. The terminal voltage is regulated in spite of varying rotor speed and different load conditions. The proposed scheme does not require any real time computation for generating reference currents. This low cost high performance controller is suitable for constant voltage variable frequency loads. The digital simulation results show satisfactory operation of induction generators under the proposed control scheme.

A static VAR compensator with supply side current sensors and improved transient response using feed-forward control

The static VAR power compensators (SVCs) based only on the supply current sensing and indirect reactive power estimation, require lesser number of current sensors and use simpler control technique. However, the transient response of these compensators is poor as compared to SVCs, based on load current and supply current sensing. This paper presents two simpler feedforward techniques for improving the transient response of a SVC based on supply current sensing. The SVC has been simulated for both the techniques to study and compare their transient and steady-state performance. The compensator is simulated for various values of feed-forward gain. The results are presented to demonstrate the transient performance and stability of the converter. Experimental results support the simulation results.

High resolution absolute position Vernier shaft encoder suitable for high performance PMSM servo drives

PMSM drives are suitable for high performance servo applications, as in robotics. This, however, requires an accurate position feedback, which is not possible with the existing absolute position encoders, unless one is prepared to compromise on the size of the encoder. This paper proposes a new encoding scheme, based on the simple Vernier principle. Computer simulations and experimental work have shown that a suitable modification of the Vernier concept can result in an encoder, which is superior to the existing ones. Details of this work are presented.

A low cost square fed delta modulator suitable for three phase FHP AC drives

Delta modulation offers a number of unique advantages in static PWM inverter applications in variable speed AC drives such as inherent constant volts per hertz control for a preset frequency range, smooth transition between the constant volts per hertz and constant volts modes of operation and severe attenuation of low order harmonics from the load voltage. In FHP drive range the control circuit cost is significant when compared with the total inverter cost. The main objective of this paper is to reduce the drive cost still maintaining the adequate performance for such drives. The scheme proposed here is square fed delta modulation technique which operates at predetermined switching frequency, simplifying the output filter design. Most of the advantages of conventional delta modulation technique are maintained with reduction in cost. This reduction is significant at low power ratings. The FHP drive employing this modulation technique and permanent magnet synchronous motor has potential in energy saving applications. The scheme is suitable for any AC motor and will favor the trend of using V/F control from energy cost point of view in even common applications. The analysis, simulation and experimental results for square fed delta modulator are presented in this paper.

Compensation of rotor position estimation error due to stator winding resistance in signal injection based sensor less PMSM drives

Signal injection techniques are popular to extract rotor position information from low speed to stand still, however these techniques have error in rotor position estimation. In the literature estimated rotor position information neglect the stator winding resistance; this work analyzes the stator winding resistance effect on position estimation accuracy and proposes compensation technique to reduce the position estimation error introduced by stator winding resistance. Proposed compensation technique is validated by simulation results. This work also analyzes the position estimation error resulting from neglecting stator winding resistance and torque reduction.