Showing papers by "Kamalesh Hatua published in 2020"

Digitally Controlled Gate Current Source-Based Active Gate Driver for Silicon Carbide MOSFETs

Abstract: Silicon carbide (SiC) MOSFETs are viable alternatives for silicon (Si) insulated-gate bipolar transistors (IGBTs). However, direct retrofitting of SiC MOSFETs in Si IGBT-based converters is not feasible due to the presence of a higher amount of parasitic inductance. A large voltage and current overshoot along with oscillation are noticed in such attempts as SiC MOSFETs switch very fast. An active gate driver (AGD) can meet the conflicting requirements of faster switching speed and lower overshoot and ringing. A switched current source-based AGD is designed and extensively tested in a 50-kVA voltage source inverter made with SiC MOSFET power modules. The control methodology is discussed and the experimental results are presented in this article.

An Asymmetric Nine-Phase Induction Motor for LCI-Fed Medium Voltage Drive Applications

Abstract: This article presents a new asymmetric nine-phase induction motor-based load commutated inverter (LCI)-fed drive configuration as an alternative to the popular LCI-based synchronous motor drive topology in medium voltage (MV), high power applications. The proposed machine has three sets of three phase windings, two of which are designed to carry the rated active power from the LCI at MV levels. The other three phase winding is designed to handle all the reactive power requirement of the machine at a standard low voltage level from an insulated gate bipolar transistor (IGBT)-based voltage source inverter (VSI). The VSI also assists the LCI operation by supplying some additional reactive power required for safe commutation of the thyristors of the LCI. A smooth torque profile is also ensured by using the VSI to cancel out the low frequency harmonics in the quasi-square-shaped LCI currents. A laboratory prototype of the machine rated 75 kW, 1650/1650/400 V is designed and built to verify the proposed drive and the experimental results obtained are presented in this article.

An Induction Machine With Tapped Stator Windings for LCI-Fed Medium Voltage Drive Applications

Abstract: The search for thyristor-based load commutated inverter (LCI) fed induction motor drives for medium voltage (MV) applications has been ongoing since the past few decades, and several new topologies have been proposed. Low cost, better efficiency, and greater ruggedness are the definite advantages of these drives. Since leading power factor is an absolute necessity for load commutation, most of these drives supply additional auxiliary reactive power at the motor terminals. However, in MV applications, this would require the auxiliary source of reactive power (typically a capacitor bank or voltage source inverter (VSI)), also to be rated for MV. To overcome this issue, a new topology using a tapped stator winding induction machine is proposed in this article. Here, a low voltage tapping on the stator winding is used to connect a low voltage VSI which supplies reactive power to the machine. The LCI is used to provide all the active power required from the main stator terminals rated for the MV operation. This article describes the proposed machine and drive configuration and the vector control method for the LCI fed drive. Experimental verification is done using a 75-kW, 3.3-kV prototype machine with a 350 V tapping on the stator winding.

Low-cost analogue active gate driver for SiC MOSFET to enable operation in higher parasitic environment

Abstract: Operating silicon carbide (SiC) metal–oxide–semiconductor field-effect transistor (MOSFET) at its rated switching speed may not be always feasible due to excessive voltage and current overshoot and ringing caused by layout parasitic inductance and load parasitic capacitance. This study proposes a low-cost analogue active gate driver technique for switching SiC MOSFET in the presence of moderate amount of layout parasitic inductance (<200 nH) and load parasitic capacitance (<300 pF). In this study, a d i / d t based closed-loop active gate driver circuit is implemented using low-cost signal level transistors. The present work explains the working of the gate driver during turn-on and turn-off switching transients. A detailed design methodology for the gate driver is presented using its high-frequency model. The proposed active gate driver (AGD) has been verified in hardware platform using a double pulse test setup and in a boost converter test setup. Cree make 1200 V, 36 A SiC MOSFET (C2M0080120D) is used for evaluating the proposed active gate driver. The proposed circuit has sufficient operating bandwidth to drive SiC MOSFET and it is realised with low-cost transistors.

Quick and seamless transition method for I-f to sensorless vector control changeover and on-the-fly start of PMSM drives

Abstract: A smooth changeover from the I-f method to closed-loop sensorless vector control is a critical requirement for permanent magnet synchronous motor (PMSM) drives using a back-emf based sensorless algorithm for medium- to high-speed range control. The existing methods provide a smooth transition by aligning the angle generated by I-f control to the sensorless estimated angle. However, the overall start-up time increases due to the additional transition interval, which limits the usability of these methods for applications requiring a quick start-up. Furthermore, the use of a direct transition method to reduce the changeover time results in speed and current oscillation if the estimated position using sensorless algorithm is having an error. In the proposed method, the inverter pulses are disabled for a short duration and the machine back-emf is measured after the stator current falls to zero. Therefore, a quick and seamless transition is achieved in the proposed method by accurately estimating the rotor position from the sensed back-emf. The proposed method is also extended to perform on-the-fly start for power failure ride through during short time power supply interruption. The performance of the proposed method is verified using simulation and experiment on a 25 kW PMSM drive.

Design Considerations for an Active–Reactive Induction Motor for Medium-Voltage Applications

Abstract: The active–reactive induction motor (ARIM) has been introduced in the literature as a low-cost and high-efficiency alternative to the synchronous motor in load commutated inverter (LCI) fed drives. ARIM is a squirrel cage machine with two sets of dissimilar three-phase stator windings. While one winding is rated for high voltage and power, the other winding is rated for a lower voltage and power. The low-voltage winding fed from a voltage source inverter (VSI) supplies only reactive power to the machine such that a leading power factor appears at the high-voltage terminals, enabling LCI-fed operation at this winding. Since the ARIM is fundamentally an induction motor, the conventional induction machine design process is applicable. However, due to the nonconventional arrangement of stator windings and being intended specifically for an LCI-fed topology, this new class of induction machines requires some critical design considerations. It is shown in this article that the leakage inductances play a pivotal role in determining the ratings of the low-voltage windings and the VSI. Therefore, an iterative design procedure to obtain the correct ratings for the flux winding and the low-voltage components is proposed. It is also required to know the correct value of the leakage inductance in order to design the control loops for reliable operation. This article proposes experimental methods to determine these leakage inductances. The proposed methods are validated by designing a 3.3-kV, 75-kW prototype and experimental results are presented.

Parameter Estimation in Sensorless Vector controlled Induction motor Drives

Abstract: Induction motor drives operating on the sensorless vector control mode are widespread in the industrial sector, owing to the better dynamic performances it provides over the other methods and the significant reduction in cost, mounting space and maintenance it provides due to the lack of encoder. But the method's performance is hugely dependent on the accurate measurement or estimation of motor parameters. This paper deals with the estimation of essential motor parameters for the proper operation of the control mode. It is a combination of standstill and rotational modes to estimate parameters by developing a self-commissioning method for industrial drives using the already existing current sensors and DC voltage sensor such that the estimated parameters can be used for both star and delta connections without any further recalculations and minimal motor name plate data. The paper deals with the verification of sensorless vector control method with the estimated parameters by using simulation results for a 15kW motor. Further hardware results on 5.5kW motor load setup are detailed which further validate the method's effectiveness.