Bhakti M. Joshi

Time discretization issues in induction machine model solving for real-time applications

The Euler numerical integration method is used very commonly to solve the dynamic equations of the induction machine in real-time on digital processors. The need to solve the machine model also arises in real-time hardware-in-loop simulations, and in electric load emulation. The Euler method is often preferred in such applications due to its fast, simple single-step, explicit nature. However, Euler integration can result in large errors in transient and steady state response calculations, even with practical integration time steps. This paper aims at providing an analytical approach to studying the steady state errors caused by the Euler method in solving the induction machine model. It is shown analytically that the least error occurs when the machine model is solved in the synchronous reference frame. The effect of these errors on the closed loop decoupled control of induction machines is analysed in detail. The paper also gives a new formulation of Feedback Linearization Control (FLC) in the synchronous reference frame to reduce the effect of the discretization error. Analyses and simulations are validated through experiments.

Machine interactions in field oriented controlled multi-machine three phase induction motor drives

This paper is concerned with the interactions between the induction motors of a single-inverter, two-machine field-oriented drive system. The machine interactions considered here are those through the field oriented controller. The paper considers a multi-machine field-oriented controller that is based on a machine model which is the average of the models of the two machines. Interactions that occur due to load torque differences are described for machines of different ratings. Also considered in detail are machine interactions due to a small stator turns fault in one machine. A faulty machine, when controlled by a field-oriented controller, shows unbalance in currents and voltages. These affect the currents and field-orientation in the parallely connected healthy machine as well. An experimentally validated dynamic model of an induction machine with stator faults is used to analyse these interactions. The paper presents a detailed analysis and experimental results of these machine interactions.

Power failure ride-through in multi-machine drives

Power failure ride-through capability is an essential feature of adjustable speed drives to avoid production loss due to momentary power failure. Field oriented controlled induction motor drives are one of the ideal choices for implementing the ride-through capability due to their fast torque dynamics. This paper deals with implementation of the power failure ride-through capability in multi-machine single-inverter induction motor drives which are widely used for applications such as electric traction. Effect of choice of control structure on the ride-through performance is studied for field-oriented, two-machine, single-inverter drives for a range of machine ratings. Analysis and simulations are supported by experimental results.

Vector Control of Two-motor Single-inverter Induction Machine Drives

Abstract Multi-machine single-inverter induction motor drives are attractive in situations in which all machines are of similar ratings and operate at approximately the same load torques. The advantages include their small size compared to multi-machine multi-inverter systems, lower weight, and overall cost. This article presents a consolidated study and comparison of vector control methods applied to multi-machine drives along with relevant simulation and experimental results. The mean control method and its modifications prove to be superior to the other control approaches.

Review of fault modeling methods for permanent magnet synchronous motors and their comparison

Modeling of Permanent Magnet Synchronous Motors (PMSM) is required for the mathematical representation of the machine in order to analyze the behaviour of the machine under different operating conditions. This paper gives a detailed study of various fault modeling methods of PMSMs and their comparison in terms of accuracy and computational time. Based on a thorough review, the fault modeling methods are classified into Electrical Equivalent Circuit (EEC) based methods, Magnetic Equivalent Circuit (MEC) based methods and Numerical Methods (NMs). This paper describes an in-depth study and analysis for each of the modeling methods and further summarizes them into a comparative study. It also draws an inference about methods which are preferable for different types of faults.

Modeling and analysis of coupled coils for Wireless Power Transfer

This paper focuses on determination of parameters like self inductance, mutual inductance, leakage inductance and coupling coefficient for a pair of helical coils for wireless power transfer applications. These parameters are important in designing and analyzing a wireless power transfer system based on the phenomenon of inductive/resonant inductive coupling. Here we present a simple approach based on fundamental laws of physics for determining the coupled coil parameters for single layered helical coils. The results obtained by numerical integration are validated with the help of an experimental set-up. Further, this analysis is used to study the effect of change in coil diameter and change in distance between coils on parameters like self and mutual inductance of coupled coils which is of great importance in Wireless Power Transfer applications.

Overview of real-time power management strategies in DC microgrids with emphasis on distributed control

In DC microgrids, effective power management in real time is important for optimum management of energy, resources, storage elements and loads. Power imbalance in the grid may also lead to fluctuation of grid voltage, which will adversely affect the reliability of the microgrid and may damage the loads. In this paper, different strategies for power management in the DC microgrids will be classified and reviewed. Emphasis will be given to distributed power management strategies, which are reliable and also cost-effective and thus are more suitable for remote Indian villages.

Average torque error as a fault diagnostic index for vector-controlled induction motor drives with stator inter-turn fault

Fault diagnostic index is a quantity which is sensed or calculated in order to diagnose and quantify the extent of fault. With increasing use of closed loop drives in industrial applications, online fault diagnosis has become a critical requirement. This paper focusses on exploring the average error in torque as a fault diagnostic index in field-oriented-controlled induction motor drives with stator inter-turn short circuit fault. Effects of controller parameters and motor operating point on the error magnitude are discussed, and modifications are suggested to the method to make it load-independent. Relevant numerical simulation results are presented in the paper.

Optimal low-switching frequency pulsewidth modulation of dual modular multilevel converter for medium-voltage open-end stator winding induction motor drive

The first dual multilevel converter (MLC) topology for medium-voltage (MV) open-end stator winding induction motor (OESW-IM) drives was proposed in 1990s. Till now, MLC topologies to generate three-level, five-level, seven-level, and nine-level voltage waveforms for OESW-IM drives have been proposed. This paper proposes a new topology for OESW-IM drives based on modular multilevel converter (MMC) topology. The control requirements of the proposed topology are as follows: balancing floating capacitor voltages, removal of common-mode current components in stator current, and low-switching frequency operation with nearly sinusoidal machine stator currents. In this paper, synchronous optimal pulsewidth modulation (SOP) has been improved to satisfy the control requirements of the proposed topology. The proposed method has been validated using a low power experimental setup of dual three-level MMC.

A review of modeling, analysis and control methods of Brushless DCMotors

Brushless Direct Current (BLDC) motors are increasingly being used in industrial applications and electric vehicles. In order to design and control the machine for high dynamic performance, as well as for real-time fault diagnosis of the BLDC drives, analytical modeling is often the first step. This paper presents a survey of different ways of modeling and analysis of BLDC motors along with their control methods. Along with the conventional BLDC control, different modern control algorithms like state feedback control mechanism and novel technique of IC based control algorithm are widely being used for controlling the motor, which are reported in the paper as well. BLDC motor is modeled and simulated and the simulations results are included in the paper. Lastly, major applications of BLDC motors are listed.