Power Electronics and Drive Systems

Assignment Brief

Module: KD7069 – Power Electronics and Drive Systems

Requirements

Write a report within 16 pages (including diagrams, contents, references etc.) to include responses to the tasks from Section 2. You can use technical publications, books or any other usual University Library resources, but you must not make verbatim extracts from these. Sources of information should be acknowledged and appropriately referenced in your report

You must complete the Assignment Submission Form available there. A copy of the form will be returned to you as a receipt, which you should keep as proof that you have submitted the Assignment. Note that the University Regulations state that in case of a late submission without a proven good cause, your assignment will incur fail or zero mark. In the event that you submit late but with a genuine reason, you must obtain and complete an appropriate form from the above Office, and have it authorised/signed by the module tutor prior to submission

2.1 Design and simulation of a boost converter

A boost converter supplies a resistive 20Ω load at 240V from a 96V DC supply. The switching frequency is 100 kHz. A filtering inductor and smoothing capacitor are used to limit the peak-to-peak ripple in inductor current and output voltage, respectively

1. If inductor ripple current is limited to less than 0.04 A and the ripple voltage of the capacitor is less than 0.05 V, calculate the inductance and capacitance. (10%)

2. Build and simulate the circuit model in Matlab/Simulink to check whether the simulated results are agreeable with the theoretical analyses. (10%)

3. If the filtering inductor has a resistance of 0.2 Ω, calculate the average current drawn from the supply and the efficiency of the converter. Simulate the updated circuit and compare the numerical and calculated results. (10%)

4. Develop and simulate a closed-loop boost converter model in Matlab/Simulink. Compare the simulation results with the corresponding analytical predictions for the open-loop boost converter. Based on this comparison, comment on whether closed-loop feedback control is needed in the converter design.

2.2 Performance of a space-vector PWM IGBT inverter-fed induction motor drive. A Simulink block diagram of the drive system with V/f control referenced above is shown in Figure 1. The corresponding parameters are given in the Appendix

1. The successive speed reference values defined by the user are 1000 rev/min, 1705 rev/min and 1200 rev/min, the respective time set-points being 0s, 1s and 3.5s, respectively. In order to account for the fixed load torque variations, the timer block is set to [0 1.5 2.5] (s), and the corresponding load torque levels are [0 12 8] Nm. Under these operating conditions, simulate the detailed system model in the time interval 0-5s and analyse the dynamic performance of the stator current, rotor speed, and torque of the motor as well as the converter DC link voltage using the respective waveforms. Try to explain the underlying physical phenomena rather than just making pure observations in your answers

2. Using the approximate equivalent circuit, show that the torque vs slip characteristic of a conventional 3-phase induction machine is nearly linear at small slips for a given supply voltage and frequency. Apply this approximation to find the rotor frequency of the motor under consideration in this assignment at 12 Nm load torque. What voltage should be applied to the stator terminals to run the motor at nominal speed for the same load?

3. Verify that induction motors with constant V/f control have electromagnetic torque virtually proportional to the slip frequency for normal steady-state operation. Bearing this in mind, calculate the applied voltage and speed of the fully-loaded motor (see Appendix for specifications) at 45 Hz. If the motor is now used to drive a variable speed centrifugal pump, determine the stator frequency required at 64% of rated load torque.

Sample Answer

Power Electronics and Drive Systems Report

Introduction

Power electronics plays a crucial role in modern electrical and electronic engineering, particularly in applications that require conversion and control of electrical energy. This report focuses on two major components of power electronic systems: the boost converter and the space-vector PWM IGBT inverter-fed induction motor drive. Both systems are essential in renewable energy systems, electric vehicles, and industrial automation, where efficiency, stability, and control are key.

The first part of this report analyses the design, simulation, and performance of a boost converter using MATLAB/Simulink. The second part examines the performance of an inverter-fed induction motor drive using space-vector pulse-width modulation (SVPWM). Each section includes theoretical calculations, simulation analyses, and discussions about efficiency and control performance.

Design and Simulation of a Boost Converter

Overview

A boost converter is a type of DC-DC converter that steps up the input voltage to a higher output voltage. It is commonly used in power supplies, battery systems, and renewable energy applications. In this case, the converter supplies a resistive load of 20 ohms at an output voltage of 240 V from a 96 V DC input supply. The switching frequency is 100 kHz. The main components of the converter are the inductor, capacitor, switch, diode, and load resistor.

Theoretical Analysis

The basic voltage relationship for a boost converter is given by:

Vout = Vin / (1 − D)

where Vout is the output voltage, Vin is the input voltage, and D is the duty cycle.

Substituting the given values:

Vout = 240 V and Vin = 96 V

The duty cycle D can be calculated as:

• D = 1 − (Vin / Vout)

• D = 1 − (96 / 240)

• D = 0.6

Hence, the converter operates at a 60 percent duty cycle.

Inductor and Capacitor Design

The inductor is designed to limit the peak-to-peak ripple current to less than 0.04 A. The ripple current in the inductor is given by:

ΔI = (Vin × D) / (L × f)

Rearranging for inductance L:

L = (Vin × D) / (ΔI × f)

Substituting the given values:

• Vin = 96 V, D = 0.6, ΔI = 0.04 A, f = 100000 Hz

• L = (96 × 0.6) / (0.04 × 100000)

• L = 0.0144 H

Therefore, the inductor should have a value of approximately 14.4 mH.

To ensure the output voltage ripple is less than 0.05 V, the required capacitor value is calculated using:

ΔV = (Iout × D) / (C × f)

Rearranging for capacitance C:

C = (Iout × D) / (ΔV × f)

First, the output current Iout is:

Iout = Vout / R = 240 / 20 = 12 A

Substituting values:

• C = (12 × 0.6) / (0.05 × 100000)

• C = 0.00144 F or 1440 µF

Thus, the capacitor should have a value of approximately 1440 microfarads.

Continued...