Applied Mechanics and Materials Vol. 785 (2015) pp 141-145 © (2015) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.785.141
Submitted: 2014-12-17 Revised: 2015-03-23 Accepted: 2015-04-04 Online: 2015-08-24
Design and Analysis of a Digital Controller for Boost Converter with Renewable Energy Sources for Domestic DC Load O. Ibrahim1 a *, N.Z. Yahaya2, b, N. Saad3, c, K.Y.Ahmed4, d 1234
Universiti Teknologi PETRONAS (UTP), Bandar Seri Iskandar, Perak 31750, Malaysia a
[email protected], b
[email protected], c
[email protected], d
[email protected]
Keywords: DC load, DC-DC boost converter, digital compensator, closed loop response
Abstract: Renewable energy sources like solar PV produces DC voltage which is converted to AC before connecting to domestic grid network. The conversion process from DC to AC and back to DC at load end introduce additional losses in the system. With increasing availability of modern DC loads and growing use of renewable energy, the use of DC network for domestic load supply is on increase in order to reduce energy conversion losses. Presented in this paper is a fast transient digital controller for DC-DC boost converter with energy source from solar PV for domestic DC loads like lightings. The boost converter was model as both steady and dynamic state. Digital controllers were designed using both digital redesign approach and direct digital redesign approach. The system demonstrated fast transient response that is essential for tightly regulated output voltage from constantly varying renewable energy generations. Introduction Domestic appliances mostly run on AC electricity supply. Recently, the use of DC supply for domestic loads is gaining popularity due to developments in power converter design, increasing availability of modern DC loads, and growing use of renewable energy [1]. Most renewable energy resources like solar photovoltaic cells and fuel cells produce DC component which can be directly connected to DC load using DC-DC converter without the need for DC-AC inverter and energy storage. Direct DC connection will eliminates harmonics injection problems from inverters and reduce energy losses from multiple conversion consequently increase system efficiency and reliability [2]. DC-DC power converters play important role in domestic DC load supply from renewable energy generations by serving as connection link and in providing necessary control in stabilizing generated power [3]. The intermittency associated to renewable energy sources results in output power with changing dynamics such as voltages, current, frequency and power flow which demands advance control schemes to fully tap their potentials [4]. The application of digital control technology in the design of the converter scheme has potential for improving its dynamic performance by allowing implementation of advance control techniques that can easily eliminate the problems of varying output power generation. This paper presents the design and analysis of digital controller for boost converter using both digital redesign and direct digital design approach. The controllers were designed based on open loop frequency response of the boost converter using Matlab-SISOtool function. The effect of the controllers on the boost converter demonstrated fast transient response that is capable of eliminating voltage fluctuations associated to solar photovoltaic generation. Operation and Modelling of Boost Converter The block diagram in Fig. 1 shows a digitally controlled boost converter with the switching elements responsible for power conversion and the control circuit for stabilizing the power flow. Control of power converters has been challenging due to non-linear nature of converter switching elements, variation of line voltage and load current. Analogue control has dominated converter control till recent time due to its design simplicity and high control bandwidth but has disadvantages like large number of parts and complex hardware configuration [5]. Development of All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 203.135.190.2-01/09/15,15:41:11)
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Recent Trends in Power Engineering
high speed digital signal processors at low cost motivates the interest of digital control of power converters [6]. Digital control systems are less sensitive to parametric variation, flexible, auto diagnosing are possible, and complexity of control is moved from hardware to software [6]. Digital compensator allows implantation of complex control algorithm essential for achieving tightly regulated output power from varying renewable energy generations [7]. L
D
iin(t)
iout(t)
iL(t)
+
ic(t) Vin
Q1
RL
Vc(t)
C
PWM
Vout(t)
-
DPWM
d(t)
Compensator
Digital Signal Processor
Vo(t)
e
H
ADC Vref
Fig.1. Digitally controlled boost converter
Steady State Model. The steady and dynamic states model of continuous current mode (CCM) operation of boost converter with parasitic parameters was derived. The model allows the development of continuous-time transfer function which was used for controller design and dynamic behavior studies of the converter [8]. IL = I
D
in
iL(t)
iin(t)
Vin
C
R LVout(t)
Vin C
RLVout(t)
Fig.2. Equivalent circuit of boost converter at 0 < t < t on Fig.3. Equivalent circuit of boost converter at ton
