Boost Converter Ripple Reduction Method and Application on Multi-String LED and BLDC Control

This dissertation presents a control design method for reduction of DC-link voltage ripple in boost converter applications. The ripple reduction is achieved by using the harmonics of the DC-link voltage to feedback control in DC-DC boost converter. The harmonics of the DC-link voltage are extracted by using a simple observer for linear systems. The observer based control is successfully implemented in multi-string LED drive and BLDC motor drive. The ripples are successfully reduced to about half of the original magnitude. Robustness of the control algorithm is also validated under different experimental conditions.;This dissertation addresses two control design objectives about voltage ripple reduction control in the application of a boost converter. The first objective is to reduce the voltage ripple on a dc-link which connects the boost converter and the inverter bridge to drive a BLDC motor. Unlike the case where a boost converter is driving a linear load and the dc-link voltage is constant, when an inverter is connected to a boost converter, the dc-link voltage has an AC component (ripple) whose frequency is related to the speed of the motor. Ripples in the dc-link are undesirable since they cause distortion of the phase voltage and current, and generate Electro-Magnetic Interference (EMI). In this dissertation, a control algorithm for voltage ripple reduction on the do-link of power electronic converters is presented. In the proposed method, a simple observer for linear system is used to extract the hannonics of the DC-link voltage. The harmonic terms are then added to existing booster converter control loop. Simulations show that the ripple is reduced to about half of the original ripple magnitude. Since the ripple frequency is directly proportional to the rotor speed, the dissertation also proposes an adaptive voltage ripple reduction method by implementing a time-varying observer whose parameters follow the speed of a BLDC motor.;The second objective is to reduce DC-link voltage ripple in multi-string LED drivers. Today's LEDs are used for backlighting in entertainment display, navigation monitor, and internal and external lights. Moreover, a number of applications require LEDs to be placed in multiple strings. A string is a group of LEDs connected in series. They have the same current. The multiple strings improve fault tolerance. This dissertation considers a multi-string configuration where a single boost converter is utilized to convert battery voltage to a higher voltage required by LED strings voltage. The electronic switching is applied to dim LEDs over a wide range, depending on the intensity of the ambient light. When a boost converter is connected to LED strings, the current drawn by the LED strings will have an AC component which frequency is the multi-string switching frequency. The AC component will cause low frequency ripple in the DC-link voltage. The magnitude of the low frequency ripple depends on the magnitude of current through LEDs. The DC-link voltage ripples have adverse effects on circuits. In the dissertation, a method for reduction of the ripple is proposed by extracting the harmonics of the ripple and using them as additional terms in feedback control to the boost converter.