CONTINOUS TIME SLIDING MODE OBSERVER FOR CAPACITOR VOLTAGE ESTIMATION

Abstract

Due to several advantages of high voltage direct current (HVDC) transmission, electricity is transmitted using HVDC. During HVDC transmission, conversion of voltage from ac to dc (at source side) and dc to ac (at load side) is done. For this, power converters are used. With increase in power level, multilevel power converters are used for better efficiency, and low harmonics level. For working of power converters, the voltage across the capacitors is to be measured and then switching pulses are to be generated. With increase in power level, number of capacitors are increased. Hence, number of voltage sensors increase, which increases the cost and complexity of the design. To reduce this, observers are designed. Here we have analysed many topologies and found that these topologies are mathematically un observable in linear sense. Moreover, these are found to be observable in non-linear sense for specific condition. Hence, the observer is designed, and simple observer is usually unable to force the output estimation error to zero due to presence of some uncertainty or unknown signals or some disturbances and the states of the observer do not converge to the states of the system. Sliding Mode Observer (SMO) presents a desirable solution to the problem. The results of the simulation prove that the designed observer gives satisfactory results. Finally, a generalized system is proposed which mimics most of the multilevel converter topologies.