S.S.Deswal et. al. / International Journal of Engineering Science and Technology Vol. 2(6), 2010, 2445-2455 IMPROVED PERFORMANCE OF AN ADJUSTABLE SPEED DRIVES DURING VOLTAGE SAG CONDITION S.S.DESWAL* Assistant Professor, EEE Department, Maharaja Agrasen Institute of Technology, Sector-22, Rohini, Delhi-110086, India satvirdeswal@hotmail.com RATNA DAHIYA Associate Professor, Department of Electrical Engineering, NIT,Kurukshetra, kurukshetra, Haryana-136119, India ratna_dahiya@yahoo.co.in D.K.JAIN Director(Technical), Guru Premsukh Memorial College of Engineering, Budhpur, Delhi-110036, India jaindk66@gmail.com Abstract: Voltage sags normally do not cause equipment damage but can easily disrupt the operation of sensitive loads such as electronic Adjustable Speed Drives (ASD’s). Voltage sags cause a momentary decrease in DC-link voltage triggering an under voltage trip leading to nuisance tripping of adjustable speed drives (ASD’s) employed in continuous-process industries which contributes to loss in revenue. A practical ride-through scheme for an adjustable speed drives based on supercapacitor during voltage sag has been presented in this paper. The supercapacitor maintains the ASD dc bus voltage under voltage sag condition. Energy storage module is connected to support the DC-link voltage during power system faults. The performance of ASD’s under normal and power system faults is first simulated in MATLab Simulink and then experimentally verified. The Data AcQuisition boards (DAQ) of National Instruments along with LabVIEW software have been used to record the observed waveforms. Keywords : Adjustable speed drives, Low voltage ride-through capability, Voltage sags, Supercapacitor, Ultracapacitor. 1. Introduction Adjustable Speed Drives (ASD’s) used in a wide variety of industrial applications. The benefits that might be provided by the ASD’s are the reason for their widespread use by the industry. Despite of its importance to the process operation, the ASD’s are sensitive to voltage sags. Undervoltage and overcurrent often follow voltage sags which may cause the ASD’s to trip bringing about the halt of the productive process and revenue losses. The ASD’s may also operate inappropriately resulting on load torque and load speed variations since the control of the current and of the output voltage are dependent on the inverter DC voltage level which decays during voltage sag [1], as shown in eqn(1). dc L r dc mot inv dV T V C dt     (1) Thus, the decrease rate of the dc bus voltage dV dc /dt depends on the capacitance C, the voltage V dc across the capacitor at the beginning of the voltage sag, the load torque T L , the motor speed ω r , the motor efficiency η mot . Different approaches to improve the ASD’s ride through by increasing the average voltage of the DC-link have been proposed [1], [5], [6], [7], [8]. The methods include the addition of capacitors to the DC- link [6], the regenerative mitigation which converts the kinetic energy from the motor and load into electric energy transferring it to the ASD’s DC-link [1], the connection of the neutral conductor of the supply source to the midpoint of the DC-link through a controlled switch [8], and the application of boost converters [1], [5], [7]. ISSN: 0975-5462 2445