International Journal of Computer Applications (0975 – 8887) Volume 87 – No 1, February 2014 9 Simulation of DTC-CBSVPWM fed SPMSM Drive with Five-level Diode Clamped Inverter G. Sree Lakshmi Research Scholar, Dept. of EEE, CVR College of Engineering, Hyderabad, India S. Kamakshaiah Former Professor & Head, Department of EEE, JNT University, Hyderabad, India G. Tulasi Ram Das Vice-Chancellor, JNT University, Kakinada, India ABSTRACT In this paper a simulation analysis of DTC-CBSVPWM of SPMSM drive using five-level diode clamped inverter is analyzed. It has simple structure and provides dynamic behavior comparable with classical DTC. Direct Torque Control (DTC) is an accurate controller for permanent magnet synchronous motor (PMSM) due to its robust and fast torque response in steady-state and transient operating condition. However, the main disadvantage of DTC is high ripples in stator current, flux linkage and torque due to the application of same active voltage vector during the whole sample period and possibly several consecutive sample intervals. This can be overcome by using proper modulation technique. Space Vector Modulation (SVM) which synthesizes any voltage vector lying inside the sextant gives good performance, but however the complexity involved is more in calculating angle and sector. To reduce the complexity involved in SVPWM, a novel modulation technique named Unified voltage modulation or carrier based space vector pulse width modulation (CBSVPWM) is described using the concept of effective time. By using this method the inverter output voltage is directly synthesized by the effective times and the voltage modulation task can be greatly simplified. The actual gating signals for each inverter arm can be easily deduced as a simple form using the effective time relocation algorithm. Keywords DTC-CBSVPWM, SPMSM, Five-Level Diode Clamped Inverter. 1. INTRODUCTION Permanent magnet synchronous motors are replacing DC and Induction motors in high performance drives due to their several advantages such as low inertia, high efficiency, high power density and good reliability. They also find increased application in robotics, ships, windmills, compressors, pumps, fans and in vehicle drives. PMSM with small size and robustness is possible due to the development of new rare- earth magnetic materials like Neodymium Iron Boron (Nd 2 Fe 14 B) and Samarium Cobalt (SmCo 5 , Sm 2 Co 17 ) which have high energy density and high resistance for demagnetization. PMSM are classified into two types, Brushless DC motors (BLDC) and PMAC. Sinusoidal PMAC machines are further classified into two groups with respect to their rotor structures as; Surface Mount Permanent Magnet (SMPM) synchronous motors and Interior Permanent Magnet (IPM) synchronous motors. IPM motors have the permanent magnets buried in the rotor core and SMPM motors have the permanent magnets mounted on the outer surface of the rotor. The reluctance variation between the direct and quadrature axes is fairly small in SPMSM. Accordingly, there is very little variation between the quadrature and direct axes inductances. This particular fact has consequence on the control operation, and characteristics of the surface mount PMSM drives. With respect to air-gap torque, IPM is better all the time compared to SMPM machines but with respect to speed range availability when the same voltage is considered, the SMPM is better compared to IPM machines. However, if the air gap power is considered, the SMPM is better in almost all the ranges compared to IPM [1][2]. Vector control is the most important, efficient and simple method to control the PMSM, which can be divided into two types. Field Oriented Control (FOC) and Direct Torque Control (DTC). In FOC, the main objective is to control the current vector and in DTC the main objective is to control the torque producing flux vector. In the middle of 1980’s Depenbrock and Takahashi was initially proposed Direct Torque Control (DTC) for induction machines and in the late 1990 French and Zhong which was then applied to PMSM [3]-[5]. The direct torque control (DTC) is an accurate controller for permanent magnet synchronous motor (PMSM) which is based on decoupled control of flux and torque which achieves robust and fast torque response in steady-state and transient operating condition, without the need of speed or position sensors, current regulator, coordinate transformation and PWM signal generator. The principle is based on the selection of voltage vectors from the difference between reference and actual value of torque and flux linkages [6]-[8]. The torque and flux errors are compared in hysteresis comparators. Although DTC has many advantages over current control, it has still some disadvantages such as high current ripples, variable switching frequency and difficulty in controlling torque and flux at very low [9]-[12]. In recent years, this can be overcome with the development of multilevel inverter proposed by Vas and Martins, a smoother torque can be expected with more voltage space vectors available to control flux and torque[13]-[15]. However, more power devices are needed to achieve a lower ripple and almost constant switching frequency. This can be obtained by using proper modulation techniques. Modified DTC schemes with constant switching frequency and low torque ripple were reported by others, where space vector modulation (SVM) is incorporated with DTC, to provide a constant inverter switching frequency. SVPWM gives good performance, but however the complexity involved is more in calculating angle and sector. To reduce the complexity involved in SVPWM, a novel modulation technique named Unified voltage modulation or carrier based space vector pulse width modulation (CBSVPWM) is described using the concept of effective. By using this method the inverter output voltage is directly by the effective times and the voltage modulation task can be greatly simplified [19]-[22]. The actual gating signals for each inverter arm can be easily deduced as a simple form using the effective time relocation algorithm. In this paper a DTC-CBSVPWM is analyzed with surface-mounted permanent magnet synchronous motor and the torque and speed response is studied by using five-level diode clamped inverter [16]-[18].