The Space Vector Modulation (SVM) technique has gained wide acceptance for many AC drive applications, due to a higher DC bus voltage utilization (higher output voltage when compared with the SPWM), lower harmonic distortions and easy digital realization. In recent years, the SVM technique was extensively adopted in multilevel inverters since it offers greater numbers of switching vectors for obtaining further improvements of AC drive performances. However, the use of multilevel inverters associated with SVM increases the complexity of control algorithm (or computational burden), in obtaining proper switching sequences and vectors. The complexity of SVM computation causes a microcontroller or digital signal processor (DSP) to execute the computation at a larger sampling time. This consequently may produce errors in computation and hence degrades the control performances of AC motor drives. This paper presents a developement of SVM modulator for three-level Cascaded H-Bridge Multilevel Inverter (CHMI) using a hybrid controller approach, i.e. with combination between the DS1104 Controller Board and FPGA. In such way, the computational burden can be minimized as the SVM tasks are distributed into two parts, in which every part is executed by a single controller. This allows the generation of switching gates performed by FPGA at the minimum sampling time 〖DT〗_2=540 ns to obtain precise desired output voltages, as can be verified via simulation and experimental results.
Multilevel inverters are progressively being used in highpower medium voltage energy control industrial drive applications due to their superior performance compared to conventional two-level inverters. There are a number of topologies applied in recent years. The most widely applied topologies are Diode Clamped Inverter (DCLI), Capacitor Clamped Inverter (CCLI) and Cascaded H-Bridge Inverter (CHBI). Three level DCLI requires additional 6 clamping diodes and CCLI requires 3 clamping capacitors that make the system bulky and quite difficult to implement while increasing the number of level. CHBI requires no additional diodes or capacitors and it is easy to implement. But it requires 2 DC sources that increases the system cost. In this paper, these three topologies for three level inverter using space vector pulse width modulation (SVPWM) technique has been modelled and simulated using MATLAB/SIMULINK and Origin 6.1 for a passive R-L load. From the simulation results, CHBI with separate DC source (CHBISEDCS) shows the better performance to the others in terms of THD. CHBI using single DC (CHBISDC) source is also presented and compared with CHBISEDC. CHBISDC shows better performance without significant increase of THD compared to CHBISEDC. Hence CHBISDC minimizes the system cost and provides better performance.
Space vector modulation (SVM) has received wide acceptance due to many benefits over other techniques such as higher output voltages, lower total harmonic distortion (THD),Voltage source inverters (VSI) have evolved as the most popular power conversion for many AC drive applications. The evolvement of VSI is in line with the development of various pulse width modulations (PWM) algorithms supported by the advent of solid state switching device technologies, fast digital signal processors, field programmable gate arrays (FPGA) and microcontrollers. Since a few decades ago, several PWM algorithms were developed to improve some performances of VSI such as high-power efficiency [1-2], high-output voltage [3][4], and low-total harmonic distortion (THD) [5][6]. Obviously, the research on VSI has not yet come to state of saturation, as novel or simplified PWM methods continue to emerge for various topology inverter circuits and multilevel inverters [7][8]. Among various modulation strategies or PWM methods, the space vector modulation (SVM) technique has received wide acceptance due to several advantages such as higher output voltages, lower THD, high-efficiency and flexible to be implemented in vector control systems [9][10].The precision on SVM control algorithm is very important to produce desired output voltages, especially for high-performance AC drive system. For example, the SVM technique is widely adopted in motor drive systems to obtain excellent torque or speed control performance. The high degree of accuracy SVM modulator is compulsory to produce proper and desired instantaneous magnitude and frequency of output AC voltages. The accuracy performance of the modulator can be determined by the reliable design of control algorithm and speed computation of processor or controller board. The reliable design of control algorithm depends on the way the SVM algorithm is formulated.In digital implementation, the SVM equations can be optimally computed if the equations eliminate the use of complex forms, e.g. trigonometry functions, exponential terms, differential equations and etc. Simplification of control algorithm is necessary for ensuring reliable data to be stored and manipulated by the controller and hence allows the computation of SVM at higher sampling rate. In the proposed development of SVM, the simple SVM based
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