Carrier Based Sinusoidal Pulse Width Modulation Control Strategy for Three Phase Nine Level Diode Clamped Multilevel Inverter and Hybrid Inverter with Reduced Components 1

Author Name(s): N.Susheela, P.Satish Kumar
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Abstract

The most widely used pulse width modulation scheme for diode clamped multilevel inverters (DCMLI) is the multicarrier based sinusoidal pulse width modulation. Though this technique is simpler and more flexible for implementation, the maximum peak of the fundamental component in the output voltage is limited to fifty percent of the voltage in the DC link. So, the hybrid multilevel inverter is proposed with superior features such as achieving more fundamental output voltage, requires fewer carrier signals, less components and gate drive circuits. Therefore, the overall cost and complexity of the hybrid inverter are greatly reduced particularly for higher inverter output voltage levels. A comparative analysis of three phase diode clamped multilevel inverter and hybrid multilevel inverter is presented in this paper using carrier based sinusoidal pulse width modulation technique. The performance of both the inverters are reported based on alternate phase opposition disposition (APOD) sinusoidal pulse width modulation (SPWM) strategy. Simulation is performed for three phase nine level diode clamped multilevel inverter and hybrid multilevel inverter using MATLAB/Simulink for induction motor load and the total harmonic distortion is evaluated at different load torques.

Keywords

Diode clamped multilevel inverter; Pulse width modulation; Hybrid inverter; Total harmonic distortion; Induction motor

Introduction

The multilevel inverters (MLI) have been attracting in recent decade due to its several benefits [1]-[5]. The commutation of the components aaggregate the multiple dc sources to gain output with higher levels. A 3-level boost converter which is connected to the inner capacitors of a 5-level diode clamped multilevel inverter (DCMLI) along with extra balancing circuit at the outer capacitors is presented using capacitor voltage balancing [6]. The carrier based multilevel PWM methods are reported to optimize or balance the utilization of the switches that are used in MLI [7]. A simple neutral point (NP) voltage regulator for a 3 level DCMLI is reported where a multiple carrier sine triangle modulator in conjunction with a closed loop controller for neutral point regulation [8]. The 3-phase front end bidirectional 5-level rectifier and rear end 5-level inverter are focused based on
multiple pole multilevel DCMLI approach to reduce the semiconductor [9]. The PWM technique is demonstrated to improve performance of a 3-phase DCMLI for 3 and 4 levels which can be extended to any levels [10]. The various hybrid techniques and its comparison is made for different applications to reduce the switches [11]. A hybrid MLI that is symmetrical is focused using modulation methods for single and three phase systems which is based on a 3-level switching cell and does not require capacitors nor diodes [12]. A combination of flying capacitor and cascaded inverters is presented which provides higher output levels with lower components with less losses [13]. An asymmetrical multi-pulse connection of uncontrolled rectifiers with hybrid MLI is elaborated to improve the input harmonic performance of adjustable-speed drives [14]. An inverter with hybrid modulation method is presented that incorporates stepped synthesis. The full bridge rectifier for single phase is discussed to analyze the performance of the MLI [15]. The NP potential regulator is discussed to determine the magnitude of variable offset voltage based upon different parameters [16]. A different topology is introduced for single phase 7 level inverter using phase disposition method for RL load to improve the performance of the inverter by compensating the disadvantages of classical MLI such as higher components, complex PWM and voltage-balancing problem [17]. As reported in the literature, the DCMLI need greater number of components. This paper presents an implementation of a three phase 9 level hybrid MLI inverter using alternate phase opposition disposition (APOD) carrier based sinusoidal pulse width modulation technique (SPWM). In classical MLI, the switches are combined to produce a high-frequency waveform in positive and negative polarities. Whereas in the hybrid multilevel inverter, all the switches need not be utilized for producing bipolar levels. This topology presented in this paper combines the level generation part and polarity generation part to generate the required nine level output.

CONCLUSION

This paper focuses on comparative analysis of two multilevel inverter topologies. One is the diode clamped multilevel inverter and the other is hybrid multilevel inverter with reduced number of components. The FFT analysis is carried out for these inverters using APOD pulse width modulation technique for nine level. The results of voltage, current, speed and torque response, stator currents and THD of voltage and current of diode clamped and hybrid inverter fed induction motor are analyzed, based on which a comparison between the diode clamped multilevel inverter and hybrid multilevel inverter is provided. The hybrid multilevel inverter has some unique features that have promoted its application in the MV drives, whereas the practical use of the diode clamped multilevel inverter seems limited due to the use of a large number of components, poor voltage THD and complex control scheme.

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