Abdul R. Beig

Modified SVPWM Algorithm for Three Level VSI With Synchronized and Symmetrical Waveforms

The objective of the present work is to improve the output waveform of three level inverters used in high-power applications, where the switching frequency is very low. This is achieved by maintaining the synchronization, half-wave symmetry, quarter-wave symmetry, and three-phase symmetry in the pulsewidth modulation (PWM) waveforms. The principles of achieving synchronization and symmetries in terms of space vectors for three level inverters are presented. A novel synchronized space vector pulsewidth modulation (SVPWM) algorithms is proposed and verified experimentally. The experimental waveforms of the inverter output voltage and motor no load current for different operating conditions of the drive are presented. The performance measure in terms of the weighted total harmonic distortion (THD) of the line voltage is computed for the linear modulation region of the drive for the proposed algorithm and compared with that of synchronized SVPWM and synchronized sine-triangle pulsewidth modulation (SPWM) technique. The comparative results show that consideration of synchronization and symmetry results in improved THD. Another significant feature of the proposed algorithm is that the symmetry and synchronization leads to self-balancing of the direct current (dc) bus capacitor voltages over every one third cycle of the fundamental

A novel CSI-fed induction motor drive

Current source inverter (CSI) fed drives are employed in high power applications. The conventional CSI drives suffer from drawbacks such as harmonic resonance, unstable operation at low speed ranges, and torque pulsation. This paper presents a novel CSI drive which overcomes all these drawbacks and results in sinusoidal motor voltage and current even with CSI switching at fundamental frequency. The proposed CSI drive uses a three-level inverter as an active filter across motor terminals replacing the bulky ac capacitors used in the conventional drive. A sensorless vector controlled CSI drive based on proposed configuration is developed. The simulation and experimental results are presented. Experimental results show that the proposed drive has stable operation even at low speeds. Comparative results show that the proposed CSI drive has improved torque ripple compared to the conventional configuration.

A novel fifteen level inverter for photovoltaic power supply system

A novel dc to ac inverter for photovoltaic power supply system is presented in this paper. The objective is to develop a low cost, reliable and efficient photovoltaic power supply unit for domestic applications. A fifteen level cascaded H-bridge configuration using low voltage MOSFETs as switching devices is used. This configuration results in sinusoidal output voltages with step modulation and fundamental frequency switching. The proposed configuration has reduced conduction loss and switching loss. Simple gate drive circuit is designed using commonly available integrated circuit components. The simulation results are presented.

Space-Vector-Based Synchronized Three-Level Discontinuous PWM for Medium-Voltage High-Power VSI

The high-power voltage source inverters are switched at low frequency to reduce the losses in the inverter. The discontinuous pulsewidth-modulation (PWM) sequences reduce the switching frequency to two-thirds compared to the conventional continuous PWM sequences. At low switching frequency, the output will be rich in harmonics, and synchronization is a must to avoid subharmonics. This paper presents four basic types of synchronized discontinuous PWM (DPWM) sequences that ensure synchronization, three-phase symmetry, and half-wave symmetry. The proposed synchronized DPWM sequences are verified through simulation and experiment on a constant- v/f open-loop induction motor drive. The performance of the proposed DPWM algorithms is studied in the entire modulation region, including the overmodulation region, and is compared with that of the conventional synchronized space vector PWM. A different type of DPWM with low common-mode voltage is suggested for low-modulation region and verified experimentally.

Synchronized SVPWM Algorithm for the Overmodulation Region of a Low Switching Frequency Medium-Voltage Three-Level VSI

In high-power applications, the output voltage of a voltage source inverter (VSI) must be synchronized with its fundamental component in order to eliminate subharmonics. With proper selection of switching states, it is possible to obtain synchronization and symmetry in the space vector pulse width modulation (SVPWM) algorithm. This paper presents an improved three-level SVPWM algorithm for the overmodulation region, which guarantees synchronization, half-wave symmetry, quarter-wave symmetry, and three-phase symmetry for all integer values of the pulse number. The proposed synchronized SVPWM algorithm is experimentally verified. The performance of the proposed algorithm is compared with other conventional algorithms. The comparative results prove that the consideration of synchronization and various symmetry results in better performance of the VSI.

Space vector based bus clamped PWM algorithms for three level inverters: implementation, performance analysis and application considerations

This paper describes the different types of space vector based bus clamped PWM algorithms for three level inverters. A novel bus clamp PWM algorithm for low modulation indices region is also presented. The principles and switching sequences of all the types of bus clamped algorithms for high switching frequency are presented. Synchronized version of the PWM sequences for high power applications where switching frequency is low is also presented. The implementation details on DSP based digital controller and experimental results are presented. The THD of the output waveforms is studied for the entire operating region and is compared with the conventional space vector PWM technique. The bus clamped techniques can be used to reduce the switching losses or to improve the output voltage quality or both.. Different issues dominate depending on the type of application and power rating of the inverters. The results presented in this paper can be used for judicious use of the PWM techniques, which result in improved system efficiency and performance.

A Multitasking Control Algorithm for Grid-Connected Inverters in Distributed Generation Applications Using Adaptive Noise Cancellation Filters

This paper proposes a multitasking control algorithm for grid-connected inverters (GCIs) in distributed generation (DG) applications. A single-phase H-bridge voltage source inverter is used as a power electronic interface between the DG system and the grid. The proposed control algorithm operates the GCI in current control mode to achieve desired active power injection to the grid. In addition to active power injection, the proposed control algorithm has current harmonics mitigation and reactive power compensation capabilities for power quality enhancement. The control algorithm utilizes only the remaining capacity of the GCI for power quality improvement. The proposed control algorithm employs a current decomposition structure based on multiple adaptive noise cancellation (ANC) filters for extraction of harmonic and reactive currents of the local loads. The extracted harmonics are used in estimating compensating currents to be injected by the GCI. A single-phase phase-locked loop (PLL) using ANC filters has been developed to synchronize the GCI at fundamental frequency, which makes the proposed control algorithm adaptive to grid frequency fluctuations and immune to grid voltage distortions. The effectiveness of the proposed control is illustrated through computer simulation and experimental results. The influence of PLL dynamics on GCI performance has also been studied using results.

Space vector based synchronized PWM algorithm for three level voltage source inverters: principles and application to V/f drives

This paper describes the synchronized PWM techniques based on space vector approach for three level voltage source inverters. The objective is to improve the output waveform of the inverters used in high power applications, where the switching frequency is very low. This is achieved by maintaining the synchronization and half wave symmetry, quarter wave symmetry, three-phase symmetry in the PWM waveforms. The principles of achieving synchronization and symmetries are presented. The proposed algorithm is implemented on TMS320F240 based digital controller and applied to V/f drive. The experimental waveforms of the inverter output voltage and motor no load current for different operating conditions of the drive are presented. The V/sub WTHD/ of the line voltage and I/sub THD/ of the no load current of the motor are computed from the experimental data. The performance measure in terms of the V/sub WTHD/ of the line voltage is computed for the entire operating region of the drive for the proposed algorithm and the synchronized SPWM technique. The comparative results show that the proposed method has improved THD over SPWM method. Another significant feature of the proposed algorithm is that the symmetry and synchronization leads to self-balancing of the DC bus capacitor voltages.

Synchronized SVPWM algorithm for overmodulation region for three-level VSI

Synchronization is essential for the satisfactory operation of VSI in high power applications. With proper selection of switching states it is possible to obtain synchronization and symmetry in space vector pulse width modulation (SVPWM) algorithm. A novel SVPWM based switching algorithm, which results in improved THD and increased fundamental voltage in overmodulation region by maintaining synchronization and symmetry is presented in this paper. A simple method to determine the switching sequence to achieve synchronization, quarter wave symmetry, half wave symmetry and three phase symmetry in overmodulation region is presented. The proposed algorithm is simulated and its performance in terms of the THD and magnitude of fundamental voltage of output is studied in the overmodulation region. The results show the improved performance of the proposed algorithm compared to the existing algorithms. The proposed algorithm is verified experimentally on a constant v/f three level VSI fed induction motor drive.

Influence of placement of small space vectors on the performance of PWM techniques for three level inverters

The performance of three level inverters depends on the PWM technique. The three level space vector PWM (SVPWM) has improved performance in terms of the THD and the D.C. bus mid point voltage balance compared to three level sine triangle PWM (SPWM). The objective of this paper is to study the importance of the space vectors, the influence of their placement in the switching sequence on the performance of the PWM techniques and address the basic issue of why the SVPWM has superior performance over SPWM technique. Such a basic understanding will help in designing optimal PWM with desired performance. The study has shown that the superior performance of SVPWM is because of the placement of the small space vectors as the beginning and ending vectors in each sequence, with equal dwell times. The simulation results are presented to validate the theoretical observations. The SVPWM is implemented on a general purpose DSP based digital controller and applied to constant v/f drive.