Ahmet M. Hava

Simple analytical and graphical methods for carrier-based PWM-VSI drives

This paper provides analytical and graphical methods for the study, performance evaluation and design of the modern carrier-based pulse width modulators (PWMs), which are widely employed in PWM voltage-source inverter (VSI) drives. Simple techniques for generating the modulation waves of the high-performance PWM methods are described. The two most important modulator characteristics-the current ripple and the switching losses-are analytically modeled. The graphical illustration of these often complex multivariable functions accelerate the learning process and help one understand the microscopic (per-carrier cycle) and macroscopic (per fundamental cycle) behavior of all the modern PWM methods. The analytical formulae and graphics are valuable educational tools. They also aid the design and implementation of the high-performance PWM methods.

A high-performance generalized discontinuous PWM algorithm

In this paper, a generalized discontinuous pulsewidth modulation (GDPWM) method with superior high modulation operating range performance characteristics is developed. An algorithm which employs the conventional space-vector PWM method in the low modulation range, and the GDPWM method in the high modulation range, is established. As a result, the current waveform quality, switching losses, voltage linearity range, and the overmodulation region performance of a PWM voltage-source inverter (PWM-VSI) drive are optimized online, as opposed to conventional modulators with fixed characteristics. Due to its compactness, simplicity and superior performance, the algorithm is suitable for most high-performance PWM-VSI drive applications. This paper provides detailed performance analysis of the method and compares it to the other methods. The experimental results verify the superiority of this algorithm to the conventional PWM methods.

Carrier-based PWM-VSI overmodulation strategies: analysis, comparison, and design

In this paper, the overmodulation region voltage-gain characteristics and waveform quality of carrier-based pulsewidth-modulated (PWM) methods are investigated. Through detailed analytical study, voltage-gain characteristics are extracted independent of carrier frequency. The influence of blanking time and minimum pulsewidth (MPW) control on the inverter gain characteristics are studied and shown to be significant. A comparative evaluation of the modulator characteristics reveals the advantageous high-modulation-range characteristics of discontinuous PWM methods and, in particular, the superior overmodulation performance of a discontinuous PWM method. The modulation methods under consideration are tested on a PWM voltage-source inverter (VSI)-fed induction motor drive in the laboratory, and the theoretical results are verified by experiments. Also, a gain linearization technique is presented and experimentally verified. The results of this study are useful in the design, performance prediction and development of high-performance overmodulation strategies for PWM-VSI drives.

Performance Analysis of Reduced Common-Mode Voltage PWM Methods and Comparison With Standard PWM Methods for Three-Phase Voltage-Source Inverters

This paper surveys the reduced common-mode voltage pulsewidth modulation (RCMV-PWM) methods for three-phase voltage-source inverters, investigates their performance characteristics, and provides a comparison with the standard PWM methods. PWM methods are reviewed, and their pulse patterns and common-mode voltage (CMV) patterns are illustrated. The inverter input and output current ripple characteristics and output voltage linearity characteristics of each PWM method are thoroughly investigated by analytical methods, simulations, and experiments. The research results illustrate the advantages and disadvantages of the considered methods, and suggest the utilization of the near-state PWM and active zero state PWM1 methods as overall superior methods. The paper aids in the selection and application of appropriate PWM methods in inverter drives with low CMV requirements.

A Near-State PWM Method With Reduced Switching Losses and Reduced Common-Mode Voltage for Three-Phase Voltage Source Inverters

The near-state pulsewidth modulation (NSPWM) method, which reduces the common-mode voltage/current, is proposed for three-phase pulsewidth modulation (PWM) inverter drives. The method is described, its optimal voltage vectors are found, and the sequence that these vectors are applied is determined. Its voltage linearity and DC bus and AC output PWM current ripple characteristics are studied. Its output line-to-line voltage pattern is carefully studied with regard to switching transients that may cause overvoltages at the motor terminals, particularly for long-cable applications. The NSPWM method is thoroughly investigated, and its performance is compared to conventional PWM methods. Theory, simulations, and experiments show that NSPWM exhibits superior common-mode performance and satisfactory input/output PWM ripple performance characteristics. It is also illustrated that even though the method has bipolar line-to-line output voltage pulses, due to the sufficient zero-voltage time intervals for the switching transients to settle, these pulses do not cause additional overvoltages at the motor terminals compared to the conventional methods. The method is feasible for motor drives, particularly for operation in the high modulation index range, where its overall performance exceeds the performances of the state-of-the-art PWM methods.

A High-Performance PWM Algorithm for Common-Mode Voltage Reduction in Three-Phase Voltage Source Inverters

A high performance PWM algorithm with reduced common mode voltage (CMV) and satisfactory overall performance is proposed for three-phase PWM inverter drives. The algorithm combines the near state PWM (NSPWM) method which has superior overall performance characteristics at high modulation index and MAZSPWM, a modified form of the active zero state PWM method (AZSPWM1), which is suitable for low modulation index range of operation. Since AZSPWM1 has line-to-line voltage pulse reversals with small zero-voltage time intervals, in its naive form it causes overvoltages, in particular in long cable motor drive applications. Obtained by re-organizing the duty cycles of the utilized voltage vectors of AZSPWM1, MAZSPWM has sufficiently long zero-voltage time intervals between pulse reversals such that overvoltages are avoided. The combined algorithm performs satisfactorily throughout the inverter operating range and the transition from NSPWM to MAZSPWM and vice versa is seamless. The performance of the proposed algorithm is proven by theory, computer simulations, and detailed laboratory experiments. The paper also shows that the proposed reduced CMV PWM algorithm is effective in reducing the motor leakage current and it is most beneficial when a small common mode inductor is included in the drive.

The matrix converter drive performance under abnormal input voltage conditions

The matrix converter (MC) is a direct frequency conversion device with high input power quality and regeneration capability. As a device without energy storage elements, it has higher power density than pulse-width modulation (PWM) inverter drives. However, for the same reason, the AC line side disturbances can degrade its performance and reliability. In this paper, the behavior of the MC drive under abnormal input line voltage conditions has been investigated. A technique to eliminate the input current distortion due to the input voltage unbalance has been developed and its feasibility proven via computer simulations and laboratory experiments. The power line failure behavior has also been investigated and the rapid restarting capability of the MC drive has been demonstrated via laboratory experiments.

Common-Mode Voltage Reduction Pulsewidth Modulation Techniques for Three-Phase Grid-Connected Converters

This paper experimentally investigates the performance of three-phase voltage source pulsewidth modulation (PWM) converter, with the grid interfaced photovoltaic energy conversion system being the main application. In such applications the ground leakage current [common mode current (CMC)] should be much less than an ampere and this is difficult to obtain in transformerless (direct) connected systems. With the target being the reduction of the common mode voltage (CMV) and CMC, the converter performance is investigated thoroughly. Conventional PWM methods [space vector PWM (SVPWM) and discontinuous PWM (DPWM)] and recently developed reduced common mode voltage PWM (RCMV-PWM) methods [active zero state PWM (AZSPWM) and near state PWM (NSPWM)] are considered. The performance of a 1-kW rated PWM rectifier with additional common-mode capacitor emulating a PV system has been experimentally investigated. It is shown that the CMV and CMC of the tested RCMV-PWM methods is significantly less than conventional methods. In particular, NSPWM yields the best overall performance including low ground leakage current, low inverter output (phase current) and input (dc-link current) ripple, and low switching losses. Accounting for the parasitic capacitance effect, the resonant frequency of the common-mode circuit is identified and it is used in the converter design for the purpose of avoiding resonances involving large CMV-CMC. This paper aims help the design engineer select the appropriate PWM method for grid-connected applications and provides some design rules of thumb.

A modified C-dump converter for variable-reluctance machines

A type of converter for variable reluctance machine (VRM) drives is described. In this converter topology the energy extracted from an offgoing phase is stored in a dump capacitor. The energy stored is consequently used to either quickly turn on the next ongoing phase or energize the conducting phase frequently during the conduction interval instead of being returned to the supply as for a conventional C-dump circuit. Since the additional switch used to pass the energy to the C-dump capacitor is switched under a relatively low voltage condition and its switching frequency is relatively low, the rating of the additional switch is modest.<<ETX>>

A high performance generalized discontinuous PWM algorithm

In this paper a generalized discontinuous pulse width modulation (GDPWM) method with superior high modulation operating range performance characteristics is developed. An algorithm which employs the conventional space vector PWM method in the low modulation range, and the GDPWM method in the high modulation range is established. As a result, the current waveform quality, switching losses, voltage linearity range and the overmodulation region voltage gain of a PWM-VSI drive are optimized online as opposed to conventional modulators with fixed characteristics. Due to its compactness, simplicity and superior performance, the algorithm is suitable for most high performance PWM-VSI drive applications. The paper provides a detailed performance analysis of the method and compares it to the other methods. Experimental results verify the superiority or this algorithm to conventional PWM methods.