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In this paper, a Pulse Width Modulation (PWM) technique for modular multilevel converter has been explored. The PWM technique is implemented using carrier based level shifted PWM strategy. It does not necessitate the calculation of duty cycles, and can be easily implemented in a DSP. With the proposed technique, harmonics in the phase voltage is shifted to twice the switching frequency. Thus, the...
Pulse width-modulated (PWM) inverters are used more and more to operate electrical machines and to interface renewable energy systems with the utility grid. However, there are abundant high-frequency harmonics in the output voltage of a PWM inverter, which increase the iron losses and result in derating of the machine or transformer connected to them. Predicting the iron losses caused by the PWM supply...
Voltage total harmonic distortion and related quadratic criteria are accepted as figures of merit of a multilevel PWM converter voltage quality. The dominating frequency domain voltage quality evaluation approach, in fact, is essentially numerical as it involves infinite double Fourier series expansion with Bessel function coefficients and requires high switching harmonics count. Suggested time domain...
This paper presents an improved asymmetric space vector modulation (ASVM) for two level voltage source converters (VSCs) when the switching frequency is only 9 times of line frequency. By adding two pulses in each line cycle when the fundamental voltage crosses zero, the total harmonic distortion (THD) of output current can be reduced significantly with very limited penalty. The applications of improved...
Randomized modulation schemes are often employed in DC-DC converters to reduce the magnitude of discrete harmonics in the output spectrum. One of these schemes is Randomized Switching Frequency modulation (RSFM) that completely eliminates the discrete harmonics by randomizing its switching period (switching frequency) to follow a uniform distribution. In this paper, we investigate RSFM with its switching...
This paper presents a novel control scheme suitable for high-power high-performance AC power supplies. The performances of the conventional current-regulated voltage-controlled system with bipolar PWM are first analyzed in detail. The proposed control scheme incorporates dual synchronous PWM technique of single-phase full-bridge inverter and multiple feedback loop. Thanks to this scheme, the AC power...
Multi-pulse converters are suitable for high power application with the merits of low switching frequency (f0) and perfect harmonic performance. But the less controllability and poor regulation has a restriction on its application. This paper proposed an AC-DC/DC-AC converter based on multi-pulse converter's structure which has the same perfect harmonic performance with a low switching frequency (3f...
This paper presents a modulation scheme in order to reduce conducted electromagnetic interference (EMI) generated by modular power converters with parallel topology. The proposed scheme is based on a combination of interleaving and Switching Frequency Modulation (SFM) techniques. The objective of this modulation scheme is to cancel certain harmonics of EMI and to reduce the amplitude of the remaining...
A typical 2-level pulse-width modulation scheme for a DC-DC converter generates a signal that has two values, that is zero and one. For a random aperiodic scheme, the switching period can be modulated in a random fashion with a known probability density function. In this paper, analytical expressions for both discrete and continuous spectrum are provided for the case where different probability density...
In order to improve the efficiency of the conventional home appliances, brushless DC motors with variable speed controller have been extensively applied to various home appliances, such as air-conditioners, refrigerators, washing machines, etc. However, existing literatures concerning power factor correction (PFC) for home appliances are limited. In this paper, a practical approach is proposed to...
In direct-drive wind turbine systems, a dual PWM converter for grid interface and its control strategy are presented. Following introducing the full-size AC-DC-AC converter, the principle and advantages of the dual inverter are analyzed. With the proposed method it not only divides high-level currents, making existing equipments apply to large-scale systems, but also reduces the current ripple amplitude...
Controlling of a specific harmonic by a switching converter with switching frequency lower than 1 kHz was originally implemented by two-level optimal pulse pattern with unsymmetrical switching angles, namely by OPUS-technique. That means, given a desired fundamental and one or more specific harmonics, the problem is to find the switching times (angles) that produce the fundamental while generating...
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