A common control method in power electronics for managing the output voltage of converters, particularly DC/AC inverters, is pulse width modulation (PWM). The basic concept behind PWM is to adjust the output pulse width in order to regulate the average output voltage. With PWM, a fixed DC input volt Contact online >>
A common control method in power electronics for managing the output voltage of converters, particularly DC/AC inverters, is pulse width modulation (PWM). The basic concept behind PWM is to adjust the output pulse width in order to regulate the average output voltage. With PWM, a fixed DC input voltage source can produce a sinusoidal output waveform with variable frequency and amplitude.
PWM methodologies in inverters provide fine control over the output voltage waveform in VSIs, enabling accurate voltage regulation as well as current regulation. This is vital for numerous applications where precise voltage control is necessary for top performance, including motor drives, renewable energy systems, and uninterruptible power supplies (UPS).
With the usage of PWM, it is also possible to control the output waveform''s harmonic distortions which ultimately leads to improved power quality and lowering system losses. In contrast to the fundamental square-wave modulation techniques, PWM in inverters offers advantages in terms of improved control over output voltage, frequency, and harmonics.
PWM comes in a variety of forms for single-phase inverters. These cleverly designed procedures take into account the inverters'' activity in only permitted switching states in order to prevent any potential damage. To prevent the source from being shorted, for instance, the switches in the same leg of VSIs are never switched on. The typical PWM methods for full-bridge single phase inverters are listed below.
Figure 24 illustrates the single-pulse width modulation; a straightforward PWM approach that includes creating gating pulses with adjustable width and position. When the modulation index M, which is the ratio of the reference signal Ar to the maximum value of the carrier signal Ac, varies, the position and breadth of this pulse inside each half-cycle also changes, or modulates.
Figure 25 depicts a single-phase full-bridge inverter. A carrier signal is compared to a reference signal to produce gating pulses for switches T1 (and T2), referred to as g1, and T3 (and T4), referred to as g4 as indicated in Figure 24. The positive magnitude of reference and carrier signal determine g1, while g4 is determined by their negative magnitudes. Figure 25 displays the output voltage as a result.
The third harmonic is prominent in this PWM. The distortion factor (DF) is defined as the ratio of the root mean square of harmonics to the fundamental component, with second-order attenuation (division by the square of each harmonic order). It takes into consideration the fact that the output filter would more effectively attenuate harmonics. DF grows as M decreases, implying lower output voltages. Finally, an acceptable value of M is approximately 0.8, where the DF is the smallest.
Three-phase inverters can be thought of as three single-phase inverters, with the output of each single-phase inverter shifted by 120-degree. Thus, the PWM methodologies discussed above for single-phase inverters are still applicable. In SPWM, for example, three sinusoidal references produced 120-degree apart are compared with the carrier signal to provide the appropriate gating signals for the phase.
The reference signal in the third-harmonic PWM for three-phase inverters is made up of the fundamental signal as well as its third harmonic, as shown in Figure 32. The third harmonic component in the neutral terminal is effectively canceled when a third harmonic component is present in each phase. By offering a fundamental component that is around 15.5% greater than that of sinusoidal PWM, third-harmonic PWM offers superior dc supply voltage consumption than sinusoidal PWM.
The fundamental distinction between SVM and traditional PWM approaches is in the mathematical formulation and production of switching patterns. The output voltage is represented as a vector in a complex plane known as the α-β plane by SVM, and the proper switching states are determined to yield the required voltage vector.
Figure 36 reflects the Sectors 1 and 2''s switching patterns and accompanying dwell periods. Similar patterns can be seen for other industries as well. Switches Q1-6 in the 3-phase bridge inverter can be triggered utilizing the gating sequence.
where PAC is AC power output and PDC is DC power input. High-quality sine wave inverters often have peak efficiencies ranging from 90 to 95%. Modified sine wave inverters of lower quality are 75–85% efficient. High frequency inverters typically outperform their low frequency equivalents in terms of efficiency.
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