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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
oxide trap obtain a higher output voltage. Overmodulation occurs when the control (or modulation) signal magnitude exceeds the magnitude of the triangle carrier signal that it is being compared to and the number of pulses begin to drop out. This does introduce greater output voltage distortion. oversampling sampling a continuous-time signal at more than the Nyquist frequency. oversampling converter A/D converter that samples frequencies at a rate much higher than the Nyquist frequency. Typical oversampling rates are 32 and 64 times the sampling rate that would be required with the Nyquist converters. overshoot the amount by which an output value momentarily exceeds the ideal output value for an underdamped system. overstress failure failure mechanisms due to a single occurrence of a stress event when the intrinsic strength of an element of the product is exceeded. overvoltage a voltage having a value larger than the nominal voltage for a duration greater than 1 minute. overvoltage relay a protective relay that operates on overvoltage. over-excitation limiter tion limiter. See maximum excita-
Introduction to Inverters and Their Control
Published in R. Krishnan, Permanent Magnet Synchronous and Brushless DC Motor Drives, 2017
When the modulating signal rises above the magnitude of the carrier signal peak, the mode of operation is known as overmodulation. The gain of the inverter becomes nonlinear under such operating conditions and the magnitude of the fundamental output voltage does not rise in proportion to the modulating signal. It is crucial to have a higher fundamental and in step with modulating signal to have a highly responsive inverter for control applications. Operational waveforms in overmodulation region are given in Figure 2.20. Note the fundamental magnitude from the spectrum. It could be improved by many methods.
Electronic Communications
Published in Dale R. Patrick, Stephen W. Fardo, Electricity and Electronics Fundamentals, 2020
Dale R. Patrick, Stephen W. Fardo
When the peak amplitude of a modulating signal is less than the peak amplitude of the carrier, modulation is less than 100%. If the modulation component and carrier amplitudes are equal, 100% modulation is achieved. A modulating component greater than the carrier will cause overmodulation. An overmodulated wave has an interrupted spot in the carrier wave. Overmodulation causes increased signal bandwidth and additional sidebands to be generated, thus causing interference with adjacent channels.
Performance evaluation of single-phase induction motor controlled by variable frequency drive at non-ideal voltage conditions
Published in Australian Journal of Electrical and Electronics Engineering, 2019
M. Ishtiaque Rahman, Khosru M. Salim
Figure 4 shows the VFD connected motor-pump system. The VFD comprises of a double-arm rectifier and inverter with a dc link capacitor bank in between. Pulse width modulation (PWM) is used to provide the gating signals to the IGBT inverter. On the PWM generator block, the modulation index is varied each time in order to change the rms output voltage of the inverter. Using the same circuit of Figure 4 but with the load disconnected the rms output voltage (Vrms) was found for a range of modulation indexes (m) so as to determine a relationship between modulation index and rms output voltage. The curve presented in Figure 5 is obtained from simulation for modulation indexes ranging from 0 to 2.5 (overmodulation) with steps of 0.01. Examining the shape of the curve, the following equation has been identified for the system under consideration.