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Generator dc - schoolphysics
Generator dc - schoolphysics

... press against a split ring of copper. This means that a varying but unidirectional e.m.f will be produced. A d.c generator and its output is shown in simplified form in Figure 1. As with the a.c. generator, the d.c. machine usually uses rotating field coils, a series of them being wound round in the ...
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... of Imminent Voltage Collapse Voltage collapse is a phenomenon that occurs due to lack of reactive power. Frequently it is difficult to detect from voltage measurements because the system “controls” the voltage. In today’s (smart grid) terminology this is called Synchrophasor (or AMI). ...
harmonic current compensation in self excited induction generator
harmonic current compensation in self excited induction generator

... Abstract: The paper presents the concept of wind power generation system inverter as SAF under balanced and unbalanced conditions. PV based systems are practically inactive during the night time, Because of the system cannot conserve the energy on the night time. During the night time, the PV-SAF pr ...
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... QX5241 is a step-down high-brightness LED constant-current driver with high accuracy. A high-side current-sense resistor adjusts the output current, which minimizes the number of external components while delivering an LED current with ±1% accuracy, and a dedicated PWM input (DIM) makes a wide range ...
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Calibrating Voltage Input Signal Conditioners Using the Fluke 787
Calibrating Voltage Input Signal Conditioners Using the Fluke 787

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Pulse-width modulation



Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique used to encode a message into a pulsing signal. Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors. In addition, PWM is one of the two principal algorithms used in photovoltaic solar battery chargers, the other being MPPT.The average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast rate. The longer the switch is on compared to the off periods, the higher the total power supplied to the load.The PWM switching frequency has to be much higher than what would affect the load (the device that uses the power), which is to say that the resultant waveform perceived by the load must be as smooth as possible. Typically switching has to be done several times a minute in an electric stove, 120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into the tens or hundreds of kHz in audio amplifiers and computer power supplies.The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on.The main advantage of PWM is that power loss in the switching devices is very low. When a switch is off there is practically no current, and when it is on and power is being transferred to the load, there is almost no voltage drop across the switch. Power loss, being the product of voltage and current, is thus in both cases close to zero. PWM also works well with digital controls, which, because of their on/off nature, can easily set the needed duty cycle.PWM has also been used in certain communication systems where its duty cycle has been used to convey information over a communications channel.
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