What Is the Power Process?

Power refers to the amount of work that an object does in a unit of time, that is, power is a physical quantity that describes the speed of the work. The amount of work is constant, the shorter the time, the greater the power value. The formula for finding power is power = work / time. Power is a physical quantity that indicates how quickly the work is performed. The work done in unit time is called power, and it is expressed by P. Therefore, the power is equal to the scalar product of the applied force and the speed of the object's force point ^[1] .

Physic Entity: Indicates how fast or slow an object is doing work

Power can be divided into

1

Overview

The device for measuring power is called a power meter. According to the frequency of the measured signal, the power meter can be divided into: DC power meter, power frequency power meter, variable frequency power meter,

The input end of the switching power supply usually uses a rectifier filter circuit composed of a rectifier diode and a filter capacitor. After 220V AC input to the mains, it is directly connected to the capacitor filter to obtain a smoother DC voltage.

However, the rectifier filter circuit composed of a rectifier diode and a filter capacitor is a combination of a non-linear element and an energy storage element. Although the waveform Vi of the AC input mains voltage is sinusoidal, the conduction angle of the rectifier element is less than 180o, and generally only Around 60 °, the input AC current waveform is severely distorted and pulsed. The rectifier filter circuit composed of a rectifier diode and a filter capacitor mainly has the following problems:

(1) A large inrush current is generated during startup, which is about ten times to dozens of times the normal working current.

(2) In normal operation, due to the small conduction angle of the rectifier diode, a narrow pulse of high amplitude is formed, the current crest factor (CF) is high, and the current total harmonic distortion (THD) is usually more than 100%, which also causes the grid voltage Distortion of the waveform.

(3) The power factor (PF) is low, generally around 0.5 to 0.6.

The pulsed input current contains a lot of harmonic components, but only the fundamental current in the AC input current does work, and the remaining harmonic components do no work, that is, the average power of each harmonic component is zero, but a large number of harmonics The current component will increase the harmonic noise of the circuit. A filter needs to be added at the input of the rectifier circuit, which is expensive, bulky and heavy. At the same time, a large amount of harmonic current components flow back into the power grid, which will cause harmonic "pollution" of the power grid. One produces a "secondary effect", that is, harmonic current flowing through the line impedance causes a harmonic voltage drop, which in turn will distort the grid voltage waveform (originally a sine wave), and the second will cause the input current The increase of the effective value causes the lines and transformers to overheat, and at the same time, harmonic currents will also cause LC resonance of the power grid, or higher harmonic currents flow through the high-voltage capacitors of the power grid, causing them to overcurrent and explode. For three-phase AC power supply, due to the large amount of harmonic current components, the neutral line potential will also be shifted, and the neutral line current will overcurrent and cause a fault. Inductive or capacitive loads will cause additional phase shifts in the AC input voltage and current, which will reduce the line power factor and power utilization; non-resistive loads will also cause severe harmonic distortion and cause interference to the power grid.