1, carrier or carrier frequency (carrier frequency) is a physical concept. It is a radio wave with a specific frequency in hertz. It is an electromagnetic wave modulated by frequency, amplitude or phase, which is used to transmit language, music, images or other signals.

2. Fundamental wave: In complex periodic oscillation, it includes fundamental wave and harmonic wave. The sine wave component equal to the longest period of oscillation is called the fundamental wave. The frequency corresponding to this period is called the fundamental frequency. A sine wave component with a frequency equal to an integer multiple of the fundamental frequency is called harmonic.

3. Harmonic refers to various components obtained by Fourier series decomposition of periodic non-sinusoidal alternating current, which is more than an integer multiple of the fundamental frequency, and is usually called higher harmonic. Fundamental refers to the same component as the power frequency (50Hz). High-order harmonic interference is a big "public hazard" that affects the power quality in the current power system, and it is urgent to take countermeasures.

Extended data:

The main causes of harmonics are as follows: because sinusoidal voltage is applied to nonlinear load, the fundamental current is distorted to produce harmonics. The main nonlinear loads are UPS, switching power supply, rectifier, frequency converter and inverter.

Overtone is a kind of physical harmonic, but the definition of numbers is slightly different. Audio with twice the fundamental frequency is called the first overtone, audio with three times the fundamental frequency is called the second overtone, and so on. The frequency of harmonics must be equal to an integer multiple of the fundamental frequency. Waves with 3 times the fundamental frequency are called third harmonics, waves with 5 times the fundamental frequency are called fifth harmonics, and so on. No matter how many harmonics, they are sine waves.

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