Contents
How do you calculate voltage distortion?
The individual harmonic voltage distortion levels can be established by performing this calculation for the p.u. current associated with each harmonic number. The Voltage Total Harmonic Distortion [THD] is then calculated by establishing the square root of the sum of the squares of these individual Voltage harmonics.
What causes voltage distortion?
Voltage distortion occurs when an AC output is purely sinusoidal but has small levels of voltage harmonics in addition to the fundamental sinewave frequency. This low level of voltage distortion is often difficult to see on an oscilloscope and requires a power analyzer or harmonics analyzer to quantify.
What is voltage distortion?
Voltage distortion is any deviation from the nominal sine waveform of the AC line voltage. The distorted waveform repeats itself with some basic frequency. The sine wave associated with this frequency, which is usually 60 Hz, is called the fundamental.
How current distortion affects voltage distortion?
The current harmonics (distorted waveform) flow through system impedance (source and line impedances) and cause harmonic voltage drop across the impedances. This will distort the supply voltage waveform. Thus voltage harmonics are generated.
What is fundamental voltage?
A Fundamental Waveform (or first harmonic) is the sinusoidal waveform that has the supply frequency. We can see that a sinusoidal waveform is an alternating voltage (or current), which varies as a sine function of angle, 2πƒ. The waveforms frequency, ƒ is determined by the number of cycles per second.
What are VFD harmonics?
Harmonics are defined from the Fourier series that defines any periodic wave shape. Typically a three-phase, six-pulse VFD will draw nonlinear current that introduces the fifth and seventh harmonics on top of the fundamental frequency. The symptoms of the VFD related harmonics are evident as a distorted line voltage.
What is current distortion voltage?
Voltage harmonics do not originate directly from non-linear loads. The current harmonics (distorted waveform) flow through system impedance (source and line impedances) and cause harmonic voltage drop across the impedances. This will distort the supply voltage waveform. Thus voltage harmonics are generated.
What to do about voltage total harmonic distortion?
The main task of the control system in a UPS unit is to minimize the output voltage total harmonic distortion in different loading profiles. In addition, it should provide the proper mechanism to recharge the battery set and maintain high input power factor and low total input current harmonic distortion.
How is voltage distortion expressed in an AC power source?
Distortion is typically expressed in percentage (%) of the fundamental, based on the ratio between RMS amplitude of the higher harmonics versus the RMS amplitude of the first harmonic or fundamental (h=1). The lower the Vthd %, the better the programmable AC power source.
Why do PWM power sources have voltage distortion?
Since the switch mode amplifier dead time is typically fixed, the impact of it will increase as the programmed output frequency is raised as it becomes a larger fraction of the decreasing sine wave period. Thus, all PWM AC power sources have higher distortion specs at higher frequencies.
Why does a pure resistive load cause voltage distortion?
There are several possible factors that can contribute to voltage distortion, some of which having to do with the effect of non-linear loads. However, to compare the relative performance of a programmable AC source, it is best to use a pure resistive load so effects of load on the power source’s performance is neutralized.