Investigation On Harmonic Model And Attenuation Effect Of Single-phase Diode Bridge Rectifier Loads

In recent years, single-phase power electronic loads with switching power supply or variable frequency device have been immediately increasing with the development of power electronic technology as well as the wider attention of energy saving. These loads are small from an energy point of view. However, they typically have high ITHDs, in the range of 100%, and are distributed all over an electric network. Collectively, they bring a great impact on harmonic voltage and current levels in distribution system, and consequently have raised serious concern as distributed harmonic sources. Traditional harmonic current source model has difficulties in investigating the interaction of the voltage and current distortion, i.e. attenuation effect, and can result in significant overestimation of the harmonic distortion levels. This paper developed a generic harmonically coupled admittance matrix model for single-phase diode-bridge converter-based loads such as desktop PC, with which attenuation characteristic of such loads is investigated.1) Based on the PC's generic circuit, this paper developed a frequency-domain harmonic model, which transfers nonlinear characteristics of PCs in the time-domain to linear admittance matrices in the frequency-domain. Besides the application on frequency domain harmonic power flow solution, the model can also be used to analyze the impact of the harmonic voltages on the harmonic currents, i.e. attenuation effect, since it couples all harmonic voltages and currents. Furthermore, the presented model can be extended to other loads employing the similar circuit since it was derived by the generic circuit. This model was verified by simulations and measurements as well.2) An approach for estimating the parameters in a general equivalent circuit that represents the single-phase diode-bridge converter-based loads was presented. The parameters can be estimated by using measurements taken under any voltage, and the obtained equivalent circuit can be extended to perform harmonic assessment under any other distorted voltages. This paper also presented a frequency domain harmonic model for this type of loads, based on which an iterative harmonic power flow calculation approach was carried out. Both the parameter estimation approach and the frequency-domain harmonic model were verified by simulations and measurements.3) Investigation of the attenuation characteristics for such loads with the presented model indicated that: the occurrence of the attenuation effect is dependent only on the phase angle, while the effect's severity is dependent on the magnitude of the harmonic voltage; the current harmonics produced by these loads produce voltage harmonics that partially correct their ITHD through attenuation effect; supply voltage crest factor is a better predictor of ITHD than VTHD.