This paper proposes a comprehensive analytical passive LCL filter design method for three-phase two-level power factor correction rectifiers (PFCs). The high frequency converter current ripple generates the high frequency current harmonics that need to be attenuated with respect to the grid standards. Studying the high frequency current of each element proposes a non-iterative solution for designing a passive LCL filter. In this paper, the converter current ripple is thoroughly analyzed to generalize the current ripple behavior and find the maximum current ripple for sinusoidal PWM and third-harmonic injection PWM. Consequently, the current ripple is used to accurately determine the required filter capacitance based on the maximum charge of the filter capacitor. To choose the grid-side inductance, two methods are investigated. First method uses the structure of the damping to express the grid-side filter inductance as a function of the converter current ripple. Reducing the power loss in the filter and optimizing the grid-side filter inductance is the main focus of the second method which is achieved by employing line impedance stabilization network (LISN). Accordingly, two passive LCL filters are designed for a 5 kW silicon-carbide (SiC) based threephase PFC. Various experimental scenarios are performed to verify the filters attenuation and performance.
- AC-DC power conversion
- Passive filters
- Power filters
- Pulse width modulated power converters.
Fig. 1. (a) The schematic of a three-phase two-level PFC and (b) the generic equivalent circuit of the filter.
Fig. 2 Configuration I: the harmonic performance of the (a) converter current (b) grid current. Configuration II: (c) the current behavior of the filter capacitor, converter side induct or, and damping branch (d) grid current and its harmonic.
This paper has presented a comprehensive analytical method for designing LCL filter of a three-phase power factor correction rectifier (PFC). The method is explained by the converter current and the voltage behavior. The converter current ripple determines all the filter parameters and defines a suitable margin for them. A general equation is derived for the maximum converter current ripple which is applicable for sinusoidal PWM and third-harmonic injection PWM. The analysis is performed for unity power factor. It is proved that for modulation index higher than 0.845 the maximum current ripple occurs at zero crossing otherwise it appears at peak current. Consequently, the maximum charge of the filter capacitor is analytically obtained. Unlike the normal method on the literature in which the maximum filter capacitance is defined by absorbed reactive power. In this paper, the minimum filter capacitance is chosen according to the converter current analysis. Two methods are proposed for deriving the grid-side filter inductance. The first method uses the properties of the damping method and derives the required grid-side inductance as a function of the damping resistor and the converter current ripple. The second method focuses on reducing the power loss in the filter and optimizing it by employing line impedance stabilization network (LISN). Since in this paper, silicon-carbide switches (SiC) are used for designing the converter, consequently the switching frequency is in the order of couple of 10 kHz. Therefore, LISN can actively provide well-define impedance for switching sideband harmonics. Using LISN easily gives the grid-side filter inductance independent from the grid impedance. Two LCL filters for the 5 kW three-phase SiC based PFC have been designed and tested for different scenarios. The experimental results are match with the analysis.
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