Design of LCL Filter
As the interface between renewable energy power generation system and the power grid, the grid-connected inverter is used to convert the dc power to the high-quality ac power and feed it into the power grid. In the grid-connected inverter, a filter is nee
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Design of LCL Filter
Abstract As the interface between renewable energy power generation system and the power grid, the grid-connected inverter is used to convert the dc power to the high-quality ac power and feed it into the power grid. In the grid-connected inverter, a filter is needed as the interface between the inverter and the power grid. Compared with the L filter, the LCL filter is considered to be a preferred choice for its cost-effective attenuation of switching frequency harmonics in the injected grid currents. To achieve high-quality grid current, the LCL filter should be properly designed. In this chapter, the widely used pulse-width modulation (PWM) schemes are introduced, including the bipolar sinusoidal pulse-width modulation (SPWM), unipolar SPWM and harmonic injection SPWM. The spectrums of the output PWM voltage with different SPWM are studied and compared. A design procedure for LCL filter based on the restriction standards of injected grid current is presented and verified by simulations.
Keywords Grid-connected inverter LCL filter (PWM) Total harmonics distortion (THD)
Pulse-width modulation
As the interface between renewable energy power generation system and the power grid, the grid-connected inverter is used to convert the dc power to the high-quality ac power and feed it into the power grid. In the grid-connected inverter, a filter is needed as the interface between the inverter and the power grid. Compared with the L filter, the LCL filter is considered to be a preferred choice for its cost-effective attenuation of switching frequency harmonics in the injected grid currents. To achieve high-quality grid current, the LCL filter should be properly designed. In this chapter, the widely used pulse-width modulation (PWM) schemes are introduced, including the bipolar sinusoidal pulse-width modulation (SPWM), unipolar SPWM and harmonic injection SPWM. The spectrums of the output PWM voltage with different SPWM are studied and compared. A design procedure for LCL filter based on the restriction standards of injected grid current is presented and verified by simulations.
© Springer Nature Singapore Pte Ltd. and Science Press 2018 X. Ruan et al., Control Techniques for LCL-Type Grid-Connected Inverters, CPSS Power Electronics Series, DOI 10.1007/978-981-10-4277-5_2
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Fig. 2.1 Single-phaseLCLtype grid-connected inverter
Q1 Vin /2
Q3
L1
A vinv
O
L2 C
vg
B
Vin /2
Q2
2.1
Design of LCL Filter
Q4
PWM for Single-Phase Full-Bridge Grid-Connected Inverter
Figure 2.1 shows the topology of a single-phase full-bridge LCL-type gridconnected inverter, where switches Q1–Q4 compose the two bridge legs, and inductors L1, L2 and capacitor C compose the LCL filter. Note that the two switches in the same bridge leg are switched in a complementary manner. Generally, the bipolar SPWM and unipolar SPWM are usually used for single-phase full-bridge inverter. For convenience of illustration, the dc input voltage Vin is split into two ones equally, and the midpoint O is defined as the base potential
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