In order to minimize the effect of the grid harmonic voltages, harmonic compensation is usually adopted for a gridtied inverter. However, a large variation of the grid inductance challenges the system stability in case a high-order passive filter is used to connect an inverter to the grid. Although in theory, an adaptive controller can solve this problem, but in such case the grid inductance may need to be detected on-line, which will complicate the control system. This paper investigates the relationship between the maximum gain of the controller that still keeps the system stable and the Q-factor for a grid-tied inverter with an RL series or an RC parallel damped high-order power filter. Then, a robust passive damping method for LLCL-filter based grid-tied inverters is proposed, which effectively can suppress the possible resonances even if the grid inductance varies in a wide range. Simulation and experimental results are in good agreement with the theoretical analysis.
For a transformerless grid-tied converter using pulse width modulation, the harmonics of grid-injected current, the leakage current, and the electromagnetic interference (EMI) noise are three important issues during designing of the output filter. In this paper, the common mode and the differential mode EMI noises are investigated for the LCL-and LLCL-filter-based single-phase full-bridge grid-tied inverters. Based on this, a modified LLCLfilter topology is proposed to provide enough attenuation on the conducted EMI noise as well as to reduce the dc-side leakage current. The parameter design method of the filter is also developed. The comparative analysis and discussion on four filter cases (the conventional LCL filter, the conventional LLCL filter, the modified LCL filter, and the modified LLCL filter) are carried out and verified through simulations and experiments on a 0.5-kW, 110 V/50 Hz single-phase full-bridge grid-tied inverter prototype.
For a transformerless grid-tied converter using pulse width modulation, the harmonics of grid-injected current, the leakage current, and the electromagnetic interference (EMI) noise are three important issues during designing of the output filter. In this paper, the common mode and the differential mode EMI noises are investigated for the LCL-and LLCL-filter-based single-phase full-bridge grid-tied inverters. Based on this, a modified LLCLfilter topology is proposed to provide enough attenuation on the conducted EMI noise as well as to reduce the dc-side leakage current. The parameter design method of the filter is also developed. The comparative analysis and discussion on four filter cases (the conventional LCL filter, the conventional LLCL filter, the modified LCL filter, and the modified LLCL filter) are carried out and verified through simulations and experiments on a 0.5-kW, 110 V/50 Hz single-phase full-bridge grid-tied inverter prototype.
Grid-tied inverters have been widely used to inject the renewable energies into the distributed power generation systems. However, a large variation of the grid impedance challenges the stability of the high-order power filter based grid-tied inverter. Many passive and active damping methods have been proposed to overcome this issue. Recently, a composite passive damping method for a high-order power filter based grid-tied inverter with an RC parallel damper and an RL series damper was presented to eliminate this problem, but at the cost of more material and power losses. In this paper, a hybrid damping method with a digital filter and an RC parallel damper is proposed. The design of the digital filter is developed using a normalized method. The validity is verified through the simulations and the experiments on a 500 W, 110 V/50 Hz prototype, while the grid inductance varies from 0.15 mH to 5 mH. I.
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