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会员 An Improved Grid Voltage Feedforward Compensation Scheme of Grid-Connected Inverter in Weak Grid
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  • 2018/01/01
摘要
The grid voltage feedforward control strategy is widely used in the grid-connected inverter, aiming to reduce the disturbance of grid voltage distortion and suppress the impulse current of inverter at startup. However, an extra positive feedback channel will be introduced into the current control loop in weak grid, bringing low harmonics and even instability in the inverter. Many schemes available in literatures are proposed to deal with this problem. In [2], an adaptive grid voltage feedforward algorithm based on online impedance detection is proposed, overcoming the effect of positive feedback on the stability of the system, and realizing stable operation of the grid-connected inverter. In [3], the phase margin (PM) of grid-connected inverter is enhanced by adding phase leading block to the current control loop. However, the differential term is introduced in this scheme, amplifying the noise in practical application. Another class of improved algorithm is to add compensation block in the traditional grid voltage feedforward control strategy, such as weighting coefficient [4], low-pass filter (LPF) [5] or second-order generalized integrator (SOGI) [6]. In [4], the weighting coefficient is introduced into the feedforward to weaken the positive feedback channel. Actually, it is a tradeoff between no proportional voltage feedforward and proportional voltage feedforward. In [5], an improved voltage feedforward based on LPF is proposed to passivate the positive feedback channel and hence improved the PM of the system. In [6], a SOGI block which centered on the fundamental frequency is placed on the grid voltage feedforward path, and the stability is also greatly improved. Reviewing the publications, there is no related literature to summarize the basic principle and control strategy of the improved voltage feedforward control. In this paper, the above improved algorithms are compared and it is concluded that the steady-state and dynamic performance of the system cannot be balanced with the existing method. For example, well steady-state performance can be achieved with the voltage feedforward control based on SOGI, however, its dynamic performance is worse than that of weighting coefficient and LPF. In this paper, an improved voltage feedforward compensation control strategy is given by incorporating the existing scheme based on weighting coefficient and LPF. Compared with existing scheme, the proposed scheme in this paper has better steady state performance. Meanwhile, the dynamic performance of the proposed scheme is better than that of the SOGI technique. The effectiveness of the proposed scheme is verified by theoretical analysis and experiments.
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