A current feedback control strategy for parallel-connected single-phase inverters using a third-order general-integrator crossover cancellation method

Virtual impedance is usually introduced to the control system of parallel inverters in order to change the inverter equivalent output impedance and to enhance control accuracy and power sharing. In this paper, a current feedback control strategy using a third-order general-integrator crossover-cancellation method that can be implemented in a virtual impedance loop is proposed. This method consists of 2 parts: a crossover-cancellation feedback network, which achieves the band-pass effect, and a multilevel TOGI-OSG link, which acts as a filter. Compared with the conventional virtual impedance method, the proposed method can avoid derivation of output current, reduce system calculating burden, and enhance dynamic response. Additionally, this method can reduce the THD of output voltage in the case of nonlinear load and can also drastically restrain the impact of DC component on output voltage. A prototype consisting of 2 sets of 2-kW photovoltaic inverters operating in parallel was built in the laboratory. Simulated and experimental results are examined to verify the effectiveness and feasibility of this method.

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[1] Yazdanian M, Sani AM. Distributed control techniques in microgrids. IEEE T Smart Grid 2014; 5: 2901-2909.
[2] Rocabert J, Luna A, Blaabjerg F, Rodriguez P. Control of power converters in AC microgrids. IEEE T Power Electron 2012; 27: 4734-4749.
[3] Olivares DE, Sani AM, Etemadi AH, Canizares CA, Iravani R, Kazerani M, Hajimiragha AH, Bellmunt OG, Saeedifard M, Behnke RP et al. Trends in microgrid control. IEEE T Smart Grid 2014; 5: 1905-1919.
[4] Guerrero JM, Vicuna LG, Matas J, Castilla M, Miret J. A wireless controller to enhance dynamic performance of parallel inverters in distributed generation systems. IEEE T Power Electron 2004; 19: 1205-1213.
[5] Vasquez JC, Guerrero JM, Savaghebi M, Garcia JE, Teodorescu R. Modeling, analysis, and design of stationaryreference-frame droop-controlled parallel three-phase voltage source inverters. IEEE T Ind Electron 2013; 60: 1271- 1280.
[6] Hasanzadeh A, Onar OC, Mokhtari H, Khaligh A. A proportional-resonant controller-based wireless control strategy with a reduced number of sensors for parallel-operated UPSs. IEEE T Power Deliver 2010; 25: 468-478.
[7] Zhong QC. Robust droop controller for accurate proportional load sharing among inverters operated in parallel. IEEE T Ind Electron 2013; 60: 1281-1290.
[8] Tao Y, Liu QW, Deng Y, Liu XH, He XN. Analysis and mitigation of inverter output impedance impacts for distributed energy resource interface. IEEE T Power Electron 2015; 30: 3563-3576.
[9] Guerrero JM, Vasquez JC, Matas J, Castilla M, Vicuna LG. Control strategy for flexible microgrid based on parallel line-interactive UPS systems. IEEE T Ind Electron 2009; 56: 726-736.
[10] He JW, Li YW. Generalized closed-loop control schemes with embedded virtual impedances for voltage source converters with LC or LCL filters. IEEE T Power Electron 2012; 27: 1850-1861.
[11] Guerrero JM, Matas J, Vicuna LG, Castilla M, Miret J. Decentralized control for parallel operation of distributed generation inverters using resistive output impedance. IEEE T Ind Electron 2007; 54: 994-1004.
[12] Li YW, Kao CN. An accurate power control strategy for power-electronics-interfaced distributed generation units operating in a low-voltage multibus microgrid. IEEE T Power Electron 2009; 24: 2977-2988.
[13] He JW, Li YW. Analysis, design, and implementation of virtual impedance for power electronics interfaced distributed generation. IEEE T Ind Appl 2011; 47: 2525-2538.
[14] Zhang Y, Yu M, Liu FR, Kang Y. Instantaneous current-sharing control strategy for parallel operation of UPS modules using virtual impedance. IEEE T Power Electron 2013; 28: 432-440.
[15] Kim J, Guerrero JM, Rodriguez P, Teodorescu R, Nam K. Mode adaptive droop control with virtual output impedances for an inverter-based flexible AC microgrid. IEEE T Power Electron 2011; 26: 689-701.
[16] Guerrero JM, Vicuna LG, Matas J, Castilla M, Miret J. Output impedance design for parallel-connected UPS inverters with wireless load sharing control. IEEE T Ind Electron 2005; 52: 1126-1135.
[17] Yao W, Chen M, Matas J, Guerrero JM, Qian ZM. Design and analysis of the droop control method for parallel inverters considering the impact of the complex impedance on the power sharing. IEEE T Ind Electron 2011; 58:576-586.
[18] Matas J, Castilla M, Vicuna LG, Miret J, Vasquez JC. Virtual impedance loop for droop-controlled single-phase parallel inverters using a second-order general-integrator scheme. IEEE T Power Electron 2010; 25: 2993-3002.
[19] Bowtell L, Ahfock A. Direct current offset controller for transformerless single-phase photovoltaic grid-connected inverters. IET Renew Power Gen 2010; 4: 428-437.
[20] He GF, Xu DH, Chen M. A novel control strategy of suppressing DC current injection to the grid for single-phase PV inverter. IEEE T Power Electron 2015; 30: 1266-1274.
[21] Fedele G, Ferrise A, Muraca P. An adaptive quasi-notch filter for a biased sinusoidal signal estimation. In: 2011 9th IEEE International Conference on Control and Automation; 1921 December 2011; Santiago, Chile. Piscataway,NJ, USA: IEEE. pp. 1060-1065.