The Research On Photovoltaic Grid-connected Inverter

The development of new energy is promoted, with the deterioration of environment and the depletion of conventional resource. Solar energy, with the characteristic of sustainable development, is being developed faster and faster by policies and measures introduced in most countries. Amongst other things, photovoltaic grid-connected system has far-reaching theoretical value and practical significance. The total installed capacity of photovoltaic grid-connected system has reached thousands of megawatts only in the past five years. Photovoltaic grid-connected inverter, which connects the photovoltaic array and grid, is the key to the photovoltaic system.The DC-DC and DC-AC two steps grid-connected inverter is proposed based on the characteristic of the invert and the output of photovoltaic arrays. DC-DC and DC-AC are analyzed elaborately and respectively, as well as new control strategy being proposed, based on the relatively independence of DC-DC and DC-AC. In the converter of DC-DC, Boost circuit is used for modulating the output of photovoltaic array and tracking the maximum power point of photovoltaic system. The three dots least square method, as a new method of maximum power point tracking is proposed, against the disadvantage of constant voltage method and perturbation method, which is proved to track maximum power point accurately and quickly by simulation, as well as improving the utilization efficiency of system and stabilizing the output voltage. In the converter of DC-AC, with the control of output current, based on the disadvantage of SPWM(sine pulse width modulation), the SVPWM(space vector pulse width modulation) is used to control the invert, improving the utilization of DC voltage, reducing harmonic. Result shows that the output current can keep the same phase with the grid voltage and proves the algorithm is feasible, by establishing the system model based the principle of SVPWM.Base on the new control strategy, the hardware of the 2kW three-phase grid- connected inverter is designed, including the main circuit DC-DC and DC-AC, driven circuit, the detection circuit of voltage and current and the detection circuit of zero and so on. The design provides reference for the similar structure of photovoltaic grid-connected invert.