The Reserach Of Three-phase Grid-connected Inverters And Their Parallel Operation

In the inverter-driven motor systems, the motor maybe dragged by the mechanical load and in the power generation state. For energy saving and security considerations, the power stored in the DC link capacitor should be converted to three-phase AC and then transmitted to power grid. There're some typical three-phase power feedback application:"Elevator energy conservation devices", "pumping special four-quadrant inverter", "Crane power brake feedback unit," "continuous feedback power dynamometer unit" and so on. In wind energy, solar energy and other new energy domain, energy feedback device is one of the core parts of these systems.Energy conservation is China's basic national policy, and energy shortage is an undisputable reality. Therefore, feed the power energy due to the mechanical load back to power grid, is not only feasible, but a realistic demand. With the increased environmental awareness, there were increasing calls for green power. For the ordinary converter such as diode uncontrolled rectifier, these devices, and will inject a lot of harmonics into power grid while running, resulting the pollution of grid. Therefore,for converters, the concept of "green" should include the network harmonic pollution-free, unit power factor, and power control systems should be of high-performance, high stability, high efficiency.At first, this paper outlines some basic concepts of energy feedback, and special for three-phase direct grid-connected inverter (GCI), analyze its topology, mathematical models and techniques commonly used in current control, space vector pulse width modulation (SVPWM) will be detailly analyzed. Based on the principle of One-Cycle-Controlled (OCC), propose the idea of current envelope waveform. From the perspective of hybrid systems, based on precise mathematical expression, discuss the possible combination of working mode which may control the phase current to go along with the envelope waveform. Based on the single inverter, analyze the model of circulating current due to the GCI's parallel operation, based on this circulation model propose a method named variable zero vector control to suppress the circulating current. Some simulations were made to show the feasibility and effectiveness of those proposed algorithm In MATLAB. Finally, elaborate the design principles and organizational structure of software control system, list the program flow of the control algorithm...