| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 100 === The thesis focuses on developing the control technology of parallel operations of multiple three-phase inverters and applies such technology to three-phase grid-connected power system as well as standalone AC power supply. The advantages of parallel operation increase the capacity and reliability of operation.The grid-connected inverters are capable of switching power flow bidirectionally, supplying DC micro-grid-connected power, and transmitting renewable energy on the DC side to the grid-connected power system.By doing so, buying and selling electricity can be achieved. Moreover, the three-phase AC voltage source is able to supply power to the AC load while the utility power fails. As for the control strategy of the standalone power supply, one of the inverter modules accomplishes the closed-loop control of q-d axis voltages by adopting synchronous frame transformation and AC voltages feedback as well. Another inverter module can be used to control the real power or average-current-sharing. Accordingly, the power which the load requires can be supplied while the rate of AC output voltage regulation can be reduced as well. The control strategy of grid-connected power system adopts the feedback of voltages and currents on the AC side to achieve the voltage phase angle detection, the q-d axis current closed-loop control, the controllable real power with software. In addition, this technology has a DC voltage closed-loop control strategy which stabilizes the DC voltage which is used to regulate the DC grid-connected voltage.
This thesis used a 32-bits digital controller as a control core to implement one inverter module. The control strategy of grid-connected power and standalone system will be accomplished by programming with C language. Each inverter module will communicate with a personal computer(PC) via CAN-bus and will be displayed on a monitor of the PC not only to show the simultaneous status of voltage, current and power, but also to execute power commands as well as setting up the operation modes. The three-phase 110V 1kVA inverter was built. Experimental result was provided from two parallel-connected inverters, which verifies the validity of the proposed control strategy.
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