Design And Study On Single-phase And High-power Inverter

The single-phase and high-power permanent- magnet petrol generator can provide electric power for many large-scale or centralized agricultural productions such as the large-scale farm breeding, the dry and refrigerated storage of agricultural products, the agricultural irrigation and the facility agriculture when the load capacity of the distribution network is insufficient or the power is cut. At present, both technology and market of the permanent-magnet petrol generator which is single-phase and high-power are occupied by some companies from the developed countries such as the U.S.A. and Japan, which causes high product price and difficult maintenance, and the domestic electromagnetic diesel generator which is single-phase and high-power is unsuited to mobile operation on account of its heavy weight and big volume. These factors restrict the application of the single-phase and high-power generator in the agricultural production. For alleviating the current contradiction between supply and demand and further meeting the demand of the agricultural production, it is necessary to develop the domestically single-phase and high-power permanent-magnet petrol generator. Its technology core is the single-phase and high-power inverter whose design performance has great influence on the usability of the generator, so it has important engineering value and practical significance to study the inverter.This paper carried out design and study on the 10 kVA single-phase and high-power inverter of the permanent- magnet petrol generator. By means of AC-DC-AC method, first the three-phase medium-frequency alternating voltage output directly by the permanent-magnet petrol generator is converted to the direct voltage via the three-phase diode rectifier and the filter capacitor, and then the digital control system using PIC18F23K20 as the controlling core inverts the direct voltage to 220V/50 Hz single-phase sinusoidal voltage by the full-bridge inverter circuit and the output filter circuit.According to the design requirements and the theoretical analysis, this paper designed and calculated the parameters of the hardware system of the inverter, including the parameter calculation for the filter capacitor on the direct voltage side and LC filter on the output side and the design of the voltage sampling circuit, the current sampling circuit and the temperature sampling circuit. Moreover, the design of the power switch and its driver adopted the modularized integrated circuit to simplify the hardware circuit structure and improve the working performance of the inverter.For obtaining the standard sinusoidal voltage, the controller controls the on-off of the power switch by the SPWM(sinusoidal pulse width modulation, SPWM) control technology. Furthermore, the reference sinusoidal voltage is discretized and made the table to store into the microcontroller for lookup. Based on the analysis to the mathematical model of the inverter circuit, the control system takes the closed-loop control for the output voltage of the inverter by sampling the instantaneous output voltage and adjusting the output duty cycle in real time for making the output voltage stable. Establishing the simulation model under the rated working condition using MATLAB and the simulation analysis results indicated that the feedback control for the instantaneous output voltage could improve the waveform quality of the output sinusoidal voltage and make it meeting the high technical index. Meanwhile, for keeping the whole inverter system working safely, the anti-interference design of both hardware and software is considered, and the control system has the short-circuit protection, low-voltage protection, overcurrent protection and over-temperature protection.After debugging the hardware and the software, the performance tests of the inverter had been carried out. The tests results showed that when the inverter output the rated 10 kVA, the effective value and frequency of the output voltage were 220.2V and 50 Hz respectively, and the inversion efficiency was 91.8% which met the design requirements.