變頻式冷氣機的系統模擬和設計

Abstract

本論文以top-down的方式來建立一套完整的變頻式冷氣系統的設計技術， 我們應用建築物參數和氣候資料，以及採用CLF/CLTD方法來計算因熱源所 需要的冷負載。接著藉著結合Matlab裡的房屋熱體模型以及上述冷負載的 估算，提出了一套實用的熱模型。我們並為此空調模型設計三種控制器 ：(1)ON-OFF 控制器，(2)P 控制器，(3)PI 控制器，最後模擬結果提示 只要使用P控制器即可達到不錯的效果。為了研究設計空調機用的變頻驅 動器，因此如何規畫合適的PWM信號控制變頻器也是我們研究的課題。為 此我們從PWM理論比較了五種三相調變波：正弦波、加上三次諧波的正弦 波、2/5梯形波、空間向量波和新的梯形波。在以(1)最大直流鏈電壓使用 率，(2)修改過的整體諧波失真因子THD'，(3)波形是否易實現評估後，我 們以2/5梯形波做為我們最佳的選擇。以這樣的波形為基礎，我們試圖 以8051的最大工作能力去實現電路，最後我們所提出的PWM波形產生方法 是以查表的方式實現之。由於所需要的資料都已經事先計算好，大大地縮 短了指令的時間，因此PWM調制載波頻率較以傳統的PWM調變的方法提高 了2~3倍，而使頻率調變比可高達21~23。實驗的結果則印證了查表方式產 生PWM波形的可行性。 In this thesis we propose a top-down design method for air- conditioners drivenby inverters. We adopt the CLF/CLTD method and use the parameters of the structu and collected data of the weather to calculate the cooling load induced from heat sources. We modified the thermal equivalent model in Matlab and propose a practical model which includes the calculation of cooling load. Using this new method, we design three temperature controllers, those are(1) ON-OFF controller, (2) P controller. and (3) PI controller. The simulation results show that P controller already works very well. We also study the method to design the inverter for the air-conditioner. The inverter with three-phase PWM outputsis our choice. Five different modulation waveforms have been considered and analyzed here, those are sinusoidal wave, sinusoidal wave with the third harmoniccomponent, "2/5" trapezoidal wave, space vector wave, and modified trapezoidalwave. After the comparison of the five associated utilization of the dc voltages and the accumulated total harmonic distortions, we find that the 2/5 trapezoidal modulation wave is the best choice in our design. We use the circuit board with 8051 CPU to implement the function of the inverter. By carefully evaluating the performance of 8051, we propose a look-up table method to synthesize three-phase 2/5 trapezoidal PWM waves.The results have shown that our method can utilize the performance of 8051 to the upmost.The frequency modulation indices can be designed up to 21~23. This result shows our implementation method is pretty practical.