Study On RC Load Approach And The Motor Losses For Linear Compressors

Since1980s, more and more small regenerative cryocoolers are applied in military and space fields, meanwhile more rigid requirements such as long life, low vibration have been raised to cryocoolers. Stirling cooler and Stirling-type pulse tube cooler have gradually become the most popular coolers in these fields. Linear compressor is the key component which insure the long-life and low-vibration operation of Stirling type coolers.At the beginning of1980s, for the first time people from Oxford introduced flexure spring in place of traditional spring to Stirling cooler, which can insure the long-life operation of cooler because of the immensely reduction of friction between piston and cylinder, so this has an epoch-making meaning in history of linear compressor. After that, cryocoolers driven by linear compressors have been developed in many research units, even several have been put into service. Owing to some shortages and open questions in linear compressor, several issues are discussed in this thesis as follows:1. Linear compressors employed in cryocoolers since1908s in different institutes are introduced, and its evolution process and solutions for various problems are analyzed. The parameters of input power per swept volume are compared and analyzed between different institutes and different kinds of coolers.2. Based on electrical model, the match mechanism between linear compressor and cold head is analyzed, and high efficiency match approach is discussed. The whole system is divided into three parts in this analysis:electrical, mechanical and acoustic parts, linked by transformer elements, and each parameter of them is transformed into an electrical part by analogy. This model makes it clear to see complex relations between each parts. Based on this, match characteristics between compressor and cold head are analyzed.3. Aimed at Stirling type cry coolers, RC load approach is established to test the performance of linear compressors. Compared with piston position sensor, RC load can simulate the impedance conditions of cold heads, it’s a non-contact method and simple to assemble, which can provide reference to impedance match between linear compressors and cold heads. Linear compressor model is built and experiments are carried out. Experimental results are very close with computational results, which prove the dependability of RC load method. In addition, experiments are carried out on a linear compressor taken LVDT position sensor and RC load method respectively Results show that PV power at the compressor outlet (that is the inlet of a regenerator) obtained by RC approach is5%-25%lower than the PV power on piston face obtained by LVDT method.4. Iron losses in two kinds of linear motors with different frequency and piston displacement are compared by measuring iron core losses (include hysteresis losses and eddy current losses). Results show that there is a1.6and1.3power function between frequency and iron loss in a single-magnet and a double-magnet linear motor respectively; The iron loss comes up with the copper loss which is known as I2R at75Hz in a single-magnet linear motor and it occupies68%of the total motor loss at120Hz, while this proportion is only as high as15%in a double-magnet liner motor.