Abstarct: Among the topics that are highly regarded in the quantum thermodynamics, is quntum thermal machine that include refrigerators, heat pump and engines. Such as the recently much attention has been thermal machines is the smallest possible self-contained quantum thermal machines. In the this thesis, from three kinds of self-contained thermal machines, we specifically focus only on the smallest self-contained refrigerator, it will be reviewed. We will explain function of how by entering the physical tool that called virtual qubit and virtual temperature. In the master equation of refrigerator, we furthermore have been proposed model of dissipation in papers [7-11], we have provided other dissipation model and according to it we have obtained the master equation governing the dynamic of refrigerator. We have demonstrated according to both dissipation models that self-contained three-qubit quantum refrigerator (three-qubit QR) can reach the Carnot efficiency, and the efficiency of the self-contained QR is always universal at the Carnot limit and away from it. We have also according to concepts of virtual qubit propsed a new fiter for self-contained three-qubit Qr. We demonstrated for this new filter that the self-contained three-qubit QR reaches again Carnot efficiency And, according to two filters presented, we shown the most general chrateristics of self-contained three-qubit QR. In the paper [7] be has been claim, that essentially only the smallest machines can approach Carnot efficiency. We verify this claim by raised self-contained four-qubit QR, and we have shown that according to concepts of virtual qubit, can reach maximum efficiency or means Carnot efficiency. But itʼs efficiency, such as self-contained three-qubit QR is not universal. We also investigated a special case of self-contained four-qubit QR, in other words self-contained four-qubit QR with two hot baths in same temperature. We demonstrated itʼs efficiency has the form as efficiency of self-contained three-qubit QR. In other words this particular model from the prespective of efficiency, equivalent to self-contained three-qubit QR. We also demonstrate the efficiency of this particular model in the Carnot limit and different from is independent from details of system model, but it is dependent on the environmental temperatures. We according to the model of self-contained four-qubit QR, generalize the our results to self-contained n-qubit QR. We demonstrate for specific case, the itʼs efficiency is equivalent with efficiency self-contained three-qubit QR.