Thermal Limit Analysis of Radial AMB by Using Finite Difference Method

Load capacity of an active magnetic bearings (AMBs) includes the static load capacity, peak transient load capacity and dynamic load capacity. In this paper, a simulation software, SimRaMB, is proposed to estimate the static load capacity which is constrained by the thermal limit of coils. A finite difference method (FDM) algorithm is adopted for the thermal limit analysis of radial AMB. The thermal limit of an eight poles radial magnetic bearing is simulated by SimRaMB and ANSYS, respectively. A thermal test unit of the radial magnetic bearing was built up in which the temperature distributions are measured by 12 thermal couples. The simulation results showed that the difference of temperature at steady-state between SimRaMB and ANSYS is within 0.8° C. The experimental result also showed that the difference of temperature between SimRaMB and experiment is within 0.89°C at lower driving current. However, when the driving current comes to 1.5A and 1.8A, the simulation results of SimRaMB and ANSYS are 8.09°C and 8.58°C higher than experimental data, respectively. The reason could be that the present study doesn’t take into account the influence of temperature to thermal conductivity of material. In order to improve the simulation result, a table of temperature-dependent thermal conductivity will be included in the future.