Some Key Technologies Of Fluid Machinery Supported By Active Magnetic Bearings

Fluid machineries such as blowers, compressors and pumps are very important in many fields of national economy. However, they are the one of the most energy-intensive equipments which consumes about 40% of industrial electricity power. Some backward equipment such as roots blowers and low speed centrifugal blowers are behind the time. Recently, with the advantages of small size, high efficiency, and high reliability, the high speed centrifugal blowers are widely used for industrial applications. However, the transmission agent, which is indispensable for the traditional high speed centrifugal blower, consumes about 10% of device power. By using high speed maglev permanent magnet synchronous motor(PMSM) as the driver, the efficiency of the high speed centrifugal blower can be improved about 10 to 15 percent. This paper investigates some key technologies for the high speed PMSM and magnetic bearing relevant to save energy.First of all, as the poor dynamic performance of the traditional V/F control method, two sensorless control methods based on hypothetical reference frame for the high speed PMSM are presented. One method combines hypothetical reference frame with state observer. In this control method, the state observer is used to estimate the components of electromotive force(EMF) in the different coordinate axis, which is concerned with rotor position. Thus, the PMSM can be operated in the condition of id=0 without any speed or position sensor. The other proposed control method is developed on the basis of the instantaneous voltage equation of the PMSM in the hypothetical reference frame. This control algorithm can estimate the angular difference between hypothetical and actual rotor position by computation the difference between the actual and the ideal current. Therefore, self-synchronization is possible by reducing the angular difference to zero. The simulations and experiments are carried out to verify the adequacy of the above two methods. And a verification test is also accomplished on a high speed maglev centrifugal blower with the rated power of 75 k W. The results indicate that both the above two sensorless control methods can be implemented only with the conventional current sensor for the proposed sensorless operation, moreover, the copper loss of the PMSM is much lower than the traditional V/F control method with the same load condition at the speed of 27000r/min.According to the high running cost of the traditional active magnetic bearing, this paper works on a six-pole heteropolar radial hybrid magnetic bearing(HMB), which can be practiced with permanent magnets and traditional three-phase voltage source inverters. Its configuration and working principle are introduced. The mathematical model is built based on equivalent magnetic circuit and coordinate transformation method. A design principle for bias flux density is presented based on maximization of load capacity in different directions, through which a prototype six-pole HMB for a five degrees of freedom magnetic bearing system is designed and assembled. Both the simulation and experimental results show that the rotor can be suspended steadily and the whole control system has good dynamic and static performance. Finally, the power losses tests were done. As a result, the total power consumption of this six-pole HMB is only 9.85% for a traditional eight-pole active magnetic bearing with a 2.2kg rotor.In order to determine the performance and characteristics of the PMSM, a dynamometer is required for the load test. Conventional dynamometers, such as eddy dynamometer require a reduction gearbox for the high speed PMSM, besides they waste energy and water during the test. In this paper, a novel energy-saving electric dynamometer system for the high speed PMSM is presented. In this scheme, two identical high speed PMSMs are mechanically connected by a high speed torque meter. The PMSM under test(MUT) is driven as motor by the sensorless field-oriented control(FOC), speed close-loop, while, the other one worked as a load motor(LM) also employs FOC technology but torque close-loop to supply load torque. And the two electric machines are electrically connected with a common-DC-bus to implement energy circulating. To verify the performance of the proposed electric dynamometer system, a back-to-back test platform is developed with two high speed maglev PMSMs. And the experimental results show that the load of MUT is applied by the generator, and the regenerated power can be feedback to the MUT successfully.