Investigation of Issues Related to Electrical Energy Efficiency of Pump and Fan Drives in Buildings

Doctoral thesis, 2011

This thesis deals with issues regarding energy efficiency of building related pump and fan drive systems. Different Induction Motor (IM) and permanent magnet motor drive systems are analyzed with focus on energy efficiency. A 4-pole, 4kW IM is the focus of the IM investigation, where different motor efficiency labels, (eff1/IE2, eff2/IE1 and eff3), different control strategies and switching schemes of the frequency converter are analyzed. Simulations as well as measurements are performed and a close correlation of the results is found. Furthermore, efficiency consideration regarding sizing of the IM for a given load are analyzed. It is shown that an oversized IM gives a higher efficiency than using one with the proper rating, provided that an adequate control of the motor supply is used. A commercially available 375W BLDC and a 4kW PMSM are analyzed using FEM calculations coupled with circuit simulations, evaluating a large range of current control strategies. It is shown that different zero voltage vector placements have a large impact on the iron losses in the motor as well as on the switching losses in the converter, especially at light load. It is further shown that the efficiency of a BLDC motor can be increased at rated operation by controlling it as a PMSM. A comparison of inner and outer rotor BLDC motor is done. It is found that the efficiency easily can be increased for the 375W BLDC motor by changing the design to an outer rotor motor. It is shown that the outer rotor motor is more suitable when using ferrite magnet materials, increasing the potential of making a more energy efficient motor. Furthermore, the impact of iron grade and magnet material is quantified with respect to energy efficiency and power density. An investigation of the energy efficiency difference between a 1.2kW BLDC and a 1.2kWPMSM motor is carried out. Two motor types are designed and constructed, showing that the BLDC motor has the highest efficiency in the whole operating range, as well as the lowest losses in the inverter stage due to decreased switching losses. The simulation result also verifies the modeling methods which includes a good accuracy regarding the iron loss modeling. The simulation results of the IM are used in order to analyze the potential saving for different load profiles. The general conclusion is that economical savings will be made iii during the life time of the drive system, both for an IM and frequency converter replacement. The analysis also show that the choice between an eff2 and eff1 IMalways generate the highest energy saving for the eff1 IM in economical terms, for the given load profiles, including the increased cost for an eff1 motor. The potential savings between a 4kW IM and a 4kWcommercially available PMSM are also quantified. It is shown that the PMSM in general is the best choice, for the given load profiles, providing an annual energy saving of 700-2600kWh. Finally quantification of the potential savings between a 375W IM, a 375Wcommercially available BLDC motor and a proposed 375WBLDC outer rotor motor are presented. The result presents an annual saving of 200-400kWh when replacing a commercially IM with the BLDC motor. In addition, 200-400 kWh can be saved annually using the proposed BLDC motor design compared with the original BLDC motor.