Brushless permanent magnet (PM) motors are preferable choice in many applications due to low weight and volume, high torque and power density, excellent controllability and reliability, simplicity and ruggedness, high efficiency and low maintenance. They have superior advantages in variable speed and load applications compared with induction, switched- and variable-reluctance motors. In recent years, poly-phase PM motors of 3-, 4-, 5-, 6- and 7-phase configurations have been investigated. Some of these motor configurations have shown promise to improve performance over three-phase configurations.
Extensive research has been carried out in radial, axial, transverse and Halbach array flux architectures. The radial flux motors (RFM) has been widely used in the industry due to relative ease in manufacturing. Axial flux motors (AFM) have been difficult to manufacture due to the high expense of fabricating lamination stacks. Axial flux motors have shown superior performance over radial flux motors under a narrow set of circumstances and additionally where length of the motor is less than 30% of the diameter (length/diameter<0.3). Transverse flux motors (TFM) are more difficult to design and manufacture. Halbach array motors have shown promise for operations requiring significantly higher speed and are not considered suitable for low speed, high torque operations.
Several control methods exist today for control of PM machines. Trapezoidal control injects trapezoidal current waveforms into the motor windings. Sinusoidal control injects sinusoidal current. Field oriented control (FOC) converts poly-phase motor currents into a Cartesian coordinate system which rotates with the motor’s synchronous speed. This results in direct control of air gap flux and hence torque. FOC has been known to improve a motor’s dynamic performance substantially. Space vector control is known to increase DC bus voltage utilization by as much as 15% by clever application of the available bus voltage.
Studies of 3-, 5- and 7-phase inverters for low voltage applications have been conducted. The study stated that the 5- and 7-phase inverters resulted in lower current per phase and leg resulting in higher reliability, better DC bus voltage utilization resulting in more output power, and better utilization of harmonics resulting in more torque. The study showed significant improvement in performance of 5-phase inverters over 3-phase inverters. The performance of 7-phase inverters was marginal over the 5-phase inverters.
Substantial innovations have taken place in the field of power electronics in the last decade. These innovations have continually churned out better semiconductor devices, thermal management systems, and materials. These breakthroughs have allowed smaller and more efficient inverters. Some tougher and space constrained applications have demanded a tight integration between motors and inverters. We will briefly discuss such innovations and their applications.
This workshop will cover simulation, algorithm and software development methodology and tools for brushless permanent magnet motor systems. Under algorithm development, we will cover the principles of FOC (field oriented control, or vector control), followed by various advanced implementation techniques for high performance and energy efficiency including predictive current control, decoupling control, space vector modulation, field weakening operation, as well as modeling and simulation This section will also cover control system analysis and compensation – open loop transfer function, stability criteria, Type 1, 2 and 3 Amplifiers, and K factor technique for stability analysis if time permits.
In this section we would briefly discuss use of such tools as dSPACE™, VISSIM™ etc. This section will also provide Software development examples based on Agile Software Development Model. Under hardware development, we will focus on MCU/DSP selection criteria, FPGA based designs, power stage design and achieving the desired performance from PM machines when integrated with an Inverter. This section will cover selection of power devices, PCB layout, safety, EMI/EMC, environmental and reliability considerations, thermal analysis, mechanical and manufacturing considerations.
Rakesh Dhawan is a twenty-two years veteran of motors and motor drive Industry. He has developed critical understanding and published on a wide range of motors, motor drives, high frequency electromagnetic components, electric vehicles and switch mode power systems. He has co-authored over 25 publications in various refereed journals and conference proceedings and is an inventor on 7 issued or pending US patents. He has served on the Technical committee of the Applied Power Electronics Conference (APEC). He received the B. Tech (Electrical Engineering) degree from Indian Institute of Technology (IIT), Kharagpur, India. He received his MS degrees from University of Minnesota under the tutelage of Power Electronics pioneer Prof. Ned Mohan. He received his MBA from Old Dominion University.
He has been directly responsible for over twenty five successful product launches in his career many of them involving brushless permanent magnet motor systems. Rakesh has conducted several workshops in the recent past in the field of motors and motor drives. His interests include brushless permanent magnet motor systems, light electric vehicles, electric bicycles, switch mode power supplies, solar inverters, simulation, statistics, project management and new and ultra-fast product development methodologies. Rakesh is a high energy individual with a difference; he combines technology excellence, leadership and professional management skills with his inborn entrepreneurial instincts.
Rakesh is a member of IEEE and the Entrepreneur’s Organization (Washington-DC Chapter) and is very keen on nurturing innovation and entrepreneurial talent in the field of technology development and management.