ABSTRACT
Synchronous machines can be classified as conventional, permanent-magnet, variablereluctance, etc. The authors are focused on the high-performance electromechanical (mechatronic) systems. Therefore, this chapter concentrates on permanent-magnet synchronous machines which possess superior performance and capabilities surpassing any other electric machines such as permanent-magnet DC electric machines, induction motors, etc. Conventional synchronous machines are covered in Refs. [1-6]. In synchronous motors, the electromagnetic torque results due to the interaction of time-
varying magnetic filed established by the stator windings and stationary magnetic field produced by the windings or magnets on the rotor [1-6]. There exist synchronous reluctance machines which exhibit, in general, low performance as documented in Chapter 3. In high-performance drives, servos and power generation systems (up to 100 kW rated
and 500 kW peak), three-phase permanent-magnet synchronous machines (motors and generators) is the preferable choice. In high-power (from hundreds of kW to MW range) generation systems, conventional three-phase synchronous generators are utilized [2-5]. There exist translational (linear) and rotational synchronous machines. Due to the fact
that a great majority of mechatronic systems utilize rotational electric machines, we concentrate on the rotational motion devices. In this chapter, we consider radial and axial topology permanent-magnet synchronous machines. Two-and three-phase radial machines are illustrated in Figure 6.1a and b. We examine the energy conversion, torque production, control, and other important
issues. The angular velocity of synchronous motors is fixed with the frequency of the supplied phase voltages to the stator windings. The phase voltages must be applied as functions of the rotor angular displacement ur. The steady-state torque-speed characteristics can be represented as a family of horizontal lines as depicted in Figure 6.1c. The electrical angular velocity is equal to the synchronous angular velocity ve¼ 4pf=P. The designer examines the maximum load torque TL max to satisfy Te rated>TLmax or Tepeak>TLmax. For a short period of time (1 min for many permanent-magnet synchronous motors), one may significantly overload motors, and the ratio Tepeak=Te rated could be from 2 to 10. If Te critical<TL, the rotor magnetic field is no longer locked to the stator magnetic field (motor cannot produce the needed torque due to the constraints imposed including rated voltage and current of power converters). For Te critical<TL, the rotor magnetic field slips behind the stator field. Due to the loss of synchronization, the electromagnetic torque developed by the motor reverses (surges). Therefore, the condition Te critical>TL must be
Analysis, and Design with
always guaranteed, and the peak power converter capabilities (peak voltage and current) must be met. Though the permanent magnet synchronous machines can be overloaded by the factor of 10, the maximum current overloading capabilities of pulse-width modulation (PWM) amplifiers is usually up to2, while the peak voltage cannot exceed the bus voltage. Radial and axial topology permanent-magnet synchronous machines are widely used as
actuators (motors) and generators. The motors are controlled by power converters (PWM amplifiers). The implications of microelectronics to motion devices have received meticulous consideration as technologies to fabricate various advanced machines are becoming developed and widely deployed. Mini-and micromachines have been fabricated utilizing CMOS-centered and micromachining technologies and processes. The images of 2 and 4 mm in diameter permanent-magnet synchronous machines are reported in Figure 6.2a and b. These permanent-magnet synchronous machines are smaller than the operational amplifier or ICs-centered electronics to control them. However, to guarantee rotation and actuation, the condition Te>TL and Fe> FL must be satisfied. Correspondingly, the operating envelope (torque=force, load, load profile, angular velocity, etc.) defines Te thereby resulting in the motor dimensionality. The acceleration capability, which defines the settling time and repositioning, depends on the ratio (TeTL)=J. The torque and power densities, rated angular velocity, and other characteristics are
defined by the machine design, dimensionality, materials, technologies, and other factors. For a preliminary power estimate, one may assume that the power density 1 W=cm3 can be achieved. Figure 6.2c documents the images of a permanent-magnet synchronous motor in the computer hard drive and VHS with the monolithic ICs driver. A two-phase permanent magnet synchronous motor (stepper motor) with the monolithic controller=driver is reported in Figure 6.2d. We address and solve a spectrum of problems in analysis and control of various
synchronous machines. A coherent analysis results in deriving sound control concepts ensuring best performance and achievable capabilities. For example, maximum efficiency, minimal losses, maximum torque and power densities, vibrations and noise minimization, as well as other critical improvements can be achieved for mechatronic systems.
