IEEE TRANSACTIONS ON EDUCATION, VOL. 48, NO. 1, FEBRUARY 2005 47 Virtual Torque and Inertia Loading of Controlled Electric Drive Alon Kuperman and Raul Rabinovici, Senior Member, IEEE Abstract—This paper presents a simple method to obtain effects similar to those obtained by real mechanical loading and real in- ertia variation but without any mechanical parts supplementary to the electric motor of the studied electric drive. The electric motor itself produces the load torque and the inertia variation using dig- ital signal processing software. Therefore, the electric drive is vir- tually torque and inertia loaded, while its behavior is similar to that of the actual loaded drive. The present method could be used to test the implementation of control algorithms or for didactic purposes using motion control kits found on the market. The present method is used with laboratory works of the DSP Fundamentals in Power Electronics course at the Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Is- rael. Index Terms—Digital control, load and inertia emulation. I. INTRODUCTION A CONTROLLED electric drive consists principally of an electric motor supplied by a power electronics source and operated by a digital signal processor (DSP) with a suitable con- trol algorithm [1]. However, the control algorithm and the elec- tric drive as a whole should be tested in conditions of mechanical loading and inertia variation. A real mechanical load is quite dif- ficult to implement even it is as simple as a constant torque one. The real mechanical loading becomes even more cumbersome when the load torque should change in time, e.g., a sinusoidal change. In addition, there are servo drive applications where the inertia has a large variation, e.g., in robotics the inertia range could be as wide as 1:10 [2]. Therefore, the system should be also tested under inertia variations. However, these changes are difficult to implement mechanically. The use of torque-controlled load dynamometers, which is common in engine test beds or in the testing of electrical ma- chines [3]–[6], is often impossible in an educational laboratory because of the high price and complexity. Authors faced this problem teaching the DSP Fundamentals in Power Electronics course at the Ben-Gurion University of the Negev, Beer-Sheva, Israel. The course consists of three parts: DSPs for power elec- tronics control, motion control, and control of power converters. Each part ends with laboratory work [13]. In order to imple- ment a motor speed control system under load torque change, a load machine is needed. The method, proposed in this paper, was developed to allow emulating the effect of load torque without using a real load machine. Manuscript received March 16, 2003; revised December 3, 2003. The authors are with the Department of Electrical and Computer Engineering, Ben-Gurion University of the Negev, Beer-Sheva 84105, Israel. Digital Object Identifier 10.1109/TE.2004.832881 Fig. 1. BLDC speed control block diagram. DSPs have developed rapidly over the past years and have become an inseparable part of almost any motor drive system, performing real-time generation of space-vector mod- ulated waveforms, online speed and current acquisitions, programmable soft-start, dynamic braking, and intelligent con- trol. A DSP was used to emulate a mechanical load or inertia variation using a controlled motor set, as shown in this paper. Fields of electric drive and power engineering are generally considered by students as unattractive and old-fashioned. How- ever, this present course and the laboratory attached to it seem able to change this situation. The DSP connection to power elec- tronics and controlled electric drive attract a large number of students to these fields. For example, the first time the course was given, seven students were enrolled, while one year later, 20 students attended it. The students’ reactions to the course were extremely positive. They were fascinated by possibilities of introducing DSP fea- tures to the area of power engineering. The DSP seems to act as a temptation, attracting students familiar with signal processing and control to the field of power electronics. It is quite impor- tant to attract students with a background of signal processing and of computers and control in order to introduce their skills and knowledge to the area of motion control and power elec- tronics. Furthermore, the presented approach of virtual loading and inertia change is used by students to validate experimentally different control algorithms in their senior projects. II. METHOD PRESENTATION A general closed-loop brushless dc (BLDC) motor speed con- trol system, which consists of the motor itself and a proportional integral derivative (PID) controller, is shown in Fig. 1 [7], where is the reference speed, is the motor speed, is the speed error, is the PID controller output voltage, is the PID controller transfer function, is the motor voltage to speed transfer function, and is the Laplace operator. The motor speed is sensed and compared with a reference value. The difference is applied to the controller (usually imple- mented using DSP software), which outputs the voltage driving the motor. 0018-9359/$20.00 © 2005 IEEE