Laboratory Workstation to Prepare Students for Industrial Application of Electric Drives

Laboratory Workstation to Prepare Students for Industrial Application of Electric Drives Todd D. Batzel Pennsylvania State University, Altoona College Abstract This paper presents the development of workstations to be used in the laboratory component of a course on electric drives for electro-mechanical engineering technology (EMET) students at the Pennsylvania State University, Altoona College. The primary goal of this laboratory revision is to provide students a hands-on experience with the operation and application of industrial electric drives. The revision also better supports ABET criterion for curriculum content, which states that engineering technology program curriculum must focus on the applied aspects of engineering science and engineering. Lab workstation hardware and associated software used to support the lab component of the course are identified, and the student experiments used in the revised lab are described. Finally, a student survey is used to confirm the effectiveness of the course updates in better preparing students for practical application of electric motors and drives. Introduction It is estimated that nearly half of the global electrical power is consumed by electric motors [1]. This means that substantial energy savings are possible by improving electric motor operating efficiency. It is also established in [2], [3], and [4] that the use of variable speed electric drives, which consist of a motor and power electronic converter, can significantly increase operating efficiency in motor driven systems and can offer significant energy savings. As a result, the use of electric drives in industry has been rapidly increasing for several decades [5]. Historically, in electrical engineering education, many courses on electric motors have focused on line-driven machines. More recently, in response to the proliferation of variable speed electric drives, some electrical engineering programs have introduced electric drive courses into their curriculum [6]. To address the need for graduates prepared to apply electric drives in industry, the Electro-Mechanical Engineering Technology (EMET) program at Penn State University updated the curriculum in 2011 by replacing a traditional motors course with an electric drives offering. The course has an associated two hour weekly laboratory component. In the original implementation of the electric drives course, the laboratory exercises for this course used hardware in the loop (HIL) tools and a rapid prototyping environment for algorithm development. With this approach, students created motor control algorithms graphically (using Simulink) and then downloaded the compiled code to the HIL hardware to execute and test. With this approach, students could quickly construct a functional electrical drive for any desired motor type and in the process develop a good understanding of the theoretical aspects of motor controls and electric drives. However, this approach also left students without exposure to the practical application and operational capabilities of commercially available industrial drives. Therefore, a recent decision was made to revise the lab component of the course to provide exposure to use and application of industrial electric drives. There are various approaches that have been reported for use in electric motor drives laboratories. Those approaches are generally categorized as: simulation only [7], virtual or webbased labs [8], hardware in the loop (HIL) [9] or DSP development boards [10] connected to a three-phase power inverter, and adoption of industrial electric drives and motors. Of these four general approaches, the first three are very well-suited for undergraduate or graduate electrical engineering programs where the main objective is to enforce theoretical concepts of electric drives introduced in lecture. For engineering technology programs where applied aspects of engineering science and engineering are essential (per ABET accreditation criteria), the industrial drives option is appealing. A potential disadvantage of industrial drive use in educational labs is that they are not designed for ease of student experimentation. Also, many signals that are useful in an educational lab may not be accessible or directly controllable in an industrial drive. However, industrial drives afford opportunities to introduce students to industry practices that would be very challenging to implement using each of the other laboratory equipment approaches. The use of industrial drives in educational labs is an attractive option since cost is moderate and it is arguably the best approach to prepare students for practice in industry. For the laboratory component of the electric drives course at Penn State Altoona, the foremost objectives are to enforce concepts introduced in the classroom, and to prepare students for industry practice. For this reason, new workstations and lab exercises are being developed using industrial electric drives. The hardware and software components used in the electric drive workstations is described in this paper, and student experiments are described in detail. Finally, a student survey is used to assess the effectiveness of the electric drives lab in meeting the stated objectives. Laboratory Workstation for Electric Drives Design Requirements Laboratory work plays a very important role in engineering technology education [11]. The principal objectives of laboratory courses in engineering technology include: verify concepts and theories learned in lecture through experimentation; develop technical skills in conducting experiments, collecting data, observing results, and using standard lab instrumentation; and develop teamwork and communication skills [12,13]. The overall objectives for the electric drives lab revisions are closely aligned with those more general objectives summarized in [12]: • Students will learn to use and apply industrial electric drives. • Lab assignments will demonstrate how theories from lecture are applied in practice. • Laboratory exercises should contribute toward the development of skills in communication and teamwork, experimentation, and computation. • Laboratory activities should be interesting to students to stimulate academic curiosity and motivate further study. • Laboratories should culminate in a project, possibly in collaboration with a concurrent course on mechanical drives. The electric drive workstations to meet these objectives must be capable of operating the following motors under test (MUT): DC, Permanent Magnet Synchronous, Brushless DC, AC Induction, and stepper motors. The workstation should also be capable of applying a variable load torque to the MUT. Some institutional restrictions include maximum motor power rating of 480W due to the capability of the DC power supplies available in our electrical laboratories. Furthermore, each workstation must not be capable of returning current into the lab power supplies during regeneration since this can result in exceeding the supply voltage rating. Hardware Prior to the revisions, the electric drives lab at Penn State Altoona used the HIL approach, where Simulink and dSpace were used to supply PWM signals to an associated power inverter [6]. This approach was quite effective in many aspects, but did not expose engineering technology students to the practical application and motion control capabilities of commercially available industrial drives. The motors used in the new workstation were retained from our previous implementation, and consist of 250 Watt DC, Brushless DC, Permanent Magnet Synchronous, and AC induction motors. To provide a variable load to the motor under test (MUT), the shaft of a 250 Watt DC generator is coupled directly to the MUT shaft. A safety guard is placed over the shaft coupler. Each machine is equipped with a 1000 count encoder, and Hall effect feedback is added for the BLDC machine. Fig. 1 shows the motor/generator set used at each student workstation. Fig. 1. Motor/Generator set for electric drives workstation. The industrial electric drives selected to operate the MUT should ideally be able to drive each type of motor in torque, velocity and position control modes as applicable. The Digiflex® series of drives from Advanced Motion Controls (AMC) meets this requirement. This series of drives supports networked communication and features programmable digital and analog I/O that facilitate interfacing with external controllers and devices. Furthermore, the integration of fully programmable homing routines coupled with the drives ability to store and execute userspecified motion trajectories allows for straightforward demonstration and implementation of multi-axis motion applications without the need for an external motion controller. The DPRALTE 020B080 operates at DC link voltages from 20 to 80V, and delivers 10 A. This model, shown in Fig. 2, was selected due to its compatibility with the lab motors. Fig. 2. Industrial motor drive. Driveware® software is available at no cost to provide a host computer interface with Digiflex drives. Driveware can be used to setup, configure, tune, troubleshoot, and monitor the performance the motor controller. This tool also provides virtual oscilloscopes and meters that allow students to view motor phase currents, voltages, position and velocity feedback, Hall sensor states, and more. Driveware also supports the management of user-specified motion profiles, providing motion control functionality at the drive level. As shown in Fig. 2, the connections on the industrial motor drive are not convenient for the repeated connection/disconnection required in an educational laboratory. Therefore, a user interface board was constructed that breaks out critical signals to provide more suitable connections, such as banana jack, BNC, and scope probe clips. The board also contains on-board phase current and voltage sensors with outputs routed to BNC connectors so that these measurements can be taken when the drives are running standalone (without Driveware). Other functionality on the interface board includes the required DC bus bulk capacitance (48,000 uF), a multi-turn potentiometer to provide analog command for torque, velocity, or position control modes, and a drive disable switch. All motor and DC source connections are accessible through the banana jack connectors, as shown in Fig. 3. Fig. 3. Motor Drive Interface Board. To provide a variable load to the MUT, a DC generator driven by a torque controller capable of regenerative current capability is required. The AMC model Z12A8 was selected to perform this function. This model is a printed circuit board mount current controller that operates at DC voltages from 20-80V, and supplies continuous current up to 6A. The torque controller operates from the same DC voltage source as the MUT drive, where under typical operating conditions, the motor drive will draw current from the DC source (quadrant 1), while torque controller will return current to the source (quadrant 4). The Z12A8 is shown in Fig. 4a, while Fig. 4b shows the drive mounted on an interface board that provides convenient connections in a student lab environment. Banana plugs are used for fast connection to both the DC link voltage and the motor terminals. The controller accepts a torque command from either an external analog signal via a BNC connector, or from an on-board multi-turn potentiometer. A current monitor signal is also available on a separate BNC connector. Note that there is no bulk capacitance on the DC link voltage since this function is provided on the MUT drive interface board shown in Fig. 3. Fig. 4a) Load Torque Control Drive. b) Drive mounted on user interface board. Laboratory Experiments The main objective of the laboratory experiments is for students to learn to apply, operate, and troubleshoot industrial motor drives. The laboratory experiments must also be synchronized with the course lecture and should connect lecture topics to practice. In this section, the experiments used in the revised electric drive lab are described. A typical lab workstation setup is shown in Fig. 5. Lab Equipment Familiarization The first lab meeting is used to introduce students to lab workstation equipment and software. In this lab, students load a provided configuration file into the MUT drive and examine these parameters and settings. The motor is then operated at no load to familiarize students with typical measurements that will be required in forthcoming experiments. These measurements are obtained from both Driveware and using the various signal test points provided on the drive interface board. In addition, students operate the DC machine in both torque and velocity control modes to gain an awareness of the difference in those control objectives. Fig. 5. Electric Drive Lab Workstation. PWM and H-Bridge Operation The second lab experiment is presented concurrently with the lecture topics covering pulse width modulation (PWM), power conversion, H-Bridges, and 3-phase inverters. This experiment links the theory in lecture to the operation of the power section of an industrial drive. The PWM signal is not typically accessible or directly controllable in an industrial drive. However, the PWM duty ratio can still be controlled indirectly by operating the industrial drive unloaded, in DC motor current control mode, and with zero integral or derivative gain. In this configuration, the current command is proportional to the duty ratio of the PWM signals so that the input command can vary the effective duty ratio from 0 to 100%. Thus, students can measure average output voltage of the drive over a range of PWM duty ratios and compare the measured output voltage values with those predicted by theory. Students also use lab oscilloscopes to view the switched drive output voltage. This exercise can be extended to demonstrate 3-phase inverter operation by changing the drive to PMSM configuration and connecting an encoder to the controller. With this configuration, the three output voltages can be shown to be a function of the encoder position as well as the PWM duty ratio command. DC Motor Parameter Determination In this experiment, the motor drive is configured for speed control mode. At several speed settings, students operate the DC Motor over a range of load settings while measuring motor voltage and current. Load torque is varied using the generator torque controller. The measured data is plotted, and a linear fit allows for the determination of voltage (and therefore torque) constant and the armature resistance. For each operating point, generator voltage and current are also recorded, which allows students to determine the generator parameters. Also, the importance of efficiency and the concept of regeneration is also introduced since the motor power and generator power are easily computed from the measurements, and the total power delivered from the DC Supply total power is directly measured. A series of similar measurements taken at no load allows the system friction parameters to be computed. Finally, a coast-down test is performed to determine the total system inertia. At the conclusion of this lab, students will have obtained the electrical parameters (R, L, torque and voltage constants) of the DC motor under test, the torque constant of the generator, and the mechanical parameters (inertia and friction) of the entire motor/generator set. Brushless DC Motor and PMSM Operation In this experiment, the BLDC torque and voltage constants are first determined by measuring the voltage and speed at the terminals of a back-driven motor. Students use the measured data and theoretical model of the BLDC discussed in lecture to compute these constants. Students also use Driveware to perform autocommutation on the BLDC, where only Hall effect sensors are used for shaft position feedback (no encoder). This automated process slowly rotates the motor shaft while monitoring position and Hall effect sensor state. After at least a full rotation, the drive automatically configures the commutation parameters for the BLDC. With commutation properly configured, the drive is then operated in both current and velocity control modes at various load while the trapezoidal currents and Hall state are observed on the Driveware scope. This allows students to observe the relation between BLDC current amplitude and frequency to torque and speed. The current amplitude and commanded load torque are used to verify the experimentally determined torque constant. The Hall sensor state and phase current plots also shows how the Hall sensors are used to select the active phase windings in the BLDC. Similar experiments are then performed on the PMSM, where an encoder is used along with the Hall sensors to drive the BLDC with sinusoidal waveform. Induction Motor Operation No-load and locked rotor tests are performed to determine the induction motor (IM) equivalent circuit parameters. These parameters are then entered into the industrial drive and act as a starting point for the tuning of the flux (direct axis current) and torque (quadrature axis) loops. The industrial drive uses a field oriented control approach and operates only in closed loop torque, velocity, or position modes. Therefore, classic open loop volts per Hz control experiments are not an easily performed. After the flux and torque controllers are tuned using the Driveware tools, students are able to operate the IM in torque control, as well as velocity and position control modes. In each case, by measuring motor speed, voltage (amplitude and frequency), current and power factor, the induction motor model obtained experimentally can be used to confirm the accuracy of the measured results. Motion Control Application The objective of this lab is to introduce students to standard industrial practice for motion control. In this lab, the motor under test is operated in position control mode, and students are introduced to homing routines, position control, jogging, indexing, and the creation and execution of a motion profile using a sequence of PVT (position, velocity, time) triplets. Students first connect two limit switches and a home switch to the industrial drive to experiment with the programmable homing sequence. They can verify that the system repeatedly arrives at the same location each time the homing routine is performed. The system is then operated in position control mode - initially with a potentiometer serving as the position command. Then, to demonstrate automated processes such as multi-axis motion control, students use programmable motion trajectories to generate and execute assigned motion trajectories. The use of signals that support multi-axis coordination (e.g. in-position flag, following error, index selection inputs) is also presented. Final project Although this has yet to be implemented, we plan to assign a final project for this lab in the future. Students in the electrical drives course concurrently take a mechanical drives class. A collaborative final project would allow students to design a mechanical system and use an industrial drive to control it using the appropriate control methodology. Assessment The workstation and laboratory experiments described have been deployed in the electric drives lab starting in spring of 2025. A student perception survey was presented to the cohort of students in the pilot offering of the course to assess the effectiveness of the electric drive lab. The results, as shown in Fig. 6, indicate that students consider that the electric drive labs are preparing them well for industrial practice, and enforcing concepts presented in lectures. Table 1. Student Perception Survey Results. Strongly Disagree Disagree Neutral Agree Strongly Agree The lab component of Electric Drives is preparing you for industry practice, including application, operation, and troubleshooting of industrial electric motor drives 0 0 0 12 6 The laboratory component of Electric Drives helps to enforce topics and theories discussed in lecture 0 0 0 10 8 Conclusion Toward the overall objective of preparing students for industrial application of electric drives, new laboratory workstations using industrial electric drives have been designed and deployed in the Spring of 2025 at Penn State Altoona. As confirmed in a student survey, the new workstation and supporting laboratory experiments described in this paper appear to be instilling confidence in students that they are being well-prepared for industrial practice in the operation, application, and troubleshooting of electric motors and drives. 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