Test Stand Drives
UNICO’s Test Stand Drive is an all-digital AC flux vector drive engineered for test stand and dynamometer applications. It consists of a UNICO 2000 Series Performance Vector Drive that incorporates software specifically designed for operating transmission test stands, engine dynamometers, engine test stands, component test stands, emissions dynamometers, and chassis dynamometers. The drive’s revolutionary technology and modular design make it the ideal choice where superior performance, flexibility, and ease of operation are desired.
A software velocity observer determines motor speed and acceleration with or without a motor transducer. When a transducer is not used, the observer estimates speed and acceleration using measured motor currents and voltages. Estimates are based upon a model of the motor and load using information measured automatically during initial drive setup. If a motor-mounted transducer is used, motor velocity and acceleration are measured directly down to zero speed.
A torque estimator feature eliminates the need for expensive and mechanically complicated torque-measuring devices. Using motor currents and voltages, the estimator calculates motor electrical torque, which can then be translated into the torque that would be measured by an in-line torque transducer if the appropriate inertia and friction information has been provided. This torque estimate may be output as an analog signal that can be used to replace load cells in many applications. The torque estimator functions down to zero speed.
For systems that rely on the torque estimator to provide a measure of motor torque, the drive provides the ability to deadweight calibrate the torque estimator output. Deadweight calibration is done by loading an arm attached directly to the motor shaft with calibration weights.
Fast Vector Rotator
A hardware/software option extends the speed range of the drive to accommodate the high motor speeds required by some test stand applications. A second digital signal processor (DSP) is added to the main controller to regulate the vector control of the motor. This enables the drive to update its AC sine wave output to the motor at rates approaching the switching frequency of the IGBTs. Frequency commands as high as 1,000 Hz (60,000 rpm for a two-pole induction motor) can be achieved.
An inertia simulator makes it easy to test a unit under varying inertial conditions without the use of custom inertia wheels. The user specifies the amount of inertia to simulate, and the drive adjusts its torque command to the motor to make it appear as if the requested inertia were present at the motor shaft or at a given reference load point.
A unique design incorporating a proprietary digital current regulator and a state-of-the-art controller allows the drive to operate any AC induction, AC synchronous, or brushless DC motor without the current-loop setup required by conventional drives.
Once routine electrical connections have been made, the simple-to-use autotuning features adjust virtually all motor and inertial parameters to the given motor and connected load. Simply enter a few values from the motor nameplate, and the advanced setup routines do the rest. The drive is completely tuned within minutes.
A modular bus design provides space, cost, and energy savings in many applications. The drive consists of separate rectifier and inverter units. The rectifier is comprised of a full-wave diode bridge, a bus-charging circuit, a dynamic braking circuit, and a capacitor bank. A fully regenerative front end is available as an option. The inverter consists of a six-IGBT, four-quadrant PWM amplifier that operates from the DC bus of the rectifier unit. High-power inverters are comprised of three separate poles.
Multiple inverter units can be operated from one rectifier unit. This allows applications that naturally share regenerative energy, such as the power and load sides of a transmission test stand, to reuse the energy, rather than dissipate it as heat through resistors. Consequently, a much smaller rectifier is needed than would be required using two integrated drives. An inverter can be used in place of the rectifier to regenerate power to the power lines.
The drive incorporates a link choke to provide near-unity power factor and low harmonic currents at all motor speeds. A 12-pulse rectifier option is available to further eliminate harmonic currents in critical applications. When a regenerative inverter is used in place of the rectifier, unity power factor is achieved and virtually all harmonic currents are eliminated.
Optically Isolated Digital I/O
All digital inputs and outputs are optically isolated. Depending upon the controller, as many as 32 individually isolated digital I/O are locally provided, each of which can be programmed by the application to be an input or output. The voltage of each can be selected from a wide range of AC/DC values.
The drive can operate with or without a feedback transducer. Typically, an incremental encoder is used for feedback, although multiturn absolute encoders and single-turn resolvers are also supported. For less demanding velocity-loop applications, the drive offers a transducerless mode of operation.
The drive can be configured for torque-, velocity-, and position-control servo applications. Its controller can be customized with analog and digital I/O, feedback, and serial communication options appropriate to the requirements of a system. A programming option allows customization for unique applications using IEC 1131 open-standard ladder diagram, function block diagram, sequential function chart, structured text, and/or instruction list languages.