An AC dynamometer is not a frequency converter + motor.
From the perspective of electrical drives, an AC dynamometer is an application of AC drives, i.e., a frequency converter. Due to the special nature of the equipment and the singularity of its application, dynamometers have long been regarded simply as load simulation and energy absorption devices for power testing. Consequently, they have habitually been viewed as "frequency converter + motor." This is a very one-sided view, much like viewing radar as a simple radio receiving and transmitting device.
From the perspective of control equipment, both AC drives and AC dynamometers use frequency converters to control asynchronous motors, but they differ significantly in terms of the controlled object, operating mode, and technical requirements. Currently, usage is still largely limited to the simple application of frequency converters, and the following issues need to be addressed in the control and application of AC dynamometers.
(1) AC drive mainly controls speed, with the aim of achieving stepless speed regulation. At this time, the motor works in motoring mode. AC dynamometer mainly controls torque, with the aim of simulating the load of the prime mover, i.e., loading. At this time, the motor works in braking mode, controlling the torque of the prime mover and absorbing its output energy.
While all frequency converters offer excellent speed control characteristics and accuracy, they lack consideration for AC dynamometer applications and therefore lack torque control functionality. Thus, determining the appropriate strategy to control the torque of the loaded motor to achieve rapid and accurate loading is the core issue and key technical challenge in AC dynamometer control.
(2) An AC dynamometer is an electric loader that has both motor and dynamometer working modes. This gives rise to many loading methods that are not available in traditional dynamometers, such as transient loading, reverse drag switching, dynamic stall, load start-up, and inertia simulation. These new loading methods are the characteristics and highlights of AC dynamometers. However, how to design them in a standardized manner and apply them flexibly is the key issue for promoting and applying AC dynamometers.
(3) In most cases, AC drives are only used for speed change or speed stabilization. However, AC dynamometers are used for power testing. During operation, the torque or speed of the loaded motor needs to be constantly adjusted and changed according to the requirements of the test process in order to test the performance parameters and characteristic curves of the prime mover under different loading conditions.
Parameters such as speed, torque, power, and efficiency during the loading process need to be acquired and analyzed in real time by a computer. Therefore, the question arises of how to achieve automatic control and data transmission of all measurement and control equipment, including the AC dynamometer, torque sensor, and power analyzer, and the integrated application of the AC dynamometer with the power testing system.
Synthesis Instruments
A 2002 report submitted by the U.S. Department of Defense to Congress stated that next-generation telemetry, tracking, and command (TT&C) systems must be based on modular hardware and software using readily available commercial technologies (COTS), emphasizing the active role of software. To this end, the new concept of Synthetic Instrumentation was proposed. Its aim is to further improve the versatility, flexibility, and reliability of TT&C systems, while saving development costs and time, and reducing equipment costs.
Based on the same design concept, we modularized all the hardware and software required for the AC dynamometer controller, and finally developed a new type of D8001 high-speed programmable AC dynamometer controller, which provides a new solution for the control and application of AC dynamometers and a high-performance, fully functional, simple to operate and easy to use measuring and control instrument.
The D8001 is a new product created by Gaobiao Company, filling a gap in the domestic and international markets where such products are not yet available. All the technologies we use are at the world's most advanced level in AC dynamometer testing, including the latest industry standard technologies, laboratory technologies, and proprietary intellectual property technologies.
The standard and optional modules used in the D8001 are as follows. All modules are installed in a 19-inch 2U standard chassis, featuring advanced technology, compact structure, and ease of use. The torque closed-loop control module is a software module, directly installed in the inverter's mainboard memory. The programming interface program is used in conjunction with the communication module, installed on a computer, and can be called by applications such as LabVIEW and C++ to achieve automatic control and data transmission of the D8001 by the computer.
Display unit: High-brightness fluorescent digital display (VFD) shows setpoints, actual values, and controller status.
Logic unit: Programmable Logic Controller (PLC), used for setting the function of the controller, state transition and logic control.
Control unit: High-speed programmable digital signal processor (DSP) for dynamometer data acquisition and analysis.
Power supply unit: +5V, +24V, +12V and ±15V DC power supply for the control unit and external sensors.
Optional modules: pulse encoder adapter, Ethernet communication module, extended digital and analog input/output modules, etc.
Application: DynoCON AC dynamometer application macro.
Control program: PI-DTC torque closed-loop control software module.
Programming interface: DynoAPI dynamic link library file (DLL).
Customized procedures: Pass/Fail product qualification/fail inspection.
Control and Application
With the D8001 controller, we can easily operate the AC dynamometer. Because the D8001 clearly defines all the functions for controlling and applying the AC dynamometer, both manual and automatic operation are very simple and convenient.
Switches and buttons
name | English abbreviation | Function Description |
power switch | POWER | D8001 Controller Main Power Switch |
Fault Reset | RESET | When the display shows a fault in the frequency converter or controller, press the reset button. |
Motor steering | FOR/REV | FOR: Motor rotates forward (clockwise), REV: Motor rotates backward (counterclockwise). Note: The actual direction of the motor rotation needs to be adjusted on-site. |
Control Mode | DTC/PID | DTC: Open-loop torque control; PID: Closed-loop torque control Note: Torque closed-loop control requires a torque sensor and a dedicated control program. |
Loading mode | TOR/SPE | TOR: Loading (constant torque control), SPE: Reverse drag (constant speed control) |
function keys | F1/F2 | Pre-defined special control functions, such as dynamic stall or start-up under load. |
Manually given | UP-DOWN | Torque or speed increment/decrement buttons, each increment is 1 rpm or 0.1 Nm. |
Start-stop control | DEC-INC | The speed and torque setting knob can be pressed once to start and once to stop. |
Speed and torque settings
The D8001 controller uses the same knob for both torque and speed settings, and it automatically switches between speed and torque settings depending on the selected operating mode. The manual knob uses a pulse generator, ensuring accurate settings, ease of use, and excellent tactile feedback.
Start and stop
The speed and torque setting knobs have a start/stop function; pressing the knob once starts the operation, and pressing it again stops it.
show
The dual-line, 40-character high-brightness fluorescent digital display (VFD) can show the set values, actual values, calculated values, and operating status of various parameters. Special display content can be customized, such as product pass/fail status.
Work mode
Operating mode | Control methods | Instructions for use |
Transient loading | Constant torque control | Loading operation is a commonly used control mode. In this mode, the loading motor operates in a braking state, using its braking torque to control the output torque of the prime mover and absorb the energy output by the prime mover. Because the torque dynamic response of the DTC AC dynamometer is very fast, it is referred to as transient loading in other countries. |
Reverse drag switching | Constant speed control | During no-load or loaded operation, the dynamometer is switched to an electric motor. At this time, the loaded motor works in electric mode and drives the prime mover to rotate. |
Dynamic stall | Zero speed control | Quickly force the prime mover, whether unloaded or under load, to a zero-speed stall state. This type of stall does not require a brake and is a dynamic state, hence it is called dynamic stall. |
Start-up under load | Constant torque control | A load torque is preset, and the load torque remains constant during startup. |
Product Inspection | Parameter control | According to the predetermined inspection parameters and operating mode, the system automatically detects and calculates during operation, and gives the product's pass/fail judgment (PASS/FAIL). This function needs to be customized depending on the testing process. |
Auto-loading | Computer control | It is controlled by a computer via Ethernet and automatically loaded according to the test procedure. With the help of computer testing software, various complex loading operation modes can be realized, such as pulse loading, oblique loading, and curve loading, providing advanced loading test methods for the time domain and frequency domain characteristic analysis of special motors and components such as servo systems. |
Application Examples
CMTS is a new type of servo system characteristic analysis and testing platform designed and manufactured by Gaobiao Company using an AC dynamometer. It is primarily used for the integrated testing of servo motors and servo drives. Gaobiao's proprietary torque closed-loop control strategy and the application of the D8001 programmable AC dynamometer controller achieve a perfect combination of DTC (Direct Torque Control) and torque closed-loop control, greatly improving the control accuracy and dynamic response characteristics of the measurement and control system. It provides a technologically advanced, fully functional, simple-to-operate, and user-friendly intelligent instrument for laboratory and production line applications. It differs from traditional motor testing platforms in terms of testing accuracy, testing speed, and testing methods, and has broad versatility, flexibility, and practicality.
The electrical connections of the CMTS motor testing system are shown in the figure. All testing and control equipment is modular and flexible. The main equipment includes:
n ABB ACS800 series frequency converter, energy absorption type.
n ABB three-phase asynchronous motor with pulse encoder.
n D8001 High-speed programmable AC dynamometer controller.
n Torque sensor from ETH company in Germany.
n CMTS 8.0 motor testing software.
Conclusion
By comprehensively redeveloping the software and hardware of ABB frequency converters and using the design concept of synthetic instruments, a brand-new solution and a multi-functional measuring and control instrument are provided for the control and application of AC dynamometers.
With its highly flexible programming capabilities and a wide range of optional modules, the D8001 can meet the needs of various AC dynamometer applications. The D8001 can be used independently, manually, or in conjunction with computers and other measurement and control equipment to create a modular, intelligent, and flexible power testing and control system.
