Design and implementation of virtual instrument testing system for motor performance
Abstract: The modern virtual instrument technology is applied in the field of motor performance testing, which gives full play to the characteristics of high development efficiency, strong flexibility, compatibility and high reuse of virtual instrument technology. The on-line test of multi-channel parallel motor is designed and implemented, and PID control algorithm is used to control the calibration parameters. Finally, TCP/IP protocol is used to realize the remote sharing of test data and the user’s remote control of the test system.
Key words: Virtual instrument motor test PID TCP/IP In recent years, with the rapid development of computer technology, motor computer-aided test (CAT) system has been popularized in the motor industry [1].
Computer-based motor performance testing has gradually replaced the traditional manual motor testing, and is developing towards automation and intelligence. However, the auto-test system based on the traditional development platform often faces the shortcomings of long development cycle, high cost, weak compatibility and expansibility, which also hinders the wide application of the auto-test system. With the introduction of modern virtual instrument technology, computer and standardized virtual instrument hardware are combined through virtual instrument application software, so as to realize the softwareization and modularization of traditional instrument functions, so as to achieve the purpose of automatic testing and analysis [2]. By using virtual instrument technology, users can easily complete the functions of signal conditioning, process control, data acquisition, analysis, display and storage, fault diagnosis and network communication of test objects through the graphical programming environment and operation interface, which greatly reduces the system development cycle. At the same time, the compatibility and expansibility of the test system have been greatly enhanced by adopting standardized virtual instrument hardware and software. In addition, the flexibility and reuse of virtual instrument technology can minimize the scale of the user’s test system, and it is easy to upgrade and maintain, and users can even use existing hardware to form another test system, thereby reducing unnecessary repeated investment and reducing the development cost of the system. The motor performance virtual instrument testing system is used by the United States National instrument onmouseover=” cc.style.visibility= “;” style=”COLOR: #ff0066; TEXT-DECORATION: underline”> Company
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(National Instruments, NI) LabVIEW and LabVIEW RT virtual instrument software platforms, And the supporting NI PCI data acquisition board, NI SCXI signal conditioning equipment and NI compact FieldPoint (cFP) distributed I/O real-time system hardware. The performance of multi-channel power tools is tested in parallel. And can automatically complete real-time monitoring of load, torque, speed, power and body temperature according to user Settings; Finally, TCP/IP protocol is used to realize the remote sharing of test data and the remote control of the test system by users. The system has the characteristics of short development cycle, high efficiency and low cost, and has strong system scalability and reusability, and has strong application value.
1. System composition and working principle
1.1. System composition
The motor performance virtual instrument test system is mainly composed of four parts: main control module, cFP real-time monitoring module, dynamometer module and motor module to be tested. The main control module module is a DELL workstation, which is used to provide graphical user interface, complete the configuration of system hardware and the setting of user interface and control parameters. The waveform display of each index parameter is updated in real time, and the motor characteristic curve is obtained after curve fitting, and the test data is recorded at last. At the same time, the main control computer also completes the measurement of non-control parameters, such as input voltage and working current, through the embedded NI PCI data acquisition card. The cFP real-time monitoring module consists of two NI cFP distributed I/O systems, which communicate with the master computer through TCP/IP protocol, obtain control parameter commands from the master computer to control the dynamometer, and return the data signal collected from the dynamometer module to the master computer for processing. Module A is used to complete real-time automatic loading and measurement of control index parameters, and provides emergency measures such as overload protection, emergency shutdown and system reconstruction after illegal shutdown. Module B is used to complete the real-time monitoring of the body surface temperature of the measuring motor. The dynamometer module is composed of hysteresis dynamometer and magnetic powder dynamometer, which are respectively suitable for different types of motor under test. They are used to provide A certain load for the motor under test, and the internal sensing equipment converts the torque, speed and output power of the motor under the load into the voltage signal acceptable to cFP real-time monitoring module A.
1.2. Working principle
The motor performance virtual instrument test system can be operated in two working modes: automatic working mode and manual working mode. The main test items are: 1) Motor input voltage curve 2) motor input current curve 3) motor input power curve 4) motor torque curve 5) motor speed curve 6) motor output power curve 7) motor body surface temperature 8)
In the automatic working mode of the internal temperature of the motor body, the main control machine first waits for the user to complete the setting and configuration of the hardware and software. Then ask the user to choose load test or fixed parameter test, load test users need to set load curve, load time, cycle time and test time and other test parameters; Under the fixed parameter test, the user can choose to specify the torque, speed or power, and set the corresponding calibration parameters, control parameters and test time. After completing the above steps, you can start the test program, the test system is automatically loaded according to the user’s load and complete the performance test of the test motor; Or maintain the stability of the calibration parameters by a certain control algorithm and automatically test the motor under this state. While the system is running, users can observe the waveform display of each index parameter to the time in the real-time monitoring chart, get the motor characteristic curve after curve fitting, and can export the interested chart to save. When the test time is completed, the system automatically terminates the test. In manual mode, the working principle of the system is basically similar to that of the automatic mode, except that the system does not carry out cyclic testing, but provides an interactive test environment, and waits for further operations of the user after completing the specified test project.
2. Hardware structure
2.1. Master computer
The main control machine uses a DELL workstation, embedded with an Intel Pentium 4 2.6G CPU, a NI PCI-6052 multi-function data acquisition card and a NI PCI-4070 high-precision flexible digital multimeter card. The PCI-6052 multi-function data acquisition card is premounted with two NI SCXI-1120 signal conditioning cards and a matching NI SCXI-1327 attenuating terminal, which is used to collect the input signals of the working voltage and working current of the multi-channel motor to be measured. The NI PCI-4070 high-precision flexible digital multimeter card is premounted with a NI SCXI-1127 multiway switch card and a matching NI SCXI-1331 multiway terminal, which is used to scan the rotor winding of the multi-way motor to be measured, and then measure the internal rotor temperature of the motor according to the corresponding algorithm.
2.2. Real-time monitoring module
The real-time monitoring module uses NI cFP distributed I/O real-time system. As an industrial control system, cFP is equipped with FIFO data queue, power failure data cache, watchdog status monitoring, and high impact and disturbance resistance, which is used to complete the core real-time acquisition and control part of the system [3]. The cFP-2020 module is selected as the Real-Time system controller, which is embedded with a microprocessor, 32M DRAM and 256M Flash flash chip, and supports the LabVIEW real-time module, which can be detached from the LabVIEW programming environment. The application program downloaded to the controller memory is run independently in real time, and the test data is shared through the 10/100Base TX Ethernet interface embedded in the controller. A cFP DI-330 is used to respond to the emergency stop switch, emergency shutdown system, to prevent accidents; A cFP DO-403 is used to control the SSR of the solid-state relay connected to each motor to be tested, so as to realize the system to close or disconnect the working circuit; A cFP AO-210 is used to provide loading signals for the dynamometer to increase or decrease the load borne by the motor to be measured, so as to control the motor under a certain load; A cFP AI-210 is used to collect the voltage signal corresponding to the motor torque output by the dynamometer sensing equipment, and measure the actual torque of the motor to be measured. A piece of cFP-CTR-502 is used to collect the TTL level signal corresponding to the motor speed output by the dynamometer sensor, and measure the actual speed of the motor to be measured.
2.3. Real-time temperature measurement module
The real-time temperature measurement module also uses the NI cFP distributed I/O real-time system. It adopts CFP-2020 controller and four cFP TC-120 8-channel thermocouple modules, which can be directly used to measure standard J, K, T, N, R, S, E and B type hot spot couples, and provide corresponding signal conditioning, double insulation isolation, input noise filtering, cold end compensation and temperature algorithms of various hot spot couples. It is used to implement front-end data sampling at the working end of the motor, and realizes remote data sharing by using the distributed I/O network sharing function based on TCP/IP protocol, which is conducive to the implementation of remote real-time monitoring on the industrial site.
2.4. Dynamometer
The dynamometer is designed according to the principle of balance between action and reaction [4]. When the torque received by the stator of the motor dynamometer is equal to the torque of the measured motor, the torque value of the measured motor is read directly and accurately by the single chip microcomputer data acquisition system. When the measured motor rotates with the rotor of the dynamometer, if DC excitation voltage is added to the dynamometer, there is a magnetic field in the dynamometer, then the rotor of the dynamometer rotates and cuts the magnetic force line to produce armature current, and the interaction between armature current and magnetic flux generates braking torque, while the stator of the dynamometer is subjected to a torque effect in the opposite direction, compressive stress will be generated on the sensor shaft of the dynamometer. In the normal operating range, the compressive stress is proportional to the torque borne by the sensor shaft. If the resistance strain gauge is attached to the direction of the maximum compressive stress of the sensor shaft, the resistance value at the strain will change with the size of the compressive stress, and then the strain gauge can be connected to a certain bridge circuit to convert the change of the compressive stress into a voltage signal, so that the torque can be measured. The photoelectric speed sensor is used to measure the speed of the motor, which has high resolution, small inertia and wide application. The combination of single chip microcomputer and photoelectric sensor makes the measurement of the speed of the motor simple and strong anti-interference ability. The photoelectric sensor is mounted on the motor shaft with a disk with N evenly distributed serrations, which is projected to the photosensitive tube by the light, when the motor rotates a week, N pulse signals are obtained, and the frequency or period of the pulse signal is measured, and the speed of the motor can be obtained. Two types of dynamometers are used here: hysteresis dynamometers and magnetic powder dynamometers. Hysteresis dynamometer torque measurement range is relatively small, the maximum torque is 10N.m, but the speed is large, the maximum speed is 12000rpm; Magnetic powder dynamometer torque measurement range is large, the maximum torque is 20N.m, but the speed measurement range is small, the maximum speed is 4000rpm, the two types of dynamometer complement each other can be applied to a variety of types of motor performance test.
2.5. Control the cabinet
The control cabinet is mainly composed of the control switch, switching power supply, filter and connection line, which provides corresponding multi-channel interfaces for each sensing module to connect with the motor to be tested, and provides auxiliary functions such as safe system power supply, excitation injection, signal isolation, amplitude adjustment and air cooling control, providing strong current support and system emergency measures for the entire motor test system.
3. Software structure and algorithm
3.1. Software structure
The virtual instrument testing system of motor performance adopts a client/server (CS) structure based on TCP/IP protocol. The server architecture is NI cFP distributed I/O system, and the embedded independent real-time system is used to realize the signal sampling of the target parameters, and to complete the real-time monitoring and control of the target parameters. The client adopts the general PC structure, runs the Windows multi-threaded operating system, uses the LabVIEW virtual instrument platform, realizes by TCP/IP protocol, communicates with the server control parameters and detection data, and provides a GUI graphical user interface to realize human-computer interaction and complete the input of control parameters. And analysis, calculation and chart display of detection data.
The system operation process is as follows: After power-on, the server automatically starts the LabVIEW RT real-time program built in the memory, and listens to the client’s “start test” command in real time; Start the main program of motor performance virtual instrument test on the client. After completing user login, hardware configuration, selecting test items and setting test parameters, start the test program; After listening to the client’s “start test” command, the server starts real-time control and data collection according to the hardware configuration, test items and test parameters formulated by the client, and sends the experimental data to the client through TCP/IP protocol. The client sends PID control command, and analyzes and processes the experimental data sent by the server. After PID control is completed, the test is carried out according to the test project, and the test data is analyzed and processed, and the experimental results are displayed in a chart. After the test is completed, the client issues a command to end the test, and the server receives the confirmation to end the test.
3.2. PID control algorithm
Three PID control algorithms are tested in this system: positional PID control algorithm, incremental PID control algorithm and integral separation PID control algorithm [5].
1) Positional PID control algorithm
The positional PID control algorithm is described as follows: where, = 0,1,2… Is the sampling sequence number; Is the computer output value at the time of the first sampling; Is the deviation value entered at the time of the first sampling; Is the deviation value entered at the time of the first sampling; Is the integration coefficient; Is the differential coefficient; Is the proportional coefficient; Is the integral time constant; Is the differential time constant; Indicates the sampling period. The advantage of this algorithm is that the principle is simple, just the classical PID algorithm theory is discretized, applied to computer-aided measurement, the structure is simple and easy to implement; The disadvantage is that each output is related to the past state, the calculation must be accumulated, the computer calculation workload is large; Moreover, because the computer output corresponds to the actual position of the actuator, if the computer fails, a large change will cause the position of the actuator to be large