Shaoyang High School 1 Shaoyang High School 1 Journal of Electric Power Measurement Influencing Factors Analysis Shaoyang Shaoyang College of Electrical Engineering, Shaoyang 4220M, Hunan, China Main article discussed the impact of non-sinusoidal input voltage on the performance of dynamometer motors. Measures for adverse effects AC variable frequency speed motor type electric power dynamometer is a kind of new type of dynamometer that appeared in the 1980s. It is the product of electromechanical technology, and it is the electrical machinery design machinery design power electronics technology detection technology computer technology and many other aspects The comprehensive application of knowledge, its research results have a strong application value, its technical performance indicators than the world's most advanced human AC frequency conversion power dynamometer more months, belonging to, science and technology products, due to its price Relatively cheap is about 1314. Therefore, it is more viable in the current economic environment. It also has the strength to participate in the international competition. The power dynamometer is mainly composed of the device control device and the dynamometer motor. A full-featured variable frequency speed control system with a main vertical axis as a high-level test equipment for torque and power, to be completed The dynamometer system should be adopted in terms of components, iJJfic, fPWM3clil0iJiiJ ftiff.iiJxijitJL0jiniAEfeJ ±. TJ near sine wave, to reduce the purpose of harmonics, in the control device, a reasonable choice of pulse width modulation strategy, so that the internal frequency harmonic power supply is greatly suppressed. As a tester, Tun Cancan designed it as an anti-harmonic old step motor as much as possible. The motor still has better performance under the power supply of the variable frequency power supply with harmonic components.
1 Frequency conversion power supply is the main harmonic source of electricity The frequency conversion device is the main non-sinusoidal power receiving device of the power grid. The power source it takes from the AC power system is non-sinusoidal, and its voltage waveform can be decomposed into fundamental waves according to the Fourier series. And series of harmonics of different frequencies and amplitudes, these harmonics will bring the following series of adverse effects to the motor.
The pulsating torque appears due to the non-sinusoidal input voltage of the variable-frequency power supply. According to the Foucault-decomposed fundamental wave and the series of higher harmonics, the respective voltages are generated in the motor to generate 5, 1 reverse rotating magnetic field and torque. The 7th harmonic voltage generates +7,1 positive rotating magnetic field and torque is the largest, they will interact with the rotating magnetic field of the stator 10, respectively, to generate 61 pulsation torque, these 61 pulsation torque values Although not large, it will cause pulsation of the output torque of the dynamometer motor. Especially at light load and low speed operation, the effect of torque ripple is more obvious, resulting in uneven motor speed and a sense of stepping to cause vibration of the dynamometer motor. And noise.
1.2 Various loss increases The time harmonics generated by waveform distortion of the variable frequency power supply are superimposed on the spatial higher harmonics caused by the motor's cogging, so that the magnetic flux in the air gap of the motor contains higher harmonics. The harmonics will cause the copper loss of the dynamometer motor to increase the mechanical loss and the additional loss, although the total increase of the core loss due to the time harmonic flux is insignificant in the total iron loss, but the end leakage flux Pass and chute leakage flux at harmonic frequencies may produce a very substantial core loss, and the skin effect causes the resistance of the stator and rotor to increase, resulting in an increase in copper consumption, and the mechanical loss increases with rotation speed. However, when the frequency of the power supply continues to rise, the additional loss also increases, so the efficiency of the motor has decreased. 5 The output power has been reduced, the temperature rise of the motor has also been improved, and the performance of the test engine has decreased. , 1.3 Voltage imbalance occurs When the variable frequency power supply is used, the voltage of each phase added to the dynamometer motor is generally balanced. However, due to the malfunction of the switching elements and the differences in the characteristics of the phase rectifying elements and the control elements, It may cause the dynamometer motor to appear voltage imbalance phenomenon at a certain moment. Coupled with the shaft voltage caused by the unbalance of the magnetic circuit of the motor and the high frequency voltage on the rotor, static electricity will be generated in the capacitor formed by the bearing oil film on the ground. The accumulation of the Dutch. A large shaft card will be generated on the shaft so that the generated current will flow off the oil between the shaft and shaft 1 . Oil stocks will be destroyed due to large flow through, which will shorten the bearing life and endanger the safe operation of the motor. 2 Common measures for improving the bad factors The dynamometer motor needs to be powered by a special variable frequency power supply to ensure the quietness of its motor. Characteristics and speed range, so it should take some common measures to improve the bad factors.
From the optimal starting of the system to suffer from the selection of the rated value of the voltage frequency power efficiency of the dynamometer motor, it is not limited by the power frequency grid of the power supply.
When the air gap flux is kept constant during operation, the maximum torque does not change substantially.
3 The motor must have sufficient stiffness to g, pulsed torque, for the current type inverter, the leakage resistance of the motor should be small; for the voltage type inverter, the leakage resistance of the motor should be large.
In order to reduce various losses, the motor core should be made of high-quality thin Gui steel sheet, and the stator or rotor slot shape must be skewed, and the slot fit and slot shape should be selected correctly. Forced air cooling is the best choice.
3 Concluding remarks AC frequency conversion dynamometer dynamometer motor as an AC variable frequency speed regulation power dynamometer system in an important part, because it requires a dedicated variable frequency power supply, so the design principle can not be equivalent to the ordinary asynchronous motor, should be based on electronic and motor Part of the technical and economic rationality is taken into consideration and determined with the overall best requirements.
1 Hu Duo, 7. The modern exchange adjustment technique, 1. North. 1; mechanical industry outlets. 1999 2 Tibetan and British Jie. AC motor speed control elbow. Beijing China Railway Publishing House, 1984 3, Liquan et al. 35 Dynamic Power System Project Evaluation Analysis 1.992 4 Cheng Licei. Discussion on Electromagnetic Computation and Design of Variable Frequency Asynchronous Motors . Electronic Technology Magazine. 445 Siemens 6870 Inverter Operation Manual Responsibility Editor Qian Guanmin
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