The essential difference between ordinary generators and digital inverter generators Part-II

- Feb 09, 2018-

Second, the characteristics of inverter generator

1, electromagnetic design For ordinary asynchronous generators, the main consideration when redesigning the performance parameters are overload capability, starting performance, efficiency and power factor. The inverter generator, as the critical slip ratio is inversely proportional to the power supply frequency, the critical slip rate close to 1 when the direct start, therefore, overload and start-up performance is not too much need to be considered, but the key issue to be solved is how to improve power generation Machine non-sine wave power adaptability. 

The general method is as follows: 

1) As much as possible to reduce the stator and rotor resistance. Reduce the stator resistance can reduce the fundamental copper consumption, to make up for higher harmonic caused by copper consumption increase 

2) In order to inhibit the higher harmonic current, the generator inductance should be increased appropriately. However, the rotor slot leakage greater than the skin effect is also large, higher harmonic copper consumption also increased. Therefore, the size of the generator leakage reactance should take into account the rationality of the impedance matching within the entire speed range. 

3) The main magnetic circuit of inverter generator is generally designed to be in an unsaturated state. One is to consider the higher harmonics will deepen the saturation of the magnetic circuit. The other is to consider increasing the output voltage of the inverter in order to increase the output torque at low frequency.

2. Structural Design When structural design is re-designed, the influence of non-sinusoidal power supply characteristics on the insulation structure, vibration and noise cooling of inverter generator shall also be considered. 

Generally, the following problems are to be noticed: 

1) The insulation grade is generally class F or more High, to strengthen the ground insulation and turn insulation strength, in particular, to consider the impact of insulation resistance to voltage capability. 

2) For the vibration and noise of the generator, it is necessary to fully consider the rigidities of the generator components and the whole structure, and make every effort to increase the natural frequency of the generator so as to avoid the resonance phenomenon with all the force waves. 

3) Cooling: The general forced air cooling, the main generator cooling fan using an independent generator drive. 

4) to prevent the shaft current measures, the capacity of more than 160KW generator insulation bearings should be used measures. Mainly easy to produce magnetic circuit asymmetry, will produce shaft current, when the combination of the current generated by other high-frequency components together, the shaft current will greatly increase, resulting in bearing damage, so generally take insulation measures. 

5) constant power inverter generator, when the speed exceeds 3000 / min, the special high temperature grease should be used to compensate for the bearing temperature.