1. The permanent magnet generator refers to a power generation device that converts mechanical energy from thermal energy into electrical energy. It was first developed by France.
In today’s DC motors, the excitation method that uses DC current to generate the main pole magnetic field is called current excitation; if permanent magnets are used instead of current excitation to generate the main pole magnetic field, this type of motor is called a permanent magnet motor.
Brushless can be achieved in many cases, so it is mostly used in small and micro motors. When using variable frequency power supply, permanent magnet motors can also be used in speed-regulated transmission systems. With the continuous improvement and improvement of the performance of permanent magnet materials, permanent magnet motors have been widely used in various fields such as household appliances, medical equipment, automobiles, aviation, and national defense.
2. System structure of permanent magnet synchronous generator with voltage adjustment
The system that uses a double-winding transformer to regulate a permanent magnet synchronous generator mainly consists of a prime mover, a permanent magnet synchronous generator, a multi-tap double-winding transformer, and a transformation ratio controller. The tap switch is turned off using thyristors. It mainly uses thyristors to turn off large rated currents, high-rated voltages, no arc generation and can realize many advantages of high-frequency conversion.
3. Working principle of voltage regulation
The high-voltage side of the three-phase double-winding transformer is connected to the output end of the permanent magnet generator, and the different taps of the high-voltage winding are connected to the output end through the control switch. When the generator output voltage is higher than the rated voltage of the load, the high-voltage side winding of the transformer increases the number of winding turns through the control switch; otherwise, decreases the number of winding turns through the control switch. Thereby realizing the adjustment of different transformation ratios.
Each tap of the high-voltage winding of the transformer is controlled by a thyristor. The voltage detection device feeds the output voltage back to the controller. The controller provides corresponding thyristor gate voltage signals under different voltage ranges. The thyristor is triggered to conduct, that is, the tap is realized. Change the connection and use the transformer ratio to adjust the voltage so that the voltage changes within an acceptable range.
When the detected output voltage U is within the following range, the corresponding transformer transformation ratio K is as follows:
Through the above control device, when the voltage of the generator is 0.87 to 1.25 times the rated voltage, the secondary side voltage is stabilized within the range of Un2 (1±2.5%) by utilizing the adjustment function of switching the high-voltage winding tap of the transformer, that is, Realize rate output voltage regulation.
4. System simulation experiment
In order to verify the feasibility of this article’s solution, according to the above ideas, a mathematical model of the system was established using the Simulink toolbox under the Matlab platform, and simulation experiments were conducted. Due to the symmetry of the three-phase voltage, this simulation only conducts simulation experiments on one-phase voltage. In order to simplify the model, the permanent magnet synchronous generator is replaced by an AC voltage source. In the experiment, the change in the output voltage of the permanent magnet synchronous generator caused by changes in the magnetic field is simulated by adjusting the effective voltage value of the AC voltage source.
In practice, after a permanent magnet synchronous generator is used for a long time, the magnetic field of the permanent magnet will become weaker, resulting in a smaller output voltage. However, it is also possible that interference from external magnetic fields may be received during use, causing the magnetic field to strengthen. There will eventually be two results: as time goes by, the effective value of the output voltage gradually becomes smaller; as time goes by, the effective value of the output voltage gradually becomes larger. All these changes are the result of accumulation over a long period of time. For a permanent magnet machine used for a short period of time, its output voltage will generally not change, but the output voltage will deviate greatly from the rated value. The two figures respectively reflect the changing trend of the effective value of the load voltage under two conditions, with and without a regulating device. In the simulation experiment, we used 380V as the rated voltage.
As the output voltage changes. When there is an adjustment device, different transformation ratios are achieved through the adjustment device, so that the difference from the rated voltage of 380V is very small, and the maximum difference is less than 30V (the difference is less than 10%) to achieve the voltage regulation effect. Without a regulating device, the output voltage changes greatly over time. In this case, the load often cannot operate normally due to the voltage being too high or too low.
Through comparison, it can be known that the voltage regulating device designed in this article can adjust the output voltage within a small range of deviation from the rated voltage, and plays the role of voltage regulation.
5. Conclusion
This article proposes a method for external regulation and control of the output voltage of a permanent magnet generator. It uses a multi-tap transformer connected in series with the generator. The output voltage is changed by adjusting the taps of the transformer, avoiding the use of expensive and complex hybrid excitation machines. Thyristors are used to achieve contactless tap switching, so that there is no danger of arcing during switching, and high-frequency changes can be achieved. Finally, the method was simulated to verify the feasibility of the method.