bipolar pwm
In the previous article in this series we saw that the most appropriate motor for an electric car is a 400Hz three phase induction motors. Operated at a fixed frequency supply of this type is essentially a constant speed motor. To be able to vary the speed of our car we have to vary the frequency of feeding. The speed motor is proportional to frequency. To prevent engine damage from the mains voltage must be varied in proportion to the frequency. The device to achieve this is called a variable speed drive (VSD). There are several types, but most suitable for our purposes is the type that uses bipolar transistors insulated gate (IGBT) to form a three-phase inverter with pulse width modulation (PWM). The easiest way is to buy a VSD with the engine. These are be designed to operate at 200 volts or 208 volts three-phase AC power. If you're planning to use a battery of your car, you have to remove, or bypass, the rectifier on the input side. If you are electronically inclined, you may want to create your own. In my website you will find references a number of useful papers on the subject.
If You are not electronically inclined, it may be best to buy a motor of 200 volts, 60Hz complete with CIV game. It will be considerably heavier than a suit of 400Hz, but still acceptable for a local runabout. There are several manufacturers in the eastern end can provide good units at a reasonable price. If you are able to connect to a grid system Talbot, they will be adequate. If you must use a battery will need 200-volt lithium-ion. Usually, they lose storage capacity by 20% per year and must be replaced at intervals of three to four years. The cost will be comparable with the use of gasoline. Those east of the Atlantic, where the standard 3-phase supply voltage is 400 or 415, there is a wide choice of engines 50Hz and VSD ranging from 60 watts to 350kW. These are ideal for heavy vehicles. The operation of these from a battery is not recommended that the battery will to be huge.
Several helpful articles are found in the Wikipedia entry on the Variable Frequency.
By John Talbot
(Under the direction the Lord Jesus, Prov 3:6, Colossians 3:17)
The Lord Jesus Christ appeared to the author, John Talbot, in a vision, on September 30th 1974 and called him to follow Him. He is the author of several books on the subject. He is now the CEO of Talbot Electric (Pty) Limited, a South African company devoted to the development of electric transport systems. For more information visit http://www.johntal.com/home.htm
Arduino Stepper Motor Controller (Bipolar) – First Test…
