> All it says is they use pwm for controlling via x72 x80 x82 etc. > > I forgot to what most buy as you say it doesn't matter really. > > I am more interested in how pwm works.
Half way turned on there are plenty of losses in transistor so it is either fully turned on or fully turned of with some margin. Usually there are half bridges so that phase voltage could be either connected to positive voltage or negative voltag or maybe left floating, then switching connection from negative to positive there must be some margin in between there both transistors are fully turned off or there will be a really good short circuit with a loud bang since there usually is quite a large capacitance with low impedance connected to half bridges. It's a duty cycle. A number telling how many percent or whatever unit is used of the period voltage should be connected to positive or negative voltage. As electric motor have some inductancem, average voltage is what is important though where will be some more or less triangular current ripple there amplitude depend on how often transistors are swicthed. Other method is to use comparator on current measurement to control at which current transistors should be switched. Lower and higher limit is one method. Turn on periodically and turn off then a certain current is reached, peak current control is another method, vaguely remember something about sub harmonic oscillation then this method is used for power supplies. To read a book about power electronics is good method to learn more, you probably only have to read a small part of it to understand half bridges commonly used in inverters for electric motors, dead times in half bridges add a small but iritating problem as do voltage drop due to current direction, SVM modulation there voltage is kept either to lower or higher DC bus level may add some more interesting problems, common mode voltage is another one. Read a book about electric motors add more useful information, the DC motor is particularly important as the equations for other motors is very similar to DC motor then viewed in rotor magnetic field "coordinate system" even though cross coupling is added for 3-phase motors, cross coupling add complications for control but should not matter to much for the basic understanding. Nicklas SB Karlsson _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
