I have a question which I know is going to be more opinion biased than factual. I know this isn't the purpose of the forum, but I would really appreciate some extra opinions so I'm going to ask it anyway.

*Note that I will be practically building this circuit eventually, not just designing the circuit on computer software, simulation etc.

As part of a project I want to design a basic voltage regulator circuit for a diesel genset (3 phase alternator). So basically I am controlling the field voltage, and current with electronics to vary the produced 3 phase voltages. Now I know there are numerous ways to do this.

I am trying to find a easier method to do some basic initial testing as the genset in not available yet. As a basic alternator field winding is simply a copper wound coil containing a series DC resistance and inductance, it would be more practical if I could use an equivalent inductor at a bench with similar values of a typical field winding, instead of starting/running a diesel genset.

Do you think there would be a big difference in operation between the alternator's field winding when rotating, compared with an equivalent valued stationary inductor?

Some issues I can think of, for example, is when the alternator is rotating, the field inductance will change as the air gap varies.

Or temperature increases inside the alternator when supplying 3 phase loads may affect field winding resistance.

Or armature magnetic flux interaction will affect field inductance.

But as the system will need to be closed loop, in theory these above issues shouldn't pose much of an issue for good microcontroller software. Testing can also be done safer with equipment at a bench.

What is your opinions? Thanks.


The alternator will have to provide the supply for the field excitation when running after a battery has flashed the field winding initially. I am considering using thyristors for controlled rectification of the 3 phase voltages to create only the required DC field power depending on the generator's load. By modifying the firing angles, the rectified DC voltage can be varied and filtered.

If the field's power requirement is very low (don't know what the alternator specs are yet), I could create a varying DC link according to the load demands and use a power switch like MOSFET or IGBT with PWM, or a BJT to switch the DC voltage across the field, and let the field winding's natural inductance filter the current to something reasonably constant.

I will probably use a variac to step down mains voltage for initial testing.

  • \$\begingroup\$ Please tell a bit more about how you are going to control the produced voltages and currents. \$\endgroup\$ – Stefan Wyss May 13 at 10:20
  • \$\begingroup\$ @StefanWyss I edited my question to try and add some information about voltage & current control. \$\endgroup\$ – David777 May 13 at 21:26

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