[SOLVED] Four Quadrant Operation

[electronicsman]

I am bit confused about the motor operating in the four quadrants. Is this operation specific only to DC motor or applicable to synchronous AC motors as well? Please advise.

 

[KlausST]

Hi,

"Four quadrants" refer to a diagram with two axis...and each of the axis may have positive as well as negative values.

Quadrant 1: X = pos, Y = pos
Q2: X =neg, Y = pos
Q3: Y = neg, Y = neg
Q4: X = pos, Y = neg

Now it depends what your both axis are. This is not clear in your question.

For the contol circuit of a DC motor the axis could be: X = voltage and Y = current.

Then the four operation modes can be:
Q1: normal motor operation in forward direction, CW rotation.
Q2: rotation forward, but current = negative = motor operating as generator
Q3: normal motor operation in reverse direction, CCW rotation.
Q4: rotation reverse, but current = positive = motor operating as generator

Klaus

 

[FvM]

Obviously the general quadrant definition also applies to AC machines. But in contrast to DC, the quadrant isn't simply related to voltage and current polarity. Instead direction of three phase voltage system and phase angle between voltage and current respectively real power sign matters.

 

[Easy peasy]

motors normally operate in 2 of 4 quadrants, i.e. motoring, with V & I in phase, or generating, 180 deg apart...

a power supply can be a 4 quadrant type, i.e. V+ with current in or out, and V- on terminals with current in or out ...

 

[electronicsman]

Thank you for the clarifications. One question is if i am switching the 3 phase synchronous motor in the motor operation, i will be making the 6 switches ON and OFF (PWM) and applying the torque to run the load using the battery. I understand that, but let us say the load is capable of moving (ex engine) then the back emf will be generated and it will charge the battery, my question is does the charging of the battery happens even if i switch OFF completely the 6 switches? I mean does it conduct through diodes of the switches? Is it possible to completely stop flowing the current in reverse direction? Please advise.

 

[KlausST]

Hi,

An AC motor control power stage needs a DC bus.
Usually the DC bus voltage is higher than the AC peak voltage.
Thus - as long as the RPM is within the usual range - the generated voltage should be smaller than the DC voltage...the diodes never become active, no current.

But if the DC supply is switched OFF, then there will be current flow.

Klaus

 

[electronicsman]

Thus - as long as the RPM is within the usual range - the generated voltage should be smaller than the DC voltage.

RPM to generated voltage will be characteristic of the motor Am I correct? If I read the motor specifications can i get this information?

the diodes never become active,

One other question is can i also switch in the generator mode? Will it be any advantage? Please advise.

 

[FvM]

You didn't tell about the involved synchronous machine, is it PMSM or DC excited? Inverter bridge starts to charge the battery if e.m.f. peak is exceeding the bus voltage.

One other question is can i also switch in the generator mode?

If e.m.f. can't be sufficiently reduced by excitation control, the usual way to switch to a safe operation point is to short the motor terminals. According to SM characteristic, the machine will source a limited reactive current.

 

[electronicsman]

It is PMSM motor.

 

[KlausST]

Hi,

RPM to generated voltage will be characteristic of the motor Am I correct? If I read the motor specifications can i get this information?

Some BLDC datasheets give this information. I doubt that all do.
But true AC motors don't have permanent magnets, thus the generated voltage is not defined.

One other question is can i also switch in the generator mode? Will it be any advantage? Please advise.

If you use it as a generator ... it will generate electrical energy...that's the main advantage.

Klaus

 

[Easy peasy]

if the nominal motor emf ( pk -pk ) at full speed is lower than the DC bus - the diodes will not carry current.

to brake the motor here, you can short out all the lower devices ( assuming they can handle the current ) and use the motor resistance to absorb all the rotational energy until it stops, OR,

you can change the control scheme such that the motor windings serve as boost chokes and pump up the DC rail ( each half bridge leg acts as a boost converter ) - it is usual to switch in a large power resistor across the DC rail ,at the same time, to absorb the energy thus transferred ...