OPA549: Scheme correcting circuit op amp control three-phase brushless motor .

Hello Aleskei,

I started a TINA Spice simulation for one phase of your OPA549 brushless motor driver. Some issue became immediately apparent. The motor specifications indciate an Lphase of 0.225 mH, which has a very low inductive reactance of +j0.075 Ohms at 53 Hz, and +j0.15 Ohms at 106 Hz. Thus, the peak current is going to be mostly dictated by the very low Rphase resistance which you indicate is only 0.75 Ohms. That being the case, if the full peak output is 12 Vpk, the approximate peak current Ipk will be 12 Vpk/ 0.75 Ohms, or 16 Amps. That exceeds the peak output capability of the OPA549 which is rated at 10 Amps. When I set up these condition in a TINA simulation circuit the OPA549 output clips at 8 Amps where I set the ILIM. Additionally, the simulation model shows high frequency oscillation on the clipped output peaks which isn't too surprising.

It appears that I don't fully understand the intended operating conditions. When I check the Maxon 118889 datasheet I find that the maximum continuous current is 2.46 Amps, the terminal resistance is 1.39 Ohms, and a nominal operating voltage of 24 V (+/-12 Vpk?) is specified. Please verify the conditions that you intend to run the motor in. Once they are defined, I can re-run the simulations and see what the results are.

I will address your questions once the circuit requirements are fully applied.

Regards, Thomas

Precision Amplifiers Applications Engineering

Therefore when desired speed = 53(Hz) ua=4.8*sin(2*pi*53*t) ub=4.8*sin(2*pi*53*t-2*pi/3)
uc=4.8*sin(2*pi*53*t+2*pi/3) and motor have counterelectromotive force (ea = 4.21*sin(2*pi*53*t)
eb=4.21*sin(2*pi*53*t-2*pi/3) ec=4.21*sin(2*pi*53*t+2*pi/3)) peak current op amp < 2.0(A).

Therefore when desired speed = 106(Hz) ua=10.5*sin(2*pi*53*t) ub=10.5*sin(2*pi*53*t-2*pi/3)
uc=10.5*sin(2*pi*53*t+2*pi/3) and motor have counterelectromotive force (ea = 8.6*sin(2*pi*53*t)
eb=8.6*sin(2*pi*53*t-2*pi/3) ec=8.6*sin(2*pi*53*t+2*pi/3)) peak current op amp < 3.0(A).

In catalog Maxon R and L is measured between two phase. I is given date motor for scheme replacement
datum equipment. Please answer on questiones 1-4.

Hello Aleksei,

I am having some difficulty interpreting each motor winding impedance, Zm = Rphase + jωLphase. The original information you provided listed Rphase as 0.75 Ohms, and Lphase as 0.225 mH. The diagram shown above indicates that Rphase would be 0.75 Ohms, and Lphase would actually be 1.5x the 0.225 mH, or 0.383 mH. Please let me know an equivalent series Rphase + Lphase values so that I can represent the output load as a series RL network. If the motor load impedance per winding is Zm = Rphase + jωLphase with an Lphase of 0.383 mH, then Zm = 0.75 +j0.13 Ohms at 53 Hz, and Zm = 0.75 +j0.26 at 106 Hz. That is the kind of information I need.

Additionally, you listed: "Therefore when desired speed = 106(Hz) ua=10.5*sin(2*pi*53*t)... you show 53 Hz being used in the equation. Did you intend to use 53 Hz, instead of 106 Hz?

Regarding your questions; I can only answer them somewhat at this point:

1. What correcting circuit is needed for op amp? That can only be determined once I know the output load conditions. - Please indicate the load impedance (Zm), the expected putput current, and peak-topeak voltage that we be developed across Zm.
2. What scheme replacement op amp is become for datum equipment? - I do not understand this question. Please clarrify.
3. What is dependency Zout op amp of frequency? - The OPA549 open-loop output impedance (Zo) when unloaded is about 200 milliohms, from dc to a frequency in excess of 10 kHz. This will decrease as the loop is closed and the output drive current increases. The closed-loop ouput impedance (Zcl) will likely be in the hundreds of micro-ohms, depending on the closed-loop gain and current.
4. What scheme op amp is good for datum equipment (noninverting amplifier
or inverting amplifier)? - Either should work. It is just a matter of what is needed in terms of an inverted, or non-inverted, output. Let me know what you prefer and we will use that in an analysis.

Regards, Thomas

Precision Amplifiers Applicaitons Engineering

Hello. Zm = 0.75 + jω*1.5x*0.225mH. Scheme op amp is inverting amplifier.
Please verify when desired speed = 53(Hz) and when desired speed = 106(Hz).

What scheme replacement op amp is become for datum equipment? - I do not understand this question. Please clarrify.
Clarrify: what is additional element (resistor, capacitor,...) add in scheme theoretical op amp for understand
work opa549 when jump small signal is supplied to in opa549.

Hello Aleskei,

I have constructed a simple OPA549 driver circuit having an equivalent motor load consisting of a 0.75 Ohm resistor, in series with a 0.383 mH inductor. An output snubber RC circuit was included as shown in Fig. 8 of the datasheet. Then a stability analysis was performed to determine the phase margin with the expected load. The results from the TINA simulation are shown below.

The phase margin is 69 degrees which occurs at 512 kHz (loop gain = 0 dB) and is more than adequate to assure stability. The inductive reactance at 53 and 106 Hz is so low that it isn't having much effect on the phase margin. Even if the motor impedance changes somewhat with the operating conditions a high phase margin provides some room for the imepdance to change and the circuit still remains stable.

Additonally, I ran a small-signal transient response per your request. The results indicate very little overshoot on the output waveform, which coincides with a high phase margin.

Do be sure that the output swing is not made to high with the primarily 0.75 Ohm resistive load. Otherwsie, the OPA549 may go into current limiting, or thermal shutdown.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hello. Thank you for help. Topic is closed.