Howto: Running a Permanent Magnet (PM) Motor with a WJ200 VFD

[hvontres]

I was able to get my WJ200 to run a Permanent Magnet motor by following the attached supplement from hitachi. The motor spins, but I am still trying to figure out all of the parameters. The picture shows a 2Hp Servo Motor next to the 1HP three phase motor it will be replacing Note all of the lovely red crud still attached to the old motor. I am planing to run the motor in my lathe and replace the step pulley with a single pulley setup and run the motor in Variable speed mode. I should have a lot more information by the end of the weekend. The motor was a freebe at work (~$600 on fleabay). I used the Autotuning feature to measure the motor parameters since I don't have the datasheet for this exact motor available.



Some potential issues that still need to be sorted out:
1) Long Spin-up / Ramp down time: The motor seems to take a long time to spin up and the time does not seem to be affected by the standard ramp parameters. I think this has to do with the sensorless control scheme used.
2) Some Audible noise. There is still some high frequency squealing even at full speed. This may be less of an issue if the motor is loaded down and mounted in the cabinet, but it is something I would like to reduce.
3) the Wiring I will be ordering the correct connector tonight. I just wanted to make sure the motor actually worked before investing a whole lot into getting it to run



View attachment WJ200 Additonal_function_Ver2_2.pdf

 

[Senna]

Wow I didn't expect a manual from a major player like Hitachi would be so poorly translated!!

I suspect it was written and translated in China rather than Japan.

Anyway, it seems there are numerous limitations on how effectively the Hitachi can function as a drive for a PM motor. I look forward to further reports on your results, thoughts, and experiences.

Thanks.

 

[hvontres]

Wow I didn't expect a manual from a major player like Hitachi would be so poorly translated!!

I suspect it was written and translated in China rather than Japan.

Anyway, it seems there are numerous limitations on how effectively the Hitachi can function as a drive for a PM motor. I look forward to further reports on your results, thoughts, and experiences.

Thanks.

Jeah, that manual could use a bit of a rewrite. I think if I didn't already have the motor, I would not have botherd But knowing the work we had to put into running our servos at work with feedback, I think it is kinda cool to be able to run a sensorless Vector drive with a relatively small amount of tinkering. Also, I think PM motors are better at delivering high torque at low speeds. But that would get into a whole discussion of how induction motors work And that is a whole different ball of wax..

 

[hvontres]

Quick update:

I finally got the motor back in the lathe and was able to tweak the parameters to get it to start up most of the time. Every so often It will stall out on startup. I will need to tinker with it some more over time. The good news is that I can run the motor from 20-150 Hz once it gets going. Also, the DC braking can stop the lathe with an 8" Cushman 3 Jaw in 5s, possibly less, but I haven't tried to push it yet.

Here are some pictures of the finished install:


One other thing I wound up doing on this build is using a DB-25 cable to connect the Logic terminals on the WJ200 to my Box. This works really well, since there are exactly 25 signals in the drive The current box is using a cheap +/-200 mV panel meter to display the RPMs based on the analog output of the drive. I think I need a bit more filtering because the meter will sometimes overrange. This might be due to PWM noise coupling into the signal, but I haven't had a chance to drag my scope over to check yet.


Overall, I would say that unless you happen to have a large brushless motor laying around in your junk pile, a good Inverter Rated Induction motor with a 10:1 speed rating would probably be a better choice for most people. The Hitachi documentation is a bit lacking at this point, especially for people unfamiliar with how motors work. I have been around Brushless motors at work for almost 20 years now (yikes...) and I was still mostly just guessing at what might or might not help. On the other hand, the monitoring tools in the Hitachi setup software are a really great help. It is really nice to be able to monitor the motor current during startup to see if the latest parameter change had any effect on reducing the peaks during startup or not.

Future Enhancements that I have planned for include:
- Improve Startup performance - I will probably play with the parameters some more to see if I can't get the motor to start on every try.
- Seperate 24V supply - I really wish the hitachi drives could supply more than the measly 100mA. That's not even enought to light my two indicators !!!
- Replace panel meter with two line LCD - I want to setup a small micro controller (TI msp430) with a two line LCD display to show both speed and load. I think I will be using the pulse output (EO) for speed and the 0-10V signal for load.
- Wire up second indicator as overload warning - I think the second indicator will be used to indicate the drive running at ~90% of peak output. That way I know when I am trying to take too deep a cut

 

[Windscreen]

Henry,

Any updates on your experiences with the WJ200? I have a mill that uses a 3 hp PM motor on the spindle, with hall feedback to a proprietary built in drive. The drive doesn't seem to provide any means to adjust its PID speed control parameters, and the speed control is quite crummy on transient loads (like entering a cut!). This seems like a potential solution to me, but the documentation (in its awesome English) seems to suggest this shouldn't be used in a constant torque application, like a spindle motor.

What do you think?

Thanks,
-Windscreen