I am struggling to find differences betwenn thos components.

To start, what's the difference between PM240P-2 and PM240-2? I can't find the difference, for example :

6SL3210-1RE28-8AL0(PM240P-2) VS.6SL3210-1PE28-8AL0(PM240-2)

Then difference between:6SL3243-0BB30-1FA0(CU230P-2) VS.6SL3244-0BB12-1FA0(CU240E-2)

The only difference I have found is CU240E-2 has safety inputs, while CU230P-2 does not have safety inputs and it's slightly expensiver than CU240E-2.

Let's say that I wan't to install 45kW blower fan with induction motor, very high fan rotor inertia. Which way should I go? What are benefits of using P series instead of using standard one. Which special functions regarding HVAC the S series have?

Can I combine PM240P-2 and CU240E-2 together? I wold like to have a safe torque off on the inverter without of the use of safety CPU (by means of F-DI on the CU240E-2).

I have read ton of manuals, but still don't find any relevant differences.

Controlling the inertia of thes blowers requires some braking, I am thinking this is a blower with a large diameter, sometimes used for gas pressure regulation from landfill.

Use a fully rated PM240-2, with braking resistor, this will make the dynamic response for speed control or pressure regulation less problematic when it comes to commissioning this stuff on site.

I have made some assumptions here, so I hope I have interpreted the application correctly.

Thanks for replies, but still there is no simple cofrontation on differences, so I had spent many hours to find some major differences:

PM240-2 has a built in a braking chopper, while PM240P-2 doesn't have.

CU240E-2 has many different modes of control:

[0] U/f control with linear characteristic

[1] U/f control with linear characteristic and FCC

[2] U/f control with parabolic characteristic

[3] U/f control with parameterizable characteristic

[4] U/f control with linear characteristic and ECO

[5] U/f control for drives requiring a precise freq. (e.g. textiles)

[6] U/f control for drives requiring a precise frequency and FCC

[7] U/f control for a parabolic characteristic and ECO

[19] U/f control with independent voltage setpoint

[20] Speed control (encoderless)

[22] Torque control (encoderless)

Application functions:

- Technology controller

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CU230P-2 has:

[0] U/f control with linear characteristic

[1] U/f control with linear characteristic and FCC

[2] U/f control with parabolic characteristic

[4] U/f control with linear characteristic and ECO

[7] U/f control for a parabolic characteristic and ECO

[20] Speed control (encoderless)

Application functions:

- Technology controller

- HVAC functions : real time clock, Essential Service Mode, Stagging, Multizone controller, Bypass, Energy saving mode

- Free blocks: Logic functions, Arithmetic functions, Time functions, Memory functions, Switch functions, Control functions, Complex functions

- Conveyor technology: limit switch

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tractor:

Installing a breaking resistor is not a viable solution, sicnce it is not important how many time it takes the fan to decelerate. I can take 10 s or 10 min, it doesn't matter.

I have found problems with some other brand inverter:

- when switching off the deceleration ramp has to be very slow to limit the generator voltage

- instead when using free run stop with flying restart, it trips when starting while fan is not completely standstill

- when starting up, at some point the fan starts cavitating/oscilating, so at the first moment it seems that fan is sudden accelerated over the setpoint speed when felt in a turbolence - sudden loss of load. The inverter want's to lower the speed and it gets into a generator mode thus it trips in DC link overvoltage. I had tried to put the inverter in vector mode as well and limit the torque in generator quadrants to zero, but it didn't helped.

All I want to acheive is:

- Start with a ramp that outputs nominal torque - no fast dynamics

- Stop with a ramp that doesn't put the system in generator mode - just the same as free run stop

- If there is a speed deviation the inverter has to accelerate with nominal torque and decelerate with zero torque.

Marko

All I want to acheive is:

- Start with a ramp that outputs nominal torque - no fast dynamics

With the type of load you have, the referred inertia is considerable, this is the ratio between the rotor inertia (motor) and the load inertia (blower), and if this 'blower' is directly coupled then this can exceed 10:1. Ideally for an asynchronous motor this should be less than 5:1, but we often can get away with more.

In your system then you will probably have a high dynamic mismatch, which means that the rotor of the motor will experience some difficulty achieving a steady state of synchronism, and possibly rotor stall.

- Stop with a ramp that doesn't put the system in generator mode - just the same as free run stop

Stopping the rotating mass requires control; relying on 'windage & friction to stop the load is not practical, because the torque to stop will change as the blower reduces in speed. As the blower speed reduces, (I am assuming this is a centrifugal blower), the load, call it 'windage', will reduce as the blades go into 'stall', after which point the load becomes inertial; due to the mass of the blower. At the low speeds then the ability of the asynchronous rotor of the motor to maintain synchronism with the supply becomes difficult, due to the rotor power factor, which at this point will be poor, and it will 'stall' early, and control will be lost.

- If there is a speed deviation the inverter has to accelerate with nominal torque and decelerate with zero torque.

Acceleration is achieved due to the rotor slip, and is a stable state of control, if within motor characteristic. As I have discussed above, deceleration is complicated by the mismatch of inertia, and change of load.

An inverter drive with a braking resistor will provide stability, and reliability for this application I believe.

I have made a few assumptions here, in order to avoid a 'yo yo' of E Mail traffic, but I hope this explanation 'clears the air' somewhat.

Thanks Marko, for the response.

tractror:

Thanks for the valuable answer. Still, there are some points that I disagree. 

1. I know that best thing would be a PM250 with regeneration, or maybe PM240-2 with chopper and braking resistor. But, the HVAC inverter with PM240P-2 is without a chopper, cheaper. Further, it is not needed any kind of regenerative braking, it's just a fan. My preasumption was that these inverters with P letter are promoted as HVAC, Fan, Pump,.. inverters. A 45kW fan is not a such unique, I would say it is still low power fan. As a fan it has big inertia. So I was expecting that CU230P-2 has some special operating mode that copes with those specific needs as promoted filed of insterest.

2. You are talking about inertia mismatch. It's an obvious fact that motor rotor can't have not nearly the same inerta as blower turbine.Also, this is not an issue, because the rotor and the blower are rigid coupled, so now the sum of both inertias are the total inertia. This fact is somehow different and problematic if there is an elastic coupling in between, but this is not the case.

Vector control has the ability to control both magnetization (d-axis) and torque (q-axis). I could use a cheap evaluation board to proove that I could accelerate with nominal current (Iq=In) and decelerate with zero torqe (Iq=0) . This is a very basic task that vector control can do. What surprises me, is that multi k€ inverter fails on this simple task. (Note: it wasn't a G120)

Hi Marko

Perhaps I am making too many assumptions regarding your application, such that you are selecting an inverter drive to change speed, and therefore, flow or pressure. The dynamic changes would be accommodated certainly with the PM250 or the PM240-2 with braking resistor.

The PM240P is a competent HVAC device, which can provide 'start on the fly'; and 'coast to stop', functions which requires no regeneration capability. Provided the speed changes can be achieved at a rate which requires limited effort from the drive system. I am not aware that the CU230P-2, has any 'special' feature which will prevent the device from tripping with over voltage due to regenerated energy form the motor.

My impression of this application is a motor 45kW, directly coupled to a 'blower', which is, or may be a centrifugal fan, designed to provide some pressure to air or gas. I assume this is a backward curved fan unit, which will have no stall point if operating within its design specification. The fan, at 45kW for the motor power, will have a considerable mass, and it is the mass which I was concerned about. The motor is coupled directly to the fan assembly with no flexible coupling, here the rotor of the motor is controlling the fan of the blower, the inertia mismatch will be large, and here the rotor must maintain synchronsm with the inverter derived supply, without exceeding the specified slip, and stalling.

However if the dynamic control required for this application is low, and not a dynamic application, then my concern is probably misplaced, and the vector control will cope with any induced instability. 

My apologies if I am making too much of this application, but it is good to discuss these things with colleagues.

Thanks Marko.

Hi tractor,

Perhaps you misunderstood me. I am very thankfull for your answer and your effords. There is nothing wrong or bad interpreted in your answers. I am jus struggling to find how these P series inverters without breaking chopper and resistor decelerate. I thought by some special algorithm dedicated to this P series, maybe?

The blower acts exactly in the manner you described it. If I issue a free run stop, the blower speed goes rapidly down due to the drag, but then spins free for a very long time due to the inertia.

So, the acceleration and decelereration ramps here, make just troubles. If the investitors decide to put a G120P, then I will report the behaviour and steps to fulfill those needs. (that won't be soon) .

Thanks Tractor.

Marko

The P Series devices:

The power module, PM230P, has been designed to service the HVAC market which is sensitive to supply harmonic distortion. To this end modules have been designed with low DC link capacitance, which permits Siemens to compete with harmonic statements relevant to supply impedance values, and when calculating the harmonic predictions this has a marked beneficial effect.

A low DC link capacity make the design vulnerable to load shocks, however variable torque loads usually mitigate the risk here.

The Control units, both CU230P and CU240E, are both sensitive to High DC link voltages, able to modify ramp time to mitigate tripping. Also 'start on the fly', works well without too many surprises, connecting a VFD to a spinning motor.