Control method for machine with inverter-operated electric drive unit

Abstract

A method for controlling a machine with at least one inverter-operated electric drive unit includes determining the instantaneous mains frequency of the mains supply to the machine and a deviation of the determined mains frequency over a standard frequency of the mains supply, determining a frequency correction value for adjusting the target drive frequency at which the electric motor of the machine is operated by weighting the deviation with a factor k, the factor k being specified dynamically as a function of at least one process variable of the drive load and/or of the operated drive process, and operating the machine at the adjusted target frequency.

Claims

1. A method for controlling a machine having at least one inverter-operated electric drive unit, comprising the steps of: determining by the machine an instantaneous network frequency of a network supply of the machine; determining a deviation of the instantaneous network frequency with respect to a standard frequency of the network supply; determining a factor k dynamically as a function of at least one process variable of a drive load, a drive process or the drive load and the drive process for which the machine is being operated; determining a frequency correction value for the adjustment of a desired drive frequency at which an electric motor of the electric drive unit of the machine is operated by weighting the deviation with the factor k; applying the frequency correction value to the desired drive frequency to generate a corrected desired drive frequency; and operating the electric motor at the corrected desired drive frequency.

2. The method as claimed in claim 1, wherein the machine is a centrifugal pump, and the factor k is determined in dependence at least upon one variable of the drive process of the centrifugal pump: motor frequency, pump capacity, delivery volume, delivery pressure, medium temperature and energy input.

3. The method as claimed in claim 2, wherein the centrifugal pump is a heating circulating pump.

4. The method as claimed in claim 3, wherein the factor k is determined in a range from 0 to 50.

5. The method as claimed in one claim 3, wherein the factor k is reduced as a flow rate of the pump increases.

6. The method as claimed in claim 3, wherein the factor k is reduced as a delivery volume of the pump increases.

7. The method as claimed in claim 1, wherein the instantaneous network frequency of the network supply is estimated from a measurement parameter, and the measurement parameter includes a measured voltage signal at the input of the electric drive unit.

8. The method as claimed in claim 1, wherein the corrected desired drive frequency is obtained by adding the frequency correction value to the desired drive frequency.

9. The method as claimed in claim 2, wherein the corrected desired drive frequency is not limited by upper or lower limit values.

10. A machine, comprising: a centrifugal pump, and a controller configured to perform the method as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The FIGURE schematically illustrates control curves associated with a heating circulating pump in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

(2) Specifically—without the invention being limited thereto—one exemplary embodiment for a heating circulating pump is proposed which has an internal electric pump drive that is supplied with the necessary energy by means of the regular network alternating voltage. Usually the alternating voltage of a supply network is applied in the case of pumps of this type which operate at a standard frequency of 50 Hz or 60 Hz.

(3) The circulating pump determines an estimated value of the instantaneous network frequency by means of the internal electronic control system. For this purpose, only a measured voltage signal of the electric input side of the drive unit is used. On the basis of this estimated value, described below as f.sub.estimate, the frequency deviation δ.sub.f is then calculated as follows:
δ.sub.f=f.sub.estimate−f.sub.N

(4) wherein f.sub.N in this case represents the standard frequency of the supply network. The calculated deviation δ.sub.f is then used to generate the necessary correction value f.sub.corr for the desired drive frequency f.sub.des of the internal rotational speed control of the heating circulating pump. The correction frequency f.sub.corr is in this case determined via a factor k from the frequency deviation δ.sub.f. The formula below defines the calculation regulations for this correction frequency value:
f.sub.corr=k*δ.sub.f.

(5) This correction frequency value f.sub.corr is then added to the currently requested desired direct frequency f.sub.des. The electric drive unit of the circulating pump is then operated at this new frequency f.sub.drive or at the corresponding rotational speed.
F.sub.drive=f.sub.des+f.sub.corr.

(6) In this case, the term f.sub.corr is intentionally not limited. Theoretically therefore corr this value can be arbitrarily large. However, in practice this value can remain small as expected since the network frequency always deviates only a little from the network frequency f.sub.N.

(7) Moreover, the invention provides for a dynamic adjustment of the correction factor k and in fact in such a manner that the desired stabilization of the network has as little effect as possible on the pumping process itself. For this purpose, the numerical value of the correction factor k is varied in the range from 0 to 2 (or also even higher) in dependence at least on a process variable of the circulating pump.

(8) In this case, the following are to be mentioned as possible process variables:

(9) Pump motor frequency,

(10) Pump capacity,

(11) Pump delivery volume,

(12) Pump delivery pressure,

(13) Pump medium temperature,

(14) Pump energy input or the heat flow conveyed by the pump (Q*δT).

(15) The influence of these process variables on the factor k is illustrated by way of example with the aid of the delivery volume Q by means of the diagram in the single FIGURE. The FIGURE illustrates the operating range 1 of a heating circulating pump and its system curve 2 in the case of fully opened thermostatic valves. Such a system curve 2 is also described as a minimal system curve.

(16) Also included in the diagram are different control curves for the operation of the heating circulating pump, in other words the rotational speed of the circulating pump is set in dependence upon different control algorithms. In this case, the first control curve 3 represents a constant pressure control mode and the control curve 4 represents a proportional pressure control mode. The control curve 5 represents an “eco-mode” pump control mode during which a further reduction in the rotational speed depending upon requirements is performed in order to save energy.

(17) However, in the case of all three operating modes in accordance with the control curves 3, 4, 5, the distance between each of the control curves 3, 4, 5 and the minimal system curve 2 is the greatest in the case of low flow rates and reduces respectively as the flow rate increases. The probability of an undersupply (if the operating point of the pump drops below the minimal system curve 2) is consequently in the case of a low flow rate less than in the case of a high flow rate. Consequently, it is expedient in the case of a heating circulating process to select a correction factor k>1 in the case of small delivery volumes, whereas in the case of large delivery volumes the factor k is reduced to the value 1.

(18) The method in accordance with the invention and the associated digitalized function in the drive unit, in particular in the pump drive unit, renders it possible to stabilize the network in a purposeful manner, wherein the scope of the network stabilizing function is dynamically adjusted to suit the customer process of the consumer.

(19) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.