Method for determining the supply voltages of a load, and load

Abstract

In order to reliably determine the supply voltages (U.sub.i) of the individual phases (L1, L2, L3) of a load (4) in a multiphase supply network (2), in particular a three-phase supply network, a measuring module (6) is provided and is used to determine the supply voltages (U.sub.i) from measuring voltages (U.sub.i,mess) with the aid of a matrix operation. The matrix operation is used, in particular, to compensate for potential differences or potential shifts between the measuring system and the supply network (2) without the need for hardware measures, for example a voltage transformer.

Claims

1. A load, comprising: sub loads connected to a plurality of phases of a multiphase supply network in one-to-one correspondence; and an integrated measuring module configured to: measure a voltage against a common measurement potential for each of the phases to thereby determine a measured voltage for each phase; determine supply voltages from the measured voltages using a matrix mapping process with the aid of a correcting matrix; correct the presence of a potential difference for each of the supply voltages of a pertaining sub load; and compensate the potential difference.

2. The load of claim 1, constructed in the form of an electric motor with an integrated measuring module.

3. A method for determining supply voltages of a load using a measuring module, comprising: connecting a load to a multiphase supply network having a plurality of phases; measuring a voltage against a common measurement potential for each of the phases to thereby determine a measured voltage for each phase; determining supply voltages from the measured voltages using a matrix mapping process with the aid of a correcting matrix; correcting the presence of a potential difference for each of the supply voltages of a pertaining sub load; and compensating the potential difference.

4. The method of claim 3, for use in a condition or energy monitoring system.

5. The method of claim 3, further comprising using different correcting matrices for different operating situations.

6. The method of claim 5, further comprising storing the different correcting matrices within the measuring module, and selecting a respective one of the correcting matrices as a function of a current operating situation.

7. The method of claim 5, further comprising automatically identifying the different operating situations, and automatically using the correcting matrices respectively assigned to the operating situations to construct a matrix.

8. The method of claim 7, further comprising determining, in the context of a measuring cycle, the operating situation and selecting the one of the correcting matrices assigned to the operating situation for constructing the matrix, and reiterating the measuring cycle repeatedly.

9. The method of claim 8, wherein the measuring cycle is reiterated in an interval of a few seconds, while the load is in operation.

10. The method of claim 3, further comprising selecting as a function of a change-over signal, which transfers the load from a first operating mode into a second operating mode, a respective one of the correcting matrices assigned to a respective one of the operating modes.

11. The method of claim 10, further comprising selectively operating the load in a connection selected from the group consisting of star connection and a delta connection, as a function of the change-over signal, and selecting a respective one of the correcting matrices assigned to the connection.

12. The method of claim 3, further comprising measuring a neutral conductor voltage, when a connection of a neutral conductor is detected, and determining a respective one of the supply voltages from a difference between the measured voltage and the neutral conductor voltage for each phase, using a first correcting matrix in accordance with U.sub.i=U.sub.i,messU.sub.n,mess, wherein U.sub.i is the supply voltage, U.sub.i,mess is the measured voltage, and U.sub.n,mess is the neutral conductor voltage.

13. The method of claim 3, further comprising automatically confirming a connection of a neutral conductor as a function of a value of a voltage applied at a neutral conductor input of the measuring module.

14. The method of claim 3, wherein the supply voltage assigned to a respective one of the measured voltages is constructed from a difference between the respective one of the measured voltages and a mean value of the measured voltages for each phase, using a second correcting matrix in accordance with U.sub.i=U.sub.i,messQ, wherein U.sub.i is the supply voltage, U.sub.i,mess is the respective one of the measured voltages, and Q is the mean value.

15. The method of claim 14, wherein the mean value is constructed from a quotient of a sum of the measured voltages divided by a quantity of the measured voltages in accordance with Q=U.sub.i,mess/A, wherein A is the quantity of the measured voltages.

16. The method of claim 3, wherein at least one of the supply voltages is used for calculating a power of the load.

17. The method of claim 3, wherein the correcting matrix is realized in the form of a 34 matrix, when a three-phase supply network is involved.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) In the following, the invention is described in detail and explained on the basis of the exemplary embodiments represented in the figures.

(2) These show, in greatly simplified representations in each case, the following:

(3) FIG. 1 a three-phase supply network with a connected load and with a measuring module, and also

(4) FIG. 2 a flow diagram to explain the method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(5) FIG. 1 shows a three-phase electricity or supply network to which a load 4 is connected. The supply network 2 is a three-phase supply network with three supply phases L1, L2, L3. Each supply phase L1, L2, L3 has a voltage source V1, V2, V3 assigned to it in each case.

(6) Furthermore, FIG. 1 shows a measuring module 6 which is preferably integrated in to the load 4 as represented schematically in FIG. 1 by means of the broken line. The measuring module 6 has a total of three conductor inputs 8, and also a neutral conductor input 9, by way of which the measuring module can be connected to one of the phases L1, L2, L3 of the supply network 2 in each case and where appropriate to a neutral conductor N. In FIG. 1, the supply network 2 is shown without a neutral conductor N, the said neutral conductor merely being indicated by means of a broken line for illustrative purposes.

(7) The load 4 is preferably an electric motor driven by three-phase current or some other load driven by three-phase current.

(8) The measuring module 6 forms part of a monitoring system for monitoring and checking the load 4, in particular with regard to its condition, such as for example wear etc., in the context of a condition monitoring process and preferably, but also with regard to an energy monitoring process, to obtain information about energy, consumption and power of the load 4. To this effect, a respective supply voltage U1, U2, U3 is ascertained in a respective supply phase L1, L2, L3 with the aid of the measuring module 6. To this effect, for example, a measured voltage U.sub.i,mess is determined, i=1, 2, 3, for each individual supply phase L1, L2, L3 with the measuring circuit represented in the figures, and transmitted to an analysis unit 10 of the measuring module 6, in a first step. A supply voltage U.sub.i is then calculated for each phase L1, L2, L3 from these measured voltages U.sub.i,mess in the said analysis unit by means of the matrix operation described above.

(9) To determine the measured voltages U.sub.i,mess, each phase L1, L2, L3 is allocated a voltage divider constructed of two resistors R, between which a voltage tap takes place for a respective voltmeter 12. All the voltmeters 12 are connected to a common potential realized in the form of a measurement potential P.

(10) In the exemplary embodiment, the measuring module 6 has its own voltage source 14 which defines the measurement potential P and is itself in turn grounded by being connected to ground potential GND. The measured voltages U.sub.i,mess measured by the voltmeters 12 are transmitted to the analysis unit 10 in a manner not represented here in detail. As with the connections of the conductor phases L1, L2, L3, the voltage level on the neutral conductor connection N is also tapped and the value measured by the voltmeter 12 is transmitted to the analysis unit 10 as the neutral conductor voltage U.sub.n,mess.

(11) The tapped voltages of the conductor phases L1, L2, L3, in the range 100 to around 700 Volt, for example, are fed back to the voltage level of the measuring system by way of the voltage dividers. Due to the individual voltage dividers being connected to the common measurement potential P, the said voltage dividers are more or less connected in a virtual star. In the exemplary embodiment, this voltage potential P is shifted by a fixed potential in relation to the ground potential GND due to the voltage source 14. The customarily star-shaped arrangement and the star-shaped connection of the load 4 are replicated with this measuring arrangement.

(12) However, the as-measured voltages U.sub.i,mess only coincide with the actual supply voltages U.sub.i in strictly symmetrical operation, and in particular also only on the condition that there is no potential difference between the measurement potential P and a reference potential of the load 4 (network potential). Such potential differences are frequently present, however, and usually operation is not strictly symmetrical, i.e. the amplitudes of the voltages in the individual supply phases L1, L2, L3 are not identical and/or the phase relationships between the individual conductor phases L1, L2, L3 do not lie precisely 120 apart.

(13) Due to the measuring module 6, errors of this type are, as described previously, compensated for exclusively by the matrix operations described. The values obtained for the supply voltages U.sub.i are then used for the monitoring system. The method for executing the matrix operation is implemented in the analysis unit 10. This is realized in particular in the form of an integrated circuit or includes such a circuit. In particular, the integrated circuit is a microchip or an Application-Specific Integrated Circuit (ASIC). The algorithm is therefore implemented permanently in the semiconductor structure of the integrated circuit. This integrated circuit is also referred to here as a power ASIC in order to indicate that in this instance the circuit is realized for measuring power for a monitoring system. A memory 16, in which different matrices M are deposited, is preferably also implemented in this integrated circuit.

(14) For the purpose of ascertaining and determining the supply voltages U.sub.i, a measuring cycle is carried out regularly, as explained below on the basis of FIGS. 2 and 3. The measuring cycle starts in the first step S1. This start-up is prompted, for example, by switching on the load 4 or at recurring time intervals while the load 4 is in operation. In the subsequent step S2, a voltage measurement takes place initially on the neutral conductor N. In step S3, a check is then performed as to whether the voltage value of the neutral conductor input 9 determined by the corresponding measuring module 12 is greater than a predetermined threshold. If so, a decision is made in step S4 that a neutral conductor N is present. In the next step S5, a selection of an assigned correcting matrix then takes place, for example the first correcting matrix M.sub.1. In the following process, the determination of the value for the supply voltage U.sub.i for each phase is then determined continuously for the monitoring system, or at time intervals predetermined by the monitoring system, with the aid of the selected correcting matrix M.sub.n.

(15) If the threshold value interrogation in step S3 establishes that the amount of the as-measured neutral conductor voltage U.sub.n,mess falls below or does not reach the threshold value, then this is analyzed in step S6 to the effect that a neutral conductor N is not present.

(16) In a further decision step S7, a check is then performed as to whether a potential shift should be compensated for. This decision is preset by means of a device-specific configuration, for example, that is to say it is decided in a device-dependent manner according to the implementation. If a potential shift is not to be taken into account, a conventional calculation takes place in step S8, for example by way of the correcting matrix M.sub.5 in the case of a star connection or M.sub.2 in the case of a delta connection. Alternatively, the decision rule as to whether a potential shift should be compensated for can also be decided by way of an algorithm. To this effect, for example, the as-measured individual measured voltages U.sub.i,mess are analyzed and a check is performed as to whether these are identical in terms of their amounts. If not, this is taken as an indication that there is a potential shift present.

(17) If a potential shift is to be compensated for, then in step S9 the supply voltages U.sub.i are determined from the as-measured voltage values U.sub.i,mess by making use of a correspondingly selected correcting matrix, for example the second correcting matrix M.sub.2.