Method for regulating paralleled alternators in order to distribute reactive load

Abstract

Method for regulating a bank of alternators comprising at least two alternators that deliver their output in parallel to a load (C), said alternators each being provided with a regulator (12, 13) that is configured to deliver an output signal representative of the reactive power level of the corresponding alternator divided by its nominal reactive power, and a control law allowing the reactive power level of the alternator to be modified depending on an input signal, method wherein a weighted signal employed as the input signal of these regulators is generated from the output signals representative of the reactive power level of each of the alternators, i.e. the signals delivered by the corresponding regulators, so as to make each of the alternators converge to a predefined reactive power level (T.sub.rp).

Claims

1. A method for regulating a bank of alternators comprising at least two alternators that deliver their output in parallel to a load, said alternators each being provided with a regulator configured to deliver an output signal representative of a reactive power level of a corresponding alternator divided by its nominal reactive power, and a control law allowing the reactive power level of the alternator to be modified depending on an input signal, the method comprising: generating a weighted signal from the output signals delivered by the corresponding regulators, and receiving the weighted signal as the input signal to the regulators so as to make each of the alternators converge to a predefined reactive power level.

2. The method according to claim 1, the weighted signal being the arithmetic mean of the output signals representative of the reactive power level of each of the alternators.

3. The method according to claim 1, a new voltage setpoint being calculated by each regulator depending on a discrepancy between the current reactive power level and the level corresponding to the input signal, this new voltage setpoint allowing the reactive power level of the alternator to be shifted in order to bring it closer to the predefined reactive power level.

4. The method according to claim 1, the output signals being weighted in an analog manner.

5. The method according to any of claim 1, the output signals being weighted in a digital manner.

6. A bank of alternators comprising at least two alternators that deliver their output in parallel to a load, said alternators each being provided with a regulator configured to deliver an output signal representative of a reactive power level of a corresponding alternator divided by its nominal reactive power, and a control law allowing the reactive power level of the alternator to be modified depending on an input signal, the regulators receiving as the input signal a weighted signal generated from the output signals representative of the reactive power level of each of the alternators so as to make each of the alternators converge to a predefined reactive power level.

7. The bank according to claim 6, each alternator delivering its reactive power level via an analog output configured to deliver a voltage.

8. The bank according to claim 7, the input of each regulator being configured to receive a voltage.

9. The bank according to claim 7, the output signals being weighted by an analog centralization circuit.

10. The bank according to claim 9, the centralization circuit joining at a common point connected to the analog inputs the various analog outputs coming from the regulators using resistors.

11. The bank according to claim 6, the output signals being weighted by a digital centralization circuit.

12. The bank according to claim 11, the centralization circuit being an external system of programmable-logic-controller type.

13. The bank according to claim 11, each regulator delivering the reactive power level of its alternator over a digital communication bus.

14. The bank according to claim 13, the centralization circuit reading the reactive power level of each regulator, determining a weighted signal and sending it to each regulator via said digital communication bus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will be better understood on reading the following description of nonlimiting examples of implementation thereof, and on examining the appended drawing, in which:

(2) FIG. 1, which was described above, shows a so-called “reactive-droop” voltage control-law curve according to the prior art,

(3) FIG. 2, which was described above, schematically illustrates a set of paralleled alternators regulated using the cross-current-compensation method according to the prior art,

(4) FIGS. 3 and 4 are schematics of a bank of alternators according to the invention, with an analog and digital centralization circuit, respectively,

(5) FIG. 5 illustrates an example of distribution of reactive load according to the invention, and

(6) FIG. 6 shows an example control law according to the invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

(7) FIG. 3 schematically shows a bank of N alternators delivering their output in parallel to a load C via a bus 11. Each alternator comprises a regulator 21, 22, 23, 24.

(8) In this example, each alternator delivers, via an analog output 12, 13, 14, 15 configured to deliver a voltage, its reactive power level divided by its nominal reactive power.

(9) An analog centralization circuit 20, which weights the output signals representative of the reactive power level of each of the alternators, is formed by joining at a common point the various analog outputs 11, 12, 13, 14 coming from each regulator 21, 22, 23, 24 by way of resistors R.sub.A, R.sub.1, R.sub.2 . . . Rn.

(10) These resistors R.sub.A, R.sub.1, R.sub.2 . . . Rn are advantageously of identical resistance if the weighted signal corresponds to the arithmetic mean of the output signals representative of the reactive power level of each of the alternators. In one variant, the resistors R.sub.A, R.sub.1, R.sub.2 . . . Rn have different resistances.

(11) The common point of the centralization circuit 20 is then joined to an analog input 16, 17, 18, 19 of each regulator 21, 22, 23, 24, which input is configured to receive a voltage, in order to measure a weighted reactive power level of all the paralleled alternators.

(12) Preferably, the weighted level corresponds to an average level.

(13) As explained above, a control law is then applied by each of the regulators 21, 22, 23, 24 so as to make each of the alternators converge to a predefined reactive power level.

(14) Preferably, the predefined reactive power level corresponds to the average of the reactive powers of all the paralleled alternators.

(15) FIG. 4 schematically shows the case where the N alternators are connected to a digital centralization circuit 30 via a digital communication bus 31 of the type called a fieldbus. In the described example, the digital centralization circuit 30 is an external system of programmable-logic-controller type.

(16) Each regulator 21, 22, 23, 24 delivers over the fieldbus 31 the reactive power level of the corresponding alternator.

(17) The centralization circuit 30 reads the reactive power level of each alternator, calculates a weighted reactive power level and sends it to each regulator 21, 22, 23, 24 via the fieldbus 31.

(18) Preferably, the weighted reactive power level corresponds to the average reactive power level of all the paralleled alternators.

(19) As explained above, a control law is then applied by each of the regulators 21, 22, 23, 24 so as to make each of the alternators converge to a predefined reactive power level. Preferably, the predefined reactive power level corresponds to the average of the reactive powers of all the paralleled alternators.

(20) FIG. 5 illustrates an example of distribution of reactive load according to the invention.

(21) Two alternators 1 and 2 of different nominal reactive powers, equal to 100 kVAr and 200 kVAr, respectively, deliver their output to a reactive load C of 125 kVAr via a bus 11. The reactive powers measured on the two alternators at the time t are 75% and 25% of their nominal powers, respectively. The average value of the reactive power level at this time is 50%. The predefined reactive power level T.sub.rp is, in this example, 41.6%, corresponding to an equilibrium point calculated by dividing the value of the load C by the sum of the nominal reactive powers of the two alternators 1 and 2: T.sub.rp=125/(100+200)×100=41.6%.

(22) The control law of the regulator 1 will make the reactive power of the alternator 1 decrease and the control law of the regulator 2 will make the reactive power of the alternator 2 increase, such that the two alternators converge to 41.6% of their nominal reactive power.

(23) FIG. 6 shows an example voltage control law according to the invention. The x-axis corresponds to the discrepancy between the reactive power level of the voltage in question and the weighted level of the reactive powers of all the paralleled alternators.

(24) As explained above, the control law advantageously calculates, at any given time, the difference between the current reactive power level of an alternator, in particular expressed in percent of its nominal reactive power, and the weighted level of the reactive powers of all the paralleled alternators. Depending on this difference, the voltage set point of the alternator in question is preferably modified along a straight line of parameterizable gradient, as shown in FIG. 6, in order to bring the reactive power level of the alternator closer to the predefined power level.

(25) By way of example, the voltage regulation of the two alternators of FIG. 5 has been shown in FIG. 6. The difference in power level, represented on the x-axis, which, as described above, corresponds to the difference between the reactive power level of each alternator and the predefined reactive power level, is equal to T.sub.r1=75−41.6=33.6% for the first alternator 1 and T.sub.r2=25−41.6=−16.6% for the second alternator 2. The projection of the straight voltage-setpoint line onto the y-axis gives the respective voltage values u.sub.1 and u.sub.2 with which the set-point voltages of the two alternators 1 and 2 delivered as input to the regulators 12 and 13 must be modified in order to achieve a balanced load distribution according to the invention.

(26) The invention is not limited to the example that has just been described. For example, other regulating measures may be combined with the invention.

(27) The alternators of the bank of alternators according to the invention may be identical, or vary in size, nominal power and/or model. The invention in particular relates to any alternator regulator comprising one or more microcontrollers.