In a method for measuring and controlling the output power of a multiphase AC generator (21) and its prime mover, said generator being connected in parallel with another multiphase AC generator (21') through a power bus (24) having at least three phase lines .phi..sub.a,.phi..sub.b,.phi..sub.c for feeding power to loads (23a-23c) through connect/disconnect means (80d-82d), each one of said generators having distinct criteria for the nominal output power, the magnitude and sign of the power factor (PF), the RMS voltage V.sub.rms, the RMS current I.sub.rms, and their fundamental frequency f, and said criteria having specified, allowable deviation ranges within set trigger points, the improvement comprising:
- sensing (25,25') the sinusoidal voltage signals, having said fundamental frequency f, between said phases .phi..sub.a,.phi..sub.b and .phi..sub.b,.phi..sub.c, and producing raw sinusoidal voltage signals V.sub.ab,V.sub.bc (30,32), respectively;
- sensing (26,26') the sinusoidal current signals in said phases .phi..sub.a,.phi..sub.c and producing raw sinusoidal current signals I.sub.a,I.sub.c (33, 35), respectively;
- shaping (27,28,29,50,51,54,55) by shifting, band limiting, and attenuating said raw voltage signals V.sub.ab,V.sub.bc and said raw current signals I.sub.a,I.sub.c, and producing therefrom corresponding attenuated sinusoidal voltage and current signals V.sub.ab,V.sub.bc,I.sub.a,I.sub.c (38,39,40,41);
- using phase-locked loops (PLL) (51) for generating corresponding, respective, synchronized, voltage and current square-wave signals V.sub.ab,V.sub.bc,I.sub.a,I.sub.c (42,43,44,45), containing information on said fundamental frequency f, and a square wave signal V.sub.ab (46) having a fixed, high-multiple frequency of said fundamental frequency f;
- using under the control of software a micro-processor/ micro-controller (M-P/M-C) means (22) including:
- an electronic read-only memory (ROM) (60), a random-access memory (RAM) (61), analog-to-digital (A/D) converter means, high-speed inputs (HSIs) for receiving said square wave signals V.sub.ab,V.sub.bc,I.sub.a,I.sub.c (42-45), an external interrupt (EXINT) input for receiving said high frequency square wave signal V.sub.ab (46), high-speed outputs (HSOs), hi-directional input-output (I/O) ports (P1), a configuration network (62) coupled to said ROM (60) and to said RAM (61) through an address/data bus (63) for configuring said micro-processor/micro-controller means (22) to control the output power of its associated generator in accordance with said generator's particular criteria values and set points, said network including binary-coded rotary configuration switches, each switch being mechanically adjustable for a particular criterion value and its set points, and each switch acting as a mechanical ROM occupying memory address space in said electronic ROM and being readable as an electronic ROM;
- using said (A/D) converter means to digitize said attenuated sinusoidal voltage and current signals V.sub.ab,V.sub.bc,I.sub.a,I.sub.c (38,39,40,41) into corresponding digital representations thereof;
- using said M-P means (22) to digitize said square wave signals V.sub.ab,V.sub.bc,I.sub.a,I.sub.c (42-46) into respective digital representations thereof containing information on said power factor's direction and on said fundamental frequency f of said raw voltage signal V.sub.ab (30);
- using said M-P means (22) to
- digitally measure for each sample, N times per cycle, starting when said high-frequency square wave signal (46) transits from low to high, the instantaneous values v.sub.ab,V.sub.bc of said attenuated sinusoidal voltage signals V.sub.ab,V.sub.bc (38,39), and the instantaneous values i.sub.a,i.sub.c of said attenuated sinusoidal current signals I.sub.a,I.sub.c (40,41),
- digitally calculate for each sample the instantaneous power p.sub.as in said phase .phi..sub.a from pas=(v.sub.ab ia) and the instantaneous power p.sub.cs in said phase .phi..sub.c from P.sub.cs =(V.sub.bc ic),
- digitally calculate the mean power per cycle p.sub.am /cyc in said phase .phi..sub.a from p.sub.am /cyc=.SIGMA.p.sub.as /N, the mean power per cycle p.sub.cm /cyc in said phase .phi..sub.c from p.sub.cm /cyc=.SIGMA.p.sub.cs /N, and the resultant mean power per cycle of P.sub.m /cyc from P.sub.m /cyc=p.sub.am +p.sub.cm,
- digitally calculate
- 1) from said instantaneous voltages v.sub.ab,v.sub.bc and said instantaneous currents i.sub.a,i.sub.c, the root-mean-square RMS value of the voltage per cycle between
- (a) said phases .phi..sub.a,.phi..sub.b from v.sub.abmrms /cyc=.sqroot..SIGMA.v.sub.ab.sup.2 /N,
- (b) said phases .phi..sub.b,.phi..sub.c from v.sub.bcmrms /cyc=.sqroot..SIGMA.v.sub.bc.sup.2 /N,
- 2) the root-mean-square RMS value of the current per cycle in
- (a) said phase .phi..sub.a from i.sub.amrms /cyc=.sqroot..SIGMA.i.sub.a.sup.2 /N,
- (b) said phase .phi..sub.c from i.sub.cmrms /cyc=.sqroot..SIGMA.i.sub.c.sup.2 /N,
- 3) the mean root-mean-square RMS value of the voltage per cycle on said bus from V.sub.mrms /cyc=(v.sub.abrms +v.sub.bcrms)/2,
- 4) the mean root-mean-square RMS value of the current per cycle in said bus from I.sub.mrms /cyc=(i.sub.arms +i.sub.crms)/2, and
- 5) the power factor value per cycle in said bus from PF/cyc=P.sub.m /(1.73 V.sub.mrms .times.I.sub.mrms), said PF/cyc being positive (+) when said square wave signals I.sub.a,I.sub.c (40,41) lead said square wave signals V.sub.ab,V.sub.bc (38,39), respectively, and, conversely, said PF/cyc being negative (-) when said square wave signals I.sub.a,I.sub.c (40,41) lag said square wave signals V.sub.ab,V.sub.bc ;
- using said (M-P/M-C) means (22), under the control of said software and of said settings on said configuration switches, to continuously digitally compare one or more of said measured components of power, including:
- said instantaneous phase powers p.sub.a and p.sub.c, said mean power per cycle P.sub.m, said phase RMS voltages per cycle v.sub.abmrms and v.sub.bcmrms, said mean RMS voltage per cycle V.sub.mrms, said RMS phase currents per cycle I.sub.amrms and I.sub.cmrms, said mean RMS current per cycle I.sub.mrms, and said power factor per cycle PF and its sign (+/-), against their corresponding comparable criteria values stored in said electronic ROM, and when the result of such comparison yields a result, which is either under or over one of said stored set point values in said ROM, to trigger said M-C means to output from said I/O bi-directional ports a digital control signal for tripping, in a timely fashion, one or more of said connect/disconnect means (80d-82d) thereby to cause appropriate successive sheddings of said loads from said bus or, if said load sheddings are insufficient, to completely break the tie between the controlled overloaded generator (21) and said power bus (24), so as to reduce from said overloaded generator a temporary, excessive, high-power load demand, and protecting the remaining generator (21' ) and its prime mover;
- and
- adjustably delaying said load sheddings by discrete time intervals before generating said control signals.