GB2504971A

GB2504971A - Calculating the reduction in power consumption or energy usage provided by a voltage optimizer

Info

Publication number: GB2504971A
Application number: GB1214556.1A
Authority: GB
Inventors: Jihong Wang
Original assignee: University of Warwick
Current assignee: University of Warwick
Priority date: 2012-08-15
Filing date: 2012-08-15
Publication date: 2014-02-19
Also published as: GB201302819D0; WO2014027198A1; GB2505019A; GB2519719A; GB201503690D0; GB2519719B; GB201214556D0

Abstract

The power consumption reduction or energy saving arising from the use of a transformer type voltage regulation device is calculated from the power induced on the primary winding from the secondary winding and a parameter based on the number of turns in the primary and secondary windings. The voltage regulation or optimization device comprises a transformer with primary and secondary windings. The power induced on the primary winding from the secondary winding is calculated by measuring the voltage on the primary winding and either the primary winding current i3 directly or by measuring the supply current i1 and the secondary current i2. The induced power may be the real power or reactive power. RMS values may be used for the voltage and current. The invention allows the effect of the voltage regulator to be monitored while in use, without needing a separate measurement of power consumed when the voltage regulator is not connected.

Description

Monitoring power consumption and/or energy usage

Description

The present invention relates to a method of and apparatus for determining an amount by which power consumption is reduced and/or an amount of energy saved arising from use of a vokage regulation device.

A vokage regifiation device (which may also be referred to as a "voltage controfler" or "voltage optimiser") can be used to control the voltage of an dectrica supp'y to a toad.

to Voltage regulation devices can be used in industria', commercial and domestic environments to reduce power consumption. V&tage reguthtion devices can also improve performance of dectrical appliances and may even help to pr&ong their life.

A voltage regulation device keeps an output voltage at a pre-set desired value which is stepped-down or stepped-up from the input voltage.

Figures 1 to 3 illustrate v&tage regulation devices 1.

Referring to Figures 1 to 3, a voltage regulation device 1 comprises a step-down transformer 2 having primary and secondary coils (or "windings") 3, 4 wound around a core 5. Each winding 3, 4 has two or more terminals 6, 7. As shown in Figures 1 to 3, a transformer 2 may comprise a single coil which is used to provide both the primary and secondary coils 3, 4 and such an arrangement is commonly known as an "autotransformer" The transformer 1 is connectable to a power supply 8 and a load 9.

Referring in particular to Figure 1, a transformer 1 may have a fixed-turn ratio.

Referring in particular to Figure 2, a transformer 1 may have a tapped structure to provide a variable-turn ratio. For example, one or more connection points (or "taps") 10 may be made to the primary coil 3, each connected to additional input terminals 6.

This arrangement can provide variable voltage regulation.

Referring in particular to Figure 3, a series chain of switches ii, arranged into pairs, is provided between the input terminals 6. A midpoint 12 of the chain of switches ii is 3s attached to one 13 end of the primary coil 3. This arrangement can be used to provide pulse width modulation (PWM) control of a transformer for continuous variable voltage regolation. WO 2007/017618 Ai describes an examp'e of a voltage regulation device which uses PWM control. Other forms of control can be used, such as phase angie switching.

Referring also to Figure 4, an arrangement 14 is shown for determining the amount by which power consumption is reduced due to a voltage regulation device 1.

The arrangement includes a power supply 8 and first and second loads 9, 9. A voltage io regulation device 1 (which may be one of the devices shown in Figures 1 to 3) is placed between the power supply 8 and the second load 92.

First and second power measuring devices 15, 152 are used to measure power supplied to the loads, 92. The power measuring devices l5, 152 provide respective values of power consumption to a comparator i6 which determines the reduction in power arising from using the voltage regulation device 1 and outputs a value for display on a visual display 17.

To obtain an accurate measurement of the power consumption reduction and/or energy saved, the loads 9', 9 should be identical. However, this can be difficult to achieve and so there is a problem that it is difficult to determine how much power consumption is reduced or how much energy is saved by using the voltage regulation device.

The present invention seeks to address this problem.

According to a first aspect of the present invention there is provided a method comprising calculating a power reduction or ener saving resulting from use of a vokage reguthtion device which comprises a transformer comprising primary and secondary windings, wherein calculatingthe power reduction includes determining a power induced in the primary winding from the secondary winding which depends on pnmary winding current and voltage across the primary winding, and adjusting the power based on number of turns in the primary winding and number of turns in the second winding and storing and/or displaying the power reduction.

Thus, a value of power consumption reduction can be obtained simply by using measurements of currents and/or voltages in the primary and secondary coils obtained from the voltage regulation device during use. In particular, measurements of current and/or voltage while the voltage regulation device is not being used are not required.

i The method may comprise receiving measurement(s) of primary winding current and calculating the power induced using the measurements of primary winding current.

The method may comprise receiving measurement(s) of current from the power source and receiving measurement(s) of secondary winding current. Calculating the power induced may include using the measurements of the current from the power source and secondary winding current.

Thus, the secondary winding current may be measured directly or obtained from measurements of current from power source and primary winding.

The method may comprise receiving measurement(s) of voltage across the primary winding. Calculating the power induced may inchide using the measurement(s) of voltage across the primary winding.

The power supply may be single-, three-or multiple-phase supply.

The vokage regdation device may comprise a fixed turn transformer, a tapped transformer or a pdse width modulation power àlectronic switch controlled transformer.

s Calculating the power reduction may comprise calculating: i\ 1 fl-N' /1_NzFt) N, L. N)/ " where: iV1 is the number of turns in the primary winding, N. is the number of turns in the second winding, and p is the induced power through the primary winding.

The induced power, d,maybe constant over a duration of time and so maybe considered not to be time-varying, i.e. ] maybe used instead of d(i).

io The induced power, , ,may be instantaneous power, p11(t) , active power, P, or reactive power, Q. The instantaneous power, Pr1 (t) may be calculated using: p11(t) = v(t)i3(t or p11(t)=i'(t)[11(t)-i2(t)] where The active power, P, may be calculated using: = lKii9)'3(Mf9) COS( The active power, F, may vary with time, i.e. F(s), and active power at a given time, P(t) may be ca1cuated using: The reactive power, Q, maybe cakailated using: = (RMX)'I(RMXj sin4) The reactive power, Q, may vary with time, i.e. Q(e), and reactive power at a given time, Q(t),maybe cakifiated using: Q () = V(pjf)(t)I3(pjfg)(t)S1fl(t) where v(t) is the voltage across the primary winding (and source) i (t) is the current from the power source 12(t) is the secondary winding current i3t) is the primary winding current is kTRW, is the RMS voltage across the primary winding is the RMS current through the primary winding 4) is the phase angk between the primary winding current and the voltage across the primary winding Cakuating the energy saving may comprise integrating power consumption reduction over time.

The method may comprise receiving measurement(s) of primary winding current and cakulating the power induced using the measurements of primary winding current.

The method may comprise receiving measurement(s) of current from the power source and receiving measurement(s) of secondary winding current. Caictilating the power induced may include using the measurements of the current from the power source and secondary winding current.

The method may comprise receiving measurement(s) of voltage across the primary winding. Calcuthting the power induced may include using the measurement(s) of vciltage across the primary winding.

The method may comprise obtaining the voltage and/or current of the primary winding from available measurements of the voltage regulation device using state estimation, state prediction or state observer technique.

Calculating the energy saving may comprise calculating: IN[1 [iY -N2 -N, ]P(t)dt x,rhere: i is the number of turns in the primary winding, N is the number of turns in the second winding, d is the induced power through the primary winding, s is a start time for energy accumulation, and 1, is an end time for energy accumulation.

The method may comprise transmitting the calculated results for power reduction and/or energy saving to a remote location, for example, to a power supply network operator server. Thus, the operator is informed about how much power or energy is reduced from the user side by using the voltage regulation devices. In reverse, the operator can also send information to the voltage regulation device to participate in user side regulation actions. This can be integrated into a smart grid frame for optimising supply and load balance.

According to a third aspect of the present invention there is provided a computer program for performing the method.

According to a fourth aspect of the present invention there is provided a computer program product comprising a computer-readable medium storing the computer program.

According to a fifth aspect of the present invention there is provided a device configured to perform the method.

The device may comprise memory and processor(s). The processor(s) is (are) configured to perform the method. The device may further comprise an interface for receiving current and/or voltage measurements. The interface may include an analog-to-digital converter.

io According to a sixth aspect of the present invention there is provided apparatus comprising a voltage regulating device comprising a transformer comprising primary and secondary windings, meters for measuring or determining supply voltage and primary winding current, and the device.

Certain embodiments of the present invention will now be described, byway of example, with reference to the accompanying drawings, in which: Figure 1 illustrates an autotransformer with a fixed-turn ratio; Figure 2 illustrates a tap changing autotransformer; Figure 3 illustrates a pulse width modulation power electronics switch-controlled autotransformer; Figure 4 illustrates an arrangement for determining power saving arising from the use of a voltage regulation device; Figure 5 illustrates an arrangement comprising an autotransformer and current meters io for measuring currents, i, i,, i flowing from the source and through the secondary and primary windings respectively; Figure 6 illustrates simulated plots of currents, i1, i2, i3 for the autotransformer 1 shown in Figure 5; Figure 7 illustrates an arrangement comprising an autotransformer, a voltage meter for i measuring the voltage across the primary coil and a current meter for measuring current, i, ,flowing through the secondary winding; Figure 8 illustrates simulated plots of primary winding voltage, v, and primary winding current i, for the autotransformer 2 shown in Figure 7; Figure 9 shows simulated time-dependent values of instant power, Pr1,active power, f, ,and reactive power, Q1,obtained from the primary winding of the autotransformer; Figure 10 iflustrates an arrangement comprising the fixed-turn ratio autotransformer, a current meter and a voltage meter; Figure 11 is a block diagram of an arrangement for determining power saving arising from the use of a voltage regulation device; and Figure 12 is a block diagram of a data processing system.

Referring to Figures 1 to 3, the electrical current passing through the primary winding 3 almost has a 180° phase shift compared with the current through the secondary winding 4. Thus, the voltage applied across the primary winding 3 and the current flowing through the primary coil 3 almost have a 1800 phase difference and so the overall power calculated from the voltage and current is negative.

A negative power can be;qewed as the primary winding 3 drawing negative power from the power suppiy 8 and so the power consumed by the toad 9 is reduced accordingly.

Figure 5 shows an arrangement which comprises a fixed turn ratio autotransformer 2 and first, second and third current meter l9i, 192, 19 arranged to measure the current, 1, from the power source 8, the current, 1, in the secondary winding 3 and the current, i,in the primary winding 3. Power consumption reduction and/or energy saving can be calculated from a measured primary winding current, i, and the primary winding voltage, v, only. Alternatively, power consumption reduction and/or energy saving can to be calculated from the measurement of current from the power source supply, 1, and the secondary winding current, 1,.

Figure 6 illustrates simidated p'ots of currents, i, 1,, 1 flowing into and through the autotransformer 2 shown in Figure 5.

As shown in Figure 6, the primary winding current, i, 1,, /,leads (or kgs) the secondary winding current, 1,, and the current, 1, from the source 8 by 1800.

Figure 7 shows another arrangement 20 comprising the fixed turn ratio autotransformer 2, the second current meter 192 and a voltage meter 21 arranged to measure the voltage, v, across the primary winding 3.

Figure 8 illustrates simulated plots of primary winding voltage, v, and secondary winding current 2 for the autotransformer 2 shown in Figure 7.

As shown in Figure 8, the primary wmding voltage, i', and current, i, almost have a phase difference 1800 and so a calculation of instant power, p, is negative over the time period shown in Figure 8. This can be qewed as power being "fed back" to the power supply 8 from the load side. Therefore, the same load 9 consumes less power (and, thus, uses less energy) when the voltage regulation device 1 is connected between the power source 8 and load 9. -10-

Power reduction can be calculated using the transformer primary-side voltage, v, and its current, /,. An active power, F, and a reactive power, Q11, can also be calculated based on the phase angle between the voltage and the current.

The power consumption reduction, iF, can be calculated in the following two ways: Firstly, taking the measurement of the primary voltage, 1', and current, [, as shown in Figure 8, the power consumption reduction, iF, and energy saving, zIE, can be calculated by using the measured voltage, v, and the current, /3* Using root mean to square (rms) values of voltage and current, the instantaneous power, Pri(t) active power, 1(r) ,and the reactive power, Q1(t) ,can be obtained using the foflowing equations: P1 (t) = v(t)4 (t) (1) I (t) = (t)I3(JL,c)(t) cosp(t) (2) Q,. (t) = RtfS) (t)hi(Rvc) (t) sinp(t) () Figure 9 shows simulated time-dependent values of instant power, p1(t),active power, .1(t) ,and reactive power, Q1(t) ,calculated using Equations (i) to (3).

Active power, 1t) ,and reactive power, Q11(t) , inv&ve tacking an average and so, for constant voltage and current, the values take about two periods to reach steady values.

For a power supply which has a sinusoidal waveform, the active power, 1(t) ,and reactive power, Q (t) , are obtained using harmonic analysis can be obtained simp'y by measuring the voltages and currents over time, obtaining the rms values and multip'ying by cosine or sine of the phase angle, 4, between the primary winding current and the main voltage. For a power supply which has a non-sinusoidal waveform, active power, (t), and reactive power, Qri (t) , are obtained by measuring the valtages and currents over time and using harmonic analysis. -11-

Figure 10 shows yet another arrangement 21 comprising the fixed turn ratio autotransformer 2, the second current meter 192 and a voltage meter 21 arranged to measure the voltage, 1', across the primary winding 3.

In a second way of calculating the power reduction, by measuring the main and the load current as shown in Figure 10, the current difference between i and 1, can be obtained, which represents the current, i, on the primary side 3. Using the RMS values of the voltage and current, the active power, 1(t) , and reactive power, Q1(t) ,can be obtained by p1(t) = v(t)[11Q)-12(t)] () 3(JMS) (t) = RMS{i1 (it) -i2 (t)} () = kI)(t)i3(F\i)(t)CoSt(t) (6) Q.1(t) = T'Kvn(t)I3(Kus)(t)Sfl(P(t) (,) v(t) is the primary winding/supply voltage, 13(t) is the primary winding current, i1(t) is the current from the power source supply, 20) is the secondary winding current, p,1(1) is the power induced on the primary winding 3 from the secondary winding 4, RMS is the Root Mean Square value, P is the active power induced on the primary winding 3, is the reactive power induced on the primary winding 3, and is the phase angle between the primary winding current and the main voltage.

Equations (i) to () and () to () work with different types of loads including resistive, capacitive and inductive loads and non-linear and emf electrical machinery type.

-12 -Based on the above analysis, the power induced from the secondary winding 4 of the autotransformer to the primary winding 3 can be calculated. The energy saving, ziE, can be calculated using: (Odt ft (8) (t)dt (9) JQe)th ft (10) With voltage reduction, the load power is proportionally reduced to around to ((N -N,)/ N1)2 times of its original power consumption, i.e. compared to the case without the vokage regulation device 1 connected, where N1 and N2 are the number of turns in the primary and secondary windings 3, 4 respectively.

A portion (A1W1) of the load current is induced back to the primary winding side. The i power consumption reduction, iF, when using a voltage regulation device can be estimated by: :[ -[ N1-W2 (ii) 1_Il /1(t) N) / N) (12) -1v2 /J -V2 t (t) N1) / r (13) where N, and N2 are the number of turns in the primary and secondary w]ndings 3,4 respectively.

The energy saving, lIE, can be calctilated by: -13 -f2[ [v_N j]/[1_w2 JPiWdt (14) nV1 -N, /H -N2 J1N2 A) R N1 (5) 1 A - / A -N1 (141 i1 N2 N, ) / N1 (16) where t, is a start time for the energy saving calculation and t2 is the end time for the energy saving calculation. Typically, (12-It) is at least of the order of hours, e.g. days or weeks. Multiple calculations can be made for different durations and calculations may overlap. For example, calculations may be made for the preceding week and the preceding month or year.

In equations (i) to (i6), instant power, Pri,active power, P,and reactive power, Q1, are shown as time-varying signals, i.e. p11 (t), (t) and Qjt). However, instant power, p11, active power, I, and reactive power, Q1, may be constant (or considered to be constant) over a duration of time, e.g. over one or several cycles or thnger. For example, power may be considered to be constant and, thus, have a fixed value for the whole duration between t. and t1. Alternatively, the duration between t. and t1 can be divided in intervals (which may be equal or unequal in ength) and power may have respective fixed vahies for each interval.

Equations (ii) to (16) provide accurate solutions if idea] transformers are used or all the transformer tosses can be ignored. Considering transformer losses, the calculated power consumption reduction, AP, and energy saving, AE, may be sllghtly tess than the true values. That is, a true energy saving may be slightly higher than the estimated value in some cases. From simifiation analysis, the calculation error is no more than 5% of the true value.

Referring to Figure 11, an arrangement 23 is shown for determining and displaying power consumption reduction and/or energy saving.

-14 -The arrangement 23 includes a power supp'y 8 and toad 9. A voltage regulation device 1 is pthced between the power supp'y 8 and the load 9. The voltage regulation device 1 continuously outputs measured values 24, 25, 26, 27 of primary winding current, 1$, supp'y vollage, v1, load current, 12, and toad vokage, v2. In some cases, the voltage regulation device 1 does not continuously output measured values 24, 25, 26, 27 but outputs measured values 24, 25, 26, 27 at intervals. For power reduction and energy saving calculation, the measured load current, 12, and load voltage, v2, are not needed.

These values 24, 25, 26, 27 are fed into a processing and display unit 28.

io The processing and display unit 28 comprises an analog-to-digital converter (ADC) 29 which digitizes the measured values 24, 25, 26, 27 at suitably high sampling rate and supplies digitized values 24, 25, 26, 27 to a calculation module 30.

The calculation module 30 calculates values 31, 32 of power consumption reduction, SP, using Equation 11, 12 or 13 above and and/or energy saving, SE, using Equation 14, or i6 and outputs the value(s) 31, 32, for example, in numerical form and/or graphically on a display 33. The calculation module 30 may also output values of current and voltage measurements and instant, active and reactive power.

Values can be updated in real time by selecting a preferred time interval, i.e. t1 and t2.

Referring to Figure 12, the processing and display unit 28 may be implemented using a data processing system 34.

The data processing system 34 includes at least one processing core 35, memory 36 and input/output interface 37 interconnected by a bus system 38. The data processing system 34 includes non-volatile storage 39 which stores software 40 for implementing the calculation module 30 and data 41 such as values of power reduction and energy saving. The data processing system 34 also includes a data interface 42 which may include the ADC 29. The processing core 35, memory 36, input/output interface 37, bus system 38, non-volatile storage 39 and data interface 40 may be imp'emented in a microcontroller 43.

The data processing system 34 also includes user input device 44, such as a keypad, s which can be used to input start and end points for the calculation and the display 33, for example, in the fomi of a Bquid crysta' dispthy or light-emitting diode.

-15 -The computer system 34 may indude a wired network interface 45, such as a USB interface, and a wirdess interface, such as Bhietooth interface 46 to aflow data to be transmifted via a remote device (not shown) such as a person& computer, tab'et computer or mobile phone.

The processing and display unit 28 maybe provided as a separate, stand-alone product which can be connected to the voltage regulation device 1. However, processing and display unit 28 and the voltage regulation device 1 may be integrated into a single unit.

It will be appreciated that many modifications may be made to the embodiments hereinbefore described.

The voltage regulation device may comprise a step-up transformer and power consumption reduction and/or energy saving may be determined for a voltage regulation device involving stepping-up a supply voltage.

The measurements may be provided in the form of data, for example, stored on a data carrier or memory, or carried in a signal.

Parameters, such as induced power, d' RMS voltage, V(pJs) and current, I(RMS), may be constant over a duration of time. Thus, parameters need not be treated as time-varying, but as a constant. Thus, a fixed value for a parameter, for example d (1) , may be used instead of a time-varying value for the parameter, such as d (t).

Claims

-i6 -Claims 1. A method comprising: c&culating an energy saving and/or a power reduction resulting from use of a voltage regulation device which comprises a transformer comprising primary and secondary windings, wherein calculating the energy saving and/or power reduction includes determining a power induced in the priinaiy winding from the secondary winding which depends on primary winding current and voltage across the priinaiy winding, and adjusting the power based on number of turns in the primary winding io and number of turns in the second winding; and storing and/or displaying the energy saving and/or power reduction.
2. A method according to claim 1, comprising: receiving measurement(s) of primary winding current; and calculating the power induced using the measurements of primary winding current.
3. A method according to claim 1, comprising: receiving measurement(s) of current from the power source; receiving measurement(s) of secondary winding current; calculating the power induced using the measurements of the current from the power source and secondary winding current.
4. A method according to claim 2 or 3, further comprising: receiving measurement(s) of vokage across the primary winding; wherein calculating the power induced indudes using the measurement(s) of voltage across the primary winding.
5. A method according to any preceding daim, wherein cakidating the power reduction comprises: 1_1_N2i /1_N2t N2 N)/L\ Y) where: N1 is the number of turns in the primary winding, 2 is the number of turns in the second winding, and Fd(t) is the induced power.
6. A method according to any preceding claim, wherein calculating the energy saving comprises: ? 1_112 /12P2(t)dt iV)/ IV where: N1 is the number of turns in the primary winding, to N1 is the number of turns in the second winding, d(t) is the induced power, t1 is a start time, and 2 is an end time
7. A method according to any preceding claim, wherein the induced power, d (t), is instantaneous power, p1 (t)
8. A method according to any preceding claim wherein the induced power, f, is active power, P.
9. A method according to any preceding claim, wherein the induced power, d, is reactive power, Q.
10. A computer program for performing a method according to any one of claims 1 to9.
ii. A computer program product comprising a computer-readable medium storing a computer program according to claim 10.
12. A device configured to perform a method according to any one of claims 1 to 9.
13. A device according to claim 12, comprising: memory; and -i8 -processor(s); wherein the processor(s) is (are) configured to perform the method.
14. A device according to claim 12 or 13, further comprising: an interface for receiving current and/or voltage measurements.
15. Apparatus comprising: a voltage regulating device comprising a transformer comprising primary and secondary windings; io voltage and/or current meters for measuring or determining supply voltage and primary winding current; and a device according to claim 14.