GB2520336A

GB2520336A - Voltage regulation

Info

Publication number: GB2520336A
Application number: GB1320345.0A
Authority: GB
Inventors: Darryl Schofield
Original assignee: ADVANCED ELECTRONIC SOLUTIONS Ltd
Current assignee: ADVANCED ELECTRONIC SOLUTIONS Ltd
Priority date: 2013-11-18
Filing date: 2013-11-18
Publication date: 2015-05-20
Also published as: GB201322575D0; GB201320345D0

Abstract

A voltage regulation device has a transformer 2 with a set of independent primary windings P1, P2, P3 and a secondary coil S1 in series with the unregulated input voltage. Relays 10, 12, 14, 16 on the low current primary side are switched by a control processor 20 to energize selected primary coils P1, P2, P3 in order to add or subtract from the input voltage by a predetermined amount, delivering a regulated voltage output. The primary windings P1, P2, P3 can be bypassed if no correction is required. A current monitor 50, 52 may be provided, as may a temperature monitor 54, to determine the control of the relays 10, 12, 14, 16, which may be latch relays. A time delay may be imposed before adjusting the voltage correction, which may be inversely proportional to the size of the correction required. A micro-generator, such as a solar cell, may be detected by the controller 20 by measuring the phase of the current waveform, and an energy consumption unit, such as a water heater, may be activated to consume surplus energy from the micro-generator.

Description

Voltage Regulation

Technical Field

[0001] The present invention relates to a device or apparatus to supply a regulated voltage for domestic use in circumstances where the supply voltage provided by a regional electric company has significant allowed variation. This variation is due to the resistance of cables and the varying consumer loads causing voltage to be dropped in the cables.

[0002] Most electrical appliances are designed to operate optimally at 220 V and although it may tolerate variations in the range 209V to 253V, in some cases up to 264 V, it may draw more energy, which is wasted, and the non-optimal supply voltage may reduce the operating life of the app Ii an ces.

[0003] One cause of voltage fluctuations can be the use of microgeneration systems, most commonly photovoltaic (PV) grid tied inverter systems. The voltage dropped in the supply cables is reversed during microgeneration, thus the dwelling may be presented with an unacceptably high supply voltage. A microgeneration system, such as a PV system is usually connected to the consumer unit just as a load will be connected on the regulated side of any voltage regulator.

[0004] It is therefore desirable to supply a reduced but steady voltage to compensate for the variations in the supplied voltage.

Background Art

[0005] An apparatus for this purpose is described in WO 201 3/079962 A (APEX CABLES LIMITED) 06.06.2013 the disclosure of which is incorporated herein by reference.

[0006] A solution using a single transformer excited by a variable supply voltage, connected in series with the supply, in order to generate a variable voltage which compensates for the variation in the incoming supply is described in WO 2007/017618 A (ENERGETIX VOLTAGE CONTROL LTD) 15.02.2007.

[0007] One or more automatic autotransformers may be used to select the voltage reduction. Typically, these are fixed ratio autotransformers, which are adjusted manually.

[0008] In Apex, the circuit requires a fully-rated bypass relay switch.

[0009] Another technical problem associated with existing voltage regulators is that of cycling between settings. This causes the nuisance of lights dimming and brightening frequently. It also reduces the economic performance of the device.

[0010] When a conventional voltage regulator is presented with an unacceptably high voltage as a result of microgeneration, that voltage is reduced.

However, as the grid voltage rises towards the safe limit, the microgeneration system becomes unable to generate and its energy is lost.

Disclosure of Invention

[0011] The scope of the invention is defined in the appended claims.

[0012] By providing that all switching is carried out on a low current primary side of the transformer, the need for any fully rated switches is avoided.

[0013] In a preferred embodiment, an automatic mechanism is provided for reducing the effective regulation when the transformer becomes hot. The approach of the present inventions uses a step change by transformer tap selection has advantages over systems using digital electronics to generate either pulse width modulation (PWM) or phase angle variation to adjust the supply voltage. The present device is simpler, more reliable and more readily passes the EMC (electromagnetic compatibility) tests due to lower emissions.

[0014] A control circuit preferably introduces a delay before allowing a change in the voltage reduction. This delay is inversely proportional to the presently required voltage change. In its limit, there is no delay in response to a demand for a large change in supply voltage.

Brief Description of Drawings

[0015] In order that the invention may be well understood, two embodiments thereof will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: [0016] Figure 1 shows a circuit diagram of the regulator module in accordance with the invention; [0017] Figure 2 shows an example of how the regulator circuit could be incorporated into a consumer panel unit; and [0018] Figure 3 shows diagrams to explain the formula for delay calculation.

Mode(s) for Carrying Out the Invention [0019] The regulation circuit as shown in Figure 1 has a transformer 2 connected to a supply voltage from a meter 4. This circuit could be supplied in an independent protective housing (not shown) or integrated into a consumer panel unit or distribution panel 6 as indicated in Figure 2. This eliminates the need to run two fully rated neutral cables to the unit. A single lower-rated neutral cable is sufficient.

[0020] The primary winding of the transformer consists of three separate windings P1, P2 and P3 which can be selected in varying combinations depending on the state of relay switches 10, 12, 14, 16. The switches are controlled by a microprocessor controller 20 in order to select different taps from the transformer. The secondary winding Si is connected in series with the supply voltage. The secondary winding Si produces a low voltage at high current. This low induced voltage is added to or subtracted from the supply voltage in order to provide a regulated voltage at high current for the dwelling. By automatically selecting different taps on the primary side, the subtracted voltage may be varied, providing the required automatically regulated supply. All of the relays are provided on the low current primary side of the transformer only. This has the advantage of saving a great deal of high current interconnections and switchgear. The bypass function is achieved by shorting the transformer primary winding by closing relayi6, yielding a virtual short-circuit at the secondary and an effective bypass without the need for a heavy duty bypass switch. This ensures that the regulator circuit is simpler and less expensive. It is more reliable and easy to build since the only physically large connections are the main supply and main load cables to the transformer.

[0021] In one example, the number of turns of the secondary winding is 10 with P1, P2 and P3 respectively having 220, 110 and 110 turns. Selection of one or more of the primary windings, delivers one or more selectable reduction ratios. Using the three windings illustrated in Figure 1 at a nominal VIN of 220 V, 5,10 or 20 V reductions could be achieved in addition to the bypass of OV reduction. It will be appreciated that use of appropriate ratios allows different reductions sets to be offered such as 0, 2,4018 V; 0, 3, 60112 V; and 0, 6, 12 or 18 V.A smaller set could also be offered. Appropriate voltages for use in the UK would be the 0, 12 or 18 V. In Australia, 0, 16 22V would be a useful set. Some Middle Eastern Indian regions could use -15, 0 -i-15V. These options can all be selected by transformer winding configurations, optimised according to the region where the device will be used. Using more than four relays would allow other options for reductions sets depending on the number of switchable correction voltages required. By selecting the transformer turns ratios as a binary selection to provide output adjustments of 0, n, 2n, 3n, a large correction voltage may be applied yet a small regulation achieved with few windings. The relays can be of an inexpensive variety, as they only need to carry the primary side current, which is approximately one tenth of the load current.

[0022] The invention is equally applicable to single phase supplies and three-phase supplies. It will be appreciated that a three-phase embodiment could be simply achieved by the use of three circuits as shown in Figure 1, one per phase.

[0023] Figure 2 shows an embodiment in which a voltage regulator module comprising a circuit 22 as illustrated in Figure lisa component of the consumer unit 6. In this embodiment the transformer secondary winding is interposed between the incoming RCD (residual current device) or isolator 30, and the live bus bar 40 of the consumer unit.

[0024] An advantage of this embodiment is that the neutral cable 42 to the voltage regulator module 22 does not carry the load current, but only the transformer primary current. With a smaller, single, neutral cable 42, there is no need for a separate isolator switch or terminals inside the module.

This saves space and cost and makes installation easier.

Operation [0025] The electric circuit between the electricity meter and the consumer unit is interrupted and the voltage regulator circuit shown in Figure 1 is interposed. The electricity supply from the electricity meter is presented to the input VIN of the voltage regulator and the regulated output VOUT is presented to the consumer unit 6, providing the entire dwelling with a regulated electricity supply.

[0026] The voltage Voul is equal to the supplied voltage VIN plus or minus the voltage developed across the transformer secondary winding Si.

[0027] The processor 20 measures the outgoing voltage and closes only one of the 4 relays in order to select the transformer ratio best able to deliver the required output voltage.

[0028] Load current is measured via a small inductor 50 located on a printed circuit board for the module adjacent to the transformer neutral connection.

This field is proportional to the load current so a simple and inexpensive inductor fulfils the function of a current transformer to measure the load current. An amplifier 52 converts the inductor current into a voltage suitable for measurement by an ADC (analogue to digital converter) input of the processor 20. This provides a representation of the load current. In the event that the load current exceeds the transformer rating for the selected ratio, the transformer will begin to heat up, transformer temperature is monitored using a built-in thermistor 54. A voltage measuring ADC input to the control processor 20 is also provided at 56.

This allows the control processor to detect the zero voltage instant.

[0029] By design, the output voltage Voui may be greater or less than the input voltage. Whether the secondary voltage is added or subtracted is selected by reversing the phase of any of the windings, Si, Ri, P2 and/or P3. In some regions, where the electricity supply voltage is sometimes low, such as in India and the Middle East, it is helpful to offer a voltage boost function. In most, it is more helpful to offer a variety of voltage reduction selections.

[0030] The transformer is also designed to optimise rating for economy. The secondary winding Si is rated to carry bOA, enabling the transformer to safety connect to the supply head fuse and to deliver iOOA continuously when in bypass mode, whilst dissipating minimal heat from copper losses.

OV mode is achieved by closure of the OV switch 16, which reflects a low impedance, with zero volts, to the secondary winding.

[0031] An appropriate rating for the transformer when used in a residential installation is 1000 VA. In this case, the transformer may deliver 100A at 5V, lOOAat 1OV, or5OAat2OV.

Relay Operation Timings [0032] The switching elements 10, 12, 14, 16 used in the design are latching relays. Each relay may be driven OPEN or CLOSED by a signal from the control processor 20. Latching relays consume no energy except when being opened or closed, yet have high current rating and rapid well-defined switching times. When a tap change is required, the control processor 20 drives the relays with precise timing, synchronised to the mains voltage waveform, so that the switching transient is minimised.

[0033] Figure 3 shows a typical timing diagram, where the relay operation occurs near to the zero voltage point on the AC voltage waveform, and the changeover between voltage as a brief 2mS time with both contacts open.

This can be illustrated by considering the operation of the switches indicated in Figure 3 as A and B, where A and B could each represent any of the switches 10, 12, 14, 16 in Figure 1.

[0034] The voltage measuring ADO 56 in the microprocessor detect the zero voltage instant and begins a short delay 60. When this delay is complete, the relay drive pulses from the control processor begin. The relays used in this design open in 6mS and close in 8m5 so are driven after a delay of 2mS in order to achieve the timings in the diagram. The A relay opens 8mS after the zero voltage crossing and the B relay closes lOmS after the zero voltage crossing. In this way contact bounce and switch closure arcing are minimised and with real loads applied the 2mS gap in supply becomes imperceptible. Also, the relays operating at or near the zero voltage point in the AC waveform suffer much less than their rated contact switching duty.

Nuisance delay [0035] In order to prevent the nuisance caused by repeated switching, the control processor is programmed to introduce a variable delay between detecting a change in the output voltage and initiating a change in tap selection. This delay is inversely proportional to the difference between the output voltage and the ideal output voltage. The delay is zero in response to a large change in output voltage but is greater for the smaller changes as the voltage may change again during that delay and therefore an unnecessary switch can be avoided.

[0036] Supposing that the ideal output voltage is VREQ and the time delay before switching is indicated is TDEL and the maximum delay is indicated by TMM This maximum delay will be typically 1000 seconds and can be pre-programmed into the control processor. The gain G is a fixed integer representing the sensitivity of the control system. A typical value will be and this would yield a delay reduction of 200 seconds per volt. The delay can then be expressed by the function: [0037] TDEL = TMAX -(G*modulus(VREQVouT)).

M icropeneration [0038] A microgeneration units such as a photovoltaic device, may be connected to the consumer unit 6. This unit can continue to operate even when the grid voltage is high because the regulator 22 is has reduced the voltage at the microgeneration inverter. The generated energy can therefore be used locally. If the local load is not consuming the locally generated energy, it will be passed to the grid. The controller 20 can analyse the phase of the current on the regulated live line and therefore detect the direction of energy supply. The controller is programmed such that in these circumstances, if the grid voltage would rise beyond the safe limit for microgeneration, the voltage regulator is set to bypass. This causes the microgeneration inverter to shut down.

[0039] The controller may also be programmed so that on detection of energy supply to the grid, it will generate a remote control signal, by wired or wireless means, to switch on a water heater or other heat store device deliberately to consume locally generated energy thereby preventing locally generated surplus energy from being delivered to the grid. This option is particularly desirable in circumstances where the grid voltage is such that the microgeneration inverter would shut down and its operation could be limited to those circumstances. a

Claims

Claims 1. A voltage regulation device comprising a transformer (2) having a set of independent primary windings (P1, P2, P3) and a secondary winding in series with an unregulated input voltage; relays (10, 12, 14, 16) provided on a low current primary side of the transformer only; and a control processor (20) for switching the relays to select the voltage added to or subtracted from the input voltage from a set of predetermined values and zero (bypass) in order to deliver a regulated output voltage.
2. A device as claimed in claim 1, wherein the bypass function is achieved by shorting the transformer primary windings.
3. A device as claimed in any one of the preceding claims, further comprising a current monitor (50, 52) for providing an indication of the of the load current in the transformer to the control processor (20).
4. A device as claimed in any one of the preceding claims, further comprising a temperature monitor (54) associated with the transformer and connected to the control processor (20) in order to allow the transformer to cool if the temperature exceeds a predetermined value.
5. A device as claimed in any one of the preceding claims, wherein the delay time preventing use a voltage changing is calculated to be inversely proportional to the difference between output voltage and an ideal output voltage.
6. A device as claimed in any one of the preceding claims, wherein the transformer turns ratios are arranged as a binary selection to provide output adjustments of 0, n, 2n, 3n, where n is in the range 2 to 5.
7. A device as claimed in any one of the preceding claims, wherein the controller analyses the phase of the current waveform to detect the presence of microgeneration delivering voltage to the grid.
8. A device as claimed in claim 7, further comprising means for switching on an energy consumption unit if surplus locally generated energy would cause the grid voltage to rise excessively, and/or for the purpose of preferentially consuming the energy locally.
9. A voltage regulation device for a three-phase supply comprising a device as claimed in any one of the preceding claims for each phase.
10. A voltage regulation device as claimed in any one of the preceding claims, supplied in a housing to be connected between an electricity meter and a consumer unit.
11. A consumer unit (6) having a housing incorporating a voltage regulation device (22) as claimed in any one of the preceding claims, where the unregulated input voltage is taken downstream of an isolator (30) and the output voltage is connected to a live bus bar (40) of the consumer unit.