GB2555869A

GB2555869A - A control device for controlling the operation of a valve

Info

Publication number: GB2555869A
Application number: GB1619330.2A
Authority: GB
Inventors: Mack Ben
Original assignee: Cistermiser Ltd
Current assignee: Cistermiser Ltd
Priority date: 2016-11-15
Filing date: 2016-11-15
Publication date: 2018-05-16
Anticipated expiration: 2036-11-15
Also published as: GB2555869B

Abstract

A control circuit comprising: a voltage source; a capacitor 207; means of charging the capacitor to a higher voltage than the voltage source; and, means for regulating the current flow from the capacitor to a solenoid valve to control the operation of the valve. The means for charging the capacitor may be a switched-mode boost circuit 201, which may comprise: an inductor 210; a switch 211; and, a diode 212, and may be controlled using feed-forward current control which can generate a variable frequency pulse width modulation (PWM) signal for controlling the switch. The means for regulating may be a switch-mode drive circuit, potentially including an H-bridge (215-218, Fig. 2c). The control circuit may provide three current control regions. The first region may provide a predetermined PWM duty cycle, which may be 100 percent, until a predetermined solenoid current is met. The second control region may have a lower PWM duty cycle to maintain the solenoid current at a constant value. The third control region may have a larger PWM duty cycle than the second region. The capacitor can supply power to allow the solenoid to be placed in a fail-safe or fail-secure state if electrical power to the control circuit fails.

Description

(71) Applicant(s):

Cistermiser Limited (Incorporated in the United Kingdom)

Unit 1, Woodley Park Estate, 59-69 Reading Road, Woodley, READING, Berkshire, RG5 3AN,

United Kingdom (72) Inventor(s):

Ben Mack (74) Agent and/or Address for Service:

Maucher Jenkins

Caxton Street, LONDON, SW1H ORJ,

United Kingdom (51) INT CL:

H01F7/18 (2006.01) (56) Documents Cited:

EP 1953372 A2 DE 102010027989 A1 JP 2011089551 A JP3714155

F16K 31/06 (2006.01)

EP 1065677 A2 JP 2014060266 A US 20040041110 A1 (58) Field of Search:

INT CLF16K, G05D, H01F Other: WPI, EPODOC & TXTA (54) Title of the Invention: A control device for controlling the operation of a valve Abstract Title: Solenoid valve control circuit with a voltage boosted capacitor (57) A control circuit comprising: a voltage source; a capacitor 207; means of charging the capacitor to a higher voltage than the voltage source; and, means for regulating the current flow from the capacitor to a solenoid valve to control the operation of the valve. The means for charging the capacitor may be a switched-mode boost circuit 201, which may comprise: an inductor 210; a switch 211; and, a diode 212, and may be controlled using feed-forward current control which can generate a variable frequency pulse width modulation (PWM) signal for controlling the switch.

The means for regulating may be a switch-mode drive circuit, potentially including an H-bridge (215-218, Fig. 2c). The control circuit may provide three current control regions. The first region may provide a predetermined PWM duty cycle, which may be 100 percent, until a predetermined solenoid current is met. The second control region may have a lower PWM duty cycle to maintain the solenoid current at a constant value. The third control region may have a larger PWM duty cycle than the second region. The capacitor can supply power to allow the solenoid to be placed in a fail-safe or fail-secure state if electrical power to the control circuit fails.

FIG. 2a

At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.

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ΊΓΕ FOR CONTROLLING THE OPERATION OF A VALVE lie present invvnrion rckifc'. to a control device, in particular a control device for controlling the opeuniou of a \iOnmd \al\c, la the inimo of reducing waic* wastage, die use of adtoniaiie Sow control devices arc increasingly being used to control water ’low from a fluid regulating device, for example a tap, sv.-u.ro tbs* flow control devices seguiute water flow based on the proximity of an individual io the fluid monkfoug device

To control water flow, typically a latching solenoid valve is used with, electrical power being used to activate the operation of the vahe, whore a solenoid behaves as a large inductor, with an additional back EMb generated by the motion of the valve actuator.

The force generated to operate ahotohoid valve is proportional to the current flowing, where a latching solenoid valve is .normally operated by apply ing a constant voltage pulse for a fixed period of time, for example 6 V for 50msee§, However, this is relatively inefficient, as the current. Increases slowly at the start, of the pulse due to the solenoid inductance (which is typically when fiiaximum force is required io unstick the vafic and get the valve actuator moving}, and continues rising after the valve actuator has started moving (when less force Is needed to keep the valve actuatpr moving). Most of th® energy is lost in the internal resistance, losses being, proportional to the square of the current (P ^:1²R) and foe length of the pulse.

Typically a latching solenoid uses a permanent magnet to latch the valve open, anil when closing, the solenoid coil must generate just enough magnetic flux to cancel the flux from the magnet, and allow a spring to close the valve. If the current rises too high (due to a high supply voltage), then the magnetic flux from the solenoid exceeds the flux from the permanent magnet and pulls the slug back to the open position, leaving foe valve open instead of closed. This phenomenon known as ceserw pull-in’

Additionally, if electrical power to the control device fails this can result in the flow control valve remaining in whichever state it was in prior to the power failure, This can be a problem If for example the valve controls the water supply to a washroom, and the valve fails closed , ··?

.leaving the washroom wlthonf water, or it controls a tap or toilet flush, anti the valve fails ©pen, leaving water flowing.

To address this problem, typically an automatic flow control device will include afaibsafe 5 system that uses a battery or large capacitor to store sufficient charge, at the solenoid operating voltage (for example, 6VDCk to allow operation of the solenoid after the power supply has failed. However this requires a relatively large and expensive capacitor or battery.

In accordance with an ©spec the accompanying claims.

of the present ir.scnuon there ts provided a controflcr according ίο

The present invention provides the advantage puwnlntg tail-safe circuitry within an.-automatic flow control device that is able to use a small, low: cost capacitor for operating a solenoid vahe within the automatic flow control device ifillowing W efeelrical power failure, where the solepetdi valve: is left in a safe state if the power supply to the solenoid valve fails.

The present invention will now be described, by way of example, with reference to 'the accompanying drawings, in which:

Figure 1 illustrates an embodiment of a solenoid valve with an associated control device according to an embodiment of the present invention;

Figure 2 illustrates a circuit schematic for a control device according to an embodiment of the present invention;

Figured illustrates electrical character is tits fora solenoid salve and control dc\ Tc accn.duig to an embodiment©! the present nneaOon, he picwnt -„mbocumcm dewmbes an automata ikm control cevue but -nJcues a kuhmc 30 solenoid valve lor controlling the flow of a fluid, and a control device that stores electrical energy locally wlthm the device. When the control device detects a power failure it operates the valve using the local energy store to place the valve in a sale state. The control device is user configurable to allow a user to pre-set the safe state, where: the control device can. be configured to clos_v ιΐκ» \ .fisc, open foevahe or flaw the vaho in to· current petition upon the eotmvi deuce detecting a power failure.

Figure } iliustrates an embodiment of a latched solenoid valve 100 coupled to a control device

IS (not shown) cohfigured to control the operation of the valve 100. The solenoid valve 100 includes a valve body 1, an inlet port 2 to allow a fluid to How into the valve 100, an outlet port 3 to allow the fluid to flow out of the vahe 100, coil windings 5. lead wires 6, u spring 8, an. orifice ^ST a plunger 7 (otherwise known as a valve actuator) for controlling the flow of fluid K'-wcen u-c mat port 2 and the outlet port '> s ta the orifice, and a permanent usacne· mot show-si

IQ that is used to maintain the plunger 7 in a set position^ when current is not flowing through the coil windings 5. The coil windings 5 are coupled to the lead wires 6, which in turn are coupled to the control device·.

The control device controls current flow through the coil windings X which results in a magnetic field being generated by the. coil windings 5. The magnetic field is used for controlhng the position ot the plunger 7. where the Hunger wfil tvpic.tHy he nude than a high permeable material, for example electrical steel ,s well known to a person skilled in the art.

In operation, when current flows in one direction through the coil windings 5 of the solenoid, the rnegnedc field generated by the solenoid adds to the pul I of the permanent magnet resulting in fire plunger 7 being attracted to the magnet. Once the plunger 7 has moved and is in contact with the magnet it will remain in tins position without further electrical power. In other words, the plunger 7 is held in position by the -permanent magnet. To release the plunger the-magnetic attraction, between, the plunger 7 and permanent magnet is cancelled by sending a current through the coil windings 5 in the opposite direction.

Although the present embodiment describes latched direct operated solenoid s alve, any suitable solenoid valve may be used, To?- example a pilot operated valve,

Figure 2 illustrates a circuit schematic for the control device 200, The control device 200 includes a switch-mode boost circuit 201, a solenoid driver 202. a microprocessor 203. a passive infrared sensor 204, a 38NET driver 205 that is a combined 2··wire power and data bus for allowing multiple devices to communicate with each other using 6VDC sup ph wires, and an ICU sensor 206, which Is an infra red remote controTthat cap be used tor umfiguring the control device. As the passive- infrared sensor 204, the 38 NET driver 205 and the ICU sensor 206 are not wlesant foi Πκ- undcr.uanding of the present invention no further description et >!a< features will be nude.

The power leads for the control device are connected to a DC power source, which in the. present embodiment Is a 6VDC power source;

The control device 200 uses a small low-cost electrolytic capacitor 207, which in this -embodiment is a 1 .ivuul· 16V elecuvlytic capacitor, for providing an efectrie eorremtO: the solenoid coil wiuduigs 5 if a power failure of the ΓΧ’ power source occurs, thereby allowing the vahe to be placed in a safe state upon power failure to the control device 200.

The energy stored on the capacitor 207 is increased by using the switch-mode boost circuit 201 to charge the capacitor 207 to a higher voltage than the DC power source to which the control dewee is connected to for the purposes of the preset? embodiment the capacitor 2Π⁷ i? chained to approximately 15YDC. As the energy stored on the capacitor 2«)7 is proportional to the square of the voltage (where the formula is given by EVd€V’,s, by boosting the voltage from 6V to 15V this results in an increase in stored energy by a factor of 6.

Although the present embodiment describes the use of a 6VDC power source and a capacitor voltage of 15 V any suitable voltages may be used that result in the stored energy on the capacitor 2d7 being increased relume jo the input voltage to the control device 200. The use of the switch«rode boost cireult 201 allows the use. of a smaller, lower-cost capacitor to be used for storing: the same energy as a bigger, more expensive capacitor charged to a lower voltage,

2.5

A second capacitor 208 provides energy storage for the microprocessor 203 to allow the microprocessor 203 to continue to operate following a IX'' power failure, to allow the microprocessor 203 to control the operation of the switch-mode boost circuit 201 and the solenoid driver 202. as described below.

Additionally diode 209 provides reverse polarity supply protection ibr both the above circuits, and prevents discharge of capacitor 208 hack into the supply during power failure.

The. witch-mode boost circuit 201 ebmists of an i«ductor2i:0, a switch. 211 and a diode 21¾ where the microprocessor 203 is used to control the operation of the switch 211 for performing PWM control Boost voltage feedback is provided by resistors 2: 1 214 and an analog to digital eo'ocski MX vLitom isncfi^pnLes’of 2Ο\simbi'y cristoss 225. 22o and t it MX rnw.de supply voltage monitoring. The microprocessor 203 is arranged to generate a variable frequency PWM the; muv.nuses the peak current in the tndueter 310 throughout the boost cycle without .saturating the inductor 210. using feed-forward current control based on the supply and boost voltages.

The solenoid driver 202 utilises the charge stored oh the Capacitor 207 to control eurresffiow through the solenoid coil windings 5. where the solenoid ikw·! 202 makes optimal use of the stored energy. as described below. This allows for a further reduction in the size and cost of the storage capacitor.

1> Ί o inasrn'ss, eifiueney and nwmnssv wirtne io wes when oneunm- the sotone'.d s -. \ e fellow ing a power failure,, the solenoid driver 202 is used to regulate the solenoid current to provide three dritoreut solenoid \nl\o control nylons over -he solenoid pulse duration, where the microprocessor 20? w arranged to eontrol the solenoid driver current profiles with an appropriate i'WX! duty w.-Je during each e-.-otrei region.

Figure 3 provides an illustration of a solenoid pulse .for operating the plunger 7 according to an embodiment of the present invention. where line A corresponds to solenoid current t25rnAdlivision). line B corresponds to the capacitor 207 supply voltage {1 V/division). line € corresponds to the solenoid voltage (1 Vfolvisfon) and line D corresponds to a PWM duty cycle (10%/division)

With reference to figure 3, in a first control region defined by time period 1 mS to 2 toS, at the start of the pulse (i.e. at time I mS) the solenoid dri ver 202 uses the high initial voltage stored on. the capacitor 207 to rapidly increase solenoid current by providing a 100 percent PWM duty cycle. This results in a sharp increase in current that creates a magnetic field to overcome the magnetic force of the permanent magnet and allows the plunger 7 to move. The rise in current is performed as quickly as possible to reduce energy loss that would occur as the current is increasing to a value that: allows: fee plunger 7 to overcomes the magnetic force: of the permanent magnet. The longer it takes for the current to reach a value that causes the plunger 7 to ovetobme the magnetic force ofthe permanent magnet the greater the loss of energy.

The microprocessor 203 uses current regulation to limit magnetic flux and avoid the ntagpcile 5 flux* .from the solenoid exceeding the flux from the permanent magnet to cause the plunger 7 to be pulled hack into the open position, leaving the valve open instead of closed, thereby avoiding a condition known as reverse pull-in.

Qftee the current has reached a predetermined a «due ri e at time ?tnS). which will allow ihe_:

TO plunger io <tart mot lug. In a second control region defined Hy the time period 2 mS to 9 mS, the PWM dins e.cle is reduced, ip maintain smflc.cr.t current to generate the required magnetic flux n· keep the plunger “ m-wing in tire third control region defined hy the time period 9 rnS to 10 mS. the microprocessor 203 modifies the PWM duty cycle as the voltage from the storage capacitor decays, maintaining the current tail required to keep the plunger moving. This makes best use of the energy stored on the Capacitor 207, providing the required magnetic flux down io a very low voltage, In this instance it operates down to 2K whereas a conventional solenoid drive only operates reliably down to approximately 43 V..

Due to the current pulse profile (sharp starting kick and om raised tail) described above and illustrated in f igure 3. a much shone·· pulse duration n required, in this instance around ISmS, compared to SOmS for a conventional drive. This also significantly reduces the energy storage required..

A more detailed description of the control device 200 and its operation will now be described. As illustrated in Figure 2, the solenoid drive consists via MOSI-'L f H-bridgc formed by switches'

215. 216. 217 and 218. whose supply comes from energy .-'forage capautor 207,

To drive the solenoid valve into an open position, switch 215 is turned on for the duration of the solenoid drive pulse, and switch 218 is pulse width modulated to regulate the solenoid current as described above. During the PWM off period, solenoid flyback current goes through a body diode of switch 21 d to the supply. Conversely, to close the solenoid valve, switch 216 is turned on and switch 217 is pulse width modulated, with flyback through the body diode of switch 215,.

Resistors 219 and 220 are arranged to provide overload protection. If the solenoid wiring is short-circuited, or a solenoid fails internally, then as the current rises the voltage drop across resistors 219 and 220 reduces the gate voltage of swatches 217 and 218 until the switches come cut of saturation. providing a hoe.tr current bmit m around 8 \ J post thus -uvurriitg, power dissipation in switches 217 and 218 can peak around 100W, far exceeding their continuous rating' of 1 \V. The microprocessor detects this condition by monitoring the drain voltage of switches 2 s 7 and 218 during the Ρλλ M on pc: tods, λ m resistor networks 221 and the ADC I'he microprocessor 20,1 can detect an overload and switch off the FWM within 200uS, thus limiting

ID the heat in.-switches 217 and 218 to around fflmJ or any other value:that is within the safe opening broils Idr the respective switches.

To minimise resistive losses the inverter switches In the ii»bridge MOSFETs have low Rds(on) values (for example switches 215 and 216 have a resistance of I'SrrtR, while witches 217 and

218 h,o c a rosi Mance of 2 I roR k u'emtimgh, ev en h,o iug 1 80mR current sensing resistors 219 and 220. the total drive resistance will only around ?5PmR, which typie-iliy will K- ueghgible compared to the soli, not· I wmdmg resistance of abound I SR.

Switching losses are minimised by leaving the high-side P-channel EFT? tin other words

2D sw itches 2 1 5 ami 21% on conrinuouslv during a solenoid drive pulse, and driving the gates of the low-safe fe-chormel FT fv tin other words switches 217 2F8> Fund, direeth from tK microprocessor 225 with no gate resistor. Preferably the microprocessor 203 PWM outputs have rise and fail times around 5nS, and switches 217 and 218 have rise and fall times around 6nS. emmnng that l’\\ M <vm.bmg occurs muddy

I he following de'-utbes prclcncdt features for .he Pw M functionality pcrfevmcu by the microprocessor 203,

I he PWM runs at a fixed frequency of 20 kllz. switching the solenoid between the supply voltage from the capacitor 207 (which starts around 15V and decays during the pulse) during (he on perioe, and a flyback \ ullage of mound -0.8V during the effperiuJ. I he PA M duty melc varies from around 45% to 100% during the pulse, as illustrated in Figure 3.

Feed-forward current control is achieved by monitoring the supply voltage front the capacitor 20? via resistors 213 and 214 and the Λ DC in microprocessor 203, and then calculating the solenoid current throughout the pulse bawd on the ruppiy cubage. the PWM dun cycle, and the solenoid inducttoCevThis allows the tnicroproce^^ir 203 to control PWM to regulate ^uk-nnid $ current without the need to measure the current, fins ailow> the control dev ice to regulate current. In a plurality of solenoids at the same time, where current measurements for each solenoid would not be known.

At the beginning of the pulsefthe: PWM drives the solenoid voltage to the full boost voltage across capacitor 207» until the feed-forward current control predicts that the solenoid current has reached a nominal target, I his minimises the current rise time and so makes best use ol the avail,iNv energy stored on the capacitor 207,

For the second region or phase of the pulse, the PWM maintains a constant solenoid current by .adapting its duty cycle as the supply voltage from the capacitor 207 decays.

For the third and last region or phase of the pulse, alter the solenoid plunger has started mo\ mg. the PWM allows, the solenoid current to decay. thus extending the poise duration by slowing the voltage decay across the - capacitor 2d?, while maintaining enough current to keep the plunger moving.

By boosting the voltage in the storage capacitor 207, the energy storage density is increase, which in the present embodiment is bv s factor of b,

By controlling the solenoid current profile in the manner described above resistive losses in the solenoid are minimised.

By optimising the current pulse profile the pulse duration is minimised» thereby further reducing theenesgv storage requirements.

These features allow a smaller, lower cost capacitor to be used within the fail sale mechanism of the control dev ice.

Claims

1. A control device for controlling the operation of a solenoid valve, the control device comprising means arranged to he coupled to a first voltage source having a first voltage,

5 a capacitor, means for storing energy on the capacitor to charge the capacitor to a higher voltage than the first voltage, and means for regulating the current flow from the capacitor to a solenoid valve for controlling the operation of the valve,

2. A control device according to claim 1, wherein the means for storing energy is a

10 switehed-mode boost circuit.

3. A control device according to claim 2, wherein the switehed-mode boost circuit includes an inductor, a switch and a diode.

15

4. A control device according to claim 2 or 3, wherein the swiiched-utode boost circuit is controlled using feed-forward current control.

5. A control device according to claim 4, wherein the feed-forward current control is used to generate a variable frequency pulse width, modulation signal for controlling operation of

20 the switch.

6. A. control device according to any preceding claims, wherein the solenoid valve includes a valve actuator for controlling fluid flow through the valve, wherein die means for regulating the current flew is arranged to control the operation of a valve actuator,

7. A control device according to any preceding claims, wherein the means for regulating includes a switch-mode drive circuit.

8. A fail safe control circuit according to any one of the preceding claims, wherein for a third region for controlling current that follows the second control region the pulse width modulation duty cycle is increased.

CM

Intellectual

Property

Office

Application No: GB1619330.2 Examiner: Nathan John

8. A control device according to claim 7, wherein the switch mode drive circuit includes an

30 H-hridge.

9. A control device according to claim 6, wherein the means for regulating is arranged to provide three current control region, wherein for the first region the means for regulating is arranged to provide a predetermined pulse width modulation duty cycle until the solenoid current reaches a predetermined value that allows the valve actuator to move.

10. A control device according to claim 9, wherein the predetermined pulse width modulation depth is maintained at a substantially 100 percent duty cycle within a first control region for controlling current.

ILA control device according to claim 9 or 10, wherein tor a second control region for controlling current that follows the first region the pulse width modulation duty cycle is reduced to maintain the solenoid current at a. substantially constant value.

12, A control device according to any one of claims 9 to 11, wherein for a third region for controlling current that follows the second region the pulse width modulation duty cycle is increased,

12 12 17

AMENDMENTS TO CLAIMS HAVE BEEN FILED AS FOLLOWS

1. A fail safe control circuit for use within an automatic flow control device that regulates water flow, wherein the fail safe control circuit is arranged to place a solenoid valve in a predetermined position if a power supply to the solenoid valve fails, the fail safe control circuit comprising means arranged to be coupled to a first voltage source having a first voltage, a capacitor, switched-mode boost circuit for storing energy on the capacitor to charge the capacitor to a higher voltage than the first voltage, and a driver for regulating the current flow from the capacitor to a solenoid valve for controlling the operation of the valve, wherein the driver is arranged to provide three current control regions, wherein for the first control region the driver for regulating is arranged to provide a predetermined pulse width modulation duty cycle until the solenoid current reaches a predetermined value that allows a valve actuator to move, wherein for a second control region for controlling current that follows the first control region the pulse width modulation duty cycle is reduced to maintain the solenoid current at a substantially constant value.

2. A fail safe control circuit according to claim 1, wherein the switched-mode boost circuit includes an inductor, a switch and a diode.

3. A fail safe control circuit according to claim 1 or 2, wherein the switched-mode boost circuit is controlled using feed-forward current control.

4. A fail safe control circuit according to claim 3, wherein the feed-forward current control is used to generate a variable frequency pulse width modulation signal for controlling operation of the switch.

5. A fail safe control circuit according to any preceding claims, wherein the driver for regulating includes a switch-mode drive circuit.

6. A fail safe control circuit according to claim 5, wherein the switch mode drive circuit includes an H-bridge.

7. A fail safe control circuit according to any one of the preceding claims, wherein the predetermined pulse width modulation depth is maintained at a substantially 100 percent duty cycle within a first control region for controlling current.