WO2019016748A1

WO2019016748A1 - Charge initiator

Info

Publication number: WO2019016748A1
Application number: PCT/IB2018/055374
Authority: WO
Inventors: Richard Underwood
Original assignee: REDT Limited (Dublin, Ireland)
Priority date: 2017-07-19
Filing date: 2018-07-19
Publication date: 2019-01-24
Also published as: GB201811784D0; GB2572024B; GB2572024A; GB201711593D0

Abstract

A circuit for initiating charging of a redox flow battery with an under-voltage lockout battery charger, the initiator circuit comprising: a conductive path via which charge can be passed from the charger to the battery; a controllable series-pass element in the conductive path; a source of voltage; a unidirectional element connected between the source of voltage and the conductive path on a charger side of the series-pass element for applying voltage above an under-voltage lockout threshold from the source to the charger, and; means for detecting fall in current in the unidirectional element and/or change in voltage across it, on change of state of the charger from under-voltage lockout state to charging state, and for controlling the series-pass element from an initial OFF state for application of the voltage to the charger to an ON state for application of charge to the battery.

Description

CHARGE INITIATOR

The present invention relates to a charge initiator circuit As used herein the term "under-voltage lockout battery charger" means a battery charger adapted to not pass charge to a battery exhibiting less than a threshold voltage. The threshold voltage is set to a level below which the battery is not expected to be able to be recharged from and at which application of the charge is likely to result merely in overheating of the battery, such as with an old, sulphated lead acid battery.

Most industrial battery chargers are under-voltage lockout battery chargers.

Redox flow batteries can be charged safely from a total discharge state, and need to be so at least on initial commissioning and on re-balancing, if required. As such they exhibit no voltage when totally discharged. They can be safely charged from this state, but under-voltage lockout battery chargers will not start charging them. The object of the present invention is to provide an initiator circuit via which an under-voltage lockout battery charger can be utilised to charge a redox flow battery.

According to the invention there is provided a circuit for initiating charging of a redox flow battery with an under-voltage lockout battery charger, the initiator circuit comprising:

• a conductive path via which charge can be passed from the charger to the battery,

• a controllable series-pass element in the conductive path,

· a source of voltage,

• a unidirectional element connected between the source of voltage and the conductive path on a charger side of the series-pass element for applying voltage above an under-voltage lockout threshold from the source to the charger and

• means for detecting fall in current in the unidirectional element and/or change in voltage across it, on change of state of the charger from under-voltage lockout state to charging state, and for controlling the series-pass element from an initial OFF state for application of the voltage to the charger to an ON state for application of charge to the battery.

The series-pass element can be a bipolar transistor. However such a transistor allows current flow one direction only, which is adequate for charging but does not allow discharging through the same conductive path. Preferably the series-pass element is a unipolar transistor such as field effect transistor. This allows both charging and discharging through the same conductive path, whereby the charger can be an inverter-charger, taking charge from the battery and returning it as required. Alternatively, two oppositely arranged bipolar transistors in parallel could be provided. To enable the individual components to carry the charging and discharging current of the battery, multiple series-pass elements in parallel can be provided.

The unidirectional element, preferably a diode, could be incorporated in the voltage source together with detection and control means. Alternatively it could be external to the voltage source, which is preferable in enabling the circuit components, aside from the source of voltage to be housed separately from the latter.

In the first embodiment described below, the detection means comprises an initially OFF sensing transistor arranged to detect change in voltage across the unidirectional element as a rise in voltage in the conductive path, and concomitant fall in current in the unidirectional diode, in the case where the battery charger would normally draw current for its control circuit from the battery to which it is connected. The base of the transistor is connected to the voltage source with the voltage in the conductive path across the emitter and collector, whereby the transistor switches ON with voltage rise in the conductive path.

Preferably the transistor is one of a Sziklai pair of transistors. In the second embodiment described below, the detection means comprises an initially ON sensing transistor arranged to pass current to the conductive path via the unidirectional diode for powering the control circuit of the battery charger and connected to switch OFF a further transistor in the conductive path, until current in the diode ceases on voltage rise in the conductive path, whereupon the further transistor is switched ON.

Preferably the further transistor is a field effect transistor. In the third embodiment, the detection means again includes a transistor and a pulse width modulation controller controlled by the sensing transistor to progressively switch on the series pass element.

To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which:

Figure 1 is a block diagram of a flow battery connected to an inverter-charger with an initiator circuit in accordance with the invention;

Figure 2 is a further diagram showing the components of the initiator circuit of Figure 1;

Figure 3 is a diagram similar to Figure 2 showing a second initiator circuit in accordance with the invention; and

Figure 4 is another similar diagram showing a third initiator circuit in accordance with the invention

Referring to Figures 1 & 2, a Redox flow battery 1, as typically described in our WO2003/069692, is connected to an inverter-charger 3 of the under-voltage lockout type - also known as a Power Converter System (PCS), a main controller 4, and initiator circuit 5 of the invention comprising source a power supply unit (PSU) 6 as a source of voltage and associated circuitry 7.

The associated circuitry 7 includes: • a conductive path 11 from the PCS 3 to the battery 1, via an in line ruse 12. (One conductor only is shown, the return being via earth with the negative terminal of the battery being earthed);

• a power transistor 14 as a series-pass element in the conductive path;

• a relay 15 parallel with the transistor 15, the relay being under the control of the main controller 4;

• a sensing transistor 16 connected to the conductive path between the PCS and the power transistor, as a Sziklai pair, that is with

• the power transistor 14, typically a BUT30V, being an NPN transistor having its collector connected to the conductive path from the PCS and its emitter connected to the battery (via the fuse) and

• the sensing transistor 16, typically an NJW0302G, being a PNP

transistor having its emitter also connected to the conductive path and its collector connected to the base of the power transistor.

This arrangement provides that when the sensing transistor is OFF the power transistor also is OFF. When the sensing transistor is ON the power transistor also is on;

• a diode 17, typically an IN4002, is provided in line between the PSU and the conductive path;

• a high resistance 18, typically 100ΚΩ, is connected between the PSU's connection to the diode 17 and earth;

• a low resistance 19, typically 100Ω, is connected in parallel with the diode 17 from the PSU to the base of the sensing transistor 16;

• an even lower base biasing resistance 20, typically 10Ω to ensure that the power transistor 14 is off when the sensing transistor 16 is not on, and a protection diode 21, typically an IN4002, are connected across the base and the emitter of the power transistor.

When the battery is to be charged from the zero volts at its positive terminal, the relay 15 is controlled to be open circuit and the PCS and PSU are both connected to a mains electricity supply (or the equivalent). Without the initiator circuit of the invention, the PCS would detect zero battery volts and its under-voltage lockout would not connect its rectified voltage to the battery - or at least the conductive path. (The lockout can be thought of as a latching relay which will not normally latch and make the connection in the absence of battery voltage).

The initiator circuit applies the PSU voltage, typically 48 volts for a nominal 48 volts battery, to the conductive path via the diode 17. In reality, the voltage applied to the conductive path will be just below 48 volts due to the PCS's control circuitry drawing a current, causing a voltage at sensing transistor emitter slightly below 48 volts. The resistances 19, 100Ω, is chosen to limit the base current of the sensing transistor 16 to a suitable value, if the PSU 6 is of a type which will sink current as the conductive path 11 voltage rises. If the PSU 6 does not sink current, then the resistance 18 100ΚΩ ensures sufficient base current for transistor 16 to switch on as conductive path 11 voltage rises. Resistance 18 also ensures the PSU voltage falls to zero when it is switched off. Resistance 20 10Ω ensures that the power transistor 14 switches off when the sensing transistor 16 is no longer on.

Consequently, when the sensing transistor is reverse biased and initially OFF and the series-pass power transistor is also off.

The PCS detects a voltage equivalent to a chargeable lead acid battery and its lockout latches. The voltage at the conductive path rises above the PSU voltage, the diode now being reverse biased and not allowing the PSU voltage to rise. The sensing transistor is now forwards biased and switches ON, in turn switching ON the power transistor 14. We have established that this process does not occur instantaneously, but sufficiently progressively for the voltage of the battery to rise and prevent the voltage of the PCS falling below the lockout level. Should this happen the initiation cycle would repeat.

Once the voltage at the battery has stabilised, as detected on line 22 via the main controller, the relay is switched in to provide for charging current to no longer pass through the power transistor. The PSU can then also be switched off by the controller.

Turning now to Figure 3, a second, alternative initiator circuit is described. It comprises in addition to the PCS: a conductive path 111 from the PCS 103 to the battery 101, via an in line fuse 112. (One conductor only is shown, the return being via earth with the negative terminal of the battery being earthed);

a power MOSET transistor 114, typically a SUM110P06-07L, as a series-pass element in the conductive path;

an PNP sensing transistor 116, typically an NJW0302G, connected to the PSU 106 at its emitter and the to the gate of the MOSFET transistor at its collector,

a low,parallel resistance 119, typically 100Ω, across the emitter and gate of the transistor;

a diode 117, typically an IN4002, connecting the PSU via the resistance to the conductive path between the PCS and the MOSFET transistor;

a high, base biasing, typically 100ΚΩ, resistance 120 connecting the gate of the MOSFET to earth and

a 15V Zener diode 121 protecting the gate of the MOSFET power transistor.

As in the first embodiment, with the battery discharged, for charging the PCS and PSU are switched on under control of the main controller 104. The arrangement of emitter to base current path from the PSU 106 to the PCS 103 initially saturates the sensing transistor ON, as the current flows initially through it via its emitter-base junction and thence through the diode. When sensing transistor 116 is ON, the MOSFET is OFF. As the voltage in the conductive path rises, the diode becomes reverse biased and the voltage across resistance 119 drops. The sensing transistor switches OFF. This results in the voltage across resistance 120 dropping as well and the MOSFET switching on.

Turning to Figure 4, a third embodiment is shown. It should be particularly noted that in this embodiment, both terminals of the battery 201 are floating as opposed to the negative terminal being grounded. The initiator circuit includes:

· a conductive path 211 from the PCS 203 to the battery 201. In this

embodiment, the conductive path has a positive limb 2111, including a 47UH inductance 231 and an inline fuse 2121, and a negative limb 2112; • a power, N-channel MOSFET transistor 214, typically an STH31 ON 10F7, as a series-pass element in the negative limb 2112 of the conductive path, together with a second inline fuse 2122;

• a sensing, PNP transistor 216, typically an MPSA56G, connected between the limbs of the conductive path via:

• a low emitter resistance 232, typically 1 Ω, to the positive limb 2111 between the positive terminal of the PCS 203 and the inductance 231 and

• a high collector resistance 233 comprised of a voltage dividing pair 2331, typically 33ΚΩ, 2332, typically 10 Ω, to the negative limb 2112 of the conductive path between the MOSFET 214 and the negative terminal of the PCS;

• a base resistor 234, typically 10ΚΩ, connects the sensing transistor to the positive terminal of PSU 206;

• a diode 217, typically a V801 OOP W, is provided in line between the positive terminal of PSU 206 and the positive limb 21 1 1 of the conductive path;

• a pulse width modulation (PWM) controller 235, typically a TL494, is

provided between the junction of the voltage dividing pair 2331 ,2332 and the gate of the MOSFET 214, via a gate resistor 236. The PWM is powered from that main controller 204;

• a Schottky diode 237, typically a V801 OOP W, is connected between the

conductive path limbs to act a flywheel circuit with the inductance 231;

• a 5.1 V Zener 238 is provided for protecting the PWM controller 235 and also to limit the control voltage input range to that of the PWM controller, with a capacitor 239, typically 100N, in parallel; and

• a further capacitance 240, typically 47,000UF, is provided across the

terminals of the PCS 203.

With the PCS, the PSU and the PWM controller switched to charge the battery from zero charge state, under control of the main controller, the positive terminal of the PCS experiences a voltage less than that of the PSU by the voltage drop of the diode 217. The sensing transistor is off due to reverse bias of the emitter-base junction and the PWM controller input is zero leading to permanent low output to the MOSFET, which is switched OFF. As the PCS output switches on, the sensing transistor switches on as well and the PWM Control Voltage starts to rise. As current flows under control of the PWM controller when the gate is pulsed high, current flows in the battery, reducing the PCS voltage. This is limited by the capacitance 240, which prevents the PCS from locking out again. The circuit is arranged for the ON pulses to increase in proportion to the OFF spaces until the battery is taking full charge and exhibiting enough voltage for the PCS to remain ON.

The invention is not intended to be restricted to the details of the above described embodiments, which are given by way of example of the present invention. For instance whereas a single STH310N10F7 power, N-channel MOSFET transistor 214 is shown, in practice, in the interests of power capacity, several of them can be provided in parallel.

Claims

CLAIMS:

1. A circuit for initiating charging of a redox flow battery with an under-voltage lockout battery charger, the initiator circuit comprising:

• a controllable series-pass element in the conductive path,

• a source of voltage,

2. A charge initiator circuit as claimed in claim 1 , wherein a plurality of the series- pass elements are provided in parallel.

3. A charge initiator circuit as claimed in claim 1 or claim 2, wherein the

unidirectional element, preferably a diode, is incorporated in the voltage source.

4. A charge initiator circuit as claimed in claim 1 or claim 2, wherein the

unidirectional element, preferably a diode, together with the detection and control means is housed separately from the voltage source.

5. A charge initiator circuit as claimed in any preceding claim, wherein the or each series-pass element is a bipolar transistor.

6. A charge initiator circuit as claimed in any preceding claim, wherein the or each series-pass element is a unipolar transistor preferably an N-channel field effect transistor.

7. A charge initiator circuit as claimed in any preceding claim, wherein the detection means comprises a sensing transistor arranged to be initially OFF for detecting change in voltage across the unidirectional element as a rise in voltage in the conductive path, and concomitant fall in current in the unidirectional diode, in the case where the battery charger would normally draw current for its control circuit from the battery to which it is connected.

8. A charge initiator circuit as claimed in claim 7, wherein the base of the sensing transistor is connected to the voltage source with the voltage in the conductive path across the emitter and collector, whereby the transistor switches ON with voltage rise in the conductive path.

9. A charge initiator circuit as claimed in claim 8, wherein the or each series-pass element is a bipolar transistor.

10. A charge initiator circuit as claimed in claim 8, wherein the sensing transistor is one of a Sziklai pair of transistors, the other being the series pass element.

11. A charge initiator circuit as claimed in any one of claims 7 to 10, including a relay in parallel with the series pass element for conducting charge to the battery after initiation of charge.

12. A charge initiator circuit as claimed in any one of claims 7 to 11 , wherein the unidirectional element is a diode and including:

• a high resistance connected between the voltage source's connection to the diode 17 and a return;

• a low resistance connected in parallel with the diode from the PSU to the base of the sensing transistor;

· a base biasing resistance and a protection diode are connected across the base and the emitter of the power transistor.

13. A charge initiator circuit as claimed in any one of claims 1 to 6, wherein the detection means comprises a sensing transistor arranged to be initially ON for passing current to the conductive path via the unidirectional diode for powering the control circuit of the battery charger and connected to switch OFF a further transistor in the conductive path, until current in the diode ceases on voltage rise in the conductive path, whereupon the further transistor is switched ON.

14. A charge initiator circuit as claimed in claim 13, wherein the or each series-pass element is a unipolar transistor, preferably an N-channel field effect transistor.

15. A charge initiator circuit as claimed in claim 14, wherein the sensing transistor is a PNP transistor and there is provided:

• a parallel resistance across the emitter and gate of the transistor and

• a base biasing resistance connecting the gate of the MOSFET to return.

16. A charge initiator circuit as claimed in any one of claims 1 to 6, wherein the detection means includes a sensing transistor and a pulse width modulation controller controlled by the sensing transistor to progressively switch on the series pass element.

17. A charge initiator circuit as claimed in claim 15, wherein the or each series-pass element is a unipolar transistor, preferably an N-channel field effect transistor.

18. A charge initiator as claimed in claim 17, wherein the sensing transistor is a PNP transistor and it has provided:

• a low emitter resistance to a positive limb of the conductive path between a positive terminal of the battery charger and the battery,

· a high collector resistance comprised of a voltage dividing pair to a negative limb of the conductive path between the unipolar transistor and a return path to the battery charger and

• a base resistor to a positive terminal of the source of voltage.

19. A charge initiator as claimed in claim 17 or claim 18, including:

· an inductance connected to the battery in the positive limb of the conductive path and

• a Zener diode 237 is connected between the conductive path limbs, the inductance and the Zener diode being arranged to act as a flywheel circuit for smoothing pulsed modulation of switching of charging.

20. A charge initiator circuit as claimed in any one of claims 16 to 19, including a capacitance provided across the terminals of the battery charger.