WO2021217211A1

WO2021217211A1 - Battery charging method and controller

Info

Publication number: WO2021217211A1
Application number: PCT/AU2021/050391
Authority: WO
Inventors: Igor Abramov; Timothy Fosdike
Original assignee: Redarc Technologies Pty Ltd
Priority date: 2020-05-01
Filing date: 2021-04-30
Publication date: 2021-11-04

Abstract

A method for charging a battery comprising the steps of: receiving at a processor a target rate of charging for the battery; delivering charge to the battery from a power supply unit; and repeating until a terminal charging condition is reached: i.) receiving at the processor a measure of battery voltage during charging; ii.) monitoring, by the processor, a rate of change of battery voltage during charging; and iii.) responsive to the monitored rate of change of battery voltage exceeding the target rate of charging, the processor controlling the power supply to reduce the charge delivered to the battery.

Description

Battery charging method and controller Technical Field

[0001] The present disclosure relates to a method and controller for charging a battery. It relates particularly but not exclusively to a method and controller for charging battery having unknown condition, while connected with a load that may be unknown and with unpredictable behaviour, in a manner which reduces risk of battery damage by controlling the rate of charge.

Background of Invention

[0002] Charging batteries is not a straightforward task. Overcharging and charging too quickly can affect battery health which reduces useful battery life and can create dangerous conditions. Overcharging a battery can cause corrosion and gassing with associated risk of explosion. Many battery charging methods and devices have been developed to mitigate this problem by terminating charging before battery capacity is exceeded.

[0003] Charging a battery too quickly can cause damage because of the limited speed of chemical reactions within the cells of the battery. For this reason, most battery types have a specified charge rate e.g. C1 or C10 measured in amp-hours (Ahr), which is based on the natural absorption rate for the surface chemical reaction within the battery cells. From this, a minimum “safe” charging time in hours can be determined. Charging a battery at an excessive rate can lead to undesirable secondary chemical reactions causing generation of hydrogen in lead-acid batteries or creation of metallic lithium dendrites in lithium-ion batteries. Additionally, charging a battery at an excessive rate can cause overcharging of some cells within a battery leading to damage by gassing or overheating, distortion of plates due to heat from ohmic losses and creation of charge gradients in electrolytes, also leading to local overcharging. These conditions cause battery damage including limitation of battery capacity and lead to rapid decline in battery health.

[0004] The gentlest process to charge a battery is achieved with a rate of charging approaching zero. Flowever, this is impractical in most applications since available charge time is limited. [0005] Previous attempts to improve safe charging of batteries have, in some instances, achieved good results. However, these methods typically require special equipment, setup, or knowledge. For example, some techniques require the battery to be standalone (i.e. not connected to a load), require measurement of battery current, and/or require prior knowledge of the battery condition such as its discharge state. Unique and unresolved challenges exist for safe charging of batteries, particularly when connected to a load, especially when the load is unknown, variable and/or of unknown behaviour in that it may have active and/or passive load elements.

[0006] It would be desirable to provide a charging method and/or controller that addresses one or more of these limitations. It would be particularly desirable to provide a charging method that does not require measurement of battery current or prior knowledge of battery condition and does not require removal of the load.

[0007] The discussion of the background to the invention included herein including reference to documents, acts, materials, devices, articles and the like is included to explain the context of the present invention. This is not to be taken as an admission or a suggestion that any of the material referred to was published, known or part of the common general knowledge in Australia or in any other country as at the priority date of any of the claims.

Summary of Invention

[0008] Viewed from one aspect, the present disclosure provides a method for charging a battery comprising the steps of: (a) receiving at a processor a target rate of charging for the battery; (b) delivering charge to the battery from a power supply unit; and (c) repeating, until a terminal charging condition is reached: receiving at the processor a measure of battery voltage during charging, monitoring, by the processor, a rate of change of battery voltage during charging, and responsive to the monitored rate of change of battery voltage exceeding the target rate of charging, the processor controlling the power supply to reduce the charge delivered to the battery.

[0009] In some embodiments, also received at the processor is a terminal charging condition which is stored in a memory component associated with the processor. The memory component may store more than one terminal charging condition, selected from a group including but not limited to minimum bulk charging duration, maximum bulk charging voltage, and a timeout duration of charging. Thus, when the terminal charging condition is met, the processor controls the power supply to stop delivering charge to the battery.

[0010] Typically, the battery has a connected load during charging. The connected load may have one or more characteristics including the load is unknown, is variable, has non-linear behaviour, has one or more of active and reactive components. In some embodiments, the load is permanently connected to the battery.

[0011] In some embodiments, the method includes the step of the processor receiving from a communicatively coupled interface device one or more battery configuration parameters selected from a group including but not limited to battery chemistry; specified battery charge rate; and nominal battery voltage.

[0012] In some embodiments, the method further includes, as part of step (c) and responsive to the monitored rate of change of battery voltage being less than the target rate of charging, the processor controlling the power supply to increase the charge delivered to the battery.

[0013] In some embodiments, the processor controls the power supply to reduce or increase the charge delivered to the battery by a predetermined voltage step. The voltage step may be in a range of tens of mV e.g. 1mV to 100mV, or it may be determined as a percentage of the starting voltage or the preceding voltage step.

[0014] In some embodiments, the method includes the processor monitoring for disturbances to the load and, responsive to the processor detecting a disturbance to the load, interrupting and re-starting step (c).

[0015] In some embodiments, the processor uses feedback control having a set point and a process variable. Thus, the processor may complete a closed loop feedback control system using a method such as Proportional/Integral (PI) control, or fuzzy control, wherein the set point is the target rate of charging for the battery and the process variable is the monitored rate of change of voltage across the battery during charging.

[0016] The measure of voltage may, in some embodiments, be determined by an analogue to digital converter. [0017] Typically, the method delivers charge to the battery only during a bulk charging phase of a three-phase charge profile.

[0018] Ideally, the method is performed in the absence of determining discharge state of the battery. The method may also be performed in the absence of knowledge of battery temperature and battery age.

[0019] Viewed from another aspect, the present disclosure provides a controller for charging a battery, the controller comprising: (a) a memory component storing a target rate of charging for the battery; and (b) a processor; the processor being in communicative coupling with the memory component, a voltage detector for determining battery voltage during charging, and a power supply unit delivering charge to the battery; wherein the processor is configured to monitor a rate of change of battery voltage during charging and, responsive to the monitored rate of change of battery voltage exceeding the target rate of charging, control the power supply unit to reduce charge delivered to the battery.

[0020] In some embodiments, the memory stores a terminal charging condition, and the processor is configured, responsive to the terminal charging condition being met, to control the power supply unit to stop charge being delivered to the battery.

[0021] Typically, the processor is configured to monitor a rate of change of battery voltage during charging of the battery while connected to a load, and the load optionally has one or more of the following characteristics: is unknown; is variable; has non-linear behaviour; has one or more of active and reactive components; and is permanently connected to the battery.

[0022] In some embodiments, the controller further includes an interface device in communicative coupling with the processor, the interface device receiving from an operator one or more battery configuration parameters to be stored in the memory, the parameters including one or more of: battery chemistry; a specified battery charge rate (as may be specified by a manufacturer) and nominal battery voltage. The interface device may also receive from an operator or other communicatively coupled system or device, one or more terminal charging conditions to be stored in the memory. [0023] In some embodiments, the processor is configured to, responsive to the monitored rate of change of battery voltage being less than the target rate of charging, control the power supply unit to increase the charge delivered to the battery.

[0024] In some embodiments, the processor is configured to monitor for disturbances to the load and, responsive to the processor detecting a disturbance to the load, recalculate the rate of change of battery voltage to determine control of the power supply unit.

[0025] In some embodiments, the processor uses feedback control having a set point and a process variable. Thus, the processor may complete a closed loop feedback control system using a method such as Proportional/Integral (PI) control, or fuzzy control, wherein the set point is the target rate of charging for the battery, and the process variable is the monitored rate of change of voltage across the battery during charging.

[0026] The processor may be an analogue or digital processor. Typically, the processor is configured to control the power supply unit to charge the battery according to aspects of the present disclosure only during a bulk charging phase of a three-phase charge profile.

[0027] Ideally, the processor controls the power supply unit in the absence of an input corresponding to a discharge state of the battery. Control may also be in the absence of knowledge of battery temperature and battery age.

[0028] It is to be noted that any one of the aspects mentioned above may include any of the features of any of the other aspects mentioned above and may include any of the features of any of the embodiments described below, as appropriate. For instance, features and steps of the method according to a first aspect may be incorporated into features of the controller according to a second aspect, and vice versa.

Brief Description of Drawings

[0029] Embodiments will now be described in greater detail with reference to the accompanying drawings. It is to be understood that the embodiments shown are examples only and are not to be taken as limiting the scope of the invention as defined in the claims appended hereto.

[0030] Fig 1 is an electric circuit diagram representing components charging a battery with a connected load.

[0031] Fig 2 (Prior Art) represents an ideal charge curve, and a more realistic charge curve corresponding to a prior art charging method.

[0032] Fig 3A is a schematic illustration of a method of charging according to one embodiment. Fig 3B is a schematic illustration of a method of charging according to another embodiment.

[0033] Fig 4 illustrates a charge profile delivered according to embodiments of the disclosure.

[0034] Fig 5 is a schematic illustration of a controller according to an embodiment of the disclosure.

[0035] Fig. 6 is a schematic illustration of components of a processor according to embodiments of the disclosure.

[0036] Table 1 is a guide from battery manufacturer Exide as obtained from the world wide web at http://www2. exide. com/Media/files/Location%20Data/Battery%20Charging%20%26% 20Storage%20Specs%20%2011_13_15.pdf.

Detailed Description

[0037] The present disclosure relates to a method and controller for charging a battery. Typically, the battery is in a condition of static installation. That is, the battery (or a plurality of interconnected batteries) is permanently connected to a load. Typically, the battery is connected to a load and the load is unknown.

Advantageously, the method and controller can also be used to charge a battery in circumstances when the load is variable and may exhibit linear and non-linear behaviour due to the presence of active and reactive components in the load. In some embodiments, the load may be zero. Relevantly, the current disclosure is directed specifically to what is known in the art as the bulk charging phase of the lUoU charge profile defined in the standard known as DIN 41773-1. For completeness, other terms of art also used to refer to the bulk charging phase include the Ί-phase’, constant current phase, or Stage 1 of the lUoU charge profile.

[0038] In order to charge a battery safely it is advisable to adhere closely to the battery manufacturer’s recommended process and specifications for charging. Most manufacturers provide a comprehensive guide including specifications for the charge rate (C), battery chemistry, maximum voltage, maximum charge current, minimum charge time, temperature conditions and the like. As an example, a comprehensive guide from Exide is provided in a table at

20Stor¾qe¾20Specs%20%2011 13 15. pdf. Table 1 contains details from the Exide guide for a Standard Flooded/Wet Automotive SLI (Calcium) battery. Similar guides are provided for Exide (and other manufacturers) for a range of lead-acid and other battery types and could be used as a guide for safe charging of those batteries and for similar batteries where manufacturer specifications are incomplete or unavailable. Based on the specifications in Table 1 , the quickest bulk charging time is 2 hrs, with a maximum voltage for the bulk charging phase of 14.8V.

[0039] The present disclosure is based on use by the inventor of a capacitor- based model 100 of the battery 103 to describe the relationship between capacitance (representing a battery), change of battery voltage and battery current. An example is shown in the electric circuit diagram of Fig 1 , in which a power supply unit 101 drives a voltage source 102 which charges a battery 103 connected to a load 104. Current from power supply unit 101 (Ipsu) is split to supply battery 103 with battery current Ibat, and to supply load 104 with load current lload. The potential across battery 103 and load 104 can be measured as battery voltage Vbat. The model shown in Fig. 1 can be used to describe the relationship between the capacitance C (representing battery 103), change of voltage AV and battery current Ibat as:

Ibat = Cbat * (AV / At) (Equation 1 )

[0040] Unlike previous inventions which require battery condition (Cbat) and Ibat to be known in order to calculate safe and fast charging voltage, the inventor of the current method and controller has determined that it is sufficient to know only Ibat/Cbat. Further, the inventor has determined, advantageously, that this can be measured indirectly by monitoring AV/At during the bulk charging phase, since Equation 1 can be rearranged as:

Ibat / Cbat = AV / At (Equation 2)

[0041] The present disclosure is predicated on the proposition that in order to avoid delivering excess current (Ibat) to the battery (Cbat) during bulk charging, the rate of voltage rise should ideally be limited by the quantity AV / At. Prolonged deviation from this target to a faster rate of charging will cause significant damage to the battery. Deviation to a slower rate will reduce the speed of battery charging.

[0042] Relevantly, during charging of a battery with a connected load, the rate of charging changes as the load changes, e.g. drawing current away from the battery with increasing load. Thus, the embodiments disclosed provide a feedback-controlled system for charging a battery, typically having a connected load, which provides regular monitoring of the rate of charging. If the monitored dynamic charging rate exceeds the target AV / At, charging energy delivered to the battery is reduced to at or below the target AV / At. The rate of charging target AV / At can be calculated using parameters supplied by the battery manufacturer, or it may be assumed for a given class of batteries. The present disclosure recognises the importance of the rate of charging not only for determining the start and/or end point of the bulk charging phase, but throughout the duration of the bulk charging cycle for batteries connected to a load.

[0043] In examples using the battery manufacturer’s specifications, AV / At can be calculated using Equation 3:

AV = Vend - Vstart (Equation 3) where Vstart is battery voltage at the start of bulk charging phase and Vend is the maximum Vbat for the bulk charging phase.

[0044] Taking an example battery from Table 1 at 90% SOC:

Vstart = 12.77V Vend = 14.8V At = 2hours (based on 10x I20)

AV / At = (14.8 - 12.77) / (2 * 3600) = 0.28 mV/sec (Equation 4)

Thus, the target safe charge rate, AV / At, for the example battery is 0.28 mV/sec.

[0045] It is widely accepted that accurate battery voltage measurements require the battery to be rested in the open circuit. This enables the battery chemistry and temperature to settle as both impact the accuracy of measurements of battery voltage. In many cases, it is recommended for the battery to be rested for a minimum of 4 hours. However, this is impractical for a battery in active use. Advantageously, the present disclosure does not require measurement of absolute state of charge of the battery, or absolute voltage. Rather, the disclosed embodiments monitor the change in state of charge over time, obviating the need for resting before determining battery voltage.

[0046] A difficulty arises in many approaches to safe battery charging during the bulk charging phase due to the fact that the battery voltage can be a property of the battery itself and/or a property of potential delivered by power supply unit 101 via voltage source 102. Some existing systems set a power supply voltage to deliver a voltage profile based on the characteristics of the battery to be charged. For example:

Vterminal = Vstart + (AV / At) * (t-tO) (Equation 5)

[0047] Where to is the time at which charging is started, Vstart is the starting voltage of the battery at to, and Vterminal is the output voltage of the charger (approximately equal to the terminal voltage applied to the battery). In cases where a load is applied after charging is started, the power supply output becomes insufficient and the charger is unable to supply Vterminal. This results in undercharge at the beginning of the charge cycle during application of the load, followed by overcharge as the charger attempts to reach the target value of Vterminal. A similar scenario arises in reverse sequence if a load is present on the battery at the start of charging and then removed after the charging voltage profile has been pre-determ ined.

[0048] The graph of Fig 2 represents the ideal charge curve 201 for the target rate of charge AV / At. Also shown in Fig 2 is a typical charge curve 202 exhibited for the prior art charge profile described above. During the initial and middle charging stages, the rate of change of charge at A remains below the target AV / At. However, toward the end of the 2-hour charge duration, curve 202 inclines steeply and from t=tB the rate of change of charge shown by B exceeds the target AV / At, potentially damaging the battery.

[0049] In contrast to the end-point driven techniques of the prior art, the present disclosure involves a feedback-controlled method in which there is stepwise feedback control of the charging energy delivered to the battery throughout the duration of charging. Because the charging profile is feedback controlled, the rate of charging can be maintained at or near the target rate of charging AV / At even with a variable load, protecting the battery from excessive rates of charging.

[0050] Fig 3A is a schematic illustration of a method 300 of charging a battery according to an example of the disclosure. In a first step 301 , data concerning the required safe charging limits of the battery are received at a processor. This data comprises principally the target rate of charging AV / At for the battery. The target rate of charging may be received directly by the processor, or it may be calculated by the processor which instead receives battery parameters such as the C-rate or safe charge rate, and nominal battery voltage for the battery being charged. In some embodiments, a terminal charging condition may also be received at the processor although it is to be understood that termination of charging may be determined in a variety of ways.

[0051] Using the example from Table 1, for the bulk charging phase of a 12V Standard Flooded/Wet Automotive SLI (Calcium) the maximum charge duration is 1 0xl2o at the recommended current (i.e. 2hr) and the terminal charging condition is the indicated maximum voltage of 14.8V. Assuming the battery has 90% State of charge, the starting voltage is 12.77V. From this, the processor can determine the target rate of charging AV / At as 0.28 mV per second, as illustrated in Equations 3 and 4. In other embodiments, the target rate of charging AV / At is calculated by the processor after determining the actual starting voltage as measured from the battery before bulk charging commences.

[0052] In a step 301a, the processor determines if a terminal charging condition has been reached. When this condition has not been met, in a step 302 charge is delivered from a power supply unit under the control of the processor. In a step 303, the processor receives a measure of battery voltage, VBAT after a first time period Ati and monitors the rate of change of the battery voltage during the first time period by determining, in a step 304, if the rate of change of battery voltage (D /BAT/DΪI ) exceeds the target of AV / At. If the target is not exceeded, the control returns to step 301 a. If the target is exceeded, in a step 305 the processor controls the power supply to reduce charge delivered to the battery and control returns to step 301a. This process is repeated until the terminal charging condition, e.g. minimum bulk charging duration (according to manufacturer’s specifications) or maximum bulk charge voltage is reached, and bulk charging is terminated at step 306. In some embodiments, the processor may be programmed with second or overriding terminal charging condition such as a time out, which terminates charging after a pre-programmed time duration of charging has elapsed. A pre-programmed time duration for a time out terminal charging condition may be e.g. 2 hours, 3 hours, or 4 hours.

[0053] Fig 3B illustrates a modification of the embodiment illustrated in Fig 3A, wherein the further step of the processor determining, in a step 307, if the rate of change of battery voltage (AVBAT/Ati) is less than the target of AV / At. If the target rate is not exceeded, in a step 308 the processor controls the power supply to increase charge delivered to the battery and control returns to step 301a.

[0054] In some embodiments, the processor also receives, in step 301 , one or more battery configuration parameters selected from a group including, for example, battery chemistry and nominal battery voltage. These, and other battery parameters such as the C-rate or safe charge rate, and nominal battery voltage for the battery being charged may be received by the processor from an interface device operated by a user, or from another device that is communicatively coupled with the processor for transmission of or access to configuration data, algorithms and other features to be deployed by the processor for safe charging of the battery. In some embodiments, the processor utilises one or more received configuration parameters stored in a memory component associated with or in communication with the processor, to determine a terminal charging condition for use in step 301a. The configuration parameters may be stored in a look-up table or similar and associated with specific battery types to which they relate. Thus, in some embodiments an operator can select, using an interface device in communication with the processor, the battery type to be charged and the processor will access or calculate from parameters stored in the memory component, the appropriate target rate of charging for that battery.

[0055] In some embodiments, the processor also determines, during charging, if there has been a disturbance to the load and, responsive to the processor detecting a disturbance to the load, interrupting the control and returning to step 303 to measure battery voltage VBAT. Disturbances may include, e.g. sudden a drop in battery voltage due to sudden increases in load, or due to failure of the power supply delivering charge to the battery.

[0056] Fig 4 illustrates a charge profile delivered according to embodiments of the disclosure, where curve 203 represents the charge delivered to battery 103. Every voltage step in the charge profile 203 begins with measuring battery voltage Vbat as in step 303. For the first time period DT 1 , voltage Vstepl is measured without waiting for the battery voltage to settle. Unlike previous approaches which require complete disconnection of the power supply and the connected load, embodiments of the present disclosure permit step-like ramping up of the voltage by determining Vbat during charging. Interruptions caused by disturbances are able to be dealt with elegantly by the processor re-calculating the appropriate control.

[0057] If, for the first time period T1 , the measured battery voltage Vbatl indicates the actual rate of charging determined as (D Vbatl +Vstep1 )/ DT 1 remains below the target AV / At, the processor controls the power supply to increase battery voltage by Vstep2 and control returns to step 301a. The process is repeated for time period DT2 and so on, adding power to the power supply unit to increase charge delivered to the battery as shown in Fig 4 as long as the rate of charging remains substantially below the target represented by curve 201. Following this algorithm will keep the rate of charging close to the ideal charge curve 201 , overcharging the battery only temporarily and by very small amounts. If the time periods AT are kept short the steps will be small and any consequential short time spent in overcharge (when the rate of charging exceeds the target) will not cause serious or lasting battery damage.

[0058] The voltage step (increase or decrease) may be determined as a percentage of the starting voltage or the preceding voltage step. Alternatively, the voltage step is a value of tens of mV, e.g. in a range of 1mV to 100mV for example 5mV, 10mV, 15mV, 20mV, 25mV, 30mV, 35mV, 40mV, 45mV or 50mV 55m V, 60mV, 65mV, 70mV, 75m V, 800V, 85mV, 90m V, 95mV or 100mV. Typically, the size of the voltage step or a method for determining the voltage step (e.g. a percentage of preceding voltage step) is programmed into the processor at manufacture, or programmable into the processor using an interface device.

[0059] Referring now to Fig 5, there is shown a schematic illustration of a controller 500 for charging battery 503, according to an embodiment of the disclosure. The controller has a processor 520 and a memory component (hereinafter “memory”) 521 storing a target rate of charging AV / At for the battery. Processor 520 and memory 521 are communicatively coupled as is usual in processor-controlled systems. Processor 520 is also in communicative coupling with voltage detector 502 which determines battery voltage during charging, and power supply unit (PSU) 501 which delivers charge to the battery. Processor 520 is configured to monitor a rate of change of battery voltage during charging and, responsive to the monitored rate of change of battery voltage exceeding the target rate of charging, control the PSU to reduce charge delivered to the battery. Typically, voltage detection is provided by an Analogue-to-Digital converter element of a microcontroller operating as processor 520.

[0060] PSU 501 may be supplied by any suitable sources of electricity, such as but not limited to an alternator (such as a vehicle alternator), solar panel, 240V or 12V power outlet or the like. Additionally, PSU 501 contains the requisite AC-DC convertors, rectifiers, regulators, and other components for delivering suitable DC charge to battery 503 during charging, as would be understood by one of skill in the art. In some embodiments, PSU 501 is operable as a switched mode power supply wherein increasing the length of the conduction pulse or Duty Cycle increases voltage delivered to battery 503. Processor 520 may be operable to control the duration of the conduction pulse according to a desired charging step width. Additionally, processor 520 may be operable to control the magnitude of each pulse, thus increasing the voltage delivered in a step-like shift on charge curve 203.

[0061] In some embodiments, interface device 522 is in communicative coupling with processor 520. Interface device 522 may be in the form of a keypad, touch screen, voice-controlled receiver or other means coupled directly or indirectly (e.g. wirelessly) with the processor. Interface device 522 is utilised by an operator to provide inputs to the controller 500 such as one or more battery configuration parameters to be stored in the memory 521 and used by processor 520 in the control of PSU 501 to deliver charge to battery 503. Parameters that may be received by interface device 522 include, but are not limited to, one or more of a terminal charging condition which causes termination of the bulk charging phase, battery chemistry, and nominal battery voltage. Interface device 522 also allows for selection, by an operator, of a battery type to be charged. A selection made in this way causes processor 520 to access or calculate from a look-up table or other data stored in memory 521 , the appropriate target rate of charging for that battery. The battery type may be entered by the operator selecting, using interface device 522, one or more of battery chemistry, nominal battery voltage, battery make and battery model.

[0062] In some embodiments, processor 520 is configured, responsive to the terminal charging condition being met, to control PSU 501 to stop charge being delivered to battery 503. Similarly, processor 520 may be configured, responsive to the monitored rate of change of battery voltage being less than the target rate of charging, to control PSU 501 to increase the charge delivered to the battery 503. In some embodiments, processor 520 also monitors for disturbances to the load and, responsive to detecting such a disturbance, interrupts control to recalculate the rate of change of battery voltage and thus determine any required change to the control of PSU 501.

[0063] In one example, processor 520 is a digital PI (Proportional-Integral) controller 600 as shown in the schematic illustration of Fig 6, wherein the set point is the target rate of charging for battery 503, and the process variable is the monitored rate of change of voltage across the battery (d/dt) (see reference numeral 620) during charging. At block 621 , the controller determines if there is a difference between the set point and the monitored rate of change of voltage across the battery 620 and modifies the control of PSU 601 using amplifier 622. The control signal from amplifier 622 is further augmented at block 623 by passing the signal through integrator 624, limiter 625 and amplifier 626 to ensure smoother control of the control signal delivered to PSU 601. The purpose of the limiter 625 is to prevent integral ‘wind-up’ which could cause the controller to exceed the charge rate of the battery. This has an effect similar to dealing with disturbances to the load. The processor may be converted to a Proportional-Integral-Differential (PID) controller by adding a differential branch to improve response time if, for example, heavy switching loads are expected in the system. Alternative automatic control methods, such as state-space or fuzzy methods, may be used for the same purpose, as would be understood by one of skill in the art.

[0064] Processor 520 may be implemented by analogue electronic components, or by a digital microprocessor as is more typical in modern control systems. A hybrid processor is also contemplated, as would be understood by one of skill in the art. Similarly, memory 521 may be implemented in analogue or digital components, typically following the design of processor 520

[0065] It is to be understood that processor 520 is configured to control PSU 501 to charge the battery according to methods described herein only during a bulk charging phase of a three-phase charge profile. It is to be further understood that processor 520 may be further programmed (with instructions stored in memory or otherwise) to control other phases of the three-phase charge profile however these are outside the scope of the present disclosure.

[0066] Embodiments of the present disclosure provide several advantages over prior art battery charging systems. For example, the methods and controller disclosed herein enable charging of a battery of unknown rating and condition, which may be connected to an unknown and unpredictable load. Further, said charging can be conducted with high degree of speed while minimising likelihood of endangering the battery by charging too quickly. This is important for reliable service and long battery life. Additionally, the embodiments disclosed herein handle variable loads more gracefully.

[0067] Advantageously, the processor controls the power supply unit in the absence of an input or knowledge corresponding to a discharge state of the battery. Thus, unlike prior art charging systems it is not necessary to know the discharge state of the battery to control safe charging. Additionally, prior knowledge of battery temperature or battery age are not required.

[0068] Where the terms “comprise”, “comprises”, “comprised” or “comprising” are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components or group thereof.

[0069] It is to be understood that various modifications, additions and/or alterations may be made to the parts previously described without departing from the ambit of the present invention as defined in the claims appended hereto.

Notes:

1 ) State of Charge (SOC) is a highly variable number. Data should be taken as reflective of technology listed, but actual performance may be plus/minus 0.10 volts. 2) The reference to C20 in the table above means 20 hour capacity as measured in amp-hours (Ahr). Similarly, I20 refers to the current discharge rate for 20 hour capacity. For example, a C20 of 100 Ahr would have an I20 of 5 amps (5 amps times 20 hours = 100 Ahr)

Table 1

Claims

1. A method for charging a battery comprising the steps of: a. receiving at a processor a target rate of charging for the battery; b. delivering charge to the battery from a power supply unit; and c. repeating, until a terminal charging condition is reached: i. receiving at the processor a measure of battery voltage during charging; ii. monitoring, by the processor, a rate of change of battery voltage during charging; and iii. responsive to the monitored rate of change of battery voltage exceeding the target rate of charging, the processor controlling the power supply to reduce the charge delivered to the battery.

2. A method according to claim 1, wherein at least one terminal charging condition is stored in a memory component associated with the processor and is selected from a group including minimum bulk charging duration, maximum bulk charging voltage and a timeout duration of charging.

3. A method according to claim 1 or claim 2, wherein the battery has a connected load during charging and has one or more of the following characteristics: a. is unknown; b. is variable; c. has non-linear behaviour; d. has one or more of active and reactive components; and e. is permanently connected to the battery.

4. A method according to any one of the preceding claims, including the step of the processor receiving from an interface device one or more battery configuration parameters selected from a group including: a. battery chemistry; b. specified battery charge rate; and c. nominal battery voltage.

5. A method according to any one of the preceding claims, including, in method step c. and responsive to the monitored rate of change of battery voltage being less than the target rate of charging, the processor controlling the power supply to increase the charge delivered to the battery.

6. A method according to any one of the preceding claims, wherein the method includes the processor monitoring for disturbances to the load and, responsive to the processor detecting a disturbance to the load, interrupting and re-starting method step c.

7. A method according to any one of claims 1 to 5, wherein the processor uses feedback control having a set point and a process variable, and wherein the set point is the target rate of charging for the battery, and the process variable is the monitored rate of change of voltage across the battery during charging.

8. A method according to any one of the preceding claims, wherein the measure of battery voltage is determined by an analogue to digital converter.

9. A method according to any one of the preceding claims, wherein the method delivers charge to the battery only during a bulk charging of a three-phase (lUoU) charge profile.

10. A method according to any one of the preceding claims, wherein the method is performed in the absence of determining one or more of discharge state of the battery, knowledge of battery temperature and knowledge of battery age.

11. A method according to any one of the preceding claims, wherein the processor controls the power supply to reduce or increase the charge delivered to the battery by a predetermined voltage step.

12. A controller for charging a battery, the controller comprising: a. a memory component storing a target rate of charging for the battery; and b. a processor; the processor being in communicative coupling with: the memory component; a voltage detector for determining battery voltage during charging; and a power supply unit delivering charge to the battery; wherein the processor is configured to: monitor a rate of change of battery voltage during charging and, responsive to the monitored rate of change of battery voltage exceeding the target rate of charging, control the power supply unit to reduce charge delivered to the battery.

13. A controller according to claim 12, wherein the memory stores a terminal charging condition, and the processor is configured to, responsive to the terminal charging condition being met, control the power supply unit to stop charge being delivered to the battery.

14. A controller according to claim 12 or claim 13, wherein the processor is configured to monitor a rate of change of battery voltage during charging of the battery while connected to a load, and the load optionally has one or more of the following characteristics: a. is unknown; b. is variable; c. has non-linear behaviour; d. has one or more of active and reactive components; and e. is permanently connected to the battery.

15. A controller according to any one of claims 12 to 14, further including an interface device in communicative coupling with the processor, the interface device receiving from an operator one or more battery configuration parameters to be stored in the memory, the parameters including one or more of: a. battery chemistry; b. specified battery charge rate; and c. nominal battery voltage.

16. A controller according to any one of claims 12 to 15, wherein the processor, responsive to the monitored rate of change of battery voltage being less than the target rate of charging, controls the power supply unit to increase the charge delivered to the battery.

17. A controller according to any one of claims 12 to 16, wherein the processor monitors for disturbances to the load and, responsive to the processor detecting a disturbance to the load, recalculates the rate of change of battery voltage to determine control of the power supply unit.

18. A controller according to any one of claims 12 to 16, wherein the processor uses feedback control having a set point and a process variable, and wherein the set point is the target rate of charging for the battery, and the process variable is the monitored rate of change of voltage across the battery during charging.

19. A controller according to any one of claims 12 to 18, wherein the processor is an analogue processor.

20. A controller according to any one of claims 12 to 19, wherein the processor is configured to control the power supply unit to charge the battery according to the method or controller of any one of claims 1 to 19 only during a bulk charging phase of a three-phase charge profile.

21. A controller according to any one of claims 12 to 20, wherein the processor is configured to control the power supply unit to reduce the rate of charging when the target rate of charging is exceeded, in the absence of an input corresponding to one or more of a discharge state of the battery, knowledge of battery temperature and knowledge of battery age.