Battery charging circuit and method

Abstract

The present invention relates to a battery charger for providing a charging current to a battery, the battery charger comprising a switched mode power converter and a controller adapted to vary the switching frequency, thereby providing a current having a desired waveform.

Description

[0001] This application is a divisional application of the invention patent application with Chinese application number "201780058047.5", application date "July 20, 2017", and applicant "Battery Charging Circuit and Method". Technical Field

[0002] Embodiments of the present invention relate to methods and systems for battery charging. Background Art

[0003] Basic battery charging systems for recharging batteries, such as lithium-ion batteries, typically apply constant electrical power or pulsed electrical power to the terminals of the rechargeable battery. Typically, a charging cycle for a lithium-ion battery may include an initial constant current operation during which the battery charging system is controlled to achieve a substantially constant supply current to the battery during a first time period of the charging cycle. Once the voltage across the battery terminals has reached a predetermined level, conventional battery charging systems are typically controlled to achieve a constant voltage or even constant power across those terminals during a second time period of the charging cycle (i.e., constant voltage operation of the charging cycle). Ultimately, once the battery is substantially fully charged, either the charging cycle is terminated or an occasional supply of electrical power may be provided to the battery to maintain maintenance or standby operation to compensate for self-discharge.

[0004] Most conventional chargers switch from constant current to constant voltage or even constant power operation for the charging cycle when the battery is between 60% and 80% of full charge.

[0005] Without wishing to be bound by theory, it is believed that ions that pass through the positive electrode of a recharged battery to the negative electrode of the battery tend to pile up before inserting into or toward the boundary of the negative electrode, which faces the positive electrode (i.e., at the solid electrolyte interphase (SEI) layer). It is believed that this pile-up slows the insertion of ions into the negative electrode and creates a higher resistance in the battery.

[0006] Conventional charging also typically causes the SEI layer to grow (ie, become thicker), which, when thick enough and followed by many charging cycles, causes the growth of the SEI layer to reduce the charge capacity of the battery and eventually cause the battery to fail.

[0007] Conventional battery charging systems use relatively complex circuits to provide the constant voltage or even constant power and current operation required for conventional charging cycles, and require additional electronic circuits to provide power factor correction. These complex electronic circuits use many relatively expensive components. Summary of the invention

[0008]

[0006] It would therefore be desirable to alleviate one or more problems associated with conventional battery charging cycles and systems.

[0009] Thus, one aspect of the invention provides a method for charging a battery, the method comprising the steps of: providing a charging current to a battery; determining a characteristic of the battery substantially continuously during charging; and varying the characteristic of the charging current in accordance with the determined characteristic of the battery. By measuring the characteristic of the battery substantially continuously, the charging current supplied to the battery is subsequently varied substantially in real time to provide a more optimized battery charging current, allowing minimization of safe battery charging time. In general, more than one battery characteristic may be determined to provide information about the battery state, which can assist in determining the desired charging current characteristic. Optionally, the charging current has an oscillating DC waveform. Optionally, the charging current has a pulsed DC waveform. Using a DC charging current that varies with time - for example these can allow characteristics (such as the internal impedance of the battery) to be more easily measured without interrupting the charging process. For efficiency, at least a portion of the waveform has the form of a substantially rectified sine wave. Optionally, at least a portion of the waveform has the form of a substantially sine square wave. These waveforms can provide advantageous battery charging with a high power factor that is easy to generate. Optionally, the waveform has a minimum value, which occurs at a current value of less than about 0.5 amperes, preferably less than about 0.1 amperes, and more preferably at a current value of about zero amperes. By having a waveform with a minimum value of about zero amperes, the effects of static buildup and / or internal potential rise in battery characteristics can be weakened. Optionally, the determined characteristic is determined from the current waveform. The current waveform is relatively directly measured and can be used to determine more characteristics of the battery. Optionally, the determined characteristic is determined at least at the frequency of the waveform. The characteristics are determined at least at the frequency of the waveform that provides monitoring of the battery characteristics substantially continuously, and these characteristics are determined at least once per waveform cycle. This allows frequent or substantially continuous updates of the charging current to prevent any overloading of the battery. Optionally, these determined characteristics are determined during the rising portion of the waveform. For accuracy, the determined characteristics are determined by starting the measurement at the minimum value of the waveform. The minimum value of the waveform provides a convenient starting point for measurement and can result in a larger measurement change in the characteristic, thereby reducing relative errors. Optionally, the determined characteristic is determined during the falling portion of the waveform. Measuring the characteristic during the falling portion of the waveform in addition to during the rising portion of the waveform allows the characteristic to be determined from different starting points, which can help detect or reduce errors. Optionally, the waveform is provided at a frequency that is approximately an integer multiple of the voltage supply frequency. Providing a waveform at an integer multiple of the power supply voltage can result in a higher power factor, improving the efficiency of charging. Optionally, providing a waveform at a frequency of approximately twice the power supply voltage supply frequency can provide more efficient charging. Optionally, the waveform is locked to the power supply voltage supply frequency. By providing a waveform locked to the power supply frequency, in this way it means that the minimum value of the current waveform and the zero value of the voltage waveform occur at substantially the same time, and a higher power factor can be provided.Optionally, the internal impedance of the battery is determined based on the current change measured at the battery and the measured voltage change. This allows the internal impedance to be measured indirectly. Optionally, the determined characteristics of the battery include the internal impedance of the battery cell. Optionally, the determined characteristics of the battery include the maximum battery cell impedance. Wherein, the battery includes a plurality of battery cells, and the battery cell impedance of each battery cell may be different. The battery cell with the highest impedance will determine the limit of the safe charging current. Optionally, the determined characteristics of the battery include the battery temperature. Optionally, the determined characteristics of the battery include the battery cell temperature. The battery temperature and / or the battery cell temperature can indicate information about the battery state and / or the battery cell state, for example, whether the charging current currently used is safe. Optionally, the characteristics of the change include: current average value, current maximum value, current amplitude, duty cycle, and / or charging mode. Changing these characteristics of the current can change the power supplied to the battery, keeping it within safe limits while minimizing the battery charging time. Optionally, the method further includes the following steps: measuring the time when the battery has been charged, thereby determining the amount of charge received by the battery. This allows monitoring the state of the battery charge. Optionally, the battery is a lithium-ion battery. Lithium ion batteries are used in a variety of different applications. According to another aspect of the present invention, a battery charging system is provided comprising: a current source, which can be adapted to provide a charging current to a battery; and a control unit, wherein the control unit is configured to determine a characteristic of the battery substantially continuously during charging, wherein the control unit is configured to vary the characteristic of the charging current according to the determined characteristic of the battery. The control unit allows the charging current to vary based on the substantially continuously determined battery characteristic to provide a charging current, the characteristic of which is effective for charging while also remaining within safety limits so as not to damage the battery. Optionally, the charging current is provided as an oscillating DC waveform. Optionally, the charging current is provided as a pulsed DC waveform. The use of DC charging currents that vary with time enables these currents to allow characteristics such as the internal impedance of the battery to be more easily measured without interrupting the charging process. Optionally, at least a portion of the waveform has the form of a substantially rectified sine wave. Optionally, at least a portion of the waveform has the form of a substantially sine squared. These waveforms can provide advantageous battery charging while being simple and easy to generate. Optionally, the waveform has a minimum value that occurs at a current value of less than about 0.5 amperes, preferably less than about 0.1 amperes, and more preferably about zero amperes. This can reduce the effects of static buildup of battery characteristics and / or internal potential rise. For efficiency, the determined characteristic is determined from the current waveform. The current waveform is relatively directly measured and can be used to determine more characteristics of the battery. For safety, one or more of these determined characteristics are determined at least at the frequency of the waveform. Optionally, one or more of these determined characteristics are determined at least at twice the frequency of the waveform. The characteristics are determined at least at the frequency of the waveform to provide substantially continuous monitoring of the battery characteristics, with the characteristics being determined at a frequency of at least once per waveform cycle.This allows frequent or substantially continuous updating of the charging current to prevent any overloading of the battery. Optionally, these determined characteristics are determined during the rising portion of the waveform. For accuracy, the determined characteristics are determined based on measurements starting from the minimum of the waveform. The waveform minimum provides a convenient starting point for measurement and can result in a greater characteristic change in the measurement, thereby reducing relative errors. Optionally, the determined characteristics are determined during the falling portion of the waveform. Measuring the characteristics during the falling portion of the waveform in addition to the rising portion of the waveform allows the characteristics to be determined from different starting points, which can help detect or reduce errors. For ease of generation, the waveform is provided at a frequency that is an integer multiple of the voltage supply. Optionally, the waveform is provided at a frequency that is approximately twice the voltage supply. Optionally, the waveform is provided as locked to the frequency of the voltage supply. This provides a high power factor and improves efficiency. Optionally, the current source includes a flyback converter. A flyback converter is used to generate a current waveform that can reduce or eliminate the need for a bulk capacitor to generate the charging current. Optionally, the system also includes a voltage measuring device and / or a current measuring device. Determining the current and voltage (or the current change and the voltage change) can allow the characteristics of the battery to be determined without interrupting the current supply to the battery. Optionally, in order to indicate the state of the battery, one or more determined characteristics of the battery include the battery internal impedance. The internal impedance can be used to indicate the state of the battery. Optionally, the internal impedance of the battery is calculated from the current change measured across the battery and the measured voltage change. This allows the internal impedance of the battery to be determined indirectly. Optionally, the determined characteristics of the battery include one or more battery cell internal impedances. Optionally, the determined characteristics of the battery include the maximum battery cell impedance. Wherein, the battery includes a plurality of battery cells, and the battery cell impedance of each battery cell may be different. The battery cell with the highest impedance will determine the limit of the safe charging current. Optionally, the determined characteristics of the battery include the battery temperature. The battery temperature and / or the battery cell temperature can indicate information about the battery state. Optionally, the changing characteristics include at least one of the following: current average value, current maximum value, current amplitude, duty cycle, and / or charging mode. Changing these characteristics of the current can change the power supplied to the battery to keep it within safe limits while minimizing the battery charging time. Optionally, the system further comprises a clock, wherein the clock is configured to measure the time when the battery has been charged, thereby determining the amount of charge received by the battery. This allows the state of charge of the battery to be monitored. In order to enable self-learning and self-updating, the control unit can be configured to store a plurality of determined characteristics of the battery in a database and / or a lookup table. According to yet another aspect of the invention, there is provided a method for monitoring the internal impedance of a battery during charging, the method comprising the steps of: providing a current that varies with time to the battery; measuring the change in the current substantially continuously; measuring the corresponding change in the voltage substantially continuously; and determining the internal impedance of the battery from the change in the current and the corresponding change in the voltage.Optionally, the time-varying current is provided in the form of an oscillating DC waveform. Optionally, at least a portion of the waveform has a substantially sinusoidal square wave form. These waveforms can provide advantageous battery charging while being easy to generate. Optionally, for accuracy, the waveform has a minimum value occurring at a current value of less than about 0.5 amperes, preferably less than about 0.1 amperes, and more preferably about zero amperes. This can reduce the static construction of the measurement of the current change and the voltage change and / or the effect of the internal potential rise. Optionally, the impedance is determined at least at the frequency of the waveform. This provides a substantially continuous determination of the battery impedance. Optionally, the change in current and / or the change in voltage is measured during the rising portion of the waveform. For accuracy, the change in current and / or the change in voltage is measured starting at the minimum of the waveform. The waveform minimum provides a convenient starting point for measurement and can result in a larger measured change in current, thereby reducing relative errors. For flexibility, the change in current and / or the change in voltage is measured during the falling portion of the waveform. According to another aspect of the present invention, a battery charger is provided, the battery charger being adapted to provide a current having an oscillating waveform, wherein the waveform minimum is 0A or close to 0A. Optionally, the waveform minimum is less than 0.1A, more preferably less than 0.01A, and more preferably less than 0.001A. Providing a waveform minimum at 0A or close to 0A can reduce static charge and / or internal potential accumulated in the battery. Optionally, the peak-to-peak value of the current is greater than 1A, and preferably between about 10A and about 30A. Providing a large peak-to-peak value current can improve the accuracy of impedance measurement. For accuracy, at least 0.5ms of each oscillation cycle of the waveform is 0A or close to 0A, preferably at least 1ms, more preferably at least 5ms, and more preferably at least 10ms. For accuracy, at least 0.5% of the cycle time period of each oscillation cycle of the waveform is 0A or close to 0A, preferably at least 1%, more preferably at least 5%, and more preferably at least 10%. Optionally, a plurality of battery charging systems are provided, each battery charging system being configured to receive input from a single phase of a multi-phase input and generate a common output. According to another aspect of the present invention, a method for charging a battery is provided, the method comprising converting an AC power source into a charging current to the battery, wherein the current has an oscillating waveform, the waveform minimum being 0A or close to 0A. Optionally, the waveform corresponds to one or more waveforms described above according to other aspects of the present invention. According to another aspect, a battery charger for providing a charging current to a battery is provided, the battery charger comprising a switching mode power converter and a controller, the controller being adapted to vary the switching frequency and / or duty cycle to provide a current having a desired waveform. By varying the switching frequency and / or duty cycle, the current provided can vary over time; this can provide a current having a desired waveform.Charging a battery using a specific waveform can benefit for many reasons, including optimization of the current taken by the battery, reducing battery heating, assessing battery health, reducing battery charging time, and optimizing battery life. The controller may be adapted to change the switching frequency and / or duty cycle after one or more duty cycles of the power converter of the switching mode. By changing the switching frequency and / or duty cycle relatively frequently, a smooth waveform can be achieved. In order to smooth the waveform, the controller may be adapted to change the switching frequency and / or duty cycle after each duty cycle of the switching mode power converter. The controller may be adapted to change the switching frequency and / or duty cycle according to the voltage oscillation of the AC power source. This can effectively generate an oscillating current waveform. Because it can be achieved to rely on a high power factor. This can avoid the need for power factor correction hardware, which may be bulky, large and heavy. The controller may be adapted to change the switching frequency and / or duty cycle multiple times during each voltage oscillation of the AC power source, preferably at least three times during each voltage oscillation, preferably at least 10 times, more preferably at least 100 times during each voltage oscillation, and more preferably at least 800 times during each voltage oscillation. This can achieve good replication of voltage oscillations. For accuracy, the battery charger may also include a voltage sensor adapted to provide an indication of the voltage of the AC power source to the controller. For accuracy, the voltage sensor may be adapted to sense the voltage at least as frequently as the controller changes the switching frequency. The switching frequency and / or duty cycle may be changed according to the voltage oscillation after rectification (preferably after full-wave rectification) of the AC power source. Rectification can double the oscillation frequency and ensure that the oscillation does not change polarity, which is conducive to changing the switching frequency according to the voltage oscillation. The desired waveform may have a frequency of about an integer multiple of the frequency of the AC power source, preferably about twice the frequency of the AC power source. This can provide an oscillating current waveform that is particularly effective in generating a particularly high power factor. For efficiency, the desired waveform may be locked to the frequency of the AC power source. The desired waveform may be a sine wave, a full-wave rectified sine wave, a sine square wave, or a combination of the above. These waveforms can provide favorable battery charging while being easy to generate. The switching mode power converter may be a flyback transformer. The flyback transformer can provide an appropriate switching frequency and / or duty cycle range. For effectiveness, the switching mode power converter may be adapted to operate in a critical conduction mode. The switching frequency and / or duty cycle may vary in the range of 1 to 1000 kHz, and preferably in the range of 10 to 500 kHz, and more preferably in the range of 40 to 200 kHz. This is higher than the typical mains supply frequency of 50 or 60 Hz and 100 or 120 Hz rectification frequency, and thus can smoothly produce the desired waveform with a frequency between 25 and 150 Hz. For adaptability, the controller may be adapted to vary the switching frequency and / or duty cycle depending on the desired maximum charging current to the battery.The desired maximum charging current may depend on one or more of the following: battery temperature, battery voltage, battery current, battery voltage variation, battery current variation, battery impedance, charging time, and accumulated battery charge. These may be conditions or situations that indicate that relatively high or relatively low charging currents may be advantageous. The controller may be adapted to change the switching frequency and / or duty cycle so that the minimum charging current provided to the battery is less than 1A, preferably less than 0.1A, more preferably less than 0.01A, and more preferably about 0A. This can reduce hysteresis effects and enable favorable battery behavior and charging. The controller may be adapted to change the switching frequency and / or duty cycle so that the peak-to-peak current provided to the battery is greater than 1A, preferably between about 10A and about 30A. This can enable effective charging of batteries (e.g., lithium-ion batteries, batteries for handheld devices) without excessive and dangerous currents. The current charger may also include a smoother that is adapted to smooth the output current from the power converter. Each of the plurality of battery chargers may be configured to be connected to a plurality of inputs and may be connected to a common output. This can generate a smoothed waveform from a rectified waveform. A smooth waveform is beneficial for battery charging because it enables efficient charging. According to another aspect, a method for charging a battery is provided, comprising: using a switching mode power converter to change an AC power source to a charging current to a battery; wherein the switching frequency and / or duty cycle is varied according to a desired waveform. By varying the switching mode and / or duty cycle, the current provided can vary over time; this can provide a current with a desired waveform. Using a specific waveform to charge a battery can be beneficial for many reasons, including optimizing the current taken by the battery, reducing battery heating, assessing battery health, reducing battery charging time, and optimizing battery life. The switching frequency and / or duty cycle can be varied after one or more duty cycles of the switching mode power converter, preferably after each duty cycle. A smooth waveform can be achieved by varying the switching frequency relatively frequently. The switching frequency and / or duty cycle can be varied according to the voltage oscillation of the AC power source. This can achieve efficient generation of an oscillating current waveform. Because reliance on a high power factor can be achieved. This can avoid the need for power factor correction hardware, which can be bulky, large and heavy. During each voltage oscillation of the AC power source, the switching frequency and / or the duty cycle may be varied multiple times, preferably at least three times during each voltage oscillation, more preferably at least 10 times, more preferably at least 100 times, and even more preferably at least 800 times during each voltage oscillation. This enables good replication of the voltage oscillation. For accuracy, the method may further include sensing the voltage of the AC power source, and varying the switching frequency and / or the duty cycle according to the voltage, and preferably includes sensing the voltage at least as frequently as varying the switching frequency.The switching frequency and / or duty cycle can be varied in the range of 1 to 1000 kHz, preferably in the range of 10 to 500 kHz, and more preferably in the range of 40 to 200 kHz. Compared with the typical mains supply frequency of 50 to 60 Hz and the rectification frequency of 100 or 120 Hz, the aforementioned frequency is higher, and thus it is possible to smoothly generate the desired waveform with a frequency between 25 and 150 Hz. The switching frequency and / or duty cycle can be varied according to the rectified (preferably full-wave rectified) voltage oscillation of the AC power source. Rectification can double the oscillation frequency and ensure that the oscillation does not change polarity, which is conducive to varying the switching frequency according to the voltage oscillation. For adaptability, the switching frequency and / or duty cycle can be varied according to the expected maximum charging current to the battery, optionally, wherein the expected maximum charging current depends on one or more of the following: battery temperature, battery voltage, battery current, battery voltage variation, battery current variation, battery impedance, charging time, and accumulated battery charge. These may in particular indicate conditions or circumstances where relatively high or relatively low charging currents may be advantageous. The switching frequency and / or duty cycle may be varied so that the minimum charging current provided to the battery is less than 1 A, preferably less than 0.1 A, more preferably less than 0.01 A, and even more preferably about 0 A. This can reduce hysteresis effects and achieve advantageous battery behavior and charging. The switching frequency may be varied so that the peak-to-peak current provided to the battery is greater than 1 A, and preferably between about 10 A and about 30 A. According to another aspect, a battery charging system is provided, comprising one or more of the following features:.

[0010] A transformer, preferably comprising a first main winding and / or a first secondary winding;

[0011] - a main switching device, preferably configured to control current delivered to the transformer, for example current from an electrical power supply to the first main winding;

[0012] a terminal configured to receive electrical power from the transformer (e.g. from a primary winding of the transformer) and configured to be connected to a battery to be charged;

[0013] A control subsystem configured to control the operation of the main switching device;

[0014] A control subsystem configured to control the main switching device so that the transformer provides electrical power to the terminal through a current waveform having a peak-to-peak current greater than about 1A;

[0015] A control subsystem configured to determine an electrical impedance of a battery to be charged using the current waveform;

[0016] A control subsystem configured to control a primary switching device based at least in part on the determined electrical impedance of the battery to be charged;

[0017] A current waveform having a frequency greater than about 60 Hz, preferably about 100 Hz to 120 Hz;

[0018] A current waveform having a peak-to-peak current of about 10A to about 30A;

[0019] A current waveform that varies between a low current of about 0A and a peak current;

[0020] a current waveform having a frequency substantially twice the frequency of the electrical power supply;

[0021] a primary switching device that operates according to a frequency and / or duty cycle that varies based at least in part on a determined electrical impedance of the battery to be charged;

[0022] • the envelope of the pulse or pulses of current delivered to the transformer substantially follows the voltage waveform of the electrical power supply;

[0023] ●The transformer is a flyback transformer;

[0024] Determining the electrical impedance of the battery to be charged at a frequency greater than about 60 Hz, and preferably between about 100 Hz and about 120 Hz;

[0025] A transformer, which can be connected to a rectified AC electrical power supply;

[0026] a control subsystem configured to control the main switching device so that the transformer provides electrical power to the terminals having a current waveform having a substantially rectified sinusoidal waveform current and / or a constant root mean square sinusoidal waveform;

[0027] A control subsystem configured to control the main switching device so that the transformer provides electric power to the terminals with a current waveform having a frequency substantially twice that of a voltage supplied with the AC electric power.

[0028] a control subsystem configured to control the main switching device so as to actuate the main switching device between an on state and an off state at a frequency that varies over time; and

[0029] ●A control subsystem configured to control the main switching device so as to actuate the main switching device between an on state and an off state at a frequency that depends on the amplitude of the voltage of the AC electric power supply and / or the amplitude of the battery current and / or the amplitude of the battery voltage.

[0030] According to another aspect, a method of operating a battery charging system is provided, the battery charging system including one or more of the following features:

[0031] The battery charging system comprises a transformer, preferably comprising a first main winding, a secondary winding,

[0032] • the battery charging system comprises a main switching device, the main switching device preferably being configured to control the current passed from the electrical power supply to the first main winding;

[0033] a terminal configured to receive electrical power from the primary winding of the transformer and configured to be connected to a battery to be charged;

[0034] A control subsystem configured to control the operation of the main switching device;

[0035] ● controlling the main switching device so that the transformer provides electrical power having a current waveform with a peak-to-peak current greater than about 1 A to the terminal;

[0036] ● Determine the electrical impedance of the battery to be charged using the current waveform;

[0037] • controlling the main switching device further based at least in part on the determined electrical impedance of the battery to be charged;

[0038] • controlling the main switching device includes controlling the main switching device so that the current waveform has a frequency greater than about 60 Hz, preferably about 100 Hz to 120 Hz;

[0039] ● controlling the main switching device includes controlling the main switching device so that the current waveform has a peak-to-peak current of about 10A to about 30A;

[0040] ● controlling the main switching device includes controlling the main switching device so that the current waveform varies between a low current of about 0A and a peak current;

[0041] • controlling the main switching device comprises controlling the main switching device such that the current waveform has a frequency that is substantially twice the frequency of the electrical power supply;

[0042] • controlling the main switching device further comprises controlling the main switching device such that a frequency and / or a duty cycle of the main switching device varies based at least in part on the determined electrical impedance of the battery to be charged;

[0043] • controlling the main switching device comprises controlling the main switching device such that the envelope of one or more pulses of current delivered to the transformer substantially follows the voltage waveform of the electrical power supply; and

[0044] - Determining the electrical impedance of the battery to be charged at a frequency greater than about 60 Hz, and preferably at a frequency between about 100 Hz and about 120 Hz.

[0045] As used herein, DC preferably refers to a voltage and / or current with a constant polarity. The DC voltage and / or current may vary over time, for example in a pulsed, oscillating or other varying waveform. In a switched mode current converter, a change in the switching frequency results in a change in the duty cycle, and vice versa. The changing switching frequency may be achieved by changing the duty cycle, and vice versa. Wherein, herein refers to a change in the switching frequency, which may be replaced by a change in the duty cycle. The present invention extends to a battery charger and / or a battery charging system substantially as described herein and / or as shown with reference to the accompanying drawings. The present invention also extends to a method for charging a battery substantially as described herein and / or as shown with reference to the accompanying drawings. The present invention also extends to a method for determining the impedance of a battery substantially as described herein and / or as shown with reference to the accompanying drawings.

[0046] Any apparatus features as described herein are also provided as method features, and vice versa.As used herein, means-plus-function features may be represented alternatively to their corresponding structures.

[0047] Any feature of one aspect of the present invention may be applied to other aspects of the present invention in any appropriate combination. In particular, method aspects may be applied to device aspects, and vice versa. Moreover, any, some and / or all features in one aspect may be applied to any, some and / or all features in any other aspect in any appropriate combination.

[0048] It should be understood that specific combinations of various functions described and defined in any aspect of the present invention may be independently implemented and / or provided and / or used. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Embodiments of the invention are described, by way of example only, with reference to the accompanying drawings, in which:

[0050] Figure 1a and Figure 1b schematically illustrates the processes believed to occur during conventional battery charging;

[0051] Figure 2 An embodiment of the present invention is shown;

[0052] Figures 3a to 3f shows a graphical representation of current and voltage during operation of an embodiment;

[0053] Figures 4 to 7 A battery charging system and portions thereof are shown according to some embodiments;

[0054] Figures 8 to 10 shows the current through the first main winding of the flyback transformer during a charging cycle according to some embodiments; and

[0055] Figures 11a to 11c A graphical representation of the current delivered to the battery, the voltage across the battery terminals, and the compressed ripple voltage signal is shown.

[0056] Fig.12 A step-by-step process for charging a battery is shown.

[0057] Fig.13 A schematic example of a single cellular battery control unit in use is shown.

[0058] Fig.14 A schematic illustration of a plurality of cellular battery control units in use is shown.

[0059] Fig.15 A schematic example of a three-phase input to a battery charger of some embodiments is shown. DETAILED DESCRIPTION

[0060] The term "battery" as used herein will be interpreted as referring to one or more battery cells that are capable of storing an electric charge and being recharged after the charge is discharged. If the battery includes a plurality of battery cells, those battery cells may be connected together in a circuit to form a battery. The circuit may be a series circuit (where the battery cells are connected together in series), or a parallel circuit (where the battery cells are connected together in parallel), or a series-parallel circuit (where the battery cells are connected together in series, with multiple groups of series-connected battery cells connected in parallel to each other), or any combination of these circuits.

[0061] As used herein, the terms "multiple battery terminals," "battery terminals," "terminals of a battery," and "multiple terminals of a battery" will be interpreted as referring to electrical terminals or multiple terminals of a battery through which the battery can deliver electrical power to one or more circuits and / or through which electrical power can be provided to the battery in order to recharge the battery.

[0062] The terms "anode" and "negative electrode" are used herein substantially interchangeably and are to be interpreted as referring to the internal portion of a battery cell that forms the anode of the battery cell. Similarly, the terms "cathode" and "positive electrode" are used herein substantially interchangeably and are to be interpreted as referring to the internal portion of a battery cell that forms the cathode of the battery cell.

[0063] Embodiments of the present invention will be described with reference to a "battery", but it should be understood that this is generally with reference to operations and processes in a single battery cell, and a battery including multiple battery cells may have corresponding multiple anodes and multiple cathodes, and similar operations and processes may occur in each battery cell of the battery.

[0064] The batteries (and thus the battery cells) as described herein may be lithium-ion batteries (or battery cells), but it is contemplated that other forms of batteries (and battery cells) may be used with embodiments of the invention.

[0065] refer to Figure 1a and Figure 1b , and again without wishing to be bound by theory, these figures schematically illustrate the processes believed to occur in a battery during a conventional charging cycle using constant current operation.

[0066] As can be seen from Figure 1a and Figure 1b As seen in , battery 1 includes a battery cell 11, and the battery cell 11 includes an anode 111 and a cathode 112 in an electrolyte 115. A separator 113 can be positioned between the anode 111 and the cathode 112. The anode 111 can be connected in electrical communication with the negative terminal 12 of the battery 1, and the cathode 112 can be connected in electrical communication with the positive terminal 13 of the battery 1.

[0067] A solid electrolyte interphase (SEI) layer 114 is located at or toward the boundary of the anode 111 .

[0068] During charging of the battery 1, a voltage is applied across the terminals 12, 13 of the battery 1 so that ions 3 pass from the cathode 112 (e.g., through the separator 113 and the electrolyte 115) to the anode 111 and are inserted into the anode 111 through the SEI layer 114 (during discharge, of course, the flow of ions 3 is in the opposite direction within the battery 1).

[0069] It is believed that ions 3 cannot be inserted into the anode 111 as quickly as ions 3 are supplied to the SEI layer 114 under a conventional charging cycle during constant current operation. Therefore, accumulation of ions 3 occurs at the boundary of the anode 111 or at the boundary toward the anode 111 (i.e., in the region of the SEI layer 114). This Figure 1b It is schematically shown in FIG.

[0070] As explained herein, it is believed that this, in turn, increases the resistance within the battery 1 and / or causes growth of the SEI layer 114. It is believed that this causes additional heating of the battery 1 during the charging cycle, which again affects the speed at which the battery 1 can be charged, the nature of the charging cycles that can be used, the efficiency of the charging process, the safety of the charging process, and / or the life of the battery in terms of the number of charging cycles that the battery 1 can undergo before the charge capacity drops below an acceptable level.

[0071] refer to Figure 2, an embodiment of the present invention therefore includes a battery charging system 100, which is configured to supply a current, also referred to as a charging current, to a battery 1, wherein the current may be a waveform of an average current with a variation amplitude that is generally non-zero, and may be a waveform with a substantially constant average current (and the waveform may be, for example, substantially sinusoidal). Further examples of suitable waveforms include an oscillating DC waveform or a pulsed DC waveform. Such a waveform may, for example, be supplied by a switching mode power converter with a controller adapted to vary the switching frequency, thereby providing a current with a desired waveform.

[0072] Figure 3a to Figure 3c 1 shows the current delivered to the battery 1 by the battery charging system 100 of some embodiments for a main power supply 102 having an RMS voltage of about 85V ( Figure 3a ), the voltage of the power supply 102 ( Figure 3b ), and the current drawn from the electrical power supply ( Figure 3c ). Figure 3d to Figure 3f 1 shows the current delivered to the battery 1 by the battery charging system 100 of some embodiments for a main power supply 102 having an RMS voltage of about 265V ( Figure 3d ), the voltage of the main power supply 102 ( Figure 3e ), and the current drawn from the electrical power supply ( Figure 3f ).

[0073] The frequency of the current supplied to the battery 1 by the battery charging system 100 may generally be twice the frequency of the electric power supplied to the battery charging system 100 and / or the current supplied to the battery 1 by the battery charging system 100 may have a waveform in a rectified form (e.g., a full-wave rectified form) that substantially corresponds to the waveform of the supply voltage. The frequency of the current supplied to the battery 1 may be, for example, 100 Hz or 120 Hz. The amplitude of the current supplied to the battery 1 may generally be equal to the peak current supplied to the battery 1.

[0074] Accordingly, in an embodiment of the present invention, the battery charging system 100 may be configured to supply electric power to the battery 1 during a charging cycle in the first operation as described above. The battery charging system 100 may be configured to supply electric power to the battery 1 during the same charging cycle in a second operation in which, for example, electric power is supplied using a substantially constant voltage or even a constant power.

[0075] As can be Figure 3a to Figure 3c and Figure 3d to Figure 3f As seen in the example, the power supply voltage (V ac) may be the mains AC power supply voltage available in many countries - its voltage and frequency may vary in different countries (e.g. 85-265V RMS, and 50-60Hz). Thus, V ac Typically, it is in the form of a sinusoidal curve centered at 0 V. The current (I bat ) can be a ac The frequency of the waveform is related to the frequency of V, and the waveform may be substantially V ac twice the frequency, or about V ac The current supplied to the battery 1 (I bat ) may have a non-zero average value (i.e., may have an offset from 0 A), and may be generally sinusoidal in form—as described herein. The current (I bat ) can be roughly the supply voltage V ac In the form of a full-wave rectified waveform, therefore, in some embodiments, the lower peak value of the waveform may be, for example, Figure 3d and Figure 3e The one shown in is sharper.

[0076] The current I supplied to battery 1 bat The waveform of the battery 1 may vary between a low current (i.e., the lowest current of the waveform) and a peak current (i.e., the highest current of the waveform). The low current may be substantially 0A. The peak current may be between about 1A and about 30A, or between about 10A and about 30A, or between about 20A and about 30A. The current I supplied to the battery 1 bat The peak-to-peak variation (i.e., the difference between the peak current and the low current) can be greater than about 1A, or greater than about 10A, or greater than about 20A, or about 30A. Generally speaking, this peak battery charging current is about 10 times the battery capacity. For example, the battery we used is 2.6Ah. Therefore, with an average battery charging current of about 16 amps, the peak current is about 26 amps.

[0077] Current I bat The waveform may oscillate repeatedly between a low current and a peak current. In some embodiments, such a waveform is substantially a smooth waveform. In some embodiments, the waveform is substantially a full-wave rectified sinusoidal shape. In some embodiments, the waveform partially has the form of a rectified sine wave and partially has the form of a sine square wave. For example, the portion of the waveform around the waveform maximum may substantially have the form of a rectified sine wave, and the portion of the waveform around the waveform minimum may substantially have the form of a sine square wave (also referred to herein as a square sine wave).

[0078] It can be considered that the non-zero average current waveform (I bat) helps to reduce the above-mentioned accumulation of ions. This in turn reduces the resistance of the battery 1 during the charging cycle. This improves the charging efficiency of the battery 1, reduces the heat generated during the charging process, and enables safer charging of the battery 1 with a higher overall charging current. In addition, the first operation of the charging cycle can be used until the battery 1 has a relatively larger charge level than some traditional charging cycles (e.g., 80% or more, or 90% or more of the full charge capacity, or between 90% and 95% of the full charge capacity).

[0079] In fact, in some embodiments, the second operation of the charging cycle may be omitted entirely.

[0080] Some embodiments may include a third operation of the charging cycle in which electric power is occasionally (eg, periodically) supplied to the battery 1 to compensate for self-discharge of the battery 1 .

[0081] As will be appreciated, the battery charging system 100 may be implemented in many different ways. However, in some embodiments, additional benefits may be achieved by implementing the battery charging system 100 in accordance with the specific embodiments described herein - as will become apparent.

[0082] refer to Figures 4 to 7 , embodiments of the battery charging system 100 will be discussed in more detail.

[0083] Some embodiments of the battery charging system 100 may include a flyback transformer (also referred to herein as a flyback converter) 101. The flyback transformer 101 may be configured to be connected in electrical communication with a main power supply 102. The main power supply 102 may be a power supply with a supply voltage V ac AC mains power supply delivering electrical power. The battery charging system 100 may include a rectifier circuit 103 configured to receive electrical power from the mains power supply 102 and rectify the electrical power from the mains power supply 102 for delivery to the flyback transformer 101 .

[0084] The electromagnetic interference filter 104 of the battery charging system 100 may be connected in electrical communication between the main power supply 102 and the flyback transformer 101. In some embodiments, the electromagnetic interference filter 104 and the rectifier circuit 103 may be combined into a single circuit.

[0085] The battery charging system 100 may further include a buffer circuit 105. The buffer circuit 105 may be connected between the main power supply 102 and the flyback transformer 101, and in particular may be connected between the electromagnetic interference filter 104 and / or the rectifier circuit 103 and the flyback transformer 101. The buffer circuit 105 may be configured to mitigate voltage spikes (which may otherwise damage the main switching device 101a of the flyback transformer 101) and / or to recirculate current from the flyback transformer 101.

[0086] The main switching device 101a of the flyback transformer 101 is configured to control the transfer of electric power from the main power supply 102 (and, for example, the rectifier circuit 103 and / or the electromagnetic filter 104 and / or the snubber circuit 105) to the first main winding 101b of the flyback transformer 101.

[0087] The flyback transformer 101 further comprises a primary winding 101 c - the flow of current through the first main winding 101 b is configured to induce the flow of current in the primary winding 101 c.

[0088] The first primary winding 101 c is connected in electrical communication to an output rectifier circuit 106 that is configured to rectify the electric power output from the flyback transformer 101 (ie, the current induced in the first primary winding 101 c ).

[0089] The battery charging system 100 includes a terminal 107 configured to be connected to the terminals 12, 13 of the battery 1 (in some embodiments, the terminal 107 of the battery charging system 100 can be configured to be selectively connected to the terminals 12, 13 of the battery 1). The terminal 107 of the battery charging system 100 is electrically connected to the primary winding 101c. The connection is via the output rectifier circuit 106, so that the output rectifier circuit 106 is configured to rectify the electric power through the primary winding 101c for delivery to the battery 1 (which is connected to the terminal 107 of the battery charging system 100).

[0090] In some embodiments, the output rectifier circuit 106 is a synchronous rectifier circuit that includes one or more switching devices—eg, transistor devices (eg, MOSFETs).

[0091] In some embodiments, the battery charging system 100 may include a smoothing circuit 108 that is electrically connected between the first winding 101c and a terminal 107 of the battery charging system 100. The smoothing circuit 108 is configured to filter and / or smooth the current and / or voltage of the electric power that is delivered to the terminal 107 of the battery charging system 100 (and to the battery 1).

[0092] In some embodiments, the smoothing circuit 108 may include one or more capacitors and / or inductors. In some embodiments, one or more capacitors are provided and connected in parallel between the terminals 107 of the battery charging system 100, such that the capacitors form a capacitor reservoir. In some embodiments, which may or may not include a capacitor reservoir as part of the smoothing circuit 108, the smoothing circuit 108 includes at least one inductor connected in series between the first winding 101c and one of the terminals 107 of the battery charging system 100.

[0093] The one or more capacitors of the smoothing circuit 108 may include one or more polymer electrolytic capacitors and may have low internal resistance and be capable of high ripple currents.

[0094] In some embodiments, the battery charging system 100 may further include an isolating switch 109, which is configured to disconnect one or both of the terminals 107 of the battery charging system 100 from electrical communication with at least the first winding 101c, but may also disconnect the or each terminal 107 from electrical communication with the output rectifier circuit 106 and / or the smoothing circuit 108 (or a portion thereof).

[0095] The battery charging system 100 may further include a control subsystem 110. The control subsystem 110 is configured to control the operation of the battery charging system 100, which includes, for example, one or more flyback transformers 101 (e.g., main switching devices 101a thereof), a rectifier circuit 103, an output rectifier circuit 106, and an isolation switch 109.

[0096] The control subsystem 110 may also include one or more sensor circuits and / or elements, each of which is configured to measure and / or determine one or more characteristics associated with the operation of the battery charging system 100 and / or the battery 1, so that the control subsystem 110 can control the operation of the battery charging system 100 based at least in part on information received from the one or more sensor circuits and / or elements. For example, the characteristics of the charging current can be varied according to the determined characteristics, so that the impedance of the battery is determined substantially continuously during charging, for example.

[0097] The one or more sensor circuits and / or elements may include a power supply voltage sensor circuit 1111 configured to sense the voltage of the main power supply 102, which may be the voltage after being rectified by the rectifier circuit 103 (if provided). The power supply voltage sensor circuit 1111 may include a potential voltage divider circuit configured to reduce the voltage to a level that can be used by other parts of the control subsystem 110.

[0098] The one or more sensor circuits and / or elements may include a main winding current sensor circuit 1112 configured to sense a current delivered to the first main winding 101b of the flyback transformer 101. For example, the main winding current sensor circuit 1112 may include a shunt loop. The main winding current sensor circuit 1112 may be configured to sense a current flowing from the first main winding 101b through the main switching device 101a to ground or to the main power supply 102.

[0099] The one or more sensor circuits and / or elements may include a battery terminal voltage sensor circuit 1113 configured to sense a voltage V across the terminals 107 of the battery charging system 100 and thus across the terminals 12, 13 of the battery 1 connected thereto. bat The battery terminal voltage sensor circuit 1113 may include a potential voltage divider circuit configured to reduce the voltage to a level that can be used by other portions of the control subsystem 110 .

[0100] The one or more sensor circuits and / or elements may include a battery terminal current sensor circuit 1114 configured to sense current delivered to or returned from at least one terminal 107 of the battery charging system 100 and thus delivered to the battery 1 connected thereto. The battery terminal current sensor circuit 1114 may include, for example, a shunt circuit. The battery terminal current sensor circuit 1114 may be configured to determine a current flowing from the terminal 107 of the battery charging system 100 through the output rectifier circuit 106 to the primary winding 101c of the flyback transformer 101.

[0101] In some embodiments, the control subsystem 110 may include a primary-side controller or input-side controller 1115 and a secondary-side controller or output-side controller 1116. The primary-side controller 1115 may be configured to communicate with the output-side controller 1116, and / or vice versa, via a communication channel that may include an optocoupler circuit 1117. The optocoupler circuit 1117 may be configured to allow communication between the primary-side controller 1115 and the secondary-side controller 1116 while maintaining electrical isolation between the two controllers 1115, 1116. As will be appreciated, therefore, the optocoupler circuit 1117 may include a light emitting diode controlled by the primary-side controller 1115 and a phototransistor connected to the secondary-side controller 1116.

[0102] In some embodiments, a second main winding or first "bias" winding 101d is provided as part of the flyback transformer 101. The second main winding 101d can be configured to be associated with the first main winding 101b so that current flowing through the first main winding 101b also induces current in the second main winding 101d. Therefore, the electrical power induced in the second main winding 101d can be used to provide electrical power to one or more parts of the control subsystem 110 - for example, to the primary-side controller 1115. A first bias circuit 101e can be provided to ensure that the electrical power is properly delivered to the primary-side controller 1115. The voltage from the output of the second main winding 101d is referred to herein as the "primary bias voltage" V bias-primary Furthermore, the second main winding or the first bias winding is used to detect the magnetic state of the flyback transformer, thereby ensuring the critical conduction mode of operation of the flyback converter.

[0103] In some embodiments, the flyback transformer 101 may include a secondary winding 101g or a second "bias" winding. The secondary winding 101g may be configured to be associated with the first main winding 101b so that current flowing through the first main winding 101b will also induce current in the secondary winding 101g. Thus, the electrical power induced in the secondary winding 101g may be used to provide electrical power to the control subsystem 110—for example, to the secondary controller 1116. A second bias circuit 101f may be provided to ensure that electrical power is properly delivered to the secondary controller 1116. The voltage from the output of the secondary winding 101g is referred to herein as the "secondary bias voltage" V bias-secondary .

[0104] In the illustrated embodiment, the first bias circuit 101e and the second bias circuit 101f are depicted as multiple parts for simplicity of representation, but it should be understood that they may be separate single circuits or connections.

[0105] The secondary-side controller 1116 is configured to compare a signal representative of the voltage across the terminals 107 of the battery charging system 100 (eg, output from the battery terminal voltage sensor circuit 1113 ) to a reference voltage at the battery terminals.

[0106] The secondary side controller 1116 may also be configured to compare a signal representation of current delivered to or returned from at least one terminal 107 of the battery charging system 100 (e.g., an output from a battery terminal current sensor circuit 1114) with a battery reference current.

[0107] The secondary side controller 1116 can be configured to use the comparison results of the voltage and / or current to determine an operating mode for the battery charging system 100. The operating mode can include determining which of the first operating mode, the second operating mode, or the third operating mode of the charging cycle will be used. In some embodiments, multiple charging modes and / or duty cycles are available.

[0108] In some embodiments, the secondary-side controller 1116 may be configured to receive a signal indicative of the temperature of the battery 1, such as from a battery temperature sensor 1118, which is configured to sense the temperature of the battery 1 or a parameter representative of the temperature and output a signal accordingly. The secondary-side controller 1116 in these embodiments may use the signal indicative of the temperature of the battery 1 to determine which of a variety of operations of the charging cycle to use (in addition to or as an alternative to using one or more comparisons discussed above).

[0109] Thus, the secondary side controller 1116 is configured to output a control signal C. The control signal C may be communicated to the primary side controller 1115 (eg, via the optocoupler circuit 1117 ), and the primary side controller 1115 may use the control signal C to control the operation of the flyback transformer 101 —as discussed herein.

[0110] The secondary side controller 1116 can also be configured to operate the isolation switch 109 if one or more predetermined conditions occur, and these conditions may include one or more specific currents delivered to or received from the battery 1 (the specific current exceeds or is lower than a predetermined threshold current), and / or the voltage across the terminals 12, 13 of the battery 1 (the voltage exceeds or is lower than a predetermined threshold voltage), and / or the battery temperature (the battery temperature exceeds or is lower than a predetermined threshold temperature).

[0111] The secondary side controller 1116 may be configured to control the operation of the output rectifier circuit 106 (which may be a synchronous rectifier circuit) based on a signal indicative of the current delivered to the terminal 107 of the battery charging system 100 (i.e., delivered to the battery 1 connected thereto) and / or based on a signal indicative of the current flowing through the output rectifier circuit 106. As will be appreciated, the signal may be an output from the battery terminal current sensor circuit 1114. In some embodiments, the secondary side controller 1116 is configured to actuate the output rectifier circuit 106 to an on state when the flyback transformer 101 is discharging to the terminal 107 of the battery charging system 100, and to disable the output rectifier circuit 106 to an off state when the flyback transformer 101 is not discharging to the terminal 107.

[0112] The primary side controller 1115 is configured to control the operation of the flyback transformer 101, and in particular, to control the actuation of the primary switching device 101a. The primary side controller 1115 is configured to control the operation of the flyback transformer 101 based at least in part on one or more of the following: the control signal C, a signal representative of the current delivered to the first main winding 101b (e.g., the output of the main winding current sensor circuit 1112), the voltage (V ) of the main power supply 102 after being rectified by the rectifier circuit 103, and the current of the main power supply 102. ac ) (e.g., the output of the power supply voltage sensor circuit 1111), and the AC bias voltage V before the bias rectifier circuit bias .

[0113] The primary side controller 1115 is configured to operate the flyback transformer 101 in a critical conduction mode of operation.

[0114] Accordingly, the primary side controller 1115 may be configured to actuate the primary switching device 101a to an open state (so that electrical power may flow through the primary power supply 102 to the first primary winding 101b) once it has been determined that the energy stored in the flyback transformer 101 (e.g., in windings 101b, 101c, 101d and any of the above) has been dissipated—i.e., is delivered to the terminal 107 of the battery charging system 100 and to the battery 1 (or is otherwise lost).

[0115] With the main switching device 101 in its on state, electrical power is delivered to the first main winding 101b, causing energy stored in the flyback transformer 101 to accumulate, which in turn is delivered as electrical power to the terminal 107 of the battery charging system 100 via the first winding 101c, and to any battery 1 connected thereto.

[0116] The main side controller 1115 can also be configured to actuate the main switching device 101a to an off state (so as to substantially prevent or hinder the transmission of electrical power from the main power supply 102 to the first main winding 101b) when the signal indication of the current delivered to the first main winding 101b has reached a certain value (which value depends on the signal indication of the voltage of the main power supply 102 and the control signal C).

[0117] Therefore, the master-side controller 1115 may be configured to actuate the master switching device 101a to have a switching frequency (ie, a frequency of switching between the on state and the off state) that varies with time.

[0118] The primary side controller 1115 may actuate the primary switching device 101a so that the current flowing through the first primary winding 101b may generally have an envelope that follows the voltage (or rectified primary power supply voltage) of the primary power supply 102. Within the envelope, the current flowing through the first primary winding 101b may have pulses of varying frequency and / or duty cycle (which determines the amplitude of the current), and the frequency and / or duty cycle is controlled by actuation of the primary switching device 101a. Figure 8 A graphical representation of the current delivered to the first main winding 101 b is shown, and the envelope of this current is shown. Fig. 9 and Fig.10 Pulses of current forming part of this envelope are shown at different times.

[0119] Accordingly, during the initial time period, the frequency of actuation of the main switching device 101a (and thus the current in the first main winding 101b) may be relatively high (see, for example, Fig. 9 ) (and / or the duty cycle may be relatively low), the frequency of actuation decreases as the amplitude of the current envelope decreases (see again for example Fig. 9 ) and then increases again (and / or the duty cycle decreases), the frequency of actuation increases with the amplitude of the current envelope (see, for example, Fig.10 ) decreases (and / or the duty cycle increases). Accordingly, the frequency and / or duty cycle of the actuation of the main switching device varies with time, and at any given time the frequency and / or duty cycle depends on the supply voltage V at that time. ac The amplitude.

[0120] Such operation of the master-side controller 1115 and the master switching device 101a helps ensure an improved power factor, which may be 0.9 or above.

[0121] In some embodiments, using e.g. Figure 7The circuit depicted in can implement the main side controller 1115. In this embodiment, the main side controller 1115 includes a variable gain amplifier 1115a, which is configured to receive a signal representative of the voltage of the main power supply 102 and is configured to reduce or amplify the signal using the control signal C. The output from the variable gain amplifier 1115a is passed to the first comparator 1115b of the main side controller 1115 (e.g., passed to its non-inverting input). The signal representative of the current delivered to the first main winding 101b can be passed to the inverting input of the first comparator 1115b. The output of the first inverter 1115b can be connected to the reset input of the set-reset flip-flop 1115c of the main side controller 1115. The bias voltage (or a signal representing the bias voltage) can be connected to the inverting input of the second comparator 1115d of the main side controller 1115. The non-inverting input of the second comparator 1115d can be connected to ground. The output of the second comparator 1115d may be connected to the set input of the set-reset flip-flop 1115c, and the output of the set-reset flip-flop 1115c may be connected to the master switching device 101a to control actuation thereof.

[0122] In some embodiments, the main switching device 101a is a transistor device, such as a power MOSFET, and in such embodiments, the output of the set-reset flip-flop 1115c may be connected to the gate of the MOSFET forming the main switching device 101a.

[0123] In some embodiments, the flyback transformer 101 is a gapped ferrite core flyback type, which may have four interleaved windings - to reduce leakage inductance. The flyback transformer 101 may, for example, be a high frequency transformer 101 configured to operate at up to 150W per core.

[0124] The first bias circuit 101 e may include one or more fast rectifier diodes to provide electrical power to the main controller subsystem 110 .

[0125] The frequency of operation of the flyback transformer 101 (eg, the switching frequency of the main switching device 101a) may vary between approximately 40 KHz and 200 KHz.

[0126] As will be appreciated, many conventional battery charging systems 100 use Schottky rectifier diodes in the output rectifier circuit 106. However, in some embodiments of the present invention, the use of synchronous rectifiers eliminates the need for such Schottky rectifier diodes - which can reduce cost, improve efficiency, eliminate the need for heat sinks, and reduce the physical space required for the circuit.

[0127] The controller subsystem 110 may be configured such that the current delivered to the terminals 107 of the average battery charging system 100 (and to the battery 1) is approximately 16 A. The controller subsystem 110 may be configured such that the current delivered to the terminals 107 of the battery charging system 100 (and to the battery 1) varies between 0 A and 30 A.

[0128] Controller subsystem 110 may be configured such that isolation switch 109 is actuated to its off state when a signal indicative of a voltage across terminals 107 of battery charging system 100 reaches or exceeds approximately 4V and / or when battery 1 is disconnected from terminals 107 .

[0129] In some embodiments, the secondary-side controller 1116 functions as a master controller that is configured to control the operation of the primary-side controller 1115—thus, the primary-side controller 1115 may be referred to as a slave controller. In such embodiments, the secondary-side controller 1116 may be configured to communicate with one or more systems external to the battery charging system 100 to control one or more aspects of the operation of the battery charging system 100.

[0130] The secondary side controller 1116 (as well as the primary controller 1116) can be configured to change the characteristics of the charging current during charging according to the determined characteristics of the battery. The determined characteristics of the battery and the characteristics of the charging current are given below.

[0131] In some embodiments, the control subsystem 110 is configured to monitor the electrical impedance of the battery 1. Subsequently, the charging system 100 may deliver a charging current to the battery 1 based at least in part on the electrical impedance of the battery 1 to charge the battery 1. Therefore, the characteristics of the charging current may depend on the determined electrical impedance of the battery 1.

[0132] As discussed above, in some embodiments, the secondary side controller 1116 may be configured to determine an operating mode for the battery charging system 100. Accordingly, the secondary side controller 1116 may be configured to monitor the electrical impedance of the battery 1 and use this information to control an aspect of the current delivered by the charging system 100 to the battery 1.

[0133] More specifically, in some embodiments, the secondary-side controller 1116 is configured to receive a signal I representing a current delivered to or returned from at least one terminal 107 of the battery charging system 100. bat(e.g., output from the battery terminal current sensor circuit 1114). Alternatively or additionally, the secondary-side controller 1116 is configured to receive a signal representing a change in current delivered to or returned from at least one terminal 107 of the battery charging system 100 during a portion of the charging current waveform delivery. An example of such a change in current can be the difference in charging current between a peak (maximum) and a valley (minimum). In an embodiment where the minimum current is zero amperes, the difference is equal to the maximum current measured.

[0134] The current I of the battery 1 connected to the terminal 107 according to the current waveform described herein bat The delivery of causes the voltage across the terminals 12, 13 of the battery 1 to increase due to the electrical impedance Z of the battery. bat In some examples of using the present invention, this can be Fig.11a and Fig.11b It can be seen that among them Fig.11a I bat ,and Fig.11b The voltage V across the terminals 12, 13 of the battery 1 is shown bat .

[0135] Thus, the secondary-side controller 1116 may be configured to use a signal representing the voltage across the terminals 107 of the battery charging system 100 (e.g., the output from the battery terminal voltage sensor circuit 1113) to determine the electrical impedance Z of the battery 1 connected to those terminals 107 (via its terminals 12, 13). bat .

[0136] More specifically, the secondary side controller 1116 may be configured to receive a signal representing a voltage across the terminals 107 of the battery charging system 100 over a first time period. The secondary side controller 1116 may be configured to determine a DC component of the signal (and therefore the voltage it represents). This may be achieved, for example, by determining an average value of the signal over the first time period and taking that as the DC component. The DC component is then subtracted from the signal to generate a voltage ripple signal ΔV representing a ripple voltage across the terminals 107 of the battery charging system 100 (and therefore across the terminals 12, 13 of the connected battery 1). bat The signal may be amplified and / or filtered to improve the signal representation of the ripple voltage. For example, the frequency of the ripple voltage is expected to be substantially equal to the frequency of the current delivered to or returned from the at least one terminal 107; therefore, one or more filters may be used to reduce frequency components of the ripple voltage signal above and / or below this frequency. In e.g. Fig.11c An example of a voltage ripple signal can be seen in .

[0137] The secondary side controller 1116 may be configured to represent the ripple voltage ΔV bat The signal ΔI is divided by the current ΔI transmitted to or returned from the at least one terminal 107 of the battery charging system 100. bat The changing signal thus obtains the electrical impedance of the battery 1 connected to those terminals 107.

[0138] In some embodiments, the current I delivered to or returned from the terminal 107 of the battery charging system 100 is bat can vary from 0A to the peak (maximum) current (before returning to 0A following the waveforms described in this article). bat The signal representation can be substantially equal to ΔI bat However, in some embodiments, I bat varies between a non-zero lower value and the peak current. Thus, in some embodiments, ΔI bat Not equal to I bat In such an embodiment, the secondary-side controller 1116 may be configured to determine the current I delivered to or received from the terminal 107. bat The signal representation is used to determine ΔI bat .

[0139] Fig.11a and Fig.11b The current and voltage at the battery terminals are shown as charging progresses. As the battery undergoes charging, the baseline voltage, superimposed with the ripple caused by the oscillating input current, increases steadily. To determine the battery impedance at a given point in time, only the ripple in the voltage is relevant and is evaluated separately from the increasing voltage baseline. Fig.11c A graphical representation of a voltage ripple is shown. To determine the amplitude of the ripple, for example a linear baseline voltage is fitted to the voltage curve and the deviation from the baseline is evaluated. This deviation results in a flat ripple. Subsequently, the flat ripple can be evaluated to determine the effect of the impedance on the voltage. The amplitude of the ripple voltage divided by the amplitude of the battery current gives the amplitude of the impedance. In another example, the average value of the voltage signal in one cycle is determined and this value is subtracted from the voltage signal; this again gives a ripple that is different from the baseline voltage. In the case of non-oscillating steady charging, the battery voltage increases steadily and no signal indicative of the impedance of the battery is available.

[0140] When the battery is being charged, the internal impedance of the battery and the internal cell voltage of the battery are usually not directly measurable. By dividing the voltage change with the current change, the internal cell impedance of the battery can be determined without knowing the internal cell voltage.

[0141] The secondary-side controller 1116 may be configured to periodically use the above process to determine the electrical impedance of the battery 1. In some embodiments, the secondary-side controller 1116 is configured to determine the electrical impedance of the battery 1 at a frequency that is substantially equal to the frequency of the signal representing the current delivered to or received from the terminal 107 of the battery charging system 100. In other words, the secondary-side controller 1116 may be configured to determine the electrical impedance of the primary battery 1 for each peak in the signal representing the current delivered to or received from the terminal 107 of the battery charging system 100, thereby effectively determining the electrical impedance of the battery 1 substantially continuously.

[0142] In some embodiments, the secondary-side controller 1116 may be configured to determine the electrical impedance of the battery 1 at a frequency that is substantially at least equal to the frequency of the signal representing the current delivered to or received from the terminal 107 of the battery charging system 100, thereby effectively determining the electrical impedance of the battery 1 substantially continuously. In such embodiments, the secondary-side controller 1116 may be configured to use a signal representing I bat The impedance of the battery 1 is determined by the peak-to-peak value change of the rising or falling signal.

[0143] In some embodiments, the secondary-side controller 1116 is configured to determine the impedance of the battery 1 at a frequency between about 100 Hz and 120 Hz, or at a frequency of about 120 Hz, or between 100 Hz and 200 Hz, or at a frequency of about 200 Hz, or between 120 Hz and 240 Hz, or at about 240 Hz, or any combination of the upper and lower boundaries of these ranges.

[0144] As will be appreciated, in some embodiments, when the determination of the impedance of the battery 1 in absolute terms is periodic, the determination is substantially continuous with respect to the frequency at which the secondary-side controller 1115 is configurable to cause I to change during a charging cycle. bat It will be appreciated that this remains valid if the impedance of the battery is not determined at exactly the frequency of the charging current waveform, but rather is determined at a frequency substantially relative to the frequency at which the secondary side controller 1115 is configured to cause I bat The frequency of the changes is continuous.

[0145] The current change and voltage change supplied to the battery 1 can be measured in the rising current portion of the current waveform. The minimum value of the current waveform can provide a convenient starting point to measure these characteristic forms. Alternatively or additionally, these changes can be measured in the falling current portion of the current waveform. When these characteristics are measured in both the rising and falling portions of the waveform, the secondary side controller 1115 can compare the results to determine whether an error occurs.

[0146] The control subsystem 110 may include a lookup table 1119. The lookup table 1119 may be stored on a computer readable medium 1119a of the control subsystem 110, or on a component accessed by the control subsystem 110. In some embodiments, the lookup table 1119 may be accessible to the secondary-side controller 1116.

[0147] Lookup table 1119 may store information associated with battery condition and / or state of charge to a charging mode. Accordingly, control subsystem 110 (e.g., secondary-side controller 1116) may use lookup table 1119 to determine an appropriate charging mode for battery 1 based on determined characteristics of battery 1 that is available to control subsystem 110.

[0148] The determined characteristics available to the control subsystem 110 (eg, to the secondary-side controller 1116) may include one or more of the following: bat 、V bat , ΔI bat , ΔV bat , and Z bat The information may also include the temperature T of the battery 1 bat In embodiments where the battery includes multiple cells, these characteristics for each cell may be used to control the subsystem in addition to or alternatively to the full battery characteristics.

[0149] In some embodiments, the information available to the control subsystem 110 (e.g., the secondary-side controller 1116) may include an identification of the battery 1—which may be determined, for example, by a battery identification code communicated to the control subsystem 110. The battery identification code may be, for example, an identification code that is unique or substantially unique to the battery 1 (e.g., a serial number), or may be a more general identification code that is unique or substantially unique to the manufacturer of the battery 1 or the model of the battery 1 or the configuration of the battery 1. The identification may be communicated to the control subsystem 110 (e.g., the secondary-side controller 116) by transmitting one or more signals from the battery 1 to the control subsystem 110 (e.g., via a communication link therebetween), or may be manually entered by a user.

[0150] The control subsystem 110 may also include a time measurement device, such as a clock. This may be used to measure the time that the battery 1 has been charged. By integrating the time that the charging current has been charging the battery 1, the total charge delivered to the battery may be determined. This integration may be performed digitally, for example. The total charge may be used to determine the state of charge of the battery 1.

[0151] The control subsystem 110 (e.g., the secondary-side controller 1116) may use the determination characteristics available to it (see above) to determine the current state of charge and / or state of health of the battery 1. As will be appreciated, the state of health of the battery 1 is a measure of the proper operation of the battery 1 (e.g., its ability to hold a charge). The current state of charge of the battery 1 may additionally be referred to as the current state of the battery 1 or the battery state of charge (SOC). These may be used to determine whether and how the charging current supplied to the battery 1 should be changed.

[0152] In some embodiments, the battery impedance is not determined, instead, the current change ΔI can be used directly bat and voltage change ΔV bat The current state of charge and / or state of health of the battery is determined, thereby determining whether and how the charging current should be changed.

[0153] In some embodiments, the lookup table 1119 provides a duty cycle and / or frequency for operation of the primary switching device 101a based on determined characteristics available to the control subsystem 110 (e.g., to the secondary controller 1116)—see above. In some embodiments, the lookup table 1119 is used to provide the desired I2C value for the state and / or health status of the battery 1. bat The query table 1119 may, for example, provide C (see above). Other characteristics of the battery charging current may also be provided in the query table, such as: current average, current maximum, current amplitude, duty cycle, and / or charging mode.

[0154] For example, a fully discharged battery 1 will have a relatively high electrical impedance, and therefore the lookup table 1119 may specify a relatively low I bat To avoid the risk of overheating and / or otherwise damaging the battery 1. Similarly, if the impedance is low, then the lookup table 1119 may specify a relatively high I bat .

[0155] The above description of the operation of the control subsystem 110 refers to the monitoring of the electrical impedance of the battery 1. As mentioned above, this will be interpreted as monitoring the electrical impedance of one or more cells 11 of the battery 1.

[0156] In some embodiments, the battery 1 includes a plurality of battery cells 11. In such embodiments, the impedance of each battery cell 11 may be determined (the above operation is performed for each battery cell 11 in the battery 1), and the charging mode may be determined based on the information determined for more than one battery cell 11 of the battery 1.

[0157] Embodiments of the invention have been described with reference to flyback transformer 101, but it will be appreciated that these and other embodiments may be implemented using converters having different topologies.Such converters are capable of high frequency operation (eg, in the range of 40 to 200 kHz).

[0158] A single battery charging system 100 has been described herein. However, it should be understood that a plurality of such battery charging systems 100 may be provided in parallel connection with each other and configured to supply current (I bat ). In such an arrangement, all battery charging systems 100 may be controlled by a common control subsystem 110. In some embodiments, such an arrangement may include a primary-side controller 1115 for each battery charging system 100, but may also include a single secondary-side controller 1116 configured to control the operation of all primary-side controllers 1115.

[0159] As will be appreciated, the embodiment supplies a current I having a waveform bat For the purpose of determining the electrical impedance of the battery, this waveform allows the electrical impedance of the battery 1 to be frequently determined without requiring the I bat any additional operation. In other words, the current used to charge the battery and form the main current for charging the battery 1 (i.e. the charging current) can be used to determine the electrical impedance of the battery. This is different from, for example, a current of relatively small amplitude, which is deliberately added to the constant or substantially constant main charging current to determine the electrical impedance of the battery. In such a hypothetical arrangement, the maximum frequency at which the electrical impedance of the battery 1 can be determined is much lower than the frequency in some embodiments of the present invention. In addition, the small amplitude current does not make a substantial contribution to the charging of the battery 1 (for example, only at the level of a few hundred milliamperes). Therefore, such a low amplitude current does not form part of the main charging current (compared to the current I bat In some embodiments of the invention, the variation in current is of an order of magnitude that affects the charging of the battery 1 and therefore forms part of the main charging current.

[0160] In some embodiments, the control subsystem 110 is configured to communicate with a remote server 210. The communication may be via a communication network—e.g., a local area network and / or a wide area network, and may include the Internet. The remote server 210 may, for example, store a query table 1119 or a portion thereof. In some embodiments, the remote server 210 includes a computer-readable medium 1119a. In some embodiments, the control subsystem 110 is configured to at least partially download the query table 1119 (e.g., to a local computer-readable medium 1119a). The control subsystem 110 (e.g., the secondary-side controller 1116) may be configured to request all or part of the query table 1119 from the remote server 210, and may be able to upload information about the battery 1 to the remote server 210.

[0161] The remote server 210 may be configured to maintain the lookup table 1119, and this may include receiving information about the battery 1 or type of battery 1 from the control subsystem 110, and then updating the lookup table 1119 based on the information. This may include updating the lookup table about the particular battery 1 and / or the type of battery 1 (e.g., based on the configuration of the battery 1, the make and / or model of the battery 1). The remote server 210 may be configured to collate the received information about the plurality of batteries 1 to modify the lookup table 1119 or portions thereof, thereby optimizing one or more aspects of the operation of the battery charging system 100 using the lookup table 1119—this may include ensuring the maximum amount of charge stored in the battery 1, ensuring the maximum life (i.e., number of charging cycles) of the battery 1, and / or ensuring that the battery charging system 100 uses electrical power most efficiently.

[0162] Fig.12 A step-by-step process for charging a battery is shown. The process attempts to provide high power efficiency as well as safely minimize battery charging time.

[0163] 1. Initialization

[0164] ●Identify battery type (total battery voltage Vbat and total battery capacity Cbat)

[0165] ●View the database and evaluate the battery's state of charge (SOC)

[0166] ● Check the database and determine the maximum allowable battery cell voltage V cell_max

[0167] ●Measure all battery cell voltages Vcell_open

[0168] ● Check the database and determine the initial battery charging current Ibat(av)_initial

[0169] 2. Start charging

[0170] ●Start the clock

[0171] ● Start charging using rectified sinusoidal current waveform and Ibat(av)_initial

[0172] 3. Measurement

[0173] ●Measure the voltage in each individual battery cell and the battery current at the bottom of the charging current waveform

[0174] ●Store the measured values ​​Vcell_bottom and Ibat_bottom

[0175] ●Measure the voltage in each individual battery cell and the battery current at the top of the charging current waveform

[0176] ●Store the measured values ​​Vcell_top and Ibat_top

[0177] 4. Calculation

[0178] ● Calculate the difference ΔVcell = Vcelltop - Vcellbottom

[0179] ● Calculate the difference ΔIbat=Ibat_top-Ibat_bottom

[0180] ● Calculate the impedance of each individual battery cell Zcell = ΔVcell / ΔIbat

[0181] 5. Fully charge

[0182] ● Assign Z_weak_cell to the weakest cell (with the highest impedance)

[0183] ● Check the database according to Z_weak_cell and determine the maximum safe battery charging current Ibat_max_safe

[0184] ● Continuously charge the battery, continuously measure and calculate the above items, fully utilize the charger potential and safely minimize the battery charging time

[0185] ●Continuously measure the temperature Tcell of each individual battery cell

[0186] 6. Stop

[0187] ●Continuously check the database and modify Vcell_max and lbat_max_safe according to the hottest battery cell Tcell_max

[0188] ● Stop charging when the voltage of the first battery cell reaches Vcell_max

[0189] 7. Management

[0190] ● Calculate the time-ampere integral and specify the total charge received by the battery

[0191] ●Display battery SOC

[0192] ●Store information in a database

[0193] Storing the determined characteristics of the battery in a database (which may reside, for example, in a lookup table stored in a controller / control unit memory) can allow the battery charging system to associate these characteristics for future use in charging other batteries and / or recharging the same battery.

[0194] The determined characteristics can be stored, for example, with the identification data, associating the characteristics with that particular battery. When charging that particular battery in the future, these characteristics can be used to determine the battery state and / or required charging current characteristics.

[0195] Alternatively or additionally, the stored determined characteristics may be aggregated into a data set from which battery characteristic associations may be determined for a class and / or type of battery. These associations may be used when charging batteries of the same type and / or class to determine / assess the battery state and / or required charging current characteristics.

[0196] By storing the determined characteristics and using them to assist in future battery charging events, the system can be said to be self-learning.

[0197] Fig.13 A schematic example of a single battery control unit in use is shown. The secondary controller (main CPU) drives a current source (e.g., a flyback converter) to use a charging current (I cell ) charges the battery at a frequency of about twice the line frequency (e.g., a current having an oscillating DC waveform such as a rectified sinusoidal waveform). This direct (i.e., always positive) but time-varying current can have a minimum value of less than about 0.5 amperes, preferably less than about 0.1 amperes, more preferably about 0 amperes, and a maximum value of about 30 amperes.

[0198] Since the battery internal impedance Z cell , this “ripple” battery charging current produces a ripple battery cell voltage ΔV cell . Battery internal impedance Z cell can depend on, for example, the battery cell state of charge, the battery cell temperature T cell , battery cell voltage V cell and battery cell history status.

[0199] The ripple battery voltage ΔV cellcan be filtered and amplified and used to transfer battery status information to the secondary controller. This can be combined with I cell (and / or current change ΔI cell , if the minimum value of the charging current is not zero) to calculate Z cell The controller uses this information along with other determined characteristics such as the battery cell temperature T cell and the battery cell voltage V cell The appropriate charging mode is selected from the lookup table. The secondary controller can then change the characteristics of the charging current according to the battery cell status by, for example, changing the duty cycle of the primary controller.

[0200] For example, when a battery is fully discharged, the internal impedance of the battery may increase. The secondary controller uses the ripple charge current and the voltage ripple induced by the current to calculate the battery impedance. The secondary controller then determines the required charging mode from the lookup table. To avoid overheating and / or damage to the battery cells, the lookup table indicates that a different charging mode is required. The secondary controller sends another charging mode with a reduced duty cycle to the primary controller, thereby reducing the battery charging current.

[0201] The battery cells themselves effectively "decide" the best mode for charging at each moment.

[0202] Fig.14 1 shows a schematic example of a multi-cell battery control unit in use. In this example, the battery includes n battery cells connected in parallel and / or in series. Fig.13 The example described above functions in a similar manner, except that the voltage V across each battery cell is measured. cell(i) , the change in voltage across each battery cell ΔV cell(i) , and the temperature T of each battery cell cell(i) The current through each battery cell I cell The measurement of all battery cells and the current I cell (and / or current change ΔI cell ) are transmitted to the secondary controller together. The voltage change ΔV across the battery cell can be divided by the current (or current change) cell(i) Calculate the battery internal impedance Z of each battery cell cell(i) .

[0203] The controller uses this information to select the most appropriate battery charging mode from a lookup table and to change the duty cycle of the main controller taking into account the conditions of all battery cells.

[0204] In some embodiments of the invention, the battery is charged using a rectified sinusoidal current, and the voltage ripple properties of this charging method are used (along with the current) to measure the internal impedance of the battery cells. This allows for substantially continuous monitoring of the internal impedance of the battery cells, allowing the controller to continuously monitor the battery health by calculating the internal impedance and to change the charging mode on the fly.

[0205] In some embodiments, a main controller is used to control the battery charging current. The main controller is composed of a programmable chip device.

[0206] Its sensing:

[0207] ● Sense grid input voltage via high voltage divider

[0208] ● Sensing the flyback main current by connecting the main current shunt at the main MOSFET source

[0209] ●Control signal from the main controller via isolation optocoupler

[0210] ●Bias voltage from flyback transformer

[0211] The arrangement and function of the circuit are as follows:

[0212] 1. The grid input voltage after the high voltage divider is amplified or attenuated by the control signal through the variable gain amplifier inside the programmable chip.

[0213] 2. The output of this amplifier is fed to the non-inverting input of a comparator inside the programmable chip.

[0214] 3. The voltage from the main current shunt (connected to the main MOSFET source) is connected to the inverting input of the comparator.

[0215] 4. The output from this comparator is the reset signal to the set-reset flip-flop inside the programmable chip.

[0216] 5. The output from the bias winding of the flyback transformer is connected to the inverting input of another comparator inside the programmable chip.

[0217] 6. The non-inverting input of the comparator is grounded.

[0218] 7. The output from this comparator is the set signal to the flip-flop.

[0219] 8. The output from the flip-flop is connected to the gate of the main power MOSFET.

[0220] So: the gate signal to the main power MOSFET can be:

[0221] ● starts when all the energy stored in the flyback transformer has been transferred to the battery; and

[0222] ●Terminated when the voltage of the main current shunt (connected to the main MOSFET source) has reached the value of the input voltage, divided down (by the high voltage divider), and amplified or attenuated by the control signal (from the main controller through the isolation optocoupler).

[0223] The grid current can be in phase with the grid voltage (PFC converter) in this way. The control signals are generated by the main controller (which is also another programmable chip) from: grid input voltage, main peak current, battery voltage, battery current, battery temperature.

[0224] In some embodiments, a multi-phase charger 300 may be provided by connecting multiple battery charging systems 100 in parallel between a multi-phase input 301 and an output 302. Thus, in some such embodiments, a multi-phase charger 300 may include multiple battery charging systems 100 (e.g., as described herein). A battery charging system 100 may be provided for each phase of the multi-phase input 301. Accordingly, in a three-phase system having a multi-phase input 301 with three phases, three battery charging systems 100 may be provided in the multi-phase charger 300.

[0225] Each battery charging system 100 can be electrically connected between a single phase of the multi-phase input 301 and the output 302. In some embodiments, the output 302 is common to all battery charging systems 100 of the multi-phase input 301. Accordingly, the terminals 107 of each battery charging system 100 can be connected to provide a common output 302 (which can have a common ground terminal and a common active terminal). Therefore, in some embodiments, as described herein, the combined output of the battery charging systems 100 from the multi-phase charger 300 can provide a charging current. Therefore, the battery charging systems 100 of the multi-phase charger 300 can be controlled accordingly to achieve this effect. In this way, the control subsystem 110 of each battery charging system 100 (if provided) can be communicatively coupled. In some embodiments, the multi-phase input 301 provides approximately 200 and approximately 800V RMS The output 301 can be between about 100 and about 800V DC between.

[0226] When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. These terms will not be interpreted as excluding the presence of other features, steps or components.

[0227] The features disclosed in the foregoing description, or claims, or drawings are represented in their specific forms, or in terms of devices for performing the disclosed functions, or appropriate methods or processes for obtaining the disclosed results, and can be used independently or in any combination of these features to implement the present invention in its diverse forms.

Claims

1. A battery charger for providing a charging current to a battery, the battery charger comprising a switching mode power converter and a controller adapted to vary a switching frequency so as to provide a current having a desired waveform.

2. The battery charger of claim 1, wherein: The battery charger is configured to be connected to an AC power source having a sinusoidal waveform; The switched mode power converter is a flyback converter; The controller is adapted to change the switching frequency of the flyback converter at least 100 times during each voltage oscillation of the AC power source; The desired waveform is a squared sine wave, which is the square of the waveform of the AC power source.

3. A battery charger according to any preceding claim, further comprising a voltage sensor adapted to provide an indication of the voltage of the AC power source to the controller.

4. The battery charger of claim 3, wherein the voltage sensor is adapted to sense the voltage at least as frequently as the controller changes the switching frequency.

5. A battery charger according to any one of the preceding claims, wherein the switched mode power converter is adapted to operate in critical conduction mode.

6. A three-phase battery charger comprising three battery chargers according to any one of the preceding claims, wherein each of the three battery chargers is configured to be connected to a single phase of a three-phase input and to a common output.

7. The three-phase battery charger of claim 6, wherein each of the three battery chargers is connected to a respective single phase of the three-phase input.

8. The three-phase battery charger of claim 7, wherein the charging current provided to the battery is a combined output of three square sine wave currents provided by the three battery chargers.

9. A method for charging a battery, comprising: converting an AC power source into a charging current to a battery using a switching mode power converter; The switching frequency is changed according to the desired waveform.

10. The method according to claim 9, wherein: The AC power source has a sinusoidal waveform; The switched mode power converter is a flyback converter; During each voltage oscillation of the AC power source, the switching frequency of the flyback converter changes at least 100 times; and The desired waveform is a squared sine wave, which is the square of the waveform of the AC power source.

11. The method according to claim 9 or 10, wherein: Converting the AC power source into a charging current to the battery includes converting three alternating polarity outputs of a three-phase AC power source into corresponding charging currents, each alternating polarity output being a respective single phase of the three-phase AC power source; The method also includes generating a combined output from the respective charging currents and providing the combined output to the battery.

12. A method for monitoring the internal impedance of a battery during charging, the method comprising the steps of: providing a time-varying current to the battery; The current change is measured essentially continuously; The corresponding voltage changes are measured substantially continuously; as well as The internal impedance of the battery is determined from the current change and the corresponding voltage change.

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