Battery charging system and method

Abstract

1. A method of charging a battery, the method comprising the steps of: supplying a charging current to the battery; substantially continuously determining a characteristic of the battery during charging; and varying a characteristic of the charging current in dependence on the determined battery characteristic. [Selected Figure] Figure 2

Description

[Technical field]

[0001] SUMMARY OF THE DISCLOSURE Embodiments of the present invention relate to methods and systems for use in charging batteries. [Background technology]

[0002] Traditionally, a basic battery charging system for recharging a battery (such as a lithium-ion battery) can provide a constant or pulsed power to the terminals of a rechargeable battery. Typically, a charging cycle for a lithium-ion battery can include an initial constant current operation in which the battery charging system is controlled to provide a substantially constant current to the battery during a first charging cycle. Once the voltage across the terminals of the battery reaches a predetermined level, the traditional battery charging system is typically controlled to provide a constant voltage or power across these terminals during this second charging cycle (i.e., a constant voltage charging cycle operation). Finally, the charging cycle can be terminated when the battery is substantially fully charged, or a maintenance or standby operation can be maintained to provide power to the battery from time to time to compensate for self-discharge. Summary of the Invention [Problem to be solved by the invention]

[0003] Most conventional chargers switch from a constant current charge cycle to a constant voltage or power charge cycle when the battery is 60% to 80% of full charge.

[0004] Without wishing to be bound by any particular theory, it is believed that ions migrating from the positive electrode of a battery to the negative electrode of the same battery during recharging tend to pile up before intercalating at or near the boundary of the negative electrode facing the positive electrode (i.e., at the solid-electrolyte interphase (SEI) layer). This pile-up is believed to slow down the intercalation of ions at the negative electrode, increasing the electrical resistance of the battery.

[0005] Additionally, conventional charging typically causes the SEI layer to grow (i.e., thicken) until it eventually becomes thick enough after multiple charging cycles, causing a loss in the battery's charge capacity and ultimately battery failure.

[0006] Conventional battery charging systems use relatively complex electronic circuits to achieve the constant voltage or power and constant current operation required for a conventional charging cycle, and require additional electronic circuits to provide power factor correction. These complex electronic circuits use numerous and relatively expensive components.

[0007] It would therefore be desirable to alleviate one or more of the problems associated with conventional battery charging cycles and systems. [Means for solving the problem]

[0008] Accordingly, one aspect of the present invention provides a method of charging a battery, the method comprising the steps of: providing a charging current to the battery; determining a characteristic of the battery substantially continuously during charging; and varying a characteristic of the charging current depending on the determined battery characteristic. By measuring the battery characteristic substantially continuously, the charging current provided to the battery can be varied in substantially real time to further provide an optimal battery charging current, allowing safe minimization of battery charging time. In general, a number of battery characteristics can be determined to provide information about the battery state that can aid in determining a required charging current characteristic. Optionally, the charging current has an oscillating DC waveform. Optionally, the charging current has a pulsed DC waveform. Using such a time-varying DC charging current, characteristics such as the battery's internal impedance can be more easily measured without interrupting the charging process. For efficiency, at least a portion of the waveform has a substantially rectified sine wave shape. Optionally, at least a portion of the waveform has a substantially squared sine wave shape. These waveforms can be simply generated while providing advantageous battery charging with a high power factor. Optionally, the waveform has a minimum occurring at a current value of less than about 0.5 amps, preferably less than about 0.1 amps, and more preferably about zero amps. Having a waveform with a minimum of about 0 amps can reduce the effect of charging and / or internal potential build-up on the battery characteristics. Optionally, the determined characteristic is determined from the current waveform. The current waveform is relatively easy to measure and can be used to determine further battery characteristics. Optionally, the determined characteristic is determined at least at the frequency of the waveform. By determining the characteristic at least at the frequency of the waveform, substantially continuous monitoring of the battery characteristics is performed, with the characteristic being 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, the determined characteristic is determined during the rising portion of the waveform. For accuracy, the determined characteristic is determined from measurements starting from the minimum of the waveform.The minimum of the waveform may provide a favorable starting point for the measurement, allowing for greater variation in the measured characteristic, and therefore reducing slight 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 the rising portion of the waveform allows the characteristic to be determined from a different starting point, which may aid in detecting or reducing errors. Optionally, the waveform is provided at a frequency that is approximately an integer multiple of the frequency of the voltage source. Providing a waveform at an integer multiple of the utility voltage source may provide a higher power factor, improving charging efficiency. Optionally, the waveform is provided at a frequency that is approximately twice the frequency of the utility voltage source, which may provide more efficient charging. Optionally, the waveform is fixed to the frequency of the utility voltage source. Providing a waveform fixed to the frequency of the utility voltage source means that the minimum of the current waveform and the zero voltage waveform occur substantially simultaneously, which may provide a higher power factor. Optionally, the determined characteristic of the battery includes the internal impedance of the battery. This internal impedance may be used to indicate the condition of the battery. Optionally, the internal impedance of the battery is determined from the measured change in current and the measured change in voltage in the battery, allowing the internal impedance to be measured indirectly. Optionally, the determined battery characteristics include the internal impedance of the cells. Optionally, the determined battery characteristics include the maximum cell impedance. If the battery includes multiple cells, the cell impedance may vary from cell to cell. The cell with the highest impedance determines the limit of a safe charging current. Optionally, the determined battery characteristics include the battery temperature. Optionally, the determined battery characteristics include the cell temperature. The temperature of the battery and / or the cells may indicate information about the state of the battery and / or the cells, such as whether the currently used charging current is safe. Optionally, the various characteristics include the current average value, the current maximum value, the current amplitude, the duty cycle and / or the charging mode. Varying these current characteristics may vary the power supplied to the battery to minimize the charging time of the battery while keeping it within safe limits.Optionally, the method further comprises determining the amount of charge received by the battery by measuring the time the battery has been charging. This allows the state of charge of the battery to be monitored. Optionally, the battery is a lithium ion battery. Lithium ion batteries are used in a wide range of applications. According to another aspect of the invention, there is provided a battery charging system comprising a current source suitable for supplying a charging current to the battery and a control unit, the control unit configured to determine a characteristic of the battery substantially continuously during charging and to vary a characteristic of the charging current depending on the determined battery characteristic. The control unit varies the charging current based on the substantially continuously determined battery characteristic to provide a charging current having characteristics that are efficient for charging and at the same time within safety limits so as not to damage the battery. Optionally, the charging current is supplied as an oscillating DC waveform. Optionally, the charging current is supplied as a pulsed DC waveform. Using such a time-varying DC charging current, characteristics such as the internal impedance of the battery can be more easily measured without interrupting the charging process. Optionally, at least a portion of the waveform has a substantially rectified sine wave shape. Optionally, at least a portion of the waveform has a substantially squared sine wave shape. These waveforms are simple to generate while still providing advantageous battery charging. Optionally, the waveforms have a minimum occurring at a current value of less than about 0.5 amps, preferably less than about 0.1 amps, and more preferably about zero amps. This reduces the effect of charging and / or internal potential build-up on the battery characteristics. For efficiency, the determined characteristics are determined from the current waveform. The current waveform is relatively easy to measure and can be used to determine further battery characteristics. For safety, one or more of the determined characteristics are determined at least at the frequency of the waveform. Optionally, one or more of the determined characteristics are determined at least twice the frequency of the waveform. By determining the characteristics at least at the frequency of the waveform, substantially continuous monitoring of the battery characteristics is performed, with the characteristics being determined at least once per waveform cycle.This allows the charging current to be updated frequently or substantially continuously to prevent any overloading of the battery. Optionally, the determined characteristic is determined during a rising portion of the waveform. For accuracy, the determined characteristic is determined from a measurement starting from a minimum of the waveform. The minimum of the waveform may provide an advantageous starting point for the measurement to increase the change in the measured characteristic and therefore reduce slight errors. Optionally, the determined characteristic is determined during a falling portion of the waveform. Measuring the characteristic during the falling portion of the waveform in addition to the rising portion of the waveform allows the characteristic to be determined from a different starting point, which may help detect or reduce errors. For ease of generation, the waveform is provided at a frequency that is about an integer multiple of the voltage source. Optionally, the waveform is provided at a frequency that is about twice the frequency of the voltage source. Optionally, the waveform is provided at a frequency that is fixed to the voltage source. This provides a high power factor for increased efficiency. Optionally, the current source includes a flyback converter. Using a flyback converter to generate the current waveform. The requirement for a bulk capacitor to generate the charging current may be reduced or eliminated. Optionally, the system further comprises voltage measuring means and / or current measuring means. Determining the current and voltage or current and voltage changes allows for determining a characteristic of the battery without interrupting the supply of current to the battery. Optionally, the one or more determined battery characteristics include an internal impedance of the battery to indicate the state of the battery. This internal impedance may be used to indicate the state of the battery. Optionally, the internal impedance of the battery is determined from a measured change in current and a measured change in voltage in the battery. This allows for an indirect determination of the internal impedance of the battery. Optionally, the determined battery characteristics include one or more internal impedances of the cells. Optionally, the determined battery characteristics include a maximum cell impedance. If the battery includes multiple cells, the cell impedance may vary from cell to cell. The cell with the highest impedance determines the limit of a safe charging current. Optionally, the determined battery characteristics include a battery temperature. The temperature of the battery and / or the cells may indicate information regarding the state of the battery. Optionally, the various characteristics include at least one of current average, current maximum, current amplitude, duty cycle and / or charging mode. Varying these current characteristics can vary the power delivered to the battery to minimize the charging time of the battery while keeping it within safety limits. Optionally, the system further comprises a clock configured to determine the amount of charge received by the battery by measuring the time the battery has been charging. This allows the state of charge of the battery to be monitored. To enable self-learning and updating, the control unit can be configured to store the plurality of determined battery characteristics in a database and / or look-up table.According to yet another aspect of the present invention, there is provided a method of monitoring the internal impedance of a battery during charging, comprising the steps of: supplying a time-varying current to the battery, measuring the change in current substantially continuously, measuring the corresponding change in voltage substantially continuously, and determining the internal impedance of the battery from the change in current and the corresponding change in 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 squared sine wave shape. These waveforms can be generated simply while still providing advantageous battery charging. Optionally, for accuracy, the waveform has a minimum occurring at a current value of less than about 0.5 amps, preferably less than about 0.1 amps, and more preferably about zero amps. This allows for less effect of electrostatic charge and / or internal potential build-up on the measurement of the current change and the corresponding voltage change. Optionally, the impedance is determined at least at the frequency of the waveform. This allows for a substantially continuous determination of the battery impedance. Optionally, the change in current and / or the change in voltage are measured during the rising portion of the waveform. For accuracy, the change in current and / or the change in voltage are measured starting from a minimum of the waveform. The minimum of the waveform may provide a favorable starting point for the measurement to allow a larger change in measured current and thus reduce slight errors. For flexibility, the change in current and / or the change in voltage are measured during the descending portion of the waveform. According to yet another aspect of the present invention, there is provided a battery charger adapted to supply a current having an oscillating waveform, the minimum of the waveform being 0 A or approximately 0 A. Optionally, the minimum of the waveform is less than 0.1 A, more preferably less than 0.01 A, more preferably less than 0.001 A. By providing a minimum of the waveform of 0 A or approximately 0 A, the build-up of static charge and / or internal potential within the battery may be reduced. Optionally, the peak-to-peak current is greater than 1 A, preferably between about 10 A and about 30 A. Supplying a large peak-to-peak current may increase the accuracy of the impedance measurement.For accuracy, at least 0.5 ms, preferably at least 1 ms, more preferably at least 5 ms, and more preferably at least 10 ms per oscillation period of the waveform are at or near 0 A. For accuracy, at least 0.5%, preferably at least 1%, more preferably at least 5%, and more preferably at least 10% of the periods per oscillation period of the waveform are at or near 0 A. Optionally, a plurality of battery charging systems are provided, each battery charging system configured to receive an input from a single phase of a polyphase input and generate a common output. According to yet another aspect of the invention, there is provided a method of charging a battery, comprising converting an AC power source into a charging current for a battery, the current having an oscillatory waveform, the minimum of the waveform being at or near 0 A. Optionally, the waveform is in accordance with one or more of the waveforms described above in relation to other aspects of the invention. According to another aspect, there is provided a battery charger for providing a charging current to a battery, the battery charger comprising a switch mode power converter and a controller adapted to vary a switching frequency and / or a duty cycle to provide a current of a desired waveform. By varying the switching frequency and / or duty cycle, the current delivered can be varied over time, thereby providing a current having a desired waveform. Charging a battery with a particular waveform can be useful for several reasons, including optimizing current draw by the battery, reducing battery heating, assessing battery health, reducing battery charge time, and optimizing battery life. The controller can be adapted to vary the switching frequency and / or duty cycle after one or more duty cycles of the switch mode power converter. By varying the switching frequency and / or duty cycle relatively frequently, a smooth waveform can be achieved. The controller can be adapted to vary the switching frequency and / or duty cycle after each duty cycle of the switch mode power converter for a smooth waveform.The controller can be adapted to vary the switching frequency and / or duty cycle depending on the voltage oscillations of the AC power source, which can effectively generate an oscillating current waveform. A high power factor can be achieved due to the dependency, which can avoid the need for power factor correction hardware, which can be large and heavy. The controller may be adapted to vary the switching frequency and / or duty cycle multiple times during each voltage oscillation of the AC source, preferably at least 3 times during each voltage oscillation, preferably at least 10 times, more preferably at least 100 times during each voltage oscillation, more preferably at least 800 times during each voltage oscillation. This may allow good replication of the voltage oscillation. For accuracy, the battery charger may further include a voltage sensor adapted to provide the controller with an indication of the voltage of the AC source. For accuracy, the voltage sensor may be adapted to sense the voltage at least as frequently as the controller varies the switching frequency. The switching frequency and / or duty cycle may vary depending on the rectified (preferably full-wave rectified) voltage oscillation of the AC source. The rectification may double the frequency of the oscillation and ensure that the polarity does not change with the oscillation, which is advantageous for varying the switching frequency depending on the voltage oscillation. The desired waveform may have a frequency that is about an integer multiple of the frequency of the AC source, preferably about twice the frequency of the AC source. This may allow particularly efficient generation of oscillating current waveforms with particularly high power factors. For efficiency, the desired waveform may be fixed at the frequency of the AC power source. The desired waveform may be a sine wave, a full wave rectified sine wave, a squared sine wave, or a combination thereof. These waveforms may be simple to generate while still providing advantageous battery charging. The switch mode power converter may be a flyback transformer. The flyback transformer may accommodate a suitable switching frequency and / or duty cycle range. For effectiveness, the switch mode power converter may be adapted to operate in critical conduction mode. The switching frequency and / or duty cycle may be varied within the range of 1 kHz to 1000 kHz, preferably within the range of 10 kHz to 500 kHz, and more preferably within the range of 40 kHz to 200 kHz.This range is relatively higher than typical mains frequencies of 50 or 60 Hz and rectified frequencies of 100 or 120 Hz, and thus may allow smooth generation of desired waveforms having frequencies between 25 Hz and 150 Hz. For adaptability, the controller may be adapted to vary the switching frequency and / or duty cycle depending on a desired maximum charging current to the battery. The desired maximum charging current may depend on one or more of battery temperature, battery voltage, battery current, change in battery voltage, change in battery current, battery impedance, charging time, and accumulated battery charge, among others. These may indicate conditions or circumstances in which a relatively large or small charging current may be advantageous. The controller may be adapted to vary the switching frequency and / or duty cycle such that the minimum charging current delivered 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 may reduce hysteresis effects to allow favorable battery behavior and charging. The controller may be adapted to vary the switching frequency and / or duty cycle such that the peak-to-peak current delivered to the battery is greater than 1 A, preferably between about 10 A and about 30 A. This may allow for effective charging of batteries, such as lithium ion batteries, handheld device batteries, etc., without using excessively large and dangerous currents. The battery charger may further comprise a smoother adapted to smooth an output current from the power converter. Each of the plurality of battery chargers may be configured to be connected to a multi-phase input and connected to a common output. This may allow for a smooth waveform to be generated from the rectified waveform. A smooth waveform may allow for effective charging, which is advantageous for charging the battery. According to another aspect, a method of charging a battery is provided, comprising converting an AC power source to a charging current to the battery using a switched mode power converter, the switching frequency and / or duty cycle being varied depending on a desired waveform.By varying the switching frequency and / or duty cycle, the current delivered can be varied over time, thereby providing a current having a desired waveform. Charging a battery with a particular waveform can be useful for several reasons, including optimizing current draw 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 switch mode power converter, preferably after each duty cycle. By varying the switching frequency relatively frequently, a smooth waveform can be achieved. The switching frequency and / or duty cycle can be varied depending on the voltage oscillations of the AC power source. This allows for efficient generation of an oscillating current waveform. Due to the dependence, a high power factor can be achieved. This avoids the need for power factor correction hardware, which can be large and heavy. The switching frequency and / or duty cycle can be varied 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, and even more preferably at least 800 times during each voltage oscillation. This allows for good replication of the voltage oscillations. For accuracy, the method may further comprise the steps of sensing the voltage of the AC power supply and varying the switching frequency and / or duty cycle in dependence on the voltage, preferably at least at the frequency at which the switching frequency is varied. The switching frequency and / or duty cycle may vary within the range of 1 kHz to 1000 kHz, preferably within the range of 10 kHz to 500 kHz, more preferably within the range of 40 kHz to 200 kHz. This range is relatively higher than the typical mains frequency of 50 or 60 Hz and the rectified frequency of 100 or 120 Hz, and thus may allow smooth generation of a desired waveform having a frequency of 25 Hz to 150 Hz.The switching frequency and / or duty cycle can be varied depending on the rectified (preferably full-wave rectified) voltage oscillation of the AC power source. Rectification doubles the oscillation frequency and can ensure that the polarity does not change with the oscillation, which is advantageous for varying the switching frequency depending on the voltage oscillation. For adaptability, the switching frequency and / or duty cycle can be varied depending on the desired maximum charging current to the battery, which optionally depends on one or more of the following: battery temperature, battery voltage, battery current, change in battery voltage, change in battery current, battery impedance, charging time, and accumulated battery charge. These may indicate conditions or situations where a relatively large or small charging current may be advantageous, among others. The switching frequency and / or duty cycle can be varied such that the minimum charging current supplied 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 to allow for favorable battery behavior and charging. The switching frequency can be varied so that the peak-to-peak current delivered to the battery is greater than 1 A, preferably between about 10 A and about 30 A. According to another aspect, there is provided a battery charging system including one or more of the following features. The transformer preferably comprises a first primary winding and / or a first secondary winding. A primary switch element is preferably configured to control current provided from a power source to a first primary winding of a transformer, etc. A terminal is configured to receive power, such as from a first secondary winding of a transformer, and is configured to be connected to a battery to be charged. A control subsystem is configured to control operation of the primary switch element. A control subsystem is configured to control a primary switch element such that the transformer delivers power to the terminals having a current waveform having a peak-to-peak current greater than about 1 A. A control subsystem is configured to use the current waveform to determine the electrical impedance of a battery to be charged. A control subsystem is configured to control a primary switch element based at least in part on the determined electrical impedance of the battery to be charged. The current waveform has a frequency greater than about 60 Hz, preferably between about 100 Hz and 120 Hz. The current waveform has a peak-to-peak current of about 10 A to about 30 A. The current waveform varies between a low current of approximately 0A and a peak current. · The current waveform has a frequency that is effectively twice that of the power supply. The primary switch element operates according to a frequency and / or duty cycle that varies based at least in part on the identified electrical impedance of the battery to be charged. The envelope of one or more pulses of current supplied to the transformer substantially follows the voltage waveform of the power supply. The transformer is a flyback transformer. The electrical impedance of the battery to be charged is determined at a frequency higher than about 60 Hz, preferably between about 100 Hz and about 120 Hz. The transformer can be connected to a rectified AC power source. The control subsystem is configured to control the primary switch elements such that the transformer supplies power to the terminals in the form of a substantially rectified sinusoidal waveform current and / or a current waveform having a constant root-mean-square sinusoidal waveform. A control subsystem is configured to control the primary switch elements such that the transformer supplies power to its terminals in the form of a current waveform having a frequency substantially twice the frequency of the voltage of the AC power source. A control subsystem is configured to control the primary switch element to operate between on and off states at a time-varying frequency. A control subsystem is configured to control the primary switch element to operate between an on state and an off state at a frequency that is dependent on the magnitude of the voltage of the AC power source and / or the magnitude of the battery current and / or the magnitude of the battery voltage.

[0009] According to another aspect, there is provided a method of operating a battery charging system including one or more of the following features. The battery charging system preferably includes a transformer including a first primary winding and a first secondary winding. The battery charging system preferably includes a primary switch element configured to control current provided from the power source to the first primary winding. A terminal is configured to receive power from a first secondary winding of the transformer and is configured to be connected to a battery to be charged. A control subsystem is configured to control operation of the primary switch element. The primary switch element is controlled so that the transformer supplies power to the terminals having a current waveform having a peak-to-peak current greater than about 1A. · The current waveform is used to determine the electrical impedance of the battery to be charged. Controlling the primary switch element based at least in part further on the determined electrical impedance of the battery to be charged. Controlling the primary switch element includes controlling the primary switch element such that the current waveform has a frequency greater than about 60 Hz, preferably between about 100 Hz and 120 Hz. Controlling the primary switch element includes controlling the primary switch element such that the current waveform has a peak-to-peak current of about 10 A to about 30 A. Controlling the primary switch element includes controlling the primary switch element such that the current waveform varies between a low current of about 0 A and a peak current. Controlling the primary switch element includes controlling the primary switch element such that the current waveform has a frequency substantially twice the frequency of the power supply. Controlling the primary switch element further includes controlling the primary switch element to vary a frequency and / or a duty cycle of the primary switch element based at least in part on the determined electrical impedance of the battery to be charged. Controlling the primary switch element includes controlling the primary switch element such that an envelope of one or more pulses of current supplied to the transformer substantially follows a voltage waveform of the power supply. The electrical impedance of the battery to be charged is determined at a frequency higher than about 60 Hz, preferably between about 100 Hz and 120 Hz.

[0010] DC as used herein preferably means a voltage and / or current with constant polarity. The DC voltage and / or current may vary in time, for example in the form of a pulsed, oscillating or otherwise varying waveform. In a switched mode power converter, varying the switching frequency varies the duty cycle and vice versa. A change in switching frequency may be achieved by varying the duty cycle and vice versa. Wherever reference is made herein to a change in switching frequency, this may be substituted with a change in duty cycle. The invention extends to a battery charger and / or battery charging system substantially as herein described and / or as illustrated with reference to the Figures. The invention also extends to a method of charging a battery substantially as herein described and / or as illustrated with reference to the Figures. The invention also extends to a method of determining the impedance of a battery substantially as herein described and / or as illustrated with reference to the Figures.

[0011] Any apparatus features described herein may also be provided as method features, and vice versa. Means-plus-function functions may also be expressed herein in other ways in terms of their corresponding structural aspects.

[0012] Any feature in one aspect of the invention may be applied to any other aspect of the invention in any suitable combination. In particular, a method aspect may be applied to an apparatus aspect and vice versa. Furthermore, 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 suitable combination.

[0013] It should also be understood that certain combinations of the various features described and defined in any aspect of the present invention may also be implemented and / or provided and / or used alone.

[0014] The invention will now be described, by way of example only, with reference to the following illustrative drawings. [Brief description of the drawings]

[0015] [Figure 1a] FIG. 1 illustrates generally what would occur during conventional battery charging. [Figure 1b] FIG. 1 illustrates generally what would occur during conventional battery charging. [Diagram 2] FIG. 1 illustrates an embodiment of the present invention. [Figure 3a] 4 is a graphical representation of current and voltage during operation of an embodiment. [Figure 3b] 4 is a graphical representation of current and voltage during operation of an embodiment. [Figure 3c] 4 is a graphical representation of current and voltage during operation of an embodiment. [Figure 3d] 4 is a graphical representation of current and voltage during operation of an embodiment. [Figure 3e] 4 is a graphical representation of current and voltage during operation of an embodiment. [Figure 3f] 4 is a graphical representation of current and voltage during operation of an embodiment. [Figure 4] FIG. 1 illustrates a battery charging system and portions thereof according to some embodiments. [Diagram 5] FIG. 1 illustrates a battery charging system and portions thereof according to some embodiments. [Figure 6] FIG. 1 illustrates a battery charging system and portions thereof according to some embodiments. [Figure 7] FIG. 1 illustrates a battery charging system and portions thereof according to some embodiments. [Figure 8] FIG. 2 illustrates a diagram showing the current through a first primary winding of a flyback transformer during a charging cycle in accordance with some embodiments. [Figure 9] FIG. 2 illustrates a diagram showing the current through a first primary winding of a flyback transformer during a charging cycle in accordance with some embodiments. [Figure 10] FIG. 2 illustrates a diagram showing the current through a first primary winding of a flyback transformer during a charging cycle in accordance with some embodiments. [Figure 11a] 4 is a graphical representation of the current delivered to the battery, the voltage across the battery terminals, and the extracted ripple voltage signal. [Figure 11b] 4 is a graphical representation of the current delivered to the battery, the voltage across the battery terminals, and the extracted ripple voltage signal. [Figure 11c] 4 is a graphical representation of the current delivered to the battery, the voltage across the battery terminals, and the extracted ripple voltage signal. [Figure 12] FIG. 1 illustrates a step-by-step procedure for charging a battery. [Figure 13] FIG. 1 shows a schematic example of a single cell battery control unit in use. [Figure 14] FIG. 1 shows a schematic example of a multi-cell battery control unit in use. [Figure 15] FIG. 2 illustrates a schematic example of a three-phase input to a battery charger of some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The term "battery" as used herein should be interpreted to mean one or more cells capable of storing an electric charge and recharging it after discharging it. When a battery includes multiple cells, the cells can be connected together in a circuit to form a battery. The circuit can be a series circuit (cells connected together in series), a parallel circuit (cells connected together in parallel), a series-parallel circuit (cells connected together in series with multiple groups of the series-connected cells connected together in parallel), or any combination of such circuits.

[0017] As used herein, the terms "battery terminals," "battery terminal," "terminal of a battery," and "terminals of a battery" should be taken to mean electrical terminals or battery terminals that enable a battery to provide power to one or more circuits and / or that allow power to be provided to a battery for recharging the battery.

[0018] The terms "anode" and "negative electrode" are used herein substantially interchangeably and should be construed to mean the internal component of a cell that forms the cathode of that cell. Similarly, the terms "cathode" and "positive electrode" are used herein substantially interchangeably and should be construed to mean the internal component of a cell that forms the anode of that cell.

[0019] Although embodiments of the invention are described with reference to a "battery," it will be understood that the invention typically refers to operations and processes in a single cell, and that a battery including multiple cells may have corresponding multiple cathodes and anodes, and similar operations and processes may occur in each cell of the battery.

[0020] Although the batteries (and thus cells) described herein may be lithium-ion batteries (or cells), it is contemplated that embodiments of the present invention may be used with other forms of batteries (and cells).

[0021] Referring to Figures 1a and 1b, again without wishing to be bound to any particular theory, these figures show generally what is believed to occur within a battery during a conventional charging cycle using constant current operation.

[0022] 1a and 1b, the battery 1 includes a cell 11, which includes a cathode 111 and an anode 112 in an electrolyte 115. A separator 113 may be located between the cathode 111 and the anode 112. The cathode 111 may be electrically connected to the negative terminal 12 of the battery 1, and the anode 112 may be electrically connected to the positive terminal 13 of the battery 1.

[0023] Located at or near the boundary of the cathode 111 is a solid electrolyte interface (SEI) layer 114 .

[0024] During charging of the battery 1, a voltage is applied between the terminals 12, 13 of the battery 1, and ions 3 move from the anode 112 through the separator 113, the electrolyte 115, etc. to the cathode 111, and intercalate into the cathode 111 through the SEI layer 114 (naturally, during discharging, the flow of ions 3 within the battery 1 is reversed).

[0025] It is believed that under a conventional constant current charging cycle, the ions 3 cannot intercalate into the cathode 111 quickly enough to be delivered to the SEI layer 114. Thus, a pile-up of ions 3 occurs at or near the boundary of the cathode 111 (i.e., in the region of the SEI layer 114). This pile-up is shown diagrammatically in FIG. 1b.

[0026] As described herein, this is believed to further increase the electrical resistance within battery 1 and / or cause the growth of SEI layer 114. This is believed to cause further heating of battery 1 during a charging cycle, further affecting the rate at which 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 useful life of the battery in terms of the number of charging cycles that battery 1 can undergo before the charge capacity drops below an acceptable level.

[0027] Thus, the embodiment of the invention shown in Figure 2 includes a battery charging system 100 configured to supply a current, also referred to as a charging current, to a battery 1, which may be a waveform of varying amplitude with a generally non-zero average current, as well as a waveform with a substantially constant average current (which may, for example, be substantially sinusoidal). Further examples of suitable waveforms include oscillating or pulsed DC waveforms. Such waveforms may be supplied, for example, by a switched mode power converter in conjunction with a controller adapted to vary the switching frequency to supply a current of the desired waveform.

[0028] Figures 3a-3c show the current supplied to the battery 1 by the battery charging system 100 of some embodiments (Figure 3a), the voltage of the utility power source 102 (Figure 3b), and the current drawn from the power source (Figure 3c) for a utility power source 102 with an RMS voltage of about 85V. Figures 3d-4f show the current supplied to the battery 1 by the battery charging system 100 of some embodiments (Figure 3d), the voltage of the utility power source 102 (Figure 3e), and the current drawn from the power source (Figure 3f) for a utility power source 102 with an RMS voltage of about 265V.

[0029] The frequency of the current supplied to the battery 1 by the battery charging system 100 may be approximately twice the frequency of the power source 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 that substantially corresponds to a rectified form of the waveform of the supply voltage (e.g., a full-wave rectified form). The frequency of the current supplied to the battery 1 may be, for example, 100 Hz or 120 Hz. The magnitude of the current supplied to the battery 1 may approximately correspond to the peak current supplied to the battery 1.

[0030] Thus, in an embodiment of the present invention, the battery charging system 100 may be configured to power the battery 1 in a first operation during a charging cycle as described above. The battery charging system 100 may also be configured to power the battery 1 in a second operation during the same charging cycle, for example, where a substantially constant voltage or power is provided.

[0031] As can be seen from the examples of FIGS. 3a to 3c and 4a to 4c, the power supply voltage (V ac ) may be typical of commercial AC power voltages available in many countries, the voltage and frequency of which may vary from country to country (e.g., 85 to 265 V RMS, 50 to 60 Hz). Thus, V ac Typically, the current supplied to battery 1 (I bat ) is V ac The waveform may have a frequency related to the frequency of, for example, substantially ac or V ac As described herein, the current supplied to the battery 1 (I bat ) may have a non-zero average value (i.e., it may be offset from 0 A) and may have an approximately sinusoidal shape. bat ) is approximately the supply voltage V ac4a and 4b, and thus in some embodiments, for example, the lower peak of the waveform may be sharper than shown in FIGS. 4a and 4b.

[0032] Current I supplied to battery 1 bat The waveform of the battery 1 can 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 can be substantially 0 A. The peak current can be about 1 A to about 30 A, about 10 A to about 30 A, or about 20 A to about 30 A. The current I supplied to the battery 1 can be bat The peak-to-peak variation (i.e., the difference between the peak current and the low current) can be greater than about 1 A, greater than about 10 A, greater than about 20 A, or greater than about 30 A. Typically, this peak battery charging current is about 10 times the capacity of the battery. For example, the battery used is 2.6 Ah. Thus, the peak current is about 26 amps, resulting in an average battery charging current of about 16 amps.

[0033] current I bat The waveform may oscillate between low and peak currents. In some embodiments, the waveform is a substantially smooth waveform. In some embodiments, the waveform is substantially in the shape of a full-wave rectified sine wave. In some embodiments, a portion of the waveform has the shape of a rectified sine wave and a portion has the shape of a sine squared wave. For example, a portion of the waveform around a maximum of the waveform may have the shape of a substantially rectified sine wave and a portion of the waveform around a minimum of the waveform may have the shape of a substantially sine squared wave (also referred to herein as a squared sine wave).

[0034] Battery 1 has a non-zero average current waveform (I bat) is believed to help reduce the pile-up of ions as discussed above. In addition, this reduces the electrical resistance of the battery 1 during the charging cycle. This improves the charging efficiency of the battery 1, reduces heat generated during the charging process, and allows the overall charging current to be increased to more safely charge the battery 1. Also, the first operation of the charging cycle can be used until the relative charge level of the battery 1 is higher than with some conventional charging cycles (e.g., 80% or more of the total charge capacity, or 90% or more of the total charge capacity, or 90%-95% of the total charge capacity).

[0035] In fact, in some embodiments, the second operation of the charging cycle may be omitted entirely.

[0036] Some embodiments may include a third operation of the charging cycle in which power is supplied to the battery 1 from time to time (eg, periodically) to compensate for self-discharge of the battery 1.

[0037] As will be appreciated, the battery charging system 100 can be implemented in a number of different ways, however, in some embodiments, additional advantages may be achieved by implementing the battery charging system 100 in accordance with certain embodiments described herein, as will become apparent below.

[0038] An embodiment of the battery charging system 100 will be described in further detail with reference to FIGS.

[0039] 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 electrically connected to a utility power source 102. The utility power source 102 may have a supply voltage V acThe battery charging system 100 may be an AC utility power source that provides power at 100 Hz to 100 Hz. The battery charging system 100 may include a rectifier circuit 103 configured to receive power from the utility power source 102 and rectify and provide the power from the utility power source 102 to the flyback transformer 101.

[0040] An electromagnetic interference filter 104 of the battery charging system 100 may be electrically connected between the utility power source 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.

[0041] The battery charging system 100 may further include a snubber circuit 105. The snubber circuit 105 may be connected between the utility power source 102 and the flyback transformer 101, specifically between the electromagnetic interference filter 104 and / or the rectifier circuit 103 and the flyback transformer 101. The snubber circuit 105 may be configured to attenuate voltage spikes that may damage the primary switch element 101a of the flyback transformer 101 and / or to recirculate current from the flyback transformer 101.

[0042] The primary switch element 101a of the flyback transformer 101 is configured to control the supply of power from the commercial power source 102 (as well as the rectifier circuit 103 and / or the electromagnetic filter 104 and / or the snubber circuit 105, etc.) to the first primary winding 101b of the flyback transformer 101.

[0043] The flyback transformer 101 further includes a first secondary winding 101c, where a current flow through the first primary winding 101b is configured to induce a current flow in the first secondary winding 101c.

[0044] The first secondary winding 101c is electrically connected to an output rectifier circuit 106 configured to rectify the power output from the flyback transformer 101 (i.e., the current induced in the first secondary winding 101c).

[0045] The battery charging system 100 includes terminals 107 configured to be connected to the terminals 12, 13 of the battery 1 (in some embodiments, the terminals 107 of the battery charging system 100 can be configured to be selectively connected to the terminals 12, 13 of the battery 1). The terminals 107 of the battery charging system 100 are electrically connected to the first secondary winding 101c. This connection is via an output rectifier circuit 106, which is configured to rectify and supply the power output by the first secondary winding 101c to the battery 1 (connected to the terminals 107 of the battery charging system 100).

[0046] In some embodiments, the output rectifier circuit 106 is a synchronous rectifier circuit that includes one or more switch elements, such as transistor elements (eg, MOSFETs).

[0047] In some embodiments, the battery charging system 100 can include a smoothing circuit 108 electrically connected between the first secondary 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 power provided to the terminal 107 of the battery charging system 100 (and, in turn, to the battery 1).

[0048] 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 across the terminals 107 of the battery charging system 100 to form a capacitor bank. In some embodiments, which may or may not include a capacitor bank as part of the smoothing circuit 108, the smoothing circuit 108 includes at least one inductor connected in series between the first secondary winding 101c and one of the terminals 107 of the battery charging system 100.

[0049] The one or more capacitors of the smoothing circuit 108 may include one or more polymer electrolytic capacitors having a low internal resistance and capable of high ripple current.

[0050] In some embodiments, the battery charging system 100 may further include a disconnect switch 109 that can disconnect one or both of the terminals 107 of the battery charging system 100 from electrical connection with at least the first secondary winding 101c, while also disconnecting the or each terminal 107 from electrical connection with the output rectifier circuit 106 and / or the smoothing circuit 108 (or a portion thereof).

[0051] 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, including, for example, one or more of the flyback transformer 101 (e.g., its primary switch element 101a), the rectifier circuit 103, the output rectifier circuit 103, and the isolation switch 109.

[0052] The control subsystem 110 may further include one or more sensor circuits and / or sensor elements, each 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, and may thus 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 sensor elements. For example, the characteristics of the charging current may change depending on the characteristics, such as the battery impedance, that are determined substantially continuously during charging.

[0053] The one or more sensor circuits and / or sensor elements may include a source voltage sensor circuit 1111 configured to sense the voltage of the utility power source 102, which may be the voltage after rectification by a rectifier circuit 103, if provided. The source voltage sensor circuit 1111 may include a potential divider circuit configured to step down the voltage to a level usable by other components of the control subsystem 110.

[0054] The one or more sensor circuits and / or sensor elements may include a primary winding current sensor circuit 1112 configured to sense a current supplied to the first primary winding 101b of the flyback transformer 101. The primary winding current sensor circuit 1112 may include, for example, a shunt circuit. The primary winding current sensor circuit 1112 may be configured to sense a current flowing from the first primary winding 101b through the primary switch element 101a to ground or the utility power source 102.

[0055] The one or more sensor circuits and / or sensor elements may include a battery terminal voltage sensor circuit 1113 configured to sense the voltage Vbat across the terminals 107 of the battery charging system 100 and therefore the voltage across the terminals 12, 13 of a battery 1 connected to the battery charging system 100. The battery terminal voltage sensor circuit 1113 may include a potential divider circuit configured to step down the voltage to a level usable by other components of the control subsystem 110.

[0056] The one or more sensor circuits and / or sensor elements may include a battery terminal current sensor circuit 1114 configured to sense a current supplied to or returned from at least one of the terminals 107 of the battery charging system 100 and thus to a battery 1 connected to the battery charging system 100. 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 first secondary winding 101c of the flyback transformer 101.

[0057] In some embodiments, the control subsystem 110 can include a primary or input side controller 1115 and a secondary or output side controller 1116. The primary side controller 1115 can be configured to communicate to the output side controller 1116 and / or vice versa via a communication channel that can include an optical coupler circuit 1117. The optical coupler circuit 1117 can be configured to allow communication between the primary and secondary side controllers 1115, 1116 while keeping them electrically isolated. Thus, as can be appreciated, the optical coupler circuit 1117 can include a light emitting diode controlled by the primary side controller 1115 and a phototransistor connected to the secondary side controller 1116.

[0058] In some embodiments, a second primary winding or a first "bias" winding 101d is provided as part of the flyback transformer 101. The second primary winding 101d may be configured in conjunction with the first primary winding 101b such that a current flowing through the first primary winding 101b also induces a current in the second primary winding 101d. The power induced in the second primary winding 101d may then be used to power one or more components of the control subsystem 110, such as the primary side controller 1115. A first bias circuit 101e may also be provided to ensure proper power supply to the primary side controller 1115. The voltage at the output from the second primary winding 101d is referred to herein as a "primary bias voltage" V bias-primary Also, the second primary winding or the first bias winding is used to sense the magnetic state of the flyback transformer and thus ensure the critical conduction mode of operation of the flyback converter.

[0059] In some embodiments, the flyback transformer 101 may include a second secondary winding 101g, or a second "bias" winding. The second secondary winding 101g may be configured in conjunction with the first primary winding 101b such that a current passing through the first primary winding 101b also induces a current in the second secondary winding 101g. The power induced in the second secondary winding 101g may then be used to power one or more components of the control subsystem 110, such as the secondary side controller 1116. A second bias circuit 101f may also be provided to ensure proper power supply to the secondary side controller 1116. The voltage at the output from the second secondary winding 101g is referred to herein as a "secondary bias voltage" V bias-secondary It is called.

[0060] In the illustrated embodiment, the first and second bias circuits 101e and 101f are shown with multiple components for simplicity of presentation, however, it will be understood that these circuits may also be single circuits or connections of each other.

[0061] 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, the output from the battery terminal voltage sensor circuit 1113) to a battery terminal reference voltage.

[0062] The secondary side controller 1116 may be further configured to compare a signal representative of the current supplied to or returned from at least one of the terminals 107 of the battery charging system 100 (e.g., an output from the battery terminal current sensor circuit 1114) to a battery reference current.

[0063] The secondary side controller 1116 can be configured to use the results of these voltage and / or current comparisons to determine an operating mode of the battery charging system 100. The operating mode can include determining whether the first, second or third operation of the charging cycle should be used. In some embodiments, multiple charging modes and / or duty cycles can be utilized.

[0064] In some embodiments, the secondary-side controller 1116 may be configured to receive a signal indicative of the temperature of the battery 1, for example from a battery temperature sensor 1118 configured to sense the temperature of the battery 1 or a parameter indicative thereof and output a signal accordingly. The secondary-side controller 1116 of these embodiments may use this signal indicative of the temperature of the battery 1 (in addition to or alternatively to using one or more comparisons as described above) to determine which of multiple operations of a charging cycle should be used.

[0065] Accordingly, the secondary side controller 1116 is configured to output a control signal C. This control signal C can be communicated (e.g., via an optocoupler circuit 1117) to the primary side controller 1115, which can use this control signal C to control the operation of the flyback transformer 101 as described herein.

[0066] The secondary side controller 1116 may be further configured to operate the cut-off switch 109 when one or more predetermined conditions occur, which may include one or more of: a particular current supplied to or received from the battery 1 rising above or falling below a predetermined threshold current, and / or a voltage across the terminals 12, 13 of the battery 1 rising above or falling below a predetermined threshold voltage, and / or a battery temperature falling below or rising above a predetermined threshold temperature.

[0067] 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 the output of a signal indicative of the current provided to the terminal 107 of the battery charging system 100 (i.e., to the battery 1 connected to the terminal 107) and / or a signal indicative of the current through the output rectifier circuit 106. As will be appreciated, this signal may be an output from the battery terminal current sensor circuit 1114. In some embodiments, the secondary side controller 1116 is configured to activate the output rectifier circuit 106 to an ON state when the flyback transformer 101 is discharging the terminal 107 of the battery charging system 100 and deactivate the output rectifier circuit 106 to an OFF state when the flyback transformer 101 is not discharging the terminal 107.

[0068] The primary side controller 1115 is configured to control the operation of the flyback transformer 101, specifically the actuation of the primary switch element 101a. The primary side controller 1115 receives a control signal C, a signal representative of the current supplied to the first primary winding 101b (e.g., the output of the primary winding current sensor circuit 1112), the voltage of the commercial power source 102 after rectification by the rectifier circuit 103 (V ac ), and a signal representing the AC bias voltage V bias The flyback transformer 101 is configured to control operation of the flyback transformer 101 based at least in part on one or more of the following:

[0069] The primary side controller 1115 is configured to operate the flyback transformer 101 in a critical conduction mode of operation.

[0070] Thus, the primary side controller 1115 can be configured to operate the primary switch element 101a to an on state (so that power flows from the utility power source 102 to the first primary winding 101b) when it is determined that energy stored in the flyback transformer 101 (e.g., in the windings 101b, 101c, 101d and any of their cores) has been dissipated, i.e., provided (or otherwise lost), to the terminals 107 and battery 1 of the battery charging system 100.

[0071] When the primary switch element 101a is in the on state, power is supplied to the first primary winding 101b, increasing the energy stored in the flyback transformer 101. This energy is then supplied as power via the first secondary winding 101c to the terminal 107 of the battery charging system 100 and to any one of the batteries 1 connected to the terminal 107.

[0072] The primary side controller 1115 may be further configured to actuate the primary switch element 101a to an off state (so as to substantially prevent or block power from flowing from the commercial power source 102 to the first primary winding 101b) when a signal representing the current supplied to the first primary winding 101b reaches a value that depends on the signal representing the voltage of the commercial power source 102 and the control signal C.

[0073] Thus, the primary side controller 1115 may be configured to operate the primary switch element 101a to have a switching frequency (ie, the frequency at which it switches between on and off states) that varies over time.

[0074] The primary side controller 1115 can operate the primary switch element 101a such that the current through the first primary winding 101b has an envelope that can generally follow the voltage of the utility 102 (or the rectified utility voltage). The current through the first primary winding 101b can be pulsed at various frequencies and / or duty cycles within this envelope (these frequencies and / or duty cycles determine the magnitude of the current), which are controlled by the operation of the primary switch element 101a. Figure 8 shows a graphical representation of the current supplied to the first primary winding 101b and the envelope of this current. Figures 9 and 10 show pulses of current that form part of this envelope at different times.

[0075] Thus, during an initial period, the operating frequency of the primary switch element 101a (and thus the current in the first primary winding 101b) may be relatively high (e.g., see FIG. 9) (and / or the duty cycle may be relatively low), the operating frequency may decrease (e.g., see FIG. 10) (and / or the duty cycle may become higher) as the magnitude of the current envelope increases, and then the operating frequency may again become higher (e.g., see FIG. 9) (and / or the duty cycle may become lower) as the magnitude of the current envelope decreases. Thus, the operating frequency and / or operating duty cycle of the primary switch element may vary over time, and the frequency and / or duty cycle at any given time may vary depending on the power supply voltage V at that time. ac It depends on the size of

[0076] This operation of the primary side controller 1115 and primary switch element 101a helps to ensure an improved power factor (which can be 0.9 or better).

[0077] In some embodiments, the primary-side controller 1115 may be implemented using a circuit as shown in FIG. 7. In this embodiment, the primary-side controller 1115 includes a variable gain amplifier 1115a configured to receive a signal representative of the voltage of the utility power source 102 and attenuate or amplify the signal using a control signal C. The output from the variable gain amplifier 1115a is passed to (e.g., to its non-inverting input) a first comparator 1115b of the primary-side controller 1115. An inverting input of the first comparator 1115b may receive a signal representative of the current provided to the first primary winding 101b. The output of the first comparator 1115b may be connected to a reset input of a set-reset flip-flop 1115c of the primary-side controller 1115. A bias voltage (or a signal representative of the bias voltage) may be connected to an inverting input of a second comparator 1115d of the primary-side controller 1115. The non-inverting input of the second comparator 1115d may be connected to ground. The output of the second comparator 1115d may be connected to the set input of a set-reset flip-flop 1115c, the output of which may be connected to the primary switch element 101a to control the operation of the primary switch element 101a.

[0078] In some embodiments, the primary switch element 101a is a transistor element 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 that forms the primary switch element.

[0079] In some embodiments, the flyback transformer 101 is of a gapped ferrite core flyback type that may have four alternating windings to reduce leakage inductance. The flyback transformer 101 may be, for example, a high frequency transformer 101 configured to operate at up to 150 W per core.

[0080] The first bias circuit 101 e may include one or more fast rectifier diodes to provide power to the primary controller subsystem 110 .

[0081] The operating frequency of the flyback transformer 101, for example the switching frequency of the primary switch element 101a, can vary between about 40 kHz and about 200 kHz.

[0082] As will be appreciated, many conventional battery charging systems 100 use a Schottky rectifier diode in the output rectifier circuit 106. However, some embodiments of the present invention may eliminate the need for this Schottky rectifier diode by using a synchronous rectifier, reducing cost, improving efficiency, eliminating the need for a heat sink, and reducing the physical space required for the circuit.

[0083] The controller subsystem 110 can be configured such that the current delivered to the terminals 107 of the battery charging system 100 (and thus to the battery 1) on average is approximately 16 A. The controller subsystem 110 can be configured such that the current delivered to the terminals 107 of the battery charging system 100 (and thus to the battery 1) varies between 0 A and 30 A.

[0084] The controller subsystem 110 can be configured to operate the cutoff switch 109 to an off state when a signal indicative of the voltage across the terminals 107 of the battery charging system 100 reaches or exceeds approximately 4 V and / or when the battery 1 is disconnected from the terminals 107.

[0085] In some embodiments, the secondary side controller 1116 acts as a master controller configured to control the operation of the primary side controller 1115, and thus the primary side controller 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.

[0086] The secondary-side controller 1116 (and the primary controller 1116) can be configured to vary the charging current profile during charging depending on the determined battery characteristics, examples of which are described below regarding the determined battery characteristics and charging current profile.

[0087] In some embodiments, the control subsystem 110 is configured to monitor the electrical impedance of the battery 1. The charging current provided by the charging system 100 to the battery 1 to charge the battery 1 may be based at least in part on the electrical impedance of the battery 1. Thus, characteristics of the charging current may depend on the determined electrical impedance of the battery 1.

[0088] As mentioned above, in some embodiments, the secondary side controller 1116 can be configured to determine the operating mode of the battery charging system 100. Thus, the secondary side controller 1116 can be a secondary side controller 1116 configured to monitor the electrical impedance of the battery 1 and use this information to control how the charging system 100 provides current to the battery 1.

[0089] Specifically, in some embodiments, the secondary side controller 1116 controls the current I supplied to or returned from at least one of the terminals 107 of the battery charging system 100. bat. Alternatively, or in addition, the secondary side controller 1116 is configured to receive a signal representative of a change in current provided to or returned from at least one of the terminals 107 of the battery charging system 100 during a portion of the charging current waveform delivery. An example of such a current change may be the difference between the peak (maximum) charging current and the trough (minimum) charging current. In an embodiment where the minimum current is zero amps, this difference is equal to the maximum measured current.

[0090] A current I flows through the battery 1 connected to the terminal 107 in accordance with the current waveform described herein. bat When the battery is supplied with bat As a result, the voltage between the terminals 12 and 13 of the battery 1 becomes ripple. bat 11a showing a voltage V between the terminals 12, 13 of the battery 1 in an example of use of some embodiments of the present invention. bat This can be seen in FIG.

[0091] Thus, the secondary side controller 1116 uses a signal representative of 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 calculate the electrical impedance Z of the battery 1 connected to those terminals 107 (by terminals 12, 13). bat The method may be configured to identify:

[0092] In particular, the secondary side controller 1116 can be configured to receive a signal representing the voltage across the terminals 107 of the battery charging system 100 over a first time period. The secondary side controller 1116 can be configured to determine a DC component of this signal (and thus the voltage it represents), for example by averaging the signal over the first time period and interpreting this value as the DC component. This DC component can then be subtracted from the signal to determine the ripple voltage ΔV across the terminals 107 of the battery charging system 100 (and thus across the terminals 12, 13 of the connected battery 1). bat 107。 This 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 the same as the frequency of the current supplied to or returned from at least one of the terminals 107, and one or more filters may be used to attenuate frequency components of the ripple voltage signal above and / or below this frequency. An example of a voltage ripple signal can be seen, for example, in Figure 11c.

[0093] The secondary side controller 1116 calculates the ripple voltage ΔV bat A signal representing a current ΔI is supplied to or returned from at least one of these terminals 107. bat The signal may be configured to divide by a signal representing a change in

[0094] In some embodiments, the current I supplied to or returned from at least one of the terminals 107 of the battery charging system 100 may be bat can vary from 0A to a peak (maximum) current (before returning to 0A according to the waveforms shown herein). Thus, I bat The signal representing is essentially ΔI bat , and can be used as such. However, in some embodiments,bat varies between a lower non-zero value and the peak current. Thus, in some embodiments, ΔI bat I bat In such an embodiment, the secondary side controller 1116 is configured to operate in a manner such that the current I bat From the signal representing ΔI bat The method may be configured to identify:

[0095] 11a and 11b show the current and voltage at the battery terminals as charging progresses. As the battery is charged, the baseline voltage steadily increases, and the oscillating input current causes a ripple to be superimposed. Only the voltage ripple is relevant for determining the impedance of the battery at a given time, and therefore this ripple is evaluated separately from the increase in the voltage baseline. FIG. 11c shows the voltage ripple. To determine the magnitude of the ripple, for example, a linear baseline voltage is fitted to the voltage curve and the deviation from this baseline is evaluated. This deviation indicates a flat ripple. This flat ripple can then be evaluated to determine the effect of the impedance on the voltage. The magnitude of the ripple voltage is divided by the magnitude of the battery current to find the magnitude of the impedance. In another example, the voltage signal is averaged over a period of time and subtracted from the voltage signal, which also shows a ripple different from the baseline voltage. In the case of a steady charge without oscillations, the battery voltage steadily increases and no signal indicative of the impedance of the battery is available.

[0096] Generally, the internal impedance and the internal battery voltage of a battery cannot be measured directly while the battery is being charged. By dividing the change in current by the change in voltage, the internal battery impedance of a battery can be determined without needing to know the internal battery voltage.

[0097] 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 substantially equal to the frequency of the signal representative of the current supplied to or received from the terminals 107 of the battery charging system. In other words, the secondary side controller 1116 may be configured to determine the electrical impedance of the battery 1 once for each peak of the signal representative of the current supplied to or received from the terminals 107 of the battery charging system 100, thereby effectively determining the electrical impedance of the battery 1 substantially continuously.

[0098] In some embodiments, the secondary side controller 1116 can be configured to determine the electrical impedance of the battery 1 at least at a frequency substantially equal to the frequency of a signal representative of the current supplied to or received from the terminals 107 of the battery charging system, thereby effectively determining the electrical impedance of the battery 1 substantially continuously. bat The impedance of the battery 1 can be determined using the rising or falling peak-to-peak variation of the signal representing

[0099] In some embodiments, the secondary side controller 1116 is configured to determine the impedance of battery 1 at a frequency of about 100 Hz, at a frequency between about 100 Hz and 120 Hz, at a frequency of about 120 Hz, at a frequency between 100 Hz and 200 Hz, at a frequency between about 200 Hz, at a frequency between 120 Hz and 240 Hz, at a frequency of about 240 Hz, or any combination of the upper and lower limits of these ranges.

[0100] As will be appreciated, in some embodiments, the determination of the impedance of the battery 1 is absolutely periodic, but may vary over a period of time during a charging cycle. batThe frequency at which the secondary-side controller 1115 can be configured to cause a change in I is substantially continuous, see below. This specification is because the impedance of the battery is not precisely specified with the frequency of the charging current waveform, but rather with respect to the frequency at which I bat It will be appreciated that this still effectively applies when specified at a substantially continuous frequency with respect to the frequency at which the secondary side controller 1115 can be configured to cause a change in

[0101] The change in current and the change in voltage supplied to the battery 1 can be measured during the rising current portion of the current waveform. The minimum of the current waveform can provide an advantageous starting point for measuring these characteristics. Alternatively, or in addition, these changes can be measured during the falling current portion of the current waveform. Once these characteristics are measured during both the rising and falling portions of the waveform, the secondary side controller 1115 can compare the results to determine if an error exists.

[0102] The control subsystem 110 may include a lookup table 1119. The lookup table 1119 may be stored in a computer readable medium 1119a of or accessible by the control subsystem 110. In some embodiments, the lookup table 1119 may be part of the secondary controller 1116 or may be accessible by the secondary controller 1116.

[0103] The lookup table 1119 can store information indicating a correlation between a battery state and / or a charging state and a charging mode. Thus, the control subsystem 110 (e.g., the secondary side controller 1116) can use the lookup table 1119 to determine an appropriate charging mode for the battery 1 based on identified characteristics of the battery 1 available to the control subsystem 110.

[0104] The identified characteristics available to these control subsystems 110 (e.g., secondary controller 1116) include: bat , V bat , ΔI bat , ΔV bat and Z bat This information may include one or more of the following: bat 1. In embodiments where the battery includes multiple cells, the control subsystem can utilize these characteristics for each cell in addition to or instead of the complete battery characteristics.

[0105] In some embodiments, information available to the control subsystem 110 (e.g., secondary side controller 1116) may include the identity of the battery 1, which may be determined, for example, by a battery identifier communicated to the control subsystem 110. The battery identifier may be, for example, an identifier that is unique or substantially unique to this battery 1 (such as a serial number), or a more general identifier that is unique or substantially unique to the manufacturer of this battery 1, the model of this battery 1, or the configuration of this battery 1. This identity may be communicated to the control subsystem 110 (e.g., secondary side controller 116) by one or more signals transmitted from the battery 1 to the control subsystem 110 (e.g., via a communication link therebetween), or may be manually entered by a user.

[0106] The control subsystem 110 may further include a time measurement means, such as a clock, which may be used to measure the time the battery 1 has been charging. By integrating the time the battery 1 has been charging with respect to the charging current, the total charge delivered to the battery may be determined. This integration may be performed, for example, numerically. The total charge may be used to determine the state of charge of the battery 1.

[0107] The control subsystem 110 (e.g., secondary side controller 1116) can use available determined characteristics (see above) to determine the current state of charge and / or health of the battery 1. As will be appreciated, the health of the battery 1 is a measure of the correct operation of the battery 1 (such as its ability to hold a charge). The current state of charge of the battery 1 can also be referred to differently as the current state of the battery 1 or the battery's state of charge (SOC). These can be used to determine whether and how the charging current supplied to the battery 1 should be changed.

[0108] In some embodiments, rather than determining the battery impedance, the change in current ΔI bat and the change in voltage ΔV bat can be used directly to determine the current state of charge and / or health of the battery and therefore whether and how the charging current should be changed.

[0109] In some embodiments, the lookup table 1119 provides a duty cycle and / or frequency for operation of the primary switch element 101a based on determined characteristics (see above) available to the control subsystem 110 (e.g., secondary side controller 1116). In some embodiments, the lookup table 1119 provides a desired I bat The lookup table 1119 may provide, for example, C (see above). The lookup table may also provide other battery charging current characteristics such as current average value, current maximum value, current amplitude, duty cycle and / or charging mode.

[0110] For example, a fully discharged battery 1 will have a relatively large electrical impedance, and therefore the look-up table 1119 may select a relatively small I batSimilarly, the lookup table 1119 may specify a relatively large I bat You can also specify:

[0111] The above description of the operation of the control subsystem 110 refers to monitoring the electrical impedance of the battery 1. As noted above, the above description should be interpreted as monitoring the electrical impedance of one or more cells 11 of the battery 1.

[0112] In some embodiments, the battery 1 includes multiple cells 11. In such embodiments, the above operations can be performed for each cell 11 of the battery 1 to determine the impedance of each cell 11, and a charging mode can be determined based on the determined information for the multiple cells 11 of the battery 1.

[0113] Although embodiments of the invention have been described with reference to a flyback converter 101, it will be appreciated that these and other embodiments can also be implemented using converters of different topologies. Such converters are capable of high frequency operation (e.g., operation in the range of 40 kHz to 200 kHz).

[0114] A single battery charging system 100 has been described herein. However, the batteries may be connected in parallel to each other and supply current (I bat It will be appreciated that multiple such battery charging systems 100 may be provided, each configured to provide a single primary side controller 1115. In such a configuration, all of the battery charging systems 100 may be controlled by a common control subsystem 110. In some embodiments, such a configuration 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 of the primary side controllers 1115.

[0115] As will be appreciated, embodiments may use I to determine the electrical impedance of a battery. bat A current I having a waveform that allows the electrical impedance of the battery 1 to be frequently determined without the need for further manipulation. bat In other words, the current used to charge the battery and forming 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 current is different from a relatively small current that is intentionally added to, for example, a constant or substantially constant main charging current to determine the electrical impedance of the battery. In such a hypothetical configuration, the maximum frequency at which the electrical impedance of the battery 1 can be determined may be much lower than that of some embodiments of the present invention. Also, the small current does not contribute much to the charging of the battery 1 (e.g., only at the level of a few hundred milliamperes). Thus, such a small current does not form part of the main charging current, and the current I of some embodiments of the present invention that forms part of the main charging current by virtue of the magnitude at which a change in the current affects the charging of the battery 1. bat is different.

[0116] In some embodiments, the control sub-system 110 is configured to communicate with the remote server 210. This communication can be via a communication network, such as a local area network and / or a wide area network, which can include the Internet. The remote server 210 can store, for example, the look-up table 1119 or a portion thereof. In some embodiments, the remote server 210 includes a computer-readable medium 1119a. In some embodiments, the control sub-system 110 is configured to download at least a portion of the look-up table 1119 (e.g., to the local computer-readable medium 1119a). The control sub-system 110 (e.g., the secondary side controller 1116) can be configured to request all or a portion of the look-up table 1119 from the remote server 210 and can also upload information about the battery 1 to the remote server 210.

[0117] The remote server 210 can be configured to maintain a lookup table 1119, which can include receiving information about the battery 1 or the type of battery 1 from the control subsystem 110 and updating the lookup table 1119 based on the information. This can include updating the lookup table for the particular battery 1 and / or the type of battery 1 (e.g., based on the configuration of the battery 1, the manufacturer and / or the model of the battery 1). The remote server 210 can be configured to collate the received information about the multiple batteries 1 to use the lookup table 1119 to modify the lookup table 1119, or a portion thereof, to optimize one or more aspects of the operation of the battery charging system 100, which can include ensuring that a maximum charge is stored in the battery 1, ensuring a maximum useful life (i.e., number of charging cycles) of the battery 1, and / or ensuring the most efficient use of power by the battery charging system 100.

[0118] A step-by-step procedure for charging the battery is shown in Figure 12. The procedure is intended to provide high power efficiency and safely minimize battery charging time. 1.Initialization -Recognizes battery type (total battery voltage Vbat and capacity Cbat) - Estimate battery state of charge (SOC) by consulting a database · Look up the database to determine the maximum allowed cell voltage Vcell_max -Measure all cell voltages Vcell_open Look up the database to determine the initial battery charge current Ibat(av)_initial 2.Start charging -Start the clock Starts charging using a rectified sinusoidal current waveform and Ibat(av)_initial 3. Measurement Measure the voltage and battery current at the bottom of the charge current waveform for each individual cell · Store the measured values ​​Vcell_bottom and Ibat_bottom Measure the voltage and battery current at the top of each individual cell's charging current waveform · Stores the measured values ​​Vcell_top and Ibat_top 4.Calculation Calculate the difference ΔVcell = Vcelltop-Vcellbottom ·Calculate the difference ΔIbat=Ibat_top-Ibat_bottom Calculate the impedance of each individual cell Zcell = ΔVcell / ΔIbat 5. Fully charged · Assign the weakest cell Z_weak_cell (with the highest impedance) According to Z_weak_cell, look up the database to determine the maximum safe battery charging current Ibat_max_safe -Continuously charges the battery and continuously measures and calculates all of the above to maximize the charger potential and safely minimize battery charging time Continuously measure the temperature of each individual cell, Tcell 6.Stop -Continuously check the database and modify Vcell_max and Ibat_max_safe according to the highest temperature cell Tcell_max - Stop charging when the voltage of the first cell reaches Vcell_max 7. Management Calculates the time ampere integral and specifies the total charge received by the battery -Displays battery SOC -Store information in database

[0119] Storing the characteristics of the identified battery in a database, which may be present, for example, in a look-up table stored in the memory of the controller / control unit, allows the battery charging system to correlate these characteristics so that they can be used in the future to charge other batteries and / or recharge the same battery.

[0120] The determined characteristics may be stored, for example along with identification data that may associate the characteristics with this particular battery. When charging this particular battery in the future, the characteristics may be used to determine the battery condition and / or required charging current characteristics.

[0121] Alternatively or additionally, the stored determined characteristics may be aggregated into a data set from which correlations of battery characteristics may be determined for a class and / or type of battery. These correlations may be used to identify / estimate battery condition and / or required charging current characteristics when charging batteries of the same type and / or class.

[0122] By storing identified characteristics and using these characteristics to aid in future battery charging events, the system is said to be self-learning.

[0123] A schematic example of a single cell battery control unit in use is shown in Figure 13. A secondary controller (master CPU) drives a current source, such as a flyback converter, to generate a charging current (I) at approximately twice the line frequency, e.g., a current having an oscillating DC waveform, such as a rectified sinusoidal waveform. cell ) to charge the battery cells. This direct (i.e., always positive) but time-varying current can have a minimum value of less than about 0.5 amps, preferably less than about 0.1 amps, and more preferably about 0 amps, and a maximum value of about 30 amps.

[0124] This "ripple" battery charging current is proportional to the battery's internal impedance Z cell Ripple battery cell voltage ΔV cell The battery internal impedance Z cell is, for example, the state of charge of the battery cell, the temperature of the battery cell T cell , the battery cell voltage V cell , and the history of the battery cells.

[0125] This ripple battery voltage ΔV cell can be filtered and amplified and used to transfer battery status information to a secondary controller. This ripple battery voltage is called I cell (and / or the change in current ΔI if the minimum charging current is not zero) cell ) with Z cell The controller uses this information to calculate the battery cell temperature T cell and the battery cell voltage V cell etc. to select an appropriate charging mode from a look-up table. At this time, the secondary controller can vary the characteristics of the charging current depending on the condition of the battery cells, for example by changing the duty cycle of the primary controller.

[0126] For example, fully discharging a battery can increase the battery's internal impedance. The secondary controller uses the ripple charging current and the voltage ripple that this current induces to calculate the battery impedance. The secondary controller then determines the required charging mode from a look-up table. The look-up table indicates that a different charging mode is required to avoid overheating and / or damage to the battery cells. The secondary controller sends a different charging mode with a lower duty cycle to the primary controller, thereby lowering the battery charging current.

[0127] In effect, the battery cells themselves are constantly "determining" what the best mode for charging is.

[0128] A schematic example of a multi-cell battery control unit in use is shown in Figure 14. In this example, a battery contains n cells arranged in parallel and / or series. This example shows the voltage V between each cell. cell(i) , the change in voltage between each cell Δ cell(i) , and the temperature of each cell T cell(i) This works similarly to the example described above in connection with FIG. 13, except that the current I cellis the same for each cell. The measurements from all cells are cell (and / or change in current ΔI cell ) to the secondary controller. The battery internal impedance Z cell(i) is the change in voltage between the cells ΔV cell It can be calculated by dividing by

[0129] The controller uses this information to select the optimal battery charging mode from a look-up table and varies the duty cycle of the primary controller to take into account the conditions of all the battery cells.

[0130] In some embodiments of the invention, a rectified sinusoidal current is used to charge the battery, and the voltage ripple inherent in this charging method is used (along with the current) to measure the cell's internal impedance, allowing a substantially continuous monitoring of the cell's internal impedance, and enabling the controller to continually monitor the battery's health through calculations of the internal impedance and change the charging mode on the fly.

[0131] In some embodiments, a primary controller is used to control the battery charging current. The primary controller is implemented using a programmable chip device. The primary controller senses: Grid input voltage through a high voltage divider Flyback primary current through the primary current shunt connected to the primary MOSFET source Control signal coming from the primary controller through an isolated optical coupler Bias voltage from the flyback transformer

[0132] The circuit is configured and functions as follows. 1. Through the variable gain amplifier in the programmable chip, the grid input voltage after the high voltage divider is amplified or attenuated according to the control signal. 2. The output of this amplifier is fed to the non-inverting input of a comparator in the programmable chip. 3. Connect the voltage from the primary current shunt (connected to the primary MOSFET source) to the inverting input of this comparator. 4. The output from this comparator is the reset signal to a set-reset flip-flop in the programmable chip. 5. Connect the output from the bias winding of the flyback transformer to the inverting input of another comparator in the programmable chip. 6. Ground the non-inverting input of this comparator. 7.The output from this comparator is the set signal to a flip-flop. 8. Connect the output of the flip-flop to the gate of the primary power MOSFET.

[0133] Therefore, the gate signal to the primary power MOSFET is It starts when all the energy stored in the flyback transformer is delivered to the battery. Termination can occur when the voltage across the primary current shunt (connected to the primary MOSFET source) reaches the value of the input voltage divided (by a high voltage divider) and amplified or attenuated by the control signal (coming from the primary controller through an isolated optocoupler).

[0134] In this way the grid current can be in phase with the grid voltage (PFC converter). The control signal is formed by the primary controller (also a separate programmable chip) according to the grid input voltage, the primary peak current, the battery voltage, the battery current and the battery temperature.

[0135] 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, the 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. Thus, in a three-phase system having a three-phase poly-phase input 301, three battery charging systems 100 may be provided within the multi-phase charger 300.

[0136] Each battery charging system 100 may be electrically connected between a single phase of the multi-phase input 301 and an output 302. In some embodiments, the output 302 is common to all battery charging systems 100 of the multi-phase input 301. Thus, the terminals 107 of each battery charging system 100 may be connected together to provide a common output 302 (which may have a common ground and a common charging terminal). Thus, in some embodiments, the combined output from the battery charging systems 100 of the multi-phase charger 300 may provide a charging current as described herein. Thus, the battery charging systems 100 of the multi-phase charger 300 may be controlled to achieve this effect. Thus, the control subsystems 110 (if provided) of each battery charging system 100 may be communicatively coupled. In some embodiments, the multi-phase input 301 may be connected to a common power supply 302 of about 200 to about 800 V. RMS The output 301 supplies an input voltage of about 100 to about 800 V. DC It can be said that:

[0137] When used in the present specification and claims, the terms "comprises" and "comprising", as well as variations thereof, mean that the specified features, steps or integers are included. These terms are not to be interpreted as excluding the presence of other features, steps or components.

[0138] The features disclosed in the above description, or in the following claims, or in the accompanying drawings are presented in their specific form or in terms of means for performing a disclosed function, or a method or process for achieving a disclosed result, and may be used separately or in any combination of such features as appropriate to realize the invention in these various forms. [Explanation of symbols]

[0139] 1 Battery 3. Aeon 4. Voltage 11 Cell 12 negative terminal 13 Positive terminal 111 Cathode 112 Anode 113 Separator 114 Solid electrolyte interface (SEI) layer 115 Electrolytes

Claims

1. 1. A multi-phase battery charger for providing charging current to batteries, the battery charger including a plurality of battery charging systems, Each of the battery charging systems comprises: receiving an input from a single phase of a polyphase AC input having a sinusoidal waveform; configured to provide a current having an oscillating waveform to a common output; the minimum value of the vibration waveform is 0 A or approximately 0 A, the vibration waveform has a squared sine wave shape, the squared sine wave being a waveform of the AC input squared; a combined output from said battery charging system providing said charging current; 1. A multi-phase battery charger comprising:

2. The minimum value of the vibration waveform is less than 0.1 A, less than 0.01 A, or less than 0.001 A; 2. The multi-phase battery charger of claim 1.

3. The peak-to-peak variation of the current having an oscillatory waveform is Greater than 1A 10 A to about 30 A, or At least one of:

3. A multi-phase battery charger as claimed in claim 1 or 2.

4. At least 0.5 ms, at least 1 ms, at least 5 ms, or at least 10 ms per vibration period of the vibration waveform is at 0 A or approximately 0 A; A multi-phase battery charger according to any one of claims 1 to 3.

5. 1. A method for charging a battery, comprising: converting a plurality of alternating polarity outputs of a polyphase AC power source into respective charging currents, each alternating polarity output having a sinusoidal waveform and being a single phase of the polyphase AC power source; generating a combined output from each of the charging currents; providing the combined output to the battery; each charging current has an oscillating waveform, the minimum value of said oscillating waveform being at or near 0 A, said oscillating waveform having a shape of a squared sine wave, said squared sine wave being a square of the waveform of each AC polarity output of said polyphase AC power source; A method comprising:

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