WO2018009071A1 - Pulse battery charger arranged for charging a battery - Google Patents

Pulse battery charger arranged for charging a battery Download PDF

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Publication number
WO2018009071A1
WO2018009071A1 PCT/NL2017/050459 NL2017050459W WO2018009071A1 WO 2018009071 A1 WO2018009071 A1 WO 2018009071A1 NL 2017050459 W NL2017050459 W NL 2017050459W WO 2018009071 A1 WO2018009071 A1 WO 2018009071A1
Authority
WO
WIPO (PCT)
Prior art keywords
solar array
voltage
threshold
battery
solar
Prior art date
Application number
PCT/NL2017/050459
Other languages
French (fr)
Inventor
Douglas KALKWARF
Original Assignee
Kallara B.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from NL2017137A external-priority patent/NL2017137B1/en
Priority claimed from NL2017131A external-priority patent/NL2017131B1/en
Application filed by Kallara B.V. filed Critical Kallara B.V.
Publication of WO2018009071A1 publication Critical patent/WO2018009071A1/en

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/007—Regulation of charging or discharging current or voltage
    • H02J7/00711—Regulation of charging or discharging current or voltage with introduction of pulses during the charging process
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/02—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries for charging batteries from ac mains by converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2207/00—Indexing scheme relating to details of circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J2207/20—Charging or discharging characterised by the power electronics converter
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J7/00—Circuit arrangements for charging or depolarising batteries or for supplying loads from batteries
    • H02J7/34—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering
    • H02J7/35—Parallel operation in networks using both storage and other dc sources, e.g. providing buffering with light sensitive cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

  • the present invention is related to a pulse battery charger arranged for charging a battery.
  • Pulse battery chargers are known in the art and are arranged to feed a charge current to the battery in pulses.
  • the charging rate can be controlled by varying the width of the pulses.
  • short rest periods between pulses allow the chemical actions in the battery to stabilise by equalising the reaction throughout the bulk of the electrode before recommencing the charge.
  • One of the challenges of pulse chargers is to improve the efficiency of the pulse chargers.
  • the invention provides in a pulse battery charger arranged for charging a battery, said pulse battery charger comprising:
  • said main transformer including a primary winding connected to an input stage and a secondary winding connected to an output stage;
  • switching means for switching an input voltage of an input power source to said main transformer
  • a battery for storing electrical energy from said secondary winding of said main transformer
  • a capacitor arranged for storing electrical energy from an input power source, when connected;
  • an input voltage sensor for determining said input voltage of said input power source
  • an output current sensor for determining an output current provided by said secondary winding of said transformer; an output voltage sensor for determining an output voltage, said output voltage being a voltage over said battery;
  • control means for generating a control signal to control the switching operation of said switching means, wherein said control signal is a square wave signal having a duty cycle and a frequency, and wherein said control means are arranged to vary said duty cycle and said frequency based on said determined input voltage, said determined output current and said determined output voltage thereby causing said transformer to produce a dynamically changing output voltage which is applied to said battery.
  • the switching means may be any electronic switching device such as a Field Effect Transistor, FET, a Metal Oxide Semiconductor, MOS, FET or a transistor.
  • the shock voltage should be construed in such a way that it is only a fraction of the ON-time itself, for example 0,2% - 3% of the total period. And the shock voltage should have a magnitude which exceeds the magnitude of the ON-time substantially. The shock voltage ensures that the battery gets reinitialized again.
  • the result of the above is that it is possible to charge the battery more quickly, causing the battery to store more energy and to increase the number of charging cycles the battery is able to withstand.
  • control means may comprise a microcontroller, a microprocessor, a Field Programmable Gate Array, FPGA, or anything alike.
  • said control means are arranged to generate said control signal in such a way that said produced output voltage comprises:
  • the shock voltage i.e. the voltage during the SHOCK-time
  • the shock voltage needs to be of a magnitude far larger than the output voltage during the ON-time. This ensures that the battery gets reinitialized again such that the battery does not loose any capacitance value.
  • the shock voltage is provided to the battery right after the ON-time of the period. This improves the recovery process of the battery.
  • control means are arranged to
  • the advantage of this example is that the frequency of the control means will automatically be set to allow for a more efficient current draw from the input power source. This is especially true in case the input power source is a solar array.
  • the pulse battery charger operates in a mode in which the substantially maximum power is drawn from the input power source.
  • said output current sensor is arranged for determining an output current provided by said secondary winding of said transformer at least during an ON-time of said produced output voltage, and wherein said control means are arranged to generate said control signal based on charge conditions of said battery.
  • control means are arranged to read out, or be provided with, the current delivered via the secondary winding of the transformer during the charging period of the battery.
  • the charging period of the battery equals the ON-time of the produced output voltage. This means that the battery is under charging conditions.
  • control means may either increase or decrease the charge current.
  • the charge conditions may be measured, for example real time, and may equal, for example, the voltage over the battery or the total amount of energy in the battery.
  • the charge conditions may also be predefined, for example the maximum allowed current to be provided to the battery or the like.
  • the output voltage sensor is arranged for determining said output voltage before a start of an ON-time of said produced output voltage, and wherein said control means are arranged to adjust a duty cycle of said control signal based on said determined output voltage.
  • control means are arranged to read out, or be provided with, the output voltage, i.e. the voltage over the battery.
  • the output voltage i.e. the voltage over the battery. This voltage is measured just before the ON-time of the period corresponding to the duty cycle meaning that the battery is not under charging conditions at this time.
  • the battery thus, had a maximum period of rest, i.e. the OFF-time, and the output voltage will thus equal the exact charge state of the battery. That is, the voltage measured by the output voltage sensor will accurately measure the voltage over the battery.
  • control means may be arranged to:
  • the battery is any of a lead crystal, lead acid and/or lithium Ion battery type.
  • the pulse battery charger comprises said input power source, wherein said input power source is any of a Grid, a wind turbine, a Generator and a solar array.
  • control signal is a square wave signal having a duty cycle and a frequency
  • control signal is a square wave signal having a duty cycle and a frequency
  • said step of generating comprises: generating said control signal in such a way that said produced output voltage comprises:
  • the step of generating comprises: decreasing said frequency of said control signal whenever said input voltage sensor has determined a drop in said input voltage thereby reducing current flowing in said primary winding of said transformer allowing said input power source to recover, and to
  • said step of determining said output current comprises:
  • step of generating comprises:
  • said step of determining said output voltage comprises:
  • step of generating comprises:
  • said step of adjusting comprises:
  • the present disclosure is also related to a solar array based pulse load charger.
  • Pulse chargers are known in the art and are arranged to feed a charge current to the battery in pulses.
  • the charging rate can be controlled by varying the width of the pulses.
  • short rest periods between pulses allow the chemical actions in the battery to stabilise by equalising the reaction throughout the bulk of the electrode before recommencing the charge.
  • One of the challenges of pulse chargers with respect to solar arrays is to improve the efficiency of the pulse chargers.
  • the disclosure provides in a solar array based pulse load charger arranged for operating around predetermined threshold values, said pulse load charger comprising a plurality of charge circuits,
  • each charge circuit comprises:
  • an inductor in the form of a transformer to store the input energy and to transform the input voltage at a desired ratio, said main transformer including a primary winding connected to an input stage and a secondary winding connected to an output stage;
  • switching means for switching said input voltage to said main transformer
  • control means for generating a control signal to control the switching operation of said switching means
  • said rectifying means are arranged for connecting a secondary winding of said transformer of said charge circuit to a secondary winding of a transformer of a next charge circuit of said plurality of charge circuits, such that each of said loads of said charge circuits are connected in series for providing a boosted voltage compared to said input voltage;
  • said input stage is arranged to be connected to an output of a solar array, said input stage comprising:
  • a solar output switch for connecting/disconnecting said solar array to said transformer
  • solar array control means connected to said voltage sensor, for disconnecting said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.
  • the efficiency of the pulse load charger is increased in case the output from the solar array is maximized as much as possible.
  • a substantially maximized output is achieved, using the solar array control means monitoring the solar array voltage while current is being drawn from the array and, at the point where the voltage starts to drop, the draw on the output power from the solar panel array is temporarily suspended by the solar array control means by causing the solar output switch to disconnect the solar array from the transformer. This will stop the current flow and cause the solar array voltage to begin to increase.
  • the output power will again be applied to any of the charge circuits by the solar array control means by causing the solar output switch to connect said solar array to said transformer.
  • the voltage sensor is feeding the solar array control means with the solar array voltage.
  • the solar array control means will sense this drop of the voltage, i.e. it fall below the first threshold, and will automatically open the solar output switch such that the transformer is disconnected from the solar array. This will stop any current from flowing in the primary windings of the transformer and will allow the solar array voltage to recover again.
  • the solar output switch will be closed again to allow the current to flow to the primary windings of the transformer again. This thus means that the frequency and duration of the control will automatically adjust to allow for maximum power drawn from the solar array.
  • the solar array control means are arranged to control the switching of the solar output switch in such a way that the power drawn from the solar array is maximized as much as possible, by making sure that the voltage drop of the solar array voltage is within predefined thresholds.
  • the inventors have found that maximum power is drawn from the solar array in case there actually is a voltage drop of the solar array voltage.
  • the voltage drop may be set once in the solar array control means using the first threshold and the second threshold.
  • Another advantage of the solar array based pulse load charger in accordance with the present disclosure is that the system is able to cope with very low solar output voltage, for example even below 0, 1 volts.
  • the inventor has found that is may be beneficial to have a plurality of charge circuits for boosting the voltage instead of a single charge circuit, having a single boost converter, for boosting the voltage. Utilizing multiple charge circuits in parallel, i.e. the loads of which are connected in series, is beneficial as it improves the efficiency of the solar array based pulse load charger over the whole voltage output range of the solar panel.
  • each of the charge circuits remain balanced during the charging cycle. That is, each of the loads are charged simultaneously, and at the same rate, such that each of the loads, i.e. batteries, provide roughly the same voltage. These voltages are then summed up as the batteries are placed in series, to provide for a single output voltage.
  • each of the batteries of the charge circuits are charged to about 12 volts.
  • Four charge circuits may be present in the solar array based pulse load charges such that the total single output voltage of the solar array based pulse load charger is about 48 volts.
  • each of the batteries are able to provide power at the same time that the batteries are charged.
  • the predetermined first threshold is between 75% - 90% of said solar array voltage.
  • the inventors have found that it is likely that maximum power is drawn from the solar array in case such an amount of current is drawn from the solar array that the solar array voltage drops until about 75% - 90% of the solar array voltage in case no load is applied.
  • the second threshold is between 1 % - 10% of solar array voltage higher than said first threshold.
  • the advantage of this example is that the solar output switch is not continuously being switched from connecting the solar array output to the transformer to disconnecting the solar array output to the transformer, and vice versa.
  • the solar output switch is stressed less in case the second threshold is higher compared to the first threshold.
  • the first threshold equals the second threshold such that it is more likely that maximum power is drawn continuously from the solar array.
  • each charge circuit further comprises an output current sensor for determining an output current
  • said control means are arranged generate said control signal to control the switching operation of said switching means based on said measured output current.
  • the output current is measured during the duty cycle. This means that the load, for example battery, is under full charging conditions at that time.
  • the control means may either increase or decrease the charge current. This can be done by increasing or decreasing the duty cycle of the pulse.
  • each charge circuit further comprises an output voltage sensor arranged for determining an output voltage at said secondary winding of said transformer, and said control means are arranged to generate said control signal to control the switching operation of said switching means based on said measured output voltage.
  • the output voltage sensor will measure the output voltage and will feed that voltage back to the control means.
  • the control means are arranged to measure the output voltage just before the duty cycle begins. This means that the battery will not be under charging conditions at this time and will have had a period of rest, and the output voltage sensor will measure the exact charge state of the load, i.e. the battery. Based on this information, the control means may either increase or decrease the duty cycle.
  • control means may be arranged to:
  • the effect of the above is that the charge rate is slowly decrease as the battery gets more charged, thereby improving the storing capabilities of the battery.
  • the pulse load charger comprises four charge circuits.
  • the disclosure provides in a method of operating a solar array based pulse load charger according to any of the examples as disclosed above, said method comprising the steps of:
  • the predetermined first threshold is between 75% - 90% of said solar array voltage.
  • the second threshold is between 1 % - 10% of solar array voltage higher than said first threshold.
  • the first threshold equals said second threshold.
  • each charge circuit further comprises an output current sensor for determining an output current, and wherein said control means are arranged generate said control signal to control the switching operation of said switching means based on said measured output current.
  • each charge circuit further comprises an output voltage sensor arranged for determining an output voltage at said secondary winding of said transformer, and wherein said control means are arranged to generate said control signal to control the switching operation of said switching means based on said measured output voltage.
  • said load is a battery
  • said control means are arranged to:
  • Figure 1 shows, in a schematic form, a circuitry with respect to the pulse battery charger 1 in accordance with the present invention
  • Figure 2 shows, in a schematic form, a chart indicating a output waveform according to the present invention.
  • Figure 3 shows, in a schematic form, a chart indicating a maximum power point at which a solar array is to be operated according to the present invention.
  • Figure 4 shows, in a schematic form, a circuitry with respect to the solar array based pulse load charger in accordance with the present invention.
  • Figure 1 shows, in a schematic form, a circuitry with respect to the pulse battery charger 1 in accordance with the present invention.
  • the pulse battery charger 1 is arranged for charging a battery 12, more specifically a battery of any of a lead crystal, lead acid and/or lithium Ion battery type.
  • the pulse battery charger 1 is arranged in such a way that the lifetime, the capacity and the charge time of the battery 12 is improved.
  • the pulse battery charger 1 comprises a single charge circuit.
  • a charge circuit is characterized in that it comprises a transformer 6, switching means 5 and each of the components depicted on the right of the transformer 6. Multiple charge circuits may be deployed, wherein the batteries 12 are cascaded in series. This ensures that the voltages of the batteries 12 can be added up.
  • Each of the charge circuits is then to be coupled to the input power source at a time.
  • Each of the charge circuits is thus coupled to the input power source one after the other. This coupling process is obtained using the control means 5 present in each of the charge circuits.
  • Each charge circuit thus comprises the transformer 6 for transforming an input voltage at a desired ratio, the transformer including a primary winding 7 connected to an input stage and a secondary winding 8 connected to an output stage.
  • An advantage of using a transformer 6 is that a transformer 6 provides for an isolation between the input stage and the output stage.
  • switching means 5 are provided for switching the input voltage to the transformer 6.
  • the switch When the switch is closed, the primary winding 7 of the transformer 6 is directly connected to the input power source. The current through the primary winding 7 of the transformer 6 and the corresponding magnetic flux in the transformer 6 will then increase, storing energy in the transformer 6.
  • the voltage induced in the secondary winding 8 of the transformer 6 is negative, so that the rectifying means 9, for example a diode, is reverse-biased, i.e. blocked.
  • the switch is opened, the current through the primary winding 7 of the transformer 6 and thus also the magnetic flux in the transformer 6, drops. The voltage induced in the secondary winding 8 of the transformer 6 is then positive allowing the current to flow from the transformer 6 via the rectifying means 9.
  • the switching means 5 comprise a Field Effect Transistor
  • FET Metal Oxide Semiconductor FET
  • MOSFET Metal Oxide Semiconductor
  • Each charge circuit further comprises a battery 12 for storing electrical energy from said secondary winding 8 of said main transformer 6.
  • the battery 12 is typically a lead crystal battery, a lead acid battery or a lithium Ion battery.
  • the batteries of each of the charge circuits are connected in series such that the output of all the charge circuits combined provides for an increased output voltage.
  • a capacitor 4 is provided in the input stage for, at least temporarily, storing electrical energy from the input power source, and for providing said stored energy to the transformers 6, if/when required. Further an input selector 2 is provided in case more than one type of input power source is connected to the pulse battery charger 1 .
  • an input voltage sensor 3 is provided for determining the input voltage of the input power source
  • an output current sensor 1 1 is provided for determining an output current provided by the secondary winding 8 of the transformer 6, and an output voltage sensor 10 is provided for determining an output voltage, the output voltage being the voltage over the battery 12.
  • Each of the measurement are provided to control means 13, 14.
  • the control means 13, 14 are arranged for generating a control signal to control the switching operation of the switching means 5, wherein the control signal is a square wave signal having a duty cycle and a frequency as is explained below with reference to figure 2.
  • the control means 13, 14 are arranged to vary the duty cycle and the frequency based on the determined input voltage, the determined output current and the determined output voltage thereby causing the transformer to produce a dynamically changing output voltage which is applied to the battery 12.
  • the control means 13, 14 may, for example, be arranged to decrease said frequency of said control signal whenever said input voltage sensor has determined a drop in said input voltage thereby reducing current flowing in said primary winding of said transformer allowing said input power source to recover, and to increase said frequency of said control signal whenever said input voltage sensor has determined an increase in said input voltage thereby increasing current flowing in said primary winding of said transformer.
  • Figure 2 shows, in a schematic form, a chart indicating a output waveform 51 according to the present invention.
  • the control signal generated by the control means in accordance with figure 1 , are arranged to generate a control signal in such a way the produced output voltage comprises a duty cycle / period.
  • the period corresponding to the duty cycle, as depicted in figure 2, comprises an ON-time 52 between 10% - 35%, preferably around 20%, of the total period.
  • the battery 12 is being charged using a voltage output indicated with reference numeral 55.
  • the inventors have found that it is beneficial in case the ON-time 52 is followed by a SHOCK-time 53 between 0,2% - 3% of the period, more specifically around 1 % of the period. During this time a SHOCK voltage 59 is generated, and provided to the battery 12 to ensure that the battery is reinitialised. This is advantageous for the total capacity of the battery 12. That is the total capacity of the battery 12 will not, or hardly, degrade over time.
  • the ratio of the magnitude of the SHOCK voltage 59 with respect to the voltage output during the ON-time 52, i.e. as indicated with reference numeral 55, is preferably about 5: 1 .
  • the battery 12 is able to recover such that, et the end of the OFF-time 54, the voltage provided by the battery 12 is roughly the steady state voltage of the battery 12 itself.
  • the control means will either increase or decrease the charge current.
  • the output voltage sensor is arranged to measure the output voltage at least at the end of the OFF-time 54, i.e. at the end of the rest time. This is indicated with reference numeral 58 in figure 2.
  • This information may be used by the control means to control the duty cycle of the control signal. More specifically, the duty cycle the control signal may be increase in case said output voltage is below a predetermined charge threshold, for example below eighty percentage charge voltage or the like.
  • the control means may also continuously decrease a duty cycle of said control signal in case said output voltage exceeds a predetermined charge threshold, for example exceeding the eighty percentage charge voltage, in such a way that when the battery is approximately fully charged said duty cycle is approximately zero.
  • Figure 3 shows, in a schematic form, a chart 1 indicating a maximum power point 106 at which a solar array is to be operated according to the present invention.
  • the inventors have found that the solar array should be utilized in such a manner that a substantially maximized power is drawn therefrom. As such, it was the insight that increase power is drawn from the solar array when the output voltage of the solar array begins to drop. This is indicated with the chart 101 shown in figure 3.
  • the output voltage of the solar array i.e. the solar array voltage
  • the vertical axis 102 is scaled with a numerical output. That is, for the solar array voltage 103 the vertical axis is divided in, for example, 0 - 6 volts DC.
  • the horizontal axis 107 is scaled with the total current drawn from the solar array.
  • the total power drawn from the solar array is indicated with reference numeral 104. Substantially most power is drawn from the solar array when the solar array voltage 3 starts to drop. This is indicated with reference numerals 105 and 106. It was the insight that the solar array based pulse load charger should function in such a way that as much as possible power is drawn from the solar array in a continuous manner. In other words, the pulse load charger should make sure that the power that the solar array is providing is around the maximum power as indicated with reference numeral 105.
  • FIG. 4 shows, in a schematic form, a circuitry with respect to the solar array based pulse load charger 21 in accordance with the present invention.
  • the solar array 22 based pulse load charger 21 is arranged for operating around predetermined threshold values. More specifically, the solar array based pulse load charger 21 is arranged to operate around the substantially maximum power point as indicated with reference numeral 105 in figure 3.
  • the pulse load charger 21 comprises a plurality of charge circuits. In the present situation two charge circuits 46, 47 are shown. Typically, about four charge circuits 46, 47 may be used. According to the present invention, only one charge circuit 46, 47 is coupled to the solar array 22 at a time. Each of the charge circuits 46, 47 is thus coupled to the solar array 22 one after the other. This coupling process is explained in more detail hereafter.
  • Each charge circuit 46, 47 comprises a transformer 30, 41 for transforming an input voltage at a desired ratio, said main transformer 30, 41 including a primary winding connected to an input stage and a secondary winding connected to an output stage.
  • An advantage of using a transformer 30, 41 is that a transformer 30, 41 provides for an isolation between the input stage and the output stage.
  • switching means 32, 42 are provided for switching the input voltage to the transformers 30, 41 , respectively.
  • the switch When the switch is closed, the primary winding of the transformer 30, 41 is directly connected to the solar array output. The current through the primary winding of the transformer 30, 41 and the corresponding magnetic flux in the transformer will then increase, storing energy in the transformer 30, 41 .
  • the voltage induced in the secondary winding of the transformer 30, 41 is negative, so that the rectifying means 34, 40, for example a diode, is reverse-biased, i.e. blocked.
  • the switching means 32, 42 comprise a Field Effect
  • Each charge circuit 46, 47 further comprises a load 35, 37 for storing, or consuming, electrical energy from said secondary winding of said main transformer.
  • the load 35, 37 is typically a battery, for example a lead crystal battery, a lead acid battery of a lithium Ion battery.
  • the batteries of each of the charge circuits 46, 47 are connected in series such that the output 45 of all the charge circuits 46, 47 combined provides for an increased output voltage.
  • Control means 29, 31 , 44, 43 are provided for generating a control signal for controlling the switching operation of the switching means 32, 42, respectively, the control signal is, for example, a square wave having a certain duty cycle.
  • the duty cycle is about 20 - 25% for each of the switching means 32, 42, respectively.
  • the duty cycles are further shifted in time with respect to each other to make sure that none of the switching means 32, 42 are closed at the same time. This prevents that power is drawn from the solar array 22 by two or more charge circuits 46, 47 at the same time.
  • the input stage 48 of the solar array 22 based pulse load charger 21 is arranged to be connected, or is actually connected, to an output of the solar array 22.
  • a capacitor 24 is provided in the input stage 48 for, at least temporarily, storing electrical energy from the solar array 22, and for providing said stored energy to any of the transformers 30, 41 , if/when required.
  • a solar output switch 23 is provided for either connecting or disconnecting the solar array 22 to any of the transformers 30, 41 .
  • the basic concept here is that the solar array 22 should disconnect any transformer 30, 41 each time too much current is drawn from the solar array 22. That is, the solar array 22 is operated at the right side of the substantially maximum power point as indicated with reference numeral 105 of figure 3. This allows the solar array 22 to recover again such that the output voltage of the solar array, i.e. the solar array voltage, starts to increase again.
  • the solar output switch 23 is closed again such that power is drawn from the solar array 22.
  • the solar output switch 23 may be a relay or the like.
  • a voltage sensor 25 for determining a solar array voltage of said solar array 22 is provided as well as solar array control means 26, 27, 28, connected to said voltage sensor, for disconnecting said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch 23 in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.
  • the first threshold and the second threshold may be the same, i.e. a voltage corresponding to the point indicated with reference numeral 106.
  • the first threshold may differ from the second threshold.
  • some sort of hysteresis loop is provided.
  • the first threshold is between 75% - 90% of the steady state voltage output of the solar array, and the second threshold is about 1 % - 5% higher than the first threshold.

Abstract

A solar array based pulse load charger arranged for operating around predetermined threshold values, said pulse load charger comprising a plurality of charge circuits and an input stage, said input stage comprising a capacitor arranged for storing electrical energy from said solar array, when connected, a solar output switch for connecting/disconnecting said solar array to said transformer, a voltage sensor for determining a solar array voltage of said solar array, solar array control means, connected to said voltage sensor, for disconnecting said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.

Description

Title: Pulse battery charger arranged for charging a battery
Description
The present invention is related to a pulse battery charger arranged for charging a battery.
Pulse battery chargers are known in the art and are arranged to feed a charge current to the battery in pulses. The charging rate can be controlled by varying the width of the pulses. During the charging process, short rest periods between pulses allow the chemical actions in the battery to stabilise by equalising the reaction throughout the bulk of the electrode before recommencing the charge. One of the challenges of pulse chargers is to improve the efficiency of the pulse chargers.
One of the challenges of the present disclosure is to charge the battery faster compared to conventional battery chargers designed for the same battery type. Another challenge is to cause the battery to store more energy compared to the case when it is charged with conventional battery chargers. Yet a further challenge is to increase the number of charging cycles the battery is able to withstand if it were charged by a conventional battery charger for the same battery type.
In a first aspect, the invention provides in a pulse battery charger arranged for charging a battery, said pulse battery charger comprising:
- a transformer for transforming an input voltage at a desired ratio, said main transformer including a primary winding connected to an input stage and a secondary winding connected to an output stage;
switching means for switching an input voltage of an input power source to said main transformer;
- rectifying means for rectifying an output voltage from said secondary winding of said main transformer;
a battery for storing electrical energy from said secondary winding of said main transformer;
a capacitor arranged for storing electrical energy from an input power source, when connected;
an input voltage sensor for determining said input voltage of said input power source;
an output current sensor for determining an output current provided by said secondary winding of said transformer; an output voltage sensor for determining an output voltage, said output voltage being a voltage over said battery;
control means for generating a control signal to control the switching operation of said switching means, wherein said control signal is a square wave signal having a duty cycle and a frequency, and wherein said control means are arranged to vary said duty cycle and said frequency based on said determined input voltage, said determined output current and said determined output voltage thereby causing said transformer to produce a dynamically changing output voltage which is applied to said battery.
It was the insight of the inventors that the frequency and the duty cycle of the control signal should be varied dynamically such that the wave form being applied to the switching means causes the output of the transformer to produce a dynamically changing pulsed output which is being applied to the battery being charged.
In the context of the present disclosure, the switching means may be any electronic switching device such as a Field Effect Transistor, FET, a Metal Oxide Semiconductor, MOS, FET or a transistor.
Using the invention, it is possible to construe the characteristics of the output signal at the secondary winding of the transformer in such a way that a shock voltage occurs after each ON-time of the period. The shock voltage should be construed in such a way that it is only a fraction of the ON-time itself, for example 0,2% - 3% of the total period. And the shock voltage should have a magnitude which exceeds the magnitude of the ON-time substantially. The shock voltage ensures that the battery gets reinitialized again.
The result of the above is that it is possible to charge the battery more quickly, causing the battery to store more energy and to increase the number of charging cycles the battery is able to withstand.
In accordance with the present invention, the control means may comprise a microcontroller, a microprocessor, a Field Programmable Gate Array, FPGA, or anything alike.
In an example, said control means are arranged to generate said control signal in such a way that said produced output voltage comprises:
a period having an ON-time between 10% - 35%, preferably around 20%, of said period;
a SHOCK-time between 0,2% - 3% of said period;
an OFF-time during a remainder of said period;
- a first output voltage during said ON-time of said period;
substantially no output voltage during said OFF-time of said period;
a second output voltage during said SHOCK-time of said period, wherein said second output voltage is oppositely directed to said first output voltage, and wherein a magnitude of said second output voltage is between four - eight times higher than a magnitude of said first output voltage, thereby dislodging any impurities within said battery.
The example disclosed above describes a detailed implementation of an advantageous embodiment. That is, the shock voltage, i.e. the voltage during the SHOCK-time, needs to be of a magnitude far larger than the output voltage during the ON-time. This ensures that the battery gets reinitialized again such that the battery does not loose any capacitance value.
In accordance with the present example, the shock voltage is provided to the battery right after the ON-time of the period. This improves the recovery process of the battery.
In another example, said control means are arranged to
decrease said frequency of said control signal whenever said input voltage sensor has determined a drop in said input voltage thereby reducing current flowing in said primary winding of said transformer allowing said input power source to recover, and to
increase said frequency of said control signal whenever said input voltage sensor has determined an increase in said input voltage thereby increasing current flowing in said primary winding of said transformer.
The advantage of this example is that the frequency of the control means will automatically be set to allow for a more efficient current draw from the input power source. This is especially true in case the input power source is a solar array.
In other words, in accordance with this example, the pulse battery charger operates in a mode in which the substantially maximum power is drawn from the input power source. In another example, said output current sensor is arranged for determining an output current provided by said secondary winding of said transformer at least during an ON-time of said produced output voltage, and wherein said control means are arranged to generate said control signal based on charge conditions of said battery.
The above entails that the control means are arranged to read out, or be provided with, the current delivered via the secondary winding of the transformer during the charging period of the battery. The charging period of the battery equals the ON-time of the produced output voltage. This means that the battery is under charging conditions.
Depending on the charge conditions of the battery, the control means may either increase or decrease the charge current. The charge conditions may be measured, for example real time, and may equal, for example, the voltage over the battery or the total amount of energy in the battery. The charge conditions may also be predefined, for example the maximum allowed current to be provided to the battery or the like.
In a further example, the output voltage sensor is arranged for determining said output voltage before a start of an ON-time of said produced output voltage, and wherein said control means are arranged to adjust a duty cycle of said control signal based on said determined output voltage.
The above entails that the control means are arranged to read out, or be provided with, the output voltage, i.e. the voltage over the battery. This voltage is measured just before the ON-time of the period corresponding to the duty cycle meaning that the battery is not under charging conditions at this time. The battery, thus, had a maximum period of rest, i.e. the OFF-time, and the output voltage will thus equal the exact charge state of the battery. That is, the voltage measured by the output voltage sensor will accurately measure the voltage over the battery.
Using this information, the control means may be arranged to:
increase a duty cycle of said control signal in case said output voltage is below a predetermined charge threshold;
continuously decreasing a duty cycle of said control signal in case said output voltage exceeds a predetermined charge threshold in such a way that when the battery is approximately fully charged said duty cycle is approximately zero. This has the effect of slowly decreasing the charge rate as the battery gets more charged. This will achieve the objective of increasing the energy stored in the battery, and increase the life expectancy of the battery as a whole.
In another example, the battery is any of a lead crystal, lead acid and/or lithium Ion battery type.
In yet a further example, the pulse battery charger comprises said input power source, wherein said input power source is any of a Grid, a wind turbine, a Generator and a solar array.
In a second aspect, there is provided a method of operating a pulse battery charger according to any of the previous claims, said method comprising the steps of:
determining, by said input voltage sensor, said input voltage of said input power source;
determining, by said output current sensor, said output current provided by said secondary winding of said transformer;
determining, by said output voltage sensor, said output voltage, said output voltage being said voltage over said battery;
generating, by said control means, said control signal to control the switching operation of said switching means, wherein said control signal is a square wave signal having a duty cycle and a frequency, and varying, by said control means, said duty cycle and said frequency based on said determined input voltage, said determined output current and said determined output voltage thereby causing said transformer to produce a dynamically changing output voltage which is applied to said battery.
In an example of the method, said step of generating comprises: generating said control signal in such a way that said produced output voltage comprises:
a period having
an ON-time between 10% - 35%, preferably around 20%, of said period;
a SHOCK-time between 0,2% - 3% of said period;
an OFF-time during a remainder of said period;
a first output voltage during said ON-time of said period; substantially no output voltage during said OFF-time of said period;
a second output voltage during said SHOCK-time of said period, wherein said second output voltage is oppositely directed to said first output voltage, and wherein a magnitude of said second output voltage is between four - eight times higher than a magnitude of said first output voltage, thereby dislodging any impurities within said battery.
In another example of the method, the step of generating comprises: decreasing said frequency of said control signal whenever said input voltage sensor has determined a drop in said input voltage thereby reducing current flowing in said primary winding of said transformer allowing said input power source to recover, and to
increasing said frequency of said control signal whenever said input voltage sensor has determined an increase in said input voltage thereby increasing current flowing in said primary winding of said transformer.
In a further example of the method, said step of determining said output current comprises:
determining said output current provided by said secondary winding of said transformer at least during an ON-time of said produced output voltage, and wherein said step of generating comprises:
generating said control signal based on charge conditions of said battery.
In yet another example of the method, said step of determining said output voltage comprises:
- determining said output voltage before a start of an ON-time of said produced output voltage,
and wherein said step of generating comprises:
adjusting a duty cycle of said control signal based on said determined output voltage.
In an even further example of the method, said step of adjusting comprises:
increasing a duty cycle of said control signal in case said output voltage is below a predetermined charge threshold; continuously decreasing a duty cycle of said control signal in case said output voltage exceeds a predetermined charge threshold in such a way that when the battery is approximately fully charged said duty cycle is approximately zero.
The above-mentioned and other features and advantages of the disclosure will be best understood from the following description referring to the attached drawings. In the drawings, like reference numerals denote identical parts or parts performing an identical or comparable function or operation.
The invention will now be explained in more detail with reference to the appended figures, which merely serve by way of illustration of the invention and which must not be construed as being limitative thereto.
The present disclosure is also related to a solar array based pulse load charger.
Pulse chargers are known in the art and are arranged to feed a charge current to the battery in pulses. The charging rate can be controlled by varying the width of the pulses. During the charging process, short rest periods between pulses allow the chemical actions in the battery to stabilise by equalising the reaction throughout the bulk of the electrode before recommencing the charge. One of the challenges of pulse chargers with respect to solar arrays is to improve the efficiency of the pulse chargers.
In a first aspect, the disclosure provides in a solar array based pulse load charger arranged for operating around predetermined threshold values, said pulse load charger comprising a plurality of charge circuits,
wherein each charge circuit comprises:
an inductor in the form of a transformer to store the input energy and to transform the input voltage at a desired ratio, said main transformer including a primary winding connected to an input stage and a secondary winding connected to an output stage;
switching means for switching said input voltage to said main transformer;
- rectifying means for blocking negative current flow through the secondary winding of the transformer;
a load for storing electrical energy from said secondary winding of said main transformer; control means for generating a control signal to control the switching operation of said switching means;
wherein said rectifying means are arranged for connecting a secondary winding of said transformer of said charge circuit to a secondary winding of a transformer of a next charge circuit of said plurality of charge circuits, such that each of said loads of said charge circuits are connected in series for providing a boosted voltage compared to said input voltage;
wherein said input stage is arranged to be connected to an output of a solar array, said input stage comprising:
- a capacitor arranged for storing electrical energy from said solar array, when connected;
a solar output switch for connecting/disconnecting said solar array to said transformer;
voltage sensor for determining a solar array voltage of said solar array;
solar array control means, connected to said voltage sensor, for disconnecting said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.
It was the insight of the inventors that the efficiency of the pulse load charger is increased in case the output from the solar array is maximized as much as possible. In order to do so, a substantially maximized output is achieved, using the solar array control means monitoring the solar array voltage while current is being drawn from the array and, at the point where the voltage starts to drop, the draw on the output power from the solar panel array is temporarily suspended by the solar array control means by causing the solar output switch to disconnect the solar array from the transformer. This will stop the current flow and cause the solar array voltage to begin to increase. At the point where the voltage has recovered again, i.e. has reached the second threshold, the output power will again be applied to any of the charge circuits by the solar array control means by causing the solar output switch to connect said solar array to said transformer. In other words, the voltage sensor is feeding the solar array control means with the solar array voltage. When too much current is being drawn from the solar array, the solar array voltage will drop. The solar array control means will sense this drop of the voltage, i.e. it fall below the first threshold, and will automatically open the solar output switch such that the transformer is disconnected from the solar array. This will stop any current from flowing in the primary windings of the transformer and will allow the solar array voltage to recover again. As soon as the solar array voltage has recovered, i.e. it exceeds a predetermined second threshold, the solar output switch will be closed again to allow the current to flow to the primary windings of the transformer again. This thus means that the frequency and duration of the control will automatically adjust to allow for maximum power drawn from the solar array.
The result of the above is that the power drawn from the solar array is maximized as much as possible, such that the objective of the present disclosure is achieved.
It is thus noted that, in accordance with the present disclosure, the solar array control means are arranged to control the switching of the solar output switch in such a way that the power drawn from the solar array is maximized as much as possible, by making sure that the voltage drop of the solar array voltage is within predefined thresholds. The inventors have found that maximum power is drawn from the solar array in case there actually is a voltage drop of the solar array voltage. The voltage drop may be set once in the solar array control means using the first threshold and the second threshold.
Another advantage of the solar array based pulse load charger in accordance with the present disclosure is that the system is able to cope with very low solar output voltage, for example even below 0, 1 volts. The inventor has found that is may be beneficial to have a plurality of charge circuits for boosting the voltage instead of a single charge circuit, having a single boost converter, for boosting the voltage. Utilizing multiple charge circuits in parallel, i.e. the loads of which are connected in series, is beneficial as it improves the efficiency of the solar array based pulse load charger over the whole voltage output range of the solar panel.
It is further noted that, in accordance with the present disclosure, the loads comprised by each of the charge circuits remain balanced during the charging cycle. That is, each of the loads are charged simultaneously, and at the same rate, such that each of the loads, i.e. batteries, provide roughly the same voltage. These voltages are then summed up as the batteries are placed in series, to provide for a single output voltage. In an example, each of the batteries of the charge circuits are charged to about 12 volts. Four charge circuits may be present in the solar array based pulse load charges such that the total single output voltage of the solar array based pulse load charger is about 48 volts.
The above thus entails that each of the batteries are able to provide power at the same time that the batteries are charged.
In an example, the predetermined first threshold is between 75% - 90% of said solar array voltage.
The inventors have found that it is likely that maximum power is drawn from the solar array in case such an amount of current is drawn from the solar array that the solar array voltage drops until about 75% - 90% of the solar array voltage in case no load is applied.
In another example, the second threshold is between 1 % - 10% of solar array voltage higher than said first threshold.
The advantage of this example is that the solar output switch is not continuously being switched from connecting the solar array output to the transformer to disconnecting the solar array output to the transformer, and vice versa. The solar output switch is stressed less in case the second threshold is higher compared to the first threshold.
As an alternative, the first threshold equals the second threshold such that it is more likely that maximum power is drawn continuously from the solar array.
In a further example, each charge circuit further comprises an output current sensor for determining an output current, and said control means are arranged generate said control signal to control the switching operation of said switching means based on said measured output current.
The output current is measured during the duty cycle. This means that the load, for example battery, is under full charging conditions at that time. Depending on the charge conditions of the load, i.e. battery, the control means may either increase or decrease the charge current. This can be done by increasing or decreasing the duty cycle of the pulse.
In a further example, each charge circuit further comprises an output voltage sensor arranged for determining an output voltage at said secondary winding of said transformer, and said control means are arranged to generate said control signal to control the switching operation of said switching means based on said measured output voltage.
The output voltage sensor will measure the output voltage and will feed that voltage back to the control means. The control means are arranged to measure the output voltage just before the duty cycle begins. This means that the battery will not be under charging conditions at this time and will have had a period of rest, and the output voltage sensor will measure the exact charge state of the load, i.e. the battery. Based on this information, the control means may either increase or decrease the duty cycle.
That is, in case the load is a battery, the control means may be arranged to:
increase a duty cycle of said control signal in case the load of said battery is below a predetermined charge threshold;
continuously decreasing a duty cycle of said control signal in case the load of said battery exceeds a predetermined charge threshold in such a way that when the battery is approximately fully charged said duty cycle is approximately zero.
The effect of the above is that the charge rate is slowly decrease as the battery gets more charged, thereby improving the storing capabilities of the battery.
In a preferred example, the pulse load charger comprises four charge circuits.
In a second aspect, the disclosure provides in a method of operating a solar array based pulse load charger according to any of the examples as disclosed above, said method comprising the steps of:
determining, by said voltage sensor, said solar array voltage of said solar array;
disconnecting, by said solar array control means, said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.
Preferably, the predetermined first threshold is between 75% - 90% of said solar array voltage. In an example hereof, the second threshold is between 1 % - 10% of solar array voltage higher than said first threshold. Alternatively ,the first threshold equals said second threshold.
In a further example, each charge circuit further comprises an output current sensor for determining an output current, and wherein said control means are arranged generate said control signal to control the switching operation of said switching means based on said measured output current.
In another example, each charge circuit further comprises an output voltage sensor arranged for determining an output voltage at said secondary winding of said transformer, and wherein said control means are arranged to generate said control signal to control the switching operation of said switching means based on said measured output voltage.
In an even further example, said load is a battery, wherein said control means are arranged to:
- increase a duty cycle of said control signal in case the load of said battery is below a predetermined charge threshold;
continuously decreasing a duty cycle of said control signal in case the load of said battery exceeds a predetermined charge threshold in such a way that when the battery is approximately fully charged said duty cycle is approximately zero.
The above-mentioned and other features and advantages of the disclosure will be best understood from the following description referring to the attached drawings. In the drawings, like reference numerals denote identical parts or parts performing an identical or comparable function or operation.
The disclosure will now be explained in more detail with reference to the appended figures, which merely serve by way of illustration of the invention and which must not be construed as being limitative thereto.
Brief Description of the Drawings
Figure 1 shows, in a schematic form, a circuitry with respect to the pulse battery charger 1 in accordance with the present invention
Figure 2 shows, in a schematic form, a chart indicating a output waveform according to the present invention.
Figure 3 shows, in a schematic form, a chart indicating a maximum power point at which a solar array is to be operated according to the present invention. Figure 4 shows, in a schematic form, a circuitry with respect to the solar array based pulse load charger in accordance with the present invention.
Detailed Description
Figure 1 shows, in a schematic form, a circuitry with respect to the pulse battery charger 1 in accordance with the present invention.
The pulse battery charger 1 is arranged for charging a battery 12, more specifically a battery of any of a lead crystal, lead acid and/or lithium Ion battery type.
In accordance with the present invention, the pulse battery charger 1 is arranged in such a way that the lifetime, the capacity and the charge time of the battery 12 is improved.
The pulse battery charger 1 comprises a single charge circuit. A charge circuit is characterized in that it comprises a transformer 6, switching means 5 and each of the components depicted on the right of the transformer 6. Multiple charge circuits may be deployed, wherein the batteries 12 are cascaded in series. This ensures that the voltages of the batteries 12 can be added up.
Each of the charge circuits is then to be coupled to the input power source at a time. Each of the charge circuits is thus coupled to the input power source one after the other. This coupling process is obtained using the control means 5 present in each of the charge circuits.
Each charge circuit thus comprises the transformer 6 for transforming an input voltage at a desired ratio, the transformer including a primary winding 7 connected to an input stage and a secondary winding 8 connected to an output stage. An advantage of using a transformer 6 is that a transformer 6 provides for an isolation between the input stage and the output stage.
Further, switching means 5 are provided for switching the input voltage to the transformer 6. When the switch is closed, the primary winding 7 of the transformer 6 is directly connected to the input power source. The current through the primary winding 7 of the transformer 6 and the corresponding magnetic flux in the transformer 6 will then increase, storing energy in the transformer 6. The voltage induced in the secondary winding 8 of the transformer 6 is negative, so that the rectifying means 9, for example a diode, is reverse-biased, i.e. blocked. When the switch is opened, the current through the primary winding 7 of the transformer 6 and thus also the magnetic flux in the transformer 6, drops. The voltage induced in the secondary winding 8 of the transformer 6 is then positive allowing the current to flow from the transformer 6 via the rectifying means 9.
Typically the switching means 5 comprise a Field Effect Transistor,
FET, a Metal Oxide Semiconductor FET, MOSFET, a transistor or anything alike.
Each charge circuit further comprises a battery 12 for storing electrical energy from said secondary winding 8 of said main transformer 6. The battery 12 is typically a lead crystal battery, a lead acid battery or a lithium Ion battery. The batteries of each of the charge circuits are connected in series such that the output of all the charge circuits combined provides for an increased output voltage.
A capacitor 4 is provided in the input stage for, at least temporarily, storing electrical energy from the input power source, and for providing said stored energy to the transformers 6, if/when required. Further an input selector 2 is provided in case more than one type of input power source is connected to the pulse battery charger 1 .
Further, an input voltage sensor 3 is provided for determining the input voltage of the input power source, and an output current sensor 1 1 is provided for determining an output current provided by the secondary winding 8 of the transformer 6, and an output voltage sensor 10 is provided for determining an output voltage, the output voltage being the voltage over the battery 12. Each of the measurement are provided to control means 13, 14.
The control means 13, 14 are arranged for generating a control signal to control the switching operation of the switching means 5, wherein the control signal is a square wave signal having a duty cycle and a frequency as is explained below with reference to figure 2.
The control means 13, 14 are arranged to vary the duty cycle and the frequency based on the determined input voltage, the determined output current and the determined output voltage thereby causing the transformer to produce a dynamically changing output voltage which is applied to the battery 12.
The control means 13, 14 may, for example, be arranged to decrease said frequency of said control signal whenever said input voltage sensor has determined a drop in said input voltage thereby reducing current flowing in said primary winding of said transformer allowing said input power source to recover, and to increase said frequency of said control signal whenever said input voltage sensor has determined an increase in said input voltage thereby increasing current flowing in said primary winding of said transformer.
Figure 2 shows, in a schematic form, a chart indicating a output waveform 51 according to the present invention.
The control signal, generated by the control means in accordance with figure 1 , are arranged to generate a control signal in such a way the produced output voltage comprises a duty cycle / period.
The period corresponding to the duty cycle, as depicted in figure 2, comprises an ON-time 52 between 10% - 35%, preferably around 20%, of the total period. During this ON-time the battery 12 is being charged using a voltage output indicated with reference numeral 55.
The inventors have found that it is beneficial in case the ON-time 52 is followed by a SHOCK-time 53 between 0,2% - 3% of the period, more specifically around 1 % of the period. During this time a SHOCK voltage 59 is generated, and provided to the battery 12 to ensure that the battery is reinitialised. This is advantageous for the total capacity of the battery 12. That is the total capacity of the battery 12 will not, or hardly, degrade over time.
The ratio of the magnitude of the SHOCK voltage 59 with respect to the voltage output during the ON-time 52, i.e. as indicated with reference numeral 55, is preferably about 5: 1 .
During the OFF-time 54, i.e. the rest time, the battery 12 is able to recover such that, et the end of the OFF-time 54, the voltage provided by the battery 12 is roughly the steady state voltage of the battery 12 itself.
The inventors have found that, during the ON-time 52, the output current is measured by the output current sensor which is indicated by reference numeral 57. Depending on charge conditions of the battery, the control means will either increase or decrease the charge current.
The output voltage sensor is arranged to measure the output voltage at least at the end of the OFF-time 54, i.e. at the end of the rest time. This is indicated with reference numeral 58 in figure 2.
This information may be used by the control means to control the duty cycle of the control signal. More specifically, the duty cycle the control signal may be increase in case said output voltage is below a predetermined charge threshold, for example below eighty percentage charge voltage or the like. The control means may also continuously decrease a duty cycle of said control signal in case said output voltage exceeds a predetermined charge threshold, for example exceeding the eighty percentage charge voltage, in such a way that when the battery is approximately fully charged said duty cycle is approximately zero.
Figure 3 shows, in a schematic form, a chart 1 indicating a maximum power point 106 at which a solar array is to be operated according to the present invention.
As mentioned before, the inventors have found that the solar array should be utilized in such a manner that a substantially maximized power is drawn therefrom. As such, it was the insight that increase power is drawn from the solar array when the output voltage of the solar array begins to drop. This is indicated with the chart 101 shown in figure 3.
The output voltage of the solar array, i.e. the solar array voltage, is indicated with reference numeral 103. The vertical axis 102 is scaled with a numerical output. That is, for the solar array voltage 103 the vertical axis is divided in, for example, 0 - 6 volts DC. The horizontal axis 107 is scaled with the total current drawn from the solar array.
The total power drawn from the solar array is indicated with reference numeral 104. Substantially most power is drawn from the solar array when the solar array voltage 3 starts to drop. This is indicated with reference numerals 105 and 106. It was the insight that the solar array based pulse load charger should function in such a way that as much as possible power is drawn from the solar array in a continuous manner. In other words, the pulse load charger should make sure that the power that the solar array is providing is around the maximum power as indicated with reference numeral 105.
Figure 4 shows, in a schematic form, a circuitry with respect to the solar array based pulse load charger 21 in accordance with the present invention.
The solar array 22 based pulse load charger 21 is arranged for operating around predetermined threshold values. More specifically, the solar array based pulse load charger 21 is arranged to operate around the substantially maximum power point as indicated with reference numeral 105 in figure 3.
The pulse load charger 21 comprises a plurality of charge circuits. In the present situation two charge circuits 46, 47 are shown. Typically, about four charge circuits 46, 47 may be used. According to the present invention, only one charge circuit 46, 47 is coupled to the solar array 22 at a time. Each of the charge circuits 46, 47 is thus coupled to the solar array 22 one after the other. This coupling process is explained in more detail hereafter.
Each charge circuit 46, 47 comprises a transformer 30, 41 for transforming an input voltage at a desired ratio, said main transformer 30, 41 including a primary winding connected to an input stage and a secondary winding connected to an output stage. An advantage of using a transformer 30, 41 is that a transformer 30, 41 provides for an isolation between the input stage and the output stage.
Further, switching means 32, 42 are provided for switching the input voltage to the transformers 30, 41 , respectively. When the switch is closed, the primary winding of the transformer 30, 41 is directly connected to the solar array output. The current through the primary winding of the transformer 30, 41 and the corresponding magnetic flux in the transformer will then increase, storing energy in the transformer 30, 41 . The voltage induced in the secondary winding of the transformer 30, 41 is negative, so that the rectifying means 34, 40, for example a diode, is reverse-biased, i.e. blocked.
When the switch is opened, the current through the primary winding of the transformer 30, 41 and thus also the magnetic flux in the transformer 30, 41 , drops. The voltage induced in the secondary winding of the transformer 30, 41 is then positive allowing the current to flow from the transformer via the rectifying means 34, 40.
Typically the switching means 32, 42 comprise a Field Effect
Transistor, FET.
Each charge circuit 46, 47 further comprises a load 35, 37 for storing, or consuming, electrical energy from said secondary winding of said main transformer. The load 35, 37 is typically a battery, for example a lead crystal battery, a lead acid battery of a lithium Ion battery. The batteries of each of the charge circuits 46, 47 are connected in series such that the output 45 of all the charge circuits 46, 47 combined provides for an increased output voltage.
Control means 29, 31 , 44, 43 are provided for generating a control signal for controlling the switching operation of the switching means 32, 42, respectively, the control signal is, for example, a square wave having a certain duty cycle. In case of, for example, four charge circuits, 46, 47, the duty cycle is about 20 - 25% for each of the switching means 32, 42, respectively. The duty cycles are further shifted in time with respect to each other to make sure that none of the switching means 32, 42 are closed at the same time. This prevents that power is drawn from the solar array 22 by two or more charge circuits 46, 47 at the same time.
The input stage 48 of the solar array 22 based pulse load charger 21 is arranged to be connected, or is actually connected, to an output of the solar array 22.
A capacitor 24 is provided in the input stage 48 for, at least temporarily, storing electrical energy from the solar array 22, and for providing said stored energy to any of the transformers 30, 41 , if/when required.
Additional components are incorporated in the input stage 48 in order to make sure that the solar array 22 based pulse load charger 21 is operating around the maximum power point as indicated in figure 3. These components, and their functionality, will be explained in more detail here below.
First, a solar output switch 23 is provided for either connecting or disconnecting the solar array 22 to any of the transformers 30, 41 . The basic concept here is that the solar array 22 should disconnect any transformer 30, 41 each time too much current is drawn from the solar array 22. That is, the solar array 22 is operated at the right side of the substantially maximum power point as indicated with reference numeral 105 of figure 3. This allows the solar array 22 to recover again such that the output voltage of the solar array, i.e. the solar array voltage, starts to increase again.
Once the output voltage of the solar array 22 has increased again to the point indicated with reference numeral 106, i.e. corresponding to the substantially maximum power point as indicated with reference numeral 105 of figure 3, the solar output switch 23 is closed again such that power is drawn from the solar array 22.
In accordance with the present invention, the solar output switch 23 may be a relay or the like.
In order to accomplish the above, a voltage sensor 25 for determining a solar array voltage of said solar array 22 is provided as well as solar array control means 26, 27, 28, connected to said voltage sensor, for disconnecting said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch 23 in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.
The first threshold and the second threshold may be the same, i.e. a voltage corresponding to the point indicated with reference numeral 106. In order to prevent chattering of the solar output switch 23, the first threshold may differ from the second threshold. As such, some sort of hysteresis loop is provided. Typically, the first threshold is between 75% - 90% of the steady state voltage output of the solar array, and the second threshold is about 1 % - 5% higher than the first threshold.
The present invention has been explained in the foregoing by means of a number of examples. As those skilled in the art will appreciate, several modifications and additions can be realised without departing from the scope of the invention as defined in the appended claims.

Claims

1 . A solar array based pulse load charger arranged for operating around predetermined threshold values, said pulse load charger comprising a plurality of charge circuits and an input stage,
wherein each charge circuit comprises:
a transformer for transforming an input voltage at a desired ratio, said main transformer including a primary winding connected to an input stage and a secondary winding connected to an output stage;
- switching means for switching said input voltage to said main transformer;
rectifying means for blocking negative current flow through the secondary winding of the transformer;
a load for storing electrical energy from said secondary winding of said main transformer;
control means for generating a control signal to control the switching operation of said switching means;
wherein said rectifying means are arranged for connecting a secondary winding of said transformer of said charge circuit to a secondary winding of a transformer of a next charge circuit of said plurality of charge circuits, such that each of said loads of said charge circuits are connected in series for providing a boosted voltage compared to said input voltage;
wherein said input stage is arranged to be connected to an output of a solar array, said input stage comprising:
- a capacitor arranged for storing electrical energy from said solar array, when connected;
a solar output switch for connecting/disconnecting said solar array to said transformer;
voltage sensor for determining a solar array voltage of said solar array;
solar array control means, connected to said voltage sensor, for disconnecting said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.
2. A solar array based pulse load charger according to claim 1 , wherein said predetermined first threshold is between 75% - 90% of said solar array voltage.
3. A solar array based pulse load charger according to any of the previous claims, wherein said second threshold is between 1 % - 10% of solar array voltage higher than said first threshold.
4. A solar array based pulse load charger according to any of the claims 1 - 2, wherein said first threshold equals said second threshold.
5. A solar array based pulse load charger according to any of the previous claims, wherein each charge circuit further comprises an output current sensor for determining an output current, and wherein said control means are arranged generate said control signal to control the switching operation of said switching means based on said measured output current.
6. A solar array based pulse load charger according to any of the previous claims, wherein each charge circuit further comprises an output voltage sensor arranged for determining an output voltage at said secondary winding of said transformer, and wherein said control means are arranged to generate said control signal to control the switching operation of said switching means based on said measured output voltage.
7. A solar array based pulse load charger according to claim 6, wherein said load is a battery, wherein said control means are arranged to:
increase a duty cycle of said control signal in case the load of said battery is below a predetermined charge threshold;
continuously decreasing a duty cycle of said control signal in case the load of said battery exceeds a predetermined charge threshold in such a way that when the battery is approximately fully charged said duty cycle is approximately zero.
8. A solar array based pulse load charger according to any of the previous claims, wherein said pulse load charger comprises four charge circuits.
9. A method of operating a solar array based pulse load charger according to any of the previous claims, said method comprising the steps of:
determining, by said voltage sensor, said solar array voltage of said solar array; disconnecting, by said solar array control means, said solar output switch in case said determined solar array voltage falls below a predetermined first threshold thereby letting said solar array voltage recover, and for connecting said solar output switch in case said determined solar array voltage exceeds a predetermined second threshold thereby increasing power drawn from said solar array such that said solar array voltage decreases.
10. A method according to claim 9, wherein said predetermined first threshold is between 75% - 90% of said solar array voltage.
1 1 . A method according to any of the claims 9 - 10, wherein said second threshold is between 1 % - 10% of solar array voltage higher than said first threshold.
12. A method according to any of the claims 9 - 10, wherein said first threshold equals said second threshold.
13. A method according to any of the claims 9 - 12, wherein each charge circuit further comprises an output current sensor for determining an output current, and wherein said control means are arranged generate said control signal to control the switching operation of said switching means based on said measured output current.
14. A method according to any of the claims 9 - 13, wherein each charge circuit further comprises an output voltage sensor arranged for determining an output voltage at said secondary winding of said transformer, and wherein said control means are arranged to generate said control signal to control the switching operation of said switching means based on said measured output voltage.
15. A method according to any of the claims 9 - 14, wherein said load is a battery, wherein said control means are arranged to:
- increase a duty cycle of said control signal in case the load of said battery is below a predetermined charge threshold;
continuously decreasing a duty cycle of said control signal in case the load of said battery exceeds a predetermined charge threshold in such a way that when the battery is approximately fully charged said duty cycle is approximately zero.
PCT/NL2017/050459 2016-07-08 2017-07-10 Pulse battery charger arranged for charging a battery WO2018009071A1 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
NL2017137A NL2017137B1 (en) 2016-07-08 2016-07-08 A pulse battery charger arranged for charging a battery, as well as a corresponding method.
NL2017131 2016-07-08
NL2017131A NL2017131B1 (en) 2016-07-08 2016-07-08 A solar array based pulse load charger arranged for operating around predetermined threshold values as well as a corresponding method.
NL2017137 2016-07-08

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WO2018009071A1 true WO2018009071A1 (en) 2018-01-11

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60216730A (en) * 1984-04-11 1985-10-30 関西電力株式会社 Solar bight generator apparatus
WO2004114433A2 (en) * 2003-06-17 2004-12-29 Ecosol Solar Technologies, Inc. A two stage energy storage device
US20120187920A1 (en) * 2009-09-17 2012-07-26 Beijing Anruode Mechanical And Electrical Apparatus Ltd Method And Device For Charging Multiple Battery Packs

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS60216730A (en) * 1984-04-11 1985-10-30 関西電力株式会社 Solar bight generator apparatus
WO2004114433A2 (en) * 2003-06-17 2004-12-29 Ecosol Solar Technologies, Inc. A two stage energy storage device
US20120187920A1 (en) * 2009-09-17 2012-07-26 Beijing Anruode Mechanical And Electrical Apparatus Ltd Method And Device For Charging Multiple Battery Packs

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