Charging system and a method of charging an electrical energy storage device

Some embodiments are directed to charging system (100) comprising converter switches for electrically coupling to a first electrical energy storage device, a filter circuit comprising a series inductor and a parallel capacitor, a coupling device for coupling to a second electrical energy storage device comprising a detection device for detecting a connection status of the coupling device, switches arranged for selectively electrically coupling, when switched on, the filter circuit with an alternating current voltage source, and a controller, configured, based on the connection status of the coupling device, to switch on switches and control the converter switches such that the time periodical voltage signal and the current through the series inductor are in phase, or to switch off switches and control the converter switches for providing a current signal to the second electrical energy storage device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national phase filing under 35 C.F.R. § 371 of and claims priority to PCT Patent Application No. PCT/EP2017/084548, filed on Dec. 22, 2017, the contents of which is hereby incorporated in its entirety by reference.

BACKGROUND

Some embodiments of the presently disclosed subject matter relate to a charging system, a charging station and a method of charging a first electrical energy storage device and a second electrical energy storage device via the charging system.

Recent drive to abate emissions of automotive vehicles has increased the use of electrical vehicles which are driven by electric motors. Electric motors are supplied by batteries which are periodically charged from a charging station or electrical outlet.

However, in some areas, there may be limited availability of grid power to charge the batteries of electrical vehicles. Such areas may be for example remote areas with weak grid connection. Furthermore, when batteries of large capacity need to be charged in short time, for example in case of commercial buses or trucks, charging of the batteries in such areas may require additional time compared to charging such batteries with stable grid connections.

In commercial activities, for example in the transport of passengers or goods, any extra delay introduced in the transport of passengers or good cost time and money. For example, if the battery of an electrical bus for the transportation of passengers is charged at the completion of a route, the same bus needs to be immediately available at the start of a new planned route after the charge of the battery. If charging of the battery is insufficient due to a weak grid connection, the bus service may be disrupted or critically delayed.

This makes the passenger unhappy and the company delivering the service less productive.

In order to overcome this issue a system has been proposed, for example in US2013/0221918A1, in which a vehicle energy storage system is charged either by an external energy source, for example a utility or a grid, or by stationary energy storage system. The grid or utility would allow for a slow charge of the vehicle energy storage system. The stationary energy storage system would allow for a fast charge of the vehicle storage system.

In US2013/0221918A1, the stationary energy storage system is charged by an external energy source by a step transformer and an alternating current (AC) to direct current (DC) converter and the vehicle energy storage is charged by the stationary energy storage by a DC to DC converter.

However, the solution proposed in US2013/0221918A1 may be dispendious in terms of both cost and hardware resources. In fact the solution proposed in US2013/0221918A1 requires the use of a high power AC to DC converter with dedicated controller and a high power DC to DC converter also with a dedicated controller and filter.

SUMMARY

One aspect of some embodiments of the presently disclosed subject matter therefore is to reduce the size and cost of the existing charger systems. Embodiments are defined in the dependent claims.

Accordingly, some embodiments provide a charging system. The charging system includes a switching converter, a filter circuit, a first set of switches, a coupling device and a controller for controlling the first set of switches and the converter. The switching converter includes converter switches coupled to each other at a converter terminal. The switching converter is for electrically coupling to a first electrical energy storage device for power conversion between the switching converter and the first electrical energy storage device. The filter circuit includes a series inductor and a parallel capacitor. The series inductor has a first inductor terminal and a second inductor terminal electrically coupled to the converter terminal. The parallel capacitor has a first capacitor terminal electrically coupled to the first inductor terminal and a second capacitor terminal. The first set of switches is arranged for selectively electrically coupling, when switched on, the filter circuit with an alternating current voltage source. The alternating current voltage source provides a time periodical voltage signal. The coupling device selectively electrically couples a second electrical energy storage device to the filter circuit via at least the first inductor terminal. The coupling device includes a detection device configured to detect a connection status of the coupling device and send, based on the status, a coupling signal indicating whether the second electrical energy storage device is connected to the coupling device. The controller is configured to receive the coupling signal from the detection device, and based on the coupling signal, to switch on the switches of the first set and control the converter switches such that the time periodical voltage signal and the current through the series inductor are in phase, or to switch off the switches of the first set and control the converter switches for providing a current signal to the second electrical energy storage device for charging the second electrical energy storage device from the first electrical energy storage device.

A single switching converter can be used to transfer power between the alternating current voltage source and the first electrical energy storage device, and between the first electrical energy storage device and the second electrical energy storage device. Control of the switches of the first set based on the connection status of the coupling device together with a different control of the switching converter allows to charge the first electrical energy storage device from the alternating current voltage source or the second electrical energy storage device from the first electrical energy storage device.

When the first electrical energy storage device is charged from the alternating current voltage source, the switching converter is controlled as an AC to DC converter by for example making using of a pulse width modulated signal. The reactance value of the filter circuit together with the correct amplitude of the time periodical voltage signal allows to adjust a ratio of the active power to reactive power, i.e. the so-called power factor, transferred between the alternating current voltage source and the charging system. In this way power can be efficiently transferred, with less power losses, between the alternating current voltage source and the first electrical energy storage device.

When the second electrical energy storage device is charged from the first electrical energy storage device, the same switching converter is controlled as a DC to DC converter. The series inductor of the filter circuit is used to store energy in a first control cycle and to release energy in a second control cycle. The released energy is in the form of a substantially direct current signal delivered to the second electrical energy storage device through the series inductor. Such current can have in practice still some ripple which can be further attenuated by the parallel capacitor of the filter circuit.

In some embodiments, the first electrical energy storage device is a stationary battery and the second electrical energy storage device is a mobile battery, for example a vehicle battery.

In some embodiments, the ripple may be attenuated by using a multiple phase switching converter and optionally by interleaving the different multiple phases.

In some embodiments, the controller is configured, when the coupling signal indicates that the second electrical energy storage device is connected to the coupling device, to switch off the switches of the first set and control the converter switches in buck mode for converting a first voltage of the first electrical energy storage device into a second voltage of the second electrical energy storage device, the first voltage being higher than the second voltage

In some embodiments, the charging system further includes a second set of switches, a third set of switches and a fourth set of switches. The coupling device is configured for selectively electrically coupling the positive terminal of the second electrical energy storage device to the first inductor terminal, and the negative terminal of the second electrical energy storage device to the second capacitor terminal via the second set of switches. The coupling device is further configured for selectively electrically coupling the positive terminal of the second electrical energy storage device to a positive terminal of the first electrical energy storage device, and the negative terminal of the second electrical energy storage device to a negative terminal of the first electrical energy storage device via the third set of switches and the fourth set of switches.

By selectively connecting the coupling device to the filter circuit via the second set of switches and to the first electrical energy storage device via the third set of switches and fourth set of switches, it is also possible to directly charge the vehicle battery from the alternating current voltage source with the same switching converter. In other words, advantageously, the switching converter can still be controlled as an AC to DC converter and the vehicle battery be charged from the alternating current voltage source.

In some embodiments, the charging system may include an electrical energy monitoring device. The electrical energy monitoring device may be configured to monitor an electrical energy level of the first electrical energy storage device and to send an electrical energy signal to the controller indicating the electrical energy level. For example, the electrical energy monitoring device may be a voltmeter device or a power meter which may constantly monitor the level of the first electrical energy storage device. The electrical energy monitoring device may be wirelessly or wired connected to the controller, e.g. via respective interfaces and/or transmitter and receiver devices. The electrical energy signal is received by the controller.

The controller acknowledges via the coupling signal that the second electrical energy storage device has been connected to the coupling device and that the second electrical energy storage device requires charging. However, if, upon receiving the electrical energy signal, the controller acknowledges that the electrical energy level of the first electrical energy storage device has dropped below a predetermined electrical energy threshold, the controller may establish, for example, that the second electrical energy storage device cannot be charged directly from the first electrical energy storage device but can be charged directly from the alternating current voltage source. Thus, for example, the second electrical energy storage device can be charged from the alternating current voltage source when the electrical energy signal indicates that the electrical energy level of the first electrical energy storage device is not sufficient to charge the second electrical energy storage device. This can be done by electrically decoupling the first electrical energy storage device from the (output of) switching converter by e.g. the fourth set of switches, electrically decoupling the second electrical energy storage device from the (input of) filter circuit by e.g. the second set of switches and further, by electrically coupling the second electrical energy storage device to the (output) switching converter by e.g. the third set of switches. Similarly, for example, the second electrical energy storage device can be charged directly from the first electrical energy storage device when the electrical energy signal indicates that the electrical energy level of the first electrical energy storage device is sufficient to charge the second electrical energy storage device. For example, the sufficient electrical energy level may be higher than the electrical energy level of the second electrical energy storage device.

Another aspect of some other embodiments provide a charging station.

A further aspect of some other embodiments provide a method of charging a first electrical energy storage device and a second electrical energy storage device via a charging system.

It should be noted that items which have the same reference numbers in different Figures, have the same structural features and the same functions, or are the same signals. Where the function and/or structure of such an item has been explained, there is no necessity for repeated explanation thereof in the detailed description.

LIST OF REFERENCE NUMERALS IN FIGS.1-9

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1schematically shows an example of some embodiments of a charging system100.

Charging system100may be used to charge a first electrical energy storage device60and a second electrical energy storage device70.

The first and second electrical energy storage device may be batteries, capacitors, ultra-capacitors or any type of device suitable for storing electrical energy.

In some embodiments, first electrical energy storage device60is a stationary battery60and second electrical energy storage device70is a mobile battery. Stationary battery60may be a fixed battery, for example installed in a charging station for the charge of second electrical energy storage device70. The mobile battery may be the battery of a vehicle, for example an electrical vehicle.

In the text we will refer to the first electrical energy storage device as to stationary battery60and to the second electrical energy storage device as to vehicle battery70.

Stationary battery60may be charged by an alternating current voltage source22which provides a time periodical voltage signal to the system. Alternating current voltage source22may be part of an electrical grid network. The electrical grid network supplies electricity to end-users.

Vehicle battery70may be charged either by stationary battery60or, in some embodiments shown later directly by alternating current voltage source22.

In some embodiments, stationary battery60may be charged by alternating current voltage source22in a first phase and vehicle battery70may be charged by stationary battery60in a second phase. For example, energy provided by alternating current voltage source22may be generated by sustainable energy sources such as wind, solar, geothermal sources. Such sustainable energy sources are not always available or are not available with sufficient power to charge vehicle battery70within a reasonable amount of time. In the first phase, stationary battery60may be charged by the grid source, subsequently vehicle battery70may be charged with a higher power by stationary battery60. This feature allows that the available charging power is independent of the grid connection power requirement.

In some embodiments, after the stationary battery60is charged, power of stationary voltage may be higher than the power of vehicle battery70. Vehicle battery70may be then charged by this higher power.

In some embodiments, alternating current voltage source22includes a grid transformer10. Primary of grid transformer10is electrically coupled to a grid source15. Grid source15represents the power provided by the grid network, e.g. by the sustainable energy sources discussed above. Grid source15thus generates a source time periodical grid voltage i.e. an alternating current (ac) voltage signal. Grid transformer10provides, at the secondary of grid transformer10, a time periodical grid voltage signal having amplitude which is scaled with respect to the amplitude of the source signal.

In some embodiments, grid transformer10may provide electrical isolation between the grid network and the charging system. For example, the secondary from the transformer may be electrically isolated from the primary and the charging system electrically floating with respect to the earth potential.

For example, the time periodical grid signals may be a sinusoidal voltage signals. If the sinusoidal voltage signal at the primary has an amplitude of 10 kV, root mean square (RMS) line-line value, the voltage signal may be scaled down by the grid transformer10to a voltage with a amplitude lower than 10 kV RMS, for example 400 V RMS. Grid transformer10may include a pair of wire windings such that the amplitude of the voltage signal at the primary is scaled down at the secondary proportionally to a ratio between the wire winding turns of the pair.

Charging system100includes a first set20of switches20a,20b, coupling device30, a filter circuit40, a switching converter50and a controller80. Charging system100may optionally include grid transformer10

In some embodiments, the filter circuit may be a multiple phase filter, the switching converter may be a multiple phase converter and the controller may be a multiple phase controller.

Single switching converter50includes converter switches1,2, for example connected to each other in series at a first converter terminal. Switching converter50converts between AC power and DC power or between DC power and DC power. Switching converter50is electrically coupled to stationary battery60. For example, the series of converter switches1and2is connectable in parallel to stationary battery60. In other words, converter switches1and2are arranged in an inverter configuration where converter switch1is the high side switch and converter switch2is the low side switch. Converter switches1and2are switched on and off complementarily, i.e. when converter switch1is switched on, converter switch2is switched off, and vice versa.

Switching converter50is arranged to convert power between the grid network and stationary battery60. Grid transformer10may provide, in use, electrical isolation between the grid network and stationary battery60.

In some embodiments, the switching converter may include a transformer, e.g. a high frequency transformer. The high frequency transformer may provide electrical isolation of the stationary battery from the earth potential. Thus, the high frequency transformer may provide electrical isolation from the earth potential in place of the grid transformer.

Filter circuit40is arranged between grid transformer10and switching converter50. The converter terminal is electrically coupled to the secondary via the filter circuit40.

Filter circuit40includes at least a series inductor45and a parallel capacitor48(an LC filter). Series inductor45has first inductor terminal and a second inductor terminal. The second inductor terminal is electrically coupled to the converter terminal. Parallel capacitor48has a first capacitor terminal and a second capacitor terminal. The first capacitor terminal is electrically coupled to the first inductor terminal. The second capacitor terminal is electrically coupled to a reference terminal of the filter circuit.

For example, as shown inFIG. 1, the second capacitor terminal may be directly coupled to a negative terminal of stationary battery60in which case the reference terminal corresponds to the negative terminal of stationary battery60.

In some embodiments, the second capacitor terminal is directly coupled to the negative terminal of stationary battery60and directly coupled at a reference terminal of low side converter switch2.

In some embodiments, the filter circuit may include any type of LC low pass filter. For example, instead of one series inductor two or more series inductors may be arranged in series and a parallel capacitor connected between the series inductors. Thus the filter circuit may be a LCL filter circuit, a LCLCL filter circuit, etc.

In some embodiments shown later, the filter is a multiple phase filter arranged in a star configuration. In the star configuration, the second capacitor terminal is not directly electrically coupled to the reference terminal of the low side converter switch, but electrically coupled thereto via another switch.

In some embodiments shown later, the filter is a multiple phase filter arranged in a delta configuration. In the delta configuration, the second capacitor terminal is electrically coupled to the inductor terminal of the successive phase. Thus the reference terminal of each phase corresponds, in this embodiment, to a terminal of another phase.

In further embodiments, the series of converter switches1and2may be not directly arranged in parallel with stationary battery60but via a set of switches.

First set20of switches20a,20bis arranged between grid transformer10and filter circuit40. Switches20a,20bselectively electrically couple, when switched on, filter circuit40in series with alternating current voltage source22. In this example, switches20,20belectrically couple capacitor48in parallel to alternating current voltage source22. Switches20,20belectrically couple the secondary of grid transformer10to the first capacitor terminal and the second capacitor terminal of capacitor48. However, other configurations are possible as long as, when stationary battery60or vehicle battery70are charged by source2, a time periodical voltage signal can be applied to the series inductor thereby generating an alternating current flow through the series inductor.

Coupling device30includes a detection device30c. Detection device is configured to detect a connection status of coupling device30and to send, based on this status, a coupling signal to controller80indicating whether vehicle battery70is connected to coupling device30.

For example, coupling device30may include one or more couplers30aand30b. Couplers30aand30bselectively electrically couple, when the couplers are connected to vehicle battery70, the positive terminal of vehicle battery70to the first inductor terminal and the negative terminal of vehicle battery70to the reference terminal of the filter circuit.

In some embodiments shown inFIG. 1, coupling device30, e.g. couplers30a,30b, is directly coupled to the first inductor terminal and the reference terminal, respectively.

In some other embodiments shown later, coupling device30, e.g., couplers30a,30b, are coupled to the first inductor terminal and the reference terminal via a second set of switches.

In some other embodiments shown later, coupling device30, e.g. couplers30aand30badditionally selectively electrically couple, when the couplers are connected to vehicle battery70, the positive terminal of vehicle battery70to a positive terminal of the stationary battery and the negative terminal of vehicle battery70to a negative terminal of stationary battery. Coupling device, e.g. couplers30aand30b, may be coupled to the positive and negative terminal of stationary battery60via a third set and a fourth set of switches. The third and fourth set of switches are for example used to decouple stationary battery60from the charging system and to couple vehicle battery70in parallel to the switching converter such that vehicle battery70can also be charged from alternating current voltage source22.

In some embodiments ofFIG. 1, when couplers30aand30bare connected to vehicle battery70, capacitor48is arranged in parallel to vehicle battery70.

In some embodiments, couplers30aand30bmay manually or automatically selectively couple vehicle battery70to at least the filter circuit. For example, the vehicle battery may be connected to corresponding input terminals of the couplers. The positive and negative terminals of the vehicle battery may be connected to the couplers via, e.g., a plug. The couplers may include, e.g., a socket into which the plug can be inserted. In some embodiments, the couplers can electrically couple the vehicle battery to the filter and/or the stationary battery automatically when, for example, the plug is plugged into the socket

In some embodiments, couplers may further include a switch, for example a mechanical coupler or electromechanical switch or an electrical switch, which may be manually activated, e.g. switched on, by a user after the positive and negative terminals of the vehicle battery are electrically connected to the couplers, for example after the plug is inserted into the socket.

Detection device30cdetects a connection status of couplers30aand30band sends a coupling signal to controller80. The coupling signal indicates to controller80whether vehicle battery70, e.g. a positive and negative terminal thereof, is connected to couplers30aand30b. Controller80receives the coupling signal and establishes for example whether a battery has been connected or disconnected to the couplers.

Controller80is used to control first set20of switches20a,20band switching converter50.

In some embodiments, controller80is configured to switch on first set20of switches20aand20bwhen controller80receives a coupling signal that couplers30aand30bhave been disconnected e.g. a battery is not connected or has been disconnected from couplers30aand30b. Stationary battery60can be charged from alternating current voltage source22. Controller80is thus configured to control the switching converter such that the time periodical voltage signal and the current flowing through the first series inductor are in phase, for charging stationary battery60from alternating current voltage source22, e.g. from grid source15via grid transformer10. By controlling the relative phase of the voltage and the current, an optimal power transfer between the grid network and the charging system can be obtained.

In some embodiments, controller80is configured to switch off first set20of switches20aand20bwhen controller80receives a coupling signal that couplers30aand30bhave been connected, e.g. a battery is connected to couplers30aand30b. Vehicle battery70can be charged from the stationary battery60. Controller80is thus configured to switch off first set20of switches20aand20band control the converter switches1and2for providing a current signal to vehicle battery70for charging vehicle battery70from stationary battery60. The current signal is filtered by filter circuit40. The current signal may indeed have a ripple due the relatively high switching frequency of the converter. This ripple can be attenuated or eliminated by the filter circuit. Filter circuit is a low pass filter which cut-off frequency may be designed to be lower than the switching frequency of the converter in order to filter out the undesired current ripple and provide a constant current for charging the vehicle battery.

In some embodiments, the charging system may include an electrical energy monitoring device (not shown inFIG. 1). The electrical energy monitoring device may be configured to monitor an electrical energy level of the stationary battery and to send an electrical energy signal to the controller indicating the electrical energy level. For example, the electrical energy monitoring device may be a voltmeter device or a power meter which constantly monitors the level of the stationary battery. The electrical energy monitoring device may be wirelessly or wired connected to the controller, e.g. via respective interfaces and/or transmitter, receiver devices. The electrical energy signal is received by the controller.

The controller acknowledges via the coupling signal that a vehicle battery has been connected to the coupling device and that the vehicle battery requires charging. However, if, upon receiving the electrical energy signal, the controller acknowledges that the electrical energy level of the stationary battery has dropped below a predetermined battery threshold, the controller may establish, for example, that the vehicle battery cannot be charged directly from the stationary battery but can be charged directly from the grid network. The predetermined threshold may be equivalent to a measured electrical energy level of the vehicle battery. For example, a further electrical energy monitoring device monitoring the electrical energy level of the vehicle battery may be communicatively connected to the controller in the same manner. The controller may compare the electrical energy levels of the vehicle battery and the stationary battery.

In some embodiments shown later, where the coupling device is further selectively coupled to the stationary battery, if the electrical energy level of the stationary battery is lower than the electrical energy level of the vehicle battery, the controller may switch on switches20aand20band control the converter switches such that the time periodical voltage signal and the current through the series inductor are in phase for charging the vehicle battery directly from alternating current voltage source22. If the electrical energy level of the stationary battery is higher than the electrical energy level of the vehicle battery, then the controller may switch off switches20a,20bof the first set and control the switching converter for providing a current signal to the vehicle battery for charging the vehicle battery from the stationary battery.

In some embodiments, when the electrical energy level of the stationary battery, e.g. stationary voltage Vbstat, is higher than the electrical energy level of the vehicle battery, e.g. vehicle voltage VbEV, controller80is configured to control converter switches1and2in buck mode for converting stationary voltage Vbstatinto vehicle voltage VbEV.

When the stationary voltage's amplitude Vbstatis higher than the vehicle voltage's amplitude VbEV, vehicle battery70can be charged faster from stationary voltage70. This allows to reduce charging times during which the vehicle needs to be stopped. The vehicle can be put into operation after relatively short charging times, which increases overall productivity of the vehicle.

The inventor has realized that a single switching converter can be used to transfer power between the grid network and the stationary battery and between the stationary battery and the vehicle battery in two different phases. Control of the first switch based on the connection status of the couplers together with a different control of the switching converter allows to alternate between the two different phases.

In the first phase, when the stationary battery is charged from the grid source, the switching converter is controlled as an AC to DC converter by for example making using of a pulse width modulated signal as it will be explained in more details in some embodiments below. The reactance value of the filter circuit together with the correct amplitude of the time periodical voltage signal allows for adjusting a ratio of the active power to reactive power, i.e. the so-called power factor, transferred between the grid source and the charging system. In this way power can be efficiently transferred, with less power losses, between the grid source and the stationary battery. Additionally, this variable reactance value may be used to assist the grid provider in stabilizing the grid or compensate for grid loads with a reactive power demand.

In the second phase, when the vehicle battery is charged from the stationary battery, the same switching converter is controlled as a DC to DC converter. The filter circuit is used to store energy in a first control cycle when converter switch1is closed and converter switch2is open and to release energy in a second control cycle, when converter switch1is open and converter switch2is closed. The released energy is in the form of a substantially direct current signal delivered to the electrical vehicle battery through series inductor45. Such current can have in practice still some ripple which can be further attenuated by filter circuit40as explained above.

In still some other embodiments shown later, the ripple may be attenuated by using a multiple phase switching converter and optionally by interleaving the different multiple phases.

The inventor has further realized that by selectively connecting the couplers to the stationary battery, for example via additional switches, it is also possible to directly charge the vehicle battery from the grid network with the same switching converter. In other words, advantageously, the switching converter can still be controlled as an AC to DC converter and the vehicle battery be charged from the grid network.

FIG. 2schematically shows an example of some embodiments of a charging system200.

Charging system200differs from charging system100in that charging system200further includes an isolation monitoring device90.

Isolation monitoring device90is electrically coupled to controller80and to at least one of the positive terminal and negative terminals of stationary battery60. Isolation monitoring device90is configured to measure an impedance value of at least one of the terminals of stationary battery60with respect to the earth potential. Alternatively or in addition isolation monitoring device90may be configured to measure an impedance value of at least one of the terminals of the electrical vehicle battery70with respect to the earth potential. Isolation monitoring device90is further configured to transmit said impedance value to controller80.

Isolation monitoring device90may be, to this purpose, connectable to at least one of the terminals of the stationary battery for receiving the impedance value. Isolation monitoring device90may further include a transmitter for transmitting, for example wirelessly or via a cable connection, the impedance value to a receiver of the controller.

For example, isolation monitoring device90may be an impedance meter to measure the impedance value at said battery terminal. The impedance value may be send from the transmitter to the controller.

Thus the impedance value at the battery terminals can be monitored in order to signal any short circuit of said terminals with the earth potential. Since charging system200is electrically isolated from the earth potential and from the primary side of the grid transformer10, any short circuit of the battery terminals with the earth potential can lead to a current leakage through the earth potential and thus to a potential destructive behavior. Isolation monitoring device90prevents that the charging system is damaged upon detection of a short circuit and protects against single point isolation failures.

In some embodiments, when stationary battery60is being charged, controller80is configured to switch off switches20aand20bif the impedance value of one of the terminals of stationary battery60drops below a predetermined threshold.

For example, isolation monitoring device90may further include a comparator (not shown in the Figures) to compare such impedance value with a predetermined threshold. The comparator may produce a comparator output signal based on this comparison. The comparator output signal may be received by controller80. Switches20and30may be switched off by controller80and charging of stationary battery60be stopped based on said comparator output signal if the comparator output signal indicates that the impedance of one of the terminals of stationary battery60has dropped below a predetermined threshold.

Similarly, in some other embodiments, system200may include a second set23of switches23aand23b. Coupling device30is configured for selectively coupling the positive terminal of vehicle battery terminal to the first inductor terminal, and the negative terminal of vehicle battery70to the reference terminal via this second set of switches23aand23bwhen the switches23aand23bare switched on. When electrical vehicle battery70is being charged, controller80is configured to switch off switches23aand23bif the impedance value of one of the terminals of electrical vehicle battery70drops below a predetermined threshold.

Thus also charging of electrical vehicle battery70may be stopped when the impedance of one of the terminals of electrical vehicle battery70drops below the predetermined threshold.

In some embodiments, isolation monitoring device90is electrically coupled to controller80and to at least one of the terminals of stationary battery60. When a vehicle battery is connected through couplers30aand30bto charging system200, isolation monitoring device90may be configured to automatically monitor the impedance at the terminals of vehicle battery70.

For example, if the impedance value at one of the terminals of stationary battery60drops below the predetermined threshold, controller80may be configured to switch off switches20a,20bbut also switches23aand23b. In some other embodiments switches23aand23bare not required or the switches may be integrated with the couplers and controller80may be configured to control such switches such to electrically decouple vehicle battery70from charging system200in case the impedance value drops below the predetermined threshold.

Isolation monitoring device90increases safety of charging system200, prevent damage of batteries60and70and of switching converter50in case low impedance or short circuits are detected at the battery terminals.

FIG. 3schematically shows an example of some embodiments of a charging system300.

Charging system300allows vehicle battery70to be charged either from stationary battery60or from grid source15. For example, stationary battery may be not sufficiently charged for charging directly vehicle battery70. For example, an electrical energy level of stationary battery60may have been dropped below an electrical energy level of the vehicle battery. In either of the above situation, it may be more advantageous, for example faster, to charge the vehicle battery directly from the grid than from the stationary battery.

Charging system300differs from charging system100in that it includes additionally a second set30of switches23aand23b, a third set26of switches26aand26band a fourth set28of switches28aand28b. Charging system300further includes an electrical energy monitoring device65.

Coupling device30is configured to electrically couple the positive terminal of vehicle battery70to the positive terminal of stationary battery70and the negative terminal of vehicle battery70to the negative terminal of stationary battery60via third set26and fourth set28of switches.

Third set26of switches26aand26bis configured for selectively electrically coupling, when switches26aand26bare switched on, the series of converter switches1,2in parallel to vehicle battery70via the couplers30a,30bwhen couplers30aand30bare connected to vehicle battery70.

Fourth set28of switches28a,28bis configured for selectively electrically coupling, when switches28a,28bof fourth set28are switched on, the series of converter switches1,2in parallel to stationary battery60.

Controller80is configured to control the switches of the second, third and fourth set of switches for charging vehicle battery70directly from the alternating current voltage source22. Switches28aand28bmay be switched off to decouple stationary battery60from charging system300and switches26aand26bmay be switched to couple vehicle battery70in parallel to the switching converter, e.g. the series of converter switches1and2.

In some embodiments, electrical energy monitoring device65may be communicatively connected to controller80. Connection may be for example a wireless communication or a wired communication. Isolation monitoring device65is configured to monitor an electrical energy level of stationary battery60. Isolation monitoring device65may include a signal generator configured to generate an electrical energy signal indicating said electrical energy level and a transmitter device suitable to send the electrical energy signal to the controller. Controller80is configured, e.g. via a receiver, to receive said signal and, when vehicle battery70is connected to couplers30aand30b, to switch on first set20of switches and third set26of switches and to switch off second set23and fourth set28of switches if the electrical energy signal indicates that the electrical energy level is lower than a predetermined threshold.

In some other embodiments, controller80is configured, e.g. via the receiver, to receive the electrical energy signal from electrical energy monitoring device65and, when vehicle battery70is connected to couplers30aand30b, to switch off first set20of switches and third set26of switches and to switch on second set23and fourth set28of switches if the electrical energy signal indicates that the electrical energy level is higher than a predetermined threshold.

The predetermined threshold may be equivalent to a current electrical energy level of vehicle battery70which may be measured in a similar way by a dedicated device. For example, the electrical energy level of vehicle battery70may be measured in the vehicle and be transmitted to the controller once vehicle battery70connects to the charging system. This transmission can occur either through coupling device or by dedicated hardware in the vehicle which communicates wirelessly or with a wired communication with controller80.

Thus controller80may retrieve from stationary battery60a status of stationary battery60. Based on the status of stationary battery60and based on whether vehicle battery70is or is not electrically connected to coupling device30, controller80may be configured to control the switches of the first, second, third and fourth set such that vehicle battery70is either charged from source22or from stationary battery60.

FIG. 4schematically shows an example of some embodiments of a controller80. Controller80includes a carrier signal generator82for generating a carrier signal, a modulation signal generator84for generating a modulating signal, a comparator86coupled to the carrier signal generator82and the modulation signal generator84for comparing the carrier signal with the modulating signal, and a pulse width modulator88for generating a pulse width modulated signal based on said comparing. Controller80is configured to complementary control the converter switches (not shown inFIG. 4) with the pulse width modulated signal.

Modulation signal generator82may include a measurement device for measuring a voltage signal measured across the filter circuit, for example across the series inductor. Thus the measuring device may measure the phase difference between the voltage signals VAand Vaacross the filter circuit40(shown inFIG. 1). The measurement device may for example measure, for voltages VAand Va, two successive time points at which the respective voltage signal becomes zero (the so-called zero-crossing point) and determine the time difference between the two points. The phase difference between the time-periodical power grid voltage signal VAand the time-periodical voltage signal Vamay be determined by taking the difference between the measured two time differences.

Modulation signal generator82may further include a processor (not shown inFIG. 4) to determine a time-periodical modulating signal Vm based on the measured first phase difference.

Carrier signal generator84may include a clock generator (not shown inFIG. 4) generating a carrier signal Vfs at a predetermined switching frequency fs. The carrier signal Vfs may be a triangular periodical waveform having an oscillation frequency fs (i.e. time-periodical with period1/fs) higher than the frequency of oscillation (i.e. the grid frequency, for example 50 or 60 Hz) of the modulating signal Vm. The carrier signal Vfs may have a predetermined carrier amplitude and the modulating signal Vm a modulating amplitude, both varying with time.

Comparator86compares the modulating amplitude with the carrier amplitude so as that pulse width modulator88can output a first control voltage Vctrl1for example for controlling the lower switch1ofFIG. 1. A second control voltage for the upper switch2ofFIG. 1can be derived from the first control voltage Vctrl1via for example an inverter (not shown). The lower and upper switches1and2are alternatively switched each time the modulating amplitude becomes higher or lower than the carrier amplitude. The voltage control Vctr1is triggered to a high level each time the modulating amplitude becomes higher than the carrier amplitude, switching on the lower switch1and switching off the upper switch2, and triggered to a low level each time the modulating amplitude becomes lower than the carrier amplitude, switching off the lower switch1and switching on the upper switch2.

The zero-crossing point of the modulating signal Vm should be set by the processor with respect to the measured zero-crossing point of the phase difference between Vaand VA(shown inFIG. 1). This relative zero-crossing time reference for Vm, together with the value of its modulating amplitude, controls the switching of the switching converter such that the phase difference between the voltage signals Vaand VAis in turns controlled. This allows the control of active and reactive power by the switching converter.

The switching converter may be arranged to operate with a pulse-width-modulated (PWM) switching scheme so that the controller80is configured to control the at least two converter switches with a time-periodical switching signal having a time-varying duty cycle.

The switching converter may operate with any modulation scheme suitable for the specific implementation.

In some embodiments, the modulation scheme may be a pulse density modulation (PDM), for example the Pulse Width Modulation (PWM) described above, wherein the frequency is substantially kept constant and a width of the pulse is modulated, or in some other embodiments a Pulse Frequency Modulation, wherein the pulse width is substantially kept constant and the frequency is modulated.

FIG. 5schematically shows an example of some embodiments of a converter switch1.

Converter switch1may be implemented with a transistor7, for example a Metal-Oxide-Semiconductor Field Effect Transistors (MOSFET)7shown inFIG. 5arranged in antiparallel with a diode8.

However, other type of transistors may be used, for example Metal-Semiconductor Field Effect Transistors (MESFET's), Junction-Field Effect Transistors (J-FET's), Bipolar transistors (BJT's), Insulated-gate bipolar transistor (IGBT's) or thyristors. Also different switching converter topologies suitable for the specific implementation may be used: for example, single phase or three-phase half-bridge converters, single phase full converters, single phase or three-phase boost or buck converters etc.

FIG. 6schematically shows an example of some embodiments of a charging system400.

A primary side of the grid transformer11can be connected to a three-phase power grid voltage source25The three-phase power grid voltage source generates a first time-periodical power grid voltage Vp1, a second time-periodical power grid voltage Vp2and a third time-periodical power grid voltage Vp3at the primary of grid transformer11.

The secondary of grid transformer11provides a three-phase time-periodical power grid voltage signal. For example, the three-phase voltage signals Vp1, Vp2and Vp3may have peak-to peak amplitudes in the order of a few kilovolts, for example 10 kV root mean square (RMS) line-line. The three-phase voltage signal may periodically vary with a frequency of 50 or 60 Hz. The three-phase voltage signals may periodically vary with the same oscillation frequency and be shifted in phase between each other, for example 120 degrees from each other. The three-phase voltage signals may be sinusoidal in shape.

Three-phase grid transformer11includes winding coils coupled at the primary and secondary terminals of grid transformer11and mutually coupled between the primary and the secondary in order to scale down the three-phase power grid voltage signals Vp1, Vp2and Vp3into corresponding scaled grid voltage signals Vs1, Vs2and Vs3.

The time-periodical voltage signal Vs1, Vs2and Vs3may have a peak-to-peak amplitude lower than the time-periodical power grid voltage signals Vp1, Vp2and Vp3. The voltages Vs1, Vs2and Vs3may, as voltage signals Vp1, Vp2and Vp3, periodically vary with the same oscillation frequency and be shifted in phase between each other, for example 120 degrees from each other. The three-phase voltage signals Vs1, Vs2and Vs3may be sinusoidal in shape.

Three-phase switch21includes a separate switch for each phase. For each phase, each switch is coupled between grid transformer11and switching converter51for selectively coupling, when switched on, each voltage signal Vs1, Vs2and Vs3to filter circuit41

Filter circuit41is a three-phase low pass filter. Low pass filter41includes for each phase a series inductor La, Lb and Lc and a parallel capacitor Ca, Cb and Cc. Series inductors La, Lb and Lc have a first inductor terminal coupled to a corresponding secondary terminal of transformer11via three-phase switch21and a second inductor terminal electrically coupled to the corresponding converter terminal.

Parallel capacitors Ca, Cb and Cc have a first capacitor terminal connected to the respective first inductor terminals secondary terminal and a common second capacitor terminal connected, via a further switch95, to a negative terminal of stationary battery60. In other words, three-phase low pass filter41is connected into a star configuration where capacitors Ca, Cb and Cc have a common reference terminal.

Charging system400thus further includes further switch95, for selectively electrically coupling, when switched on, said common reference terminal to a negative terminal of the stationary battery60. Switch95is operated synchronously with second switch31. Switch95is switched on to provide a return path for the current when series inductors La, Lb and Lc are discharging, for example when one of the upper side converter switches1,3or5is switched off and one of the lower side converter switches2,4or6is switched on.

Second switch31is switched on when switching converter51is operated as three-phase DC to DC converter.

When converter51is operated as three-phase DC to DC converter, controller81controls switches1-6with periodical carrier signals having a predetermined oscillation frequency. The predetermined oscillation frequency determines the switching frequency of converter51in this operating mode. Periodical carrier signals may be, for example, triangular or rectangular carrier signals.

Each pair of converter switches1,2,3,4, and5,6is controlled complementarily, e.g. when upper side switch1is switched on, lower side switch2is switched off and vice versa.

Herein below we describe operation of converter51as DC to DC buck converter, where, for example, the stationary battery voltage VbST is higher than the vehicle battery voltage VbEV.

When the upper switch of a phase is switched on, the corresponding series inductor is charged with a current rising linearly with time at a rate proportional to the voltage across the corresponding series inductor La, Lb or Lc divided by its inductance. The voltage across the series inductor La, Lb or Lc is the input DC voltage, i.e. stationary battery voltage VbST, minus the output DC voltage, i.e. electrical vehicle battery VbEV.

When the upper switch of a phase is switched off, the lower switch is switched on pulling to the negative terminal of the stationary battery the second inductor terminal. The current flowing through the corresponding series inductor decreases due to negative voltage across the corresponding series inductor and the energy previously stored therein is discharged into the vehicle battery70.

The current flowing through each of three-phase switch31has thus a ripple with positive polarity depending on how the lower and upper converter switches are switched. In a three-phase DC to DC converter system this current ripple is reduced with respect to a single phase system.

In general, as the number of phases increase, the magnitude of the output ripple current and voltage decreases.

In some embodiments, as shown inFIG. 6, multiple phase switch31selectively couples the positive terminal of vehicle battery70to the first inductor terminal of each phase. Thus all first inductor terminals are connected to node33when multiple phase switch31is switched on.

In some embodiments, controller81is configured to apply a phase shift between periodical carrier signals associated to different phases.

In other words, converter51may be arranged in an interleaved topology and controlled by controller81accordingly. By applying a phase shift to the carrier signals also the current ripple will have a phase shift across the three-phase. Since the currents are phase shifted and summed at node33of three-phase switch31, the ripple of the current flowing through node33will be significantly reduced.

Reduction of the current ripple improves accuracy of the DC current, thereby improving charging efficiency of electrical vehicle battery70.

Thus a single vehicle battery is charged from stationary battery60. Interleaving the phase of the periodical carrier signals further improves charging of vehicle battery70.

FIG. 7schematically shows an example of some embodiments of a charging system500.

A multiple phase charging system may charge multiple batteries at the same time. For example, charging system500may charge three different batteries70,71and72at the same time. Each phase of three phase charging system500may charge a different battery. Three phase switch31electrically couples, when switched on, the positive terminals of vehicle batteries70,71and72, respectively.

Each battery70,72is coupled to the system via respective couplers30a,30b,34a,34band34c,34d. Each pair of couplers has its own detection device (which has been for a better understanding of the drawings omitted from theFIG. 7) for detecting a status of the respective couplers.

Three-phase switch32electrically couples the negative terminal of each battery70,71and72to the negative terminal of stationary battery60. Three-phase switch31, three phase switch32and further switch95are synchronously switched on and three phase switch21is switched off to allow charging of batteries70-72from stationary battery60.

Three-phase switch31, three phase switch32and further switch95are synchronously switched off and three phase switch21is switched on to allow charging stationary battery6—from grid source25.

Multiple batteries can thus be charged at the same time with the same multi-phase charging system. Charging capacity of the charging system is increased and vehicle productivity can be increased with less investment in charging infrastructure.

FIG. 8schematically shows an example of some embodiments of a charging system600.

Charging system600is similar to charging system400ofFIG. 6and includes a three-phase grid transformer11, a first three-phase switch21, a second three-phase switch31, a three-phase low pass filter42, a three phase switching converter51and a three-phase controller83.

Low pass filter42differs from low pass filter41in that it is arranged in a delta configuration.

Low pass filter42includes series inductors La, Lb, and Lc and parallel capacitors Cab, Cbc and Cca.

Series inductors La, Lb and Lc have first inductor terminals connected to corresponding terminals of first switch21and second switch31. Series inductors La, Lb and Lc have second inductor terminals connected to corresponding converter terminals.

Parallel capacitors Ca, Cb, and Cc have corresponding first capacitor terminals electrically coupled to respective first inductor terminals. Parallel capacitors Ca, Cb, and Cc have respective second capacitor terminals electrically connected to the first inductor terminal of the successive phase.

In other words, parallel capacitors Ca, Cb, and Cc are in this embodiment connected across the different phases.

The first inductor terminals are electrically coupled, when three-phase first switch21is switched on, to corresponding secondary terminals at the secondary of grid transformer11.

The first inductor terminals are electrically coupled, when three-phase first switch31is switched on, to the positive terminal of stationary battery70.

Negative terminal of vehicle battery70is electrically coupled, to the negative terminal of stationary battery60.

Controller83switches off second switch31, switches on first switch21and control switching converter51such that voltages VA, VBand VCat the first inductor terminals and currents flowing through the series inductors La, Lb and Lc are in phase, for charging stationary battery60from grid source25.

Controller83switches off first switch21, switches on second switch31and control switching converter51as DC to DC converter, preferably in buck mode, for charging vehicle battery70from stationary battery60.

With this filter topology, switch95shown inFIG. 4is not needed anymore. The filter capacitors are irrelevant to the functioning of the system in this operation mode since they are short-circuited by the three phase relay31. The filtering of the chopped DC voltages is therefore less effective than with the configuration shown inFIG. 6.

FIG. 9schematically shows an example of a charging station700. Charging station700may be a charging infrastructure where vehicles can stop for charging their batteries.

Charging station400includes any of the single phase or three-phase charging systems100,200,300,400,500and600shown with reference to theFIGS. 1-3 and 6-8, respectively. Charging station700includes a charger connector705. Charger connector makes electrical contact with the coupling device described above, e.g. with the respective couplers30aand30bshown inFIG. 1. Charger connector705is further electrically coupled and mechanically connectable to a vehicle connector710. Vehicle connector710is electrically coupled to a positive terminal and a negative terminal of a vehicle battery70.

Vehicle720may be any type of plug-in electric or hybrid vehicle, for example a passenger vehicle, a commercial vehicle, a car, a bus, a truck, a van, or the like. The stationary battery may be installed in a suitable space inside or surrounding charging station700where the vehicle720temporarily stops for charging vehicle battery70.

InFIG. 9, charging station400charges battery70of one vehicle420. Alternatively, a plurality of batteries of vehicle420may be charged or different batteries of different vehicles may be charged at the same time. This can be for example achieved by using a multiple-phase charging system as described with reference to charging systems500shown inFIG. 7.

Vehicle connector710may be mounted on a pantograph system on top of vehicle720such that when the vehicle is driving the pantograph is tilted down on the top of vehicle720and when the vehicle is stopped in the charging station, the pantograph is tilted up to contact charger connector705.

However, other types of charging stations and vehicle connectors are possible. The vehicle connector may include a plug type connector to be inserted into the charger connector705, for example a socket. The charging station may thus look more similar to a gas pump station where the charger system has an extension electrical cable connecting at one end the vehicle battery and at the end the charging system, for example the coupling device of the charging system.

FIG. 10schematically shows a flow diagram of a method800of charging a vehicle battery via a charging system. The charging system may be for example any of the charging system described with reference to theFIGS. 1-3 and 6-8.

Herein below we will be referring to charging system100ofFIG. 1.

Method800includes receiving810the coupling signal from the detection device. The coupling signal indicates a connection status of the coupling device, i.e. whether the vehicle battery has been connected or disconnected from the coupling device.

Based on the coupling signal the method may switch on820the first set20of switches20a,20band control830the converter switches such that the time periodical grid voltage and the current flowing through the series inductor are in phase.

Alternatively, based on the coupling signal, the method may switch off840the first set20of switches20a,20band control850the converter switches for providing a current signal to vehicle battery70for charging vehicle battery70from the stationary battery60. First switch20is switched on after vehicle battery70is e.g. disconnected from coupling device30to prevent any short circuit between vehicle battery terminals and secondary terminals at the secondary of grid transformer10.

Similarly, for the same reason, in method800switching off840first switch20is performed before vehicle battery70is e.g. connected to the coupling device.

It should be noted that the above-mentioned embodiments illustrate rather than limit some embodiments, and that those skilled in the art will be able to design many alternative embodiments.

For example, it is noted thatFIG. 1shows an example of a single-phase half-bridge switching converter. However, the switching converter can be arranged in any suitable configuration. For example, the switching converter may be arranged and controlled as a full-bridge converter including another pair of at two series switches for rectifying, when charging the stationary battery, also the negative cycle of the time-periodical voltage signals.

For example, set26and28of switches26a,26band28a,28bare shown inFIG. 3to couple coupling device30to stationary battery60. However, instead of using separate set26and28of switches, a single switch can be used, for example a three state switch which couple the series of converter switches1and2either in parallel to stationary battery60or with coupling device30.