Patent Publication Number: US-2022234464-A1

Title: Rapid charging device for a motor vehicle

Description:
TECHNICAL FIELD 
     The present disclosure relates to the field of charging devices for motor vehicles, such as an electric or hybrid car or bus. These charging devices are also called “charging stations” and can be installed in a variety of locations, such as private parking lots, public parking lots of stores or restaurants for example. 
     The disclosure relates more specifically to a so-called “rapid” charging station. 
     BACKGROUND 
     The development of electric or hybrid vehicles is naturally accompanied by the development of charging solutions for these vehicles. One of the points blocking growth in the use of full-electric vehicles is the charging time of these vehicles. In fact, this charging time is much longer than that required to refuel a combustion vehicle. For example, when traveling long distances, a driver is more likely to use a combustion or hybrid vehicle than a full-electric vehicle. 
     An electric (or hybrid) vehicle is charged by charging one or more batteries connected to the vehicle&#39;s electrical network. To do this, the electrical energy is typically consumed over an electrical network with AC voltage. The function of the charging station is to transform the AC voltage from the network to a voltage level suitable for the battery and to transform the AC voltage into a DC voltage. 
     A conventional charging station is connected to an electrical network operating at 220 V AC and comprises a network input connected to a transformer lowering the AC voltage to a level of about 50 V linked to an AC/DC converter connected to a charging socket of the electric vehicle. 
     With this type of widely available charging station, fully charging an electric vehicle typically takes 8 to 12 hours. 
     However, withdrawal by several charging stations on a network can lead to degraded network performance. Indeed, in an electrical network, consumption must always be balanced with generation at the risk of varying the characteristics of the network, particularly its frequency. To do this, the network operator can use primary, secondary and tertiary reserves, which operate on different time and power scales. For example, the primary reserve has an action time of less than 30 seconds, the secondary reserve has an action time of less than 15 minutes, and the tertiary reserve has an action time of 30 minutes. 
     Thus, when an imbalance is detected, the primary reserves are automatically activated based upon the frequency differences measured between the network and a reference signal produced by the operator of the transmission network. Indeed, when an imbalance occurs between generation and consumption, the network frequency deviates from the required level of 50 Hz and this deviation activates the primary reserve of the entities participating in this primary reserve. Each of these entities must increase its injection power if the frequency is less than 50 Hz or decrease its injection power or even withdraw current, if the frequency is greater than 50 Hz. A new balance point between generation and consumption is thus obtained on the network. 
     To obtain the necessary responsiveness, the primary reserve comprises reserve entities connected to the high-voltage network or medium-voltage network. In fact, an electrical power transmission network is typically structured with several voltage levels, for example high-voltage lines transport the current with a voltage between 50 kV and 400 kV, medium-voltage lines with a voltage between 1 kV and 50 kV and low-voltage lines with a voltage of 220 V. These lines are interconnected with transformer stations located between the different types of lines. 
     A system using batteries to participate as a reserve entity in the primary reserve typically includes a set of very high capacity batteries charged to half their capacity in order to inject or withdraw power from the network as required. Similarly, this system participates in voltage regulation according to the specifications of the network operator, by injecting or withdrawing reactive power. 
     The primary reserve must be proportioned to inject or release a significant portion of the network&#39;s generation and consumption. In Europe, all the reserve entities that form the primary reserve represent a capacity of 3000 MW, i.e. the generation power of the two largest nuclear reactors in service. To obtain this total power, each reserve entity must be proportioned to have a capacity of at least 1 MW. 
     More precisely, as shown in  FIG. 1 , a balancing system  100  with batteries  17  comprises a network input  11  incorporating high-voltage or medium-voltage network protection units  12  and units for measuring  13  network performance in order to detect power and voltage balancing requirements. This network input is connected to a step-down transformer  14 . For example, when the balancing system is connected to the medium-voltage network, the transformer can be configured to transform a 20 kV AC voltage into a 450 V AC voltage. The output of the transformer  14  is connected to an inverter  15  configured to convert the AC voltage into a DC voltage supplying a network  16  of batteries  17 . A supervision unit, not shown, measures the active and reactive power of the network over time and controls the charging or discharging of the batteries  17  in order to compensate for network imbalances. 
     In order to limit the contract power for connecting the system to the network, charging stations  101  for electric vehicles incorporating one or more batteries are also known, as shown in  FIG. 2 . This type of charging station  101  incorporates a transformer  12  lowering the AC voltage of the low-voltage network followed by an AC/DC converter  15  connected to a battery  17  and configured to adapt the voltage level to the battery  17 . 
     The output of the AC/DC converter  15  is also connected to a second DC/DC converter  18  connected to a charging socket of the electric vehicle and configured to adapt the voltage level to the electric vehicle. When the power demand exceeds a threshold value, the battery  17  is used to limit the strain that would be imposed on the network. 
     In addition, the battery  17  can be charged after the charging phase of an electric vehicle. Although this embodiment limits the instantaneous power withdrawn from the network, the charging time is not improved with respect to a conventional charging station. 
     To improve the charging speed, it is possible to use a charging station connected directly to the high-voltage network or to the medium-voltage network in order to supply maximum power to the electric vehicle. As shown in  FIG. 3 , this type of charging station  102  incorporates a network input  11  incorporating high-voltage or medium-voltage network protection units  12  and a step-down transformer  14 . 
     The output of the transformer  14  is connected to an inverter  15  configured to convert the AC voltage into a DC voltage supplying the charging socket of the electric vehicle. With this type of charging station, an electric vehicle can be charged in 20 minutes. 
     Although this solution is effective for improving the charging speed of an electric vehicle, the size and cost of the protection units  12  needed in order to be authorized to connect to the high-voltage or medium-voltage network are prohibitive for the deployment of this type of charging station. 
     The technical problem solved by the disclosed embodiments is therefore that of how to obtain a rapid charging station that overcomes the disadvantages of the previously disclosed devices. 
     SUMMARY OF THE DISCLOSURE 
     To address this technical problem, the disclosed embodiments propose modifying a balancing system forming part of the primary or secondary reserve so as to perform, in addition to the network balancing function, a charging function for an electric or hybrid vehicle. Thus, the protection units needed in order to be authorized to connect to the high-voltage or medium-voltage network are common to the balancing system and the charging station, and this limits the number of components required for the installation of the charging station. 
     To do this, the transformer is modified with a dedicated additional winding to supply power to the charging socket of the electric vehicle via a dedicated inverter. 
     For this purpose, according to a first aspect, the disclosed embodiments relate to a balancing system for a high-voltage or medium-voltage network comprising: 
     a network input incorporating protection units for protecting said network and units for measuring the performance of said network in order to detect the balancing requirements; 
     a transformer having a first winding connected to the output of said network input and configured to lower the voltage of said network; 
     an inverter connected to a second winding of said transformer and configured to transform an AC voltage into a DC voltage; 
     a set of batteries connected to said DC voltage; and 
     a supervision unit configured to activate said inverter and to charge or discharge said batteries when an imbalance is measured on said network by said measurement units. 
     The disclosed embodiments are characterized in that said balancing system also comprises an additional inverter connected to a third winding of said transformer, the output of which makes it possible to supply power to at least one charging socket of an electric or hybrid vehicle; and means for detecting a charging requirement of said charging socket; said supervision unit being configured to activate said additional inverter when a charging requirement is detected at said charging socket and the requirements for injection into the network are less than a threshold value. 
     Thus, the disclosed embodiments propose the use of a balancing system to charge an electric or hybrid vehicle except in the phases in which a large amount of power needs to be injected into the network. Indeed, in a balancing system, the injection and withdrawal phases are normally relatively short, often a few tens of seconds. Compared to the charging time of an electric or hybrid vehicle, these withdrawal or injection instants are very short. 
     Unlike a conventional charging station, the disclosed charging station is much faster, since it is connected to the high-voltage or medium-voltage network. Thus, although it is not available all the time, since the charging station cannot be used when the balancing system needs to inject a large amount of power into the network, the improvement of the charging speed during the other phases largely compensates for the instants during which the charging station cannot be used to charge an electric or hybrid vehicle. 
     Moreover, compared with a rapid charging station of the state of the art, the installation cost of the charging station is lower since the protection units needed in order to be authorized to connect to the high-voltage or medium-voltage network are common to the balancing system and the charging station, and this limits the number of components necessary for the installation of the charging station. 
     The disclosed embodiments are therefore the result of a discovery whereby the unavailability of the charging station at the instants of high injection of a balancing system is compensated by the gain in charging speed and does not significantly degrade the lifespan of batteries integrated in electric or hybrid vehicles. 
     Indeed, it is known that interruptions in the charging phases degrade the lifespan of batteries integrated in electric or hybrid vehicles. However, a substantially constant lifespan has been measured for lithium-ion batteries integrated in electric or hybrid vehicles, even when using a charging station according to the disclosed embodiments, i.e. with unavailability instants that may occur during the charging phases. 
     According to one embodiment, said units for measuring the performance of said network in order to detect the balancing requirements comprise a dedicated energy meter for the operator of said network and an independent energy meter. The dedicated meter for the network operator typically makes it possible, in a balancing system, to allow the network operator to check that the balancing system is active according to the contract imposed by the network operator. For example, the network operator may have imposed a constraint that the balancing system must withdraw 10% of active power when the frequency exceeds a threshold value or any other network prevention mode and, similarly, withdraw 10% of reactive power when the voltage exceeds a threshold value or any other network prevention mode. The independent meter makes it possible to check the fulfillment of the contract by the provider. Additionally, the independent meter can be used to measure the power withdrawn from the network to supply power to the charging station and not to balance the network. 
     According to one embodiment, said transformer is delta-wired at the first winding, delta-wired at the second winding and star-wired at the third winding. This embodiment makes it possible to obtain maximum power at the set of batteries via a delta/delta coupling that does not allow the neutral to be transmitted. Conversely, for the charging station, it may be necessary to have access to the neutral and the delta/star coupling makes it possible to transmit the neutral without degrading the delta/delta coupling that supplies the set of batteries. 
     To implement the disclosed embodiments, it is necessary to configure the supervision unit to allow injection into and withdrawal from the network while using the same network to supply power to the second inverter in the phases for which maximum injection is not required. The easiest way to do this is to allow the second inverter to operate when the charging socket is in use and maximum injection into the network is not required. 
     In this embodiment, said means for detecting a charging requirement of said charging socket correspond to a probe configured to detect a consumption at said charging socket. 
     Alternatively, the control of the two inverters can depend on both the balancing requirements of the network and the withdrawal requirements of the charging station. Thus, a compromise can be sought between these two requirements when the requirements for injection into the network are not maximal. 
     In this embodiment, said means for detecting a charging requirement of said charging socket correspond to a probe for measuring the requested charging power at said charging socket. 
     Additionally, in this embodiment, said balancing system preferably comprises a probe disposed between said transformer and said additional inverter so as to measure an instantaneous power consumed by said charging socket. Similarly, said balancing system preferably comprises a probe disposed between said inverter and said set of batteries so as to measure an instantaneous power consumed by said charging socket. 
     With these two probes, the supervision unit is able to detect the power used on each output of the transformer to balance the withdrawal from the network based upon the withdrawal requirements in order to supply power to the charging socket and to maintain the set of batteries at the balance point corresponding approximately to half of the total capacity of each of the batteries. 
     For this purpose, according to a second aspect, the embodiments relate to a method for managing a balancing system according to the first aspect, said method comprising the following steps: 
     measuring the difference between a voltage measurement, a frequency measurement and a current measurement of the network and the nominal values in order to determine the active and/or reactive power injection and/or withdrawal requirements; 
     determining a control power of the inverter connected to the set of batteries based upon the injection and/or withdrawal requirements; 
     if the injection requirements are greater than a maximum injection power, deactivating the additional inverter and activating the inverter connected to the set of batteries in order to inject said maximum injection power, 
     if the injection requirements are less than a maximum injection power, deactivating the additional inverter and activating the inverter connected to the set of batteries in order to inject said control power, 
     if the withdrawal requirements are less than a requested charging power at said charging socket and the charge level of the set of batteries is greater than a threshold value, deactivating the inverter connected to the set of batteries and activating the additional inverter in order to withdraw said control power, and 
     if the withdrawal requirements are greater than a requested charging power at said charging socket and the charge level of the set of batteries is less than a threshold value, activating the two inverters until the charge level of the set of batteries is greater than said threshold value. 
     Preferably, said control power is determined based upon load losses estimated from measurements taken from two probes respectively disposed between said transformer and said additional inverter and between said inverter and said set of batteries. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The way of implementing the embodiments and the advantages resulting therefrom shall be apparent from the following embodiments, given as non-limiting examples, in support of  FIGS. 1 to 6 , which constitute: 
         FIG. 1  is a schematic depiction of a balancing system with batteries of the state of the art; 
         FIG. 2  is a schematic depiction of a charging station with batteries of the state of the art; 
         FIG. 3  is a schematic depiction of a “rapid” charging station of the state of the art; 
         FIG. 4  is a schematic depiction of a balancing system according to a first embodiment; 
         FIG. 5  is a schematic depiction of a balancing system according to a second embodiment; and 
         FIG. 6  is a flowchart of the management steps of a supervision unit of the balancing system of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 4  shows a balancing system  10   a  which also forms a charging station for an electric or hybrid vehicle. This balancing system  10   a  typically comprises a network input  11  incorporating protection units  12  and measurement units  13 . The network input  11  can be connected to the high-voltage or medium-voltage network. For example, the network input  11  may be connected to two separate power cables each carrying a voltage of 20 kV. Additionally, the network input  11  may also include a network outlet allowing one of the two cables to pass through the network input  11  so as to form a balancing system through which the network passes. 
     The protection units  12  typically correspond to high-voltage or medium-voltage circuit-breakers, for example controlled circuit-breakers capable of disconnecting a current of 400 A in order to protect the balancing system  10   a.  Preferably, the network cables enter the network input  11  via manual circuit-breakers allowing maintenance operations to be performed in the balancing system  10   a.  An automatic circuit-breaker is preferably installed at the output of these manual circuit-breakers so as to cut off the current flowing through the network input  11  when the inrush currents inside the balancing system  10   a  are greater than a threshold value. Thus, these protection units  12  are preferably coupled with measurement units  13  in order to detect the instants at which it is necessary to cut off the current flowing through the network input  11 . 
     These measurement units  13  also have the function of measuring the frequency, the voltage and the phase shift between the current and this voltage, in order to detect the active and reactive power balancing requirements of the network. Preferably, these measurement units  13  incorporate several energy meters: one energy meter associated with the network operator and one independent energy meter associated with the operator of the balancing system  10   a.  These energy meters are preferably connected to a wired or wireless communication network. 
     Thus, the network operator can obtain information about the balancing requirements in real time using the measurements taken by the measurement units  13  of the balancing system  10   a.  Similarly, the measurements taken by the independent energy meter can be transmitted to the operator of the balancing system  10   a  to control the amount of energy injected into or withdrawn from the network. 
     The measurement units  13  transmit at least three pieces of information to a supervision unit  22 : a voltage measurement mU, a frequency measurement mF and a current measurement ml, the supervision unit  22  being configured to calculate the phase shift between the current and the voltage. Alternatively, the measurement units  13  may comprise means for automatically detecting the phase shift between the voltage and the current and this phase shift may be transmitted to the supervision unit  22 . 
     The primary function of the supervision unit  22  is to identify the network balancing requirements AU, AF, and Al and to fulfill these requirements based on the state of charge of the batteries  17  integrated in the balancing system  10   a.  This supervision unit  22  can be in the form of a microcontroller or a microprocessor associated with a sequence of instructions. In addition, this supervision unit  22  can be remotely controlled, for example by the operator of the balancing system  10   a  in order to update the balancing strategies or the authorizations to charge the electric or hybrid vehicles. 
     In order to perform the balancing or charge of an electric or hybrid vehicle, the output of the network input  11  is connected to a transformer  21  comprising three windings. The first winding is preferably delta-wired and receives the 20 kV voltage from the network. This first winding is coupled to a second winding preferably also delta-wired with a voltage lowered to 450 V. 
     This lowered AC voltage is connected to an inverter  15 , which makes it possible to transform this AC voltage into a DC voltage that supplies the set  16  of batteries  17 . Preferably, the output of the inverter  15  has a DC voltage level between 700 and 1000 volts. 
     The transformer  21  also has a third winding that is preferably star-connected is linked to an additional inverter  23 . This additional inverter receives a voltage lowered to 400 V and transforms this AC voltage into a DC voltage suitable for charging a motor vehicle, for example 50 V. Thus, the output of the additional inverter  23  is connected to a charging socket of an electric or hybrid vehicle  24 . Of course, the voltage levels at the network input  11 , transformer  21  and inverters  15 ,  23  can vary without deviating from the contemplated embodiments. 
     In addition to these features which are essential to the embodiment described, other features may be implemented to improve the safety or the control strategies of the balancing system  10   a.  For example,  FIG. 5  shows probes disposed after the transformer  21  in order to measure power at various points in the balancing system  10   b.  More precisely, a probe is disposed at the output of the inverter  15  in order to measure the power at the set of batteries Peq, i.e. after the losses associated with the transformer  21  and the inverter  15 , and a probe is disposed between the third winding of the transformer  21  and the additional inverter  23  in order to measure the power consumed Pre by the charging socket  24 . 
     To adapt the balancing strategy of the two inverters  15  and  23 , it suffices to detect a consumption or, at the very least, a presence on the charging socket  24  by means of a signal Ep, as shown in  FIG. 4 . Preferably, as shown in  FIG. 5 , the charging power requested Prrve by the charging socket  24  is measured by a probe disposed at the charging socket  24  in order to provide information to the supervision unit  22 . 
     Based on these various pieces of information transmitted to the supervision unit  22 , the supervision unit  22  can determine the strategy to be followed by the inverters  15  and  23 . 
     In addition to these structural features that make it possible to charge an electric or hybrid vehicle and to balance the network, the balancing system  10   a - 10   b  can incorporate conventional features of a balancing system, such as a cooling unit making it possible to cool the transformer  21  or the set of batteries  17 , an alarm, a fire protection unit, etc. 
       FIG. 6  shows an example of a method for managing the two inverters  15  and  23  implemented by the supervision unit  22 . In a first step  50 , this method measures the difference between the voltage mU, frequency mF, and current ml and nominal values to detect the reactive and/or active power injection or withdrawal requirements ΔU, Δl, ΔF of the network. Thus, when the difference between a nominal value and a measured value mU, mF, ml exceeds a threshold value, an injection or withdrawal requirement is determined based upon this difference. The second step  51  aims to determine the power to be applied to the inverter  15  based upon the injection or withdrawal requirements Pc 1  and a coefficient k. These requirements Pc 1  are then specified in a second determination step  52  by taking into account the real losses at the transformer  21 . These real losses can be estimated by the different probes based upon the state of the inverters  15  and  23 . 
     The requirements Pc 2  obtained from step  52  can be applied based upon several predefined scenarios, for example: 
     if the injection requirements ΔU, ΔF, Δl are greater than a maximum injection power Pmax, deactivating the additional inverter  23  and activating the inverter  15  connected to the set of batteries  17  in order to inject the maximum injection power Pmax, 
     if the injection requirements ΔU, ΔF, Δl are less than a maximum injection power Pmax, deactivating the additional inverter  23  and activating the inverter  15  connected to the set of batteries  17  in order to inject the control power Pc 1  or Pc 2 , 
     if the withdrawal requirements ΔU, ΔF, Δl are less than a requested charging power Prrve at the charging socket  24  and the charge level of the set of batteries  17  is greater than a threshold value, deactivating the inverter  15  connected to the set of batteries  17  and activating the additional inverter  23  in order to withdraw the control power Pc 1  or Pc 2 , and 
     if the withdrawal requirements ΔU, ΔF, Δl are greater than a requested charging power Prrve at the charging socket  24  and the charge level of the set of batteries  17  is less than a threshold value, activating both inverters  15 ,  23  until the charge level of the set of batteries  17  is greater than the threshold value. 
     The disclosed embodiments thus make it possible to obtain a balancing system  10   a - 10   b  which makes it possible, in addition to balancing the network, to charge an electric or hybrid vehicle very rapidly since the balancing system is connected directly to the high-voltage or medium-voltage network. The disclosed embodiments thus make it possible to obtain a “rapid” charging station that is less expensive since it reuses existing components in the balancing system  10   a - 10   b,  particularly at the network input  11 .