Description

Long-distance journey time with electrical vehicles is strongly dependent on the power delivered by charging stations. To illustrate this, consider a journey from Amsterdam to Berlin, a distance of about 660 km. A typical Electrical Vehicle, EV, battery has a capacity of about 60 kWh and when driving 100 km per hour they may have a typical power consumption of 20 kWh. This implies that the driving range is about 240 km (assuming a typical battery charge level of about 80% after a battery recharge). Hence, to travel from Amsterdam to Berlin, a driver will have to make two stops, each stop adding waiting time that depends on the power of the charging station. The total journey time, including this power-dependent waiting time, is 6.6 hours for a petrol or diesel car, with 0 stops, 32.5 hours for a 3.7 kW charged EV, 15.3 hours for a 11 kW charged EV, 8.5 hours for a 50 kW charged EV, alle including 2 stops. These journey times are applicable for current generation EV charging, whereas future EV charging at 150 kW will lower the journey time to 7.2 hours, including 2 stops. The 3.7 kW charging is currently considered a standard for domestic single phase charging whereas the 11 kW may be considered the current standard for public charging and currently on 2% of Dutch public charges are suitable for 50 kW charging.

The above comparison illustrates that with the deployment of fast 150 kW charges, the journey times will be comparable to those obtained with traditional petrol/diesel fuelled vehicles. Indeed, plans are made to deploy such stations in for example the Netherlands to stimulate a broader adoption of EVs.

Clearly, fast charging stations are required. However, the costs for these charging stations are very high. Meanwhile, more rapid charging requires extracting higher peak power from the grid. This is not always available and can work out very expensive. Half the cost of a new charging station can be the cost of grid connection. These factors may considerably slow down their accessibility in the charging infrastructure. A typical solution for fast charging stations is shown in Figure 1. To achieve a constant non-varying demand, the station is equipped with a local battery and a DC/DC power converter.

About 40% of the equipment cost of the charging station is determined by this power converter, whose total cost can run up to €60,000. A major additional factor is the cost for the connection to the distributed electricity grid at the medium voltage level (left side of Figure 1) which can easily exceed €100,000 at the higher end.

Known charging stations arranged for fast EV charging of 150 kW or more, rely on either circuitry which is either bulky, large, has lots of components and is inefficient. As such, there is a need for an improved EV charging system which is efficient, arranged for fast charging of 150 kW or more, at lower costs.

In a first aspect of the present disclosure, there is provided an electric vehicle charging system, comprising: a rectifier stage, configured for connecting at an input with an Alternating Current, AC, power supply network, and rectifying the AC into Direct Current, DC, for connecting with a battery pack of an electric vehicle at an output; a buffering battery pack, connected in parallel with the output of the rectifier stage; a DC/DC converter stage, connected in series with the buffering battery and the output of the rectifier stage; wherein the buffering battery pack comprises a primary and an auxiliary battery pack, wherein an output of the DC/DC converter stage is connected in series between with the primary battery pack and the output of the rectifier stage, and the auxiliary battery pack is connected in parallel with an input of the DC/DC converter stage.

To achieve a broader adoption of Electric Vehicles, EVs, fast charging stations (delivering very high power) must be deployed in the charging infrastructure. But the equipment costs of these fast-charging stations are very high, slowing down their accessibility. To further increase adoption of EVs fast charging stations are essential, and as such, there is a need for an EV charging systems which are suitable for such fast-charging at very high power, at a high efficiency but at reduced costs.

To this end, an EV charging system may employ a Reduced Dissipation Converter, RDC, which lowers the costs as it has much lower heat losses and requirements for cooling.

A goal of an EV charging system design is to reduce high-peak power demand from the grid and thereby grid connection costs. To this end, an EV charging system may comprise a local battery which is coupled to a DC/DC converter.

The RDC utilizes a serial link between the battery pack of the EV and a local battery, also referred to as buffering battery or buffering battery pack as is may comprise several batteries. The serial link is configured to only provide the voltage difference ad control the charging current. Thus, the RDC only processes the partial charging power instead of a traditional DC/DC converter that processes the full charging power, thereby reducing cost on components and components dimensions and complexity.

As the RDC has to handle both voltage differences between the buffering battery pack and the battery pack of the EV, the DC/DC converter may be configured as an isolated DC/DC converter, wherein the output of the DC/DC converter is connected in series with the buffering battery pack, while the input is connected in parallel with this buffering battery pack, or alternatively, in parallel with the battery pack of the EV. To prevent short-circuiting the DC/DC converter is to be galvanically isolated, which needs to use complex topology. Due to the number components and complexity in design, the efficiency of such a design is far from optimal.

The proposed Electric Vehicle, EV, charging system has an increased efficiency, at lower costs. The proposed EV charging system is arranged or configured to be connected with an Alternating Current, AC, power supply network to receive AC power and convert the AC power into DC power with a rectifier stage and to make the power match a battery pack of an electric vehicle which can be charged accordingly. The system and in particular the rectifier is configured to meet a certain dimension of charging, e.g. fast charging at 150 kW or more.

The inventor had the insight that by splitting the battery pack into a primary and an auxiliary battery pack, of which an output of the DC/DC converter stage is connected in series between with the primary battery pack and the output of the rectifier stage, and the auxiliary battery pack is connected in parallel with an input of the DC/DC converter stage, the local buffering by the battery pack is fully utilized and allows to implement the partial power processing using a non-isolated DC/DC convert. The local buffering is thus split in two, or more, batteries and the input of the DC/DC converter is connected to the auxiliary battery or also referred to as Bat1.

In an example, the buffering battery pack is comprised in a reduced dissipation converter.

The reduced dissipation converter is a type of power electronic converter that is arranged to minimize the amount of energy dissipated during its operation. In other words, it is a converter that is designed to be more efficient than conventional converters.

Power electronic converters are used to convert electrical power from one form to another and commonly used in a wide range of applications, including electric vehicles and charging systems thereof. Typically, during the conversion process, some of the electrical energy is lost in the form of heat, which is dissipated in the converter. This results in a decrease in the overall efficiency of the system.

The reduced dissipation converter is designed to minimize the amount of energy that is lost in the form of heat. In an example, this may be implemented by using various techniques such as soft switching, resonant switching, or other control techniques that reduce the amount of energy dissipated in the switching devices. They may also use high-frequency switching to reduce the size of the passive components, which can further improve the efficiency of the converter. The effect of the use of a reduced dissipation converter may include lower energy consumption, reduced heat generation, and longer lifespan of the electronic components. They are especially useful the present application in which energy efficiency and heat dissipation is a critical factor.

Use of a reduced dissipation converter in electric vehicle charging systems are beneficial as electric vehicle charging systems require high power and efficiency to ensure that the vehicle can be charged quickly and cost-effectively. By using the reduced dissipation converter, the overall efficiency of the charging system can be improved, which can reduce the cost of charging for the user.

In addition, reduced dissipation converters can also help to minimize the size and weight of the charging system, which is important in the design of charging stations and onboard chargers. By reducing the amount of energy that is dissipated in the converter, the size and weight of the passive components, such as capacitors and inductors, can be reduced, which can help to make the system more compact and lightweight.

In an example, the reduced dissipation converter comprising the buffering battery pack comprises the auxiliary battery pack and at least one further auxiliary battery pack.

The reduced dissipation converter may comprise, in an example, one but preferably at least two batteries or battery packs. Hence, the reduced dissipation converter may comprise the auxiliary battery pack and one further auxiliary battery pack. As such, the system, in this example, is comprised of three separate batteries or battery packs, i.e. the main primary battery, the auxiliary battery and a further auxiliary battery. In yet another examples, yet another further auxiliary battery or battery pack may be included.

The further auxiliary battery or battery pack, and preferably also the corresponding control or switching circuitry, allows the reduced dissipation converter to output power at a much wider voltage range. As such, the system is arranged for different electric vehicles with different batteries or battery packs. This is very beneficial for fast DC charging. The corresponding circuitry, control or switching circuitry, can further prevent a reverse voltage polarity, which is not possible without such circuitry. Absence of such circuitry, may result in larger reverse inrush currents and may destroy the converter as well as the batteries. With the circuitry, this is prevented.

In an example, the reduced dissipation converter further comprises a switching circuitry for control of the auxiliary battery pack and the at least one further auxiliary battery pack.

The switching circuitry may be comprised of a plurality of switches and capacitors, wherein each battery, i.e. the auxiliary battery and the further auxiliary battery may have a respective capacitor connected parallel over the respective battery, and two switches implemented as transistors, field effect transistors, FETs, or MOSFETS.

In an example, the switching circuitry comprises switches for turning on and turning off the auxiliary battery pack and the at least one further auxiliary battery pack..

In an example, the switching circuitry arranged for operating in a first and second operational modus, wherein the switching circuitry comprises first switching sub-circuitry for connecting the at least one further auxiliary battery pack in series with the primary battery pack in the first operational modus, and the switching circuit comprises a second switching sub-circuitry for connecting the at least one further auxiliary battery pack in series with the auxiliary battery pack in the second operational modus respectively.

In an example, the DC/DC converter stage is configured as a non-isolated DC/DC converter.

In contrast with known EV charging systems which comprise DC/DC converter stages which are isolated by for example a transformer to eliminate short circuit due to the direct DC path between the input and the output, the proposed EV charging system may comprise a non-isolate DC/DC converter which amongst other advantages enables IC integration and makes large, analogue and non-efficient components such as galvanic isolators superfluous.

In an example, the DC/DC converter stage is configured as a bidirectional buck-converter. The DC/DC converter stage is preferably configured as a non-isolated switching DC to DC converter and in particular comprising a buck-converter topology, buck-boost converter topology, Cuk converter topology, SEPIC converter topology or zeta converter topology.

A Cuk converter is a type of DC/DC converter that can be used to efficiently step up or step down voltage levels in electronic circuits. Using a Cuk converter may have the effect that a higher efficiency is obtained in voltage conversion because they use a coupled inductor to transfer energy between the input and output, reducing the energy losses that occur in other types of converters. Also, Cuk converters may have the effect of being small in size and light in weight because they require little components to achieve the a certain voltage conversion. Using Cuk converters also results in a low input ripple because they use a capacitor to filter the input voltage, which reduces the high-frequency noise that may cause problems in electronic circuits. Cuk converters may also be considered advantageous for having a wide input voltage range and having good output voltage regulation making them suitable for use as DC/DC converter of the proposed system.

SEPIC (Single-Ended Primary Inductor Converter) converter are also a type of DC/DC converter that can be used to efficiently step up or step down voltage levels in electronic circuits and also have several advantages of using a SEPIC converter which include having a high efficiency in voltage conversion because they use a capacitor to store energy, which reduces the energy losses that occur in other types of converters, they utilize a wide input voltage range, making them suitable for use in the proposed system, especially for charging batteries having a variety of voltage levels. Other advantages are they have good output voltage regulation, which is beneficial for the present application, they have low input ripple, because of the use of the capacitor to filter the input voltage and to reduce the high-frequency noise that may cause problems in further circuitry. They also have a simple design making them easy to use, design and manufacture. Similar to the SEPIC, the Zeta converter also has corresponding advantages like high efficiency, low input ripple, wide input voltage range, simple design and small footprint. Preferably, the DC/DC converter is a switched-mode power supply, and more preferably, a buck converter or step-down converter comprising switching means, a capacitor and an inductor, of which the switching means preferably comprise two transistors.

In an example, the DC/DC converter stage is arranged for regulating the current obtained from the buffering battery pack in accordance with a maximum power output according to which the rectifier stage is configured.

The DC/DC converter may be configured to control the current to the battery pack of the EV and thus also the current drawn from the primary and auxiliary battery pack and subsequently the current drawn from the rectifier stage.

In an example, a capacity of the primary battery pack is larger than the capacity of the auxiliary battery pack.

In an example, the DC/DC converter stage is configured for providing a fraction of the power, in particular approximately 20%, drawn for charging the battery pack of the electric vehicle.

In an example, the rectifier stage is configured for connecting with a three- phase AC power supply network.

In an example, the electric vehicle charging system further comprises: a power transformer, configured for connecting between the input AC power supply network and the rectifier stage, and configured as a delta-wye step-down power converter for lowering a medium voltage from the input AC power supply network to a lower voltage at an input of the rectifier stage. In an example, the system is configured for charging the battery pack of the electric vehicle at 150 kW or above.

In a second aspect there is provided a DC/DC converter configured for connecting in series with a buffering battery and an output of a rectifier stage rectifying AC into DC for connecting at the output the DC with a battery pack of an electric vehicle; wherein the buffering battery pack comprises a primary and an auxiliary battery pack, wherein an output of the DC/DC converter stage is connected in series between with the primary battery pack and the output of the rectifier stage, the auxiliary battery pack being connected in parallel with an input of the DC/DC converter stage.

The present disclosure will now be explained by means of a description of an embodiment of a fast charging station in accordance to the present disclosure, in which reference is made to the following figures, in which:

Fig. 1A discloses an embodiment of a fast charging station in accordance with the prior art;

Fig. 1 B discloses another embodiment of a fast charging station in accordance with the prior art;

Fig. 2 discloses an embodiment of a fast charging station in accordance with the present disclosure;

Fig. 3A discloses an embodiment of the fast charging station of Fig. 1A, in accordance with the prior art;

Fig. 3B discloses another embodiment of the fast charging station of Fig. 1A, in accordance with the prior art;

Fig. 4A discloses in more detail elements of the fast charging station of Fig. 3A, in accordance with the prior art;

Fig. 4B discloses in more detail elements of the fast charging station of Fig. 3B, in accordance with the prior art;

Fig. 5 discloses an embodiment of a dual active bridge converter in accordance with the prior art;

Fig. 6a discloses an embodiment of the fast charging station of Fig. 2, in accordance with the present disclosure comprising an auxiliary battery pack; Fig. 6b discloses an embodiment of the fast charging station of Fig. 2, in accordance with the present disclosure comprising an auxiliary battery pack Bat1 and a further auxiliary battery pack Bat_s;

Fig. 7a discloses in more detail the fast charging station of Fig. 6, in accordance with the present disclosure comprising control circuitry for control of the auxiliary battery pack Bat1 ;

Fig. 7b discloses in more detail the fast charging station of Fig. 6, in accordance with the present disclosure comprising control circuitry for control of the auxiliary battery pack Bat1 and for control of the further auxiliary battery pack Bat_s;

Fig. 7c discloses the detailed fast charging station of Fig. 7b, operating in the first operation modus;

Fig. 7d discloses the detailed fast charging station of Fig. 7b, operating in the second operation modus;

Fig. 8 discloses the voltage variation of Tesla EV battery Vs SoC;

Fig. 9 discloses the key voltage waveforms during the charging process;

Fig. 10 discloses the key power waveforms during the charging process;

Fig 11A discloses the key energy during the charging process, i.e. the energy from BAT1 ;

Fig 11 B discloses the key energy during the charging process, i.e. the energy from BAT2;

Fig 11C discloses the key energy during the charging process, i.e. the energy loss due to the energy transfer from BAT 1 to output of RDC.

The fast charging station 1 in accordance with the prior art is shown in figure 1A and 1 B. To reduce the high-peak power demand from the grid and thereby the grid connection cost, the station is equipped with a local battery BAT that is coupled through a DC/DC converter as shown in figure 1 A or coupled through a AC/DC converter as shown in figure 1 B.

The electric vehicle charging system or fast charging station 1 in accordance with the present disclosure comprises a rectifier stage AC/DC, configured for connecting at an input with an Alternating Current, AC, power supply network, and rectifying the AC into Direct Current, DC, for connecting with a battery pack of an electric vehicle EV at an output; a buffering battery pack BAT, connected in parallel with the output of the rectifier stage AC/DC; a DC/DC converter stage RDC, connected in series with the buffering battery and the output of the rectifier stage. The buffering battery pack BAT comprises a primary BAT2 and an auxiliary battery pack BAT1 , wherein an output of the DC/DC converter stage is connected in series between with the primary battery pack BAT2 and the output of the rectifier stage, and the auxiliary battery pack BAT 1 is connected in parallel with an input of the DC/DC converter stage.

The fast charging station 1 further comprises a power transformer, configured for connecting between the input AC power supply network and the rectifier stage AC/DC, and configured as a delta-wye step-down power converter for lowering a medium voltage MV from the input AC power supply network to a lower voltage LV at an input of the rectifier stage.

The concept of the DC/DC converter stage or Reduced Dissipation Converter RDC concept is shown in Figure 2. It utilizes a serial link between the local buffering battery BAT and the Electric Vehicle EV to only handle their voltage difference and control the charging current. Thus, the RDC only processes the partial charging power instead of a traditional DC/DC converter that processes the full charging power. Given the fact that the converter cost is closely correlated with the power it processed, the RDC is able to reduce the converter cost by 70%.

The Reduced Dissipation Converter RDC has to handle the voltage difference between the local buffering battery BAT and the battery in EV. In order to achieve that, the existing solutions utilize an isolated DC/DC converter, where the output is connected in series with the local buffering battery BAT, while the input is connected in parallel with the local buffering battery BAT, as shown in figure 3A or in parallel with the EV battery, as shown in figure 3B. The DC/DC converter is galvanically isolated between the input or output, as without it, it will cause a short circuit, as indicated by figure 4. As a result, such a converter circuit has to use very a complicated topology, such as a dual active bridge converter 3 as shown in figure 5. Due to lots of components in the isolated converter circuit, the cost reduction of known solutions is incremental and efficiency improvement is very limited. The fast charging station 1 in accordance with the present disclosure fully utilizes the local buffering battery BAT storage, and propose a novel configuration that allows to implement the Reduced Dissipation Converter RDC using the non-isolated DC/DC converter, as shown in figure 6. The local buffering battery is split into two units, BAT1 and BAT2, and the input of DC/DC converter is connected to the BATI . One of the possible implementations of the Reduced Dissipation Converter RDC is shown in figure 7, in which a buck converter is used.

In Fig. 6a the electric vehicle charging system of the present disclosure, implemented for use as a fast charging station, is comprised of the primary battery pack Bat2, and the auxiliary battery pack Bat1 , which auxiliary battery pack Bat1 is comprised in the reduced dissipation converter, RDC. The RDC is at least comprised of a DC/DC converter and the auxiliary battery pack Bat1. In Fig. 6b, the electric vehicle charging system of the present disclosure, implemented for use as a fast charging station, is embodied with a further auxiliary battery pack Bat_s. The skilled person will appreciate that in further examples, more branches of such auxiliary battery pack may be comprised in the RDC. The RDC, besides Bat1 , the DC/DC converter and Bat_s as further auxiliary battery pack, may also comprise control circuitry or switching circuitry, also referred to in the figures as embedded switching network, ESN. With the ESN the RDC can control the operation of the respective auxiliary battery packs, Bat1 and Bat_s, and the ESN may be implemented as shown in Fig. 7b, showing an additional capacitance C2, and additional switches S3 and S4, similar to the circuitry layout for control of the single auxiliary battery pack as shown in Fig. 7a. With the ESN, as thus for example implemented according to the example of Fig. 7b, the system, or more in particular, the ESN, may be operated according to two modes of operation as shown in Fig. 7c and 7d. In Fig. 7c the first mode of operation, or mode I, is shown, where Bat_s can be treated as part of Bat2 (S4 is turned off and S3 is turned on, while S1 and S2 are operated at a constant switching frequency). In Fig. 7d, the second mode of operation, or mode II, is shown where Bat_s can be treated as Bat1 (S1 is turned off and S2 is turned on, while S3 and S4 are operated at a constant switching frequency) Accordingly, two modes of operation are provided, with operation mode I, as shown in Fig. 7c Bat_s can thus be treated as part of Bat2 (S4 is turned off and S3 is turned on, while S1 and S2 are operated at a constant switching frequency), and in operation mode II, as shown in Fig.7d where Bat_s can be treated as Bat1 (S1 is turned off and S2 is turned on, while S3 and S4 are operated at a constant switching frequency). These two modes of operation have the advantage that: the ESN allow RDC to output a much wide voltage range (i.e., v1+v2 in Fig. 6b has wider voltage range), which can adapt to different electric vehicles with different battery (which is a very important aspect and beneficial in fast DC charging). Further, the ESN can prevent the reverse voltage polarity(i.e. , v1 <0) when v2>vEv. In comparison with the configuration shown in Fig. 7a, the converter has no controllability when v2>vEv, which result large reverse inrush current, and may destroy the converter as well as all the batteries. Therefore the use of such an ESN provides a significant improvement.

Assuming the output voltage of the Reduced Dissipation Converter RDC is v1 , output voltage of Bat 2 is v2 , the EV battery voltage is VE , and the charging current is i ₀ . According to the Kirchhoff Voltage Law (KVL), we have

'i + ''2 = ''/.■ (Eq. 1)

By multiplying the charging current on both sides of Eq. 1 , yields

As seen, the Reduced Dissipation RDC only processes fractional part of the charging power PRDC, while most of the power is directly transferred from BAT2 to EV, i.e., PBAT2. Therefore, power rating of the RDC is greatly reduced so does its cost.

By integrating the terms on both sides of Eq. 2, yields, (Eq. 3) Eq. 3 shows the energy distribution between BAT1 and BAT2.

Take the Tesla EV battery as example, the voltage variation of VE VS State of Charge SoC is shown in figure 8.

Assume the charging starts from 5% of the State Of Charge SoC to prevent over-discharge, the key voltage waveforms of RDC output voltage v1 , output voltage of BAT2 v2 , the EV battery voltage VE can be obtained according to Eq. 1 , as shown in figure 9, where the voltages are normalized. The power processed by RDC can also be obtained according to Eq. 2, as shown in figure 10. Given that the power processed by the RDC is only a fractional part of the total power transferred, the cost and power loss can be greatly reduced.

As energy is the integration of the power, the energy provided from BAT 1 , BAT2 and the energy loss is shown by the shaded area in figure 11 A, 11 B, and 11C respectively, which further confirms the reduced energy loss.

To achieve a broader adoption of electric vehicles (EVs), fast charging stations (delivering very high power) must be deployed in the charging infrastructure. But the equipment costs of these fast-charging stations are very high, slowing down their accessibility. This invention can reduce their greatly costs by a Reduced Dissipation Converter (RDC), a cheaper solution which has much lower heat losses and requirements for cooling.