DE102020208432A1 - Voltage transformation system and method for charging electric vehicles - Google Patents

Abstract

A voltage transformation system for charging devices (LV1...LV6) for charging electric vehicles is proposed. This includes a transformer device (MST) for providing voltage for the individual charging devices (LV1...LV6) and a transformer (T1, T2) for transforming the voltage into a lower voltage range. In addition, a switching device for connecting the transformer (T1, T2) to the voltage supply of one of a plurality of charging devices (LV1...LV6) as required is provided, whereby the corresponding charging device is supplied with voltage from the lower voltage range. The invention enables individual charging devices to be designed and optimized for an upper voltage range, but the lower voltage range is not represented individually for each charging device in terms of components, but a common provision for a plurality of charging devices is realized by switching on as required.

Description

The invention relates to a system for voltage transformation for charging devices for charging electric vehicles and a method for charging an electric vehicle using such a system.

Conventional AC charging stations for electric vehicles have an output of 10-22 kW, which means a charging time of 2-4 hours (see https://www.autoscout24.de/informieren/ratgeber/e-mobilitaet/ladedauer /) .

Compared to refueling petrol-powered vehicles, this long charging time means a significant limitation for the vehicle owner in several respects and stands in the way of a greater willingness to switch to electromobility.

Current efforts are therefore aimed at enabling significantly faster loading. Specific developments relate to DC charging stations with significantly higher power.

A different concept is pursued with DC charging stations than with AC charging stations.

When charging using AC charging stations, the alternating current in the vehicle is converted into direct current for the vehicle battery. Since rectifiers become bulkier and heavier with increasing power, there are limits to the charging power of AC charging stations. But even with low charging power, the vehicle becomes heavier due to the inverter electronics and takes up space for other uses.

Therefore, with DC charging columns, rectification is shifted to the column and direct current is provided at the column, so that rectification in the vehicle is not necessary. This means that the restrictions on dimensioning that exist with AC charging stations no longer apply, i.e. greater charging capacities and thus shorter charging times can be used.

The usual charging power of most DC charging stations is currently around 50 kW, which leads to charging times of around half an hour to an hour.

Concepts for even faster charging are known under the designation HPC (high power charger). HPC charging systems are available from Tesla and IONITY, a joint venture founded by several automotive companies. The output power of HCP charging stations can currently be up to 350 kW, which means that a charging time of less than 10 minutes can be achieved.

An HPC charging site typically includes a medium-voltage connection. Using a mains transformer, the medium voltage is converted into low voltage, which supplies several HPC charging stations. The individual charging stations typically each include a rectifier, a DC/DC converter for setting the charging voltage and a payment terminal.

There is a need for further increases in the efficiency of charging systems for electric vehicles. It is the object of the invention to contribute to this.

The task is solved by a system for voltage transformation for charging devices (typically charging stations) for charging electric vehicles. Advantageous developments are specified in the dependent claims. The invention also includes two methods using a voltage transformation system according to the invention for charging an electric vehicle.

A voltage transformation system for charging devices (typically charging stations) for charging electric vehicles is proposed. This is formed with a transformer device for providing voltage (e.g. low voltage in the range of 1000 V) for the individual charging devices and includes a transformer for transforming the voltage into a lower voltage range (lower voltage provided in relation to the transformer device). For example, the transformer device may comprise a plurality of low-voltage windings each for supplying voltage to a charging device. In addition, a switching device is provided for connecting the transformer to the voltage supply as required for one charging device of a plurality of charging devices, as a result of which a supply of voltage from the lower voltage range is realized for the corresponding charging device. The switching device is designed for switching on the transformer as required, e.g. with switches (e.g. load-break switch or solid-state relay), which are opened or closed by means of a controller.

In this case, charging of electric vehicles by the charging devices in the lower voltage range and an upper voltage range is preferably provided, and the system is then for switching on the transformer for charging in the lower voltage range and switching off ten designed for charging in the upper voltage range.

A central inventive idea is that individual charging devices are designed and optimized for the upper voltage range, but the lower voltage range is not represented individually for each charging device in terms of components, but a common provision for a plurality of charging devices is realized by switching on as required. This means that the lower or lower voltage range is allocated to the charging device that currently needs it. This not only saves resources with regard to the number or dimensioning of the electronic components of the charging devices, but also allows a more targeted and thus better optimization of the electronics of the charging devices for charging in the upper voltage range. A charging system that includes a system for voltage transformation according to the invention can be designed, for example, to implement a DC charging voltage in the upper voltage range by possibly connecting a plurality of DC controllers consecutively. These DC converters can then be optimized for the most efficient charging possible in the upper voltage range.

The system preferably includes a controller and is designed to switch the transformer on and off by means of the controller based on a two-point controller algorithm. A discontinuously operating controller with two output states is understood as a two-point controller. Depending on whether the voltage value is below or above a limit value between two voltage ranges (lower or lower and upper or higher voltage range), the system switches between charging with an intermediate transformer and charging without an intermediate transformer.

The transformer is preferably a variable or stepped transformer for the provision of different voltage levels from the lower voltage range.

According to a development, the system for voltage transformation includes a plurality of transformers for transforming voltage into the lower voltage range, and each transformer is associated with a plurality of charging devices in terms of circuitry. This development aims in particular at supplying a large number of charging devices. Depending on the number of charging devices, it can be advantageous to provide more than one transformer. This means that a smaller number of transformers is provided for a larger number of charging devices, with each transformer being assigned to a subset of charging devices and set up or integrated for a corresponding connection to the power supply as required. Both the number and the assignment of the transformers can be optimized according to the circumstances (e.g. number of charging devices and frequency of charging processes). It is an advantage of the solution according to the invention that retrofitting with an additional transformer (in order to take into account an increased average number of charging processes, for example) is relatively easy. The assignments of transformers to subsets of charging devices can either be disjoint subsets or, with regard to redundancies to compensate for the failure of a transformer, overlaps are provided in the assignment.

A development of the system for voltage transformation according to the invention is designed to delay the charging process of charging an electric vehicle at a charging device. As a rule, the charging process is delayed as long as another charging device requires the transformer for a charging process that started earlier or, in the case of a plurality of transformers, requires a transformer that is jointly assigned to both charging devices. In this way, access conflicts with regard to the (assigned) transformer are avoided.

This application also relates to two methods in which a voltage transformation system according to the invention is used to charge an electric vehicle.

In the first method, a first charging process of a first electric vehicle is initiated at a first charging device. To charge the first electric vehicle in the second, lower voltage range, the transformer (if there is more than one transformer, the associated one) is switched on. A charging process of a second electric vehicle at a second charging device is (typically after the start and before completion of the first charging process) initialized (ie preparations for this charging process such as possible authorization, handshake, etc. are made). The beginning of the charging process of the second electric vehicle is then delayed until the (possibly associated) transformer for charging the first electric vehicle is no longer required. The (possibly associated) transformer is then switched on for charging the second electric vehicle in the second, lower voltage range. This avoids access conflicts. It would also be conceivable, as part of a tariff strategy, to immediately interrupt the th charging process when initializing a second charging process that is prioritized according to the tariff. In the case of heavily loaded loading systems, this concept could also be further developed in the sense of a queue. In this case, the first load might be considered the load placed in the queue immediately before the second load.

It may be that electric vehicles initiate a charging process even though the vehicle battery is still relatively well charged. In this case, charging in the lower voltage range may not be necessary. Another method for charging an electric vehicle with the aid of a system for voltage transformation according to the invention takes this into account. In this case, a charging process for a battery-powered electric vehicle is initiated at a first charging device, and the state of charge of the battery is used to check whether charging in the lower voltage range is necessary. The (possibly assigned) transformer is then only switched on if charging has to take place in the lower voltage range.

• 1: Lade/Entladekurve einer Li-Ion-Batterie,
• 2: Beispiel U/I/P-Anforderung an High Power Charger (HPC-Charger) ,
• 3: Effizienz-Kurve eines klassischen DC/DC-Wandlers,
• 4: Variabel oder gestufter einstellbarer Spartrafo (verschiedene Spannungen abgreifbar),
• 5: Effizienz-Kurve eines aus mehreren Wandlern zusammengeschalteten Gesamt-Wandlers, welcher in einen oberen und einen unteren Spannungsbereich aufgeteilt ist,
• 6: Schaltplan-Schema bzw. Schaltplan-Prinzip für eine Konstruktion der beschriebenen Erfindung (konkretes Beispiel:
  • sechs EV Ladestellen mit zwei Spartrafos, welche nach Anforderung jeweils zwischen drei Ladestellen wechseln können),
• 7: erfindungsgemäßes Vorgehen beim Laden eines Elektofahrzeuges.

The invention is described in more detail below within the scope of an exemplary embodiment with reference to figures. Show it:

• 1 : charge/discharge curve of a Li-Ion battery,
• 2 : Example U/I/P request for High Power Charger (HPC-Charger) ,
• 3 : Efficiency curve of a classic DC/DC converter,
• 4 : Variable or stepped adjustable autotransformer (different voltages can be tapped),
• 5 : Efficiency curve of an overall converter made up of several converters, which is divided into an upper and a lower voltage range,
• 6 : Circuit diagram scheme or circuit diagram principle for a construction of the invention described (specific example:
  • six EV charging points with two autotransformers, which can switch between three charging points as required),
• 7 : procedure according to the invention when charging an electric vehicle.

In 1 a charge/discharge curve of a Li-ion battery is shown. The abscissa shows the state of charge SOC (state of charge), while the ordinate indicates the battery voltage in VDC (volts direct current).

As in 1 illustrated, the lower voltage range of an almost empty battery is passed through relatively quickly in HPC charging systems in relation to the total charging time. Accordingly, the switchable voltage adjustment in the lower voltage range is only required for a very limited time, which in turn allows multiple uses of this device for multiple charging points.

The changing battery voltage places demands on the working range of the charging system. This is based on 2 can be seen, in which a U/I/P diagram for an HPC charging system with working curves for charging powers P of 150 kW, 250 kW and 350 kW is shown as an example. It must be taken into account that the maximum possible charging power usually also depends on the current state of charge (SOC) of the battery. In the edge areas, mostly below 20% and above 80%, the power is throttled to protect the battery cells.

As a result, there are significant requirements with regard to the wide-range voltage output, which typically causes a reduction in the efficiency of the overall system.

There are different design approaches for the electronics of HPC chargers. For example, an AC bus can be used. With this approach, the secondary side of a transformer feeds multiple AC/DC converters, which in turn feed their own DC/DC stages. Alternatively, a DC bus design can be used. This approach uses only one AC/DC stage to generate the DC output to power all DC/DC stages. Galvanic isolation between the HPC charging points is required by the standard, which is why the design approaches either operate with separate low-voltage outlets on the transformer or galvanically isolated DC/DC converters.

DC/DC converters (also referred to as DC controllers in this context) are used for the individual DC/DC stages. It should be noted that these converters are typically optimized for a specific power range or have their highest efficiency there (cf. 3 ).

The invention is based on the observation that, especially for HPC charging devices, at the beginning of the charging process when charging an empty battery, the battery voltage increases rapidly in a first phase until it transitions into a second phase of a slower voltage increase. This also applies in particular to solid-state batteries, which are expected to increasingly replace Li-ion batteries in electromobility become gene. In the case of solid-state batteries, the battery based on glass as the electrolyte is particularly promising. This can be charged to 100% SOC in minutes, with a very fast run through the lower voltage range.

According to the invention, the voltage range is divided into a lower and an upper voltage range in accordance with the charging phases discussed above. this is in 1 indicated where a range is marked in which switching between the lower and upper voltage range is provided. This can be implemented using a two-point controller, for example. As is also indicated there, there is a hysteresis behavior when the voltage is switched using a two-point controller. It is in 1 a threshold value SOC(Ug) is specified by which the actual value must change in order to switch to the opposite state. The voltage U rises strictly monotonically as the charge SOC (state of charge) increases in the transition range between the lower and upper voltage range, so that the threshold value SOC(Ug) is assigned the limit voltage Ug. Also because of the hysteresis, both voltage ranges are not necessarily sharply delimited, but can overlap around the limit voltage Ug or possibly also vary depending on the electronics or control method used. Accordingly, the terms "lower voltage range" and "upper voltage range" are to be interpreted in such a way that the majority of the voltage values of the lower voltage range are below those of the upper voltage range and vice versa. There are currently two voltage levels for electric vehicles, 400V and 800V. For an 800V system, the threshold or limit voltage Ug would be 550-600V, for example. However, the principle is also conceivable for 400V systems, in which case the voltage Ug would be more in the 200-250V range.

All charging stations in a charging park must design their components for the upper voltage range. Since the first charging phase is short compared to the second, it is sufficient to represent the lower voltage range only a few times in terms of components and to switch it on if necessary. In the best case, the lower voltage range only needs to be mapped once. If there are several lower voltage ranges that are structurally available, it may then be the case that some of them are idle because they are not currently being used. Here it is important to find an optimum for you (according to the project). It is also not a problem to simply retrofit with regard to the lower voltage range.

The lower voltage range is implemented using a transformer. That is, the lower voltage range is represented, for example, by a variable or stepped autotransformer ( 4 ). This is comparatively cheap and can be removed from the circuit using a load isolator or solid-state relay.

Thus, the voltage adjustment for charging an electric vehicle in the lower range is realized at least for the most part by the autotransformer. In the upper area, for example, there are several DC stages or DC controllers in order to achieve the highest possible efficiency through consecutive use or their interconnection. This is through 5 illustrated.

In 6 an overall system with a voltage transformation according to the invention is shown. An HPC charging system is powered by medium voltage. A medium-voltage transformer MST supplies charging devices or charging columns LV1...LV6 with low voltage by means of low-voltage windings NSW1...NSW6. These charging stations include the AC/DC conversion (indicated by the AC/DC label) and have connection points EV1 ... EV6 for connection to electric vehicles to be charged (charging cables typically attached to the station).

The individual supply branches are switched through with main switches HS1, ..., HS1 (typically molded case circuit breakers or MCCBs). The autotransformers T1 and T2 are switched on as required for the power supply in the lower voltage range. The autotransformer T1 is responsible for the charging columns LV1 to LV3 and the autotransformer T2 for the charging columns LV4 to LV6. This is illustrated by the dashed lines. The voltage supply is formed with switches in such a way that the transformers can be switched into the supply path of each of the charging stations for which the respective transformer is responsible. The figure shows switches S1 to S6, with which the direct supply of the charging stations LV1 to LV6 can be interrupted for the purpose of connecting one of the transformers. In contrast, only switches S31 and S32 for connecting the transformer T1 to supply the charging device LV3 and switches S41 and S42 for connecting the transformer T2 to supply the charging device LV4 are shown in the figure for reasons of clarity. In fact, however, switches for connecting the responsible transformer to all charging devices are to be provided. The charging process is controlled by a controller CU (CU: Control Unit), which is formed, for example, with a microcontroller (MCU).

The autotransformers T1 and T2 are in 6 shown as separate elements from the charging columns LV1...LV6. However, it would also be possible, for example, for the transformers to be purely structural or would be physically integrated into a correspondingly expanded charging device (e.g. LV1 and LV6).

A loading process is now based on the 7 explained. In step S1 an electronically operated vehicle docks at the connection point EV3 (at this time the relevant switches S3, S31 and S32 are open). Typically, a protocol then runs to start or initialize the charging process, in which, for example, authentication takes place and the payment mode is specified. After this initialization, it is checked in step S2 whether the transformer T1 is available or is being used in the course of another charging process. This can be queried, for example, by the controller CU via the switch positions.

It is also conceivable that in the course of the initialization the state of charge of the vehicle is determined and, on this basis, it is checked whether charging in the lower voltage range is necessary at all (e.g. charging in the lower voltage range is not necessary if the battery still has more than 20 % is loaded). This is indicated by step S0.

If charging in the lower voltage range is required and the transformer T1 is available, the charging process can be started immediately in step S3. Otherwise, in step S4, there is a wait until the transformer T1 is available again (step S5). This can be detected, for example, by the opening of switches via which the transformer T1 is connected to another charging device. It is also conceivable at this point that the vehicle is not charged directly at the connection point EV3, but another waiting vehicle. Prioritization can be used for this purpose, which typically takes place in accordance with the order in which loading processes are initialized. For charging in the lower voltage range, switches S31 and S32 are closed in step S6 so that charging (step S7) can take place.

If it is now recognized (e.g. by means of a two-point controller algorithm) that a transition to charging in the upper voltage range should take place (query S8), switches S31 and S32 are opened in step S10 in order to fully couple transformer T1. In step S11, charging then takes place in the upper voltage range until the charging process is complete. Then the switch S3 is opened again (step S12).

The procedure described using the exemplary embodiment has several advantages. By dividing the power curve into two voltage levels, it is possible that only the upper part of the efficiency curve is used for each converter or converter, which means that the components can also be designed more efficiently. It is also possible to interconnect several smaller converters in order to achieve the best efficiency over the entire working range.

Furthermore, this invention - as mentioned above - is strongly aimed at future battery developments, since it is currently expected that solid-state batteries will increasingly replace Li-ion batteries in EVs.

Charging stations must design their components for the upper voltage range. However, the lower stress range only needs to be represented a few times in terms of component technology. This results in lower system costs, since the entire voltage range does not have to be mapped for all charging stations, which in turn leads to component savings and better utilization of the components.

In addition, a better overall efficiency is achieved through the different treatment of the lower and upper voltage range, since components must or can be designed for the optimal (significantly limited) working range.

The lower voltage range for an empty battery is passed through relatively quickly in relation to the total charging time, e.g. in a few minutes. How fast depends on the overall system consisting of charging power, battery type and battery capacity. Above all, this rapid cycling through the lower battery voltage occurs in HPC charging systems, for which this invention is particularly suitable. In the case of home wallboxes with a small charging capacity, the advantages are less.

Another advantage is the possibility of using a comparatively low-cost autotransformer. The battery is quickly brought out of its low voltage level by means of the autotransformer and an AC/DC converter trimmed for efficiency. After that, only efficient converters work in parallel or in series. (The autotransformer is then removed from the circuit again.)

The system can be used e.g. for electric cars (typically minimum battery voltage 200 VDC) and for electric buses and electric trucks (typically minimum battery voltage 450 VDC). With a minimum battery voltage of 450 VDC, the system works even more efficiently, since the dwell time in the lower voltage range is relatively short with a correspondingly high charging station output (approx. > 300kW).

Claims (11)

Voltage transformation system for chargers (LV1...LV6) for charging electric vehicles, with - A transformer device (MST) for providing voltage for each of the individual charging devices (LV1 ... LV6), - A transformer (T1, T2) for transforming the voltage into a lower voltage range, and - A switching device for switching on the transformer (T1, T2) as required in the power supply of one charging device of a plurality of charging devices (LV1...LV6), whereby a supply of voltage from the lower voltage range is realized for the corresponding charging device. Stress transformation system claim 1 , characterized in that - charging of electric vehicles by charging devices (LV1...LV6) is provided in the lower voltage range and an upper voltage range, and - the system for switching on the transformer (T1, T2) for charging in the lower Voltage range and switching off for loading in the upper voltage range is designed. Stress transformation system claim 1 or 2 , characterized in that - it comprises a controller (CU), and - the system for switching the transformer (T1, T2) on or off by means of the controller (CU) is designed on the basis of a two-point controller algorithm. Stress transformation system according to one of Claims 1 until 3 , characterized in that the transformer (T1, T2) is a variable or stepped transformer designed to provide different voltage levels from the lower voltage range. System for voltage transformation according to one of the preceding claims, characterized in that the switching device is formed with switches (S31, S32, S41, S42) for switching on the transformer (T1, T2) as required, which switches are opened or closed by means of a controller (CU). . getting closed. Voltage transformation system according to one of the preceding claims, characterized in that it comprises a transformer device (MST) with a plurality of low-voltage windings (NSW1...NSW6) each for supplying voltage to a charging device (LV1...LV6). Voltage transformation system according to one of the preceding claims, characterized in that - it comprises a plurality of transformers (T1, T2) for transforming voltage into the lower voltage range, and - each transformer (T1, T2) of a plurality of charging devices (LV1. ..LV6) is assigned switching technology for the required connection. System for voltage transformation according to one of the preceding claims, characterized in that the system is designed for a delay in the charging process of charging an electric vehicle at one charging device (LV1...LV6) as long as another charging device (LV1...LV6) is available for a charging process started earlier requires the transformer (T1, T2). Charging system for electric vehicles, - with a large number of charging devices (LV1...LV6), and - with a system for voltage transformation according to one of the preceding Claims 1 until 8th , which is designed for a realization of a DC charging voltage in the upper voltage range by a possibly consecutive interconnection of a plurality of DC controllers. Method for charging an electric vehicle using a voltage transformation system according to one of Claims 1 until 8th , in which - a first charging process of a first electric vehicle is initiated at a first charging device (LV1...LV6), - the transformer (T1, T2) is switched on for charging the first electric vehicle in the second, lower voltage range, - a charging process of a second electric vehicle is initialized at a second charging device (LV1...LV6), - the beginning of the charging process of the second electric vehicle is delayed until the transformer (T1, T2) is no longer required for charging the first electric vehicle, and - then the transformer is switched on for charging the second electric vehicle in the second, lower voltage range. Method for charging an electric vehicle using a voltage transformation system according to one of Claims 1 until 8th , in which - a charging process of a battery-powered electric vehicle at a first charging device (LV1...LV6) is initiated, - based on the state of charge (SOC) of the battery, it is checked whether charging in the lower voltage range is necessary, and the transformer (T1, T2) is only switched on when charging in the lower voltage range is required.

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