Stationary DC charging device for electrically powered vehicles, method for providing a DC charging device for electrically powered vehicles

Abstract

The invention relates to a stationary DC charging device for electrically powered vehicles, which has a first circuit for connection to an AC network, which is designed to convert the AC voltage provided by the network into a first DC voltage, and a second circuit, which is functionally connected to the first circuit and is designed such that the first DC voltage is supplied to it in such a way that it converts the first DC voltage into a second DC voltage that is galvanically isolated from the AC network, in which the ratio of the magnitude of the galvanically isolated second DC voltage to the magnitude of the first DC voltage is kept constant regardless of the magnitude of the first DC voltage, in particular at a value >1, wherein a third circuit is functionally connected to the second circuit, which is designed such thatthat the galvanically isolated second DC voltage is supplied to the third circuit in such a way that the galvanically isolated second DC voltage is converted into the charging voltage and is applied to an output of the third circuit for a charging process on the electrically driven vehicle, wherein the first circuit, the second circuit and / or the third circuit are designed and functionally interconnected in such a way that the magnitude of the first DC voltage can be varied depending on the magnitude of the charging voltage used.

Description

[0001] The invention relates to a DC charging device for electrically powered vehicles according to the preamble of claim 1 and to a method for providing a DC charging device for electrically powered vehicles according to the preamble of claim 10.

[0002] It is known that stationary DC chargers for electric vehicles usually consist of a so-called mains front end, which is designed as an AC-DC converter, and at least one galvanically isolated DC-DC converter, i.e. a DC-DC converter.

[0003] The grid front end converts the AC grid voltage into a first DC voltage, while the DC-DC converter(s) are responsible for generating a galvanically isolated second DC voltage from this first DC voltage, which is used to charge the EV. It is also known that a DC charger is generally designed to charge different battery systems, particularly those with both 400V and 800V. Therefore, the charger must cover a very wide voltage range, particularly 200-920V.

[0004] The disadvantage is that achieving such a wide voltage range with good efficiency is very complex. This is due to the fact that the required DC-DC converter topologies, such as those provided by LLC converters, phase-shift full bridges, or dual active bridges, achieve very high efficiency rates at their nominal operating point, but this efficiency drops significantly when operated outside the nominal voltage.

[0005] One solution to this problem is to generate two electrically isolated second voltages for charging, usually using either two DC-DC converters or a single DC-DC converter with two outputs. The voltages are connected in parallel in the lower voltage range and in series in the upper voltage range. The resulting reduced voltage range reduces the efficiency loss outside the nominal operating point.

[0006] However, this solution also has disadvantages. For example, additional costs arise because relays are required for switching between parallel and series voltage connections, and a compensating control system is required to compensate for component variations between the output stages. Depending on the requirements, other factors that drive higher costs may also arise. For example, the power electronics often have to be designed for a higher maximum current to ensure maximum power can be delivered within the switching voltage range. This disadvantage is particularly evident in implementations that operate according to the "High Power Charging" (HPC) standard.

[0007] The object underlying the invention is therefore to provide a solution that at least partially overcomes the disadvantages of the prior art. In particular, the object is to provide a technical solution that improves the efficiency of DC chargers.

[0008] This object is achieved by the DC charging device for electrically powered vehicles according to the preamble of claim 1, starting from the features of the preamble by its characterizing features, and by a method for providing a DC charging device for electrically powered vehicles according to the preamble of claim 10, starting from the features of the preamble by its characterizing features.

[0009] The stationary DC charging device for electrically powered vehicles according to the invention has a first circuit for connection to an AC network, which is designed to convert the AC voltage provided by the network into a first DC voltage, and a second circuit which is functionally connected to the first circuit and is designed such that the first DC voltage is supplied to it in such a way that it converts the first DC voltage into a second DC voltage that is galvanically isolated from the AC network, wherein the ratio of the magnitude of the galvanically isolated second DC voltage to the magnitude of the first DC voltage is kept constant regardless of the magnitude of the first DC voltage, in particular at a value >1, wherein a third circuit is functionally connected to the second circuit, which is designed such thatthat the galvanically isolated second DC voltage is supplied to the third circuit in such a way that the galvanically isolated second DC voltage is converted into the charging voltage and is applied to an output of the third circuit for a charging process on the electrically driven vehicle, wherein the first circuit, the second circuit and / or the third circuit are designed and functionally interconnected in such a way that the magnitude of the first DC voltage can be varied depending on the magnitude of the charging voltage used.

[0010] The invention forms a multi-stage topology which ensures that the output voltage of the rectifier is not converted directly into the charging voltage, but that the converted voltage is first raised to an intermediate level and only converted to the charging voltage by the third circuit. This allows circuit design measures to increase efficiency and flexibility, while also reducing the costs and complexity of prior art circuits. One advantage of the invention is, for example, that the fixed transformation ratio and the high voltage level, particularly in the range of 700V-950V, mean that the second circuit, and thus the entire topology, operates very efficiently. A further increase in efficiency in the topology is achieved by making it possible for the first DC voltage, the output voltage of the rectifier, to vary depending on the required charging voltage.This adaptation also has the beneficial effect of reducing the voltage load on semiconductors used in the circuit during operation that requires low charging voltage, thus extending their service life.

[0011] Advantageous embodiments and further developments of the invention are specified in the dependent claims.

[0012] If the stationary DC charging device according to the invention is further developed such that the first circuit is designed as a two- and / or three-phase rectifier, it can be connected to conventional AC voltage sources and widely used. If the stationary DC charging device according to the invention is further developed such that the second circuit is designed as a transformer circuit and the ratio is determined by the transformer's transformation ratio, a simple implementation is obtained that is very well suited to the multi-stage topology of the invention.

[0013] Preferably, the stationary DC charging device according to the invention is advantageously further developed such that the second circuit is designed as a so-called DC-DC full-bridge converter, thus providing an efficient and adaptable variant of a transformer circuit which is suitable and usable for various requirements of the charging device and whose efficiency, considered across all requirements, is better than according to the prior art.

[0014] A further preferred advantageous development of the stationary DC charging device according to the invention provides that the third circuit is designed as a so-called step-down converter circuit, in particular as a DC-DC buck converter. This provides a particularly suitable circuit for bringing the second galvanically isolated DC voltage, converted to the intermediate level, to the desired charging voltage level. Furthermore, the buck converter can adjust the charging voltage without a load connected to the output, thus maintaining a charging current of 0A. This low-cost, no-load capability is particularly advantageous shortly before the start of the charging process.

[0015] If the stationary DC charging device according to the invention is further developed in such a way that this step-down converter circuit is formed from a first DC-DC step-down converter and a second DC-DC step-down converter connected in parallel, this provides further degrees of freedom in dimensioning and increasing efficiency.

[0016] In a further preferred advantageous development of the stationary DC charging device according to the invention, the two-phase rectifier, the three-phase rectifier, the transformer circuit, and / or the step-down converter circuit are configured such that the directed blocking function, particularly provided by diodes, is at least partially implemented by transistors, particularly power transistors, preferably designed using MOSFET technology. This also supports the efficiency of the multi-stage topology according to the invention and also allows the orchestration of the individual and / or all stages, so that further improvements / adaptations can be realized.

[0017] An alternating and thus a kind of "interleaved" orchestrated solution is provided by the development of the stationary DC charging device according to the invention, in which the first DC-DC buck converter and the second DC-DC buck converter are functionally connected and operated in such a way that the blocking function of the second DC-DC buck converter, realized by the MOSFET transistors, is always connected in a complementary manner with respect to the reverse direction of the first DC-DC buck converter, realized by the MOSFET transistors, with a reversal of the reverse direction occurring at a recurring, adjustable time interval. This achieves, among other things, that the two parallel converters clock with a time offset from one another, allowing for smaller output chokes.

[0018] Preferably, the stationary DC charging device according to the invention can be further developed such that the time interval, i.e. the cycle, is selected as a function of the value of a current flowing into the third circuit, in particular such that the reversal is triggered at a current value of 0A. This therefore ensures that the switching frequency of this converter, unlike the other conversion stages, is not kept constant, but is adjusted such that the converter is always switched on at current = 0A, thus preventing switch-on losses. This advantage is particularly evident when using silicon carbide semiconductors, since at a given operating point, more switch-on losses occur than switch-off losses, whereby the operating mode according to this development achieves high efficiency values.

[0019] Further advantages and details of the invention are explained with reference to the embodiment of the invention shown in the single figure. FIGURE schematically shows a circuit diagram of an embodiment of the arrangement according to the invention in the form of a multi-stage topology for charging an electrically powered vehicle.

[0020] The exemplary embodiments and functions partly shown and partly only explained in the FIGURE below are a preferred embodiment and further developments of the arrangement according to the invention and the method according to the invention.

[0021] In the exemplary embodiments, the described components of the embodiments each represent individual features of the invention that are to be considered independently of one another, which also further develop the invention independently of one another and are therefore to be regarded as part of the invention individually or in a combination other than that shown.

[0022] Furthermore, the described embodiments can also be supplemented by further features of the invention already described.

[0023] The FIGURE shows a schematic circuit diagram of an embodiment of the stationary DC charging device according to the invention. It can be seen that the topology according to the invention has a multi-stage structure. For this purpose, the individual stages are indicated in the figure by dashed rectangles.

[0024] One exemplary embodiment of the first circuit according to the invention, which represents the first stage, is a rectifier circuit GL. It is connected to a power grid NT at its inputs. It thus forms the grid front end of the multi-stage topology according to the invention. At the outputs of this grid front end, the second circuit according to the invention is configured as a DC-DC full-bridge converter DC-DC-VBW, at whose outputs, as the final stage, the third circuit according to the invention is connected to two parallel-connected DC-DC buck converters, to whose common output an electric vehicle can be connected for charging purposes.

[0025] It can also be seen that the power grid provides a three-phase alternating voltage, for which the rectifier GL has three correspondingly labeled inputs for each of the three phases L1...L3. An identical branch is provided for each phase, with the corresponding phase connected between two transistors for each branch. The first branch is formed by a first MOSFET mains front-end transistor of TN1_1 and a second MOSFET mains front-end transistor TN1_1. The second branch is formed by a third MOSFET mains front-end transistor TN2_1 and a fourth MOSFET mains front-end transistor TN2_2, and finally, the third branch is formed by a fifth MOSFET mains front-end transistor TN3_1 and a sixth MOSFET mains front-end transistor TN3_2. All three second branches are connected in parallel to a capacitor CN forming the output of the mains front-end, the terminals of which also form the terminals for the subsequent second stage DC-DC-VBW.

[0026] By using MOSFET transistors TN1_1...TN1_3, TN2_1...TN2_3 instead of diodes for converting the AC voltage components, the GL rectifier enables control of the converter, particularly its current flow. This control can be achieved by a so-called driver circuit designed and dimensioned for this purpose. This driver circuit (not shown) is connected in a manner known to those skilled in the art, particularly to the transistors to be controlled. One of the advantages of this design variant is that it enables improved efficiency.

[0027] The full-bridge converter DC-DC-VBW is also constructed in a variant known to those skilled in the art with MOSFET transistors, so that this second stage DC-DC-VBW can also be controlled; with the aforementioned advantages.

[0028] It can be seen that the circuit of the full-bridge DC-DC converter VBW is formed symmetrically around a transformer TF. As is typical for a transformer TF, this has a primary coil / winding and a secondary coil / winding. The circuit is thus divided into a primary circuit and a secondary circuit, which are constructed symmetrically to each other.

[0029] In the primary circuit, a first MOSFET primary circuit transistor TVp1_1 is connected to a terminal of the mains front-end GL capacitor CN. A second MOSFET primary circuit transistor TVp1_2 is connected in series, and the second MOSFET primary circuit transistor TVp1_2 is connected to the mains front-end GL in such a way that the series-connected first and second MOSFET primary transistors TVp1_1, TVp1_2 are connected in parallel to the capacitor CN. Furthermore, a primary-side capacitor Cp is connected between the series-connected first and second primary transistors TVp1_1, TVp1_2 on the input side, and its output is connected to an input of the primary coil / winding of the transformer TF.

[0030] The output of the primary coil / winding of the transformer TF is connected between a third MOSFET primary circuit transistor TVp2_1 and a fourth MOSFET primary circuit transistor TVp2_2 connected in series with it. The third and fourth primary circuit transistors TVp2_1 and TVp2_2 connected in series are also connected in parallel to the mains front-end GL output capacitor CN.

[0031] Since the secondary side is symmetrically constructed, it features a first MOSFET secondary circuit, transistor TVs1_1, and a second MOSFET secondary circuit, transistor TVs1_2, connected in series with it. These circuits are connected in parallel to the output of the full-bridge DC-DC converter VBW. Also connected in parallel are a third MOSFET secondary circuit, transistor TVs2_1, and a fourth MOSFET secondary circuit, transistor TVs2_2, connected in series with it.

[0032] Between the third and fourth secondary circuit transistor TVs2_1, TVs2_2 a secondary circuit capacitor Cs is connected, which in turn is connected on the output side to the input of the secondary coil / winding of the transformer TF, whereby the output of the secondary coil / winding is connected between the first secondary circuit transistor TVs1_1 and the second secondary circuit transistor TVs1_2.

[0033] A full-bridge DC converter is also called a buck-boost converter. The name comes from the fact that it is a power electronics circuit that can be used to convert a DC voltage to both higher voltage levels (boost mode) and lower voltage levels (buck mode).

[0034] The full-bridge DC converter uses a bridge circuit, as shown in the figure. This essentially consists of switches, diodes, inductors (coils), and capacitors to achieve DC-DC conversion. Four switches are arranged in the bridge configuration, and each switch can be independently turned on or off to control the energy flow.

[0035] This is how the full-bridge converter operates, which involves switching the switches on and off in specific sequences to generate a pulsating DC voltage. Filtering with inductors and capacitors ensures that the pulsating DC voltage is converted into a stabilized DC voltage.

[0036] By using MOSFET technology according to the exemplary embodiment to replace the switches and diodes of a full-bridge converter, these switching processes can be controlled in an efficient manner to regulate the output voltage at the output of the full-bridge DC-DC converter. It also supports the flexibility of the inventive multi-stage topology, for example, with regard to providing different charging voltages.

[0037] A DC-DC-TSS buck converter circuit consisting of two buck converters connected in parallel, hereinafter referred to as buck converter branches, is connected to this output as the third stage.

[0038] The DC-DC step-down converter DC-DC TSS, also known as a buck converter or step-down converter, is a circuit in power electronics that is used to reduce the input voltage to a lower output voltage.

[0039] An input capacitance Cein can be seen connected between the outputs of the full-bridge converter DC-DC-VBW, i.e., parallel to its circuit. A first MOSFET transistor TC1 of the first branch, relating to the control, is connected to the input of the capacitor Cein forming the input capacitance. A first MOSFET transistor TC1 of the first branch, relating to the control, is connected in series to this first MOSFET transistor TS1, relating to the synchronization. A first coil L1 is connected between these first transistors TC1, TS1. The output capacitance Cout is connected to the terminals of the first coil L1, which is connected on the output side to an output capacitance Cout. The charging voltage with which the electrically powered vehicle to be charged can be charged is applied to the terminals of the first coil L1.

[0040] The second branch is now closed in parallel in such a way that a second control transistor TC2, a second synchronization transistor TS2 and a second coil L2 are connected in a manner analogous to the first branch and are connected to the input capacitance Cein and the output capacitance Cout.

[0041] With this arrangement, the buck converter, which otherwise typically consists of a switch, a diode, an inductor and a capacitor, is made efficient and controllable according to the method according to the invention by using MOSFET technology, which replaces the switches and diodes.

[0042] The basic functionality of the buck converter remains the same. For example, a typical periodic switching of the switch on and off occurs through the appropriate timing of the control transistors TC1, TC2 and the synchronization transistors TS1, TS2. This timing results in current flowing through the inductance of branch L1, L2, also known as the choke, in one phase and charging the capacitor Cout. In the complementary phase, the energy flow is maintained and the voltage across the capacitor Cout is transferred to the output VeF.

[0043] By changing the turn-on times, i.e., the clock duration, the output voltage VeF of the DC-DC-TSS buck converter can be regulated. With the parallel connection of two buck converter branches according to the invention, this means that the turn-on times for both branches must be changed equally.

[0044] It is therefore advantageous that the MOSFET transistors of the third stage (TS1, TS2, TC1, TC2) can also be controlled, thus contributing to efficiency. The control is implemented in such a way that the entire arrangement is orchestrated according to the method of the invention.

[0045] For this purpose, for example, a cross-stage driver circuit and / or individual driver circuits for each stage GL, DC-DC-VBW, DC-DC-TSS can be provided.

[0046] However, the invention is not limited to what has been described and illustrated. Rather, the exemplary embodiment represents only one of the many possible implementations of the multi-stage topology and method according to the invention with regard to the design of the stages, for example, the type and polarity of the transistors and / or other circuit elements. These implementations may differ in circuit details, for example, according to dimensioning specifications and / or optimized for specific applications.For example, the MOSFET transistors could also be designed, in whole or in part, not as so-called enhanced n-channel MOSFET transistors as shown in the circuit diagram, but could be replaced, in whole or in part, by other electronic elements providing the switching function, which usually also leads to analogous adaptations of the other elements of the topology, which the person skilled in the art who intends to make such a change to the circuit can always take into account and easily carry out.

[0047] This method according to the invention is interlinked with a multi-stage arrangement in which the first DC voltage converted by the network front end Gl is not converted directly, for example by a full-bridge converter, into the charging voltage VeF, but is first converted by the full-bridge converter according to the invention in an intermediate stage into a galvanically isolated second DC voltage, which is not provided directly as charging voltage, but is only made available as charging voltage after conversion in a third stage.

[0048] The second DC voltage has a fixed voltage ratio to the output voltage of the mains front end GL, which corresponds to the transformation ratio of the transformer TF.

[0049] This fixed transformation ratio and the generally high voltage level, which is, for example, in the range of 700-950V, make this DC-DC full-bridge converter very efficient. To further increase system efficiency, the invention provides that the first DC voltage, i.e., the DC output voltage present at the output of the mains front end GL, can be varied via the mains front end GL depending on the required charging voltage.

[0050] This adjustment option is also used to reduce the voltage stress on the semiconductors at low charging voltages (VeF), thus extending their service life (keyword: cosmic radiation).

[0051] According to the method according to the invention, the second DC voltage is converted into the charging voltage VeF of the electrically driven vehicle via a third stage, for example via a DC-DC step-down converter DC-DC-TSS.

[0052] According to an embodiment of the inventive arrangement, the DC-DC buck converter is designed and operated according to an embodiment of the inventive method in such a way that it converts in an interleaved or alternating manner. This means that it consists of two parallel converters that are clocked with a time offset from one another, allowing the output chokes L1 and L2 to be designed smaller.

[0053] According to an advantageous development, the switching frequency of this third-stage DC-DC-TSS converter is not constant, unlike the other conversion stages GL and DC-DC-VBW, but is adjusted or adjustable such that the step-down DC-DC-TSS converter is always switched on at current = 0A. This advantageously prevents switch-on losses.

[0054] As a result, the invention achieves high efficiency values, for example, even when implemented with silicon carbide (SiC) semiconductors, which have the property that more turn-on losses than turn-off losses occur at the same operating point.

[0055] This design and the operation of the DC-DC TSS step-down converter also allow an output voltage VeF to be set even without any load on the output side, thus maintaining a charging current of 0A. This achieves a no-load capability that is typically required shortly before the start of the charging process, for example, to comply with the charging protocol between the electric vehicle and the charger. The no-load capability achieved in this way is achieved with significantly less effort than would be the case with state-of-the-art topologies.

[0056] A further advantage of the invention is that the entire topology has a high efficiency over the entire voltage range.

[0057] Furthermore, the invention offers a further advantage over prior-art DC chargers, which exhibit higher efficiencies at their nominal operating points but lower efficiencies in voltage ranges outside the nominal operating points. The invention ensures that losses, especially at maximum power, are lower at the least efficient operating point than in comparable prior-art chargers thanks to the topology according to the invention. This also allows for smaller cooling dimensions and lower cost.

[0058] The invention also enables better utilization of the 1200V blocking voltage of SiC semiconductors, which are still preferred in the current state of gallium nitride semiconductors due to the high switching frequencies required. In contrast to the topologies often used in the prior art, such as the so-called LLC converter and the so-called phase-shift full bridge, which are only suitable for bidirectional operation to a limited extent or require greater complexity, the invention is easily suitable for bidirectional operation.

[0059] In other words, the invention has the following advantages: • Very good voltage utilization of 1200V semiconductors • A nearly constant efficiency across the entire voltage range, making it advantageous during charging / discharging and enabling advantageous thermal design, as there is no operating point that generates particularly high losses and for which the cooling system would have to be dimensioned • The semiconductors of the output stage can be designed based on the maximum required charging current, so that over-dimensioning is not necessary • Idle capability is immediately available, as no base load is required at the output • Bypassing relays for voltage range switching is possible • Bypassing a balancing control between multiple DC / DC converters is possible • Identical system properties and identical operating characteristics are provided for both charging and discharging operations

Claims

[1] Stationary DC charging device for electrically powered vehicles, which has a first circuit for connection to an AC network, which is designed to convert the AC voltage provided by the network into a first DC voltage, and a second circuit which is functionally connected to the first circuit and is designed such that the first DC voltage is supplied to it in such a way that it converts the first DC voltage into a second DC voltage which is galvanically isolated from the AC network, characterized bythat the ratio of the magnitude of the galvanically isolated second direct voltage to the magnitude of the first direct voltage is kept constant regardless of the magnitude of the first direct voltage, in particular at a value >1, wherein a third circuit is functionally connected to the second circuit and is designed such that the galvanically isolated second direct voltage is supplied to the third circuit in such a way that the galvanically isolated second direct voltage is converted into the charging voltage and is present at an output of the third circuit for a charging process on the electrically driven vehicle, wherein the first circuit, the second circuit and / or the third circuit are designed and functionally interconnected in such a way that the magnitude of the first direct voltage can be varied depending on the magnitude of the charging voltage used. [2] Stationary DC charging device according to the preceding claim characterized by that the first circuit is designed as a two- and / or three-phase rectifier. [3] Stationary DC charging device according to one of the preceding claims, characterized by that the second circuit is designed as a transformer circuit and the ratio is determined by the transformation ratio of the transformer. [4] Stationary DC charging device according to the preceding claim, characterized by that the second circuit is designed as a so-called DC-DC full-bridge converter. [5] Stationary DC charging device according to one of the preceding claims, characterized by that the third circuit is designed as a so-called step-down converter circuit, in particular as a DC-DC step-down converter. [6] Stationary DC charging device according to the preceding claim characterized bythat the step-down converter circuit is formed from a first DC-DC step-down converter and a second DC-DC step-down converter connected in parallel. [7] Stationary DC charging device according to one of the preceding claims, characterized by that the two-phase rectifier, the three-phase rectifier, the transformer circuit and / or the step-down converter circuit are designed such that the directional blocking function, effected in particular by diodes, is at least partially realized by transistors, in particular power transistors, preferably designed according to MOSFET technology. [8] Stationary DC charging device according to the preceding claim, characterized bythat the first DC-DC buck converter and the second DC-DC buck converter are functionally connected to one another and operated in such a way that the blocking function of the second DC-DC buck converter realized by the MOSFET transistors is always connected in a complementary manner with respect to the blocking direction of the first DC-DC buck converter realized by the MOSFET transistors, wherein a reversal of the blocking direction takes place at a repeating adjustable time interval. [9] Stationary DC charging device according to the preceding claim, characterized by that the time interval is selected as a function of the value of a current flowing into the third circuit, in particular such that the reversal is triggered at a current value of 0A.

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