Charging circuit for a vehicle-side electrical energy storage system

Abstract

Charging circuit (LS) for a vehicle-side electrical energy storage device (ES), wherein the charging circuit comprises: an AC terminal (WA), at least two smoothing capacitors (C1, C2), a configuration device (KV) and a rectifier (GR) via which the AC terminal (WA) is connected to the configuration device (KV), wherein the configuration device (KV) connects the rectifier (GR) to the smoothing capacitors (C1, C2) and is configured to connect the smoothing capacitors (C1, C2) to each other in either a parallel or series configuration, wherein the AC terminal has a neutral conductor terminal (N) which is connected to the configuration device (KV) via a diode circuit (DE), wherein the configuration device (KV) has two switches (S1, S2) which are provided in the configuration device (KV) such that, in the closed state, they connect the smoothing capacitors (C1, C2) to each other in parallel and the configuration device (KV) has a diode (DS).which is provided in the configuration device (KV) such that the diode (DS) connects the smoothing capacitors in series with respect to the different potentials (P+, P-) of the rectifier (GR) in the forward direction, wherein the diode circuit (DE) has at least two diodes (D1, D2), of which at least one first diode (D1) connects the neutral conductor terminal (N) via a first connection point between the first switch (S1) of the two switches and the diode (DS) to a first of the smoothing capacitors (C1), and of which at least one second diode (D2) connects the neutral conductor terminal (N) via a second connection point between the second switch (S2) of the two switches to a second of the smoothing capacitors (C2).

Description

[0001] Vehicles with electric drive, meaning purely electric vehicles and hybrid vehicles, have an electrical energy storage system, primarily in the form of a battery. To enable charging via external means, some of these vehicles are equipped with an AC connection. This AC connection is designed to draw energy from an AC power grid, such as a public utility network, to charge the vehicle. Such vehicles are also known as "plug-in vehicles."

[0002] Firstly, for technical reasons, the energy storage device must be charged with direct current, so rectification is required, and secondly, adjustments may be necessary between the operating or nominal voltage of the energy storage device on the one hand and the level of the alternating voltage or the rectified voltage generated from it on the other.

[0003] Document US 2018 / 0041061A1 describes a three-phase AC system connected to a rectifier at the input, with two DC-DC converters connected downstream of the rectifier. Diodes of the rectifier are connected at the input to the phases and to the neutral conductor (star point) of the AC system. The inputs of the DC-DC converters are switchable and can be connected either to a negative potential of the rectified voltage or to the neutral conductor of the AC system.

[0004] Publication US 2012 / 0 087 163 A1 also shows a rectifier and downstream (galvanically isolated) DC-DC converters, wherein the inputs of the inverters (choppers) of the DC-DC converters are connected in series via a diode and in parallel via two switches to allow the inputs of the inverters to be connected either in parallel or in series.

[0005] Furthermore, it is desirable that the vehicle's energy storage system can be charged with both single-phase and multi-phase alternating current in order to achieve the shorter charging time made possible by the higher chaining factor of three-phase current.

[0006] In addition to these requirements, the costs of semiconductors and other components suitable for the corresponding charging circuits, both in terms of current carrying capacity and voltage withstand, must be considered. Particularly with regard to these costs, the task is to demonstrate a method for charging a vehicle's energy storage system using cost-effective components.

[0007] This problem is solved by the charging circuit in claim 1. Further features, embodiments, properties and advantages are described in the dependent claims.

[0008] The charging circuit described here comprises two smoothing capacitors that can be connected in parallel or series using a configuration device. A rectifier is connected to the AC terminal and thus connects (rectifying) the AC terminal to the smoothing capacitors. The AC terminal, and therefore also the rectifier, can be operated with different numbers of phases, for example, single-phase or three-phase. This results in different line-to-line factors (which, as is known, depend directly on the number of phases, i.e., the number of phase-shifted currents used). Consequently, different voltage levels across the smoothing capacitors result from the different line-to-line factors when the rectifier or the AC terminal is operated with different numbers of phases.

[0009] The option of configuring the smoothing capacitors in either parallel or series allows for cost-effective design (with a relatively low rated voltage) while still enabling optimization based on the voltage to be smoothed or the operation of the rectifier. For single-phase operation (corresponding to a low rectified voltage), a parallel configuration is preferred to achieve a high capacitance. Conversely, for multi-phase operation (of the AC connection or rectifier) ​​and thus a higher (rectified) voltage compared to single-phase operation, a series configuration is used, ensuring that each capacitor is subjected to only a portion of the total voltage for smoothing.

[0010] To connect the neutral conductor of the AC power supply appropriately to each configuration, a diode circuit is provided. This circuit connects the neutral conductor of the AC power supply to the configuration device. The configuration device itself connects the rectifier to the smoothing capacitors and is thus connected to them. In multi-phase operation, the diode circuit allows the removal of asymmetrical components from the phases of the AC power supply and thus serves as a filter. In multi-phase operation or in a series configuration, the diode circuit therefore serves to remove unwanted components.

[0011] In asymmetrical operation, for example, in single-phase operation, the diode circuit serves to connect the neutral conductor as a surge arrester or return conductor. While one, several, or all phase terminals of the AC connection are connected to a phase or the same phase of the AC system, the neutral conductor forms the return conductor, as with typical single-phase loads in a 230-volt AC network. The diodes in the diode circuit thus allow a connection to the (parallel) connected smoothing capacitors to complete this return path (or supply path). The diode circuit includes at least one diode located between the neutral conductor terminal and the configuration device. In particular, the diode circuit includes at least one diode connected in series (where the series connection refers to the connection relative to the neutral conductor terminal).The diode circuit can have several diodes connected in series from the neutral terminal to the configuration device. At least two diodes are connected in opposite directions (in series) between the neutral terminal and the configuration device, relative to the neutral terminal.

[0012] The previously mentioned connection of the neutral conductor via the diode circuit allows for the distribution of the smoothing capacitors, particularly to enable operation at high voltages with capacitors whose maximum voltage rating is lower than the maximum rectified voltage. By dividing the capacitors in series, each smoothing capacitor only receives a portion of the rectified voltage. This allows the smoothing capacitors to be designed for a lower rated or maximum voltage, resulting in cost savings. The diode circuit enables a switchless connection of the neutral conductor. In multi-phase operation of the AC connection or rectifier, this connection serves to dissipate asymmetrical components, while in single-phase operation (of the AC connection or rectifier) ​​it serves to mitigate the effects of the rectified voltage.of the rectifier) ​​the diode circuit serves as a connection between the configuration device (and thus ultimately an energy storage connection) and the individual phase potential.

[0013] A charging circuit for a vehicle-mounted electrical energy storage device is described, comprising an AC connection, at least two smoothing capacitors, a configuration device, and a rectifier. The AC connection is connected to the configuration device via the rectifier. The configuration device connects the rectifier to the smoothing capacitors. In other words, the configuration device is positioned between the rectifier and the smoothing capacitors. The configuration device is designed to connect the smoothing capacitors either in parallel or in series.The smoothing capacitors are thus connected to the configuration device in such a way that in a first circuit state the smoothing capacitors are connected in parallel to each other, and in a second state (corresponding to the serial configuration) are connected in series to each other.

[0014] The AC power supply has a neutral conductor connection. This is connected to the configuration device via a diode circuit. The neutral conductor connection is thus connected to the smoothing capacitors via the diode circuit. The configuration device is located between the neutral conductor connection and the smoothing capacitors.

[0015] The diode circuit comprises several diodes. These are connected to different connection points of the configuration device (e.g., between switches). One, several, or all of the diodes in the circuit is / are connected to the neutral terminal. This at least one diode is connected in series between the neutral terminal and the configuration device, in particular between connection points within the configuration device.

[0016] Preferably, the diode circuit is configured as a rectifier circuit. The diode circuit can be a diode bridge circuit, for example in the form of a half-bridge, which may have an intermediate point to which the neutral conductor is connected. The rectifier circuit formed by the diode circuit can have an AC side, for example in the form of the connection point. This AC side is connected to the neutral conductor terminal. The rectifier circuit formed by the diode circuit can have a DC side that is connected to the configuration device (and thus also to the capacitors). The rectifier circuit is, in particular, a full-wave rectifier circuit.

[0017] The diode circuit comprises at least two diodes. These different diodes are connected to different smoothing capacitors. The diodes are connected in opposite directions (forward or reverse bias) relative to the neutral terminal. One of the two diodes connects the neutral terminal to the first of the smoothing capacitors. The second of the at least two diodes connects the neutral terminal to the second of the smoothing capacitors. Viewed from the neutral terminal, the forward biases of the two diodes are opposite to each other. This ensures that both half-waves are conducted by the diodes, with the different diodes conducting half-waves of opposite polarity (to the capacitors). The connection between the smoothing capacitors and the diodes forms a series circuit of each diode with the smoothing capacitor.This allows for a particularly cost-effective representation of the diode circuit, which is equally suitable for single-phase and multi-phase charging.

[0018] The configuration device has at least one switch. In its closed state, this switch connects the smoothing capacitors in parallel. The at least one switch therefore establishes the parallel connection between the smoothing capacitors. The configuration device also includes a diode that connects the smoothing capacitors in series in the forward direction.

[0019] The configuration device comprises two switches and a diode. The two switches can also be described as parallel elements, since, when closed, they connect the smoothing capacitors in parallel. The diode of the configuration device can also be described as a series element, since, in the forward direction, it connects the smoothing capacitors in series. The two switches and the diode are connected in series, specifically in a series circuit. This series circuit is connected to different potentials of the rectifier. In other words, the two switches and the diode are connected in series, which is connected in parallel to the rectifier.

[0020] The switches are connected to each other via the diode in a series circuit. The switches thus have terminals that are directly connected to the different potentials of the rectifier. In this context, "rectifier potentials" refers to DC voltage potentials, that is, the DC side of the rectifier. Since the diode is connected between the switches, and the switches are directly connected to the two potentials, the diode is not directly connected to the potentials, but rather via the switches. The rectifier potentials correspond to the rectified voltage, which results from the voltage at the AC terminal and the relevant line-to-line voltage factor. The different potentials are typically a positive and a negative potential, but can also be a ground potential and a positive potential.

[0021] The charging circuit preferably includes a control unit that is connected to the configuration device. The configuration device is equipped with switches. The control unit is connected to these switches. In a parallel configuration state (for the charging control device), the control unit is configured to close only the switch(es) of the configuration device through which the smoothing capacitors are connected between two different potentials of the rectifier. In other words, in the parallel configuration state, the control unit is configured to close only the switch(es) of the configuration device that, when closed, connects the smoothing capacitors to each other in parallel (and thus also to the two different potentials).In the parallel configuration state, each of the smoothing capacitors is connected individually between the two different potentials and thus receives the full potential difference or voltage between the two different potentials.

[0022] The control unit can be configured to detect single-phase and multi-phase occupancy states of the AC power supply. Alternatively, the control unit can be configured to detect single-phase and multi-phase operating states of the rectifier. Furthermore, the control unit can be configured to acquire a signal indicating a single-phase or multi-phase target state of the charging circuit. In other words, the control unit can distinguish between single-phase and multi-phase states (of the AC power supply or the rectifier). The control unit can also be configured to connect the smoothing capacitors in parallel in one of the single-phase states. Additionally, the control unit can be configured to connect the smoothing capacitors in series in one of the multi-phase states.

[0023] Alternatively, the control device can be configured to connect the smoothing capacitors in series (using the configuration device) when a rectified voltage applied to the DC side of the rectifier exceeds a predetermined threshold, and to connect the smoothing capacitors in parallel (also using the configuration device) when the voltage does not exceed the threshold. This allows the smoothing capacitors to be connected in series even for elevated voltages that do not result from an increased line-to-line factor (i.e., a line-to-line factor > 1), thus ensuring that only a portion of the rectified voltage is present at each capacitor. The control device can therefore include a comparator that compares the rectified voltage of the rectifier with the threshold value.The threshold value is preferably a predetermined margin below a maximum voltage of the capacitors, which is determined by the design of the capacitor.

[0024] Furthermore, the charging circuit may include several DC-DC converters. Each of these converters has a clocked switching unit and an intermediate circuit capacitor. The intermediate circuit capacitor of a first DC-DC converter is formed by a first smoothing capacitor. The intermediate circuit capacitor of a second DC-DC converter is formed by a second smoothing capacitor. This allows the smoothing capacitors to be used as intermediate circuit capacitors for different DC-DC converters. The clocked switching unit comprises at least one controllable switch, in particular two controllable switches, which serve to alternately connect an element. The DC-DC converter may, for example, include an inductor (or a capacitor) as a temporary storage element.Preferably, each DC-DC converter has a converter inductor connected upstream or downstream of the switched-mode unit. The DC-DC converters can be configured as boost converters, buck converters, or synchronous converters. The DC-DC converters are preferably constructed in the same way.

[0025] The DC-DC converters have terminals that connect to a DC power supply. This DC power supply is designed to connect the energy storage device (to the charging circuit). The terminals of the DC-DC converters are connected in parallel. Therefore, during charging, the DC-DC converters operate in parallel, and the output currents add up at the DC power supply. For example, a positive and a negative terminal are provided, with both DC-DC converters connected to the positive terminal, or their positive potentials connected to the negative terminal. The same applies to the negative terminal or ground connection.

[0026] The rectifier can be a controllable rectifier. The controllable rectifier can be directly connected to the AC power supply. The rectifier unit includes transistors, but no dedicated energy storage devices such as coils.

[0027] Alternatively, the rectifier can be a power factor correction filter. This has a controllable rectifier unit connected to the AC power supply via inductors (such as coils). Within the power factor correction filter, these inductors act as temporary energy storage devices. Each phase of the AC power supply is connected to the rectifier unit via its own (series-connected) inductor.

[0028] The vehicle's electrical system may include a charging circuit and an energy storage device connected to the charging circuit via its DC input. If no DC-DC converters are used, the DC input (for connecting the energy storage device) is directly connected to the DC side of the rectifier, i.e., to the potentials between which the smoothing capacitors are located.

[0029] The Fig. Figure 1 schematically shows an embodiment of a charging circuit connected to a (vehicle-side) energy storage device.

[0030] The charging circuit LS comprises an AC connection WA with three phase connections L1 to L3 and a neutral connection N. These are connected to one AC side of a rectifier GR. The rectifier GR comprises a rectifier unit GE with diodes, as well as three upstream (phase-specific) inductors I1 to I3. The inductors I1 to I3 connect the AC connection WA to the rectifier unit GE and, in particular, connect the different phase connections L1 to L3 of the AC connection to the rectifier unit GE. The rectifier unit GE comprises only rectifier elements in the form of diodes or, in particular, in the form of controllable transistors.The phase-individually connected inductors I1 to I3 together with the rectifier unit form a power factor correction filter, i.e. a rectifier GR, which in addition to the rectification function also implements functions such as harmonic attenuation and / or power factor correction and / or boost converters.

[0031] The rectifier GR comprises a DC side GS, which is opposite to the AC side. The rectifier GR connects the AC terminal WA to the two individual ends of smoothing capacitors C1 and C2. A diode circuit DE is provided, comprising a first diode D1 and a second diode D2. These are connected in series via a junction point, to which the neutral conductor N is connected. From this junction point, diodes D1 and D2 (in opposite forward bias directions) are connected to a configuration device KV.

[0032] The configuration device KV comprises a series connection of two switches S1 and S2 and a diode DS. These are connected in series. The resulting series connection is connected to the DC side of the rectifier GR. Specifically, one end of this series connection of switches S1, S2, and diode DS is connected to the positive potential P+ and the negative potential P-. The positive potential P+ and the negative potential P- are the DC voltage potentials of the rectifier GR and the DC side GS of the rectifier GR, respectively. The series connection of switches S1, S2, and the diode, and thus the configuration device KV, is connected in parallel (with the ends of the configuration device KV) to the potentials P- and P+. The diode DS connects switches S1 and S2 together.Switches S1 and S2 are each permanently connected to one of the two potentials, with switch S1 connected to the positive potential P+ and switch S2 to the negative potential P-. Diodes D1 and D2 are connected in series, in parallel with diode DS, which is connected in series between switches S1 and S2.

[0033] In other words, the diode circuit DE is connected in parallel to the diode DS. The diode circuit DE forms a diode bridge for full-wave rectification, particularly for single-phase operation. The junction of the diodes in the diode circuit DE is connected to the neutral conductor N.

[0034] The connection point between switch S1 and diode DS is connected to a first smoothing capacitor C1. The connection point between diode DS and switch S2 is connected to a second smoothing capacitor C2. Smoothing capacitors C1 and C2 are therefore only connected in series when diode DS is conducting. When switches S1 and S2 are closed, capacitors C1 and C2 are connected in parallel.

[0035] If only one phase is connected, the line-to-line factor is 1, and capacitors C1 and C2 can be connected in parallel to increase their capacitance. If the AC connection WA is used in a three-phase configuration (where phase connections L1 to L3 are connected to different phases of a three-phase system), the line-to-line factor is greater than 1, and capacitors C1 and C2 are connected in series by the configuration device KV. This results in only half the smoothed voltage for capacitors C1 and C2 (due to voltage division across the capacitors). Therefore, each capacitor C1 and C2 can be designed with a lower rated voltage than the maximum voltage in three-phase operation. The smoothing capacitors preferably have the same (rated) capacitance and / or the same rated voltage.

[0036] In single-phase operation, the neutral conductor N can be connected to a corresponding terminal of the three-phase system, while the phase terminals L1 to L3, or only phase terminal L2 (or even only phase terminals L1 and L2), are connected to one and the same phase of the connectable network. In this case, the line-to-line factor is 1. If more than one phase terminal L1 to L3 is connected to the same phase of a connectable AC network, then the respective terminals L1, L2, and L3 are connected to each other accordingly. Since no phase currents out of phase with each other are used, and no phase terminals out of phase are connected, this is also referred to as single-phase operation. Preferably, in single-phase operation, the terminals L1, L2, and L3 are connected to the same phase (i.e., connected to each other) so that all phases of the rectifier GR can contribute to the current flow.

[0037] In this embodiment, the smoothing capacitors C1 and C2, or the DC side of the rectifier GR, are directly connected to the energy storage device ES, and the DC connection GA of the charging circuit LS. Here, the energy storage device ES is not necessarily part of the charging circuit, but can be another component of the vehicle's electrical system in which the charging circuit is located.

[0038] The example shown includes a DC / DC converter unit comprising two DC / DC converters, GW1 and GW2. Each DC / DC converter, GW1, includes a switching unit, SE1 and SE2. This unit contains clocked switching elements of the DC / DC converter, as well as (here in Fig. (1 not shown) a temporary energy storage device such as an inductor. The intermediate circuit capacitors associated with the DC-DC converter are implemented by capacitors C1 and C2. Thus, the first DC-DC converter GW1 is formed by capacitor C1 as the intermediate circuit capacitor and the switching unit SE1. Similarly, the DC-DC converter GW2 is formed by the switching unit SE2 and capacitor C2.

[0039] A control unit C is connected to switches S1 and S2. Furthermore, this control unit C can have an input at which it can detect signals relating to the number of active (different) phases of the rectifier GR. These signals can represent the occupancy status of the AC terminal, the number of active and phase-shifted phases of the rectifier GR, or a command to execute single-phase or multi-phase operation, the latter signal indicating the number of (different) phases. In another embodiment, the control unit C is configured to detect the voltage on the DC side of the rectifier and to determine whether the voltage exceeds a threshold value, in order to then configure the configuration device KV for serial operation (of capacitors C1 and C2).If the voltage is lower than the threshold value, the configuration device for parallel connection of capacitors C1 and C2 is set to increase the total capacitance of these capacitors.

[0040] The DC-DC converter unit is shown schematically only. The DC-DC converters GW1 and GW2, or switching units SE1 and SE2, are connected in parallel at the output, i.e., on the DC input side (GA). However, a series connection of the converters is also possible. Converters GW1 and GW2 can be either galvanically conductive or galvanically isolating / isolating. This depends primarily on the interconnection on the DC input side (GA).

[0041] Finally, it should be noted that the Fig.1 can be considered the vehicle electrical system, which includes the charging circuit LS and the connected energy storage device ES. The energy storage device ES can be a battery, in particular a lithium-based battery. The energy storage device ES is preferably a traction battery. The charging circuit is designed for a power output of at least 1 kW, 5 kW, 10 kW, or 50 kW. This refers to the power output when connected to a three-phase system.

Claims

[1] Charging circuit (LS) for a vehicle-side electrical energy storage device (ES), wherein the charging circuit comprises: an AC terminal (WA), at least two smoothing capacitors (C1, C2), a configuration device (KV) and a rectifier (GR) via which the AC terminal (WA) is connected to the configuration device (KV), wherein the configuration device (KV) connects the rectifier (GR) to the smoothing capacitors (C1, C2) and is configured to connect the smoothing capacitors (C1, C2) to each other in either a parallel or series configuration, wherein the AC terminal has a neutral conductor terminal (N) which is connected to the configuration device (KV) via a diode circuit (DE), wherein the configuration device (KV) has two switches (S1, S2) which are provided in the configuration device (KV) such that, in the closed state, they connect the smoothing capacitors (C1, C2) to each other in parallel and the configuration device (KV) has a diode (DS).which is provided in the configuration device (KV) such that the diode (DS) connects the smoothing capacitors in series with respect to the different potentials (P+, P-) of the rectifier (GR) in the forward direction, wherein the diode circuit (DE) has at least two diodes (D1, D2), of which at least one first diode (D1) connects the neutral conductor terminal (N) via a first connection point between the first switch (S1) of the two switches and the diode (DS) to a first of the smoothing capacitors (C1), and of which at least one second diode (D2) connects the neutral conductor terminal (N) via a second connection point between the second switch (S2) of the two switches to a second of the smoothing capacitors (C2). [2] Charging circuit (LS) according to claim 1, wherein the two switches (S1, S2) and the diode (DS) are connected in a series circuit which are connected to the different potentials (P+, P-) of the rectifier (GR), wherein the switches (S1, S2) are connected to each other within the series circuit via the diode (DS). [3] Charging circuit (LS) according to claim 1 or 2, wherein the diode circuit (DE) is configured as a rectifier circuit having an AC side connected to the neutral terminal (N) and a DC side connected to the configuration device (KV). [4] Charging circuit (LS) according to one of the preceding claims, further comprising a control device (C) which is connected to the configuration device (KV) in a controlling manner, wherein the configuration device (KV) is equipped with the switches (S1, S2) and the control device (C) is configured, (i) in a parallel configuration state to close the switches (S1, S2) of the configuration device (KV) through which the smoothing capacitors (C1, C2) are each connected between two different potentials (P+, P-) of the rectifier (GR), and (ii) to provide the switches (S1, S2) of the configuration device (KV) in an open state in a serial configuration state, which are closed in a parallel configuration state. [5] Charging circuit (LS) according to claim 4, wherein the control device (C) is configured to determine a single-phase and a multi-phase occupancy state of the AC connection (WA), to determine a single-phase and a multi-phase operating state of the rectifier (GR) or to detect a signal that represents a single-phase or multi-phase target state of the charging circuit, wherein the control device (C) is configured to connect the smoothing capacitors (C1, C2) to each other in parallel configuration in one of the single-phase states and to connect them to each other in series configuration in one of the multi-phase states. [6] Charging circuit (LS) according to one of the preceding claims, wherein the charging circuit comprises several DC-DC converters (GW1, GW2), each comprising a clocked switching unit (SE1, SE2) and an intermediate circuit capacitor, wherein the intermediate circuit capacitor of a first of the DC-DC converters (GW1) is formed by a first of the smoothing capacitors (C1) and the intermediate circuit capacitor of a second of the DC-DC converters (GW2) is formed by a second of the smoothing capacitors (C2). [7] Charging circuit (LS) according to claim 6, wherein the DC-DC converters (GW1, GW2) have terminals which are connected to a DC terminal (GA) set up for connecting the energy storage device (ES), wherein the terminals of the DC-DC converters (GW1, GW2) are connected in parallel to each other. [8] Charging circuit (LS) according to one of the preceding claims, wherein the rectifier (GR) is a controllable rectifier comprising a controllable rectifier unit (GE) directly connected to the AC terminal (WA), or wherein the rectifier (GR) is a power factor correction filter comprising a controllable rectifier unit (GE) connected to the AC terminal (WA) via inductors (I1 - I3).

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