WO2021115576A1

WO2021115576A1 - Vehicular power supply system

Info

Publication number: WO2021115576A1
Application number: PCT/EP2019/084490
Authority: WO
Inventors: Ahmed ABDELHAKIM; Frans Dijkhuizen
Original assignee: Abb Schweiz Ag
Priority date: 2019-12-10
Filing date: 2019-12-10
Publication date: 2021-06-17

Abstract

A vehicular power system (1) comprises a battery unit (2), a high-capacity unit (3), and first and second connectors (4) for supplying a first output voltage and a second, different output voltage, wherein each connector is arranged to receive one or more parallel daughter boards (7). A daughter board comprises circuitry forming a DC-to-DC converter across the battery unit when the daughter board is received in the connector. The DC-to-DC converter is configured to supply the respective output voltage.

Description

VEHICULAR POWER SUPPLY SYSTEM TECHNICAL FIELD

[0001] The present disclosure relates to the field of electric power supply systems for vehicles, and in particular to a modularizable power supply system where the energy source is batteries and at least one super-capacitor.

BACKGROUND

[0002] Power supply systems in electric vehicles, including automated guided vehicles (AGVs) and automated mobile robots (AMRs), utilize batteries for powering the different elements or loads within the system, such as motors, computers, controllers, and sensors. Such elements require different voltage levels, such as 3.3 V, 5 V, 12 V and 24 V, and some of them can handle a voltage up to 60 V, such as motor drivers. Then, many converters have to be utilized within the system wherever a different voltage level is desired in order to obtain these different voltages. Power supply systems based on this design approach have poor modularity, and the type and power level of each converter may be different from one product to another. This drives cost of the AGV and AMR products.

[0003] Further, these power supply systems are usually fed from a 24-V battery system and one of the desired voltage levels is the 24 V itself. Hence, a regulating stage with both buck and the boost capabilities is utilized to stabilize the battery output, which otherwise has a voltage variation from 20 V to 30 V approximately. This results in quite bulky and expensive system.

[0004] Among the different loads in the system, motors are seen to be the main or biggest power consumer, requiring high current and/or high power during acceleration, which may have short durations such as 1-3 seconds. Most of today’s batteries can deliver satisfactory acceleration current but will see their useful lifetime reduced when doing so repeatedly. Over and above that, regenerated power with high current amplitude occurs frequently during braking or deceleration, and this is seen as a significant issue for conventional batteries. Since not all available batteries can absorb currents of high amplitude, braking choppers are utilized to dissipate rather than store the braking energy. The alternative is to use batteries with high capacity rating for both charging and discharging, which is a costly option. As a result, some known vehicular power supply systems include super-capacitors (or super-caps) to manage positive and negative power peaks of short duration, e.g., due to acceleration, deceleration or start of different motors. Super-caps may be connected to the load side over an additional DC-to-DC converter. With this additional circuitry, the requirements on the batteries are relaxed, so that cost-efficient batteries with a moderate capacity rating can be used. Since the super-caps absorb the current peaks, the battery lifetime may increase. The additional converter, with several semiconductor components, however represents an additional cost.

[0005] As a conclusion from the prior discussion, the following demerits are seen behind the existing power supplies of different AGV and AMR systems:

- different power converters/components must be utilized to fulfil the system needs, resulting in a suboptimal power system that is also expensive and bulky;

- each power converter must handle the maximum power requirements of each element, where these maximum powers are not occurring simultaneously, resulting in oversizing;

- buck and boost capabilities are mandatory for regulating the battery voltage for 24 V systems;

- expensive batteries with high capacity rating must be utilized, especially for absorbing higher currents during regeneration;

- extra complexity and volume for integrating an on-board charger; and

- each power supply system has highly case-oriented characteristics.

SUMMARY

[0006] It is an objective of the invention to make available a vehicular power system that suffers to a lesser extent from the above demerits. The object is achieved by the invention by a vehicular power system with the technical features according to claim 1.

[0007] In an aspect of the invention, a power system for vehicles comprises a battery unit, a high-capacity unit as well as a first connector for supplying a first output voltage and a second connector for supplying a second output voltage, which is different from the first output voltage. Each of the connectors is arranged to receive one or more daughter boards. A daughter board susceptible to be received in the connector comprises circuitry which forms a DC-to-DC converter across the battery unit when the daughter board is received in the connector. The DC-to-DC converter thus formed receives electric energy from the battery unit and is able to convert the battery voltage into one of the output voltages to be supplied to the load side; it may also be capable of stabilization when the battery voltage varies as a result of changing momentary load.

[0008] Because uniform requirements apply for all daughter boards, this power supply system is highly modularizable. It is also possible to replace, add or remove daughter boards after the original manufacture, so as to accommodate later needs or to refresh the system in the future using circuitry that has become available more recently. Further, this aspect of the invention provides a multi-port system for supplying multiple voltages.

[0009] In one embodiment, there is provided a vehicular power system with the above characteristics, wherein a suitable number of daughter boards are received in the connectors.

[0010] In one embodiment, all daughter boards received in the connectors are structurally similar. It is possible to configure at least some of the structurally similar daughter boards to be functionally different. In particular, two daughter boards which are deployed at different connectors of the vehicular power system may operate differently, e.g., to supply different nominal voltages. Such a system may be regarded as modular with regard to the daughter boards.

[0011] In a further aspect of the invention, there is provided an AMR or an electric vehicle, such as an AGV, which comprises a vehicular power system with the above characteristics.

[0012] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to “a/an/the element, apparatus, component, means, step, etc.” are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, on which: figure l is a schematic circuit diagram of a vehicular power supply system, in which m connectors are shown; figure 2 is a more detailed view, showing in particular local controllers, of a vehicular power system for supplying three distinct output voltages in addition to the battery voltage, wherein the stepped-down output voltages are supplied at respective connectors and the system further comprises a high-capacity unit with circuitry for on-board charging from an alternating current (AC) source; figure 3 shows a simple daughter board example, suitable for being received in one of the connectors of the power system shown in figure 2; figure 4 shows a battery-powered vehicular power system in which a sequence of partially overlapping buck converters is formed when the daughter boards are received in the connectors; figure 5 shows a vehicular power system powered by a battery unit and high-capacity unit; figure 6 shows alternative circuitry for on-board charging from a direct current (DC) source; figures 7 and 8 illustrate an example pulse-width modulation (PWM) control approach and safety monitoring arrangement suitable for vehicular power systems of the type disclosed herein; figure 9 shows an alternative structure of the vehicular power system of figure 5, wherein a diode replaces one of the switches; figure 10 shows a further alternative structure, which includes switches for selecting a power source; figure 11 shows a still further alternative structure, in which a boost converter is used to integrate a high-capacity unit; figure 12 shows a vehicular power system in which a DC source is connected over a high-capacity unit for charging; and figure 13 shows an alternative structure of the vehicular power system in figure 12, in which an input AC charger is connected to the high-capacity unit via a transformer and a rectifier. DETAILED DESCRIPTION

[0014] The aspects of the present disclosure will now be described more fully with reference to the accompanying drawings, on which certain embodiments of the invention are shown. These aspects may, however, be embodied in many different forms and the description thereof should not be construed as limiting; rather, the embodiments are provided by way of example, so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0015] In accordance with one embodiment, figure 1 shows a vehicular power system 1 with the following components arranged on respective parallel branches: a battery unit 2, a high-capacity unit 3 and an arbitrary number of connectors 4.1, 4.2, ..., 4.m. As suggested by the lines extending from the right side of each connector and then downward in figure 1, the connectors 4.1, 4.2, ..., 4.1h are configured to supply respective output voltages to components (not shown) in a load side of the system 1. The number of connectors, m, may correspond to the number of different output voltages. The high-capacity unit 3 comprises at least one super-capacitor and may comprise additional circuitry, such as a DC-to-DC converter and controllable switches, which allow the super-capacitor to absorb and inject current into the load side in various operating conditions. As used herein, a super-capacitor is one with relatively high energy storage capacity per unit volume or unit mass; a specific energy of at least 1 mJ/mms is preferred. Alternatively or additionally, a super-capacitor is able to accept and inject current at a higher rate than a conventional rechargeable battery. The high-capacity unit 3 may further comprise interfaces for charging the super-capacitor from an AC or DC source.

[0016] Each connector 4 is arranged to receive one or more daughter boards 7. As will be explained in more detail with reference to figure 2, each daughter board 7 comprises circuitry forming a DC-to-DC converter across the battery unit 2 when the daughter board 7 is received in the connector 4. The DC-to-DC converter has the ability of converting the voltage over the battery unit 2 into one of the output voltages to be supplied to the load side, including stabilizing the battery unit 2 when the momentary load is varying. To this end, the DC-to-DC converter may include switches, inductive and capacitive components, wherein the output voltage depends on timings which apply to a periodic switching behaviour of the DC-to-DC converter. The system 1 may be adapted for the requirements of a particular use case by configuring such timings, such as by adjusting control parameters in software or assigning values to control voltages controlling the switching behaviour; this allows a uniform hardware to be adapted for changing use cases. At least some of the DC-to- DC converters may be of a bidirectional type in the sense that the input and output sides of the DC-to-DC converter may alternatingly be energized and energizing. For example, the DC-to-DC converter may serve as interface for connecting a high- capacity unit 3 with a capacitor, which during operation absorbs and releases energy in different periods of time. A DC-to-DC converter which serves to stabilize the voltage of a battery may have a switching behaviour with adaptive timings, which are adjusted in response to variations in the current drawn from the battery by the momentary load. Such a battery balancer may be available as a prefabricated and easily sourceable component for voltages 24 V and 48 V. Structurally, each or all DC- to-DC converters may be a boost converter, a buck-boost converter, a step-down converter or a flyback converter.

[0017] Furthermore, the system 1 may be adapted for a current rating applying for a connector 4.j by selecting the number n_; of daughter boards 7 to be received in that connector. In figure 1, the first connector 4.1 is fitted with n_t daughter boards 7.1.1, 7.1.2, ..., 7.1. n_t, the second connector 4.2 is fitted with n₂ daughter boards 7.2.1, 7.2.2, ..., 7.2 n₂ and so forth. The m^th connector 4.1h is shown fitted with n_m daughter boards 7.m.i, 7.m.2, ..., y.m.n_m. The current rating for the output of a connector 4 may be dependent on the number of parallel daughter boards. The parallel daughter boards may then be operated in a coordinated manner as regards their switching behaviour, preferably synchronously. Multiple parallel daughter boards configured to supply a common output voltage may be operated in an interleaved fashion; this may help distribute the load over the daughter boards in periods where the output current is less than the maximum design load, so as to delay component wear and allocate thermal power more evenly.

[0018] In embodiments, all daughter boards received in the connectors are structurally similar. As mentioned, at least some of the structurally similar daughter boards may be configured to be functionally different, wherein two daughter boards which are deployed at different connectors of the vehicular power system may operate differently. Different nominal voltages may be supplied from different daughter boards, and combinations of daughter boards may be arranged in parallel to withstand a larger total current. The vehicular power system 1 can be described as modular with regard to the daughter boards 7, which may be manufactured in a uniform fashion and individualized later in accordance with different use cases. A use case may be a specific deployment, e.g. a robot model or autonomous vehicle model, or for a class of models whose sets of electric components have approximately uniform sets of electric requirements as regards voltages and currents.

[0019] In one embodiment, a suitable nominal voltage of the battery unit 2 is 48 V. Since several merits with the utilization of the 48 V battery system instead of the 24 V one are seen, such as the utilization of simple buck converters to handle the needed voltage levels, and the reduced copper area for big loads that can handle a non-regulated 48-V DC link, a vehicular power system 1 according to the present embodiment utilizes a 48-V battery system in a modular way. In addition to that, it integrates a super-capacitor (in the high-capacity unit 3) within the system 1 to manage intermittent excessive power requirements.

[0020] The vehicular power system 1 may be arranged on a main board, which may be referred to as mother board, and as many as needed of identical DC-to-DC converter boards, i.e. daughter boards 7. The daughter boards 7 are grouped together into different groups, where each group supplies a certain voltage level. On top of that, one daughter board 7, which may be extended into a group of parallel daughter boards, is connected to the high-capacity unit 3 for the sake of injecting any excessive need of power. On the other hand, when no excessive power is needed, the high- capacity unit 3 may be recharged to its nominal level. Moreover, in case of power regeneration, e.g. at braking of the vehicle, a resulting excessive power may be handled by the high-capacity unit 3, after which the high-capacity unit 3 is returned to its nominal level.

[0021] Figure 2 is a more detailed view of a vehicular power system 1 for supplying three stepped-down output voltages, 24 V, 12 V and 5 V, in addition to the battery voltage 48 V over the poles of the battery unit 2. The j^th connector 4.j in figure 2 comprises an input sub-connector 4-j-i, an output sub-connector 4.j-o and a controller 8.j. The stepped-down output voltages are supplied at the output sub connectors 4.1-0, 4.2-0, 4.3-0, respectively by means of rq, n₂ and n₃ parallel daughter boards 7 with a switching behaviour configured in view of the nominal voltage levels 24 V, 12 V and 5 V. The controller 8.j may control the switching behaviour of the daughter boards that are received in the j* connector 4.j. The controller 8.j may be pre-programmed and operated either by an open-loop control strategy, or by closed-loop automatic control, wherein actual currents, voltages and other relevant local or general state variables are taken into account to control the switching behaviour. As will be disclosed with reference to figure 3, a daughter board 7 may include sensors for capturing the state variables which are made available to the controller. The state variables may also be obtained by external sensors or in a centralized fashion. Furthermore, the controller 8.j may operate in accordance with signals received from a central controller (not shown) of the vehicular control system 1, which may reflect user input, a current state of the vehicle (e.g., accelerating, braking), a change of operating mode or other relevant factors. Alternatively, the controller 8.j is dynamically configured by a central controller (not shown). Each of the controllers 8 and the central controllers may be in an asymmetric primary/secondary control relationship.

[0022] At their input sub-connectors 4.1-i, 4.2-i, 4.3-i, the daughter boards 7 are connectable to the battery unit 2 and to a high-capacity unit 3. The input sub connectors 4.1-i, 4.2-i, 4.3-i may be consecutive sections of a common bus structure of the vehicular power system 1. The high-capacity unit 3 comprises a super-capacitor 5 and circuitry 6 for charging, in particular on-board charging, from a connectable AC source (not shown). The AC source may for example supply no or 220 V at 50 or 60 Hz. The charging circuitry 6, which comprises a transformer interfacing with the AC source, a rectifying bridge and a current -limiting inductor, is connected over the terminals of the super-capacitor 5. The super-capacitor 5 is furthermore connected, via an associated daughter board 7.0, with the battery unit 2 and the input sub connectors 4.1-i, 4.2-i, 4.3-i.

[0023] In a variation of the present embodiment, the circuitry 6 is replaced with the alternative circuitry 6’ shown in figure 6, which allows charging from a DC source. The alternative circuitry 6’ includes a serially arranged inductor, which may limit intermittent high currents. The alternative circuitry 6’ further includes a unidirectionally conducting component across the connectors towards the DC source, which are located in the upper portions of figure 6. [0024] Figure 3 shows a simple example of a daughter board 7 suitable for being received in one of the connectors of the power system shown in figure 2. The daughter board 7 includes an input-side terminal 31-i and an output-side terminal 31- o, adapted for interfacing, respectively, with an input sub-connector 4.j-i and output sub-connector 4.j-o of the connector 4.j where the daughter board 7 is received. The daughter board 7 further comprises circuitry 30 suitable for acting as a DC-to-DC converter. While other DC-to-DC converter types may be suitable for use in the described system 1, the circuitry 30 shown in figure 3 may be generally described as a buck converter or step-down converter. The circuitry 30 includes a capacitor 37 across the poles of the output-side terminal 31-0, an inductor 36 and two switches 34, 35 across the poles of the input-side terminal 31-i. The switches 34, 35 may be implemented as transistors, such as metal oxide semiconductor field effect transistors (MOSFETs) or insulated-gate bipolar transistors (IGBTs). In this embodiment, the lower switch 34 is configured to act as a unidirectionally conducting component allowing current to flow in the upward direction; in a simplified embodiment, which may have higher losses and may perform less well during regenerative braking, the lower switch 34 may be replaced by a diode. The upper switch 35 alternates between an on-state, during which magnetic energy is accumulated in the inductor 36, and an off-state, during which this energy is released. As is well known to those skilled in the art, the output voltage at the output-side terminal 31-0 is related to the voltage at the input-side terminal 31-i and the ratio (duty cycle) of the respective durations of the on-state and off-state. In particular, for a given input voltage, the output voltage may vary linearly with the duty cycle.

[0025] Proposed controlling of the switches 34, 35 will be discussed below in detail with reference to figures 7 and 8. In the embodiment shown in figure 3, the circuitry 30 comprises a second capacitor 33 across the poles of the input-side terminal 31-i, which is optional as far as the voltage conversion is concerned. The embodiment further comprises one or more voltage and/or current sensors 32 for supporting the control of the switches 34, 35.

[0026] All in all, the embodiment shown in figures 2 and 3 offers a 48-V-fed modular DC supply with hybrid storage and an optional on-board charging capability for AGV and AMR systems, in which galvanic isolation is not needed. This solution can be realized simpler and cheaper if it utilizes a modular structure with identical daughter boards. It is also expandable for a wide range of output power levels.

[0027] Figure 4 shows a vehicular power system 1 powered by a battery unit 2, where a sequence of partially overlapping buck converters is formed when the daughter boards 7 are received in the connectors 4. The unregulated battery voltage of 48 V is supplied directly. A first connector 4.1 comprises an input sub-connector 4.1-i and an output sub-connector 4.1-0 for supplying 3.3 V voltage; in the first connector 4.1, there is received a first daughter board comprising a switch S'₃, an inductor 36.1 and a capacitor 37.1. A second connector 4.2 comprises an input sub connector 4.2-i and an output sub-connector 4.2-0 for supplying 5 V voltage; in the second connector 4.2, there is received a second daughter board comprising a switch S₃, an inductor 36.2 and a capacitor 37.2. A third connector 4.3 comprises an input sub-connector 4.3-i and an output sub-connector 4.3-0 for supplying 12 V voltage; in the third connector 4.3, there is received a third daughter board comprising a switch S₅, an inductor 36.3 and a capacitor 37.3. A fourth connector 4.4 comprises an input sub-connector 4.4-i and an output sub-connector 4.4-0 for supplying 24 V voltage; in the fourth connector 4.4, there is received a fourth daughter board comprising a switch S₁₂, an inductor 36.3 and a capacitor 37.3.

[0028] In this structure, four DC-to-DC converters are formed by overlapping components. For example, a first DC-to-DC converter comprises switches S'₃ andS₃, inductor 36.1 and capacitor 37.1, and a second DC-to-DC converter comprises switches S₃ and S₅, inductor 36.2 and capacitor 37.2. As such, the switch S₃ supports the supply of both the 3.3 V and 5 V voltages. Compared with known circuits for this and similar purposes, the structure shown in figure 4 represents a significant reduction of the number of installed semiconductor components. If the DC-to-DC converters are ordered by decreasing output voltages, the overlap is compatible with the sequential operation of the converters to be described below with reference to figure 7. The DC-to-DC converters may be characterized as buck converters or step- down converters.

[0029] It is noted that the embodiment shown in figure 4 does not include any input-side capacitor similar to capacitor 33 in figure 3. The vehicular power system further comprises a switch S₂₄ arranged between the fourth input 4.4-i sub-connector and the high side of the battery unit 2. The low side of the battery unit 2 is at basic system potential. A high-capacity unit is optional in the embodiment shown in figure 4.

[0030] It is noted that the circuitry of the vehicular power system 1 has inventive merit independently of the modularity. Accordingly, an embodiment of the invention, for which the applicant claims protection, provides the circuitry of figure 4 without the modular structure of the connectors and daughter boards. In this embodiment, more precisely, the interface between an input-side terminal 31-i of a daughter board 7 and an input sub-connector 4-1 of a connector 4 and/or the interface between an output-side terminal 31-0 and an output sub-connector 4-0 may be a conventional electric connection, such as a fixed connection.

[0031] Figure 5 shows a vehicular power system 1 comprising a battery unit 2 and a high-capacity unit 3. Because, in many respects, the structure of this system 1 is similar to the one shown in figure 4 and may be operated in the same manner, it is not necessary to describe all of this system in detail. The battery unit 2 has a nominal voltage of 48 V but may be designed for fluctuations between 40 and 60 V during operation. The high-capacity unit 3 comprises a super-capacitor 5, an inductor arranged serially therewith and a switch 51 allowing the battery unit 2 to be intermit tently disconnected from the input sides of the DC-to-DC converters. Intermittent disconnection may help protect the battery unit 2 from excessive current; it may also allow the super-capacitor 5 to absorb electric energy from one or more of the DC-to- DC converters, such as during regenerative braking of the vehicle. The super capacitor 5 may be designed to be operated with a voltage between 30 V and 60 V.

[0032] A PWM control approach suitable for vehicular power systems of the type disclosed herein will now be described with reference to figure 7. The left half of the figure shows a portion of the vehicular power system 1 according to figure 4 or 5, with the same notation. The battery unit 2 and optional high-capacity unit 3 are implicit. Each of the switches S₂₄, S₁₂, S₅ and S₃ is controlled on the basis of a comparison of a momentary value of a carrier signal u(t) and a reference voltage specific to the switch. The output of each comparison passes through a logic circuit, which governs the state of each switch. Accordingly, the reference voltages control the voltages at the output side of the connectors.

[0033] The carrier signal is exemplified in figure 7 by a triangular signal, which maybe advantageous for limiting turn-on losses; alternatively, the carrier signal may be a trailing-edge sawtooth waveform. The reference voltages are shown in the top portion as horizontal lines and are denoted V₂ ^* ₄, V^₂, V₃ and V₃. The respective duty cycles are graphically illustrated and denoted d₂₄ , d₁₂, d₅ and d₃. It is noted that the switches, and thus the daughter boards to which they belong, are operated sequentially. In particular, shorter duty cycles may be contained in the longer ones.

As shown in figure 7, a duty cycle of a daughter board received in a connector relatively more distant from the battery unit (i.e., connected at points relatively closer to the basic potential of the system) is contained in a duty cycle of a daughter board received in a connector relatively closer to the battery unit.

[0034] To increase a duty cycle, the corresponding reference voltage is increased. It is noted that the reference voltages are related to the duty cycle of each DC-to-DC converter but may not correspond directly to the nominal output voltages. For instance, a reference voltage of V₂₄ = 0.5 theoretically achieves a duty cycle of d₂₄ = 0.5 (as a fraction of the full period of the carrier signal u(t )) and will cause the DC-to- DC converter to supply an output voltage that is approximately equal to 0.5 x 48 V = 24 V.

[0035] As already mentioned, the switch S'₃ is operated in zero-voltage switching.

[0036] Figure 8 illustrates a safety arrangement for the vehicular power system 1. In applications, it may be of interest to monitor the load current and protect the vehicular power system 1 from short-circuit events. For this purpose, the system 1 may include circuitry for predicting the current in each output by utilizing one current sensor at the input side (denoted i , in upper left corner) with multiple sample-and-hold units (S&H), which record each momentary current at the turn-on point in time. Linear combinations of digital representations of the recorded momentary currents are used as predicted currents, which may subsequently be compared with actual measured currents to detect a short-circuit event. The digital representations may be provided by analog-to-digital converters (ADCs).

[0037] Figure 9 shows an alternative structure of the vehicular power system 1 of figure 5, wherein a diode 90 replaces the switch S'₃. The alternative structure is simpler but the voltage drop which is to be expected across the diode 90 may detract from the overall energy efficiency. Likewise, the system 1 may have a less symmetric performance when it is operated bidirectionally. The system 1 further differs from the one shown in figure 5 by the placement of the 48-V output terminals; in figure 9, these terminals are arranged across the super-capacitor 5.

[0038] Figure 10 shows a vehicular power system 1 similar to those previously described. The present structure is equipped with two switches 101, 102 which allow the battery unit 2 or the super-capacitor 5, or both, to be connected to the load side including the chain of DC-to-DC converters. The three different configurations may correspond to strong acceleration, normal operation and regenerative braking of the vehicle.

[0039] Unlike the system shown in figure 5, the super-capacitor 5 does not have any associated, serially arranged inductor. Instead of using a current -limiting inductor to limit momentary current through the super-capacitor 5, the serially arranged switch 101 may disconnect the super-capacitor 5 if excessive current is detected or can be expected to occur.

[0040] Figure 11 shows vehicular power system 1 with a still further alternative structure, in which a boost converter is used to integrate the super-capacitor 5. The boost converter avoids the need to include an extra balancing circuit for the super capacitor 5. The boost converter includes a capacitor 133, two controllable switches 134, 135 arranged across the capacitor 133, and an inductor 136 arranged in series with the super-capacitor 5. The switches 134, 135 may be operated in a manner which is conventional in boost converters, so that a higher voltage is obtained over the capacitor 133 than the actual voltage over the super-capacitor 5. For example, the higher voltage may be approximately equal to a nominal battery voltage of 48 V.

Since this enables the super-capacitor 5 to release stored energy even in conditions where the momentary voltage is 48 V, its dynamic range increases. This way, the stored energy can be utilized more completely in the system 1.

[0041] In a variation, the system 1 according to figure 11 includes multiple super capacitors arranged in parallel.

[0042] Figure 12 shows a vehicular power system in which a DC source 120 is connected over a high-capacity unit for charging. An optional inductor is arranged in series with the DC source. This solution may enable on-board charging. Figure 12 may be seen to illustrate a charging mode of the system 1 shown in figure 2, wherein the AC charging circuitry 6 is replaced by a simplified variant of the DC-oriented alternative circuitry 6’, which is shown in figure 6, and the DC source 120 is connected.

[0043] Figure 13 shows a vehicular power system 1 with an AC source applied to the high-capacity unit 5 via a transformer and a rectifier. Figure 13 has similarities with the system 1 shown in figure 2, and the charging circuitry 6 has been indicated analogously. This solution may enable on-board charging.

[0044] The aspects of the present invention have mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. A vehicular power system (1) comprising: a battery unit (2), a high-capacity unit (3), and first and second connectors (4) for supplying a first output voltage and a second, different output voltage, respectively, wherein each connector is arranged to receive one or more daughter boards (7), each daughter board comprising circuitry (30) forming a DC-to-DC converter across the battery unit when the daughter board is received in the connector.

2. The vehicular power system of claim 1, wherein all daughter boards are structurally similar, such as structurally identical.

3. The vehicular power system of claim 1 or 2, wherein the DC-to-DC converter is a bidirectional converter.

4. The vehicular power system of any of the preceding claims, wherein the DC-to- DC converter is one in the group comprising: a boost converter, a buck-boost converter, a step-down converter, a flyback converter.

5. The vehicular power system of any of the preceding claims, wherein the high- capacity unit is connected to the vehicular power system over a daughter board.

6. The vehicular power system of claim 5, wherein the high-capacity unit interfaces with an output side of the daughter board.

7. The vehicular power system of any of the preceding claims, wherein the high- capacity unit comprises a high-capacity capacitor (5), such as a super-capacitor.

8. The vehicular power system of claim 7, wherein the high-capacity unit comprises a charging interface (6).

9. The vehicular power system of any of the preceding claims, wherein a nominal voltage of the battery unit is 48 V.

10. The vehicular power system of any of the preceding claims, wherein at least one of the connectors is arranged to receive two or more daughter boards.

11. The vehicular power system of claim 10, wherein the two or more daughter boards received at the connector are arranged parallel to each other.

12. The vehicular power system of claim 10 or n, wherein the two or more daughter boards received at the connector are operated similarly, such as identically.

13. The vehicular power system of any of claims 10 to 12, wherein a number of daughter boards are received at each connector, said number being in accordance with a maximum current to be supplied for the output voltage of the respective connector.

14. The vehicular power system of any of the preceding claims, wherein: the connectors are arranged sequentially in relation to the battery unit; and said DC-to-DC converter is formed by a combination of the circuitry of a daughter board received in a connector and a portion of the circuitry of a daughter board received in an adjacent connector.

15. The vehicular power system of claim 14, wherein the circuitry of the daughter boards is such that a sequence of partially overlapping buck converters or step-down converters is formed when daughter boards are received in the connectors.

16. The vehicular power system of claim 14 or 15, wherein daughter boards received in different connectors are operated sequentially in time.

17. The vehicular power system of claim 16, wherein the daughter boards are operated such that a duty cycle of a daughter board received in a connector relatively more distant from the battery unit is contained in a duty cycle of a daughter board received in a connector relatively closer to the battery unit.

18. The vehicular power system of any of the preceding claims, wherein the high- capacity unit is arranged in parallel with the battery unit, the system further comprising a switch (51, S24) for selectively connecting the battery unit and the high- capacity unit as input.

19. An automated mobile robot (AMR) or an electric vehicle, in particular an autonomous guided vehicle (AGV), comprising the vehicular power system of any of the preceding claims.