A hybrid energy storage power supply system

Abstract

A system for supplying electric power to an electric load, the system comprising: a low-voltage terminal, a high-voltage terminal, and an output terminal. The system further including a first energy storage module and a second energy storage module of a different type than the first energy storage module, placed in parallel to the first energy storage module. A first unidirectional power converter being provided between the high-voltage terminal and the output terminal. A first discharge unit being provided between the first energy storage module and the second energy storage module. A first switching element being provided between the second energy storage module and the output terminal. A pre-charging unit comprising a second switching element and a third unidirectional power converter, wherein the pre-charging unit is configured to allow charging the second energy storage module. The system comprising a second discharge unit comprising a resistor and a third switching element.

Description

A hybrid energy storage power supply systemField of the invention

[0001] The present invention relates to an electric system for supplying electric power to an electric load connected thereto, an electric machine comprising the electric circuit, and to a method of providing an electric power to the machine using the electric system.Background art

[0002] Hybrid energy storage power supply systems are known from the prior art. Such systems combine two different energy storage module types, for example, a battery and a supercapacitor for supplying an electric load connected to the system with electric power. In such systems, the battery is usually used as a primary source of electric power to supply power directly to the electric load while the supercapacitor is used as a secondary source for quickly charging the battery. It is also possible to realize a system wherein a supercapacitor is the primary source of power while the battery is used as the secondary source of power. At least one of the two energy storage elements may be connected directly to a DC bus while the other one is connected to the DC bus via a bi-directional power converter. Depending on a number of bi-directional converters, the system may be passive (without converters), semi-active (only one converter), and active (two converters). The converters are used to control power output from each of the energy storage elements making the system less prone to failures and more controllable.

[0003] One such hybrid energy storage system is shown in Fig. 1. Fig. 1 illustrates a hybrid energy power supply system 1 including a battery 2, such as a lithium-ion battery, and a supercapacitor 4. The battery 2 is connected between a high-voltage terminal H being at high voltage VH and a low-voltage terminal L at a low voltage VL, wherein the high voltage VH is higher than the low voltage Vi_to allow current flow in the system 1. The battery 2 supplies a motor 8 of an electric vehicle with an electric power. The motor 8 is connected to the system 1 between an output terminal O and the low-voltage terminal L. Between the battery 2 and the output terminal O, a first bi-directional power converter 3 is connected to the system 1 . The first bi-directional power converter 3 ensures that a constant power is delivered to the motor 8 from the battery 2. At the same time, during breaking action, for example, the power generated by this action may be transferred to the battery 2 via the same first bi-directional power converter 3. The bi-directional power flow through the first bi-directional power converter 3 is indicated in Fig. 1 by a double arrow placed next to a symbol for a bi-directional power converter.

[0004] The supercapacitor 4 is connected in parallel to the battery 2 together with a second bi-directional power converter 5 connected in series with the supercapacitor 4. The second bi-directional power converter 5 allows for a power transfer from and towards the supercapacitor 4. In this manner, the supercapacitor 4 can be used to charge the battery 2 via the first bi-directional power converter 3. Additionally, the battery 2 can be used to charge the supercapacitor 4 if that is needed. The system 1 further includes a discharge unit, wherein the discharge unit comprises a switching element 6 and a resistor 7, connected between the supercapacitor 4 and the low-voltage terminal O. Upon closing the switching element 6, the supercapacitor 4 can be discharged at the low-voltage terminal O.

[0005] The use of the bi-directional power converters in not desired as these elements are bulky and costly, significantly increasing size and price of such hybrid energy storage systems. Additionally, due tocomplex structure of these converters to allow power transfer in both direction, significant power losses occur in these systems.

[0006] Additionally, in the systems according to the prior art, only one of the two energy storage modules is used as main module for supplying electric power directly to the electric load while the other one is use only for charging / discharging the main module. This is undesirable as for some tasks of the electric vehicle it is better to use one type of the energy storage module while for other tasks a different type. For example, for moving the electric vehicle at a constant speed it is desired to use battery that can supply a steady and constant power to the motor. However, fora rapid acceleration it would be desired to use the supercapacitor to quickly supply the motor with the electric power needed for this task.

[0007] It would be desirable to provide a hybrid energy storage system that at least partially overcomes shortcomings of the prior art.Summary of the invention

[0008] Therefore, according to a first aspect of the present invention there is a system for supplying electric power to an electric load provided according to claim 1 .

[0009] The system comprises a low-voltage terminal, a high-voltage terminal, and an output terminal configured to be connected to the electric load.

[0010] The system further includes a first energy storage module provided between the low-voltage terminal and the high-voltage terminal, wherein the first energy storage module is configured to supply electric power to the electric load upon connecting the electric load to the output terminal.

[0011] The system further includes a second energy storage module of a different type than the first energy storage module, wherein the second energy storage module is provided between the low-voltage terminal and the output terminal, and arranged in parallel to the first energy storage module, and wherein the second energy storage module is configured to supply electric power to the electric load upon connecting the electric load to the output terminal.

[0012] The system also includes a first unidirectional power converter provided between the high-voltage terminal and the output terminal, and configured to allow an electric power flow in a direction from the high-voltage terminal towards the output terminal such that a power generated by the first energy storage module is supplied via the first unidirectional power converter towards the output terminal.

[0013] The system further includes a first discharge unit provided between the first energy storage module and the second energy storage module, wherein the first discharge unit comprises a second unidirectional power converter configured to allow an electric power flow in a direction from the second energy storage module towards the first energy storage module in order to discharge the second energy storage module into the first energy storage module, and thereby to charge the first energy storage module with the power from the second energy storage module.

[0014] The system further includes a first switching element provided between the second energy storage module and the output terminal, wherein the first switching element is configured to control power supply from the second energy storage module towards the output terminal. The first switching element may be arranged in series with the second energy storage module.

[0015] The system further includes a pre-charging unit comprising a second switching element and a third unidirectional power converter, wherein the pre-charging unit is configured to allow charging the second energy storage module, for example, upon connecting a charging module, e.g. a battery, to the system.The pre-charging unit may be connected between the second energy storage module and the output terminal. The second switching element may be configured to control the charging process of the second energy storage module such that by switching the second switching element on and off, the charging process of the second energy storage module may be carried out or stopped, respectively. The third unidirectional power converter may be configured to supply power in a direction from the output terminal towards the second energy storage module or more precisely from the charging module towards the second energy storage module upon connecting the charging module to the system.

[0016] The system may further include a second discharge unit comprising a resistor and a third switching element, wherein the second discharge unit is configured to allow a discharge of the second energy storage module into the low-voltage terminal. The second discharge unit may be provided between the second energy storage module and the low-voltage terminal. Particularly, the second discharge unit may be arranged in parallel to the second energy storage module.

[0017] In an embodiment, the first discharge unit may further include a fourth switching element configured to control electric power discharge of the second energy storage module into the first energy storage module. In other words, by switching the fourth switching element on and off the discharge process may be allowed or interrupted, respectively.

[0018] In an embodiment, the system may further include a fifth switching element configured to control an electric power supply from the first energy storage module via the first unidirectional power converter and towards the output terminal. For example, by switching the fifth switching element on, a power flow from the first energy storage module towards the output terminal may be established, while by switching the fifth switching element off, the power flow from the first energy storage module towards the output terminal may be blocked.

[0019] In an embodiment, a voltage rectifying element, such as a diode, may be placed at an output of the first unidirectional power converter. Particularly, if the fifth switching element is present in the system, the voltage rectifying element may be provided in between the first unidirectional power converter and the fifth switching element. The voltage rectifying element prevents damaging the first unidirectional power converter from any kind of reverse power flow in a direction from the output terminal towards the high-voltage terminal.

[0020] In an embodiment, the system may comprise an output power control unit comprising a sixth switching element and an electrical resistor arranged in parallel, wherein the output power control unit is configured to control an electric power level at the output terminal.

[0021] In an embodiment, the system may comprise a seventh switching element configured to control an electrical connection between the system and the electric load upon connecting the electric load to the system. More precisely, the seventh switching element controls a power at the output terminal, wherein the output terminal may be electrically connected or disconnected from the rest of the system by switching the seventh switching element on and off, respectively.

[0022] In an embodiment the first energy storage module and second energy storage module may be chosen such that the system forms a hybrid energy storage system.

[0023] In an embodiment, the first energy storage module and the second energy storage module may be anyone of the following: a battery such as a lithium-ion battery and / or a lead-acid battery, and / or a capacitor such as a supercapacitor, ultracapacitor, and / or a lithium-capacitor. In a preferred embodiment, the firstenergy storage module is a battery and the second energy storage module is a capacitor, and most preferably, the first energy storage module is a lithium-ion battery and the second energy storage module is a supercapacitor.

[0024] A supercapacitor may be any capacitor based on use of electrostatic double-layer capacitance and / or electrochemical pseudo-capacitance. For example, such as disclosed in https: / / en.wikipedia.org / wiki / Supercapacitor.

[0025] In an embodiment, at least one, and preferably all, unidirectional power converters may be unidirectional voltage converters, and more preferably DC-to-DC unidirectional voltage converters such as unidirectional buck converters.

[0026] In an embodiment, a voltage at the output terminal may be in a range between 12 V and 1500 V, preferably in a range between 700 V and 900 V, and most preferably around 800 V.

[0027] In an embodiment, the unidirectional power converters may have a power in a range between 100 W and 1.5 MW, and preferably in a range between 400 kW and 600 kW, and most preferably around 500 kW.

[0028] In an embodiment, the system may further include a charging module, such as a battery, configured to charge the second energy storage device via the pre-charging unit.

[0029] In an embodiment, at least one, and preferably, all switching elements may be contactors.

[0030] According to a second aspect of the present invention, there is an electric machine provided. The electric machine comprises a system for supplying electric power according to the first aspect of the present invention, and wherein the system is used to supply the machine with the electric power.

[0031] In an embodiment, the machine may be an electric vehicle, a robotic system such as a robotic arm, and / or a heavy-duty machine such as an excavator.

[0032] According to a third aspect of the present invention, there is proved a method for supplying electric power to an electric machine according to the second aspect of the present invention.

[0033] The method includes the steps of:a. using a first energy storage module to supply power to the machine;b. using a second energy storage module, wherein the second energy storage module is a high- power energy storage module such as a supercapacitor, to deliver a high electric power to the machine in order to satisfy a high-power task;c. using a pre-charging unit to charge the second energy storage module; andd. using a first and a second discharging unit to discharge the second energy storage module at the first energy storage module or at a low-voltage terminal, respectively.

[0034] A high-power task may be any task that requires higher power than an average power value to be output at the output terminal during a working cycle and / or normal operation of the electric machine. The high-power task may have a pre-determined power requirement needed for performing such a task.

[0035] In an embodiment, the high-power task may be a rapid acceleration of the machine, loading or unloading weight, moving weight, digging, drilling, hammering, etc.

[0036] In an embodiment, the step a. of the method according to the present invention may be carried out by configuring a first unidirectional power converter to control a power supply from the first energy storage module towards the output terminal such that a power at the output terminal correspond to a first power value.

[0037] In an embodiment, the step b. of the method may be carried out by configuring a first switching element to connect the second energy storage module to the system by switching on the first switching element. The second energy storage module may be configured such that the power at the output terminal upon switching on the first switching element increases to a second power value. The second power value may be chosen to satisfy the power requirement for the high-power task such as the rapid acceleration of the machine, loading or unloading weight, and / or moving weight.

[0038] Conventional hybrid energy storage systems supply power to any electric machine using bidirectional DC-DC voltage converters and the same bi-directional DC-DC voltage converters are used to charge energy storage modules of the system. This is not only costly but it is also difficult to find matching and safely operating bi-directional DC-DC voltage converters which could be used to control power outputs of each of the energy storage modules of the system due to their different types / technologies.

[0039] Furthermore, in conventional systems only one type of energy storage module within the hybrid energy storage system is considered as the primary source of power for supplying power to any electric machine while the others are considered as secondary source of power or backup power to support the primary source of power in case of power deficit in the primary source of energy.

[0040] The present invention is related to simple and low cost utilization of any hybrid energy storage system (which may include but not limited to combinations of any lithium-ion and / or lead-acid and / or supercapacitors and / or ultracapacitors and / or lithium-capacitors technologies) using combinations of unidirectional power converters such as unidirectional voltage converting devices, preferably unidirectional DC-to-DC converters and switching elements, such as but not limited to contactors, to supply power directly to any electric machine.

[0041] According to a fourth aspect of the present invention there is a hybrid energy storage system provided.

[0042] The hybrid energy storage system may consist of combinations of at least two energy storage modules of different chemistries. At least one energy storage module may be a high-energy storage module (for example, a Semi-Solid State Battery) and at least one other energy storage module may be a high-power storage module. According to the invention, each of the at least two energy storage modules may serve as the primary source of power and can supply power directly to any electric machine using combinations of unidirectional power converters and switching elements as disclosed in the present application.

[0043] An electric machine may include but not limited to any electric vehicle. A power may be supplied to the vehicle from any one of the at least two energy storage modules directly such that, for example, in case of normal traction / operation the high-energy storage module may be used, while in case of high power requirements such as but not limited to rapid acceleration in a short period of time and / or loading / unloading weights, the high-power storage module may be used by controlling a switching element.

[0044] Therefore, the main focus of the present invention is to simplify electrical and operational architecture of any hybrid energy storage system, minimizing costs by replacing bulky bi-directional DC-to-DC voltage converters with specific combinations of unidirectional power converters and switching elements.

[0045] In an embodiment, the system comprises a high-energy type (HE) energy storage module, for example, a semi-solid state battery, that is connected to a switching element, which can connect ordisconnect the HE energy storage module from the rest of the system. The switching element is connected to the HE energy storage module via a unidirectional voltage converter, for example, a DC-to-DC voltage converter, and a voltage rectifying element to block power flow from the opposite direction and prevent from any damage the unidirectional power converter.

[0046] In an embodiment, the HE energy storage module may supply power to the electric machine via an output power control unit, which may comprise a switching element and a resistor arranged in parallel to limit inrush currents through the electric machine and prevent it from any damage. Furthermore, a switching element may be provided, wherein the switching element is configured to connect or disconnect the electrical machine from the system.

[0047] The HE storage module may be configured to supply power to auxiliary devices, such as on-board computers and sensors, via a switching element, wherein the switching element is configured to connect or disconnect the auxiliary devices from the rest of the system. The supply of the power to the auxiliary devices may be carried out via a unidirectional power converter to supply power at a constant current to the auxiliary devices.

[0048] The electrical architecture may also comprise a high-power type (HP) energy storage module, such a s a supercapacitor, that may be connected to a switching element, wherein the switching element may be configured to connect or disconnect the HP energy storage module the rest of the system.

[0049] The HP energy storage module can also supply power to the electric machine directly via output power control unit to limit inrush currents through the electric machine and prevent it from any damage. Furthermore, the switching element may be provided to connect or disconnect the electrical machine from the system.

[0050] The HP energy storage module can be rapidly charged (within 1-2 minutes) through a pre-charging unit comprising a switching device (which can connect or disconnect itself from the HP type energy storage device) and a unidirectional power converter (for example a DC-to-DC voltage converter) at a constant charging current.

[0051] The HP energy storage module may be rapidly discharged (within 1-2 minutes) into the HE energy storage module through a first discharge unit comprising a switching device (which can connect or disconnect itself from the HP energy storage module) and a unidirectional power converter (for example, a DC-to-DC power converter) at a constant discharging current.

[0052] The HP energy storage module can be slowly discharged (within minutes to hours) into a power dissipating device (for example but not limited to a resistive element) through a second discharge unit comprising a switching device (which can connect or disconnect itself from the HP energy storage module).

[0053] The present invention relates to any hybrid energy storage system / devices, which may include but not limited to any combination of lithium-ion batteries, and / or lead-acid batteries, and / or supercapacitors, and / or ultracapacitors, and / or lithium-capacitors. The system according to the present invention can supply power directly to any electric machine using simple and low cost combinations of unidirectional voltage converting devices (such as but not limited to DC-DC converters) and switching devices (such as but not limited to contactors). Moreover, such hybrid energy storage system / devices may consist of combinations of at least two or more than two energy storage devices of different chemistries such that but not limited to at least one energy storage device should be a high-energy type energy storage device and at least the other energy storage device should be a high-power type energy storage device where each of theindividual energy storage devices within the hybrid energy storage system / de vices can serve as the primary source of power and can supply power directly to any electric machine using combinations of unidirectional voltage converter and switching elements.

[0054] Further advantages of the disclosed invention will become evident in the following.Brief description of the drawings

[0055] The present invention will be discussed in more detail below, with reference to the attached drawings, in which:

[0056] Fig. 1 depicts in a schematic view a hybrid energy storage system according to prior art;

[0057] Fig. 2 depicts in a schematic view a hybrid energy storage system according to a first embodiment of the present invention;

[0058] Fig. 3 depicts in a schematic view a hybrid energy storage system according to a second embodiment of the present invention.Description of embodiments

[0059] The invention will be explained in more detail below with reference to drawings in which illustrative embodiments thereof are shown. The drawings are intended exclusively for illustrative purposes and not as a restriction of the inventive concept which is to cover all modifications, equivalents, and alternatives falling within the scope of the present invention. The scope of the invention is only limited by the definitions presented in the appended claims.

[0060] Furthermore, in the present description the terms “current flow”, “power flow”, “power transfer”, “power supply” are used. The skilled person understands that for a current flow to occur in a system or an electric circuit it is necessary for the system / circuit to be closed. In other words, it is necessary that an electric load is connected to the system / circuit. Nonetheless, the system and / or the electric circuit is an independent entity from the electric load. Furthermore, the system and / or the electric circuit according to the present invention may be arranged and / or are readily designed to be connectable to different types of electric loads.

[0061] It is further noted that in the present description the terms “charge”, “current”, “power”, “energy” refer to electric charge, electric current, electric power, and electric energy, respectively.

[0062] Fig. 2 shows a hybrid energy storage system 10 according to a first embodiment of the present invention for supplying electric power to an electric load 36 connected the system 10. For example, the electric load 36 may be an electric motor, and furthermore, the electric motor 36 may be part of an electric vehicle.

[0063] The system 10 has a low-voltage terminal L, a high-voltage terminal H, and an output terminal O. The high-voltage terminal H is at a high voltage VH, while the low-voltage terminal L is at a low voltage VL being lower than the high voltage VH,. Preferably, the low-voltage terminal L is connected to the ground. The motor 36 is connected between the output terminal O and the low-voltage terminal L.

[0064] The system 10 includes two energy storage modules 12, 14 of different types and / or different technologies. Fig. 2 illustrates an example wherein a first energy storage module 12 is a battery while the second energy storage module 14 is a supercapacitor. However, this is only one of the possibilities. The skilled person understands that, for example, the first energy storage module 12 may be a battery of a first type such a lithium-ion battery while the second energy storage module 14 may be a battery of a differenttype such as a lead-acid battery. Alternatively, the first energy storage module 12 may be a electrostatic double-layer capacitor while the second energy storage module 14 may be a hybrid capacitor.

[0065] Nonetheless, it is advantageous to combine energy storage technologies with complementary characteristics, especially in terms of energy and power, to achieve performance improvement and size reduction of the system according to the present invention in comparison to power supply systems according to prior art. For example, it is advantageous to combine a high-energy storage device, such as a battery, with a high-power storage device such as a capacitor, and preferably a supercapacitor.

[0066] Although the embodiment shown in Fig. 2 depicts only two energy storage modules 12,14, the system 10 according to the present invention may have more than two energy storage modules. At least one of these energy storage modules has to be of a different type and / or technology with respect to the other energy storage modules.

[0067] The first energy storage module 12 is connected to the system 10 between the high-voltage terminal H and the low-voltage terminal L.

[0068] In this embodiment, the bi-directional power converters used in the prior art solutions are replaced with unidirectional power converters 16, 22, 26. Unidirectional power converters are smaller, less complex than the bi-directional power converters thereby resulting in smaller power losses during their operation. However, unlike the bi-directional power converters, the unidirectional power converters can operate only in one direction. In the figures, a direction in which the power flow is carried out is depicted by an arrow located next to the symbol indicating a power converter. For example, in Fig. 2 a first unidirectional power converter 16 is depicted with the same symbol as a bi-directional converter 3, 5 shown in Fig. 1 but with an single-sided arrow under the symbol, wherein the single-sided arrow is in a direction from the high-voltage terminal H towards the output terminal O (left to right). This arrow indicates that the power flow is carried out only in this direction. In other words, unidirectional power converters cannot operate in an opposite direction, i.e., in a direction from the output terminal O towards the high-voltage terminal H (right to left). This means that, for example, in the case of an electric vehicle, a power generated by braking cannot be transferred to the energy storage module 12, 14. Nonetheless, the inventors have found out that this shortcoming of unidirectional power converters is at least partially overcome by smaller losses generated in or by them. This is particularly the case in the systems with a plurality of unidirectional power converters (replacing a plurality of bi-directional power converters).

[0069] The first unidirectional power converter 16 is located between the high-voltage terminal H and the output terminal O. The first unidirectional power converter 16 is further configured to control power supply between the first energy storage module 12 and the output terminal O. Thus, when an electric load is connected to the output terminal (more precisely, between the output terminal O and the low-voltage terminal L), such as the motor 36, the first energy storage module 12 may supply the motor 36 with a power needed for functioning of the motor 36. The power supply from the first energy storage module 12 is controlled by the first unidirectional power converter 16.

[0070] Furthermore, the system 10 includes the second energy storage module 14. The second energy storage module 14 is connected between the low-voltage terminal L and the output terminal O, and in parallel to the first energy storage module 12. The second energy storage module 14 may be further configured to directly supply the motor 36 with power (i.e. independently of the first energy storage module 12).

[0071] A first switching element 18 may be connected between the second energy storage module 14 and the output terminal O. The first switching element 18 is configured to control the power supply from the second energy storage module 14 towards the output terminal O. In other words, upon switching on the first switching element 18, an electric connection between the second energy storage module 14 and the output terminal O is formed allowing current flow, and thereby power supply, from the second energy storage module 14 towards the motor 36. Upon switching off the first switching element 18, this electrical connection is interrupted and the current cannot flow via the first switching element 18.

[0072] The system 10 further includes a first discharge unit 20. The first discharge unit 20 comprises a second unidirectional power converter 22. The first discharge unit 20 may be provided between the first and second energy storage modules 12, 14 and configured to allow discharge of the second energy storage module 14 into the first energy storage module 12. Consequently, the first energy storage module 12 is charged using the second energy storage module 14. In this manner the first energy storage module 12 can be quickly charged within minutes.

[0073] It is also noted that the second unidirectional power converter 22 does not allow a power transfer in an opposite direction, i.e. from the first energy storage module 12 towards the second energy storage module 14.

[0074] The system 10 further includes a pre-charging unit 32 for charging the second energy storage module 14. The pre-charging unit 32 may be connected between the output terminal O and the second energy storage module 14, and in parallel to the first switching element 18.

[0075] The pre-charging unit 32 depicted in Fig. 2 includes a second switching element 24 and a third unidirectional power converter 26. The third unidirectional power converter 26 is configured to control power supply in a direction from the output terminal and towards the second energy storage module 14.

[0076] In an example, a charging module (not shown), such as a battery, may be connected to the system 10 and configured for charging the second energy storage module 14. In such an embodiment, the second switching element 24 may be used to control an electric connection between the charging module and the second energy storage module 14. Upon switching on the second switching element 24, an electric connection between the charging module and the second energy storage module 14 is established and the second energy storage module 14 may be charged via the third unidirectional power converter 26 from the charging module.

[0077] The system 10 further includes a second discharging unit 34 configured for discharging the second energy storage module 14 into the low-voltage terminal L.

[0078] The second discharging unit 34 may be arranged in parallel to the second energy storage module 14 and may comprise a third switching element 28 and an electric resistor 30. Upon switching on the third switching element 28, the second energy storage module 14 may be discharged via the resistor 30 at the low-voltage terminal L. A resistance of the resistor 30 may be selected such to allow for an optimal discharge time of the second energy storage module 14.

[0079] Advantageously, the second discharge unit 34 allows to discharge the second energy storage module 14 when the system 10 is not in use, making the system 10 safer.

[0080] The system 10 may further comprise a control unit (not depicted). The control unit may be configured to control switching actions of each of the switching elements 18, 24, 28. For example, thecontrol unit may comprise a processor configured to automatically switch on and off each of the switching elements 18, 24, 28.The control unit may be connected to the system 10 via a wire connection or wirelessly.

[0081] Together with the pre-charging unit 32 and the second discharge unit 34, the second energy storage module 14 may be charged and discharged. This makes it particularly useful for, for example, using the second energy storage module 14 for quickly delivering power to the motor 36 when high-power tasks are required in a short amount of time.

[0082] In the depicted non-limiting example, the system 10 is a part of the electric vehicle. The battery 12 may be used to supply power to the motor 36 for moving the electric vehicle at a constant speed. However, if a rapid acceleration is required, the system 10 may fulfil this high-power task by using the supercapacitor 14. The supercapacitor 14 can be quickly charged via the pre-charging unit 32 and deliver power to the motor 36 in a short amount of time for performing the rapid acceleration task by switching on the first switching element 18 to establish an electrical connection between the supercapacitor 14 and the output terminal O. If any charge is left in the supercapacitor 14 after the rapid acceleration is performed, that charge may be either discharged into the battery 12 or it may be discharged via the second discharge unit 34 into the low-voltage terminal L. In either case, the supercapacitor 14 is discharged when not in use resulting in a safer system 10. The control unit may be used to control switching the switching elements on and off to allow performance of these actions.

[0083] The system 10 as disclosed here-above is advantageous over the prior art systems as it can be made in a very compact form due to absence of bi-directional power converters. Furthermore, the systems according to present invention are also much cheaper than the prior art systems with same and / or similar functionalities. As the power conversion is carried out only in one direction, a power conversion range of each of the unidirectional power converters may be narrower. This results not only in lower costs but also in overall better functionality of the system.

[0084] Fig. 3 shows another embodiment of the present invention.

[0085] A system 10’ shown in Fig. 3 may be realised by adding additional electrical components to the system 10 disclosed in Fig. 2. Therefore, the components in Fig. 3 appearing also in Fig. 2 and having the same reference signs, perform the same functions in Fig. 3 as well, and to avoid repletion, we will not describe them again.

[0086] Although system 10’ is shown as one embodiment in Fig. 3, the skilled person understands (and particularly as it will be clear from the rest of this description) that each of the additional components shown in Fig. 3 and not appearing in Fig. 2 performs a specific function in Fig. 3 and can be added or omitted from the system 10’ independently of other additional components.

[0087] The system 10’ may comprise an output power control unit 48. The output power control unit may comprise a sixth switching element 46 and a control resistor 44 arranged in parallel. The output power control unit 48 may be configured to control and / or maintain a power level at the output terminal O steady. The power level at the output terminal O may vary due to, for example, by in addition to or instead of using the first energy storage module 12 for supplying power to the motor 36 using the second energy storage module 14. During this transitional period, the power level at the output terminal O may experience a sudden jump which can damage the motor 36. This is particularly the case when a supercapacitor is used to quickly supply power to the motor 36. To prevent such a scenario, during tasks that require additional power and / or switching between the two energy storage modules 12, 14, the sixth switching element is switched off suchthat the power is delivered to the motor 36 via the control resistor 44. A resistance of the control resistor 44 may be chosen such that a power delivered via the control resistor 44 does not exceed a certain, predetermined value. To determine this value, a capacitance, the output voltage, as well as, and electric load parameters may be used.

[0088] Once a stable power output has been reached, the sixth switching element 46 may be switched on such that the most of the power is supplied to the motor 36 via the sixth switching element 46.

[0089] The system 10’ may further include a seventh switching element 44 configured to connect and disconnect the electric load 36 from the rest of the system 10’. In this manner, when the power supply to the electric load 36 is not needed, it is not needed to physically detach the electric load 36 from the output terminal O but simply switch off the seventh switching element 44. This operation may be controlled by the control unit.

[0090] The first discharge unit 20 may further comprise a fourth switching element 38. The forth switching element 38 may the configured to control discharge of the second energy storage module 14 at the first energy storage module 12 and thereby charging the first energy storage module 12.

[0091] The fourth switching element 38 may be controlled by the control unit to automatically switch on and off the first discharge unit 20.

[0092] The system 10’ may further include a voltage rectifying element 40 such as a diode. The voltage rectifying element 40 may be provided at an output of the first unidirectional power converter 16. The voltage rectifying element 40 may be configured to block power transfer or flow towards the first unidirectional power converter 16. It is noted that the first unidirectional power converter 16 by itself does not allow power transfer in a direction from the output terminal O towards the first energy storage module 12. Nonetheless, during a sudden power surge in the system 10’ it may happen that the first unidirectional power converter 16 malfunction resulting in a power transfer towards the first energy storage module 12 and thereby damaging the first unidirectional power converter 16. To prevent such a scenario, the first voltage rectifying element 40 is added.

[0093] Additionally, auxiliary devices 54 such as a computer, sensors may be connected to the high-voltage terminal H of the system 10’ for supplies these devices with power. The auxiliary devices may be connected to the system 10’ via a forth unidirectional power converter 50 allowing power transfer in a direction from the high-voltage terminal H towards the auxiliary devices 54. In this manner the auxiliary devices may be easily connected to the system 10’. The system 10’ may also include an eight switching element 52 configured to control a power supply from the first energy storage module 12 towards the auxiliary devices 54 such that the auxiliary devices 10’ may be easily connected and disconnected from the system 10’.

[0094] The unidirectional power converters 16, 22, 26, 50 may be configured to convert a source of direct current from one voltage level to another thereby controlling a power supply in the system 10, 10’.

[0095] In particular, each one of the unidirectional power converter 16, 22, 26, 50 may be a unidirectional voltage converter, and preferably a DC-to-DC unidirectional voltage converter. Such a converter is configured to convert a converter input voltage at an input side of the converter to a converter output voltage at an output side of the converter. For example, the converter input voltage may correspond to the high voltage and the converter output voltage may correspond to an output voltage at the output terminal.Furthermore, the unidirectional power converter may be configured such that the converter output voltage corresponds to a specified voltage of the electric load (for optimal working of the electric load).

[0096] In an embodiment, the unidirectional power converter is a unidirectional buck voltage converter.

[0097] The switching elements 18, 24, 28, 38, 42, 46, 52 may be any type of elements configured to establish and interrupt an electrical connection between elements and / or sections of the system 10, 10’. For example, the switching elements 18, 24, 28, 38, 42, 46, 52 may be manual switching elements and / or automatic switching elements such as breakers. In a preferred embodiment, the switching elements may be contactors such as mechanical contactors, electrical contractors, and / or solid-state contactors. Particularly, the contactors may be configured to be controlled by the control unit such that the switching on and off of each of the contactors is automatically controlled by the control unit.

[0098] It is also noted that if the switching element is switched off and an electrical connection between a component and rest of the circuit / system is interrupted, the component is still considered as to be “connected” to the circuit / system in the broadest sense as the interruption is only temporary and will be established again by switching on the switching element.

[0099] The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive to the inventive concept. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice. In addition, many modifications may be made to adapt a particular configuration or material to the teachings of the invention without departing from the essential scope thereof.

[0100] All modifications which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

1. Claims1. A system for supplying electric power to an electric load, the system comprising:3.• a low-voltage terminal;4.• a high-voltage terminal;5.• an output terminal configured to be connected to the electric load;6.• a first energy storage module7.o provided between the low-voltage terminal and the high-voltage terminal, and o configured to supply electric power to the electric load upon connecting the electric load to the output terminal;8.• a second energy storage module of a different type than the first energy storage module, wherein the second energy storage module is9.o provided between the low-voltage terminal and the output terminal, o in parallel to the first energy storage module, and10.o configured to supply electric power to the electric load upon connecting the electric load to the output terminal;11.• a first unidirectional power converter12.o provided between the high-voltage terminal and the output terminal, and o configured to allow a power flow in a direction from the high-voltage terminal towards the output terminal;13.• a first discharge unit14.o provided between the first energy storage module and the second energy storage module,15.o wherein the first discharge unit comprises a second unidirectional power converter configured to allow a power flow in a direction from the second energy storage module towards the first energy storage module;16.• a first switching element17.o provided between the second energy storage module and the output terminal, and18.o configured to control power supply from the second energy storage module towards the output terminal;19.• a pre-charging unit comprising a second switching element and a third unidirectional power converter, wherein20.o the pre-charging unit is configured to allow charging the second energy storage module, and21.o the charging is controlled by the second switching element; and • a second discharge unit comprising a resistor and a third switching element, wherein the second discharge unit is configured to allow a discharge of the second energy storage module into the low-voltage terminal.

2. The system according to claim 1 , wherein the first discharge unit further includes a fourth switching element configured to control electric power discharge of the second energy storage module into the first energy storage module.

3. The system according to claim 1 or claim 2, wherein the system further includes a fifth switching element configured to control an electric power supply from the first energy storage module via the first unidirectional power converter and towards the output terminal.

4. The system according to claim 3, wherein a voltage rectifying element, such as a diode, is placed in between the first unidirectional power converter and the fifth switching element.

5. The system according to any of the preceding claims, wherein the system comprises an output power control unit comprising a sixth switching element and an electrical resistor arranged in parallel, and wherein the output power control unit is configured to control an electric power level at the output terminal.

6. The system according to anyone of the preceding claims, wherein the system comprises a seventh switching element configured to control an electrical connection between the system and the electric load upon connecting the electric load to the system.

7. The system according to any one of the preceding claims, wherein the first energy storage module and second energy storage module form a hybrid energy storage system.

8. The system according to any one of the preceding claims, wherein the first energy storage module and second energy storage module are anyone of the following: a battery such as a lithium-ion battery and / or a lead-acid battery, and / or a capacitor such as a supercapacitor, ultracapacitor, and / or a lithium-capacitor.

9. The system according to any one of the preceding claims, wherein the first energy storage module is a battery and the second energy storage module is a capacitor, and preferably, wherein the first energy storage module is a lithium-ion battery and the second energy storage module is a supercapacitor.

10. The system according to any one of the preceding claims, wherein at least one, and preferably all, unidirectional power converters are unidirectional voltage converters, and more preferably DC-to-DC unidirectional voltage converters such as unidirectional buck converters.

11. The system according to any one of the preceding claims, wherein a voltage at the output terminal is in a range between 12 V and 1500 V, preferably in a range between 700 V and 900 V, and most preferably around 800 V.

12. The system according to any one of the preceding claims, wherein the unidirectional power converters have a power in a range between 100 W and 1.5 MW, and preferably in a range between 400 kW and 600 kW, and most preferably around 500 kW.

13. The system according to any one of the preceding claims, wherein the system further includes a charging module, such as a battery, configured to charge the second energy storage device via the pre-charging unit.

14. The system according to any of the preceding claims, wherein at least one, and preferably, all switching elements are contactors.

15. An electric machine comprising a system for supplying electric power according to any one of the preceding claims, and wherein the system is used to supply the machine with the electric power.

16. The machine according to claim 15, wherein the machine is an electric vehicle, a robotic system such as a robotic arm, and / or a heavy-duty machine such as an excavator.

17. A method for supplying electric power to an electric machine according to claim 15 or 16, wherein the method includes the steps of:36.a. using a first energy storage module to supply power to the machine;37.b. using a second energy storage module, wherein the second energy storage module is a high-power energy storage module such as a supercapacitor, to deliver a high electric power to the machine in order to satisfy a high-power task;38.c. using a pre-charging unit to charge the second energy storage module; and39.d. using a first and a second discharging unit to discharge the second energy storage module at the first energy storage module or at a low-voltage terminal, respectively.

18. The method according to claim 17, wherein the high-power task is a rapid acceleration of the machine, loading or unloading weight, and / or moving weight.

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