Abstract:
Electrical energy buffering system, comprising an energy source for delivering electrical energy, an energy buffer for buffering electrical energy delivered from the energy source, the energy buffer comprising a plurality of supercapacitors, and control logic for controlling the operation of the energy buffer by selectively switching the supercapacitors, wherein the plurality of supercapacitors are switchably connected in parallel to each other in a circuit comprising the energy source and an electrical power output, and the control logic comprises a buffer monitor for monitoring a parameter representing the charge or discharge state, respectively, of each of the supercapacitors and is adapted to sequentially switch single supercapacitors or groups of supercapacitors on, responsive to the detection of a first predetermined charge or discharge state, respectively, and to switch them off, responsive to the detection of a second predetermined charge or discharge state, respectively.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to EP Patent Application No. 11157409.1, filed Mar. 9, 2011. The entire disclosure of the prior application is considered to be part of the disclosure of the instant application and is hereby incorporated by reference herein. 
       TECHNICAL FIELD 
       [0002]    Embodiments of the invention are related to electrical energy buffering, storing and management systems and are, in particular, applicable in the fields of renewable energy electric drives for vehicles, boats and submarines. 
       BACKGROUND OF THE INVENTION 
       [0003]    According to the heavily growing importance of renewable energy in global energy production on the one hand and of electric and hybrid drives for cars on the other, the development of sophisticated energy buffering and storing systems has become a crucial aspect. Whereas wind farms and solar energy plants produce a rapidly increasing share of electrical energy in a couple of developed countries, the buffering of the energy produced by such power plants and the smart management of future electrical power supply systems (“smart grids”) is, to a large extent, still unresolved. Likewise, the smart buffering and management of electrical energy is crucial for a significant market share and for an ecologically beneficial operation of electric cars on a broad scale. Such systems have to be tailored both to the typically discontinuous production or consumption of electrical energy and to the physico-chemical peculiarities and restraints of available battery systems. 
         [0004]    In electronics and low-voltage systems, capacitors, and in particular electrolytic capacitors, have long been known as devices for storing energy. However, relatively low capacitances and, resulting therefrom, low energy storage capacities preclude capacitors from use in electrical energy supply systems. Recently, electrochemical double layer capacitors (EDLC), or supercapacitors, have been used in “energy smoothing” applications and momentary-load devices, and have further been used for energy-storage in vehicles and in smaller power-plant applications, like home solar energy systems. 
       SUMMARY 
       [0005]    It is an object of the invention to provide a sophisticated electrical energy buffering system on the basis of supercapacitors which, more specifically, is usable for power generation control applications, as well as for power consumption control applications, on an industrial scale. 
         [0006]    It is a further object of the invention to provide an electrical storing system, making use of supercapacitors, which allows to store electrical energy generated from renewable energy sources in an efficient manner on an industrial scale. 
         [0007]    It is a further object of the invention to provide an electrical energy storing system, making use of supercapacitors as essential part of an improved electric or hybrid drive in vehicles etc. which are equipped with rechargeable batteries. 
         [0008]    Still further, it is an object of the invention to provide an electrical energy management system, making use of supercapacitors, which allows for a smart management of electrical energy in electric and hybrid drives and with respect to other loads which are typically connected to up-to-date energy supply systems. 
         [0009]    In embodiments of the invention, an electrical energy buffering system of claim  1  is provided, as well as an electrical energy storing system of claim  9 , and an electrical energy management system of claim  12 . Further embodiments of the invention are subject of the respective dependent claims. 
         [0010]    According to an aspect of the invention, an energy buffer of the proposed system comprises a plurality of supercapacitors and control logic for controlling the operation of the energy buffer by selectively switching the supercapacitors according to a specific scheme. According to a further aspect of the invention, the plurality of supercapacitors are switchably connected in parallel to each other in a circuit comprising an energy source and an electrical power output. The control logic comprises a buffer monitor for monitoring a parameter representing the charge or discharge state, respectively, of each of the supercapacitors and is adapted to sequentially switch single supercapacitors or groups of supercapacitors on or off, respectively. 
         [0011]    According to a further aspect of the invention, the switching on is responsive, at least in part, to the detection of a first predetermined charge or discharge state of the respective supercapacitor or group, and the switching off is responsive, at least in part, to the detection of a second predetermined charge or discharge state, respectively. 
         [0012]    In at least one embodiment of the invention, the energy source may comprise a photovoltaic converter or may comprise a fuel cell. However, these examples are not exhaustive, and further useful applications related to renewable energies and beyond are possible. In other arrangements, the energy source may comprise a rechargeable battery, preferably of the Li-ion type or NiMH type or NiCd type or metal/air type. 
         [0013]    In an embodiment of the invention, the control logic comprises a threshold discriminator provided at the respective outputs of the monitor, for providing a switch-on or switch-off signal, respectively, responsive to the detection of a parameter value above a predetermined upper threshold value or below a predetermined lower threshold value. More specifically, herein the threshold discriminator comprises programming for adjustably setting a respective threshold value. 
         [0014]    In a further embodiment, the buffer monitor may be adapted for monitoring the output voltage of each of the supercapacitors. 
         [0015]    In yet another embodiment, the control logic may be adapted to immediately combine a switching-off of a first supercapacitor or group of supercapacitors with a switching-on of a second supercapacitor or group of supercapacitors, essentially without delay time. Insofar, a “chain” of off-on switching operations may be implemented, ensuring an uninterrupted delivery of sufficient electrical power for buffering an electrical energy generating, storing and/or consuming process. 
         [0016]    According to a further embodiment, the control logic may comprise a source monitor for monitoring a performance parameter of the energy source, such as an output voltage and/or output current thereof, and for providing an auxiliary control signal for influencing the switching-on of supercapacitors or groups of supercapacitors responsive to a detected value of the performance parameter. 
         [0017]    The proposed electrical energy storing system, in principle, may comprise an energy storage device connected to the power output of the above-explained electrical energy buffering system. Herein, output side switches may be provided for each of the supercapacitor or group of supercapacitors, and the control logic may be adapted to sequentially actuate the output-side switches for connecting the supercapacitors or groups of supercapacitors to the energy storage device responsive, at least in part, to the detection of a third predetermined charge or discharge state, respectively, and for disconnecting them from the energy storage device responsive to the detection of a fourth predetermined charge or discharge state, respectively. 
         [0018]    In some embodiments of the invention, the energy storage device may comprise a rechargeable battery, preferably of the Li-ion type or NiMH type or NiCd type or metal/air type (referenced further above as an energy source, related to the basic energy buffering system). In further embodiments, the energy storage device may comprise an electrical motor for converting electrical energy into mechanical energy and a mechanical energy storage device coupled to the motor. Flywheels are a well-known example of an energy storage device of this type. 
         [0019]    The proposed electrical energy management system, in principle, in addition to the above-specified electrical energy buffering system, comprises a load that may consume electrical energy, and further may be connected to the power output of the buffering system. Herein, output side switches may be provided for each of the supercapacitor or group of supercapacitors, and the control logic may be adapted to sequentially actuate the output-side switches for connecting the supercapacitors or groups of supercapacitors to the load responsive to the detection of a third predetermined charge or discharge state, respectively, and for disconnecting them from the load responsive to the detection of a fourth predetermined charge or discharge state. 
         [0020]    In an embodiment of the invention, a switchable direct connection may be provided between the energy source and the load, and the control logic may be adapted to selectively switch-on and switch-off either the direct connection between the energy source and the load or a connection via a supercapacitor or group of supercapacitors. 
         [0021]    According to another aspect of the electrical energy management system, the load may be connected to an additional power output of the buffering system, provided in addition to its output for connecting the energy storage device. Herein, output side switches may be provided for each of the supercapacitor or group of supercapacitors, and the control logic may be adapted to sequentially actuate the output-side switches. On the one hand, this actuation may connect the supercapacitors or groups of supercapacitors to the load responsive to the detection of a third predetermined charge or discharge state, respectively, and for disconnecting them from the load responsive to the detection of a fourth predetermined charge or discharge state. Furthermore, the energy management system may comprise a switchable direct connection between the energy storage device and the load, wherein the control logic may be adapted to selectively switch on or off either the direct connection between the energy storage device and the load or the connection between the energy source and the load via a supercapacitor or a group of supercapacitors. 
         [0022]    In one embodiment, the load may include an electric motor, such as an electric motor of a vehicle drive, boat drive or submarine drive. 
         [0023]    The invention may provide, at least in some embodiments, a simpler and more efficient energy buffering in electrical energy supply and drive systems and, more specifically, in renewable energy applications. This may be due to the sophisticated embedding of supercapacitors by making use of their specific advantages over electrochemical cells. The insensitivity of capacitors to charging conditions and the simplicity of defining and monitoring the basic parameters for controlling such systems may provide for a simplified construction of charger and converter components and ensure a robust system operation over a broad range of environmental and operating conditions, resulting in an increased overall efficiency and utilization of the electrical energy provided by several types of energy sources. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    Further embodiments and advantages, as well as important aspects of the invention, become apparent from the following description of embodiments of the invention according to the figures. 
           [0025]      FIG. 1  shows a diagram of a prior art electrical energy management system. 
           [0026]      FIG. 2  shows a diagram of an electrical energy management system of the present invention. 
           [0027]      FIG. 3  shows a diagram of an electrical energy buffering circuit arrangement of an embodiment of the invention. 
           [0028]      FIG. 4  shows the structure of a controller of such buffering circuit in more detail. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIG. 1  schematically shows the structure of a conventional electrical energy utilization or management system  1 , which e.g. can be used in an electric or hybrid car or a home renewable energy system. The energy management system  1  comprises a system input (energy source input)  3 , to which a system battery block (energy storage device)  5  is connected via a system battery charger block  7 . A wind generator or solar panel can be connected to the system input  3  in energy supply applications, whereas a combustion engine is connected to the input in a hybrid car (and even in a conventional car). Furthermore, the system battery block  5  is connected to an output  9  via a DC-AC converter block  11 , for supplying stored electrical energy to a load, which can be an electric motor or any other electrically driven equipment. For controlling the battery charging and discharging operations, as well as the DC-AC conversion and further functions of the system, a control unit  13  is provided. 
         [0030]      FIG. 2  is a block diagram illustrating the general structure of an energy management system  1 ′ according to an embodiment of the present invention. Identical or similar components to those in  FIG. 1  are designated with the same or corresponding reference numerals. In  FIG. 2 , an energy source  15  and a load  17  are shown as components of the overall system, whereas in  FIG. 1  these components have not been shown. On the other hand, in  FIG. 2  any DC-DC or DC-AC converter components are omitted. Please refer to  FIG. 3  and details provided further below. 
         [0031]    In the electrical energy management system  1 ′ of  FIG. 2 , a supercapacitor block  19  may comprise a number of supercapacitors  19   i  connected in parallel. A supercap charging unit  8  and a supercap discharging unit  10  are associated with the supercapacitor  19 , and both the charging and discharging units  8 ,  10  may comprise a “channel” structure corresponding to the structure of block  19  and may provide individual charging and discharging operations for each of the supercapacitors  19   i.    
         [0032]    In the figure, it is shown that an output of the supercap charging unit  8  may be connected to the load  17 , via the discharging unit  10  and the (first) output  9 , and likewise an output of the supercap discharging unit  10  may be connected to the battery block  5  via the charging unit  8  and the (second) output  12 . This second output  12  may also be connected to the supercap charging unit  8 , which may have an input function, as explained below. The arrangement and mutual connections of the supercap charging unit  8 , the supercap discharging unit  10 , the system battery block  5  and the load  17  may be adapted to provide for multiple energy supply paths from the energy source  15  to the system battery block  5  and/or to the load  17 , via the supercapacitor block  19 , or from the system battery block  5  to the supercapacitor  19  and/or to the load  17 , as explained further above in the general part of the description. 
         [0033]    A modified control and monitoring unit  13 ′ may be provided for controlling the respective energy flows and, more specifically, the consecutive charging/discharging operations of the supercapacitors  19   i , to provide the outstanding system performance. The control and monitoring unit  13 ′ may comprise an industrial standard programmable logic controller (PLC) and may be equipped with remote control, both for programming its operation and for implementing at least part of its monitoring functions. Such remote control may be implemented both as short-distance remote control, via WLAN or Bluetooth or similar standards, e.g. in home renewable energy applications, or as long-distance remote control, via mobile telecommunications networks, i.e. for implementing distributed renewable energy applications and smart grids. In  FIG. 2  it is also illustrated that within the overall energy management system  1 ′ and energy buffering system  1 A′—including the energy source  15  but not including the supercap discharge unit  10 , the system battery block  5  and the load  17 —and an energy storing system  1 B′—including all components except the load  17 —may be defined as sub-systems. 
         [0034]      FIG. 3  shows an electrical energy storing system  101  that may comprise a battery  103 , an energy source input  105 , a load output  107 , a power source step-up/step-down DC-DC converter  109 , a 12V/24V DC-DC converter  111 , and an energy buffering sub-system  113 . 
         [0035]    The energy buffering sub-system  113  comprises n supercapacitors C 1  . . . Cn connected between the power input  105  and the load output  107  in parallel, via charging switches SC 1  . . . SCn at the input side and discharging switches SD 1  . . . SDn at the output side. Additionally, at the output side of each supercapacitor branch, a Schottky diode  115  may be provided, for blocking any reverse current flow. A toggle switch TG may be provided at the circuit&#39;s output, for switching the output voltage between the two predetermined levels 12V or 24V. 
         [0036]    For controlling the operation of the energy buffering sub-system  113 , a buffering controller  117  may be provided, which delivers control signals for actuating the supercapacitor charging switches SC 1  to SCn and discharging switches SD 1  to SDn to a capacitors commutator (switch actuator)  119 . Charging feedback signals A and discharging feedback signals B may be provided to respective inputs of the buffering controller  117  from the charging switches block  121  or discharging switches block  123 , respectively. Besides those feedback signals, the buffering controller  117  monitors input (power source) voltages on the one hand and output (load) voltages on the other and controls the charging or discharging switches responsive to the result of a predetermined internal processing of the signals gained through its monitoring function. 
         [0037]    The buffering controller  117  may control the charging switches SC 1  to SCn such that, upon application of a sufficient source voltage, charging of the supercapacitors C 1  to CQn starts with the first supercapacitor C 1 , up to a predetermined upper threshold voltage. Once this upper threshold voltage is achieved, the respective charging switch SC 1  may be opened, immediately followed by closing the second charging switch SC 2 , associated to the second supercapacitor C 2 , until the second supercapacitor reaches its upper threshold voltage, and so forth. 
         [0038]    Vice versa, if a load disconnected to the output  107  and the buffering controller  117  is instructed to provide electrical energy to the load, discharging of the supercapacitors may start with actuating the discharging switch SD 1  associated to the first supercapacitor C 1 , until a predetermined lower threshold voltage is reached. At this point of time, the first discharging switch SD 1  may be opened, immediately followed by closing the second discharging switch SD 2  to discharge the second supercapacitor C 2  to the load, and so forth. 
         [0039]    In an operation scheme of the energy buffering sub-system  113 , assuming that an energy source and a load are connected to the second arrangement  101  at the same time, charging and discharging operations of the supercapacitors may be carried out consecutively, i.e. the discharging of one of the supercapacitors down to a predetermined output voltage is immediately followed by starting its re-charging up to a predetermined voltage, when at the same time the next one of the supercapacitors is being discharged, and so forth. This process may, assuming that no failure appears, continue until the system is powered off or a connected energy source is no longer able to provide a minimum amount of energy (input voltage). In such a situation, the buffering sub-system will be waiting until a lower input voltage level is reached, to automatically re-start its operation. 
         [0040]    If no load is connected to the output on the circuit arrangement, a corresponding operation scheme may be applied for charging the internal battery  103 . The battery under 3 may even be charged in parallel to the consecutive charging of the supercapacitors, depending on the implemented specific control scheme, and optionally on a monitor charge/discharge state of the supercapacitors. Furthermore, the buffering controller  117  can actuate the charging switches and discharging switches such that the battery  103  is discharged through the output  107 , in this way serving as (secondary) energy source for supplying electrical energy to a load connected to the output  107 . 
         [0041]    The power source step-up/step-down DC-DC converter  109  provides for a broad range of usable input voltages (6V DC . . . 32V DC), in a preferred embodiment with an efficiency&gt;92% and an output current up to 10 A. The converter  109  may comprise a pulse charge controller  25  bidirectionally connected to a conversion monitor  127 , which latter is connected to the input  105 , in parallel to a switch device  129 . The switch device  129  provides, at an output SW thereof, a signal to the conversion monitor  127 , whereas it receives, besides the voltage applied to the input  105 , a control signal from a step-up/step-down DC-DC converter  131 . Furthermore, the converter  109 , may comprise a system monitor  133 , inputs of which are connected to respective outputs of the controller  131 , a current sensor  135  and the power line  137  connecting the input  105  to the supercapacitors C 1  to Cn. 
         [0042]    The converter  109  acts on power switches  139  provided in the power line  137 . Given that supercapacitors are being used, the maximum voltage of which is 16.2V, the converter output voltage is set to 15.5V, so that the supercapacitors C 1  to Cn will charge up to approximately 15.2V. As far as the detailed operation scheme of the converter  109  is concerned, such type of converters is, known to those of ordinary skill in the art, and additional detail may be omitted. 
         [0043]    The configuration of the 12V/24V DC-DC converter  111  may be similar to the converter  109 , i.e. it may comprise a pulse charge controller  141 , a conversion monitor  143 , a switch device  145 , a step-up/step-down DC-DC controller  147 , and a system monitor  149 , and it may receive signals from a (second) current sensor  151  and (second) power line  153  and acts on power switches  155 . At its input side, the converter  111  may be connected to the battery  103 , instead of an external energy source, and at its output side it may be connected to the system output  107 , through the toggle switch TG. In a preferred embodiment equipped with standard ICs, it can be operated with an efficiency up to 95% and an output current up to 6 A. 
         [0044]      FIG. 4  shows a controller structure of the arrangement illustrated in  FIG. 3  in more detail. The buffering controller  117  may comprise a charging controller part  117 A and discharging controller part  117 B, each part comprising an integrated logic as its core, the signal inputs and outputs IN 1  to IN 4  and OUT 1  to OUT 4  of both parts being connected in a feedback manner to provide for the step-up/step-down operation of the (exemplified four) supercapacitors of the system in the above-explained consecutive operating scheme. In each of the respective parallel output lines, connected to a single control signal output  117 C, a charging relay RC 1  to RC 4  or discharging relay RD 1  to RD 4 , each followed by a relays current limiting device CL 1  to CL 8 , are arranged. 
         [0045]    The embodiments and aspects of the invention explained above are not determined to limit the scope of the invention, which is exclusively to be determined by the attached claims. Many modifications of the inventive concept may be possible within the scope of the claims and, more specifically, arbitrary combinations of the several claim features are considered to be within the scope of the invention.