Abstract:
A supervisory system controller for controlling and monitoring the generation of electrical energy from renewable sources and management methods for the storage of energy so generated and interconnecting the energy-generating elements, storage and load. The supervisory system controller operates to maximum the power transfer from a wind turbine to a battery by automatically varying the threshold levels at which turbine dump loads are switched based on system inputs and measurements. The method conserves generator fuel by delaying a scheduled generator maintenance running period such that it to occurs when renewable energy availability is predicted to be low and battery is in a reduced state of charge. Further modifications and management methods are also provided.

Description:
1. PRIORITY CLAIM 
       [0001]    This application is a continuation of and claims priority under 35 U.S.C. §120 and/or 35 U.S.C. §365 to co-pending PCT Application No. PCT/GB2009/050543 having an international filing date of May 20, 2009, which claims priority to Great Britain Application No. 0809235.5 filed on May 21, 2008. 
     
    
     2. FIELD OF THE INVENTION 
       [0002]    The present invention relates to a Supervisory System Controller (SSC) for controlling and monitoring the generation of electrical energy from renewable sources, managing the storage of energy so generated and interconnecting the energy generating elements, storage and load. 
       3. RELATED ART 
       [0003]    One type of radio communications system is a cellular communications system. In a cellular communications system, the area over which service is provided is divided into a number of smaller areas called cells. Typically each cell is served from a base transceiver station (BTS) which has a corresponding antenna or antennas for transmission to and reception from a user station, normally a mobile station and a backhaul connection for routing of communications to a fixed switching centre for onward transmission to fixed user terminals or other communications networks. Presently established cellular radio communications systems include Global System for Mobile communications (GSM), Code Division Multiple Access (CDMA), Worldwide Interoperability for Microwave Access (WiMAX), and also the Universal Mobile Telecommunication System (UMTS). 
         [0004]    Such base transceiver stations and their associated equipment require electrical power to operate. Typically this power has been provided by connection to an electrical grid, or in cases where this is not available connection to a standalone diesel generator. More recently power generated from renewable means such as wind turbines or to photovoltaic (PV) arrays has been used as an alternative to diesel generators for sites without a grid connection. 
         [0005]    While this offers considerably advantages in operational costs over a diesel generator their performance is very dependant on the prevailing weather conditions and significant energy storage is required to provide a reserve for periods of low renewable energy generation. The disadvantage with these systems is that in order to provide the high level of power availability required for reliable operation of a radio communications system the size of both the generation equipment and the storage capacity has to be considerably increased over that of a system that is not required to provide continuous power. 
         [0006]    Renewable energy generators such as wind turbines and PV arrays require electronic control systems to regulate their performance and to ensure that batteries used for energy storage are charged according to the correct profile for the size, type of cell technology employed in the battery, and environmental factors such as temperature. Whilst PV controllers exist that perform this function, when a wind turbine and PV system are combined together the usual mode of operation is for the turbine controller to err on the side of under charging the batteries as its control is based on fixed voltage level thresholds that do not take account of battery condition or temperature. When these thresholds are exceeded, dump loads are switched in to dissipate excess energy and to prevent damage occurring to the battery by charging it with too high a current. The use of fixed thresholds for controlling dump loads is wasteful of energy and can lead to the over sizing of both turbines and battery systems to compensate. 
         [0007]    In a system described above it is normal to provide a means of preventing the batteries from becoming deeply discharged or to prevent discharge below a certain defined state of charge to extend the batteries operating life. This is provided by a low voltage disconnect device that will remove all loads from the batteries when the batteries terminal voltage drops below a preset voltage threshold. Hysteresis is provided in the detection circuitry to prevent the loads reconnecting again until the battery is being recharged. This hysteresis is also of a preset, fixed value. The use of fixed thresholds for the control and switching of loads offers none of the flexibility required to permit the most efficient implementation of a renewable energy powered telecommunications system. 
         [0008]    Present control systems do not permit the automatic, selective operation of disconnect devices to remove loads of a specific type for the purpose of prolonging the operation of a higher priority load, thereby permitting the use smaller batteries. Neither do existing systems permit an operator to remotely command a disconnect device to remain connected, to override a low voltage disconnect, and provide additional reserves of power under exceptional circumstances should it be required. 
         [0009]    Existing systems have no means of receiving predicted weather data or correlating such weather data with the local micro climate to predict the availability and quantity of renewable energy at the site. Neither do they accurately determine the state of charge of batteries and use this data together with the energy prediction data to control the loads to within the system, either by variable power control or by means of selective disconnection and reconnection. Existing systems do not permit communications between the telecommunications equipment and the system controller for the purpose of power control or the passing of data, monitoring and alarm information. 
         [0010]    Due to the failings mentioned above it is also not possible to obtain the most efficient use of a fossil fuelled backup generator, both in fuel usage and service maintenance intervals. 
         [0011]    Existing systems do not offer dual or N+1 redundancy of critical components in the renewable energy components, for example splitting individual PV panels between multiple PV controllers for the purpose of failure tolerance. Neither are critical components that ensure reliability of supply to the telecommunications equipment duplicated to ensure the highest levels of reliability. Although multiple strings of batteries are occasionally used in such systems they are not configured to permit the automatic removal and testing of an individual battery string or the automatic removal of a battery string that has developed a fault. 
       SUMMARY 
       [0012]    The present invention addresses some or all of the above disadvantages. 
         [0013]    According to one aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources, managing the storage of energy so generated and interconnecting the energy generating elements, storage and load. 
         [0014]    According to another aspect of the present invention, there is provided a method of receiving weather forecast data and using said data to predict renewable energy availability at a site for the purpose of connecting, disconnecting or controlling the power consumption of loads connected to a battery. 
         [0015]    According to another aspect of the present invention, there is provided a method of more efficiently controlling a fossil fuelled backup generator by overriding or delaying the operation of said fossil fuelled generator to recharge a battery if predicted weather data indicates that renewable energy will become available within an acceptable timeframe. 
         [0016]    According to another aspect of the present invention, there is provided a method to conserve generator fuel and extend generator servicing intervals by delaying a scheduled generator maintenance running period, that may be required to preserve generator condition and starting capability, such that it occurs when weather data is predicting low renewable energy availability and a battery is in a reduced state of charge. 
         [0017]    According to another aspect of the present invention, there is provided a plurality of independent disconnection devices that are controlled by an algorithm that uses voltage levels, battery charge status, a real time clock, predicted renewable energy availability and operator remote commands to control said devices. 
         [0018]    According to another aspect of the present invention, there is provided a control system that can dynamically vary the disconnection thresholds of one or more disconnect devices to remove power load from a DC bus to make available a greater proportion of energy to one or more specific loads that may remain connected. This may specifically include the disconnection of a base station to make available a greater proportion of battery energy to backhaul communications equipment. 
         [0019]    Further aspects of the invention are as claimed in the dependent claims. Additional specific advantages are apparent from the following description and figures which relate to a merely exemplary embodiment of the present invention. 
         [0020]    The present invention is applicable to, but not limited to, radio communication systems such as the Global System for Mobile communications (GSM), Code Division Multiple Access (CDMA), Worldwide Interoperability for Microwave Access (WiMAX), and also the Universal Mobile Telecommunication System (UMTS). 
         [0021]    According to another aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources, which operates to maximise the power transfer from a wind turbine to a battery by automatically varying the threshold levels at which turbine dump loads are switched based upon system inputs and measurements. 
         [0022]    According to another aspect of the present invention, there is provided an apparatus which varies the threshold levels at which turbine dump loads are switched according to the precise state of charge of the battery and the usage pattern of the battery preceding the charge period. 
         [0023]    According to another aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources that can communicate with a remote device to obtain weather forecast data for the purpose of predicting future renewable energy generation capability. 
         [0024]    According to another aspect of the present invention, there is provided an apparatus which correlates local micro climate conditions with forecasted weather data for the purpose of predicting future energy availability. 
         [0025]    According to another aspect of the present invention, there is provided an apparatus that uses predicted renewable energy availability for the purpose of connecting, disconnecting or controlling the power consumption of loads connected to a battery. 
         [0026]    According to another aspect of the present invention, there is provided an apparatus that can override or delay the operation of a fossil fuelled generator to recharge a battery if predicted energy data indicates that renewable energy will become available within an acceptable timeframe. 
         [0027]    According to another aspect of the present invention, there is provided a method to conserve generator fuel and extend generator servicing intervals by delaying a scheduled generator maintenance running period, that may be required to preserve generator condition and starting capability, such that it occurs when renewable energy availability is predicted to be low and a battery is in a reduced state of charge. 
         [0028]    According to another aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources that has plurality of disconnect devices to allow independent disconnection of individual loads from a DC bus according to an algorithm that uses voltage levels, battery state of charge, time and override command. 
         [0029]    According to another aspect of the present invention, there is provided an apparatus that uses the measure of battery state of charge for the purpose of connecting, disconnecting or controlling the power consumption of loads connected to a battery. 
         [0030]    According to another aspect of the present invention, there is provided an apparatus wherein one or more said disconnect devices can have their operating thresholds adjusted to remove power load from a DC bus to make available a greater proportion of energy to one or more specific loads that may remain connected. 
         [0031]    According to another aspect of the present invention, there is provided an apparatus that that may dynamically vary the disconnection threshold of a disconnect device controlling a base station to make available a greater proportion of battery energy to backhaul communications equipment. 
         [0032]    According to another aspect of the present invention, there is provided an apparatus that can be commanded to override the normal operation of battery protection disconnect devices to provide additional operational power under an emergency condition. 
         [0033]    According to another aspect of the present invention, there is provided an apparatus that can communicate with telecommunications equipment to command said equipment to reduce its power consumption. 
         [0034]    According to another aspect of the present invention, there is provided an apparatus whereby a communications system comprises two BTSs, one providing BCCH carriers and a second with additional capacity, that can exercise power control by disconnecting the second BTS. 
         [0035]    According to another aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources that has a plurality of PV arrays and individually switched and controlled PV controllers to offer redundancy of power supply in the event of a PV array or PV controller failure by disconnecting the failed device from the remainder of the functioning system and communicating the failure to the system controller. 
         [0036]    According to another aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources that has a plurality of contactor devices to offer redundancy of power connection in the event of a contactor or central controller failure. 
         [0037]    According to another aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources that has a plurality of batteries to offer redundancy of battery power in the event of a fault within an individual battery string. 
         [0038]    According to another aspect of the present invention, there is provided an apparatus that has a plurality of batteries to permit automatic, periodic removal and capacity measurement of an individual battery string without interruption of normal operation. 
         [0039]    According to another aspect of the present invention, there is provided an to apparatus that has a plurality of batteries to permit battery replacement at the batteries end of life without affecting the normal operation of the communications equipment. 
         [0040]    According to another aspect of the present invention, there is provided An apparatus for controlling and monitoring the generation of electrical energy from renewable sources that has redundant contactors to improve reliability for the switching of safety devices such as mast warning lights to assist in aircraft collision avoidance. 
         [0041]    According to another aspect of the present invention, there is provided an apparatus that controls redundant contactors for the switching of safety devices, such as mast warning lights used to assist in aircraft collision avoidance, continue to receive power when other system loads have been disconnected. 
         [0042]    According to another aspect of the present invention, there is provided an apparatus for controlling and monitoring the generation of electrical energy from renewable sources that has a plurality of individually switched and controlled wind turbines to offer redundancy of power supply in the event of a turbine failure by disconnecting the failed device from the remainder of the functioning system and communicating the failure to the system controller. 
         [0043]    Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the figures, like reference numerals designate corresponding parts throughout the different views. 
           [0045]      FIG. 1  is an exemplary illustration of a radio communications site powered by renewable energy generated by a wind turbine and photovoltaic array, containing a supervisory system controller for monitoring and controlling the system according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    The embodiment hereinafter described relates to a renewable energy powered storage system for powering radio communications systems. 
         [0047]    In  FIG. 1 , the components contained in the dotted box represent a Supervisory System Controller  100 . A software enabled system controller  101  has a control interface  115  for the control of interconnect and switching of externally housed batteries  105  and turbine dump loads  106 . Control is also provided to switch mast warning light contactors  120  for the supply of power to aircraft warning lights  125  mounted on the radio mast  119 , backhaul equipment contactors  121  for the supply of power to backhaul equipment  124 , and Base Station contactors  122  for the supply of power to the Base Station  118  from a DC bus  114 . 
         [0048]    The system controller  101  also possesses a generator control interface  109  to permit the start and stop control of an optional generator  102  and also to receive status information from the generator if one is present. A maintenance interface  110  is provided to permit the connection of a local maintenance terminal  112  for the purpose of software upgrades, changing site control parameters and the monitoring of system performance data. A security interface  111  is provided for the connection of site security monitoring devices  113 . The SSC management interface  116  provides connection to a remote maintenance terminal  117  for the provision of remote access to the controller for software upgrades, changing site control parameters and the monitoring of system performance data. 
         [0049]    A BTS signaling interface  123  is provided to permit two-way signalling between the SSC and the base station  118  for the purpose of base station power control and the reporting of status and alarms. 
         [0050]    The SSC  100  has provision for the connection of a PV array  103  via one or more PV controllers  108  and for the connection of a wind turbine  104  to the DC bus  114  via interconnect and switching  107 . 
         [0051]    Under normal operation the SSC  100  will manage the renewable energy power from the PV array  103  and wind turbine  104  to maintain power to the system loads of the base station  118 , backhaul equipment  123 , mast warning lights  119 , and to charge the batteries  105 . The PV controllers  108  control all aspects of battery charging from the PV array  103  to prevent over charge when surplus power is available from this source. When surplus power is available from the wind turbine  104  one or more of the dump loads  106  are switched on to dissipate the excess energy and prevent overcharge of the batteries  105  for the duration of the excess power being available. The voltage thresholds at which these loads are switched on and off are dynamically controlled based on the state of charge of the battery  105  to improve the capture of turbine power. 
         [0052]    When insufficient power is available from renewable sources the system loads take their power from the batteries  105  which are sized to maintain normal operation for a specified period of time. When renewable power becomes available again the system will revert to normal operation as described above. 
         [0053]    The system controller  101  can receive weather forecast data from the remote maintenance terminal  117  which it uses to efficiently manage the power system. In a system that does not have a generator  102 , if renewable energy is not available and the forecast is not predicting renewable energy becoming available in the required timescale, the SSC can implement a number of power saving options to maximise the system&#39;s operating time. The SSC  100  can command the base station  118  to implement any power reduction features that it may possess such as turning off non-BCCH transceivers. The SSC  100  can also disconnect the base station  118  via the contactors  122  during off-peak times, such as at night, to conserve battery power for the periods of maximum demand. For remote sites carrying little or no night time traffic, a controlled nightly shut down can give considerable savings in required energy generation elements and battery capacity. 
         [0054]    Another option available to conserve power is to configure two, lower power base stations onto one site in place of one larger capacity base station and configured so one base station provides the BCCH carriers and the second one peak hour capacity. The SSC  100  can then exercise power control by disconnecting the second base station from the battery at off-peak times or as remotely commanded by the operator. 
         [0055]    Ultimately, if no renewable power becomes available, the system controller  101  will perform a low voltage disconnect, where it commands the contactors  120 ,  121  and  122  to disconnect their respective loads from the DC bus  114  to prevent the battery  105  from discharging to a level where it will sustain damage. 
         [0056]    In a system that does have a generator  102 , if renewable energy is not available and the forecast is not predicting energy becoming available in the required timescale, the SSC  100  can start the generator  102  and this will provide power to the system loads and also to charge the battery  105 . Once the battery is charged, or renewable energy is forecast to become available in the required timescale, the SSC  100  will stop the generator  102  to conserve fuel. Similarly, if generator usage is low and a generator maintenance run is required to preserve generator condition and starting capability, the SSC  100  can automatically schedule this to occur at a time when the battery capacity is reduced and weather data is predicting low renewable energy availability. This ensures the energy produced during the generator maintenance run will be absorbed by the battery and is not wasted. 
         [0057]    The SSC can also inhibit a low voltage disconnect and postpone a generator start for a short period of time if renewable energy is predicted to become available but after the normal low voltage disconnect point for the load. This offsets a generator start against occasionally running the battery to a slightly lower state of charge but conserves fuel and extends generator service intervals. 
         [0058]    In some situations the backhaul equipment  124  links on to provide connection for routing of communications for other base station sites to a fixed switching centre for onward transmission to fixed user terminals or other communications networks (daisy chaining) In the event of the system controller  101  determining there insufficient power being available to operate the radio site continuously, it is desirable to provide a longer period of battery operation to this backhaul equipment than to the site base station  118 . The SSC  100  can independently control how long each load will remain connected to the dc bus  114 . By disconnecting the base station  118  after a predetermined time period the SSC  100  will reduce the power load on the battery and so extend the time backhaul equipment  124  can operate before the battery  105  becomes discharged to the point where a low voltage disconnect will occur. The SSC has the ability to vary the operating time of the base station  118  to increase or decrease the operating time of the backhaul equipment  124 . 
         [0059]    In the event of the energy sources sustaining damage, and power generation becoming limited or unavailable, an operator can remotely command the SSC  100  to disconnect base station  118  power immediately in the interest of maintaining communications in the remainder of his network for a much longer period. The SSC  100  also has the option to override one or more of the low voltage disconnects to power the base station and/or the backhaul equipment to provide additional operating time at the expense of potentially damaging the batteries by deep discharge. This feature would only be exercised in extreme conditions where the potential cost of replacement batteries is considered acceptable to meet the operational need, for example, in the event of a natural disaster where life may depend upon working communications. 
         [0060]    High levels of reliability and availability are achieved by configuring the PV array  103  to be split between multiple PV controllers  108 , such that a failure in one PV controller  108  will not remove all of the available solar power to the SSC  100 . The SSC also employs dual redundant low voltage disconnect components,  121 ,  122 , to ensure that a contactor failure will not remove a load from the battery. The battery  105 , may also be configured as two or more strings of cells to permit automatic, periodic removal and capacity measurement of one battery string whilst the system continues to operate from the remaining battery string(s). The use of multiple battery strings also permits the removal of an individual battery string in the event of a fault within an individual cell whilst maintaining operation from the remaining battery string(s). Additionally it facilitates the replacement of the batteries at end of life without the need to take the site off air. 
         [0061]    While various embodiments of the invention have been described, it will be apparent to those of ordinary skill in the art that many more embodiments and implementations are possible that are within the scope of this invention. In addition, the various features, elements, and embodiments described herein may be claimed or combined in any combination or arrangement.