GB2421127A

GB2421127A - Power supply system having energy conversion unit and central control unit

Info

Publication number: GB2421127A
Application number: GB0427275A
Authority: GB
Inventors: Jens-Otto Ravn Andersen; Jan Nielsen
Original assignee: EC Power AS Norway
Current assignee: EC Power AS Norway
Priority date: 2004-12-13
Filing date: 2004-12-13
Publication date: 2006-06-14
Anticipated expiration: 2024-12-13
Also published as: GB0427275D0; WO2006064214A1; GB2421127B; RU2355091C2; EP1829181A1; CN101120497A; RU2007123529A

Abstract

A method of operating a power supply system comprising a central control unit 5 and an energy conversion unit 2. The central control unit has access to operating parameters of the energy conversion unit and is arranged to receive a power request from a consumer 1, determine the amount of power the energy conversion unit should produce and to issue a power request. In response to the power request the energy conversion unit responds to the central control unit indicating the amount of power it can produce. The energy conversion unit may have an energy conversion unit controller 8 associated with it. More than one energy conversion unit may be connected to, or in communication with, the central control unit (see figure 2). The energy conversion unit controller may transmit status information, relating to its associated energy conversion unit, to the central control unit. The energy conversion unit may be a CHP unit and/or a fuel cell.

Description

Power Supply Control Apparatus The present invention relates to a control

apparatus for controlling energy conversion units and in particular for controlling combined heat and power (CHP) units.

Combined heat and power units are used in various applications ranging from domestic applications, such as in the home, to larger scale applications such as factories, hospitals and the like. A CHP unit in its basic form typically comprises an internal combustion engine (I.C.) mechanically coupled to an electrical generator. As the engine operates heat is generated which is removed from the cooling circuit of the engine and used to heat radiators whilst electricity generated by the generator is used to power electrical appliances.

A CHP unit can thereby provide both electricity and heating for an installation from a single source local to the consumer or user.

A typical installation of such a system may comprise a plurality of energy conversion units. It may be desirable to be able to combine varying types of power sources for an individual site or installation.

In addition, it may also be desirable to be able to change the capacity or even type of energy conversion unit for a given installation. For example, a consumer may want to change a energy conversion unit from a 20kW diesel powered CHP unit to a 45kW gas powered generating unit as the power requirements of an installation change.

Existing power supply systems, particularly for use with combined heat and power systems, do not provide any flexibility or adaptability for users. There is therefore a need for a power supply control system capable of overcoming the problems associated with existing systems.

Thus, viewed from a first aspect there is provided a method of operating a power supply system comprising a central control unit and an energy conversion unit, the central control unit having access to data indicating operating parameters of the energy conversion unit, wherein A) the central control unit receives a power request from a consumer indicating a power demand, B) in response to the power request the central control unit determines, based on the data, the amount of power the energy conversion unit should produce, C) the central control unit communicates a corresponding power request to the energy conversion unit; and D) in response to the power request the energy conversion unit responds to the central control unit indicating the amount of power it can produce.

Thus, the present invention provides a power supply control system in which the central control unit can control different energy conversion units irrespective of type or capacity so as to meet the demands of a consumer. Furthermore, the energy conversion units can be replaced or upgraded without the need to adapt or change the central control unit.

Still further, the present invention allows for the operation of a system having a plurality of electrical and/or heat generating units each being controlled by a common central control. unit. For example, a power supply system may comprise a CHP unit and a boiler.

The term power request is intended to refer to an indication received by the central control unit indicating the power which is being or is to be consumed by the user. For example, the request may be in the form of a signal issued from the consumer for power or may be an indication received from a consumption meter measuring the power consumption of the consumer.

It can be seen that a controller according to the present invention can control a plurality of energy conversion units which need not be the same. For example, a single or plurality of CHP units may be controlled by the central controller together with a boiler, heat pump or other heat only energy conversion unit. Alternatively, the controller may control one or more heat generating units and at least one CHP unit.

Thus, in this way the electrical and heating demands of a user carl be met.

Furthermore, the present invention can also keep maintenance costs down since the energy conversion units can be changed without the need to adapt the central control unit and the system can be controlled to operate in the most economical way. These are important considerations for CHP units which have to compete with other energy conversion units such as boilers and the like which have no moving parts and which are therefore extremely reliable.

The energy conversion unit may in fact be any unit capable of supplying all or part of the power required by the consumer. The energy conversion unit may be any suitable prime mover including a fuel cell. Preferably, the energy conversion unit is a combined heat and power unit capable of generating heat and electricity. This may, for example, be an internal combustion engine connected to an electrical generator and to a heat exchanger.

Alternatively, the energy conversion unit may supply only electricity or only heat. For example, the energy conversion unit may be a heat pump or boiler arranged to supply heat in the form of hot water or steam.

The energy conversion unit may alternatively be in the form of an energy consuming unit such as an electrical load. Thus, excess electricity can be consumed when only heat is required by the installation.

The system may comprise a single energy conversion unit or may comprise a plurality of units each arranged to provide power to the consumer and each arranged to receive power request signals from the central control unit.

Preferably, each of the energy conversion units is provided with a local control arrangement arranged to control the specific energy conversion unit. There is thereby provided a two-level control arrangement, the first level being control between the central control unit and the local control unit and a second level being local control of the energy conversion unit by the local control arrangement using energy conversion unit specific instructions and commands.

The central control unit may issue power generation requests to each of the energy conversion units in a form specific to each energy conversion unit.

Preferably, the central control unit will issue power generation requests in a energy conversion unit independent format i.e. a common format for all energy conversion units. The format of the power request signals may be an industry standard protocol or a protocol compatible with existing manufacturers' products such that the control unit can be used in conjunction with existing equipment.

The power generation requests may be in the form of requests to switch on or switch of an energy conversion unit. For example, the energy conversion unit may be a heat pump or the like which can be activated or deactivated by a request from the central control unit.

In this arrangement the energy conversion unit can be controlled directly by the central control unit.

Preferably, the power generating requests are received by an energy conversion unit controller associated with each energy conversion unit. The energy conversion unit controller (hereinafter referred to as a local controller' or local control unit') is preferably arranged to control the operation of the energy conversion unit in response to requests from the central control unit.

Thus, viewed from another aspect, an invention disclosed herein provides a power supply apparatus comprising a central control unit and at least one energy conversion unit having an energy conversion unit controller associated therewith, wherein the central control unit is arranged to issue power generation requests to each of said energy conversion units in a format common to all energy conversion units and wherein each of said energy conversion unit controllers is arranged to control the associated energy conversion unit in response to said requests.

In this way the central control unit can issue requests to one or more energy conversion units using a unit independent format or protocol. The local control unit can, in turn, control individual energy conversion units in response to the requests using unit specific instructions. It is thereby possible to increase the number of energy conversion units within the system without changing the central control unit.

The central control unit may be located on the same site as the installation and energy conversion units or may, alternatively, be located elsewhere. For example, the installation and energy conversion units may be arranged to communicate with the central control unit via a local server, router and wide area network. Thus, the central control unit may be located at a central control centre which may be in the same country as the installation or overseas. Thus, the power supply to the installation and control of the individual energy conversion units can be controlled and administered remotely from the installation and may be administered by a third party. Preferably however the central control unit is located near to the installation.

The term consumer is used herein to mean an installation having an energy load such as a shop/factory/house or the like having a heat arid or electrical demand. References to requests from the consumer include the switching on or off of electrical and/or heating appliances and may be by manual or computer based control.

The installation may be a single location (e.g. a single building) or, alternatively, may be a distributed installation having more than one location (e.g. a number of buildings).

The installation may he arranged to receive power from each of the energy conversion units independently.

For example, the installation may have a conduit connecting each of the energy conversion units to the installation so as to receive heat in the form of hot water or steam. Similarly, the installation may be arranged to receive electricity via conductive cables directly connecting the installation to each of the energy conversion units.

Preferably, the energy conversion units are arranged to supply power to a common supply connecting the energy conversion units to the installation. For example, heat may be supplied to a common store, pipe or conduit carrying hot water or Steam. Similarly, electricity may be supplied from the energy conversion units to the installation by a ring main or loop connecting all parts of the installation having an electrical demand. This thereby simplifies the supply network and provides flexibility in adding additional locations, installations and also energy conversion units to the network or system.

The energy conversion units may be provided with a common heat store arranged to receive heat generated from each unit to a common store such as a tank.

Alternatively, there may be a plurality of heat stores each associated with one or more of the energy conversion units and arranged to receive heat therefrom.

Similarly, the installation or distributed installations may be arranged to receive heat from one or more of the heat stores.

The heat store(s) may be provided with a heat controlling unit arranged to communicate with the central control unit and with the energy conversion units. The heat controlling unit may for example be arranged so as to communicate information to the central control unit indicating the status of the heat store(s) This information can thus be used by the central control unit in determining the operational strategy of the energy conversion units.

Alternatively, each of the energy conversion units may be provided with a heat controlling unit associated with that energy conversion unit.

The central control unit preferably receives indications of the power required by the installation (the power demand) from sensors located at the installation. For example, the installation may be provided with an electricity meter to sense electrical demand and the central control unit may be arranged to receive a signal from the electricity meter. Similarly, the installation may be provided with thermostats indicating the thermal needs of the installation.

Preferably, the central control unit is arranged to only receive an indication of the electrical demand of the installation and matches electrical supply to the electrical demand. The thermal demand of the installation is preferably matched by supply from the heat store(s) . Thermal demand may, for example, be met using thermostatic valves connected by conduits to the common heat store. The thermal demand of the installation can thereby be met automatically with no control from the central control unit.

Power demand information received by the installation may indicate instantaneous demand information or a prediction or schedule of expected demand. For example, the central control unit may be provided with a schedule of power requirements over a 24 hour period.

The central control unit may determine, based on demand, to operate particular energy conversion units or to select a particular combination of energy conversion units operating at a particular output level.

Furthermore, the central control unit may operate the energy conversion units so as to match a particular electrical or heating demand. For example, the central control unit may operate the energy conversion units S according to an expected (that is predicted) heating and or electrical demand by, for example, filling the heat store(s) Power demand information may be received constantly i.e. in real time, at intervals or alternatively only when there is a change in demand. The information may be provided automatically from a reference or consumption meter at the installation or may be provided manually to the central control unit by a user. Where the installation is in the form of a number of locations then the central control unit may be arranged to receive indications from each location and may be arranged to sum the demands.

Communication between the central control unit and the installation may be physical. For example, there may be an electrical connection connecting the central control unit to the installation (and to each location thereof) . The connection may for example he a local area network or the like. Alternatively, communication between the central control unit arid the installation may be by means of a wireless communication system.

The power demand information may be stored on a hard disk within the central control unit, and/or may be stored on solid state random access memory (RAM) or other form of storage within the central control unit.

In general, the central control unit may be in the form of, or similar to, the processing unit of a personal computer, having read only memory (RaM) , RAM, a microprocessor, a bulk storage device such as a hard disk drive and so forth. There may be ports for - 10 - attaching a keyboard or other input device. The central control unit is preferably provided with a user interface including a visual display and input device allowing the user to monitor and control the central S control unit.

The central control unit may alternatively be in the form of a programmable logic controller (PLC) or other suitable control arrangement. Similarly, the local control unit may be any suitable control arrangement.

The central control unit may also preferably be provided with an external communication interface and arranged to receive additional information from external sources. This information may include fuel price information, electricity market price information, weather information, geographical fuel tax information, servicing information etc. This information is preferably stored by the central control unit and may be received from a number of different sources and accessed, for example, over a wide area network (WAN) The communication interface may be linked to hubs, switches and routers as desired and may communicate with a local server, through that server to a remote server, or through a router and a suitable wide area network with a remote server.

Communication may be one-way i.e. the central control unit may only be arranged to receive information. Alternatively, communication may be twoway i.e. the central control unit may issue requests for information and then receive information from the external information source.

information may alternatively, or additionally, be received via direct communication with a utility company - 11 - or service provider or from a central server or database.

The central control unit may further be arranged to communicate with an external service provider such as a maintenance provider by one or twoway communication using any suitable protocol. The central control unit may be arranged to communicate information indicating the instantaneous status of the energy conversion units and/or historical status information.

The central control unit is preferably arranged to communicate with each of the energy conversion units.

Communication between the central control unit and the energy conversion units may be one-way such that the energy conversion units only receive power production requests from the central control unit. Preferably, the communication is two-way such that the energy conversion units can return information back to the central control unit in response to the power production requests.

The central control unit may communicate with the or each of the energy conversion units in the same way that the central control unit communicates with the installation. For example, communication between the central control unit and the energy conversion units may be physical i.e. there may be an electrical connection connecting the central control unit to each of the energy conversion units. The connection may for example be a local area network or the like or, dial-up connection, mobile phone connection (e.g. GSM) each using suitable hardware e.g. modems. Alternatively, communication may be by means of a wireless communication system such as by radio, WiFi or the like.

Communication between the installation and central control unit and central control unit and energy - 12 conversion units (and any other component of the system) may be by means of any suitable communication protocol such as, for example, RS-485, CAN or TCP/IP.

The central control unit is preferably arranged to receive information indicating the performance characteristics (hereinafter referred to as unit specific data') for each of the energy conversion units.

This may be communicated to the central control unit from each of the energy conversion units or may be provided by the user by means of a user interface connected to the central control unit. Alternatively, the information may be preprogrammed into the central control unit or may be received from an external source such as, for example, the manufacturer or maintenance/service provider.

The unit specific data preferably provides the central control unit with information relating to the type and performance of each of the energy conversion units. This information is preferably stored within the central control unit.

The unit specific information may include - the type of power which the unit can produce eg.

heat, electricity or both.

- the maximum arid minimum operating capacities of the unit e. g. in terms of kw1 and/or kw - the type of fuel which the unit requires e.g. diesel, natural gas, electricity etc. - fuel consumption data indicating fuel consumption levels for specific electrical/heat loads (this may, for example, be in the form of an algorithm or look-up

table)

- service intervals required for each unit and hours to next service. 13 -

- the operational life of the unit.

The central control unit preferably receives the power request information (from the installation) and the unit specific information (from the energy conversion units) and processes the information to determine the most appropriate energy conversion unit or combination of units from which to request power. In effect the central control unit determines an operational strategy preferably comprising a load sharing strategy' to share the power load requested by the installation across the energy conversion units.

The load may for example be spread equally across all units or may, alternatively, be split between a combination of units.

The central control unit preferably determines the operational strategy and load sharing strategy so as to meet the power request of the installation in the most efficient way using the energy conversion units available.

The energy conversion units receive the power generation request and preferably return a response signal indicating if the request can he met. The response may, in its simplest form, be the production of the power requested by the central control unit (for example where the energy cor1version unit is a heat pump or the like with no local control unit) . if the request cannot be met the energy conversion un1it may respond indicating the amount of power which can be supplied.

The response signal is preferably used by the central control unit to adapt the strategy accordingly. Thus, the central control unit can adapt the strategy according to responses from the energy conversion units so as to maintain an uninterrupted and efficient supply of power to the installation.

- 14 - The responses received from the energy conversion units is preferably communicated to an external party such as, for example, a maintenance provider.

S

The operational strategy is preferably determined using the specific power needs of the consumer (in terms of heat and electricity) and the unit specific information. For example, the central control unit may determine hOW to share the load between generating units (that is the proportion of power to be generated by each unit) based on the efficiency of each unit for the type of power and the power level requested by the installation.

The central control unit may also be arranged to receive updates or additional information indicating changes in the efficiency or power generating capacity of each of the energy conversion units. This may be received continuously, at regular time intervals or as and when the efficiency of each unit changes.

The central control unit may thereby compensate for changes in efficiency and alter the operational strategy accordingly.

Thus, the central control unit can determine a strategy using the most efficient combination off energy conversion units to meet the power demands of the installation.

The central control unit may be arranged to receive further information from the energy conversion unit(s) relating to the status of the unit. For example, the energy conversion units may communicate fault information or service requests in addition to, or in combination with, the response to the power demand - 15 - request received from the central control unit.

The local control arrangement may for example determine that a service is required and may issue a service request signal to the central control unit.

Viewed from another aspect, an invention disclosed herein provides a control apparatus comprising a central control unit and at least one energy conversion unit having an energy conversion unit controller associated therewith, wherein the energy conversion unit controller is arranged to determine status information relating to the energy conversion unit and to communicate signals to the central control unit indicating the status of the unit.

Such status information may include requests for service or maintenance or may indicate malfunctions.

The energy conversion unit controller (the local control arrangement) is preferably arranged to control and monitor the energy conversion unit and to determine maintenance requirements and/or fault conditions for the subcomponents of the unit. For example, the local control unit may issue a signal to the central control unit indicating a problem or malfunction or may issue requests for servicing or maintenance.

The central control unit may be arranged to issue corresponding requests to the user. Preferably, the central control unit issues requests directly to external sources such as, for example, maintenance providers. Maintenance of the energy conversion units can thereby be requested without the intervention of the user and, furthermore, can be planned so as to cause the minimum of inconvenience or disruption to the user e.g. by scheduling maintenance at periods of low demand.

- 16 - The local control arrangement may further be arranged to determine the efficiency of the energy conversion unit and to communicate this information to the central control unit.

The central control unit may use this information to schedule services, maintenance or outages for the individual units. Alternatively, the central control unit may communicate information received from the energy conversion units, for example efficiency information, to an external party e.g. a maintenance provider via a wide area network or the like.

The operational strategy is preferably determined by the central control unit so as to minimise the cost of operating the energy conversion units to meet the power demands of the installation. This may for example be by minimising the fuel costs of meeting demand.

Alternatively, the operational strategy may be determined by a strategy provided to the central control unit. For example, the central control unit may be provided with a strategy defining when particular energy conversion units should or should not be used or may be provided with parameters (e.g. hours of the day) during which particular energy conversion units can or cannot be used.

The central control unit may be arranged to determine, based on the unit specific information for each of the generating units and fuel price information, the cost in monetary terms of running each of the individual energy conversion units. The central control unit can thereby determine the most efficient way to share the load not just in terms of fuel used by the energy conversion units but also in monetary terms.

- 17 - Thus, the total cost of meeting the power demands of the installation can be minimised.

The central control unit may further be provided with maintenance intervals and maintenance costs for each of the energy conversion units. This may also be used in determining the operational strategy.

The central control unit may still further be Jo provided with information relating to the external market price of electricity or pool price' (that is the cost. of purchasing electricity from the local electricity grid or network) . The central control unit may further be arranged to compare the cost of meeting the installation's power demands using the power generation units and the cost of purchasing the equivalent electricity from the grid and to adapt the strategy accordingly.

The installation is preferably arranged to selectively receive power directly from the grid such that if the central control unit determines that it is more economical to purchase electricity, then the installation can receive part or all of its power demand from the grid. The installation may be connected to the grid via a suitable switch, relay or switchgear, the switch, relay or switchgear being controlled by the central control unit.

Similarly, the central control unit may be provided with information relating to the price at which the external electricity network or grid will purchase electricity. The central control unit may be arranged to issue power production requests to the energy conversion units such that power, normally in the form of eLectricity, can be sold to the grid. The central control unit can thereby generate a revenue for the - 18 consumer if and when there is spare power production capacity.

The central control unit may further be arranged to S receive data indicating the operational characteristics and/or status of the components or units consuming energy within the installation and further may be provided with means to issue power consumption requests to the energy consuming units. An energy consuming unit (such as a freezer for example)may further be provided with a local control arrangement arranged to communicate with the central control unit arid arranged to control the energy consuming unit in response to requests.

Thus, in this way the central control unit can adapt the operational strategy to match demand with supply as well as supply with demand by issuing consumption requests to the energy consuming units.

Specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which Figure 1 shows a first embodiment of the present invertjori comprising a single energy conversion unit.

Figure 2 shows a second embodiment of the present invention comprising a plurality of energy conversion units.

Figure 3 shows a common heat store and heat control unit.

Figure 1 shows a first embodiment of the invention in which an installation receives power from a single energy conversion unit.

- 19 - In figure 1, the installation i requires power in the form of heating and electricity which are supplied by the energy conversion unit 2 which, in this embodiment, is a combined heat and power unit capable of S generating electricity and heating from a diesel internal combustion engine. The subcomponents of the CHP unit, that is the internal combustion engine, electrical generator, heat exchanger etc. are not shown.

The CHP unit 2 is arranged to provide electricity to the installation via conductive cables 3a and 3b and heat to the installation via conduits 4a and 4b. In operation the cables 3a and 3b provide an electrical circuit between the electrical generator and the electrical load in the installation. Similarly, the heating conduits 4a and 4b provide a heating circuit connecting the heat exchanger of the CHP unit (not shown) to the heating circuit of the installation e.g. radiators.

Figure 1 also shows the central control unit 5 which receives a power demand indication from the installation i on communication line 6.

Communjcatioi line 6 is connected to an electrical load meter within the installation which determines the instantaneous power demand (in the form of an electrical demand signal) of the building.

In the embodiment shown in figure 1, there is a single CHP unit 2 arranged to Supply the power needs of the installation. The central control unit is preprogrammed with performance data relating to the CHP unit 2 which is stored in RAM in the central control unit.

The central control unit receives the power demand - 20 - signal and forwards, via the central control unit's microprocessor and interface, a power request signal to the CHP unit on communication line 7. The CHP unit comprises a local controller 8 which is arranged to receive the power request signal. Local controller 8 comprises a microprocessor and is specific to the CHP unit. Upon receipt of the power request signal the local controller 8 determines if the power request can be met. If there is sufficient capacity the unit will control the diesel engine so as to match the demand which is then provided to the installation on lines 3a, 3b, 4a and 4b. If the CHP unit does not have sufficient capacity the local controller 8 will return a response signal to the central control unit 5 on communication line 7 indicating that the demand cannot be met together with information indicating why the demand cannot be met and the power level which can be supplied.

The central control unit 5 receives the response from the local controller 8 and stores the information received which can be used for fault diagnosis.

As an example, the dialogue between the installation the central control unit and CHP may be as follows Signal from Electrical Load Meter in Installation: "Electrical load = 15 kw111." Central Control Unit to CHP: "Please generate 15 kw11 CHP to Central Control Unit "Not possible. Reason - engine temperature high, flue gas heat exchanger malfunction. Can produce 10 - 21 - kW1 II The central control unit determines that the power production deficit is 5 kw10. In order to meet the demand in the embodiment shown in figure 1 (where only a single energy conversion unit is provided), the installation matches demand for electricity by receiving the remaining 5kw from the external grid 11.

In this example the heat generated as a consequence of running the diesel engine to match the electrical demand is fed to the installation on conduits 4a and 4b.

Thermostatic valves within the installatjoi (not shown) use the heat from the circuit formed from conduits 4a and 4b as required. The conduits 4a and 4b are connected to an internal heat store or tank within the CHP unit (not shown).

Where there has been a failure by the CHP unit to match the demand requested by the central control unit, the central control unit will record that there has been a failure to match supply and demand and stores the reason, as provided by the local control unit (in this example a flue gas heat exchanger malfunctioi) . This information is then forwarded to a maintenance provider who can monitor the unit and schedule a service. If the maintenance provider receives the information and determines that it is urgent they may arrange immediate servicing of the unit rather than scheduling a service.

In the embodiment described above (with reference to figure 1) there is a single power generation unit controlled by the central control unit. Any deficit in supply must therefore be provided by the external electricity grid 11.

- 22 - Figure 2 shows a second embodiment of the invention where the central control unit is arranged to control three independent generating units.

S In figure 2 there are 2 separate CHP units 21, 22, each capable of supplying electricity and heat to the installation 23. The first CHP unit 21 is powered by diesel and the second CHP unit 22 is by natural gas.

The third energy conversion unit 24 is a boiler arranged to supply heat only in the form of hot water. Boiler 24 is powered by electricity only. The CHP units 21, 22 are connected to a common electrical supply 25 and to common heating supply 26. Boiler 24 is connected to common heating supply 26 only. Common electrical and heating supplies 25, 26 are both connected to the installation 23.

As discussed with reference to figure 1, the central control unit 28 receives an indication from an electrical load meter of the electrical demand of the installation. This is received on communicatioii line 27.

In this embodiment central control unit 28 is connected by a local area network to each of the 3 energy conversion units 21, 22, 24 by communication line 29 (a local area network) . Central control unit 28 is also connected to a router 30 and wide area network to a maintenance provider 31 and to a utility company 32 (providing external electricity market prices) . The central control unit 28 is also provided with a user interface 33 arranged as part of the control unit.

In the embodiment shown in figure 2, the control unit is also connected to an external electricity power supply switch 34 by communication line 35 which allows the central control unit to selectively connect the - 23 external grid 36 to the installation 23. The switch 34 may be any suitable switching means such as a relay.

The system operates as follows The system is first initialised by connecting each of the energy conversion units 21, 22, 24 to the central control unit 28 via local area network communication line 29. A handshaking process takes place and information is provided from each of the energy conversion units to the central control unit listing the following energy conversion unit specific data i) the type of power which the individual unit can produce e.g. heat, electricity or both.

ii) the type of fuel which the unit requires e.g. diesel, natural gas, electricity etc. iii) the maximum and minimum operating capacities of the unit e.g. in terms of kWheat and/or kwiecti.ic iv) fuel consumption data indicating fuel consumption levels for specific electrical/heat loads (which may be in the form of an algorithm or look-up

table)

v) service intervals and hours to next service and the operational life of the unit.

This data is stored in a database in the RAN of the central control unit 28. The user inputs the current fuel prices for each of the fuels used by each of the power generation units (except electricity price - see below) using the user interface 33. This data is also stored in the database against the relevant energy conversion unit data.

In a load following mode of operation i.e. where the central control unit is arranged to match supply and demand the central control unit operates as follows: - 24 - The central control unit receives the power demand indication from the installation and interrogates the database of energy conversion unit data, fuel prices and S maintenance cost data and determines the most cost effective way of meeting the installationTs demands i.e. it determines the most efficient strategy. The central control unit then issues power production requests onto the communication line 29 for each of the energy conversion units. The power production requests are received by the local control units 21c, 22c and 24c associated with each of the energy conversion units 21, 22 and 24.

The local control units 21c, 22c and 24c are unit specific controllers and are arranged to control the operation of each of the energy converting units. For example, in a CHP unit the controller will be arranged to control the fuel and circulation pumps or the engine and to monitor the status of the sub-components of the CHP unit.

The power request signal is generic to all units and simply indicates the power that is requested from the unit. The local control unit receives the request and determine locally if the request can be met.. Each of the local control units is specific to its associated energy conversion unit i.e. it acts as a bridge between the generic signals from the central control unit and converts them to unit specific instructions.

The local control unit determines the current capacity of the individual energy conversion units and responds to the power request indicating if the request can be met. This is received and stored by the central processing unit.

- 25 - The following example illustrates a cycle in the control of the energy conversion units.

The central control unit receives a signal from an electrical demand meter in the installation requesting kWeiecricity. The central control unit compares the fuel prices and the operating costs of each unit (based on operating life, service interval and service cost data) and determines that the two CHP units 21, 22 should produce 1OkWietiity. The central controller issues power requests to the two units capable of producing electricity i.e. CHP units 21 and 22 which respond as follows: CHP Unit 21: 1 Okweictrcity ok CHP Unit 22: Can only produce 5 kwiecijv; reason: heat exchanger efficiency low, engine temperature high.

The central control unit then receives this information and redetermines the most efficient way to meet demand using the database information arid the new information The central control unit notes that the CHP unit 22 is malfunctioning and that its load should be reduced or removed altogether. Thus, the central control unit will issue a new power request increasing the request for production from CHP unit 21 to 15kweiectity. CHP unit 22 can then be requested to produce 5kwictricity It will be appreciated that in some circumstances the electricity provided by the CHP units could be used to power electrically powered energy conversion units such as boilers or heat pumps and the like.

- 26 - This process is repeated continuously, based on changes in demand from the installation and changes to data in the database to as to maintain the most S efficient production of power whilst meeting the demands of the installation.

In the example above, the central control unit will issue a maintenance request to the external maintenance supplier 31 together with the malfunction reason provided by the CHP unit 22. Maintenance can then be scheduled to repair the malfunctioning unit.

If the energy conversion units are unable to meet the demands of the installation then the central control unit is able to supplement the electricity produced by the units directly from the external electricity supply 36. In this situation electricity is supplied directly from the grid 36. Heat can be provided by powering boiler 24 with electricity from the grid 36.

The user interface 33 allows the user to monitor and control the central control unit and to adapt the central control unit strategy. For example, the user may instruct the central controller to adopt a load following strategy as described above. Alternatively, the user may instruct the central control unit to adopt an alternative strategy.

:30 Example 1

The user may instruct the central control unit to adopt a strategy of maximum operating life or maximum service intervals so as to maintain supply to the installation with the minimum of disruption. The control unit would then apply the strategy so as to use energy conversion units with the largest service - 27 - intervals whenever possible.

Example 2

The user may instruct the central control unit to S adopt a maximum monetary return strategy rather than a load following strategy i.e. matching supply with the installation!s demands. As shown in figure 2 the control unit also receives, from the external source 32 via router 30, the current market prices for buying and selling electricity from the external grid. This data is continuously downloaded and stored in the database so that the control unit has a constantly up to date value for buying and selling electricity. The central control unit then assesses the spare capacity of each of the energy conversion units and sells the surplus electricity back to the external grid 36 when a buy price is received from the utility company 32 which covers the cost of running the energy conversion units according to the database information. The spare capacity of the energy conversion units can thereby provide a financial return for the consumer.

Figure 3 shows a further arrangement of the present invention in which the system is provided with a common heat store and heat control unit.

Figure 3 shows two CHP units 301, 302 each generating electricity arid heat. As in figure 1 and 2, the CHP units are connected to central control unit by a communication line 304. Central control unit 303 is similarly arranged to receive an indication of electrical demand from the installation on communication line 306. In this arrangement the heat output from the CHP unit 301, 302 is directed to a common heat store by conduit 308. The electrical output from each CHP unit is connected directly to the installation 305 by - 28 - electrical connection 309.

The heat store 307 is connected to the installation 305 by conduit 310 and to a boiler 311 by conduit 312.

S The heat store is further provided with a heat store controller 313 which communicates with the central controller 303 using communication line 314.

As is known in the field of CHP system, a CHP unit

JO can only generate electricity when there is sufficient cooling capacity in the heat store. If the heat store is full i.e. it has reached its thermal capacity, then the CHP prime movers (internal combustion engines or the like) cannot operate since they would overheat. In the iS arrangement shown in figure 3 the heat generated by the CHP units 301, 302 is handled centrally by the heat store 307 and heat store controller 313 and not independently by the CHP units. Heat store controller 313 monitors the temperature of each of the CHP units via temperature signals received on communication lines 315, 316 and issues a signal indicating the status of the heat store to the central control unit 303 on communication line 314. The central control unit can thereby adapt the operational strategy according to the status of the heat store which, when used with a CHP units as an energy conversion unit, is essential for continued operation.

Three possible situations which may influence the operational strategy are as follows Situation 1: The heat store has not reached thermal capacity.

Normal operation can continue and heat can be generated as required.

- 29 - In this situation the heat store has capacity to receive heat which is produced above that required by the installation. The surplus heat can be stored in the heat store which has not yet reached full thermal capacity.

Situation 2: The heat store has reached thermal capacity. Stop CHP unit immediately. 1 0

In this situation the heat control unit 313 will issue a signal to the central control unit indicating the status of the store. Thus, even if the central control unit has determined that the most efficient way to meet demand will be to run the CHP units this part of the strategy will be adapted on receipt of the information from the heat control unit 313. The central control unit would then have to meet demand for electricity from external supply (discussed above with reference to figures 1 and 2) Situation 3: The heat store is empty and no heat can be supplied to the installation.

This situation may arise where there is no electrical demand from the installation but some heating demand may remain. The central control unit will therefore not initiate a power request from either of 3() the CHP units. Instead the central control unit will issue a power request to the heat controller which will either supply heat to the installation from the heat store or will activate a boiler 311 to supply heat to the installation, heat being supplied via conduit 317 and 310.

- 30 - In each of the embodiments the central control unit is arranged to receive electrical demand requests only.

Heat is produced as a by-product of producing electricity and is used by the installation as required.

The common heat store is connected by conduits to the installation which can remove heat from the conduits (effectively forming a heating circuit) as required for example using thermostatic valves as discussed above with reference to figures 1 and 2.

Claims

- 31 - Claims 1. A method of operating a power supply system comprising a

central control unit and an energy conversion unit, the central control unit having access to data indicating operating parameters of the energy conversion unit, wherein A) the central control unit receives a power request from a consumer indicating a power demand, B) in response to the power request the central control unit determines, based on the data, the amount of power the energy conversion unit should produce, C) the central control unit communicates a corresponding power request to the energy conversion unit; and D) in response to the power request the energy conversion unit responds to the central control unit indicating the amount of power it can produce
2. A method as claimed in claim 1, wherein the energy conversion unit communicates with the central control unit indicating it is able to produce the power requested and/or supplies the power requested to the consumer.
3. A method as claimed in claim 1, wherein the energy conversion unit communicates with the central control unit indicating it is unable to produce the power requested and the central control unit communicates a further request to the energy conversion unit and/or obtains power from an external power source.
4. A method as claimed in claimed in any preceding claim, wherein the central control unit receives the operating parameters for the energy conversion unit from the energy conversion unit.

- 32 -
5. A method as claimed in any of claims 1 to 3, wherein the central control unit receives the operating parameters for the energy conversion unit from a source external to the system.
6. A method as claimed in any preceding claim wherein the power supply system comprises a plurality of energy conversion units.
7. A method as claimed in claim 6, wherein the central control unit is able to communicate power requests to and receive responses from all of said energy conversion units.
8. A method as claimed in any preceding claim, wherein the amount of power requested from the energy conversion unit(s) is determined by the central control unit so as to meet the power demand of the consumer in a manner determined to be most cost-effective.
9. A power supply apparatus comprising a central control unit and at least one energy conversion unit having an energy conversion unit controller associated therewith, wherein the central control unit is arranged to issue power generation requests to each of said energy conversion units in a format common to all energy conversion units and wherein each of said energy conversion unit controllers is arranged to control the associated energy conversion unit in response to said requests.
10. An apparatus as claimed in claim 9, wherein the energy conversion unit controller is arranged to determine the operating status of the energy conversion unit and to provide the central control unit with information relating to the status of the unit.

- 33 -
11. An apparatus as claimed in claim 10, wherein the status of the energy conversion unit includes information relating to maintenance requirements of the unit.
12. An apparatus comprising a central control unit and at least one energy conversion unit having an energy conversion unit controller associated therewith, wherein the energy conversion unit controller is arranged to determine status information relating to the energy conversion unit and to communicate signals to the central control unit indicating the status of the unit.
13. An apparatus as claimed in claim 12, wherein the status information includes information relating to maintenance and/or malfunct ions.