Method for operating a combined heat and power plant on a power grid, as well as communication device and combined heat and power plant

Abstract

Method for operating a combined heat and power plant (10) on a power grid (11), wherein a call signal (14) for negative secondary control power is received via a communication device (13) and a setpoint signal (16) for electrical power (12) to be supplied by the combined heat and power plant (10) to the power grid (11) is generated depending on the call signal (14) and the electrical power (12) actually supplied by the combined heat and power plant (10) to the power grid (11) is adjusted by means of the setpoint signal (16), characterized in that the generation of the setpoint signal (16) is based on a predetermined full-power value and this is reduced by a call value of the call signal (14) and a demand signal (24) for primary control power to be provided is determined and the setpoint signal (16) is additionally generated depending on the demand signal (24).by incorporating a demand value (27) of the demand signal (24) from the full-power value (25) and the call-off value (26) of the call-off signal (14), so that simultaneous provision and / or provision assurance of primary control power and secondary control power by means of the combined heat and power plant (10) is enabled.

Description

The invention relates to a method for operating a combined heat and power (CHP) plant on a power grid. While the CHP plant feeds electrical power into the grid, it also provides negative secondary control power depending on a call signal. The invention also includes a communication device for specifying a setpoint signal for the CHP plant, as well as a CHP plant with such a communication device. The concepts of positive and negative control power are described, for example, in DE 10 2014 201 406 B3. This document further discloses that primary control power must be available from a power plant within a few seconds. The essence of primary control power (PCP) lies in the fact that it can be called upon within 30 seconds for up to 15 minutes, after which the so-called secondary control system takes over to maintain stability in the electrical grid. The secondary control system for providing secondary control power can therefore be operated with lower control dynamics or a larger time constant. German patent DE 10 2015 201 085 A1 describes how several energy generators can be combined into an aggregation system in order to provide primary control reserve and short-circuit power for an energy transmission network using a central control unit. The different energy generators can be based on different technologies, including a combined heat and power plant. It is known from WO 2015 / 010 895 A1 that both primary and secondary control can be implemented by means of a power plant connected to a power grid. From the publication by SOBIERAJSKI, M. and ROJEWSKI, W. (Primary and secondary frequency control in a small power system (SPS) with rotating and static sources after islanding. In: Modern Electric Power Systems 2015 (MEPS), Wroclaw, 2015. In: IEEE Xplore [online]. DOI: 10.1109 / MEPS.2015.7477154, In: IEEE ), it is known how frequency control for power stabilization can be implemented in a small power system when switching from grid-connected operation to islanding operation. From DE 10 2015 014 117 A1 it is known that primary and secondary control power can be provided to stabilize an AC grid by means of a combination unit consisting of an energy storage device and an energy generator. The invention is based on the objective of upgrading a combined heat and power plant to provide control power. The problem is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are described by the dependent claims, the following description, and the figure. The invention provides a method for operating a combined heat and power (CHP) plant on an electrical power grid or transmission network. In the CHP plant, a communication device receives a call signal for negative secondary control power. Negative secondary control power is required when the power grid is oversupplied, i.e., when more electrical power is fed in than is needed by consumers. This undesirably increases the grid frequency of the AC voltage. When the call signal is received, a setpoint signal for the electrical power to be supplied to the power grid by the CHP plant is generated, depending on the call signal. The setpoint signal thus determines the power output of the CHP plant. Negative secondary control power means that the CHP plant reduces its electrical power output.Accordingly, the electrical power actually fed into the grid by the combined heat and power plant is reduced by means of the setpoint signal relative to a full-power value. This contributes to reducing the aforementioned oversupply. Since secondary control power, as described, may be provided with a control dynamics lower than those for primary control power, the response to the call signal does not pose a technical problem for a combined heat and power (CHP) plant. However, the invention now additionally provides for primary control power to also be provided by the CHP plant. The method according to the invention utilizes the setpoint signal, which, as described, specifies the power output of the CHP plant. The setpoint signal is generated based on the aforementioned predetermined full-power value. This full-power value can, for example, correspond to 100 percent of the rated power of the CHP plant and, more generally, be the power value that must be provided independently of primary and secondary control.The full power output is provided if no primary or secondary control power is supplied. The full power output is reduced by a call-off value from the call-off signal. The call-off value is the current signal value of the call-off signal. The call-off signal indicates, as described, how much negative secondary control power is required by the combined heat and power plant. Starting with the full power output, this is then reduced by the call-off value of the call-off signal. The full power output therefore corresponds to 100 percent. The call-off value can be a percentage, generally x percent. This method of generating the setpoint signal provides sufficient flexibility to also deliver primary control reserve using the combined heat and power (CHP) plant. For this purpose, a demand signal for the required primary control reserve is determined. The setpoint signal is then additionally generated based on this demand signal by incorporating a demand value (e.g., y percent) from the demand signal, starting with the full-power value (e.g., 100 percent) and the call-up value (e.g., x percent). This incorporation can be done, for example, as a subtraction (for negative control reserve). Thus, the setpoint signal can indicate the actual electrical power to be delivered as: 100 percent - x percent - y percent (100% - x% - y%). In other words, the setpoint signal is modulated by the demand signal for primary control reserve.Thus, the simultaneous provision and / or provision of primary (PRL) and secondary control reserve (SRL) is feasible using a single combined heat and power (CHP) plant. The invention offers the advantage that, without requiring any modifications to a combined heat and power (CHP) plant, it can be enabled to provide primary control reserve to the extent permitted by modifying or manipulating the setpoint signal. This is achieved by combining the demand signal for primary control reserve with the call signal for negative secondary control reserve. For example, a full-power value is used as the starting point, and this value is reduced by the call value x of the call signal and the demand value y of the demand signal (reduction - y percent for negative primary control reserve, where y is a positive absolute value). The demand value represents the current signal value of the demand signal. The invention also includes embodiments that offer additional advantages. One embodiment provides that when generating the setpoint signal, if the demand value indicates negative primary control power, the full-power value is further reduced by the demand value y (100 percent - x percent - y percent). The demand value y itself can have a positive absolute value, and the negative sign in the calculation indicates that it is negative primary control power. Negative primary control power means that the actual electrical power output of the combined heat and power (CHP) plant is to be reduced. As with secondary control power, this occurs in the event of an oversupply of electricity to the grid. Using this embodiment, the CHP plant can therefore be used to provide negative primary control power. The combined heat and power (CHP) plant therefore only needs to provide negative control reserve (both secondary and primary control reserve). This is referred to as asymmetric provision. However, primary control reserve is preferably marketed or offered as a symmetric product. Therefore, according to one embodiment, a virtual power plant is formed by at least one aggregator or at least one additional power source, which also supplies the positive portion of the required primary control reserve in the same grid control area (here: TenneT). Such a power source could, for example, be a biogas plant that increases its electrical output when positive primary control reserve is called upon (grid frequency lower than a setpoint frequency, where the setpoint frequency could be, for example, 50 Hz or 60 Hz). One embodiment provides for the CHP plant to be operated together with at least one additional electrical power source.This joint operation constitutes aggregation in the sense described above. If positive secondary control power is requested via the call signal and / or if the demand value of the primary control power signal exceeds the full-load value (100% - x% + y% > 100%), at least the electrical power exceeding the full-load value—for example, the portion above 100% (if the full-load value is 100%)—is fed into the grid by controlling at least one other electrical power source. The electrical power that would exceed the full-load value of the combined heat and power plant is thus provided by at least one other power source through aggregation, as it cannot be provided by the combined heat and power plant itself.Thus, aggregation allows for the provision of fully functional positive and negative secondary control reserve and positive and negative primary control reserve. However, the secondary control reserve can also be marketed separately as positive and negative control reserve. One embodiment provides that the communication device receives the request signal for secondary control power via a mobile network connection and / or an internet connection. The communication device is thus controlled from outside the combined heat and power plant (CHP) by means of a request signal that can be transmitted to the CHP plant via a mobile network connection and / or an internet connection. For this purpose, the communication device can, for example, include a mobile communication module and / or a WLAN radio module (WLAN - Wireless Local Area Network) and / or a NIC (Network Interface Controller). In addition, the communication device is preferably operated in conjunction with the power grid. Using a built-in mains frequency meter, the communication device then determines the current mains frequency of the power grid.If the grid frequency exceeds a predetermined setpoint, the communication device also generates the demand signal for primary control power, depending on the deviation of the determined grid frequency from the predetermined setpoint. In other words, the communication device can combine the call signal for secondary control power with the demand signal for primary control power. Advantageously, a single setpoint signal for power output can be provided, which incorporates both the call signal and the demand signal. Therefore, the rest of the combined heat and power plant does not need to be adapted to this process. One embodiment provides that, in the case of the combined heat and power (CHP) plant, a permissible power range is defined by the aforementioned full-load power value and by a correspondingly smaller minimum possible power output value. The minimum possible power output value is greater than zero, specifically greater than 45 percent of the full-load power value. The CHP plant may only be operated within this power range, i.e., between the minimum possible power output value and the full-load power value. However, it is further stipulated that the maximum secondary control power that can be called up via the activation signal is limited to a maximum value that is smaller than the power range. The operational power range is thus divided into a power range for negative secondary control power and a power range for negative primary control power. There is no overlap.In other words, the system prevents the call-up signal from triggering such a large amount of secondary control reserve that the combined heat and power (CHP) plant uses its entire power range exclusively for providing secondary control reserve, thus reducing its output from full capacity to the absolute minimum. Instead, the maximum callable value is smaller than the power range, ensuring that a difference between the maximum value and the power range always remains as a control reserve or power reserve for providing primary control reserve. This power reserve can be defined, for example, based on the prequalification of the CHP plant, which then indirectly determines the remaining maximum value for secondary control reserve. One embodiment provides that the combined heat and power (CHP) plant has a maximum possible change in its output power that can be achieved within a predetermined time interval. In other words, the CHP plant can only change its output power by a predetermined maximum amount within this time interval (e.g., 30 seconds) because, for example, the inertia of a turbine and / or generator in the CHP plant prevents a faster change. This time interval is typically between 10 and 50 seconds. A 30-second interval is particularly relevant for primary control reserve. Depending on the maximum possible change value, a corresponding maximum available primary control reserve is then determined.The primary control reserve is therefore set to a value that can be implemented with the available control dynamics of the combined heat and power plant, so that the primary control reserve can be provided, changed, or adjusted as required within the time interval, for example, within 30 seconds. This ensures that the provision of the primary control reserve is adapted to the control dynamics of the combined heat and power plant. To implement the inventive method in a combined heat and power (CHP) plant, the invention provides a communication device by means of which a setpoint signal for a CHP plant can be specified or generated. The communication device is configured to receive a request signal for negative secondary control power and, depending on the received request signal, to generate the setpoint signal for the CHP plant. The communication device also includes a computing unit configured to execute an embodiment of the inventive method. The computing unit can be implemented on the basis of at least one microcontroller and / or at least one microprocessor.The computing device can have program code containing program instructions that, when executed by the computing device, carry out the embodiment of the method according to the invention. The program code can be stored in a data memory of the computing device. The communication device can, for example, be designed as an electronic circuit. For receiving the retrieval signal, the communication device can, for example, include a mobile communication module and / or a WLAN radio module and / or a NIC. The invention also includes a combined heat and power (CHP) plant for operation on an electrical power grid or transmission network. The CHP plant is characterized by the fact that it incorporates a communication device according to the invention. Thus, the setpoint signal for adjusting the electrical power to be supplied to the power grid can be specified by a communication device that takes into account both a request signal for negative secondary control power and a demand signal for primary control power. The invention also includes combinations of the features of the described embodiments. Further features of the invention will become apparent from the claims, the figures, and the description of the figures. The features and combinations of features mentioned above in the description, as well as the features and combinations of features mentioned below in the description of the figures and / or shown in the figures alone, are not only usable in the combinations specified, but also in other combinations or on their own. An embodiment of the invention is described below. The single figure shows a schematic representation of an embodiment of the combined heat and power plant according to the invention. Fig. 1 shows a combined heat and power (CHP) plant 10 that can be operated on an electrical transmission network or power grid 11. The power grid 11 is symbolically represented here by a power pylon. The power grid can be a public power grid with a multiphase alternating voltage of over 10 kilovolts. The CHP plant 10 can feed electrical power 12 into the power grid 11. Conversely, a CHP plant 10 cannot draw electrical power from the power grid as a consumer. However, it can reduce the electrical power 12 it feeds in if necessary, for example, because the power grid 11 is overloaded, i.e., too much electrical power is being fed into the power grid 11. For this purpose, the combined heat and power plant 10 can have a communication device 13 that can receive an external call signal 14 for negative secondary control power. The call signal 14 can, for example, originate from a signal source 15, which can, for instance, represent the operator of the electricity grid 11. Depending on the call signal 14, the communication device 13 can generate a setpoint signal 16, by which the actual combined heat and power process 17 of the combined heat and power plant 10 can be controlled or monitored. For example, a controller 18 can be provided that regulates the output electrical power 12 according to the setpoint signal 16 with respect to the power value. For example, the controller 18 can control a generator 19 and / or a turbine 20. Additionally, for example, the communication device 13 can determine a current grid frequency value 21 based on the grid frequency f of the AC voltage of the power grid 11. The communication device 13 can be coupled to the power grid 11 for this purpose. If the determined grid frequency value 21 deviates from a target frequency value 22, the target signal 16 can additionally include a component corresponding to the provision of primary control power by the combined heat and power plant 10. The target frequency value 22 can, for example, be 50 Hertz or 60 Hertz. The calculation of a component of a target signal for providing primary control power as a function of the grid frequency value 21 is known in the prior art. The communication device thus enables a method for the simultaneous provision and / or provision assurance of primary (PRL) and secondary control reserve (SRL) by means of a single combined heat and power plant 10 (CHP). This results in a grid frequency deviation 23, from which a demand signal 24 is generated using a known calculation method for the primary control reserve. The setpoint signal 16 can be calculated from a full-power value 25 of the combined heat and power plant 10 by subtracting a current call-up value 26 of the call-up signal 14 and a current demand value 27 of the demand signal 24. In the combined heat and power plant 10, a permissible power interval can be defined by the full power value 25 and a minimum possible minimum power value, and a maximum secondary control power that can be called up by means of the call signal 14 can be limited to a maximum value that is smaller than the power interval. In Germany, there are currently no projects for the simultaneous provision of primary and negative secondary control reserve using a CHP plant. CHP plants are currently marketed for their minute reserve and secondary control reserve capacity. In contrast, in the combined heat and power plant 10, the grid frequency f is measured locally for the provision of PRL (primary load), and a setpoint signal is generated from this to specify a power setpoint. The setpoint signal can be updated every second. According to this setpoint specified by the setpoint signal, the power output of the CHP plant can be varied proportionally to the grid frequency f in accordance with the requirements of the prequalification for the PRL. If the CHP plant 10 is operated in power-led mode (full power value at 100% power) and therefore a further increase in power is not possible, only the part of the grid frequency deviation 23 that results in a power reduction of the CHP plant 10 can be compensated (asymmetric primary control power provision in the case of an oversupplied grid with grid frequency values ​​e.g. f > 50 Hz). At the same time, the CHP plant 10 enables the provision of negative secondary control power. In this context, the plant can be "remotely controlled" by means of the call-off signal 14, e.g., in a pool or aggregation of a marketing partner according to the specifications of the transmission system operator of the electricity grid 11, the CHP plant 10 can be reduced from its current operating point in power generation ("call-off") or, at the end of the call-off, brought back to its original operating point. Significantly reduced prices for providing balancing power, particularly in minute reserve or secondary control reserve, are lowering revenues from marketing energy flexibility. Providing primary control reserve currently offers the highest returns; however, not all CHP plants are technically or operationally suitable for this purpose. Primary control reserve provision requires plants to be able to handle load changes on a second-by-second basis. Additionally, primary control reserve must be provided symmetrically around its operating point, corresponding to the 50 Hz grid frequency deviation. Marketing primary control reserve has not previously been possible for plants operating in a current-controlled mode (e.g., full power at 100% output), but this is now possible for CHP plant 10. Simultaneous provision of primary control reserve (PCR) and asymmetrical primary control reserve (PCR) during current-controlled operation of CHP plant 10 means that CHP plant 10 continuously provides primary control reserve x% in accordance with the grid frequency deviation, but only asymmetrically, for example, in the form of a power reduction of 100% - x%. Additionally, individual calls for secondary control reserve y% can be fulfilled. Here, in addition to providing PCR, CHP plant 10 is reduced by a further y% from its current power value during a call and then ramped up to its original power value at the end of the call. The current target power value as a percentage of the nominal power (full power value) is therefore calculated as 100% - x% - y%, where x% (PCR) represents the demand and y% (PCR) represents the demand. The control of the CHP plant 10 for the provision of control power can be carried out via a common communication interface of a communication device if this is able, in addition to the necessary communication between the CHP plant 10 and the marketing partner (represented by the signal source 15), to also measure the grid frequency deviation in the power grid 11 and to generate a setpoint signal 16 to specify a setpoint for the CHP plant 10. The advantage lies in the optimized yield achieved through the simultaneous use of two control reserve segments (PRL and SRL). In secondary control reserve marketing, a capacity price is paid for the mere provision of CHP plant 10, while individual calls for power are compensated with an energy price. In primary control reserve, there is no distinction between capacity and energy prices. Here, compensation is based solely on a capacity price, which is determined by the plant's potential marketable output. This, in turn, is established during the prequalification process for the plants. In summary, the invention makes it possible to provide and / or ensure asymmetric primary and negative secondary control power simultaneously using a combined heat and power (CHP) plant.

Claims

Method for operating a combined heat and power plant (10) on a power grid (11), wherein a call signal (14) for negative secondary control power is received via a communication device (13) and a setpoint signal (16) for electrical power (12) to be supplied by the combined heat and power plant (10) to the power grid (11) is generated depending on the call signal (14) and the electrical power (12) actually supplied by the combined heat and power plant (10) to the power grid (11) is adjusted by means of the setpoint signal (16), characterized in that the generation of the setpoint signal (16) is based on a predetermined full-power value and this is reduced by a call value of the call signal (14) and a demand signal (24) for primary control power to be provided is determined and the setpoint signal (16) is additionally generated depending on the demand signal (24).by incorporating a demand value (27) of the demand signal (24) from the full-power value (25) and the call-off value (26) of the call-off signal (14), so that simultaneous provision and / or provision assurance of primary control power and secondary control power by means of the combined heat and power plant (10) is enabled. Method according to claim 1, wherein when generating the setpoint signal (16) in the case of a demand value (27) which signals a negative primary control power, the full power value (25) is additionally reduced by the demand value (27). Method according to one of the preceding claims, wherein the combined heat and power plant (10) is operated together with at least one further electrical power source and in the event that positive secondary control power is requested by the call signal (14) and / or in the event that the full power value is exceeded by the demand value (27) of the demand signal (24) for the primary control power, at least one electrical power exceeding the full power value (25) is fed into the power grid (11) by controlling the at least one further electrical power source. Method according to one of the preceding claims, wherein the communication device (13) receives the call signal (14) for the secondary control power via a mobile communication connection and / or an internet connection, and wherein the communication device (13) is operated coupled to the power grid (11) and determines a current grid frequency value (21) of a grid frequency (f) of the power grid (11) and generates the demand signal (24) for the primary control power as a function of a grid frequency deviation (23) of the determined grid frequency value (21) from a predetermined target frequency value (22). Method according to one of the preceding claims, wherein in the combined heat and power plant (10) a permissible power interval is defined by the full power value (25) and a minimum possible minimum power value and a maximum secondary control power that can be called up by means of the call signal (14) is limited to a maximum value that is smaller than the power interval. Method according to one of the preceding claims, wherein in the combined heat and power plant (10) a maximum possible change in the output power (12) is given within a predetermined time interval, which is in a range of 10 seconds to 50 seconds, and depending on a value of the change, a currently available maximum primary control power is determined. Communication device (13) for generating a setpoint signal (16) for a combined heat and power plant (10), wherein the communication device (13) is configured to receive a call signal (14) for negative secondary control power and to generate the setpoint signal (16) for the combined heat and power plant (10) depending on the received call signal (14), characterized in that the communication device (13) has a computing device configured to carry out a method according to one of the preceding claims. Combined heat and power plant (10) for operation on a power grid (11), wherein a communication device (13) according to claim 7 is provided.

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