Hybrid power plant for providing electrical power and frequency response to an electrical grid

Abstract

a hybrid power plant for providing electrical power and frequency response to a grid by generating electrical energy with active and reactive power by operating a generator system (3), with a gas turb

Description

The invention relates to hybrid power plant system designed to provide electrical power and frequency response to an electrical grid, addressing the challenges posed by the evolving energy landscape, including the integration of renewable energy sources and the phase-out of conventional power plants. The invention aims to optimize the interactions between different power generation and storage systems within the plant, allowing for a controlled and centralized response to grid demands . Today's electricity transmission grid faces several challenges resulting from changes to the grid. These include reduced generation from conventional power plants (e.g. phase-out), increased generation from renewables (e.g. wind and solar), a shift from predominantly synchronous generation to generation with power electronic converters and the use of variable speed generators in modern wind farms instead of synchronous generators. The consequences of these challenges include the loss of mass inertia (the rotor speed of the turbine is decoupled from the grid frequency) and the reduction of short-circuit power (limited short-circuit current output). To address these challenges, it is possible to combine a range of technologies as a hybrid. At present gas turbine plants meet the requirements of global grid codes for required frequency response of the plant and other technologies are installed (e.g. Battery Energy Storage Systems, flywheels and / or synchronous condensers) at separate locations to provide fast frequency response. In hybrid solutions with a single connection point to the grid, several different systems can be combined. For example, a gas turbine with the added inertia energy of a flywheel and / or the stored energy of a BESS (battery energy storage system), both of which can provide inherent frequency response and fast frequency response. Independently, gas turbines do not provide a fast frequency response. A flywheel in combination with a generator provides inertial frequency response for a short period of time and a BESS provides fast frequency response with a time limitation depending on the amount of stored energy in the batteries. Because each system requires its own control system, the interactions that the systems have with each other regarding power control (active and reactive power) and frequency control (fast and inherent) cannot be managed by the overall control system of the hybrid power plant at a single connection point to the grid. The object of the invention is to provide a hybrid power plant and a method of operating a hybrid power plant in which the interactions that the systems have with each other are optimized and the response provided to the grid operator can be controlled and provided at a single location meaning the grid operator does not need to control different technologies across multiple locations in the grid. In addition, it is object of the invention to optimize the performance, avoid negative interactions of the systems with each other, and reduce costs by equipment sizing. The object regarding a device is solved by a hybrid power plant system for providing electrical power and frequency response to an electrical grid according claim 1. The hybrid power plant system comprises a generator system, with a gas turbine that is connected frictional to a generator via a common shaft, to generate electrical energy with active and reactive power. It further comprises a BESS (battery energy storage system) with a battery, an inverter, and an inverter controller, and is electrically coupled to the generator system via a source bus and configured to store and discharge electrical energy to provide fast frequency response. It further comprises a plant controller communicatively coupled to the generator system and the BESS and is equipped to monitor the frequency of the electrical grid, and to determine a frequency error based on a deviation from a reference frequency. The hybrid power plant system according to the invention is characterized in, that the plant controller controls a BESS controller and a generator system controller, whereby the BESS controller is equipped to adjust a real power reference for the BESS based on the frequency error, to control an adaptive PI controller for inverter control of the BESS to reduce the frequency error by adjusting the discharge of electrical energy from the BESS, and to coordinate the frequency response of the generator system and the battery energy storage system to provide a frequency response to the electrical grid. Core of the invention is the combination of a conventional generator system with a BESS so that the hybrid power plant can give a comprehensive instant frequency response to the grid at a single location. This is achieved by the BESS controller and the generator controller being controlled directly by the plant controller, allowing control from a single location. The invention is based on the understanding that the negative interactions of the systems of each other can be minimized by a direct control by the plant controller which controls the BESS controller and the generator controller, so that the adaptive PI controller can adjust the discharge of electrical energy from the BESS, and the frequency response of the generator system to provide a frequency response to the electrical grid can be controlled by the real and reactive power reference for the BESS based on the frequency error. The adaptive PI (Proportional Integral) controller for inverter according to the invention, controls the battery energy storage system (BESS) to maintain grid stability by regulating the frequency. Adaptive PI controllers dynamically adjust the discharge rate of the electrical energy from the BESS to correct deviations in the grid frequency. The PI controller does this by adjusting the output based on the frequency error (the difference between the actual frequency and the target frequency). The proportional component reacts to the current frequency error, while the integral component addresses the accumulation of past errors, providing a smooth and steady response. The adaptive feature of the controller allows it to adjust its control parameters (proportional and integral gains) in real-time based on the changing dynamics of the grid and the BESS. This adaptability is crucial for dealing with varying load demands and other external disturbances that affect the grid frequency. The use of an adaptive PI controller for the BESS inverter ensures that the battery's output is finely adjusted in real-time based on the grid's frequency needs . The adjustment loop functions by continuously monitoring the frequency of the electrical grid. When a deviation from the reference frequency is detected, this frequency error is processed by the BESS controller. The controller adjusts the real power reference for the BESS accordingly. This adjustment is aimed at compensating for the frequency deviation, either by increasing or decreasing the BESS's discharge rate and reactive / real power output. These power adjustments are executed through an adaptive Proportional-Integral (PI) controller, which fine-tunes the output based on the magnitude and duration of the frequency error. This ensures that the response is both precise and timely, mitigating the frequency error effectively. This dynamic adjustment capability allows the system to effectively respond to fluctuating grid conditions and load demands. The invention reduces the first-time costs of the hybrid power plant system because the required response time of the BESS can be slower and thus the BESS can be designed more cost-effectively. This is possible because the inertia of the generator system can be considered by the plant controller and the hybrid power plant system can be controlled in such a way that a common and comprehensive instant frequency response to the grid at a single location can be provided. The invention optimizes the use of stored energy in the BESS, discharging power only when necessary to correct frequency errors. This efficient utilization helps in prolonging battery life and reducing operational costs. The modular nature of the hybrid power plant system according to the invention, with the ability to add components like flywheels and synchronous condensers, provides flexibility in design and scalability. This allows the hybrid power plant system to be tailored to specific grid requirements and to be upgraded easily as technology advances or as grid demands evolve . According to a further embodiment of the invention the generator system further comprises a flywheel which is frictional connected with the generator and the gas turbine on the common shaft, and communicatively coupled to the plant controller to provide additional inherent frequency response to the electrical grid. The further integration of a flywheel with the generator and gas turbine on a common shaft provides additional inherent frequency response, enhancing the grid’s stability without requiring immediate power output changes from the BESS or gas turbine. In a further embodiment of the invention the hybrid power plant system, further comprises a synchronous condenser which is electrically coupled to the source bus, and communicatively coupled to the plant controller, to provide additional reactive power to the electrical grid. The inclusion of a synchronous condenser offers additional reactive power support, improving voltage stability and the ability to handle short-circuit conditions. In a further embodiment of the invention the BESS controller is equipped to process the frequency error in an adjustment loop, to compensates the deviation in the frequency and adjusts the real power reference. The effect of the adjustment is monitored, and the feedback is used to further refine the control actions, ensuring precise control over the grid frequency. The object with regard to a method is solved by a method of operating a hybrid power plant for providing electrical power and frequency response to an electrical grid according claim 5. The advantages of the method claims according to the invention are the same as those of the device claims according to the invention. The method of operating a hybrid power plant for providing electrical power and frequency response to an electrical grid comprises the steps of: - generating electrical energy with active and reactive power by operating a generator system, with a gas turbine that is connected frictional to a generator via a common shaft, and controlled by a generator system controller; - storing electrical energy in a battery which is part of a BESS, electrically coupled to the generator system via a source bus, and controlled by a BESS controller; - monitoring the frequency of the electrical grid by a plant controller, which is communicatively coupled to the generator system and the BESS; - determining a frequency error by the plant controller based on a deviation from a reference frequency; - adjusting a real power reference for the BESS by the BESS controller based on the frequency error; - controlling an adaptive PI controller by the BESS controller to reduce the frequency error by adjusting the discharge rate of electrical energy from the BESS; and - coordinating the frequency response between the generator system and the BESS to provide a combined frequency response to the electrical grid, by discharging the stored electrical energy from the BESS through an inverter controlled by an 5 inverter controller. According to an embodiment of the invention further inertial frequency response is added to the electrical grid for a short period of time, by a flywheel which is frictional 10 connected with the generator and the gas turbine on the common shaft, and communicatively coupled to the plant controller. In a further embodiment of the invention additional reactive 15 power to the electrical grid is added by a synchronous condenser which is electrically coupled to the source bus, and communicatively coupled to the plant controller. In an additional embodiment of the invention the BESS 20 controller is equipped to determine the frequency error in an adjustment loop to compensates the deviation in the frequency and adjusts the real power reference. In the following embodiments of the invention are further 25 described in figures. Figure 1 and 2 show diagrams with the same x-axis and the same event of a hybrid power plant. Figure 1 shows the deviation of frequency from the grid frequency in percentage 30 over time and figure 2 shows the power in MW in percentage over time. In both figures the hybrid power plant is connected to the grid and supplies electrical power and frequency support. Here, the frequency of the grid 19 and the frequency response provided by the hybrid power plant 20 is 35 equal. Figures 1 and 2 shall illustrate the behave of electrical frequency of the grid 19 versus the frequency response provided by the hybrid power plant 20 according to the invention. In phase A the hybrid power plant supplies electrical power and frequency response 20 at 100% of the grid demand with active and reactive power by generator system, comprising a gas turbine that is connected frictional to a generator via a common shaft. The generator system is controlled by a generator system controller. Further in phase A electrical energy generated by the generator system is stored in a battery which is part of a BESS. The BESS is electrically coupled to the generator system via a source bus and controlled by a BESS controller. In phase B, the grid is affected by an event or a loss of energy. As a result, the grid frequency 19 drops in phase C to values between 98% and 99%. The plant controller, which is communicatively coupled to the generator system and the BESS, monitors the frequency of the electrical grid 19 and determines a frequency error based on a deviation from a reference frequency. Based on the frequency error 13 the BESS controller adjusts a real power reference for the BESS and controls an adaptive PI controller to reduce the frequency error by adjusting the discharge rate of electrical energy from the BESS. The BESS controller also coordinates the frequency response between the generator system and the BESS to provide a combined frequency response to the electrical grid 20 by discharging the stored electrical energy from the BESS through an inverter controlled by an inverter controller. Within milliseconds the hybrid power plant supplies in phase C frequency response 20 by synchronous inertial response 21 with its rotating masses (gas turbine, shaft, and generator). Within seconds after the event of phase B the synchronous inertial response 21 is consumed, and in phase D the BESS takes over as a fast frequency response. In this stage the gas turbine power is ramped up. In phase E the frequency support by the BESS decreases and the load and power of the gas turbine increases. In phase F the gas turbine is on full load and supplies electrical power and secondary frequency support. In phase G, the grid frequency 19 stabilizes again to 100%. Figure 3 shows a schematic diagram of an embodiment of a hybrid power plant according to the invention. The hybrid power plant comprises a generator system 3, a BESS 7, and a plant controller 12. The generator system 3 comprises a gas turbine 4 that is connected frictional to a generator 5 via a common shaft 6, to generate electrical energy with active and reactive power. The BESS 7 comprises a battery 8, an inverter 9, and is controlled by an inverter controller. The Bess 7 is electrically coupled to the generator system 3 via a source bus 11 and configured to store and discharge electrical energy to provide fast frequency response. The plant controller 12 is communicatively coupled to the generator system 3 and the BESS 7 and equipped to monitor the frequency 19 of the electrical grid 2, and to determine a frequency error 13 based on a deviation from a reference frequency 14. The plant controller 12 comprises and controls a BESS controller 11 and a generator system controller 16. The plant controller 12 with the BESS controller 11 and the generator system controller 16 can be designed in one unit. The BESS controller 11 is equipped to adjust a real power reference 17 for the BESS 7 based on the frequency error 13, to control an adaptive PI controller 18 for inverter control of the BESS 7 to reduce the frequency error 13 by adjusting the discharge of electrical energy from the BESS 7, and to coordinate the frequency response 20 of the generator system 3 and the BESS to provide a frequency response 20 to the electrical grid 2. Figure 4 shows a schematic diagram with a further development of a hybrid power plant. Addition to the generator system 3, the BESS 7, and the plant controller 12, the hybrid power plant comprises further a synchronous condenser 22, which is electrically coupled to the source bus 11, and communicatively coupled to the plant controller 12, to provide additional reactive power to the electrical grid 2. The synchronous condenser 22 is controlled by a synchronous condenser controller 23. The plant controller 12 with the BESS controller 11, the generator system controller 16, and the synchronous condenser controller 23 can be designed in one unit. In a further embodiment of the invention the generator system 3 further comprises flywheel 30 which is frictional connected with the generator 5 and the gas turbine 4 on the common shaft 6, and communicatively coupled to the plant controller 12 to provide additional inherent frequency response to the electrical grid 2. Figure 5 shows a diagram of the plant controllers 12 control circuitry. The plant controller 12 comprises of the BESS controller 15, the generator system controller 16, and in a further development of the invention optionally of the synchronous condenser controller 23. The BESS controller 15 comprises sub-controller for active and reactive power control 24 and frequency control 25. The generator system controller 16 has governor control 26 (real power and frequency), droop capability control 27, and reactive power control 28. The synchronous condenser controller 23 consists of SC terminal voltage control 29. The BESS controller 15 first generates reference frequency 14 for real and reactive power. The reference real and reactive power values are then compared to the systems measured real and reactive power values. Then, the difference is passed through the PI controller to reduce error and generate I values for inverter control. In this architecture, apart from using the general architecture of using real and reactive power reference values, the system frequency is tracked, and the frequency error adjustment loop is introduced. The loop compensates for the deviation in the system frequency and adjusts the real power reference. An adaptive PI controller is used to reduce errors, which can calculate the P, I value adaptively with the change in system parameters and outputs. The system generates reference real and reactive power values based on the difference between the load and the output of the two generators. The real power reference is adjusted based on the frequency deviation. The real and reactive power is passed through adaptive PI controllers to generate I values for inverter control. To control the reactive power of the synchronous generators, field voltage is tracked and compared with the reference voltage. The generators reactive power is also tracked and compared with the reference reactive power. Both differences, (the difference between the field voltage and reference voltage and the difference between measured reactive power and reference reactive power) is passed through an adaptive PI controller. The sum of the reference voltage and the output of the adaptive PI controller are taken as adjusted field voltage. The invention provides a hybrid power plant in which the interactions that the components have with each other are optimized. The response provided to the grid can be controlled and provided at a single location meaning the grid operator does not need to control different technologies across multiple locations in the grid. With the invention the performance can be optimized, and costs can be reduced by equipment sizing. The invention significantly improves the frequency behavior of conventional gas turbine systems, with integrated fast frequency response and greatly damps any frequency oscillations. In addition, a higher frequency nadir is achieved after a loss of energy (generation) event on the power system.

Claims

1. Hybrid power plant system (1) for providing electrical power and frequency response to an electrical grid (2), comprising:- a generator system (3), with a gas turbine (4) that is connected frictional to a generator (5) via a common shaft (6), to generate electrical energy with active and reactive power,- a BESS (7), comprising a battery (8), an inverter (9), and an inverter controller (10), electrically coupled to the generator system (3) via a source bus (11) and configured to store and discharge electrical energy to provide fast frequency response,- a plant controller (12) communicatively coupled to the generator system (3) and the BESS (7), and equipped to monitor the frequency of the electrical grid (2), and to determine a frequency error (13) based on a deviation from a reference frequency, characterized in, that the plant controller (12) controlls a BESS controller (11) and a generator system controller (16), whereby the BESS controller (15) is equipped to- adjust a real power reference (17) for the BESS (7) based on the frequency error (13),- control an adaptive PI controller (18) for inverter control (10) of the BESS (7) to reduce the frequency error (13) by adjusting the discharge of electrical energy from the BESS (7), and- coordinate the frequency response of the generator system (3) and the battery energy storage system to provide a frequency response to the electrical grid (2).

2. Hybrid power plant system (1) according to claim 1, whereby the generator system (3) further comprises flywheel (30) which is frictional connected with the generator (5) and the gas turbine (4) on the common shaft (6), and communicatively coupled to the plant controller (12) toprovide additional inherent frequency response to the electrical grid (2).

3. Hybrid power plant system (1) according to claim 1 or 2, further comprising a synchronous condenser (20) electrically coupled to the source bus (11), and communicatively coupled to the plant controller (12), to provide additional reactive power to the electrical grid (2).

4. Hybrid power plant system (1) according to one of the previous claims, whereby the BESS controller (15) is equipped to process the frequency error (13) in an adjustment loop, to compensates the deviation in the frequency and adjusts the real power reference.

5. Method of operating a hybrid power plant (1) for providing electrical power and frequency response to an electrical grid (2), comprising the steps of:- generating electrical energy with active and reactive power by operating a generator system (3), with a gas turbine (4) that is connected frictional to a generator (5) via a common shaft (6), and controlled by a generator system controller (16), - storing electrical energy in a battery (8) which is part of a BESS (7), electrically coupled to the generator system (3) via a source bus, and controlled by a BESS controller (15),- monitoring the frequency of the electrical grid (2) by a plant controller (12), which is communicatively coupled to the generator system (3) and controls the BESS (7),- determining a frequency error (13) by the plant controller (12) based on a deviation from a reference frequency,- adjusting a real power reference (17) for the BESS (7) by the BESS controller (15) based on the frequency error (13) ,- controlling an adaptive PI controller (18) by the BESS controller (15) to reduce the frequency error (13) by adjusting the discharge rate of electrical energy from the BESS (7), and- coordinating the frequency response between the generator system (3) and the BESS (7) to provide a combined frequency response to the electrical grid (2), by discharging the stored electrical energy from the BESS (7) through an inverter (9) controlled by an inverter controller (10).

6. Method (1) according to claim 5, whereby further inertial frequency response is added to the electrical grid (2) for a short period of time, by a flywheel (30) which is frictional connected with the generator and the gas turbine on the common shaft (6), and communicatively coupled to the plant controller (12).

7. Method (1) according to claim 5 or 6, whereby additional reactive power to the electrical grid (2) is added by a synchronous condenser (20) which is electrically coupled to the source bus (11), and communicatively coupled to the plant controller (12).

8. Method (1) according to one of the claims 5 to 7, whereby the BESS controller (15) is equipped to determine the frequency error (13) in an adjustment loop to compensates the deviation in the frequency and adjusts the real power reference.16

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