Flywheel energy storage system and fire storage combined frequency modulation energy storage system

Abstract

The invention provides a flywheel energy storage system and a fire storage combined frequency modulation energy storage system. The flywheel energy storage system comprises a plurality of flywheel energy storage units, a plurality of bidirectional power regulation systems and an energy management master control system. The flywheel energy storage units which are high in response speed, high in gradeability and flexible in power output serve as quick response energy storage to improve the primary frequency modulation performance index, the online rate of the energy storage system is improved through the arrangement of the multiple flywheel energy storage units connected in parallel, it is guaranteed that the frequency modulation requirement can still be met when a single flywheel energy storage unit is shut down and overhauled, and the service life of the flywheel energy storage units is prolonged. And meanwhile, a bidirectional power regulation system and an energy management master control system are combined to realize a whole set of array control technology, so that the flywheel energy storage system is effectively ensured to respond to a primary frequency modulation instruction of a unit step by step.

Description

Technical Field

[0001] The present disclosure relates to the technical field of power grid frequency regulation, and in particular, to a flywheel energy storage system and a thermal-storage combined frequency regulation energy storage system. Background Art

[0002] Traditional power grid frequency regulation is often achieved through thermal power units or hydropower units. Wind power and photovoltaic power generation units not only do not have the ability to regulate themselves, but their intermittent power output also increases the frequency regulation burden on the power grid.

[0003] The power grid is a huge inertial system. When there is a shortage of active power, the rotor of the generator will accelerate, and the power grid frequency will increase. Conversely, the power grid frequency will decrease. Primary frequency regulation technology refers to dynamically ensuring the balance of active power in the power grid. When the power grid frequency increases, the primary frequency regulation technology helps the unit reduce the grid-connected active power. Conversely, it assists the unit to increase the grid-connected active power. If the proportion of new energy power generation units such as photovoltaic is relatively small, the power grid can easily control the deviation amplitude relying on system inertia; conversely, if the proportion of new energy power generation units such as photovoltaic is relatively large, the power grid cannot be balanced through system inertia, and the power grid frequency cannot be controlled within a stable range.

[0004] Therefore, when the proportion of new energy installed capacity in the power grid reaches a certain level, if the power generation unit itself cannot quickly adjust the frequency, it will bring frequent peak shaving and valley filling pressures to the overall power dispatching, and it is also easy to cause major accidents such as grid disconnection in the power grid area, posing an increasingly serious challenge to the frequency safety of the current power grid. Summary of the Invention

[0005] The purpose of the embodiments of the present disclosure is to provide a flywheel energy storage system and a thermal-storage combined frequency regulation energy storage system to solve the problems in the prior art.

[0006] The embodiments of the present disclosure adopt the following technical solutions: A flywheel energy storage system at least includes: a plurality of flywheel energy storage units, a plurality of bidirectional power regulation systems, and an energy management master control system; wherein, all the flywheel energy storage units are connected in parallel, and the flywheel energy storage units are connected to the bidirectional power regulation systems; each bidirectional power regulation system at least includes: a converter system and a step-up transformer. The converter system at least includes a plurality of parallel-connected converter units, and the converter units are used to realize the bidirectional conversion of electric energy between the flywheel energy storage units and the step-up transformer. The step-up transformer is connected to the plant working bus through an energy storage bus; the energy management master control system is communicatively connected to all the flywheel energy storage units and the bidirectional power regulation systems, and is used to coordinate the charge and discharge logic and monitor the system state.

[0007] In some embodiments, the flywheel energy storage unit at least includes: a flywheel rotor for storing rotational kinetic energy; a magnetic levitation bearing for supporting the flywheel rotor and reducing mechanical friction; a bidirectional motor coaxially connected to the flywheel rotor for realizing the conversion between electrical energy and mechanical energy; and a vacuum chamber for accommodating the flywheel rotor, the magnetic levitation bearing and the bidirectional motor.

[0008] In some embodiments, the flywheel energy storage unit further includes: a vacuum maintenance module connected to the vacuum chamber through a vacuum pipeline for maintaining the vacuum degree in the vacuum chamber; a cooling module including a liquid cooling circulation pipeline surrounding the vacuum chamber and the bidirectional motor.

[0009] In some embodiments, the converter unit is a bidirectional converter module, and the bidirectional converter module at least includes: a grid-side converter connected to the step-up transformer through a converter system bus and a DC link for regulating the voltage and frequency of the converter system bus; a plurality of machine-side converters connected in parallel, connected to the grid-side converter through a converter unit bus, and each machine-side converter is connected to one flywheel storage unit for controlling the charge and discharge power of the flywheel energy storage unit.

[0010] In some embodiments, an isolation capacitor is provided between the machine-side converter and the grid-side converter.

[0011] In some embodiments, the single capacity of the flywheel storage unit is 500kW / 50kWh, the rated power of the machine-side converter is 630kw, the rated power of the grid-side converter is 1250kw, and each grid-side converter is connected to two machine-side converters simultaneously.

[0012] In some embodiments, the step-up transformer is a box-type transformer.

[0013] In some embodiments, it further includes: a protection switch and a filtering device connected to the energy storage bus.

[0014] The embodiments of the present disclosure further provide a thermal energy storage combined frequency regulation energy storage system, which at least includes:

[0015] A thermal power generating unit connected to an external power grid system; the flywheel energy storage system as described above, connected to the thermal power generating unit through the plant service bus.

[0016] In some embodiments, the power capacity of the flywheel energy storage system is 3% of the rated power of the thermal power generating unit.

[0017] The beneficial effects of the embodiments of the present disclosure are as follows: By using a flywheel energy storage unit with fast response speed, strong climbing ability, and flexible power output as a fast-response energy storage to improve the primary frequency modulation performance index, and by setting multiple parallel flywheel storage units, the online rate of the energy storage system is improved, ensuring that the frequency modulation demand can still be met even when a single flywheel energy storage unit is out of service for maintenance. At the same time, combined with a bidirectional power regulation system and an energy management master control system, a complete set of array control technologies are realized, effectively ensuring that the flywheel energy storage system responds to the primary frequency modulation commands of the unit in unison. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in one or more embodiments of this specification or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in this specification. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 Structural schematic diagram of the flywheel energy storage system provided for one or more embodiments of this specification;

[0020] Figure 2 Structural schematic diagram of the flywheel energy storage unit provided for one or more embodiments of this specification;

[0021] Figure 3 Structural schematic diagram of the bidirectional power regulation system provided for one or more embodiments of this specification;

[0022] Figure 4 Actual built structure schematic diagram of the flywheel energy storage system provided for one or more embodiments of this specification;

[0023] Figure 5 Principle diagram of the thermal storage combined frequency modulation energy storage system provided for one or more embodiments of this specification. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] In order to enable those skilled in the art to better understand the technical solutions in one or more embodiments of this specification, the following will clearly and completely describe the technical solutions in one or more embodiments of this specification in conjunction with the drawings in one or more embodiments of this specification. Obviously, the described embodiments are only a part of the embodiments of this specification, rather than all the embodiments. Based on one or more embodiments of this specification, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of this document.

[0025] Traditional power grid frequency regulation is often achieved through thermal power units or hydroelectric power units. Wind power and photovoltaic power generation units not only do not have the ability to regulate themselves, but their intermittent power output also increases the frequency regulation burden on the power grid.

[0026] The power grid is a huge inertial system. When there is a shortage of active power, the rotor of the generator will accelerate, and the power grid frequency will increase. Conversely, the power grid frequency will decrease. Primary frequency regulation technology refers to dynamically ensuring the balance of active power in the power grid. When the power grid frequency increases, the primary frequency regulation technology helps the unit reduce the grid-connected active power. Conversely, it assists the unit to increase the grid-connected active power. If the proportion of new energy generation units such as photovoltaics is relatively small, the power grid can easily control the offset amplitude relying on the system inertia; conversely, if the proportion of new energy generation units such as photovoltaics is relatively large, the power grid cannot be balanced through system inertia, and the power grid frequency cannot be controlled within a stable range.

[0027] Therefore, when the installed capacity of new energy in the power grid reaches a certain proportion, if the generator set itself cannot quickly regulate the frequency, it will bring frequent peak shaving and valley filling pressures to the overall power dispatch, and it is also easy to cause major accidents such as grid area disconnection, posing an increasingly serious challenge to the current power grid frequency safety.

[0028] To solve the above problems, the first embodiment of the present disclosure provides a flywheel energy storage system, the structural schematic diagram of which is as Figure 1 shown, mainly including a plurality of flywheel energy storage units 10, a plurality of bidirectional power regulation systems 20, and an energy management master control system 30; wherein, all the flywheel energy storage units 10 are connected in parallel, and the flywheel energy storage unit 10 is connected to the bidirectional power regulation system 20; each bidirectional power regulation system 20 at least includes: a converter system 21 and a step-up transformer 22, the converter system 21 at least includes a plurality of parallel-connected converter units 210, and the converter unit 210 is used to realize the bidirectional power conversion between the flywheel energy storage unit 10 and the step-up transformer 22, and the step-up transformer 22 is connected to the plant working bus 50 through the energy storage bus 40; the energy management master control system 30 is communicatively connected to all the flywheel energy storage units 10 and the bidirectional power regulation system 20, and is used to coordinate the charge and discharge logic and system status monitoring. It should be noted that the connection relationship between the energy management master control system 30 and the flywheel energy storage unit 10 and the bidirectional power regulation system 20 is Figure 1 shown by a dotted line in, and its actual connection method can be realized by a wired or wireless communication connection method that conforms to the on-site conditions, and this embodiment does not make specific limitations.

[0029] Figure 2 shows the structural schematic diagram of the flywheel energy storage unit in this embodiment. As Figure 2, in this embodiment, the flywheel energy storage unit 10 at least includes: a flywheel rotor for storing rotational kinetic energy; a magnetic levitation bearing for supporting the flywheel rotor and reducing mechanical friction; a bidirectional motor coaxially connected to the flywheel rotor for realizing the conversion between electrical energy and mechanical energy; and a vacuum chamber for accommodating the flywheel rotor, the magnetic levitation bearing and the bidirectional motor. Further, the flywheel energy storage unit further includes: a vacuum maintenance module connected to the vacuum chamber through a vacuum pipeline for maintaining the vacuum degree in the vacuum chamber; a cooling module including a liquid cooling circulation pipeline surrounding the vacuum chamber and the bidirectional motor.

[0030] In this embodiment, as Figure 3 shown, the converter unit 210 is a bidirectional converter module, which at least includes a grid-side converter 211 and a plurality of machine-side converters 212 connected in parallel. Among them, the grid-side converter 211 is connected to the step-up transformer 22 through the converter system bus 23 and the DC link 24 for realizing the voltage and frequency regulation on the converter system bus 23; while the machine-side converter 212 is connected to the grid-side converter 211 through the converter unit bus 25, and each machine-side converter 212 is connected to a flywheel storage unit 10 for controlling the charge and discharge power of the flywheel energy storage unit. When actually building a flywheel energy storage system, the flywheel PCS (Power Conversion System) system can be directly used as the converter system 21 to implement, which simultaneously includes a machine-side converter, a grid-side converter, as well as a flywheel control system and a communication system, and can simultaneously meet the connection with the flywheel energy storage unit 10, the step-up transformer 22, and the energy management main control system 30. The step-up transformer 22 is used to step up the power compensated by the flywheel energy storage unit and output it to the energy storage bus.

[0031] In some embodiments, an isolation capacitor is further provided between the grid-side converter 211 and the machine-side converter 212 for realizing high-frequency noise suppression and electromagnetic interference (EMI) isolation.

[0032] Figure 4 shows a schematic diagram of the actual built structure of a flywheel energy storage system according to an embodiment of the present disclosure. As Figure 3As shown, the number of flywheel energy storage units 10 is 16, and the single-unit capacity of each flywheel storage unit is 500kW / 50kWh. Accordingly, the number of machine-side converters 212 corresponding to the number of flywheel energy storage units is also 16. The rated power of the machine-side converter 212 can be selected as 630kw to meet the 500kW flywheel energy storage unit regulation, and the number of machine-side converters 212 in each converter unit 210 is 2. In order to meet the frequency regulation of the two machine-side converters 212, the rated power of the grid-side converter 211 can be selected as 1250kw equipment for implementation. For each converter system 21 including 4 parallel converter units 210, 2 converter systems 21 can be actually set, with a total of 8 converter units 210, to achieve the control of 16 flywheel energy storage units 10.

[0033] At the same time, the step-up transformer 22 can be implemented with a 4500kVA box-type transformer, and the converter system bus 23 can be implemented with a 450V bus. Corresponding to the number of converter systems 21, the number of converter system bus 23 is 2, which are respectively connected to a step-up transformer 22 to achieve connection with the energy storage bus 40. The flywheel outlet voltage is DC, which is converted into AC by the converter system and then merged into the low-voltage side of the box-type transformer. After being stepped up to 10kV by the box-type transformer, it is sent to the 10kV distribution room and then connected to the existing working power grid through a 10kV cable line. At the same time, the energy storage bus 40 and the plant working bus 50 are connected through the plant power switch S, so that a total of 8MW flywheel energy storage units are connected to the plant working bus and participate in the primary frequency regulation. Figure 4 As shown, in some embodiments, a protection switch and a filter device 60 may be further connected to the energy storage bus. This embodiment does not limit the specific structure of the protection switch and the filter device 60, and they can be specifically configured according to actual needs.

[0034] The flywheel energy storage system of this embodiment has the advantages of fast response speed, strong climbing ability, flexible power output, strong plasticity, high regulation accuracy, etc. The use of fast response energy storage to improve the unit's primary frequency regulation performance index, namely the target comprehensive performance Kp, is an effective measure to ensure the frequency safety of the power grid under the new form. in, is the frequency modulation response time, is the frequency modulation action rate, is the primary frequency modulation response accuracy. In this embodiment, and The value of can be calculated based on the following formula:

[0035]

[0036]

[0037] Among them,

[0038]

[0039] (1) Primary frequency regulation response time

[0040] It is used to measure whether the time taken for the output of the market entity to change to 10% of the total primary frequency regulation amount from the start when the frequency exceeds the primary frequency regulation dead zone meets the requirements. The calculation formula is as follows.

[0041] If the value of is less than 0.1, then take 0.1;

[0042] In the formula, is the lag time when market entity i participates in primary frequency regulation for the jth time;

[0043] t N,d is the standard lag time, t N,d is 1 s.

[0044] (2) Primary frequency regulation action rate

[0045] It is used to measure whether the rate during the process of the output of the market entity reaching the primary frequency regulation target value when the frequency exceeds the primary frequency regulation dead zone and the output of the market entity returning to the starting value when the frequency returns to the primary frequency regulation dead zone meets the requirements. The calculation formula is as follows:

[0046]

[0047] In the formula, V N,i is the standard response rate, and the market entity should reach the target value or return to the starting value within 4 seconds each time it adjusts; V i.j is the actual response rate when market entity i reaches the target value for the jth time, V i.jh is the actual response rate when market entity i returns to the starting value for the jth time.

[0048] If the value of is less than 0.1, then take 0.1.

[0049] (3) Primary frequency regulation response accuracy

[0050] It is used to measure the deviation between the actual output value and the theoretical target value after the primary frequency regulation response of the market entity reaches stability. The calculation formula is as follows:

[0051]

[0052] where P i.j is the stable actual output value of the market entity i for the jth adjustment, and P E is the theoretical target value of the output for the jth adjustment of the market entity i; if the calculated value is less than 0.1, then take 0.1.

[0053] Standard time t N,d = 1 s. The flywheel energy storage system uses a high-precision and fast frequency detection device. The frequency detection, operation, and communication time do not exceed 170 ms. The time for the flywheel energy storage system to reach 10% of the theoretical active power regulation amount P E does not exceed 30 ms. Therefore, the flywheel energy storage system can achieve full-power charging to full-power discharging within 100 ms (including communication time). The value of the flywheel energy storage system actually tests the ability of the system to track power commands. The measured dynamic accuracy error of tracking power does not exceed 10%. In this embodiment, it is calculated according to a 20% tracking power dynamic error. According to the detection report provided by the flywheel device, the worst tracking accuracy value in the full-power range is 1.2%. Considering the influence of the power consumption of other devices in the system on power accuracy, the system response accuracy is considered according to 10%. The target comprehensive performance Kp = 1.8 * 1.8 * 1.8 = 5.832, with relatively high performance.

[0054] In this embodiment, a flywheel energy storage unit with fast response speed, strong climbing ability, and flexible power output is used as a fast-response energy storage to improve the primary frequency modulation performance index. The online rate of the energy storage system is improved by setting multiple parallel flywheel storage units, ensuring that the frequency modulation demand can still be met when a single flywheel energy storage unit is out of service for maintenance. At the same time, a complete set of array control technologies is realized by combining a two-way power regulation system and an energy management master control system, effectively ensuring that the flywheel energy storage system responds to the primary frequency modulation commands of the unit in unison.

[0055] For example, when the flywheel energy storage device is under maintenance, when a single flywheel with a monomer capacity of 500 kW / 50 kWh is out of service, only 0.5 MW of frequency modulation power is reduced, and it can still meet the requirements of the primary frequency modulation market operation. However, when a single flywheel with a monomer capacity of 4 MW / 100 kWh is out of service, 4 MW of frequency modulation power is reduced, that is, a unit cannot participate in the primary frequency modulation market.

[0056] Based on the same inventive concept, the second embodiment of the present disclosure provides a combined thermal energy and energy storage frequency modulation energy storage system, which combines the flywheel energy storage system of the first embodiment of the present disclosure with a thermal power generating unit to achieve dynamic frequency modulation of an external power grid. Specifically, the thermal power generating unit is directly connected to the external power grid system, while the flywheel energy storage system is connected to the thermal power generating unit through the auxiliary power working bus. By charging or discharging from the auxiliary power working bus according to the unit DCS instruction by the energy storage system, the real-time load of the auxiliary power is changed, thereby changing the grid-connected power of the unit, as Figure 5 shown.

[0057] In some embodiments, an energy storage facility with a power capacity of about 3% of the rated power of the unit is connected to the auxiliary power bus section, that is, the power capacity of the flywheel energy storage system is 3% of the rated power of the thermal power generating unit. The thermal power generating unit mainly refers to a coal-fired power generating unit. This embodiment utilizes the technical characteristics of the flywheel energy storage system, such as short output power response time and high power regulation accuracy, to shorten the unit response time, improve the regulation rate and regulation accuracy, so as to improve the comprehensive performance index of frequency modulation.

[0058] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present disclosure, and are not intended to limit them; although the present disclosure has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A flywheel energy storage system, characterized in that, At least including: Multiple flywheel energy storage units, multiple bidirectional power conditioning systems, and an energy management master control system; wherein, All the flywheel energy storage units are connected in parallel, and the flywheel energy storage units are connected to the bidirectional power conditioning systems; Each of the bidirectional power conditioning systems at least includes: a converter system and a step-up transformer. The converter system at least includes multiple parallel-connected converter units. The converter units are used to achieve bidirectional power conversion between the flywheel energy storage units and the step-up transformer. The step-up transformer is connected to the auxiliary power working bus through an energy storage bus; The energy management master control system is communicatively connected to all the flywheel energy storage units and the bidirectional power conditioning systems, and is used to coordinate the charge and discharge logic and monitor the system status.

2. The flywheel energy storage system according to claim 1, wherein The flywheel energy storage unit at least includes: A flywheel rotor for storing rotational kinetic energy; A magnetic levitation bearing for supporting the flywheel rotor and reducing mechanical friction; A bidirectional motor coaxially connected to the flywheel rotor for achieving the conversion between electrical energy and mechanical energy; A vacuum cavity for accommodating the flywheel rotor, the magnetic levitation bearing, and the bidirectional motor.

3. The flywheel energy storage system according to claim 2, wherein, The flywheel energy storage unit further includes: A vacuum maintenance module connected to the vacuum cavity through a vacuum pipeline for maintaining the vacuum degree in the vacuum cavity; A cooling module including a liquid cooling circulation pipeline surrounding the vacuum cavity and the bidirectional motor.

4. The flywheel energy storage system according to claim 1, wherein The converter unit is a bidirectional converter module. The bidirectional converter module at least includes: A grid-side converter connected to the step-up transformer through a converter system bus and a DC link for regulating the voltage and frequency of the converter system bus; Multiple parallel-connected machine-side converters connected to the grid-side converter through a converter unit bus. Each machine-side converter is connected to one of the flywheel storage units for controlling the charge and discharge power of the flywheel energy storage unit.

5. The flywheel energy storage system according to claim 4, characterized in that An isolation capacitor is provided between the machine-side converter and the grid-side converter.

6. The flywheel energy storage system according to claim 4, wherein The single capacity of the flywheel storage unit is 500kW / 50kWh, the rated power of the machine-side converter is 630kw, the rated power of the grid-side converter is 1250kw, and each grid-side converter is connected to two machine-side converters simultaneously.

7. The flywheel energy storage system according to claim 6, wherein The step-up transformer is a box-type transformer.

8. The flywheel energy storage system according to any one of claims 1 to 7, characterized in that, It further includes: A protection switch and a filtering device connected to the energy storage bus.

9. A combined thermal energy storage and frequency regulation energy storage system, characterized in that, At least including: A thermal power generating unit connected to an external power grid system; The flywheel energy storage system according to any one of claims 1 to 8 is connected to the thermal power generating unit through the auxiliary power working bus.

10. The combined thermal energy and energy storage frequency regulation energy storage system according to claim 9, wherein The power capacity of the flywheel energy storage system is 3% of the rated power of the thermal power generating unit.

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