Energy storage system for cooperatively outputting power to power grid and power output method

Abstract

The invention relates to an energy storage system for outputting power to a power grid cooperatively and a power output method.The energy storage system comprises a gravity energy storage subsystem, a compressed air energy storage subsystem, a power generator and a motor, and gravitational potential energy of the gravity energy storage subsystem is converted into mechanical energy for driving the power generator through the compressed air energy storage subsystem; the generator driven by the mechanical energy outputs electric energy to a power grid; the power output method comprises the following steps: receiving a power input demand of a power grid side and judging the demand; when the power grid demand output power N is greater than or equal to 0, the gravity energy storage subsystem, the compressed air energy storage subsystem and the generator work; when the power grid demand output power N is less than 0, the motor and the compressed air energy storage subsystem work in sequence; through power distribution and operation state switching between the two sub-systems, cooperative control over the two sub-systems in the gravity compressed air energy storage system is achieved, and therefore the respective advantages of the gravity and compressed air energy storage system are brought into full play.

Description

Technical Field

[0001] The present invention relates to the technical field of power management systems, and in particular to an integrated management system for power grid technical transformation projects. Background Art

[0002] With the transformation of the global energy structure and the rapid development of new power systems, energy storage technology plays an increasingly critical role in the modern power industry. The balance of power supply and demand faces many challenges, such as the intermittent and volatile nature of renewable energy (such as wind and solar energy), which leads to large differences in power supply on different time scales. In order to ensure the stable operation of the power system, improve energy efficiency, and promote the large-scale grid connection of renewable energy, efficient and reliable energy storage technology has become an urgent need for the development of the industry.

[0003] As an emerging energy storage method, gravity energy storage has outstanding advantages such as long service life of cyclic charging and discharging, high safety, large capacity, no pollution, and large-scale construction, but the response speed is slow. Although compressed air energy storage has a fast response speed, long service life, and low operation and maintenance costs, it has certain energy losses and a high degree of system complexity. Therefore, how to give full play to the advantages of the two energy storage methods and coordinate the two energy storage methods is a technical problem that needs to be solved at present. Summary of the invention

[0004] The purpose of the present invention is to solve the above-mentioned problems of the prior art and to propose an energy storage system and energy storage method for collaboratively outputting power to a power grid. The specific technical solution is as follows:

[0005] An energy storage system for collaboratively outputting power to a power grid comprises a gravity energy storage subsystem, a compressed air energy storage subsystem, a generator and an electric motor. The gravitational potential energy of the gravity energy storage subsystem is converted into mechanical energy for driving the generator by the compressed air energy storage subsystem. The generator driven by the mechanical energy outputs electrical energy to the power grid. The electrical energy on the power grid side is converted into high-pressure gas internal energy by the electric motor and the compressed air energy storage subsystem.

[0006] The compressed air energy storage subsystem includes a compressor, an expander and a high-pressure gas storage chamber. The compressor compresses air to output high-pressure gas, which is stored in the high-pressure gas storage chamber. The high-pressure gas with internal energy output by the high-pressure gas storage chamber is converted into mechanical energy for driving the generator through the expander; the electric energy on the grid side is converted into mechanical energy for driving the compressor through the electric motor, and the air compressed by the compressor is stored in the high-pressure gas storage chamber to form high-pressure gas with internal energy.

[0007] A further design of the energy storage system is that the gravity energy storage subsystem includes a plurality of weight blocks with gravitational potential energy, and the plurality of weight blocks fall down at equal time intervals to convert the gravitational potential energy of the weight blocks into mechanical energy for driving the compressor.

[0008] A further design of the energy storage system is that the model of the gravity energy storage subsystem is expressed as:

[0009] Where, T i is the mechanical torque provided to the generator by the ith weight block, m is the unit weight block mass; g is the gravitational acceleration; v is the weight block velocity, η is the efficiency of converting gravitational potential energy into electrical energy; S n is the rated capacity of the gravity energy storage unit, T m is the total torque provided to the generator by all the weights; T m_gra is the input mechanical torque of the generator, T e is the electromagnetic torque of the generator; T j is the inertia time constant of the generator, D is the damping coefficient of the gravity energy storage unit, δ is the power angle of the generator; ω0 is the synchronous speed of the generator; ω is the electrical angular velocity of the generator.

[0010] A further design of the energy storage system is that the time interval constraint is:

[0011] t on_i =t on_1 +(i-1)Δt

[0012] In the formula, i is the number of the weight block, t on_1 is the time for the first weight block to be put into operation, t on_i is the operation time of the i-th weight block, and Δt is the interval time between weight blocks.

[0013] A further design of the energy storage system is that the expander outputs a torque T m for:

[0014]

[0015] Where G is the flow rate, kg / s; Cp is the constant pressure specific heat capacity; T is the total temperature of the centripetal turbine, K; π is the centripetal turbine expansion ratio; k is the heat capacity ratio, k for air is 1.4; η is the centripetal turbine efficiency; n is the speed, r / s; T m is the output torque, kN·m.

[0016] The energy storage system is further designed in that the stator voltage of the generator has a component u on the d-axis. d and the q-axis component u q It is obtained from the following formula:

[0017]

[0018] Where: i sd 、i sqare the components of the stator current on the d-axis and q-axis respectively; ψ f is the rotor flux, which is a constant; R s is the stator resistance; L d , L q are the stator direct-axis and quadrature-axis inductances.

[0019] A further design of the energy storage system is that the generator operates in the following mode:

[0020] Stator mechanical motion mode:

[0021]

[0022] in,

[0023]

[0024] Ignoring the stator copper loss and iron loss, the active power P s and electromagnetic power P e The relationship model is:

[0025] P s =P e =ω r T e

[0026] The relationship between electrical angular velocity and rotor mechanical angular velocity:

[0027] ω s =pω r

[0028] Electrical angular velocity mode when the expander is directly connected to the generator:

[0029]

[0030] Where: L d is the stator direct axis inductance, L q is the quadrature-axis inductance, ω s is the electrical angular velocity, ω r is the rotor mechanical angular velocity, p is the number of generator pole pairs, J is the rotor moment of inertia, T e is the electromagnetic torque, T m is the mechanical torque and n is the rotor speed.

[0031] An energy storage method as described above for the energy storage system comprises:

[0032] When the power grid requires output power N≥0, several weight blocks fall at equal time intervals to generate mechanical energy to drive the compressor. The compressor is driven to work and output high-pressure gas with internal energy. The internal energy of the high-pressure gas is converted into mechanical energy to drive the generator through the expander. The driven generator outputs power to the grid, and the energy storage system is in an energy release state.

[0033] When the grid demand output power N is less than 0, the grid's electric energy drives the motor to work, the compressor is driven by the motor to work, the output high-pressure gas is stored in the high-pressure gas storage chamber, and the energy storage system is in an energy storage state.

[0034] The present invention has the following beneficial effects:

[0035] According to the given power demand of the power grid, the present invention invests in a gravity energy storage subsystem and a compressed air energy storage subsystem or only invests in a compressed air energy storage subsystem, and realizes coordinated control of the two subsystems in the gravity compressed air energy storage by allocating power and switching the operating states between the two subsystems, thereby giving full play to the respective advantages of the gravity energy storage system and the compressed air energy storage system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a topological structure diagram of the energy storage system of the present invention;

[0037] Figure 2 The method of the energy storage system of the present invention outputting and inputting electric energy to a power grid;

[0038] Figure 3 It is a simulation diagram of the output power of the invented energy storage system. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Example 1

[0041] This embodiment relates to an energy storage system that outputs power to a power grid in a coordinated manner, such as Figure 1 The energy storage system includes a gravity energy storage subsystem, a compressed air energy storage subsystem, a generator and an electric motor. The gravitational potential energy of the gravity energy storage subsystem is converted into mechanical energy for driving the generator by the compressed air energy storage subsystem. The generator driven by the mechanical energy outputs electrical energy to the power grid. The electrical energy on the power grid side is converted into high-pressure gas internal energy through the electric motor and the compressed air energy storage subsystem.

[0042] The compressed air energy storage subsystem comprises a compressor, an expander and a high-pressure gas storage chamber. The compressor compresses air to output high-pressure gas, which is stored in the high-pressure gas storage chamber. The high-pressure gas with internal energy output by the high-pressure gas storage chamber is converted into mechanical energy for driving the generator through the expander; the electric energy on the grid side is converted into mechanical energy for driving the compressor through the electric motor, and the air compressed by the compressor is stored in the high-pressure gas storage chamber to form high-pressure gas with internal energy.

[0043] The gravity energy storage subsystem comprises a plurality of weight blocks having gravitational potential energy, and the plurality of weight blocks fall down at equal time intervals to convert the gravitational potential energy of the weight blocks into mechanical energy for driving the compressor.

[0044] The model of the above gravity energy storage subsystem is expressed as:

[0045]

[0046] Where, T i is the mechanical torque provided to the generator by the ith weight block, m is the unit weight block mass; g is the gravitational acceleration; v is the weight block velocity, η is the efficiency of converting gravitational potential energy into electrical energy; S n is the rated capacity of the gravity energy storage unit, T m is the total torque provided to the generator by all the weights; T m_gra is the input mechanical torque of the generator, T e is the electromagnetic torque of the generator; T j is the inertia time constant of the generator, D is the damping coefficient of the gravity energy storage unit, δ is the power angle of the generator; ω0 is the synchronous speed of the generator; ω is the electrical angular velocity of the generator.

[0047] Due to the physical characteristics of the gravity energy storage subsystem, there is a fixed time interval between each weight block being put into operation or withdrawn from operation. The time interval constraint for each weight block being put into operation in the present invention is:

[0048] t on_i =t on_1 +(i-1)Δt

[0049] In the formula, i is the number of the weight block, t on_1 is the time for the first weight block to be put into operation, t on_i is the operation time of the i-th weight block, and Δt is the interval time between weight blocks.

[0050] The above expander is the work-doing device of the system, which converts the pressure energy and heat energy contained in the air into mechanical energy. Its output power is related to the inlet air pressure, temperature and flow rate. The output work and output torque T m for:

[0051] Where G is the flow rate, kg / s; Cp is the constant pressure specific heat capacity; T is the total temperature of the centripetal turbine, K; π is the centripetal turbine expansion ratio; k is the heat capacity ratio, k for air is 1.4; η is the centripetal turbine efficiency; n is the speed, r / s; T m is the output torque, kN·m.

[0052] This embodiment uses a permanent magnet synchronous generator directly connected to the expander to convert mechanical energy into electrical energy. The stator voltage of the generator on the d-axis is u d and the q-axis component u q It is obtained from the following formula:

[0053]

[0054] Where: i sd 、i sq are the components of the stator current on the d-axis and q-axis respectively; ψ f is the rotor flux, which is a constant; R s is the stator resistance; L d , L q are the stator direct-axis and quadrature-axis inductances.

[0055] The above generator works in the following mode:

[0056] 1) Stator mechanical motion mode:

[0057]

[0058] in,

[0059]

[0060] 2) Active power P after ignoring stator copper loss and iron loss s and electromagnetic power P e The relationship model is:

[0061] P s =P e =ω r T e

[0062] 3) Relationship model between electrical angular velocity and rotor mechanical angular velocity:

[0063] ω s =pω r

[0064] 4) Electrical angular velocity mode when the expander is directly connected to the generator:

[0065]

[0066] Where: L dis the stator direct axis inductance, L q is the quadrature-axis inductance, ω s is the electrical angular velocity, ω r is the rotor mechanical angular velocity, p is the number of generator pole pairs, J is the rotor moment of inertia, T e is the electromagnetic torque, T m is the mechanical torque and n is the rotor speed.

[0067] Example 2

[0068] like Figure 2 This embodiment is a method for outputting power of an energy storage system based on the above-mentioned embodiment 1, comprising:

[0069] Accept power input requirements from the grid side and make judgments on the requirements;

[0070] When the power grid requires output power N ≥ 0, the gravity energy storage subsystem, the compressed air energy storage subsystem and the generator work in sequence, and the energy storage system is in an energy release state of outputting electric energy to the power grid;

[0071] When the grid demand output power N is less than 0, the motor and the compressed air energy storage subsystem work in sequence, and the energy storage system is in an energy storage state of absorbing grid electricity.

[0072] The more specific process of the above output power method is as follows:

[0073] Accept power input requirements from the grid side and make judgments on the requirements;

[0074] When the power grid requires output power N≥0, several weight blocks fall at equal time intervals to generate mechanical energy to drive the compressor. The compressor is driven to work and output high-pressure gas with internal energy. The internal energy of the high-pressure gas is converted into mechanical energy to drive the generator through the expander. The driven generator outputs power to the grid, and the energy storage system is in an energy release state.

[0075] When the grid demand output power N is less than 0, the grid's electric energy drives the motor to work, the compressor is driven by the motor to work, the output high-pressure gas is stored in the high-pressure gas storage chamber, and the energy storage system is in an energy storage state.

[0076] Simulation Example

[0077] This embodiment is based on Figure 1 The simulation results of the energy storage system are shown in Figure 2.

[0078] like Figure 3At 5s in the simulation, the power demand instruction on the grid side changes from 0MW to 0.6MW; at 15s in the simulation, the power demand instruction on the grid side changes from 0.6MW to 0MW; at 17s in the simulation, the power demand instruction on the grid side changes from 0MW to -0.5MW. Based on the power demand instruction on the grid side and the coordinated control strategy of gravity compressed air energy storage, the output power of the gravity compressed air energy storage system is obtained as follows: Figure 3 shown.

[0079] According to the above-mentioned power demand on the grid side, at 5s, the grid side needs gravity compressed air energy storage to emit power. At this time, the gravity pressure block drops, and the gravity compressed air energy storage presents the output power operation characteristics of gravity energy storage. At 5s, the first weight block is put into use, and the external power output is 0.2MW. Due to the output power characteristics of the gravity energy storage itself, it takes 4s to put in the second weight block, that is, at 9s, the second weight block is put into use, and the external output power of the gravity compressed air energy storage changes from 0.2MW to 0.4MW. Subsequently, at 13s, the third weight block is put into use, and the external output power of the gravity compressed air energy storage changes from 0.4MW to 0.6MW. At this time, the energy storage completes the power demand of the first stage on the grid side.

[0080] At 15s, the power demand on the grid side changes from 0.6MW to 0. At this time, the gravity energy storage part needs to be shut down, and the output power of the gravity compressed air energy storage switches from 0.6MW to 0 power operation state. At 17s, the power demand on the grid side changes from 0MW to -0.5MW. At this time, the compressed air energy storage part is put into operation. The compressed air energy storage has instantaneous response characteristics, and its output power has no minimum power output characteristic limit. It can directly absorb 0.5MW to meet the power demand on the grid side.

Claims

1. An energy storage system for collaboratively outputting power to a power grid, characterized in that: It includes a gravity energy storage subsystem, a compressed air energy storage subsystem, a generator and an electric motor. The gravitational potential energy of the gravity energy storage subsystem is converted into mechanical energy for driving the generator by the compressed air energy storage subsystem. The generator driven by the mechanical energy outputs electrical energy to the power grid. The electrical energy on the power grid side is converted into high-pressure gas internal energy through the electric motor and the compressed air energy storage subsystem.

2. The energy storage system according to claim 1, characterized in that: The compressed air energy storage subsystem includes a compressor, an expander and a high-pressure gas storage chamber. The compressor compresses air to output high-pressure gas, which is stored in the high-pressure gas storage chamber. The high-pressure gas with internal energy output by the high-pressure gas storage chamber is converted into mechanical energy for driving the generator through the expander; the electric energy on the grid side is converted into mechanical energy for driving the compressor through the electric motor, and the air compressed by the compressor is stored in the high-pressure gas storage chamber to form high-pressure gas with internal energy.

3. The energy storage system according to claim 2, characterized in that: The gravity energy storage subsystem includes a plurality of weight blocks with gravity potential energy. The plurality of weight blocks fall down at equal time intervals to convert the gravity potential energy of the weight blocks into mechanical energy for driving the compressor.

4. The energy storage system according to claim 3, characterized in that: The model expression of the gravity energy storage subsystem is: Where, T i is the mechanical torque provided to the generator by the ith weight block, m is the unit weight block mass; g is the gravitational acceleration; v is the weight block velocity, η is the efficiency of converting gravitational potential energy into electrical energy; S n is the rated capacity of the gravity energy storage unit, T m is the total torque provided to the generator by all the weights; T m_gra is the input mechanical torque of the generator, T e is the electromagnetic torque of the generator; T j is the inertia time constant of the generator, D is the damping coefficient of the gravity energy storage unit, δ is the power angle of the generator; ω0 is the synchronous speed of the generator; ω is the electrical angular velocity of the generator.

5. The energy storage system according to claim 3, characterized in that: The time interval constraint is: on_i =t on_1 +(i-1)Δt In the formula, i is the number of the weight block, t on_1 is the time for the first weight block to be put into operation, t on_i is the operation time of the i-th weight block, and Δt is the interval time between weight blocks.

6. The energy storage system according to claim 2, characterized in that: The expander output torque T m for: Where G is the flow rate, kg / s; Cp is the constant pressure specific heat capacity; T is the total temperature of the centripetal turbine, K; π is the centripetal turbine expansion ratio; k is the heat capacity ratio, k for air is 1.4; η is the centripetal turbine efficiency; n is the speed, r / s; T m is the output torque, kN·m.

7. The energy storage system according to claim 1, characterized in that: The stator voltage of the generator on the d-axis component u d and the q-axis component u q It is obtained from the following formula: Where: i sd 、i sq are the components of the stator current on the d-axis and q-axis respectively; ψ f is the rotor flux, which is a constant; R s is the stator resistance; L d , L q are the stator direct-axis and quadrature-axis inductances.

8. The energy storage system according to claim 1, characterized in that: The generator works in the following mode: Stator mechanical motion mode: in, Ignoring the stator copper loss and iron loss, the active power P s and electromagnetic power P e The relationship model is: P s =P e =ω r T e The relationship between electrical angular velocity and rotor mechanical angular velocity is as follows: oh s =pω r Electrical angular velocity mode when the expander is directly connected to the generator: Where: L d is the stator direct axis inductance, L q is the quadrature-axis inductance, ω s is the electrical angular velocity, ω r is the rotor mechanical angular velocity, p is the number of generator pole pairs, J is the rotor moment of inertia, T e is the electromagnetic torque, T m is the mechanical torque and n is the rotor speed.

9. The power output method of the energy storage system according to claims 1-8, characterized in that: include: Accept power input requirements from the grid side and make judgments on the requirements; When the power grid requires output power N≥0, several weight blocks fall at equal time intervals to generate mechanical energy to drive the compressor. The compressor is driven to work and output high-pressure gas with internal energy. The internal energy of the high-pressure gas is converted into mechanical energy to drive the generator through the expander. The driven generator outputs power to the grid, and the energy storage system is in an energy release state. When the grid demand output power N is less than 0, the grid's electric energy drives the motor to work, the compressor is driven by the motor to work, the output high-pressure gas is stored in the high-pressure gas storage chamber, and the energy storage system is in an energy storage state.

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