A large-capacity energy storage power station connected to the grid via a synchronous motor

Abstract

The present invention provides a large-capacity energy storage power station connected to the grid via a synchronous motor, drawing on the large-capacity and naturally grid-friendly grid-connected characteristics of synchronous motors in power systems; the energy storage power station is composed of ≥1 power station units, and the power station unit is composed of an energy storage system, a PCS, a first motor, a coupling, and a second motor. The first motor and the second motor can operate as both motors and generators and form a motor group through a coupling; the second motor is a synchronous motor and is connected to a medium-voltage and high-voltage power grid; the PCS can quickly adjust the operating state of the first motor, and the second motor adjusts its own excitation system to emit or absorb active power and reactive power to the AC power grid, thereby realizing bidirectional energy flow and four-quadrant operation, participating in frequency regulation, peak regulation, and voltage regulation of the power system, and serving as a black start power supply for the power system, and is suitable for the construction of a 100-megawatt-class battery energy storage power station.

Description

Technical Field

[0001] The present invention relates to the field of energy storage power stations using battery packs and supercapacitors as energy storage devices, and in particular to a large-capacity energy storage power station similar to a pumped storage power station using battery packs and supercapacitors as energy storage devices, which is connected to the grid with synchronous motors to assist the power grid in peak regulation, frequency regulation, voltage regulation, and black start. Background Art

[0002] my country has built several 10 million kilowatt-level renewable energy power generation bases. With the rapid development of energy internet, large-scale energy storage technology has become a key supporting technology for the utilization of renewable energy power generation with randomness, intermittency and volatility. For the access of large-scale renewable energy power generation, on the one hand, the randomness can be reduced and its adjustability can be improved by combining energy storage technology with renewable energy power generation; on the other hand, the adaptability of the power grid to renewable energy power generation can be enhanced through grid-level energy storage applications.

[0003] Pumped storage is the most mature and cost-effective energy storage method in the current power system, but it is limited by geographical location. Battery energy storage has flexible configuration and is not restricted by geographical location. As the cycle life and cost-effectiveness of batteries continue to improve, energy storage power stations using batteries as energy storage devices have received attention and demonstrated applications.

[0004] In regional power grids rich in renewable energy generation, the capacity requirement for battery energy storage is usually more than tens of MW, or even more than 100 MW. The National Wind, Solar, Storage and Transmission Demonstration Project is currently the world's largest renewable energy project integrating wind power, photovoltaic power generation, energy storage and transmission projects, with a development scale of 500 MW of wind power, 100 MW of solar photovoltaic power generation, and 110 MW of chemical energy storage.

[0005] At present, battery energy storage is mainly connected to the grid by power electronic converters. With the large-scale development and utilization of new energy, a large number of power electronic converters are connected to the grid, the trend of power system power electronics is becoming more and more obvious, the operation characteristics of the power grid have changed significantly, and the safety and stability of the power system are becoming increasingly prominent. In some areas where new energy is concentrated and connected to the grid, sub / super synchronous oscillations often occur. Different from the low-frequency oscillation mode dominated by synchronous machines, it is difficult to analyze and suppress them.

[0006] Drawing on the natural and friendly grid-connected characteristics of synchronous motors, the virtual synchronous machine technology of power electronic converters has received great attention. Virtual synchronous machine technology introduces synchronous machine rotor motion and electromechanical transient equations in the control link of power electronic converters, and configures energy storage units or uses the inertia of wind turbines to simulate the primary frequency regulation and excitation control mechanism of synchronous generators, realizes automatic adjustment of active and reactive power, adaptively participates in system frequency and voltage regulation, and damps system frequency oscillations, so as to achieve the purpose of improving the safe and stable operation level of regional power grids. Many scientific research institutions and enterprises have conducted extensive research and demonstration applications on it, and have made certain progress.

[0007] However, the application of virtual synchronous machines also encounters inherent limitations. The adaptability of large-scale access to the power grid is still unclear, and they also face the problems of correlated coupling and mutual excitation under complex power electronic environment conditions. When a short circuit occurs in the power grid, traditional synchronous motors can support larger short-circuit currents, while virtual synchronous machines are limited by the overcurrent characteristics of power electronic devices and cannot support larger short-circuit currents. Due to the limitation of overload capacity, the voltage control capability is also not as good as that of conventional synchronous motor groups. Summary of the invention

[0008] In view of the defects of the existing technology and the trend of large-scale and high-proportion grid connection of new energy in the energy transformation that has been booming all over the world, the present invention provides a large-capacity energy storage power station solution and implementation example via synchronous motor grid connection, drawing on the large capacity and naturally grid-friendly grid connection characteristics of synchronous motors in power systems, replacing the defects caused by large-scale grid connection of traditional power converters, similar to the functions of pumped storage power stations but with greater flexibility and faster response speed, and capable of providing peak shaving, frequency regulation, voltage regulation, black start and other services for power grids that accept large-scale renewable energy power generation, thereby improving the grid's acceptance of energy storage power stations and renewable energy power generation and improving the safety of the power system.

[0009] The energy storage power station is composed of ≥1 power station units, and the power station unit is composed of an energy storage system, a PCS, a first motor, a coupling, and a second motor. The energy storage system is connected to the PCS, and the PCS is connected to the first motor. The first motor and the second motor are connected through a coupling to form a motor group. The second motor is a synchronous motor and is incorporated into the medium voltage and high voltage power grids for operation.

[0010] After the second motor is connected to the grid, it generates or absorbs reactive power by adjusting its own excitation system to control the reactive power between it and the grid. At the same time, the speeds of the second motor and the first motor remain basically unchanged due to the constraints of the grid. The PCS controls the operating state of the first motor to make the first motor work in the motor state or the generator state. When the first motor works in the motor state, the PCS absorbs DC power from the energy storage system to drive the first motor, and the first motor drives the second motor to be connected to the grid and generate electricity through the coupling, and transmits active power to the grid. When the first motor works in the generator state, the second motor operates as a motor, absorbs active power from the grid, drives the first motor to generate electricity, and the PCS converts the AC power generated by the first motor into DC power to charge the energy storage system.

[0011] The power station unit responds to the grid AGC (automatic generation control) and AVC (automatic voltage control) instructions in real time or autonomously adjusts the operating status of the first motor and the second motor's own excitation system according to the voltage and frequency of the grid connection point, sends active power to the AC grid or absorbs active power and reactive power, realizes two-way flow of energy and four-quadrant operation, participates in the frequency regulation, peak regulation and voltage regulation of the power system, and serves as the black start power supply of the power system.

[0012] The first motor and the second motor are both three-phase AC motors, which can be operated as motors or generators; the first motor is one of a permanent magnet synchronous motor, a synchronous motor, and an asynchronous motor, and the second motor is a synchronous motor.

[0013] Since the motor group transmits energy bidirectionally, the first motor and the second motor have the same rated power and rated speed, and the rated speed is the synchronous speed of the second motor when it emits 50Hz or 60Hz alternating current.

[0014] Since the first motor and the second motor transmit power through a coupling and have electrical isolation, the rated voltages of the first motor and the second motor are independent of each other. The second motor is connected to the grid through medium voltage and high voltage to improve the conversion efficiency of the system, reduce losses and equipment costs such as step-up transformers, and the rated voltages of the second motor include 3.15kV, 6.3kV, 10.5kV, 13.8kV, 15.75kV, 18kV and 20kV.

[0015] The energy storage system of the energy storage power station consists of ≥2 energy storage units. One energy storage unit includes one energy storage device and one bidirectional DC / DC converter. The energy storage device includes battery packs of different chemical systems (such as lithium battery packs, lead-acid battery packs, lead-carbon battery packs, and liquid flow battery packs) and high-power density supercapacitor modules. The positive and negative electrodes of the energy storage device are respectively connected to the input positive and negative electrodes of the bidirectional DC / DC converter, and the output positive and negative electrodes of the bidirectional DC / DC converter are the positive and negative electrodes of the energy storage unit.

[0016] There are two types of bidirectional DC / DC converters: isolated and non-isolated. The insulation level of the isolated bidirectional DC / DC converter is the same as that of the connected first motor, so that the energy storage device is insulated from the first motor.

[0017] PCS has two topological structures: modular multilevel converter (MMC) and cascaded H-bridge converter (CHC). PCSs with different topological structures correspond to different energy storage unit access methods.

[0018] The PCS based on the MMC topology has three phases and six bridge arms. The upper and lower bridge arms constitute one phase. A wire is drawn out from the connection point of the upper and lower bridge arms to connect to one phase of the first motor. Each bridge arm consists of N sub-modules (SM) and a current-limiting reactance.

[0019] The PCS based on the MMC topology has medium-voltage and high-voltage DC busbars. Since the output voltage of a single energy storage unit is too low to be directly connected to the DC busbar, several energy storage units are connected in series or parallel to form a large-capacity energy storage system and then connected to the DC busbar. The output port of the bidirectional DC / DC converter serves as the interface between the energy storage device and the PCS, and is controlled as a voltage source with simulated internal resistance. Its output voltage is related to its output current and simulated internal resistance. Specifically, the output voltage = the output voltage when the output current of the energy storage unit is zero minus the voltage obtained by multiplying the simulated internal resistance by the discharge current, or the voltage obtained by multiplying the simulated internal resistance by the charging current.

[0020] The PCS is based on a cascaded H-bridge topology and has three phases, which are connected in a star shape. Each phase is connected to a phase of a first motor. Each phase is formed by N H-bridge converters connected in series, and each H-bridge converter is connected to one energy storage unit.

[0021] The grid-connected mode of the power station unit of the energy storage power station is related to the topological structure, economy and reliability of the PCS. There are two grid-connected modes.

[0022] The first method starts from the energy storage system side: the energy storage system provides energy for the PCS, which drives the first motor to operate with variable frequency and speed regulation through the PCS, thereby adjusting the frequency and phase of the output voltage of the second motor; and adjusting the second motor's own excitation system to control the output voltage of the second motor, and connecting to the grid after the output voltage of the second motor meets the synchronization conditions with the grid voltage.

[0023] The second method is to start from the grid side: the second motor is equipped with an auxiliary starting device to assist the second motor in starting as an electric motor and inputting it into the grid, driving the first motor to run to the synchronous speed. This method is suitable for situations where the PCS based on the MMC topology is not convenient for frequency conversion to start the first motor.

[0024] Compared with the prior art, the present invention has the following beneficial effects.

[0025] Energy storage power stations are connected to the grid through synchronous generators, which have inertia for the grid and can stabilize the grid frequency. They can replace power electronic converters for grid connection, improve the quality of electric energy, solve the adaptability problem of large-scale power electronic converters for grid connection, and use traditional and effective theoretical analysis of subsynchronous oscillations of power systems to solve subsynchronous / supersynchronous oscillations generated by large-scale power electronic converters for grid connection. When a short-circuit fault occurs in the grid, a larger short-circuit current is provided, which is beneficial to grid recovery. In areas where new energy sources are concentrated and connected to the grid, the grid is often a weak grid with a small short-circuit current. The short-circuit current of the weak grid can be increased by connecting synchronous motors to the grid, which is beneficial to the stability of the power system and ultra-high voltage direct current transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Other features, objectives and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting implementation examples made with reference to the following accompanying drawings.

[0027] Figure 1 This is a structural diagram of a power station unit of a large-capacity energy storage power station connected to the grid via a synchronous motor proposed by the present invention.

[0028] Figure 2 The PCS schematic diagram is based on the MMC (modular multi-level) topology structure disclosed in the embodiment of the present invention.

[0029] Figure 3 The schematic diagram of the energy storage system disclosed in the implementation example of the present invention connected to a PCS based on an MMC (modular multi-level) topology structure.

[0030] Figure 4 A schematic diagram of a PCS in which an energy storage system disclosed in an embodiment of the present invention is connected to a cascaded H-bridge (CHC) topology structure. DETAILED DESCRIPTION

[0031] The present invention is described in detail below in conjunction with specific implementation examples. The following implementation examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0032] See also Figure 1The present invention discloses a power station unit of a large-capacity energy storage power station connected to the grid via a synchronous motor. The power station unit consists of an energy storage system, an energy conversion system (PCS), a first motor, a coupling, and a second motor. The energy storage system is connected to the PCS, and the PCS is connected to the first motor. The first motor and the second motor are connected to form a motor group through a coupling. The second motor is a synchronous motor and is connected to the medium-voltage and high-voltage power grids for operation.

[0033] After the second motor is connected to the grid, it controls the reactive power between itself and the grid by adjusting its own excitation system, thereby emitting or absorbing reactive power. At the same time, the speeds of the second motor and the first motor remain basically unchanged due to the constraints of the grid, and the PCS controls the operating state of the first motor, so that the first motor works in the motor state or the generator state. When the first motor works in the motor state, the PCS absorbs DC power from the energy storage system to drive the first motor, and the first motor drives the second motor to connect to the grid and generate electricity through the coupling, thereby delivering active power to the grid. When the first motor works in the generator state, the second motor operates as a motor, absorbs active power from the grid, drives the first motor to generate electricity, and the PCS converts the AC power emitted by the first motor into DC power to charge the energy storage system.

[0034] The power station unit responds to the grid AGC (automatic generation control) and AVC (automatic voltage control) instructions in real time or autonomously adjusts the operating status of the first motor and the second motor's own excitation system according to the voltage and frequency of the grid connection point, sends or absorbs active power and reactive power to the AC grid, realizes two-way flow of energy and four-quadrant operation, participates in the frequency regulation, peak regulation and voltage regulation of the power system, and serves as the black start power supply of the power system.

[0035] The first motor and the second motor are both three-phase AC motors, which can be operated as motors or generators; the first motor is one of a permanent magnet synchronous motor, a synchronous motor, and an asynchronous motor, and the second motor is a synchronous motor.

[0036] Since the motor group transmits energy bidirectionally, the first motor and the second motor have the same rated power and rated speed, and the rated speed is the synchronous speed of the second motor when it emits 50Hz or 60Hz alternating current.

[0037] The first motor and the second motor transmit power through a coupling, which has an electrical isolation effect. Therefore, the rated voltages of the first motor and the second motor are independent of each other. To improve the conversion efficiency, the second motor is connected to the grid through medium voltage and high voltage, which can save a first-level step-up transformer. Preferably, the rated voltage of the second motor includes 3.15kV, 6.3kV, 10.5kV, 13.8kV, 15.75kV, 18kV and 20kV.

[0038] See also Figure 2, a schematic diagram of a PCS based on an MMC (modular multi-level) topology structure disclosed in an embodiment of the present invention, wherein the PCS has three-phase six bridge arms, wherein the upper and lower bridge arms constitute one phase, and a lead wire is drawn out from the connection point of the upper and lower bridge arms to connect to one phase of the first motor, and each bridge arm consists of N sub-modules (SM) and a current-limiting reactance.

[0039] See also Figure 3 , which is a schematic diagram of the energy storage system disclosed in the implementation example of the present invention being connected to a PCS based on an MMC (modular multi-level) topology structure.

[0040] The energy storage system consists of ≥2 energy storage units. One energy storage unit includes one energy storage device and one bidirectional DC / DC converter. The energy storage device includes battery packs of different chemical systems (such as lithium battery packs, lead-acid battery packs, lead-carbon battery packs, and liquid flow battery packs), and high-power density supercapacitor modules. The positive and negative electrodes of the energy storage device are respectively connected to the input positive and negative electrodes of the bidirectional DC / DC converter, and the output positive and negative electrodes of the bidirectional DC / DC converter are the positive and negative electrodes of the energy storage unit.

[0041] There are two types of bidirectional DC / DC converters: isolated and non-isolated. The insulation level of the isolated bidirectional DC / DC converter is the same as that of the connected first motor, so that the energy storage device is insulated from the first motor.

[0042] Since the PCS based on the MMC topology has medium-voltage and high-voltage DC buses, the output voltage of a single energy storage unit is too low to be directly connected to this DC bus. Therefore, several energy storage units are connected in series and parallel to form a large-capacity energy storage system and then connected to this DC bus; the output port of the bidirectional DC / DC converter serves as the interface between the energy storage device and the PCS, and is controlled as a voltage source with simulated internal resistance. Its output voltage is related to its output current and simulated internal resistance. Specifically, the output voltage = the output voltage when the output current of the energy storage unit is zero minus the voltage obtained by multiplying the simulated internal resistance by the discharge current, or the voltage obtained by multiplying the simulated internal resistance by the charging current. The external characteristics of the battery are simulated in the above manner to facilitate the series and parallel connection of energy storage units, similar to the battery being connected in series and parallel to form a battery pack with higher voltage level and higher capacity.

[0043] The power station unit has two ways of being put into grid connection: the first is to start from the energy storage system side, the energy storage system provides energy for the PCS, the PCS drives the first motor to operate with variable frequency speed regulation, thereby adjusting the frequency and phase of the output voltage of the second motor, and adjusting the second motor's own excitation system to control the output voltage of the second motor, and connecting to the grid after the output voltage of the second motor meets the synchronization condition with the grid voltage;

[0044] The second method is to start from the grid side. The second motor is equipped with an auxiliary starting device to assist the second motor in starting as an electric motor and putting it into the grid, driving the first motor to run to the synchronous speed. This method is suitable for situations where the PCS based on the MMC topology is not convenient for frequency conversion to start the first motor.

[0045] See also Figure 4 , which is a PCS schematic diagram of an energy storage system connected to a cascaded H-bridge (CHC) topology structure disclosed in an embodiment of the present invention.

[0046] The energy storage system is composed of ≥2 modular energy storage units, one energy storage unit includes one energy storage device and one bidirectional DC / DC converter, the energy storage device includes battery packs of different chemical systems (such as lithium battery packs, lead-acid battery packs, lead-carbon battery packs, liquid flow battery packs), and high power density supercapacitor modules, the positive and negative electrodes of the energy storage device are respectively connected to the input positive and negative electrodes of the bidirectional DC / DC converter, and the output positive and negative electrodes of the bidirectional DC / DC converter are the positive and negative electrodes of the energy storage unit.

[0047] There are two types of bidirectional DC / DC converters: isolated and non-isolated. The insulation level of the isolated bidirectional DC / DC converter is the same as that of the connected first motor, so that the energy storage device is insulated from the first motor.

[0048] The PCS is based on a cascaded H-bridge topology and has three phases, which are connected in a star shape. Each phase is connected to a phase of a first motor. Each phase is formed by N H-bridge converters connected in series, and each H-bridge converter is connected to one energy storage unit.

[0049] The power station unit has two ways of being put into the grid: the first is to start from the energy storage system side. The energy storage system provides energy for the PCS. The PCS drives the first motor to operate with variable frequency and speed regulation to adjust the frequency and phase of the output voltage of the second motor, and adjust the second motor's own excitation system to control the output voltage of the second motor. The second motor is connected to the grid after the output voltage of the second motor meets the synchronization condition with the grid voltage. The second is to start from the grid side. The second motor is equipped with an auxiliary starting device to assist the second motor in starting as an electric motor and putting it into the grid, driving the first motor to run to the synchronous speed.

Claims

1. A large-capacity energy storage power station connected to the grid via a synchronous motor, characterized in that: include: The energy storage power station is composed of ≥1 power station unit, and the power station unit is composed of an energy storage system, an energy conversion system PCS, a first motor, a coupling, and a second motor. The energy storage system is connected to the PCS, and the PCS is connected to the first motor. The first motor and the second motor are connected through a coupling to form a motor group. The second motor is a synchronous motor and is incorporated into the medium voltage and high voltage power grid for operation; After the second motor is connected to the grid, it controls the reactive power between itself and the grid by adjusting its own excitation system, and emits or absorbs reactive power. At the same time, the speed of the second motor is constrained by the grid, and the PCS controls the operating state of the first motor, so that the first motor works in the motor state or the generator state. When the first motor works in the motor state, the PCS absorbs DC power from the energy storage system to drive the first motor, and the first motor drives the second motor to connect to the grid and generate electricity through the coupling, and transmits active power to the grid. When the first motor works in the generator state, the second motor operates as a motor, absorbs active power from the grid, drives the first motor to generate electricity, and the PCS converts the AC power generated by the first motor into DC power to charge the energy storage system. The power station unit responds to the automatic generation control AGC and automatic voltage control AVC instructions of the power grid in real time or autonomously adjusts the operating state of the first motor and the self-excitation system of the second motor according to the voltage and frequency of the grid connection point, sends or absorbs active power and reactive power to the AC power grid, realizes the two-way flow of energy and four-quadrant operation, participates in the frequency regulation, peak regulation and voltage regulation of the power system, and serves as the black start power supply of the power system; The energy storage system is composed of ≥2 energy storage units, one energy storage unit includes one energy storage device and one bidirectional DC / DC converter, the energy storage device includes a battery pack and a super capacitor, the positive electrode and negative electrode of the energy storage device are respectively connected to the input positive electrode and negative electrode of the bidirectional DC / DC converter, and the output positive electrode and negative electrode of the bidirectional DC / DC converter are the positive electrode and negative electrode of the energy storage unit.

2. A large-capacity energy storage power station connected to the grid via a synchronous motor according to claim 1, characterized in that: The first motor and the second motor are both three-phase AC motors, which can be operated as motors or generators; the first motor is one of a permanent magnet synchronous motor, a synchronous motor, and an asynchronous motor, and the second motor is a synchronous motor; The first motor and the second motor have the same rated power and rated speed, and the rated speed is the synchronous speed of the second motor when it generates 50 Hz or 60 Hz alternating current; The first motor and the second motor transmit power through a coupling, which has electrical isolation; the rated voltages of the first motor and the second motor are independent of each other; the second motor is connected to the grid through medium voltage and high voltage, and the rated voltages of the second motor include 3.15kV, 6.3kV, 10.5kV, 13.8kV, 15.75kV, 18kV and 20kV.

3. A large-capacity energy storage power station connected to the grid via a synchronous motor according to claim 1, characterized in that: The bidirectional DC / DC converter has two types: isolated and non-isolated. The insulation level of the isolated bidirectional DC / DC converter is the same as the insulation level of the first motor connected thereto, so that the energy storage device is insulated from the first motor. The PCS has two topological structures: modular multi-level MMC and cascade H-bridge. PCSs with different topological structures correspond to different energy storage unit access methods: The PCS based on the MMC topology has three phases and six bridge arms, wherein the upper and lower bridge arms constitute one phase, and a lead wire is drawn from the connection point of the upper and lower bridge arms to connect to one phase of the first motor, and each bridge arm is composed of N submodules and a current limiting reactance; The PCS based on the MMC topology has medium-voltage and high-voltage DC buses. A number of energy storage units are connected in series or parallel to form a large-capacity energy storage system and then connected to the DC bus. The output port of the bidirectional DC / DC converter serves as an interface between the energy storage device and the PCS and is controlled as a voltage source with simulated internal resistance. Its output voltage is related to its output current and simulated internal resistance. Specifically, the output voltage = the output voltage when the output current of the energy storage unit is zero minus the voltage obtained by multiplying the simulated internal resistance by the discharge current, or the voltage obtained by multiplying the simulated internal resistance by the charging current. The PCS based on the cascaded H-bridge topology has three phases, which are connected in a star shape. Each phase is connected to a phase of the first motor. Each phase is formed by N H-bridge converters connected in series, and each H-bridge converter is connected to one energy storage unit.

4. A large-capacity energy storage power station connected to the grid via a synchronous motor according to claim 1, characterized in that: The power station unit has two ways of being put into the grid; The first method starts from the energy storage system side: the energy storage system provides DC power to the PCS, and the PCS drives the first motor to operate with variable frequency speed regulation to adjust the frequency and phase of the second motor's output voltage; and adjusts the second motor's own excitation system to control the second motor's output voltage, and the second motor is put into grid connection after the output voltage of the second motor meets the synchronization condition with the grid voltage; The second method is starting from the grid side: the second motor is equipped with an auxiliary starting device to assist the second motor in starting as an electric motor and inputting into the grid.

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