Energy storage type phase modifier with damping structure and system

Abstract

The invention discloses an energy storage type phase modifier with a damping structure and a system, and belongs to the technical field of electric power equipment. The brush doubly-fed motor comprises a stator and a rotor. An air gap is formed between the stator and the rotor; three-phase symmetrical windings are arranged in the stator and the rotor; the damping structure is made of an electric conductor material and is arranged along the circumference of the notch of the rotor; the damping structure can be equivalent to a three-phase winding, and in the equivalent three-phase winding of the damping structure, each phase is self-short-circuited. The damping structure optionally comprises at least one of the following structures: a slot wedge made of an electric conductor, a cage bar and an end ring. According to the invention, the energy storage type phase modifier has the capabilities of suppressing the excitation current peak value and improving the short-circuit current on the premise of ensuring the high inertia supporting function, so that an excitation system is effectively protected, and the short-circuit voltage supporting capability of the motor is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of power equipment technology, and more specifically, relates to a synchronous condenser with a damping structure and a system thereof. Background Technology

[0002] The demand for electricity from the power grid has been increasing year by year, gradually forming a pattern in which new energy units are the main body and power transmission relies on high-voltage direct current transmission. Power systems built with a high proportion of new energy units have problems such as lack of rotational inertia and insufficient short-circuit capacity due to the widespread use of power electronic converters, which significantly increases the risk of grid frequency exceeding limits and the probability of voltage faults.

[0003] To address these challenges, the current power grid primarily relies on deploying synchronous condensers (SCDCs) near renewable energy power plants to resolve voltage and frequency support issues. However, traditional SCDC systems only offer reactive power compensation, have limited inertia support capabilities, and are far less effective at suppressing frequency fluctuations than traditional synchronous generator sets. Therefore, an energy storage-type SCDC system based on AC excitation technology has been proposed as an improvement over traditional SCDCs. This system achieves high inertia support through wide-range speed regulation and the mechanical energy storage of the motor rotor or coaxial flywheel, significantly reducing the grid frequency variation rate. However, limited by the current carrying capacity of the rotor-side AC excitation system, under severe fault conditions such as three-phase symmetrical short circuits, the excitation system is prone to triggering overcurrent protection mechanisms, leading to the unit's self-protection and grid disconnection, making it difficult to maintain continuous voltage support during fault periods.

[0004] Overall, existing energy storage synchronous condenser systems are unable to simultaneously provide the power system with effective resistance to frequency fluctuations and transient voltage support during short-circuit faults. Summary of the Invention

[0005] In view of the shortcomings of the existing technology and the need for improvement, the present invention provides an energy storage type synchronous condenser and system with a damping structure. The purpose is to enable the energy storage type synchronous condenser to suppress the peak excitation current and improve the short-circuit current while ensuring the high inertia support function, thereby effectively protecting the excitation system and enhancing the short-circuit voltage support capability of the motor.

[0006] To achieve the above objectives, according to one aspect of the present invention, an energy storage type synchronous condenser with a damping structure is provided, comprising: a brushed doubly fed motor and a damping structure; A brushed doubly fed motor consists of a stator and a rotor; there is an air gap between the stator and the rotor; both the stator and the rotor are equipped with three-phase symmetrical windings. The damping structure is made of an electrical conductor material and is arranged along the circumference of the rotor slots; the damping structure can be equivalent to a three-phase winding, and each phase in the equivalent three-phase winding of the damping structure is self-short-circuited.

[0007] In some alternative embodiments, the damping structure includes slot wedges disposed at the rotor slot openings; each slot wedge is made of an electrically conductive material.

[0008] In some alternative embodiments, the damping structure further includes at least one of the following: Cage bars; cage bars are installed at the rotor slot openings and located outside the slot wedges; each cage bar is made of an electrically conductive material; End ring; the end ring is disposed on the axial end face of the rotor; and the end ring is made of an electrically conductive material.

[0009] In some alternative embodiments, the damping structure includes at least one of the following: Cage bars; cage bars are installed at the rotor slot openings; each cage bar is made of an electrically conductive material; End ring; the end ring is disposed on the axial end face of the rotor; and the end ring is made of an electrically conductive material.

[0010] Furthermore, the electrical conductor material is copper.

[0011] According to another aspect of the present invention, an energy storage type synchronous condenser system is provided, comprising: a step-up transformer, an excitation transformer, an excitation converter, and an energy storage type synchronous condenser; The energy storage type synchronous condenser is the energy storage type synchronous condenser with damping structure provided by the present invention; The excitation converter includes a grid-side converter and a machine-side converter; the grid-side converter and the machine-side converter share a DC bus; The rotor winding of the energy storage type synchronous condenser is connected to the AC side of the machine-side converter, and the stator winding of the energy storage type synchronous condenser is connected to the low-voltage side of the step-up transformer; the low-voltage side of the excitation transformer is connected to the AC side of the grid-side converter, and the high-voltage side of the excitation transformer is connected to the low-voltage side of the step-up transformer; the high-voltage side of the step-up transformer is connected to the power grid.

[0012] According to another aspect of the present invention, a power system is provided, comprising: a power grid and an energy storage type synchronous condenser system provided by the present invention.

[0013] In summary, through the above-described technical solutions of this invention, by setting a damping structure at the rotor slot of the brushed doubly fed motor, the energy storage synchronous condenser operates at synchronous speed during steady-state operation. Since the damping structure has no induced current, it does not affect motor control. The synchronous condenser can still regulate the active and reactive power of the motor by adjusting the rotor excitation current. Therefore, the energy storage synchronous condenser provided by this invention has the ability to suppress grid frequency fluctuations. During transient faults caused by grid voltage drops, the damping structure can reduce the transient reactance of the motor and share the fault current, increasing the short-circuit capacity on the stator side while reducing the transient current stress on the generator-side converter. Therefore, the energy storage synchronous condenser provided by this invention has the ability to support grid voltage. Because the energy storage-type synchronous condenser provided by this invention has the ability to suppress grid frequency fluctuations and support grid voltage, it can provide high equivalent inertia and large short-circuit capacity. It effectively solves the problems of low-voltage fault ride-through difficulty and difficulty in providing effective voltage support in voltage drop scenarios. The synchronous condenser system can still operate reliably and provide reactive power support capability when there are serious faults such as grid short circuits. As a result, the frequency stability and voltage stability of the high proportion of new energy power system are greatly improved. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the energy storage condenser with damping structure provided in Embodiment 1 of the present invention.

[0015] Figure 2 This is a schematic diagram of the damping structure in the energy storage type synchronous condenser with damping structure provided in Embodiment 2 of the present invention.

[0016] Figure 3 This is a schematic diagram of the energy storage type synchronous condenser system provided in Embodiment 3 of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0018] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0019] High-inertia energy storage synchronous condenser systems based on AC excitation technology have limited excitation capacity. When the grid voltage drops significantly, the excitation system struggles to withstand the high short-circuit current stress and is forced to shut down, thus failing to provide effective voltage support to the grid. To address the problem that existing energy storage synchronous condenser systems cannot simultaneously provide effective system resistance to frequency fluctuations and transient voltage support during short-circuit faults, this invention provides an energy storage synchronous condenser and system with a damping structure. Based on a brushed doubly-fed induction generator (DFIG), a damping structure is introduced into the rotor. This damping structure effectively suppresses short-circuit transient currents in the rotor windings. Therefore, while retaining the high inertia support capability of the energy storage synchronous condenser, it reduces converter fault current and provides continuous voltage support during severe grid voltage dips, thereby effectively protecting the excitation system and enhancing the motor's short-circuit voltage support capability.

[0020] The following is an example.

[0021] Example 1: A type of energy storage synchronous condenser with a damping structure, such as Figure 1 As shown, it includes: a brushed doubly fed motor and a damping structure; A brushed doubly fed motor includes a stator and a rotor; there is a uniform air gap between the stator and the rotor; both the stator and the rotor are equipped with three-phase symmetrical windings, the magnetic circuit / electrical circuit is symmetrical, and the rotor winding current is fed in through slip rings mounted on the rotor; The damping structure is made of an electrical conductor material and is arranged along the circumference of the rotor slots; the damping structure can be equivalent to a three-phase winding, and each phase in the equivalent three-phase winding of the damping structure is self-short-circuited.

[0022] Traditional applications of doubly-fed induction generators (DFIGs) include wind turbine generators and pumped-storage generators. In these applications, DFIGs require a wide range of speed regulation. Damping windings in these DFIGs experience significant losses under large slip, thus reducing the motor's speed regulation capability. Therefore, damping windings are not used in traditional DFIG applications. However, in high-inertia energy storage synchronous condensers, the motor operates at synchronous speed for extended periods, only changing speed during severe grid frequency faults. Therefore, the damping winding has minimal impact on motor operation. Furthermore, in the event of a short-circuit fault, the damping winding reduces the current stress on the generator-side converter, thereby improving the motor's voltage support capability. Therefore, adding a damping winding is beneficial for high-inertia energy storage synchronous condensers.

[0023] Based on the above considerations, this embodiment achieves a high-inertia energy storage synchronous condenser by setting a damping structure at the rotor slot of the brushed doubly-fed motor. During steady-state operation, the energy storage synchronous condenser operates at synchronous speed. Since the damping structure has no induced current, it does not affect motor control. The condenser can still regulate the active and reactive power of the motor by adjusting the rotor excitation current. Therefore, the energy storage synchronous condenser provided by this invention has the ability to suppress grid frequency fluctuations. During transient faults caused by grid voltage drops, the damping structure can reduce the transient reactance of the motor and share the fault current, increasing the short-circuit capacity on the stator side while reducing the transient current stress on the generator-side converter. Therefore, the energy storage synchronous condenser provided by this invention has the ability to support grid voltage.

[0024] Depending on the application scenario, different types of damping windings can be used. In scenarios with more severe frequency fluctuations, weaker damping windings can be used to ensure that the motor is less affected by the damping windings when it actively accelerates or decelerates. In scenarios with more severe voltage fluctuations, stronger damping windings can be used to improve the short-circuit capacity of the synchronous condenser.

[0025] like Figure 1 As shown, in this embodiment, the damping structure includes slot wedges disposed at the rotor slot openings; each slot wedge is made of an electrically conductive material. Motor rotor windings generally require slot wedges for fixation. This embodiment reuses these slot wedges as the damping structure, simply by replacing the material of the slot wedges with electrically conductive materials such as copper, iron, or alloys. As an optional implementation, in this embodiment, the slot wedges embedded in the rotor slot openings are made of copper. The eddy current effect of the slot wedges provides a damping effect, acting as a damping winding. In practical applications, the strength of the damping winding is adjustable. Adjustments to the strength of the damping winding include adjusting the number of slot wedges using conductive materials and adjusting the type of conductor material.

[0026] In other embodiments of the present invention, the damping structure may also be implemented in other ways, such as installing end rings or adding extra cage bars at both ends of the rotor.

[0027] Example 2: A synchronous condenser with a damping structure. This embodiment is similar to Embodiment 1 above, except that the damping structure in this embodiment does not reuse the rotor slot wedges in the brushed doubly-fed motor. Figure 2 As shown, in this embodiment, the damping structure includes: Cage bars; cage bars are installed at the rotor slot openings; each cage bar is made of an electrically conductive material; End ring; the end ring is disposed on the axial end face of the rotor; and the end ring is made of an electrically conductive material.

[0028] The cage bars and end rings used in the damping structure can be made of electrical conductor materials such as copper, iron, or alloys; optionally, in this embodiment, the cage bars and end rings in the damping structure are both made of copper.

[0029] It is easy to understand that, depending on the required damping strength, the damping structure may only have cage bars, or only end rings, or it may be composed of cage bars or end rings and rotor slot wedges made of electrical conductor material, or it may be composed of cage bars, end rings and rotor slot wedges made of electrical conductor material, or it may be configured in other forms as needed, which will not be listed here.

[0030] Example 3: An energy storage type synchronous condenser system, such as Figure 3 As shown, it includes: a step-up transformer, an excitation transformer, an excitation converter, and an energy storage type synchronous condenser; The energy storage type synchronous condenser is the energy storage type synchronous condenser with damping structure provided in Embodiment 1 or 2 above, wherein the three-phase windings equivalent to the damping structure are in a natural short-circuit form. The excitation converter includes a grid-side converter and a machine-side converter; the grid-side converter and the machine-side converter share a DC bus; The rotor winding of the energy storage type synchronous condenser is connected to the AC side of the machine-side converter, and the stator winding of the energy storage type synchronous condenser is connected to the low-voltage side of the step-up transformer; the low-voltage side of the excitation transformer is connected to the AC side of the grid-side converter, and the high-voltage side of the excitation transformer is connected to the low-voltage side of the step-up transformer; the high-voltage side of the step-up transformer is connected to the power grid.

[0031] Figure 3 The power system in question can be located at the common connection point of the sending-end system, which is composed of a high proportion of new energy generating units; or near the sending-end and receiving-end converter stations of a high-voltage direct current transmission system, etc.

[0032] Example 4: An electric power system includes: a power grid and the energy storage type synchronous condenser system provided in Embodiment 3 above.

[0033] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A phase modifier of the energy storage type with a damping structure, characterized in that, The application relates to a brush double-fed motor and a damping structure. The brush double-fed motor comprises a stator and a rotor; an air gap is arranged between the stator and the rotor; three-phase symmetrical windings are arranged in the stator and the rotor. The damping structure is made of an electric conductor material and is arranged along a circumference of a slot of the rotor; the damping structure can be equivalent to three-phase windings, and each phase of the equivalent three-phase windings of the damping structure is self-short-circuited. The damping structure comprises slot wedges arranged at the rotor slot; each slot wedge is made of an electric conductor material.

2. The energy storage phase modifier with damping structure as claimed in claim 1, wherein, The damping structure further comprises at least one of the following:

3. The energy storage type synchronous condenser with damping structure as described in claim 2, characterized in that, cage bars; the cage bars are arranged at the rotor slot and are located outside the slot wedges; each cage bar is made of an electric conductor material; end rings; the end rings are arranged at axial end faces of the rotor; and the end rings are made of an electric conductor material. The damping structure comprises at least one of the following:

4. The damper-structured energy storage phase modifier of claim 1, wherein, cage bars; the cage bars are arranged at the rotor slot; each cage bar is made of an electric conductor material; end rings; the end rings are arranged at axial end faces of the rotor; and the end rings are made of an electric conductor material. The electric conductor material is copper.

5. The phase modifier with damping structure according to any one of claims 1 to 4, wherein The application relates to a boost transformer, an excitation transformer, an excitation current transformer and an energy storage type phase modifier.

6. An energy storage type synchronous condenser system, characterized in that, The energy storage type phase modifier is the energy storage type phase modifier with the damping structure as claimed in any one of claims 1 to 5. The excitation current transformer comprises a grid-side current transformer and a machine-side current transformer; the grid-side current transformer and the machine-side current transformer share a direct-current bus; a rotor winding of the energy storage type phase modifier is connected with an alternating-current side of the machine-side current transformer; a stator winding of the energy storage type phase modifier is connected with a low-voltage side of the boost transformer; a low-voltage side of the excitation transformer is connected with an alternating-current side of the grid-side current transformer; a high-voltage side of the excitation transformer is connected with the low-voltage side of the boost transformer; and a high-voltage side of the boost transformer is connected with a power grid. The application relates to a power grid and the energy storage type phase modifier system as claimed in claim 6. ​ 7. A power system characterized by, ​ ​

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