Metro flywheel energy storage system with direct-current ice melting function and ice melting energy storage method

Abstract

The invention discloses a subway flywheel energy storage system with a direct-current ice melting function, which comprises a medium-voltage looped network, a contact network, a running rail, a positive bus, a negative bus, a subway rectifier module and a flywheel energy storage module, the subway rectification module is connected with the positive and negative buses. The positive bus is connected with a contact network, and the negative bus is connected with a walking rail; the flywheel energy storage module is connected with the positive bus, the negative bus and the walking rail. The flywheel energy storage module is further connected with the contact net through a circuit breaker QF, and the contact net is connected with the walking rail through a far-end short-circuit switch K3. The invention further discloses an ice melting and energy storage method applying the subway flywheel energy storage system with the direct-current ice melting function. The device has two functions of direct-current ice melting and flywheel energy storage charging and discharging, time division multiplexing is controlled by the two functions through a switch, efficient utilization of equipment is achieved, and the cost performance is improved.

Description

Technical Field

[0001] The present invention relates to the field of transportation technology, and in particular to a subway flywheel energy storage system with a direct current ice melting function and an ice melting energy storage method. Background Art

[0002] As a daily mode of transportation, subways offer numerous advantages, leading to their rapid development. However, this rapid development also presents challenges. The first is how to recover regenerative braking energy in subways. This is crucial for reducing energy consumption, suppressing catenary voltage fluctuations, and improving power supply system stability. Among the current mainstream technologies for utilizing regenerative braking energy in subways, flywheel energy storage is the optimal solution. Its basic principle is that when subway braking generates regenerative braking energy and raises the DC catenary voltage, the flywheel energy storage device stores the regenerative braking energy that cannot be absorbed by neighboring vehicles as mechanical energy. When the DC grid voltage drops due to subway traction, this stored mechanical energy is converted into electrical energy for release, thereby achieving energy savings and voltage stability. The second challenge is that when subway vehicles are powered by overhead catenary systems, rain, snow, and freezing weather can have a particularly significant impact on the catenary. The catenary is a crucial power supply for subway traction. Ice on the catenary surface can severely affect the normal current collection of the pantograph, reducing the reliability of the subway power supply and threatening driving safety. Small areas of line ice can be removed manually or mechanically (such as hammering with tools like a mallet) or with high-pressure steam. However, for large, long-distance lines, these methods are inefficient and ineffective. Therefore, installing advanced and reliable ice-melting equipment in traction substations to safely and quickly remove ice from large-scale contact lines is of great economic and social significance. Based on current domestic and international technological advancements, DC ice-melting technology is the most mature and feasible method. Its basic principle is to melt ice by harnessing the heat energy generated by the DC current flowing through the conductors.

[0003] Flywheel energy storage devices have been researched and applied to urban rail transit systems both domestically and internationally. DC de-icing technology has been successfully applied in power transmission lines, and research has also been conducted on DC de-icing for electrified railway catenary systems. Manufacturers such as Zhuzhou Electric Locomotive Works and Xuji Group have also conducted research on DC de-icing for catenary systems. However, there are currently no examples of DC de-icing technology being used on urban rail transit lines nationwide. In recent years, a DC de-icing device with reactive power compensation (SVG) has attracted attention. This device combines reactive power compensation and DC de-icing functions, offering easy switching and cost-effectiveness. It typically utilizes half-bridge, full-bridge, and hybrid MMC topologies.

[0004] Existing subway energy regenerative devices and DC de-icing devices have relatively limited functionality. For example, subway energy regenerative devices only recover regenerative braking energy from the subway and stabilize DC catenary voltage. DC de-icing devices, on the other hand, only melt ice when the catenary is iced, leaving them idle for extended periods. A traction substation requiring both functions would require two sets of equipment, which occupies a large area and incurs high procurement costs.

[0005] Existing flywheel energy storage devices and DC de-icing systems have relatively limited functionality. For example, flywheel energy storage devices only store energy, charge, and discharge energy, while DC de-icing devices only melt ice. These devices are only used when the catenary is iced, leaving them idle for extended periods of time. A traction substation requiring both functions must be equipped with two separate sets of equipment, which occupies a large area and incurs high procurement costs. Summary of the Invention

[0006] The purpose of the present invention is to provide a subway flywheel energy storage system and ice melting energy storage method with DC ice melting function, which has both DC ice melting and flywheel energy storage charging and discharging functions. The two functions are time-shared and multiplexed through switch control to achieve efficient utilization of the equipment and improve cost performance.

[0007] A subway flywheel energy storage system with DC ice melting function, comprising: The subway rectifier module steps down the AC power from the medium-voltage ring network and then outputs stable DC power through high-efficiency rectification and voltage regulation technology; The flywheel energy storage module converts regenerative braking energy through a converter cabinet, converting DC power into six-phase AC power to drive a permanent magnet synchronous motor. The permanent magnet synchronous motor accelerates the flywheel rotor, storing this energy as mechanical energy. Furthermore, when the DC grid voltage drops due to subway traction, the flywheel rotor drives the permanent magnet synchronous motor to decelerate, converting the stored mechanical energy into electrical energy. The resulting six-phase AC power is converted to DC power through the converter cabinet and released to the contact network. The subway rectifier module is connected to the positive and negative busbars; the positive busbar is connected to the contact network, and the negative busbar is connected to the running rails; the flywheel energy storage module is connected to the positive busbar, negative busbar and running rails respectively; The flywheel energy storage module is also connected to the contact network through a circuit breaker QF, and the contact network is connected to the running rail through a remote short-circuit switch K3; The flywheel energy storage module adopts two sets of three-phase active neutral-point clamped three-level topology, in which one phase is connected in series with an inductor and in parallel with a capacitor to form a buck-type DC / DC circuit; six such bridge arms in the converter cabinet form a six-way buck-type DC / DC circuit.

[0008] Furthermore, the flywheel energy storage module includes a switch cabinet K1, an isolating switch cabinet K2, a converter cabinet, a contactor KM and a flywheel cabinet; The converter cabinet is connected to the switch cabinet K1 and the negative busbar via the isolation switch cabinet K2, and the switch cabinet K1 is also connected to the positive busbar; The converter cabinet is also connected to the flywheel cabinet via a contactor KM.

[0009] Furthermore, the two groups of three-phase active neutral point clamped three-level topology structures include group A and group B, which have the same structure; Group A includes three bridge arms, namely bridge arm A, bridge arm B, and bridge arm C; and also includes inductor L1, inductor L2, inductor L3, capacitor C1, capacitor C2, capacitor C3, capacitor C4, and capacitor C5; In bridge arm A, the collector of power switch Q3 is connected to the DC+ point, the emitter of power switch Q3 is connected to the collector of power switch Q4, the emitter of power switch Q4 is connected to the collector of power switch Q5 at point a1, the emitter of power switch Q5 is connected to the collector of power switch Q6, and the emitter of power switch Q6 is connected to the DC- point. The midpoint between power switch Q3 and power switch Q4 is connected to the collector of power switch Q1; the emitter of power switch Q1 and the collector of power switch Q2 are connected to point a2, and point a2 is connected to the midpoint O of bus capacitor C1 and bus capacitor C2; the midpoint of power switch Q5 and power switch Q6 is connected to the emitter of power switch Q2; one end of capacitor C1 is connected to the DC+ point, and the other end is connected to the neutral point O; One end of capacitor C2 is connected to the DC-point, and the other end is connected to the neutral point O; the structures of bridge arms A, B and C are the same; all power switches are connected in reverse parallel with a diode, and the anode of each diode is connected to the emitter of the power switch, and the cathode of each diode is connected to the collector of the power switch; The connection point a1 in bridge arm A corresponds to b1 in bridge arm B and c1 in bridge arm C; One end of inductor L1 is connected to point a1 in bridge arm A, and the other end is connected to capacitor C5 and contactor KM; one end of inductor L2 is connected to point b1 in bridge arm B, and the other end is connected to capacitor C4 and contactor KM; one end of inductor L3 is connected to point c1 in bridge arm C, and the other end is connected to capacitor C3 and contactor KM.

[0010] Furthermore, the subway rectifier module includes a step-down transformer, a rectifier unit, and several switches; One end of the step-down transformer is connected to the medium voltage ring network, and the other end is connected to one end of the rectifier unit; the other end of the rectifier unit is connected to the positive and negative busbars respectively; the positive busbar is connected to the contact network respectively, and the negative busbar is connected to the running rail.

[0011] A method for melting ice and storing energy in a subway flywheel energy storage system with a DC ice melting function, characterized by comprising the following steps: When contactor KM is closed and circuit breaker QF is opened, the system starts the flywheel energy storage charging and discharging mode. In this mode, when subway braking generates regenerative braking energy and raises the DC contact network voltage, the regenerative braking energy that cannot be absorbed by neighboring vehicles is converted through the converter cabinet, and the DC power is converted into six-phase AC power to drive the permanent magnet synchronous motor. The permanent magnet synchronous motor drives the flywheel rotor to accelerate and store this energy in the form of mechanical energy. When the DC network voltage drops due to subway traction, the flywheel rotor drives the permanent magnet synchronous motor to start decelerating, converting the stored mechanical energy into electrical energy. The generated six-phase AC power is converted into DC power through the converter cabinet and released to the contact network, thereby achieving energy saving and voltage stabilization. When the circuit breaker QF is closed and the contactor KM is opened, the system starts the DC ice melting mode. In this mode, DC power is output to the contact network, and the contact network and the far end of the running rail are short-circuited through the switch K3. In the DC ice melting mode, this switch is in the closed state. The output DC power forms a loop between the contact network and the running rail. The DC current flowing through the contact network generates Joule heat, which has the effect of melting the ice.

[0012] A set of circuit topologies in the converter cabinet of the device of the present invention realizes time-sharing multiplexing of two functions. In the DC / AC working mode of the flywheel energy storage charging and discharging mode converter cabinet, six-phase alternating current is output to drive the permanent magnet synchronous motor. The permanent magnet synchronous motor drives the flywheel rotor to accelerate and stores electrical energy in the form of mechanical energy. In the AC / DC working mode of the flywheel energy storage charging and discharging mode converter cabinet, six-phase alternating current is converted into direct current and released to the contact network, thereby achieving energy saving and voltage stabilization. In the DC / DC working mode of DC de-icing, the converter cabinet outputs direct current, forming a current loop between the upstream and downstream contact networks or between the contact network and the running rails, generating heat to melt the ice on the contact network.

[0013] The DC / DC mode of this invention can simultaneously melt ice on the running rails and the contact network, increasing the adhesion coefficient of the running rails and preventing subway cars from slipping. This invention uses two three-phase active neutral-point clamped three-level circuits in parallel to achieve six DC outputs through switching control modes. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The system topology of the present invention Figure 1 ; Figure 2 This is the electrical topology diagram of the flywheel energy storage module of the present invention; Figure 3 This is a circuit diagram of one phase in the DC ice melting mode of the present invention. DETAILED DESCRIPTION

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the existing known technologies. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0016] like Figure 1 As shown, the subway flywheel energy storage system with DC ice-melting capabilities includes a medium-voltage ring network, catenary, running rails, and positive and negative busbars. It also includes a subway rectifier module, which steps down the incoming AC power from the city grid and then outputs stable DC power through efficient rectification and voltage regulation technology, meeting the power supply needs of high-power, long-distance subway lines. The subway rectifier module includes a step-down transformer, a rectifier unit, and several switches. One end of the step-down transformer is connected to the medium-voltage ring network, and the other end is connected to one end of the rectifier unit. The other end of the rectifier unit is connected to the positive and negative busbars, respectively. The positive busbar is connected to the catenary, and the negative busbar is connected to the running rails.

[0017] like Figure 1 As shown in the figure, the subway system draws medium-voltage 35kV AC power from the city grid. After being stepped down by a step-down transformer in the traction substation, it is fed into the rectifier unit. Using efficient rectification and voltage regulation technology, it outputs stable 1500V DC power, meeting the power supply requirements of high-power, long-distance subway lines. The positive output power of the rectifier unit is connected to the positive busbar, with switches K8 and K9 controlling the line's on / off. The negative output power of the rectifier unit is connected to the negative busbar, with a voltage level of 1500V DC. Switches K4, K5, K6, and K7 control the connection between the positive and negative busbars and the subway overhead line and running rails.

[0018] The flywheel energy storage module, on the one hand, converts the regenerative braking electric energy through the converter cabinet, converting DC into six-phase AC to drive the permanent magnet synchronous motor. The permanent magnet synchronous motor drives the flywheel rotor to accelerate and stores this energy in the form of mechanical energy. On the other hand, when the DC network voltage drops due to subway traction, the flywheel rotor drives the permanent magnet synchronous motor to start decelerating, converting the stored mechanical energy into electrical energy. The generated six-phase AC is converted into DC through the converter cabinet and released to the contact network.

[0019] The flywheel energy storage module includes a switch cabinet K1, an isolating switch cabinet K2, a converter cabinet, a contactor KM and a flywheel cabinet; the converter cabinet is connected to the switch cabinet K1 and the negative busbar through the isolating switch cabinet K2, and the switch cabinet K1 is also connected to the positive busbar; the converter cabinet is also connected to the flywheel cabinet through the contactor KM.

[0020] like Figure 2As shown, the flywheel energy storage module consists of two three-phase active neutral-point-clamped three-level inverter circuits connected in parallel, Group A and Group B, which output or input two sets of three-phase AC power. The three-phase active neutral-point-clamped three-level inverter circuit has three bridge arms, each with six power switches. Due to the clamping effect of the two neutral-point-clamped switches on the left side of each phase arm, the voltage stress of each switch is half the total DC bus voltage.

[0021] Group A includes three bridge arms, namely bridge arm A, bridge arm B, and bridge arm C; and also includes inductor L1, inductor L2, inductor L3, capacitor C1, capacitor C2, capacitor C3, capacitor C4, and capacitor C5; In bridge arm A, the collector of power switch Q3 is connected to the DC+ point, the emitter of power switch Q3 is connected to the collector of power switch Q4, the emitter of power switch Q4 is connected to the collector of power switch Q5 at point a1, the emitter of power switch Q5 is connected to the collector of power switch Q6, and the emitter of power switch Q6 is connected to the DC- point. The midpoint between power switch Q3 and power switch Q4 is connected to the collector of power switch Q1; the emitter of power switch Q1 and the collector of power switch Q2 are connected to point a2, and point a2 is connected to the midpoint O of bus capacitor C1 and bus capacitor C2; the midpoint of power switch Q5 and power switch Q6 is connected to the emitter of power switch Q2; one end of capacitor C1 is connected to the DC+ point, and the other end is connected to the neutral point O; One end of capacitor C2 is connected to the DC-point, and the other end is connected to the neutral point O; the structures of bridge arms A, B and C are the same; all power switches are connected in reverse parallel with a diode, and the anode of each diode is connected to the emitter of the power switch, and the cathode of each diode is connected to the collector of the power switch; The connection point a1 in bridge arm A corresponds to b1 in bridge arm B and c1 in bridge arm C.

[0022] One end of inductor L1 is connected to point a1 in bridge arm A, and the other end is connected to capacitor C5 and contactor KM; one end of inductor L2 is connected to point b1 in bridge arm B, and the other end is connected to capacitor C4 and contactor KM; one end of inductor L3 is connected to point c1 in bridge arm C, and the other end is connected to capacitor C3 and contactor KM.

[0023] like Figure 2 As shown, group B and group A have the same structure and will not be described further.

[0024] The flywheel energy storage module is installed in the traction substation. The positive input terminal of the converter cabinet is connected to the positive busbar, while the negative input terminal is connected to the negative busbar and the running rails. A 1500V switchgear K1 controls the line's on / off function, while an isolating switchgear K2 provides electrical isolation. The converter cabinet has two outputs. One outputs six-phase AC power, which is connected to the permanent magnet synchronous motor in the flywheel cabinet through contactor KM. The permanent magnet synchronous motor drives the flywheel rotor, and vice versa. The other outputs DC power, which is connected to the contact network through circuit breaker QF. The running rails and the contact network are remotely shorted via switch K3. When KM is closed and QF is opened, the device enters the flywheel energy storage charging and discharging mode. In this mode, when subway braking generates regenerative braking energy and raises the DC catenary voltage, the regenerative braking energy that cannot be absorbed by neighboring trains is converted through the converter cabinet. This DC power is converted into six-phase AC power to drive the permanent magnet synchronous motor, which accelerates the flywheel rotor, storing this energy as mechanical energy. When the DC grid voltage drops due to subway traction, the flywheel rotor decelerates the permanent magnet synchronous motor, converting the stored mechanical energy into electrical energy. The resulting six-phase AC power is converted to DC power by the converter cabinet and released to the catenary, achieving energy savings and voltage stability. When QF is closed and KM is disconnected, the device enters DC de-icing mode. In this mode, DC power is output to the catenary, short-circuiting the catenary and the far end of the running rails via switch K3. When this switch is closed in DC de-icing mode, the DC power forms a circuit between the catenary and the running rails. The DC current flowing through the catenary generates Joule heating, which melts the ice.

[0025] Figure 3 This is a circuit diagram of one of the six-phase DC outputs of this system in DC ice-melting mode. This circuit is actually one phase of a three-phase active neutral point clamped (ANPC) three-level circuit, with an inductor connected in series and a capacitor in parallel, forming a buck DC / DC circuit. The converter cabinet contains six such bridge arms, forming a six-way buck DC / DC circuit. The parallel output DC current is fed into the catenary. Closing the remote shorting switch K3 between the catenary and the running rails creates a current loop, effectively melting ice on the catenary.

[0026] The present invention utilizes a set of circuit topologies in a set of systems to realize two functional modes, which can not only solve the problem of utilizing the regenerative braking energy of the subway and achieve the effects of energy saving and voltage stabilization, but also increase the utilization rate of equipment and improve the economy. The use of this subway flywheel energy storage device with DC ice melting function is convenient, fast and efficient. In normal times, it is used as a flywheel energy storage device to realize the real-time power compensation function. In extreme environments, when the contact network is covered with ice, it can also play an important role as a DC ice melting device to prevent the pantograph from losing power to the contact network due to poor contact between the pantograph and the contact network. The two modes often do not need to be carried out at the same time, so two switches need to be set on the output side to control the mode selection, which is convenient, simple and efficient.

[0027] The active neutral point clamped three-level circuit employed within the converter cabinet of this invention offers numerous advantages. Compared to a two-level circuit, the voltage stress of each switching transistor is only half the DC bus voltage. This allows the selection of switching transistors with a lower withstand voltage rating for the same DC bus voltage level. Furthermore, since the dv / dt during the switching process of each switching transistor is significantly reduced, system electromagnetic interference is improved. Compared to neutral point clamped (NPC) three-level circuits, replacing the clamping diodes with switching transistors solves the problem of uneven heat distribution.

[0028] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A subway flywheel energy storage system with DC ice melting function, characterized in that: include: The subway rectifier module steps down the AC power from the medium-voltage ring network and then outputs stable DC power through high-efficiency rectification and voltage regulation technology; The flywheel energy storage module converts regenerative braking energy through a converter cabinet, converting DC power into six-phase AC power to drive a permanent magnet synchronous motor. The permanent magnet synchronous motor accelerates the flywheel rotor, storing this energy as mechanical energy. Furthermore, when the DC grid voltage drops due to subway traction, the flywheel rotor drives the permanent magnet synchronous motor to decelerate, converting the stored mechanical energy into electrical energy. The resulting six-phase AC power is converted to DC power through the converter cabinet and released to the contact network. The subway rectifier module is connected to the positive and negative busbars; the positive busbar is connected to the contact network, and the negative busbar is connected to the running rails; the flywheel energy storage module is connected to the positive busbar, negative busbar and running rails respectively; The flywheel energy storage module is also connected to the contact network through a circuit breaker QF, and the contact network is connected to the running rail through a remote short-circuit switch K3; The flywheel energy storage module adopts two sets of three-phase active neutral-point clamped three-level topology, in which one phase is connected in series with an inductor and in parallel with a capacitor to form a buck-type DC / DC circuit; six such bridge arms in the converter cabinet form a six-way buck-type DC / DC circuit.

2. The subway flywheel energy storage system with DC ice melting function according to claim 1 is characterized in that: The flywheel energy storage module includes a switch cabinet K1, an isolating switch cabinet K2, a converter cabinet, a contactor KM and a flywheel cabinet; The converter cabinet is connected to the switch cabinet K1 and the negative busbar via the isolation switch cabinet K2, and the switch cabinet K1 is also connected to the positive busbar; The converter cabinet is also connected to the flywheel cabinet via a contactor KM.

3. The subway flywheel energy storage system with DC ice melting function according to claim 1 is characterized in that: The two groups of three-phase active neutral point clamped three-level topology structures include group A and group B, which have the same structure; Group A includes three bridge arms, namely bridge arm A, bridge arm B, and bridge arm C; and also includes inductor L1, inductor L2, inductor L3, capacitor C1, capacitor C2, capacitor C3, capacitor C4, and capacitor C5; In bridge arm A, the collector of power switch Q3 is connected to the DC+ point, the emitter of power switch Q3 is connected to the collector of power switch Q4, the emitter of power switch Q4 is connected to the collector of power switch Q5 at point a1, the emitter of power switch Q5 is connected to the collector of power switch Q6, and the emitter of power switch Q6 is connected to the DC- point. The midpoint between power switch Q3 and power switch Q4 is connected to the collector of power switch Q1; the emitter of power switch Q1 and the collector of power switch Q2 are connected to point a2, and point a2 is connected to the midpoint O of bus capacitor C1 and bus capacitor C2; the midpoint of power switch Q5 and power switch Q6 is connected to the emitter of power switch Q2; one end of capacitor C1 is connected to the DC+ point, and the other end is connected to the neutral point O; One end of capacitor C2 is connected to the DC-point, and the other end is connected to the neutral point O; the structures of bridge arms A, B and C are the same; all power switches are connected in reverse parallel with a diode, and the anode of each diode is connected to the emitter of the power switch, and the cathode of each diode is connected to the collector of the power switch; The connection point a1 in bridge arm A corresponds to b1 in bridge arm B and c1 in bridge arm C; One end of inductor L1 is connected to point a1 in bridge arm A, and the other end is connected to capacitor C5 and contactor KM; one end of inductor L2 is connected to point b1 in bridge arm B, and the other end is connected to capacitor C4 and contactor KM; one end of inductor L3 is connected to point c1 in bridge arm C, and the other end is connected to capacitor C3 and contactor KM.

4. The subway flywheel energy storage system with DC ice melting function according to claim 1 is characterized in that: The subway rectifier module includes a step-down transformer, a rectifier unit and several switches; One end of the step-down transformer is connected to the medium voltage ring network, and the other end is connected to one end of the rectifier unit; the other end of the rectifier unit is connected to the positive and negative busbars respectively; the positive busbar is connected to the contact network respectively, and the negative busbar is connected to the running rail.

5. An ice melting and energy storage method using the subway flywheel energy storage system with DC ice melting function as claimed in claim 2, characterized in that: The following steps are involved: When contactor KM is closed and circuit breaker QF is opened, the system starts the flywheel energy storage charging and discharging mode. In this mode, when subway braking generates regenerative braking energy and raises the DC contact network voltage, the regenerative braking energy that cannot be absorbed by neighboring vehicles is converted through the converter cabinet, and the DC power is converted into six-phase AC power to drive the permanent magnet synchronous motor. The permanent magnet synchronous motor drives the flywheel rotor to accelerate and store this energy in the form of mechanical energy. When the DC network voltage drops due to subway traction, the flywheel rotor drives the permanent magnet synchronous motor to start decelerating, converting the stored mechanical energy into electrical energy. The generated six-phase AC power is converted into DC power through the converter cabinet and released to the contact network, thereby achieving energy saving and voltage stabilization. When the circuit breaker QF is closed and the contactor KM is opened, the system starts the DC ice melting mode. In this mode, DC power is output to the contact network, and the contact network and the far end of the running rail are short-circuited through the switch K3. In the DC ice melting mode, this switch is in the closed state. The output DC power forms a loop between the contact network and the running rail. The DC current flowing through the contact network generates Joule heat, which has the effect of melting the ice.

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