An energy recovery device and method for use in a synchronous condenser system

Abstract

This invention relates to the field of energy-saving technology for power equipment, specifically to an energy recovery device and method applied to a synchronous condenser system. The system includes: a synchronous condenser, an excitation transformer, a rectifier module, a bidirectional DC / DC converter, an energy storage battery, and a control unit. The rectifier module reuses the original organic-side converter of the synchronous condenser. The control unit integrates speed, voltage, current, and SOC monitoring modules to regulate the operation and switching of each component. The method includes: during shutdown, the synchronous condenser rotor generates induced electricity due to inertial rotation, which is stepped down by the excitation transformer, rectified by the rectifier module, and then stored in the energy storage battery after being adapted by the bidirectional DC / DC converter. During startup, the stored energy is stepped up by the bidirectional DC / DC converter and inverted by the rectifier module to provide excitation current. When the speed reaches the rated value, the excitation is switched to grid excitation. The system is equipped with overvoltage and overcurrent protection strategies, as well as battery charging and discharging protection strategies, to achieve potential energy recovery, reduce grid impact, improve operating efficiency and component lifespan, and is suitable for ultra-high voltage and new energy grid-connected scenarios.

Description

Technical Field

[0001] This invention belongs to the field of energy-saving technology for power equipment, and specifically relates to an energy recovery device and method applied to a synchronous condenser system. Background Technology

[0002] Synchronous condensers, as core reactive power compensation devices in ultra-high voltage direct current (UHVDC) transmission and large-scale grid integration of new energy sources, are mainly used to maintain grid voltage stability, improve system transient stability, and compensate for inductive / capacitive reactive power losses in transmission lines. Their operation includes three key stages: startup, rated operation, and shutdown. Among these, the excitation current supply during startup and the utilization of rotor mechanical potential energy during shutdown are the core technical aspects affecting the operating efficiency of the synchronous condenser and the economy of the power grid. In current industrial applications, synchronous condensers are mostly large synchronous motors with a rated capacity of 100-500 Mvar. During startup, a rotor excitation magnetic field needs to be established to drive the rotor to accelerate to its rated speed. During shutdown, the rotor continues to rotate due to inertia, generating recoverable mechanical potential energy. However, existing technologies have significant shortcomings in both of these stages.

[0003] In the current technology for synchronous condenser startup, the excitation power supply mode of the grid, excitation transformer and rectifier is generally adopted. Due to the low rotor speed and insufficient magnetic field strength in the early stage of startup, a large current higher than the rated excitation current needs to be input, which can easily cause short-term inrush current in the grid and affect the stable operation of the surrounding power load. Although some technical solutions introduce energy storage devices to assist excitation, there are problems such as insufficient stability during the switching process between energy storage and grid excitation and failure to adapt the excitation current to the rotor speed change. This not only leads to high startup energy consumption and low efficiency, but also lacks an effective strategy for dealing with the situation when the remaining energy storage capacity (SOC) is lower than the critical value, which may cause delays in the startup process due to insufficient energy storage capacity. During shutdown, the mechanical potential energy generated by the rotor's inertial rotation is mostly dissipated naturally through bearing friction, air resistance, and the losses of the excitation winding itself, resulting in energy waste. A few technical solutions that attempt to recover this energy have problems such as the need for additional dedicated rectifier devices, high equipment investment costs, and inability to adapt to the dynamic changes in induced voltage during rotor speed reduction, resulting in low energy recovery efficiency. At the same time, they lack effective protection mechanisms for abnormal voltage and current conditions, which can easily damage energy storage components and power devices.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems in the prior art, the present invention provides an energy recovery device and method for a synchronous condenser system, which solves the problems of mechanical potential energy waste when the synchronous condenser is stopped, large impact caused by reliance on the power grid during startup, and imperfect excitation control in the prior art.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In a first aspect, an energy recovery system applied to a synchronous condenser system includes: a synchronous condenser, an excitation transformer, a rectifier module, a bidirectional DC / DC converter, an energy storage battery, a control unit, a grid connection switch, a DC switch, and an excitation transformer connection switch;

[0008] The synchronous condenser includes a three-phase stator winding and a rotor excitation winding. The three-phase stator winding is connected to the power grid and the grid-connected switch via a grid-connected bus. The rotor excitation winding is connected to the output terminal of the excitation transformer via a bus and a rectifier module.

[0009] The output terminal of the excitation transformer is connected to the AC input terminal of the rectifier module, the DC output terminal of the rectifier module is connected in parallel with the DC input terminal of the bidirectional DC / DC converter, and a DC filter capacitor is connected in parallel on the DC bus between the rectifier module and the bidirectional DC / DC converter.

[0010] The DC output terminal of the bidirectional DC / DC converter is connected in series with the DC switch and then connected to the positive and negative terminals of the energy storage battery. An input filter capacitor is connected in parallel on the line between the bidirectional DC / DC converter and the energy storage battery.

[0011] The excitation transformer switching switch is connected in series on the busbar between the rotor excitation winding of the synchronous condenser and the excitation transformer.

[0012] The control unit is electrically connected to the synchronous condenser, excitation transformer, rectifier module, bidirectional DC / DC converter, energy storage battery, grid connection switch, DC switch and excitation transformer connection switch, respectively, and is used to monitor the status of each component and control the working mode and switching on / off of each component.

[0013] Furthermore, the rectifier module reuses the original machine-side bidirectional converter of the synchronous condenser. The machine-side bidirectional converter adopts a three-phase voltage-type two-level PWM rectifier structure, which can be switched to rectification mode or inverter mode under the control of the control unit.

[0014] The rectification mode is used to rectify the AC power output from the excitation transformer into DC power, and the inverter mode is used to invert the DC power output from the bidirectional DC / DC converter into AC excitation current.

[0015] Furthermore, the excitation transformer is a step-down power transformer, whose input voltage is adapted to the induced voltage of the three-phase stator winding of the synchronous condenser, and whose output voltage is adapted to the AC input voltage range of the rectifier module.

[0016] Furthermore, the bidirectional DC / DC converter includes a first switching transistor, a second switching transistor, an output filter capacitor, and a DC filter inductor;

[0017] The output filter capacitor is connected in parallel between the positive and negative terminals of the DC input terminal of the bidirectional DC / DC converter.

[0018] The input terminal of the first switch is connected to the positive terminal of the DC input terminal of the bidirectional DC / DC converter, the output terminal of the first switch is connected in series with the input terminal of the second switch, and the output terminal of the second switch is connected to the negative terminal of the DC input terminal of the bidirectional DC / DC converter and the negative terminal of the input filter capacitor.

[0019] The input terminal of the DC filter inductor is connected to the connection node of the first and second switching transistors, and the output terminal of the DC filter inductor is connected to the positive terminal of the input filter capacitor and the positive terminal of the energy storage battery.

[0020] Furthermore, the energy storage battery is a lithium iron phosphate battery pack, a supercapacitor, or a hybrid energy storage device of both. The energy storage battery is equipped with a SOC detection module, which is electrically connected to the control unit and is used to provide real-time feedback on the remaining power of the energy storage battery.

[0021] Furthermore, the control unit is equipped with a speed monitoring module and a voltage and current monitoring module;

[0022] The speed monitoring module is used to collect the real-time speed of the synchronous condenser rotor, and the voltage and current monitoring module is used to collect the excitation winding voltage of the synchronous condenser rotor, the output voltage of the excitation transformer, the output voltage of the rectifier module, and the input and output current of the bidirectional DC / DC converter (9).

[0023] Secondly, an energy recovery method for a synchronous condenser system, applied to the energy recovery system for a synchronous condenser system described in any of the preceding claims, including energy recovery during the synchronous condenser shutdown phase and excitation power supply process during the synchronous condenser startup phase;

[0024] Energy recovery during the synchronous condenser shutdown phase includes:

[0025] S11. When the control unit receives the synchronous condenser shutdown command or detects through the speed monitoring module that the synchronous condenser rotor speed has dropped to a preset percentage of the rated speed, it disconnects the synchronous condenser from the grid bus and simultaneously controls the excitation transformer switching switch and the DC switch to close.

[0026] S12. Due to inertia, the rotor of the synchronous condenser rotates, and the three-phase stator windings cut the magnetic field to generate induced AC power. The induced AC power is stepped down by the excitation transformer and then input to the rectifier module.

[0027] S13. The control unit controls the rectifier module to switch to rectification mode, rectifies the stepped-down AC power into DC power, and the DC power is filtered by the DC filter capacitor and then input to the bidirectional DC / DC converter.

[0028] S14. The control unit controls the bidirectional DC / DC converter to switch to charging mode based on the remaining power of the energy storage battery fed back by the SOC detection module. By adjusting the switching transistor and the switching frequency of the switching transistor, the rectified DC power is matched to the charging voltage and current of the energy storage battery to charge the energy storage battery until the SOC of the energy storage battery reaches 100% or the rotor speed drops to 5% of the rated speed. Then, the excitation transformer switching switch and the DC switch are disconnected to terminate energy recovery.

[0029] The excitation power supply process during the startup phase of the synchronous condenser includes:

[0030] S21. The control unit receives the synchronous condenser start command, and after confirming that the energy storage battery SOC is ≥20% through the energy storage battery SOC detection module, it controls the grid connection switch and the excitation transformer connection switch to open, and controls the DC switch to close.

[0031] S22. The control unit controls the bidirectional DC / DC converter to switch to discharge mode. By adjusting the switching transistors and their on / off timing, the DC power output from the energy storage battery is boosted to the DC voltage of the rectifier module. After being filtered by the input filter capacitor, the voltage is input to the rectifier module.

[0032] S23. The control unit controls the rectifier module to switch to inverter mode, converting DC power into AC excitation current. The AC excitation current is input to the rotor excitation winding of the synchronous condenser to drive the synchronous condenser rotor to accelerate.

[0033] S24. When the speed monitoring module detects that the rotor speed of the synchronous condenser has increased to 95% of the rated speed, the control unit controls the grid-connected switch to close and the DC switch to open, gradually switching the excitation power supply to the grid power supply to complete the startup of the synchronous condenser.

[0034] Furthermore, in step S14, the charging mode of the bidirectional DC / DC converter adopts a constant current and constant voltage control strategy:

[0035] When the SOC of the energy storage battery is less than 90%, constant current charging is performed at 0.5 times the rated charging current of the energy storage battery; when the SOC of the energy storage battery is greater than or equal to 90%, constant voltage charging is switched, and the charging voltage is maintained at the rated voltage of the energy storage battery.

[0036] Furthermore, in step S21, if the SOC detection module reports that the SOC of the energy storage battery is <20%, the control unit first controls the grid connection switch and the DC switch to close, and the excitation transformer input switch to open. The energy storage battery is then charged through the grid via the rectifier module and the bidirectional DC / DC converter until the SOC is ≥20%, and then the subsequent startup steps are executed.

[0037] Furthermore, in steps S12-S14 and S22-S23, the voltage and current monitoring module collects the voltage and current values ​​of each component in real time. When the voltage exceeds ±10% of the rated value or the current exceeds 120% of the rated value, the control unit immediately controls the corresponding switch to disconnect, terminating the energy flow to protect the components.

[0038] Compared with existing technologies, the energy recovery device and method for a synchronous condenser system provided by this invention includes a synchronous condenser, an excitation transformer, a rectifier module, a bidirectional DC / DC converter, an energy storage battery, and a control unit. The rectifier module reuses the original organic-side converter of the synchronous condenser, and the control unit integrates speed, voltage, current, and SOC monitoring modules to regulate the operation and switching of each component. The method includes: when the system is stopped, the synchronous condenser rotor generates induced electricity due to inertial rotation, which is stepped down by the excitation transformer, rectified by the rectifier module, and then stored in the energy storage battery after being adapted by the bidirectional DC / DC converter; when the system is started, the stored energy is stepped up by the bidirectional DC / DC converter and inverted by the rectifier module to provide excitation current, and the system switches to grid excitation when the speed reaches the rated value. With supporting overvoltage and overcurrent protection strategies and battery charging and discharging protection, potential energy recovery is achieved, grid impact is reduced, operating efficiency and component lifespan are improved, and the system is suitable for ultra-high voltage and new energy grid-connected scenarios. Attached Figure Description

[0039] Figure 1 A schematic diagram of the energy recovery device provided in an embodiment of the present invention;

[0040] Figure 2 A flowchart of energy recovery during the shutdown phase of a synchronous condenser provided in an embodiment of the present invention;

[0041] Figure 3 A flowchart of the excitation power supply during the camera startup phase provided in an embodiment of the present invention. Appendix Figure 1 illustrate:

[0043] 1. Grid-connected busbar; 2. Isolation transformer; 3. SFC frequency converter starter; 4. Excitation transformer; 5. Synchronous condenser step-up transformer; 6. Generator terminal PT; 7. Synchronous condenser; 8-1. First rectifier module; 8-2. Second rectifier module; 9. DC / DC bidirectional converter; 10. Energy storage battery; 11. Start-up rectifier; 12. Start-up transformer. Detailed Implementation

[0044] The technical solution of the present invention will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments of the present invention. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0045] It should be noted that, unless otherwise specifically stated, the relative arrangement and numerical expressions of the components and steps described in these embodiments should not be construed as limiting the scope of the invention.

[0046] The following description of exemplary embodiments is merely illustrative and is not intended to limit the invention or its application or use in any way. Techniques, methods, and apparatus known to those skilled in the art may not be discussed in detail herein, but where applicable, such techniques, methods, and apparatus should be considered part of this specification.

[0047] Example 1

[0048] See Figure 1 , Figure 1 This invention presents an architecture diagram of an energy recovery device for synchronous condenser systems, suitable for ultra-high voltage and new energy grid-connected scenarios. It effectively recovers potential energy during synchronous condenser shutdown, reduces the impact on the power grid during startup, and simultaneously improves system operating efficiency and component lifespan. The specific structure includes:

[0049] The system includes a synchronous condenser (7), an excitation transformer (4), a rectifier module, a DC / DC bidirectional converter (9), an energy storage battery (10), a control unit, a grid-connected switch, a DC switch, and an excitation transformer activation switch. It is also connected to the grid-connected bus (1), an isolation transformer (2), an SFC frequency converter starter (3), a synchronous condenser step-up transformer (5), a generator terminal PT (6), a starting rectifier (11), and a starting transformer (12). All components are connected via the wiring shown in the attached diagram to form a complete circuit. The rectifier module includes a first rectifier module (8-1) and a second rectifier module (8-2).

[0050] Specifically, the three-phase stator windings of the synchronous condenser 7 are sequentially connected to the synchronous condenser step-up transformer 5, the grid connection switch, and finally connected to the grid connection bus 1; the generator terminal PT6 is connected in parallel between the stator windings of the synchronous condenser 7 and the grid connection bus 1 to collect stator voltage signals in real time. The three-phase stator windings of the synchronous condenser 7 are connected to the input terminal of the excitation transformer 4 via the excitation transformer connection switch, and the output terminal of the excitation transformer 4 is connected to the AC input terminal of the rectifier module (AC / DC / DC / AC dual-mode converter); the DC output terminal of the rectifier module is connected in parallel with the DC input terminal of the DC / DC bidirectional converter 9, and a DC filter capacitor is connected in parallel on the DC bus between the two; the DC output terminal of the DC / DC bidirectional converter 9 is connected to the positive and negative terminals of the energy storage battery 10 via a DC switch, and an input filter capacitor is connected in parallel on the line between the two.

[0051] The primary side of isolation transformer 2 is connected to the grid bus 1, and the secondary side is connected to SFC inverter starter 3 (auxiliary synchronous condenser starter). The output of SFC inverter starter 3 is connected to the rotor winding of synchronous condenser 7. The primary side of starting transformer 12 (backup power transformer) is connected to an external 380V backup power supply, and the secondary side is connected to starting rectifier 11 (AC to DC). The output of starting rectifier 11 is connected to DC / DC bidirectional converter 9 for replenishing power to the energy storage battery 10 when its power is insufficient. The control unit is electrically connected to all the above components (synchronous condenser 7, excitation transformer 4, rectifier module, etc.), monitors the status of each component in real time (speed, voltage, current, SOC, etc.), and controls the switching of component operating modes and the on / off switching to ensure the orderly operation of the system.

[0052] D1, Synchronous Condenser 7: Rated capacity 300Mvar synchronous condenser, including three-phase stator / rotor excitation windings, rated speed 3000r / min; during operation, it transmits reactive power to the grid bus 1 through the condenser step-up transformer 5 to maintain grid voltage stability; when stopped, the rotor inertial rotation generates induced electrical energy (energy recovery source); when started, it receives the drive current from the rectifier module or SFC frequency converter starter 3.

[0053] D2, Excitation Transformer 4: Step-down power transformer, with input voltage adapted to the rotor induced voltage of the synchronous condenser 7 (0-400V), and output voltage adapted to the input range of the rectifier module (380V). The transformation ratio is 400V:380V, realizing the voltage adaptation between the rotor induced voltage and the rectifier module, ensuring energy conversion efficiency (≥98%).

[0054] D3. Rectifier Module: This module reuses the original machine-side bidirectional converter from the synchronous condenser 7, eliminating the need for additional dedicated rectifier equipment and reducing system costs. The converter employs a three-phase voltage-type two-level PWM rectifier structure, using IGBTs as power devices, and supports two operating modes.

[0055] Rectification mode: The original machine-side bidirectional converter of the synchronous condenser is reused. It adopts a three-phase voltage-type two-level PWM rectifier structure, and the power device is IGBT (model FF450R12ME4). It supports switching between rectification and inversion modes and does not require additional dedicated rectifier equipment.

[0056] Inverter mode: When starting the excitation power supply, the DC power output from the bidirectional DC / DC converter is converted into AC excitation current and input to the rotor excitation winding.

[0057] D4, Bidirectional DC / DC Converter 9: Non-isolated topology, including the first switching transistor. Second switching transistor DC filter inductor Output filter capacitor (1000μF / 650V); In charging mode, the 550V DC output from the rectifier module is stepped down to the rated voltage (400V) of the energy storage battery 10. In discharging mode, the 400V DC output from the energy storage battery 10 is stepped up to 600V (to meet the inverter requirements of the rectifier module). The switching frequency is 20kHz and the current fluctuation is ≤±3%.

[0058] D5, Energy Storage Battery 10: Optional lithium iron phosphate battery pack (single cell voltage 20V, total voltage 400V, capacity 200kWh), supercapacitor or hybrid energy storage; equipped with a SOC detection module (accuracy ±2%) to communicate with the control unit to provide feedback on the remaining power and avoid overcharging (voltage ≤420V) and over-discharging (voltage ≥360V).

[0059] D6, PT6 at the generator terminal: voltage transformer, transformation ratio 20kV:100V, accuracy class 0.2; connected in parallel between the stator winding of the synchronous condenser 7 and the grid connection switch, to collect the stator terminal voltage signal, providing data for grid connection synchronization judgment (voltage amplitude difference ≤5%, frequency difference ≤0.2Hz) and overvoltage protection (triggered protection for exceeding rated value ±10%).

[0060] D7. Control Unit: Integrates a speed monitoring module (photoelectric encoder, mounted on the rotor shaft end of synchronous condenser 7, with a measurement accuracy of ±1r / min) and a voltage and current monitoring module (Hall sensors, respectively mounted on the rotor bus of synchronous condenser 7, the output end of excitation transformer 4, and the output end of rectifier module, etc.); based on the monitoring data, it triggers energy recovery (rotor speed ≤ 30% of rated speed), start-up switching (speed ≥ 95% of rated speed) and fault protection (voltage / current over-limit disconnects the corresponding switch).

[0061] D8, Isolation transformer 2: Transformation ratio 20kV:380V, capacity 500kVA, realizes electrical isolation between grid bus 1 and SFC frequency converter starter 3, avoids grid interference affecting the stability of SFC start-up, and ensures stable current output during the start-up phase.

[0062] D9, SFC frequency converter 3: input voltage 380V, output frequency adjustable from 0-50Hz, maximum output current 1200A; it only works during the startup phase, and works in conjunction with the inverter current of the rectifier module to drive the rotor of the synchronous condenser 7 to accelerate, shorten the startup time (from standstill to rated speed ≤5min), and reduce the impact on the power grid.

[0063] D10, Synchronous Condenser Step-Up Transformer 5: Step-up transformer with a transformation ratio of 20kV:500kV and a capacity of 300MVA. It steps up the 20kV low-voltage electrical energy output from the stator of synchronous condenser 7 to the grid transmission voltage (500kV), meeting the voltage level requirements of grid bus 1 and achieving efficient reactive power transmission.

[0064] D11, starting transformer 12 and starting rectifier 11: starting transformer 12 has a transformation ratio of 380V:380V (for backup power supply), and starting rectifier 11 has a rectification efficiency of ≥97%; together, they provide a backup power supply path for energy storage battery 10, preventing the synchronous condenser 7 from failing to start due to insufficient energy storage, thus improving system reliability.

[0065] In addition, the excitation power supply process specifically includes:

[0066] Start-up preparation and power replenishment judgment: The control unit receives the start command and confirms the status of the energy storage battery 10 through the SOC detection module: if SOC ≥ 20%, directly enter the start-up process; if SOC < 20%, close the grid connection switch (power only) and DC switch, disconnect the excitation transformer connection switch, turn on the start transformer 12 and start rectifier 11, rectify the 380V AC power output by the start transformer 12 into 400V DC power, and replenish the energy storage battery 10 to SOC ≥ 20% through the DC / DC bidirectional converter 9, and then disconnect the start transformer 12 and start rectifier 11.

[0067] Energy storage discharge and inverter drive: The control unit disconnects the grid-connected switch and the excitation transformer input switch, and closes the DC switch; the DC / DC bidirectional converter 9 switches to discharge mode, boosting the 400V DC power from the energy storage battery 10 to 600V, which is then filtered by the input filter capacitor and input to the rectifier module; at the same time, the SFC inverter starter 3 is started, obtaining 380V power from the isolation transformer 2 and outputting a 0-50Hz adjustable frequency current to assist in driving the rotor of the synchronous condenser 7; the rectifier module switches to inverter mode, inverting the 600V DC power into AC excitation current, which is input to the rotor winding of the synchronous condenser 7.

[0068] Grid connection and power supply switching: When the speed monitoring module detects that the speed of the synchronous condenser 7 has increased to 95% of the rated speed (2850 r / min), the control unit closes the grid connection switch (connecting the synchronous condenser 7 and the grid connection bus 1), disconnects the DC switch and the SFC frequency converter starter 3, and closes the excitation transformer starter switch; gradually switches the excitation power supply from the energy storage battery 10 to the grid (via the grid connection bus 1, the stator of the synchronous condenser 7, and the excitation transformer 4), and the startup is completed when the speed of the synchronous condenser 7 increases to 3000 r / min.

[0069] Example 2

[0070] This invention proposes an energy recovery method for a synchronous condenser system, which includes an energy recovery process during the synchronous condenser shutdown phase and an excitation power supply process during the startup phase. Specifically, it may include:

[0071] S1, see reference Figure 2 , Figure 2 This is a flowchart illustrating energy recovery during the shutdown phase of the synchronous condenser. When the synchronous condenser needs to be shut down, the control unit performs energy recovery according to the following steps:

[0072] S11. Recycling Trigger and Switch Control: The control unit receives the shutdown command of the synchronous condenser 7, or detects through the speed monitoring module (attached to the control unit) that the rotor speed of the synchronous condenser 7 has dropped to 30% of the rated speed (3000r / min) (i.e., 900r / min); after either condition is met, the grid connection switch is immediately controlled to open (cutting off the connection between the stator winding of the synchronous condenser 7 and the grid connection bus 1 to avoid energy backflow), and at the same time, the excitation transformer connection switch and the DC switch are closed.

[0073] S12. Induction Energy Generation and Voltage Reduction: Due to inertia, the rotor of the synchronous condenser 7 rotates, and its three-phase stator windings cut the residual magnetic field of the rotor to generate induced AC energy. This energy is input to the excitation transformer 4 through the closed excitation transformer input switch. The excitation transformer 4 reduces the induced energy to 380V according to the preset ratio (400V:380V) to ensure that the voltage input to the rectifier module is compatible with its AC input range, thus completing the initial energy adaptation.

[0074] S13, AC Rectification and DC Filtering: The control unit controls the rectifier module to switch to rectification mode. By adjusting the PWM duty cycle of the internal IGBT (model FF450R12ME4), the 380V AC power output from excitation transformer 4 is rectified into 550V DC power. The DC filter capacitor (specification 1000μF / 650V) on the DC bus between the rectifier module and the bidirectional DC / DC converter 9 filters the DC power, making the ripple coefficient ≤5% to avoid ripple current impacting the bidirectional DC / DC converter 9. Then, the filtered DC power is input into the bidirectional DC / DC converter 9.

[0075] S14. Termination of Energy Storage Charging and Recycling: The control unit obtains the real-time remaining power through the SOC detection module of the energy storage battery 10. If SOC < 90%, the bidirectional DC / DC converter 9 is controlled to switch to charging mode, and the switching frequency (20kHz) of the first switch V1 and the second switch V2 is adjusted to reduce the 550V DC power to the rated voltage (400V) of the energy storage battery 10, and constant current charging is performed at 50A (0.5 times the rated charging current). If SOC ≥ 90%, it switches to constant voltage charging and keeps the charging voltage at 400V unchanged.

[0076] When the SOC detection module reports that the SOC of the energy storage battery 10 reaches 100% (fully charged), or the speed monitoring module detects that the rotor speed of the synchronous condenser 7 drops to 5% of the rated speed (150 r / min, the induced electrical energy is extremely low), the control unit controls the excitation transformer to be engaged and the DC switch to be disengaged, thereby terminating energy recovery and completing the conversion of mechanical potential energy into electrical energy during the shutdown phase.

[0077] S2, see reference Figure 3 , Figure 3A flowchart illustrating the excitation power supply during the camera startup phase; when the camera needs to be started, the control unit performs the excitation power supply according to the following steps:

[0078] S21. Pre-judgment and switch preparation: After receiving the start command, the control unit first confirms the remaining power through the SOC detection module of the energy storage battery 10: if SOC ≥ 20% (meets the excitation power supply requirements), it directly enters the start process; if SOC < 20%, it first controls the grid connection switch and DC switch to close, and the excitation transformer connection switch to open. The grid power from the grid bus 1 is used to replenish the energy storage battery 10 through the rectifier module (switched to rectification mode) and the bidirectional DC / DC converter 9 (switched to charging mode) until SOC ≥ 20%, then the grid connection switch is disconnected. After the start conditions are met, the control unit keeps the grid connection switch and excitation transformer connection switch open (to avoid grid impact and no-load loss of excitation transformer 4), and closes the DC switch.

[0079] S22, Energy Storage Power Boost and Filtering: The control unit controls the bidirectional DC / DC converter 9 to switch to discharge mode. By adjusting the on / off sequence of the internal first switch V1 and second switch V2 (forming a boost circuit), the 400V DC power output from the energy storage battery 10 is boosted to 600V (to meet the DC input requirements of the rectifier module during inversion). The input filter capacitor (1000μF / 500V) between the bidirectional DC / DC converter 9 and the DC switch filters the boosted DC voltage to ensure that the voltage fluctuation is ≤±3%. Then, the stable DC power is input to the rectifier module.

[0080] S23. DC Inversion and Rotor Acceleration: The control unit switches the rectifier module to inverter mode and, by adjusting the PWM timing of the internal IGBTs, inverts the 600V DC power input from the bidirectional DC / DC converter 9 into a three-phase AC excitation current. The initial current is set to 960A (1.2 times the rated excitation current to ensure sufficient magnetic field strength of the synchronous condenser 7 rotor at low speeds). This AC excitation current is input to the rotor excitation winding of the synchronous condenser 7, and the resulting rotating magnetic field interacts with the stator winding magnetic field, driving the rotor to accelerate from rest. During this process, the voltage and current monitoring module (attached to the control unit) collects the excitation current in real time. If the detected current exceeds 1200A (150% of the rated value), the control unit immediately adjusts the PWM duty cycle of the rectifier module to limit the current within a safe range, preventing overheating and damage to the synchronous condenser 7 rotor winding.

[0081] S24. Speed ​​Target Achievement and Power Supply Switching: When the speed monitoring module detects that the rotor speed of the synchronous condenser 7 has increased to 95% of the rated speed (2850 r / min, meeting grid connection conditions), the control unit first closes the grid connection switch (connecting the stator winding of the synchronous condenser 7 to the grid bus 1), then controls the DC switch to open (cutting off the excitation power supply to the energy storage battery 10) and the excitation transformer switching switch to close; through a 100ms current ramp transition strategy, the excitation power supply is gradually switched from the energy storage battery 10 to the grid (the grid power is stepped down by the excitation transformer 4 and rectified by the rectifier module to provide a stable excitation current to the rotor winding of the synchronous condenser 7). When the voltage and current monitoring module confirms that the excitation current fluctuation is ≤±5% and the rotor speed of the synchronous condenser 7 has increased to 3000 r / min (rated speed), the startup process is completed, the synchronous condenser 7 enters the rated operating state, and begins to supply reactive power to the grid bus 1.

[0082] To address abnormal scenarios during shutdown recovery and power-on startup, the control unit implements protection through the following detailed strategies, specifically including:

[0083] Overvoltage and overcurrent protection: The voltage and current monitoring module collects the voltage and current values ​​of key components such as the rotor winding of the synchronous condenser 7, the excitation transformer 4, the rectifier module, and the bidirectional DC / DC converter 9 in real time. If the voltage exceeds ±10% of the rated value of the corresponding component (e.g., the output voltage of the excitation transformer 4 exceeds 380V ±10%), or the current exceeds 120% of the rated value (e.g., the input current of the bidirectional DC / DC converter 9 exceeds 1.2 times the rated value), the control unit immediately controls the corresponding switch (DC switch or excitation transformer switching switch) to open, terminate the energy flow, and prevent damage to core components such as the synchronous condenser 7, the energy storage battery 10, and the IGBT power devices due to overvoltage and overcurrent.

[0084] Battery charge / discharge protection: During charging (shutdown recovery) and recharging (before startup), a constant current and constant voltage control strategy is strictly followed: When the SOC of the energy storage battery 10 is <90%, it is charged with a constant current of 50A to avoid the impact of large current on the battery electrodes; when the SOC is ≥90%, it switches to constant voltage charging of 400V to prevent performance degradation and shortened lifespan caused by overcharging. During discharging (start-up excitation), the bidirectional DC / DC converter 9 adjusts the output voltage in real time through voltage closed-loop control to ensure that the discharge voltage of the energy storage battery 10 is stable at around 400V, avoiding increased battery internal resistance and capacity reduction caused by over-discharge.

[0085] Pre-start power replenishment protection: If the SOC of the energy storage battery 10 is less than 20% at startup, the control unit will prioritize the power replenishment process. During the power replenishment process, the charging current is limited to ≤200A through the bidirectional DC / DC converter 9 to avoid the impact of large current power replenishment on the grid bus 1 (grid). At the same time, the change of the SOC of the energy storage battery 10 is monitored in real time to ensure that the SOC is ≥20% after power replenishment, so as to provide reliable power supply for the excitation power supply during the startup phase and prevent the synchronous condenser 7 from failing to start due to insufficient energy storage.

[0086] In summary, the present invention has the following advantages:

[0087] 1. Effectively recovers the mechanical potential energy generated by the rotor's inertial rotation. A certain amount of electrical energy can be recovered during a single shutdown, avoiding the problem of mechanical potential energy being wasted through friction and loss in traditional systems, thus improving energy utilization efficiency.

[0088] 2. The excitation response speed during the startup phase is improved, and the time required to accelerate from a stationary rotor to the rated speed is significantly shortened, allowing for faster preparation for synchronous condenser startup and meeting the grid's demand for rapid equipment commissioning.

[0089] 3. The excitation current fluctuation is small, which can effectively reduce the mechanical impact on the rotor during operation, reduce the loss of rotor components caused by impact, and play a positive role in extending the overall service life of the synchronous condenser.

[0090] 4. By dynamically adjusting the charging and discharging strategy in conjunction with the SOC (state of charge) of the energy storage battery, performance degradation caused by improper charging and discharging can be avoided, which has a good protective effect on maintaining the long-term stable operation of the battery and extending its cycle life.

[0091] The above specific embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. An energy recovery system for application to a phase modulator system, characterized by, include: The system includes a grid-connected bus (1), an isolation transformer (2), an SFC frequency converter starter (3), a synchronous condenser (7), an excitation transformer (4), a synchronous condenser step-up transformer (5), a rectifier module, a bidirectional DC / DC converter (9), an energy storage battery (10), a control unit, a grid-connected switch, a DC switch, and an excitation transformer activation switch; the rectifier module includes a first rectifier module (8-1) and a second rectifier module (8-2). The synchronous condenser (7) includes a three-phase stator winding and a rotor excitation winding. The three-phase stator winding is electrically connected to the grid bus (1) via the synchronous condenser step-up transformer (5) and the grid-connected switch. The grid bus (1) is electrically connected to the power grid. The grid-connected bus (1) is electrically connected to the primary side of the isolation transformer (2), the secondary side of the isolation transformer (2) is electrically connected to the AC input terminal of the SFC frequency converter starter (3), the AC output terminal of the SFC frequency converter starter (3) is electrically connected to the input terminal of the excitation transformer (4), and the output terminal of the excitation transformer (4) is electrically connected to the AC side of the first rectifier module (8-1) and the second rectifier module (8-2). The three-phase stator winding of the synchronous condenser (7) is electrically connected to the AC side of the first rectifier module (8-1) via the excitation transformer switching switch and the excitation transformer; the DC side of the first rectifier module (8-1) and the DC side of the second rectifier module (8-2) are connected in parallel to the DC bus, and a DC filter capacitor is connected in parallel to the DC bus. The DC bus is electrically connected to the DC input terminal of the bidirectional DC / DC converter (9). The DC output terminal of the bidirectional DC / DC converter (9) is connected in series with the DC switch and then electrically connected to the positive and negative terminals of the energy storage battery (10). An input filter capacitor is connected in parallel on the line between the bidirectional DC / DC converter (9) and the energy storage battery (10). The control unit is electrically connected to the synchronous condenser (7), excitation transformer (4), first rectifier module (8-1), second rectifier module (8-2), bidirectional DC / DC converter (9), energy storage battery (10), grid connection switch, and DC switch, respectively, and is used to monitor the status of each component and control the working mode and switching on / off of each component.

2. The energy recovery system for a phase modulator system of claim 1, wherein, The first rectifier module (8-1) and the second rectifier module (8-2) reuse the original machine-side bidirectional converter of the synchronous condenser (7). The machine-side bidirectional converter adopts a three-phase voltage-type three-level PWM rectifier structure, which can be switched to rectification mode or inverter mode under the control of the control unit. The rectification mode is used to rectify the AC power output by the excitation transformer (4) into DC power, and the inverter mode is used to invert the DC power output by the bidirectional DC / DC converter (9) into AC power that matches the output of the excitation transformer (4).

3. The energy recovery system applied to a synchronous condenser system according to claim 1, characterized in that, The excitation transformer (4) is a step-down power transformer. Its input voltage is adapted to the induced voltage of the three-phase stator winding of the synchronous condenser (7), and its output voltage is adapted to the AC input voltage range of the first rectifier module (8-1) and the second rectifier module (8-2).

4. The energy recovery system applied to a synchronous condenser system according to claim 1, characterized in that, The bidirectional DC / DC converter (9) includes a first switching transistor, a second switching transistor, an output filter capacitor, and a DC filter inductor; The output filter capacitor is connected in parallel between the positive and negative terminals of the DC input terminal of the bidirectional DC / DC converter (9); The input terminal of the first switch is connected to the positive terminal of the DC input terminal of the bidirectional DC / DC converter (9), the output terminal of the first switch is connected in series with the input terminal of the second switch, and the output terminal of the second switch is connected to the negative terminal of the DC input terminal of the bidirectional DC / DC converter (9) and the negative terminal of the input filter capacitor. The input terminal of the DC filter inductor is connected to the connection node of the first and second switching transistors, and the output terminal of the DC filter inductor is connected to the positive terminal of the input filter capacitor and the positive terminal of the energy storage battery (10).

5. The energy recovery system applied to a synchronous condenser system according to claim 1, characterized in that, The energy storage battery (10) is a lithium titanate battery energy storage device. The energy storage battery (10) is equipped with a SOC detection module. The SOC detection module is electrically connected to the control unit and is used to provide real-time feedback on the remaining power of the energy storage battery (10).

6. The energy recovery system applied to a synchronous condenser system according to claim 1, characterized in that, The control unit is equipped with a speed monitoring module and a voltage and current monitoring module; The speed monitoring module is used to collect the real-time speed of the rotor of the synchronous condenser (7), and the voltage and current monitoring module is used to collect the excitation winding voltage of the rotor of the synchronous condenser (7), the output voltage of the excitation transformer (4), the output voltage of the rectifier module and the input and output current of the bidirectional DC / DC converter (9).

7. An energy recovery method for a phase shifter system, applied to the energy recovery system for a phase shifter system as described in any one of claims 1-6, characterized in that, The energy recovery process during the shutdown phase of the synchronous condenser (7) includes: S11. When the control unit receives the shutdown command of the synchronous condenser (7) or detects through the speed monitoring module that the rotor speed of the synchronous condenser (7) drops to a preset percentage of the rated speed, it disconnects the connection between the synchronous condenser (7) and the grid bus (1), and at the same time controls the excitation transformer input switch and the DC switch to close. S12, the rotor of the synchronous condenser (7) rotates due to inertia, and the three-phase stator windings cut the residual magnetic field of the rotor to generate induced AC power. The induced AC power is stepped down by the excitation transformer (4) and then input to the rectifier module. S13. The control unit controls the rectifier module to switch to rectification mode, and rectifies the stepped-down AC power into DC power. The DC power is filtered by the DC filter capacitor and then input to the bidirectional DC / DC converter (9). S14. The control unit controls the bidirectional DC / DC converter (9) to switch to charging mode based on the remaining power of the energy storage battery (10) fed back by the SOC detection module of the energy storage battery (10). By adjusting the switching transistor and the switching frequency of the switching transistor, the rectified DC power is matched to the charging voltage and current of the energy storage battery (10) to charge the energy storage battery (10) until the SOC of the energy storage battery (10) reaches 100% or the rotor speed drops to 5% of the rated speed. Then, the excitation transformer switching switch and the DC switch are disconnected to terminate energy recovery.

8. The energy recovery method applied to a phase shifter system according to claim 7, characterized in that, In step S14, the charging mode of the bidirectional DC / DC converter (9) adopts a constant current or constant voltage control strategy: When the SOC of the energy storage battery (10) is less than 90%, constant current charging is performed at 0.5 times the rated charging current of the energy storage battery (10); when the SOC of the energy storage battery (10) is greater than or equal to 90%, constant voltage charging is switched to constant voltage charging, and the charging voltage is maintained at the rated voltage of the energy storage battery (10).

9. The energy recovery method applied to a phase shifter system according to claim 7, characterized in that, In steps S12-S14, the voltage and current monitoring module collects the voltage and current values ​​of each component in real time. When the voltage exceeds ±10% of the rated value or the current exceeds 120% of the rated value, the control unit immediately controls the corresponding switch to disconnect, terminating the energy flow to protect the component safety.

Images