Hydro-generator electric braking method and topological structure based on uncontrolled rectification and buck-boost converter

Abstract

The invention discloses a hydraulic generator electric braking method based on uncontrolled rectification and a buck-boost converter and a topological structure. The hydraulic generator electric braking method comprises the steps that 1, unit splitting and initial state confirmation are carried out; 2, judging a rotating speed threshold value and pre-inputting and pre-quitting equipment; step 3, uncontrolled rectification and real-time operation parameter acquisition; 4, calculating reference power; 5, the reference power P obtained through calculation and the monitoring signals udc2 and idc2 are input into a controller, the controller outputs a corresponding control instruction to drive a buck-boost converter according to a variable power control algorithm based on the rotating speed of the water turbine, and the storage battery starts to be charged; meanwhile, the battery management system BMS monitors the voltage, the current and the temperature of the storage battery in real time; if the equipment is abnormal, entering step 6; step 6, carrying out equipment fault switching; step 7, switching a braking mode; while the electromagnetic power output by the water turbine is rapidly tracked, efficient recovery of braking energy is achieved, the loss of a mechanical braking module is reduced, and the operation and maintenance cost is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrical braking of a hydro-generator, and particularly to a method and topology of electrical braking of a hydro-generator based on uncontrolled rectification and a boost-buck converter. BACKGROUND

[0002] As the core mechanical equipment of a hydropower station, the performance of a hydro-turbine unit directly determines the development and utilization rate of hydropower resources. After the hydro-turbine unit is decoupled from the external power system, if the shutdown process only relies on its own friction to stop naturally, it will take a long time, and when the unit speed drops to a low-speed operation state, the oil film of the bearing bush will be in a dry friction state, causing wear to the unit bearing. Therefore, in order to reduce the duration of the unit at low speed, it is necessary to use a mechanical braking and electrical braking assisted shutdown method for the hydro-turbine unit. The electrical braking is used when the unit speed is high, and the electrical braking is turned off when the unit speed is low, and the mechanical braking mode is used.

[0003] However, in existing applications, the electrical braking mainly reduces the speed of the generator by short-circuiting the three-phase stator of the generator, and the part of the rotating energy is converted into heat energy dissipation of the generator stator bar, resulting in energy waste. Some existing research has proposed a hydro-generator braking energy recovery and reuse scheme combining power electronic devices and energy storage devices, and the topology of the scheme is as shown in Figure 1 However, the above electrical braking scheme is generally put into use when the speed reaches 50% of the rated value, and is cut off at 15%, and the energy recovery rate is still low. The reliability and success rate of electrical braking directly determine the wear and replacement cycle of the braking module in mechanical braking. If the energy recovery efficiency of electrical braking can be increased, the service life of the mechanical braking module can also be indirectly extended, and the operation and maintenance cost can be reduced. Specifically, the existing technology has the following disadvantages: 1. In the existing electrical braking method, whether it is the electrical braking method of dissipating energy by short-circuiting the three-phase stator of the generator, or the method of absorbing electrical energy by using a hydro-turbine unit braking energy recovery system, there is a lot of energy waste.

[0004] 2. The output voltage during the shutdown process of the hydro-generator will continue to decay as the speed decreases, and a large range of output voltage changes requires a higher requirement for the control strategy design of the recovery rectification module, the voltage resistance of the hardware device, and the overload capacity, which indirectly leads to a shorter time for the actual braking energy recovery scheme to be put into application (put into use when the speed reaches 50% of the rated value, and cut off at 15%). According to the energy kinetic formula, when the speed is only 50% of the rated value, the kinetic energy has been wasted by 75% compared to the rated value. It can be seen that the existing scheme still has a lot of energy waste.

[0005] ​3、Based on the cause analysis of the failure of electric braking, the existing related researches put forward optimization and improvement suggestions on how to improve the reliability and stability of the electric braking system. But most of them focus on the research on the software control level such as automatic control strategy [1] , unit protection locking logic [2] , parameter adjustment of excitation system [3]、[4] , etc. The above-mentioned schemes mostly need to modify and optimize the original hardware and software of the water turbine unit or circuit, and less optimize and improve the hardware and software of the electric braking equipment itself without changing the existing operation and maintenance, so as to improve the energy recovery rate and reduce the burden on the operation and maintenance personnel after the addition of the extra electric braking equipment.

[0006] The references in the background art are as follows: [1] QIU Enhua. Electric braking method and application of water turbine generator unit considering protection and safety control [D]. Chongqing: Chongqing University, 2014. [2] TAN Juan, LIU Guangquan, YANG Yan. Application of electric braking technology of large-scale water turbine generator unit in Three Gorges Hydropower Station [J]. Hydropower Automation and Dam Monitoring, 2012, 36(1): 34-37. [3] YANG Xiujie, WANG Fang. Design and application of electric braking system in Xiaolangdi Hydropower Station [J]. Large Electric Machine Technology, 2002, 32(1): 60-63. [4] YANG Chengwan, PAN Rui, JI Jianpei, et al. A water turbine generator unit braking energy recovery system and method [P]. Hubei: CN202310557354.5, 2023-08-15. SUMMARY The purpose of the present application is to overcome the above-mentioned deficiencies and provide a water turbine generator electric braking method and topology structure based on uncontrolled rectification and boost-buck converter to solve the problems in the background art.

[0007] To solve the above-mentioned technical problems, the technical scheme adopted by the present application is as follows: a water turbine generator electric braking method based on uncontrolled rectification and boost-buck converter, comprising the following steps: Step 1: Unit splitting and initial state confirmation: after the water turbine generator unit receives the shutdown instruction, the load is gradually reduced to 0, the generator outlet switch is turned off, and the unit is split from the power grid. The local control unit LCU of the unit sends a signal to the energy recovery system controller to trigger system self-checking, and judges whether to enter the next step according to the self-checking result; Step 2: Speed threshold judgment and device pre-throw-off: the local control unit LCU of the unit collects the unit speed n in real time, and sends an instruction to make the controller complete the closing operation of the energy recovery system related switch when the speed drops to the set threshold, to establish an energy transmission channel; Step 3: Uncontrolled rectification and real-time operating parameter acquisition: AC power output by the generator stator is input into the uncontrolled rectification circuit after being stepped down by the excitation transformer to convert it into DC power, and real-time acquisition of the operating parameters of the energy recovery system and the hydro-turbine unit is performed; Step 4: Reference power calculation: based on the operating parameters acquired in Step 3, the loss power and electromagnetic power are calculated to obtain the reference power for the control strategy P ; Step 5: the reference power P calculated in Step 4 and the monitoring signal u dc2 、 i dc2 are input into the controller, the controller outputs corresponding control instructions to drive the boost-buck converter according to the variable power control algorithm based on the hydro-turbine speed to start charging the battery; at the same time, the battery management system BMS monitors the battery voltage, current and temperature in real time; if an abnormality occurs in the equipment, Step 6 is entered; Step 6: equipment fault switching: if a fault in the braking energy recovery system is detected during operation, the controller disconnects the relevant switches and sends an instruction to the unit local control unit to stop charging the battery, and at the same time, the braking switch is closed to short-circuit the three-phase of the generator stator, the traditional energy consumption braking resistor is heated to assist braking, and Step 7 is entered; Step 7: braking mode switching: the unit local control unit monitors the unit speed in real time, and when the speed drops to the set exit threshold, an instruction is sent to stop the energy recovery system from operating, the battery is switched to the floating state, and the mechanical brake is put into operation to reduce the unit speed to 0.

[0008] Preferably, in Step 1, the system self-checking specifically detects the fault states of the uncontrolled rectification circuit, the boost-buck converter, the battery pack and the current / voltage sensor in sequence, the fault states include device short circuit, device open circuit and battery bulging; if any of the equipment has a fault, the controller feeds back to the unit local control unit that the “energy recovery system is abnormal”, the system automatically exits, and the unit is switched to the traditional electrical braking process; if all the equipment is in good condition, the next step is entered.

[0009] More preferably, the traditional electrical braking process is to short-circuit the three-phase of the generator stator to heat the traditional energy consumption braking resistor to assist braking.

[0010] Preferably, Step 2 specifically includes that the unit local control unit acquires the unit speed n in real time, and when the speed drops to 70% of the rated speed, an “allow energy recovery to be put into operation” instruction is sent; the controller closes the connection switch between the energy recovery system and the generator stator side, so that the uncontrolled rectification circuit is connected to the output end of the generator; at the same time, the switch between the battery pack and the boost-buck converter is closed to establish an energy transmission channel.

[0011] Preferably, step 3 specifically involves: the AC power output from the generator stator is stepped down by the excitation transformer and then input into the uncontrolled rectifier circuit to convert the AC power into DC power. u dc1 Simultaneously, other parameters of the energy recovery system and turbine parameters are collected in real time, including the output voltage of the uncontrolled rectifier. u dc1 DC output voltage u dc2 Charging current i dc2 Stator short-circuit current I g Real-time speed of turbine rotor n Excitation current I f For later use.

[0012] Preferably, step 4 specifically involves: based on the real-time detected stator short-circuit current... I g Real-time speed of turbine rotor n Excitation current I f Calculate power loss and electromagnetic power P e And calculate the reference power used to execute the control strategy based on the obtained power loss. P This is used to perform subsequent steps.

[0013] More preferably, the power loss includes friction loss P1 caused by generator stator ventilation and heat dissipation, bearing friction loss power P2, stator winding copper loss P3, and eddy current and hysteresis loss P4 in the stator core.

[0014] More preferably, a reference power for implementing the control strategy is calculated based on the obtained power loss. P The specific process is as follows: Let the real-time rotational speed of the turbine rotor be... n Then there is frictional loss caused by the ventilation and heat dissipation of the generator stator. P The calculation formula is as follows: (1); in, K 1 represents the stator ventilation friction coefficient; Bearing friction loss power P The formula for calculating 2 is as follows: (2); in, K 2 represents the bearing friction coefficient; Meanwhile, the magnitude of the stator current during electric braking can be expressed by the following formula: (3); wherein, I g is the stator output current, E is the stator potential, X d is the direct axis synchronous reactance of the generator, R is the equivalent resistance in the stator circuit, and there is the direct axis synchronous reactance X d The calculation formula of is: (4); wherein, f is the fundamental potential frequency, L is the direct axis synchronous inductance of the generator; and f , the rotational speed n and the number of magnetic pole pairs p The relationship is: (5); The potential generated on the stator side of the generator can be expressed as: (6); In the above formula, N is the total number of turns of the stator per-phase winding in series, is the fundamental magnetic flux of the stator per pair of magnetic poles; Substituting formula (4), (5) and (6) into (3) can obtain: (7); Although the equivalent resistance of the stator circuit will change due to the influence of the boost-buck converter during the process of braking energy recovery, according to the motor theory, the stator circuit resistance is much smaller than the direct axis synchronous reactance, and then the above formula (7) can be simplified as: (8); In the entire electrical braking process, the stator current calculation formula is a constant, that is, when the excitation current is constant, the stator current is also constant; according to the Joule law, the calculation formula of the copper loss P 3 of the stator winding and the eddy current and hysteresis loss P 4 in the stator core are: (9); (10); wherein, I g and I f represent the stator output current and the alternating current excitation current of the stator respectively, R g and R f represent the stator winding resistance and the excitation winding resistance respectively; In the above power conversion process, the rotor excitation loss is not considered, which is supplied by the excitation power supply and is not calculated; Based on the above derivation, the maximum recoverable power of the hydroelectric generator set electrical braking energy recovery system can be determined P For: (11).

[0015] Preferably, the variable power control algorithm based on the speed of the water turbine in step 5 is specifically: Step 5.1, voltage and power outer loop control: With the target terminal voltage of the battery U dc2 * As a reference, compare it with the actual detected terminal voltage U dc2 Calculate the voltage deviation; take the current power P * As a reference, compare it with the actual detected DC / DC charging power, calculate the power deviation as an auxiliary control signal; Step 5.2, deviation processing and reference current generation: The voltage outer loop PI controller performs proportional integral operation on the voltage deviation and outputs a current value as the control reference quantity of the current inner loop control; Similarly, the power outer loop PI controller performs proportional integral operation on the power deviation and outputs the current correction value corresponding to the power deviation. After superimposing the current reference value generated by the voltage outer loop controller, the total reference current i * is obtained, which is used for subsequent current inner loop controller calculation; Step 5.3, execute current inner loop control: take the reference current obtained by adding the current signals output by the voltage and power outer loop controls as the control target, compare it with the current actual charging current i dc2 , calculate the current deviation; the current inner loop PI controller performs operation on the current deviation and outputs the control signal for pulse width modulation PWM, and then changes the duty cycle of the power device in the boost-buck converter to adjust the charging circuit, and finally obtains a large enough DC output voltage U dc2 , stable DC output current i dc2 , to ensure that the battery can absorb as much braking energy as possible during the speed reduction of the hydroelectric generator set.

[0016] Preferably, the brake energy recovery system failure in step 6 includes diode breakdown and MOSFET tube damage.

[0017] Preferably, the step 7 is specifically: the unit local control unit monitors the unit speed in real time, when the speed drops to 10% of the rated speed, sends the "electrical brake exit" instruction; the controller disconnects the switch, stops the energy recovery system operation, at the same time sends the "float charging" instruction to the BMS, the BMS controls the storage battery to turn into the floating state, standby next shutdown or black start, at the same time, the mechanical brake device is put into operation, so that the speed of the hydraulic turbine unit is reduced to 0.

[0018] In addition, the application also discloses a recovery rectification module topology based on uncontrolled rectification and a boost-buck converter, which is applied to the water turbine generator electrical braking method and comprises an excitation transformer, an uncontrolled rectification circuit, a boost-buck converter, a DC side capacitor and a storage battery. The high-voltage side of the excitation transformer is connected with the stator winding of the water turbine generator, and the low-voltage side is connected with the AC input end of the uncontrolled rectification circuit. The DC output end of the uncontrolled rectification circuit is connected with the DC side capacitor in parallel, and the DC output end of the uncontrolled rectification circuit is connected with the DC input end of the boost-buck converter through a wire. The DC output end of the boost-buck converter is connected with the storage battery. The uncontrolled rectification circuit adopts diodes as power electronic devices, which are used for converting the AC power output by the excitation transformer into DC power, and the DC side capacitor is used for filtering the DC power output by the uncontrolled rectification circuit. The boost-buck converter is used for realizing the step-down operation in the initial stage of the braking energy recovery, i.e. when the AC input voltage is large, and realizing the step-up operation in the later stage of the braking energy recovery, i.e. when the AC input voltage is small, so as to ensure that the storage battery can be reliably and stably charged in the whole braking process.

[0019] The application has the following beneficial effects: 1. The application is put into operation in advance and withdrawn in delay, and the energy recovery rate is improved: by improving the energy recovery starting speed from 50% of the rated speed to 70% and lowering the withdrawal speed from 15% to 10%, and combining the variable power control strategy, the energy recovery time is prolonged by more than 30%, and the recovery rate is improved by 25%-40% compared with the prior art.

[0020] 2. The hardware topology and equipment are simplified, and the control strategy is optimized: the uncontrolled rectification is adopted to replace the controllable rectification, the use of controllable devices such as IGBT is reduced, and the hardware failure rate is reduced; the variable power control strategy does not need complex excitation current adjustment, the control logic is simplified, and the operation and maintenance personnel only need to check the storage battery and sensor state regularly.

[0021] 3. The application improves the reliability of unit shutdown: sets up multi-dimensional switching mechanism of equipment failure, power grid power failure, abnormal speed, etc., ensures that the unit can be safely shut down under any working condition, and has black start power support capability, improving the risk resistance of power station.

[0022] 4. The application solves the problems of complex parameter setting of power devices, limitations of overcurrent and voltage resistance, ensures that the electrical scheme can be put into the water turbine braking process earlier from the hardware level, designs a variable power control strategy based on the speed of the water turbine, realizes efficient recovery of braking energy while quickly tracking the output electromagnetic power of the water turbine, improves the recovery rate of water turbine braking energy from the software design level, indirectly reduces the loss of mechanical braking module, and reduces the operation and maintenance cost. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Fig. 1 is a topological diagram of an electrical braking energy recovery and recycling system for a water turbine generator set. Figure 2 Fig. 2 is a topological structure diagram of a recycling rectifier module based on uncontrolled rectification and boost-buck converter. Figure 3 Fig. 3 is a variable power control block diagram based on the speed of the water turbine. Figure 4 Fig. 4 is a flowchart of an electrical braking method for a water turbine generator based on uncontrolled rectification and boost-buck converter. DETAILED DESCRIPTION

[0024] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0025] Embodiment 1: In the original Figure 1 In the electrical braking energy recovery and recycling system, the deceleration process of the water turbine generator set still conforms to the calculation formula of the effective value of the synchronous generator stator winding excitation electromotive force: ; In the formula, f is the fundamental potential frequency, N is the total number of turns of each phase winding of the stator in series, is the fundamental flux of each pair of magnetic poles of the stator, which can change the size of the magnetic flux by adjusting the excitation current, thereby changing the size of the electromotive force. And f , the speed n and the number of magnetic pole pairs p are related as follows: ; As can be seen from the above formula, the rotor excitation current needs to be continuously increased during the braking energy recovery to maintain the output voltage of the hydroelectric generating set and ensure the reliable operation of the recovery rectifier module, but this process ignores the saturation effect of the magnetic material itself, that is, when the rotor excitation current is large enough, the ferromagnetic material will reach the over-saturation region, at which time the magnetic induction intensity of the rotor core will no longer change with the magnetic field intensity. The actual control effect of increasing the excitation current to increase the rotor output voltage is not ideal. Therefore, the application replaces the recovery rectifier module with a form of uncontrolled rectification and boost-buck converter cascade, and the specific scheme topology is shown in Figure 2

[0026] Among them, the alternating current energy output by the excitation transformer of the generator is injected into the uncontrolled rectification circuit as an alternating current input, and the alternating current input voltage is u ac , and the uncontrolled rectification output voltage after rectification is u dc1 , u dc1 The stable direct current output voltage u dc2 is obtained through the boost-buck converter, and the charging current of the storage battery is i dc2 . At the same time, in addition to being connected to the recovery rectifier module topology proposed in the application, the storage battery can also be connected to the self-use power bus or the braking rectifier cabinet through the AC / DC module or the DC / DC module respectively in parallel, to supply power to other loads and fully utilize the braking recovery energy.

[0027] In the process of braking energy recovery, the output power of the hydroelectric generator and the output voltage of the uncontrolled rectification circuit u dc1 also continuously decrease due to the continuous decrease of the hydroelectric generator speed, so it is necessary to connect a boost-buck converter at the output end of the uncontrolled rectification circuit to ensure that the boost-buck converter output voltage u dc1 is constant while the voltage variation range is large. u dc2

[0028] In addition, considering that the output power of the hydroelectric generator is continuously decreasing, the traditional constant voltage, constant current or droop control strategy of constant control target has been difficult to adapt to the adjustment requirement under this working condition, and the application further proposes a variable power control strategy based on the speed of the hydroelectric generator, so that the braking energy recovery system can automatically adjust the charging and discharging power according to the speed and the uncontrolled rectification circuit output voltage u dc1 to maintain the stability of the output voltage u dc2 . ​​

[0029] During electric braking, the braking torque of the turbine unit includes not only the braking torque generated by the recovery of braking energy, but also the wind resistance torque caused by the ventilation and heat dissipation of the generator stator, the wear and loss of the turbine bearings, and the copper loss of the stator and rotor. The magnitude of these braking torques and braking power are all related to the rotational speed.

[0030] The following describes in detail an electrical braking method for a hydro-generator based on uncontrolled rectification and step-up / step-down converter, comprising the following steps: like Figure 4 As shown, an electrical braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter includes the following steps: Step 1: Unit disconnection and initial state confirmation: After receiving the shutdown command, the hydro-generator unit gradually reduces the load to 0, disconnects the generator outlet switch, disconnects from the grid, and the unit's local control unit (LCU) sends a signal to the energy recovery system controller to trigger the system self-test. Based on the self-test results, it is determined whether to proceed to the next step. Step 2: Speed ​​threshold judgment and equipment pre-operation / de-operation: The unit's local control unit (LCU) collects the unit's speed n in real time. When the speed drops to the set threshold, it sends a command to the controller to complete the closing operation of the relevant switches of the energy recovery system and establish an energy transmission channel. Step 3: Uncontrolled rectification and real-time operating parameter acquisition: The AC power output from the generator stator is stepped down by the excitation transformer and then input into the uncontrolled rectifier circuit to be converted into DC power. At the same time, the operating parameters of the energy recovery system and the turbine unit are acquired in real time. Step 4: Reference power calculation: Based on the operating parameters collected in Step 3, calculate the power loss and electromagnetic power to obtain the reference power used for the control strategy. Step 5: Calculate the reference power. P and monitoring signals u dc2 , i dc2 The input controller outputs corresponding control commands based on the variable power control algorithm of the turbine speed to drive the step-up / step-down converter to start charging the battery; at the same time, the battery management system (BMS) monitors the battery voltage, current and temperature in real time; if the equipment malfunctions, proceed to step 6. Step 6: Equipment Fault Switching: If a brake energy recovery system fault is detected during operation, the controller disconnects the relevant switch and sends a command to the local control unit of the unit to stop charging the battery. At the same time, the brake switch is closed to short-circuit the three phases of the generator stator. The conventional energy consumption brake resistor heats up to assist braking, and then proceeds to Step 7. Step 7: Braking mode switching: The local control unit monitors the unit speed in real time. When the speed drops to the set exit threshold, it sends a command to stop the energy recovery system, controls the battery to switch to float charging mode, and engages mechanical braking to reduce the unit speed to 0.

[0031] Preferably, in step 1, the system self-test specifically involves sequentially detecting the fault status of the uncontrolled rectifier circuit, buck-boost converter, battery pack, and current / voltage sensor. The fault status includes short circuit, open circuit, and battery bulging. If any device is faulty, the controller reports "energy recovery system abnormality" to the local control unit of the unit, the system automatically exits, and the unit switches to the conventional electric braking process. If all devices are fault-free, proceed to the next step.

[0032] Preferably, the conventional electric braking process involves short-circuiting the three phases of the generator stator and using the heat generated by the conventional energy-consuming braking resistor to assist braking.

[0033] Preferably, step 2 specifically involves: the local control unit of the unit collecting the unit speed n in real time; when the speed drops to 70% of the rated speed, sending a "allow energy recovery to be activated" command; causing the controller to close the connection switch between the energy recovery system and the generator stator side, so that the uncontrolled rectifier circuit is connected to the generator output terminal; at the same time, closing the switch between the battery pack and the step-up / step-down converter to establish an energy transmission channel.

[0034] Preferably, step 3 specifically involves: the AC power output from the generator stator is stepped down by the excitation transformer and then input into the uncontrolled rectifier circuit to convert the AC power into DC power. u dc1 Simultaneously, other parameters of the energy recovery system and turbine parameters are collected in real time, including the output voltage of the uncontrolled rectifier. u dc1 DC output voltage u dc2 Charging current i dc2 Stator short-circuit current I g Real-time speed of turbine rotor n Excitation current I f For later use.

[0035] Preferably, step 4 specifically involves: based on the real-time detected stator short-circuit current... I g Real-time speed of turbine rotor n Excitation current I f Calculate power loss and electromagnetic power P eAnd calculate the reference power used to execute the control strategy based on the obtained power loss. P This is used to perform subsequent steps.

[0036] More preferably, the power loss includes friction loss P1 caused by generator stator ventilation and heat dissipation, bearing friction loss power P2, stator winding copper loss P3, and eddy current and hysteresis loss P4 in the stator core.

[0037] More preferably, a reference power for implementing the control strategy is calculated based on the obtained power loss. P The specific process is as follows: Let the real-time rotational speed of the turbine rotor be... n Then there is frictional loss caused by the ventilation and heat dissipation of the generator stator. P The calculation formula is as follows: (1); in, K 1 represents the stator ventilation friction coefficient; Bearing friction loss power P The formula for calculating 2 is as follows: (2); in, K 2 represents the bearing friction coefficient; Meanwhile, the magnitude of the stator current during electric braking can be expressed by the following formula: (3); in, I g For stator output current, E For stator potential, X d Here, R is the direct-axis synchronous reactance of the generator, and R is the equivalent resistance in the stator circuit, and there is a direct-axis synchronous reactance. X d The calculation formula is: (4); In the formula, f The fundamental potential frequency, L For the generator direct-axis synchronous inductor; and f Rotation speed n With the number of magnetic pole pairs p The relationship is: (5); The electromotive force generated on the stator side of the generator can then be expressed as: (6); In the above formula, N is the total number of turns in series in each phase of the stator winding. This refers to the fundamental magnetic flux per pair of stator poles; Substituting equations (4), (5), and (6) into (3) yields: (7); Although the equivalent resistance of the stator circuit changes due to the influence of the step-up / step-down converter during the regenerative braking process, according to motor theory, the stator circuit resistance is much smaller than the direct-axis synchronous reactance. Therefore, equation (7) can be simplified as follows: (8); Throughout the entire electric braking process, the stator current calculation formula remains constant; that is, when the excitation current is constant, the stator current is also a constant value. According to Joule's law, the stator winding copper loss can be obtained. P 3. Eddy current and hysteresis losses in the stator core P The formula for calculating 4 is: (9); (10); In the formula, I g and I f These represent the stator output current and the stator AC excitation current, respectively. R g and R f These represent the stator winding resistance and the excitation winding resistance, respectively. In the above power conversion process, rotor excitation loss is not considered. This part of the loss is supplied by the excitation power supply, so it is not included in the calculation. Based on the above derivation, the maximum recoverable power of the hydro-turbine generator set's electrical braking energy recovery system can be determined. P for: (11).

[0038] As the rotor speed decreases, the power that the regenerative braking system can absorb also decreases. Therefore, a corresponding control strategy must be matched to achieve stable and reliable charging of the battery. As can be seen from the above power conversion process, during electric braking, the maximum recoverable power... P It is directly related to the rotor speed n, and the speed n directly determines the stator output electromotive force. E Therefore, in actual operation, only the stator output current, voltage, and rotational speed n need to be monitored to calculate the reference power input P required by the proposed variable power control strategy, i.e., the maximum recoverable power. The specific control strategy flow is as follows: Figure 3 As shown in the figure, u* dc2This is the reference voltage for the buck-boost converter, and this value can be determined from the battery's charging voltage curve. Although the DC output voltage... u dc2 While the system can be directly powered by batteries, it is necessary to maintain a constant DC bus voltage to avoid DC voltage fluctuations caused by changes in turbine speed during charging. Therefore, a dual closed-loop control strategy for voltage and current is adopted. Simultaneously, to ensure adjustable power absorption, a power control loop is added at the outer voltage loop output to ensure that the step-up / step-down converter can adjust its transmission power in accordance with the turbine speed.

[0039] Specifically, the variable power control algorithm based on the turbine speed in step 5 is as follows: Step 5.1, Voltage and Power Outer Loop Control: Based on the target terminal voltage of the battery U dc2 * Using this as a reference, compare it with the actual detected terminal voltage. U dc2 By comparing the values, the voltage deviation was calculated; based on the current power output P of the turbine unit... * Based on this, the power deviation is calculated by comparing it with the actual detected DC / DC charging power, and used as an auxiliary control signal. Step 5.2, Deviation Processing and Reference Current Generation: The voltage outer-loop PI controller performs proportional-integral calculations on the voltage deviation and outputs a current value as the control reference quantity for the current inner-loop control. Similarly, the power outer-loop PI controller performs proportional-integral calculations on the power deviation and outputs a current correction value corresponding to the power deviation. This correction value is then superimposed on the current reference quantity generated by the voltage outer-loop controller to obtain the total reference current i. * These are used together for subsequent calculations of the inner current controller. Step 5.3: Execute inner current control: Use the reference current obtained by adding the current signals output from the outer voltage and power control loops as the control target, and compare it with the current actual charging current i. dc2 The current deviation is calculated; the inner-loop PI controller calculates the current deviation and outputs a control signal for pulse width modulation (PWM), which in turn changes the duty cycle of the power devices in the buck-boost converter to adjust the charging circuit, ultimately obtaining a sufficiently large DC output voltage U. dc2 Stable DC output current I dc2 This ensures that the battery can absorb as much braking energy as possible during the deceleration of the turbine unit.

[0040] Preferably, the braking energy recovery system faults in step 6 include diode breakdown and MOSFET damage.

[0041] Preferably, step 7 specifically involves: the local control unit of the unit monitoring the unit speed in real time; when the speed drops to 10% of the rated speed, sending an "electric brake disengagement" command; the controller disconnects the switch to stop the energy recovery system from operation, and simultaneously sends a "float charging" command to the BMS; the BMS controls the battery to switch to float charging mode, ready for the next shutdown or black start. Simultaneously, the mechanical braking device is engaged to reduce the turbine unit speed to 0.

[0042] Example 2: As Figure 2 As shown, this embodiment also discloses a recovery rectifier module topology based on uncontrolled rectifier and buck-boost converter, applied to the above-mentioned hydro-generator electrical braking method, which includes an excitation transformer, an uncontrolled rectifier circuit, a buck-boost converter, a DC-side capacitor, and a battery; The high-voltage side of the excitation transformer is connected to the stator winding of the hydro-generator, and the low-voltage side is connected to the AC input terminal of the uncontrolled rectifier circuit. The DC output terminal of the uncontrolled rectifier circuit is connected in parallel with the DC-side capacitor, and the DC output terminal of the uncontrolled rectifier circuit is connected to the DC input terminal of the buck-boost converter through a wire. The DC output terminal of the buck-boost converter is connected to the battery. The uncontrolled rectifier circuit uses diodes as power electronic devices to convert the AC power output from the excitation transformer into DC power, and the DC-side capacitor is used to filter the DC power output from the uncontrolled rectifier circuit. The buck-boost converter is used to achieve buck operation in the early stage of regenerative braking, when the AC input voltage is relatively high, and buck operation in the later stage of regenerative braking, when the AC input voltage is relatively low, so as to ensure that the battery can be reliably and stably charged throughout the braking process.

[0043] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. An electrical braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter, characterized in that, Includes the following steps: Step 1: Unit disconnection and initial state confirmation: After receiving the shutdown command, the hydro-generator unit gradually reduces the load to 0, disconnects the generator outlet switch, disconnects from the grid, and the unit's local control unit (LCU) sends a signal to the energy recovery system controller to trigger the system self-test. Based on the self-test results, it is determined whether to proceed to the next step. Step 2: Speed ​​threshold judgment and equipment pre-operation / de-operation: The unit's local control unit (LCU) collects the unit's speed n in real time. When the speed drops to the set threshold, it sends a command to the controller to complete the closing operation of the relevant switches of the energy recovery system and establish an energy transmission channel. Step 3: Uncontrolled rectification and real-time operating parameter acquisition: The AC power output from the generator stator is stepped down by the excitation transformer and then input into the uncontrolled rectifier circuit to be converted into DC power. At the same time, the operating parameters of the energy recovery system and the turbine unit are acquired in real time. Step 4: Reference Power Calculation: Based on the operating parameters collected in Step 3, calculate the power loss and electromagnetic power to obtain the reference power used for the control strategy. P ; Step 5: Calculate the reference power. P and monitoring signals u dc2 , i dc2 The input controller outputs corresponding control commands based on the variable power control algorithm of the turbine speed to drive the step-up / step-down converter to start charging the battery; at the same time, the battery management system (BMS) monitors the battery voltage, current and temperature in real time. If the device malfunctions, proceed to step 6; Step 6: Equipment Fault Switching: If a brake energy recovery system fault is detected during operation, the controller disconnects the relevant switch and sends a command to the local control unit of the unit to stop charging the battery. At the same time, the brake switch is closed to short-circuit the three phases of the generator stator. The conventional energy consumption brake resistor heats up to assist braking, and then proceeds to Step 7. Step 7: Braking mode switching: The local control unit monitors the unit speed in real time. When the speed drops to the set exit threshold, it sends a command to stop the energy recovery system, controls the battery to switch to float charging mode, and engages mechanical braking to reduce the unit speed to 0.

2. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 1, characterized in that, In step 1, the system self-test specifically involves sequentially detecting the fault status of the uncontrolled rectifier circuit, buck-boost converter, battery pack, and current / voltage sensor. The fault status includes short circuit, open circuit, and battery bulging. If any device is faulty, the controller reports "energy recovery system abnormal" to the local control unit of the unit, the system automatically exits, and the unit switches to the conventional electric braking process. If all devices are fault-free, proceed to the next step.

3. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 2, characterized in that, The traditional electric braking process involves short-circuiting the three phases of the generator stator and using the heat generated by the traditional energy-consuming braking resistor to assist braking.

4. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 1, characterized in that, Step 2 specifically involves: the local control unit of the generator set collecting the generator speed n in real time; when the speed drops to 70% of the rated speed, sending a "allow energy recovery to be activated" command; causing the controller to close the connection switch between the energy recovery system and the generator stator side, allowing the uncontrolled rectifier circuit to be connected to the generator output terminal; at the same time, closing the switch between the battery pack and the step-up / step-down converter to establish an energy transmission channel.

5. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 1, characterized in that, Step 3 specifically involves: the AC power output from the generator stator is stepped down by the excitation transformer and then input into the uncontrolled rectifier circuit to convert the AC power into DC power. u dc1 Simultaneously, other parameters of the energy recovery system and turbine parameters are collected in real time, including the output voltage of the uncontrolled rectifier. u dc1 DC output voltage u dc2 Charging current i dc2 Stator short-circuit current I g Real-time speed of turbine rotor n Excitation current I f For later use.

6. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 1, characterized in that, Step 4 specifically involves: based on the real-time detected stator short-circuit current... I g Real-time speed of turbine rotor n Excitation current I f Calculate power loss and electromagnetic power P e And calculate the reference power used to execute the control strategy based on the obtained power loss. P This is used to perform subsequent steps.

7. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 6, characterized in that, The power loss includes friction loss P1 caused by generator stator ventilation and heat dissipation, bearing friction loss power P2, stator winding copper loss P3, and eddy current and hysteresis loss P4 in the stator core.

8. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 6, characterized in that, Calculate the reference power used to implement the control strategy based on the obtained power loss. P The specific process is as follows: Let the real-time rotational speed of the turbine rotor be... n Then there is frictional loss caused by the ventilation and heat dissipation of the generator stator. P The calculation formula is as follows: （1）； in, K 1 represents the stator ventilation friction coefficient; Bearing friction loss power P The formula for calculating 2 is as follows: （2）； in, K 2 represents the bearing friction coefficient; Meanwhile, the magnitude of the stator current during electric braking can be expressed by the following formula: （3）； in, I g For stator output current, E For stator potential, X d Here, R is the direct-axis synchronous reactance of the generator, and R is the equivalent resistance in the stator circuit, and there is a direct-axis synchronous reactance. X d The calculation formula is: （4）； In the formula, f The fundamental potential frequency, L For the generator direct-axis synchronous inductor; and f Rotation speed n With the number of magnetic pole pairs p The relationship is: （5）； The electromotive force generated on the stator side of the generator can then be expressed as: （6）； In the above formula, N is the total number of turns in series in each phase of the stator winding. This refers to the fundamental magnetic flux per pair of stator poles; Substituting equations (4), (5), and (6) into (3) yields: （7）； Although the equivalent resistance of the stator circuit changes due to the influence of the step-up / step-down converter during the regenerative braking process, according to motor theory, the stator circuit resistance is much smaller than the direct-axis synchronous reactance. Therefore, equation (7) can be simplified as follows: （8）； Throughout the entire electric braking process, the stator current calculation formula remains constant; that is, when the excitation current is constant, the stator current is also a constant value. According to Joule's law, the stator winding copper loss can be obtained. P 3. Eddy current and hysteresis losses in the stator core P The formula for calculating 4 is: （9）； （10）； In the formula, I g and I f These represent the stator output current and the stator AC excitation current, respectively. R g and R f These represent the stator winding resistance and the excitation winding resistance, respectively. In the above power conversion process, rotor excitation loss is not considered. This part of the loss is supplied by the excitation power supply, so it is not included in the calculation. Based on the above derivation, the maximum recoverable power of the hydro-turbine generator set's electrical braking energy recovery system can be determined. P for: （11）。 9. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 1, characterized in that, The variable power control algorithm based on turbine speed in step 5 is as follows: Step 5.1, Voltage and Power Outer Loop Control: Based on the target terminal voltage of the battery U dc2 * Using this as a reference, compare it with the actual detected terminal voltage. U dc2 By comparing the results, the voltage deviation can be calculated. With the current power output P of the turbine units * Based on this, the power deviation is calculated by comparing it with the actual detected DC / DC charging power, and used as an auxiliary control signal. Step 5.2, Deviation Processing and Reference Current Generation: The voltage outer-loop PI controller performs proportional-integral calculations on the voltage deviation and outputs a current value as the control reference quantity for the current inner-loop control. Similarly, the power outer-loop PI controller performs proportional-integral calculations on the power deviation and outputs a current correction value corresponding to the power deviation. This correction value is then superimposed on the current reference quantity generated by the voltage outer-loop controller to obtain the total reference current i. * These are used together for subsequent calculations of the inner current controller. Step 5.3: Execute inner current control: Use the reference current obtained by adding the current signals output from the outer voltage and power control loops as the control target, and compare it with the current actual charging current i. dc2 The current deviation is calculated. The inner-loop PI controller calculates the current deviation and outputs a control signal that is pulse-width modulated (PWM). This PWM signal then changes the duty cycle of the power devices in the buck-boost converter to regulate the charging circuit, ultimately resulting in a sufficiently large DC output voltage U. dc2 Stable DC output current i dc2 This ensures that the battery can absorb as much braking energy as possible during the deceleration of the turbine unit.

10. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 1, characterized in that, The faults in the regenerative braking system mentioned in step 6 include diode breakdown and MOSFET damage.

11. The electric braking method for a hydro-generator based on uncontrolled rectifier and step-up / step-down converter according to claim 1, characterized in that, Step 7 specifically involves: the local control unit of the unit monitoring the unit speed in real time, and when the speed drops to 10% of the rated speed, sending an "electric braking off" command; the controller disconnects the switch to stop the energy recovery system from running, and at the same time sends a "float charging" command to the BMS, the BMS controls the battery to switch to float charging state, ready for the next shutdown or black start, and at the same time engages the mechanical braking equipment to reduce the turbine speed to 0.

12. A topology for a recovery rectifier module based on uncontrolled rectification and a buck-boost converter, applied to the electric braking method of a hydro-generator as described in any one of claims 1 to 11, characterized in that, It includes an excitation transformer, an uncontrolled rectifier circuit, a step-up / step-down converter, a DC-side capacitor, and a battery; The high-voltage side of the excitation transformer is connected to the stator winding of the hydro-generator, and the low-voltage side is connected to the AC input terminal of the uncontrolled rectifier circuit. The DC output terminal of the uncontrolled rectifier circuit is connected in parallel with the DC-side capacitor, and the DC output terminal of the uncontrolled rectifier circuit is connected to the DC input terminal of the buck-boost converter through a wire. The DC output terminal of the buck-boost converter is connected to the battery. The uncontrolled rectifier circuit uses diodes as power electronic devices to convert the AC power output from the excitation transformer into DC power, and the DC-side capacitor is used to filter the DC power output from the uncontrolled rectifier circuit. The buck-boost converter is used to achieve buck operation in the early stage of regenerative braking, when the AC input voltage is relatively high, and buck operation in the later stage of regenerative braking, when the AC input voltage is relatively low, so as to ensure that the battery can be reliably and stably charged throughout the braking process.

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