A method and system for controlling a drop-out of a rig bus

Abstract

The present application relates to the field of drilling rig variable frequency drive, and particularly relates to a drilling rig bus anti-drop control method and system. A bidirectional DC / DC converter is arranged between a drilling rig frequency converter DC bus and a super capacitor module, and current limiting charging is performed during normal power supply. When power supply disturbance occurs, a bus energy gap state is determined based on bus voltage, drop slope, load state, super capacitor voltage and power supply side disturbance state, super capacitor energy compensation is controlled, and torque limiting, soft speed reduction are driven in linkage. After disturbance is removed, current limiting recharging, soft return and secondary drop back-off are performed. The present application can improve bus transient support capability, reduce under-voltage trip, secondary drop and mechanical impact risk.

Description

Technical Field

[0001] This invention relates to the field of frequency conversion drive for drilling rigs, specifically a method and system for controlling the anti-fall of drilling rig busbars. Background Technology

[0002] During drilling operations, winches, rotary tables, mud pumps, and other high-power equipment are typically driven by frequency converters. The power supply to the drilling site may be a generator set or a weak power grid. When there are sudden load changes, insufficient generator speed control response, abnormal frequency, instantaneous generator power loss, contactor switching, or upstream power sags, the power available to the frequency converter input side decreases, and the DC bus voltage of the frequency converter drops accordingly. When the DC bus voltage drops to near the undervoltage protection threshold, the frequency converter is prone to triggering undervoltage protection, leading to the shutdown of critical drilling loads or interruption of operations.

[0003] Input reactors can suppress input-side peak currents, improve some harmonic currents, and limit current surges, but they do not provide a sustainable release of electrical energy. For energy gaps caused by short-term voltage dips, instantaneous undervoltage, generator power loss, or frequency disturbances, relying solely on the input reactor cannot compensate for the energy deficit created by the DC bus capacitor releasing power to the load. Therefore, it cannot fundamentally prevent inverter undervoltage tripping.

[0004] Adding an energy storage device to the DC bus side of the drilling rig's frequency converter can replenish energy to the DC bus. However, if the charging and discharging of the energy storage device is controlled solely based on the DC bus voltage threshold, the following problems still exist: First, the triggering logic is lagging, and energy replenishment is only initiated after the DC bus voltage is close to the undervoltage protection threshold, making it difficult for the bidirectional DC / DC converter's replenishment current to be established in time; second, the available energy of the supercapacitor module is limited by the energy window, and simple energy replenishment cannot continuously cover the high power load demand of the drilling rig; third, if the frequency converter speed and torque are immediately restored after the fault is cleared, the recharge power and the load restoration power will be superimposed, which may cause the secondary bus to drop; fourth, the drilling rig has a large load inertia, and sudden changes in speed or torque may cause mechanical shock. Summary of the Invention

[0005] The purpose of this invention is to provide a solution to the aforementioned problems existing in the prior art. Specifically, this invention is achieved through the following technical solution: A method for controlling the drop of a drilling rig busbar includes the following steps: Step 1: During normal power supply, collect the DC bus voltage of the drilling rig inverter, the voltage of the supercapacitor module, the load status of the inverter, and the disturbance status on the power supply side. Control the bidirectional DC / DC converter connected between the DC bus of the drilling rig inverter and the supercapacitor module to charge the supercapacitor module with current limiting, so that the voltage of the supercapacitor module is kept within the voltage range corresponding to the supercapacitor energy window. Step 2: Determine the bus energy gap state based on the DC bus voltage of the drilling rig frequency converter and the corresponding drop slope, the load state of the frequency converter, the voltage of the supercapacitor module, and the power supply side disturbance state. Step 3: When the bus energy gap state is established and the supercapacitor module voltage is within the discharge window, a replenishment reference quantity is generated based on the bus energy gap state, the supercapacitor energy window, and the allowable current of the bidirectional DC / DC converter. After applying current slope limiting processing to the replenishment reference quantity, the replenishment reference quantity is written into the current control input or power control input of the bidirectional DC / DC converter corresponding to the type of the replenishment reference quantity, so that the supercapacitor module replenishes energy to the DC bus of the drilling rig frequency converter. Step 4: During the energy replenishment period, determine the load power matching state based on the voltage drop state of the supercapacitor module, the DC bus voltage recovery state of the drilling rig inverter, and the load state of the inverter; when the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, write the reduced torque upper limit and the soft speed reduction ramp given by adjusting the speed according to the limited slope to the drilling rig inverter. Step 5: After the power supply disturbance is resolved, the recharge permission state is determined based on the bus recovery margin formed by the DC bus voltage of the drilling rig frequency converter, the voltage of the supercapacitor module, the load state of the frequency converter, and the stable state of the generator. The recharge permission state is established when the bus recovery margin is higher than the recharge safety margin, the generator is stable, the frequency converter load state is in the recharge safety zone, and the voltage of the supercapacitor module is lower than the target standby voltage. After the recharge permission state is established, the bidirectional DC / DC converter is controlled to current-limit the recharge of the supercapacitor module, keeping the upper limit of torque limited. The recovery speed is initially given according to the soft return speed ramp, and the upper limit of torque is gradually widened according to the torque recovery ramp when the return stability condition is established. Step six: Perform a second drop-back. During the recharge or soft return, when the bus energy gap state is re-determined to be established, suspend recharge and return to the energy replenishment state; when the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, enter the energy replenishment and derated state.

[0006] Furthermore, the power supply side disturbance state includes at least one of the generator frequency abnormal state and the generator instantaneous power loss state; the bus energy gap state is jointly determined by the decrease in the DC bus voltage of the drilling rig frequency converter relative to the sag trigger voltage, the over-limit state of the sag slope relative to the sag slope limit, the power supply side disturbance state, the frequency converter load state, and the margin of the supercapacitor module voltage relative to the discharge lower limit.

[0007] Furthermore, the sag trigger voltage is determined based on the rated DC bus voltage of the drilling rig inverter, the undervoltage protection threshold, and the safety margin; the sag slope limit is determined based on the DC bus capacitance, the inverter load state, the sampling period, and the response capability of the bidirectional DC / DC converter.

[0008] Furthermore, the bus energy shortage status includes a warning level, a replenishment level, and a replenishment and derating level; the warning level is used to put the bidirectional DC / DC converter into a fast response standby state; the replenishment level is used to generate the replenishment reference quantity, which is a replenishment current command or a replenishment power reference value; the replenishment and derating level is used to simultaneously generate the replenishment reference quantity, the torque upper limit, and the soft speed reduction ramp.

[0009] Furthermore, the energy replenishment reference quantity is an energy replenishment current command or an energy replenishment power reference; the energy replenishment reference quantity is subject to the combined constraints of the maximum allowable current of the bidirectional DC / DC converter, the allowable discharge current of the supercapacitor module, the voltage margin of the supercapacitor module relative to the discharge lower limit, the temperature state of the bidirectional DC / DC converter, the overvoltage limit of the DC bus of the drilling rig frequency converter, and the current slope limit.

[0010] Furthermore, after the energy replenishment reference value is written into the bidirectional DC / DC converter, the energy replenishment reference value is corrected according to the feedback value of the current of the bidirectional DC / DC converter and the feedback value of the DC bus voltage of the drilling rig inverter; when the DC bus voltage of the drilling rig inverter recovers to the target holding range corresponding to the target holding voltage of the bus, the energy replenishment reference value is reduced according to the current slope limit.

[0011] Furthermore, the load power matching state is determined jointly based on the rate of decrease of the supercapacitor module voltage, whether the energy replenishment reference quantity reaches the allowable current limit or allowable power limit of the bidirectional DC / DC converter corresponding to the type of the energy replenishment reference quantity, whether the DC bus voltage of the drilling rig inverter recovers to the target holding range formed by the target holding voltage of the bus, and the load state of the inverter. When the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, the torque limit written to the drilling rig inverter is reduced in a graded manner, and the speed setpoint is adjusted down according to the soft speed reduction ramp.

[0012] Furthermore, the recharge safety zone is determined based on the inverter load rate, DC bus current, estimated load power, speed recovery stage, and the limited state of the torque upper limit in the inverter load state. It is used to characterize the load state range in which the superposition of recharge power and load recovery power does not cause the bus recovery margin to be lower than the recharge safety margin. When the inverter load state exits the recharge safety zone, the recharge current reference is reduced or the current-limited recharge is suspended.

[0013] Furthermore, the current-limited recharge includes: in the initial stage after the recharge permission state is established, recharging the supercapacitor module with a first recharge current limit; when the bus recovery margin is continuously higher than the recharge safety margin and the inverter load state is continuously in the recharge safety zone, increasing the recharge current limit to a second recharge current limit; when the supercapacitor module voltage enters the recharge termination interval determined by the target standby voltage and the recharge termination margin, decreasing the recharge current limit to a third recharge current limit; and stopping recharge when the supercapacitor module voltage is not lower than the target standby voltage.

[0014] Furthermore, the return stabilization conditions include: the bus recovery margin continuously exceeding the recharge safety margin, the supercapacitor module voltage being within the standby window formed by the target standby voltage or the recharge permission state being continuously established, the inverter load state being continuously within the recharge safety zone, and the generator stabilization state being continuously established; the soft return speed ramp is executed before the torque recovery ramp.

[0015] Furthermore, the secondary dropback includes: during the current-limited recharge or soft return, continuously collecting the DC bus voltage of the drilling rig inverter, the drop slope, the power supply side disturbance state, the inverter load state, and the supercapacitor module voltage; when the bus energy gap state is re-determined, the recharge current reference is reduced, the reduction includes clearing the recharge current reference to zero, and switching the bidirectional DC / DC converter to the energy replenishment direction.

[0016] Furthermore, the bidirectional DC / DC converter switches between standby state, replenishment state, replenishment and derating state, current-limited recharge state, paused recharge state, and protection isolation state; before switching from replenishment state to current-limited recharge state, it is confirmed that the current of the bidirectional DC / DC converter meets the direction switching conditions, and the charging and discharging direction, current change slope, and minimum mode hold time are interlocked and controlled.

[0017] Furthermore, the direction switching conditions include: the current of the bidirectional DC / DC converter drops to the allowable commutation range, the bus recovery margin is higher than the recharge safety margin, the voltage of the supercapacitor module is lower than the target standby voltage, and the protection interlock state allows commutation; before the current direction of the bidirectional DC / DC converter is reversed, the current reference in the current direction is first reduced to the allowable commutation range by a slope, and then the current reference in the opposite direction is enabled.

[0018] Furthermore, when overvoltage of the DC bus of the drilling rig inverter, overcurrent of the bidirectional DC / DC converter, overvoltage of the supercapacitor module, over-discharge of the supercapacitor module, over-temperature of the supercapacitor module, or sampling communication failure is detected, the output of the energy replenishment reference quantity and the recharge current reference quantity is limited or prohibited, and the DC bus voltage of the drilling rig inverter, the voltage of the supercapacitor module, the current of the bidirectional DC / DC converter, the load status of the inverter, the disturbance status of the power supply side, and the status switching flag are recorded as fault waveform objects.

[0019] A drilling rig bus anti-drop control system, used to execute the aforementioned drilling rig bus anti-drop control method, includes: a supercapacitor module, a bidirectional DC / DC converter, a bus sampling unit, a supercapacitor sampling unit, a power supply side disturbance sampling unit, a frequency converter load status acquisition unit, a frequency converter interface unit, and a controller. The bus sampling unit, the supercapacitor sampling unit, the bidirectional DC / DC current acquisition unit, the power supply side disturbance sampling unit, the inverter load status acquisition unit, and the inverter interface unit are respectively connected to the controller; the bidirectional DC / DC converter is connected between the DC bus of the drilling rig inverter and the supercapacitor module. The bus sampling unit is used to collect the DC bus voltage of the drilling rig inverter and form the voltage drop slope of the DC bus voltage of the drilling rig inverter. The supercapacitor sampling unit is used to collect the voltage of the supercapacitor module; The bidirectional DC / DC current acquisition unit is used to acquire the current of the bidirectional DC / DC converter; The power supply side disturbance sampling unit is used to collect the power supply side disturbance status; The inverter load status acquisition unit is used to acquire the inverter load status; The inverter interface unit is used to write the torque upper limit, soft speed reduction ramp, soft return speed ramp and torque recovery ramp to the drilling rig inverter. The controller is configured to determine the bus energy gap state, load power matching state, recharge permission state, return stability condition, and secondary drop-back state. Based on the type of the energy replenishment reference quantity, the controller writes the energy replenishment reference quantity through the current control input or power control input of the bidirectional DC / DC converter, and writes the recharge current reference through the current control input of the bidirectional DC / DC converter. The controller also writes the torque upper limit, the soft speed reduction ramp, the soft return speed ramp, and the torque recovery ramp to the drilling rig frequency converter through the frequency converter interface unit.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects: This application not only determines the energy replenishment triggering conditions based on the DC bus voltage, but also combines the DC bus voltage drop slope, power supply side disturbance status, inverter load status, and supercapacitor module voltage to determine the bus energy gap status, thereby enabling the identification of DC bus energy insufficiency trends before undervoltage protection is activated.

[0021] This application further determines the load power matching state during the power replenishment period based on the voltage drop status of the supercapacitor module, the DC bus voltage recovery status, and the inverter load status. When the load power extraction exceeds the replenishment capacity, a torque upper limit and a soft speed reduction ramp are written to the drilling rig inverter. Therefore, the replenishment capacity of the supercapacitor module and the inverter load power extraction are matched under the same control state machine, reducing the risk of continued DC bus voltage drops during the power replenishment period.

[0022] This application only performs current-limited recharge when the bus recovery margin, supercapacitor module voltage, inverter load status, and generator stability all meet the recharge permission requirements. During current-limited recharge, the speed setpoint is restored first, and then the torque limit is gradually increased. If the controller re-determines the bus energy gap status during recharge or soft return, recharge is suspended and the system reverts to replenishment mode. This reduces the risk of secondary bus drop caused by the superposition of recharge power and load recovery power during the recovery phase, and also reduces mechanical impact on the drilling rig. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart illustrating a method for controlling the drop of a drilling rig busbar. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are for illustrative purposes only and are not intended to limit the invention. It should be noted that this invention is already in the actual research and development stage.

[0025] Example 1 like Figure 1 As shown, a method for controlling the drop of a drilling rig busbar includes the following steps: Step 1: During normal power supply, collect the DC bus voltage of the drilling rig inverter, the voltage of the supercapacitor module, the load status of the inverter, and the disturbance status on the power supply side. Control the bidirectional DC / DC converter connected between the DC bus of the drilling rig inverter and the supercapacitor module to charge the supercapacitor module with current limiting, so that the voltage of the supercapacitor module is kept within the voltage range corresponding to the supercapacitor energy window. Step 2: Determine the bus energy gap state based on the DC bus voltage of the drilling rig frequency converter and the corresponding drop slope, the load state of the frequency converter, the voltage of the supercapacitor module, and the power supply side disturbance state. Step 3: When the bus energy gap state is established and the supercapacitor module voltage is within the discharge window, a replenishment reference quantity is generated based on the bus energy gap state, the supercapacitor energy window, and the allowable current of the bidirectional DC / DC converter. After applying current slope limiting processing to the replenishment reference quantity, the replenishment reference quantity is written into the current control input or power control input of the bidirectional DC / DC converter corresponding to the type of the replenishment reference quantity, so that the supercapacitor module replenishes energy to the DC bus of the drilling rig frequency converter. Step 4: During the energy replenishment period, determine the load power matching state based on the voltage drop state of the supercapacitor module, the DC bus voltage recovery state of the drilling rig inverter, and the load state of the inverter; when the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, write the reduced torque upper limit and the soft speed reduction ramp given by adjusting the speed according to the limited slope to the drilling rig inverter. Step 5: After the power supply disturbance is resolved, the recharge permission state is determined based on the bus recovery margin formed by the DC bus voltage of the drilling rig frequency converter, the voltage of the supercapacitor module, the load state of the frequency converter, and the stable state of the generator. The recharge permission state is established when the bus recovery margin is higher than the recharge safety margin, the generator is stable, the frequency converter load state is in the recharge safety zone, and the voltage of the supercapacitor module is lower than the target standby voltage. After the recharge permission state is established, the bidirectional DC / DC converter is controlled to current-limit the recharge of the supercapacitor module, keeping the upper limit of torque limited. The recovery speed is initially given according to the soft return speed ramp, and the upper limit of torque is gradually widened according to the torque recovery ramp when the return stability condition is established. Step six: Perform a second drop-back. During the recharge or soft return, when the bus energy gap state is re-determined to be established, suspend recharge and return to the energy replenishment state; when the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, enter the energy replenishment and derated state.

[0026] Specifically, under normal power supply conditions, the drilling rig frequency converter is powered normally by the power supply side, the DC bus voltage is within the normal range, the generator frequency or the power supply side frequency is not abnormal, and the frequency converter load is within the allowable operating range.

[0027] The controller collects data on the DC bus voltage of the drilling rig's frequency converter, the voltage of the supercapacitor module, the current of the bidirectional DC / DC converter, the load status of the frequency converter, and the disturbance status on the power supply side. When the supercapacitor module voltage is lower than the lower limit corresponding to the target standby voltage, the controller writes a limited recharge current reference to the bidirectional DC / DC converter, causing the bidirectional DC / DC converter to charge the supercapacitor module from the DC bus of the drilling rig's frequency converter with limited current. When the supercapacitor module voltage enters the target standby voltage range, the controller reduces or stops the recharge current, keeping the supercapacitor module within the supercapacitor energy window.

[0028] In this state, the bidirectional DC / DC converter does not act as the primary control source for rigidly controlling the DC bus voltage under normal conditions. Instead, it performs slave control actions such as current-limited charging, standby, or current-controlled operation. This setting is used to avoid control conflicts caused by simultaneous strong control of the same DC bus by the power supply side bus control and the bidirectional DC / DC converter control.

[0029] The controller identifies the bus energy gap status based on the DC bus voltage of the drilling rig frequency converter, the DC bus voltage drop slope, the power supply side disturbance status, the supercapacitor module voltage, and the frequency converter load status.

[0030] In one implementation, the controller first determines the sag trigger voltage, the target holding voltage of the bus, and the lower limit of the bus protection based on the rated DC bus voltage of the drilling rig inverter, the inverter's undervoltage protection threshold, and the safety margin. The sag trigger voltage is higher than the inverter's undervoltage protection threshold, and the lower limit of the bus protection is located within the protection range before the inverter's undervoltage protection operates. The sag slope limit is determined based on the DC bus capacitance, the inverter's load state, the sampling period, and the response capability of the bidirectional DC / DC converter.

[0031] When the DC bus voltage of the drilling rig inverter drops relative to the sag trigger voltage, and the sag rate exceeds the sag rate limit, the controller determines that the DC bus has a rapid energy deficit trend. If there is also an abnormal generator frequency, a generator instantaneous power loss, or an AC input sag, the controller increases the level of the bus energy deficit status. If the inverter load status indicates a high load power, and the supercapacitor module voltage is still above the discharge lower limit, the controller allows entry into the energy replenishment state.

[0032] If the bus voltage only experiences a short-lived noise spike without a sustained drop slope exceeding the limit, or if the power supply disturbance condition is not established and the inverter load is relatively light, the controller can remain in standby mode or enter an early warning mode, without outputting a supplementary energy reference value. This process is used to reduce false triggering and ineffective discharge of the supercapacitor module.

[0033] In one implementation, the controller categorizes the bus energy shortage status into three levels: a warning level, a replenishment level, and a replenishment and derating level. The warning level initiates a fast-response standby state for the bidirectional DC / DC converter; the replenishment level outputs a replenishment reference value; and the replenishment and derating level synchronously outputs the replenishment reference value, torque limit, and soft speed reduction ramp. Hysteresis and minimum hold conditions are set between the different levels to avoid frequent state switching when the bus voltage fluctuates near the threshold.

[0034] When the bus energy gap condition is established and the supercapacitor module voltage is within the discharge window, the controller enters the energy replenishment state. The controller generates an energy replenishment reference quantity based on the bus energy gap condition, the supercapacitor energy window, and the current constraint of the bidirectional DC / DC converter.

[0035] The energy replenishment reference quantity is either an energy replenishment current command or an energy replenishment power reference. The controller determines the candidate energy replenishment reference quantity based on the deviation between the DC bus voltage of the drilling rig frequency converter and the target holding voltage of the bus, the sag slope of the DC bus voltage, the margin of the supercapacitor module voltage relative to the discharge lower limit, the allowable current of the bidirectional DC / DC converter, the allowable discharge current of the supercapacitor module, and the temperature status.

[0036] The candidate energy replenishment reference is subject to the following limits: maximum allowable current of the bidirectional DC / DC converter, allowable power of the bidirectional DC / DC converter, allowable discharge current of the supercapacitor module, voltage margin of the supercapacitor module relative to the lower discharge limit, temperature limit of the bidirectional DC / DC converter, DC bus overvoltage limit, and current change slope limit. The controller writes the energy replenishment reference after limit constraints into the current control input or power control input of the bidirectional DC / DC converter.

[0037] When the energy replenishment reference is an energy replenishment current command, the bidirectional DC / DC converter tracks the energy replenishment current command using its inner current loop. When the energy replenishment reference is an energy replenishment power reference, the bidirectional DC / DC converter converts the energy replenishment power reference into a current control quantity based on the current DC bus voltage, and is subject to current limiting and current slope limiting constraints.

[0038] The controller adjusts the energy replenishment reference value based on the current feedback from the bidirectional DC / DC converter and the bus voltage feedback. If the current tracking error of the bidirectional DC / DC converter exceeds the allowable range, the controller reduces the energy replenishment reference value and checks the power stage status. If the bus voltage recovers to the target holding range corresponding to the target holding voltage of the bus, the controller reduces the energy replenishment reference value by the slope. If the bus voltage recovery is insufficient and the supercapacitor module voltage is still within the discharge window, the controller can increase the energy replenishment reference value within the allowable range and coordinate with load derating control.

[0039] During the power replenishment period, the controller determines the load power matching status based on the voltage drop status of the supercapacitor module, the DC bus voltage recovery status of the drilling rig frequency converter, and the load status of the frequency converter.

[0040] In one implementation, the controller determines the rate of energy consumption of the supercapacitor based on the rate of voltage drop of the supercapacitor module, assesses the margin of the energy replenishment branch based on whether the energy replenishment reference amount has reached the upper limit of the allowable current or the upper limit of the allowable power of the bidirectional DC / DC converter corresponding to the type of energy replenishment reference amount, judges the energy replenishment effect based on whether the DC bus voltage of the drilling rig inverter has recovered to the target holding range formed by the target holding voltage of the bus, and determines the load energy demand based on the load status of the inverter. When the rate of voltage drop of the supercapacitor module increases, the energy replenishment reference amount has reached the upper limit of the allowable current or the upper limit of the allowable power of the bidirectional DC / DC converter corresponding to the type of energy replenishment reference amount, and the DC bus voltage has not yet recovered to the target holding range, the controller determines that the load energy extraction exceeds the energy replenishment capacity.

[0041] When the load power matching state indicates that the load's energy extraction exceeds its replenishment capacity, the controller writes a reduced upper torque limit to the torque limit interface of the drilling rig's frequency converter. The reduction range of the upper torque limit is determined based on the supercapacitor module voltage drop state, the bus voltage recovery state, and the derating range allowed by the drilling rig's processes. If the drilling rig's processes do not allow an immediate reduction to a lower torque, the controller can reduce the upper torque limit in stages while maintaining the lower limit of bus protection and supercapacitor discharge.

[0042] The controller also writes a soft deceleration slope to the speed ramp interface of the drilling rig's frequency converter, causing the speed setpoint to decrease at a limited slope. The soft deceleration slope is determined based on load inertia, mechanical shock tolerance, and bus energy deficit level. This soft deceleration action is tied to the energy replenishment status and is only performed in the bus energy deficit state or in the replenishment and derating state, and is not used as a normal speed adjustment during normal operation.

[0043] Through the above processing, the power drawn from the DC bus by the inverter load side is reduced in a controlled manner, and the supplementary power output from the supercapacitor module through the bidirectional DC / DC converter can cover the remaining energy gap. This processing enables the supercapacitor module, the bidirectional DC / DC converter, and the drilling rig inverter load control interface to jointly participate in the DC bus energy balance, rather than having the supplementary power branch bear all the disturbance power alone.

[0044] Once the power supply disturbance is resolved, the controller does not immediately perform a high-current recharge or fully restore the inverter's speed and torque. Instead, it enters a recovery and stability assessment state. This state confirms that both the power supply and load sides are ready for recovery.

[0045] The controller generates a bus recovery margin based on the DC bus voltage of the drilling rig's frequency converter. This bus recovery margin can be determined by the margin of the current DC bus voltage relative to the recharge safety lower limit, the target bus holding voltage, or the normal bus voltage range. The recharge safety lower limit is higher than the frequency converter's undervoltage protection threshold and allows for a margin to account for voltage drops caused by recharge power absorption.

[0046] The controller also determines the generator's stable state based on the generator frequency, generator power, or the power recovery status of the power supply side. The generator's stable state indicates that the generator frequency and generator power are within the recovery range, and that no further power loss or frequency anomalies occur within the set holding conditions. In weak grid power supply scenarios, the generator's stable state can be characterized by the power supply side's frequency stability state and power recovery status.

[0047] Simultaneously, the controller determines whether the load is within the safe recharge zone based on the inverter's load status. The safe recharge zone characterizes the load state range where the sum of the recharge power and the load recovery power will not cause the bus recovery margin to fall below the safe recharge margin. The controller determines whether the inverter load status is within the safe recharge zone based on the inverter load rate, DC bus current, estimated load power, speed recovery stage, and the limitation status of the torque upper limit.

[0048] The controller determines that the recharge permission state is established only when the bus recovery margin is higher than the recharge safety margin, the generator is in a stable state, the inverter load is in the recharge safety zone, and the supercapacitor module voltage is lower than the target standby voltage.

[0049] In one implementation, the controller uses a single-step rolling prediction method to predict the bus recovery margin for the next control cycle. For the first... In each control cycle, the controller calculates the current bus recovery margin based on the DC bus voltage of the drilling rig's frequency converter collected during that control cycle. ; in, Indicates the first The current bus recovery margin for each control cycle. Indicates the first The DC bus voltage of the drilling rig frequency converter is collected in each control cycle. This indicates the lower limit voltage of the safe recharge voltage that allows entry into or maintenance of current-limited recharge.

[0050] The controller restores margin based on the current bus. As the initial state for prediction, the bus recovery margin for the next control cycle is predicted according to the following formula: ; in, Indicates the predicted first Bus recovery margin for each control cycle. Indicates the first The estimated available power supply is restored on the power supply side within each control cycle. This indicates the bus-side recharge power corresponding to the recharge current reference. This indicates the predicted load recovery power for the next control cycle. This represents the equivalent capacitance of the DC bus of the drilling rig's frequency converter. Indicates the control cycle.

[0051] Each control cycle recalculates the current bus recovery margin based on the currently acquired DC bus voltage of the drilling rig inverter, and performs single-step prediction for the next control cycle accordingly. The bus recovery margin predicted in the previous control cycle is not used as the recursive input for this control cycle. In the first effective control cycle after entering the recovery and stabilization state, the controller calculates the current bus recovery margin based on the DC bus voltage of the drilling rig inverter acquired in that control cycle. .

[0052] Based on the inverter load rate, DC bus current, estimated load power, speed recovery phase, and torque limit constraint, the controller estimates the load recovery power for the next control cycle as follows: ; in, Indicates the first The load recovery power for the next control cycle is predicted in the previous control cycle. This represents the estimated load power obtained from the inverter's load condition. Indicates DC bus current. Indicates the speed recovery phase. This indicates a limited state for the upper limit of torque. This represents the load recovery power increment corresponding to the speed recovery phase. This represents the load recovery power increment corresponding to the torque upper limit limitation state. and The settings are pre-tuned based on the drilling rig load process constraints, speed recovery phase, and torque upper limit release phase, or determined through the control strategy table.

[0053] Based on the recharge power, load recovery power, and power supply recovery available on the power supply side, the controller predicts the bus recovery margin for the next control cycle as follows: ; in, This indicates the predicted bus recovery margin for the next control cycle. This indicates the estimated power supply that has been restored to the power supply side, which is obtained from at least one of the generator frequency recovery status, generator power recovery status, AC input power, or bus input power. This indicates the bus-side recharge power corresponding to the recharge current reference. This represents the equivalent capacitance of the DC bus of the drilling rig's frequency converter; This indicates the control period. This formula is used in the recovery stabilization judgment or current-limited recharge candidate stage when the DC bus voltage of the drilling rig frequency converter is higher than the recharge safety lower limit voltage. It is used to make a first-order prediction of the bus recovery margin within the control period, and is not limited to the only prediction model.

[0054] The controller determines the recharge safety zone marker according to the following formula: ; in, This indicates that the inverter load is in the safe charging zone. This indicates that the inverter has exited the recharge safety zone due to load status. Indicates the safety margin during recharging; Indicates the inverter load rate; This indicates the upper limit of the allowable load rate, which is jointly determined by the speed recovery phase and the torque upper limit limitation state. This indicates the upper limit of the allowable DC bus current, which is determined jointly by the speed recovery phase and the torque upper limit limitation state.

[0055] when When the controller determines that the inverter load state is in the recharge safety zone; when When the inverter load status is determined to be out of the safe recharge zone, the controller reduces the recharge current reference or suspends current-limited recharge.

[0056] In one implementation, the controller determines the recharge permission status according to the following formula: ; in, This indicates that the recharge permission has been granted. This indicates that the recharge permission status is invalid. Indicates the generator's stable state. This indicates that the voltage of the supercapacitor module is lower than the target standby voltage. This indicates that the busbar recovery margin is higher than the recharge safety margin.

[0057] in: ; ; in, Indicates the first The voltage of the supercapacitor module within each control cycle This indicates the target standby voltage. This indicates that the generator has reached a stable state. This indicates that the generator's stable state is not established; It is determined by whether the generator frequency and generator power are within the recovery range, or by the stable frequency and power recovery state of the power supply side in a weak power grid supply scenario.

[0058] The controller determines the recharge termination interval marker and stop conditions as follows: ; ; in, This indicates that the supercapacitor module voltage has entered the recharge termination range determined by the target standby voltage and the recharge termination margin. This indicates that the conditions for stopping recharging have been met. This indicates the recharge termination margin. The recharge termination margin is determined based on the supercapacitor module voltage sampling error, the target standby voltage allowable deviation, the recharge control accuracy of the bidirectional DC / DC converter, and the supercapacitor module protection margin.

[0059] During the current-limited recharge process, the controller determines the recharge current reference according to the following formula: ; in, Indicates the first Each control cycle outputs a recharge current reference to the bidirectional DC / DC converter; This indicates that the energy gap condition of the busbar is established. This indicates that the energy gap condition of the busbar is not valid; This indicates that the conditions for recharging and upgrading have been met. This indicates that the recharge boosting condition is not met; the recharge boosting condition is formed when the bus recovery margin is continuously higher than the recharge safety margin and the inverter load state is continuously in the recharge safety zone. This indicates the first charging current limit. This indicates the second charging current limit. This indicates the third charge current limit; the first, second, and third charge current limits are all set based on the power supply side recovery capability, the allowable current of the bidirectional DC / DC converter, the allowable charge current of the supercapacitor module, and the bus recovery margin.

[0060] when When the controller determines that a bus energy gap occurs again during the current-limited recharge or soft return period, the controller reduces the recharge current reference, which includes clearing the recharge current reference to zero and controlling the bidirectional DC / DC converter to return to the energy replenishment direction; when the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, the controller enters the energy replenishment and derated state.

[0061] The above-mentioned formulaic judgment can also be implemented using a control strategy table. The control strategy table should at least use the inverter load rate, DC bus current, estimated load power, speed recovery stage, and torque upper limit limitation state as indexes, and output a recharge safety zone flag; when using a control strategy table, its output results should satisfy the above... The judgment logic.

[0062] When the recharge permission is established, the controller controls the bidirectional DC / DC converter to provide current-limited recharge to the supercapacitor module from the DC bus of the drilling rig frequency converter. Current-limited recharge is used to restore the standby energy of the supercapacitor module, while preventing the recharge current from absorbing too much power from the power supply side during the recovery process, which could cause a drop in the secondary bus.

[0063] In one implementation, the current-limited recharge process is divided into an initial recharge phase, an enhanced recharge phase, and a target approach phase. The initial recharge phase uses a first recharge current limit. This first recharge current limit is used to verify the power supply side's recovery capability and the bus recovery margin, and its value is less than the second recharge current limit in the enhanced recharge phase. If the bus recovery margin remains higher than the recharge safety margin and the inverter load remains within the recharge safety zone, the controller increases the recharge current limit to the second recharge current limit to shorten the time it takes for the supercapacitor module to recover to the standby energy window. When the supercapacitor module voltage enters the recharge termination range determined by the target standby voltage and the recharge termination margin, the controller decreases the recharge current limit to the third recharge current limit; when the supercapacitor module voltage is not lower than the target standby voltage, the controller stops recharge. The third recharge current limit is not greater than the first recharge current limit and is used to reduce charging shocks before and after entering the recharge termination range.

[0064] If the bus recovery margin decreases, the generator stability fails, or the inverter load condition exits the safe charging zone during the current-limited charging period, the controller lowers the charging current reference or suspends charging. If the controller re-determines that the bus energy deficit condition is established, the controller immediately suspends current-limited charging and reverts to the energy replenishment state.

[0065] Soft return is used to controllably restore the speed setpoint and torque limits of the drilling rig inverter after the power supply disturbance is resolved and the recharge conditions are confirmed. The controller does not release all limits simultaneously, but executes them in stages according to the speed ramp and torque recovery ramp.

[0066] In one implementation, during the current-limited recharge period, the controller maintains the torque upper limit in a restricted state and first restores the speed setpoint using a soft return speed ramp. During the speed setpoint restoration process, the controller continuously monitors the DC bus voltage of the drilling rig's frequency converter, the voltage of the supercapacitor module, the frequency converter load status, and the generator stability status. When the above statuses continuously meet the return stability conditions, the controller then gradually relaxes the torque upper limit using a torque recovery ramp.

[0067] The conditions for returning to stability may include: the bus recovery margin continuously exceeding the recharge safety margin; the supercapacitor module voltage remaining in the standby window or recharge permission state; the inverter load state continuously remaining within the recharge safety zone; and the generator stability state continuously being established. The inverter load state continuously remaining within the recharge safety zone means that the recharge safety zone flag is 1 in each control cycle during the period of maintaining the return to stability conditions; the maintenance period is determined based on the sampling period, generator recovery response, and drilling rig load recovery inertia. The soft return speed ramp is executed before the torque recovery ramp to avoid the simultaneous superposition of speed recovery and torque recovery, which could impact the generator and mechanical transmission chain.

[0068] If the controller re-determines the bus energy gap state during the soft return period, the controller pauses the soft return and returns to the energy replenishment state; if the load power matching state indicates that the load energy intake exceeds the energy replenishment capacity, the controller enters the energy replenishment and derated state.

[0069] The secondary dropback is used to handle situations where a short-term power supply disturbance occurs again during current-limited recharge or soft return. During this phase, the controller continuously collects data on the drilling rig inverter DC bus voltage, DC bus voltage drop slope, power supply disturbance status, inverter load status, and supercapacitor module voltage.

[0070] When the controller re-determines that the bus energy gap is established, it immediately suspends current-limited recharge, lowers the recharge current reference (including clearing the recharge current reference to zero), and switches the bidirectional DC / DC converter to the energy replenishment direction. If the inverter load status indicates that the load energy extraction still exceeds the energy replenishment capacity, the controller enters the energy replenishment and derating state, rewriting the reduced torque upper limit and soft speed ramp to the drilling rig inverter.

[0071] Secondary dropout backoff is not a normal protection shutdown action, but rather a state machine backoff path that re-enters the power replenishment and derating state machine during the recovery process. Through this path, the system can avoid continuing to absorb recharge power or continue to restore load power before the power supply is fully stable, thereby reducing the risk of secondary undervoltage tripping.

[0072] Example 2 The bidirectional DC / DC converter switches between at least the following states: standby, power replenishment, power replenishment and derating, current limiting recharge, paused recharge, and protection isolation.

[0073] Before switching from the recharge state to the current-limited recharge state, the controller confirms that the bidirectional DC / DC converter current meets the direction switching conditions. These conditions include: the bidirectional DC / DC converter current dropping to the allowable commutation range; the bus recovery margin exceeding the recharge safety margin; the supercapacitor module voltage falling below the target standby voltage; and the protection interlock allowing commutation. The controller interlocks the charging / discharging direction, current change slope, and minimum mode hold time to prevent frequent switching between recharge and recharge modes.

[0074] When the bus voltage fluctuates near the sag trigger voltage, the controller limits state jitter through hysteresis and minimum hold conditions. When the bidirectional DC / DC converter current direction reverses, the controller first reduces the current reference in the current direction to the allowable commutation range by a slope, and then enables the current reference in the opposite direction. This method can reduce inductor current reverse surges and DC bus oscillations.

[0075] Example 3 The controller or protection interlock unit detects the following abnormalities: overvoltage of the drilling rig inverter DC bus, undervoltage of the drilling rig inverter DC bus entering the protection zone, overcurrent of the bidirectional DC / DC converter, overtemperature of the bidirectional DC / DC converter, overvoltage of the supercapacitor module, over-discharge of the supercapacitor module, overtemperature of the supercapacitor module, abnormal status of the protection switch, sampling value exceeding the limit, sampling communication failure, and control interface communication failure.

[0076] When an anomaly occurs, the controller limits or disables the output of the energy replenishment reference and the recharge current reference based on the anomaly type. For over-discharge of the supercapacitor module, the controller stops or reduces energy replenishment in the discharge direction and writes a stricter torque limit and soft speed ramp to the drilling rig frequency converter. For overcurrent or overtemperature of the bidirectional DC / DC converter, the controller reduces the current reference and enters a protective isolation state. For sampling communication failure, the controller disables energy replenishment and recharge actions relying on the failed sampling quantity and puts the system into a preset safe state.

[0077] The controller records fault waveforms based on the DC bus voltage of the drilling rig's frequency converter, the voltage of the supercapacitor module, the current of the bidirectional DC / DC converter, the load status of the frequency converter, the disturbance status on the power supply side, and the status switching flags. These fault waveform records are used to subsequently determine whether the execution processes of the bus energy gap status, energy replenishment reference quantity, torque limiting and soft speed reduction, current limiting recharge, and soft return meet the preset control logic.

[0078] Example 4 A drilling rig bus anti-fall control system includes a supercapacitor module, a bidirectional DC / DC converter, a bus sampling unit, a supercapacitor sampling unit, a bidirectional DC / DC current acquisition unit, a power supply side disturbance sampling unit, a frequency converter load status acquisition unit, a frequency converter interface unit, a controller, and a protection interlocking unit.

[0079] The supercapacitor module is used to store the energy required for short-term replenishment. The supercapacitor module is connected to the energy storage side of the bidirectional DC / DC converter. The bus side of the bidirectional DC / DC converter is connected to the DC bus of the drilling rig's frequency converter. The bidirectional DC / DC converter transfers energy in the discharge direction based on the replenishment reference output from the controller, and in the charging direction based on the recharge current reference output from the controller.

[0080] The bus sampling unit outputs the DC bus voltage of the drilling rig inverter to the controller. The controller uses the bus voltage output from the bus sampling unit to determine the sag slope and bus recovery margin. The supercapacitor sampling unit outputs the supercapacitor module voltage to the controller and can simultaneously output the supercapacitor module current and temperature. The bidirectional DC / DC current acquisition unit outputs the bidirectional DC / DC converter current to the controller. The power supply side disturbance sampling unit outputs generator frequency abnormality status, generator instantaneous power loss status, or AC input sag status to the controller. The inverter load status acquisition unit outputs the inverter load status to the controller.

[0081] The inverter interface unit is used to receive the upper torque limit, soft speed reduction ramp, soft return speed ramp and torque recovery ramp output by the controller, and write the above control quantities into the torque limit interface and speed ramp interface of the drilling rig inverter.

[0082] The controller determines the bus energy gap status based on the bus voltage, sag slope, supercapacitor module voltage, bidirectional DC / DC converter current, power supply side disturbance status, and inverter load status. The controller generates a supplementary energy reference value based on the bus energy gap status, supercapacitor energy window, and bidirectional DC / DC converter current constraint, and writes this supplementary energy reference value into the current control input or power control input of the bidirectional DC / DC converter.

[0083] The controller determines the load power matching state based on the supercapacitor module voltage drop state, bus voltage recovery state, and inverter load state, and writes the torque upper limit and soft speed reduction ramp to the drilling rig inverter through the inverter interface unit. The controller determines the recharge permission state based on the bus recovery margin, supercapacitor module voltage, inverter load state, and generator stability state, and writes the recharge current reference to the bidirectional DC / DC converter when the recharge permission state is established. The controller determines the return stability condition based on the drilling rig inverter DC bus voltage, supercapacitor module voltage, and inverter load state, and writes the soft return speed ramp and torque recovery ramp to the drilling rig inverter through the inverter interface unit.

[0084] The protection interlocking unit outputs the protection status to the controller. The controller limits or prohibits the energy replenishment reference and the recharge current reference based on the protection status, and can control the bidirectional DC / DC converter to enter the protection isolation state.

[0085] Specifically, in one embodiment, the transient energy support system for the DC bus of the drilling rig frequency converter is applied in a drilling rig frequency converter drive scenario. The DC bus of the drilling rig frequency converter is the DC energy convergence node between the rectifier side and the inverter side of the drilling rig frequency converter, including a bus capacitor and a bus voltage sampling point connected to the DC bus; the drilling rig frequency converter is used to drive the winch, rotary table, mud pump, or other motor loads in the drilling rig. The system includes a supercapacitor module, a bidirectional DC / DC converter, a bus sampling unit, a supercapacitor sampling unit, a bidirectional DC / DC current acquisition unit, a power supply side disturbance sampling unit, a frequency converter load status acquisition unit, a controller, a frequency converter interface unit, and a protection interlocking unit.

[0086] A bidirectional DC / DC converter is connected between the DC bus of the drilling rig's frequency converter and the supercapacitor module, serving as a DC-DC conversion device capable of controlled power transmission in both directions. The first DC terminal of the bidirectional DC / DC converter is connected to the DC bus of the drilling rig's frequency converter, and the second DC terminal is connected to the supercapacitor module. The bidirectional DC / DC converter has at least a current control input or a power control input for receiving the energy replenishment reference and recharge current reference output from the controller, and features charge / discharge direction control, overcurrent protection, overvoltage protection, and temperature protection functions. Under normal power supply conditions, the bidirectional DC / DC converter receives the recharge current reference and performs current-limited charging of the supercapacitor module. Under bus energy shortage conditions, the bidirectional DC / DC converter receives the energy replenishment reference, causing the supercapacitor module to output energy replenishment current or power to the DC bus of the drilling rig's frequency converter.

[0087] The supercapacitor module is composed of multiple supercapacitor cells connected in series, parallel, or series-parallel, and can be configured with voltage equalization circuits, temperature sampling circuits, voltage sampling circuits, current sampling circuits, and protection switches. The controller establishes a supercapacitor energy window based on the target standby voltage, discharge lower limit, recharge termination interval, and recharge stop condition, ensuring the supercapacitor module operates within its permissible range during standby, discharge, and recharge. The target standby voltage is determined based on the required disturbance duration, the supercapacitor module's rated voltage, the bidirectional DC / DC converter's input range, and lifespan requirements. The discharge lower limit is determined based on the supercapacitor module's minimum permissible operating voltage, the bidirectional DC / DC converter's boost capability, load support requirements, and protection margin. The recharge termination interval determines the final stage of current-limited recharge, and the recharge stop condition determines the timing of stopping current-limited recharge. The recharge termination interval and the recharge stop condition are determined by the target standby voltage, the recharge termination margin, the supercapacitor energy window, and the supercapacitor module's protection margin.

[0088] During the determination of the energy window of the supercapacitor module, the controller can estimate the available energy of the supercapacitor module according to the following formula: ; in, This indicates the energy that the supercapacitor module can release within the energy window. This represents the equivalent capacitance of the supercapacitor module. This indicates the high-side operating voltage when the supercapacitor module is in standby mode. This indicates the lowest operating voltage to which the supercapacitor module can discharge. In actual control, the controller can directly use the voltage window, look up the energy window from a table, or calculate the available energy level to determine whether the supercapacitor module is within the discharge window, recharge range, or target standby voltage range.

[0089] The bus sampling unit is connected to the DC bus of the drilling rig's frequency converter to collect the DC bus voltage of the frequency converter and output the sampled bus voltage value to the controller. The controller generates the DC bus voltage sag slope based on the continuously sampled bus voltage. The sag slope can be obtained through differential calculation of adjacent sample values, sliding window differential calculation, filtered differential calculation, or equivalent slope calculation method preset in the controller.

[0090] A supercapacitor sampling unit is connected to the supercapacitor module and is used to acquire at least one of the following: supercapacitor module voltage, supercapacitor module current, and supercapacitor module temperature. A bidirectional DC / DC current acquisition unit is used to acquire the bidirectional DC / DC converter current; the bidirectional DC / DC converter current can be obtained from the internal current detection circuit of the bidirectional DC / DC converter, an external current sampling circuit, or a current feedback value read from the bidirectional DC / DC converter by the controller. The controller uses the bidirectional DC / DC converter current to limit, correct feedback, confirm direction switching, and determine protection interlocks for the energy replenishment reference or recharge current reference.

[0091] The power supply side disturbance sampling unit is used to collect generator frequency, AC input frequency, generator power, AC input voltage, or power supply side power loss signal. The controller forms the power supply side disturbance state based on the signal output by the power supply side disturbance sampling unit; the power supply side disturbance state can at least manifest as an abnormal generator frequency state, a generator instantaneous power loss state, an AC input voltage sag state, an AC input voltage interruption state, or a power supply side power decrease state. The abnormal generator frequency state can be determined by the generator output frequency, AC input frequency, frequency deviation, or frequency change rate; the instantaneous generator power loss state can be determined by the generator controller output signal, changes in AC input active power, changes in rectified input power, or the bus input power estimation result.

[0092] The inverter load status acquisition unit is used to acquire the inverter load status, which characterizes the amount of energy the drilling rig inverter draws from the DC bus and the mechanical load requirements. The inverter load status can be obtained from at least one of the following quantities: motor current, inverter output power, motor torque feedback, speed setpoint, actual speed, DC bus current, estimated DC bus power, and the inverter's internal load rate. The controller can read the inverter's internal status through the communication interface, or estimate the inverter load power based on the bus voltage, bus current, and inverter output status.

[0093] The inverter interface unit is used to write torque limit, soft speed ramp, soft return speed ramp, and torque recovery ramp to the drilling rig inverter. The inverter interface unit can use a communication interface, analog interface, or digital interface, as long as it allows the controller to write control values ​​to the inverter's torque limit and speed ramp inputs. If the specific engineering system uses a fieldbus, analog channel, or digital channel, the interface type and refresh cycle are determined by the actual open interfaces of the inverter.

[0094] The protection interlock unit is used to detect overvoltage on the DC bus of the drilling rig frequency converter, overcurrent in the bidirectional DC / DC converter, overvoltage in the supercapacitor module, over-discharge in the supercapacitor module, over-temperature in the supercapacitor module, abnormal status of the protection switch, and failure of sampling communication. When the protection interlock unit outputs a protection signal, the controller limits or disables the output of the energy replenishment reference and the recharge current reference, and enters the protection isolation state according to the fault type.

[0095] The controller is connected to the above units respectively and performs bus energy gap status identification, energy replenishment reference quantity generation, torque limiting and soft speed reduction control, recharge permission status determination, current limiting recharge, soft return, secondary drop back and protection isolation control. The bus energy gap status is determined by the controller based on the DC bus voltage, DC bus voltage drop slope, power supply disturbance status, supercapacitor module voltage, and inverter load status. It is used to characterize the insufficient energy and undervoltage trip risk of the drilling rig inverter's DC bus under the current power supply and load conditions. The load power matching status is determined by the controller during energy replenishment based on the supercapacitor module voltage drop status, drilling rig inverter DC bus voltage recovery status, and inverter load status. It is used to characterize the degree of matching between the energy replenishment capacity provided by the supercapacitor module through the bidirectional DC / DC converter and the energy demand of the inverter load. The recharge permission status is determined by the controller after the power supply disturbance is cleared based on the bus recovery margin, supercapacitor module voltage, inverter load status, and generator stability status. The secondary drop back status is determined by the controller when the bus energy gap status is re-established during current-limited recharge or soft return.

[0096] During the recovery and current-limited recharge process, the controller also generates a recharge safety zone flag, a recharge termination interval flag, and a recharge stop condition. The recharge safety zone flag is determined by the inverter load rate, DC bus current, estimated load power, speed recovery stage, and the limited torque limit. It characterizes whether the sum of the recharge power and load recovery power at the current load recovery stage still ensures that the bus recovery margin is not lower than the recharge safety margin. The load recovery power is caused by speed setpoint recovery, torque limit release, and changes in drilling rig load status, and is determined by the speed recovery stage, the limited torque limit state, the inverter load rate, DC bus current, and the estimated load power. The recharge termination interval is formed by the target standby voltage and the recharge termination margin. The recharge stop condition is formed when the supercapacitor module voltage is not lower than the target standby voltage. The recharge termination margin is determined based on the supercapacitor module voltage sampling error, the target standby voltage allowable deviation, the bidirectional DC / DC converter recharge control accuracy, and the supercapacitor module protection margin.

[0097] The method of this application can be executed via a state machine. The state machine includes at least the following states: normal standby state, early warning state, power replenishment state, power replenishment and derating state, recovery and stabilization state, current limiting and recharging state, soft return state, secondary fallback state, and protection isolation state. These are shown in the table below: The control principle of this state machine is as follows: the response should be timely when entering the energy replenishment state; the judgment should be conservative when exiting the energy replenishment state and entering the recharge state; if a bus energy gap occurs again during the recharge and soft return period, the recharge should be suspended first and the energy replenishment should be restored instead of continuing to execute the original recovery sequence.

[0098] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling the drop of a drilling rig busbar, characterized in that, Includes the following steps: Step 1: During normal power supply, collect the DC bus voltage of the drilling rig inverter, the voltage of the supercapacitor module, the load status of the inverter, and the disturbance status on the power supply side. Control the bidirectional DC / DC converter connected between the DC bus of the drilling rig inverter and the supercapacitor module to charge the supercapacitor module with current limiting, so that the voltage of the supercapacitor module is kept within the voltage range corresponding to the supercapacitor energy window. Step 2: Determine the bus energy gap state based on the DC bus voltage of the drilling rig frequency converter and the corresponding drop slope, the load state of the frequency converter, the voltage of the supercapacitor module, and the power supply side disturbance state. Step 3: When the bus energy gap state is established and the supercapacitor module voltage is within the discharge window, a replenishment reference quantity is generated based on the bus energy gap state, the supercapacitor energy window, and the allowable current of the bidirectional DC / DC converter. After applying current slope limiting processing to the replenishment reference quantity, the replenishment reference quantity is written into the current control input or power control input of the bidirectional DC / DC converter corresponding to the type of the replenishment reference quantity, so that the supercapacitor module replenishes energy to the DC bus of the drilling rig frequency converter. Step 4: During the energy replenishment period, determine the load power matching state based on the voltage drop state of the supercapacitor module, the DC bus voltage recovery state of the drilling rig inverter, and the load state of the inverter; when the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, write the reduced torque upper limit and the soft speed reduction ramp given by adjusting the speed according to the limited slope to the drilling rig inverter. Step 5: After the power supply disturbance is resolved, the recharge permission state is determined based on the bus recovery margin formed by the DC bus voltage of the drilling rig frequency converter, the voltage of the supercapacitor module, the load state of the frequency converter, and the stable state of the generator. The recharge permission state is established when the bus recovery margin is higher than the recharge safety margin, the generator is stable, the frequency converter load state is in the recharge safety zone, and the voltage of the supercapacitor module is lower than the target standby voltage. After the recharge permission state is established, the bidirectional DC / DC converter is controlled to current-limit the recharge of the supercapacitor module, keeping the upper limit of torque limited. The recovery speed is initially given according to the soft return speed ramp, and the upper limit of torque is gradually widened according to the torque recovery ramp when the return stability condition is established. Step six: Perform a second drop-back. During the recharge or soft return, when the bus energy gap state is re-determined to be established, suspend recharge and return to the energy replenishment state; when the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, enter the energy replenishment and derated state.

2. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The power supply side disturbance state includes at least one of the generator frequency abnormal state and the generator instantaneous power loss state; the bus energy gap state is determined by the amount of the decrease in the DC bus voltage of the drilling rig frequency converter relative to the sag trigger voltage, the over-limit state of the sag slope relative to the sag slope limit, the power supply side disturbance state, the frequency converter load state, and the margin of the supercapacitor module voltage relative to the discharge lower limit.

3. The method for controlling the drop of a drilling rig busbar according to claim 2, characterized in that, The sag trigger voltage is determined based on the rated DC bus voltage of the drilling rig frequency converter, the undervoltage protection threshold, and the safety margin; the sag slope limit is determined based on the DC bus capacitance, the frequency converter load state, the sampling period, and the response capability of the bidirectional DC / DC converter.

4. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The bus energy shortage status includes a warning level, a replenishment level, and a replenishment and derating level; the warning level is used to put the bidirectional DC / DC converter into a fast response standby state, the replenishment level is used to generate the replenishment reference quantity, and the replenishment and derating level is used to simultaneously generate the replenishment reference quantity, the torque upper limit, and the soft deceleration ramp.

5. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The energy replenishment reference quantity is either an energy replenishment current command or an energy replenishment power reference; the energy replenishment reference quantity is subject to the combined constraints of the maximum allowable current of the bidirectional DC / DC converter, the allowable discharge current of the supercapacitor module, the voltage margin of the supercapacitor module relative to the discharge lower limit, the temperature state of the bidirectional DC / DC converter, the overvoltage limit of the DC bus of the drilling rig frequency converter, and the current slope limit.

6. The method for controlling the drop of a drilling rig busbar according to claim 5, characterized in that, After the energy replenishment reference value is written into the bidirectional DC / DC converter, the energy replenishment reference value is corrected according to the feedback value of the current of the bidirectional DC / DC converter and the feedback value of the DC bus voltage of the drilling rig frequency converter. When the DC bus voltage of the drilling rig frequency converter recovers to the target holding range corresponding to the target holding voltage of the bus, the energy replenishment reference value is reduced according to the current slope limit.

7. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The load power matching state is determined jointly based on the rate of decrease of the supercapacitor module voltage, whether the energy replenishment reference quantity reaches the allowable current limit or allowable power limit of the bidirectional DC / DC converter corresponding to the type of the energy replenishment reference quantity, whether the DC bus voltage of the drilling rig inverter recovers to the target holding range formed by the target holding voltage of the bus, and the load state of the inverter. When the load power matching state indicates that the load energy extraction exceeds the energy replenishment capacity, the torque limit written to the drilling rig inverter is reduced in a graded manner, and the speed setpoint is adjusted down according to the soft speed reduction ramp.

8. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The recharge safety zone is determined based on the inverter load rate, DC bus current, estimated load power, speed recovery stage, and the limited state of the torque upper limit in the inverter load state. It is used to characterize the load state range in which the superposition of recharge power and load recovery power does not cause the bus recovery margin to be lower than the recharge safety margin. When the inverter load state exits the recharge safety zone, the recharge current reference is reduced or the current-limited recharge is suspended.

9. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The current-limited recharge includes: in the initial stage after the recharge permission state is established, recharging the supercapacitor module with a first recharge current limit; when the bus recovery margin is continuously higher than the recharge safety margin and the inverter load state is continuously in the recharge safety zone, increasing the recharge current limit to a second recharge current limit; when the supercapacitor module voltage enters the recharge termination interval determined by the target standby voltage and the recharge termination margin, decreasing the recharge current limit to a third recharge current limit; and stopping recharge when the supercapacitor module voltage is not lower than the target standby voltage.

10. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The conditions for returning to stability include: The bus recovery margin is continuously higher than the recharge safety margin, the supercapacitor module voltage is in the standby window formed by the target standby voltage or the recharge permission state is continuously established, the inverter load state is continuously in the recharge safety zone and the generator stable state is continuously established; the soft return speed ramp is executed before the torque recovery ramp.

11. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The secondary fallback includes: During the current-limited recharge or soft return, the DC bus voltage of the drilling rig inverter, the drop slope, the power supply side disturbance state, the inverter load state, and the supercapacitor module voltage are continuously collected; when the bus energy gap state is re-determined to be established, the recharge current reference is reduced, which includes clearing the recharge current reference to zero and switching the bidirectional DC / DC converter to the energy replenishment direction.

12. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, The bidirectional DC / DC converter switches between standby state, replenishment state, replenishment and derating state, current-limited recharge state, paused recharge state, and protection isolation state. Before switching from replenishment state to current-limited recharge state, it is confirmed that the current of the bidirectional DC / DC converter meets the direction switching conditions, and the charging and discharging direction, current change slope, and minimum mode hold time are interlocked and controlled.

13. The method for controlling the drop of a drilling rig busbar according to claim 12, characterized in that, The direction switching conditions include: The bidirectional DC / DC converter current drops to the allowable commutation range, the bus recovery margin is higher than the recharge safety margin, the supercapacitor module voltage is lower than the target standby voltage, and the protection interlock state allows commutation; before the bidirectional DC / DC converter current direction reverses, the current reference in the current direction is first reduced to the allowable commutation range by a slope, and then the current reference in the opposite direction is enabled.

14. The method for controlling the drop of a drilling rig busbar according to claim 1, characterized in that, When overvoltage of the DC bus of the drilling rig inverter, overcurrent of the bidirectional DC / DC converter, overvoltage of the supercapacitor module, over-discharge of the supercapacitor module, over-temperature of the supercapacitor module, or sampling communication failure is detected, the output of the energy replenishment reference and the recharge current reference is limited or prohibited, and the DC bus voltage of the drilling rig inverter, the voltage of the supercapacitor module, the current of the bidirectional DC / DC converter, the load status of the inverter, the disturbance status of the power supply side, and the status switching flag are recorded as fault waveform objects.

15. A drilling rig busbar anti-drop control system, characterized in that, A drilling rig bus anti-fall control method for executing any one of claims 1-14 includes: a supercapacitor module, a bidirectional DC / DC converter, a bus sampling unit, a supercapacitor sampling unit, a power supply side disturbance sampling unit, a frequency converter load status acquisition unit, a frequency converter interface unit, and a controller. The bus sampling unit, the supercapacitor sampling unit, the bidirectional DC / DC current acquisition unit, the power supply side disturbance sampling unit, the inverter load status acquisition unit, and the inverter interface unit are respectively connected to the controller; the bidirectional DC / DC converter is connected between the DC bus of the drilling rig inverter and the supercapacitor module. The bus sampling unit is used to collect the DC bus voltage of the drilling rig inverter and form the voltage drop slope of the DC bus voltage of the drilling rig inverter. The supercapacitor sampling unit is used to collect the voltage of the supercapacitor module; The bidirectional DC / DC current acquisition unit is used to acquire the current of the bidirectional DC / DC converter; The power supply side disturbance sampling unit is used to collect the power supply side disturbance status; The inverter load status acquisition unit is used to acquire the inverter load status; The inverter interface unit is used to write the torque upper limit, soft speed reduction ramp, soft return speed ramp and torque recovery ramp to the drilling rig inverter. The controller is configured to determine the bus energy gap state, load power matching state, recharge permission state, return stability condition, and secondary drop-back state. Based on the type of the energy replenishment reference quantity, the controller writes the energy replenishment reference quantity through the current control input or power control input of the bidirectional DC / DC converter, and writes the recharge current reference through the current control input of the bidirectional DC / DC converter. The controller also writes the torque upper limit, the soft speed reduction ramp, the soft return speed ramp, and the torque recovery ramp to the drilling rig frequency converter through the frequency converter interface unit.

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