Oilfield micro power network switching control system and method

Abstract

The invention discloses an oil field micro power grid switching control system and method. The system comprises a pumping unit inverter, an energy consumption resistor and a photovoltaic power supply which are respectively connected with a direct current bus circuit; the direct current bus can output electric energy to an external power grid or input electric energy from the external power grid through the controllable rectifier; the monitoring device is used for acquiring alternating-current voltage and direct-current bus voltage in real time; the control device is used for controlling the pumping unit frequency converter, the energy consumption resistor and the controllable rectifier, and the preset rule comprises the steps that after an active isolated network is executed, when the current direct current bus voltage is lower than a preset value and it is monitored that the pumping unit is converted into a down stroke, the pumping unit inverter is controlled to reversely generate power to the direct current bus; in an isolated network, when the oil pumping unit is in a down stroke and the current internal network direct current bus voltage is higher than another preset value, the energy consumption resistor is put into use. According to the method, the failure probability of the active isolated network can be reduced by rescuing the failure of the isolated network, and the abnormal shutdown of oil extraction operation is reduced.

Description

Technical Field

[0001] This invention relates to the field of power systems, and in particular to a switching control system and method for oilfield microgrids. Background Technology

[0002] In the process of promoting the integrated development of new energy and traditional energy, as the penetration rate of new energy continues to increase, a large number of enterprises' power systems are being converted into new power systems with a high proportion of new energy and a high proportion of power electronic equipment connected.

[0003] Currently, the power sources in the new power systems of oilfield production systems can include: external power grid connected to the internal power grid, and photovoltaic power connected to the internal power grid through photovoltaic inverters for coordinated power supply.

[0004] New energy power generation equipment (such as photovoltaic power sources) and electrical equipment (such as frequency converters) in the internal power grid all use power electronic components as energy conversion elements. These power electronic components are susceptible to voltage dips (i.e., voltage sags). When voltage waveform distortions such as voltage sags occur, in order to avoid equipment damage, the existing technology generally adopts the method of cutting off the fault and shutting down the machine, and then reconnecting to the grid after power supply is restored.

[0005] The inventors discovered through research that existing technologies still have at least the following shortcomings:

[0006] A shutdown due to a malfunction results in losses in oil production, and restarting the equipment after a shutdown places a significant impact on the equipment.

[0007] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0008] The purpose of this invention is to reduce the failure rate of active islanding and reduce abnormal downtime in oil production operations.

[0009] This invention provides a micro-power grid switching control system for oilfields, comprising a DC bus, a photovoltaic power source, multiple pumping units equipped with pumping unit frequency converters, energy-consuming resistors, a controllable rectifier, a monitoring device, and a control device, wherein:

[0010] The pumping unit inverter, energy-consuming resistor, and photovoltaic power supply are respectively connected to the DC bus circuit; the DC bus can output power to or input power from the external power grid through a controllable rectifier; the monitoring device is used to acquire the AC voltage of the connected external power grid and the DC bus voltage of the internal power grid in real time; the control device is used to control the frequency of the pumping unit inverter, the switching action of the energy-consuming resistor, and the voltage of the controllable rectifier according to preset rules, the preset rules including:

[0011] Set the response time of the islanded grid shutdown relay protection to be no less than the time required for the downstroke of the pumping unit;

[0012] When the AC voltage is lower than a first preset value, active islanding is executed;

[0013] In islanded mode, when the current DC bus voltage is lower than the second preset value and the pumping unit is detected to switch to the downstroke, the pumping unit inverter is controlled to generate electricity back to the DC bus.

[0014] In isolated network mode, when the pumping unit is in the downstroke and the current internal DC bus voltage is higher than the third preset value, the energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated.

[0015] Preferably, in this invention, the preset rule further includes:

[0016] If the duration for which the DC voltage of the grid is lower than the second preset value exceeds the response time of the islanded grid shutdown relay protection, or if the DC bus voltage is still lower than the second preset value after the downstroke is completed, the islanded grid shutdown relay protection will be activated.

[0017] In another aspect of the present invention, a method for switching control of an oilfield microgrid is also provided, for use in the oilfield microgrid switching control system as described above, comprising the following steps:

[0018] S11. Set the response time of the islanded grid shutdown relay protection to be no less than the time required for the downstroke of the pumping unit;

[0019] S12. When the AC voltage is lower than the first preset value, active islanding is performed;

[0020] S13. In islanded mode, when the current DC bus voltage is lower than the second preset value and the pumping unit is detected to switch to the downstroke, control the pumping unit inverter to generate electricity back to the DC bus.

[0021] S14. In the isolated network state, when the pumping unit is in the downstroke and the current internal network DC bus voltage is higher than the third preset value, the energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated.

[0022] Preferably, in this invention, it further includes:

[0023] S15. When the duration of the DC voltage being lower than the second preset value exceeds the response time of the islanded grid shutdown relay protection, or when the DC bus voltage is still lower than the second preset value after the downstroke is completed, the islanded grid shutdown relay protection action is executed.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The inventive concept of this invention includes: when an external power grid fails, oil production operations are not interrupted; instead, an active islanding grid is implemented to form an independent DC microgrid. Then, when the DC bus voltage falls below the warning value for islanding failure (i.e., the second preset value, located at the voltage value corresponding to the peak position of the photovoltaic power characteristic curve), this invention does not directly initiate islanding shutdown relay protection. Instead, when the pumping unit enters its downstroke phase, the pumping unit inverter is activated to generate electricity back to the DC bus, raising the DC bus voltage until it exceeds the voltage value required for the highest power operating point in the photovoltaic power characteristic curve. This achieves recovery from islanding failure, reducing the probability of active islanding failure and minimizing abnormal shutdowns in oil production operations. Meanwhile, when the DC bus voltage rises too high, the present invention can quickly reduce the voltage by appropriately adding energy-consuming resistors, thereby avoiding the shutdown of equipment such as photovoltaic power supplies and frequency converters due to power fluctuations. Since the present invention can effectively improve the stability of the internal power grid in the islanded state, it can also reduce the interruption of oil production operations caused by power fluctuations, and thus reduce the economic losses such as equipment wear and operational losses caused by the interruption of oil production operations.

[0026] Furthermore, the present invention also includes additional triggering conditions for performing active islanding. The magnitude of the voltage change rate is used to determine whether a fault has occurred in the external power grid, thereby enabling active islanding to be performed as early as possible when the voltage and power quality of the internal power grid are good, thus reducing the probability of active islanding failure.

[0027] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it according to the contents of the specification, and to make the above and other objects, technical features and advantages of the present invention easier to understand, one or more preferred embodiments are listed below and described in detail with reference to the accompanying drawings. Attached Figure Description

[0028] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the oilfield micro power grid switching control system described in this embodiment of the invention;

[0030] Figure 2 This is a schematic diagram of the photovoltaic power supply characteristic curve described in the embodiments of the present invention;

[0031] Figure 3This is a flowchart illustrating the steps of the oilfield microgrid switching control method described in this embodiment of the invention;

[0032] Figure 4 This is another step diagram of the oilfield micro power grid switching control method described in this embodiment of the invention. Detailed Implementation

[0033] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0034] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0035] In this document, the terms "first," "second," etc., are used to distinguish two different elements or parts, and are not used to define specific positions or relative relationships. In other words, in some embodiments, the terms "first," "second," etc., can also be used interchangeably.

[0036] Example 1

[0037] In order to reduce the probability of active grid isolation failure and reduce abnormal downtime in oil production operations, such as Figure 1 As shown, this embodiment of the invention provides a switching control system for an oilfield micro power grid.

[0038] Includes a DC bus 01, a photovoltaic power supply 02, multiple oil pumps 03 equipped with pumping unit frequency converters, a controllable rectifier 04, a power-consuming resistor 05, a monitoring device 06, and a control device 07, wherein:

[0039] The pumping unit inverter 03, energy-consuming resistor 05, and photovoltaic power supply 02 are respectively connected to the DC bus 01 circuit; the DC bus 01 can output power to or input power from the external power grid 08 through the controllable rectifier 04; the monitoring device 06 is used to acquire the AC voltage of the connected external power grid 08 and the DC bus voltage of the internal power grid in real time; the control device 07 is used to control the frequency of the pumping unit inverter 03, the switching action of the energy-consuming resistor 05, and the voltage of the controllable rectifier 04 according to preset rules, the preset rules including:

[0040] Set the response time of the islanded grid shutdown relay protection to be no less than the time required for the downstroke of the pumping unit;

[0041] When the AC voltage is lower than a first preset value, active islanding is executed;

[0042] In islanded mode, when the current DC bus voltage is lower than a second preset value and the pumping unit is detected to be in its downstroke phase, the pumping unit inverter 31 is controlled to generate electricity back to the DC bus; in this embodiment of the invention, the second preset value used for early warning of islanded failure can be set to the photovoltaic power characteristic curve (e.g., ...). Figure 2 The voltage value corresponding to the vertex position (as shown in the figure) is the maximum output point of the photovoltaic power source.

[0043] In the isolated grid state, when the pumping unit is in the downstroke and the current internal grid DC bus voltage is higher than the third preset value (e.g., 620V), the energy-consuming resistor 05 is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor 05 is deactivated.

[0044] The control device in this embodiment of the invention can be a device with data processing capabilities, such as a computer or PLC; it can generate various required control instructions through preset programs and algorithms.

[0045] The inventive concept of this invention includes that when the islanded grid fails, instead of directly performing islanded grid shutdown relay protection, the islanded grid is salvaged by using the electrical energy generated by the reverse generator of the pumping unit 03. In view of this, in this embodiment of the invention, the response time of the islanded grid shutdown relay protection will be appropriately extended to allow time to enter the subsequent islanded grid salvage process.

[0046] In this embodiment of the invention, the timing for islanding failure recovery occurs during the downstroke of the pumping unit. If the DC bus voltage still cannot return to the normal operating level (second preset value) after the pumping unit 03 completes its downstroke, the equipment needs to be protected by the islanding shutdown relay protection. Therefore, in practical applications, the response time of the islanding shutdown relay protection can be set to be equal to or slightly greater than the downstroke time required by the pumping unit, based on the downstroke time setting.

[0047] In this embodiment of the invention, the external power grid 08 is connected to the DC bus 01 of the internal power grid as a power supplier through a controllable rectifier 04. In addition, the photovoltaic power supply 02 is also connected to the DC bus 01 of the internal power grid as another power supplier. In this embodiment of the invention, an energy-dissipating resistor 05 is also provided to reduce the equipment impact caused by power fluctuations by dissipating energy.

[0048] In this embodiment of the invention, the presence or absence of a fault in the external power grid 08 is determined by detecting the AC voltage of the external power grid 08. Specifically, when the AC voltage is lower than a first preset value, the external power grid 08 is considered to have faulted. In this case, the oil extraction operation is not interrupted, but active islanding is implemented to form an independent DC microgrid. The voltage of the internal power grid is stabilized by utilizing the principle that the output power of the photovoltaic power source 02 fluctuates with the DC bus voltage, thereby achieving automatic tracking of the bus voltage value by the photovoltaic output power. Specifically, based on the photovoltaic power source characteristic curve (refer to...), Figure 3 As can be seen, in the monotonically decreasing range on the right side of the photovoltaic power supply characteristic curve, after islanding, the output power of photovoltaic power supply 02 decreases as the DC bus voltage increases and increases as the DC bus voltage decreases. Thus, when pumping unit 03 is working in the downstroke, it is in reverse generation mode, the DC bus voltage increases, the output power of photovoltaic power supply 02 decreases, and the DC bus voltage decreases. When pumping unit 03 is working in the upstroke, it is in power consumption mode, the power consumption is greater than the photovoltaic output power, and the DC bus voltage will decrease. When the DC bus voltage decreases, the output power of photovoltaic power supply 02 increases as the DC bus voltage decreases, that is, the output of photovoltaic power supply 02 increases, which will increase the DC bus voltage again, thus maintaining the DC bus voltage balance (self-balancing).

[0049] It should be noted that, in this embodiment of the invention, the range of the first preset value can be 340V-360V, such as 350V.

[0050] During the oil production operation of pumping unit 03, the current stroke status of pumping unit 03 can be monitored in real time, that is, it can be determined whether pumping unit 03 is currently in the upstroke or downstroke.

[0051] During active islanding or after entering islanding mode, islanding failure may occur due to excessively low voltage on the DC bus 01. Generally, excessively low DC bus voltage often occurs during the upstroke of the pumping unit 03. When the voltage is too low, the pumping unit 03 lacks sufficient power, leading to overload of the pumping unit inverter 31. When the DC bus voltage is too low, the photovoltaic power supply 02 is in the non-operating region, causing system instability. In this embodiment of the invention, the second preset value used for early warning of islanding failure can be set as the voltage value corresponding to the peak position of the photovoltaic power supply characteristic curve, which is the maximum output point of the photovoltaic power supply 02. When the voltage of the DC bus 01 is lower than the second preset value, it will be in the monotonically increasing range on the left side of the photovoltaic power supply characteristic curve, and the increase in the voltage of the DC bus 01 will cause an increase in the output of the photovoltaic power supply 02.

[0052] In existing technologies, islanding failure triggers rapid islanding shutdown relay protection. However, in this embodiment of the invention, the electrical energy generated by the pumping unit 03 under gravity after an islanding failure is cleverly utilized to boost the voltage of the DC bus 01. During an islanding failure, the pumping unit 03 is in its upstroke phase, at which point the pumping unit inverter 31 blocks its output to prevent further load pull on the DC voltage, which could lead to a DC voltage collapse. After the pumping unit 03 transitions from its upstroke to its downstroke phase, it triggers a pulse in the pumping unit inverter 31, which then begins charging the DC bus 01. During an islanding failure, the pumping unit 03 is in its downstroke phase, allowing it to directly begin charging the DC bus 01.

[0053] In islanded mode, to prevent the reverse power generation from rising too quickly and burning out related equipment, in this embodiment of the invention, the power fluctuation of the microgrid can also be reduced by switching the energy-consuming resistor 05. Specifically:

[0054] In the isolated grid state, when the pumping unit is in the downstroke and the current internal grid DC bus voltage is higher than the third preset value, the energy-consuming resistor 05 is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor 05 is deactivated; in practical applications, the third preset value can be set to 620V.

[0055] In this embodiment of the invention, when the pumping unit 03 is in the reverse power generation mode during the downstroke, the DC bus voltage will increase. If the photovoltaic power supply 02 responds too slowly to the decrease in its output power or the decrease is insufficient, the DC bus voltage will exceed the reasonable range, which may easily cause damage to the equipment or affect the normal operation of the pumping operation.

[0056] In the isolated grid state, the controllable rectifier 04, which was originally used to transmit power to the external power grid 08, is in a malfunctioning state, and excess power cannot be transmitted. In view of this, in this embodiment of the invention, an energy-dissipating resistor 05 is set on the DC bus 01. In this way, when the reverse generator causes an impact on the DC bus voltage of the internal power grid, the voltage can be effectively stabilized by putting in the energy-dissipating resistor 05, so as to avoid the DC bus voltage from exceeding the standard.

[0057] It should be noted that, in this embodiment of the invention, the resistance value of the energy-consuming resistor 05 can be matched and set according to the magnitude of the reverse power generation of the pumping unit 03; in addition, it can also be obtained by those skilled in the art based on experience or a limited number of experiments.

[0058] In addition, when the pumping unit switches to the upstroke, the pumping unit 03 will be in an energy-consuming state. In order to make full use of the output of the photovoltaic power source 02, in this embodiment of the invention, the energy-consuming resistor 05 needs to be disconnected in a timely manner.

[0059] In this embodiment of the invention, the output frequency of the oil pump inverter 31 is calculated based on the oil pump rotation speed; specifically, the output frequency of the oil pump inverter 31 is k% of the electric frequency of the oil pump rotation speed, and the value range of k can be: 70 < k < 90; the smaller the value of k, the more reverse power generation, and the larger the value of k, the less reverse power generation.

[0060] When the grid fails, the voltage of DC bus 01 is in the monotonically increasing range to the left of the photovoltaic power supply characteristic curve (i.e., to the left of the peak of the photovoltaic power supply characteristic curve). At this time, the increase in the voltage of DC bus 01 will increase the output of photovoltaic power supply 02. In this embodiment of the invention, the photovoltaic panels and the pumping unit's reverse generator work together to charge the DC bus voltage. When the voltage of DC bus 01 rises to the monotonically decreasing range to the right of the photovoltaic power supply characteristic curve, the microgrid after the grid failure will return to its normal operating voltage range, meaning the grid failure is successfully resolved. After successful grid failure, there is no need for grid shutdown relay protection, and the pumping unit 03 will also return to normal operation.

[0061] Preferably, in this embodiment of the invention, the preset rule may further include:

[0062] If the duration for which the DC voltage of the grid is lower than the second preset value exceeds the response time of the islanded grid shutdown relay protection, or if the DC bus voltage is still lower than the second preset value after the downstroke is completed, the islanded grid shutdown relay protection will be activated.

[0063] If the recovery from the islanding failure is not completed during the downstroke of pumping unit 03, it indicates that the DC bus voltage will drop further. To avoid equipment damage caused by sudden voltage drop, the equipment can be protected by the islanding shutdown relay protection.

[0064] Furthermore, in this embodiment of the invention, the number of energy-consuming resistors 05 can be multiple; specifically, by successively putting on and taking off multiple energy-consuming resistors 05 and simultaneously monitoring the DC bus voltage, the energy consumption value put on can be matched with the fluctuation amplitude of the abnormal voltage fluctuation of the DC bus 01, thereby obtaining a better voltage stability effect.

[0065] Preferably, in this embodiment of the invention, the internal power grid may further include a photovoltaic tracking system (not shown in the figure) capable of adjusting the output of the photovoltaic power source; thus, the voltage can be stabilized by adjusting the output of the photovoltaic power source through the photovoltaic tracking system. Specifically:

[0066] In islanded grid mode, when the pumping unit is in its downstroke phase and the current DC bus voltage of the internal grid is higher than the third preset value (e.g., 620V), all energy-consuming resistors 05 are activated. When the DC voltage stabilizes between the third preset value and the low-power operating point, the photovoltaic tracking system is adjusted until the DC bus voltage stabilizes at the low-power operating point, such as 610V, far from the third preset value, thus increasing the stability margin. When the DC voltage stabilizes below the low-power operating point, the photovoltaic tracking system does not adjust.

[0067] If the DC bus voltage continues to decrease, reaching the high-power operating point (e.g., 570V), then all energy-consuming resistors 05 are removed. This indicates that during the formation of the isolated grid, energy-consuming resistors 05 consumed excessive energy. After all energy-consuming resistors 05 are removed, the DC bus voltage rises to a certain low-power operating point (e.g., 605V), and N-1 energy-consuming resistors 05 are then connected (N being the total number of energy-consuming resistors). When the DC voltage stabilizes below the third preset value but above the low-power operating point, the photovoltaic tracking system is adjusted until the DC bus voltage stabilizes at the low-power operating point (e.g., 610V). When the DC voltage stabilizes below the low-power operating point, the photovoltaic tracking system is not adjusted. If the DC bus voltage continues to decrease, the operation of reducing the number of energy-consuming resistors is repeated until the DC voltage stabilizes below the third preset value but above the low-power operating point. The photovoltaic tracking system is then adjusted to stabilize the DC bus voltage at the low-power operating point (e.g., 610V). When the DC voltage stabilizes below the low-power operating point, the photovoltaic tracking system is not adjusted. During the adjustment of the photovoltaic tracking system, the working angle is always between ±θ to prevent excessive fluctuations in the photovoltaic operating conditions; θ can be 15°.

[0068] Switching the energy-consuming resistors can quickly regulate the voltage, with a relatively large single adjustment range. A photovoltaic tracking system can track the sun's position, improving photovoltaic power generation efficiency. In this embodiment of the invention, a photovoltaic tracking system is used to regulate the output of the photovoltaic power source. Since the control mechanism of the photovoltaic tracking system uses a mechanical transmission device, its adjustment speed is on the same order of magnitude as the stroke of an oil pump. Therefore, the method of regulating voltage by controlling the output of the photovoltaic power source through the photovoltaic tracking system allows for precise adjustment, but the response speed is relatively slow. In this embodiment of the invention, a method is adopted to first adjust the number of energy-consuming resistors for rapid coarse adjustment, and then finely adjust the photovoltaic tracking system to more accurately stabilize the DC bus voltage, thereby improving the voltage stability effect.

[0069] Furthermore, to reduce the probability of islanding failure, this embodiment of the invention may also include additional triggering conditions for active islanding, so that a fault in the external power grid equipment is predicted in advance before the AC voltage of the external power grid drops to the minimum operating point of the AC voltage. Specifically, this includes:

[0070] During the upstroke, the AC voltage is lower than the fourth preset value, and the rate of voltage drop dU / dt is greater than the threshold V. J1 The fourth preset value is higher than the first preset value.

[0071] or,

[0072] During the downstroke, the DC bus voltage is higher than the fifth preset value, and the rate of voltage rise, dU / dt, is greater than the threshold value V. J2 The fifth preset value is higher than the third preset value.

[0073] In existing microgrid systems, the triggering conditions for islanding are stringent, and the timing of islanding execution is relatively delayed, which easily leads to islanding failure. In this embodiment of the invention, the rate of change of grid voltage is calculated to help determine whether equipment failure has occurred in the external grid, thereby effectively reducing the response time for fault judgment. This allows for earlier execution of active islanding, when the internal grid is less affected by external factors, thus reducing the probability of islanding failure.

[0074] In this embodiment of the invention, an AC voltage acceleration criterion is used during the upstroke, including: setting a threshold (i.e., a third preset value) higher than the conventional minimum operating point of AC voltage (i.e., a first preset value) as a voltage reference point; during the upstroke of the pumping unit, when the AC voltage drops to the third preset value, if the absolute value of the voltage change rate dU / dt still increases and the absolute value is greater than the threshold V... J1 When the AC voltage continues to decrease rapidly, it indicates that an equipment failure has occurred in the external power grid, and active grid isolation is initiated. In practical applications, when the first preset value is generally below 350V, the fourth preset value can be in the range of 360V-370V; V J1 The absolute value can be 60V / s.

[0075] Furthermore, in this embodiment of the invention, a DC bus voltage acceleration criterion can be used during the downstroke, including: during the downstroke, the pumping unit generates electricity back to the external power grid. After a failure of the external power grid equipment, the DC power cannot be fed back to the external power grid, and the DC bus voltage will rise. When the DC bus voltage rises to a fourth preset value, if the absolute value of the voltage change rate dU / dt still increases and the absolute value is greater than the threshold V... J2 When the AC voltage continues to decrease rapidly, it indicates that an equipment failure has occurred in the external power grid, and active grid isolation is initiated. In practical applications, when the third preset value is 620V, the fifth preset value can be 625V. J2 The absolute value can be 70V / s.

[0076] As can be seen from the above, the embodiments of the present invention can effectively improve the stability of the internal power grid in the isolated state, thereby reducing the interruption of oil production operations caused by power fluctuations, and thus reducing economic losses such as equipment wear and operational losses caused by the interruption of oil production operations.

[0077] Furthermore, in this embodiment of the invention, additional triggering conditions for active grid isolation are provided. The magnitude of the voltage change rate is used to determine whether a fault has occurred in the external power grid. This allows active grid isolation to be performed as early as possible when the voltage anomaly in the internal power grid is still low, thereby reducing the probability of active grid isolation failure.

[0078] The inventive concept of this invention includes: when an external power grid fails, oil production operations are not interrupted; instead, an active islanding grid is implemented to form an independent DC microgrid. Then, when the DC bus voltage is lower than the warning value for islanding failure (i.e., the second preset value, whose value is the voltage value corresponding to the peak position of the photovoltaic power characteristic curve), this invention does not directly perform islanding shutdown relay protection. Instead, when the pumping unit switches to the downstroke, the pumping unit inverter is turned on to generate electricity back to the DC bus, causing the DC bus voltage to rise until it exceeds the voltage value required for the highest power operating point in the photovoltaic power characteristic curve. This achieves recovery from islanding failure, reducing the probability of active islanding failure and minimizing abnormal shutdowns in oil production operations. Meanwhile, in this embodiment of the invention, when the DC bus voltage rises too high, the voltage is quickly reduced by appropriately activating a power-consuming resistor, thereby avoiding the shutdown of equipment such as photovoltaic power supplies and frequency converters due to power fluctuations. Since this invention can effectively improve the stability of the internal power grid in the islanded state, it can also reduce the interruption of oil production operations caused by power fluctuations, and thus reduce the economic losses such as equipment wear and operational losses caused by the interruption of oil production operations.

[0079] Furthermore, this embodiment of the invention also includes additional triggering conditions for performing active grid isolation. The magnitude of the voltage change rate is used to determine whether a fault has occurred in the external power grid, thereby enabling active grid isolation to be performed as early as possible when the voltage and power quality of the internal power grid are good, thus reducing the probability of active grid isolation failure.

[0080] Example 2

[0081] Corresponding to the above embodiment of the oilfield microgrid switching control system, another aspect of the present invention provides an oilfield microgrid switching control method; the oilfield microgrid switching control method in the present invention is applicable to the oilfield microgrid switching control system in embodiment one;

[0082] like Figure 3 As shown, the oilfield microgrid switching control method in this embodiment of the invention may specifically include the following steps:

[0083] S11. Set the response time of the islanded grid shutdown relay protection to be no less than the time required for the downstroke of the pumping unit;

[0084] The inventive concept of this invention includes that when the islanded grid fails, instead of directly performing islanded grid shutdown relay protection, the islanded grid is salvaged by using the electrical energy generated by the reverse generator of the pumping unit 03. In view of this, in this embodiment of the invention, the response time of the islanded grid shutdown relay protection will be appropriately extended to allow time to enter the subsequent islanded grid salvage process.

[0085] In practical applications, the response time of the islanded grid shutdown relay protection can be set according to the downstroke time of the pumping unit, and the response time of the islanded grid shutdown relay protection can be set to be equal to or slightly greater than the downstroke time required by the pumping unit.

[0086] S12. When the AC voltage is lower than the first preset value, active islanding is performed;

[0087] In this embodiment of the invention, the external power grid 08 is faulty by detecting its AC voltage. Specifically, when the AC voltage is lower than a first preset value, the external power grid 08 is considered to be faulty. In this case, the oil extraction operation is not interrupted, but active islanding is implemented to form an independent DC microgrid. The voltage of the internal power grid is stabilized by using the principle that the output power of the photovoltaic power source 02 fluctuates with the DC bus voltage to achieve automatic tracking of the bus voltage value.

[0088] S13. In islanded mode, when the current DC bus voltage is lower than the second preset value and the pumping unit is detected to switch to the downstroke, control the pumping unit inverter to generate electricity back to the DC bus.

[0089] During active islanding or after entering islanding mode, islanding failure may occur due to excessively low voltage on the DC bus 01. Generally, excessively low DC bus voltage often occurs during the upstroke of the pumping unit 03. When the voltage is too low, the pumping unit 03 lacks sufficient power, leading to overload of the pumping unit inverter 31. When the DC bus voltage is too low, the photovoltaic power supply 02 is in the non-operating region, causing system instability. In this embodiment of the invention, the second preset value used for early warning of islanding failure can be set as the voltage value corresponding to the peak position of the photovoltaic power supply characteristic curve, which is the maximum output point of the photovoltaic power supply 02. When the voltage of the DC bus 01 is lower than the second preset value, it will be in the monotonically increasing range on the left side of the photovoltaic power supply characteristic curve, and the increase in the voltage of the DC bus 01 will cause an increase in the output of the photovoltaic power supply 02.

[0090] S14. In the isolated network state, when the pumping unit is in the downstroke and the current internal network DC bus voltage is higher than the third preset value, the energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated.

[0091] In this embodiment of the invention, when the pumping unit 03 is in the reverse power generation mode during the downstroke, the DC bus voltage will increase. If the photovoltaic power supply 02 responds too slowly to the decrease in its output power or the decrease is insufficient, the DC bus voltage will exceed the reasonable range, which may easily cause damage to the equipment or affect the normal operation of the pumping operation.

[0092] In the isolated grid state, the controllable rectifier 04, which was originally used to transmit power to the external power grid 08, is in a malfunctioning state, and excess power cannot be transmitted. In view of this, in this embodiment of the invention, an energy-dissipating resistor 05 is set on the DC bus 01. In this way, when the reverse generator causes an impact on the DC bus voltage of the internal power grid, the voltage can be effectively stabilized by putting in the energy-dissipating resistor 05, so as to avoid the DC bus voltage from exceeding the standard.

[0093] It should be noted that, since the oilfield microgrid switching control method in this embodiment is the specific usage of the oilfield microgrid switching control system in Embodiment 1, its specific implementation and beneficial effects can be referred to the oilfield microgrid switching control system in Embodiment 1, and will not be repeated here.

[0094] Example 3

[0095] Based on Example 2, such as Figure 4 As shown, the embodiments of the present invention may further include the following steps:

[0096] S15. When the duration of the DC voltage being lower than the second preset value exceeds the response time of the islanded grid shutdown relay protection, or when the DC bus voltage is still lower than the second preset value after the downstroke is completed, the islanded grid shutdown relay protection action is executed.

[0097] If the recovery from the islanding failure is not completed during the downstroke of pumping unit 03, it indicates that the DC bus voltage will drop further. To avoid equipment damage caused by sudden voltage drop, the equipment can be protected by the islanding shutdown relay protection.

[0098] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A switching control system for an oilfield microgrid, characterized in that, This includes a DC bus, photovoltaic power supply, multiple oil pumps equipped with pumping unit frequency converters, energy-consuming resistors, controllable rectifiers, monitoring devices, and control devices, wherein: The pumping unit inverter, energy-consuming resistor, and photovoltaic power supply are respectively connected to the DC bus circuit; the DC bus can output power to or input power from the external power grid through a controllable rectifier; the monitoring device is used to acquire the AC voltage of the connected external power grid and the DC bus voltage of the internal power grid in real time; the control device is used to control the frequency of the pumping unit inverter, the switching action of the energy-consuming resistor, and the voltage of the controllable rectifier according to preset rules, the preset rules including: Set the response time of the islanded grid shutdown relay protection to be no less than the time required for the downstroke of the pumping unit; When the AC voltage is lower than a first preset value, active islanding is executed; In islanded mode, when the current DC bus voltage is lower than the second preset value and the pumping unit is detected to switch to the downstroke, the pumping unit inverter is controlled to generate electricity back to the DC bus. In isolated network mode, when the pumping unit is in the downstroke and the current internal DC bus voltage is higher than the third preset value, the energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated.

2. The oilfield microgrid switching control system according to claim 1, characterized in that, The preset rules also include: If the duration for which the DC voltage of the grid is lower than the second preset value exceeds the response time of the islanded grid shutdown relay protection, or if the DC bus voltage is still lower than the second preset value after the downstroke is completed, the islanded grid shutdown relay protection will be activated.

3. The oilfield microgrid switching control system according to claim 2, characterized in that, The control of the pumping unit inverter to generate electricity from the DC bus includes: The output frequency of the pumping unit inverter is determined according to a preset algorithm, which includes: The inverter output frequency is k% of the pumping unit's rotational speed electrical frequency; where 70 < k < 90.

4. The oilfield microgrid switching control system according to claim 3, characterized in that, The triggering conditions for executing active isolated network also include: During the upstroke, the AC voltage is lower than the fourth preset value, and the rate of voltage drop dU / dt is greater than the threshold V. J1 The fourth preset value is higher than the first preset value. or, During the downstroke, the DC bus voltage is higher than the fifth preset value, and the rate of voltage rise, dU / dt, is greater than the threshold value V. J2 The fifth preset value is higher than the second preset value.

5. The oilfield microgrid switching control system according to claim 4, characterized in that, The energy-consuming resistors include multiple types; Multiple energy-consuming resistors are switched on and off in succession.

6. The power grid control system for an oilfield production system according to claim 5, characterized in that, The range of the first preset value is: 340V-360V, preferably 350V.

7. The power grid control system for an oilfield production system according to claim 6, characterized in that, The range of the second preset value is: The voltage value corresponding to the peak position of the photovoltaic power supply characteristic curve.

8. The power grid control system for an oilfield production system according to claim 7, characterized in that, The third preset value is 620V.

9. The power grid control system for an oilfield production system according to claim 8, characterized in that, The range of the fourth preset value is: 360V-370V.

10. The power grid control system for an oilfield production system according to claim 8, characterized in that, The fifth preset value is 625V.

11. A method for switching control of a microgrid in an oilfield, applicable to the switching control system of a microgrid in an oilfield as described in any of claims 1 to 10, characterized in that, Including the following steps: S11. Set the response time of the islanded grid shutdown relay protection to be no less than the time required for the downstroke of the pumping unit; S12. When the AC voltage is lower than the first preset value, active islanding is performed; S13. In islanded mode, when the current DC bus voltage is lower than the second preset value and the pumping unit is detected to switch to the downstroke, control the pumping unit inverter to generate electricity back to the DC bus. S14. In the isolated network state, when the pumping unit is in the downstroke and the current internal network DC bus voltage is higher than the third preset value, the energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated.

12. The oilfield microgrid switching control method according to claim 11, characterized in that, Also includes: S15. When the duration of the DC voltage being lower than the second preset value exceeds the response time of the islanded grid shutdown relay protection, or when the DC bus voltage is still lower than the second preset value after the downstroke is completed, the islanded grid shutdown relay protection action is executed.

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