Voltage control system and method for an internal grid of a microgrid

Abstract

The application discloses a voltage control system and method for an internal power grid of a micro-grid, wherein the method comprises the following steps: acquiring an alternating voltage of an accessed external power grid in real time; performing active isolated grid operation when the alternating voltage is lower than a first preset value; acquiring a direct-current bus voltage of the internal power grid and a current stroke state of a pumping unit in real time in the isolated grid state; when the pumping unit is in a down stroke and the current internal power grid direct-current bus voltage is higher than a second preset value, a preset energy consumption resistor is connected; the energy consumption resistor is connected with the direct-current bus; and when the pumping unit is switched to an up stroke, the energy consumption resistor is cut off. When the direct-current bus voltage is too high in the isolated grid state, the voltage can be quickly lowered by properly connecting the energy consumption resistor, thereby avoiding the problem that photovoltaic power supply and frequency converters and other devices are caused to exit due to voltage fluctuation. Since the application can effectively improve the stability of the internal power grid in the isolated grid state, the oil production operation caused to be interrupted due to voltage fluctuation can be reduced.

Description

Technical Field

[0001] This invention relates to the field of power systems, and particularly to a voltage control system and method for the internal power grid of a microgrid. 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 microgrids with a high proportion of new energy and a high proportion of power electronic equipment.

[0003] Currently, the power sources in the microgrid of an oilfield production system 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] Both new energy power generation equipment (such as photovoltaic power sources) and electrical equipment (such as frequency converters) in the internal power grid use power electronic components as energy conversion elements. These power electronic components are susceptible to voltage dips (i.e., voltage sags). When voltage waveform distortion occurs due to voltage dips, the phase-locked loop (PLL) cannot function properly, photovoltaic systems may block control signals and shut down. When a voltage dip occurs, the DC bus voltage of the frequency converter decreases, causing the frequency converter to shut down.

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

[0006] When power electronic equipment experiences power fluctuations, the reliability of the equipment operation deteriorates, which can easily lead to problems such as the shutdown of photovoltaic power supplies and frequency converters, and consequently cause oil pumping production to be interrupted.

[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 improve the operational reliability of power electronic equipment during power fluctuations.

[0009] This invention provides a voltage control method for the internal power grid of a microgrid, comprising the following steps:

[0010] S11. Real-time acquisition of the AC voltage of the external power grid and the DC bus voltage of the internal power grid;

[0011] S12. When the AC voltage is lower than the first preset value, active islanding is performed;

[0012] S13. 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 second preset value, the preset energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated; the energy-consuming resistor is connected to the DC bus.

[0013] Preferably, in this invention, the triggering condition for executing active isolated network further includes:

[0014] During the upstroke, the AC voltage is lower than the third preset value, and the rate of voltage drop dU / dt is greater than the threshold V. J1 The third preset value is higher than the first preset value.

[0015] or,

[0016] During the downstroke, the DC bus voltage is higher than the fourth preset value, and the rate of voltage rise, dU / dt, is greater than the threshold voltage V. J2 The fourth preset value is higher than the second preset value.

[0017] Preferably, in this invention, the preset rule further includes:

[0018] When the pumping unit is operating in the upstroke, the operating voltage of the DC bus is adjusted to a preset high-power operating point by the voltage control command, and the output frequency to the pumping unit is increased by the frequency control command to increase the load of the pumping unit.

[0019] Preferably, in this invention, it further includes:

[0020] When the AC voltage is higher than a first preset value, coordinated power supply is executed; the coordinated power supply includes: photovoltaic power and external power grid jointly supplying power to the oil pumping unit through internal power grid;

[0021] In the coordinated power supply mode, when the pumping unit is working in the downstroke, the operating voltage of the DC bus is regulated to the preset low power operating point through the controllable rectifier. In addition, the reverse power generation of the pumping unit is reduced by increasing the output frequency of the pumping unit inverter.

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

[0023] When the pumping unit is operating in the upstroke phase, the working voltage of the DC bus is adjusted to a preset high-power operating point through the pumping unit inverter. Furthermore, the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

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

[0025] This invention is applicable to microgrids in oilfield operations. The inventive concept includes: when an external power grid fails, oil production operations are not interrupted; instead, an active islanded grid is implemented to form an independent DC microgrid. Under normal circumstances, this invention utilizes the principle that the output power of the photovoltaic power source fluctuates with the DC bus voltage to automatically track the bus voltage value, thus stabilizing the voltage of the internal power grid. Furthermore, to prevent excessively high voltage caused by slow response to changes in the output power of the photovoltaic power source, this invention also uses an appropriate energy-dissipating resistor to quickly reduce the voltage when the DC bus voltage rises too high, thereby avoiding the shutdown of equipment such as photovoltaic power sources and frequency converters due to power fluctuations. Since this invention can effectively improve the stability of the islanded grid within the internal power grid, it can reduce oil production operation interruptions caused by power fluctuations, thereby reducing economic losses such as equipment wear and operational losses caused by oil production operation interruptions.

[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] Furthermore, to avoid the load impact on the controllable rectifier caused by the superposition of the pumping unit's reverse power generation and the photovoltaic power output, this invention appropriately reduces the reverse power generation and the photovoltaic power output during the pumping unit's reverse power generation, thereby reducing the capacity requirement of the controllable rectifier. In addition, this invention eliminates the need for a converter for the photovoltaic power under the power grid control system, thus effectively reducing equipment costs.

[0028] Furthermore, the present invention also improves the energy utilization rate of photovoltaic power by increasing the output of photovoltaic power and the load of the pumping unit during the upstroke of the pumping unit.

[0029] Furthermore, by controlling the up and down strokes of the pumping unit differently, this invention can significantly reduce the load fluctuation of the controllable rectifier, thereby effectively reducing the operating losses of the controllable rectifier, extending its service life, and saving maintenance costs.

[0030] 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

[0031] 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.

[0032] Figure 1 This is a step diagram of the voltage control method for the internal power grid of a microgrid as described in an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the voltage control system for the internal power grid of a microgrid as described in an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of the photovoltaic power supply characteristic curve described in an embodiment of the present invention. Detailed Implementation

[0035] 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.

[0036] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprising" shall be understood to include the stated elements or components without excluding other elements or other components.

[0037] 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.

[0038] Example 1

[0039] To improve the stability of the internal power grid in islanded conditions and reduce oil production interruptions caused by power slumps, such as... Figure 1 As shown, this embodiment of the invention provides a voltage control method for the internal power grid of a microgrid, including the following steps:

[0040] S11. Real-time acquisition of the AC voltage of the external power grid and the DC bus voltage of the internal power grid;

[0041] The applicable scenarios for this invention embodiment are microgrids used in oilfield operations, such as... Figure 2As shown, the internal power grid applicable to this embodiment of the invention may include a DC bus 01, a photovoltaic power source 02, multiple pumping units 03 equipped with pumping unit inverters 31, a controllable rectifier 04, a power dissipation resistor 05, a monitoring device 06, and a control device 07; wherein: the power dissipation resistor 05, the pumping unit inverters 31, and the photovoltaic power source 02 are respectively connected to the DC bus circuit 01; 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 generate control commands according to preset rules; the control commands include: switching commands for the power dissipation resistor 05, frequency control commands for the pumping unit inverters 31, and voltage control commands for the controllable rectifier 04;

[0042] In this embodiment of the invention, the external power grid 08 is connected to the DC bus 04 of the internal power grid as a power supplier through a controllable rectifier 04. In addition, the photovoltaic power source 02 is also connected to the DC bus 01 of the internal power grid as another power supplier.

[0043] The monitoring device 06 can acquire the AC voltage of the connected external power grid and the current DC bus voltage in real time.

[0044] S12. When the AC voltage is lower than the first preset value, active islanding is performed;

[0045] In this embodiment of the invention, the external power grid 08 is faulty if its AC voltage is detected. Specifically, if the AC voltage is lower than a first preset value, the external power grid is considered faulty. In this case, oil extraction is not interrupted; instead, active islanding is implemented to form an independent DC microgrid. The internal power grid voltage is stabilized by utilizing the principle that the output power of the photovoltaic power source 02 fluctuates with the DC bus voltage 01. 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 03 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 03 increases as the DC bus voltage decreases, that is, the output of photovoltaic power supply 03 increases, which will cause the DC bus voltage to increase again, thereby maintaining the DC bus voltage balance (self-balancing).

[0046] In practical applications, the first preset value, which is the lowest operating point of AC voltage, is generally below 350V. For example, when the AC voltage of the external power grid 08 is detected to be as low as 350V, the lowest operating point of AC voltage, it is determined that the external power grid equipment has failed and active grid isolation needs to be performed.

[0047] S13. 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 second preset value, the preset energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated; the energy-consuming resistor is connected to the DC bus.

[0048] 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.

[0049] When the pumping unit 03 is in the downstroke and the current DC bus voltage of the internal network is higher than the second preset value, the preset energy-consuming resistor 05 is activated.

[0050] 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.

[0051] 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 quickly stabilized by putting in the energy-dissipating resistor 05, so as to avoid the DC bus voltage from exceeding the standard.

[0052] In practical applications, the energy-consuming resistor 05 in the invention embodiment can be connected to the DC bus through a thyristor SCR switch.

[0053] 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.

[0054] 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.

[0055] Furthermore, in this embodiment of the invention, the number of energy-consuming resistors 05 can be multiple; specifically, by switching multiple energy-consuming resistors on and off, and simultaneously monitoring the DC bus voltage, the value of the resistors on can be matched with the fluctuation amplitude of the abnormal voltage fluctuation of the DC bus 01, thereby obtaining a better voltage stabilization effect.

[0056] 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:

[0057] 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 second preset value (e.g., 620V), all energy-consuming resistors are activated. When the DC voltage stabilizes between the second 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 second preset value, thus increasing the stability margin. When the DC voltage stabilizes below the low-power operating point, the photovoltaic tracking system is not adjusted.

[0058] If the DC bus voltage continues to decrease, reaching the high-power operating point (e.g., 570V), all N energy-consuming resistors will be taken out of operation. This indicates that the energy-consuming resistors were too large during the formation of the isolated grid. After the N energy-consuming resistors are taken out, the DC bus voltage will rise to a certain low-power operating point (e.g., 605V), and N-1 energy-consuming resistors will be put back in. When the DC voltage stabilizes below the second preset value but above the low-power operating point, the photovoltaic tracking system will be 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 will not be adjusted. If the DC bus voltage continues to decrease, the reduction of resistors will be repeated until the DC voltage stabilizes below the second preset value but above the low-power operating point. The photovoltaic tracking system will then be 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 will not be adjusted. During the adjustment of the photovoltaic tracking system, the operating angle remains between ±θ to prevent excessive fluctuations in the photovoltaic operating conditions; θ can be set to 15°.

[0059] 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.

[0060] 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:

[0061] First, during the upstroke, the AC voltage is lower than the third preset value, and the rate of voltage drop dU / dt is greater than the threshold V. J1 The third preset value is higher than the first preset value.

[0062] Secondly, during the downstroke, the DC bus voltage is higher than the fourth preset value, and the rate of voltage rise, dU / dt, is greater than the threshold V. J2 The fourth preset value is higher than the second preset value.

[0063] 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.

[0064] 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 third preset value can be in the range of 360V-370V; VJ1 The absolute value can be 60V / s.

[0065] 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 second preset value is 620V, the fourth preset value can be 625V. J2 The absolute value can be 70V / s.

[0066] 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.

[0067] 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.

[0068] Example 2

[0069] Based on Embodiment 1, further embodiments of the present invention may include the following steps:

[0070] When the AC voltage is higher than a first preset value, coordinated power supply is executed; the coordinated power supply includes: photovoltaic power and external power grid jointly supplying power to the oil pumping unit through internal power grid;

[0071] In the coordinated power supply mode, when the pumping unit is working in the downstroke, the operating voltage of the DC bus is regulated to the preset low power operating point through the controllable rectifier. In addition, the reverse power generation of the pumping unit is reduced by increasing the output frequency of the pumping unit inverter.

[0072] The inventive concept of this invention includes: In a coordinated power supply state, firstly, this invention receives electrical energy from the photovoltaic power source through the DC bus, thus eliminating the need for a photovoltaic power converter; secondly, in this invention, by reducing the reverse power generation of the pumping unit during its downstroke and the output of the photovoltaic power source, the peak current of the DC bus transmitting power to the external power grid is reduced, thus eliminating the need for a large-capacity controllable rectifier and saving equipment costs.

[0073] In a specific example, the specific working process of this embodiment of the invention can be as follows:

[0074] The control device in this embodiment of the invention can be a device with data processing and computing functions. Through preset programs and algorithms, it can generate control commands that can control components such as pumping unit inverters and controllable rectifiers.

[0075] In practical applications, the stroke status of the pumping unit can be obtained through the operating condition monitoring unit, that is, the pumping unit is currently in the upstroke or downstroke through real-time monitoring.

[0076] When the control device detects that the pumping unit is about to enter the downstroke, it generates voltage control commands and frequency control commands corresponding to the downstroke.

[0077] During the downstroke of the pumping unit, reverse power generation occurs. At this time, the internal power grid switches to power output mode. The photovoltaic power and the power generated by the reverse power generation of the pumping unit are rectified by a controllable rectifier and then transmitted to the external power grid. During this time, the load on the controllable rectifier is at its peak. In order to reduce the load on the controllable rectifier when the pumping unit enters the downstroke, in this embodiment of the invention, on the one hand, the operating voltage of the DC bus is adjusted to a preset low-power operating point by the controllable rectifier to reduce the output of the photovoltaic power; on the other hand, the output frequency of the pumping unit to the DC bus is increased by the pumping unit inverter, thereby reducing the reverse power generation of the pumping unit. This effectively reduces the overall load on the controllable rectifier when the pumping unit enters the downstroke.

[0078] It should be noted that, in the embodiments of the present invention, the reduction in photovoltaic power output and the reduction in reverse power generation of the oil pump can be determined by those skilled in the art based on actual operating conditions (e.g., the current capacity of the controllable rectifier and the actual output power of the photovoltaic power source), and no specific limitation is made.

[0079] In practical applications, the voltage value of the low-power operating point in the embodiments of the invention can preferably be in the range of 605-615V.

[0080] In this embodiment of the invention, the operating range of the DC bus operating voltage is located within the photovoltaic power supply characteristic curve (reference). Figure 3The monotonically decreasing interval in the curve indicates that the smaller the DC bus operating voltage, the greater the output of the photovoltaic power supply. The peak of the curve is the position of the extreme value of the photovoltaic power supply output. Then, as the operating voltage increases, the output of the photovoltaic power supply will decrease accordingly. Therefore, the operating voltage value corresponding to the low power operating point can be determined based on the set decrease range of the photovoltaic power supply output.

[0081] Furthermore, in this embodiment of the invention, the efficiency of electrical energy utilization can be improved by performing corresponding control when the pumping unit is operating in the upstroke phase. Specifically:

[0082] When the pumping unit is operating in the upstroke phase, the working voltage of the DC bus is adjusted to a preset high-power operating point through the pumping unit inverter. Furthermore, the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

[0083] Within the monotonically decreasing range, the higher the operating voltage of the DC bus, the lower the output of the photovoltaic power supply. The peak of the curve represents the extreme value of the photovoltaic power supply's output. Subsequently, as the operating voltage increases, the output of the photovoltaic power supply will decrease accordingly. Therefore, the position near the peak of the curve can be determined as the operating voltage value corresponding to the high-power operating point. In practical applications, the voltage range of the high-power operating point in the embodiments of the invention is preferably 560-570V.

[0084] When the pumping unit enters its upstroke phase, it switches to energy-consuming mode. At this time, the combined power from the photovoltaic (PV) power source and the external grid is supplied to the pumping unit via its inverter. To fully utilize the capabilities of the PV power source, in this embodiment, on one hand, a controllable rectifier adjusts the DC bus voltage to a preset high-power operating point to fully utilize the PV power output; on the other hand, the pumping unit inverter increases the output frequency to the pumping unit. This allows for a corresponding increase in the PV power output by increasing the pumping unit's load. Through these controls, the maximum capacity of the PV power source can be fully utilized during the pumping unit's upstroke, thereby improving its efficiency.

[0085] In summary, in this embodiment of the invention, oil production operations are not interrupted during external power grid failures. Instead, an active islanded grid is implemented to form an independent DC microgrid. Under normal circumstances, this embodiment utilizes the principle that the output power of the photovoltaic power source fluctuates with the DC bus voltage to automatically track the bus voltage value, thereby stabilizing the voltage of the internal power grid. Furthermore, to prevent excessively high voltage caused by slow response to changes in the output power of the photovoltaic power source, this embodiment also uses an appropriate energy-dissipating resistor to quickly reduce the voltage when the DC bus voltage rises too high, thus avoiding the shutdown of equipment such as photovoltaic power sources and frequency converters due to power fluctuations. Since this embodiment can effectively improve the stability of the islanded grid within the internal power grid, it can reduce oil production operation interruptions caused by power fluctuations, thereby reducing economic losses such as equipment wear and operational losses caused by oil production operation interruptions.

[0086] Furthermore, to avoid the load impact on the controllable rectifier caused by the superposition of the pumping unit's reverse power generation and the photovoltaic power output, in this embodiment of the invention, the reverse power generation and the photovoltaic power output are appropriately reduced during the pumping unit's reverse power generation, thereby reducing the capacity requirement of the controllable rectifier. In addition, in this embodiment of the invention, there is no need to set up a converter for the photovoltaic power under the power grid control system, so the invention can effectively reduce equipment costs.

[0087] Furthermore, embodiments of the present invention also improve the energy utilization rate of photovoltaic power by increasing the output of photovoltaic power and the load of the pumping unit during the upstroke of the pumping unit.

[0088] Furthermore, by controlling the up and down strokes of the pumping unit differently, the embodiments of the present invention can significantly reduce the load fluctuation of the controllable rectifier, thereby effectively reducing the working loss of the controllable rectifier, extending its service life, and saving maintenance costs.

[0089] Example 3

[0090] Corresponding to the above-described embodiment of the voltage control method for the internal power grid of a microgrid, another aspect of this invention provides a voltage control system for the internal power grid of a microgrid, such as... Figure 2As shown, the system includes a DC bus 01, a photovoltaic power source 02, multiple pumping units 03 equipped with pumping unit inverters 31, a controllable rectifier 04, a power-consuming resistor 05, a monitoring device 06, and a control device 07. The power-consuming resistor 05, the pumping unit inverters 31, and the photovoltaic power source 02 are connected to the DC bus circuit 01. The DC bus 01 can output power to or receive power from the external power grid 08 via 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 generate control commands according to preset rules. The control commands include: switching commands for the power-consuming resistor 05, frequency control commands for the pumping unit inverters 31, and voltage control commands for the controllable rectifier 04.

[0091] In this embodiment of the invention, the external power grid 08 is connected to the DC bus 04 of the internal power grid as a power supplier through a controllable rectifier 04. In addition, the photovoltaic power source 02 is also connected to the DC bus 01 of the internal power grid as another power supplier.

[0092] The monitoring device 06 can acquire the AC voltage of the connected external power grid and the current DC bus voltage in real time.

[0093] The preset rules include: determining whether to perform active islanding or coordinated power supply based on whether the current AC voltage is higher than a first preset value; in the islanding state, when the pumping unit 03 is in the downstroke and the current internal DC bus voltage is higher than a second preset value, the preset energy-consuming resistor 05 is activated; when the pumping unit 03 switches to the upstroke, the energy-consuming resistor 05 is deactivated; the energy-consuming resistor 05 is connected to the DC bus 01.

[0094] 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.

[0095] 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 quickly stabilized by putting in the energy-dissipating resistor 05, so as to avoid the DC bus voltage from exceeding the standard.

[0096] In practical applications, the energy-consuming resistor 05 in the embodiment of the invention can be connected to the DC bus 01 through a thyristor SCR switch.

[0097] It should be noted that, in the embodiments of the present invention, the resistance value of the energy-consuming resistor can be matched and set according to the magnitude of the reverse power generation of the oil pumping unit; in addition, it can also be obtained by those skilled in the art based on experience or a limited number of experiments.

[0098] In addition, when the pumping unit 03 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 supply 02, in this embodiment of the invention, it is necessary to disconnect the energy-consuming resistor 05 in a timely manner.

[0099] Furthermore, in this embodiment of the invention, the number of energy-consuming resistors 05 can be multiple; specifically, by successively putting multiple energy-consuming resistors into the system and simultaneously monitoring the DC bus voltage, the input resistor value can be matched with the fluctuation amplitude of the abnormal voltage fluctuation of the DC bus 01, thereby obtaining a better voltage stability effect.

[0100] 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:

[0101] 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 second preset value (e.g., 620V), all energy-dissipating resistors are engaged. When the DC voltage stabilizes between the second 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 second preset value, thus increasing the stability margin. When the DC bus voltage falls below 620V, the energy-dissipating resistors are gradually deactivated, including when the DC voltage stabilizes below the low-power operating point, in which case the photovoltaic tracking system does not adjust.

[0102] When one energy-consuming resistor is removed, if the DC bus voltage continues to decrease and reaches the high-power operating point (e.g., 570V), then all N energy-consuming resistors should be taken out of operation. This indicates that the energy-consuming resistors were too large during the formation of the isolated grid. After the N energy-consuming resistors are removed, the DC bus voltage rises to a certain low-power operating point (e.g., 625V-605V), and N-1 energy-consuming resistors are then connected. When the DC voltage stabilizes below the second 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 resistors is repeated until the DC voltage stabilizes below the second 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°.

[0103] 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, the method of controlling the output of the photovoltaic power source to regulate the voltage allows for fine adjustment, but the response speed is slow. In this embodiment of the invention, a method of first adjusting the number of energy-consuming resistors for coarse adjustment, and then fine-tuning by adjusting the photovoltaic tracking system, is used to more accurately stabilize the DC bus voltage, thereby improving the voltage stability effect.

[0104] Preferably, in the embodiments of the present invention, under the cooperative power supply state, when the pumping unit is working in the upstroke, the operating voltage of the DC bus is regulated to a preset high power operating point by a controllable rectifier, and the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

[0105] Preferably, in this embodiment of the invention, under coordinated power supply, when the pumping unit is working in the upstroke, the working voltage of the DC bus is regulated to a preset high-power operating point by the pumping unit inverter, and the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

[0106] It should be noted that, since the voltage control method for the internal power grid of the microgrid in the embodiments of the present invention is a specific usage of the voltage control system for the internal power grid of the microgrid in Embodiments 1 and 2, its specific implementation and the beneficial effects can be referred to the voltage control system for the internal power grid of the microgrid in Embodiments 1 and 2, and will not be repeated here.

[0107] The inventive concept of this invention includes: In a coordinated power supply state, firstly, this invention receives electrical energy from the photovoltaic power source through the DC bus, thus eliminating the need for a power converter; secondly, in this invention, by reducing the reverse power generation of the pumping unit during its downstroke and the output of the photovoltaic power source, the peak current of the DC bus transmitting power to the external power grid is reduced, thus eliminating the need for a large-capacity controllable rectifier and saving equipment costs.

[0108] The control device in this embodiment of the invention can be a device with data processing and computing functions. Through preset programs and algorithms, it can generate control commands that can control components such as pumping unit inverters and controllable rectifiers.

[0109] In practical applications, the stroke status of the pumping unit can be obtained through the operating condition monitoring unit, that is, the pumping unit is currently in the upstroke or downstroke through real-time monitoring.

[0110] When the control device detects that the pumping unit is about to enter the downstroke, it generates voltage control commands and frequency control commands corresponding to the downstroke.

[0111] During the downstroke of the pumping unit, reverse power generation occurs. At this time, the internal power grid switches to power output mode. The photovoltaic power and the power generated by the reverse power generation of the pumping unit are rectified by a controllable rectifier and then transmitted to the external power grid. During this time, the load on the controllable rectifier is at its peak. In order to reduce the load on the controllable rectifier when the pumping unit enters the downstroke, in this embodiment of the invention, on the one hand, the operating voltage of the DC bus is adjusted to a preset low-power operating point by the controllable rectifier to reduce the output of the photovoltaic power; on the other hand, the output frequency of the pumping unit to the DC bus is increased by the pumping unit inverter, thereby reducing the reverse power generation of the pumping unit. This effectively reduces the overall load on the controllable rectifier when the pumping unit enters the downstroke.

[0112] It should be noted that, in the embodiments of the present invention, the reduction in photovoltaic power output and the reduction in reverse power generation of the oil pump can be determined by those skilled in the art based on actual operating conditions (e.g., the current capacity of the controllable rectifier and the actual output power of the photovoltaic power source), and no specific limitation is made.

[0113] In this embodiment of the invention, the operating range of the DC bus operating voltage is located within the photovoltaic power supply characteristic curve (reference). Figure 2The monotonically decreasing interval in the curve indicates that the smaller the DC bus operating voltage, the greater the output of the photovoltaic power supply. The peak of the curve is the position of the extreme value of the photovoltaic power supply output. Then, as the operating voltage increases, the output of the photovoltaic power supply will decrease accordingly. Therefore, the operating voltage value corresponding to the low power operating point can be determined based on the set decrease range of the photovoltaic power supply output.

[0114] Furthermore, in this embodiment of the invention, the efficiency of electrical energy utilization can be improved by performing corresponding control when the pumping unit is operating in the upstroke phase. Specifically:

[0115] When the pumping unit is operating in the upstroke phase, the working voltage of the DC bus is adjusted to a preset high-power operating point through the pumping unit inverter. In addition, the output frequency to the pumping unit is increased through the controllable rectifier to increase the load of the pumping unit.

[0116] Within the monotonically decreasing range, the higher the operating voltage of the DC bus, the lower the output of the photovoltaic power supply. The peak of the curve represents the extreme value of the photovoltaic power supply's output. Subsequently, as the operating voltage increases, the output of the photovoltaic power supply will decrease accordingly. Therefore, the position near the peak of the curve can be determined as the operating voltage value corresponding to the high-power operating point. In practical applications, the voltage range of the high-power operating point in the embodiments of the invention is preferably 560-570V.

[0117] When the pumping unit enters its upstroke phase, it switches to energy-consuming mode. At this time, the combined power from the photovoltaic (PV) power source and the external grid is supplied to the pumping unit via its inverter. To fully utilize the capabilities of the PV power source, in this embodiment, on one hand, a controllable rectifier adjusts the DC bus voltage to a preset high-power operating point to fully utilize the PV power output; on the other hand, the pumping unit inverter increases the output frequency to the pumping unit. This allows for a corresponding increase in the PV power output by increasing the pumping unit's load. Through these controls, the maximum capacity of the PV power source can be fully utilized during the pumping unit's upstroke, thereby improving its efficiency.

[0118] 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 voltage control method for the internal power grid of a microgrid, characterized in that, Including the following steps: S11. Real-time acquisition of the AC voltage of the external power grid and the DC bus voltage of the internal power grid; S12. When the AC voltage is lower than the first preset value, active islanding is performed; S13. 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 second preset value, the preset energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated; the energy-consuming resistor is connected to the DC bus.

2. The control method for an internal power grid in an oil field according to claim 1, characterized in that, The triggering conditions for executing active isolated network also include: During the upstroke, the AC voltage is lower than the third preset value, and the rate of voltage drop dU / dt is greater than the threshold V. J1 The third preset value is higher than the first preset value. or, During the downstroke, the DC bus voltage is higher than the fourth preset value, and the rate of voltage rise, dU / dt, is greater than the threshold voltage V. J2 The fourth preset value is higher than the second preset value.

3. The control method for an internal power grid in an oil field according to claim 2, characterized in that, Also includes: S14. When the AC voltage is higher than the first preset value, perform coordinated power supply; The coordinated power supply includes: photovoltaic power and external power grid jointly supplying power to the oil pumping unit through internal power grid; S15. In the coordinated power supply state, when the pumping unit is working in the downstroke, the operating voltage of the DC bus is regulated to the preset low power operating point through the controllable rectifier, and the reverse power generation of the pumping unit is reduced by increasing the output frequency of the pumping unit inverter.

4. The control method for an internal power grid in an oil field according to claim 3, characterized in that, Also includes: S16. During coordinated power supply, when the pumping unit is working in the upstroke, the working voltage of the DC bus is adjusted to the preset high power operating point through the pumping unit inverter, and the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

5. The control method for an internal power grid in an oil field according to claim 4, characterized in that, The energy-consuming resistors include multiple types; The preset energy-consuming resistors include: multiple energy-consuming resistors being continuously switched on and off.

6. The control method for an internal power grid in an oil field according to claim 5, characterized in that, After inserting the preset energy-consuming resistor, it also includes: The DC bus voltage can be controlled by adjusting the output of the photovoltaic power source through a photovoltaic tracking system.

7. The voltage control system for the internal power grid of a microgrid according to claim 6, characterized in that, The positions of the second preset value, the fourth preset value, the high-power operating point, and the low-power operating point are: The monotonically decreasing range of the photovoltaic power source characteristic curve.

8. The voltage control system for the internal power grid of a microgrid according to claim 7, characterized in that, The location of the high-power operating point includes: The position near the peak in the monotonically decreasing range of the photovoltaic power source characteristic curve.

9. The voltage control system for the internal power grid of a microgrid according to claim 8, characterized in that, The location of the low-power operating point is: The position below the high-power operating point in the monotonically decreasing range of the photovoltaic power supply characteristic curve.

10. A voltage control system for the internal power grid of a microgrid, comprising a DC bus, a photovoltaic power source, multiple pumping units equipped with pumping unit frequency converters, a controllable rectifier, a power-consuming resistor, a monitoring device, and a control device, wherein: The energy-consuming resistor, the oil pumping unit inverter, and the photovoltaic power supply are respectively connected to the DC bus circuit; the DC bus can output power to the external power grid or input power from the external power grid through a controllable rectifier; the monitoring device is used to obtain 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 generate control commands according to preset rules; The control commands include: switching commands for the energy-consuming resistor, frequency control commands for the pumping unit inverter, and voltage control commands for the controllable rectifier; The preset rules include: The decision to perform active islanding or coordinated power supply is based on whether the current AC voltage is higher than a first preset value. 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 second preset value, the preset energy-consuming resistor is activated; when the pumping unit switches to the upstroke, the energy-consuming resistor is deactivated; the energy-consuming resistor is connected to the DC bus.

11. The voltage control system for the internal power grid of a microgrid according to claim 10, characterized in that, The preset rules also include: When the pumping unit is operating in the upstroke phase, the operating voltage of the DC bus is adjusted to a preset high-power operating point by a controllable rectifier. Furthermore, the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

12. The control system for an internal power grid in an oil field according to claim 11, characterized in that, The energy-consuming resistor is connected to the DC bus via a thyristor SCR switch.

Images