Multi-device voltage coordination control system and method for microgrid

Abstract

The application discloses a multi-device voltage coordination control system and method for a micro-grid, wherein the system comprises a DC bus, a photovoltaic power supply, a plurality of pumping units provided with frequency converters, a controllable rectifier, and a control device; the frequency converters and the photovoltaic power supply are respectively connected with a DC bus circuit; the DC bus outputs electric energy to an external power grid through the controllable rectifier; the control device is used for generating a control instruction according to a preset rule; the control instruction comprises a frequency control instruction of the frequency converter and a voltage control instruction of the controllable rectifier; the preset rule comprises: when the pumping units work in a downstroke, the working voltage of the DC bus is regulated to a preset low-power working point, and the output frequency of the pumping unit frequency converter is increased to reduce the downstroke power generation of the pumping units. The application appropriately reduces the downstroke power generation and the output of the photovoltaic power supply when the pumping units generate power in a downstroke, reduces the demand for the capacity of the controllable rectifier, and reduces the use of the rectifier, so that the equipment cost can be effectively reduced.

Description

Technical Field

[0001] This invention relates to the field of power systems, and in particular to a multi-device voltage coordination control system and method for 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, microgrids used in oilfield production systems, as a typical new type of power system, can specifically include: while the external power grid is connected to the internal power grid, there is also photovoltaic power connected to the internal power grid through photovoltaic inverters to provide auxiliary power supply.

[0004] In existing technologies, the pumping unit speed is adjusted by controlling the pumping unit inverter according to different operating conditions, thereby improving energy utilization.

[0005] The reverse power generated during the downstroke of the oil pumping unit is returned to the internal power grid. At this time, the internal power grid is in the power transmission state. That is, the reverse power generated during the downstroke of the oil pumping unit and the power generated by the photovoltaic power source are transmitted to the external power grid through the rectifier.

[0006] The inventors discovered through research that existing technologies still have at least the following shortcomings:

[0007] When the internal power grid is in the state of power transmission, the reverse power generated by the pumping unit during the downstroke and the power generated by the photovoltaic power source will be superimposed, which will cause the peak load of the rectifier to be very large. In order to avoid the risk of overload, it is necessary to increase the capacity of the rectifier, which will make the equipment cost too high.

[0008] 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

[0009] The purpose of this invention is to reduce the equipment cost of the internal power grid in a new type of power system for oilfield production systems.

[0010] This invention provides a multi-device voltage coordination control system for microgrids, including a DC bus, a photovoltaic power source, multiple oil pumps equipped with frequency converters, a controllable rectifier, and a control device, wherein:

[0011] The oil pumping unit inverter and photovoltaic power supply are respectively connected to the DC bus circuit; the DC bus outputs power to the external power grid or receives power from the external power grid through a controllable rectifier.

[0012] The control device generates control commands according to preset rules; the control commands include frequency control commands for the pumping unit inverter and voltage control commands for the controllable rectifier; the preset rules include:

[0013] When the pumping unit is operating in the downstroke, the operating voltage of the DC bus is adjusted to a preset low-power operating point by the voltage control command, and the output frequency of the pumping unit inverter is increased by the frequency control command to reduce the reverse power generation of the pumping unit.

[0014] Preferably, in this invention, the preset rule further includes:

[0015] 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 through the voltage control command, and the output frequency of the pumping unit inverter is increased through the frequency control command to increase the load of the pumping unit.

[0016] Preferably, in this invention, it further includes:

[0017] After each preset number of pumping cycles, the pumping unit enters intermittent pumping mode.

[0018] During intermittent pumping mode, the operating voltage of the DC bus is adjusted to a preset high power point, and the pumping unit is shut down by blocking the output of the pumping unit inverter.

[0019] In another aspect of the invention, a multi-device voltage coordination control method for a microgrid is also provided, for use in the multi-device voltage coordination control system for a microgrid as described above, comprising the following steps:

[0020] When the pumping unit is working in the downstroke, the working voltage of the DC bus is regulated to the preset low power operating point through the pumping unit inverter. In addition, the reverse power generation of the pumping unit is reduced by increasing the output frequency of the pumping unit inverter.

[0021] When the pumping unit is operating in the upstroke phase, the operating voltage of the DC bus is regulated to a preset high-power operating point through a controllable rectifier, and the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

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

[0023] Each time the pumping unit completes a preset number of strokes, it enters the intermittent pumping mode. During the intermittent pumping mode, the operating voltage of the DC bus is regulated to the preset high power point through the controllable rectifier, and the output of the pumping unit is blocked through the pumping unit inverter to keep the pumping unit in a shutdown state.

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

[0025] To avoid the load impact on the controllable rectifier caused by the combined output of the pumping unit's reverse power generation and the photovoltaic power, this invention appropriately reduces the reverse power generation and the output of the photovoltaic power during the reverse power generation, thereby reducing the capacity requirement of the controllable rectifier. In addition, this invention eliminates the need for a rectifier for the photovoltaic power under the power grid control system, thus effectively reducing equipment costs.

[0026] 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.

[0027] 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.

[0028] 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

[0029] 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.

[0030] Figure 1 This is a schematic diagram of the structure of the multi-device voltage coordination control system for microgrids described in this embodiment of the invention;

[0031] Figure 2 This is a schematic diagram of the photovoltaic power supply characteristic curve described in an embodiment of the present invention;

[0032] Figure 3 This is a flowchart illustrating the steps of the multi-device voltage coordination control method for microgrids 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] To reduce the equipment cost of the internal power grid in the new power system of oilfield production systems, such as Figure 1 As shown, this embodiment of the invention provides a multi-device voltage coordination control system for a microgrid, including a DC bus 01, a photovoltaic power source 02, multiple oil pumps 03 equipped with oil pump inverters 31, a controllable rectifier 04, and a control device 05, wherein:

[0038] The oil pumping unit inverter 31 and photovoltaic power supply 02 are respectively connected to the DC bus 01 circuit; the DC bus 01 can output power to the external power grid 06 or receive power from the external power grid 06 through the controllable rectifier 04.

[0039] Control device 05 is used to generate control commands according to preset rules; the control commands include frequency control commands for the pumping unit inverter 31 and voltage control commands for the controllable rectifier 04; the preset rules include:

[0040] When the pumping unit is operating in the downstroke, the operating voltage of the DC bus is adjusted to a preset low-power operating point by the voltage control command, and the output frequency of the pumping unit inverter is increased by the frequency control command to reduce the reverse power generation of the pumping unit.

[0041] The inventive concept of this invention includes: First, this invention receives electrical energy from photovoltaic power through a DC bus, thus eliminating the need for a photovoltaic converter; second, this invention reduces the back-generated power and photovoltaic output when the pumping unit is operating in the downstroke phase, thereby reducing the peak current of the DC bus transmitting power to the external grid. This eliminates the need for a large-capacity controllable rectifier, thus saving equipment costs.

[0042] In a specific example, the specific working process of this embodiment of the invention can be as follows:

[0043] The control device 05 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 the pumping unit inverter 31 and the controllable rectifier 04.

[0044] In practical applications, the stroke status of the pumping unit 03 can be obtained through the operating condition monitoring unit (not shown in the figure), that is, the pumping unit 03 can be determined to be in the upstroke or downstroke through real-time monitoring.

[0045] When the pumping unit 03 is detected to be about to enter the downstroke, the control device 05 generates voltage control command and frequency control command corresponding to the downstroke.

[0046] During the downstroke of the pumping unit 03, reverse power generation occurs. At this time, the internal power grid switches to power output mode. The electrical energy generated by the photovoltaic power source 02 and the reverse power generation of the pumping unit 03 is rectified by the controllable rectifier 04 and then transmitted to the external power grid 06. At this time, the load of the controllable rectifier 04 is at its peak. In order to reduce the load of the controllable rectifier 04 when the pumping unit 03 enters the downstroke, in this embodiment of the invention, on the one hand, the operating voltage of the DC bus 01 is adjusted to a preset low power operating point by the controllable rectifier 04 to reduce the output of the photovoltaic power source 02; on the other hand, the output frequency of the pumping unit inverter 31 is increased to reduce the reverse power generation of the pumping unit 03. This effectively reduces the overall load of the controllable rectifier 04 when the pumping unit 03 enters the downstroke.

[0047] 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.

[0048] 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.

[0049] 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 2 The monotonically decreasing interval in the curve (i.e., the monotonically decreasing interval to the right of the maximum power point in the photovoltaic power supply characteristic curve) means 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 output of the photovoltaic power supply. 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 according to the set decrease range of the photovoltaic power supply output.

[0050] 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:

[0051] The preset rules also include: when the pumping unit 03 is working in the upstroke, the voltage control command controls the rectifier 04 to adjust the working voltage of the DC bus 01 to the preset high power working point, and the frequency control command increases the output frequency to the pumping unit inverter 31 to increase the load of the pumping unit 03.

[0052] Within the monotonically decreasing range, the higher the operating voltage of DC bus 01, the lower the output of the photovoltaic power supply. The peak of the curve is the location of the extreme output value of photovoltaic power supply 02. Subsequently, as the operating voltage increases, the output of photovoltaic power supply 02 will decrease accordingly. Therefore, the position near the peak of the curve (i.e., the maximum power point in the photovoltaic power supply characteristic 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 this embodiment of the invention can preferably be 560-570V.

[0053] It should be noted that in the photovoltaic power supply characteristic curve, the high-power operating point should be located to the upper left of the low-power operating point.

[0054] When pumping unit 03 enters its upstroke, it switches to energy-consuming mode. At this time, the combined power from photovoltaic power source 02 and external power grid 06 supplies power to pumping unit 03 via pumping unit inverter 31. To fully utilize the power supply capacity of photovoltaic power source 02, in this embodiment of the invention, on the one hand, the operating voltage of DC bus 01 is adjusted to a preset high-power operating point by controllable rectifier 04 to fully utilize the output of photovoltaic power source 02; on the other hand, the output frequency to pumping unit is increased by pumping unit inverter 31. In this way, the increased output of photovoltaic power source 02 can be matched by increasing the load on pumping unit 03.

[0055] By employing the above-mentioned controls, the maximum function of the photovoltaic power source can be fully utilized during the upstroke of the oil pumping unit to improve the utilization efficiency of the photovoltaic power source.

[0056] In summary, to avoid the load impact on the controllable rectifier caused by the combined output of the pumping unit's reverse power generation and the photovoltaic power generation, this embodiment of the invention appropriately reduces the reverse power generation and the output of the photovoltaic power generation during the reverse power generation of the pumping unit, 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 rectifier for the photovoltaic power generation under the power grid control system. Therefore, this embodiment of the invention can effectively reduce equipment costs.

[0057] 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.

[0058] 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.

[0059] Example 2

[0060] Based on Embodiment 1, further in this embodiment of the invention, the preset rules may include the following:

[0061] After each preset number of pumping units is completed, the pumping unit enters the intermittent pumping mode. During the intermittent pumping mode, the operating voltage of the DC bus is adjusted to the preset high power point, and the output is blocked by the pumping unit inverter to keep the pumping unit in a shutdown state.

[0062] In this embodiment of the invention, the pumping unit is set to operate in a combination of rapid pumping and intermittent pumping mode. This achieves maximum utilization of photovoltaic power while avoiding the drawbacks of insufficient liquid volume and low-load operation of the pumping unit in the rapid pumping mode. At the same time, this embodiment of the invention also maximizes the output of photovoltaic power during the intermittent pumping mode of the pumping unit and transmits the electrical energy to the external power grid so that the photovoltaic energy can be effectively utilized.

[0063] It should be noted that, in the embodiments of the present invention, in the mode of rapid pumping plus intermittent pumping, the preset number of continuous rapid pumping sprints can be set by those skilled in the art according to the actual working conditions of the oilfield.

[0064] Example 3

[0065] Corresponding to the above-described embodiment of a multi-device voltage coordination control system for microgrids, another aspect of this invention provides a method for multi-device voltage coordination control in microgrids, such as... Figure 3 As shown, the steps include:

[0066] S11. When the pumping unit is working in the downstroke, the working voltage of the DC bus is regulated to the preset low power operating point through the pumping unit inverter. In addition, the reverse power generation of the pumping unit is reduced by increasing the output frequency of the pumping unit inverter.

[0067] S12. When the pumping unit is working in the upstroke, the working voltage of the DC bus is regulated 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.

[0068] Preferably, in embodiments of the present invention, it may further include:

[0069] S13. After each preset number of pumping units is completed, the pumping unit enters the intermittent pumping mode. During the intermittent pumping mode, the operating voltage of the DC bus is adjusted to the preset high power point through the controllable rectifier, and the output of the pumping unit is blocked through the pumping unit inverter to keep the pumping unit in a shutdown state.

[0070] It should be noted that, since the multi-device voltage coordination control method for microgrids in the embodiments of the present invention is a specific usage of the multi-device voltage coordination control system for microgrids in Embodiments 1 and 2, its specific implementation and beneficial effects can be referred to the multi-device voltage coordination control system for microgrids in Embodiments 1 and 2, and will not be repeated here.

[0071] 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 multi-device voltage coordination control system for microgrids, characterized in that, This includes a DC bus, photovoltaic power supply, multiple oil pumping units equipped with pumping unit inverters, a controllable rectifier, and a control device, wherein: The oil pumping unit inverter and photovoltaic power supply are respectively connected to the DC bus circuit; the DC bus outputs electrical energy to the external power grid or inputs electrical energy from the external power grid through a controllable rectifier. The control device generates control commands according to preset rules; the control commands include frequency control commands for the pumping unit inverter and voltage control commands for the controllable rectifier; the preset rules include: When the pumping unit is operating in the downstroke, the operating voltage of the DC bus is adjusted to a preset low-power operating point by the voltage control command, and the output frequency of the pumping inverter is increased by the frequency control command to reduce the reverse power generation of the pumping unit.

2. The multi-device voltage coordination control system for microgrids according to claim 1, 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 through the voltage control command, and the output frequency of the pumping unit inverter is increased through the frequency control command to increase the load of the pumping unit.

3. The multi-device voltage coordination control system for microgrids according to claim 2, characterized in that, Also includes: After each preset number of pumping cycles, the pumping unit enters intermittent pumping mode. During intermittent pumping mode, the operating voltage of the DC bus is adjusted to a preset high power point, and the pumping unit is shut down by blocking the output of the pumping unit inverter.

4. The multi-device voltage coordination control system for microgrids according to claim 3, characterized in that, The location of the high-power operating point is: The position near the peak in the monotonically decreasing range of the photovoltaic power source characteristic curve.

5. The multi-device voltage coordination control system for microgrids according to claim 4, characterized in that, The location of the high-power operating point is: The position below the high-power operating point in the monotonically decreasing range of the photovoltaic power supply characteristic curve.

6. The multi-device voltage coordination control system for microgrids according to claim 5, characterized in that, The voltage value of the low-power operating point is in the range of 605-615V.

7. The multi-device voltage coordination control system for microgrids according to claim 6, characterized in that, The voltage value of the high-power operating point is in the range of 560-570V.

8. The multi-device voltage coordination control system for microgrids according to claim 7, characterized in that, It also includes a condition monitoring unit; The operating condition monitoring unit is used to monitor operating condition information, including at least the stroke state; the stroke state includes the backstroke and the backstroke.

9. A multi-device voltage coordination control method for microgrids, applicable to power grid control systems as described in any of claims 1 to 8, characterized in that, Including the following steps: When the pumping unit is working in the downstroke, the operating voltage of the DC bus is regulated to a preset low power operating point through a controllable rectifier. In addition, the reverse power generation of the pumping unit is reduced by increasing the output frequency of the pumping unit inverter. When the pumping unit is operating in the upstroke phase, the operating voltage of the DC bus is regulated to a preset high-power operating point through a controllable rectifier, and the load of the pumping unit is increased by increasing the output frequency of the pumping unit inverter.

10. The multi-device voltage coordination control method for microgrids according to claim 9, characterized in that, Also includes: Each time the pumping unit completes a preset number of strokes, it enters the intermittent pumping mode. During the intermittent pumping mode, the operating voltage of the DC bus is regulated to the preset high power point through the controllable rectifier, and the output of the pumping unit is blocked through the pumping unit inverter to keep the pumping unit in a shutdown state.

11. The multi-device voltage coordination control method for microgrids according to claim 10, characterized in that, The location of the high-power operating point is: The position near the peak in the monotonically decreasing range of the photovoltaic power source characteristic curve.

12. The multi-device voltage coordination control method for microgrids according to claim 11, characterized in that, The location of the high-power operating point is: The position below the high-power operating point in the monotonically decreasing range of the photovoltaic power supply characteristic curve.

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