Load starting impact load variable working condition control method for oil field micro-grid system

Abstract

The invention relates to a load starting impact load variable working condition control method for an oil field micro-grid system, and belongs to the field of oil field micro-grids, the method comprises the following steps: starting an oil pumping unit, and when the rotating speed of the oil pumping unit is in a preset interval and the oil pumping unit operates stably, triggering a static rapid change-over switch STS and a seamless change-over switch to act; the STS switch switches a motor of the oil pumping unit from variable-frequency power supply to power-frequency power supply, in the switching process, electrical parameters of a variable-frequency circuit and a power-frequency circuit are monitored in real time, when it is judged that switching conditions are met, a switching instruction is sent out, and the PLL synchronous control technology is adopted to ensure that current and voltage transition of the motor is smooth at the switching moment. According to the method, power frequency starting can be achieved to stabilize the voltage of the micro-grid, impact on the micro-grid caused by large starting current is effectively restrained, and continuous and reliable power supply of the micro-grid is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of oilfield microgrid technology, and in particular to a method for load start-up impact load variable operating condition control of oilfield microgrid systems. Background Technology

[0002] In the actual operation of oilfield microgrid systems, inductive loads such as motors play a crucial role and are widely used in oilfield pumping units. However, due to their electromagnetic characteristics, inductive loads generate powerful inrush currents at startup that are several times or even more than ten times the normal operating current. For example, the peak starting current of a pumping unit motor in an oilfield can reach 5 to 8 times the rated current when started directly at power frequency.

[0003] For microgrids with relatively limited capacity, such surge loads pose a significant challenge. The power generation equipment, transmission lines, and other electrical devices within the microgrid struggle to withstand such intense current surges in a short period. When the surge current is excessive, it causes a sharp drop in microgrid voltage, exceeding the operating voltage range of the equipment. Once the voltage falls below the undervoltage protection threshold of the equipment, the protection devices in the microgrid will quickly activate, triggering a shutdown command and causing a complete shutdown of the microgrid equipment.

[0004] To address the impact load issue during the startup of inductive loads, current technologies generally employ variable frequency drives (VFDs) for reduced-voltage starting. By lowering the output voltage of the VFD during the startup phase, the starting current of the motor can be effectively reduced, thereby achieving a smooth start-up of the inductive load and mitigating the impact on the microgrid to some extent.

[0005] However, the traditional inverter-based reduced-voltage starting method has significant limitations: relying solely on inverter-based reduced-voltage starting makes it difficult to accurately match the dynamic demands of the motor as its speed increases, resulting in high energy consumption and a relatively long starting time. Therefore, it is urgent to develop a more efficient, intelligent, and adaptable method for controlling the impact load during the starting of inductive loads in microgrids under complex operating conditions. Summary of the Invention

[0006] The purpose of this invention is to at least address one of the aforementioned technical deficiencies.

[0007] Therefore, the purpose of this invention is to propose a load start-up impact load variable operating condition control method for oilfield microgrid systems, which can achieve stable microgrid voltage during power frequency start-up, effectively suppress the impact of large start-up current on the microgrid, and ensure continuous and reliable power supply to the microgrid.

[0008] To achieve the above objectives, embodiments of the present invention provide a load start-up impact load variable operating condition control method for an oilfield microgrid system, comprising:

[0009] S1, start the pumping unit. When the pumping unit's rotation speed is within the preset range and the operation is stable, trigger the static fast switching switch (STS) to seamlessly switch the operation.

[0010] S2, the STS switch switches the pumping unit's motor from variable frequency power supply to mains frequency power supply. During the switching process, the electrical parameters of the variable frequency circuit and the mains frequency circuit are monitored in real time. When the switching conditions are met, a switching command is issued.

[0011] Among them, synchronous control technology based on phase-locked loop (PLL) is adopted to ensure smooth current and voltage transition of the motor during switching. Specifically, during motor switching, the inverter voltage V is detected. FT (t) and power frequency voltage V GT The phase difference between (t) is used to dynamically adjust the output frequency of the frequency converter, so that the output frequency of the frequency converter gradually approaches the power frequency. When the frequency converter voltage V is detected, FT (t) and power frequency voltage V GT When the phase difference and frequency difference of (t) meet the switching conditions, the switching condition is determined to be met, and the switching is initiated.

[0012] Furthermore, in S1, the pumping unit is started by frequency conversion and voltage reduction.

[0013] Furthermore, in S1, the preset interval is an interval extending from the rated speed of the pumping unit to both sides by a preset value.

[0014] Furthermore, in S2, a software phase-locked loop (SPLL) synchronous control technique is used for control, including:

[0015] (1) Input signal modeling

[0016] Variable frequency voltage: V VF (t)=V m sin(ω VF t+θ VF )

[0017] Power frequency voltage: V GF (t)=V m sin(ω GF t+θ GF )

[0018] Where, ω VF For the frequency conversion voltage V FT angular frequency of (t), ω GF The power frequency voltage V GT Angular frequency of (t); θ VF For the frequency conversion voltage V FT The initial phase of (t), θ GF The power frequency voltage VGT The initial phase of (t);

[0019] (2) Calculate the frequency conversion voltage V using a phase detector FT (t) and power frequency voltage V GT Phase error of (t):

[0020] Δθ(t)=θ VF (t)-θ GF (t)

[0021] (3) Loop control equations

[0022] The control equations for the PLL are expressed as follows:

[0023] Among them, K p and K i These are the proportional and integral gains, used to adjust the response speed and stability; when Δθ→0, it indicates that the inverter output is completely synchronized with the power frequency signal, that is, when V VF (t)≈V GF When (t), the STS seamless switching switch can be switched without generating inrush current or voltage surges.

[0024] Furthermore, in step (2), the frequency conversion voltage V is calculated. FT (t) and power frequency voltage V GT After the phase error of (t) is calculated, the phase error signal is extracted through a low-pass filter and used to control the voltage control oscillator (VCO), so that the frequency converter output phase is gradually adjusted to the power frequency phase.

[0025] Furthermore, in S2, the electrical parameters of the frequency conversion circuit and the power frequency circuit include: voltage phase and frequency.

[0026] Furthermore, in S2, the frequency conversion voltage V FT (t) and power frequency voltage V GT The phase difference and frequency difference of (t) satisfy the switching condition as follows: the frequency converter voltage V FT (t) and power frequency voltage V GT The phase difference of (t) is less than the set threshold, and the frequency difference is close to zero.

[0027] Compared with existing technologies, the advantages and beneficial effects of this invention are as follows: The method of this invention successfully overcomes the problem of power frequency start-up in a microgrid environment, making power frequency start-up feasible. In the application of high-yield wells in oilfield microgrids, this solution significantly improves single-well production compared with traditional solutions. This invention overcomes the problem of power frequency start-up impact load of pumping units in oilfield microgrids. Through innovative control methods, it achieves stable microgrid voltage during power frequency start-up, effectively suppresses the impact of large start-up current on the microgrid, ensures continuous and reliable power supply to the microgrid, avoids microgrid power outages and production interruptions caused by voltage drops, significantly improves oilfield production efficiency, and reduces production costs.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0029] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0030] Figure 1 This is a flowchart of a load start-up impact load variable operating condition control method for an oilfield microgrid system according to an embodiment of the present invention. Detailed Implementation

[0031] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0032] like Figure 1 As shown in the figure, the load start-up impact load variable operating condition control method for oilfield microgrid systems according to an embodiment of the present invention includes the following steps:

[0033] S1, start the pumping unit. When the pumping unit speed is within the preset range and the operation is stable, trigger the Static Transfer Switch (STS) to seamlessly switch the operation.

[0034] In this step, the pumping unit is started using a variable frequency drive (VFD) with reduced voltage. The preset range is a range of preset values ​​extending outwards from the rated speed of the pumping unit. This preset value is set according to user needs, and the preset range can be understood as a range of values ​​close to the rated speed.

[0035] That is, the pumping unit is first started by frequency conversion and voltage reduction. After the speed approaches the rated speed and the operation is stable, the STS static fast switching switch is triggered to perform seamless switching.

[0036] S2 and STS switches switch the pumping unit's motor from variable frequency power supply to mains frequency power supply. During the switching process, the electrical parameters of the variable frequency circuit and the mains frequency circuit are monitored in real time. When the switching conditions are met, a switching command is issued.

[0037] In embodiments of the present invention, the electrical parameters of the frequency converter circuit and the power frequency circuit include voltage phase and frequency, etc. It should be noted that the electrical parameters are not limited to the examples above and can be other parameters, set as needed.

[0038] The switching conditions are determined based on the electrical parameters of the frequency converter circuit and the mains frequency circuit. Specifically, the frequency converter voltage V... FT (t) and power frequency voltage V GT The phase difference of (t) is less than the set threshold, and the frequency difference is close to zero.

[0039] In this step, an STS switch is used to switch from variable frequency power supply to mains frequency power supply. The STS seamless transfer switch has fast and precise switching capabilities, and can smoothly switch the motor from the power supply circuit of the variable frequency speed control device to the mains frequency circuit in a very short time (usually in the millisecond range).

[0040] During the switching process, precise synchronous control technology is further adopted to ensure a smooth transition of current and voltage in the motor at the moment of switching, avoiding current surges and voltage fluctuations, thereby ensuring the continuity and stability of the pumping unit operation.

[0041] Specifically, this invention employs synchronization control technology based on a phase-locked loop (PLL). A phase-locked loop is an automatic control system capable of tracking the phase of an input signal and keeping the output signal synchronized with the input signal. It consists of a phase detector (PD), a loop filter (LF), and a voltage-controlled oscillator (VCO), among other components.

[0042] During motor switching, the PLL's role is to detect the inverter voltage V. FT (t) and power frequency voltage V GT The phase difference between (t) is used to dynamically adjust the output frequency of the frequency converter, so that the output frequency of the frequency converter gradually approaches the power frequency. When the frequency converter voltage V is detected, FT (t) and power frequency voltage V GT When the phase difference and frequency difference of (t) meet the switching conditions, the switching is determined to be satisfied, and the switching is initiated. This ensures that the voltage amplitude, frequency, and phase are almost identical at the moment of switching, achieving a smooth transition.

[0043] Control is achieved using PLL synchronous control technology, including:

[0044] (1) Input signal modeling

[0045] Inverter output voltage: V VF (t)=V m sin(ω VF t+θ VF (1)

[0046] Power frequency voltage: V GF (t)=V m sin(ω GF t+θ GF (2)

[0047] Where, ω VF For the frequency conversion voltage V FT angular frequency of (t), ω GF The power frequency voltage V GT Angular frequency of (t); θ VF For the frequency conversion voltage V FT The initial phase of (t), θ GF The power frequency voltage V GT The initial phase of (t);

[0048] (2) Calculate the phase error between the two using a phase detector (PD):

[0049] Δθ(t)=θ VF (t)-θ GF (t) (3)

[0050] The frequency conversion voltage V is calculated. FT (t) and power frequency voltage V GT After the phase error of (t) is calculated, the phase error signal is extracted through a low-pass filter (LF) and used to control the voltage control oscillator (VCO) so that the frequency converter output phase is gradually adjusted to the power frequency phase.

[0051] (3) Loop control equations

[0052] The governing equations of a PLL can be expressed as:

[0053]

[0054] Among them, K p and K i These are the proportional and integral gains, used to adjust the response speed and stability. When Δθ→0, it indicates that the inverter output is completely synchronized with the power frequency signal, i.e., V VF (t)≈V GF (t) At this time, the STS seamless switching switch can be switched without inrush current or voltage surge.

[0055] To achieve precise switching control, the STS seamless transfer switch control system incorporates an advanced synchronous detection algorithm. This algorithm monitors parameters such as voltage phase and frequency of the inverter circuit and the mains frequency circuit in real time. When switching conditions are met, it quickly issues a switching command to ensure a seamless switching process. Simultaneously, a redundant protection mechanism is provided to prevent motor damage or microgrid failure due to switching failure or abnormal conditions.

[0056] To ensure a smooth switching of the motor from variable frequency power to mains frequency power, and to guarantee a smooth voltage and current transition during the switching process to avoid shocks, a synchronization detection algorithm based on a software phase-locked loop (SPLL) is adopted. Its mathematical model is consistent with the mathematical model of the aforementioned PLL synchronization control.

[0057] The principle of software phase-locked loop (SPLL) is that SPLL uses digital signal processing technology to achieve real-time tracking of the frequency and phase of the input signal, ensuring synchronization between the frequency converter and the power supply.

[0058] The core components of SPLL include:

[0059] (1) The phase detector (PD) compares the phase difference between the input signal and the local oscillator signal to generate an error signal.

[0060] (2) Loop Filter (LF): Filters the error signal, extracts effective phase difference information, and removes high-frequency noise.

[0061] (3) Numerically Controlled Oscillator (NCO): Adjusts the frequency and phase of the output signal according to the filtered error signal, so that it gradually synchronizes with the input signal.

[0062] In practical applications, SPLL is used to monitor the phase and frequency differences between the variable frequency power supply and the mains frequency power supply in real time, and dynamically adjust the output of the variable frequency power supply to synchronize it with the mains frequency power supply. When the phase and frequency differences between the two are detected to meet preset switching conditions (e.g., variable frequency voltage V...), the SPLL will automatically adjust the output. FT (t) and power frequency voltage V GT When the phase difference (t) is less than the set threshold and the frequency difference is close to zero, the control system triggers the Seamless Switching Switch (STS) to achieve a smooth switchover of the motor from the variable frequency power supply to the mains frequency power supply, avoiding current and voltage surges and ensuring the continuous and stable operation of the pumping unit. By adopting the SPLL synchronous detection algorithm, the accuracy and reliability of the switching process can be effectively improved, meeting the requirements for smooth start-up and operation of inductive loads in a microgrid environment.

[0063] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0064] It will be readily understood by those skilled in the art that this invention includes any combination of the inventive description and specific embodiments outlined in the foregoing specification, as well as the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0065] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling load start-up impact load under varying operating conditions in an oilfield microgrid system, characterized in that, include: S1, start the pumping unit. When the pumping unit's rotation speed is within the preset range and the operation is stable, trigger the static fast switching switch (STS) to seamlessly switch the operation. S2, the STS switch switches the pumping unit's motor from variable frequency power supply to mains frequency power supply. During the switching process, the electrical parameters of the variable frequency circuit and the mains frequency circuit are monitored in real time. When the switching conditions are met, a switching command is issued. Among these measures, a phase-locked loop (PLL) based synchronous control technology is employed to ensure a smooth transition of current and voltage during motor switching. Specifically, during motor switching, the inverter voltage V is detected. FT (t) and power frequency voltage V GT The phase difference between (t) is used to dynamically adjust the output frequency of the frequency converter, so that the output frequency of the frequency converter gradually approaches the power frequency. When the frequency converter voltage V is detected, FT (t) and power frequency voltage V GT When the phase difference and frequency difference of (t) meet the switching conditions, the switching condition is determined to be met, and the switching is initiated.

2. The load start-up impact load variable operating condition control method for oilfield microgrid systems according to claim 1, characterized in that, In S1, the pumping unit is started by frequency conversion and voltage reduction.

3. The load start-up impact load variable operating condition control method for oilfield microgrid systems according to claim 1, characterized in that, In S1, the preset interval is an interval extending from the rated speed of the pumping unit to both sides by a preset value.

4. The load start-up impact load variable operating condition control method for oilfield microgrid systems according to claim 1, characterized in that, In S2, a synchronization control technique based on a phase-locked loop (PLL) is used for control, including: (1) Input signal modeling Variable frequency voltage: V VF (t)=V m sin(ω VF t+θ VF ) Power frequency voltage: V GF (t)=V m sin(ω GF t+θ GF ) Where, ω VF For the frequency conversion voltage V FT angular frequency of (t), ω GF The power frequency voltage V GT Angular frequency of (t); θ VF For the frequency conversion voltage V FT The initial phase of (t), θ GF The power frequency voltage V GT The initial phase of (t); (2) Calculate the frequency conversion voltage V using a phase detector FT (t) and power frequency voltage V GT Phase error of (t): Δθ(t)=θ VF (t)-θ GF (t) (3) Loop control equations The control equations for the PLL are expressed as follows: Among them, K p and K i These are the proportional and integral gains, used to adjust the response speed and stability; when Δθ→0, it indicates that the inverter output is completely synchronized with the power frequency signal, that is, when V VF (t)≈V GF When (t), the STS seamless switching switch can be switched without generating inrush current or voltage surges.

5. The load start-up impact load variable operating condition control method for oilfield microgrid systems according to claim 4, characterized in that, In (2), the frequency conversion voltage V is calculated. FT (t) and power frequency voltage V GT After the phase error of (t) is calculated, the phase error signal is extracted through a low-pass filter and used to control the voltage control oscillator (VCO), so that the frequency converter output phase is gradually adjusted to the power frequency phase.

6. The load start-up impact load variable operating condition control method for oilfield microgrid systems according to claim 1, characterized in that, In S2, the electrical parameters of the frequency converter circuit and the power frequency circuit include: voltage phase and frequency.

7. The load start-up impact load variable operating condition control method for oilfield microgrid systems according to claim 1, characterized in that, In S2, the frequency conversion voltage V FT (t) and power frequency voltage V GT The phase difference and frequency difference of (t) satisfy the switching condition as follows: the frequency converter voltage V FT (t) and power frequency voltage V GT The phase difference of (t) is less than the set threshold, and the frequency difference is close to zero.

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