A DC microgrid system for a group of pumping wells and its coordinated control method

Abstract

The present invention provides a DC microgrid system for a well group of pumping units and a coordinated control method thereof, and belongs to the technical field of DC microgrid systems. The technical scheme is as follows: the high voltage side of the step-down transformer is connected to the three-phase power grid, the low voltage side of the step-down transformer is connected to the AC input end of the AC / DC converter one, the DC output end of the AC / DC converter one is used as a common DC bus, the output end of the photovoltaic panel is connected to the low voltage input end of the unidirectional DC / DC converter, the high voltage output end of the unidirectional DC / DC converter is connected in parallel to the common DC bus, the stator output end of the permanent magnet wind turbine generator set is connected to the AC input end of the AC / DC converter two, the DC output end of the AC / DC converter two is connected in parallel to the common DC bus, and the pumping unit and the DC / AC converter three are respectively connected in parallel to the common DC bus. The beneficial effects of the present invention are: it can effectively reduce the voltage fluctuation of the DC bus and improve the stability of the power supply system.

Description

Technical Field

[0001] The present invention relates to a direct current microgrid system, and in particular to a direct current microgrid system for a pumping well group and a coordinated control method thereof. Background Art

[0002] Most of my country's oil fields are low-permeability, low-energy, and low-yield oil fields, and their electricity consumption is relatively large compared to self-flowing oil wells. The existing network system for powering oil field pumping units mainly relies on the national grid or distributed power generation units or network power supply drawn from the national grid, which has problems with long-distance power transmission consumption and poor stability.

[0003] In recent years, in order to solve the structural contradictions and environmental pollution problems of traditional energy, achieve energy conservation and consumption reduction in oil fields, and achieve green, coordinated and sustainable development, distributed renewable energy represented by wind power and photovoltaic power generation has been widely promoted and applied. However, with the continuous penetration of distributed renewable energy such as wind power and solar power in the power grid, their obvious randomness, intermittency and dispersion have adversely affected the stable operation, safety control and power quality of the power system.

[0004] The DC microgrid system is an electrical network topology that can maximize the acceptance of distributed power sources, improve power supply reliability, and improve the emergency power supply capacity of the power grid. As an autonomous operating system, the DC microgrid can use the flexible control technology of power electronic equipment, such as the improved control method of distributed energy storage equipment and the coordinated control of multiple energy storage power sources, to actively adjust the flow within the system, thereby enhancing the stability of the distribution system and improving the efficiency of the distribution system. Therefore, the application of the DC microgrid system can not only promote the effective consumption of various types of renewable energy in the oil production area, but also improve the reliability of oil well power supply, and realize a DC microgrid power supply system that complements wind and solar power, is efficient and energy-saving, and safe and reliable.

[0005] At present, the stability and power balance of DC microgrid systems are mainly controlled by energy storage batteries and supercapacitors. The investment cost of the installation project is high, and the subsequent maintenance is difficult. At the same time, the control method of the DC microgrid system is mainly a centralized control method. The centralized control method requires the microgrid central controller to send control instructions to the controlled units after complex calculations to achieve the control objectives of the system. This control method requires a complex and costly communication network. Summary of the invention

[0006] The purpose of the present invention is to provide a dynamic power balance control method for a DC microgrid in order to address the shortcomings of the existing topological structure and control method of a DC microgrid system for a pumping well group, as well as the adverse effects of intermittent new energy output characteristics and pumping unit load fluctuation characteristics on the stability of the three-phase power grid, thereby effectively reducing the DC bus voltage fluctuation and improving the stability of the power supply system.

[0007] The present invention is realized by the following measures: a DC microgrid system for a pumping well group, characterized in that it includes a step-down transformer, a photovoltaic power generation unit, a wind power generation unit and a pumping load, wherein the photovoltaic power generation unit includes a photovoltaic panel and a unidirectional DC / DC converter, the wind power generation unit includes a permanent magnet wind power generator set and an AC / DC converter 2, and the pumping load includes a pumping unit and a DC / AC converter 3;

[0008] The high voltage side of the step-down transformer is connected to the three-phase power grid, the low voltage side of the step-down transformer is connected to the AC input end of the AC / DC converter one, the DC output end of the AC / DC converter one serves as a common DC bus, the output end of the photovoltaic panel is connected to the low voltage input end of the unidirectional DC / DC converter, the high voltage output end of the unidirectional DC / DC converter is connected in parallel to the common DC bus, the stator output end of the permanent magnet wind turbine generator set is connected to the AC input end of the AC / DC converter two, the DC output end of the AC / DC converter two is connected in parallel to the common DC bus, and the oil pump and the DC / AC converter three are respectively connected in parallel to the common DC bus;

[0009] It also includes a DC unloading resistor and a DC voltage stabilizing capacitor respectively connected in parallel to the common DC bus, and the DC unloading resistor is controlled by a controllable switch.

[0010] A reactor is connected in series between the step-down transformer and the AC / DC converter.

[0011] The coordinated control method of the DC microgrid system of the pumping well group specifically includes rectification energy consumption mode, inverter derating mode and island droop mode;

[0012] In the rectification energy consumption mode, the AC / DC converter operates in a rectification state to maintain the common DC bus voltage stable, generally at 750V, and controls the photovoltaic power generation unit and the wind turbine power generation unit to operate in a maximum power tracking state;

[0013] In the inverter derating mode, the AC / DC converter operates in an inverter feedback state, and controls the photovoltaic power generation unit and the wind turbine power generation unit to operate at reduced power;

[0014] In the island droop mode, once the AC / DC converter is locked, the photovoltaic power generation unit and the wind turbine power generation unit are controlled to output power according to the droop control coefficient.

[0015] In the inverter derating mode, the power instructions P of the photovoltaic power generation unit and the wind turbine power generation unit are PV , P wind They are set as:

[0016]

[0017] Where: P GSC_RT , P load Respectively represent the rated power of the AC / DC converter 1 and the power of the pumping unit load; k = P PV / P wind , is the power sharing coefficient, and 0≤k≤10.

[0018] In the island droop mode, when the power of the pumping unit load is greater than zero, that is, P load >0, the power instructions P of the photovoltaic power generation unit and the wind turbine power generation unit PV , P wind They are set as:

[0019] P PV =α1P load +ΔP dc1 (1)

[0020] P wind =α2P load +ΔP dc2 (2)

[0021] Where: α1 and α2 are the droop control coefficients of the photovoltaic power generation unit and the wind turbine power generation unit, respectively, and α1=k / (1+k), α2=1 / (1+k); ΔP dc1 , ΔP dc1 They are the compensation power output by the photovoltaic power generation unit and the wind turbine power generation unit participating in the bus voltage regulation, and ΔP dc1 ≥0,ΔP dc2 ≥0;

[0022] When the power of the pumping unit load is less than or equal to zero, that is, P load ≤0, the trigger pulses of the converters of the photovoltaic power generation unit and the wind turbine power generation unit are locked, and the DC unloading resistor absorbs the power fed into the common DC bus by the oil pump load.

[0023] When the secondary voltage of the step-down transformer is normal (generally the effective value of the line voltage is not less than 340V), and the load power of the pumping unit is greater than zero (i.e. P load >0), the DC microgrid system of the pumping well group operates in the rectification energy consumption mode;

[0024] When the secondary voltage of the step-down transformer is normal (generally the effective value of the line voltage is not less than 340V), and the load power of the pumping unit is less than or equal to zero (i.e. P load ≤0), the DC microgrid system of the pumping well group switches to the inverter derating mode;

[0025] When the secondary voltage value of the step-down transformer is abnormal (generally the effective value of the line voltage is lower than 340V), the DC microgrid system of the pumping well group switches to the island droop mode.

[0026] The invention also includes a control method for the AC / DC converter in each mode, specifically: firstly, the line voltage U gabc With phase current I gabc Perform synchronous coordinate transformation to obtain the d-axis and q-axis components U in the synchronous rotating coordinate system gdq ,I gdq ; Then I gdq With current reference value The difference ΔI gdq The proportional integral resonance (PIR) controller is fed into the control vector V in the synchronous rotating coordinate system by adding the feedforward compensation term. gdq ; Control vector V gdq Perform anti-synchronous coordinate transformation to obtain the control vector V in the two-phase stationary coordinate system gαβ , V gαβ The pulse signal of the AC / DC converter 1 can be obtained by sending it to the space vector modulation module. Specifically, the three-phase grid side line voltage U is measured by the existing technology. gabc The phase current I gabc ; The measured three-phase grid line voltage U gabc The phase current I gabc Perform stationary coordinate transformation to obtain the α and β axis components U in the stationary coordinate system gαβ ,I gαβ , the coordinate transformation expression is (the voltage and current expressions are consistent):

[0027]

[0028] Will U gαβ The fundamental grid angular frequency ω and grid angle signal θ are obtained through the phase-locked loop module;

[0029] Will U gabc with I gabc According to the grid angle signal θ, synchronous coordinate transformation is performed to obtain the d-axis and q-axis components U in the synchronous rotating coordinate system. gdq ,I gdq ; The coordinate transformation expression is:

[0030]

[0031] Will I gdq With current reference value The difference ΔI gdqThe proportional integral resonance (PIR) controller is fed into the control vector V in the synchronous rotating coordinate system by adding the feedforward compensation term. gdq ; The calculation formula of the feedforward compensation term is as follows:

[0032]

[0033] Where, the transfer function of the proportional integral resonant (PI R) controller is:

[0034]

[0035] Where: Kp, Ki are the proportional and integral coefficients of the PI controller respectively; Kr0 is the resonance coefficient of the 2-fold resonator; ωc0 is the cutoff frequency of the 2-fold resonator.

[0036] The control vector V gdq Perform anti-synchronous coordinate transformation to obtain the control vector V in the two-phase stationary coordinate system gαβ , V gαβ By sending it to the space vector modulation module, a pulse signal for controlling the grid-side converter can be obtained.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows: there is no need to install energy storage battery units and supercapacitor units in the DC microgrid system of the oil pumping well group, and the DC bus stability and source-load power balance are both adjusted by the control systems of the photovoltaic and wind turbine power generation units, the project investment cost is significantly reduced, and the difficulty of later maintenance is small; the collaborative control method of the DC microgrid system of the oil pumping well group can work normally under the state of oil pumping load reverse power generation or island operation, and can quickly and stably realize the grid-connected and off-grid switching process, so that the oil pumping load is not affected in any way; the switching of the control method is determined by the control system of each unit, and there is no need to set up a central controller and a communication module for real-time communication and unified control, so that the dynamic power balance of the DC microgrid can be achieved, the system operation reliability is high, and the investment cost is effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a topological structure diagram of the present invention.

[0039] Figure 2 It is a control flow chart of the present invention.

[0040] Figure 3 This is a simulation result diagram of the DC microgrid of a pumping well group under grid-connected operation conditions using traditional control methods.

[0041] Figure 4 This is a simulation result diagram of a DC microgrid of a pumping well group under grid-connected operation conditions using the control method of the present invention.

[0042] Figure 5 This is a simulation result diagram of a DC microgrid of a pumping well group adopting the control method of the present invention and switching between on-grid and off-grid operation.

[0043] Figure 6 This is the simulation result diagram of the DC microgrid of the pumping well group working in the island droop mode.

[0044] Figure 7 This is the control block diagram of the grid-side fully-controlled rectifier of the DC microgrid system for a group of pumping wells.

[0045] Among them, the figures are marked as: 1. step-down transformer; 2. AC / DC converter 1; 3. photovoltaic panel; 4. unidirectional DC / DC converter; 5. permanent magnet wind turbine; 6. AC / DC converter 2; 7. DC unloading resistor; 8. DC / AC converter 3; 9. oil pump; 10. reactor; 11. common DC bus; 12. oil pump load. DETAILED DESCRIPTION

[0046] In order to clearly illustrate the technical features of this solution, this solution is described below through a specific implementation method.

[0047] Embodiment 1:

[0048] See also Figure 1 A DC microgrid system for a pumping well group includes a step-down transformer 1, a photovoltaic power generation unit, a wind power generation unit, and a pumping load 12, wherein the photovoltaic power generation unit includes a photovoltaic panel 3 and a unidirectional DC / DC converter 4, the wind power generation unit includes a permanent magnet wind turbine generator set 5 and an AC / DC converter 6, and the pumping load 12 includes a pumping unit 9 and a DC / AC converter 8;

[0049] The high voltage side of the step-down transformer 1 is connected to the three-phase power grid, the low voltage side of the step-down transformer 1 is connected to the AC input end of the AC / DC converter 1 2, the DC output end of the AC / DC converter 1 2 serves as a common DC bus 11, the output end of the photovoltaic panel 3 is connected to the low voltage input end of the unidirectional DC / DC converter 4, the high voltage output end of the unidirectional DC / DC converter 4 is connected in parallel to the common DC bus 11, the stator output end of the permanent magnet wind turbine 5 is connected to the AC input end of the AC / DC converter 2 6, the DC output end of the AC / DC converter 2 6 is connected in parallel to the common DC bus 11, and the oil pump 9 and the DC / AC converter 3 8 are respectively connected in parallel to the common DC bus 11;

[0050] It also includes a DC unloading resistor 7 and a DC voltage stabilizing capacitor respectively connected in parallel to the common DC bus 11, and the DC unloading resistor 7 is controlled by a controllable switch.

[0051] A reactor 10 is connected in series between the step-down transformer 1 and the AC / DC converter 2.

[0052] Embodiment 2:

[0053] See also Figure 1 , Figure 2 and Figure 7 A DC microgrid system for a pumping well group includes a step-down transformer 1, a photovoltaic power generation unit, a wind power generation unit, and a pumping load 12, wherein the photovoltaic power generation unit includes a photovoltaic panel 3 and a unidirectional DC / DC converter 4, the wind power generation unit includes a permanent magnet wind turbine generator set 5 and an AC / DC converter 6, and the pumping load 12 includes a pumping unit 9 and a DC / AC converter 8;

[0054] The high voltage side of the step-down transformer 1 is connected to the three-phase power grid, the low voltage side of the step-down transformer 1 is connected to the AC input end of the AC / DC converter 1 2, the DC output end of the AC / DC converter 1 2 serves as a common DC bus 11, the output end of the photovoltaic panel 3 is connected to the low voltage input end of the unidirectional DC / DC converter 4, the high voltage output end of the unidirectional DC / DC converter 4 is connected in parallel to the common DC bus 11, the stator output end of the permanent magnet wind turbine 5 is connected to the AC input end of the AC / DC converter 2 6, the DC output end of the AC / DC converter 2 6 is connected in parallel to the common DC bus 11, and the oil pump 9 and the DC / AC converter 3 8 are respectively connected in parallel to the common DC bus 11;

[0055] It also includes a DC unloading resistor 7 and a DC voltage stabilizing capacitor respectively connected in parallel to the common DC bus 11, and the DC unloading resistor 7 is controlled by a controllable switch.

[0056] A reactor 10 is connected in series between the step-down transformer 1 and the AC / DC converter 2.

[0057] The coordinated control method of the DC microgrid system of the pumping well group specifically includes rectification energy consumption mode, inverter derating mode and island droop mode;

[0058] In the rectification energy consumption mode, the AC / DC converter operates in a rectification state to maintain the common DC bus voltage stable, generally at 750V, and controls the photovoltaic power generation unit and the wind turbine power generation unit to operate in a maximum power tracking state;

[0059] In the inverter derating mode, the AC / DC converter operates in an inverter feedback state, and controls the photovoltaic power generation unit and the wind turbine power generation unit to operate at reduced power;

[0060] In the island droop mode, once the AC / DC converter is locked, the photovoltaic power generation unit and the wind turbine power generation unit are controlled to output power according to the droop control coefficient.

[0061] In the inverter derating mode, the power instructions P of the photovoltaic power generation unit and the wind turbine power generation unit are PV , P wind They are set as:

[0062]

[0063] Where: P GSC_RT , P load Respectively represent the rated power of the AC / DC converter 1 and the power of the pumping unit load; k = P PV / P wind , is the power sharing coefficient, and 0≤k≤10.

[0064] In the island droop mode, when the power of the pumping unit load is greater than zero, that is, P load >0, the power instructions P of the photovoltaic power generation unit and the wind turbine power generation unit PV , P wind They are set as:

[0065] P PV =α1P load +ΔP dc1 (1)

[0066] P wind =α2P load +ΔP dc2 (2)

[0067] Where: α1 and α2 are the droop control coefficients of the photovoltaic power generation unit and the wind turbine power generation unit, respectively, and α1=k / (1+k), α2=1 / (1+k); ΔP dc1 , ΔP dc1 They are the compensation power output by the photovoltaic power generation unit and the wind turbine power generation unit participating in the bus voltage regulation, and ΔP dc1 ≥0,ΔP dc2 ≥0;

[0068] When the power of the pumping unit load is less than or equal to zero, that is, P load ≤0, the trigger pulses of the converters of the photovoltaic power generation unit and the wind turbine power generation unit are locked, and the DC unloading resistor absorbs the power fed into the common DC bus by the oil pump load.

[0069] When the secondary voltage of the step-down transformer is normal (generally the effective value of the line voltage is not less than 340V), and the load power of the pumping unit is greater than zero (i.e. P load >0), the DC microgrid system of the pumping well group operates in the rectification energy consumption mode;

[0070] When the secondary voltage of the step-down transformer is normal (generally the effective value of the line voltage is not less than 340V), and the load power of the pumping unit is less than or equal to zero (i.e. P load ≤0), the DC microgrid system of the pumping well group switches to the inverter derating mode;

[0071] When the secondary voltage value of the step-down transformer is abnormal (generally the effective value of the line voltage is lower than 340V), the DC microgrid system of the pumping well group switches to the island droop mode.

[0072] The invention also includes a control method for the AC / DC converter in each mode, specifically: firstly, the line voltage U gabc With phase current I gabc Perform synchronous coordinate transformation to obtain the d-axis and q-axis components U in the synchronous rotating coordinate system gdq ,I gdq ; Then I gdq With current reference value The difference ΔI gdq The proportional integral resonance (PIR) controller is fed into the control vector V in the synchronous rotating coordinate system by adding the feedforward compensation term. gdq ; Control vector V gdq Perform anti-synchronous coordinate transformation to obtain the control vector V in the two-phase stationary coordinate system gαβ , V gαβ The pulse signal of the AC / DC converter 1 can be obtained by sending it to the space vector modulation module. Specifically, the three-phase grid side line voltage U is measured by the existing technology. gabc The phase current I gabc ; The measured three-phase grid line voltage U gabc The phase current I gabc Perform stationary coordinate transformation to obtain the α and β axis components U in the stationary coordinate system gαβ ,I gαβ , the coordinate transformation expression is (the voltage and current expressions are consistent):

[0073]

[0074] Will U gαβ The fundamental grid angular frequency ω and grid angle signal θ are obtained through the phase-locked loop module;

[0075] Will U gabc with I gabc According to the grid angle signal θ, synchronous coordinate transformation is performed to obtain the d-axis and q-axis components U in the synchronous rotating coordinate system. gdq ,I gdq ; The coordinate transformation expression is:

[0076]

[0077] Will I gdq With current reference value The difference ΔI gdq The proportional integral resonance (PIR) controller is fed into the control vector V in the synchronous rotating coordinate system by adding the feedforward compensation term. gdq ; The calculation formula of the feedforward compensation term is as follows:

[0078]

[0079] Where, the transfer function of the proportional integral resonant (PI R) controller is:

[0080]

[0081] Where: Kp, Ki are the proportional and integral coefficients of the PI controller respectively; Kr0 is the resonance coefficient of the 2-fold resonator; ωc0 is the cutoff frequency of the 2-fold resonator.

[0082] The control vector V gdq Perform anti-synchronous coordinate transformation to obtain the control vector V in the two-phase stationary coordinate system gαβ , V gαβ By sending it to the space vector modulation module, a pulse signal for controlling the grid-side converter can be obtained.

[0083] Embodiment three:

[0084] See also Figure 1-Figure 7 , among which Figure 3-Figure 6 In the figure, Vabc is the three-phase voltage output by the power grid; Vdc is the DC bus voltage; Ppv is the output power of the photovoltaic power generation unit; Pwind is the output power of the wind power generation unit; Pload and Qload are the active power and reactive power of the oil pump load, respectively.

[0085] A DC microgrid system for a pumping well group includes a step-down transformer 1, a photovoltaic power generation unit, a wind power generation unit, and a pumping load 12, wherein the photovoltaic power generation unit includes a photovoltaic panel 3 and a unidirectional DC / DC converter 4, the wind power generation unit includes a permanent magnet wind turbine generator set 5 and an AC / DC converter 2 6, and the pumping load 12 includes a pumping unit 9 and a DC / AC converter 3 8;

[0086] The high voltage side of the step-down transformer 1 is connected to the three-phase power grid, the low voltage side of the step-down transformer 1 is connected to the AC input end of the AC / DC converter 1 2, the DC output end of the AC / DC converter 1 2 serves as a common DC bus 11, the output end of the photovoltaic panel 3 is connected to the low voltage input end of the unidirectional DC / DC converter 4, the high voltage output end of the unidirectional DC / DC converter 4 is connected in parallel to the common DC bus 11, the stator output end of the permanent magnet wind turbine 5 is connected to the AC input end of the AC / DC converter 2 6, the DC output end of the AC / DC converter 2 6 is connected in parallel to the common DC bus 11, and the oil pump 9 and the DC / AC converter 3 8 are respectively connected in parallel to the common DC bus 11;

[0087] It also includes a DC unloading resistor 7 and a DC voltage stabilizing capacitor respectively connected in parallel to the common DC bus 11, and the DC unloading resistor 7 is controlled by a controllable switch.

[0088] A reactor 10 is connected in series between the step-down transformer 1 and the AC / DC converter 2.

[0089] The coordinated control method of the DC microgrid system of the pumping well group specifically includes rectification energy consumption mode, inverter derating mode and island droop mode;

[0090] In the rectification energy consumption mode, the AC / DC converter operates in a rectification state to maintain the common DC bus voltage stable, generally at 750V, and controls the photovoltaic power generation unit and the wind turbine power generation unit to operate in a maximum power tracking state;

[0091] In the inverter derating mode, the AC / DC converter operates in an inverter feedback state, and controls the photovoltaic power generation unit and the wind turbine power generation unit to operate at reduced power;

[0092] In the island droop mode, once the AC / DC converter is locked, the photovoltaic power generation unit and the wind turbine power generation unit are controlled to output power according to the droop control coefficient.

[0093] In the inverter derating mode, the power instructions P of the photovoltaic power generation unit and the wind turbine power generation unit are PV , P wind They are set as:

[0094]

[0095] Where: P GSC_RT , P load Respectively represent the rated power of the AC / DC converter 1 and the power of the pumping unit load; k = P PV / P wind , is the power sharing coefficient, and 0≤k≤10.

[0096] In the island droop mode, when the power of the pumping unit load is greater than zero, that is, P load >0, the power instructions P of the photovoltaic power generation unit and the wind turbine power generation unit PV , P wind They are set as:

[0097] P PV =α1P load +ΔP dc1 (1)

[0098] P wind =α2P load +ΔP dc2 (2)

[0099] Where: α1 and α2 are the droop control coefficients of the photovoltaic power generation unit and the wind turbine power generation unit, respectively, and α1=k / (1+k), α2=1 / (1+k); ΔP dc1 , ΔP dc1 They are the compensation power output by the photovoltaic power generation unit and the wind turbine power generation unit participating in the bus voltage regulation, and ΔP dc1 ≥0,ΔP dc2 ≥0;

[0100] When the power of the pumping unit load is less than or equal to zero, that is, P load ≤0, the trigger pulses of the converters of the photovoltaic power generation unit and the wind turbine power generation unit are locked, and the DC unloading resistor absorbs the power fed into the common DC bus by the oil pump load.

[0101] When the secondary voltage of the step-down transformer is normal (generally the effective value of the line voltage is not less than 340V), and the load power of the pumping unit is greater than zero (i.e. P load >0), the DC microgrid system of the pumping well group operates in the rectification energy consumption mode;

[0102] When the secondary voltage of the step-down transformer is normal (generally the effective value of the line voltage is not less than 340V), and the load power of the pumping unit is less than or equal to zero (i.e. P load ≤0), the DC microgrid system of the pumping well group switches to the inverter derating mode;

[0103] When the secondary voltage value of the step-down transformer is abnormal (generally the effective value of the line voltage is lower than 340V), the DC microgrid system of the pumping well group switches to the island droop mode.

[0104] The following is a comparison between the traditional control method and the control method in this application:

[0105] like Figure 3The figure shows the simulation results of the DC microgrid of the oil pumping well group under the condition of grid-connected operation using the traditional control method. During the simulation, the oil pump is in the reverse power generation state at 0.3s, and the wind turbine and photovoltaic components continue to transmit power to the DC bus. At this time, the oil pump does not need power from the grid. The power generated by the motor, wind turbine, and photovoltaic are all fed back to the DC bus, causing the DC bus voltage to rise more rapidly. When it reaches 600V, the DC unloading resistor protection action is triggered. When the motor is in the upstroke at 0.6s, the DC bus voltage gradually recovers to 540V. It can be seen that under the traditional control method, since the power fluctuation of the oil pump load is not taken into account, when the oil machine reverses power generation in the downstroke, it is easy to cause the DC bus voltage to soar, endangering the safe operation of the system.

[0106] like Figure 4 The figure shows the simulation results of the DC microgrid of the oil pumping well group under the condition of grid-connected operation when the control method described in the present invention is adopted. At the beginning of the simulation, the power required by the oil pumping load is greater than zero, and the microgrid is in the rectification energy consumption mode. From 1.2s on, the oil pumping gradually enters the reverse power generation state, and the microgrid gradually switches to the inverter derating mode. Figure 3 It can be seen that the control method of the present invention can not only meet the power demand of the load, but also ensure the relative stability of the quality bus voltage (the bus voltage fluctuation during the whole process is less than 30V, and the DC unloading resistor protection action is not triggered).

[0107] like Figure 5 The figure shows the simulation results of the DC microgrid of the pumping well group using the control method of the present invention and switching between on-grid and off-grid operation. As shown in the figure, at 1 second, a short circuit fault occurred in the grid, and the system detected that the secondary voltage value of the transformer was abnormal, that is, the effective value of the line voltage was lower than 340V, and the system automatically switched to the island droop operation mode; 1.4 seconds later, the grid fault was eliminated and the system was put back into operation. The simulation test results show that the proposed control method can realize the automatic switching of the microgrid on-grid and off-grid operation states without causing large electromagnetic transient shocks.

[0108] like Figure 6 The figure shows the simulation results of the DC microgrid of the pumping well group working in the island droop mode. As shown in the figure, in this operation mode, the load power increases sharply at 1.2s. When the load power is greater than the maximum power output of photovoltaic and wind power, the DC bus voltage begins to drop rapidly; when the DC bus voltage drops to 520V, the system automatically cuts off part of the load to maintain the source-load power balance, and the DC bus voltage transitions to a stable state again. The simulation test results show that the control method can effectively improve the stability level of the DC bus voltage and ensure the safe and stable operation of the system.

[0109] Technical features not described in the present invention can be achieved through or by adopting existing technologies and will not be described in detail here. Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by ordinary technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A DC microgrid system for a pumping well group, characterized in that: It includes a step-down transformer, a photovoltaic power generation unit, a wind power generation unit and an oil pumping unit load, wherein the photovoltaic power generation unit includes a photovoltaic panel and a unidirectional DC / DC converter, the wind power generation unit includes a permanent magnet wind power generator set and an AC / DC converter 2, and the oil pumping unit load includes an oil pumping unit load and a DC / AC converter 3; The high voltage side of the step-down transformer is connected to the three-phase power grid, the low voltage side of the step-down transformer is connected to the AC input end of the AC / DC converter one, the DC output end of the AC / DC converter one serves as a common DC bus, the output end of the photovoltaic panel is connected to the low voltage input end of the unidirectional DC / DC converter, the high voltage output end of the unidirectional DC / DC converter is connected in parallel to the common DC bus, the stator output end of the permanent magnet wind turbine generator set is connected to the AC input end of the AC / DC converter two, the DC output end of the AC / DC converter two is connected in parallel to the common DC bus, and the oil pump and the DC / AC converter three are respectively connected in parallel to the common DC bus; A reactor is connected in series between the step-down transformer and the AC / DC converter; It also includes the collaborative control method of the pumping well group DC microgrid system, which specifically includes a rectification energy consumption mode, an inverter derating mode and an island droop mode; In the rectification energy consumption mode, the AC / DC converter operates in a rectification state, maintains the common DC bus voltage stable, and controls the photovoltaic power generation unit and the wind power generation unit to operate in a maximum power tracking state; In the inverter derating mode, the AC / DC converter operates in an inverter feedback state, and controls the photovoltaic power generation unit and the wind power generation unit to operate at reduced power; In the island droop mode, once the AC / DC converter is locked, the photovoltaic power generation unit and the wind power generation unit are controlled to output power according to the droop control coefficient; The invention also includes a control method for the AC / DC converter in each mode, specifically, firstly setting the line voltage of the three-phase power grid to With phase current Perform synchronous coordinate transformation to obtain the d and q axis components in the synchronous rotating coordinate system , ; then With current reference value The difference The proportional integral resonance (PIR) controller is fed into the control system and the feedforward compensation term is added to obtain the control vector in the synchronous rotating coordinate system. ; Control vector Perform anti-synchronous coordinate transformation to obtain the control vector in the two-phase stationary coordinate system ,Will The pulse signal of the AC / DC converter 1 can be obtained by sending it to the space vector modulation module.

2. The DC microgrid system for a pumping well group according to claim 1 is characterized in that: It also includes a DC unloading resistor and a DC voltage stabilizing capacitor respectively connected in parallel to the common DC bus, and the DC unloading resistor is controlled by a controllable switch.

3. The DC microgrid system for a pumping well group according to claim 2 is characterized in that: In the inverter derating mode, the power instructions of the photovoltaic power generation unit and the wind power generation unit , They are set as: (1) (2) Where: , Respectively represent the rated power of the AC / DC converter 1 and the power of the oil pumping unit load; , is the power sharing coefficient, and .

4. The DC microgrid system for a pumping well group according to claim 3 is characterized in that: In the island droop mode, when the power of the pumping unit load is greater than zero, that is, When the power instructions of the photovoltaic power generation unit and the wind power generation unit are , They are set as: (1) (2) Where: , are the droop control coefficients of the photovoltaic power generation unit and the wind power generation unit, respectively, and , ; , are the compensation powers output by the photovoltaic power generation unit and the wind power generation unit participating in the bus voltage regulation, and , ; When the power of the pumping unit load is less than or equal to zero, that is, When the trigger pulses of the converters of the photovoltaic power generation unit and the wind power generation unit are blocked, the power fed into the common DC bus by the pumping unit load is absorbed by the DC unloading resistor.

5. The DC microgrid system for a pumping well group according to claim 4 is characterized in that: When the secondary voltage value of the step-down transformer is normal and the load power of the oil pump is greater than zero, the DC microgrid system of the oil pump well group operates in the rectification energy consumption mode; When the secondary voltage value of the step-down transformer is normal and the load power of the oil pump is less than or equal to zero, the DC microgrid system of the oil pumping well group switches to the inverter derating mode; When the secondary voltage value of the step-down transformer is abnormal, the DC microgrid system of the pumping well group switches to the island droop mode.

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