CN117978015A - Low-frequency operation model prediction control method for flying capacitor modularized multi-level frequency converter - Google Patents
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Abstract
A predictive control method for a low-frequency operation model of a flying capacitor modularized multi-level frequency converter belongs to the field of electric transmission and mainly aims at inhibiting capacitance voltage and common-mode voltage of a sub-module when an oil drilling motor runs at low frequency. The method takes a permanent magnet synchronous motor as a driving object, performs model prediction control on FC-MMC through layering, establishes dq axis output current and common mode voltage prediction models in a first layer, rolls in real time to calculate the number of sub-modules to be input, and realizes motor output current and common mode voltage suppression; and a second layer establishes an SM capacitance voltage difference prediction model and a phase SM capacitance voltage prediction model between bridge arms, selects the number of sub-modules which are finally ordered according to the degrees of freedom of the bridge arms input sub-modules, realizes the suppression of the capacitance voltage fluctuation of the sub-modules, and finally realizes the operation guarantee of the permanent magnet synchronous motor under different working conditions. The method has simple structure and good output performance. The safe and stable operation of the petroleum drilling motor can be ensured.
Description
Technical Field
The invention relates to the field of variable frequency driving such as electric transmission and oil exploitation, in particular to a low-frequency operation model predictive control technology of a flying capacitor modularized multi-level frequency converter.
Background
Along with the acceleration of industrialization progress and the remarkable improvement of the living standard of people, the electric energy quality gradually becomes a focus problem of social attention, and the demand of people for electric energy is also increased, in particular to high-quality electric energy. At present, china is in an important stage of industrialization acceleration, energy demand is in an ascending trend, environmental pollution and resource shortage are a non-negligible ring in the industrial process, and improvement of the energy utilization rate of energy consumption equipment is an important link in energy revolution.
From the aspect of energy consumption ratio, the motor is used as important equipment in the industrial production link, consumes most of energy and accounts for about 70 percent. In recent years, with the continuous innovation of power electronics technology, motor speed regulation technology is rapidly developed, and variable frequency speed regulation is also applied to the field of motor control, so that great contribution is made to reducing energy consumption and improving environment.
The main device for petroleum resource development is petroleum drilling machine, which is composed of several systems of control system, working system, transmission system, power system and auxiliary system, etc. and its matched equipment. The power system provides power for the operation of the petroleum drilling machine, and the power driving equipment is mechanically driven in many cases. Because the electric power electronic technology enters, an electric drive drilling machine appears in the aspect of a petroleum drilling machine driving mode, the electric drive drilling machine greatly improves the transmission efficiency, can adapt to different load environments, is convenient to assemble and transfer during application, has a better machine tool protection function when accidents occur, is beneficial to realizing the control on the aspects of position, speed, torque and other performances, can better adapt to the development of the drilling machine to a high-automation control direction, and has incomparable performance advantages of the traditional mechanical drive drilling machine. The power driving equipment is an extremely important ring in the petroleum drilling machine set, provides power for the operation of the petroleum drilling machine, and serves three working machine sets of a winch, a turntable and a drilling pump.
The rotary table is the key device of the rotary drill and functions to power and rotate the drill bit through Fang Wachuan. Therefore, the turntable is always in a good working state, so that a condition necessary for high-quality drilling is realized. However, in the actual drilling process, as the drilling depth and the nature of the rock layer broken change, the load born by the rotary table also changes continuously. The winch mainly has the function of providing different lifting speeds and lifting weights for tripping operation so as to meet the requirements of tripping drilling tools and casing pipes, and can be used as a speed changing and transmission mechanism of another unit turntable, etc. in the actual drilling process, the load of the winch can be greatly changed due to different working condition requirements. The drill pump is called the "heart" of the rig. During the operation of the drilling machine, the drilling pump is used for circulating mud and cooling the bottom of the well, forming mud cakes on the well wall and carrying rock fragments.
For permanent magnet synchronous motors (PERMANENT MAGNET Synchronous Motor, PMSM) as oil drilling drives, the drilling process has the following requirements for the motor: first, the rotational speeds of the turntable and the winch drive motor are required to reach and stabilize at the desired rotational speed within a prescribed time, and the rotational speed can be maintained unchanged when load disturbances occur. Secondly, the rotation speed of the drilling pump driving motor needs to reach pumping according to the set time, the drilling pump driving motor can be stabilized on the expected pumping, and when the pressure of a slurry pipeline changes, the pumping is kept unchanged.
When the traditional modularized multi-level conversion (Modular Multilevel Converter, MMC) drives a motor to run at low frequency in petroleum drilling, in order to restrain the fluctuation of capacitance voltage and common mode voltage of a submodule, mathematical expressions of power difference of an upper bridge arm and a lower bridge arm are firstly analyzed, a high-frequency injection method based on modulation is provided, injection waveforms comprise sine waves, third harmonics, square waves and the like, but the injection waveforms are overmodulated, the problems of circulation of a bridge arm of an MMC type converter and increase of bridge arm current are caused, the problems are applied to a motor winding, the insulation damage of the winding is possibly caused, faults such as short circuit or grounding are extremely easy to cause, and the motor bearing is blocked, broken and the like. Therefore, the research model predictive control has important significance for realizing the safe and stable operation of the permanent magnet synchronous motor in the petroleum drilling power driving system.
Disclosure of Invention
The invention aims to replace all required control targets by cost functions, and solve the problems of parameter design of cascade connection of a plurality of PI controllers and optimal injection of high-frequency injection control. And finally, the safe and stable operation of the permanent magnet synchronous motor under the low-frequency operation condition is ensured.
The invention relates to a prediction control method for a low-frequency operation model of a flying capacitor modularized multi-level frequency converter, which establishes a system model of a flying capacitor modularized multi-level driving permanent magnet synchronous motor and comprises the following steps:
Under the condition that the influence of factors such as magnetic field saturation effect is ignored, the stator voltage equation of the surface-mounted three-phase permanent magnet synchronous motor under the two-phase rotation dq coordinate system by adopting the surface-mounted three-phase permanent magnet synchronous motor can be expressed as:
In formula (1), u d、uq is the stator phase voltage dq axis component; l d、Lq is dq axis inductance respectively; i d、iq is the stator phase current dq axis component; r s is the stator resistance; omega e is the electrical angular velocity; phi f is the permanent magnet flux linkage;
step (2): when the line impedance is ignored, according to kirchhoff voltage law KVL, a loop equation of upper and lower bridge arms and an alternating current side of the FC-MMC frequency converter can be written as follows:
In the formula (2), U dc is the direct-current side bus voltage; l is half bridge arm inductance; i j,p1、ij,p2、ij,n1、ij,n2 is the current of the upper half bridge arm and the lower half bridge arm of the j phases respectively; u j,p1、uj,p2、uj,n1、uj,n2 is the capacitance voltage of the sub-module of the upper half bridge arm and the lower half bridge arm of the j phases respectively; u j is the ac side output stator voltage, where j=a, b, c;
Step (3): and (3) respectively summing and differencing the two formulas in the step (2) to obtain a mathematical expression of the dynamic characteristics of the alternating current-direct current side of the FC-MMC frequency converter:
in the formula (3), i j is an ac side output stator current, where j=a, b, c;
Step (4): combining the step (3) and the transformation matrix of the three-phase static abc coordinate system to the two-phase rotation dq coordinate system to obtain the mathematical model of the FC-MMC frequency converter under the dq coordinate system, wherein the mathematical model comprises the following steps:
in the formula (4), C abc/dq is a transformation matrix for converting a three-phase static abc coordinate system into a two-phase rotation dq coordinate system; l is half bridge arm inductance; u j,v1、uj,v2 is the voltages of four sub-arms of abc three-phase, respectively, wherein v=n, p, p represents the upper arm, n represents the lower arm, j=a, b, c;
step (5): bringing the formula (4) into a stator voltage equation of the permanent magnet synchronous motor to obtain a dq axis current state equation of the FC-MMC driven permanent magnet synchronous motor:
Wherein (5), L eq represents an equivalent inductance, and the value is L eq＝Ld+L＝Lq +L;
The invention has the following beneficial effects:
The invention provides a new method for inhibiting capacitor voltage fluctuation of an FC-MMC submodule and reducing common-mode voltage output at low frequency, which comprises the steps of performing model prediction control on flying-span type modularization multi-level by using layering through adopting an FC-MMC converter topological structure, firstly deducing to obtain a dq-axis current output prediction model based on a driving permanent magnet synchronous motor of the FC-MMC converter, and adding an additional common-mode voltage prediction model to replace the traditional high-frequency injection method; and the low-frequency pulsation of the capacitor voltage of the submodule is restrained by combining an inter-bridge arm SM capacitor voltage difference prediction model, a phase SM capacitor voltage and a prediction model, the output of a common-mode voltage is reduced to a certain extent, and the long-term stable operation of the permanent magnet synchronous motor is ensured.
Drawings
FIG. 1 is a topology diagram of an FC-MMC frequency converter driven permanent magnet synchronous motor according to one embodiment of the invention;
FIG. 2 is a flow chart of model predictive control of a FC-MMC frequency converter driven permanent magnet synchronous motor according to one embodiment of the invention;
FIG. 3 is a block diagram of a low frequency control system of an FC-MMC type frequency converter according to one embodiment of the invention;
Detailed Description
The invention provides a fly capacitor modularized multi-level frequency converter (FC-MMC) driving permanent magnet synchronous motor which is used for inhibiting fluctuation of an alternating current side output common-mode voltage and submodule capacitor voltage under a low-frequency operation condition. The low-frequency operation of the motor is realized by adopting layering to carry out model predictive control (Model Predictive Control, MPC) on the FC-MMC. Firstly, a first layer realizes stator current output and common-mode voltage suppression of a permanent magnet synchronous motor, and the number of submodules required to be input for each half bridge arm is determined; secondly, the second layer realizes the suppression of the voltage ripple of the submodule capacitor, and the optimal free number of the submodules is circularly selected to determine the final number of the capacitor voltage sequences of the submodules. The hierarchical control strategy has simple weight coefficient design, the required control targets are replaced by cost functions, and the problem of parameter design of cascade connection of a plurality of PI controllers and the problem of optimal injection of high-frequency injection control are eliminated. And finally, the safe and stable operation of the permanent magnet synchronous motor under the low-frequency operation condition is ensured.
The following description of the embodiments of the invention will be given with reference to the accompanying drawings and examples:
as shown in fig. 1, the topology structure of the permanent magnet synchronous motor is driven by adopting an FC-MMC frequency converter. Similar to the traditional MMC, the three-phase bridge arms are included, but a capacitor C F is arranged between the middle point of the upper bridge arm and the middle point of the lower bridge arm of the traditional MMC in a flying mode, the upper bridge arm and the lower bridge arm are further divided into four half bridge arms, each half bridge arm is composed of a plurality of submodules SM and a current-limiting inductor L, and the total inductance of the upper half bridge arm and the lower half bridge arm is kept the same as the total inductance of the upper bridge arm and the lower bridge arm in the traditional MMC. The two switching devices VT 1 and VT 2 in the single SM unit shown in fig. 1 have complementary modes of operation. When switch VT 1 is on, the submodule produces voltage U c. Conversely, if the switch VT 2 is on, the SM produces zero voltage. Wherein: u dc direct current side FC-MMC voltage; i dc is direct-current side output current; i a,p1、ia,p2、ia,n1、ia,n2 is the current of the upper half bridge arm and the lower half bridge arm of the a phase respectively; i a,F is a phase a flying capacitor current; p represents an upper bridge arm, and n represents a lower bridge arm; i j is an ac side output phase current (j=a, b, c).
As shown in fig. 2, the model prediction control flow in the present invention is:
Firstly, a predictive model containing dq axis output current and common mode voltage of a first layer is established, and the number of submodules required to be put into is calculated through real-time rolling; and secondly, establishing a second layer containing an inter-bridge-arm SM capacitance voltage difference prediction model, a phase SM capacitance voltage and a prediction model, and selecting the number of the sub-modules which are finally ordered through the degrees of freedom of the sub-modules input by the bridge arms, wherein the specific flow is shown in figure 2.
As shown in fig. 3, the specific implementation steps are as follows:
the method for predicting and controlling the low-frequency model of the permanent magnet synchronous motor driven by the FC-MMC frequency converter comprises the following steps of:
Step 1: establishing a system model of the flying capacitor type modularized multi-level driving permanent magnet synchronous motor;
Step 2: discretizing a dq axis current state equation of the FC-MMC driving permanent magnet synchronous motor by using an Euler equation to obtain a dq axis current prediction model of the flying capacitor type modularized multi-level frequency converter driving permanent magnet synchronous motor at the time k+1:
In the formula (1), T s represents sampling time, and theta e is the electrical angle of the rotor permanent magnet; for the moment k+1, abc three-phase four sub-arm voltages, where v=n, p, j=a, b, c;
step 3: in order to keep the voltage balance of the submodules under the low-frequency working condition, the voltage difference of the submodules of the upper bridge arm and the lower bridge arm needs to be controlled:
In the formula (2), u ci,v1j,uci,v2j represents the capacitance voltage of each sub-module of four sub-bridge arms of the abc three-phase; s v1j,Sv2j represents the state of a switch tube of each sub-module of four sub-bridge arms of the abc three-phase; i j,v1,ij,v2 represents abc three-phase four-sub-arm current; n represents the number of sub-module power units; c represents the capacitance of the submodule; wherein v=n, p, j=a, b, c;
Step 4: in order to increase the balance of the capacitance voltage of the sub-module, the balance of the interphase capacitance voltage of the sub-bridge arm needs to be further ensured, so that the sum of the capacitance voltages of the sub-bridge arm SM is controlled:
Step 5: if only the model prediction of the sum of the SM voltage difference and the phase SM voltage between the sub-bridge arms is used, the low-frequency SM capacitance voltage cannot be effectively suppressed, and an additional term u * CMV_no is added on the basis, so that the low-frequency suppression is completed jointly. A potential difference u no, called common mode voltage expression, is formed between the midpoint of the Y-type three-phase stator winding and the reference ground as follows:
Step 6: to control the above objectives, the first layer ac side phase current and common mode voltage rejection cost function is established as follows:
In the formula (5), the amino acid sequence of the compound, A d-axis reference current representing the voltage outer loop output; /(I)A q-axis reference current representing the current inner loop; representing a common mode voltage reference value; lambda 1 is a current control weight coefficient of the dq axis of the motor; lambda 2 is the weight coefficient of the output common-mode voltage of the alternating current side; i d(k+1)、iq (k+1) represents the stator phase current dq axis component at time k+1; u no denotes the common mode voltage;
step 7: the establishment of the second layer suppression low frequency submodule capacitance-voltage cost function can be expressed as follows:
In the formula (6), the amino acid sequence of the compound, Representing the difference reference value of the capacitor voltages of the sub-bridge arms; /(I)Representing the sum reference value of the capacitor voltages of the sub-bridge arms; lambda 3 is a weight coefficient of SM capacitance voltage difference control between an upper bridge arm and a lower bridge arm; lambda 4 is the weight coefficient of phase SM capacitance voltage and control; u cjdiff (k+1) represents the difference between the j-phase SM capacitor voltages at time k+1; u cjadd (k+1) represents the sum of the j-phase SM capacitor voltages at time k+1;
Step 8: and (3) obtaining the total number of required input submodules according to the minimum value of the rolling optimization output current and the common-mode voltage cost function in the step (6), obtaining the optimal submodules according with the step (7) through degree-of-freedom circulation, and finally obtaining the final input number S op_g by capacitor voltage sequencing according to the direction judgment of the bridge arm current.
According to the invention, after the FC-MMC converter new topology is combined with the provided low-frequency model predictive control strategy, the amplitude of the common-mode voltage of the FC-MMC alternating-current side in the whole low-frequency operation stage is about 400V, and the control is reduced by 77.8% compared with that of the traditional MMC structure; compared with the traditional MMC, the voltage fluctuation of the capacitance of the sub-module is reduced by 76.9%, and under the condition of safe and stable output of the FC-MMC frequency converter, the torque fluctuation of the permanent magnet synchronous motor is small, the rotating speed is free from overshoot, and the sine degree of output current is high, so that the reliability and the safety of the whole permanent magnet synchronous motor system under different working conditions are proved by the proposed control strategy.
It should be understood that the above description is not intended to limit the invention to the particular embodiments disclosed, but to limit the invention to the particular embodiments disclosed, and that the invention is not limited to the particular embodiments disclosed, but is intended to cover modifications, adaptations, additions and alternatives falling within the spirit and scope of the invention.
Claims (1)
1. The low-frequency operation model prediction control method of the flying capacitor modularized multi-level frequency converter is characterized by comprising the following steps of:
Step 1: a system model of a flying capacitor type modularized multi-level driving permanent magnet synchronous motor is established, and the specific flow is as follows:
substep (1-1): under the condition that the influence of factors such as a magnetic field saturation effect is ignored, a stator voltage equation of the surface-mounted three-phase permanent magnet synchronous motor under a two-phase rotation dq coordinate system by adopting the surface-mounted three-phase permanent magnet synchronous motor can be expressed as:
In formula (1), u d、uq is the stator phase voltage dq axis component; l d、Lq is dq axis inductance respectively; i d、iq is the stator phase current dq axis component; r s is the stator resistance; omega e is the electrical angular velocity; phi f is the permanent magnet flux linkage;
Substep (1-2): neglecting line impedance, and writing the loop equation energy columns of the upper bridge arm and the lower bridge arm of the flying capacitor type modularized multi-level frequency converter and the alternating current output side as follows:
In the formula (2), U dc is the direct-current side bus voltage; l is half bridge arm inductance; i j,p1、ij,p2、ij,n1、ij,n2 is the current of the upper half bridge arm and the lower half bridge arm of the j phases respectively; u j,p1、uj,p2、uj,n1、uj,n2 is the capacitance voltage of the sub-module of the upper half bridge arm and the lower half bridge arm of the j phases respectively; u j is the ac side output stator voltage, where j=a, b, c;
Substep (1-3): after the two formulas in the sub step (1-2) are respectively summed and differenced, the mathematical expression of the dynamic characteristics of the alternating current and direct current sides of the flying capacitor type modularized multi-level frequency converter can be obtained:
in the formula (3), i j is an ac side output stator current, where j=a, b, c;
Substep (1-4): the mathematical model of the fly-capacitance type modularized multi-level frequency converter under the dq coordinate system can be obtained by performing matrix transformation on the two-phase rotation dq coordinate system in the sub-steps (1-3) as follows:
in the formula (4), C abc/dq is a transformation matrix for converting a three-phase static abc coordinate system into a two-phase rotation dq coordinate system; l is half bridge arm inductance; u j,v1、uj,v2 is the voltages of four sub-arms of abc three-phase, respectively, wherein v=n, p, p represents the upper arm, n represents the lower arm, j=a, b, c;
substep (1-5): the output current and the voltage of the flying capacitor type modularized multi-level frequency converter are the input current and the voltage of a stator of the three-phase permanent magnet synchronous motor, and the dq axis current state equation of the flying capacitor type modularized multi-level driving permanent magnet synchronous motor can be obtained by combining a stator voltage equation of the surface-mounted three-phase permanent magnet synchronous motor with a mathematical model of the flying capacitor type modularized multi-level frequency converter:
In the formula (5), L eq represents an equivalent inductance, and the value of the equivalent inductance is L eq＝Ld+L＝Lq +L;
Step 2: discretizing the formula (5) by using an Euler equation to obtain a dq axis current prediction model of the moment k+1 of the flying capacitor type modularized multi-level frequency converter driving permanent magnet synchronous motor:
in formula (6), T s represents a sampling time; θ e is the electrical angle of the rotor permanent magnet; for the moment k+1, abc three-phase four sub-arm voltages, where v=n, p, j=a, b, c;
step 3: in order to keep the voltage balance of the submodules under the low-frequency working condition, the voltage difference of the submodules of the upper bridge arm and the lower bridge arm needs to be controlled:
In the formula (7), u ci,v1j,uci,v2j represents the capacitance voltage of each sub-module of four sub-bridge arms of the abc three-phase; s v1j,Sv2j represents the state of a switch tube of each sub-module of four sub-bridge arms of the abc three-phase; i j,v1,ij,v2 represents abc three-phase four-sub-arm current; n represents the number of sub-module power units; c represents the capacitance of the submodule; wherein v=n, p, j=a, b, c;
step 4: in order to increase the balance of the capacitance voltage of the sub-module, the balance of the interphase capacitance voltage of the sub-bridge arm needs to be further ensured, so that the sum of the capacitance voltages of the sub-bridge arm SM is controlled:
Step 5: if only the model prediction of the SM voltage difference between the sub-bridge arms and the sum of the phase SM voltages is used, the low-frequency SM capacitance voltage cannot be effectively restrained, and additional items are added on the basis Low frequency suppression is completed together; a potential difference u no, called common mode voltage, is formed between the midpoint of the Y-type three-phase stator winding and the reference ground, expressed as follows:
Step 6: to control the above objectives, the first layer ac side phase current and common mode voltage rejection cost function can be established as follows:
In the formula (10), the amino acid sequence of the compound, A d-axis reference current representing the voltage outer loop output; /(I)A q-axis reference current representing the current inner loop; representing a common mode voltage reference value; lambda 1 is a current control weight coefficient of the dq axis of the motor; lambda 2 is the weight coefficient of the output common-mode voltage of the alternating current side; i d(k+1)、iq (k+1) represents the stator phase current dq axis component at time k+1; u no denotes the common mode voltage;
Step 7: the establishment of the second layer of suppression low frequency submodule capacitance-voltage cost function can be expressed as follows:
In the formula (11), the amino acid sequence of the compound, Representing the difference reference value of the capacitor voltages of the sub-bridge arms; /(I)Representing the sum reference value of the capacitor voltages of the sub-bridge arms; lambda 3 is a weight coefficient of SM capacitance voltage difference control between an upper bridge arm and a lower bridge arm; lambda 4 is the weight coefficient of phase SM capacitance voltage and control; u cjdiff (k+1) represents the difference between the j-phase SM capacitor voltages at time k+1; u cjadd (k+1) represents the sum of the j-phase SM capacitor voltages at time k+1;
Step 8: and (3) obtaining the total number of required input submodules according to the minimum value of the rolling optimization output current and the common-mode voltage cost function in the step (6), obtaining the optimal submodules according with the step (7) through degree-of-freedom circulation, and finally obtaining the final input number S op_g by capacitor voltage sequencing according to the direction judgment of bridge arm current.
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