CN109861268B - Nonlinear control method for layered access of extra-high voltage direct current transmission system - Google Patents
Nonlinear control method for layered access of extra-high voltage direct current transmission system Download PDFInfo
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Abstract
The invention discloses a nonlinear control method for a layered access extra-high voltage direct current transmission system, which comprises the following steps: establishing a state equation and an output equation of an extra-high voltage direct-current transmission system with a receiving end hierarchically connected to an alternating-current power grid according to equipment parameters and control system parameters of the extra-high voltage direct-current transmission system with the receiving end hierarchically connected to the alternating-current power grid; selecting coordinate transformation meeting the differential homoembryo condition, and accurately linearizing the state equation; solving a Riccati equation corresponding to the linear system according to an optimization principle in the linear system; and forming an optimal control law of a layered access extra-high voltage direct current transmission system according to the solved optimal pre-control, optimizing state feedback, and realizing nonlinear control of constant current at the rectifying side and constant arc-quenching angle at the inverting side. The invention has obvious improvement on the accurate control of the constant current at the rectifying side and the constant arc-extinguishing angle at the inverting side and the dynamic response characteristics of the pole layer and the valve layer in the direct current control system.
Description
Technical Field
The invention belongs to the technical field of extra-high voltage direct current transmission control, and particularly relates to a nonlinear control method for layered access to an extra-high voltage direct current transmission system.
Background
At present, the +/-1100 kV direct-current transmission technology is the transmission technology with the highest voltage level, the largest capacity and the farthest distance in the world, the distance reaches 3000-.
In the direct-current power transmission technology, a direct-current control protection system controls the whole process of alternating-current/direct-current power conversion and direct-current power transmission. The main control and additional control of the direct current transmission project are mostly based on the linear control theory design of single input and single output, namely a root locus method and a frequency response method. Although the controller designed by the traditional method can firstly obtain a system transfer function through an identification algorithm, then set parameters through a Berde plot and a root locus plot, and the traditional controller has a good control effect under the conditions of a steady state and small disturbance, the alternating current and direct current system has strong nonlinear characteristics. Under the condition of large disturbance, the control effect of the traditional method is not ideal, the control action time of the traditional method cannot be guaranteed to aim at the optimal performance of the whole system, and even the performance of the system is deteriorated.
In summary, a new nonlinear control method is needed.
Disclosure of Invention
The invention aims to provide a nonlinear control method for a layered access extra-high voltage direct current transmission system, so as to solve one or more technical problems. The nonlinear control method of the invention uses the optimal control formed by nonlinear function to replace the traditional combined PI controller; compared with the traditional PI controller with both sides combined, the invention has obvious improvement on the accurate control of constant current at the rectification side and constant arc-extinguishing angle at the inversion side and the dynamic response characteristics of the pole layer and the valve layer in the direct current control system.
In order to achieve the purpose, the invention adopts the following technical scheme:
a nonlinear control method for a layered access extra-high voltage direct current transmission system comprises the following steps:
s1, collecting equipment parameters and control system parameters in an extra-high voltage direct current power transmission system with a receiving end connected to an alternating current power grid in a layered mode, and drawing an equivalent circuit; collecting control strategies of a rectification side and an inversion side in pole layer control; collecting conditions and response time of constant current control, constant arc-extinguishing angle control, valve group voltage balance control and transformer tap control;
s2, selecting the actual direct current deviation and the actual arc-quenching angle deviation as performance indexes of constant current control and constant arc-quenching angle control according to the control strategies of the rectifying side and the inverting side obtained in the step S1;
s3, establishing a state equation of the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode according to the equipment parameters, the equivalent circuit and the control system parameters obtained in the step S1;
s4, establishing an output equation of the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode according to the performance indexes of the constant current control and the constant arc-quenching angle control obtained in the step S2;
s5, combining the state equation obtained in the step S3 with the output equation obtained in the step S4 to obtain a nonlinear system; selecting coordinate transformation meeting the differential homoembryo condition by adopting a state feedback accurate linearization method in a nonlinear control theory, and accurately linearizing the obtained nonlinear system to obtain a linear system;
s6, solving a Riccati equation corresponding to the linear system according to the optimization principle in the linear system; and forming an optimal control law of a layered access extra-high voltage direct current transmission system according to the solved optimal pre-control, optimizing state feedback, and realizing nonlinear control of constant current at the rectifying side and constant arc-quenching angle at the inverting side.
In the invention, the controller designed by the nonlinear control method comprises: a rectification side controller and an inversion side high-end and low-end controller; the rectification side controller includes: constant current control, constant voltage control and transformer tap control; the inverter side high-end and low-end controller comprises: high-side current control, high-side arc-extinguishing angle control, high-side constant voltage control, high-side transformer tap control, low-side current control, low-side arc-extinguishing angle control, low-side constant voltage control, low-side transformer tap control, and high-low side valve bank voltage balance control.
In the invention, when an equivalent circuit diagram of a layered access extra-high voltage direct current transmission system is established, the high-low end valve group is independently controlled, and the high-low end voltage balance control is configured.
In step 1 of the invention, the direct current voltage and direct current equation at the rectifying side is as follows:
in the formula: vaRFor rectifying the valve side AC voltage of the side converter αRTriggering a delay angle for the rectification side; dxRAnd drRThe inductive commutation voltage drop and the resistive commutation voltage drop are on the rectifying side; i isdIs direct current at the rectifying side; i isdNThe rated value is the rated value of the direct current at the rectification side; u shapeTIs the converter valve forward pressure drop; u shapedRIs a rectifying side direct current voltage; u shapedioNRAn ideal no-load voltage rated value of the rectification side; u shapedioRIs a rectifying side no-load voltage; mu.sRThe commutation side changes the phase overlap angle.
In step 1 of the invention, the equations of the direct current voltage and the direct current at the inversion side are as follows:
in the formula: vaHAnd VaLThe alternating current voltage of the inversion side high-voltage end valve and the inversion side low-voltage end valve is respectively the alternating current voltage of the inversion side high-voltage end valve and the inversion side low-voltage end valve; gamma rayHAnd gammaLConverter valve arc-quenching angles of a high-pressure end valve and a low-pressure end valve on the inversion side are set; dxIAnd drIThe voltage drop of the inductive commutation at the inverting side and the voltage drop of the resistive commutation; rdIs a direct current line resistor; u shapedioINThe ideal no-load voltage rated value of the inversion side; u shapedioIHAnd UdioILRespectively the no-load voltage of the high-voltage end valve and the low-voltage end valve of the inverter side；μHAnd muLThe phase-change overlap angles of the high-pressure end valve and the low-pressure end valve on the inversion side are respectively.
In step 2 of the invention, when the constant current controller and the constant arc-quenching angle controller act, the position of the joint is kept unchanged, and the actual direct current deviation and the actual arc-quenching angle deviation are selected as performance indexes of the constant current control and the constant arc-quenching angle control.
In the step 3 of the present invention,
the dynamic equation of the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode is as follows:
in the formula βHAnd βLLeading firing angles of the inverter side high-pressure end valve and the low-pressure end valve, respectively αOAnd βORespectively setting a triggering angle at a rectification side and a leading triggering angle at an inversion side; u. ofαFor the control variable of the firing angle of the commutation side, uHAnd uLRepresenting the triggering angle control variables of the high-pressure end valve and the low-end valve bank on the inversion side; t isαControl of the inertia time constant, T, of the converter valve on the rectifying sideβThe inverter side converter valve controls an inertia time constant.
In step 3 and step 4 of the invention, the receiving end is hierarchically connected to the space state equation of the extra-high voltage direct current transmission system of the alternating current power grid
And output equation y1,y2,y3The expression of (a) is:
in the formula: x ═ IdαRβHβL]T；ga(x)＝[0 1/Tα0 0]T；gH(x)＝[0 0 1/Tβ0]T；gL(x)＝[0 0 0 1/Tβ]T；y1Is an output variable controlled by a trigger angle of the rectification side; y is2And y3Representing the output variables of the control trigger angles of the high-pressure end valve and the low-end valve bank on the inversion side; x is the number ofcI△ I for inverting side phase-change reactanced、△γHAnd △ gammaLThe current value deviation, the high-pressure end valve extinction angle deviation and the low-pressure end valve extinction angle deviation are respectively.
The step 5 of the invention specifically comprises the following steps:
first, the following coordinate transformation z ═ Φ (x) is selected
Then, the rationality of the coordinate transformation is demonstrated, and the corresponding Jacobian matrix is obtained as follows:
wherein R is∑Is the total resistance of the DC loop, L∑Is the total reactance of the direct current loop;
the determinant of the Jacobian matrix is as follows:
under the normal operation state of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode, a determinant value is not zero, and according to a differential geometric theory, coordinate transformation of z ═ phi (x) has differential homoembryonic property;
after z ═ Φ (x) coordinate transformation, the state equation is expressed in z coordinates as:
the equation is solved according to the differential geometry theory, and the result is as follows:
the linear system is expressed as a standard:
the step 6 of the invention specifically comprises the following steps: according to the optimization control principle of a linear system, solving the Riccati equation to obtain the corresponding optimal pre-control as follows:
finally, the optimal control law of the original nonlinear system is solved as follows:
compared with the prior art, the invention has the following beneficial effects:
the control method disclosed by the invention is based on a nonlinear model, combines the requirements of performance indexes on two sides of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode with a system dynamic equation, can realize the integral optimization of a control target and dynamic quality in the direct current system, and can avoid the parameter setting problem in the traditional combined PI controller. Compared with the existing PI control, the nonlinear control realizes more accurate constant current at the rectifying side and constant extinction angle at the inverting side, has smaller state variation of the pole layer and the valve layer of the direct current control system and shorter response time under the condition of large disturbance, and improves the performance and the running stability of the layered access ultrahigh voltage direct current transmission system. The invention relates to a method for designing valve layer control of a layered access direct current system by utilizing a state feedback accurate linearization method, which belongs to the field for the first time. The nonlinear control method is characterized in that the optimal control formed by a nonlinear function replaces the traditional combined PI controller; accurately linearizing and decoupling a dynamic equation of an extra-high voltage direct-current transmission system with a receiving end connected to an alternating-current power grid in a layered mode based on a differential geometry theory, so that the control problem of an affine nonlinear system is converted into a linear control problem; solving a Riccati equation corresponding to the linear system according to an optimization principle in the linear system; and forming an optimal control law of a layered access extra-high voltage direct current transmission system according to the solved optimal pre-control, optimizing state feedback, and realizing nonlinear control of constant current at the rectifying side and constant arc-quenching angle at the inverting side. Compared with the traditional PI controller with both sides combined, the invention has obvious improvement on the accurate control of constant current at the rectification side and constant arc-extinguishing angle at the inversion side and the dynamic response characteristics of the pole layer and the valve layer in the direct current control system.
Drawings
Fig. 1 is a schematic diagram of a main loop of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode;
FIG. 2 is a schematic diagram of an equivalent circuit of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode;
FIG. 3 is a basic flow schematic block diagram of the nonlinear control method of the present invention;
fig. 4 is a schematic diagram illustrating a comparison of simulation waveforms of dc power of a dc outlet at a rectifying side after a single-phase ground at a 500kV side in the embodiment of the present invention;
fig. 5 is a schematic diagram illustrating a comparison of simulation waveforms of dc voltages of the dc outgoing line on the rectifying side after the single-phase grounding on the 500kV side in the embodiment of the present invention;
fig. 6 is a schematic diagram illustrating a comparison of simulation waveforms of dc current of the rectifying-side dc outlet after the single-phase grounding at the 500kV side in the embodiment of the present invention;
FIG. 7 is a schematic diagram illustrating a comparison of simulation waveforms of the firing angle of the rectifying side after the single-phase grounding of the 500kV side in the embodiment of the present invention;
FIG. 8 is a diagram illustrating a comparison of simulation waveforms of DC voltage of the DC outgoing line of the inverter side after single-phase grounding at the 500kV side in the embodiment of the present invention;
fig. 9 is a schematic diagram illustrating a comparison of simulation waveforms of dc current of the dc outgoing line on the inverting side after single-phase grounding on the 500kV side in the embodiment of the present invention;
FIG. 10 is a schematic diagram showing a comparison of simulation waveforms of the trigger angle of the high-end valve at the inverting side after the single-phase grounding at the 500kV side in the embodiment of the present invention;
fig. 11 is a simulation waveform comparison diagram of the triggering angle of the low-end valve of the inverter side after the single-phase grounding of the 500kV side in the embodiment of the present invention;
fig. 12 is a simulation waveform comparison diagram of an arc extinguishing angle of the Yy valve at the high-voltage end of the inverter side after the single-phase grounding at the 500kV side in the embodiment of the invention;
fig. 13 is a simulation waveform comparison diagram of the extinction angle of the Yd valve at the high-voltage end of the inverter side after the single-phase grounding at the 500kV side in the embodiment of the present invention;
fig. 14 is a simulation waveform comparison diagram of an arc extinguishing angle of the Yy valve at the low-voltage end of the inverter side after the single-phase grounding at the 500kV side in the embodiment of the invention;
fig. 15 is a comparison diagram of simulated waveforms of arc-extinguishing angles of the Yd valve at the low-voltage end of the inverter side after single-phase grounding at the 500kV side in the embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it should be noted that the embodiments of the present invention are only used for further explaining the technical solutions of the present invention, and should not be understood as limiting the scope of the present invention, and a person skilled in the art may make some insubstantial modifications and adjustments according to the contents of the embodiments.
Referring to fig. 1 to 3, a nonlinear control method of an extra-high voltage dc power transmission system with a receiving end connected to an ac power grid in a layered manner based on a state feedback accurate linearization method in a nonlinear control theory according to an embodiment of the present invention includes the following steps: according to equipment parameters and control system parameters of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode, a state equation and an output equation of the extra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in the layered mode are established, coordinate transformation meeting differential homomorphic conditions is selected, the state equation is accurately linearized, a Riccati equation corresponding to a linear system is solved according to an optimization principle in the linear system, an optimal control law with the extra-high voltage direct current transmission system connected in the layered mode is formed according to optimal pre-control of solution, state feedback is optimized, and nonlinear control of constant current on a rectifying side and constant arc-extinguishing angle on an inverting side is achieved.
The linearization method based on differential geometry theory comprises an input-to-state feedback linearization method and an input-output feedback linearization method, and has the core of feedback accurate linearization, and the method enables an affine nonlinear system to map the nonlinear system into a linear system under new coordinates under the conditions of satisfying controllability, vector field generation, involution and convexity through local differential homoembryo transformation, thereby converting the control problem of the affine nonlinear system into a linear control problem. The nonlinear control can achieve the control target more accurately and more quickly, so that the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode has a good dynamic effect under the condition of large disturbance, and the method has an important significance for improving the system performance and the operation stability. The invention provides a nonlinear control method of a layered access extra-high voltage direct current transmission system based on a state feedback accurate linearization method in a nonlinear control theory, which is characterized in that the traditional combined PI controller is replaced by the optimal control formed by a nonlinear function; accurately linearizing and decoupling a dynamic equation of a layered access extra-high voltage direct current system based on a differential geometric theory, so that the control problem of an affine nonlinear system is converted into a linear control problem; selecting a proper weight matrix according to an optimization principle in a linear system, and solving a Riccati equation corresponding to the linear system; and forming an optimal control law of a layered access extra-high voltage direct current transmission system according to the solved optimal pre-control, optimizing state feedback, and realizing nonlinear control of constant current at the rectifying side and constant arc-quenching angle at the inverting side. Compared with the traditional PI controller with both sides combined, the invention has obvious improvement on the accurate control of constant current at the rectification side and constant arc-extinguishing angle at the inversion side and the dynamic response characteristics of the pole layer and the valve layer in the direct current control system.
Examples
Referring to fig. 1, a controller designed by a nonlinear control method for a receiving-end layered access extra-high voltage direct current transmission system includes: a rectification side controller and an inversion side high-end and low-end controller; the rectifier side controller comprises constant current control, constant voltage control and transformer tap control, and the inverter side high-end and low-end controllers comprise high-end current control, high-end arc-extinguishing angle control, high-end constant voltage control, high-end transformer tap control, low-end current control, low-end arc-extinguishing angle control, low-end constant voltage control, low-end transformer tap control and high-low end valve bank voltage balance control.
(1) Precision linearization
Referring to fig. 2, an equivalent circuit diagram of a layered access extra-high voltage dc power transmission system is first established. Because the inverter side layered connection has access to two alternating current systems, the voltage fluctuation and load fluctuation conditions of the two alternating current systems are considered to be different, the indexes of the extinction angle of the high-voltage end valve bank and the low-voltage end valve bank, the transformer tap and the like are adjusted according to the conditions of the respective alternating current systems, so that the high-end valve bank and the low-end valve bank are independently controlled, the rated transmission power of the high end and the low end is the same, and the high-end and low-end voltage balance control is required to be configured.
The direct-current voltage and direct-current equation at the rectifying side is as follows:
in the formula: vaRFor rectifying the valve side AC voltage of the side converter αRTriggering a delay angle for the rectification side; dxRAnd drRThe inductive commutation voltage drop and the resistive commutation voltage drop are on the rectifying side; i isdIs direct current at the rectifying side; i isdNThe rated value is the rated value of the direct current at the rectification side; u shapeTIs the converter valve forward pressure drop; u shapedRIs a rectifying side direct current voltage; u shapedioNRFor ideal no-load voltage rating of the rectifying side；UdioRIs a rectifying side no-load voltage; mu.sRThe commutation side changes the phase overlap angle.
The inversion side direct current voltage and direct current equation is:
in the formula: vaHAnd VaLThe alternating current voltage of the inversion side high-voltage end valve and the inversion side low-voltage end valve is respectively the alternating current voltage of the inversion side high-voltage end valve and the inversion side low-voltage end valve; gamma rayHAnd gammaLConverter valve arc-quenching angles of a high-pressure end valve and a low-pressure end valve on the inversion side are set; dxIAnd drIThe voltage drop of the inductive commutation at the inverting side and the voltage drop of the resistive commutation; rdIs a direct current line resistor; u shapedioINThe ideal no-load voltage rated value of the inversion side; u shapedioIHAnd UdioILThe no-load voltages of the high-voltage end valve and the low-voltage end valve on the inversion side are respectively; mu.sHAnd muLThe phase-change overlap angles of the high-pressure end valve and the low-pressure end valve on the inversion side are respectively.
Because the constant current control at the rectifying side and the constant arc-extinguishing angle control at the inverter side are high-speed controllers, and the action time of tap control is 5-10 seconds per stage, the tap is considered to be not in time to act when the constant current control at the rectifying side and the constant arc-extinguishing angle control at the inverter side are designed, namely the action of the constant current controller and the constant arc-extinguishing angle controller is that the positions of the tap are kept unchanged.
Neglecting the effect of the direct current line capacitance, the dynamic equation of the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current grid in a layered mode is
In the formula βHAnd βLLeading firing angles of the inverter side high-pressure end valve and the low-pressure end valve, respectively αOAnd βORespectively setting a triggering angle at a rectification side and a leading triggering angle at an inversion side; u. ofαFor the control variable of the firing angle of the commutation side, uHAnd uLRepresenting the triggering angle control variables of the high-pressure end valve and the low-end valve bank on the inversion side; t isαControl of the inertia time constant, T, of the converter valve on the rectifying sideβThe inverter side converter valve controls an inertia time constant.
Definition x ═ IdαRβHβL]T. Because of the constant current control on the rectifying side and the constant extinction angle control on the inverting side, the output quantity should reflect the deviation between the actual value and the set value, and thus the output variable is defined as the difference between the actual current and the actual extinction angle and the respective set values. Space state equation of ultra-high voltage direct current transmission system with receiving end connected to alternating current power grid in layered mode
And output equation y1,y2,y3Is composed of
In the formula: y is1Is an output variable controlled by a trigger angle of the rectification side; y is2And y3Representing the output variables of the control trigger angles of the high-pressure end valve and the low-end valve bank on the inversion side; x is the number ofci△ I for inverting side phase-change reactanced、△γHAnd △ gammaLThe current value deviation, the high-pressure end valve extinction angle deviation and the low-pressure end valve extinction angle deviation are respectively.
Referring to fig. 3, since the space state equation includes a nonlinear function, a method of accurate linearization of state feedback in nonlinear control is adopted to linearize a nonlinear system. First, the following coordinate transformation z ═ Φ (x) is selected
Then the rationality of the coordinate transformation is demonstrated, and the corresponding Jacobian matrix is obtained as follows
Wherein R is∑Is the total resistance of the DC loop, L∑Is a direct currentThe total reactance of the loop.
The determinant of the Jacobian matrix is
Under the normal operation state of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode, the value of the formula (7) is not zero, and according to a differential geometric theory, the coordinate transformation of z ═ phi (x) has differential homoembryoid.
After z ═ Φ (x) coordinate transformation, the equation of state of equation (4) is expressed in z coordinates as follows:
equation (8) is solved according to differential geometry theory, and the result is as follows:
the linear system is expressed as a standard as follows:
(2) optimal control
According to the optimization control principle of a linear system, solving the Riccati equation to obtain the corresponding optimal pre-control as follows:
finally, the optimal control law of the original nonlinear system is solved as follows:
compared with the simulation result of the traditional method, the method of the invention has the following advantages:
and (3) performing simulation analysis on the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode as shown in the figure 1 by using the designed nonlinear optimal control law.
Basic situation of the two-sided communication system: the rectification side is a 750kV alternating current system, the inversion side is a 500kV and 1000kV system, and a plurality of groups of alternating current filter groups are arranged on respective alternating current buses.
Parameters of the control system: the bipolar operation rated power is 12000MW, the rated voltage is +/-1100 kV, the rated current is 5.455kA, and each station of each pole is in a double-12-pulse series structure; the rated trigger angle of the rectifying side is 15 degrees, and the normal allowable fluctuation is +/-2.5 degrees; the rated extinction angle on the inversion side is 17 degrees, and the normal allowable fluctuation is +/-2.5 degrees.
The superiority of the control method is verified by using the direct current system response after the short-time single-phase earth fault of the receiving-end 500kV power grid, and the control method for comparison comprises the following steps: nonlinear control and conventional combined PI controllers.
Referring to fig. 4 to 7, fig. 4 to 6 are simulation waveform diagrams of dc power, dc voltage and dc current of the dc outlet at the rectifying side after the single-phase grounding at the 500kV side, respectively; fig. 7 is a simulated waveform diagram of the firing angle of the rectifying side after the single-phase grounding of the 500kV side. It can be seen that, compared with the traditional combined PI controller, the nonlinear control of the present invention has smaller fluctuation range of the direct current voltage, the fluctuation range of the direct current and the fluctuation range of the trigger angle, and the direct current power is recovered to the original state in a shorter time.
Referring to fig. 8 to 11, fig. 8 and 9 are simulated waveform diagrams of the dc voltage and the dc current of the dc output line of the inverter side after the single-phase grounding of the 500kV side, respectively; fig. 10 and 11 are simulation waveform diagrams of the inverter side high-end valve firing angle and the inverter side low-end valve firing angle after single-phase grounding at the 500kV side, respectively. As can be seen from the figure, the inverter-side dc voltage, the dc current and the firing angle fluctuation range are smaller compared to the conventional combined PI controller.
Referring to fig. 12 to 15, fig. 12 to 15 are simulation waveforms of the trigger angle and the extinction angle of the high-side valve and the low-side valve of the inverter side after the single-phase grounding at the 500kV side, respectively. From the results, it can be seen that the range of the arc-quenching angle fluctuation in the nonlinear control is smaller and the influence of a healthy valve on a failed valve is much smaller than that of the conventional combined PI controller. Simulation results show that nonlinear control can reduce the oscillation amplitude and duration of a direct current system, so that an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode can recover from alternating current faults more quickly.
In summary, the embodiment of the present invention provides a nonlinear control method for a layered access extra-high voltage dc power transmission system based on state feedback accurate linearization, where the method includes the following steps: in an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode, performance indexes corresponding to control strategies of constant current on a rectifying side and constant arc-quenching angle on an inverting side are determined, a dynamic equation of the direct current transmission system connected in the layered mode is established according to equivalent circuit and equipment parameters of the direct current system, an output equation of the control system is determined according to the performance indexes, a state feedback accurate linearization method in a nonlinear control theory is adopted, the state equation connected in the direct current transmission system in the layered mode is subjected to accurate linearization, state feedback is optimized according to an optimization principle in the linear system, an optimal control law is formed, and nonlinear control of constant current on the rectifying side and constant arc-quenching angle on the inverting side is achieved. Compared with the traditional PI controller with both sides combined, the invention has obvious improvement on the accurate control of the constant current at the rectifying side and the constant arc-extinguishing angle at the inverting side and the dynamic response characteristics of the pole layer and the valve layer in the direct current control system. The method of the invention realizes the accurate control of the constant current at the rectification side and the constant arc-quenching angle at the inversion side, realizes the independent control of the high-end converter transformer and the low-end converter transformer at the inversion side, can improve the dynamic response characteristic of a pole layer or a valve layer in a direct current control system, reduces the oscillation amplitude and the duration time of the direct current system, and enables the system to recover from alternating current disturbance or fault more quickly.
According to equipment parameters and control system parameters of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode, a state equation and an output equation of the extra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in the layered mode are established, coordinate transformation meeting differential homomorphic conditions is selected, the state equation is accurately linearized, a Riccati equation corresponding to a linear system is solved according to an optimization principle in the linear system, an optimal control law with the extra-high voltage direct current transmission system connected in the layered mode is formed according to optimal pre-control of solution, state feedback is optimized, and nonlinear control of constant current on a rectifying side and constant arc-extinguishing angle on an inverting side is achieved.
Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can make modifications and equivalents to the embodiments of the present invention without departing from the spirit and scope of the present invention, which is set forth in the claims of the present application.
Claims (9)
1. A nonlinear control method for a layered access extra-high voltage direct current transmission system is characterized by comprising the following steps:
s1, collecting equipment parameters and control system parameters in an extra-high voltage direct current power transmission system with a receiving end connected to an alternating current power grid in a layered mode, and drawing an equivalent circuit; collecting control strategies of a rectification side and an inversion side in pole layer control; collecting conditions and response time of constant current control, constant arc-extinguishing angle control, valve group voltage balance control and transformer tap control;
s2, selecting the actual direct current deviation and the actual arc-quenching angle deviation as performance indexes of constant current control and constant arc-quenching angle control according to the control strategies of the rectifying side and the inverting side obtained in the step S1;
s3, establishing a state equation of the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode according to the equipment parameters, the equivalent circuit and the control system parameters obtained in the step S1;
s4, establishing an output equation of the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode according to the performance indexes of the constant current control and the constant arc-quenching angle control obtained in the step S2;
s5, combining the state equation obtained in the step S3 with the output equation obtained in the step S4 to obtain a nonlinear system; selecting coordinate transformation meeting the differential homoembryo condition by adopting a state feedback accurate linearization method in a nonlinear control theory, and accurately linearizing the obtained nonlinear system to obtain a linear system;
s6, solving a Riccati equation corresponding to the linear system according to the optimization principle in the linear system; according to the solved optimal pre-control, an optimal control law of a layered access extra-high voltage direct current transmission system is formed, state feedback is optimized, and nonlinear control of constant current at the rectifying side and constant arc-quenching angle at the inverting side is realized;
in step S1, the dc voltage and dc current equations on the rectifying side are:
in the formula: vaRFor rectifying the valve side AC voltage of the side converter αRTriggering a delay angle for the rectification side; dxRAnd drRThe inductive commutation voltage drop and the resistive commutation voltage drop are on the rectifying side; i isdIs direct current at the rectifying side; i isdNThe rated value is the rated value of the direct current at the rectification side; u shapeTIs the converter valve forward pressure drop; u shapedRIs a rectifying side direct current voltage; u shapedioNRAn ideal no-load voltage rated value of the rectification side; u shapedioRIs a rectifying side no-load voltage; mu.sRThe commutation side changes the phase overlap angle.
2. The nonlinear control method for the layered access to the extra-high voltage direct current transmission system according to claim 1, wherein the controller designed by the nonlinear control method comprises: a rectification side controller and an inversion side high-end and low-end controller;
the rectification side controller includes: constant current control, constant voltage control and transformer tap control;
the inverter side high-end and low-end controller comprises: high-side current control, high-side arc-extinguishing angle control, high-side constant voltage control, high-side transformer tap control, low-side current control, low-side arc-extinguishing angle control, low-side constant voltage control, low-side transformer tap control, and high-low side valve bank voltage balance control.
3. The nonlinear control method for the layered access of the extra-high voltage direct current transmission system according to claim 1, wherein in the step S1, when the equivalent circuit is drawn, the high-low end valve group is independently controlled, and a high-low end voltage balance control is configured.
4. The nonlinear control method for the layered access to the extra-high voltage direct current transmission system according to claim 1, wherein in step S1, the equations of the inverter side direct current voltage and the direct current are as follows:
in the formula: vaHAnd VaLThe alternating current voltage of the inversion side high-voltage end valve and the inversion side low-voltage end valve is respectively the alternating current voltage of the inversion side high-voltage end valve and the inversion side low-voltage end valve; gamma rayHAnd gammaLConverter valve arc-quenching angles of a high-pressure end valve and a low-pressure end valve on the inversion side are set; dxIAnd drIThe voltage drop of the inductive commutation at the inverting side and the voltage drop of the resistive commutation; rdIs a direct current line resistor; u shapedioINThe ideal no-load voltage rated value of the inversion side; u shapedioIHAnd UdioILThe no-load voltages of the high-voltage end valve and the low-voltage end valve on the inversion side are respectively; mu.sHAnd muLThe phase-change overlap angles of the high-pressure end valve and the low-pressure end valve on the inversion side are respectively.
5. The nonlinear control method for the layered access to the extra-high voltage direct current transmission system according to claim 2, wherein in step S2, when the constant current controller and the constant arc-quenching angle controller are operated, the position of the joint is kept unchanged, and the actual direct current deviation and the actual arc-quenching angle deviation are selected as performance indexes of the constant current control and the constant arc-quenching angle control.
6. The nonlinear control method for the layered access to the extra-high voltage direct current transmission system according to claim 4, wherein in the step S3,
the dynamic equation of the ultra-high voltage direct current transmission system with the receiving end connected to the alternating current power grid in a layered mode is as follows:
in the formula βHAnd βLLeading trigger angles of a high-pressure end valve and a low-pressure end valve on the inversion side are respectively set; l is∑And R∑α total reactance and total resistance of equivalent circuitoAnd βoRespectively setting a triggering angle at a rectification side and a leading triggering angle at an inversion side; u. ofαFor the control variable of the firing angle of the commutation side, uHAnd uLRepresenting the triggering angle control variables of the high-pressure end valve and the low-end valve bank on the inversion side; t isαControl of the inertia time constant, T, of the converter valve on the rectifying sideβThe inverter side converter valve controls an inertia time constant.
7. The nonlinear control method for the layered access of the extra-high voltage direct current transmission system according to claim 6, wherein in the steps S3 and S4, the space state equation of the extra-high voltage direct current transmission system with the receiving end layered accessed to the alternating current grid
And output equation y1,y2,y3The expression of (a) is:
in the formula: x ═ IdαRβHβL]T；ga(x)＝[0 1/Tα0 0]T；gH(x)＝[0 0 1/Tβ0]T；gL(x)＝[0 00 1/Tβ]T；y1Is an output variable controlled by a trigger angle of the rectification side; y is2And y3Representing the output variables of the control trigger angles of the high-pressure end valve and the low-end valve bank on the inversion side; x is the number ofcI△ I for inverting side phase-change reactanced、△γHAnd △ gammaLThe current value deviation, the high-pressure end valve extinction angle deviation and the low-pressure end valve extinction angle deviation are respectively.
8. The nonlinear control method for the layered access to the extra-high voltage direct current transmission system according to claim 7, wherein the step S5 specifically includes:
first, the following coordinate transformation z ═ Φ (x) is selected
Then, the rationality of the coordinate transformation is demonstrated, and the corresponding Jacobian matrix is obtained as follows:
the determinant of the Jacobian matrix is as follows:
under the normal operation state of an extra-high voltage direct current transmission system with a receiving end connected to an alternating current power grid in a layered mode, a determinant value is not zero, and according to a differential geometric theory, coordinate transformation of z ═ phi (x) has differential homoembryonic property;
after z ═ Φ (x) coordinate transformation, the state equation is expressed in z coordinates as:
the equation is solved according to the differential geometry theory, and the result is as follows:
the linear system is expressed as a standard:
9. the nonlinear control method for the layered access to the extra-high voltage direct current transmission system according to claim 8, wherein the step S6 specifically includes: according to the optimization control principle of a linear system, solving the Riccati equation to obtain the corresponding optimal pre-control as follows:
finally, the optimal control law of the original nonlinear system is solved as follows:
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