CN108539748B - Double-circuit line unified power flow controller and control method of series side converter thereof - Google Patents
Double-circuit line unified power flow controller and control method of series side converter thereof Download PDFInfo
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Abstract
The invention relates to a double-circuit unified power flow controller and a control method of a series-side converter thereof.
Description
Technical Field
The invention belongs to the technical field of high-voltage alternating-current power transmission, and particularly relates to a double-circuit line unified power flow controller and a control method of a series side converter thereof.
Background
With the rapid increase of economy in China, power systems are rapidly developed, and interconnection of various large power systems and the use of new equipment make power grid architectures become more and more large and complex, power flows among power grids are unevenly distributed and difficult to regulate and control, and some lines have overload and instability risks.
Flexible Alternating Current Transmission Systems (FACTS) are new ac Transmission technologies formed by integrating power electronic technologies, communication technologies and control technologies, and can flexibly control the voltage, impedance and phase angle of a Transmission system, thereby greatly improving the regulation and control flexibility and operation stability of the power system, and greatly improving the Transmission capacity of the existing Transmission line.
A Unified Power Flow Controller (UPFC) is a powerful member of FACTS, integrates flexible control means of many FACTS devices, and is considered as a representative of third generation FACTS, the UPFC is the most creative and comprehensive FACTS device. The unified power flow controller mainly comprises a parallel current converter and a series current converter which are connected with each other at a direct current side, has dual functions of parallel compensation and series compensation, is very flexible in operation mode, has good power flow control capability, and has the advantages of being unique in the aspects of oscillation suppression and damping compensation of an alternating current system.
Chinese patent CN104052073B, "a line power control method for unified power flow controller", includes outer loop line power control, inner loop valve side current control and converter valve control: calculating to obtain a valve side current reference value of the serial side converter according to an input line power instruction, an actually measured line voltage and an actually measured line power by the outer loop line power control; the current control of the inner ring valve side calculates and obtains a reference value of the output voltage of the converter according to a valve side current reference value output by the outer ring power control, an actually measured valve side current value and an actually measured valve side voltage; and finally, the converter outputs corresponding voltage according to the voltage reference value, and the power of the circuit is controlled to reach the reference value.
In an actual power system, in an occasion with a higher voltage level, in order to improve the power supply reliability, a double-circuit line is mostly adopted, and for a double-circuit line structure, the power flow of a power grid can be optimized only by simultaneously carrying out power flow control on the double-circuit line. When the double-circuit lines run in parallel, the two ends of the lines are connected and coupled with each other. When the power on the loop is adjusted, the voltage of the endpoint is changed, the change of the voltage of the endpoint can cause the change of the power on the other loop, and the adjustment of the power on the other loop under the action of closed-loop control can adversely affect the power conversion on the loop, so that when the double-loop is connected, the unified power flow controllers of the two loops are seriously coupled to affect the current control on the side of the inner loop valve.
Disclosure of Invention
The invention aims to provide a double-circuit line unified power flow controller and a control method of a series side converter of the double-circuit line unified power flow controller, which are used for solving the problem that the dynamic performance of current control on an inner ring valve side is poor due to the fact that the series side converter of the existing double-circuit line unified power flow controller is coupled.
In order to solve the technical problem, decoupling control needs to be performed on double-circuit power flow, the invention provides a control method of a series side converter of a double-circuit unified power flow controller, which comprises the following solutions:
the method comprises the steps of outer loop line power control and inner loop valve side current control, wherein the inner loop valve side current control is used for generating a converter output voltage reference value, a d-axis component of the converter output voltage reference value comprises a d-axis reference value first component, a d-axis reference value second component and a d-axis reference value third component, and a q-axis component of the converter output voltage reference value comprises a q-axis reference value first component, a q-axis reference value second component and a q-axis reference value third component;
the valve side d-axis current reference value and the valve side d-axis current feedback value are subjected to difference, and a first component of the d-axis reference value is obtained through a proportional-integral controller; the valve side q-axis current reference value and the valve side q-axis current feedback value are subjected to difference, and a first component of the q-axis reference value is obtained through a proportional-integral controller;
the valve side q-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a second component of the d-axis reference value; the valve side d-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a q-axis reference value second component;
the q-axis current feedback value of the other loop valve side is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the d-axis reference value; and the d-axis current feedback value at the other loop valve side and the coupling reactance of the other loop to the loop are multiplied to obtain a third component of the q-axis reference value.
According to the invention, by calculating the current decoupling terms (the third component of the d-axis reference value and the third component of the q-axis reference value) between the double loops, then adding a decoupling term considering the current of the other loop in the current inner loop of the converter on the series side of the double-loop unified power flow controller respectively, and performing combined action with the loop current inner loop PI controller and the dq-axis current decoupling term (the second component of the d-axis reference value and the second component of the q-axis reference value), the output voltage reference value of the converter is obtained and is used for controlling the line power, the power flow decoupling control between the double loops can be realized, the mutual influence during the power regulation of the double loops is reduced, the dynamic response characteristic of the system is improved, and the control structure is simple and easy to realize.
Further, the d-axis component of the converter output voltage reference value further comprises a grid-side d-axis voltage feedforward, and the q-axis component of the converter output voltage reference value further comprises a grid-side q-axis voltage feedforward.
The decoupling terms considering the current of the other loop current are respectively added to the current inner loop of the current converter on the series side of the double-loop unified power flow controller, and the decoupling terms act together with the loop current inner loop PI controller, the voltage feedforward term and the dq-axis current decoupling term to obtain the output voltage reference value of the current converter.
When the action of the voltage feedforward term is considered, the mathematical model of the current control of the inner ring valve side under the dq rotation coordinate system is as follows:
in the formula uv1dFor d-axis component, u, of converter output voltage referencev1qFor q-component of converter output voltage reference, KiPIs a proportionality coefficient, KiIIn order to be the integral coefficient of the light,
is a valve side d-axis current reference value,
for valve side q-axis current reference value, iv1dIs a valve side d-axis current feedback value iv1qIs a valve side q-axis current feedback value, Lσ1An equivalent reactance on the AC side of the current converter on the series side of the loop line, Lσ2For the coupling reactance, u, of the other loop to the loopedFor the net side d-axis voltage feed-forward, ueqFor said net side q-axis voltage feed-forward, iv2qTo another oneMeasured value of current q axis on return line valve side, iv2dThe measured value of the valve side current d axis is the other loop, and ω is the angular frequency.
Corresponding to the inner loop valve side current control, the outer loop circuit power control of the invention comprises the following steps:
and calculating to obtain a reference value of the line current under a dq rotating coordinate system through line active and reactive power instructions and actually measured line alternating voltage, and performing conversion through a series side converter equivalent to a transformation ratio of a series transformer to obtain valve side d-axis and q-axis current reference values.
Specifically, the measured active power of the line is used as a feedback value to be differenced with the instruction value of the active power of the line, and after the difference is adjusted by a PI controller, the value output after the adjustment is superposed with the d-axis current value obtained through the conversion and conversion of the transformation ratio to obtain a valve side d-axis current reference value;
and taking the actually measured reactive power of the line as a feedback value to be differenced with the reactive power instruction value of the line, adjusting the feedback value by the PI controller, and superposing the value output after adjustment and the q-axis current value obtained by conversion and conversion of the transformation ratio to obtain the valve side q-axis current reference value.
In order to solve the above technical problem, the present invention further provides a double-loop unified power flow controller, including the following solutions:
each loop is connected with a series side converter, each series side converter comprises an outer loop power control module and an inner loop valve side current control module, each inner loop valve side current control module is used for generating a converter output voltage reference value, a d-axis component of the converter output voltage reference value comprises a d-axis reference value first component, a d-axis reference value second component and a d-axis reference value third component, and a q-axis component of the converter output voltage reference value comprises a q-axis reference value first component, a q-axis reference value second component and a q-axis reference value third component;
the valve side d-axis current reference value and the valve side d-axis current feedback value are subjected to difference, and a first component of the d-axis reference value is obtained through a proportional-integral controller; the valve side q-axis current reference value and the valve side q-axis current feedback value are subjected to difference, and a first component of the q-axis reference value is obtained through a proportional-integral controller;
the valve side q-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a second component of the d-axis reference value; the valve side d-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a q-axis reference value second component;
the q-axis current feedback value of the other loop valve side is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the d-axis reference value; and the d-axis current feedback value at the other loop valve side and the coupling reactance of the other loop to the loop are multiplied to obtain a third component of the q-axis reference value.
Further, the d-axis component of the converter output voltage reference value further comprises a grid-side d-axis voltage feedforward, and the q-axis component of the converter output voltage reference value further comprises a grid-side q-axis voltage feedforward.
In this case, the mathematical model generated by the inner ring valve side current control module in the dq rotation coordinate system is:
in the formula uv1dFor d-axis component, u, of converter output voltage referencev1qFor q-component of converter output voltage reference, KiPIs a proportionality coefficient, KiIIn order to be the integral coefficient of the light,
is a valve side d-axis current reference value,
for valve side q-axis current reference value, iv1dIs a valve side d-axis current feedback value iv1qIs a valve side q-axis current feedback value, Lσ1An equivalent reactance on the AC side of the current converter on the series side of the loop line, Lσ2For the coupling reactance, u, of the other loop to the loopedFor the net side d-axis voltage feed-forward, ueqFor said net side q-axis voltage feed-forward, iv2qIs powered by another loop valveMeasured value of flow q-axis, iv2dThe measured value of the valve side current d axis is the other loop, and ω is the angular frequency.
Corresponding to the inner loop valve side current control, the outer loop circuit power control module of the invention is used for:
and calculating to obtain a reference value of the line current under a dq rotating coordinate system through line active and reactive power instructions and actually measured line alternating voltage, and performing conversion through a series side converter equivalent to a transformation ratio of a series transformer to obtain valve side d-axis and q-axis current reference values.
Specifically, the measured active power of the line is used as a feedback value to be differenced with the instruction value of the active power of the line, and after the difference is adjusted by a PI controller, the value output after the adjustment is superposed with the d-axis current value obtained through the conversion and conversion of the transformation ratio to obtain a valve side d-axis current reference value;
and taking the actually measured reactive power of the line as a feedback value to be differenced with the reactive power instruction value of the line, adjusting the feedback value by the PI controller, and superposing the value output after adjustment and the q-axis current value obtained by conversion and conversion of the transformation ratio to obtain the valve side q-axis current reference value.
Drawings
Fig. 1 is a schematic diagram of a topology of a dual-loop unified power flow controller;
fig. 2 is an equivalent circuit diagram of a two-loop unified power flow controller;
fig. 3 is a control block diagram of a double-circuit line unified power flow controller series side cross decoupling controller;
fig. 4 is a valve side current control block diagram in a double-loop unified power flow controller.
Detailed Description
The following further describes embodiments of the present invention with reference to the drawings.
The first embodiment is as follows:
the topology structure of the dual-loop unified power flow controller shown in fig. 1 includes an ac power grid at the transmitting end, a dual-loop power transmission line (referred to as a dual-loop) and a unified power flow controller, where the unified power flow controller includes a parallel side converter I and series side converters II and III, that is, each loop is connected to a series side converter.
The parallel converter I is mainly responsible for the active power balance and the alternating current bus voltage support of the unified power flow controller, usually adopts double closed-loop control, the outer loop is constant direct current voltage/constant reactive power control or constant direct current voltage/constant alternating current voltage control, and the inner loop is direct current control under a dq synchronous rotation coordinate system; the series converters II and III are mainly responsible for regulating and controlling line power flow, and because two ends of a double-circuit line accessed at the series side are connected, coupling exists between the two ends during power regulation.
Therefore, in order to eliminate the influence of coupling between the two circuit lines, the invention provides a method for controlling a series side converter of a two circuit line unified power flow controller, which comprises the following steps:
the method comprises outer loop line power control and inner loop valve side current control, wherein the outer loop line power control is used for generating valve side d-axis and q-axis current reference values, the inner loop valve side current control is used for generating a converter output voltage reference value, a d-axis component of the converter output voltage reference value comprises a d-axis reference value first component, a d-axis reference value second component and a d-axis reference value third component, and a q-axis component of the converter output voltage reference value comprises a q-axis reference value first component, a q-axis reference value second component and a q-axis reference value third component.
The valve side d-axis current reference value and the valve side d-axis current feedback value are subjected to difference, and a first component of the d-axis reference value is obtained through a proportional-integral controller; and (3) making a difference between the valve side q-axis current reference value and the valve side q-axis current feedback value, and obtaining a first component of the q-axis reference value through a proportional-integral controller.
The valve side q-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a second component of the d-axis reference value; and the valve side d-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop series side converter to obtain a second component of the q-axis reference value.
The q-axis current feedback value at the valve side of the other loop is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the d-axis reference value; and the d-axis current feedback value at the valve side of the other loop is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the q-axis reference value.
According to the invention, by calculating the current decoupling terms (the third component of the d-axis reference value and the third component of the q-axis reference value) between the double loops, then adding a decoupling term considering the current of the other loop in the current inner loop of the converter on the series side of the double-loop unified power flow controller respectively, and performing combined action with the loop current inner loop PI controller and the dq-axis current decoupling term (the second component of the d-axis reference value and the second component of the q-axis reference value), the output voltage reference value of the converter is obtained and is used for controlling the line power, the power flow decoupling control between the double loops can be realized, the mutual influence during the power regulation of the double loops is reduced, the dynamic response characteristic of the system is improved, and the control structure is simple and easy to realize.
Specifically, the d-axis component of the converter output voltage reference value is obtained by subtracting the second component of the d-axis reference value from the first component of the d-axis reference value and then subtracting the third component of the d-axis reference value; the q-axis component of the converter output voltage reference is the q-axis reference first component plus the q-axis reference second component plus the q-axis reference third component.
Further, the d-axis component of the converter output voltage reference value further comprises a grid-side d-axis voltage feedforward, and the q-axis component of the converter output voltage reference value further comprises a grid-side q-axis voltage feedforward. The decoupling terms considering the current of the other loop current are respectively added to the current inner loop of the current converter on the series side of the double-loop unified power flow controller, and the decoupling terms act together with the loop current inner loop PI controller, the voltage feedforward term and the dq-axis current decoupling term to obtain the output voltage reference value of the current converter.
When the action of the voltage feedforward term is considered, the mathematical model of the current control of the inner ring valve side under the dq rotation coordinate system is as follows:
in the formula uv1dFor d-axis component, u, of converter output voltage referencev1qFor q-component of converter output voltage reference, KiPIs a proportionality coefficient, KiIIn order to be the integral coefficient of the light,
is a valve side d-axis current reference value,
for valve side q-axis current reference value, iv1dIs a valve side d-axis current feedback value iv1qIs a valve side q-axis current feedback value, Lσ1Is the equivalent reactance, L, on the AC side of the current converter on the series side of the present loopσ2Is the coupling reactance of another loop to the present loop uedFor net side d-axis voltage feed-forward, ueqThe net side q-axis voltage is fed forward.
Corresponding to the inner loop valve side current control, the outer loop circuit power control of the invention comprises the following steps:
and calculating to obtain a reference value of the line current under a dq rotating coordinate system through line active and reactive power instructions and actually measured line alternating voltage, and performing conversion through a series side converter equivalent to a transformation ratio of a series transformer to obtain valve side d-axis and q-axis current reference values.
Specifically, the measured active power of the line is used as a feedback value to be differenced with the command value of the active power of the line, and after the difference is adjusted by the PI controller, the value output after the adjustment is superposed with the d-axis current value obtained through the conversion and conversion of the transformation ratio, so that the valve side d-axis current reference value is obtained.
And taking the actually measured reactive power of the line as a feedback value to be differenced with the reactive power instruction value of the line, adjusting the feedback value by using a PI (proportional integral) controller, and superposing the value output after adjustment and the q-axis current value obtained by conversion through the transformation ratio to obtain the valve-side q-axis current reference value.
Based on the control method of the series side converter, the invention further provides a double-loop unified power flow controller, each loop is connected with the series side converter, each series side converter comprises an outer loop power control module and an inner loop valve side current control module, the outer loop power control module is used for generating valve side d-axis and q-axis current reference values, the inner loop valve side current control module is used for generating a converter output voltage reference value, a d-axis component of the converter output voltage reference value comprises a d-axis reference value first component, a d-axis reference value second component and a d-axis reference value third component, and a q-axis component of the converter output voltage reference value comprises a q-axis reference value first component, a q-axis reference value second component and a q-axis reference value third component.
The valve side d-axis current reference value and the valve side d-axis current feedback value are subjected to difference, and a first component of the d-axis reference value is obtained through a proportional-integral controller; and (3) making a difference between the valve side q-axis current reference value and the valve side q-axis current feedback value, and obtaining a first component of the q-axis reference value through a proportional-integral controller.
The valve side q-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a second component of the d-axis reference value; and the valve side d-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop series side converter to obtain a second component of the q-axis reference value.
The q-axis current feedback value at the valve side of the other loop is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the d-axis reference value; and the d-axis current feedback value at the valve side of the other loop is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the q-axis reference value.
The outstanding substantial features of the dual-circuit unified power flow controller in the above embodiments are based on the method flow of the present invention, that is, the method for controlling the series-side converter of the dual-circuit unified power flow controller, and the description of the method is clear and complete enough, so detailed description of the dual-circuit unified power flow controller is not repeated.
Example two:
fig. 1 is a topology structure of a dual-loop unified power flow controller in the present invention, which includes a transmitting-receiving end ac power grid, a dual-loop power transmission line, and a unified power flow controller, wherein the unified power flow controller includes a parallel side converter I and series side converters II and III.
The parallel converter I is mainly responsible for the active power balance and the alternating current bus voltage support of the unified power flow controller, usually adopts double closed-loop control, the outer loop is constant direct current voltage/constant reactive power control or constant direct current voltage/constant alternating current voltage control, and the inner loop is direct current control under a dq synchronous rotation coordinate system; the series converters II and III are mainly responsible for regulating and controlling line power flow, and because two ends of a double-circuit line accessed at the series side are connected, the double-circuit line is coupled with each other during power regulation.
The control strategy adopted by the unified power flow controller series side converter is a double-loop decoupling control strategy and comprises a power outer loop controller and a cross decoupling inner loop controller.
Wherein the power outer loop controller is used for controlling the power output according to the active and reactive power instruction values P of the lineref、QrefAnd actually measured line alternating voltage, and calculating to obtain a reference value of the line current in a dq rotation coordinate system
Then converting the voltage into a current reference value of the valve side of the converter through the transformation ratio conversion of the series transformer
In the formula, v1d、v1qRespectively, dq components of the measured line alternating voltage in a dq rotation coordinate system.
In order to improve the line power control precision, a power closed-loop control part can be added in an outer-loop controller of the series side converter. The measured active power of the line is used as a feedback value, and is output as a part of the active current instruction value of the current inner loop through the regulation of a PI controller together with the active power instruction value of the line obtained by the system level control; and (3) taking the actually measured reactive power of the line as a feedback value, and outputting the feedback value and a line reactive power instruction value obtained by system-level control as a part of the current inner loop reactive current instruction through the regulation of the PI controller.
And the cross decoupling inner loop controller is used for enabling the dq-axis current to quickly track the dq-axis current reference value output by the power outer loop by adjusting the output voltage of the current converter so as to indirectly control the line power. The design of the cross-decoupling inner ring controller is derived according to a frequency domain mathematical model of a converter under a dq rotating coordinate system, and the derivation process is as follows:
fig. 2 is an equivalent circuit diagram of the topology of fig. 1, in which the effect of the parallel side converter on the line voltage current is neglected. Assuming that the bridge arm reactances of the two series converters are equal, the leakage impedances of the two series transformers are equal. According to the equivalent circuit shown in fig. 2, there is the following relation:
in the formula, XtmThe leakage reactance of the series transformer is equivalent on the secondary side, XarmIs bridge arm equivalent impedance, XsAnd XrLine equivalent impedance, U, of the transmitting and receiving end grids, respectivelyeTo receive a voltage difference between two terminals, U12For connecting the primary side voltage of the transformer in series, Uv12For voltage of secondary side of series transformer, Uv1And Uv2Output voltages, i, of series converters II and III, respectivelyv1And iv2Valve side currents, i, of series converters II and III, respectivelyLFor line current, n is the series transformer transformation ratio.
Taking the serial converter II as an example to continue analysis, the above relation is arranged and transformed to the synchronous rotating coordinate system dq, and the following are:
in the formula, Rσ1Is the equivalent resistance, L, of the AC side of the series converter IIσ1Is the equivalent reactance, L, of the AC side of the series converter IIσ1＝Ltm+Larm/2+(Ls+Lr)/n2，Ltm、Larm、Ls、LrThe series transformer equivalent reactance, the bridge arm reactance, the line equivalent reactance of the sending end power grid and the receiving end power grid are respectively; l isσ2Is the coupling reactance, L, of another loop to the present loopσ2＝(Ls+Lr)/n2And p is a differential operator.
Because the power grid voltage feedforward term is the voltage difference of an equivalent ideal voltage source of the power grids at two ends, is determined by the amplitude difference and the phase difference of the power grids at two ends, is difficult to measure and can change along with the change of the power flow, the voltage feedforward is not considered to be added in the current inner loop of the series side converter of the unified power flow controller. In addition, the sudden change of the differential terms is fast, and the transient terms are not suitable to be directly superposed on the output result of the controller as feedforward terms, so that the decoupling feedforward can be carried out only on the non-differential term part, and finally the cross decoupling inner ring controller is designed as follows:
in the unified power flow controller series side converter cross decoupling inner ring controller, the converter output voltage reference value uv1d、uv1qIs composed of three parts, in uv1dFor illustration, the first part represents a current inner loop PI controller,
and iv1dReference values and feedback values of d-axis and q-axis of valve side current, KiP、KiIProportional coefficient and integral coefficient respectively; the second part represents a dq-axis current decoupling term; the third part represents the current decoupling term between the double loops, where iv2qIs the measured value of the valve side current q axis of the other loop.
The double-circuit unified power flow controller is connected with the cross decoupling inner loop controller adopted by the converter at the series side, the power flow decoupling control between the double circuits can be realized, the mutual influence during the power regulation of the double circuits is reduced, the dynamic response characteristic of a system is improved, and the control structure is simple and easy to realize.
In order to obtain the output voltage reference value of the converter, if a voltage feedforward term is considered to be added when a cross decoupling inner ring controller is designed, a mathematical model of the cross decoupling inner ring controller of the unified power flow controller series side converter under a dq rotation coordinate system is as follows, and a control block diagram of the cross decoupling inner ring controller is shown in fig. 3 corresponding to the following mathematical model.
In the formula, the converter outputs a voltage reference uv1d、uv1qIs composed of four items of content, in uv1dFor illustration, the first term represents a current inner loop PI controller,
and iv1dReference values and feedback values of d-axis and q-axis of valve side current, KiP、KiIProportional coefficient and integral coefficient respectively; the second term represents the dq-axis current decoupling term, Lσ1Is the equivalent reactance, L, on the AC side of the current converter on the series side of the present loopσ1＝Ltm+Larm/2+(Ls+Lr)/n2，Ltm、Larm、Ls、LrThe series transformer equivalent reactance, the bridge arm reactance, the line equivalent reactance of the sending end power grid and the receiving end power grid are respectively; the third term represents the current decoupling term between the double loops, Lσ2Is the coupling reactance of another loop to the present loop, Lσ2＝(Ls+Lr)/n2，iv2qIs another loop valve side current q-axis measured value, iv2dIs the measured value of the valve side current d axis of the other loop, and omega is the angular frequency; item uedAnd ueqRepresenting the voltage feed forward term.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.
Claims (10)
1. A series side converter control method of a double-loop unified power flow controller is characterized by comprising outer loop line power control and inner loop valve side current control, wherein the inner loop valve side current control is used for generating a converter output voltage reference value, a d-axis component of the converter output voltage reference value comprises a d-axis reference value first component, a d-axis reference value second component and a d-axis reference value third component, and a q-axis component of the converter output voltage reference value comprises a q-axis reference value first component, a q-axis reference value second component and a q-axis reference value third component;
the valve side d-axis current reference value and the valve side d-axis current feedback value are subjected to difference, and a first component of the d-axis reference value is obtained through a proportional-integral controller; the valve side q-axis current reference value and the valve side q-axis current feedback value are subjected to difference, and a first component of the q-axis reference value is obtained through a proportional-integral controller;
the valve side q-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a second component of the d-axis reference value; the valve side d-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a q-axis reference value second component;
the q-axis current feedback value of the other loop valve side is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the d-axis reference value; and the d-axis current feedback value at the other loop valve side and the coupling reactance of the other loop to the loop are multiplied to obtain a third component of the q-axis reference value.
2. The method of claim 1, wherein the d-axis component of the converter output voltage reference further comprises a grid-side d-axis voltage feedforward and the q-axis component of the converter output voltage reference further comprises a grid-side q-axis voltage feedforward.
3. The series-side converter control method of the double-loop unified power flow controller according to claim 2, wherein the mathematical model of the inner loop valve-side current control under the dq rotation coordinate system is as follows:
in the formula uv1dFor d-axis component, u, of converter output voltage referencev1qFor q-component of converter output voltage reference, KiPIs a proportionality coefficient, KiIIn order to be the integral coefficient of the light,
is a valve side d-axis current reference value,
for valve side q-axis current reference value, iv1dIs a valve side d-axis current feedback value iv1qIs a valve side q-axis current feedback value, Lσ1An equivalent reactance on the AC side of the current converter on the series side of the loop line, Lσ2For the coupling reactance, u, of the other loop to the loopedFor the net side d-axis voltage feed-forward, ueqFor said net side q-axis voltage feed-forward, iv2qIs another loop valve side current q-axis measured value, iv2dThe measured value of the valve side current d axis is the other loop, and ω is the angular frequency.
4. The method of controlling a series side converter of a two-loop unified power flow controller according to claim 1, wherein the outer loop power control comprises the steps of:
and calculating to obtain a reference value of the line current under a dq rotating coordinate system through line active and reactive power instructions and actually measured line alternating voltage, and performing conversion through a transformation ratio equivalent to a series transformer through a series side converter to obtain a valve side d-axis current reference value and a valve side q-axis current reference value.
5. The method for controlling the series side converter of the double-circuit unified power flow controller according to claim 4, wherein the difference is made between the measured active power of the line as a feedback value and an active power instruction value of the line, and after the difference is adjusted by the PI controller, the value output after the adjustment is superposed with a d-axis current value obtained by the conversion of the transformation ratio to obtain a d-axis current reference value on the valve side;
and taking the actually measured reactive power of the line as a feedback value to be differenced with the reactive power instruction value of the line, adjusting the feedback value by the PI controller, and superposing the value output after adjustment and the q-axis current value obtained by conversion and conversion of the transformation ratio to obtain the valve side q-axis current reference value.
6. A double-loop unified power flow controller is characterized in that each series side converter comprises an outer loop power control module and an inner loop valve side current control module, wherein the inner loop valve side current control module is used for generating a converter output voltage reference value, a d-axis component of the converter output voltage reference value comprises a d-axis reference value first component, a d-axis reference value second component and a d-axis reference value third component, and a q-axis component of the converter output voltage reference value comprises a q-axis reference value first component, a q-axis reference value second component and a q-axis reference value third component;
the valve side d-axis current reference value and the valve side d-axis current feedback value are subjected to difference, and a first component of the d-axis reference value is obtained through a proportional-integral controller; the valve side q-axis current reference value and the valve side q-axis current feedback value are subjected to difference, and a first component of the q-axis reference value is obtained through a proportional-integral controller;
the valve side q-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a second component of the d-axis reference value; the valve side d-axis current feedback value is multiplied by the equivalent reactance of the alternating current side of the loop line series side converter to obtain a q-axis reference value second component;
the q-axis current feedback value of the other loop valve side is multiplied by the coupling reactance of the other loop to the loop to obtain a third component of the d-axis reference value; and the d-axis current feedback value at the other loop valve side and the coupling reactance of the other loop to the loop are multiplied to obtain a third component of the q-axis reference value.
7. The dual loop unified power flow controller of claim 6, wherein the d-axis component of the converter output voltage reference further comprises a grid-side d-axis voltage feedforward and the q-axis component of the converter output voltage reference further comprises a grid-side q-axis voltage feedforward.
8. The double-loop unified power flow controller according to claim 7, wherein the mathematical model generated by the inner-loop valve-side current control module under dq rotation coordinate system is:
in the formula uv1dFor d-axis component, u, of converter output voltage referencev1qFor q-component of converter output voltage reference, KiPIs a proportionality coefficient, KiIIn order to be the integral coefficient of the light,
is a valve side d-axis current reference value,
for valve side q-axis current reference value, iv1dIs a valve side d-axis current feedback value iv1qIs a valve side q-axis current feedback value, Lσ1An equivalent reactance on the AC side of the current converter on the series side of the loop line, Lσ2For the coupling reactance, u, of the other loop to the loopedFor the net side d-axis voltage feed-forward, ueqFor said net side q-axis voltage feed-forward, iv2qIs another loop valve side current q-axis measured value, iv2dThe measured value of the valve side current d axis is the other loop, and ω is the angular frequency.
9. The two-loop unified power flow controller of claim 6, wherein said outer loop power control module is configured to:
and calculating to obtain a reference value of the line current under a dq rotating coordinate system through line active and reactive power instructions and actually measured line alternating voltage, and performing conversion through a transformation ratio equivalent to a series transformer through a series side converter to obtain a valve side d-axis current reference value and a valve side q-axis current reference value.
10. The double-circuit unified power flow controller according to claim 9, wherein the difference is made between the measured active power of the line as a feedback value and the line active power command value, and after the difference is adjusted by the PI controller, the value output after the adjustment is superimposed with the d-axis current value obtained by the conversion of the transformation ratio to obtain a valve-side d-axis current reference value;
and taking the actually measured reactive power of the line as a feedback value to be differenced with the reactive power instruction value of the line, adjusting the feedback value by the PI controller, and superposing the value output after adjustment and the q-axis current value obtained by conversion and conversion of the transformation ratio to obtain the valve side q-axis current reference value.
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