CN109802380B - Low-voltage current limiting control method, system and device for high-voltage direct-current transmission - Google Patents
Low-voltage current limiting control method, system and device for high-voltage direct-current transmission Download PDFInfo
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Abstract
The invention discloses a low-voltage current-limiting control method, a system and a device for high-voltage direct-current transmission, which comprise the following steps: determining starting voltage, minimum allowable voltage, maximum allowable current and minimum allowable current according to working parameters of the high-voltage direct-current transmission system; dividing a UI characteristic curve which takes the starting voltage and the maximum allowable current as one end point and takes the minimum allowable voltage and the minimum allowable current as the other end point into N sections of sub-curves, and setting the slope of each section of sub-curve; the slope of the sub-curve corresponding to the larger voltage is greater than the slope of the sub-curve corresponding to the smaller voltage; substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a voltage-current relation to obtain the coordinate value of the intersection point of the adjacent sub-curves so as to obtain a UI characteristic curve with variable slope; and in the working process of the system, when the actual direct current voltage is smaller than the starting voltage, limiting the direct current command according to the obtained UI characteristic curve. Therefore, the method and the device avoid the continuous phase change failure of the system and ensure that the system can quickly recover to normal operation.
Description
Technical Field
The invention relates to the field of high-voltage direct-current transmission, in particular to a low-voltage current-limiting control method, a low-voltage current-limiting control system and a low-voltage current-limiting control device for high-voltage direct-current transmission.
Background
At present, the high-voltage direct-current transmission technology has great advantages in limiting the short-circuit current level of a system, isolating the fault influence between alternating-current and direct-current systems, solving the problems of large-capacity long-distance transmission and the like, so that the high-voltage direct-current transmission system is widely applied to a power grid. In the prior art, a thyristor which has no breaking capacity is generally adopted as a switching device in a high-voltage direct-current transmission system, so that a phase change failure on an inverter side of the high-voltage direct-current transmission system is a common fault, and adverse consequences such as reduction of direct-current voltage of the system, reduction of direct-current transmission power, increase of direct current, shortening of the service life of a converter valve and the like can be caused. If the control is improper after the commutation failure, the subsequent commutation failure can be caused, and finally the direct current transmission of the system is interrupted.
In order to prevent continuous commutation failure of a high-voltage direct-current transmission system, a low-voltage current-limiting control method is generally adopted in the prior art: when the direct current voltage of the system is reduced to a specified value, the direct current instruction of the system is limited, so that the direct current of the system is prevented from being rapidly increased during the fault period, the reactive requirement of the system is reduced, the maintenance or recovery of the direct current voltage of the system is facilitated, and the effect of preventing the commutation failure is achieved. Specifically, the existing low-voltage current limiting control method adopts a linear control mode, as shown in fig. 1 (in fig. 1, UDC *For system DC voltage, UH *Is a systemStarting voltage, UL *For the minimum allowable voltage of the system, Iord*Is a system DC current command, IH *For the maximum allowable current of the system, IL *The minimum allowable current for the system). However, when a system has a serious fault, the response is slow, which results in slow adjustment of the voltage on the inverter side and the direct-current transmission power, and for the increase speed of the direct-current at a low voltage level, it is still difficult to avoid the system from continuous phase commutation failure, and is not favorable for the recovery of the system after the fault is removed.
Therefore, how to provide a solution to the above technical problem is a problem that needs to be solved by those skilled in the art.
Disclosure of Invention
The invention aims to provide a low-voltage current-limiting control method, a low-voltage current-limiting control system and a low-voltage current-limiting control device for high-voltage direct-current transmission, which avoid the situation that the system fails in continuous phase commutation and ensure that the system can quickly recover to normal operation.
In order to solve the technical problem, the invention provides a low-voltage current limiting control method for high-voltage direct-current transmission, which comprises the following steps:
determining the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of a system in advance according to the working parameters of the high-voltage direct-current transmission system;
dividing a UI characteristic curve which takes the starting voltage and the maximum allowable current as one endpoint and takes the minimum allowable voltage and the minimum allowable current as the other endpoint into N sections of sub-curves, and setting the slope of each section of sub-curve; wherein the slope of the sub-curve corresponding to the larger direct current voltage is greater than the slope of the sub-curve corresponding to the smaller direct current voltage; n is an integer greater than 1;
substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to obtain the coordinate value of the intersection point of the adjacent sub-curves so as to finally obtain a variable-slope UI characteristic curve;
and in the working process of the system, when the actual direct current voltage of the system is smaller than the starting voltage, limiting the direct current instruction of the system according to the UI characteristic curve with the variable slope.
Preferably, the preset voltage-current relation comprises a current coordinate solving relation
And the voltage coordinate to obtain the relation
Wherein, I1Is the maximum allowable current, IN+1Is the minimum allowable current, 1 < I < N +1 and I is an integer, IiIs the current value corresponding to the intersection point of the i-1 th sub-curve and the i-th sub-curve, UiIs the voltage value corresponding to the intersection point of the i-1 th sub-curve and the i-th sub-curve, KiThe slope of the ith sub-curve is shown.
Preferably, after obtaining the coordinate values of the intersection points of the adjacent sub-curves and before finally obtaining the UI characteristic curve with a variable slope, the low-voltage current limiting control method further includes:
performing iterative computation on the intersection point coordinate value by using a preset iterative algorithm to obtain an optimal intersection point coordinate value;
the process of finally obtaining the UI characteristic curve with a variable slope includes:
and obtaining a UI characteristic curve with a variable slope according to the coordinate values of the two end points and the optimal intersection point coordinate value.
Preferably, the low-voltage current limiting control method further comprises:
and when the actual direct current voltage of the system is less than the starting voltage, controlling a prompting device to send out prompting information indicating that the system enters low-voltage current-limiting control.
Preferably, the prompting device is specifically an indicator light or a buzzer.
Preferably, 0.7 times the rated voltage of the system is equal to or less than 0.9 times the rated voltage, 0.1 times the rated voltage is equal to or less than 0.2 times the minimum allowable voltage, 0.1 times the rated current of the system is equal to or less than 0.2 times the minimum allowable current, and the maximum allowable current is equal to or less than the rated current.
Preferably, N ═ 6.
Preferably, the process of limiting the dc current command of the system according to the UI characteristic curve with a variable slope includes:
obtaining a direct current instruction relational expression according to the UI characteristic curve of the variable slope
Wherein, IordFor system DC current command, UDCIs the system direct current voltage;
and substituting the actual direct current voltage into a corresponding direct current instruction relational expression to obtain a direct current instruction of the system so as to control the direct current of the system according to the direct current instruction.
In order to solve the above technical problem, the present invention further provides a low voltage current limiting control system for high voltage dc transmission, including:
the end point determining module is used for determining the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of the system in advance according to the working parameters of the high-voltage direct-current power transmission system;
a curve setting module, configured to divide a UI characteristic curve, which takes the starting voltage and the maximum allowable current as one endpoint and the minimum allowable voltage and the minimum allowable current as another endpoint, into N segments of sub-curves, and set a slope of each segment of sub-curve; wherein the slope of the sub-curve corresponding to the larger direct current voltage is greater than the slope of the sub-curve corresponding to the smaller direct current voltage; n is an integer greater than 1;
the curve acquisition module is used for substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to acquire the coordinate value of the intersection point of the adjacent sub-curves so as to finally obtain a variable-slope UI characteristic curve;
and the current limiting control module is used for limiting a direct current instruction of the system according to the UI characteristic curve with variable slope when the actual direct current voltage of the system is smaller than the starting voltage in the working process of the system.
In order to solve the above technical problem, the present invention further provides a low voltage current limiting control device for high voltage dc transmission, including:
a memory for storing a computer program;
and the processor is used for realizing any one of the low-voltage current limiting control methods for high-voltage direct-current transmission when executing the computer program.
The invention provides a low-voltage current limiting control method for high-voltage direct-current transmission, which comprises the following steps: determining the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of a system in advance according to the working parameters of the high-voltage direct-current transmission system; dividing a UI characteristic curve which takes the starting voltage and the maximum allowable current as one endpoint and takes the minimum allowable voltage and the minimum allowable current as the other endpoint into N sections of sub-curves, and setting the slope of each section of sub-curve; wherein the slope of the sub-curve corresponding to the larger direct current voltage is greater than the slope of the sub-curve corresponding to the smaller direct current voltage; substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to obtain the coordinate value of the intersection point of the adjacent sub-curves so as to finally obtain a variable-slope UI characteristic curve; and in the working process of the system, when the actual direct current voltage of the system is smaller than the starting voltage, limiting the direct current instruction of the system according to the UI characteristic curve with the variable slope.
It can be seen that the UI characteristic curve of the present application includes N sub-curves having different slopes (the slope of the sub-curve corresponding to a larger dc voltage is larger). That is, when the dc voltage of the system is at a lower level, the system can provide less reactive power, and the dc current of the system should increase at a slower speed, so as to reduce the reactive power consumption during phase change and promote the recovery of the phase change voltage compared with the prior art; when the direct current voltage of the system reaches a higher level, the reactive power provided by the system is more, and the direct current of the system is increased at a higher speed, so that the recovery of the transmission power of the system is promoted, the condition that the system fails in continuous phase change is avoided, and the system is ensured to recover normal operation quickly.
The invention also provides a low-voltage current-limiting control system and device for high-voltage direct-current transmission, and the low-voltage current-limiting control system and device have the same beneficial effects as the low-voltage current-limiting control.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed in the prior art and the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a prior art UI characteristic for a low voltage current limit control;
fig. 2 is a flowchart of a low-voltage current limiting control method for high-voltage direct-current transmission according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of a model of a high-voltage direct-current power transmission system according to an embodiment of the present invention;
fig. 4 is a slope characteristic curve of a low-voltage current-limiting control UI according to an embodiment of the present invention;
fig. 5 is a block diagram of a control structure of a hvdc power transmission system according to an embodiment of the present invention;
fig. 6(a) is a simulated waveform diagram of a dc current at a receiving end three-phase ground fault using a conventional low-voltage current limiting control according to an embodiment of the present invention;
fig. 6(b) is a simulated waveform diagram of a dc voltage at a receiving end three-phase ground fault using a conventional low-voltage current-limiting control according to an embodiment of the present invention;
fig. 6(c) is a simulated waveform diagram of turn-off angle at the time of receiving end three-phase ground fault using the conventional low-voltage current limiting control according to the embodiment of the present invention;
fig. 7(a) is a simulated waveform diagram of a dc current at a receiving end three-phase ground fault using an improved low-voltage current limiting control according to an embodiment of the present invention;
fig. 7(b) is a simulated waveform diagram of a dc voltage at a receiving end three-phase ground fault using an improved low-voltage current limiting control according to an embodiment of the present invention;
fig. 7(c) is a simulated waveform diagram of turn-off angle at the time of receiving end three-phase ground fault using the improved low-voltage current limiting control provided by the embodiment of the invention;
fig. 8 is a schematic structural diagram of a low-voltage current-limiting control system for high-voltage direct-current transmission according to an embodiment of the present invention.
Detailed Description
The core of the invention is to provide a low-voltage current-limiting control method, a system and a device for high-voltage direct-current transmission, which avoid the condition of continuous commutation failure of the system and ensure that the system can quickly recover normal operation.
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 2, fig. 2 is a flowchart of a low voltage current limiting control method for high voltage dc transmission according to an embodiment of the present invention.
The low-voltage current limiting control method for high-voltage direct-current transmission comprises the following steps:
step S1: the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of the system are determined in advance according to the working parameters of the high-voltage direct-current transmission system.
Specifically, referring to fig. 3, fig. 3 is a schematic structural diagram of a model of a high-voltage direct-current power transmission system according to an embodiment of the present invention. The high-voltage direct-current transmission system comprises a rectification side alternating-current line impedance Z1, an inversion side alternating-current line impedance Z2, a direct-current line impedance ZL, a rectification side transformer T1, an inversion side transformer T2 and a controller (alpha)recFor rectifying side retardation, αinvInverter-side delay angle), rectifier, and inverter.
The working principle of the high-voltage direct-current transmission system is as follows: the controller adjusts the conduction angles of the rectifier and the inverter to realize the generation of direct voltage and direct current and the transmission of power. Usually, the controller is provided with control strategies suitable for different conditions, such as constant power control, constant current control, constant turn-off angle control, current deviation control, low-voltage current-limiting control and the like.
For low-voltage current limiting control of a high-voltage direct-current transmission system, the triggering conditions of the low-voltage current limiting control are as follows: when the system direct current voltage drops to the system starting voltage, a controller in the system enters low-voltage current-limiting control.
Based on this, this application obtains system maximum voltage and maximum current that low pressure current-limiting control corresponds at first. Specifically, the starting voltage and the minimum allowable voltage (system maximum voltage) of the system are determined according to the working parameters of the system, and the maximum allowable current and the minimum allowable current (system maximum current) of the system are determined, so that a foundation is laid for improving the UI characteristic curve in the later period.
Step S2: dividing a UI characteristic curve which takes the starting voltage and the maximum allowable current as one endpoint and takes the minimum allowable voltage and the minimum allowable current as the other endpoint into N sections of sub-curves, and setting the slope of each section of sub-curve; wherein the slope of the sub-curve corresponding to a larger dc voltage > the slope of the sub-curve corresponding to a smaller dc voltage.
Specifically, considering that when the dc voltage of the system is at a lower level, the reactive power that the system can provide is less, and when the dc current of the system is at a faster increasing speed, the reactive power that the system needs for commutation is more, when the dc voltage of the system is at a lower level, if the dc current of the system increases at a faster increasing speed, the reactive power that the system can provide is not enough for the commutation of the system, which may cause a situation that the commutation fails. On the contrary, when the system direct current voltage is at a higher level, the reactive power provided by the system is more, so that the system direct current can be increased at a higher speed, and the recovery of the system transmission power can be promoted.
Therefore, in order to avoid the occurrence of continuous phase commutation failure of the system, the application should adaptively change the increase speed of the system dc current according to the magnitude of the system dc voltage value, specifically: the increase speed of the direct current when the system direct current voltage is larger than the increase speed of the direct current when the system direct current voltage is smaller. Based on this, the low-voltage current-limiting control method of the application adopts a piecewise linear control mode, and the specific setting principle is as follows:
firstly, coordinate values of two end points of a UI characteristic curve corresponding to the low-voltage current-limiting control method are obtained (it can be understood that the starting voltage and the maximum allowable current of a system are one end point of the UI characteristic curve, and the minimum allowable voltage and the minimum allowable current of the system are the other end point of the UI characteristic curve); then, according to a control principle that the increase speed of the system direct current is faster (that is, the slope of the UI characteristic curve is larger) as the system direct current voltage is larger, the UI characteristic curve is divided into N segments of sub-curves (N is an integer larger than 1), and a slope is set for each segment of sub-curve according to a rule that the slope of the sub-curve corresponding to the larger direct current voltage is larger.
Step S3: and substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to obtain the coordinate value of the intersection point of the adjacent sub-curves so as to finally obtain the UI characteristic curve with variable slope.
It should be noted that the preset of the present application is set in advance, and only needs to be set once, and the reset is not needed unless the modification is needed according to the actual situation.
Specifically, after obtaining the coordinate values of the two end points of the UI characteristic curve and the slope of each sub-curve, the method and the device need to obtain the coordinate value of the intersection point of the adjacent sub-curves to finally obtain the complete UI characteristic curve. Therefore, the present application sets in advance a voltage-current relational expression in which the known quantity is a coordinate value of two end points of the UI characteristic curve, a slope of each sub-curve, and the unknown quantity is a coordinate value of an intersection point of adjacent sub-curves, and then after obtaining the known quantity of the voltage-current relational expression, the present application can substitute the known quantity into the voltage-current relational expression to obtain the unknown quantity of the voltage-current relational expression: the coordinate values of the intersection points of the adjacent sub-curves can obtain a complete UI characteristic curve (since the UI characteristic curve includes different slopes, it can be called as a UI variable slope characteristic curve).
Step S4: and in the working process of the system, when the actual direct current voltage of the system is smaller than the starting voltage, limiting the direct current instruction of the system according to the UI characteristic curve with the variable slope.
Specifically, in the working process of the system, the actual direct current voltage of the system is detected in real time and is compared with the starting voltage of the system, when the actual direct current voltage of the system is smaller than the starting voltage of the system, the system can be protected according to the improved low-voltage current-limiting control, namely, a direct current instruction corresponding to the actual direct current voltage of the system is obtained according to the UI variable slope characteristic curve, and the direct current of the system is controlled according to the direct current instruction, so that the current-limiting effect is achieved.
The invention provides a low-voltage current limiting control method for high-voltage direct-current transmission, which comprises the following steps: determining the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of a system in advance according to the working parameters of the high-voltage direct-current transmission system; dividing a UI characteristic curve which takes the starting voltage and the maximum allowable current as one endpoint and takes the minimum allowable voltage and the minimum allowable current as the other endpoint into N sections of sub-curves, and setting the slope of each section of sub-curve; wherein the slope of the sub-curve corresponding to the larger direct current voltage is greater than the slope of the sub-curve corresponding to the smaller direct current voltage; substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to obtain the coordinate value of the intersection point of the adjacent sub-curves so as to finally obtain a variable-slope UI characteristic curve; and in the working process of the system, when the actual direct current voltage of the system is smaller than the starting voltage, limiting the direct current instruction of the system according to the UI characteristic curve with the variable slope.
It can be seen that the UI characteristic curve of the present application includes N sub-curves having different slopes (the slope of the sub-curve corresponding to a larger dc voltage is larger). That is, when the dc voltage of the system is at a lower level, the system can provide less reactive power, and the dc current of the system should increase at a slower speed, so as to reduce the reactive power consumption during phase change and promote the recovery of the phase change voltage compared with the prior art; when the direct current voltage of the system reaches a higher level, the reactive power provided by the system is more, and the direct current of the system is increased at a higher speed, so that the recovery of the transmission power of the system is promoted, the condition that the system fails in continuous phase change is avoided, and the system is ensured to recover normal operation quickly.
On the basis of the above-described embodiment:
as an alternative embodiment, the predetermined voltage-current relationship comprises a current coordinate solving relationship
And the voltage coordinate to obtain the relation
Wherein, I1To the maximum allowable current, IN+11 < I < N +1 and I is an integer, IiIs the current value corresponding to the intersection point of the i-1 th sub-curve and the i-th sub-curve, UiIs the voltage value corresponding to the intersection point of the i-1 th sub-curve and the i-th sub-curve, KiThe slope of the ith sub-curve is shown.
Specifically, referring to fig. 4, fig. 4 is a slope characteristic curve of the low-voltage current-limiting control UI according to an embodiment of the present invention. Fig. 4 shows an example of the division of the UI characteristic into 6-segment sub-curves (N ═ 6), where in fig. 4, I1To the maximum allowable current, IN+1To a minimum allowable current, U1To the maximum allowable voltage, UN+1To a minimum allowable voltage, IiRepresenting the current values corresponding to the intersections of adjacent sub-curves.
The present application relates to coordinates (U)1，I1) And coordinates (U)2，I2) The sub-curve between the two is called the sub-curve of the 1 st segment, and the slope of the sub-curve of the 1 st segment is called K1By analogy, coordinate (U)i，Ii) And coordinates (U)i+1，Ii+1) The sub-curve between the segments is called the i-th sub-curve, the slope of the i-th sub-curve is called KiThen, IiA current value, U, corresponding to the intersection of the i-1 th sub-curve and the i-th sub-curveiIs the i-1 th sub-curve and the i-th sub-curveThe voltage value corresponding to the intersection point of (a).
Based on this, the voltage-current relation of the present application can be set as: current coordinate solving relation
And the voltage coordinate to obtain the relation
As can be seen, the coordinate values (including I) at the two end points of the UI characteristic curve are known1、IN+1) Then, the current value I corresponding to the intersection point of the adjacent sub-curves can be obtained according to the current coordinate obtaining relational expressioni. The current value I corresponding to the intersection point of the slope of each section of the sub-curve and the adjacent sub-curve is obtainediThen, the voltage value U corresponding to the intersection point of the adjacent sub-curves can be obtained according to the voltage coordinate obtaining relational expressioniAnd thus, a complete UI variable slope characteristic curve is obtained.
As an optional embodiment, after obtaining the coordinate value of the intersection point of the adjacent sub-curves, before finally obtaining the UI characteristic curve with a varying slope, the low-voltage current limiting control method further includes:
performing iterative computation on the intersection point coordinate value by using a preset iterative algorithm to obtain an optimal intersection point coordinate value;
and finally obtaining a variable-slope UI characteristic curve, wherein the variable-slope UI characteristic curve comprises the following steps:
and obtaining a UI characteristic curve with a variable slope according to the coordinate values of the two end points and the optimal intersection point coordinate value.
Further, considering that the intersection coordinate values of the adjacent sub-curves obtained by using the voltage-current relational expression are not optimal values, the application optimizes the intersection coordinate values by using an iterative algorithm, and specifically, the intersection coordinate values can be iteratively calculated by using matlab, so that the optimal intersection coordinate values are obtained.
Correspondingly, the final UI variable slope characteristic curve is obtained based on the optimal intersection point coordinate value, so that the system is protected in a more optimal low-voltage current limiting control mode.
As an optional embodiment, the low voltage current limiting control method further comprises:
when the actual direct current voltage of the system is smaller than the starting voltage, the control prompting device sends out prompting information indicating that the system enters low-voltage current-limiting control.
Further, it is known that when the actual dc voltage of the system is less than the starting voltage, the system enters low voltage current limit control. Therefore, when the actual direct current voltage of the system is smaller than the starting voltage, the control prompting device sends out prompting information indicating that the system enters the low-voltage current-limiting control, and therefore relevant personnel can know whether the system enters the low-voltage current-limiting control or not through checking the prompting information of the prompting device.
As an optional embodiment, the prompting device is specifically an indicator light or a buzzer.
Specifically, the prompting device of the present application may be selected from, but not limited to, an indicator light (the on/off state of the indicator light or the color of the light may be used to indicate that the system enters the low-voltage current limiting control) or a buzzer (the buzzer may be used to indicate that the system enters the low-voltage current limiting control), and the present application is not particularly limited herein.
As an alternative embodiment, the rated voltage of the 0.7 × system is less than or equal to the starting voltage is less than or equal to 0.9 × rated voltage, the 0.1 × rated voltage is less than or equal to the minimum allowable voltage is less than or equal to 0.2 × rated voltage, the rated current of the 0.1 × system is less than or equal to the minimum allowable current is less than or equal to 0.2 × rated current, and the maximum allowable current is equal to the rated current.
Specifically, according to engineering experience, the starting voltage of the system is usually set to be 0.7-0.9 times of the rated voltage of the system; the minimum allowable voltage of the system is required to be larger than the minimum voltage of the system, and the minimum allowable voltage of the system is usually set to be between 0.1 and 0.2 times of the rated voltage of the system; the maximum allowable current of the system is usually set equal to the rated current of the system; similarly, the minimum allowable current of the system needs to be larger than the minimum current of the system, which is usually set between 0.1 and 0.2 times of the rated current of the system.
As an alternative embodiment, N-6.
Specifically, the more the number of sub-curves divided by the UI characteristic curve of the present application is, the higher the system performance is, but the more complicated the corresponding algorithm is, so that the present application comprehensively considers the two factors to divide the UI characteristic curve into 6 segments of sub-curves. Of course, the number of divisions of the UI characteristic curve of the present application may also be other values, and the present application is not particularly limited herein and depends on the actual situation.
As an alternative embodiment, the process of limiting the dc current command of the system according to the UI characteristic curve with variable slope includes:
obtaining a direct current instruction relational expression according to the UI characteristic curve of the variable slope
Wherein, IordFor system DC current command, UDCIs the system direct current voltage;
and substituting the actual direct current voltage into the corresponding direct current instruction relational expression to obtain a direct current instruction of the system so as to control the direct current of the system according to the direct current instruction.
Specifically, knowing coordinate values of two end points of each sub-curve in the UI variable slope characteristic curve, when the system DC voltage U is obtainedDCWhen any section of sub-curve is adopted, the system direct current voltage U can be obtained according to the principle that the slopes of the same sub-curve are equalDCCorresponding direct current instruction Iord。
Suppose that the coordinates of two end points of the nth sub-curve are (U)n，In)、(Un+1，In+1) When the system DC voltage UDCWhen on the nth sub-curve, the relation can be obtained according to the principle that the slopes of the same sub-curve are equal:
thereby obtaining a DC current instruction relation for the deformation of the DC current instruction
Based on the direct current command, the detected actual direct current voltage is substituted into the corresponding direct current command relational expression to obtain the direct current command of the system, and then the direct current command is obtainedAnd controls the direct current of the system according to the direct current command. Specifically, the operation principle of the dc current command in the controller is shown in fig. 5. In FIG. 5, UDC_invFor inverting the side DC bus voltage, UDCFor compensating the post-bus voltage at the starting point, Iord_recFor rectifying the side current command, Iord_invFor inverting side current command, Id_recFor rectifying the side actual current, Id_invFor inverting the actual current on the side e_recFor rectifying the side current error signal, e_invFor inverting the side current error signal, e_γTo turn off the angle error signal, betarecFor commutation side lead angle command, betainvFor inverting side lead angle commands, alpharecFor rectifying side retardation, αinvIs the inverse side delay angle, Delta I is the offset current, Delta gamma is the offset turn-off angle, gamma_ordFor inverting side turn-off angle commands, gamma_invIs the minimum value of the periodic turn-off angle on the inverting side, betainv_γAdvance angle command, beta, for inverter side fixed turn-off angle controlinv-iThe lead angle command is the lead angle command of the current control of the inversion side. Finally, the controller will αrecAnd alphainvThe signals are respectively input to the pulse generating units on the rectifying side and the inverting side, so that the pulse generating units generate corresponding control signals.
In addition, the parameters (direct current, direct current voltage and turn-off angle) of the receiving end three-phase ground fault by using the traditional low-voltage current limiting control and the improved low-voltage current limiting control can be simulated respectively to obtain simulation graphs as shown in fig. 6(a) -7 (c), and therefore the improved low-voltage current limiting control is better in performance by analyzing comparison graphs of the traditional low-voltage current limiting control and the improved low-voltage current limiting control.
Referring to fig. 8, fig. 8 is a schematic structural diagram of a low-voltage current-limiting control system for high-voltage dc transmission according to an embodiment of the present invention.
This high voltage direct current transmission's low pressure current-limiting control system includes:
the end point determining module 1 is used for determining the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of the system in advance according to the working parameters of the high-voltage direct-current transmission system;
a curve setting module 2, configured to divide a UI characteristic curve, which takes the start voltage and the maximum allowable current as one endpoint and takes the minimum allowable voltage and the minimum allowable current as another endpoint, into N segments of sub-curves, and set a slope of each segment of the sub-curve; wherein the slope of the sub-curve corresponding to the larger direct current voltage is greater than the slope of the sub-curve corresponding to the smaller direct current voltage; n is an integer greater than 1;
the curve acquisition module 3 is used for substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to acquire the coordinate value of the intersection point of the adjacent sub-curves so as to finally obtain the UI characteristic curve with variable slope;
and the current limiting control module 4 is used for limiting a direct current instruction of the system according to the UI characteristic curve with variable slope when the actual direct current voltage of the system is smaller than the starting voltage in the system working process.
For the introduction of the low voltage current limiting control system provided by the present invention, reference is made to the above-mentioned embodiment of the low voltage current limiting control method, which is not described herein again.
The invention also provides a low-voltage current-limiting control device for high-voltage direct-current transmission, which comprises:
a memory for storing a computer program;
and the processor is used for realizing any one of the low-voltage current limiting control methods for high-voltage direct-current transmission when executing the computer program.
For the introduction of the low voltage current limiting control device provided by the present invention, reference is made to the above-mentioned embodiment of the low voltage current limiting control method, which is not described herein again.
It should also be noted that, in the present specification, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. A low-voltage current limiting control method for high-voltage direct-current transmission is characterized by comprising the following steps:
determining the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of a system in advance according to the working parameters of the high-voltage direct-current transmission system;
dividing a UI characteristic curve which takes the starting voltage and the maximum allowable current as one endpoint and takes the minimum allowable voltage and the minimum allowable current as the other endpoint into N sections of sub-curves, and setting the slope of each section of sub-curve; wherein the slope of the sub-curve corresponding to the larger direct current voltage is greater than the slope of the sub-curve corresponding to the smaller direct current voltage; n is an integer greater than 1;
substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to obtain the coordinate value of the intersection point of the adjacent sub-curves so as to obtain a UI characteristic curve with a variable slope;
in the working process of the system, when the actual direct current voltage of the system is smaller than the starting voltage, limiting a direct current instruction of the system according to the UI characteristic curve with the variable slope;
the process of limiting the direct current instruction of the system according to the UI characteristic curve with the variable slope includes:
obtaining a direct current instruction relational expression according to the UI characteristic curve with variable slope
Un+1≤UDC≤UnN is more than or equal to 1 and less than or equal to N; wherein, IordFor system DC current command, UDCIs the system direct current voltage;
and substituting the actual direct current voltage into a corresponding direct current instruction relational expression to obtain a direct current instruction of the system so as to control the direct current of the system according to the direct current instruction.
2. The method of claim 1 in which the predetermined voltage-to-current relationship comprises a current coordinate solving relationship
And the voltage coordinate to obtain the relation
Wherein, I1Is the maximum allowable current, IN+11 < I < N +1 and I is an integer, IiIs the current value corresponding to the intersection point of the i-1 th sub-curve and the i-th sub-curve, UiIs the voltage value corresponding to the intersection point of the i-1 th sub-curve and the i-th sub-curve, KiThe slope of the ith sub-curve is shown.
3. The low voltage current limiting control method for hvdc transmission according to claim 2, further comprising, after obtaining the intersection coordinate values of the adjacent sub-curves and before finally obtaining the UI characteristic curve with a variable slope, the step of:
performing iterative computation on the intersection point coordinate value by using a preset iterative algorithm to obtain an optimal intersection point coordinate value;
the process of finally obtaining the UI characteristic curve with a variable slope includes:
and obtaining a UI characteristic curve with a variable slope according to the coordinate values of the two end points and the optimal intersection point coordinate value.
4. The low voltage current limiting control method of hvdc transmission according to claim 3, further comprising:
and when the actual direct current voltage of the system is less than the starting voltage, controlling a prompting device to send out prompting information indicating that the system enters low-voltage current-limiting control.
5. The low-voltage current-limiting control method for high-voltage direct current transmission according to claim 4, characterized in that the prompting device is specifically an indicator lamp or a buzzer.
6. The method of claim 3, wherein 0.7 times the rated voltage of the system is less than or equal to 0.9 times the rated voltage, 0.1 times the rated voltage is less than or equal to 0.2 times the rated voltage, 0.1 times the rated current of the system is less than or equal to 0.2 times the rated current, and the maximum allowable current is equal to the rated current.
7. The method of claim 6 in which N is 6.
8. A low voltage current limiting control system for high voltage direct current transmission, comprising:
the end point determining module is used for determining the starting voltage, the minimum allowable voltage, the maximum allowable current and the minimum allowable current of the system in advance according to the working parameters of the high-voltage direct-current power transmission system;
a curve setting module, configured to divide a UI characteristic curve, which takes the starting voltage and the maximum allowable current as one endpoint and the minimum allowable voltage and the minimum allowable current as another endpoint, into N segments of sub-curves, and set a slope of each segment of sub-curve; wherein the slope of the sub-curve corresponding to the larger direct current voltage is greater than the slope of the sub-curve corresponding to the smaller direct current voltage; n is an integer greater than 1;
the curve acquisition module is used for substituting the coordinate values of the two end points and the slope of each section of the sub-curve into a preset voltage-current relation to acquire the coordinate value of the intersection point of the adjacent sub-curves so as to obtain a variable-slope UI characteristic curve;
the current limiting control module is used for limiting a direct current instruction of the system according to the UI characteristic curve with variable slope when the actual direct current voltage of the system is smaller than the starting voltage in the working process of the system;
the process of limiting the direct current instruction of the system according to the UI characteristic curve with the variable slope includes:
obtaining a direct current instruction relational expression according to the UI characteristic curve of the variable slope
Un+1≤UDC≤UnN is more than or equal to 1 and less than or equal to N; wherein, IordFor system DC current command, UDCIs the system direct current voltage;
and substituting the actual direct current voltage into a corresponding direct current instruction relational expression to obtain a direct current instruction of the system so as to control the direct current of the system according to the direct current instruction.
9. A low voltage current limiting control apparatus for high voltage direct current transmission, comprising:
a memory for storing a computer program;
processor for implementing the low voltage current limiting control method for high voltage direct current transmission according to any of claims 1-7 when executing the computer program.
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| DE102005024068A1 (en) * | 2005-05-25 | 2006-11-30 | Robert Bosch Gmbh | Method for controlling an electric motor fed from a DC voltage network |
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