Disclosure of Invention
The invention aims to provide a multi-section power flow control method suitable for a double-circuit line of a unified power flow controller, which is used for filling the blank of the field of double-circuit line section power flow control. Meanwhile, the invention also provides a double-circuit line unified power flow controller.
In order to achieve the above object, the scheme of the invention comprises:
the multi-section power flow control method of the double-circuit line unified power flow controller comprises the following steps: monitoring the transmission power of at least two distal sections and one proximal section simultaneously; for any loop: if any far-end section power is out of limit, the unified power flow controller is enabled to increase the transmission power; and if the power of the near-end section is out of limit, reducing the transmission power of the unified power flow controller.
Further, the following three control quantities are superposed and then used as a final required reference value of one line in the double-circuit line, namely a control reference value of a corresponding UPFC series side converter, and the three control quantities are as follows: the total control quantity of the far-end section, the total control quantity of the near-end section and the corresponding power set value of the controlled line.
Further, the number of the far-end sections is N, and the total control quantity of the total far-end sections is as follows: summing the output of the first far-end section power flow PI controller and the output of the first far-end single-circuit power PI controller, summing the output of the Nth far-end section power flow PI controller and the output of the Nth far-end single-circuit power PI controller, and negating the sum;
for a remote section, the remote section flow PI controller adjusts the difference value of a section flow set value P1_ set and an actually measured value P1_ mean, namely P1_ set-P1_ mean, as the input of the PI controller, the upper limit of the PI controller is set to be 0, and the lower limit is set to be the transmission power limit of a corresponding controlled line in the UPFC system; the remote single-circuit line power PI controller takes the minimum value of the difference value between the corresponding line power set value and the measured value as input, the upper limit of the PI regulator is set to be 0, and the lower limit is set to be the transmission power limit value of the corresponding controlled line in the negative UPFC system;
the total control quantity of the near-end section is as follows: the sum of the output of the near-end section power flow PI controller and the output of the near-end single-circuit line power PI controller;
the near-end section power flow PI controller adjusts the difference value between a section power flow set value PJ2_ set and an actually measured value PJ2_ mean, namely PJ2_ set-PJ2_ mean, as the input of the PI controller, the upper limit of the PI controller is set to be 0, and the lower limit of the PI controller is set to be the transmission power limit value of a corresponding controlled line in a negative UPFC system; the near-end single-circuit line power PI controller takes the minimum value of the difference value between the set value and the measured value of the corresponding line power as input, the upper limit of the PI regulator is set to be 0, and the lower limit is set to be the transmission power limit value of the corresponding controlled line in the negative UPFC system.
The invention also provides a double-circuit line unified power flow controller, which comprises the following modules: means for monitoring the delivered power of the distal and proximal sections simultaneously; for any loop: a module for increasing the transmission power of the unified power flow controller when the power of any far-end section is out of limit; and the module is used for reducing the transmission power of the unified power flow controller when the power of the near-end section is out of limit.
Further, the following three control quantities are superposed and then used as a final required reference value of one line in the double-circuit line, namely a control reference value of a corresponding UPFC series side converter, and the three control quantities are as follows: the total control quantity of the far-end section, the total control quantity of the near-end section and the corresponding power set value of the controlled line.
Further, the number of the far-end sections is N, and the total control quantity of the total far-end sections is as follows: summing the output of the first far-end section power flow PI controller and the output of the first far-end single-circuit power PI controller, summing the output of the Nth far-end section power flow PI controller and the output of the Nth far-end single-circuit power PI controller, and negating the sum;
for a remote section, the remote section flow PI controller adjusts the difference value of a section flow set value P1_ set and an actually measured value P1_ mean, namely P1_ set-P1_ mean, as the input of the PI controller, the upper limit of the PI controller is set to be 0, and the lower limit is set to be the transmission power limit of a corresponding controlled line in the UPFC system; the remote single-circuit line power PI controller takes the minimum value of the difference value between the corresponding line power set value and the measured value as input, the upper limit of the PI regulator is set to be 0, and the lower limit is set to be the transmission power limit value of the corresponding controlled line in the negative UPFC system;
the total control quantity of the near-end section is as follows: the sum of the output of the near-end section power flow PI controller and the output of the near-end single-circuit line power PI controller;
the near-end section power flow PI controller adjusts the difference value between a section power flow set value PJ2_ set and an actually measured value PJ2_ mean, namely PJ2_ set-PJ2_ mean, as the input of the PI controller, the upper limit of the PI controller is set to be 0, and the lower limit of the PI controller is set to be the transmission power limit value of a corresponding controlled line in a negative UPFC system; the near-end single-circuit line power PI controller takes the minimum value of the difference value between the set value and the measured value of the corresponding line power as input, the upper limit of the PI regulator is set to be 0, and the lower limit is set to be the transmission power limit value of the corresponding controlled line in the negative UPFC system.
The method is simple and practical and has high reliability, and can simultaneously monitor and control the power of a plurality of far-end and near-end sections and lines so as to ensure that the transmission power of the lines is not out of limit, and effectively inhibit the tidal current imbalance of the near-end and far-end sections so as to realize the maximum utility of the UPFC-MMC system.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings.
Fig. 1 shows a basic structure of the unified power flow controller applied to a double-circuit line: the parallel side is connected with an alternating current bus, the series side comprises two groups of current converters, and the two groups of current converters on the series side are respectively connected with one of the double-circuit lines.
Regarding the structure in which the unified power flow controller is applied to the double-circuit line, other structures described in "unified power flow controller system structure optimization analysis for double-circuit line" (period 21 in 2015 for power system automation) may also be adopted. The unified power flow controller can adopt a modular multilevel technology-based unified power flow controller MMC-UPFC or a three-phase full-bridge UPFC.
As shown in FIG. 1, the system includes two or more distal sections and one proximal section. The near-end section and the far-end section are based on a line where the unified power flow controller is located.
The basic scheme of the invention is as follows: the unified power flow controller simultaneously monitors the transmission power of the far-end section and the near-end section, and if the power of the far-end section is out of limit, the unified power flow controller increases the transmission power; if the power of the near-end section is out of limit, the unified power flow controller is enabled to reduce the transmission power; wherein, the control mode of the double-circuit line is the same.
According to the above basic scheme, a specific embodiment is given below.
Taking the structure shown in fig. 1 as an example, the unified power flow controller monitors and controls the power of the far-end and near-end sections and lines simultaneously. The series-side converter 1 is connected with a controlled line 1, and the series-side converter 2 is connected with a controlled line 2; the proximal section includes a transmission line 1 and a transmission line 2, and each distal section includes a transmission line 1 and a transmission line 2. The number of distal sections is N.
In the multi-section power flow control in the embodiment, a schematic block diagram of the section power flow control of the controlled line 1 is shown in fig. 2, and a schematic block diagram of the section power flow control of the controlled line 2 is shown in fig. 3.
The section flow control principle of the controlled line 1 and the controlled line 2 is the same, as shown in fig. 2, the section flow control of the controlled line 1:
the first remote profile flow PI controller regulates the difference between the profile flow setpoint PR1_ set and the measured value PR1_ mean, i.e., PR1_ set-PR1_ mean, as an input to the PI controller, the upper limit of which is set to 0 and the lower limit to the transmission power limit of the controlled line 1 in the negative UPFC system, i.e., -PL1_ max.
The remote single-circuit line power PI controller of the first remote section takes the minimum value of the difference value between the corresponding line power set value and the measured value as input,
i.e., min (PLR11_ set-PLR11_ mean, PLR12_ set-PLR12_ mean) is regulated as an input to a PI controller whose upper limit is set to 0 and lower limit is set to the transmission power limit of the controlled line 1 in the negative UPFC system, i.e., -PL1_ max.
The second distal cross-section, the third distal cross-section … …, the nth distal cross-section is similar to the first distal cross-section. As shown in fig. 2: and the Nth remote section flow PI controller adjusts the difference value of the section flow set value RPN _ set and the actually measured value PRN _ mean, namely PRN _ set-PRN _ mean, as the input of the PI controller, the upper limit of the PI controller is set to be 0, and the lower limit of the PI controller is set to be the transmission power limit value of the controlled line 1 in the UPFC system, namely-PL 1_ max.
The remote single-circuit line power PI controller of the Nth remote cross section takes the minimum value of the difference value between the corresponding line power set value and the measured value as input,
i.e., min (PLRN1_ set-PLRN1_ mean, PLRN2_ set-PLRN2_ mean) is regulated as an input to a PI controller whose upper limit is set to 0 and lower limit is set to the negative transmission power limit of the controlled line 1 in the UPFC system, i.e., -PL1_ max.
Similarly, the near-end section flow PI controller regulates the difference value between the section flow set value PJ2_ set and the actually measured value PJ2_ mean, namely PJ2_ set-PJ2_ mean, as the input of the PI controller, the upper limit of the PI controller is set to 0, and the lower limit is set to the transmission power limit value of the controlled line 1 in the negative UPFC system, namely-PL 1_ max.
The near-end single-loop line power PI controller takes the minimum value of the difference value between the corresponding line power set value and the actually measured value as an input, namely min (PLN1_ set-PLN1_ mean, PLN2_ set-PLN2_ mean) is used as the input of the PI controller for regulation, the upper limit of the PI regulator is set to be 0, and the lower limit is set to be the transmission power limit value of the controlled line 1 in the negative UPFC system, namely-PL 1_ max.
The following three control quantities are added as the final required reference value PCL1_ ref of the controlled line 1, i.e. the control reference value of the UPFC series-side converter, and are:
the number of the far-end sections is N, the sum of the output of the first far-end section power flow PI controller and the output of the first far-end single-circuit power PI controller is obtained, the sum of the output of the Nth far-end section power flow PI controller and the output of the Nth far-end single-circuit power PI controller is obtained, and the sum is obtained after summation; the sum of the output of the near-end section power flow PI controller and the output of the near-end single-circuit line power PI controller; controlled line 1 sets value PCL1_ set.
As shown in fig. 3, the cross-sectional power flow control of the controlled line 2 is similar to that of the controlled line 1:
the first remote profile flow PI controller regulates the difference between the profile flow setpoint PR1_ set and the measured value PR1_ mean, i.e., PR1_ set-PR1_ mean, as an input to the PI controller, the upper limit of which is set to 0 and the lower limit to the transmission power limit of the controlled line 1 in the negative UPFC system, i.e., -PL2_ max.
The remote single-circuit line power PI controller of the first remote section takes the minimum value of the difference value between the corresponding line power set value and the measured value as input,
i.e., min (PLR11_ set-PLR11_ mean, PLR12_ set-PLR12_ mean) is regulated as an input to a PI controller whose upper limit is set to 0 and lower limit is set to the transmission power limit of the controlled line 1 in the negative UPFC system, i.e., -PL2_ max.
The second distal cross-section, the third distal cross-section … …, the nth distal cross-section is similar to the first distal cross-section. As shown in fig. 2: and the Nth remote section flow PI controller adjusts the difference value of the section flow set value RPN _ set and the actually measured value PRN _ mean, namely PRN _ set-PRN _ mean, as the input of the PI controller, the upper limit of the PI controller is set to be 0, and the lower limit of the PI controller is set to be the transmission power limit value of the controlled line 1 in the UPFC system, namely-PL 2_ max.
The remote single-circuit line power PI controller of the Nth remote cross section takes the minimum value of the difference value between the corresponding line power set value and the measured value as input,
i.e., min (PLRN1_ set-PLRN1_ mean, PLRN2_ set-PLRN2_ mean) is regulated as an input to a PI controller whose upper limit is set to 0 and lower limit is set to the negative transmission power limit of the controlled line 1 in the UPFC system, i.e., -PL2_ max.
Similarly, the near-end section flow PI controller regulates the difference value between the section flow set value PJ2_ set and the actually measured value PJ2_ mean, namely PJ2_ set-PJ2_ mean, as the input of the PI controller, the upper limit of the PI controller is set to 0, and the lower limit is set to the transmission power limit value of the controlled line 1 in the negative UPFC system, namely-PL 2_ max.
The near-end single-loop line power PI controller takes the minimum value of the difference value between the corresponding line power set value and the actually measured value as an input, namely min (PLN1_ set-PLN1_ mean, PLN2_ set-PLN2_ mean) is used as the input of the PI controller for regulation, the upper limit of the PI regulator is set to be 0, and the lower limit is set to be the transmission power limit value of the controlled line 1 in the negative UPFC system, namely-PL 2_ max.
The following three control quantities are added as the final required reference value PCL2_ ref of the controlled line 1, i.e. the control reference value of the UPFC series-side converter, and are:
the number of the far-end sections is N, the sum of the output of the first far-end section power flow PI controller and the output of the first far-end single-circuit power PI controller is obtained, the sum of the output of the Nth far-end section power flow PI controller and the output of the Nth far-end single-circuit power PI controller is obtained, and the sum is obtained after summation; the sum of the output of the near-end section power flow PI controller and the output of the near-end single-circuit line power PI controller; controlled line 1 sets value PCL1_ set.
As another embodiment, the PI controllers in the control structure diagrams of fig. 2 and 3 may be adjusted according to the method of fig. 4.
In the above embodiments, the meaning of the minimum function min adopted for the power control of the near-end and far-end lines is that; (taking the near end as an example), when PLN1_ set-PLN1_ mean is a positive number, it indicates that the given value of the near-end line 1 is greater than the measured value, at this time, the line is not overloaded, and the PI controller is not required to function, so the PI controller is required to be limited to 0; when PLN1_ set-PLN1_ mean is a negative number, the given value of the near-end line 1 is smaller than the measured value, at the moment, the line is overloaded, the PI controller is required to act, the output power of the line 1 is reduced, and therefore the PI controller is required to output a negative value; since the PI controller is active when PLN1_ set-PLN1_ mean or PLN2_ set-PLN2_ mean is negative, a small negative value indicates that the overload is more severe, and the UPFC cannot separately control near-end line 1 and line 2, so using min to select the input of the PI controller is preferred.
In the above embodiment, the three control quantities are superposed to be used as the final required reference value of the controlled line, i.e. the control reference value of the UPFC series-side converter. The three control quantities are actually: the total control quantity of the far-end section, the total control quantity of the near-end section and the corresponding power set value of the controlled line. As another implementation, a specific form of the total control quantity of the far end and the entering end given in the above embodiments may also adopt different forms of line and power flow calculation.
The embodiment of the double-circuit line unified power flow controller comprises the following modules: means for monitoring the delivered power of the distal and proximal sections simultaneously; for any loop: a module for increasing the transmission power of the unified power flow controller when the power of any far-end section is out of limit; and the module is used for reducing the transmission power of the unified power flow controller when the power of the near-end section is out of limit.
The above module, in effect, is a software process programmed according to the above section flow control method, corresponding to the method steps. Therefore, it will not be described in detail below.
The present invention has been described in relation to particular embodiments thereof, but the invention is not limited to the described embodiments. In the thought given by the present invention, the technical means in the above embodiments are changed, replaced, modified in a manner that is easily imaginable to those skilled in the art, and the functions are basically the same as the corresponding technical means in the present invention, and the purpose of the invention is basically the same, so that the technical scheme formed by fine tuning the above embodiments still falls into the protection scope of the present invention.