CN115579894B - Distributed power flow controller coordinated output distribution method for reducing overall loss of device - Google Patents
Distributed power flow controller coordinated output distribution method for reducing overall loss of device Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
- H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
- H02J3/16—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by adjustment of reactive power
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
- H02J3/466—Scheduling the operation of the generators, e.g. connecting or disconnecting generators to meet a given demand
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
- H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/40—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation wherein a plurality of decentralised, dispersed or local energy generation technologies are operated simultaneously
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
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Abstract
The invention discloses a distributed power flow controller coordinated output distribution method for reducing the overall loss of a device. The invention adopts the following steps: judging whether the target value of the power flow regulation active reactive power of the controlled line is within the range of a specified constraint condition, if so, carrying out the next step; if the current exceeds the preset current limit value, the current regulation active reactive power target value of the controlled line is regulated to be within the range of the specified constraint condition; judging whether the active and reactive power flow regulation demand of the controlled line is within the adjustable range of the DPFC multi-unit system, if so, carrying out the next step; if the current is exceeded, readjusting the current regulation demand; and calculating the total required compensation voltage when the DPFC multi-unit system adjusts the active power and the reactive power of the controlled line, and then solving an objective function to obtain a DPFC coordinated output distribution scheme. The invention improves the utilization rate of the device, improves the actual output voltage of the device, improves the use capacity of the device, and reduces the overall loss of the device.
Description
Technical Field
The invention belongs to the technical field of safe and stable operation of smart power grids, and particularly relates to a distributed power flow controller coordinated output distribution method for reducing the overall loss of a device.
Background
The fluctuation and intermittence of the new energy power, the bilateral randomness of the power system containing the new energy power and the limitation of the line conveying capacity can cause overload and bidirectional tide problems of the transmission line. Meanwhile, uncontrolled power flow can cause problems of insufficient power supply in partial areas, large line transmission loss and the like, and even reduce system stability and reliability.
The distributed power flow controller (distributed power flow controller, DPFC) is also called a generalized distributed static series compensator, is a distributed series flexible alternating current transmission device (Distributed Flexible Alternative Current Transmission System, D-FACTS) which performs line compensation by utilizing superposition of low-voltage converter modules, and has low cost, high reliability, small occupied area and strong expandability compared with a centralized device. Therefore, the DPFC will be a further development direction of future flexible alternating current transmission technology, and has wide popularization and application prospect.
Aiming at DPFC multi-unit output coordination control, the methods widely adopted at present are a uniform division method and a proportional method. When the equal division output distribution method is adopted, if the capacities of the subunits are inconsistent, the utilization rate of the subunits with large capacity is low, the regulation and control range of the whole system is limited by the subunits with the smallest capacity, and the economy is low; if a proportional output distribution method is adopted, output distribution is carried out according to the capacity proportion of each subunit, but when the adjustment quantity is smaller, the overall utilization rate of the device is lower, and the loss of the device is large.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a distributed power flow controller coordinated output distribution method for reducing the overall loss of a device, which can flexibly input subunits according to actual working conditions, improve the utilization rate of the device, improve the actual output voltage of the device, improve the use capacity of the device and reduce the overall loss of a DPFC device.
Therefore, the invention adopts the following technical scheme: the distributed power flow controller coordinated output distribution method for reducing the overall loss of the device comprises the following steps:
1) Judging whether target values of the active power and the reactive power of the power flow regulation of the controlled line are within a specified constraint condition range, and if the target values are within the specified constraint condition range, performing the next step; if the current of the controlled line exceeds the range of the specified constraint condition, the current regulating active power and reactive power target values of the controlled line are regulated to be within the range of the specified constraint condition;
2) Judging whether the active and reactive power flow regulation demand of the controlled line is within the adjustable range of the DPFC multi-unit system, and if so, performing the next step; if the adjustable range of the DPFC multi-unit system is exceeded, the flow adjustment demand is readjusted;
3) Calculating the total demand compensation voltage when the DPFC multi-unit system adjusts the active power and the reactive power of the controlled line, and then solving an objective function to obtain a DPFC coordinated output distribution scheme;
4) And finally, issuing a power distribution instruction to each subunit of the DPFC, and adjusting the flow of the controlled line by each subunit of the DPFC according to the instruction.
Further, in step 3), the active power and reactive power flow at the tail end of the controlled line are set as P L 、Q L Then:
in delta sr For the voltage V at the first and the last ends of the line s And V is equal to r A phase difference; v (V) sei Injecting a voltage into the line for the ith DPFC subunit, i=1, 2,3 … n; x and R respectively correspond to equivalent reactance and resistance of the power system serial DPFC branch; v (V) s 、V r The voltages at the first end and the last end of the line are respectively;
when the DPFC multi-unit system adopts an average method, the output of each unit of the DPFC is obtained, namely the voltage V is injected into a line by a subunit i single-phase converter sei The method comprises the following steps:
wherein V is seΣ The voltage is compensated for the total demand.
Further, the overall loss calculation formula of the DPFC multi-unit system is formula (21):
when the DPFC multi-unit system adopts the proportional method, defining the total line installation capacity of the DPFC multi-unit system as S seΣ The rated capacity of the device of the subunit i is S sei A ratio coefficient of a single subunit to the total installed capacity is h i The method comprises the following steps:
the output of each unit of the DPFC is as follows:
the total loss of the DPFC device is then:
further, for actual engineering, considering the failure or the out-of-operation of the line subunit, a subunit operation state variable D is introduced i The following steps are:
according to the above formula, the force output scheme is also changed, and when an average method is adopted, the force output of each subunit is distributed as follows:
the total loss of the DPFC device is:
if a scaling method is adopted, the total capacity of the circuit installation, the scaling coefficient of the capacity and the output of the subunit are all changed, and then the method comprises the following steps:
the total loss of the DPFC device becomes:
definition of the actual use Capacity of the ith DPFC subunit as S sefi The following steps are:
when V is sei When=0, S sefi =0, dpfc subunit utilization is 0%.
Further, the search for an optimal solution from a plurality of constraints is a multi-objective optimization problem, based on which there are:
in equation (34), F (x) is a multiple objective function, F i (x) Is a sub-objective function corresponding to each constraint condition, x is an independent variable needing to be optimally designed, g j (x) Is a constraint condition of inequality of multiple objective functions, h k (x) Is a constraint of multiple objective function equation, j max 、k max The number of inequality constraints and equality constraints, respectively.
Further, in order to ensure that the DPFC subunit is normally put into operation in the line, the following specified constraint conditions are set:
line-controlled DPFC total demand compensation voltage constraint, i.e. DPFC subunit i output voltage V sei Sum and total system demand voltage V seΣ Equal:
line tide constraint:
P L,min ≤P L,ref ≤P L,max (36)
Q L,min ≤Q L,ref ≤Q L,max (37)
I L,min ≤I L ≤I L,max (38)
P L,ref active power of the controlled circuit; q (Q) L,ref Reactive power of the controlled line; i L The current of the controlled line; p (P) L,min 、P L,max And Q L,min 、Q L,max The upper limit and the lower limit of active power and reactive power of the controlled line are respectively corresponding; i L,min And I L,max The upper limit and the lower limit of the current of the controlled circuit are respectively corresponding;
device force constraints for each subunit of DPFC:
V r,i the output voltage is rated for DPFC subunit i, i=1, 2,. -%, n; k is an efficiency constraint coefficient; s is S sefi The actual capacity for DPFC subunit i; s is S sei Rated capacity for DPFC subunit i;
transformer voltage constraints:
V sei ≤V semaxi (40)
V semaxi injecting a voltage maximum value into the power transmission line allowed by the DPFC subunit i;
transformer capacity constraint:
S sefi ≤S TNi (41)
S TNi the power rating of the single-turn coupling transformer between the DPFC subunit i and the power transmission line is realized.
Further, in the device output constraint of each DPFC subunit, the output voltage and the used capacity of each DPFC subunit must not be less than 80% of the rated output voltage and the rated capacity, i.e. the efficiency constraint coefficient k takes 0.8.
Further, the power flow regulation and control task of the controlled line is completed while the DPFC subunit loss is effectively reduced, and the error square sum of the real power value of the controlled line and a given reference value P is introduced Lref -P L || 2 ,P Lref Giving a reference value for the active power of a controlled line, P L Real-time value of active power for the controlled line; defining the variable function of the number of input units as A (m 1 ) Wherein m is 1 Is the number of DPFC subunits, and a coordinated optimization function w (u) is introduced according to the operation constraint condition of the DPFC multi-unit system i ),u i Representing the control quantity of the output voltage of the ith subunit, the optimization function of the control system is:
J i =||P Lref -P L || 2 +w(u i )+A(m 1 ),i=1,...,λ (42)
wherein lambda represents the number of DPFC subunits put into operation;
the control system is a system for calculating and converting a power flow regulation target of a system layer, distributing output of each DPFC subunit and finally controlling on-off of each subunit switch to realize target voltage output;
wherein the coordination optimization function w (u i ) The equation is satisfied:
w(u i )=K(u i )+V(u i )+C(u i ) (43)
K(u i ) For DPFC subunit i, V (u) i )、C(u i ) Output voltages and use capacity assessment functions for the corresponding DPFC subunit i, respectively, and have:
wherein V is sei Outputting voltage for DPFC subunit i; v (V) r,i Rated output voltage for DPFC subunit i; s is S sefi The actual capacity for DPFC subunit i; s is S sei Rated capacity for DPFC subunit i;
by Lagrangian method for w (u) i ) The function is constructed:
wherein H (u) i )、G(u i ) Equality and inequality constraints for DPFC multi-unit system operation;G、respectively representing the upper and lower limits of each inequality condition; in meeting the requirement of the flow regulation of the controlled lineAnd establishing a global objective function under the condition of the node requirement:
find J min Corresponding control quantity u min The obtained control quantity result directly acts on the input of the DPFC multi-unit system to the line.
Further, the loss of the insulated gate bipolar transistor is directly related to the switching state of the insulated gate bipolar transistor by analyzing the loss of the converter, including the switching loss P s And working loss P w The method comprises the steps of carrying out a first treatment on the surface of the Wherein the switching loss is classified as an on loss P according to the switching action of the transistor s-on And turn-off loss P s-off Two, there are insulated gate bipolar transistor switching loss expressions:
P s =P s-on +P s-off (1)
wherein V is dc Is the capacitance voltage f of the DPFC single-phase converter s The carrier frequency is T, and the period of PWM modulated waves is T; r is R gon And R is R goff The on and off resistances of the gate electrode of the insulated gate bipolar transistor are respectively in an actual working state; e (R) gon )、E(R goff ) The losses generated in the turn-on and turn-off processes of the transistor by the IGBT gate resistance under the rated current condition are respectively; k (k) on For the transistor on loss coefficient, k off Is the turn-off loss coefficient of a transistor, S i1 (t i )、S i2 (t i ) The switching functions corresponding to the on and off of the IGBT switch are respectively realized, dead zones are not considered, and the specific form is as follows:
under the rated current condition, the energy consumption generated by the gate resistance of the IGBT switch in the switching-on and switching-off process is E (R gon_t )、E(R goff_t ) The method comprises the steps of carrying out a first treatment on the surface of the Definition E on_t 、E off_t The energy consumption generated by single turn-on and turn-off actions of the IGBT switch under the rated current condition is respectively carried out; v (V) t After the IGBT is conducted, the voltage generated between the collector and the emitter has the loss coefficients of on and off:
further, the loss generated by the IGBT in normal operation is:
in the formula (8), V CE (t) is a function of time corresponding to the voltage generated between the collector and the emitter of the transistor; i C (t) is a time function corresponding to the current flowing through the collector of the transistor, D Q (t) is the duty cycle of the transistor at time t;
in the single-phase full-bridge converter, in order to realize the follow current function, a diode and an IGBT are required to be connected in reverse parallel, and in the conducting process of the IGBT, the loss generated by the diode is expressed as:
P D =P on_D +P off_D (9)
P on_D =V F (t)I F (t)D T (10)
in the above, V F (t) is the voltage at two ends of the diode corresponding to the time function, I F (t) is a function of time corresponding to the current flowing through the diode, D T Is the duty cycle of the diode, k Dre For the corresponding loss factor when the diode is turned off, E re (R g ) Reverse recovery of energy consumption for gate resistance E re (t i ) For the diode to correspond to the switching function, V dcse The dc capacitor voltage of the current transformer is represented, and there are:
E re (t i )=S i2 (t i ) (12)
the transformer loss mainly comprises two parts of iron loss and copper loss, wherein the iron loss is calculated by the following formula:
P c =T * λ * Kf α B β (13)
wherein P is c For iron loss, K, alpha, beta are relevant empirical parameters of the iron core, T * Is the temperature coefficient of the iron core lambda * F is the working frequency of the transformer, and B is the magnetic flux density of the iron core;
the copper loss expression is:
wherein I is L The current of the controlled line connected in series for the DPFC is that ρ is the resistivity of the induction coil, L is the length of the induction coil, S coil Is the cross-sectional area of the inductance coil;
the total loss of the transformer is as follows:
P T =P cm +P c (15)
the total loss generated after the DPFC subunit device is put into operation is as follows:
P Z =P s +P w +P D +P T (16)。
the invention has the following beneficial effects: the DPFC subunit coordinated output distribution method provided by the invention can ensure that the DPFC subunit can accurately regulate the line voltage; on the premise of ensuring the working reliability of multiple subunits, compared with the traditional averaging method and the traditional proportional method, the coordinated output distribution control method provided by the invention can flexibly input the subunits according to the actual working conditions, improves the utilization rate of the device, improves the actual output voltage of the device, improves the use capacity of the device, and reduces the overall loss of the DPFC device.
Drawings
FIG. 1 is a diagram of a single subunit architecture of a prior DPFC;
FIG. 2 is a diagram of an equivalent circuit of a prior art DPFC subunit;
FIG. 3 is a diagram of a prior art DPFC multi-unit controlled power source equivalence model;
fig. 4 is a flow chart of a DPFC coordinated output distribution method of the present invention that reduces overall device loss.
Detailed Description
The technical scheme of the invention is further described in detail below with reference to the attached drawings. It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
The invention starts from a DPFC topological structure, analyzes the device loss of the DPFC in detail, considers the device capacity difference and the operation loss difference, and provides a DPFC coordinated output distribution method which can reduce the overall loss of the device and remarkably improve the subunit utilization ratio in two aspects of output voltage and use capacity.
1. DPFC topology and mathematical model
The complete DPFC system is composed of a plurality of DPFC subunits, and the specific structure of the DPFC subunits is shown in fig. 1.
The DPFC subunit consists of a single-phase voltage source converter, a single-turn coupling transformer, a filtering link, a built-in communication module and a controller module. The equivalent circuit model is shown in fig. 2.
In the figure, S A1 ,S A2 ,S B1 ,S B2 L is the switching tube on each bridge arm se R is the filter inductance of the single-phase converter se Is the equivalent resistance of the circuit, C dc Is a direct current capacitor, R loss Representing single-phase converter losses. V (V) se Output voltage of single-phase converter, V 1 Is the ground voltage of the left access point of the serial side, V 2 For the right access point to ground voltage, i R I is the output current of the converter, i is the output current of the DPFC alternating current side after passing through the LC filter circuit, C se Is a filter capacitor.
2. Loss of operation of the line in which the device is located
The DPFC multi-unit system comprises a plurality of DPFC subunits, wherein the output of each DPFC subunit distributed by a distribution controller is different according to different output distribution methods adopted by the DPFC multi-unit system, so that the loss generated by the device is also different when the units regulate the power transmission line according to the obtained output distribution. As known from the DPFC operating principle, the device losses when they are put into line compensation regulation can be divided into single-phase converters and line-coupled transformer losses. The loss of the single-phase converter mainly comprises IGBT switch and freewheeling diode loss, and the loss of the line coupling transformer comprises iron loss and copper loss.
Firstly, analyzing the loss of a converter, wherein the loss of an insulated gate bipolar transistor has a direct relation with the switching state of the insulated gate bipolar transistor, and the loss comprises a switching loss P s And working loss P w . Wherein the switching loss can be classified into an on loss P according to the switching action of the transistor s-on And turn-off loss P s-off Two, there are insulated gate bipolar transistor switching loss expressions:
P s =P s-on +P s-off (1)
wherein V is dc Is the capacitance voltage f of the DPFC single-phase converter s The carrier frequency is T, and the period of PWM modulated waves is T; r is R gon And R is R goff The on and off resistances of the gate electrode of the insulated gate bipolar transistor are respectively in an actual working state; e (R) gon )、E(R goff ) The losses generated in the turn-on and turn-off processes of the transistor by the IGBT gate resistance under the rated current condition are respectively; k (k) on For the transistor on loss coefficient, k off Is the turn-off loss coefficient of a transistor, S i1 (t i )、S i2 (t i ) The corresponding switching function is turned on and off for the IGBT switch, without considering dead zone, in the specific form as follows:
under the rated current condition, the energy consumption generated by the gate resistance of the IGBT switch in the switching-on and switching-off process is respectively E (R gon_t )、E(R goff_t ) Definition E on_t 、E off_t The energy consumption, V, generated by single turn-on and turn-off actions of the IGBT switch under the rated current condition t After the IGBT is conducted, the voltage generated between the collector and the emitter has the loss coefficients of on and off:
the loss generated by the IGBT in normal operation is as follows:
in the formula (8), V CE (t) is a function of time corresponding to the voltage generated between the collector and the emitter of the transistor; i C (t) is a time function corresponding to the current flowing through the collector of the transistor, D Q And (t) is the duty cycle of the transistor at time t. In the single-phase full-bridge converter, in order to realize the follow current function, a diode and an IGBT are required to be connected in reverse parallel, and in the conducting process of the IGBT, the loss generated by the diode can be expressed as:
P D =P on_D +P off_D (9)
P on_D =V F (t)I F (t)D T (10)
in the above, V F (t) is the voltage at two ends of the diode corresponding to the time function, I F (t) is a function of time corresponding to the current flowing through the diode, D T Is the duty cycle of the diode, k Dre For the corresponding loss factor when the diode is turned off, E re (R g ) Reverse recovery of energy consumption for gate resistance E re (t i ) The corresponding switching function of the diode is:
E re (t i )=S i2 (t i ) (12)
the transformer loss is mainly composed of two parts, namely iron loss and copper loss. Wherein, the iron loss calculation formula is:
P c =T * λ * Kf α B β (13)
wherein P is c For iron loss, K, alpha, beta are relevant empirical parameters of the iron core (generally 1 < alpha < 3 and 2 < beta < 3), T * Is the temperature coefficient of the iron core lambda * F is the working frequency of the transformer, and B is the magnetic flux density of the iron core. The invention provides a copper loss expression:
wherein I is L The current of the controlled line connected in series for the DPFC is that ρ is the resistivity of the induction coil, L is the length of the induction coil, S coil Is the inductor cross-sectional area. Therefore, the total loss of the transformer is as follows:
P T =P cm +P c (15)
in summary of the above analysis, the total loss generated after the DPFC subunit device is put into operation is:
P Z =P s +P w +P D +P T (16)
3. DPFC multi-subunit coordinated output method
The DPFC subunits are connected in series on the power line in a distributed mode, and according to different running conditions of the power line, the DPFC can have three regulation modes of impedance, voltage and tide by changing an outer ring control target. Thus, for different modes of operation of the DPFC, the corresponding DPFC loss can be expressed as a function of:
the DPFC multi-unit controlled power supply equivalent model can be expressed as shown in FIG. 3.
The reference phase selected by the value circuit is based on the phase of the line current, V sei And theta sei The magnitude and phase of the line injection voltage for the i-th DPFC subunit (i=1, 2,3 … n); x and R respectively correspond to equivalent reactance and resistance of the power system serial DPFC branch; v (V) s 、V r For the voltage delta at the first and the last ends of the line s 、δ r Respectively, its corresponding voltage amplitude and phase.
Let the active power and reactive power flow at the end of the line be P L 、Q L Then:
in delta sr For the voltage V at the first and the last ends of the line s And V is equal to r The phase difference is not difficult to see, if the active and reactive power flows of the power line need to be regulated and controlled, the most direct method is to carry out the output voltage of the line of the DPFC subunitAnd (5) controlling.
The current stage mainly comprises an average method and a proportional method aiming at a DPFC multi-unit output distribution strategy. The average method distributes average output to each unit of the DPFC according to the total output requirement of the whole multi-unit system; the proportion rule is to distribute the output by the specific capacity of each unit of DPFC.
Therefore, when the DPFC multi-unit system adopts the average method, the output force of each unit of the DPFC (namely the injection voltage V of the single-phase converter of the subunit i to the line can be obtained sei Hereinafter not described in detail) are:
V seΣ the voltage is compensated for the total line demand.
The invention provides a calculation formula of the overall loss of a DPFC multi-unit system device, which is as follows:
when the DPFC multi-unit system adopts the proportional method, the invention defines the total line installation capacity of the multi-unit system as S seΣ The rated capacity of the device of the subunit i is S sei ,h i For the single subunit and the installed total capacity scaling factor, the invention proposes:
therefore, the invention proposes that the output of each unit of the DPFC is as follows:
the invention further provides that the total loss of the DPFC device is as follows:
for practical engineering, the invention provides that the fault or the out-of-operation of the line subunit is taken into consideration, and the subunit operation state variable D is introduced i The following steps are:
according to the above formula, the force output scheme is also changed, and when an average method is adopted, the force output of each subunit is distributed as follows:
the invention provides a DPFC device total loss which is as follows:
if a scaling method is adopted, the total capacity of the circuit installation, the scaling coefficient of the capacity and the output of the subunit are all changed, and then the method comprises the following steps:
the total loss of the DPFC device becomes:
the invention defines the actual use capacity of the ith DPFC subunit as S sefi The following steps are:
when V is sei When=0, S sefi =0, dpfc subunit utilization is 0%.
Therefore, the average utilization rate of the DPFC multi-unit system can be effectively improved by the average method, and the problem that the DPFC subunits with larger capacity are limited by the DPFC subunits with small capacity can be solved by the proportional method. However, when the total demand adjustment amount of the system is relatively small, all DPFC subunits must be put into operation whether an averaging method or a proportional method is adopted, which results in low utilization rate of the DPFC subunit devices and reduced service life, thereby resulting in lower operational reliability.
The invention provides a coordinated output distribution method (hereinafter referred to as a "coordinated output method") among DPFC multi-unit system units from the aspects of DPFC subunits themselves, constraint and regulation of system conditions, demand quantity regulation and control and device utilization rate.
It can be seen that the DPFC multi-subunit system level control strategy is constrained by a plurality of conditions, and in actual analysis, the optimal solution is a multi-objective optimization problem, based on the idea that:
in equation (34), F (x) is a multiple objective function, F i (x) Is a sub-objective function corresponding to each constraint condition, x is an independent variable needing to be optimally designed, g j (x) Is a constraint condition of inequality of multiple objective functions, h k (x) Is a constraint of multiple objective function equation, j max 、k max The number of inequality constraints and equality constraints, respectively.
In order to ensure that the DPFC subunit is normally put into operation in a circuit, the invention provides the following constraint conditions:
1) DPFC total injection voltage V required for power line control seΣ Constraint (i.e. sum of output voltages of each subunit is equal to total voltage required by system):
2) Line tide constraint:
P L,min ≤P L,ref ≤P L,max (36)
Q L,min ≤Q L,ref ≤Q L,max (37)
I L,min ≤I L ≤I L,max (38)
P L,min 、P L,max and Q L,min 、Q L,max The upper limit and the lower limit of active power and reactive power of the controlled line are respectively corresponding; i L,min And I L,max And the upper limit and the lower limit of the current of the controlled circuit are respectively corresponding.
3) Device force constraints for each subunit of DPFC:
in order to improve the utilization rate of the device and reduce the loss of the device, each DPFC subunit needs to be ensured to be in a working state with higher efficiency, therefore, the invention proposes that the output voltage and the use capacity of each DPFC subunit are not less than 80 percent of the rated output voltage and the rated capacity, and therefore, the invention has the following formula
V r,i Rated output voltage for DPFC subunit i (i=1, 2,., n), k is the efficiency constraint coefficient, taking 0.8.
4) Transformer voltage constraints:
V sei ≤V semaxi (40)
V semaxi is the maximum value of the injection voltage allowed by the DPFC subunit i to the transmission line.
5) Transformer capacity constraint:
S sefi ≤S TNi (41)
S TNi the power rating of the single-turn coupling transformer between the DPFC subunit i and the power transmission line is realized.
In order to effectively reduce DPFC subunit loss and finish the load flow regulation and control task of the controlled line, the invention introduces the error square sum P of the real-time value of the load flow of the controlled line and a given reference value Lref -P L || 2 Defining input unit number variable functionNumber A (m) 1 ) Wherein m is 1 Is the number of DPFC subunits, and a coordinated optimization function w (u) is introduced according to the operation constraint condition of the DPFC multi-unit system i ) The control system optimization function is obtained as follows:
J i =||P Lref -P L || 2 +w(u i )+A(m 1 ),i=1,...,λ (42)
wherein the coordination optimization function w (u i ) The equation is satisfied:
w(u i )=K(u i )+V(u i )+C(u i ) (43)
K(u i ) For DPFC subunits corresponding to loss functions, V (u i )、C(u i ) For operating the subunit output voltage and using the capacity evaluation function corresponding to the DPFC multi-unit system respectively, there are:
the invention aims at w (u) by Lagrangian method i ) Function construction, H (u i )、G(u i ) Equations and inequality constraints for DPFC multi-unit system operation.
Wherein K (u) i ) For DPFC subunits corresponding to loss functions, H (u i )、G(u i ) For equality and inequality constraint conditions of DPFC multi-unit system operation, the invention establishes a global objective function under the condition of meeting the regulation requirement of the controlled line power flow:
find J min Corresponding control quantity u min The obtained control quantity result directly acts on the input of the DPFC multi-unit system to the line.
To sum up, the specific steps of the DPFC coordinated output distribution method of the present invention are shown in fig. 4:
(1) Judging the active and reactive power target value P of the power flow regulation of the controlled line Lref 、Q Lref If the system is within the range of the specified constraint condition, carrying out the next step, and if the system is beyond the range of the specified constraint condition, adjusting the system line power flow adjustment target to be within the constraint range;
(2) Judging whether the active reactive power flow regulation demand of the controlled line is in the adjustable range of the DPFC multi-unit system, if so, carrying out the next step, and if the active reactive power flow regulation demand exceeds the adjustable range of the DPFC multi-unit system, readjusting the power flow regulation demand;
(3) The voltage V of the total compensation when the active and reactive power of the controlled line is regulated by the DPFC multi-unit system is combined with the formula (18) and the formula (19) seΣ Calculating; then, solving an objective function (47) within the constraint condition range meeting the formulas (35) to (41) to obtain a DPFC coordinated output distribution scheme;
(4) And finally, issuing a power distribution instruction to each subunit of the DPFC, and regulating the flow of the controlled line by each subunit according to the instruction.
The DPFC subunit coordinated output distribution method provided by the invention can ensure that the DPFC subunit can accurately regulate the line voltage; on the premise of ensuring the working reliability of multiple subunits, compared with the traditional averaging method and the traditional proportional method, the coordinated output distribution control method provided by the invention can flexibly input the subunits according to the actual working conditions, improves the utilization rate of the device, improves the actual output voltage of the device, improves the use capacity of the device, and reduces the overall loss of the DPFC device.
The foregoing is only a partial embodiment of the present invention, and it should be noted that it will be apparent to those skilled in the art that modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the present invention.
Claims (9)
1. The distributed power flow controller coordinated output distribution method for reducing the overall loss of the device is characterized by comprising the following steps:
1) Judging whether target values of the active power and the reactive power of the power flow regulation of the controlled line are within a specified constraint condition range, and if the target values are within the specified constraint condition range, performing the next step; if the current of the controlled line exceeds the range of the specified constraint condition, the current regulating active power and reactive power target values of the controlled line are regulated to be within the range of the specified constraint condition;
2) Judging whether the active and reactive power flow regulation demand of the controlled line is within the adjustable range of the DPFC multi-unit system, and if so, performing the next step; if the adjustable range of the DPFC multi-unit system is exceeded, the flow adjustment demand is readjusted;
3) Calculating the total demand compensation voltage when the DPFC multi-unit system adjusts the active power and the reactive power of the controlled line, and then solving an objective function to obtain a DPFC coordinated output distribution scheme;
4) Finally, issuing a power distribution instruction to each subunit of the DPFC, and adjusting the flow of the controlled line by each subunit of the DPFC according to the instruction;
the power flow regulation and control task of the controlled line is completed while the DPFC subunit loss is effectively reduced, and the error square sum of the real power value of the controlled line and a given reference value P is introduced Lref -P L || 2 ,P Lref Giving a reference value for the active power of a controlled line, P L Real-time value of active power for the controlled line; defining the variable function of the number of input units as A (m 1 ) Wherein m is 1 Is the number of DPFC subunits, and a coordinated optimization function w (u) is introduced according to the operation constraint condition of the DPFC multi-unit system i ),u i Representing the control quantity of the output voltage of the ith subunit, the control system optimization function is:
J i =||P Lref -P L || 2 +w(u i )+A(m 1 ),i=1,...,λ (42)
wherein lambda represents the number of DPFC subunits put into operation;
wherein the coordination optimization function w (u i ) The equation is satisfied:
w(u i )=K(u i )+V(u i )+C(u i ) (43)
K(u i ) For DPFC subunit i, V (u) i )、C(u i ) Output voltages and use capacity assessment functions for the corresponding DPFC subunit i, respectively, and have:
wherein V is sei Outputting voltage for DPFC subunit i; v (V) r,i Rated output voltage for DPFC subunit i; s is S sefi The actual capacity for DPFC subunit i; s is S sei Rated capacity for DPFC subunit i;
by Lagrangian method for w (u) i ) The function is constructed:
wherein H (u) i )、G(u i ) Equality and inequality constraints for DPFC multi-unit system operation;G、respectively representing the upper and lower limits of each inequality condition; establishing a global objective function under the condition of meeting the load flow regulation requirement of the controlled line:
find J min Corresponding control quantity u min The obtained control quantity result directly acts on the input of the DPFC multi-unit system to the line.
2. The coordinated output distribution method of a distributed power flow controller according to claim 1, wherein in step 3), the active power and reactive power flows at the end of the controlled line are set to be P L 、Q L Then:
in delta sr For the voltage V at the first and the last ends of the line s And V is equal to r A phase difference; v (V) sei Injecting a voltage into the line for the ith DPFC subunit, i=1, 2,3 … n; x and R respectively correspond to equivalent reactance and resistance of the power system serial DPFC branch; v (V) s 、V r The voltages at the first end and the last end of the line are respectively;
when the DPFC multi-unit system adopts an average method, the output of each unit of the DPFC is obtained, namely the voltage V is injected into a line by a subunit i single-phase converter sei The method comprises the following steps:
wherein V is seΣ The voltage is compensated for the total demand.
3. The distributed power flow controller coordinated output distribution method according to claim 1, wherein the overall loss calculation formula of the DPFC multi-unit system is formula (21):
when the DPFC multi-unit system adopts the proportional method, defining the total line installation capacity of the DPFC multi-unit system as S seΣ The rated capacity of the device of the subunit i is S sei A ratio coefficient of a single subunit to the total installed capacity is h i The method comprises the following steps:
the output of each unit of the DPFC is as follows:
the total loss of the DPFC device is then:
4. a method of coordinated output distribution of a distributed power flow controller according to claim 3, characterized in that for actual engineering, the sub-unit operation state variables D are introduced taking into account the failure or the exit of the line sub-unit i The following steps are:
according to the above formula, the force output scheme is also changed, and when an average method is adopted, the force output of each subunit is distributed as follows:
the total loss of the DPFC device is:
if a scaling method is adopted, the total capacity of the circuit installation, the scaling coefficient of the capacity and the output of the subunit are all changed, and then the method comprises the following steps:
the total loss of the DPFC device becomes:
definition of the actual use Capacity of the ith DPFC subunit as S sefi The following steps are:
when V is sei When=0, S sefi =0, dpfc subunit utilization is 0%.
5. The method of coordinated output distribution of a distributed power flow controller according to claim 1, wherein the search for an optimal solution from a plurality of constraints is a multi-objective optimization problem, based on which:
in equation (34), F (x) is a multiple objective function, F i (x) Is a sub-objective function corresponding to each constraint condition, x is an independent variable needing to be optimally designed, g j (x) Is a constraint condition of inequality of multiple objective functions, h k (x) Is a constraint of multiple objective function equation, j max 、k max The number of inequality constraints and equality constraints, respectively.
6. The method for distributing coordinated output of a distributed power flow controller according to claim 5, wherein to ensure that the DPFC subunit is normally put into operation in a line, the following prescribed constraint conditions are set:
line-controlled DPFC total demand compensation voltage constraint, i.e. DPFC subunit i output voltage V sei Sum and total system demand voltage V seΣ Equal:
line tide constraint:
P L,min ≤P L,ref ≤P L,max (36)
Q L,min ≤Q L,ref ≤Q L,max (37)
I L,min ≤I L ≤I L,max (38)
P L,ref active power of the controlled circuit; q (Q) L,ref Reactive power of the controlled line; i L The current of the controlled line; p (P) L,min 、P L,max And Q L,min 、Q L,max The upper limit and the lower limit of active power and reactive power of the controlled line are respectively corresponding; i L,min And I L,max The upper limit and the lower limit of the current of the controlled circuit are respectively corresponding;
device force constraints for each subunit of DPFC:
V r,i the output voltage is rated for DPFC subunit i, i=1, 2,. -%, n; k is an efficiency constraint coefficient; s is S sefi The actual capacity for DPFC subunit i; s is S sei Rated capacity for DPFC subunit i;
transformer voltage constraints:
V sei ≤V semaxi (40)
V semaxi injecting a voltage maximum value into the power transmission line allowed by the DPFC subunit i;
transformer capacity constraint:
S sefi ≤S TNi (41)
S TNi the power rating of the single-turn coupling transformer between the DPFC subunit i and the power transmission line is realized.
7. The method for coordinated output distribution of distributed power flow controllers according to claim 6, wherein in the device output constraint of each DPFC subunit, the output voltage and the usage capacity of each DPFC subunit must not be less than 80% of the rated output voltage and the rated capacity, i.e. the efficiency constraint coefficient k takes 0.8.
8. The method of claim 1, wherein the analysis is performed on the loss of the converter, and the loss of the insulated gate bipolar transistor has a direct relation with the switching state of the insulated gate bipolar transistor, including the switching loss P s And working loss P w The method comprises the steps of carrying out a first treatment on the surface of the Wherein the switch is based on a transistorAction classifies switching loss as on loss P s-on And turn-off loss P s-off Two, there are insulated gate bipolar transistor switching loss expressions:
P s =P s-on +P s-off (1)
wherein V is dc Is the capacitance voltage f of the DPFC single-phase converter s The carrier frequency is T, and the period of PWM modulated waves is T; r is R gon And R is R goff The on and off resistances of the gate electrode of the insulated gate bipolar transistor are respectively in an actual working state; e (R) gon )、E(R goff ) The losses generated in the turn-on and turn-off processes of the transistor by the IGBT gate resistance under the rated current condition are respectively; k (k) on For the transistor on loss coefficient, k off Is the turn-off loss coefficient of a transistor, S i1 (t i )、S i2 (t i ) The switching functions corresponding to the on and off of the IGBT switch are respectively realized, dead zones are not considered, and the specific form is as follows:
under the rated current condition, the energy consumption generated by the gate resistance of the IGBT switch in the switching-on and switching-off process is E (R gon_t )、E(R goff_t ) The method comprises the steps of carrying out a first treatment on the surface of the Definition E on_t 、E off_t Respectively IGBT switch under rated current conditionThen, energy consumption generated by single turn-on and turn-off actions is carried out; v (V) t After the IGBT is conducted, the voltage generated between the collector and the emitter has the loss coefficients of on and off:
9. the distributed power flow controller coordinated output distribution method according to claim 8, wherein the losses generated by the IGBT in normal operation are:
in the formula (8), V CE (t) is a function of time corresponding to the voltage generated between the collector and the emitter of the transistor; i C (t) is a time function corresponding to the current flowing through the collector of the transistor, D Q (t) is the duty cycle of the transistor at time t;
in the single-phase full-bridge converter, in order to realize the follow current function, a diode and an IGBT are required to be connected in reverse parallel, and in the conducting process of the IGBT, the loss generated by the diode is expressed as:
P D =P on_D +P off_D (9)
P on_D =V F (t)I F (t)D T (10)
in the above, V F (t) is the voltage at two ends of the diode corresponding to the time function, I F (t) corresponds to the diode currentTime function, D T Is the duty cycle of the diode, k Dre For the corresponding loss factor when the diode is turned off, E re (R g ) Reverse recovery of energy consumption for gate resistance E re (t i ) For the diode to correspond to the switching function, V dcse The dc capacitor voltage of the current transformer is represented, and there are:
E re (t i )=S i2 (t i ) (12)
the transformer loss mainly comprises two parts of iron loss and copper loss, wherein the iron loss is calculated by the following formula:
P c =T * λ * Kf α B β (13)
wherein P is c For iron loss, K, alpha, beta are relevant empirical parameters of the iron core, T * Is the temperature coefficient of the iron core lambda * F is the working frequency of the transformer, and B is the magnetic flux density of the iron core;
the copper loss expression is:
wherein I is L The current of the controlled line connected in series for the DPFC is that ρ is the resistivity of the induction coil, L is the length of the induction coil, S coil Is the cross-sectional area of the inductance coil;
the total loss of the transformer is as follows:
P T =P cm +P c (15)
the total loss generated after the DPFC subunit device is put into operation is as follows:
P Z =P s +P w +P D +P T (16)。
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