CN113964840A - Power flow analysis method, device and medium based on HVST equivalent circuit model - Google Patents
Power flow analysis method, device and medium based on HVST equivalent circuit model 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
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- H—ELECTRICITY
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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
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- H—ELECTRICITY
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Abstract
The invention discloses a power flow analysis method, a device and a medium based on an HVST equivalent circuit model, wherein the method comprises the following steps: establishing an HVST single-phase equivalent circuit model according to the electrical parameters of the HVST; calculating the integral equivalent impedance of the HVST single-phase equivalent circuit model according to the impedance value of each winding and the excitation impedance value in the HVST single-phase equivalent circuit model; the integral equivalent impedance changes along with the change of the gear of the on-load voltage regulating switch; and calculating series compensation voltage output to the three-phase transmission line by the HVST according to the integral equivalent impedance, and analyzing the load flow distribution of the three-phase transmission line after the HVST is accessed. By adopting the embodiment of the invention, the leakage impedance of the HVST is fully considered, a single-phase circuit equivalent model and a three-phase power flow equation are established, and the power flow distribution of the three-phase power transmission line after the HVST is accessed is efficiently and accurately analyzed.
Description
Technical Field
The invention relates to the field of power grid dispatching operation, in particular to a power flow analysis method, a device and a medium based on an HVST equivalent circuit model.
Background
Due to the unbalanced distribution of the energy center and the load center, the power transmission network in China develops towards ultrahigh voltage and long distance. The tidal current situation of the high-voltage transmission line is complex, the situations of overload, power circulation and the like can occur, the running stability of the system is reduced, the quality of electric energy is influenced, and a large amount of economic loss can be caused. Therefore, the operation of the power system faces a great challenge, and the power transmission capacity must be increased, the system can operate stably, and the economy and reliability of the system must be improved.
At present, most methods for solving the problems are control over the operation mode of the power system, such as change of a transformer tap, adjustment of the operation mode of a generator, switching of a compensation device and the like. However, these methods have their own limitations, are greatly influenced by system operation, and have certain technical limitations. The power flow of the power system can be controlled and adjusted by using some high-power electronic equipment without greatly changing the existing power grid system. Based on the principle, the FACTS (Flexible AC Transmission System) optimizes the operation mode of the power System and improves the Transmission capacity of the Transmission System. FACTS devices have various types and functions, and especially STATCOM, SSSC, and Unified Power Flow Controller (UPFC) are most widely used.
For a High-Voltage class power system, an improved power flow controller, i.e., a High-Voltage "Sen" Transformer (hereinafter abbreviated as HVST), has better economical efficiency, and its powerful application potential is worth further research due to low cost and High reliability. At present, research on a high-voltage Sen type phase shifter mainly focuses on the aspects of circuit topology and feasible control schemes, modeling research on HVST is less, and a traditional single-core or double-core type phase-shifting transformer (PST) mathematical model cannot be directly applied to HVST modeling. The HVST is a multi-winding model, the development of various analysis and research containing the HVST is relatively complex, and even if the complex HVST analysis model is successfully established, the complexity of the model also seriously influences the calculation efficiency of the system load flow. In addition, the existing HVST model often ignores the leakage impedance of the HVST itself, which results in an inaccurate flow analysis result of the analysis model.
Disclosure of Invention
The embodiment of the invention provides a power flow analysis method, a device and a medium based on an HVST equivalent circuit model, wherein a single-phase circuit equivalent model and a three-phase power flow equation are established by considering the leakage impedance of the HVST, and the power flow distribution of a three-phase power transmission line accessed to the HVST is efficiently and accurately analyzed.
In order to achieve the above object, a first aspect of embodiments of the present application provides a power flow analysis method based on an HVST equivalent circuit model, the method including:
connecting a high-voltage side winding in three phases of HVST into a corresponding three-phase power transmission line, and enabling a medium-voltage side winding and a low-voltage side winding of any two phases of the three phases of HVST to form a residual single-phase series compensation group; the series compensation group provides series compensation voltage for the residual single phase, and the series compensation voltage is converged into the three-phase power transmission line through an isolation transformer;
establishing an HVST single-phase equivalent circuit model according to the electrical parameters of the HVST;
calculating the integral equivalent impedance of the HVST single-phase equivalent circuit model according to the impedance value of each winding and the excitation impedance value in the HVST single-phase equivalent circuit model; the integral equivalent impedance changes along with the change of the gear of the on-load voltage regulating switch;
and calculating series compensation voltage output to the three-phase transmission line by the HVST according to the integral equivalent impedance, and analyzing the load flow distribution of the three-phase transmission line after the HVST is accessed.
In a possible implementation manner of the first aspect, the electrical parameter specifically includes:
the voltages of the high voltage side, the medium voltage side and the low voltage side correspond to the voltage and the load current;
the number of turns, current, electromotive force and leakage impedance of the series winding, the common winding and the low-voltage side winding correspond to each other.
In a possible implementation manner of the first aspect, the establishing an HVST single-phase equivalent circuit model specifically includes:
and deducing an HVST single-phase voltage and current equation according to the connection form of the single-phase winding of the autotransformer, converting the electric quantity of the public winding and the low-voltage winding side to the high-voltage side winding, and establishing an HVST single-phase equivalent circuit model.
In a possible implementation manner of the first aspect, the impedance values of the respective windings are obtained through a transformer short-circuit test;
the transformer short-circuit test is that a winding on one side of a transformer is short-circuited, alternating voltage with rated frequency is added from the winding on the other side of the transformer, current in the winding of the transformer is used as a rated value, the added voltage and power are measured, and then impedance values of all windings are obtained.
In a possible implementation manner of the first aspect, the excitation impedance value is calculated after determining an HVST single-phase equivalent magnetic circuit according to a length, a permeability, and a cross-sectional area of a magnetic circuit of an iron core of the transformer.
In a possible implementation manner of the first aspect, the calculating, according to the overall equivalent impedance, a series compensation voltage output by the HVST to the three-phase power transmission line, and analyzing a power flow distribution of the three-phase power transmission line after the HVST is connected to the three-phase power transmission line specifically includes:
and establishing a compensation voltage equation according to the integral equivalent impedance and the mode that the HVST is connected into the three-phase power transmission line, obtaining a three-phase steady-state power flow equation of the three-phase power transmission line before and after compensation is carried out through series compensation voltage, and analyzing the adjustment amount and the power flow distribution of the three-phase power transmission line power flow after the HVST is connected into the three-phase power transmission line.
A second aspect of an embodiment of the present application provides a power flow analysis apparatus based on an HVST equivalent circuit model, including:
the access module is used for accessing a high-voltage side winding in three phases of HVST to a corresponding three-phase power transmission line and enabling a medium-voltage side winding and a low-voltage side winding of any two phases of the three phases of HVST to form a residual single-phase series compensation group; the series compensation group provides series compensation voltage for the residual single phase, and the series compensation voltage is converged into the three-phase power transmission line through an isolation transformer;
the circuit model building module is used for building an HVST single-phase equivalent circuit model according to the electrical parameters of the HVST;
the impedance calculation module is used for calculating the integral equivalent impedance of the HVST single-phase equivalent circuit model according to the impedance value of each winding and the excitation impedance value in the HVST single-phase equivalent circuit model; the integral equivalent impedance changes along with the change of the gear of the on-load voltage regulating switch;
and the analysis module is used for calculating the series compensation voltage output to the three-phase transmission line by the HVST according to the integral equivalent impedance and analyzing the load flow distribution of the three-phase transmission line after the three-phase transmission line is accessed to the HVST.
In a possible implementation manner of the first aspect, the establishing an HVST single-phase equivalent circuit model specifically includes:
and deducing an HVST single-phase voltage and current equation according to the connection form of the single-phase winding of the autotransformer, converting the electric quantity of the public winding and the low-voltage winding side to the high-voltage side winding, and establishing an HVST single-phase equivalent circuit model.
In a possible implementation manner of the first aspect, the analysis module is specifically configured to:
and establishing a compensation voltage equation according to the integral equivalent impedance and the mode that the HVST is connected into the three-phase power transmission line, obtaining a three-phase steady-state power flow equation of the three-phase power transmission line before and after compensation is carried out through series compensation voltage, and analyzing the adjustment amount and the power flow distribution of the three-phase power transmission line power flow after the HVST is connected into the three-phase power transmission line.
A third aspect of embodiments of the present application provides a computer-readable storage medium comprising a stored computer program; wherein the computer program, when running, controls an apparatus in which the computer-readable storage medium is located to perform the power flow analysis method based on the HVST equivalent circuit model as described above.
Compared with the prior art, the power flow analysis method, the device and the medium based on the HVST equivalent circuit model provided by the embodiment of the invention can be used for obtaining the circuit parameters of the three-phase power transmission line after the HVST is accessed so as to construct the single-phase circuit equivalent model and obtain the integral equivalent impedance expression of the HVST. And establishing a compensation voltage equation according to the mode that the HVST is accessed into the power transmission system to calculate the series compensation voltage, and writing a three-phase steady-state power flow equation of the lines before and after compensation in a row to quickly and accurately calculate the adjustment quantity of the HVST to the system power flow after the HVST is accessed into the power transmission system. As the HVST model adopted in the whole analysis and calculation process is a circuit equivalent model, the problem of multilayer complexity of the existing HVST model is avoided, the leakage impedance of the HVST model is also considered under the condition of ensuring the simplicity and effectiveness of the model, the modeling accuracy is further improved, and the accuracy of the power flow analysis and calculation is further improved.
In addition, in the embodiment of the invention, the HVST integral leakage impedance of the single-phase circuit equivalent model is changed along with the change of the gear of the on-load tap changer, so in practical application, an operator can adjust the switching position of the on-load tap changer tap of the HVST according to the adjustment quantity of the expected load flow of a circuit, namely the amplitude and the phase of the output voltage of the HVST can be adjusted, which means that related technicians can flexibly adjust the active and reactive load flows according to the load condition of the circuit.
Drawings
Fig. 1 is a schematic flow chart of a power flow analysis method based on an HVST equivalent circuit model according to an embodiment of the present invention;
FIG. 2 is a wiring diagram of an HVST access three-phase transmission line in an embodiment of the present invention;
FIG. 3 is a schematic diagram of an HVST single-phase winding provided by an embodiment of the present invention;
FIG. 4 is a schematic circuit diagram of an HVST equivalent circuit model according to an embodiment of the present invention;
FIG. 5 is a circuit schematic of an equivalent magnetic circuit of an HVST according to an embodiment of the present invention;
FIG. 6 is an equivalent circuit diagram of an HVST series-in circuit according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a compensation voltage provided by a single-phase power transmission line according to an embodiment of the present invention;
fig. 8 is a vector diagram of the head end voltage of a compensated single-phase line according to an embodiment of the present invention;
FIG. 9 is a schematic circuit diagram of a power transmission system after HVST access provided by an embodiment of the present invention;
fig. 10 is a voltage vector diagram of a power transmission system after HVST access in an embodiment of the invention;
FIG. 11 is a graphical illustration of the relationship between the HVST maximum phase shift angle and the rated voltage provided by one embodiment of the present invention.
Detailed Description
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 only a part of the embodiments of the present invention, and not all of the embodiments. 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. 1, an embodiment of the present invention provides a power flow analysis method based on an HVST equivalent circuit model, including:
s10, connecting a high-voltage side winding in three HVST phases to a corresponding three-phase power transmission line, and enabling a medium-voltage side winding and a low-voltage side winding of any two phases in the three HVST phases to form a residual single-phase series compensation group; and the series compensation group provides series compensation voltage for the residual single phase, and the series compensation voltage is converged into the three-phase power transmission line through an isolation transformer.
And S11, establishing an HVST single-phase equivalent circuit model according to the electrical parameters of the HVST.
S12, calculating the integral equivalent impedance of the HVST single-phase equivalent circuit model according to the impedance value of each winding and the excitation impedance value in the HVST single-phase equivalent circuit model; the integral equivalent impedance changes along with the change of the gear of the on-load voltage regulating switch.
And S13, calculating series compensation voltage output to the three-phase transmission line by the HVST according to the integral equivalent impedance, and analyzing the load flow distribution of the three-phase transmission line after the HVST is connected.
Referring to fig. 2, a schematic diagram of a wiring structure of an HVST and a three-phase transmission line in a three-phase power system is shown in fig. 2. The HVST main body adopts an autotransformer structure, A, B, C-phase high-voltage side windings are directly connected into corresponding three-phase power transmission lines, and head-end voltages USA, USB and USC of the power transmission lines respectively provide parallel input voltages for A, B, C phases of the high-voltage side of the transformer. The windings of the medium-voltage side connected to the load tap changer are marked as a1, b1, c1, and the windings of the low-voltage side are marked as a2, b2, c 2. And the middle and low voltage side windings of the second and third phases form series compensation voltage of the first phase, and the series compensation voltage is converged into the power transmission line through the isolation transformer. The HVST access mode proposed by this embodiment is an improvement of the structure of the Sen-type transformer, and this connection mode reduces the number of secondary windings from 9 to 6, and has a larger shift angle range than the general Sen-type phase shifter, so that the economic advantages of this connection mode are fully exerted, and the connection mode is more suitable for high-voltage power systems.
The HVST body part is equivalent to a three-winding autotransformer, and a schematic diagram of HVST single-phase winding is created according to the autotransformer structure and is shown in figure 3.
If the specific values of the winding impedance value and the excitation impedance value in the HVST single-phase equivalent circuit model are not obtained in the step S12, the series compensation voltage in the step S13 is essentially an expression related to HVST electrical parameters, and therefore a three-phase steady-state power flow equation of the lines before and after compensation is written in a series mode, and an expression of the adjustment quantity of the HVST to the system power flow after the HVST is connected into the power transmission system is obtained.
It should be noted that, when building a steady-state power flow mathematical model for HVST, considering that the parallel side of HVST provides input voltage to the power grid to perform excitation, while the series side provides output compensation voltage with three-phase symmetry, this embodiment will use the compensation voltage U of the a-phase transmission lineHVSTAFor example, a steady-state power flow mathematical model is established, wherein the isolation transformer is an ideal transformer model and only plays a role in electrical isolation.
Illustratively, the electrical parameters specifically include: the voltages of the high voltage side, the medium voltage side and the low voltage side correspond to the voltage and the load current; the number of turns, current, electromotive force and leakage impedance of the series winding, the common winding and the low-voltage side winding correspond to each other.
Illustratively, the establishing of the HVST single-phase equivalent circuit model specifically includes:
and deducing an HVST single-phase voltage and current equation according to the connection form of the single-phase winding of the autotransformer, converting the electric quantity of the public winding and the low-voltage winding side to the high-voltage side winding, and establishing an HVST single-phase equivalent circuit model.
The voltages of the high voltage side, the medium voltage side and the low voltage side are respectively as follows: u1, U2, U3, the medium side load current is I2.
The number of turns, current and electromotive force of the series winding Aa1 are respectively as follows: n1, I1, E1.
The number of turns, current and electromotive force of the common winding a1X are respectively: n2, I, E2.
The number of turns, current, and electromotive force of the low-voltage winding a2x are: n3, I3, E3.
The leakage impedances of the series winding, the medium voltage winding and the low voltage winding are respectively as follows: ZAa1, Za1X, Za2 x.
According to the definition, an HVST single-phase steady-state equivalent circuit model is established. The column write high side, medium side, low side loop voltage equations are:
the magnetomotive force of the series winding, the common winding and the low-voltage winding is as follows:
excited magnetomotive force of
Then, according to the magnetic circuit theorem, the following relationship exists:
defining the excitation current as
Excitation impedance of ZmThe voltage drop across the excitation impedance is then:
defining the transformation ratio of the high-pressure side and the medium-pressure side:
transformation ratio of high-pressure side and low-pressure side:
converting the electrical quantities of the medium-voltage side and the low-voltage side to the high-voltage side according to the transformation ratio, and then:
the single-phase equivalent circuit of HVST is established by combining the formula (1), the formula (8) and the formula (9):
from equations (10) and (11), a single-phase equivalent circuit of HVST can be derived, as shown in fig. 4. HVST is equivalent to an ideal autotransformer, high-voltage side equivalent impedance ZAa+(1-k12)Za1XDirect and converted to the equivalent impedance k on the high-voltage side12(k12-1)Za1XSeries, equivalent impedance k12Za1XEquivalent impedance k converted to high voltage side2 13Za2xForm a parallel loop, k12Za1XAnd excitation impedance ZmForming another parallel loop.
Illustratively, the impedance values of the windings are obtained through a transformer short circuit test;
the transformer short-circuit test is that a winding on one side of a transformer is short-circuited, alternating voltage with rated frequency is added from the winding on the other side of the transformer, current in the winding of the transformer is used as a rated value, the added voltage and power are measured, and then impedance values of all windings are obtained.
In practice, the applied voltage and power are measured by short-circuiting one winding (usually the low voltage side) of the transformer, applying an ac voltage of a rated frequency from the other winding (the tap is at the rated voltage position), setting the current in the transformer winding to the rated value. In this embodiment, the HVST main body adopts a self-coupling variable structure, and is divided into three windings, namely a high-voltage side winding, a medium-voltage side winding and a low-voltage side winding, and a short-circuit test should be performed on every two windings, and a non-tested coil should be open-circuited. If the capacities of the two windings are different, the rated current of the winding with the smaller capacity is introduced, and the capacity corresponding to the measured impedance voltage is noted. ) And measuring short-circuit impedances of windings on the high voltage side, the medium voltage side and the low voltage side, and determining the winding impedance value in the HVST single-phase equivalent circuit according to the short-circuit impedances.
To obtain the overall equivalent impedance in the HVST single-phase equivalent circuit, the excitation impedance of the HVST needs to be obtained. The excitation impedance of the HVST is a nonlinear impedance whose determination requires the establishment of the magnetic loop equations of the equivalent autotransformer core. The magnetic equivalent circuit is based on the magnetic equivalent circuit to obtain the magnetic circuit of the iron core of the autotransformer, and then the magnetic circuit is converted into a circuit model, so that the influence of the structure of the iron core on the exciting current of the transformer can be reflected, and the magnetic equivalent circuit is divided into two partsAnalysis of the magnetic saturation condition of HVST under different working conditions plays an important role. The proposed conversion methods include a unified Magnetic circuit model umec (unified Magnetic Equivalent circuit) method, a dual principle method, and an electromagnetic conversion method based on current decomposition and winding equivalence. The invention adopts a method based on current decomposition and winding equivalence, considers that an excitation branch model of an iron core structure is not a nonlinear inductor any more, but is formed by connecting a plurality of nonlinear inductors in series and in parallel according to different iron core structures, and establishes an HVST equivalent magnetic loop as shown in figure 5. The magnetic resistances of the series winding, the common winding and the low-voltage side winding section are sequentially connected in series, and the magnetic resistances are respectively Rm1、Rm2And Rm3Equivalent magnetic flux of phimThe magnetomotive force of the three windings is connected in series in sequence.
Illustratively, the excitation impedance value is calculated after an HVST single-phase equivalent magnetic circuit is determined according to the length, the permeability and the cross-sectional area of a magnetic circuit of an iron core of the transformer.
With reference to fig. 5, the HVST single phase magnetic loop equation can be derived:
I1N1+IN2+I3N3＝φm(Rm1+Rm2+Rm3) (12)
according to faraday's law of electromagnetic induction:
from the above equation, the calculation formula of the excitation reactance L of HVST is:
the size of the excitation reactance L is related to the number of turns of the series winding and the number of turns of the common winding and the size of the equivalent magnetic resistance of each winding section. The magnetic resistance calculation formula is as follows:
wherein mu is the magnetic conductivity of the iron core, l is the magnetic path length of the iron core, and S is the sectional area of the iron core. From this, it is understood that the magnitude of the field reactance L is determined by the magnetic permeability μ of the core. The change in permeability μ is non-linear as the saturation level of the core changes, as determined by the B-H curve of the core. The excitation reactance calculation formula can therefore be expressed as:
and then determining the leakage impedance of the HVST, wherein the leakage impedances of the series winding, the common winding and the low-voltage winding are linear impedances under the condition that the on-load tap changer is not considered to switch different gears, and are obtained by calculating the short-circuit impedances of the high-voltage winding, the medium-voltage winding, the high-voltage winding, the low-voltage winding and the medium-voltage winding. The short circuit impedance of the HVST can be measured by a short circuit test. Short circuit impedance of high and middle windings is Zk12High and low winding short circuit impedance of Zk13Short circuit impedance of middle or low winding is Zk23Then the relation between the leakage impedance and the short circuit impedance of the series winding, the common winding and the low-voltage winding is as follows:
the common winding and the low-voltage winding are respectively provided with a group of on-load voltage regulating switches, and when the switches are switched at different gears, the output voltages are different, and the equivalent impedances are also different. The switch positions of the common and low voltage windings of the HVST may take values in (0, ± 1, ± 2, …, ± m). Wherein the positive and negative signs correspond to lead adjustment and lag adjustment, respectively. According to the relation of winding voltage, current and turns, the leakage impedance of the common winding and the low-voltage winding is as follows:
wherein m is the maximum adjustable gear of the on-load voltage regulating switch2Selection of gear position for common winding, m3The gear is selected for the low voltage winding. Equivalent circuit of HVST series-connected line as shown in FIG. 6, HVST integral leakage impedance ZHVSTIs a value varying with the gear, and the calculation formula is as follows:
in the formula, Za′1XAnd Za′2xThe leakage impedance values of the common winding and the low-voltage winding are respectively changed along with the gear change of the on-load tap changer.
Illustratively, the calculating a series compensation voltage output by the HVST to the three-phase power transmission line according to the overall equivalent impedance and analyzing a power flow distribution of the three-phase power transmission line after accessing the HVST specifically includes:
and establishing a compensation voltage equation according to the integral equivalent impedance and the mode that the HVST is connected into the three-phase power transmission line, obtaining a three-phase steady-state power flow equation of the three-phase power transmission line before and after compensation is carried out through series compensation voltage, and analyzing the adjustment amount and the power flow distribution of the three-phase power transmission line power flow after the HVST is connected into the three-phase power transmission line.
When the stable power flow mathematical model is established for the HVST, considering that the parallel side of the HVST provides input voltage for an electric network to play an excitation role, and the serial side provides output compensation voltage which is three-phase symmetrical, the embodiment establishes the stable power flow mathematical model by taking the compensation voltage UHVSTA of the A-phase power transmission line as an example, wherein the isolation transformer is an ideal transformer model and only plays an electric isolation role.
The phase a compensation voltage is as shown in fig. 7, the phase B common winding B1 and the phase C low-voltage winding C2 are respectively provided with a group of on-load tap changers, the two windings are connected in series to provide a series compensation voltage UHVSTA of the phase a transmission line, and when the on-load tap changers are in different gears, the phase B common winding B1 and the phase C low-voltage winding C2 are connectedThe output voltage also varies, and the switching positions of the B-phase common winding B1 and the C-phase low-voltage winding C2 can be (0, ± 1, ± 2, …, ± m). UB2step and UC3step represent voltage vectors of the levels of the B-phase common winding B1 and the C-phase low-voltage winding C2, namely voltages between adjacent taps, respectively, and the voltage amplitude UstepA size of
Ustep＝|UB2step|＝|UC3step|＝U2N/m (21)
In the formula of U2NThe rated voltage of the common winding in the single-phase equivalent circuit of the autotransformer. When the tap of the voltage regulating switch is switched at +/-m, the amplitude of the output voltage UB2 of the B-phase common winding B1 and the amplitude of the output voltage UC3 of the C-phase low-voltage winding are both U2N。
The switching gear of the on-load voltage regulation switch of the B-phase common winding is marked as mB2The switching gear of the on-load voltage regulating switch of the C-phase low-voltage winding is marked as mC3Then the compensation voltage output by the HVST series side can be calculated as:
for example, fig. 8 is a vector diagram of the head end voltage of the a-phase line, and the input voltage of the head end of the line is UsAThe compensated voltage is UsA1, UB2 represents the output voltage of the B-phase common winding B1, and UC3 represents the output voltage of the C-phase low-voltage winding C2. When m isB2＝-2，mC3When the on-load tap changer of the B-phase common winding is switched in a-2 gear and the on-load tap changer of the C-phase low-voltage winding is switched in a +4 gear, the compensation voltage vector of the HVST connected to the A-phase is shown as UHVSTA in the figure, and the voltage vector of the head end of the compensated system is shown as voltage USA1 in the figure.
When the on-load voltage regulating switch is adjustable in +/-M levels, the number M of voltage vectors which can be output by the HVST is as follows:
M＝(2m+1)2 (23)
the analysis of the formula (23) shows that when the number of adjustable stages of the on-load tap changer is increased, the number M of compensation voltage vectors UHVST which can be output by the HVST is increased, and the adjustment accuracy of the voltage of the transmission line is also increased. However, the higher the adjustable stage number of the on-load tap changer is, the higher the device cost is, so that the adjustable stage number of the on-load tap changer is determined according to the requirement of actual power flow regulation.
And establishing an HVST three-phase steady-state power flow mathematical analysis model by the A-phase analysis embodiment, and writing a three-phase compensation voltage equation set. And defining three-phase series compensation voltages generated by HVST as UHVSTA, UHVSTB and UHVSTC, and injecting the three-phase series compensation voltages into a power transmission line through a three-phase isolation transformer. The input voltage of the head end of the transmission line is USA, USB and USC, and the compensated voltage of the line is USA1, USB1 and UsC 1. The three-phase common winding and the low-voltage winding a1, b1, c1, a2, b2 and c2 output series compensation voltages which are respectively marked as UA2, UB2, UC2, UA3, UB3 and UC 3.
The B-phase common winding B1 and the C-phase low-voltage winding C2 are connected in series through a load tap changer to provide a series compensation voltage UHVSTA of the B-phase transmission line; the C-phase common winding C1 and the A-phase low-voltage winding a2 are connected in series through the on-load tap changer to provide a series compensation voltage UHVSTB of the B-phase transmission line; the A-phase common winding a1 and the B-phase low-voltage winding B2 are connected in series through the load tap changer to provide a series compensation voltage UHVSTC of the C-phase transmission line.
The equation for the three-phase compensation voltage is:
the input three-phase voltage relationship of the power transmission line is as follows:
establishing a compensation voltage equation of the transmission line, wherein the head end voltage expression after the compensation of the transmission line is as follows:
by adjusting the position of the on-load tap changer, the series compensation voltage output by the HVST can be adjusted. In order to keep the three-phase voltage balance of the head-end input voltages USA, USB and USC of the three-phase power transmission system, the three-phase series compensation voltages generated by HVST are UHVSTA, UHVSTB and UHVSTC for ensuring that the head-end voltages USA1, USB1 and UsC1 of the compensated system also keep the three-phase voltage balance, namely the on-load voltage regulating switches of the three-phase common windings a1, b1 and c1 need to be switched in the same gear; the load tap changers of the three-phase low-voltage windings a2, b2 and c2 also need to be switched in the same gear. It should be noted, however, that the on-load tap changer positions between the common winding "a 1-b1-c 1" and the low voltage winding "a 2-b2-c 2" may be different, so that the HVST has series compensated voltage outputs of different magnitudes and phases.
It should be noted that the phase angle of the compensation voltage provided by the HVST is adjustable from-180 ° to +180 °, and the amplitude of the output voltage is adjustable from 0 to v 3. The amplitude and the phase of the HVST output voltage can be adjusted by adjusting the switching position of the on-load tap changer of the HVST, which means that related workers can flexibly adjust the active power flow and the reactive power flow according to the load condition of the line. To better demonstrate the principles and basis of HVST for system power flow regulation, the impact on power flow after access to the transmission system from the HVST will be described below.
Referring to fig. 9, fig. 9 is a schematic diagram of a power transmission system connected to an HVST, and two ends of the power transmission line are simplified into an ideal single-machine infinite system. Because the resistance of the high-voltage transmission line is very small relative to the reactance, the resistance and the capacitance of the transmission line are ignored when a steady-state power flow mathematical analysis model is established, and the equivalent reactance of the transmission line is represented by XL.
Fig. 10 is a voltage vector diagram of an HVST access power transmission system. Voltage magnitude for compensation voltage outputted from HVST to transmission line
The phase is shown as θ HVST. Before compensation, the voltage vector of the head end of the system is
Phase is 0 DEG, and system end voltage vector is
The phase is delta, namely the phase difference of the voltages at the head end and the tail end of the system before compensation is delta. After HVST compensation, the head end voltage vector of the system is
The phase difference of the first and last voltages of the system is delta'.
The power transmitted from the transmission line to the end is
Wherein the active power and the reactive power are respectively represented by PL and QL; HVST equivalent impedance is represented by ZHVSTThe end power calculation equation of the system can be obtained from fig. 7 as follows:
the equation (27) can calculate the active and reactive power flows of the tail end of the power transmission system after the power transmission system is subjected to HVST compensation, wherein the power flows are influenced by the head end voltage, the tail end voltage, the HVST compensation voltage and the line reactance value. When the HVST is not used for compensating the transmission line, namely when the output voltage UHVST of the HVST series side is equal to 0, the power transmitted to the tail end by the transmission line is
The active power and the reactive power are respectively represented by PL0 and QL0, and the terminal power calculation formula of the system is as follows:
the compensation voltage output by the system head and tail end voltage vector and the HVST is respectively as follows:
bringing equation (29) into equation (28) yields the active and reactive power at the end of the transmission system when no HVST compensation equipment is engaged:
after formula (29) is taken into formula (27) and the HVST compensation device is put into operation, the active and reactive power at the tail end of the power transmission system are as follows:
as can be seen from equations (32) and (33), after the HVST is connected to the power transmission system, the total impedance of the system is at line reactance XLOn which an impedance value Z changing with the gear of the on-load tap changer is superimposedHVSTThe active power and the reactive power at the tail end of the system are respectively superposed with a component and the amplitude U of the HVST output voltageHVSTAnd phase angle thetaHVSTIt is related.
When the system is determined, the amplitude value and the phase difference of the voltage at the head end and the tail end of the system and the reactance of a transmission line are determined, namely Us, UL, delta and XL are kept constant in the formula. After the HVST is put into use, series compensation voltage is provided for the transmission line
Phase angle theta of its output voltageHVSTAdjustable from-180 deg. to +180 deg. and output voltage amplitude UHVSTIn that
Is adjustable. On-load tap changing for HVST regulationThe amplitude and the phase of the HVST output voltage can be adjusted by switching the position of a switch tap, so that the active power flow and the reactive power flow at the tail end of the system can be flexibly adjusted.
In the embodiment, the leakage impedance of the HVST is considered when the HVST equivalent circuit model is constructed, so that the precision of the model is improved, and the subsequent analysis and calculation results are more accurate. In order to more intuitively reflect the influence of the leakage impedance of the HVST, an HVST actual model can be built in electromagnetic transient simulation software PSCAD, and the accuracy of the HVST equivalent model is verified by taking the simulation result of the model as a reference. And when the rated voltage USN of the HVST secondary winding is taken from 0-0.5 p.u., the generated maximum phase shift angle changes along with the rated voltage USN of the secondary winding. As can be seen from fig. 11, the equivalent impedance of the HVST body creates an internal phase shift angle β within it that affects its external characteristics and power flow regulation performance.
Compared with the prior art, the power flow analysis method based on the HVST equivalent circuit model provided by the embodiment of the invention obtains the circuit parameters of the three-phase power transmission line accessed to the HVST so as to construct the single-phase circuit equivalent model and obtain the integral equivalent impedance expression of the HVST. And establishing a compensation voltage equation according to the mode that the HVST is accessed into the power transmission system to calculate the series compensation voltage, and writing a three-phase steady-state power flow equation of the lines before and after compensation in a row to quickly and accurately calculate the adjustment quantity of the HVST to the system power flow after the HVST is accessed into the power transmission system. As the HVST model adopted in the whole analysis and calculation process is a circuit equivalent model, the problem of multilayer complexity of the existing HVST model is avoided, the leakage impedance of the HVST model is also considered under the condition of ensuring the simplicity and effectiveness of the model, the modeling accuracy is further improved, and the accuracy of the power flow analysis and calculation is further improved.
In addition, in the embodiment of the invention, the HVST integral leakage impedance of the single-phase circuit equivalent model is changed along with the change of the gear of the on-load tap changer, so in practical application, an operator can adjust the switching position of the on-load tap changer tap of the HVST according to the adjustment quantity of the expected load flow of a circuit, namely the amplitude and the phase of the output voltage of the HVST can be adjusted, which means that related technicians can flexibly adjust the active and reactive load flows according to the load condition of the circuit.
An embodiment of the present application provides a power flow analysis apparatus based on an HVST equivalent circuit model, including: the device comprises an access module, a circuit model establishing module, an impedance calculating module and an analyzing module.
The access module is used for accessing a high-voltage side winding in three phases of HVST to a corresponding three-phase power transmission line, and enabling a medium-voltage side winding and a low-voltage side winding of any two phases of the three phases of HVST to form a residual single-phase series compensation group; and the series compensation group provides series compensation voltage for the residual single phase, and the series compensation voltage is converged into the three-phase power transmission line through an isolation transformer.
And the circuit model establishing module is used for establishing an HVST single-phase equivalent circuit model according to the electrical parameters of the HVST.
The impedance calculation module is used for calculating the integral equivalent impedance of the HVST single-phase equivalent circuit model according to the impedance value of each winding and the excitation impedance value in the HVST single-phase equivalent circuit model; the integral equivalent impedance changes along with the change of the gear of the on-load voltage regulating switch.
And the analysis module is used for calculating the series compensation voltage output to the three-phase transmission line by the HVST according to the integral equivalent impedance and analyzing the load flow distribution of the three-phase transmission line after the three-phase transmission line is accessed to the HVST.
Illustratively, the establishing of the HVST single-phase equivalent circuit model specifically includes:
and deducing an HVST single-phase voltage and current equation according to the connection form of the single-phase winding of the autotransformer, converting the electric quantity of the public winding and the low-voltage winding side to the high-voltage side winding, and establishing an HVST single-phase equivalent circuit model.
Illustratively, the analysis module is specifically configured to:
and establishing a compensation voltage equation according to the integral equivalent impedance and the mode that the HVST is connected into the three-phase power transmission line, obtaining a three-phase steady-state power flow equation of the three-phase power transmission line before and after compensation is carried out through series compensation voltage, and analyzing the adjustment amount and the power flow distribution of the three-phase power transmission line power flow after the HVST is connected into the three-phase power transmission line.
Compared with the prior art, the power flow analysis device based on the HVST equivalent circuit model provided by the embodiment of the invention constructs the single-phase circuit equivalent model by acquiring the circuit parameters of the three-phase power transmission line accessed to the HVST, and obtains the integral equivalent impedance expression of the HVST. And establishing a compensation voltage equation according to the mode that the HVST is accessed into the power transmission system to calculate the series compensation voltage, and writing a three-phase steady-state power flow equation of the lines before and after compensation in a row to quickly and accurately calculate the adjustment quantity of the HVST to the system power flow after the HVST is accessed into the power transmission system. As the HVST model adopted in the whole analysis and calculation process is a circuit equivalent model, the problem of multilayer complexity of the existing HVST model is avoided, the leakage impedance of the HVST model is also considered under the condition of ensuring the simplicity and effectiveness of the model, the modeling accuracy is further improved, and the accuracy of the power flow analysis and calculation is further improved.
In addition, in the embodiment of the invention, the HVST integral leakage impedance of the single-phase circuit equivalent model is changed along with the change of the gear of the on-load tap changer, so in practical application, an operator can adjust the switching position of the on-load tap changer tap of the HVST according to the adjustment quantity of the expected load flow of a circuit, namely the amplitude and the phase of the output voltage of the HVST can be adjusted, which means that related technicians can flexibly adjust the active and reactive load flows according to the load condition of the circuit.
A third aspect of embodiments of the present application provides a computer-readable storage medium comprising a stored computer program; wherein the computer program, when running, controls an apparatus in which the computer-readable storage medium is located to perform the power flow analysis method based on the HVST equivalent circuit model as described above.
Preferably, the computer program may be divided into one or more modules/units (e.g., computer program) that are stored in the memory and executed by the processor to implement the invention. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used for describing the execution process of the computer program in the terminal device.
The Processor may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable Gate Array (FPGA) or other Programmable logic device, a discrete Gate or transistor logic device, a discrete hardware component, etc., the general purpose Processor may be a microprocessor, or the Processor may be any conventional Processor, the Processor is a control center of the terminal device, and various interfaces and lines are used to connect various parts of the terminal device.
The memory mainly includes a program storage area and a data storage area, wherein the program storage area may store an operating system, an application program required for at least one function, and the like, and the data storage area may store related data and the like. In addition, the memory may be a high speed random access memory, may also be a non-volatile memory, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash Card (Flash Card), and the like, or may also be other volatile solid state memory devices.
It should be noted that the terminal device may include, but is not limited to, a processor and a memory, and those skilled in the art will understand that the terminal device is only an example and does not constitute a limitation of the terminal device, and may include more or less components, or combine some components, or different components.
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
Claims (10)
1. A power flow analysis method based on an HVST equivalent circuit model is characterized by comprising the following steps:
connecting a high-voltage side winding in three phases of HVST into a corresponding three-phase power transmission line, and enabling a medium-voltage side winding and a low-voltage side winding of any two phases of the three phases of HVST to form a residual single-phase series compensation group; the series compensation group provides series compensation voltage for the residual single phase, and the series compensation voltage is converged into the three-phase power transmission line through an isolation transformer;
establishing an HVST single-phase equivalent circuit model according to the electrical parameters of the HVST;
calculating the integral equivalent impedance of the HVST single-phase equivalent circuit model according to the impedance value of each winding and the excitation impedance value in the HVST single-phase equivalent circuit model; the integral equivalent impedance changes along with the change of the gear of the on-load voltage regulating switch;
and calculating series compensation voltage output to the three-phase transmission line by the HVST according to the integral equivalent impedance, and analyzing the load flow distribution of the three-phase transmission line after the HVST is accessed.
2. The HVST equivalent circuit model-based power flow analysis method according to claim 1, wherein the electrical parameters specifically include:
the voltages of the high voltage side, the medium voltage side and the low voltage side correspond to the voltage and the load current;
the number of turns, current, electromotive force and leakage impedance of the series winding, the common winding and the low-voltage side winding correspond to each other.
3. The HVST equivalent circuit model-based power flow analysis method according to claim 1, wherein the establishing of the HVST single-phase equivalent circuit model specifically comprises:
and deducing an HVST single-phase voltage and current equation according to the connection form of the single-phase winding of the autotransformer, converting the electric quantity of the public winding and the low-voltage winding side to the high-voltage side winding, and establishing an HVST single-phase equivalent circuit model.
4. The HVST equivalent circuit model-based power flow analysis method according to claim 1, wherein the respective winding impedance values are obtained by a transformer short circuit test;
the transformer short-circuit test is that a winding on one side of a transformer is short-circuited, alternating voltage with rated frequency is added from the winding on the other side of the transformer, current in the winding of the transformer is used as a rated value, and the added voltage and power are measured to obtain impedance values of the windings.
5. The HVST equivalent circuit model-based power flow analysis method according to claim 1, wherein the excitation impedance value is calculated after determining the HVST single-phase equivalent magnetic circuit according to the length, permeability, and cross-sectional area of the magnetic circuit of the iron core of the transformer.
6. The HVST equivalent circuit model-based power flow analysis method according to claim 1, wherein the calculating of the series compensation voltage output by the HVST to the three-phase transmission line according to the overall equivalent impedance and the analyzing of the power flow distribution of the three-phase transmission line after the HVST is connected specifically comprises:
and establishing a compensation voltage equation according to the integral equivalent impedance and the mode that the HVST is connected into the three-phase power transmission line, obtaining a three-phase steady-state power flow equation of the three-phase power transmission line before and after compensation is carried out through series compensation voltage, and analyzing the adjustment amount and the power flow distribution of the three-phase power transmission line power flow after the HVST is connected into the three-phase power transmission line.
7. A power flow analysis device based on an HVST equivalent circuit model is characterized by comprising:
the access module is used for accessing a high-voltage side winding in three phases of HVST to a corresponding three-phase power transmission line and enabling a medium-voltage side winding and a low-voltage side winding of any two phases of the three phases of HVST to form a residual single-phase series compensation group; the series compensation group provides series compensation voltage for the residual single phase, and the series compensation voltage is converged into the three-phase power transmission line through an isolation transformer;
the circuit model building module is used for building an HVST single-phase equivalent circuit model according to the electrical parameters of the HVST;
the impedance calculation module is used for calculating the integral equivalent impedance of the HVST single-phase equivalent circuit model according to the impedance value of each winding and the excitation impedance value in the HVST single-phase equivalent circuit model; the integral equivalent impedance changes along with the change of the gear of the on-load voltage regulating switch;
and the analysis module is used for calculating the series compensation voltage output to the three-phase transmission line by the HVST according to the integral equivalent impedance and analyzing the load flow distribution of the three-phase transmission line after the three-phase transmission line is accessed to the HVST.
8. The HVST equivalent circuit model-based power flow analysis device according to claim 7, wherein the establishing of the HVST single-phase equivalent circuit model specifically comprises:
and deducing an HVST single-phase voltage and current equation according to the connection form of the single-phase winding of the autotransformer, converting the electric quantity of the public winding and the low-voltage winding side to the high-voltage side winding, and establishing an HVST single-phase equivalent circuit model.
9. The HVST equivalent circuit model-based power flow analysis device according to claim 7, wherein the analysis module is specifically configured to:
and establishing a compensation voltage equation according to the integral equivalent impedance and the mode that the HVST is connected into the three-phase power transmission line, obtaining a three-phase steady-state power flow equation of the three-phase power transmission line before and after compensation is carried out through series compensation voltage, and analyzing the adjustment amount and the power flow distribution of the three-phase power transmission line power flow after the HVST is connected into the three-phase power transmission line.
10. A computer-readable storage medium, characterized in that the computer-readable storage medium comprises a stored computer program; wherein the computer program controls an apparatus in which the computer-readable storage medium is located to perform the HVST equivalent circuit model-based power flow analysis method according to any one of claims 1 to 6 when executed.
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| CN103066589A (en) * | 2012-12-11 | 2013-04-24 | 天津市电力公司 | Equivalent modeling method of power system double output phase regulator |
| CN103199522A (en) * | 2013-02-25 | 2013-07-10 | 中国电力科学研究院 | Controllable phase shifter used for super /extra-high voltage circuit and parameter design method thereof |
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