CN117559460A - Middle-low voltage cloud edge cooperative voltage control method based on fusion terminal - Google Patents
Middle-low voltage cloud edge cooperative voltage control method based on fusion terminal Download PDFInfo
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Abstract
The invention relates to the technical field of power system automation, in particular to a medium-low voltage cloud edge cooperative voltage control method based on a fusion terminal, which comprises the following steps of 1, dividing any low-voltage distribution line into a plurality of nodes; step 2, under the condition that the capacity of the compensation transformer and the allowable deviation constraint of the node voltage are met, establishing a comprehensive objective function and determining the constraint condition of the comprehensive objective function; step 3, selecting a series voltage compensation device which accords with the constraint condition, carrying out optimization treatment on line power flow after the series voltage compensation device is connected, and solving device optimization configuration data when the comprehensive objective function is minimum; and 4, selecting an optimally configured series voltage compensation device, and adjusting feedback control schemes of the single-phase three-level rectifier and the single-phase full-bridge inverter to enable the series voltage compensation device to achieve a compensation effect. The invention realizes the rapid response and continuous adjustment of the load voltage regulation by providing the control method.
Description
Technical Field
The invention relates to the technical field of power system automation, in particular to a medium-low voltage cloud edge cooperative voltage control method based on a fusion terminal.
Background
According to a traditional scheme for controlling low voltage of the step switching of the transformer based on the fast switch, under the condition of low voltage, the gear of the series transformer is changed according to load voltage and current; in high voltage conditions, a bypass switch bypass is used. The scheme belongs to coarse voltage adjustment, so that the control and the structure are simple. However, the response time of the fast switch is typically in the order of ms, and a momentary undervoltage or overvoltage of the load may occur during the gear shift.
Chinese patent publication No.: CN110716601a. A voltage control device includes a charge pump, a driving circuit, and a control circuit. The charge pump provides a first voltage. The driving circuit is coupled to the charge pump and receives the first voltage and the reference voltage. The driving circuit outputs a driving signal according to the input signal, the first voltage and the reference voltage. The control circuit is coupled to the charge pump and the driving circuit. It follows that the voltage control device has the following problems: the load is easy to instantaneously undervoltage or overvoltage in the process of shifting the transformer.
Disclosure of Invention
Therefore, the invention provides a middle-low voltage cloud edge cooperative voltage control method based on a fusion terminal, which is used for solving the problem that in the prior art, the load is easy to be instantaneously under-voltage or over-voltage in the gear shifting process of a transformer.
In order to achieve the above purpose, the invention provides a method for controlling the cooperative voltage of the middle and low voltage cloud edges based on a fusion terminal, which comprises the following steps,
step S1, selecting any low-power distribution line for each point in a power grid with the same voltage level in a power system, and dividing a plurality of nodes; the node is arranged according to the conditions of a plurality of branch lines of the low-power distribution line;
step S2, under the condition that the capacity of the compensation transformer and the allowable deviation constraint of the node voltage are met, a comprehensive objective function is established according to an active loss formula and a node voltage average deviation formula of the low-power distribution line, and the constraint condition of the comprehensive objective function is determined;
step S3, selecting a series voltage compensation device which accords with the constraint condition, carrying out optimization treatment on line power flow after the series voltage compensation device is connected, and solving device optimization configuration data when the comprehensive objective function is minimum;
step S4, selecting an optimally configured series voltage compensation device according to the device optimal configuration data result, and adjusting feedback control schemes of the single-phase three-level rectifier and the single-phase full-bridge inverter;
the step S4 comprises a step S4-1 and a step S4-2;
The step S4-1 is that a double closed-loop control system is adopted for the single-phase three-level rectifier, and comprises a direct-current side voltage control outer ring and an alternating-current side current control inner ring, and hysteresis regulation is adopted for midpoint potential balance;
step S4-2, the double closed loop control system of the single-phase full-bridge inverter adopts an inductance current instantaneous value feedback inner loop and an output voltage instantaneous value feedback outer loop, and adopts dead beat control to track current in the control process, and simultaneously introduces load current compensation and output voltage cross feedback decoupling control;
in the step S4-1, a prediction function is established according to historical data, the current actual value which is the same as the trend of the prediction function is determined according to the reference current value and the current actual value at any time, deviation range judgment is performed on the current actual value which is not in the deviation range, adjustment and prediction are performed according to the prediction function, the original prediction function is predicted, the actual current value at the next sampling moment is compared, a proper prediction calculation process is determined, and coverage adjustment is performed on the original prediction function according to the using times of different prediction processes.
Further, in step S2, the active loss formula of the low-voltage distribution line is designed according to the number of nodes stored in any low-voltage distribution line, the voltage amplitude of each node, and the conductance of each branch, and the average deviation formula of the voltage of each node is designed according to the voltage amplitude of any node and the rated voltage amplitude;
The comprehensive objective function is obtained by carrying out normalization and combination on a plurality of indexes in an active loss formula of the low-power distribution line and a voltage average deviation formula of each node and then weighting;
the constraint conditions of the comprehensive objective function comprise voltage deviation constraint of each node and capacity constraint of a compensation transformer, wherein the voltage deviation constraint of each node is lower limit of allowable deviation of voltage of any node and upper limit of allowable deviation of voltage of any node, and the capacity constraint of the compensation transformer is determined according to node voltage of each compensation point, voltage reduction transformation ratio of the corresponding compensation transformer, current injected by a compensation device and capacity of a distribution transformer.
Further, in step S3, the optimizing step is:
step S301, according to distribution line parameters and load original data of each node, performing distribution line original power flow calculation by using a forward push-back substitution method of load static voltage characteristics;
step S302, taking an access point of a series voltage compensation device as a demarcation point, and dividing the distribution line into a compensation point front section and a compensation point rear section;
step S303, after the series voltage compensation device is connected, the voltage value of the compensation point is given to the head end node of the back-end line, other parameters are unchanged, and the back-end power flow calculation of the compensation point is performed;
Step S304, after the series voltage compensation device is connected, the series voltage compensation device is compensated and combined with the back-stage power flow data to obtain the complete power flow data of the line after the series voltage compensation device is connected;
step S305, repeating the steps S202-204 to calculate the power flow calculation data of different access points, and generating a plurality of groups of data;
step S306, screening out the group of data if the node voltage or the capacity of the compensation transformer is out of limit according to the constraint condition;
step S307, according to the comprehensive objective function, calculating the minimum value of the comprehensive objective function of all the data sets conforming to the constraint condition, outputting the minimum value therein, and accessing the node number of the device;
step S308, calculating the actual voltages at two sides of the compensation transformer at the moment, reserving the margin on the basis, and taking the reserved margin as the optimal configuration capacity value of the compensation transformer.
Further, in step S4-1, the current side voltage control outer loop process is: the direct-current side voltage control outer loop obtains the amplitude and phase deviation information of the input phase voltage through a phase-locked loop structure under a synchronous rotation coordinate system by the input grid voltage through a single-phase SRF-PLL, and the output phase deviation information is subjected to amplitude normalization.
Further, in step S4-1, in the process of controlling the inner loop by the ac side current, the difference between the dc voltage given value and the dc voltage sampling value is calculated, and is input into the PI regulator, and the inner loop reference current amplitude is output;
sampling the current at the network side by the alternating current side of the single-phase three-level rectifier at a fixed frequency, comparing the actual value of the current obtained by sampling this time with the predicted reference current at the next sampling moment, and obtaining the optimal control voltage.
Further, in step S4-1, recording the actual value of the current and the reference current value of any one time;
a prediction function is stored in the process of predicting the reference current at the next sampling moment, the prediction function is established according to recorded historical data, and a preset regulation value and a preset deviation range are arranged in the prediction function;
the reference current predicts the reference current at the next sampling moment according to the data condition in the historical ring ratio period, the ring ratio period is the internal value of the prediction function, and the prediction result is the current reference value.
Further, according to the reference current value and the current actual value at any time, judging the trend direction in the current actual value and the prediction function, and determining whether the current actual value is the same as the trend of the prediction function at the time;
If the current actual value is the same as the trend of the prediction function, judging the deviation range of the reference current value;
if the current actual value is different from the trend of the prediction function, trend error reporting is carried out.
Further, calculating a current error value predicted at the time according to the reference current value and the current actual value at any time;
if the sampling time is within the preset deviation range, carrying out trend judgment of the next sampling time;
if the current value is not in the preset deviation range, calculating a reference current value at the next sampling moment;
and calculating the reference current value at the next sampling moment when the prediction is performed, wherein the calculating comprises the steps of calculating a first reference current value according to a prediction function and calculating a second reference current value according to the prediction function and a preset regulation value, respectively calculating the difference value between the two reference current values and the actual current value of the current sample, judging the reference value similar to the difference value of the actual current value of the current sample, and taking the calculation process of the similar value as the calculation process of the reference current value at the next sampling moment.
Further, an adjustment period and preset adjustment times are stored for the prediction function;
The method comprises the steps that overall adjustment is conducted on a prediction function which reaches preset adjustment times in any adjustment period, the prediction function is adjusted to cover an initial prediction function according to the calculation process of calculating a reference current value for the last time, and the initial prediction function is used as the prediction function to calculate the reference current value at the next sampling moment;
and for the prediction function which does not reach the preset adjustment times in any adjustment period, performing prediction function detail adjustment, wherein the prediction function detail adjustment is to select a calculation process with more use times of two calculation modes in the adjustment period, cover the initial prediction function according to the calculation formula of the last time, and perform calculation of a reference current value at the next sampling moment by taking the initial prediction function as the prediction function.
Further, in the step S4-1, the hysteresis loop is adjusted by adding a hysteresis loop comparison link of the upper capacitance voltage deviation and a hysteresis loop comparison link of the lower capacitance voltage deviation into the midpoint balance control system, when the voltage deviation is within the tolerance range of the hysteresis loop comparator, the pulse given by the original control algorithm is still used, and if the voltage difference reaches the upper or lower tolerance limit of the hysteresis loop regulator, the converted pulse is output.
Compared with the prior art, the method has the beneficial effects that the basis is provided for the installation position and capacity configuration of the compensation device through the established multi-objective optimized mathematical model with the minimum active line loss and the minimum node average voltage deviation, the provided line power flow solving method taking the static characteristics of load voltage into account and the influence of the compensation device can quickly and accurately solve the model, and the calculation errors caused by the load voltage change and the line total power change after the compensation device is connected can be effectively reduced; the developed series voltage compensation device based on series voltage compensation control can achieve the capacity of the compensation device with the load of 1/10 line, realize the effect that the line full line voltage meets the index and the terminal voltage is raised (or lowered) by 25%, and provide a low-cost solution for the terminal low-voltage problem management of the power distribution network under a long power supply distance; the compensation device takes a rectifying inversion unit as a core, the rectifier adopts an I-shaped three-level topology, and under the double closed-loop control and the midpoint potential balance control, the direct-current voltage stabilization, the alternating-current side unit power factor control and the low injection harmonic wave are realized; the inverter adopts single-phase full-bridge topology and double closed-loop control, can realize quick response and continuous regulation of load voltage regulation, and the control method has the advantages of quick response, strong load disturbance resistance, continuous uninterrupted voltage regulation, wide-range voltage regulation capability and low-cost design.
Furthermore, the invention provides a basis for the installation position and capacity configuration of the series voltage compensation device by establishing a multi-objective optimized mathematical model with minimum active loss of the distribution line and minimum average voltage deviation of the nodes.
Furthermore, the load voltage static model is introduced into the load voltage calculation to correct the load voltage static model, the influence on the load voltage after the compensation device is connected in is considered, the load voltage after the compensation device is connected in series is calculated as a front-section line and a rear-section line of the access point, and calculation errors caused by load voltage change and total power change of the lines after the compensation device is connected in are effectively reduced.
Furthermore, when the current control is carried out on the single-phase three-level rectifier, the shape of the input current of the converter is approximate to a sine wave through dead beat prediction current control, and the phase of the network side voltage is tracked, so that the network side power factor is close to 1 or-1, and the current controller has faster transient response and satisfactory steady state characteristics.
Further, in the process of current control inner loop control at the alternating side, when current prediction is carried out, a related prediction function is established for reference current at any next sampling moment according to related conditions in a historical loop ratio period, and reference current value prediction is carried out at any sampling moment according to the function.
Further, the invention compares the variation trend of the actual current value with the variation trend of the prediction function, determines whether the reference current value and the prediction function trend accord with the actual application, records and reports errors which do not accord with the trend, and determines the deviation range of the consistent trend so as to refine the accuracy of the prediction function.
Further, the invention determines the actual current values at different positions in the preset deviation range of the prediction function, calculates the original prediction function for the reference current value at the next sampling moment of the actual current value in the preset deviation range, and adjusts the supplementary regulation value for the prediction function value for the reference current value at the next sampling moment of the actual current value not in the preset deviation range so as to improve the accuracy of the prediction function.
Furthermore, the invention can carry out integral adjustment on the prediction function so as to carry out integral coverage adjustment on the prediction function in the process of predicting the current reference value, and the calculation result of the prediction function is more approximate to the prediction result of the current error minimum value from the large direction, thereby improving the efficiency of the current control inner loop control at the alternating current side.
Furthermore, the invention adopts a midpoint potential control method based on hysteresis regulation, which essentially converts the current switch pulse combination which is unfavorable for midpoint potential balance into the pulse combination which is favorable for midpoint potential balance, thereby achieving the purpose of controlling midpoint potential.
Drawings
Fig. 1 is a step flowchart of a method for controlling a middle-low voltage cloud-edge cooperative voltage based on a fusion terminal according to the embodiment;
FIG. 2 is a block diagram of a dual closed loop control of a single phase three level rectifier according to the present embodiment;
fig. 3 is a double closed-loop control block diagram of the single-phase full-bridge inverter according to the embodiment;
fig. 4 is a current loop control block diagram of the single-phase full-bridge inverter according to the embodiment after decoupling and simplification;
FIG. 5 is a simplified voltage loop of the single-phase full-bridge inverter according to the present embodiment after load current compensation is added and the inner current loop is regarded as a constant gain;
fig. 6 is a flowchart of the optimization process of the line power flow after the series voltage compensation device is connected in the embodiment;
fig. 7 is a diagram of a phase-locked loop structure under a synchronous rotation coordinate system of the single-phase SRF-PLL according to the present embodiment.
Detailed Description
In order that the objects and advantages of the invention will become more apparent, the invention will be further described with reference to the following examples; it should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are merely for explaining the technical principles of the present invention, and are not intended to limit the scope of the present invention.
It should be noted that, in the description of the present invention, terms such as "upper," "lower," "left," "right," "inner," "outer," and the like indicate directions or positional relationships based on the directions or positional relationships shown in the drawings, which are merely for convenience of description, and do not indicate or imply that the apparatus or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.
Furthermore, it should be noted that, in the description of the present invention, unless explicitly specified and limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly, and may be either fixedly connected, detachably connected, or integrally connected, for example; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention can be understood by those skilled in the art according to the specific circumstances.
Referring to fig. 1, fig. 2, fig. 3, fig. 4, fig. 5, fig. 1 is a flow chart of steps of a method for controlling a middle-low voltage cloud edge cooperative voltage based on a fusion terminal according to the present embodiment, fig. 2 is a dual closed-loop control block diagram of a single-phase three-level rectifier according to the present embodiment, fig. 3 is a dual closed-loop control block diagram of a single-phase full-bridge inverter according to the present embodiment, fig. 4 is a current loop control block diagram after decoupling and simplifying the single-phase full-bridge inverter according to the present embodiment, and fig. 5 is a simplified voltage loop after adding load current compensation and regarding an inner current loop as a constant gain in the single-phase full-bridge inverter according to the present embodiment, wherein ZOH is a zero-order keeper for discretizing a controlled object.
The invention provides a medium-low voltage cloud edge cooperative voltage control method based on a fusion terminal, which comprises the following steps of,
step S1, selecting any low-power distribution line for each point in a power grid with the same voltage level in a power system, and dividing a plurality of nodes; the node is arranged according to the conditions of a plurality of branch lines of the low-power distribution line;
step S2, under the condition that the capacity of the compensation transformer and the allowable deviation constraint of the node voltage are met, a comprehensive objective function is established according to an active loss formula and a node voltage average deviation formula of the low-power distribution line, and the constraint condition of the comprehensive objective function is determined;
Step S3, selecting a series voltage compensation device which accords with the constraint condition, carrying out optimization treatment on line power flow after the series voltage compensation device is connected, and solving device optimization configuration data when the comprehensive objective function is minimum;
step S4, selecting an optimally configured series voltage compensation device according to the device optimal configuration data result, and adjusting feedback control schemes of the single-phase three-level rectifier and the single-phase full-bridge inverter;
the step S4 comprises a step S4-1 and a step S4-2;
the step S4-1 is that a double closed-loop control system is adopted for the single-phase three-level rectifier, and comprises a direct-current side voltage control outer ring and an alternating-current side current control inner ring, and hysteresis regulation is adopted for midpoint potential balance;
step S4-2, the double closed loop control system of the single-phase full-bridge inverter adopts an inductance current instantaneous value feedback inner loop and an output voltage instantaneous value feedback outer loop, and adopts dead beat control to track current in the control process, and simultaneously introduces load current compensation and output voltage cross feedback decoupling control;
in the step S4-1, a prediction function is established according to historical data, the current actual value which is the same as the trend of the prediction function is determined according to the reference current value and the current actual value at any time, deviation range judgment is performed on the current actual value which is not in the deviation range, adjustment and prediction are performed according to the prediction function, the original prediction function is predicted, the actual current value at the next sampling moment is compared, a proper prediction calculation process is determined, and coverage adjustment is performed on the original prediction function according to the using times of different prediction processes.
With continued reference to fig. 3, 4, and 5, an inductor current feedback loop is employed and deadbeat control is employed for current tracking.
After the output voltage feedback is introduced, the double closed-loop control system of the single-phase full-bridge inverter outputs the following control quantity of the current loop:
in the formula, v r (k) The output control quantity of the current loop at the moment k;
K DB is the gain coefficient of the inductance current loop;
L s equivalent inductance of the alternating current side of the single-phase three-level rectifier;
T s is a PWM switching period;
the inductance current target value at the moment k;
i L (k) The actual value of the inductance current at the moment k;
u 0 (k) The actual value of the output voltage at time k.
k is the current time of the control period, the discrete control current time is k, the next control period is k+1, and the previous control period is k-1.
After load current compensation is introduced, the output control quantity of the voltage loop is as follows:
wherein K is P Is the proportionality coefficient of the PI controller;
an output voltage reference value at the moment k;
an output current target value at the time k;
an output current target value at time k-1;
K I the integral coefficient of the PI controller;
i 0 (k) The actual value of the output current at time k.
The invention provides a basis for the installation position and capacity configuration of the compensation device through the established multi-objective optimization mathematical model with minimum active line loss and minimum node average voltage deviation, and the proposed line power flow solving method taking the static characteristics of load voltage and the influence of the compensation device into account can quickly and accurately solve the model, thereby effectively reducing the calculation errors caused by the load voltage change and the line total power change after the compensation device is connected; the developed series voltage compensation device based on series voltage compensation control can achieve the capacity of the compensation device with the load of 1/10 line, realize the effect that the line full line voltage meets the index and the terminal voltage is raised (or lowered) by 25%, and provide a low-cost solution for the terminal low-voltage problem management of the power distribution network under a long power supply distance; the compensation device takes a rectifying inversion unit as a core, the rectifier adopts an I-shaped three-level topology, and under the double closed-loop control and the midpoint potential balance control, the direct-current voltage stabilization, the alternating-current side unit power factor control and the low injection harmonic wave are realized; the inverter adopts single-phase full-bridge topology and double closed-loop control, can realize quick response and continuous regulation of load voltage regulation, and the control method has the advantages of quick response, strong load disturbance resistance, continuous uninterrupted voltage regulation, wide-range voltage regulation capability and low-cost design.
Specifically, in this embodiment, in step S2, the active loss formula of the low-voltage distribution line is designed according to the number of nodes in the low-voltage distribution line, the voltage amplitude of each node, and the conductance of each branch, and the average deviation formula of the voltage of each node is designed according to the voltage amplitude of any node and the rated voltage amplitude;
the comprehensive objective function is obtained by carrying out normalization and combination on a plurality of indexes in an active loss formula of the low-power distribution line and a voltage average deviation formula of each node and then weighting;
the constraint conditions of the comprehensive objective function comprise voltage deviation constraint of each node and capacity constraint of a compensation transformer, wherein the voltage deviation constraint of each node is lower limit of allowable deviation of voltage of any node and upper limit of allowable deviation of voltage of any node, and the capacity constraint of the compensation transformer is determined according to node voltage of each compensation point, voltage reduction transformation ratio of the corresponding compensation transformer, current injected by a compensation device and capacity of a distribution transformer.
The active loss formula of the low-power distribution line is as follows:
wherein f 1 Is the 1 st objective function;
P Loss active loss for low-power distribution lines;
i is the node number of node i;
j is the node number of node j;
k is the branch number;
n is the number of nodes;
U i the voltage amplitude of the node i;
U j the voltage amplitude at node j;
θ ij is the phase difference between nodes i, j;
G k is the conductance of branch k.
The average deviation formula of the voltage of each node is as follows:
wherein f 2 Is the 2 nd objective function;
U Dev the average deviation sum of the voltages of all the nodes is;
U Ni is the nominal voltage amplitude of node i.
The comprehensive objective function is:
wherein F is a comprehensive objective function;
wherein (1)>Is the 1 st objective function after normalization; p (P) Loss.min The minimum value of active loss of the distribution line; p (P) Loss.max The maximum value of active loss of the distribution line;
wherein (1)>Is the normalized 2 nd objective function; u (U) Dev.min The voltage deviation of the node is the minimum value; u (U) Dev.max Is the maximum value of the node voltage deviation;
λ 1 for normalized 1 st objective functionTaking lambda as the weight coefficient of (2) 1 ＝0.3；
λ 2 For normalized 2 nd objective functionTaking lambda as the weight coefficient of (2) 2 ＝0.7。
The node voltage bias constraint is:
U i min ≤U i ≤U i max ；
wherein U is i min A lower limit for the allowable deviation of the voltage of the node i;
U i max which is the upper limit of the allowed deviation of the voltage at node i.
The compensation transformer capacity constraint is:
wherein U is i The node voltage is the node voltage when the node i is a compensation point, and the voltage amplitude of the node i and the node voltage amplitude are the same value;
a is the step-down transformation ratio of the compensation transformer;
I i the current injected into the compensation device;
s is the capacity of the distribution transformer.
The invention provides a basis for the installation position and capacity configuration of the series voltage compensation device by establishing a multi-objective optimized mathematical model with minimum active loss of the distribution line and minimum average voltage deviation of the nodes.
Referring to fig. 6, fig. 6 is a flowchart of the optimization process of the line power flow after the series voltage compensation device is connected in the present embodiment.
Specifically, in this embodiment, in step S3, the optimization processing step is as follows:
step S301, according to distribution line parameters and load original data of each node, performing distribution line original power flow calculation by using a forward push-back substitution method of load static voltage characteristics;
step S302, taking an access point of a series voltage compensation device as a demarcation point, and dividing the distribution line into a compensation point front section and a compensation point rear section;
step S303, after the series voltage compensation device is connected, the voltage value of the compensation point is given to the head end node of the back-end line, other parameters are unchanged, and the back-end power flow calculation of the compensation point is performed;
step S304, after the series voltage compensation device is connected, the series voltage compensation device is compensated and combined with the back-stage power flow data to obtain the complete power flow data of the line after the series voltage compensation device is connected;
Step S305, repeating the steps S202-204 to calculate the power flow calculation data of different access points, and generating a plurality of groups of data;
step S306, screening out the group of data if the node voltage or the capacity of the compensation transformer is out of limit according to the constraint condition;
step S307, according to the comprehensive objective function, calculating the minimum value of the comprehensive objective function of all the data sets conforming to the constraint condition, outputting the minimum value therein, and accessing the node number of the device;
step S308, calculating the actual voltages at two sides of the compensation transformer at the moment, reserving the margin on the basis, and taking the reserved margin as the optimal configuration capacity value of the compensation transformer.
Aiming at the parameters of the selected test bench area, the compensation device is calculated by using a written calculation program and is installed at the 7 th node, and the capacity is configured to be 5kVA. After the series voltage compensation device is connected, the voltage of each node of the line after the compensation point is obviously improved, and the voltage of each node before the compensation point is slightly reduced. In comparison with the original condition of the line, the installation effect analysis of the compensation device is shown in table 1, and table 1 is an installation effect analysis table after the series voltage compensation device is connected in the embodiment.
TABLE 1
According to table 1, after the series voltage compensation device is installed, the average voltage deviation of the node is greatly reduced, the qualification rate of the node voltage reaches 100%, the active loss of the line is slightly increased, but the total power of the line is increased after the compensation device is connected, and the active loss rate of the line is reduced. The low voltage condition of the line is obviously improved in combination.
According to the load voltage static model correction method, the load voltage static model is introduced into the load voltage calculation, the influence on the load voltage after the compensation device is connected is considered, the load voltage after the series voltage compensation device is connected is calculated as a front-section line and a rear-section line of the access point, and calculation errors caused by load voltage change and line total power change after the compensation device is connected are effectively reduced.
Referring to fig. 7, fig. 7 is a diagram of a PLL structure under a synchronous rotation coordinate system of a single-phase SRF-PLL according to the present embodiment.
Specifically, in this embodiment, in the dual closed-loop control system in step S4-1, the feedback control scheme of the single-phase three-level rectifier includes: the direct-current side voltage control outer loop obtains the amplitude and phase deviation information of the input phase voltage through a phase-locked loop structure under a synchronous rotation coordinate system by the input grid voltage through a single-phase SRF-PLL, and the output phase deviation information is subjected to amplitude normalization.
The single phase SRF-PLL consists of 4 parts in total: quadrature signal generator (OSG), phase Detector (PD), loop Filter (LF), and Voltage Controlled Oscillator (VCO). The OSG generates a pair of mutually orthogonal sinusoidal signals according to the input single-phase power grid voltage signals; the PD detects the phase difference of the input and output based on synchronous rotation coordinate transformation (also referred to as αβ -dq transformation); LF adopts PI controller to realize filtering; the VCO obtains the output phase by using the integrator and feeds back to the PD for negative feedback adjustment until the deviation is 0, thereby achieving phase locking.
Specifically, in this embodiment, in step S4-1, in the process of controlling the inner loop by using the ac side current, the difference between the dc voltage given value and the dc voltage sampling value is calculated, and is input into the PI regulator, so as to output the inner loop reference current amplitude;
sampling the current at the network side by the alternating current side of the single-phase three-level rectifier at a fixed frequency, comparing the actual value of the current obtained by sampling this time with the predicted reference current at the next sampling moment, and obtaining the optimal control voltage.
AC side of single-phase three-level rectifier comprises network side power supply u s Equivalent resistance R at net side s Equivalent inductance L s 、u ab Is an ac side voltage value.
The specific implementation method comprises the following steps: first assume that from the kth sampling instant t k After a PWM switching period T s The actual value of the network side current can track the upper instruction value, namely, when one period is finished, the current is as follows:
wherein i is s To control the grid side current;
at t k A network side current command value at a moment;
t k is the sampling instant.
Because u ab Is to control the network side current i s Is controlled in a control period T s And (3) performing periodic averaging on a mathematical model of the single-phase NPC three-level rectifier to obtain:
wherein AV is an average value of one cycle;
R s the network side equivalent resistance is the network side equivalent resistance of the alternating current side of the single-phase three-level rectifier;
L s equivalent inductance of the alternating current side of the single-phase three-level rectifier;
for a control period T s Internal ac side voltage valueAn average value;
for a control period T s An average value of the internal network side power supply voltage value;
for a control period T s Inner equivalent inductance L s Average value of voltage values;
for a control period T s Inner net side equivalent resistance R s Average value of the voltage values.
Assuming that the network side voltage source is an ideal power source and the rectifier is ideal, the actual period average valueEqual to u s ，/>Equal to u ab . Since the net side resistance is typically small, it is ignored. The modulation signal can be obtained by properly transforming the formula 4-1-2 The calculation formula of (2) is as follows:
in the method, in the process of the invention,the current amplitude is referenced to the inner loop.
When the current control is carried out on the single-phase three-level rectifier, the shape of the input current of the converter is approximate to a sine wave through dead beat prediction current control, and the phase of the network side voltage is tracked, so that the network side power factor is close to 1 or-1, and the current controller has faster transient response and satisfactory steady state characteristics.
Specifically, in the present embodiment, in step S4-1, the actual current value and the reference current value of any one are recorded;
a prediction function is stored in the process of predicting the reference current at the next sampling moment, the prediction function is established according to recorded historical data, and a preset regulation value and a preset deviation range are arranged in the prediction function;
and predicting the reference current at the next sampling moment according to the data condition in the historical ring ratio period, wherein the prediction result is a current reference value.
Sampling time t k The predictive function of (2) is:
in the method, in the process of the invention,for sampling time t k A prediction function of a network side current command value;
i s (t k-1 ) For sampling time t k-1 Is the actual value of the current;
i s (t k-T ) For sampling time t k-T T is the period of the cyclic ratio
X[i s (t k-1 )、t k-1 ]For sampling time t k-1 Is provided.
In the current control inner loop control process of the alternating current side, when current prediction is carried out, a related prediction function is established for the reference current at any sampling moment according to the related conditions in the historical loop ratio period, and the reference current value prediction is carried out on any sampling moment at any sampling moment according to the function.
Specifically, in this embodiment, according to the reference current value and the current actual value at any time, the current actual value is judged to be compared with the trend direction in the prediction function, and whether the current actual value is the same as the trend of the prediction function at this time is determined;
if the current actual value is the same as the trend of the prediction function, judging the deviation range of the reference current value and the current actual value;
if the current actual value is different from the trend of the prediction function, trend error reporting is carried out.
If the sampling time t k The actual value of the current is i s (t k ) Which is equal to i s (t k-1 ) Comparing the determined change trend to increase the period, and at the sampling time t k Is the predictive function Y of (2)The current reference value derived from (a)>And if the change trend is periodic increase, judging the deviation range of the reference current value and the current actual value.
If the sampling time t k The actual value of the current is i s (t k ) Which is equal to i s (t k-1 ) Comparing the determined change trend to be period increment and decreasing, and at the sampling time t k Is a predictive function of (2)The current reference value derived from (a)>And if the change trend is periodic increase, reporting trend errors.
The invention compares the variation trend of the actual current value with the variation trend of the prediction function, determines whether the reference current value and the prediction function trend accord with the actual application, records and reports errors which do not accord with the trend, and determines the deviation range of the consistent trend so as to refine the accuracy of the prediction function.
Specifically, in this embodiment, the current error value predicted at this time is calculated according to the reference current value and the current actual value at any time;
if the sampling time is within the preset deviation range, carrying out trend judgment of the next sampling time;
if the current value is not in the preset deviation range, calculating a reference current value at the next sampling moment;
and calculating the reference current value at the next sampling moment when the prediction is performed, wherein the calculating comprises the steps of calculating a first reference current value according to a prediction function and calculating a second reference current value according to the prediction function and a preset regulation value, respectively calculating the difference value between the two reference current values and the actual current value of the current sample, judging the reference value similar to the difference value of the actual current value of the current sample, and taking the calculation process of the similar value as the calculation process of the reference current value at the next sampling moment.
Sampling time t k Is a predictive function of (2)The preset deviation range of (1) is [ P1, P2 ]]And includes P1 and P2.
When k=1, the reference current value isThe actual value of the current is i s (t 1 ),t 1 The current error value at the moment is,
if delta i s Within a preset deviation range [ P1, P2 ]]In the case, then proceed t 2 Judging the trend of time; if delta i s Is not within a preset deviation range [ P1, P2 ]]In the case, then proceed t 2 And calculating a reference current value at the moment.
Sampling time t k+1 The adjusted prediction function of (2) is:
in the method, in the process of the invention,for sampling time t k+1 A prediction function is adjusted according to the net side current command value;
X’[i s (t k )、t k 、γ]for sampling time t k A current adjustment function when adding the regulation value gamma;
gamma is the regulating value.
When t k+1 At t 2 At this time, the first reference current value Y (t 2 )＝X[i s (t 1 )、t 1 、i s (t 1-T )]The method comprises the steps of carrying out a first treatment on the surface of the Second reference current value Y at this time ′ (t 2 )＝X‘[i s (t 1 )、i s (t 1-T )、γ]The actual current value is i s (t 2 )。
|ΔY1|＝|i s (t 2 )-Y(t 2 )|；|ΔY2|＝|i s (t 2 )-Y′(t 2 )|
If |Δy1|<And (delta Y2), sampling time t k+1 Is used to adjust the prediction function of the model (c), a calculation process of a reference current value as a next sampling time; if |Δy1|>And (delta Y2), sampling time t k Is>t k-1 ]As a calculation process of the reference current value at the next sampling time.
The invention determines the actual current values at different positions of the preset deviation range of the prediction function, calculates the original prediction function for the reference current value at the next sampling moment, and adjusts the supplementary regulation value for the prediction function value for the reference current value at the next sampling moment for the actual current value which is not in the preset deviation range so as to improve the accuracy of the prediction function.
Specifically, in this embodiment, an adjustment period and a preset adjustment frequency are stored for the prediction function;
the method comprises the steps that overall adjustment is conducted on a prediction function which reaches preset adjustment times in any adjustment period, the prediction function is adjusted to cover an initial prediction function according to the calculation process of calculating a reference current value for the last time, and the initial prediction function is used as the prediction function to calculate the reference current value at the next sampling moment;
and for the prediction function which does not reach the preset adjustment times in any adjustment period, performing prediction function detail adjustment, wherein the prediction function detail adjustment is to select a calculation process with more use times of two calculation modes in the adjustment period, cover the initial prediction function according to the calculation formula of the last time, and perform calculation of a reference current value at the next sampling moment by taking the initial prediction function as the prediction function.
The invention carries out integral adjustment on the prediction function, so that the integral coverage adjustment can be carried out on the prediction function in the process of predicting the current reference value, and the calculation result of the prediction function is more approximate to the prediction result of the current error minimum value from the large direction, thereby improving the efficiency of the current control inner loop control at the alternating current side.
Specifically, in the embodiment, in the step S4-1, the hysteresis loop adjustment is to add a hysteresis loop comparison link of the upper capacitance voltage deviation and a hysteresis loop comparison link of the lower capacitance voltage deviation in the midpoint balance control system, when the voltage deviation is within the tolerance range of the hysteresis loop comparator, the pulse given by the original control algorithm is still used, and if the voltage difference reaches the upper or lower tolerance limit of the hysteresis loop regulator, the converted pulse is output.
The invention adopts a midpoint potential control method based on hysteresis regulation, which essentially converts the current switch pulse combination unfavorable for midpoint potential balance into the pulse combination favorable for midpoint potential balance, thereby achieving the purpose of controlling midpoint potential.
The LVR device based on series voltage compensation control developed by the invention is manufactured in a prototype mode and is subjected to experimental tests.
In static and dynamic tests of the high-voltage band-stop inductive load, when the mains voltage is higher than 220V, the LVR can enable the load voltage to be stabilized at about 220V, and the high-voltage regulation effect is good. The sudden increase or decrease of the load and the basically no transient process of the load voltage show that the response speed of the controller of the LVR device is very fast, and the continuous voltage regulation can be realized.
According to static and dynamic tests of the high-voltage band-stop inductive load, three groups exist.
One is, input voltage 238V, resistive load: 2kW resistance and 4kVar inductance; second, input voltage 233V, resistive load: 2kW resistance and 4kVar inductance; third, input voltage 229V, resistive load: 7kW resistance and 4kVar inductance.
For the same resistive load, different input voltage adjusting effects, the load voltage is stable at 219V; for the same input voltage, the adjusting effect of different resistance-sensing loads is achieved. As the load increases, the input voltage drops slightly from 233V to 229V, as the load current increases resulting in a decrease in the output of the autotransformer. But the load voltage is still stable around 220V. The two groups of experiments show that the LVR voltage regulating device has good load adaptability under the high-pressure condition.
In static and dynamic testing of low voltage band-stop inductive loads, when the mains input voltage is as low as 170V, the resistive inductive load is increased from 2kW resistance and 4kVar to 4kW resistance and 6kVar, and the inverter output voltage current is increased from 223.2V,4A to 250.2V,6.7A. Therefore, the output of the inverter is increased along with the increase of the load, so long as the LVR can stably maintain the load voltage to be about 220V in the capacity range of the equipment, and the voltage quality of a user is ensured.
8 months in 2020, project LVR equipment is installed and debugged at the C-phase outlet line of the low-voltage side of the 10kV water line building small pile and enlargement branch line 1#, 2# and 3# transformer stations of the Jia Musi city, betula county, heilongjiang province, and put into operation. Up to the present, the equipment has been operated on site for more than 4 months, the working state is stable, and the effect of treating the low voltage (or high voltage) at the tail end of the distribution network line is good. Mains input voltage current 248V, 46A, regulated load voltage current 220V, 50.4A.
Thus far, the technical solution of the present invention has been described in connection with the preferred embodiments shown in the drawings, but it is easily understood by those skilled in the art that the scope of protection of the present invention is not limited to these specific embodiments. Equivalent modifications and substitutions for related technical features may be made by those skilled in the art without departing from the principles of the present invention, and such modifications and substitutions will be within the scope of the present invention.
The foregoing description is only of the preferred embodiments of the invention and is not intended to limit the invention; various modifications and variations of the present invention will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The method for controlling the middle-low voltage cloud edge cooperative voltage based on the fusion terminal is characterized by comprising the following steps of,
step S1, selecting any low-power distribution line for each point in a power grid with the same voltage level in a power system, and dividing a plurality of nodes; the node is arranged according to the conditions of a plurality of branch lines of the low-power distribution line;
step S2, under the condition that the capacity of the compensation transformer and the allowable deviation constraint of the node voltage are met, a comprehensive objective function is established according to an active loss formula and a node voltage average deviation formula of the low-power distribution line, and the constraint condition of the comprehensive objective function is determined;
step S3, selecting a series voltage compensation device which accords with the constraint condition, carrying out optimization treatment on line power flow after the series voltage compensation device is connected, and solving device optimization configuration data when the comprehensive objective function is minimum;
step S4, selecting an optimally configured series voltage compensation device according to the device optimal configuration data result, and adjusting feedback control schemes of the single-phase three-level rectifier and the single-phase full-bridge inverter;
the step S4 comprises a step S4-1 and a step S4-2;
The step S4-1 is that a double closed-loop control system is adopted for the single-phase three-level rectifier, and comprises a direct-current side voltage control outer ring and an alternating-current side current control inner ring, and hysteresis regulation is adopted for midpoint potential balance;
step S4-2, the double closed loop control system of the single-phase full-bridge inverter adopts an inductance current instantaneous value feedback inner loop and an output voltage instantaneous value feedback outer loop, and adopts dead beat control to track current in the control process, and simultaneously introduces load current compensation and output voltage cross feedback decoupling control;
in the step S4-1, a prediction function is established according to historical data, the current actual value which is the same as the trend of the prediction function is determined according to the reference current value and the current actual value at any time, deviation range judgment is performed on the current actual value which is not in the deviation range, adjustment and prediction are performed according to the prediction function, the original prediction function is predicted, the actual current value at the next sampling moment is compared, a proper prediction calculation process is determined, and coverage adjustment is performed on the original prediction function according to the using times of different prediction processes.
2. The method for controlling the middle-low voltage cloud edge collaborative voltage based on the fusion terminal according to claim 1, wherein in step S2, an active loss formula of the low-voltage distribution line is designed according to the number of nodes, the voltage amplitude of each node and the conductance of each branch existing in any low-voltage distribution line, and an average deviation formula of the voltage of each node is designed according to the voltage amplitude and the rated voltage amplitude of any node;
The comprehensive objective function is obtained by carrying out normalization and combination on a plurality of indexes in an active loss formula of the low-power distribution line and a voltage average deviation formula of each node and then weighting;
the constraint conditions of the comprehensive objective function comprise voltage deviation constraint of each node and capacity constraint of a compensation transformer, wherein the voltage deviation constraint of each node is lower limit of allowable deviation of voltage of any node and upper limit of allowable deviation of voltage of any node, and the capacity constraint of the compensation transformer is determined according to node voltage of each compensation point, voltage reduction transformation ratio of the corresponding compensation transformer, current injected by a compensation device and capacity of a distribution transformer.
3. The method for controlling the cooperative voltage of the middle and low voltage cloud edges based on the fusion terminal according to claim 2, wherein in step S3, the optimizing step is as follows:
step S301, according to distribution line parameters and load original data of each node, performing distribution line original power flow calculation by using a forward push-back substitution method of load static voltage characteristics;
step S302, taking an access point of a series voltage compensation device as a demarcation point, and dividing the distribution line into a compensation point front section and a compensation point rear section;
Step S303, after the series voltage compensation device is connected, the voltage value of the compensation point is given to the head end node of the back-end line, other parameters are unchanged, and the back-end power flow calculation of the compensation point is performed;
step S304, after the series voltage compensation device is connected, the series voltage compensation device is compensated and combined with the back-stage power flow data to obtain the complete power flow data of the line after the series voltage compensation device is connected;
step S305, repeating the steps S202-204 to calculate the power flow calculation data of different access points, and generating a plurality of groups of data;
step S306, screening out the group of data if the node voltage or the capacity of the compensation transformer is out of limit according to the constraint condition;
step S307, according to the comprehensive objective function, calculating the minimum value of the comprehensive objective function of all the data sets conforming to the constraint condition, outputting the minimum value therein, and accessing the node number of the device;
step S308, calculating the actual voltages at two sides of the compensation transformer at the moment, reserving the margin on the basis, and taking the reserved margin as the optimal configuration capacity value of the compensation transformer.
4. The method for controlling the middle-low voltage cloud edge cooperative voltage based on the fusion terminal according to claim 3, wherein in the step S4-1, the control process of the feedback control scheme of the single-phase three-level rectifier is as follows: the direct-current side voltage control outer loop obtains the amplitude and phase deviation information of the input phase voltage through a phase-locked loop structure under a synchronous rotation coordinate system by the input grid voltage through a single-phase SRF-PLL, and the output phase deviation information is subjected to amplitude normalization.
5. The method for controlling the middle-low voltage cloud edge collaborative voltage based on the fusion terminal according to claim 4, wherein in step S4-1, the ac side current controls the inner loop control process, firstly calculates the difference between the dc voltage given value and the dc voltage sampling value, inputs the difference into the PI regulator, and outputs the inner loop reference current amplitude;
sampling the current at the network side by the alternating current side of the single-phase three-level rectifier at a fixed frequency, comparing the actual value of the current obtained by sampling this time with the predicted reference current at the next sampling moment, and obtaining the optimal control voltage.
6. The method for controlling the middle-low voltage cloud edge collaborative voltage based on the fusion terminal according to claim 5, wherein in step S4-1, the actual current value and the reference current value of any one are recorded;
a prediction function is stored in the process of predicting the reference current at the next sampling moment, the prediction function is established according to recorded historical data, and a preset regulation value and a preset deviation range are arranged in the prediction function;
the reference current predicts the reference current at the next sampling moment according to the data condition in the historical ring ratio period, the ring ratio period is the internal value of the prediction function, and the prediction result is the current reference value.
7. The method for controlling the middle-low voltage cloud edge collaborative voltage based on the fusion terminal according to claim 6, wherein the method is characterized in that according to the reference current value and the current actual value at any time, the current actual value is judged to be compared with the trend direction in the prediction function, and whether the current actual value is the same as the trend of the prediction function at the time is determined;
if the current actual value is the same as the trend of the prediction function, judging the deviation range of the reference current value;
if the current actual value is different from the trend of the prediction function, trend error reporting is carried out.
8. The fusion terminal-based medium-low voltage cloud edge cooperative voltage control method according to claim 7, wherein the predicted current error value is calculated according to the reference current value and the current actual value at any time;
if the sampling time is within the preset deviation range, carrying out trend judgment of the next sampling time;
if the current value is not in the preset deviation range, calculating a reference current value at the next sampling moment;
and calculating the reference current value at the next sampling moment when the prediction is performed, wherein the calculating comprises the steps of calculating a first reference current value according to a prediction function and calculating a second reference current value according to the prediction function and a preset regulation value, respectively calculating the difference value between the two reference current values and the actual current value of the current sample, judging the reference value similar to the difference value of the actual current value of the current sample, and taking the calculation process of the similar value as the calculation process of the reference current value at the next sampling moment.
9. The fusion terminal-based medium-low voltage cloud edge cooperative voltage control method according to claim 8, wherein an adjustment period and preset adjustment times are stored for the prediction function;
the method comprises the steps that overall adjustment is conducted on a prediction function which reaches preset adjustment times in any adjustment period, the prediction function is adjusted to cover an initial prediction function according to the calculation process of calculating a reference current value for the last time, and the initial prediction function is used as the prediction function to calculate the reference current value at the next sampling moment;
and for the prediction function which does not reach the preset adjustment times in any adjustment period, performing prediction function detail adjustment, wherein the prediction function detail adjustment is to select a calculation process with more use times of two calculation modes in the adjustment period, cover the initial prediction function according to the calculation formula of the last time, and perform calculation of a reference current value at the next sampling moment by taking the initial prediction function as the prediction function.
10. The method for controlling the middle-low voltage cloud-edge collaborative voltage based on the fusion terminal according to claim 5, wherein in the step S4-1, the hysteresis loop is adjusted by adding a hysteresis loop comparison link of upper capacitance voltage deviation and a hysteresis loop comparison link of lower capacitance voltage deviation in a midpoint balance control system, when the voltage deviation is within the tolerance range of a hysteresis loop comparator, the pulse given by the original control algorithm is still used, and if the voltage difference reaches the upper or lower tolerance limit of the hysteresis loop adjuster, the converted pulse is output.
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