CN106849111A - A kind of statements based on collusion circuit pressure regulation method based on photovoltaic DC-to-AC converter phase modulation - Google Patents

Abstract

The invention discloses a kind of statements based on collusion circuit pressure regulation method based on photovoltaic DC-to-AC converter phase modulation, voltage-regulation is carried out to statements based on collusion circuit using photovoltaic DC-to-AC converter generator operation as synchronous condenser ability, to the Q (U) that commonly uses andControl strategy is improved, both can at any time for power network provides reactive power support, or photovoltaic plant reduces dynamic passive compensation equipment investment, and line voltage regulation is both participated in by transferring all photovoltaic DC-to-AC converters, so that reactive absorption total amount is minimum, electric network active, reactive loss are minimum.

Description

Series supply line voltage regulating method based on photovoltaic inverter phase modulation

Technical Field

The invention belongs to the field of photovoltaic inverters, and particularly relates to a series-fed line voltage regulating method based on photovoltaic inverter phase modulation.

Background

Solar energy is regarded as renewable green energy, is inexhaustible, pollution-free and low in cost, and is considered as one of the most important new energy sources in the 21 st century. Countries around the world compete to draw huge research and development teams and huge funds to research solar power generation technology. Among them, photovoltaic power generation is favored because of its advantages such as abundant sources of battery material silicon and low cost. The basic principle is that the conversion from light energy to electric energy is realized through the photovoltaic effect on the surface of the solar cell. The photovoltaic power generation has important significance for optimizing an energy structure, promoting energy conservation and emission reduction and realizing economic sustainable development, and the grid-connected operation of the photovoltaic power generation becomes a main direction of development in the future.

The western region of China has sufficient illumination and little precipitation, and is provided with a large number of photovoltaic power stations. The load in the local power grid is light, the distance between a load point and the load point is long, and after the power is supplied in a long-distance series power supply mode, the terminal voltage of the power transmission line is obviously higher than the voltage of the head end due to the fact that the R/X value of the high-voltage power transmission line is small, and the problem of relatively serious reactive voltage exists. At present, domestic grid-connected photovoltaic power stations are required to be provided with capacitive reactive compensation devices accounting for about 20% of installed capacity and inductive reactive compensation devices accounting for about 5%, and dynamic compensation SVG is also required frequently, so that the cost is high.

With the development of power electronic technology and industrial control technology, the modulation mode and control strategy of the inverter are also greatly improved. Inverters in new energy plants, especially photovoltaic power stations, have phase modulation operation capability. The phase modulation operation capability of the inverter is effectively developed and utilized, so that reactive support can be provided for a power grid at any time, and the investment of dynamic reactive compensation equipment can be reduced for a new energy plant station adopting the inverter. General useThe voltage regulation method of (1) adopts Q (U) andthe control strategy is used for regulating voltage, the inverter absorbs or emits reactive power under the Q (U) control strategy and has no direct relation with the magnitude of photovoltaic active output and the magnitude of load, the total reactive power absorbed by the control strategy is the lowest, the loss of a power grid is reduced, all photovoltaic inverters are not mobilized to participate in voltage regulation of the power grid, and the voltage regulating capability of the whole photovoltaic system is weaker.The premise for the establishment of the control strategy is to assume that the voltage of the grid-connected point rises along with the increase of the photovoltaic active power output. When the photovoltaic active power output is large and is just the peak of the power consumption of a user, the voltage of a grid-connected point is not out of limit at the moment, and a large amount of reactive power output can increase the active power loss and the reactive power loss of a power grid.

Disclosure of Invention

The technical problem is as follows: the invention provides a series supply line voltage regulating method based on phase modulation of a photovoltaic inverter, which utilizes the phase modulation operation capability of the photovoltaic inverter to regulate the voltage of a series supply line so as to maintain the voltage of each node in a power grid within a reasonable range.

The technical scheme is as follows: in order to achieve the purpose, the invention adopts the technical scheme that:

step 1: and (3) carrying out equivalence processing on a generator, a transformer, a line and a load in the power grid, and establishing a power grid equivalence model.

Step 2: and carrying out load flow calculation on the equivalent model of the power grid, and acquiring load flow information comprising the voltage of each node and the active and reactive power of each branch.

And step 3: judging grid-connected point voltage U of photovoltaic system_iIn the range of 0.95 p.u.or less U_iAnd (4) if the temperature is less than or equal to 1.05p.u., directly ending, otherwise, performing the step 4.

And 4, step 4: according to the point based on grid connectionCalculating the reactive output value Q of the photovoltaic system by using a voltage amplitude Q (U) control strategy_uiQ (U) control strategy for directly collecting voltage U at grid-connected point of photovoltaic system_iThe expression is

In the formula: u shape₁、U₂、U₃、U₄The voltage values indicated are 0.95, 0.98, 1.02, 1.05p.u., respectively; q_imaxThe maximum value of the reactive output of the photovoltaic system during the active rated output is obtained.

According to active output basedControl strategy for calculating reactive output value Q of photovoltaic system_pi，The control strategy sets a power factor value C according to the active power output P of the photovoltaic system₁Is changed into C₂The expression is

In the formula: c₁＝1，C₂＝0.9，P_imFor rated active output value, P₁＝P_im/2，P₂＝P_im。

And 5: setting Q (U) control strategy based on grid-connected point voltage amplitude to calculate reactive output value Q of photovoltaic system_uiSetting the initial value a of weight coefficient to 1, and setting the value based on active outputControl strategy for calculating reactive output value Q of photovoltaic system_piThe initial value b of the weight coefficient is 0.

Step 6: judgment of Q_piAnd (4) directly ending the weighting coefficient b if the weighting coefficient b is more than or equal to 1, and otherwise, performing the step 7.

And 7: calculating the reactive output value Q of the photovoltaic system_iThe expression is

Q_i＝aQ_ui+bQ_pi(4)

In the formula: q_uiThe reactive output value of the photovoltaic system calculated by the Q (U) control strategy based on the voltage amplitude of the grid-connected point, a is the weight coefficient of the photovoltaic system, Q_piBased on active outputAnd b is a weight coefficient of the reactive output value of the photovoltaic system calculated by the control strategy.

And 8: judging the reactive output value Q of the photovoltaic system_iSize, if Q_i＝Q_imIf not, go to step 9, Q_imAnd the capacity is the reactive output capacity of the photovoltaic system.

And step 9: judging grid-connected point voltage U of photovoltaic system_iIn the range of 0.95 p.u.or less U_iIf the temperature is less than or equal to 1.05p.u., the operation is finished directly, otherwise, the step 10 is carried out.

Step 10: the weight coefficient a is set to a-0.05 and the weight coefficient b is set to b +0.05, and the procedure returns to step 6.

Has the advantages that: compared with the prior art, the technical scheme of the invention has the following advantages:

1. the invention provides a series supply line voltage regulating method based on photovoltaic inverter phase modulation, which effectively develops and utilizes the phase modulation operation capability of an inverter, can provide reactive support for a power grid at any time, and can reduce the investment of dynamic reactive compensation equipment for a photovoltaic power station so as to maintain the voltage of each node in the power grid within a reasonable range;

2. the invention inherits Q (U) andthe control strategy has the advantages of overcoming respective defects, and enabling the total reactive power absorption to be minimum and the active and reactive power losses of the power grid to be minimum by adjusting all the photovoltaic inverters to participate in the voltage regulation of the power grid.

Drawings

FIG. 1 is a flow chart of the present invention;

FIG. 2 is a topological diagram of a power grid in south Xinjiang;

FIG. 3 is a model of the power grid in south Xinjiang, built in DIgSILENT software.

Detailed Description

The following describes a series supply line voltage regulating method based on phase modulation of a photovoltaic inverter in detail with reference to embodiments. It should be emphasized that the following description is merely exemplary in nature and is in no way intended to limit the scope of the embodiments and their applications.

The embodiment is a power grid in south Xinjiang, and a power grid topological graph is shown in FIG. 2. The system comprises a power grid, wherein an Aksu line, a Bachu line and a Kash line are long-distance 750kV overhead lines, and the rest are 220kV overhead lines to form a typical series-supply line structure power grid, wherein an Aksu, Bachu and Kash node is provided with a 750/220/63kV three-winding transformer with the capacity of 1500MVA, and a golden deer, a Macintosh, a Shache, a Yingsha and an Oitake node are connected with a high-capacity photovoltaic system. And constructing a power grid model in DIgSILENT according to the actual power grid data, as shown in FIG. 3. And setting an Aksu node as a balance node, writing a series supply line voltage regulating method based on the phase modulation of the photovoltaic inverter into a control module in DIgSILENT, and carrying out comparative analysis on node voltage obtained by the series supply line voltage regulating method based on the phase modulation of the photovoltaic inverter.

Taking Bachu-karsch 750kV overhead line as an example, the line length is 188km, the positive and negative sequence resistance value of the unit length is 0.0138 omega/km, the positive and negative sequence reactance value of the unit length is 0.2833 omega/km, the R/X value is very small, when power flows through the line, the voltage at the tail end of the line is higher than that at the head end of the line, when only reactive compensation equipment is added at a Bachu node, the voltage of a karsch node obviously exceeds the standard and reaches 1.055p.u., and the voltage of each node is shown in table 1.

TABLE 1 Voltage regulation of each node of the power grid in the south of Xinjiang

Node name	Voltage (p.u.)	Node name	Voltage (p.u.)	Node name	Voltage (p.u.)
						Aksu	1.000	Bachu (a Chinese character of' Bachu	1.028	Kashi	1.055
Keping	1.003	Golden deer	1.033	Wheat cover handle	1.043
						Shake car	1.058	Leaf city	1.057	Miller is good at	1.058
Yingjisha	1.062	Upper atlas	1.057	Wuqi medicine	1.059
						Deep click	1.057	Second stage of karez	1.057	Three stages of karezing	1.057
Dredge and attach	1.057	Aoyitake	1.051	Cumin cover	1.049
						Mouth of Bulun	1.048

In order to better regulate the voltage of a power grid in the south of Jiang, the phase modulation operation capacity of a photovoltaic inverter with Jinlu, Maigaiti, Shache, Yixtaco nodes is utilized to regulate the voltage of a series supply line. The calculated weight coefficients a and b of the control strategy of each node are shown in table 2.

TABLE 2 control strategy weight coefficients for each node

The voltage of each node of the power grid in south of Jiang after voltage regulation is shown in Table 3. As can be seen from Table 3, the voltage of each node is maintained between 0.98 and 1.02p.u., and the requirement of the grid voltage is met. All photovoltaic inverters participate in the voltage regulation of the power grid, and the total reactive power absorption amount is comparedThe control strategy is low, and meanwhile, the active loss and the reactive loss of the power grid are small.

TABLE 3 Voltage regulation of each node of the south Jiang area grid

Claims (5)

1. A series supply line voltage regulating method based on photovoltaic inverter phase modulation is characterized by comprising the following steps:

step 1: carrying out equivalence processing on a generator, a transformer, a line and a load in a power grid, and establishing a power grid equivalence model;

step 2: carrying out load flow calculation on the equivalent model of the power grid, and acquiring load flow information which comprises the voltage of each node and the active and reactive power of each branch;

and step 3: judging grid-connected point voltage U of photovoltaic system_iIn the range of 0.95 p.u.or less U_i≤1.05pU, directly ending, otherwise, performing the step 4;

and 4, step 4: calculating a reactive output value Q of the photovoltaic system according to a Q (U) control strategy based on the voltage amplitude of the grid-connected point_uiAccording to active output basedControl strategy for calculating reactive output value Q of photovoltaic system_pi；

And 5: setting Q (U) control strategy based on grid-connected point voltage amplitude to calculate reactive output value Q of photovoltaic system_uiSetting the initial value a of weight coefficient to 1, and setting the value based on active outputControl strategy for calculating reactive output value Q of photovoltaic system_piThe initial value b of the weight coefficient is 0;

step 6: judgment of Q_piIf b is larger than or equal to 1, directly ending the process, otherwise, performing the step 7;

and 7: calculating the reactive output value Q of the photovoltaic system_iThe expression is

Q_i＝aQ_ui+bQ_pi(4)

In the formula: q_uiThe reactive output value of the photovoltaic system calculated by the Q (U) control strategy based on the voltage amplitude of the grid-connected point, a is the weight coefficient of the photovoltaic system, Q_piBased on active outputB is a weight coefficient of a reactive output value of the photovoltaic system calculated by the control strategy;

and 8: judging the reactive output value Q of the photovoltaic system_iSize, if Q_i＝Q_imIf not, go to step 9, Q_imThe capacity is the reactive output capacity of the photovoltaic system;

and step 9: judging grid-connected point voltage U of photovoltaic system_iIn the range of 0.95 p.u.or less U_iIf the temperature is less than or equal to 1.05p.u., directly ending, otherwise, performing the step 10;

step 10: and (5) adjusting the step sizes of the weight coefficients a and b, and returning to the step 6.

2. The series supply line voltage regulating method based on the photovoltaic inverter phase modulation according to claim 1, characterized in that: the adjustment step sizes of the weight coefficients a and b in the step 10 are set according to the requirement of the response speed.

3. The series supply line voltage regulating method based on the photovoltaic inverter phase modulation according to claim 2, characterized in that: in the step 10, the weight coefficients a and b are adjusted in steps of a-0.05 and b + 0.05.

4. The series supply line voltage regulating method based on the photovoltaic inverter phase modulation according to claim 1, characterized in that: in step 4, a reactive output value Q of the photovoltaic system is calculated according to a Q (U) control strategy based on the voltage amplitude of the grid-connected point_uiThe expression is

$Q_{ui}=\left\{\begin{array}{cc}{Q}_{imax}& U_i<U_1\\ \frac{Q_{imax}}{U_1-U_2}(U_i-U_1)+Q_{imax}& U_1\&le;U_i\&le;U_2\\ 0& U_2\&le;U_i\&le;U_3\\ \frac{Q_{imax}}{U_3-U_4}(U_i-U_3)& U_3\&le;U_i\&le;U_4\\ -Q_{imax}& U_i>U_4\end{array}\right.---\left(1\right)$

In the formula: q (U) control strategy for directly collecting voltage U at grid-connected point of photovoltaic system_i，U₁、U₂、U₃、U₄The voltage value represented is determined according to the actual grid requirements, Q_imaxThe maximum value of the reactive output of the photovoltaic system during the active rated output is obtained.

5. The series supply line voltage regulating method based on the photovoltaic inverter phase modulation is characterized in that: based on active output in step 4Control strategy for calculating reactive output value Q of photovoltaic system_piThe expression is as follows:

wherein,the control strategy sets a power factor value C according to the active power output P of the photovoltaic system₁Is changed into C₂The expression is as follows:

in the formula: c₁＝1，C₂＝0.9，P_imFor rated active output value, P₁＝P_im/2，P₂＝P_im。