JP4719760B2 - Control method and system for distributed power supply group - Google Patents

Description

  The present invention relates to a control method and system for a distributed power supply group. For example, a plurality of generations using natural energy or renewable energy such as wind power generation, solar power generation, small-scale hydropower generation, tidal power generation, and the like as power generation energy. The present invention relates to a control method and system for a distributed power supply group in which power supplies are installed in a distributed manner.

  Reducing carbon dioxide emissions, which is thought to cause global warming, has become a major issue. As one means of reducing carbon dioxide emissions, the introduction of distributed power sources such as wind power generation and solar power generation has become popular. These distributed power sources are often used in conjunction with the power system, but the power generation output fluctuates due to fluctuations in wind speed and solar radiation, so the voltage of the connected system and a large amount of distributed power sources When a group is introduced, there is a concern that it may affect the power quality of the interconnected power system, for example, the voltage and frequency of the power system.

  For example, as a method of suppressing voltage fluctuations at a connection point (position) when a wind power generator is connected to an electric power system via a power converter, Patent Document 1 discloses the effective power of a distributed power source. From each detected value of fluctuation and voltage fluctuation, system parameter α related to voltage fluctuation (α = ratio of resistance Req / reactance Xeq of the combined impedance on the power system side as seen from the connection point (Req / Xeq)) There is disclosed a method for suppressing voltage fluctuation by supplying reactive power from a distributed power source that estimates and cancels voltage fluctuation caused by fluctuation of active power.

  Wind power generation is often configured as a wind power generator group or wind farm composed of a plurality of wind power generators in order to improve efficiency. It can be applied to wind power generators.

  Patent Document 2 discloses a method for obtaining a system parameter related to voltage fluctuation by generating an inter-order storm wave.

JP 2007-1224779 A JP 2002-171667 A

  By the way, when applying the technique of Patent Document 1 to a distributed power supply group composed of a plurality of wind power generators, based on measurement information at each distributed power supply, preferred active power, reactive power of each distributed power supply, in other words, The power factor will be determined.

  However, even if the active power and reactive power exchanged with the power system side are the same, the sharing of reactive power among the distributed power sources becomes unbalanced, or the active power that can be extracted from the distributed power source group as a whole There are problems such as lowering.

  In addition, a distributed power source group called a mega solar equipped with a plurality of photovoltaic power generation devices also has output fluctuations due to changes in the amount of solar radiation, and voltage fluctuations at the interconnection points resulting from it. There are similar problems such as unbalanced power sharing, or a reduction in the effective power that can be extracted from the distributed power supply group as a whole.

  In view of the above-mentioned problems, the problem to be solved by the present invention is that the distributed power supply group controls the distributed power sources in a coordinated manner while suppressing voltage fluctuations at the connection points where the distributed power sources are connected to the grid. The objective is to properly allocate reactive power and optimize the operation of the distributed power supply group.

  In order to solve the above-mentioned problem, a first aspect of the present invention is to provide a plurality of distributed power sources including a power converter that converts an output of a power generation power source into a desired voltage and power and outputs the power. In a control method or system for a distributed power supply group connected to a power system via a transmission line, for each predetermined control cycle, collect measured values of the output voltage and output power of each of the distributed power supplies, A first constraint condition that absorbs the variation of the active power of each distributed power source and the voltage variation of the interconnection point of the power system by the reactive power of each of the distributed power sources, and between each of the distributed power sources It satisfies the second constraint that suppresses the cross current and the third constraint that sets the active power of each distributed power source within the upper and lower limits, and the active power for the previous control cycle at the interconnection point Each of the distributed types so as to minimize variation The source of active power and the command value of the reactive power calculated respectively and controlling the power converter of the respective decentralized power supply.

  According to this, the first constraint condition is satisfied to suppress the voltage fluctuation at the interconnection point, the second constraint condition is satisfied to suppress the cross current between the distributed power sources, and the third constraint condition is satisfied. The active power and reactive power command values of each distributed power supply in the distributed power supply group are obtained while considering the characteristics of each distributed power supply. The reactive power can be appropriately distributed and the operation of the distributed power supply group can be optimized. In particular, fluctuations in active power (output) as the entire distributed power supply group can be minimized.

  Further, the second aspect of the present invention is that each of the distributed types satisfies the first to third constraints and maximizes the effective power of each of the distributed power sources output to the power system. The power converter of each distributed power source is controlled by obtaining the active power and reactive power of the power source, respectively.

  According to this, it is possible to optimize the operation of the distributed power supply group by coordinatingly controlling each distributed power supply and appropriately distributing the active power and reactive power. There is an advantage that power (output) can be maximized.

  According to the present invention, a distributed power source is configured to appropriately distribute active power and reactive power by coordinatingly controlling each distributed power source while suppressing voltage fluctuations at a connection point where the distributed power source group is connected to the grid. The group's operation can be optimized.

  Hereinafter, the present invention will be described based on embodiments.

  FIG. 1 shows a system configuration diagram of a system in which an embodiment of the present invention is applied to a method for controlling a wind power generator group.

  As shown in FIG. 1, the wind power generator group is connected to a main system 1 of a power system via a connection line 2, and a load 3 is connected to the connection line 2. The wind power generator group is composed of a plurality of wind power generators arranged in a distributed manner. Each wind power generator includes a wind turbine 10, a power generator 9, a power converter 8, a current sensor 6, a voltage sensor 7, and a controller 20. The power converter 8 is configured to once convert the output of the generator 9 into direct current, convert the direct current into desired voltage and power (active power and reactive power), and output the converted voltage.

  The output of each wind power generator is connected to a local transmission line 11 that is a distributed power transmission line, and the local transmission line 11 is connected to the interconnection line 2 at the interconnection point 4. The on-premises power transmission line 11 is provided with a transformer 13 that boosts the voltage of the on-premises power transmission line and connects it to the interconnection line 2.

  The controller 20 of each wind power generator is connected to the overall monitoring device 5 via the communication line 12. The overall monitoring device 5 collects data related to the output voltage and output power measured by the controller 20 of each wind power generator, and based on those data, the active power is supplied to the controller 20 of each wind power generator by calculation described later. The reactive power command value is output. Each controller 20 controls the power converter 8 according to the input command value to appropriately distribute the active power and reactive power of each wind power generator so that the active power (output) of the wind power generator group as a whole is output. ) To minimize fluctuations or to maximize the effective power (output) of the entire wind power generator group.

  FIG. 2 is a block diagram showing the main equipment of the overall monitoring device 5. The overall monitoring device 5 receives the data sent from the controller 20 of each wind power generator, calculates the optimum command value of each wind power generator, and performs various processes such as operation recording and maintenance. The arithmetic processing device 212, an input device 213 that receives an input of an instruction and the like, and a display device 214 are configured.

  The arithmetic processing unit 212 is configured by a computer and includes a central processing unit, a memory, a storage device for storing a program, and the like (not shown). The arithmetic processing unit 212 is connected to a storage device for storing data and configuring the databases 221 to 225. The database includes a system constant database (DB) 221 that stores system constants necessary for calculating command values, a power transmission information DB 222 that stores the amount of power transmitted from the wind power generator group, and a weather information DB 223 that stores wind speed and the like. The operation record DB 224 for storing operation results and the failure / maintenance information DB 225 for storing information on occurrence / removal of trouble or periodic inspection are configured.

  FIG. 3 is a functional block diagram of the controller 20. The controller 20 includes a communication function 311 for exchanging information with the overall monitoring device 5, a control signal generation function 312 for generating a control signal to the power converter 8, and measured values of the current sensor 6 and the voltage sensor 7. A measurement value calculation function 313 for calculating current and voltage measurement values is provided.

  The control signal generation function 312 generates a command value for active power and reactive power, which will be described later, based on the measurement value obtained by the measurement value calculation function 313, and generates a gate signal (control signal) for the power converter 8 for control. Is output to the container 20.

  FIG. 4 is an explanatory diagram showing a part of the display screen of the display device 214 provided in the overall monitoring device 5, and shows the state of the grid connected to the operating state of each wind power generator. As shown in the figure, a schematic diagram [XXX wind farm] 400 shows a connection line 401 and each wind power generator 402, and displays a main operation state 403 such as operation or failure. The operation state 404 displays the detailed operation state of each wind power generator. As display items, name 405, active power 406, reactive power 407, voltage 408, wind condition 409, fault 410, condition 411, and the like are displayed. In addition, when a button 412 is pressed, a sub-screen (not shown in the figure) is opened, and a past history and a detailed log can be viewed. The bottom 413 of the table displays the active power, reactive power, voltage, etc. of the entire wind power generator group. When the button 414 is pressed, a trend graph of the transmitted power 415 and voltage is displayed. Further, a message field 416 is provided.

  Next, the contents of the arithmetic processing in the overall monitoring apparatus 5 according to the feature of the present embodiment will be described. A wind power generator group composed of n wind power generators will be described with reference to FIG. 5 showing an equivalent circuit of the system configuration diagram of FIG.

  First, the first constraint condition is to compensate the voltage fluctuation at the connection point Cn (interconnection point 4) due to the fluctuation of the active power of the wind power generator group by generating the reactive power as shown in Equation 1. . That is, based on the fluctuation of the active power of each wind power generator and the voltage fluctuation of the interconnection point 4, the ratio (Req) of the resistance component Req and the reactance component Xeq of the combined impedance on the power system side viewed from the interconnection point 4 / Xeq) is determined. And, it is a condition for controlling the reactive power of each wind power generator so that the total sum of the reactive power of each wind power generator becomes equal to the value obtained by multiplying the calculated system parameter and the total of the active power of the wind power generator .

ΣQi (t + 1) = − α · ΣPi (t + 1) Equation 1
Where i is the number of the wind power generator and i = 1 to n
t: Control period Pi (t + 1): Active power from each generator at time (t + 1) Qi (t + 1): Reactive power from each generator at time (t + 1) α: System parameter
The combined impedance including the interconnection line 2 and the load 3 as seen from the interconnection point 4
Anti-component (Req) / Reactance component Xeq)
Σ: A symbol for summation, which is the summation in the range [i = 1 to n].

  Supplementary explanation will be given for the system parameter α described above. In the case of the system configuration of FIG. 1, the impedance on the system side viewed from the wind power generator group (wind farm) side is given by the following equation.

1 / (Req + j Xeq) =
1 / (R1 + j X1) + 1 / (R2 + j X2) (2)
Here, j is an imaginary unit, R1 is the resistance of the interconnection impedance,
X1 is the reactance of the interconnection impedance,
R2 is the resistance component of the equivalent impedance of the load,
X2 is a reactance component of the equivalent impedance of the load. Since the load fluctuates with time, R2 and X2 fluctuate with time. However, since the second term on the right side of Equation 2 is smaller than the first term, In the order, the combined impedance may be considered to be substantially constant in time.

  Note that the active power, reactive power, and voltage (described later) at the interconnection point 4 are measured by a voltage sensor and a current sensor (not shown in the figure) attached to the transformer 13 described in FIG. Estimate using the value.

  Next, preventing the cross current between the wind power generators i is a second constraint condition. That is, cross current is prevented by setting the voltage difference between the connection point Ci to the on-site transmission line 11 to which each wind power generator i is connected and the connection point Cj (j = i + 1) adjacent to the connection point Ci to zero. The condition for this can be expressed as Equation 3. In addition, Formula 3 needs to be materialized about i = 1- (n-1).

Vj−Vi≈ {Rij ΣPk (t + 1)
+ Xij ΣQk (t + 1)} / Vi = 0 (Formula 3)
Where Vi: voltage at each connection point Ci Rij: resistance between connection points Ci and Cj Xij: reactance between connection points Ci and Cj Σ: symbol for summation, in the range of [k = 1 to i] Take the sum.

  Further, as shown in Expression 4, the upper limit of the active power of each wind power generator i is limited by the energy of the wind, and the lower limit is set in the operation range by mechanical control. Equation 4 is a third constraint condition.

Pi (n + 1) _Min ≦ Pi (n + 1) ≦ Pi (n + 1) _Max ...... Expression 4
here,
Pi (n + 1) _Max : Maximum effective power value of wind power generator i at time (t + 1) Pi (n + 1) _Min : Minimum effective power value of wind power generator i at time (t + 1) Based on such constraints, wind power While controlling the voltage fluctuation at the connection point 4 where the generator group is connected to the grid, each wind generator is coordinated to distribute the active power and reactive power appropriately and optimize the operation of the wind generator group In this embodiment, the following two evaluation conditions (1) and (2) are examined as a method to do this.
(1) Minimize temporal changes in active power transmitted from the wind power generator group.
(2) Maximize the effective power transmitted from the wind power generator group.

  The objective function F1 in the case of the evaluation condition (1) is expressed by Equation 5.

F1 = {ΣPi (t + 1) −ΣPi (t)} Equation 5
Here, Pi (t) is the active power of the i-th wind power generator at time t, and the known quantity Equation 5 is minimized at time (t + 1), in other words, Pi (t) of the previous cycle. Pi (t + 1) is determined so as to minimize the sum of fluctuations of Pi (t + 1) in the current cycle with respect to the wind power generators i to n.

  Similarly, the objective function F2 in the case of the evaluation condition (2) is expressed by Equation 6.

F2 = ΣPi (t + 1) ...... Formula 6
Pi (t + 1) is determined so as to maximize Equation 6, in other words, so as to maximize the sum of Pi (t + 1) in the current cycle.
The output command value to each wind power generator is set as an optimal solution using linear programming, with Formula 1, Formula 3, and Formula 4 as constraints, Formula 5 or Formula 6 as objective functions F1 and F2,
Pi (t + 1) and Qi (t + 1) [i = 1 to n] can be obtained.
Next, a method for obtaining an optimal solution by linear programming will be described. To apply linear programming, it must have the following characteristics:

    (a) All variables (assuming n) are non-negative.

    (b) The constraint condition is a linear inequality or an equality.

    (c) The objective function (maximizing or minimizing function) is a linear function of the variable of (a).

  In order to satisfy the above (a), variable conversion is performed as necessary. For example, Qi (t + 1) obtains a coefficient in place of a new variable whose sign has been changed.

  A method called a simplex method is used as a method for obtaining an optimal solution from the linear programming problem subjected to the above preprocessing.

  A collection of n variables satisfying the constraint condition (b) is represented by an area (called a possible area) in an n-dimensional space, and a collection of n variables belonging to it is called a possible solution. A set of variables that maximizes or minimizes the target value among possible solutions is an optimal solution.

  The linear programming problem defined in (a) to (c) uses the property that the possible region is a convex polyhedron in n-dimensional space, and the optimal solution is its vertex. In the simplex method, the object function moves along a side where the value of the objective function changes the most, and ends at a vertex where the objective function does not change. As a result, an optimal solution is obtained. Actually, the above-described processing is realized by a computer program.

  The above arithmetic processing is performed by the overall monitoring device 5, and the optimal solutions Pi (t + 1) and Qi (t + 1) are output to the corresponding controllers 20 as command values to the respective wind power generators i.

FIG. 6 shows a flowchart of processing of the overall monitoring apparatus 5. First, system information necessary for system parameter calculation for suppressing voltage fluctuation at the interconnection point 4 is acquired (600). Based on a predetermined control period, it is determined whether or not it is a control timing (601). If it is a control timing, information, such as active power, reactive power, an output voltage, a wind speed, will be acquired from each wind power generator i (602), and will be stored in a database (DB). Based on the acquired information (information such as wind speed), the maximum effective power (output) of each wind power generator i at the control timing is estimated. (604)
Next, using Equation 1, Equation 3, and Equation 4, a constraint equation for active power and reactive power related to voltage fluctuation suppression and output optimization (effective power maximization) is created (605). An objective function F1 or F2 is created using Expression 5 or 6 (606). Whether to optimize with the objective function F1 or with the objective function F2 is input in advance from the input device of the overall monitoring device 5. A solution of the optimization problem is obtained using linear programming (607). The rationality of the solution corresponding to the active power and reactive power of each wind power generator i at the next control timing is checked (608). Here, the rationality check checks whether or not the range of the limit is satisfied when the limit is set to the active power and the reactive power of each wind power generator i. If there is a problem with the rationality of the solution, replace it with the previous value or the corrected value. This is transmitted as a command value to each wind power generator i (609). Thereafter, steps 601 to 609 are repeated for each control cycle (610).

  Here, regarding the voltage fluctuation suppression, the constraint formula of Formula 1 may be satisfied, and when there is a variation in the output from each wind power generator, the maximum active power is extracted from the wind power generator with a large output, Reactive power can be distributed to wind power generators with low output.

  In FIG. 7, the graph of the example of operation | use in the wind power generator group comprised by the three wind power generators in embodiment of this invention is shown. FIG. 4A shows a case where a voltage difference of 1% at the maximum is generated at the connection point of each wind power generator. It can be seen that there is a cross current between the connection points. FIG. 5B shows a case where the voltages at the three connection points are substantially equal in the method of the present embodiment, and it is possible to eliminate the cross current.

  In the example of FIG. 1, all the wind turbine generators have been optimized. However, when the number of wind power generators is very large, grouping is performed depending on the difference in the connected transmission lines. It is conceivable to apply the optimization of FIG. 1 to the same group of wind generators.

  As described above, according to the present embodiment, the first constraint condition is satisfied to suppress the voltage fluctuation at the interconnection point, and the second constraint condition is satisfied to suppress the cross current between the wind power generators. Further, since the command values of the active power and reactive power of each wind power generator in the wind power generator group are obtained while satisfying the third constraint condition and considering the characteristics of each wind power generator, each wind power generation The active power and reactive power can be appropriately distributed by cooperatively controlling the machines, and the operation of the wind power generator group can be optimized. In particular, fluctuations in active power (output) as a whole wind power generator group can be minimized.

  In addition, each wind power generator obtains the active power and reactive power of each wind power generator so as to maximize the active power of the wind power generator that is output to the power system while satisfying the first to third constraints. Since the power converter of the generator is controlled, each wind power generator can be coordinated to effectively distribute the active power and reactive power, and the operation of the wind power generator group can be optimized. There is an advantage that the effective power (output) of the entire wind power generator group can be maximized.

  Although the overall monitoring device 5 and each distributed power controller 20 have been described as separate units so far, the function of the overall monitoring device is added to each distributed power source controller, thereby providing a separate control unit. The same effects as described above can be obtained without using a monitoring device. In addition, the functions of the general monitoring device are provided in multiple controllers, and in the unlikely event that a controller that realizes the general monitoring device function fails, other controllers having the general monitoring device function can perform the function. By doing so, it is also possible to ensure higher reliability.

It is a system configuration | structure figure of the system which applied one Embodiment of this invention to the control method of the wind power generator group. It is a block diagram which shows the structure of an integrated monitoring apparatus. It is a block diagram which shows each function of a controller. It is explanatory drawing which shows the monitoring screen of an integrated monitoring apparatus. It is an equivalent circuit of the system | strain block diagram of FIG. The flowchart which shows the process of an integrated monitoring apparatus. It is an operation | movement waveform diagram explaining the effect of embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Master system, 2 ... Interconnection line, 3 ... Load, 4 ... Connection point, 5 ... General monitoring apparatus, 6 ... Current sensor, 7 ... Voltage sensor, 8 ... Power converter, 9 ... Generator, 10 ... Wind turbine, 31 ... communication line, 20 ... controller

Claims (3)

A group of distributed power sources in which a plurality of distributed power sources each including a power converter that converts the output of the power source into desired voltage and power and outputs the power are connected to the power system via the transmission lines for the distributed power source In the control method of
Collecting measured values of output voltage and output power of each distributed power source for each predetermined control cycle,
A first constraint that absorbs the variation of the active power of each of the distributed power sources and the voltage variation of the interconnection point of the power system by the reactive power of each of the distributed power sources;
A second constraint that suppresses cross current between the distributed power sources;
Satisfying a third constraint that limits the active power of each of the distributed power sources within the upper and lower limits; and
Wherein minimizing the variation of the active power for the previous control cycle in the interconnection node, or as an evaluation condition one of maximizing the active power of each of the distributed power to be output to the electric power system, the A control method of a distributed power supply group, wherein command values of active power and reactive power of each distributed power supply are respectively obtained to control the power converter of each distributed power supply. In the control method of the distributed power supply group according to claim 1,
The first constraint condition is based on a fluctuation amount of active power of each of the distributed power sources and a voltage fluctuation amount of the interconnection point, and a resistance component Req of the combined impedance on the power system side viewed from the interconnection point and A system parameter that is a ratio of reactance component Xeq (Req / Xeq) is obtained, and the sum of reactive power of each distributed power source is equal to a value obtained by multiplying the system parameter and the total active power of each distributed power source. A control method for a distributed power supply group, characterized in that: A plurality of distributed power sources each including a power converter that converts the output of the power generation source into a desired voltage and power and outputs the power, a distributed power transmission line to which the plurality of distributed power sources are connected, and In a distributed power supply group system in which distributed power transmission lines are connected to a power system,
For each predetermined control cycle, an overall control device is provided that collects measured values of the output voltage and output power of each distributed power source and controls the power converter of each distributed power source,
The overall control device is:
A first constraint that absorbs the variation of the active power of each of the distributed power sources and the voltage variation of the interconnection point of the power system by the reactive power of each of the distributed power sources;
A second constraint that suppresses cross current between the distributed power sources;
Satisfying a third constraint that limits the active power of each of the distributed power sources within the upper and lower limits; and
Wherein minimizing the variation of the active power for the previous control cycle in the interconnection node, or as an evaluation condition one of maximizing the active power of each of the distributed power to be output to the electric power system, the A distributed power supply group system characterized in that command values of active power and reactive power of each distributed power supply are respectively obtained to control the power converter of each distributed power supply.

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