JP5074268B2 - Distributed power system - Google Patents

Description

  The present invention relates to a distributed power supply system linked to a power system.

  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 solar power generation and wind power generation has become popular. These distributed power sources are often used in conjunction with the power system, but when the power generation output fluctuates due to fluctuations in the amount of solar radiation and wind speed, the voltage of the connected system or when it is introduced in large quantities There is a concern that the frequency of the system may be affected.

  Several proposals for using reactive power have been made regarding methods for suppressing voltage fluctuations.

  Patent Documents 1 and 2 are known as methods for suppressing voltage fluctuations at a connection point (position) when a wind power generator is connected to a power system via a converter. In Patent Document 1, a parameter for determining reactive power (hereinafter referred to as a system parameter) is calculated from detected values of active power fluctuations and voltage fluctuations, and voltage fluctuations caused by active power fluctuations are canceled out. A method for suppressing voltage fluctuation by supplying reactive power is disclosed.

  Further, Patent Document 2 discloses a method for obtaining a system parameter related to voltage fluctuation using an inter-order storm surge by adding a device that generates an inter-order storm surge.

JP 2007-1224779 A JP 2002-171667 A

  There are many areas where solar power generation is suitable for introduction. In particular, in Japan, large-scale and large-scale introduction are planned. From the economical point of view regarding voltage fluctuation suppression, it is desirable to suppress voltage fluctuation by the converter itself without adding a new device as in Patent Document 2. Even if the converter itself suppresses voltage fluctuations, if the reactive power is actively changed to determine the optimal operating condition of the converter, the power system will be An artificial disturbance will be given.

  Moreover, in patent document 1, although the above-mentioned problem does not exist, the voltage fluctuation factor resulting from other than wind power generation output is removed using the periodic fluctuation of wind power, and periodicity like solar power generation is excluded. There is a possibility that a voltage variation factor caused by other than its own output fluctuation cannot be completely removed from a distributed power source that exhibits no output fluctuation.

  The present invention has been made in view of the above problems, and when a distributed power source that exhibits non-periodic output fluctuation is connected to an electric power system and operated, even if the output of the distributed power source fluctuates. An object of the present invention is to provide a distributed power supply system that can suppress voltage fluctuation caused by output fluctuation.

  In the present invention, the above object is achieved by calculating a system parameter that minimizes voltage fluctuation from the system constant of the system to which the distributed power system is connected. However, since the temperature of the transmission line changes depending on the temperature and the power flowing through the transmission line, the resistance of the transmission line fluctuates among the system constants, so using a constant value causes an error in the calculated system parameter. Become.

  In order to solve this problem, in the present invention, a distributed power supply system that is pre-recorded in a database in a distributed power supply system that includes a power generation unit and a power converter and is connected to a power system through a connection line. Based on the system constants and representative load patterns of the power system that is connected to the power system and the temperature information, system parameters that minimize voltage fluctuations are calculated, and active and reactive power command values are generated from the system parameters. The power converter is driven by generating a control signal of the power converter according to the command value.

  Furthermore, when the amount of power generated by solar power generation is large, the influence on the power passing through the transmission line cannot be ignored. For this reason, in addition to system constants, typical load patterns, and temperature information, the output power of the power converter calculated from the measured values of the voltage sensor and current sensor provided in the distributed power system is used to minimize voltage fluctuations. The system parameter to be converted is calculated.

  According to the distributed power supply system of the present invention, the optimum system parameters for minimizing the voltage fluctuation can be obtained from the system constants and representative load patterns of the interconnected system, the temperature information, and the output of the power converter. By operating the power converter based on the same system parameters, the converter can generate fluctuations in reactive power that cancel out voltage fluctuations due to output fluctuations, and has the effect of suppressing voltage fluctuations at the interconnection point .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present invention, the voltage fluctuations are obtained by determining the optimum system parameters from the system constants and representative load patterns of the interconnection system recorded in advance, the temperature information, and the output power of the power converter, and driving the converter based on the system parameters. The operation which minimizes is realized.

  FIG. 1 is a configuration diagram of a distributed power supply system having a photovoltaic power generation apparatus according to an embodiment of the present invention. The solar power generation device includes a power conversion unit (solar panel) 9 and a power converter 8. The power generation unit 9 is connected to the interconnection line 2 at the interconnection point 4 via the power converter 8, and the interconnection line 2 is connected to the main system 1. A load 3 is connected to the connection line 2. The power converter 8 is driven by a signal generated by the controller 10 based on the measured values of the current sensor 5, the voltage sensor 8, and the temperature sensor 7.

  The controller 10 includes a voltage power calculator 100, an air temperature calculator 105, a system parameter calculator 110, a power command value calculator 120, and a power controller 130. The database 20 records system constants and typical load patterns of the power system connected to the photovoltaic power generation system. The system constants are impedance (resistance component, reactance component) for each section of the transmission line, transformer transformation ratio and impedance, power generation facility output, operating power factor, and the like. Although the load varies depending on the season and within a day, it is a big difference that affects the system parameters, such as a difference in load depending on the season.

  FIG. 2 shows an example of a typical load pattern. In this example, the average load of 10:00 to 14:00, which increases the photovoltaic power generation output if it is fine, is shown for the winter, spring, summer, and fall seasons. In addition, when applying this pattern for the turn of the season, as shown by the broken line in the figure, the load gradually (linearly) during the period before and after the change of the season (for example, two weeks on one side) Treat as changing.

  The measured value calculator 100 calculates active power and reactive power from the measured values of voltage sensors and current sensors provided in the distributed power supply system. The measured values (voltage, current) are sent to the power controller 130, and the calculated power is sent to the power command value calculator 120.

  If the system parameter has not been updated, the power command value calculator 120 generates a command value for active power and reactive power using the previous system parameter, and sends it to the power controller 130. The power controller 130 generates a drive signal for the power converter 6 based on the command values of the active power and reactive power and the measured value from the measured value calculator 100.

  On the other hand, the system parameter calculator 110 obtains system constants and representative load patterns from the database 20, and the temperature calculated by the temperature calculator 105 based on the measured value of the temperature sensor 7 at a constant cycle (for example, 30 minutes). From the estimated value of the load on that day, the system constant is calculated in consideration of the temperature change, and the system parameter reflecting this is calculated.

  When the system parameters are updated, in the process of the power command value calculator 120 described above, command values for active power and reactive power are generated based on the new system parameters and sent to the power controller 130. The processing in the power controller 130 is the same as the case where the above-described system parameter is not updated.

  Next, a method for obtaining system parameters will be described. Consider the example system of FIG. The main system is approximated by the leftmost power supply (VS). A transmission line extends from the main system, and a load and photovoltaic power generation are connected near the end of the transmission line. The power transmission line can be represented by a resistance component r1 and a reactance component x1, and the load can be approximated by a resistance component r2 and a reactance component x2.

  FIG. 4 is a system model when the transmission line and the load are viewed from the photovoltaic power generation system. The transmission line and load of the system shown in FIG. 3 are equivalent to the combined impedance (resistance R, reactance X) shown in FIG. The main system voltage (V0) is constant. The voltage (VS) at the interconnection point to which the photovoltaic power generation system is connected varies depending on the output fluctuation of the photovoltaic power generation system and the fluctuation of the load.

  When the active power fluctuation ΔP and the reactive power fluctuation ΔQ occur in the photovoltaic power generation system, the fluctuation ΔVS of the connection point voltage can be expressed by Expression (1).

ΔVS≈ (ΔP · R + ΔQ · X) / VS (1)
Here, R is the resistance of the combined impedance, and X is the reactance of the combined impedance.

  If reactive power fluctuation ΔQ is generated in proportion to active power fluctuation ΔP as shown in equation (2), and α is determined as shown in equation (3), interconnection point voltage fluctuation ΔVS in equation 1 is reduced to 0. Can be. This α is called a system parameter.

ΔQ = −α · ΔP (2)
However, α = R / X (3)
Next, a method for obtaining the synthetic impedance will be described. The synthetic impedance is obtained using Thevenin's theorem. When the identification theory is applied to the circuit of FIG. 5 equivalent to the system of FIG. 3, the resistance component R and the reactance component X are given as follows.

R = A / (A · A + B · B) (4)
X = B / (A · A + B · B) (5)
here,
A = r1 / (r1 · r1 + x1 · x1) + r2 / (r2 · r1 + x2 · x2) (6)
B = x1 / (r1 · xr1 + x1 · x1) + x2 / (r2 · r1 + x2 · x2) (7)
Using R and X obtained in equations (4) and (5), a system parameter α that minimizes voltage fluctuation at the interconnection point is obtained in equation (3). The corresponding power factor PF (referred to as the optimum power factor) is given by the following equation.

PF = cos (arctan (−α)) (8)
FIG. 6 is an example of the optimum power factor when a photovoltaic power generation system is connected near the end of a transmission line of about 25 km. The temperature is assumed to be 2 ° C in winter and 31 ° C in summer. In summer, the load is high and the temperature is high, so the conductor temperature of the transmission line is high, so the electrical resistance is large and the optimum power factor is low (a value far from 1). The winter load is the second largest after summer, but the temperature is low, so the conductor temperature of the transmission line is lower than in other seasons, and the optimum power factor is high (a value close to 1).

  Next, the operation of the system parameter calculator 110 which is a part of the function of the controller 10 will be described. FIG. 7 is a flowchart showing the processing of the system parameter calculator. Processing is started in accordance with the startup of the photovoltaic power generation system. It is determined whether the day has changed (301), and the target date is changed (302). The target date is a date that serves as a reference for predicting the load.

  The system constant of the system connected to the system is acquired from the database (303). A load pattern for each season is acquired (304). The load on the target day is calculated from the target day and the acquired load pattern (305). In addition to determining which season the target day belongs to, when the target day is at the turn of the season, as shown in FIG. 2, the load is estimated on the assumption that the load gradually changes over a predetermined period. To do. The load pattern may be given in units shorter than the season (for example, monthly). The processes 302 to 305 are performed once a day.

  Next, it is determined whether it is the timing for reviewing the system parameters (306). The review timing is determined in advance, for example, once every hour. When the corresponding time is the review timing, the following series of processing is performed. The temperature is acquired from the temperature calculator 105 (307). The conductor temperature of the transmission line is calculated from the temperature and the load (308). Based on the conductor temperature of the transmission line, the system constant resistance is corrected (309). A system parameter (α) is calculated using equations (3) to (7) (310). The calculated system parameter (α) is transmitted to the power command value calculator 120 (311).

  In the power command computing unit 120, until the system parameter is changed, the previous value of the system parameter (α) is used and the command value of the active / reactive power is calculated by the above-described processing.

Next, the function of the power controller will be described. FIG. 8 is a processing block diagram of the power controller. In the block 501, three-phase two-phase conversion (formulas (9) and (10)) and rotational coordinate conversion (formulas (11) and (12)) are applied to the measured values (va, vb, vc) of the three-phase voltage. And the straight-axis and horizontal-axis voltages (vd, vq) are calculated (see the Electrical Engineering Handbook (6th edition), The Institute of Electrical Engineers of Japan, P.136).
vα = √2 / 3) · va−√ (1/6) · vb−√ (1/6) · vc (9)
vβ = √ (1/2) · vb−√ (1/2) · vc (10)
vd = cos (θ) · vα + sin (θ) · vβ (11)
vq = −sin (θ) · vα + cos (θ) · vβ (12)
Here, θ is the system voltage phase angle (angular velocity × time).

In the block 502, three-phase two-phase transformation (Equations (13), (14)) and rotational coordinate transformation (Equations (15), (16)) are applied to the measured values (ia, ib, ic) of the three-phase current. And the straight axis and horizontal axis currents (id, iq) are calculated.
iα = √2 / 3) · ia−√ (1/6) · ib−√ (1/6) · ic (13)
iβ = √ (1/2) · ib−√ (1/2) · ic (14)
id = cos (θ) · iα + sin (θ) · iβ (15)
iq = −sin (θ) · iα + cos (θ) · iβ (16)
The block 503 uses the command values of the active / reactive power obtained by the power command value calculator 120 and the direct axis and horizontal axis voltages (vd, vq) obtained in the block 501, and uses the direct axis and horizontal axis currents. Command values (id *, iq *) are calculated.

  In the block 504, the measured values of the direct axis and horizontal axis currents are compared with the command values of the direct axis and horizontal axis currents, and the proportional-integral control processing is performed according to the equations (9) and (10). The voltages (two phases) ed and eq of the converter are calculated from the equations (17) and (18).

ed = ∫k · (id-id *) · dt (17)
eq = ∫k · (iq−iq *) · dt (18)
Here, k is a proportional coefficient, and dt is a minute time.

  In 505, non-interference control, that is, voltage command values (two-phase) ed * and eq * of the voltage source converter considering the voltage change due to the direct and horizontal currents are calculated from the equations (19) and (20) To do.

ed * = ed−R · id + ω · L · iq (19)
eq * = eq−ω · L · id + R · iq (20)
Here, R is a resistance, L is an inductance, and ω is an angular frequency.

In the block 506, a three-phase voltage command value is generated by rotating coordinate inverse transformation (Equations (21) and (22)) and two-phase three-phase transformation (Equations (23) and (24)).
eα * = cos (θ) · ed * −sin (θ) · eq * (21)
eβ * = sin (θ) · ed * + cos (θ) · ed * (22)
ea * = √ (2/3) · eα * (23)
eb * =-√ (1/6) · eα * + √ (1/2) · eβ * (24)
ec * = − √ (1/6) · eα * −√ (1/2) · eβ * (25)
In a block 507, a gate signal is generated by a PWM (pulse width modulation) method for driving the power converter 8. That is, by comparing a triangular wave carrier signal (for example, frequency 3 kHz) with a voltage command value, a gate signal (driving signal) for turning on and off the switching element is generated.

  Next, voltage fluctuations when a photovoltaic power generation system was connected near the end of the transmission line of about 25 km described above were evaluated by simulation. FIG. 9 is an example when there is a fluctuation (decrease) in the photovoltaic power generation output. FIG. 10 shows the result of the simulation, and shows the result of the flow calculation of the voltage fluctuation at the interconnection point due to the output fluctuation, and shows the case where the control with the constant power factor is performed and the case where the control of the present invention is performed. In the case of constant power factor control, a voltage drop of 0.35% was observed at the connection point, but in the case of performing the control of the present invention, the voltage drop was only 0.03%.

  Until now, the case where the ratio of the photovoltaic power generation output to the load of the target system is relatively small has been dealt with. However, when the ratio of the photovoltaic power generation output increases, the influence of the photovoltaic power generation cannot be ignored.

  FIG. 11 is a configuration diagram of a distributed power supply system having a photovoltaic power generation apparatus according to the second embodiment. As in the case of FIG. 1, the controller 11 includes a voltage power calculator 100, an air temperature calculator 105, a system parameter calculator 110, a power command value calculator 120, and a power controller 130. The controller 11 is different in that the system parameter calculator 111 acquires a measured value of power from the voltage power calculator 100 in addition to the temperature.

  FIG. 12 is a flowchart showing processing in the system parameter calculator 111. In accordance with the start of the photovoltaic power generation system, it is determined whether the day has changed (401), and the target date is changed (402). The acquisition of the system constant (403), the acquisition of the load pattern for each season (404), and the calculation of the load on the target day (405) are the same as in the case of FIG.

  Next, it is determined whether it is the timing for reviewing the system parameters (406). When the corresponding time is the review timing, the following series of processing is performed. First, the temperature is acquired from the temperature calculator 105 (407). Next, photovoltaic power (effective / reactive power of the power converter) is acquired from the voltage / power calculator 100 (408). The conductor temperature of the transmission line is calculated from these temperature, load, and photovoltaic power (409). Based on the conductor temperature of the transmission line, the system constant resistance is corrected (410). A system parameter (α) is calculated using equations (3) to (7) (411). The calculated system parameter (α) is transmitted to the power command value calculator 120 (412).

  By performing the above processing, even when the photovoltaic power generation output is large with respect to the load, the optimum system parameter can be obtained, and the voltage fluctuation at the interconnection point can be suppressed.

  In the first and second embodiments, the method for calculating the air temperature from the measurement value by the temperature sensor has been described as means for obtaining the air temperature information. However, since the data for the past several years has been provided by the Japan Meteorological Agency etc. regarding the temperature in the region or the vicinity, it is also possible to use this data. That is, the average temperature of each month is obtained from the past temperature data and recorded in the database 20. When operating a power converter, it is possible to suppress the voltage fluctuation by determining what month the operation day is, obtaining the average temperature of the month from the database, and calculating the system parameters using it. System parameters can be obtained.

  Further, the solar power generation system has been described so far, but the system parameters are determined by the state of the power system and the load, and do not depend on the type of the distributed power source. Therefore, even when the wind power generation system is linked to the power system as a distributed power source, the same control as in the embodiment of FIG. 1 or FIG. 11 is possible.

The block diagram of the distributed power supply system which has a solar power generation device in Example 1 of this invention. Explanatory drawing which shows the example of a load pattern. The schematic diagram which shows the example of the system | strain which connected solar power generation. The schematic diagram which shows the condition of the system | strain and load which were seen from the solar power generation system. The equivalent circuit diagram for calculating a synthetic | combination impedance. The graph which shows the difference in the optimal power factor according to a season. The flowchart which shows the process in a system | strain parameter calculator. The block diagram which shows the process in an electric power controller. The graph which shows the example of photovoltaic power generation output fluctuation. 3 is a graph showing the effect of Example 1. The block diagram of the distributed power supply system which has a solar power generation device in Example 2 of this invention. 9 is a flowchart showing processing in a system parameter calculator according to the second embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Master system, 2 ... Interconnection line, 3 ... Load, 4 ... Connection point, 5 ... Current sensor, 6 ... Voltage sensor, 7 ... Temperature sensor, 8 ... Power converter, 9 ... Electric power generation part (sunlight Panel), 10 ... Controller, 100 ... Power voltage calculator, 105 ... Temperature calculator, 110 ... System parameter calculator, 120 ... Power command value calculator, 130 ... Power controller.

Claims (6)

In a distributed power system that consists of a power converter and a controller that converts power from the power generation unit, and is operated by connecting to the power system via a connection line,
The controller calculates a system parameter that minimizes voltage fluctuation based on a database in which system constants and representative load patterns of the power system are recorded in advance, and the system constants, representative load patterns, and temperature information. System parameter calculation means, power calculation means for calculating active / reactive power in the interconnection line from the measured voltage and current values of the power converter output, calculated system parameters and calculated active / reactive power Power command value calculation means for generating an active / reactive power command value, and a power controller for generating a control signal for a power converter according to the active / reactive power command value. the system parameters to drive calculates the load of the target date from the representative load patterns, calculate the conductor temperature of the transmission line from the load and the temperature information And, distributed power supply system and calculates to correct the resistance of the system constant by conductor temperature. In a distributed power system that consists of a power converter and a controller that converts power from the power generation unit, and is operated by connecting to the power system via a connection line,
The controller includes a database in which system constants and representative load patterns of the power system are recorded in advance, the system constants and representative load patterns, temperature information, and voltage and current measurements of the power converter output. Based on the active / reactive power of the power converter output calculated from the value, the system parameter calculating means for calculating the system parameter that minimizes the voltage fluctuation, the calculated system parameter, the measured values of the voltage and current, Power command value calculation means for generating an active / reactive power command value from the power controller, and a power controller for generating a control signal for a power converter corresponding to the active / reactive power command value. A distributed power supply system characterized by driving an electric power source. In claim 2 ,
When the active power P and the reactive power Q calculated from the measured values of voltage and current fluctuate, the system parameter α is such that the reactive power fluctuation ΔQ is proportional to the active power fluctuation ΔP, and ΔQ = −αΔ
A distributed power supply system that is calculated so as to have a relationship of P. In claim 2,
The system parameter calculates a load on a target day from the representative load pattern, calculates a conductor temperature of a transmission line from the temperature information, the load, and active / reactive power of the power converter output, and the conductor A distributed power supply system, wherein the calculation is performed by correcting the resistance of the system constant according to temperature. In any of claims 1 4, wherein the temperature information distributed power supply system is the historical average temperature data / day stored in the temperature or a database in advance, which is calculated from the measured value of the temperature sensor. In any one of Claims 1 thru | or 5 ,
The power generation unit is a distributed power supply system that is a solar power generation device.

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