JP4749433B2 - Distributed power supply system and control method thereof - Google Patents

Description

  The present invention relates to a distributed power supply system used in conjunction with a power system and a control method thereof.

  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. As a method for suppressing voltage fluctuations at a connection point (position) when a wind power generator is connected to a power system via a converter, Patent Document 1 discloses detection of fluctuations in active power and voltage fluctuations. Disclosed is a method for suppressing voltage fluctuation by calculating a parameter (hereinafter referred to as a system parameter) for determining reactive power from a value and supplying reactive power that cancels voltage fluctuation caused by fluctuation of active power. Has been.

  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.

  In Patent Document 3, a reactive power is actively changed in a converter (inverter) without adding a new device, a system parameter relating to voltage fluctuation is obtained, and effective and reactive power for suppressing voltage fluctuation is obtained. A method of generating is disclosed.

JP 2007-1224779 A JP 2002-171667 A JP 2006-158179 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. Regarding voltage fluctuation suppression, it is desirable to suppress voltage fluctuation with a converter instead of adding a new device as in Patent Document 2. Further, as in the cited document 3, when the reactive power is actively changed to determine the optimum operating condition of the converter, an artificial disturbance is applied to the power system at the stage of calculating the optimum operating condition. Will give.

  In Patent Document 1, although there is no problem as described above, the periodic fluctuation of wind power is used to remove the voltage fluctuation factor caused by other than the wind power generation output, and periodicity like solar power generation is removed. 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 object of the present invention has been made in view of the above problems, and when a distributed power source that exhibits output fluctuation without periodicity is connected to an electric power system and operated, the output of the distributed power source fluctuates. Another object of the present invention is to provide a distributed power supply system and a control method that can suppress voltage fluctuations caused by output fluctuations.

  The present invention that achieves the above object is provided in a distributed power supply system in a distributed power supply system that is operated by connecting a power converter that controls the output of a power generation unit to a power system via a connection line. From the measured value of the sensor, the fluctuation of the active power sent to the interconnection line and the voltage of the interconnection point voltage are calculated, and the system parameter for determining the ratio of reactive power to the active power from the calculated fluctuation value is The amount of deviation between the parameters and the system parameter that minimizes the voltage fluctuation is calculated, and the active / reactive power command value is generated based on the optimum system parameter obtained by correcting the deviation amount. The power converter is driven by generating a control signal for the power converter.

  Furthermore, when obtaining the amount of deviation between the system parameter that minimizes the voltage variation and the current system parameter from the measured value, an isolated variation that is a discontinuous and non-periodic variation is extracted from the measured value. The variation of the active power and the interconnection point voltage is calculated from the magnitude of the variation.

The method of the present invention that achieves the above object is a method for controlling a distributed power supply system including a power converter that is connected to a power system via a connection line and controls the output of a power generation unit. Read time series data of active power and connection point voltage in the vicinity of the connection point with the system line, and from the active power and reactive power calculated based on the active power command value, the reactive power command value, and the time series data, While obtaining a control signal for controlling the power converter,
Using the time series data, the base line of the active power and the base line of the interconnection point voltage are obtained, the amount of fluctuation of the active power and the amount of fluctuation of the interconnection point voltage, which are fluctuation amounts from the base line, are obtained, and these fluctuation amounts are A system parameter that determines the ratio of reactive power to active power only when the timing is the maximum or minimum within a predetermined time range and the timings coincide with each other, based on the active power fluctuation amount and the interconnection point voltage fluctuation amount. A correction amount is calculated, and an active power command value and a reactive power command value are obtained based on the system parameter correction amount.

  According to the distributed power supply system of the present invention, an optimum system parameter that minimizes the voltage fluctuation is obtained by obtaining the system parameter based on the measurement value related to the aperiodic fluctuation, and the power converter based on the system parameter is obtained. By performing this operation, it is possible to cause the converter to generate a fluctuation in reactive power that cancels the voltage fluctuation accompanying the output fluctuation, and to suppress the voltage fluctuation at the interconnection point.

  Hereinafter, the embodiment of the present invention will be described by taking the case where the power generation unit is photovoltaic power generation as an example. By obtaining the correction amount of the system parameter from the measurement value related to the non-periodic fluctuation, the optimum system parameter is obtained, and the converter is driven based on the optimum system parameter, thereby realizing the operation that minimizes the voltage fluctuation.

  FIG. 1 is a configuration diagram of a distributed power supply system applied to a photovoltaic power generation system as an embodiment of the present invention. The solar power generation system is connected to the interconnection line 2 at the interconnection point 4, and the interconnection line 2 is connected to the main system 1. A load 3 is connected to the connection line 2. The solar power generation system includes a power conversion unit (solar panel) 5 and a power converter 6. The power converter 6 is driven by a signal generated by the controller 20 based on the measured values of the current sensor 11 and the voltage sensor 12 near the interconnection point 4.

  The controller 20 includes a power voltage (measured value) calculator 210, a power voltage fluctuation calculator 220, a system parameter calculator 230, a power command value calculator 240, and a power controller 250.

  The power voltage calculator 210 calculates the current, voltage, active power, and reactive power at each time from the measurement values obtained by the current sensor 11 and the voltage sensor 12. The measurement cycle of the measurement value is shorter than 1 millisecond. Each calculated measurement value is sent to a power controller 250 that generates a control value for the power converter 6, and a control signal (power converter 6) is compensated for the difference between the active power command value and the reactive power command value. Gate signal) is calculated.

  On the other hand, the calculated voltage (V) and active power (P) are also sent to the power voltage fluctuation calculator 220. The power voltage fluctuation calculator 220 obtains an average value for one second from the measured values of the voltage (V) and the active power (P), and stores it as time-series data accumulated for a fixed time (for example, 5 minutes). Fluctuation amount (ΔV) and active power fluctuation amount (ΔP) are calculated and sent to the system parameter calculator 230.

  The system parameter is given by the ratio of resistance and reactance in the combined impedance of the transmission line when the main system is viewed from the photovoltaic power generation system. By supplying reactive power that matches this system parameter from the photovoltaic power generation system (power converter), voltage fluctuations at the interconnection point can be suppressed.

  The system parameter calculator 230 calculates the deviation Δα from the optimal system parameter by a method described later, and sends it to the power command value calculator 240. The power command value calculator 240 generates command values for active power and reactive power using the system parameters with the deviation amount Δα corrected, and sends the command values to the power controller 250. The power controller 250 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 power voltage calculator 210.

  Next, a method for estimating optimum system parameters from measured values will be described. The interconnection line and load in FIG. 1 are equivalent to the combined impedance (resistance Rt, reactance Xt) when the interconnection line and load are viewed from the photovoltaic power generation system in FIG. The voltage (V0) at the connection point between the main system and the interconnection line 2 is constant. On the other hand, the voltage (Vs) at the interconnection point to which the photovoltaic power generation system is connected varies due to 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 solar power generation system, the interconnection point voltage Vs can be expressed by the equation (1).
ΔVs≈ (ΔP · Rt + ΔQ · Xt) / Vs (1)
Here, Rt is the resistance component of the true combined impedance, and Xt is the reactance component of the true combined impedance.

If the reactive power fluctuation ΔQ is generated in proportion to the active power fluctuation ΔP as shown in equation (2) and the system parameter α is determined as shown in equation (3), then the interconnection point in equation (1) The voltage fluctuation ΔVs can be made zero. Α at this time is set as αt and is called a true system parameter.
ΔQ = −α · ΔP (2)
α = Rt / Xt (= αt) (3)
Therefore, equation (4) is established.
0 = (ΔP · Rt−α · ΔP · Xt) / Vs (4)
However, the true system parameters are difficult to determine from the beginning because the system conditions change. When α is a system parameter used in the current control, there is a relationship of equation (5) with the true system parameter αt.
α = αt + Δα (5)
Here, Δα is a deviation amount from the true system parameter αt. Substituting these relationships into equation (1) establishes equation (6).
ΔVs = (ΔP · Rt− (αt + Δα) · ΔP · Xt) / Vs (6)
By solving equations (4) and (6), the deviation Δα from the true system parameter αt in the current system parameter α is given by equation (7).
Δα = − (Vs / Xt) · (ΔVs / ΔP) (7)
Vs, ΔVs, and ΔP in equation (7) are obtained from the measured values. If Xt is known, the true system parameter αt can be obtained by one correction according to the equation (8).
αt = α−Δα (8)
Next, how to obtain ΔVs and ΔP will be described. Although there are various forms of changes in the output of the photovoltaic power generation system, this method focuses on solitary wave fluctuations. FIG. 3 schematically shows temporal changes in active power ((a)) and voltage ((b)) of solitary wave fluctuation. In the figure, basic fluctuations (hereinafter referred to as trends) are indicated by broken lines. The trend is obtained by, for example, obtaining a regression line.

For the active power, an average value (Avpp) of active power larger than the trend and an average value (Avlow) of active power larger than the trend are obtained, and the coefficient K is calculated by the equation (9).
K = Avlow / Avuppp (9)
As K is larger than 1, it can be regarded as a solitary wave fluctuation. In the following evaluation, the case where K was 2.5 or more was treated as a solitary wave variation.

  FIG. 4 shows the amount of change from the trend in FIG. FIG. 4A shows the change over time in the amount of change in active power. The amount of change with the maximum amount of change in the evaluation range is defined as an active power fluctuation ΔP. FIG. 4B shows the change over time of the change amount of the interconnection point voltage Vs. The amount of change that maximizes the amount of change in the evaluation range is defined as a connection point voltage ΔVs. By treating the amount of change from the trend with respect to the interconnection point voltage, it is possible to eliminate voltage fluctuations that are not caused by changes in active power.

  FIG. 5 is a flowchart showing the system parameter correction processing, and shows the functions of the blocks 220 and 230 in FIG.

  First, time series data of active power and interconnection point voltage, and further a threshold value for determination are read (301). The maximum and minimum times are calculated for the read active power and connection point voltage data. A preliminary evaluation is performed, and an evaluation range is set based on the preliminary evaluation (302).

  FIG. 6 is an example of the read data of active power and interconnection point voltage. Although there are 300 time-series data in total, the evaluation range is set to a narrower range (a range indicated by a one-dot chain line in the figure) before and after the time when the minimum value of active power is given in the preliminary evaluation. This makes it difficult for disturbance to be superimposed on the trend of active power and voltage.

  Using the data of the set evaluation range, a base line of active power and a base line of interconnection point voltage corresponding to a trend are obtained by statistical processing of the data (303). Using this base straight line, the maximum and minimum values in the evaluation range are evaluated, and the active power fluctuation amount ΔP and the interconnection point voltage fluctuation amount ΔVs are obtained (304).

  Only when the active power change amount ΔP and the interconnection point voltage change amount ΔVs are larger than the preset threshold value and the timings coincide with each other, it is determined that the voltage fluctuation has occurred due to the fluctuation of the active power. (305). That is, only when it is determined that ΔP and ΔVs are valid values, the shift amount Δα is calculated (306). Further, the corrected system parameter α is calculated from the current system parameter α and the correction amount (−Δα).

  The rationality of whether or not α thus calculated is within the assumed range is checked (307). That is, in consideration of temperature and load fluctuations, upper and lower limit values that can be taken by the system parameter α are set in advance, and if the calculated α is between the above upper and lower limit values, it is determined to be reasonable. If the rationality is confirmed, the system parameter correction amount (−Δα) is transmitted to the power command value calculator 240 of FIG. 1 (308). The power command value calculator 240 generates active power and reactive power command values so as to satisfy the expression (2). When the rationality is not confirmed, the power command value calculator 240 generates active power and reactive power command values using the previous value of α.

  The effect of applying the method of the present invention to a 40 kW solar power generation system connected to a low-voltage distribution line and connected to a 6.6 kV high-voltage distribution line by pressure increase is predicted. FIG. 6 shows measurement data when the power generation output temporarily decreases on a substantially sunny day. FIG. 6A shows the active power, FIG. 6B shows the change in the interconnection point voltage, and the straight line in the figure is the trend (base straight line).

  When the measured value of FIG. 6 is obtained, the control according to the present invention is not performed. The system parameter α related to the control at this time was 0.12. When the process of FIG. 5 was applied, the correction amount obtained from the measured value was 1.02. From this result, the estimated true system parameter is 1.14.

  In addition, about the system | strain which connected the solar power generation system, since the system | strain constant is known beforehand and the true system | strain parameter calculated | required from the known system | strain constant will be 1.23, both corresponded substantially. Therefore, it can be seen that the process of FIG. 5 is almost appropriate.

  When the reactance of the combined impedance can be predicted almost accurately as in the example of FIG. 6 described above, a value close to the true system parameter can be obtained by one correction. However, if the reactance component is estimated to be smaller than the true value in the equation (5), the correction amount (−Δα) becomes larger than the true value, and the correction is excessive. As a result, the voltage may increase as shown in FIG. Also in this case, by performing the processing described below, as shown in an example in FIG. 8, it is possible to correct to a substantially true system parameter by performing several corrections.

  FIG. 9 is a flowchart showing a process when a plurality of corrections are performed. The measurement time series data and determination threshold value reading (401), evaluation range setting (402), base straight line calculation (403), and fluctuation amount calculation (404) are the same as the processing of 301-304 in FIG. It is.

  Next, it is determined whether or not the fluctuation directions ΔP and ΔVs change in the same direction (405). If they do not match (ΔVs increases when ΔP decreases), excessive correction is performed, and effectiveness determination in the case of excessive correction is performed (407). That is, ΔVs is evaluated at the time when Vs is maximum. When the fluctuation amounts ΔP and ΔVs change in the same direction (when ΔP decreases, ΔVs decreases), the same validity determination as in 305 of FIG. 5 is performed. In this case, ΔVs is evaluated at a time when Vs is minimum.

  Next, a system parameter correction amount is calculated (408). Although the correction amount (absolute value) is decreased by several corrections, it is determined whether the value is equal to or less than a predetermined threshold value (409). If it is not less than the threshold value, the processing of 402 to 408 is repeated. If the value is below the threshold value, the correction amount (signed) obtained by several corrections is added to obtain the final correction amount. As in 307 in the case of FIG. 5, the rationality check of the corrected system parameter (410) and transmission of the system parameter correction amount (411) are performed.

  FIG. 10 is an example of a measurement value that is not an isolated waveform ((a) is active power, and (b) is a connection point voltage). For measurements that are not isolated waveforms, the correction amount is not evaluated because it is difficult to eliminate the influence of disturbance in the voltage evaluation.

Next, processing of the power controller 250 in FIG. 1 will be described. FIG. 11 is a block diagram illustrating processing functions in the power controller 250. In block 501, the three-phase voltage measurement values (va, vb, vc) are subjected to three-phase two-phase conversion according to equations (10) and (11) and rotational coordinate conversion according to equations (12) and (13). , The vertical axis and horizontal axis voltages (vd, vq) are calculated (see Electrical Engineering Handbook (6th edition), Institute of Electrical Engineers, P.136).
vα = √ (2/3) · va−√ (1/6) · vb−√ (1/6) · vc (10)
vβ = √ (1/2) · vb−√ (1/2) · vc (11)
vd = cos (θ) · vα + sin (θ) · vβ (12)
vq = −sin (θ) · vα + cos (θ) · vβ (13)
Here, θ is an angle (angular velocity × time).

In block 502, three-phase two-phase conversion according to equations (14) and (15) and rotational coordinate conversion according to equations (16) and (17) are performed on the measured values (ia, ib, ic) of the three-phase current. , Straight axis, horizontal axis current (id, iq) is calculated.
iα = √ (2/3) · ia−√ (1/6) · ib−√ (1/6) · ic (14)
iβ = √ (1/2) · ib−√ (1/2) · ic (15)
id = cos (θ) · iα + sin (θ) · iβ (16)
iq = −sin (θ) · iα + cos (θ) · iβ (17)
Here, θ is an angle (angular velocity × time).

  In block 503, the target values and measured values of active / reactive power are taken in, and the direct axis and horizontal axis current command values (id *, vq) are obtained using the direct axis and horizontal axis voltages (vd, vq) obtained in block 501. iq *).

In block 504, the measured values of the direct axis and horizontal axis currents are compared with the command value, and the proportional-integral control processing is performed according to the equations (18) and (19), and the required voltage of the voltage source converter (two-phase) ed and eq are calculated.
ed = ∫k · (id-id *) · dt (18)
eq = ∫k · (iq−iq *) · dt (19)
Here, k is a proportional coefficient, and dt is a minute time.

In block 505, voltage command values (two-phase) ed * and eq * of the voltage source converter are calculated in consideration of the non-interference control by the equations (20) and (21), that is, the voltage change due to the direct / horizontal current. To do.
ed * = ed−R · id + ω · L · iq (20)
eq * = eq−ω · L · id + R · iq (21)
Here, R is a resistance, L is an inductance, and ω is an angular frequency.

In block 506 , the rotational coordinate conversion by the equations (22) and (23) and the two-phase three-phase conversion by the equations (24), (25) and (26) are performed to generate a three-phase voltage command value.
eα * = cos (θ) · ed * −sin (θ) · eq * (22)
eβ * = sin (θ) · ed * + cos (θ) · ed * (23)
ea * = √ (2/3) · eα * (24)
eb * = − √ (1/6) · eα * + √ (1/2) · eβ * (25)
ec * = − √ (1/6) · eα * −√ (1/2) · eβ * (26)
Here, θ is an angle (angular velocity × time).

In block 507 , a gate signal for driving the power converter 8 is generated by a PWM (pulse width modulation) method. 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.

  According to the present invention, by using the photovoltaic power generation system of FIG. 1 or the like, even when there is a large variation in active power, it is possible to supply power with suppressed variation in the connection point voltage.

The block diagram of the solar energy power generation system which is one Example of this invention. Explanatory drawing which shows the principle of voltage fluctuation suppression. Explanatory drawing which shows the method of calculating | requiring a trend from a measured value. Explanatory drawing which shows the method of calculating | requiring the variation | change_quantity of measured value. The flowchart which shows the process sequence of system | strain parameter correction | amendment. The graph of the active power and interconnection point voltage which show the example of application of this invention. The graph of the connection point voltage which shows the example of application at the time of overcorrection. Explanatory drawing which shows how to obtain | require the system | strain parameter at the time of overcorrection. The flowchart which shows the process sequence which calculates | requires a system | strain parameter by multiple correction | amendment. A graph of (a) active power and (b) interconnection point voltage) that is not an isolated waveform. The block diagram which shows the processing function of an electric power controller.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Master system, 2 ... Interconnection line, 3 ... Load, 4 ... Interconnection point, 5 ... Solar panel, 6 ... Power converter, 11 ... Current sensor, 12 ... Voltage sensor, 20 ... Controller, 210 ... Power, voltage (measured value) calculator, 220 ... power voltage fluctuation calculator, 230 ... system parameter calculator, 240 ... power command value calculator, 250 ... power controller.

Claims (6)

In a distributed power supply system that is operated by connecting a power converter that controls the output of a power generation unit to a power system via a connection line,
Fluctuations in active power and interconnection point voltage sent to the interconnection line are calculated from the measured values of sensors provided in the distributed power system, and the ratio of reactive power to active power is calculated from the calculated fluctuation values. For the system parameters to determine the current system parameter and the system parameter deviation amount that minimizes the voltage fluctuation, the active / reactive power command value is generated based on the optimum system parameter that corrects the deviation amount, A distributed power system, wherein a power converter is driven by generating a control signal of a power converter according to the effective / reactive power command value.   In Claim 1, when calculating | requiring the deviation | shift amount of the present system parameter and the system parameter which minimizes a voltage variation, the isolated fluctuation | variation which is a discontinuous and aperiodic fluctuation | variation is extracted from the said measured value, and this isolation | separation is carried out. A distributed power supply system characterized in that the fluctuation of the active power and the interconnection point voltage is calculated from the magnitude of the fluctuation.   2. The distributed power supply system according to claim 1, wherein the calculation of the optimum system parameter is repeated several times until it falls within a predetermined range.   4. The distributed power supply system according to claim 1, wherein the power generation unit is a solar power generation device. In a control method of a distributed power supply system that includes a power converter that is connected to a power system through a connection line and controls an output of a power generation unit
The active power and the connection point voltage in the vicinity of the connection point between the power converter and the connection line are measured, and the active power command value and the reactive power command value obtained based on the measured value and the system parameter at the time of control are used. While generating a control signal for controlling the power converter,
Periodically, using the time series data of the active power and the connection point voltage in the vicinity of the connection point between the power converter and the connection line, obtain a base line of the active power and a base line of the connection point voltage, The active power fluctuation amount and the connection point voltage fluctuation amount, which are fluctuation amounts from the base straight line, are obtained, and the invalidity for the active power is obtained only when the fluctuation amounts are the maximum or minimum within the predetermined time range and the timing matches. For the system parameter for determining the power ratio, the deviation Δα from the optimum system parameter is calculated based on the active power fluctuation amount and the interconnection point voltage fluctuation amount, and is changed to the system parameter corrected using the deviation amount. And a control method for a distributed power system, wherein an active power command value and a reactive power command value are obtained from the system parameters.   6. The control method for a distributed power supply system according to claim 5, wherein the correction of the system parameter is repeatedly performed until it falls within a predetermined range.

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