JP3108054B2 - Inverter control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter control method and, more particularly, to a hybrid power supply system in which a distributed power supply such as a wind power generation system or a solar power generation system and a diesel generator constituting a commercial power supply are interconnected. The present invention relates to a method for controlling an inverter to be used.

[0002]

2. Description of the Related Art Generally, the quality of electric power is defined by frequency and voltage. For example, the frequency of a power system is kept constant under the balance between the capacity of a load belonging to the system and the output of a generator. ing. If the amount of power generation exceeds the load, the frequency increases, and if the amount of power generation falls below the load, the frequency decreases. That is, the frequency is kept constant by controlling the output of the generator with respect to the load amount that changes every moment. The output of distributed power sources that utilize natural energy, such as wind power and solar power, is affected by weather conditions and changes in output are steep, but the capacity of commercial power is significantly larger than its installed capacity Therefore, conventionally, frequency fluctuation has not been a problem.

However, in a hybrid power supply system in which a wind power generation system having a large output fluctuation is connected as a distributed power supply to a small-capacity diesel generator installed as a commercial power supply on an isolated island or the like, the output fluctuation of the wind power generation system is sharp. In this case, the output control of the diesel generator cannot be sufficiently followed, so that the power generation amount and the power consumption of the load cannot be balanced, and frequency fluctuation occurs. Therefore, a measure for stabilizing the frequency in a commercial system is desired.

[0004] As an example of such frequency fluctuation countermeasures,
As shown in FIG. 8, in a system system in which an arc furnace variable load 8 is connected to a diesel generator 1 constituting a commercial power supply, a flywheel is connected to a variable-speed synchronous generator 9 in order to improve frequency fluctuations caused by the arc furnace variable load 8. There is a means provided with the wheel 10. As a countermeasure against the frequency fluctuation, the apparent inertia constant of the variable speed synchronous generator 9 is increased by attaching the flywheel 10, and the frequency fluctuation is suppressed by utilizing the mechanical energy stored therein.

[0005] On the other hand, when the wind power generation system is located at the end of a commercial power system and a general customer is in proximity, a voltage fluctuation due to line impedance occurs due to an output fluctuation of the wind power generation system. In the case where the voltage fluctuation occurs as described above, conventionally, as shown in FIG. 9, the reactive power fluctuation ΔQ of the wind power generation system 2 is detected by the detection circuit 3 and the reactive power of the inverter 5 is compensated for the reactive power fluctuation. The command value is created by the command value creation circuit 4, and voltage fluctuation is suppressed by controlling the inverter 5 (for example, self-excited SVC).

[0006]

In the meantime, as shown in FIG. 8, in the case of countermeasures against frequency fluctuation by the arc furnace fluctuation load 8, the frequency fluctuation is suppressed by attaching a flywheel 10 to the variable speed synchronous generator 9. However, the flywheel 10 is large, large in noise, large in loss, and requires a large maintenance space.

[0007] Therefore, in order to stabilize the frequency of a commercial system, there is a demand for a countermeasure against frequency fluctuation in which a power storage device such as a battery and an inverter are combined. However, when suppressing frequency fluctuations in a hybrid power supply system in which a wind power generation system showing large-capacity output fluctuations is connected to a small-scale system using an inverter and a power storage device, the installed capacity of the inverter and the power storage device should be as small as possible. It is desirable to reduce equipment costs, equipment losses, and maintenance costs, respectively. As described above, the frequency of the system depends on the output adjustment capability of the diesel generator. However, since the output fluctuation of the wind power generation system is steep, if the capacity of the wind power generation system becomes large, it cannot be processed by the output adjustment capability of the diesel generator, and the frequency fluctuation exceeds the normal operation standard.

Accordingly, the present invention has been proposed in view of the above-mentioned problems, and an object of the present invention is to reduce the equipment cost when suppressing frequency fluctuations due to active power and reactive power fluctuations with an inverter and a power storage device. Another object of the present invention is to provide a method of controlling an inverter, which can reduce equipment loss and maintenance cost.

[0009]

SUMMARY OF THE INVENTION As a technical means for achieving the above-mentioned object, the present invention connects a distributed power supply or a variable load having a large fluctuation in active power or reactive power to a commercial power supply having a small capacity. In a hybrid power supply system, a method of controlling an inverter with a power storage device that suppresses frequency fluctuation and voltage fluctuation of the system by sharing with a generator constituting a commercial power supply, and detects active power fluctuation of a distributed power supply or a variable load. Then, the short-period component is extracted from the active power fluctuation by a high-pass filter having a cut-off frequency determined from the cut-off frequency of the governor characteristic of the generator constituting the commercial power supply, and the input is performed based on the short-period component. <br/> By creating an active power command value for the inverter,
Inverter that suppresses wave number fluctuation and is based on the short-period component
Voltage fluctuation with the effective power command value of
Long-period component of active power fluctuation excluding short-period component and invalid
Creates the reactive power command value for the inverter based on the power fluctuation.
The characteristic feature is that the voltage fluctuation of the system is suppressed by implementing the method.

According to the method of the present invention, of the frequency fluctuations due to the active power fluctuations of the distributed power supply or the variable load, the long-period component of the active power fluctuations that can be processed by the output adjustment capability of the commercial power supply is the commercial power supply, and the output of the commercial power supply is Short-period components that cannot be processed by the adjustment capability are shared by the inverter to suppress frequency fluctuations and reduce the capacity of the inverter and the power storage device.

[0011]

In the case where a voltage fluctuation due to line impedance occurs near the installation point of the distributed power supply or the variable load due to the output fluctuation of the distributed power supply or the variable load connected at the end of the commercial power supply, In addition to suppressing the fluctuation, it is necessary to suppress the voltage fluctuation. Therefore,
Akira is a high-pass filter with the cutoff frequency described above.
Extract the short-period component of the active power fluctuation extracted by
The active power command value of the inverter based on this short cycle component
By creating the inverter, the short period of the active power
Component, absorbing the active power generated by the line resistance.
Also contributes to improving voltage fluctuations caused by short-period components
You. In addition, the short period extracted from the active power fluctuation
Components to suppress voltage fluctuations in the
Long-period component of reactive power fluctuation and reactive power
The reactive power command value of the inverter based on the
This suppresses voltage fluctuations in the system.

Incidentally, the cut-off frequency of the high-pass filter described above.
The wave number is based on the governor characteristics of the generator that constitutes the commercial power supply.
To 1/20 to 1/2 of the toe-off frequency.
No. Here, the cutoff frequency of the high-pass filter is
Less than 1/20 of the cut-off frequency of governor characteristics
If this is the case, it is preferable to increase equipment costs and increase the size of equipment.
It is no longer a suitable means, and if it is larger than 1/2,
Providing expected effects beyond operating standards that regulate frequency fluctuations
It becomes difficult to conduct. By the way, the high-pass filter
Is the cutoff frequency of the governor characteristics of the generator.
About 1/10 of the number is preferable.

[0014]

Further, when suppressing the voltage fluctuation of the system, the voltage at the end of the line due to the long-period component of the active power fluctuation is reduced.
SVR that suppresses ascent and short circuit that SVR cannot cope with
Control with inverter that selectively compensates for voltage fluctuations
I will.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail. In the following embodiments, a case where a wind power generation system is used as a distributed power supply will be described. However, the present invention is also applied to other distributed power supplies including a stationary power supply such as a generator, a rotating machine power supply such as a flywheel, and a photovoltaic power generation. It is possible.

First, in general, a diesel generator 1 constituting a commercial power supply receives an input (fuel) of a prime mover such that a rotation speed is kept constant by a governor as described later.
Control is performed (see FIG. 5). As a result, an output of the generator according to the active power required by the load is obtained. Further, the inverter 5 is provided with a power storage device (not shown) having a battery, a battery, or the like so as to be able to absorb surplus power from the system and release insufficient power to the system in order to suppress frequency fluctuation. ing.

FIG. 1 shows how the rotation speed of the diesel generator 1 responds to a change in the active power of the load. The transfer function G (s) of the diesel generator 1 is shown in FIG.
The governor characteristic G determined by the formula (1) indicates that the governor works more effectively as the load fluctuation frequency is lower, and the rotation speed (frequency) fluctuation of the diesel generator 1 can be suppressed to be smaller. Conversely, if the load fluctuation frequency is high, the governor cannot follow the fluctuation, and the effect of suppressing the rotation speed (frequency) fluctuation of the diesel generator 1 is lost.

The inverter 5 used in the present invention has a cut-off frequency f of the governor characteristic G of the diesel generator 1.
g, a high-pass filter having a cut-off frequency fp, for example, about 1/10 of the cut-off frequency fg of the governor characteristic G determined by the transfer function G (s) of the diesel generator 1. 14 (see FIG. 5). The filter characteristic I determined by the transfer function I (s) required by the high-pass filter 14 is
Contrary to the governor characteristic G described above, the higher the load fluctuation frequency is, the more effectively the inverter 5 operates and the rotation speed (frequency) fluctuation of the diesel generator 1 can be suppressed small, and conversely, the load fluctuation frequency decreases. The lower the value, the less the effect of suppressing the fluctuation of the rotational speed (frequency) of the diesel generator 1 becomes.

The suppression of frequency fluctuation due to active power fluctuation is as follows.
It is performed in the following manner. Schematically, a transfer function F (s) = G (s) × obtained by a product of the transfer function G (s) of the diesel generator 1 and the transfer function I (s) of the high-pass filter 14. I (s), that is, the combined frequency F = G × I of the governor characteristic G of the diesel generator 1 and the filter characteristic I of the high-pass filter 14 causes the frequency fluctuation to be shared by both the diesel generator 1 and the inverter 5. And suppress.

That is, as shown in FIG. 1, when the load fluctuation frequency is low, the fluctuation suppression effect by the diesel generator 1 is large, so that the frequency fluctuation due to the active power fluctuation (FIG. 3)
） P-ΔPinv (see FIG. 4)
Is mainly absorbed by the diesel generator 1. on the other hand,
In a situation where the load fluctuation frequency is high, the fluctuation suppression effect of the inverter 5 is large, so that the short-cycle component ΔPinv (see FIG. 3) of the frequency fluctuation due to the active power fluctuation is mainly absorbed by the inverter 5.

The cut-off frequency fp of the high-pass filter 14 required for setting the filter characteristic I is as follows:
In the case described above, the cutoff frequency fg of the governor characteristic G is 1
Although it is set to about / 10, this value can be changed according to various conditions such as the capacity of the diesel generator 1 and the wind power generation system 2.

However, the cutoff frequency fp of the high-pass filter 14 is 1/20 to 1/2 of the cutoff frequency fg of the governor characteristic G of the diesel generator 1 constituting the commercial power supply.
It is desirable that Here, if the cut-off frequency fp of the high-pass filter 14 is smaller than 1/20 of the cut-off frequency fg of the governor characteristic G of the diesel generator 1, the cost of equipment increases and the equipment becomes larger. If it is larger than 手段, the combined characteristic F ′ = G × I ′ of the governor characteristic G of the diesel generator 1 and the filter characteristic I ′ of the high-pass filter 14 controls the frequency fluctuation. It becomes difficult to exhibit the intended effect beyond the standard L (see FIG. 2).

Specifically, the above-described absorption of the short-period component ΔPinv by the inverter 5 is performed based on the following configuration shown in the control block diagram of FIG. As described above, the diesel generator 1 constituting the commercial power supply controls the fuel system 24 based on the rotation speed detected by the rotation speed detector 22 so that the governor 23 keeps the rotation speed constant. Then, input (fuel) control of the prime mover 25 is performed. As a result, the output of the diesel generator 1 according to the active power required by the load is obtained.

The active power fluctuation ΔP of the wind power generation system 2 is detected by the current transformer 11 and the transformer 12 by the detection circuit 13, and the cutoff frequency of the governor characteristic G of the diesel generator 1 is reduced to about 1/10 of the cutoff frequency fg. The short-period component ΔPinv is extracted from the active power fluctuation ΔP by the high-pass filter 14 (HPF) having the off frequency fp. Note that this high-pass filter 14 is calculated by (S · Tinv) / (1 + S · Tin
v) [1 / Tinv: cut-off frequency of the inverter]. The short-period component ΔP of this active power fluctuation ΔP
Based on the inv, the command power generation circuit 15 of the inverter 5 generates the active power command value Pref to control the active power P of the inverter 5.

On the other hand, when the wind power generation system 2 is located at the end of the commercial power system and a general customer is in proximity, the voltage fluctuation due to the line impedance due to the output fluctuation of the wind power generation system 2 causes the fluctuation. Occurs near the installation point. The voltage fluctuation ΔV accompanying the output fluctuation of the wind power generation system 2 is represented by ΔP for the active power fluctuation, ΔQ for the reactive power fluctuation, and R + for the line impedance of the wind power generation system 2.
Assuming that jX [R: resistance of the commercial system, X: reactance of the commercial system], it can be approximated by ΔV = R × ΔP + X × ΔQ.

Therefore, this voltage fluctuation ΔV is
Since it is necessary to satisfy ΔV = X × Qinv in order to compensate with the reactive power of (1), the reactive power compensation amount Qinv of the inverter 5 is Qinv = (R / X) × ΔP + ΔQ. In general, the countermeasures against voltage fluctuations are performed only with the reactive power fluctuation ΔQ of the system because the resistivity (R / X) of the line is small (see FIG. 9).

In order to suppress the frequency fluctuation by the inverter 5, the short-period component ΔPinv which is a part of the active power fluctuation ΔP
In this case, the voltage fluctuation due to the long-period component (ΔP−ΔPinv) of the active power fluctuation ΔP remains. In particular, in the wind power generation system 2 which is often installed at the end of the system, the voltage fluctuation due to the resistance of the line is remarkable, so that the long-period component (ΔP−ΔPinv) of the active power fluctuation ΔP.
) Increases the voltage at the end of the line. To suppress this, SVR (Series Voltage Regulator) controls the terminal voltage to fall within the specified voltage range. If that cannot be met, however, avoid voltage rise at the terminal by changing the system configuration. ing. The high-pass filter 20 using the response time of the SVR as a time constant is represented by (S · Tsvr) /
It has the characteristic of (1 + S · Tsvr) [1 / Tsvr: SV
Cutoff frequency of R control system].

The inverter 5 responds to such a voltage rise (long-period component (ΔP−ΔPinv) of the active power fluctuation ΔP).
It is not advisable to cope with the active power compensation of the above. If the voltage fluctuation due to the active power fluctuation ΔP is dealt with by the reactive power of the inverter 5, the reactive power compensation of the resistivity (R / X) of the active power fluctuation ΔP can be completed. As a result, the capacity of the inverter 5 can be reduced.

In the method of the present invention, as described above, the active power fluctuation ΔP of the wind power generation system 2 is detected, and the cutoff frequency fg of the governor characteristic G of the diesel generator 1 constituting the commercial power supply is determined. The short-period component ΔPinv extracted from the active power fluctuation ΔP by the high-pass filter 14 having the frequency fp is given as the active power command value Pref of the inverter 5 for suppressing the frequency fluctuation. As a result, since the inverter 5 absorbs the short-period component ΔPinv of the active power fluctuation ΔP, it also contributes to the improvement of the voltage fluctuation caused by the short-period component ΔPinv of the active power fluctuation ΔP generated by the resistance (R / X) of the line. .

Therefore, the voltage fluctuation is suppressed by the short-period component ΔPinv extracted from the active power fluctuation ΔP of the wind power generation system 2, and the long-period component (ΔP−ΔPinv) of the active power fluctuation ΔP excluding the short-period component ΔP. The line impedance (Z = R + j) viewed from the wind power generation system 2
X) to the reactive power conversion value multiplied by (R / X)
The reactive power component detected from the wind power generation system 2 is added,
A reactive power command value Qref for the inverter 5 is created.

That is, the active power fluctuation ΔP of the wind power generation system 2 is detected by the current transformer 11 and the transformer 12 by the detection circuit 13, and the short-period component ΔP is obtained from the active power fluctuation ΔP.
Pinv is subtracted by the subtractor 16 to obtain a long-period component (ΔP
-ΔPinv). The long-period component (ΔP−ΔPinv) of the active power variation ΔP is multiplied by the resistivity (R / X) by the arithmetic circuit 19, and the reactive power variation ΔQ of the wind power generation system 2 detected by the detection circuit 18 is calculated as described above. The adder 17 adds the reactive power conversion value output from the arithmetic circuit 19 to the reactive power command value Qref of the inverter 5 by the command value creation circuit 21 to control the reactive power Q of the inverter 5.

FIG. 7 is a modification of FIG. 5, and in the embodiment of FIG. 5, the long period component (ΔP−ΔP
Inv) is calculated by an internal calculation, whereas the embodiment of FIG. 7 uses the current transformer 11 ′ and the transformer 12 to detect the long-period component (ΔP−ΔPinv) of the active power fluctuation ΔP. 'To detect it.

In the above embodiment, the case where the voltage fluctuation is suppressed by controlling both the active power and the reactive power has been described.
In a commercial system having a relatively short system bus 6 and a small line impedance between the power generation system 2 and the wind power generation system 2 serving as a distributed power source, voltage fluctuations do not appear significantly. In some cases, it is sufficient to suppress the fluctuations of.

[0035]

According to the present invention , the short-period component of the active power fluctuation
The active power is controlled based on the
The reactive power is controlled based on the reactive power fluctuation.
Therefore, the commercial power supply shares part of the frequency and voltage fluctuations due to the fluctuations in the active power and the reactive power, and the rest can be shared by the inverter, thereby reducing the load on the inverter. Since the capacity of the inverter can be made smaller than the capacity, and the capacity of the power storage device such as a battery can also be made smaller, the equipment cost, equipment loss and maintenance cost can be reduced, and the equipment can be made more compact. Its practical value is great.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, and is a frequency characteristic diagram showing how the rotation speed of a generator responds to a change in active power of a load.

FIG. 2 is a frequency characteristic diagram when a cutoff frequency of a high-pass filter is set to be larger than 1/2 of a cutoff frequency of a governor characteristic of a generator.

FIG. 3 is a waveform chart showing frequency fluctuation of active power.

FIG. 4 is a waveform diagram showing a state in which the frequency fluctuation of FIG. 3 is divided into a long-period component and a short-period component;

FIG. 5 is a control block diagram of an inverter according to the embodiment of the present invention.

FIG. 6 is a control block diagram of an inverter when an SVR is installed in a system.

FIG. 7 is a control block diagram of an inverter according to another embodiment of the present invention.

FIG. 8 is a configuration diagram showing a system interconnection system in which an arc furnace variable load is connected to a commercial system.

FIG. 9 is a control block diagram showing a conventional example of a countermeasure against voltage fluctuation provided with an inverter for compensating reactive power generated in a commercial system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Commercial power supply (diesel generator) 2 Distributed power supply (wind power generation system) 5 Inverter 8 Fluctuating load 14 High-pass filter G Governor characteristic I Filter characteristic ΔP Active power fluctuation ΔQ Reactive power fluctuation fg Governor characteristic cutoff frequency fp Filter characteristic Cutoff frequency ΔPinv Short-term component ΔP-ΔPinv Long-term component ΔV Voltage fluctuation Pref Active power command value Qref Reactive power command value

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor, Hayato Naruto, 5-2-1 Makiko, Urasoe, Okinawa Prefecture Inside Okinawa Electric Power Co., Inc. (72) Atsushi Irika, 5-2-1 Makiko, Urasoe, Okinawa, Okinawa Inside Electric Power Co., Inc. (72) Inventor Masaya Yoshikawa 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Kyoto Nippon Electric Co., Ltd. (72) Inventor Noriaki Tokuda 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Kyoto Nishi Electric Co., Ltd. Inventor Yoshiya Ogiwara 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Nippon Electric Co., Ltd. (56) References JP-A-2-250638 (JP, A) JP-A-Hei. JP-A-7-298497 (JP, A) JP-A-8-308248 (JP, A) JP-A-6-80389 (JP, U) JP-A-7-25407 (JP, U) Japanese Utility Model Application Hei 7-41608 (JP, U) Japanese Utility Model Application Hei 6-86109 (JP, U) Patent 2557682 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02J 3/12 -3/18 G05F 1/66-1/70 H01M 7/48

Claims (3)

(57) [Claims] In a hybrid power supply system in which a variable power supply or a variable load having large fluctuations in active power or reactive power is connected to a commercial power supply having a small capacity, the frequency fluctuation of the system by sharing with a generator constituting the commercial power supply. And a method for controlling an inverter with a power storage device that suppresses voltage fluctuations , wherein active power fluctuations of a distributed power supply or a variable load are detected, and the active power fluctuations are determined from a cutoff frequency of a governor characteristic of a generator constituting a commercial power supply. extracts the short-period component from the active power variation by a high pass filter having a cut-off frequency, this
By creating an active power command value for the inverter based on the short-period component, frequency fluctuation of the system is suppressed,
Voltage by the inverter's active power command value based on the period component
Fluctuations and the effective power excluding the short-period component.
Based on the long-period component of the power fluctuation and the reactive power fluctuation.
The reactive power command value of the
A method for controlling an inverter, which suppresses fluctuation . 2. The cut-off frequency of the high-pass filter is:
2. The control method for an inverter according to claim 1, wherein the control value corresponds to 1/20 to 1/2 of a cutoff frequency of a governor characteristic of a generator constituting a commercial power supply. 3. The method according to claim 1, further comprising :
The voltage rise at the line end due to the long period component of the active power fluctuation
SVR to suppress and short-period that cannot be dealt with by SVR
Cooperative control with an inverter that selectively compensates for voltage fluctuations
The method for controlling an inverter according to claim 1, wherein
Law.