JPH0736718B2 - Wind power generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a wind turbine that converts wind energy into power, a basket-shaped induction machine that converts this power into electric power, and a converter that regenerates generated power. Regarding a wind power generator using a converter that sends out power to the grid, as a power supply in a non-powered area,
Moreover, it is suitable for use as a power generator for hybrid with a diesel power generator on a remote island or the like for the purpose of energy saving and for peak cut in grid interconnection.

(Prior Art) Conventionally, a synchronous machine, a DC machine, an induction machine, or the like has been used as a means (generator) for converting shaft power of a wind turbine into electric power in a wind turbine generator.

However, in general, the one using a synchronous machine or a DC machine has a pitch of the wind turbine blade in the main operation range from the rated wind speed at which the rated output of the wind turbine is obtained to the power generation stop wind speed at which the wind turbine is stopped and power generation is stopped. The control performs constant rotation speed control to keep the rotation speed constant. For this reason,
As will be described later, the “peripheral speed ratio”, which is determined by the wind speed relative to the wind speed of the wind turbine, was not constant, and it could not be said that energy was effectively acquired. Moreover, as described above, in constant speed control operation, a large torque fluctuation is caused by a sudden change in wind conditions, and in order to withstand this, the structure and material must be robust, which increases costs. It was also the cause.

On the other hand, many of those using an induction machine are operated by being connected to an existing electric power system, and generally wind speed is used as an operation control means. In this case, since the generator and the point where the wind speed is measured are different, it is difficult to perform highly accurate control, and sometimes the induction machine does not operate as a generator but may operate as an electric motor. In addition, the system is driven directly, and the excitation frequency is close to the commercial frequency of 50/60 Hz.Thus, the rotation frequency of the rotor can be controlled relatively easily by the slip frequency control, but the operation is performed under the same conditions as the constant rotation speed control. Therefore, even the one using the induction machine has the same problem as the above-mentioned DC machine and synchronous machine.

In particular, the winding-type induction machine can easily control the slip frequency by the secondary excitation method, but it requires a power supply for secondary excitation separately from the excitation power supply of the stator, which increases the size of the induction machine. There has been a demand for a power generation device which has a complicated problem and which can efficiently extract the energy of the wind turbine with a simple structure and can be efficiently connected to the grid.

(Object of the Invention) The present invention has been made in view of the above problems, and absorbs torque fluctuation due to a sudden change in wind conditions by performing variable speed control in which a wind turbine is operated at a rotational speed according to an input. Then
Cost reduction in structure and material can be suppressed, large energy can be regenerated at low cost, and slip frequency control is performed using wind turbine rotation speed information, making it easy to control at a substantially constant peripheral speed ratio. It is an object of the present invention to provide a wind power generation device that is capable of achieving effective energy acquisition and that can be efficiently connected to the grid.

(Structure of the Invention) A wind turbine generator of the present invention includes a wind turbine that converts wind energy whose blade pitch angle is controllable into motive power, and a squirrel-cage induction that rotatably drives a rotor by the power of this wind turbine to generate electric power. Machine, rotation speed detection means for detecting the rotation speed of the rotor, output detection means for detecting the output of the squirrel cage induction machine, based on the detected output and the detected rotation speed, the rotor In the operating range where the number of revolutions is less than the rated number of revolutions, the ratio of the output voltage of the squirrel cage induction machine to the excitation frequency is kept constant, and in the operating range where the number of revolutions of the rotor exceeds the rated number of revolutions, The excitation frequency of the induction machine is controlled so as to be constant, and the self-excited first converter that regenerates the electric power generated by the cage induction machine, and the operation at the rated speed or less from the start of the wind turbine In the region Pitch angle control means for fixing the pitch angle of the blade to a predetermined value, and controlling the pitch angle of the blade so that the rotation speed of the rotor falls within a predetermined range set in advance in an operating range exceeding the rated rotation speed. And a self-exciting second converter that synchronizes the electric power regenerated by the first converter with the phase of the system and sends it to the system.

With this configuration, variable control operation at the rotational speed (rotational speed) of the wind turbine corresponding to the wind speed is performed below the rated rotational speed at which the rated output is generated, and torque fluctuations due to changes in wind conditions are absorbed as inertia. The output frequency is controlled by controlling the slip frequency of the induction machine according to the rotational speed of the wind turbine, and for the reasons described below, operation control can be easily performed at a substantially constant peripheral speed ratio and effective energy acquisition is possible. Become.

By controlling the rotation speed according to the wind speed,
The reason why constant peripheral speed ratio control is possible and effective energy acquisition can be achieved will be described.

The basic characteristic of the output from a propeller-type wind turbine is expressed by the following equation.

Output P = 1 / 2ρv ³ πR ² Cp (1) ρ: Air density, v: Wind velocity, Cp: Power coefficient, R: Propeller radius, ω: Angular velocity ∴ Power coefficient Cp = 2P / (ρπR ² v ³ ) …… (2) Peripheral speed ratio TSR = ωR / v …… (3) Here, to obtain the maximum efficiency as a wind turbine, the power coefficient
The maximum value of Cp should always be controlled so that the maximum effective acquisition of energy can be achieved.

FIG. 2 is a diagram showing the characteristic of the power coefficient Cp of the wind turbine with respect to the peripheral speed ratio TSR with the pitch angle β of the wind turbine blade as a parameter. As shown in the figure, the power coefficient Cp of the wind turbine is
It is a function of the peripheral speed ratio TSR that has the maximum value at a certain peripheral speed ratio TSR. The maximum values of the peripheral speed ratio TSR and the power coefficient Cp that maximize the power coefficient Cp vary depending on the pitch angle β of the wind turbine blade, but if the pitch angle β of the wind turbine blade is set to a certain value, the power coefficient Cp becomes the maximum. The peripheral speed ratio TSR can be determined.

However, since the peripheral speed ratio TSR is determined by the peripheral speed ratio ω and the wind speed v, as can be seen from the equation (3), when the peripheral speed ratio TSR is kept constant, the rotational speed also changes when the wind speed v changes. There must be.

Therefore, if the pitch angle β of the wind turbine blade is fixed to maximize the energy acquisition in accordance with the wind conditions, the rotation speed control in accordance with the wind speed, that is, the constant peripheral speed ratio control should be performed.

Now, assuming that the peripheral speed ratio TSR at which the power coefficient Cp is maximum is Ω, the output P of the wind turbine is expressed as a function of the rotational speed N as follows.

Ω = ωR / v (4) v = ωR / Ω (4 ') ω = 2π N / 60 (5) where N: Wind turbine speed (rpm) (5), (4') v = πNR / (30Ω) (6) From equations (1) and (6), P = (ρπR ² Cpmax) ・ (πRN / 30
^{Ω) 3 /2=1.8×10 -3 · (ρR} 5 N 3 Cpmax) / Ω 3 ......
(7) From this equation (7), it is understood that the output P of the wind turbine is proportional to the cube of the rotation speed N, and the constant peripheral speed ratio control may be performed using the rotation speed N as information.

Power factor Cp, output P, and rotational speed N of torque T of these wind turbines
Fig. 3 shows the characteristics for the. In the figure, the horizontal axis represents the rotation speed N, and the vertical axis represents the power coefficient at each wind speed V _{1 to} V ₇ .
Cp (solid line) shows the characteristic curve of the output P (dashed line), torque T (dashed line), the line P _L denotes a rated load. As can be seen from the figure, the output P shows the maximum value at the rotational speed N at which the maximum value (Cpmax) of the power coefficient Cp at each wind speed V _{1 to} V ₇ is obtained. Therefore, by maintaining Cpmax, the output P
Has the characteristic of curve (a), and the torque T at that time has the characteristic of curve (b). That is, by keeping the power coefficient Cp at the maximum value, the level of the output P is uniquely determined by the rotation speed N of the wind turbine. Therefore, if the slip frequency of the induction machine is controlled so that the predetermined output P determined according to the rotation speed N is obtained, energy can be effectively acquired.

In FIG. 3, N _VC is the cut-in speed corresponding to the cut-in wind speed (v _C ) at which power generation is started, and N _VL is the rated speed corresponding to the rated wind speed v _{L at} which the rated output of the wind turbine is produced. .

(Embodiment) FIG. 1 shows the construction of an embodiment of the device of the present invention. In the figure, the wind turbine 1 has a propeller-type rotor having a mechanical pitch control unit of blades and a function of transmitting the power of the rotor to a three-phase cage induction machine 2. This induction machine 2
Is connected to the first converter 3 which controls the excitation for causing it to function as an induction generator and regenerates the generated power. As the first converter 3, a three-phase converter using an active element such as a transistor as a switching element is used, and a capacitor is connected between the output lines (single phase) of the three-phase converter and regenerated by the first converter 3. The 2nd converter 4 which sends out electric power to a grid is connected. As the second converter 4, the same three-phase inverter as described above is used, and its output line (three phases) is connected to the commercial power source.
A thyristor may be used as the element of the converters 3 and 4.

Further, the rotation speed of the wind turbine 1 is detected by the rotation speed detector 5, and the detected rotation speed is converted into a voltage by the frequency-voltage (F / V) converter 6 to convert the preset rotation speed and power. Is input to the function converter 7 for performing. On the other hand, the current and voltage are detected by the current detector 8 and the voltage detector 9 by the output line of the first converter 3,
The multiplier 10 detects the generator output that the induction machine 2 acts as a generator. Then, the conversion output signal P _REF of the function converter 7 and the output (generator output) of the multiplier 10 via the amplifier 11 are compared by the first comparator 12, and the output of this comparator 12 is The second comparator 14 drives the F / V converter 6 through the compensation circuit 13 for matching the system characteristics.
It is compared with the output of the above and input to the excitation frequency command circuit 15. In the excitation frequency command circuit 15, in the following rotational speed N _VL which generates the rated output, the ratio of the generator voltage / excitation frequency is constant, the higher the rotational speed N _VL which generates the rated output, the generator voltage is constant So that a command for exciting the induction machine 2 is output by the first converter 3 and this command is sent via the gate drive circuit 16 to the first command.
It is adapted to be applied to the gate of the active element of the converter 3.

Then, as described above, the first converter 3 is driven based on the result of comparison between the value obtained by converting the rotational speed of the wind turbine to the output by the function converter 7 and the output of the generator. The slip frequency of the induction machine 2 is controlled so that the machine 2 can effectively output electric power corresponding to the input of the wind turbine. Function converter 7, current detector 8, voltage detector 9, comparison circuit
12, 14, the excitation frequency command circuit 15, the gate drive circuit 16 and the like constitute the drive means 17 for operating the first converter 3 as described above.

The output line of the second converter 4 is connected to the system 20 (commercial power supply), and the phase detection transformer 18 and the current detection means 19 are connected to this line, and the detected phase and the output of the first converter 3 are connected. The output of the amplifier 11 is the current command circuit
The output of the current command circuit 21 and the current detection value passed through the current detection amplification circuit 22 are input to the comparator 21, and are compared by the comparator 23. The comparison result is the compensation circuit 24 for matching the system characteristics.
Is input to the gate drive circuit 25 via. The output of the gate drive circuit 25 drives the active element of the second converter 4. These phase detection transformers 18,
The current detecting means 19, the current command circuit 21, the gate drive circuit 25 and the like constitute the driving means 26 of the second converter 4, whereby the second converter 4 is synchronized with the system 20 and the first converter. Three
Output, that is, the phase control is performed according to the electric power energy generated corresponding to the wind turbine input, and the function of sending electric power to the grid 20 is achieved.

Next, a control chart of the above wind turbine generator will be described with reference to FIG. In the figure, the wind velocity v on the horizontal axis, the output on the vertical axis P, represents the rotation speed N, V _S is started wind speed the wind turbine begins to rotate, V _C is the cut-in wind speed for starting the power generation, V _L is the wind turbine Rated wind speed at which rated output is obtained, V _CO is a cut-out wind speed at which wind turbine operation is stopped and feathering is performed to release wind energy, P _L is a rated output as a wind power generator, N _VC
Is the cut-in speed, N _VL is the rated speed, the blade pitch angle is constant in the operation range up to this speed, and the wind turbine speed falls within the predetermined speed range in the operation range above this speed. To control the pitch angle of the blade.
N _N unloaded set rotational speed of the wind turbine, a control engine speed range N _N ± 10% is to be controlled by the pitch control, the curve P _R A Loss Power, v _S to v _C between the mechanical loss of the generator a gear transmission loss (square curve), v _C during joined the excitation loss of the generator, v _C to v _L between the excitation loss and mechanical loss, v
_{L to} v _CO is the generator excitation loss and the mechanical loss (almost constant).

The operation status in FIG. 4 is as follows.

Standby: During wind speed 0 to v _S , power is not generated and the converter 3 is not operated.

Start: between wind velocity v _S to v _C can be used as energy to the energy of the wind rotates the windmill.

Cut-in: A state in which power generation can be started as a wind turbine generator is applied to the induction machine 2.

Load control area: During the wind speeds v _{C to} v _L , the maximum output control described in FIG. 3 is performed. That is, the generated electric power is controlled so that the rotation speed matches the situation of each wind speed. As a result, the output P exhibits an output characteristic proportional to the cube of the wind speed (rotation speed), and maximum output control is performed at each rotation speed.

The rotation speed N rises from v _S , rises in balance with the inertia moment of the wind turbine, and after v _C, the operation is performed in proportion to the wind speed. The process in which the rotation speed increases and the process in which the wind weakens and the rotation speed decreases show a hysteresis characteristic as indicated by the arrow.

Fixed load region: The output P is kept constant during the wind speed v _{L to} v _CO , the energy of the input wind is released by mechanical pitch control, and the rotational speed N is controlled within the range of N _N ± 10%.

Standby: In wind conditions above wind speed v _CO , the wind energy will exceed the equipment capacity, so the mechanical governor will use the blade pitch angle as a feather to keep the wind turbine within the set rotational speed range, allowing energy to escape and the wind turbine to be safe. Maintain good condition.

Next, the excitation of the induction machine 2 by the first converter 3 in FIG. 1 described above, that is, the operation of the induction generator will be described with reference to FIG. FIG. 5 shows the characteristics of the induction machine, where the motor region is positive, the power generation region is negative, the horizontal axis shows the excitation frequency f, and the solid curves show the output characteristics at the respective excitation frequencies f,
Each chain line curve shows torque characteristics. The operating range a of the generator is the cut-in speed N _VC to N _{N of the} wind turbine.
In order to use an induction machine of + φN and 3φ (phase) 4P (pole), the rated rotational speed N _VL of the wind turbine is 60 Hz, the electrical frequency of the induction machine.
The speed increasing ratio of the speed increaser is determined so that

In controlling the induction machine, in FIG. 5, the output voltage V / of the induction machine is changed from the cut-in speed N _VC to the rated speed N _VL.
Excitation frequency f = constant operation, rated speed N
Above _VL , operation is performed with the output voltage V = constant. That is, between the cut-in speed N _VC and the rated speed N _VL , in the load control range b for performing the output control corresponding to the input, the output and the torque are the same as those indicated by the curves (C) and (D). It is controlled so that it increases with the increase in rated speed N
_{Between VL} and the pitch control range N _N ± _ΔN of the wind turbine, in the load fixed region c where constant output control is performed, the output is constant as shown by the curve (c) and the torque is shown by the curve (d). It is controlled so as to be inversely proportional to the rotation speed.

For such control, the excitation frequency f on the side of the induction machine (generator) according to the rotational speed of the wind turbine is set to the synchronous frequency (slip is zero), and the output and torque characteristics shown in FIG. 5 are obtained.
The "slip frequency control" (the output increases as the slip increases in the negative direction) may be performed so that the slip frequency is added.

In the above embodiment, by controlling the induction machine 2 with the first converter 3 in this way, the wind turbine is consequently operated close to the constant peripheral speed ratio, enabling effective acquisition of energy and at the same time. 1 The power regenerated by the converter 3 can be directly sent to the system by performing phase control in synchronization with the system by the second converter 4 according to this power,
This enables efficient grid interconnection, improves reliability, and contributes to an improvement in the operating load factor by cutting the power peak of the grid. Further, since the generator voltage is controlled as described above according to the rotational speed of the wind turbine, the magnetic saturation of the induction machine is small, and the output performance and the reliability of the device can be improved.

In the above description, an example in which the output power of the first converter 3 is controlled by the power conversion command proportional to the cube of the rotation speed N of the wind turbine to obtain the maximum effective energy is shown. The present invention is not necessarily limited to this, and it is possible to perform constant rotation speed control as in the prior art even if control is performed by a predetermined power conversion command such as a command proportional to the rotational speed N of the wind turbine or proportional to its square. In comparison, effective energy can be acquired.

(Effects of the Invention) As described above, according to the present invention, in the operation range in which the rotation speed of the rotor rotated by the power of the wind turbine is equal to or lower than the rated rotation speed,
The pitch angle of the blade is fixed to a predetermined angle, and the first
The converter controls the excitation frequency according to the number of rotations of the rotor to keep the ratio of the output voltage of the squirrel cage induction machine to the excitation frequency constant and at the same time control the slip frequency of the squirrel cage induction machine. In the operating range where the rotation speed exceeds the rated rotation speed, the pitch angle of the blades is controlled so that the rotation speed of the rotor falls within a preset predetermined range, and the output of the cage induction machine is controlled by the first converter. Since the slip frequency control is performed while the voltage is kept constant, the wind turbine can be operated in a state close to the constant peripheral speed ratio control, and a large amount of energy can be efficiently generated. In addition, since the output of the squirrel cage induction machine is controlled by controlling the excitation frequency according to the rotation speed of the rotor, that is, the rotation speed of the wind turbine, when the torque changes abruptly due to a sudden change in wind conditions. In addition, it is possible to absorb torque fluctuations and prevent a structural increase in cost.

Further, the electric power generated by the squirrel cage induction machine is sent to the system in synchronization with the phase of the system by the second converter, so that the power generator and the system can be effectively interconnected. For example, energy as a power source for peak cut can be effectively acquired.

Furthermore, since the first and second converters are configured by self-excitation, there is no need to supply an exciting current (reactive power) from the system to the squirrel cage induction machine, the power factor is improved, and power is supplied to the system. Efficiency is improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a wind turbine generator according to an embodiment of the present invention, FIG. 2 is a characteristic diagram of a power coefficient with respect to a peripheral speed ratio in a wind turbine for explaining the present invention, and FIG. FIG. 4 is a characteristic chart of power coefficient, output, and torque with respect to the number, FIG.
FIG. 5 is a characteristic diagram of the output and torque of the generator with respect to the excitation frequency for explaining the operation of the device. 1 ... Windmill, 2 ... Induction machine, 3 ... First converter, 4 ...
Second converter, 5 ... Rotation speed detector, 7 ... Function converter,
15 ... Excitation frequency command circuit, 17 ... Driving means for the first converter 3, 26 ... Driving means for the second converter 4.

Claims (1)

[Claims] 1. A wind turbine that converts wind energy whose blade pitch angle is controllable into power, a squirrel-cage induction machine that rotatably drives a rotor by the power of the wind turbine to generate electric power, and rotation of the rotor. Rotation speed detection means for detecting the number,
Based on the output detection means for detecting the output of the squirrel-cage induction machine and the detected output and the detected rotation speed, the squirrel-cage induction machine is operated in the operating range in which the rotation speed of the rotor is equal to or lower than the rated rotation speed. The ratio of the output voltage to the excitation frequency is constant, and the induction frequency of the induction machine is controlled so that the output voltage is constant in the operating range where the rotation speed of the rotor exceeds the rated rotation speed. Self-excited first converter that regenerates the electric power generated in the induction machine, and in the operating range below the rated speed from the start of the wind turbine, the blade pitch angle is fixed to a predetermined value, and the rated speed is In an operating range exceeding, the pitch angle control means for controlling the pitch angle of the blade so that the rotation speed of the rotor falls within a predetermined range set in advance, and the electric power regenerated by the first converter is supplied to the system. Synchronized in phase Second self-excited to be sent to the system Te
A wind turbine generator comprising a converter.