JP2002335697A - Voltage control method for induction generator using variable reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage control method which can extend an upper limit of an operation speed range of a self-excitation induction generator to a value three times that of a conventional technology. SOLUTION: This voltage control method for a self-excitation induction generator changes an inductance by a variable reactor to change a value of an equivalent capacitive current so as to correspond to a revolution of the self-excitation induction generator and a load variation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a voltage control method for a self-excited induction generator used for wind power generation, for example.

[0002]

2. Description of the Related Art Conventionally, electric power is generated by burning fossil fuels such as heavy oil and coal to convert heat energy into electric energy, converting heat energy due to fission into electric energy, or converting hydraulic power into electric energy. Powered by a way to convert. In particular, a large proportion depends on the thermal energy from the combustion of the fossil fuel. In the case of using a power supply system from thermal energy generated by burning fossil fuel, there is a problem of global environmental problems due to the gradual increase of CO ₂ and also a problem of finite fossil fuel supply capacity.

[0003] Therefore, there is a strong demand for the development of a technology for using clean energy such as sunlight, solar heat, wind power, tidal power and the like. In particular, technologies for converting inexhaustible wind power into electric energy are promising, and installation of wind power plants is being promoted on a worldwide scale. An induction generator is suitable for converting wind energy into electrical energy. The induction machine has a simple structure, is durable and inexpensive.

[0004]

However, induction generators have a problem of self-excitation at low speed rotation and a problem of overexcitation at high speed rotation. Although there is a method of solving this problem by switching the capacitor bank, it is extremely difficult to continuously change the capacitor capacity according to the rotation speed of the induction generator. Conventionally, induction generators are not self-excited in the low speed range. Conversely, there is a problem that over-excitation occurs in the high-speed rotation range, and the stator winding is overheated by the capacitor current. Thus, the operable speed range of the induction generator was narrow.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a voltage control method capable of solving the above-mentioned problems in the prior art and increasing the upper limit of the operable speed range of the self-excited induction generator to three times or more that of the prior art. .

[0006]

According to a first aspect of the present invention, there is provided a voltage control method for a self-excited induction generator, the method comprising: Is a method for controlling the voltage of an induction generator using a variable reactor, wherein the magnitude is changed according to the rotation speed and load change of the self-excited induction generator.

According to a second aspect of the present invention, there is provided a voltage control method for an induction generator using a variable reactor according to the first aspect, wherein a variable flux type variable reactor is used as the variable reactor.

According to a third aspect of the present invention, as the variable reactor, the magnetic flux density of a part of the toroidal magnetic core is controlled by using another magnetic core, and the inductance of the reactor winding is continuously changed. A voltage control method for an induction generator using a variable reactor according to claim 1 or 2, wherein a variable reactor is used.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on preferred embodiments.

The self-excitation range for the rotation speed of the induction generator is determined by the induction machine constant and the capacity of an external capacitor. That is, when the rotational speed is low, the self-excitation is not performed. vice versa,
If the number of rotations is too high, over-excitation occurs, which causes overheating due to Joule heat of the stator winding due to the capacitor current. Therefore, the upper limit n _{G, max} of the operable speed of the induction generator is limited to a range that does not cause overheating due to Joule heat of the stator winding due to the capacitor current. Although the induction machine has a simple structure, is durable and inexpensive, and is suitable for wind power generation, the problem of the self-excited range must be solved in order to use the induction generator for wind power generation and the like.

The inventors operated a squirrel-cage induction motor having the following constants as a generator. The rotation speed n at this time
The relationship between the self-excitation voltage V _G and the capacitor current I _C for _G shown in FIG. 3-phase 0.75 (kW) 4-pole 200 (V) 60 (Hz) 50 (Hz) I _rate 3.2 (A) 3.5 (A) 1710 (rpm) 1430 (rpm) R ₁ = 3.1 (Ω) L ₁ + L ₂ ′ = 12.8 (mH) M = 195 (mH) R ₂ ′ = 2.33 (Ω)

FIG. 1 shows an induction generator 1800.
Is a measured value of the self-voltage V _G and the capacitor current I _C for the capacitor capacitance C when operated at a constant speed of (rpm). Here, C _O (= 33 μF) is the rated voltage V _O (=
200V). As apparent from FIG. 1, the self-excited voltage V _G is largely dependent on the capacitance of the capacitor. If the capacitor capacity is 0.94 C _O or less, it will not excite itself.

[0013] FIG. 2 shows the relationship between the rotational speed n _G and self-excited voltage V _G of the induction generator, the capacitance C as a parameter. Here, in order to be able to generate electricity even in the low speed range,
The operating range of the induction generator when the capacitor capacity is twice the capacitor capacity C _O that gives the rated voltage V _O (= 200 V) will be examined. From FIG. 2, the rated voltage V _O (=
The rotation speed n _{G, O} giving 200 V) is 1387 rpm. On the other hand, the self-excited operable lower limit speed n _{G, min} is 130
0 rpm, and the operable upper limit speed n _{G, max} is determined by the magnitude of the capacitor current which is equal to the rated current I _rate (= 3.5 A) at 50 Hz of the induction machine.
rpm.

As is apparent from these, the rated voltage V _O
(= 200V), the upper limit n _{△ +} for the rotation speed n _{G, O}
The lower limit n _{△ -} percentage _{of, n △ + = {(n} G, max -n G, O) / n G, O} × 100 = 15.4 (%) n △ - = {(n G, min −n _{G, O} ) / n _{G, O} ｝ × 100 = 6.3 (%). Further, the self-excited voltage V _G is n
There is a large change between _{G, min} and nG _{, max} , between 160 V and 270 V, indicating that voltage control is necessary to apply the induction generator to wind power generation.

[0015] To control the self-excitation voltage V _G in the induction motor, equivalent leading current I _lead, the size of _eq, may be changed in response to changes in rotational speed. Conventionally, in order to change the magnitude of the equivalent advance current I _{lead, eq} corresponding to the rotation speed of the induction machine, it has been performed to control the firing angle of the reactor to inject the lag component. . However, it has been difficult to change the inductance over a wide range with low distortion by this method.

[0016]

[Embodiment] FIG. 3 shows a basic configuration of the invention developed by the flux-controlled variable reactor L _var. This variable reactor is a system that changes the equivalent magnetic permeability of a magnetic core. In this variable reactor, a part of the magnetic path is saturated. Therefore, applying a control magnetic field from the outside on a part of the magnetic core M _M. FIG. 4 shows how the inductance changes with respect to the control current in the variable reactor used in the present invention. The inductance changes 30 times or more by the control current I _con .

FIG. 5 shows a control circuit for implementing the voltage control method for an induction motor using a variable reactor according to the present invention. In FIG. 5, V _{G, r:} own target value K _V of excitation voltage V _G: Gain epsilon _V in the detection circuit of the self-excitation voltage V _G: target value V _G of the self-excited _{voltage, r} and the detected self-voltage V
Deviation between _{G G V} (s): the target value I _con of the control current from the deviation epsilon _V, voltage error amplifier circuit for outputting a _r epsilon _I: target value I _con of the control _current, and _r, the control of the control magnetic field M _C deviation between the current _{I con} G I (s): deviation ε current error amplifier circuit for outputting a control current I _con from _I K _a: a gain in the current amplifier. As shown in FIG. 5, an induction generator I.V. G. FIG. Detecting the output voltage by the voltage detection circuit, the target value V _G of the detection value and the self-excited _voltage, and outputs a deviation epsilon _V with _r, the voltage error amplifier circuit, the target value I of the control current from the deviation epsilon _V Output _{con, r} . The target value I of this control current
_con, and comparing the control current I _con of _r and the control field at that time and outputs the deviation epsilon _I, to control the I _con control current is amplified by a current error amplifier G _I (s) and current amplifier K _A To change the inductance of the variable reactor, thereby changing the induction generator I.I. G. FIG. Output voltage of the target value V
Match with _{G, r} . Here, when configuring the PI amplifier shown a G _V (s) in FIG. 5 by the following formula, in the steady state, voltage deviation epsilon _V becomes zero, the self-excited voltage V _G corresponds to V _{G, r} / K _V . G _V (s) = K _P {1 + 1 / (sτ _I )} (1) ε _V = V _{G, r} −K _V V _G = 0 (2)

FIG. 6 shows that V _{G, r} / K _V is 180 V, 200 V
V, 220V, induction generator I. G. FIG. Shows the behavior of the self-excitation voltage V _G for the change in the rotational speed n _G. Here, G _V (s) is a PI amplifier (K _P = 0.
75, τ _I = 6.6 × 10 ⁻³ ), so that the voltage deviation in the steady state is as small as 0.25% or less. When the operable range of the induction generator at the time of voltage control is compared with the case where the capacitor capacity is 2C _O , as in the case of non-control shown in FIG. 2, the number of rotations n _G giving the rated voltage V _O (= 200V) _{, O} , the upper limit ratio n _{△ +} is more than tripled. Further, n _G, the lower limit for the _O ratio n _{△ -} is 6
As shown in (1), if a large capacitor is connected, voltage control can be performed even in a low-speed rotation region.

FIG. 7 shows terminal voltage, capacitor current and inductance current waveforms during voltage control. It can be confirmed that the distortion of the i _L waveform is small.

[0020] FIG. 8 shows a no-load state not connected the resistive load R _L, the transient characteristics of the self-excitation voltage V _G at the time of changing the rotation speed of the induction generator. At the time of non-control, 1804 rpm
Self-excitation voltage V _G for rotation speed change from 2000 rpm to
Has changed by 91.5V from 205.3V to 296.8V. On the other hand, at the time of control, a slight transient response of about one second is recognized, but the steady-state deviation is controlled to a constant voltage of 0.25% or less.

The upper limit rotational speed when no control voltage of the induction generator, when the capacitance C = 2C _O, 2
To 1600 rpm. On the other hand, when the control is performed, as shown in FIG. Since wind energy is proportional to the cube of wind speed, by controlling the voltage, (2000/1600) ³ = 1.95
Double power can be collected. Also, considering that the obtained electric power is transmitted to a power system, for example, the terminal voltage changes from 160 V to about 270 V during non-control, but becomes a voltage that matches the target value during control.
Power transmission to the power system becomes easier.

[0022]

According to the present invention, voltage control in an induction generator, which has been difficult in the past, can be facilitated, and the operable rotational speed range of the induction generator can be expanded to three times or more of that of the prior art. Application of the machine to wind power can be put to practical use.

According to the second aspect of the present invention, the current distortion is extremely small, and the inductance can be varied over a wide range of 30 times or more.

According to the third aspect of the present invention, the current distortion is extremely small, the inductance can be varied over a wide range of 30 times or more, and the variable reactor can have an extremely compact and simple structure. It is inexpensive and has excellent operability.

[Brief description of the drawings]

FIG. 1 is a graph showing a generated voltage with respect to an external capacitor during a constant speed operation.

2 is a graph showing the relationship between the self-excitation voltage V _G and the capacitor current I _C with respect to the rotational speed of the induction generator during uncontrolled

FIG. 3 is a schematic diagram showing a configuration of a variable reactor in the present invention that changes the equivalent magnetic permeability.

FIG. 4 is a graph showing a change in inductance with respect to a control current in a variable reactor.

FIG. 5 is a circuit diagram showing a voltage control circuit of the induction motor of the present invention.

FIG. 6 is a graph showing the self-excitation range with respect to the rotation speed of the induction generator during voltage control according to the present invention.

FIG. 7 is a graph showing operation waveforms during voltage control according to the present invention.

FIG. 8 is a graph showing transient characteristics of the induction generator with and without voltage control.

Claims (3)

[Claims] 1. A voltage control method for a self-excited induction generator, comprising: changing an inductance by a variable reactor to change a magnitude of an equivalent advance current according to a rotation speed and a load change of the self-excited induction generator. A voltage control method for an induction generator using a variable reactor. 2. The voltage control method for an induction generator using a variable reactor according to claim 1, wherein a magnetic flux control type variable reactor is used as the variable reactor. 3. A variable reactor, wherein the magnetic flux density of a part of the toroidal magnetic core is controlled by using another magnetic core,
3. The voltage control method for an induction generator using a variable reactor according to claim 1, wherein a variable reactor configured to continuously change the inductance of the reactor winding is used.