JPS6142520B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide an excitation control device for a brushless synchronous generator that prevents burnout of the field winding when the rotational speed decreases.

Hereinafter, the structure and operation of the present invention will be explained in detail with reference to illustrated embodiments.

FIG. 1 shows the rotation speed-field current characteristic when the output voltage is constant. As is clear from this figure, when the synchronous generator is controlled at constant voltage by an automatic voltage regulator, as the rotational speed decreases, the field current increases.
Therefore, if the device is operated for a long time in this state, the field winding will burn out. And this risk is greater with brushless than with brush. This characteristic can be expressed as a general formula as follows.

If=KV ₀ /N ² ...(1) Here, If is the field current, V ₀ is the generator output voltage,
N is the number of rotations, and K is a constant. From this equation, in order to keep If constant, it is necessary to keep V ₀ /N ² constant.

Therefore, it can be expressed as follows.

V ₀ = K N ² ...(2) This is illustrated in Figure 2. This second
As is clear from the figure, even if the rotational speed N decreases,
In order to keep the field current If constant, the generator output voltage
It is necessary to reduce V ₀ with a square curve. However, on the other hand, under normal operating conditions of the generator, the generator output voltage needs to be maintained at a constant voltage even if the rotational speed fluctuates around the rated rotational speed. FIG. 3 is a rotation speed-output voltage characteristic diagram that satisfies both of these conditions. In other words, the rated voltage is higher than the rotation speed N ₁ , which is smaller than the rated rotation speed Nr by a certain value.
Operating at Vor, output voltage V ₀ in parts smaller than N ₁
is reduced according to the square curve of the rotational speed.
However, controlling using the V ₀ ∝N ² characteristic makes the circuit complicated. Also, when driving a generator with an engine,
In general, the rotation speed fluctuation rate is about ±5% in steady state and ±10% instantaneously, so N ₁ in Fig. 3 is the rated rotation speed Nr.
If the field current is set to about 90% of N ₁ or less, the field current If
As long as the output voltage V ₀ is reduced so as not to increase, there is no practical problem even if the output voltage V 0 is not necessarily reduced according to the squared curve.In fact, if it is reduced according to the straight line b shown by the dotted line, the heating of the field winding will be reduced. , the circuit becomes simpler. At this time, the field current If decreases as shown by curve c. FIG. 4 is an example of a connection diagram of an excitation control device that performs excitation control using the characteristics of the b straight line and c curve in FIG. 3. In the figure, G is the armature of the synchronous generator,
ACEX is AC exciter, F ₁ and F ₂ are field windings, V ₀ is generator output voltage, Tr is transformer, PT is potential transformer, SCR is thyristor, SD is thyristor driver, OP is operation Amplifier, ZD is a Chener diode, D ₁ to _{D 3} are diodes, PG is a function generator that generates an output V proportional to the rotation speed N, R ₁ to _{R 5}
is a resistor and VR is a variable resistor. Also, the O terminal is a common line among the generator output lines and is an O volt line.
A feedback voltage Vg of the generator voltage is fed back between terminals B and O. With such a configuration, when the rotation speed in Fig. 3 is N ₁ or more, the output voltage V of the function generator PG
Since it becomes higher than the voltage V _ZD of the Zener diode ZD, it is cut by the diode _D1 , and the state is exactly the same as being cut off at this point. Therefore, with the voltage V _ZD of the Zener diode ZD as the reference voltage, Vg = -V _ZD , that is,
The power generation return output voltage is controlled to be a constant voltage Vor. Next, when the rotational speed falls below _N1 , the output voltage V of the function generator PG becomes lower than the Zener voltage V _ZD . For this reason, from the Zener diode ZD side
Current flows to PG due to the differential voltage (V _ZD -V).

As a result, the reference point moves from point J to point H, and control is performed using the voltage V of the function generator PG as the reference voltage. The reason is that the H point and the operational amplifier OP
In addition to the Zener diode ZD and the resistor R ₂ , the voltage drop of the resistor R ₄ (V _ZD - V) is inserted between the inverting input terminal _of the
This is because the voltage between H and B is controlled to be V. On the other hand, the voltage applied between H and B is Vg+(V _ZD -V). Therefore, since Vg+(V _ZD -V)=V, the feedback voltage Vg becomes Vg=2V-V _ZD , and changes linearly b as shown in FIG. As a result, the field current If changes according to the curve-like characteristics shown in Figure 3c, so the rotational speed of the generator changes to N ₁
Even if the field current decreases further, it will never become larger than the field current value at _N1 . In the case of the self-excited type shown by the dotted line in Figure 5, the voltage drops and the automatic voltage regulator becomes inoperable, so in reality, the output voltage Vo = O and the field current If = This shows that it becomes O.

As can be easily understood from the above explanation, the present invention can (1) prevent an increase in field current when the rotational speed decreases; (2) Since the function generator is disconnected by a diode near the rated rotation speed, it is possible to prevent constant voltage control accuracy from decreasing due to the influence of the function generator. (3) The circuit configuration is simple, inexpensive, and compact, and provides excellent effects such as improved reliability.

[Brief explanation of the drawing]

Figure 1 is a rotation speed vs. field current characteristic diagram when the generator output voltage is constant, Figure 2 is a rotation speed vs. generator output voltage characteristic diagram when the field current is constant, and Figure 3 is around the rated rotation speed. Figure 4 is an example of a connection diagram of the excitation control device according to the present invention. , FIG. 5 is an example diagram of the rotation speed-generator voltage and field current characteristics by the excitation control device of the present invention. V ₀ ... Generator output voltage, Nr... Rated rotation speed,
ZD...Cheener diode, PG...Function generator.

Claims (1)

[Claims] 1. In a brushless synchronous power generator that excites by feeding back the generator output voltage and performs automatic voltage adjustment, the first input terminal B is connected to the inverting input terminal of the operational amplifier OP, _R5 via the input resistor _R1 ; The above operational amplifier OP,
A first connection point H via a first input resistor R ₃ to the non-inverting input terminal of R ₅ ; a second input terminal J via a second input resistor R ₄ to the first connection point H; A second connection point A is further provided at the inverting input terminal of the operational amplifier OP, _R5 via another resistor _R2 , and the second input terminal J and the second connection point A are connected to each other. In between, a Zener diode ZD is connected so that the second input terminal J side becomes the anode side, and a diode _D1 is connected in the forward direction from the first connection point H,
A function generator PG that generates an output voltage proportional to the rotation speed of the generator is connected to the second connection point A so that the first connection point H is on the positive side, and further connected to the first input terminal. A feedback voltage Vg of the generator output voltage is input between B and the second input terminal J, and a field current command signal of the generator is output from the output terminal of the operational amplifier OP, _R5 . An excitation control device for a brushless synchronous generator, characterized in that an increase in field current during low rotation is prevented in this way.