JPH0332320B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an AVR protection circuit.

Engine-driven generators need to generate a constant output voltage regardless of the engine speed, so an automatic voltage regulator (hereinafter referred to as AVR) is installed to supply the field winding of the generator. The magnetic current is controlled to stabilize the output voltage.

Figure 1 shows the configuration block of a conventional AVR. In the figure, 1 is a brushless alternating current generator (hereinafter referred to as a generator), 2 is a load, 3 is a DC constant voltage circuit, 4 is a reference voltage generation circuit, 5 is a detection circuit, 6 is a comparison circuit, 7 is a control circuit, and Q ₀ is a control transistor. The generator 1 is composed of a main machine G and an exciter EX, and a field winding L of the exciter EX is supplied with a direct current from the outside.

Thus, the power generated by the generator 1 is supplied to the load 2, and the voltage is detected by the detection circuit 5, which includes a transformer T ₁ , a diode D ₁ , resistors R ₁ , R ₂ , R ₃ , a capacitor C ₁ , etc. , and is converted into a DC voltage corresponding to the output voltage (AC voltage) of the generator 1. Next, the comparison circuit 6 compares the output voltage of the detection circuit 5 with the reference voltage obtained from the reference voltage generation circuit 4, and outputs an error voltage according to the difference with the reference voltage. The control circuit 7 operates to reduce this error voltage to 0, and drives the control transistor Q ₀ as appropriate depending on the polarity and magnitude of the error voltage.
On the other hand, part of the output of the generator 1 is supplied to the DC constant voltage circuit 3.
After being converted into direct current at , the field current is supplied to the field winding L via the collector-emitter of the transistor Q ₀ .

Now, when the output voltage of the generator 1 increases for some reason, the output voltage of the detection circuit 5 increases, and when this exceeds the preset reference voltage of the reference voltage generation circuit 4, the comparison circuit 6 outputs the error voltage. In response to this, the control circuit 7 switches the transistor Q ₀
to reduce the field current by reducing the base current of
Reduce the generated voltage. Conversely, when the output voltage of the generator 1 decreases and the output voltage of the detection circuit 5 falls below the reference voltage of the reference voltage generation circuit 4, the control circuit 7 increases the base current of the transistor _Q0 to generate a field current. increases the generated voltage.
And since these actions occur extremely quickly,
The output voltage of the generator 1 will be kept constant.

Although the conventional AVR shown in FIG. 1 operates as described above and is very useful, it has the following drawbacks. In other words, since the AVR is always operating regardless of the engine speed, when the engine is rotated at low speed during warm-up, etc., the AVR works to keep the output voltage of the generator constant, and the generator If the field current continues to increase, there is a risk that a large current will flow to the field coil, and in the worst case, it may destroy the AVR.
This may cause the generator body to burn out. There are two possible ways to deal with these problems: increasing the capacity of the AVR and generator, and combining the AVR with a saturable current transformer, saturable reactor, etc. to create a differential type. The latter has the disadvantage that the overall shape is large and expensive, and on the other hand, the latter has the disadvantage that the excitation of the generator is differential, requiring two types of excitation windings, resulting in a complicated structure.

The present invention has been proposed in view of the above points, and in addition to the conventional AVR configuration, a means for detecting the engine rotation speed from the output voltage of the generator is provided,
If the rotation speed is below the specified rotation speed, the output voltage of the generator is lowered to reduce the output current of the AVR, preventing damage to the AVR and generator due to the generation of large currents, and also reducing the damage to the AVR and generator itself. Increased capacity, miniaturization, and cost reduction
Aims to provide AVR protection circuit.

That is, the present invention includes a first detection circuit that detects the output voltage of a generator, a first reference voltage generation circuit that generates a reference voltage set corresponding to the rated output voltage, a first detection circuit, and a first detection circuit that generates a reference voltage set corresponding to the rated output voltage. a first comparison circuit that compares the output voltages of the first reference voltage generation circuit, and controls the field current of the generator according to the output of the first comparison circuit to keep the output voltage of the generator constant. In the AVR configured to a second reference voltage generation circuit that generates a reference voltage set corresponding to the lower limit frequency of the machine output; and a second comparison circuit that compares the output voltages of the second detection circuit and the second reference voltage generation circuit. and when the output frequency of the generator falls below the lower limit frequency, the photocoupler is controlled on/off by the output of the second comparison circuit to control the output voltage of the first detection circuit, and the output voltage of the first detection circuit is controlled. The above object is achieved by configuring the output voltage to be lowered or maintained at the rated voltage.

Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

FIG. 2 is a block diagram showing a first embodiment of the present invention, and the same parts as in the conventional example shown in FIG. 1 are given the same reference numerals. The configuration and functions of this generator will be explained below. In FIG. 2, the output end of the generator 1 is connected to a load 2 to supply generated power, and also connects a DC constant voltage circuit 3 and a control transistor Q ₀
own field winding L through the collector emitter of
The field current is supplied to the Furthermore, the output voltage of the generator 1 is connected to the input terminals of a first detection circuit 5' for detecting voltage and a second detection circuit 9 for detecting frequency. It is configured to obtain a DC voltage corresponding to the frequency and a DC voltage corresponding to the frequency.

The first detection circuit 5' includes a transformer T ₁ that converts the output voltage of the generator 1 into an appropriate voltage, a rectifying diode D ₁ , a current limiting resistor R ₁ , and a smoothing capacitor.
Consists of C ₁ , voltage dividing resistors R ₂ and R ₃ , and further resistor R ₂
At both ends of the
The collector and emitter of Q ₁ are connected. On the other hand, the second detection circuit 9 is composed of an input section 91, a waveform shaping circuit 92, an integrating circuit 93, and a time constant circuit 94 connected in cascade, and detects the output frequency of the generator and outputs the In addition to outputting a pulse signal corresponding to the frequency, this output signal is integrated and converted into a DC signal. Next, reference numerals 4 and 8 are first and second reference voltage generation circuits, respectively, which generate comparison reference voltages for the first and second detection circuits 5' and 9. circuit 4
outputs a reference voltage corresponding to the rated output voltage, and on the other hand, the second reference voltage generating circuit 8 outputs a reference voltage corresponding to the lower limit frequency at which the operation of the AVR should be stopped.

Further, 6 and 10 are first and second comparison circuits, respectively, and the first comparison circuit 6 compares the output voltage of the first detection circuit 5' and the first reference voltage generation circuit 4 with the output voltage of the first detection circuit 5' and the first reference voltage generation circuit 4. The second comparison circuit 10 compares the output voltages of the second detection circuit 9 and the second reference voltage generation circuit 8, respectively. 7 is a control circuit, which is configured to receive the output of the first comparator circuit 6 and drive the control transistor Q ₀ connected in series with the field winding L to obtain a constant output voltage. . on the other hand,
The output terminal of the second comparator circuit 10 is directly connected to the base of the transistor Q ₂ whose emitter is grounded, and the comparator circuit 10 is connected to the resistor R ₆ inserted between the collector of the transistor Q ₂ and the power supply Vcc and the light emitting Controls energization to the diode LED.

FIG. 3 shows a specific circuit configuration of the second detection circuit 9, the second reference voltage generation circuit 8, and the comparison circuit 10. The input section 91 consists of a transformer _T2 , one end of the secondary winding is grounded, and the other end is connected to the inverting input of the amplifier _A1 of the waveform shaping circuit 92 via a series circuit of a capacitor _C3 and a resistor _R9 . connected to the terminal. Amplifier _A1 works as a zero-cross comparator, and the non-inverting input terminal of amplifier _A1 is connected to the midpoint of voltage dividing resistors _R7 and _R8 connected in series between the power supply Vcc and ground via resistor _R10. Furthermore, a resistor _R11 for providing hysteresis is connected between the midpoint of the resistors _R7 and _R8 and the output terminal of the amplifier _A1 . A resistor _R12 is connected between the output terminal of amplifier _A1 and ground to keep the wave height constant.
A series circuit of Zener diodes Z ₁ and Z ₂ connected in anti-series with is connected, and the connection point of resistor R ₁₂ and Zener diode Z ₁ is connected to one end of capacitor C ₄ that constitutes the diode pump circuit. .

The other end of capacitor _C4 is grounded via diode _D3 and connected to the amplifier via diode _D4 .
A ₂ is connected to the inverting input terminal of the amplifier A ₂
The non-inverting input terminal of is grounded. Furthermore, a capacitor C ₅ and a resistor R ₁₃ are connected in parallel between the inverting input terminal and the output terminal of the amplifier A ₂ , and these are connected to the capacitor C ₄ , diode D ₃ ,
Together with _D4 , it constitutes an integrating circuit 93. This integrating circuit 93 accumulates charge in a capacitor _C5 in the feedback loop of the amplifier _A2 according to the number of pulses applied to one end of the capacitor _C4 , and at the same time, the charge in the capacitor _C5 is
Since it is discharged by _R13 , a voltage proportional to the input pulse frequency is obtained at its output.

Next, the time constant circuit 94 is a reverse current blocking diode.
It consists of a delay circuit consisting of D ₂ , resistors R ₄ and R ₅ , and capacitor C ₂ , and by setting the relationship R ₅ ≫ R ₄ , it has fast charging and slow discharging characteristics, and the load of the motor etc. The circuit according to the present invention malfunctions due to a temporary decrease in engine speed when
This is designed to prevent the AVR from stopping.

The reference voltage generation circuit 8 includes a current limiting resistor _R14 and a Zener diode _Z3 , and obtains a desired reference voltage by a variable resistor VR connected across the Zener diode _Z3 .

The comparator circuit 10 has an inverting input terminal of the amplifier _A3 connected to the output terminal of the time constant circuit 94, and a non-inverting input terminal connected to the intermediate terminal of the variable resistor VR of the reference voltage generating circuit 8 via a resistor _R15 . Furthermore, in order to obtain hysteresis, it is grounded via a resistor _R16 , and is also connected to its own output terminal via a resistor _R17 . The reason for providing hysteresis here is to prevent the hunting phenomenon in which the circuit repeatedly turns on and off due to uneven rotation of the engine. Next, the output terminal of the comparison circuit 10 is connected to the resistor R ₁₉
is connected to the base of transistor Q ₂ through, and the emitter of transistor Q ₂ is grounded,
Further, a series circuit of a resistor _R6 and a light emitting diode LED is connected between the collector and the power supply Vcc.
Note that this light emitting diode LED constitutes a photocoupler together with the phototransistor _Q1 in the first detection circuit 5'.

The operation will be explained below based on FIGS. 2 and 3. Note that the basic operation of the AVR has already been described in the description of the conventional example, so the description thereof will be omitted to avoid duplication.

First, the output voltage of the generator 1 input to the input section 91 of the second detection circuit 9 is converted to an appropriate voltage by the transformer _T2 so as to match the subsequent circuit voltage.
Next, the waveform shaping circuit 92 performs zero-cross switching on the sinusoidal output voltage to convert it into a square wave pulse with a constant amplitude. The integrating circuit 93 receives this square wave pulse as an input, outputs a DC voltage proportional to the frequency, and sends it to the second comparison circuit 10 via the time constant circuit 94. Second reference voltage generation circuit 8
generates a voltage corresponding to the lower limit frequency set before the field current increases due to a decrease in engine speed and causes destruction of the device as described above, and the comparator circuit 10 is a second detection circuit. When the output voltage of Q 9 decreases due to a decrease in the output frequency and falls below the reference voltage, the output is changed to a high level, driving the transistor Q ₂ and lighting the light emitting diode LED.

However, when the engine is being used at a normal rotation speed, the output voltage of the second detection circuit 9 is sufficiently high and does not fall below the reference voltage generated by the reference voltage generation circuit 8, so that the light emitting diode LED is turned on. Without it, the AVR is working properly. On the other hand, when the engine rotates at low speed due to warm-up, etc., the output voltage of the detection circuit 9 decreases, and when this falls below the reference voltage, the output of the comparison circuit 10 changes to high level, turning on the transistor Q ₂ and switching on the light emitting diode. Turn on the LED. As mentioned above, the light emitting diode LED forms a photocoupler with the phototransistor _Q1 provided in the first detection circuit 5'.
When the light emitting diode LED is turned on, the phototransistor _Q1 is turned on and shoots both ends of the voltage dividing resistor _R2 . As a result, the output voltage of the first detection circuit 5' increases, and the output voltage of the generator 1 appears to increase, so that the output voltage of the generator decreases. Therefore, when the engine rotates at low speed, the amount of field current supplied is reduced, and there is no risk of large current flowing and damaging the device. Further, when the engine rotation becomes normal, the AVR is immediately released from its functional stoppage, and the AVR operates normally to maintain the output voltage of the generator 1 at a constant value.

FIG. 4 shows a second embodiment of the present invention, in which the reference voltage of the first reference voltage generation circuit is forcibly increased instead of increasing the level of the output voltage of the first detection circuit when the engine is running at low speed. The structure is such that the same effect as in the first embodiment can be obtained. That is, in the figure, the collector of transistor _Q3 in the first reference voltage generation circuit 4' is connected to the power supply.
Vcc, the emitter is the reference voltage output terminal, and the base is connected to its own collector via a resistor _R20 , and the transistor
The collector of Q ₄ is grounded through a series circuit of emitter and Zener diode Z ₄ . Also, the cathode of the Zener diode Z ₄ is connected to the resistor R ₂₁
is connected to the emitter of transistor Q ₃ through
The base of transistor Q ₄ is a voltage dividing resistor R ₂₂ connected between the emitter of transistor Q ₃ and ground,
The collector-emitter of a phototransistor _Q1 , which forms a photocoupler together with the light emitting diode LED, is connected to both ends of _the resistor _R22 . Other than that, the overall configuration is substantially the same as that in FIG. 2, but the phototransistor _Q1 in the first detection circuit 5' is unnecessary.

Transistor Q ₄ is driven by the difference between the output voltage divided by resistors R ₂₂ and R ₂₃ and the Zener voltage of Zener diode Z ₄ , and the output voltage is controlled by controlling the base current of transistor Q _3. It has a function of leading to a constant value determined by the voltage dividing resistors R ₂₂ and R ₂₃ .

When low-speed rotation of the engine is detected during warm-up, etc., and phototransistor Q ₁ is turned on, the base current of transistor Q ₄ increases, decreasing the base current of transistor Q ₃ , and lowering the reference voltage output. to stop the AVR from operating,
The generator 1 can be protected by reducing the field current.

In the above embodiments, the output voltage of the first detection circuit 5' or the reference voltage in the reference voltage generation circuit 4' is configured to be changed by the operation of the photocoupler, but the present invention is not limited to this. Of course, it can also be constructed using relays or the like.

As described above, the AVR protection circuit of the present invention includes a first detection circuit that detects the output voltage of the generator, and a first reference voltage generator that generates a reference voltage set corresponding to the rated output voltage. circuit, and a first comparison circuit that compares the output voltages of the first detection circuit and the first reference voltage generation circuit, and adjusts the field current of the generator according to the output of the first comparison circuit. An AVR that is configured to control the output voltage of the generator to keep it constant, detects the output frequency of the generator's output, outputs a pulse signal corresponding to that output frequency, integrates the output signal, and converts it into a DC signal. a second detection circuit for converting, a second reference voltage generation circuit for generating a reference voltage set corresponding to the lower limit frequency of the generator output, the second detection circuit and a second reference voltage generation circuit; The second to compare the output voltage of
A comparison circuit is provided, and when the output frequency of the generator falls below the lower limit frequency, the photocoupler is controlled on/off by the output of the second comparison circuit to control the output voltage of the first detection circuit, and the output voltage of the first detection circuit is controlled. Since the machine's output voltage is reduced or maintained at the rated voltage, there is no risk of large current flowing into the field coil when the engine rotates at low speed, and it is completely unaffected by external factors such as the surrounding ambient temperature. Therefore, destruction of the AVR and generator can be completely prevented. In addition, since there is no need to design the AVR and generator capacity to be large in advance in anticipation of the risk of destruction, it is possible to reduce the capacity and size of each of these devices, which has the effect of contributing to cost reduction. have

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a conventional AVR, Fig. 2 is a block diagram showing a first embodiment of the present invention, Fig. 3 is a specific circuit diagram of the main part of the present invention, and Fig. 4 is a block diagram of a second embodiment of the present invention. FIG. 2 is a circuit diagram of main parts showing an embodiment of the present invention. 1... Generator, 2... Load, 3... DC constant voltage circuit, 4, 4'... First reference voltage generation circuit, 5,
5'...first detection circuit, 6...first comparison circuit,
7...Control circuit, 8...Second reference voltage generation circuit, 9...Second detection circuit, 91...Input section, 9
2... Waveform shaping circuit, 93... Integrating circuit, 94...
...Time constant circuit, 10...Second comparison circuit, Vcc...
...power supply, _A1 to _A3 ...amplifier, _Q1 ...phototransistor, LED ...light-emitting diode, _Q0 , _Q2 ,
Q ₃ , Q ₄ ... Transistor, L ... Field winding, D ₁
~ _D5 ...Diode, _Z1 - _Z4 ...Zener diode, _R1 - _R23 ...Resistor, _C1 - _C5 ...Capacitor, _T1 , _T2 ...Transformer, VR...Variable resistor.

Claims (1)

[Claims] 1. A first detection circuit that detects the output voltage of the generator, a first reference voltage generation circuit that generates a reference voltage set corresponding to the rated output voltage, a first detection circuit, and a first reference voltage. a first comparison circuit that compares the output voltage of the generator circuit, and is configured to control the field current of the generator according to the output of the first comparison circuit to keep the output voltage of the generator constant. In the AVR, a second detection circuit detects the output frequency of the generator, outputs a pulse signal corresponding to the output frequency, integrates the output signal and converts it into a DC signal, and a lower limit of the generator output. a second reference voltage generation circuit that generates a reference voltage set in accordance with a frequency; the second detection circuit;
A second comparison circuit is provided to compare the output voltages of the reference voltage generation circuits, and when the output frequency of the generator falls below the lower limit frequency, the output of the second comparison circuit and the output changes to a high level and the light emitting diode lights up. , the photodiode of the first detection circuit forming a photocoupler with the light emitting diode is turned on, shorting one of the output voltage dividing resistors and increasing the voltage applied to the first comparison circuit. An AVR protection circuit characterized by being configured to stop operation.