JPH05328800A - Exciting current controller for generator - Google Patents

Abstract

PURPOSE:To reduce switching noise at the time of a low temperature and switching loss and to prevent a variation in an output of a generator at the time of a high temperature by stabilizing a switching frequency of a switching element for limiting an exciting current to a predetermined value even if a temperature of an exciting coil is varied. CONSTITUTION:An exciting current controller 6 for controlling an exciting current of an exciting coil 2 has a current regulator 9 for suppressing the exciting current to a predetermined voltage or lower. The regulator 9 detects the exciting current of the coil 2 by an exciting detector 11, and sets an OFF time of a switching element 7 by a breaking time setter 12. The setter 12 turns OFF the element 7 after a predetermined time from when an output voltage of the detector 11 exceeds a set voltage (set value), sets the OFF time to long when a difference between the output voltage of the detector 11 and the set voltage is large, and sets it to short when the difference is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exciting current control device for controlling exciting current by intermittently energizing an exciting coil of a generator.

[0002]

2. Description of the Related Art As a conventional technique, Japanese Patent Laid-Open No. 62-104
The technique disclosed in No. 500 is known. In this technique, as shown in the electric circuit of FIG. 7, the comparator 101 determines that the energization amount of the exciting coil exceeds a set value, and the comparator 101 controls when the exciting current exceeds the set value. Turn on the transistor 102 and turn on the switching element 103.
Turn OFF and stop energizing the excitation coil. The energization stop time of the exciting coil is set by the discharge time of the capacitor 104. Then, when the discharging of the capacitor 104 is completed, the switching element 103 is turned on again, the energization of the exciting coil is started, and the above is repeated. With this technique, the maximum value of the exciting current is limited to a constant value even if the temperature of the exciting coil changes. Therefore, an increase in the generator output current at low temperatures can be suppressed.

[0003]

However, in the technique described above, the switching frequency of the switching element 103 varies greatly due to the temperature change of the exciting coil. That is, since the resistance of the exciting coil is low at low temperatures, it is necessary to increase the cutoff ratio (DOFF) of the exciting coil. Therefore, the switching cycle (T) is T = t0 / DOFF (t0 is the exciting coil cutoff time determined by the discharge time of the capacitor 104). That is, at low temperatures, the switching frequency becomes high, which causes switching noise and increases switching loss. Also, at high temperatures,
The switching frequency becomes low, the exciting current fluctuates, the output of the generator fluctuates, flickering of lamps occurs, and generator noise fluctuates.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to achieve the following even if the temperature of the exciting coil changes.
It is an object of the present invention to provide an exciting current control device for a generator in which a switching frequency for controlling the exciting current to a constant current is stabilized.

[0005]

The exciting current control device for a generator of the present invention employs the following technical means. The excitation current control device includes a generator including an excitation coil that generates a magnetic field and an armature coil that rotates relative to the magnetic field generated by the excitation coil to generate electric power, and energization and interruption of the excitation coil. And an exciting current control device for repeatedly controlling the exciting current. The exciting current control device interrupts the exciting current after a delay of a predetermined time after the exciting current value of the exciting coil exceeds a set value, and a difference between the exciting current value and the set value at the time of the cutoff. Becomes longer and the breaking time becomes shorter, and as the difference between the exciting current value at the time of breaking and the set value becomes smaller, the breaking time becomes shorter.

[0006]

When the temperature of the exciting coil is low, the resistance value of the exciting coil is low. For this reason, when the exciting current control circuit cuts off the energization of the exciting coil a predetermined time after the exciting current exceeds the set value, the difference between the exciting current value and the set value at the time of the cutoff is large. The exciting current control circuit lengthens the interruption time when the difference is large. As a result, the intermittent period of energization of the exciting coil becomes longer than in the conventional case. On the contrary, when the exciting coil has a high temperature, the resistance value of the exciting coil is high. Therefore, when the exciting current control circuit cuts off the energization of the exciting coil a predetermined time after the exciting current exceeds the set value, the difference between the exciting current value and the set value at the time of the cutoff is small. And
The exciting current control circuit shortens the interruption time when the difference is small. As a result, the intermittent period of energization of the exciting coil becomes shorter than in the conventional case.

[0007]

The exciting current control device for a generator according to the present invention comprises:
As shown in the above operation, when the temperature of the exciting coil is low, the intermittent period of energization of the exciting coil becomes longer than in the conventional case, and conversely when the temperature of the exciting coil is high, in comparison with the conventional case. The intermittent cycle of energization of the exciting coil is shortened, and as a result, the intermittent cycle of energization of the exciting coil can be a stable switching cycle regardless of the temperature of the exciting coil. As a result, it is possible to reduce switching noise and switching loss at low temperatures, and to prevent output fluctuation of the generator at high temperatures.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an exciting current control device for a generator according to the present invention will be described based on an embodiment shown in the drawings. [Structure of Embodiment] FIGS. 1 to 4 show an embodiment of the present invention, and FIG. 1 is an electric circuit diagram showing the structure of an exciting current control device for an automobile generator. The generator 1 includes an exciting coil 2 that generates a magnetic field when energized, and an armature coil 3 that generates electric power by rotating relative to the magnetic field generated by the exciting coil 2. One of the armature coils 3 is driven by an engine (not shown). The alternating current generated by the armature coil 3 is converted into direct current by the rectifier circuit 4 and output to the battery 5 and each electric load 5a of the vehicle. The electric power generated by the generator 1 changes depending on the rotation speed of the engine and the energization amount (excitation current value) of the exciting coil 2. The exciting current supplied to the exciting coil 2 is the exciting current controller 6
Controlled by.

The exciting current control device 6 includes a switching element 7 for energizing and shutting off the exciting coil 2. The switching element 7 includes a comparator 8 that detects that the voltage of the battery 5 has dropped below a predetermined voltage, and a current adjustment circuit 9 that controls the switching element 7 so that the exciting current does not exceed the maximum value. It is controlled by the output of the connected NOR circuit 10. As shown in the electric circuit diagram of FIG. 2, the current adjusting circuit 9 includes an exciting current detecting circuit 11 for detecting an exciting current, and a breaking time setting circuit for setting a breaking time of the exciting current according to the detected exciting current value. It consists of 12.

The exciting current detection circuit 11 is provided with an operational amplifier 14 which differentially amplifies and outputs a voltage corresponding to the exciting current detected by the shunt resistor 13 for changing the exciting current of the exciting coil 2. On the other hand, the cutoff time setting circuit 12
Is when the output of the exciting current detection circuit 11 reaches the set voltage (when the exciting current value of the exciting coil 2 exceeds the set value),
A comparator 15 for generating a Hi output signal is provided, and a delay circuit 16 for generating a Hi output signal for turning off the switching element 7 after a delay of a predetermined time after receiving the Hi output signal from the comparator 15 is provided. In addition, the cutoff time setting circuit 12 has an operational amplifier 1 according to the exciting current value (voltage value detected by the shunt resistor 13) when the energization of the exciting coil 2 is cut off by the delay circuit 16.
4 is provided with a capacitor 18 for storing the output signal.
While the exciting current is cut off, the discharge circuit 20 discharges the capacitor 18, and the output voltage v3 of the capacitor 18 simulates the decrease in the current flowing through the exciting coil.

[Operation of the Embodiment] Next, the operation of the above embodiment will be briefly described with reference to the time charts shown in FIGS. 3 (a) and 3 (b). The exciting current flowing through the exciting coil 2 increases and the voltage v1 generated by flowing through the shunt resistor 13 is
When the voltage becomes higher than the voltage v2 applied to the negative terminal of the operational amplifier 14, the output of the operational amplifier 14 charges the capacitor 18. On the contrary, the voltage v1 changes to the voltage v2
Is smaller than this, the capacitor 18 is discharged and the voltage v2
The capacitor 18 is charged so that is equal to the voltage v1. As a result, the voltage v3 generated in the capacitor 18
Is a value proportional to the exciting current, as shown in the following equation.

## EQU1 ## v3 = k × ir (ignoring the voltage drop of the diode 21) ir is the exciting current k = R1 × (R2 + R3) / R2 R1 is the resistance value of the shunt resistor 13, and R2 and R3 are the negative terminals of the operational amplifier 14. It is the resistance value of the resistors 22 and 23 that sets the voltage applied to. Here, when the exciting current increases and the voltage v3 on the output side of the operational amplifier 14 exceeds the set voltage va, the output of the comparator 15 becomes Hi, and then the delay circuit 16 turns on the transistor 24 after a delay of a predetermined time td. , The exciting current decreases. When this transistor 24 turns on, the switching element 7
Since it is turned off, the current applied to the shunt resistor 13 is also OF
Then, the voltage v1 becomes almost 0V. Therefore, the output of the operational amplifier 14 is inverted to Low, and the voltage v3 is the discharge circuit 2
When the voltage v3 drops below the set voltage va, the output of the comparator 15 becomes Lo.
Invert to w. This turns off the transistor 24.
Then, the switching element 7 is turned on, and the exciting current flows through the exciting coil 2 again.

Here, when the time during which the switching element 7 is off is TOFF, the following equation is established.

[Formula 2] TOFF = C × SON / i where C is the capacitance of the capacitor 18 and SON is the delay time td.
The change amount of the voltage v3 at (the voltage corresponding to the difference between the exciting current value at the time of interruption and the set value), i is the discharge current value of the discharge circuit 20. Therefore, the shutoff time TOFF of the exciting current becomes a value proportional to the value (AON) of the exciting current changed during the delay time td (since AON = SON / k, TOFF = C × k).
X AON / i). In addition, the following equation holds when switching is stable.

## EQU00003 ## AOFF / td.times.TOFF = AON / td.times.TON From these results, the switching cycle T can be expressed by the following equation.

## EQU00004 ## T = A.times. (AON + AOFF) where A is a coefficient (A = C.times.k / i), and AOFF is the amount of attenuation of the exciting current at a fixed time td. Then, as can be seen from the increase and attenuation characteristics of the current of the exciting coil 2 in FIG.
The switching cycle T does not change significantly whether the exciting coil 2 is at a low temperature or at a high temperature.

[Effects of the Embodiment] In this embodiment, the switching element 7 is turned ON-OF so that the exciting current does not exceed the maximum value.
The switching cycle T to perform F can be a stable cycle as shown by the above operation. Therefore, it is possible to reduce switching noise and switching loss at low temperatures, and to prevent output fluctuations of the generator 1 and flicker of lamps at high temperatures.

[Second Embodiment] FIGS. 5 and 6 show a second embodiment, and FIG. 5 is an electric circuit diagram of the current adjusting circuit 9. In this embodiment, the exciting current detection circuit 11 integrates the voltage difference between the detected voltage of the exciting current and the set voltage v2, and outputs the voltage v3 corresponding to the value of the exciting current to the comparator 15 of the cutoff time setting circuit 12. is doing. Since the noise component included in the excitation current detection is removed from the integrated voltage v3,
The exciting current can be stably detected by the integrated voltage v3. The operation will be briefly described. As shown in FIG.
When the integrated voltage v3 exceeds the set voltage va, the delay circuit 16
The switching element 7 is delayed by the delay time td set in
It turns off and the excitation current is cut off. The interruption time is determined by the amount of change of the voltage v3 according to the exciting current value changed during the delay time td, as in the first embodiment.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing the configuration of an exciting current control device for a generator (first embodiment).

FIG. 2 is an electric circuit diagram of a current adjusting circuit (first embodiment).

FIG. 3 is a time chart for explaining the operation (first
Example).

FIG. 4 is a graph showing a characteristic of increase / decrease in current of an exciting coil (first embodiment).

FIG. 5 is an electric circuit diagram of a current adjusting circuit (second embodiment).

FIG. 6 is a time chart for explaining the operation (second)
Example).

FIG. 7 is an electric circuit diagram of a current regulating circuit (prior art).

[Explanation of symbols]

 1 generator 2 exciting coil 3 armature coil 6 exciting current control device

Claims (1)

[Claims] 1. A generator including an exciting coil that generates a magnetic field and an armature coil that generates electric power by rotating relative to the magnetic field generated by the exciting coil, and repeating energization and interruption of the exciting coil. In an exciting current control device for a generator, which comprises an exciting current control device for controlling an exciting current, the exciting current control device, after the exciting current value of the exciting coil exceeds a set value, after a predetermined time delay The current is interrupted, and the interruption time is lengthened as the difference between the exciting current value at the time of interruption and the set value increases, and the interruption time decreases as the difference between the exciting current value at interruption and the set value decreases. An exciting current control device for a generator, characterized in that