Condensive load protection device of self-excited generator

In a self-excited generator 1 including an automatic voltage regulator (AVR) 10, a condensive load protection device includes: a field current control driver 21 which is connected to the field winding 6 in series and controlled to be ON/OFF by a drive circuit 23 of the AVR 10 to supply a field current to the field winding 6; and a condensive load protecting rotor short-circuit driver 22 which is connected in parallel to the field winding 6, and supplies a short-circuit current to the field winding 6 by being turned ON, and a bootstrap circuit 30 is connected as a drive power supply of the field current control driver and the condensive load protecting rotor short-circuit driver, and the bootstrap circuit 30 includes a capacitance portion 32 in which charges are accumulated when the field current control driver 21 is ON.

TECHNICAL FIELD

The present invention relates to a control device of an engine-driven power generator (self-excited AVR synchronous generator) which adjusts a generator output by regulating a current to be supplied to a field winding by an automatic voltage regulator (AVR), and specifically, to a condensive load protection device of a self-excited generator which protects an automatic voltage regulator (AVR) from a back electromotive force caused by armature reaction when a condensive load is connected to the generator.

BACKGROUND ART

A configuration of a self-excited AVR synchronous generator including a generation winding2and an excitation winding3wound on a stator side of the generator1, a field winding6wound around a rotor5to be rotated by a drive source (engine)4, a permanent magnet7fitted to the rotor5for generating an excitation current, and an automatic voltage regulator (AVR)10which regulates a current to be supplied to the field winding6as shown inFIG. 4, is described in Patent Literature 1.

The automatic voltage regulator (AVR)10connected to the field winding6via a brush8includes a commutator11having an input side to which both ends of the excitation winding3are connected, a capacitor12provided between the commutator11and the ground to smooth an output voltage of the commutator11, a flywheel diode13connected in parallel to the field winding6, a transistor14which is controlled to be turned ON/OFF to supply a field current to the field winding6, and a field current drive circuit (field current driving means)15which PWM-controls a field current. One end of the field winding6is connected to the output side of the commutator11, and the other end of the field winding6is connected to the collector side of the transistor14.

The flywheel diode13is provided for absorbing a surge voltage caused in case of power supply stop and smoothing the field current when PWM-controlling the field current flowing in the field winding6.

The output side of the generation winding2is connected to a load9via a brush8, and is configured so that a detected output voltage is input into the field current drive circuit15.

The automatic voltage regulator (AVR)10operates to hold a voltage to be output from the generation winding2at a voltage set in advance by regulating a current to be supplied to the field winding6by turning ON/OFF the transistor14.

In the self-excited AVR synchronous generator, when a capacitive load which is a condensive load is connected as the load9, magnetization of the rotor5occurs due to armature reaction. Therefore, due to a predetermined or more condensive load current, as shown inFIG. 5B, a phenomenon occurs in which a back electromotive voltage is generated in the field winding6of the rotor5. At this time, the back electromotive voltage (overvoltage) is applied to the AVR as a rotor excitation control unit, so that when it has no protective function, a commutating device, etc., such as the capacitor12inside the AVR10may be broken by the overvoltage.FIG. 5Ais a schematic circuit diagram showing a current flowing in the excitation winding3and the field winding6in a normal state where no condensive load is connected. InFIGS. 5A and 5B, instead of the transistor14as a switching element inFIG. 4, a field current control FET14is used.

Conventionally, as a condensive load protecting short circuit for suppressing a back electromotive voltage, as shown inFIG. 6, a self-bias circuit40including two bipolar transistors Darlington-connected is used. With this circuit, due to a back electromotive force according to armature reaction of a condensive load, a base current ib flows from the rotor (field winding6) to the transistor42via a lead resistor41, and a short-circuit current is flows according to short-circuiting of the transistor43.

CITATION LIST

Patent Literature

Patent Literature 1 Japanese Published Unexamined Patent Application No. I-108-140400

SUMMARY OF INVENTION

Technical Problem

Devices such as transistors and FETs, etc., are used for forming a condensive load protecting short circuit, however, in the above-described self-bias circuit40, a sufficient gate voltage for the transistors42and43cannot be obtained with a back electromotive voltage generated in the rotor5, so that the devices cannot be used in a saturation region of operation, and a large-scale device the heat generation of which is great becomes necessary.

Further, the heat generation from the devices must be suppressed by connecting a large lead resistor41for voltage drop to the base of the transistor42.

Further, if PNP transistors and Pch-FETs which are easy to handle in the circuit are used, the cost becomes expensive, and there is no high-capacity device suitable for the circuit.

Specifically, in a self-bias circuit, a function necessary for the transistors42and43is only a short-circuiting operation, and if it is realized, heat generation of the devices inside the AVR can be suppressed and the protection device can be greatly downsized, and the possibility of circuit breakage due to a back electromotive voltage can be greatly reduced.

The present invention has been proposed in view of the above-described circumstances, and an object thereof is to provide a condensive load protection device of a self-excited generator which can be configured by using inexpensive devices, as a device for protecting an automatic voltage regulator (AVR) from a back electromotive force generated by armature reaction.

Solution to Problem

To achieve the above object, the present invention of the claim1having a first feature is a condensive load protection device of a self-excited generator (1) including an automatic voltage regulator (10) which supplies a current obtained by commutating an output of an excitation winding (3) wound in a generator to be driven by an engine to a field winding (6) according to fluctuation in a generator output voltage, comprising:

a field current control driver (21) which is connected to the field winding (6) in series and controlled to be ON/OFF by a drive circuit (23) of the automatic voltage regulator (10) to supply a field current to the field winding (6); and

a condensive load protecting rotor short-circuit driver (22) which is connected in parallel to the field winding (6), and supplies a short-circuit current to the field winding (6) by being turned ON, wherein

a bootstrap circuit (30) is connected as a drive power supply of the field current control driver and the condensive load protecting rotor short-circuit driver, and

the bootstrap circuit (30) includes a capacitance portion (32) in which charges are accumulated when the field current control driver (21) is ON.

The present invention of the claim2having a second feature is the condensive load protection device of a self-excited generator according to claim1, wherein the field current control driver (21) and the condensive load protecting rotor short-circuit driver (22) consist of N channel-MOSFETs.

The present invention of the claim3having a third feature is the condensive load protection device of a self-excited generator according to claim1, comprising a control means (24) which always operates the field current control driver (21) and the condensive load protecting rotor short-circuit driver (22) in a mutually inverted manner.

The present invention of the claim4having a forth feature is the condensive load protection device of a self-excited generator according to claim3, wherein the control means (24) voltage-drives the field current control driver (21) and the condensive load protecting rotor short-circuit driver (22) at different timings by controlling the drivers with arbitrary pulse widths in arbitrary phases.

Advantageous Effects of Invention

According to the present invention having a first feature, by providing a condensive load protecting rotor short-circuit driver (22), the AVR is prevented from being broken by a back electromotive force which is generated in the field winding (6), and the capacitance portion (23) is used as a power supply independent of the condensive load protecting rotor short-circuit driver (22).

Specifically, by using a bootstrap circuit as a drive power supply of each driver, a gate voltage sufficient for operating both of the field current control driver (21) and the condensive load protecting rotor short-circuit driver (22) in a saturation region can be secured by a power supply of one system. As a result, heat generation of each driver when it is turned ON can be suppressed, and a small-sized device can be adopted as each driver.

According to the present invention having a second feature, by using an inexpensive N channel-MOSFET as each driver, the entire device can be configured inexpensively.

According to the present invention having a third feature, by providing a control means (24) which always operates the drivers in a mutually inverted manner, the drivers can be prevented from being turned ON concurrently.

According to the present invention having a fourth feature, by controlling each driver with each arbitrary pulse width in each arbitrary phase, the drivers can be voltage-driven at different timings.

DESCRIPTION OF EMBODIMENTS

A condensive load protection device of a self-excited generator according to an embodiment of the present invention will be described with reference to the drawings.FIG. 1is a block diagram showing an essential portion configuration of a condensive load protection device of a self-excited generator of the present invention. InFIG. 1, the portions having the same configuration as inFIG. 4are designated with the same reference numerals.

As shown inFIG. 4, a self-excited generator1to which a condensive load protection device is connected is driven by an engine and includes an automatic voltage regulator10which supplies a current obtained by commutating an output of an excitation winding3wound in the generator by the commutator11to a field winding6according to fluctuation in a generator output voltage. A capacitor12is for smoothing the output voltage of the commutator11.

To the field winding6, a field current control driver21for supplying a field current to the field winding6is connected in series. This field current control driver21supplies a field current to the field winding6according to ON/OFF control by an FET drive circuit23of the automatic voltage regulator10. The field current control driver21consists of an N channel-MOSFET using conduction electrons as carriers (n-type channel).

To the field winding6, a condensive load protecting rotor short-circuit driver22which supplies a short-circuit current to the field winding6is connected in parallel. This condensive load protecting rotor short-circuit driver22is turned ON to supply a short-circuit current to the field winding6when a back electromotive force is generated in the field winding6. The condensive load protecting rotor short-circuit driver22consists of an N channel-MOSFET using conduction electrons as carriers (n-type channel).

The gate portion of the field current control driver21is connected to a CPU24via the FET drive circuit23. To the CPU24, a predetermined power supply voltage (5V DC) for driving the CPU24is supplied from a DC power supply26(15V DC) for driving the condensive load protection device via a rated voltage power supply25. To the FET drive circuit23, the DC power supply26is connected as a drive power supply via a power wire27.

Turning ON/OFF of the field current control driver21is controlled by an input of a PWM signal output the drive timing of which is adjusted into the gate portion of the field current control driver21from the FET drive circuit23, and the field current to flow in the field winding6is accordingly controlled.

The gate portion of the condensive load protecting rotor short-circuit driver22is connected to the CPU24via a bootstrap circuit30.

The bootstrap circuit30includes a diode31, a capacitance portion22, and a photo coupler33including a light emitting diode33aand a phototransistor33b, and the capacitance portion32is connected between the gate portion and the source portion of the condensive load protecting rotor short-circuit driver22, and to the gate portion of the condensive load protecting rotor short-circuit driver22and the capacitance portion32, the diode31on the forward side of the DC power supply26is connected via the power wire27.

The output portion of the photo coupler33is connected to the gate portion of the condensive load protecting rotor short-circuit driver22and the source portion of the condensive load protecting rotor short-circuit driver22(drain portion of the field current control driver21) so that the photo coupler becomes parallel to the capacitance portion32.

The photo coupler33is for electrically insulating the condensive load protecting rotor short-circuit driver22and the CPU24from each other. Specifically, when the field current control driver21is OFF, the reference potential of the condensive load protecting rotor short-circuit driver22is different from that of the CPU24, so that a drive signal of the CPU24is converted into an optical signal, and according to this optical signal, the condensive load protecting rotor short-circuit driver22is driven.

Specifically, the photo coupler33of the bootstrap circuit30and the FET drive circuit23control turning ON/OFF of the field current control driver21and the condensive load protecting rotor short-circuit driver22independently of each other in response to a drive signal from the CPU24.

Therefore, in the bootstrap circuit30, when the field current control driver21is ON (electrically continuous) and the condensive load protecting rotor short-circuit driver22is OFF (not electrically continuous) according to a drive signal from the CPU24, charges are accumulated in the capacitance portion32from the DC power supply26via the diode31, and when the field current control driver21is OFF (not electrically continuous), the drive signal from the CPU24is converted into an optical signal by the light emitting diode33a, and according to this optical signal, the phototransistor33bbecomes electrically continuous, and accordingly, the output side of the photo coupler33is short-circuited, and the condensive load protecting rotor short-circuit driver22is driven according to charges accumulated in the capacitance portion32as an independent power supply.

The field current control driver21and the condensive load protecting rotor short-circuit driver22are controlled by the CPU24by using drive pulses which are always operated in an inverted manner (ON/OFF) (either one is always ON) as shown inFIG. 2. In order to reliably prevent the drive pulses of the field current control driver21and the condensive load protecting rotor short-circuit driver22from being turned ON concurrently, by providing a dead time for delaying a rise of one drive pulse with respect to a fall of the other drive pulse, both of field and condensive load protection are realized while preventing a synchronous short-circuit of both FETs.

By turning ON either the field current control driver21or the condensive load protecting rotor short-circuit driver22, the condensive load protecting rotor short-circuit driver22is turned ON upon using a parasitic diode present between the source and the drain inside the condensive load protecting rotor short-circuit driver22as a fly diode, and the field current is synchronously commutated, and accordingly, loss can be reduced.

Next, detailed controls of the field current control driver21and the condensive load protecting rotor short-circuit driver22by the CPU24will be described.

The field current control driver21and the condensive load protecting rotor short-circuit driver22can be driven by power supplies independent of each other, so that they can be controlled with arbitrary pulse widths in arbitrary phases according to a control program of the CPU24.

In the controls of the field current control driver21and the condensive load protecting rotor short-circuit driver22according to the drive pulses, when a condensive load is connected, excitation of the rotor becomes almost unnecessary due to magnetization, so that the ON duty of the field current control driver21can be made as close to zero as possible.

Specifically, as shown inFIG. 3, in the always inverted operation (ON/OFF) of the field current control driver21and the condensive load protecting rotor short-circuit driver22, the ON time of the condensive load protecting rotor short-circuit driver22is set long, and the field current control driver21and the condensive load protecting rotor short-circuit driver22can be voltage-driven at different timings.

The field current can be properly controlled by controlling ON/OFF of the field current control driver21with an arbitrary pulse width in an arbitrary phase.

When a condensive load is connected, it is required that “the field current control driver21is OFF and the condensive load protecting rotor short-circuit driver22is ON” in a phase in which a back electromotive force is generated, and this can be easily set by a control program of the CPU24.

Next, the operation of the condensive load protection device when the field current control driver21and the condensive load protecting rotor short-circuit driver22are controlled to be ON/OFF with the drive pulses at the timings shown inFIG. 3will be described.

In the bootstrap circuit30, when the field current control driver21is ON (electrically continuous) and the condensive load protecting rotor short-circuit driver22is OFF (not electrically continuous) according to a drive signal from the CPU24, charges are accumulated in the capacitance portion32from the DC power supply26via the diode31.

When the field current control driver21is OFF (not electrically continuous) and the condensive load protecting rotor short-circuit driver22is ON (electrically continuous), a short-circuit current caused according to a back electromotive force generated in the field winding6flows in the closed circuit including the field winding6and the condensive load protecting rotor short-circuit driver22, and accordingly, the capacitor12on the AVR side is prevented from being influenced by the back electromotive force.

Specifically, according to the above-described configuration of the condensive load protection device of a self-excited generator, the field current control driver21and the condensive load protecting rotor short-circuit driver22are controlled to be ON/OFF, and by supplying a short-circuit current to the field winding6when the field current control driver21is OFF and the condensive load protecting rotor short-circuit driver22is ON, the circuit (capacitor12, etc.) of the AVR can be prevented from being broken by a back electromotive force generated in the field winding6.

According to the above-described configuration of the condensive load protection device, N channel-MOSFETs are used as the field current control driver21and the condensive load protecting rotor short-circuit driver22, and are driven individually by independent power supplies realized by the bootstrap circuit30. Therefore, a gate voltage sufficient for operation of the MOSFET of each driver in a saturation region can be secured, and both of the field current control driver21and the condensive load protecting rotor short-circuit driver22can be used in a saturation region by the DC power supply26of one system, so that heat generation of the MOSFETs is suppressed (heat generation loss is reduced). As a result, as the MOSFET, a small-sized device can be adopted, and an inexpensive high-capacity N channel-MOSFET can be used.

Comparison of the above-described condensive load protection device with a self-bias circuit40as a condensive load protecting short circuit shown inFIG. 6will be described.

First, the condensive load protection transistors (transistors42and43) which are operated by the self-bias circuit40cannot control a firing timing (passive operation). Specifically, in the case of the self-bias circuit40, unless a condensive load is connected and a back electromotive force is generated in the field winding6, the transistors42and43do not operate. Therefore, when digitizing (microcomputer-controlling) the AVR, in order to control the field current control FET14directly by a microcomputer when a condensive load is connected, a circuit and control for preventing synchronous turning ON (short-circuit) of the condensive load protection transistors (transistors42and43) and the field current control FET14are necessary.

On the other hand, according to the above-described condensive load protection device, the CPU24controls the field current control driver21and the condensive load protecting rotor short-circuit driver22by using the bootstrap circuit30, and accordingly, microcomputer control can be performed according to a predetermined program, and synchronous turning ON (short-circuit) of the drivers can be prevented by software.

In the CPU24, even when microcomputer control according to a program is not used, by driving the field current control driver21and the condensive load protecting rotor short-circuit driver22according to reverse logic by a logic circuit, the same effect (heat generation suppression and downsizing) can be obtained.

When the condensive load protecting short circuit is formed by the self-bias circuit40, as described above, unless a condensive load is connected and a back electromotive force is generated in the field winding6, the transistors42and43do not operate. A failure mode of an FET and a transistor is short-circuited, and when the field current control FET (transistor)14in the self bias circuit40fails and short-circuits, the self-excited generator1may continue power generation while its output voltage is still overvoltage.

On the other hand, according to the condensive load protection device of the present embodiment, at the timing at which either the field current control driver (FET)21or the condensive load protecting rotor short-circuit driver (FET)22fails and short-circuits, a short-circuit state is caused in both of the FETs, so that both of the FETs are broken and the unit of the AVR is broken, however, the field current does not flow and the generator output does not increase, so that the generator can be prevented from continuing power generation while the voltage is still overvoltage.

REFERENCE SIGNS LIST