In a capacitor-compensation-type generator having a rotor wound with a field winding, a stator wound with an output winding adapted to cross flux generated by the field winding to output AC power, and an internal combustion engine that drives the rotor to rotate relative to the stator, there are equipped with an actuator that changes the engine speed and an actuator controller that controls operation of the actuator in accordance with a constant voltage operation mode in which the engine speed is controlled to a desired speed such that a detected output voltage becomes a desired voltage, or a constant frequency operation mode in which the detected engine speed is controlled to a predetermined speed such that frequency of AC power outputted from the output winding becomes a desired frequency, thereby enabling to output AC power at constant voltage or frequency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a capacitor-compensation-type generator and a method for controlling the same.

2. Description of the Related Art

There is known a capacitor-compensation-type generator having a rotor wound with a field winding that is short-circuited with a diode, a stator wound with an output winding that is adapted to cross the flux generated by the field winding to produce AC power and with an exciting winding that is disposed at predetermined phase angle with respect to the output winding and is short-circuited with a phase advance capacitor, and an internal combustion engine for driving the rotor relative to the stator, as taught, for example, in Japanese Laid-Open Patent Application No. Sho 63 (1988)-227960. The generator of this type is originally a brushless single-phase synchronous generator that is also called “Nonaka-type generator”, named after the inventor thereof.

In this type of generator, current (whose phase is advanced by 90 degrees by the phase advance capacitor) flows through the exciting winding, field current (which is produced in the field winding by armature reaction) is rectified by the diode, and rotating field is produced by DC magnetizing the rotor (field), which is rotated by the engine, to the N-pole and S-pole. The output winding wound around the stator crosses the flux generated from the rotating field of the rotor, thereby producing AC power.

Since the capacitor-compensation-type generator does not require a brush, slip ring etc., and achieves simple structure, it causes wide spread in the low-price range. However, the output voltage increases with increasing speed of the engine and fluctuates in response to increase or decrease in load, disadvantageously resulting in unstable output voltage. Also, it is preferable for a certain load that frequency is constant, but this type of generator is not necessarily satisfactory in this regard.

SUMMARY OF THE INVENTION

An object of this invention is therefore to overcome the foregoing problem by providing a capacitor-compensation-type generator or method of controlling the same that can output AC power at constant voltage or frequency.

In order to achieve the object, this invention provides, in a first aspect, a capacitor-compensation-type generator having a rotor wound with a field winding that is short-circuited with a diode, a stator wound with an output winding that is adapted to cross flux generated by the field winding to output AC power and with an exciting winding that is disposed at predetermined phase angle with respect to the output winding and is short-circuited with a phase advance capacitor, and an internal combustion engine that drives the rotor to rotate relative to the stator, comprising: an engine speed detector that detects a speed of the engine; an output voltage detector that detects output voltage of the AC power outputted from the output winding; an actuator that changes the engine speed; and an actuator controller that controls operation of the actuator in accordance with one of a constant voltage operation mode in which the detected engine speed is controlled to a desired speed such that the detected output voltage becomes a desired voltage, and a constant frequency operation mode in which the detected engine speed is controlled to a predetermined speed such that frequency of AC power outputted from the output winding becomes a desired frequency.

In order to achieve the object, this invention provides, in a second aspect, a method of controlling a capacitor-compensation-type generator having a rotor wound with a field winding that is short-circuited with a diode, a stator wound with an output winding that is adapted to cross flux generated by the field winding to output AC power and with an exciting winding that is disposed at predetermined phase angle with respect to the output winding and is short-circuited with a phase advance capacitor, an internal combustion engine that drives the rotor to rotate relative to the stator and an actuator that changes the engine speed, comprising the steps of: detecting a speed of the engine; detecting output voltage of the AC power outputted from the output winding; and controlling operation of the actuator in accordance with one of a constant voltage operation mode in which the detected engine speed is controlled to a desired speed such that the detected output voltage becomes a desired voltage, and a constant frequency operation mode in which the detected engine speed is controlled to a predetermined speed such that frequency of AC power outputted from the output winding becomes a desired frequency.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A capacitor-compensation-type generator according to a preferred embodiment of the present invention will now be explained with reference to the attached drawings.

FIG. 1is a block diagram entirely showing a capacitor-compensation-type generator according to an embodiment of the invention.

InFIG. 1, reference numeral10designates the capacitor-compensation-type generator that is equipped with an internal combustion engine (hereinafter called “engine”; ENG)12and has a rated output of AC 100V-2.1 kVA. The generator10is originally a brushless single-phase synchronous generator.

The engine12is an air-cooled, spark-ignition engine that runs on gasoline. Air sucked in through an air cleaner (not shown) flows through an intake pipe12aand carburetor12b. A choke valve12cand throttle valve12dare installed in the carburetor12bto regulate the intake air.

The gasoline fuel pumped from a fuel tank (not shown) is injected through a venturi12eto be mixed with the intake air and air-fuel mixture thus generated flows into a combustion chamber12gupon opening of an intake valve12f.

The air-fuel mixture in the combustion chamber12gis ignited by a spark plug12iat predetermined ignition timing and burns, thereby driving a piston12jdownward in the drawing to rotate a crankshaft12kconnected to the piston12j. Upon opening of an exhaust valve12l, exhaust gas caused by the combustion flows through an exhaust pipe12mand is discharged to the exterior through a muffler12n.

A flywheel12ois disposed at an end of the crankshaft12k. The inner wall of the flywheel12ois fastened with permanent magnet pieces (not shown) and outside thereof is provided with a power generation coil12pand exciting coil12qthat are fastened to the body of engine12.

The throttle valve12dis connected with an actuator (hereinafter called “throttle motor”)12sthat is constituted as a stepper motor. When operated, the throttle motor12sopens or closes the throttle valve12dto change engine speed NE.

A power generation unit14is connected to the engine12to be operated thereby. As shown inFIG. 1, the power generation unit14is equipped with a rotor14athat is connected to the other end of the crankshaft12kof the engine12to be rotated with rotation of the crankshaft12k, and a stator14bfixed at an appropriate position of the body of the engine12.

The rotor14ais wound with a field winding14a2that is short-circuited with a diode14a1and the stator14bis wound with an output winding14b1that is adapted to cross the flux generated by the field winding14a2of the rotor14ato produce AC power and with an exciting winding14b3that is disposed at predetermined phase angle (electric angle), i.e., phase angle of 90 degrees with respect to the output winding14b1and is short-circuited with a phase advance capacitor14b2.

In this configuration, current (whose phase is advanced by 90 degrees by the phase advance capacitor14b2) flows through the exciting winding14b3, field current (which is produced in the field winding14a2by armature reaction) is rectified by the diode14a1, and rotating field is produced by DC magnetizing the rotor14a, which is rotated by the crankshaft12kof the engine12, to the N-pole and S-pole.

Specifically, the output winding14b1wound around the stator14bthat faces the rotor14ais adapted to cross the flux generated in the rotating field of the rotor14aand produces single-phase AC power as shown at the lower portion ofFIG. 1. The output winding14b1is connected to a load18through a terminal16. A voltage sensor20installed at the output winding14b1produces an output or signal indicative of voltage outputted from the output winding14b1.

The generator10is connected to an Electronic Control Unit (hereinafter simply referred to as “ECU”)22that is constituted as a microcomputer having a CPU, ROM, RAM, I/O (input/output) and other components. An output of the voltage sensor20is sent to the ECU22.

In the engine,12, the AC power generated by the generation coil12pis rectified by a rectification circuit (not shown) and is supplied to the ECU22as operating power, while voltage waveform of the AC power is shaped through a shaping circuit (not shown) and is sent to the ECU22. Based on an output of the rectification circuit, the ECU22detects the engine speed NE. Thus the generation coil12pproduces the output that is synchronous with the engine speed NE.

An output of the exciting coil12qis sent to an ignition circuit12tto be used as power for igniting the ignition plug12i. When it is needed to stop the engine12, the ECU22opens a switch (SW)12uto stop the ignition.

An oil switch (SW)12wis installed near the bottom of an oil pan12vplaced below the piston12jand outputs an ON signal when the oil (lubricant oil) level falls below a point where the oil switch12wis installed. An output of the oil switch12wis also sent to the ECU22.

An operation mode selector switch (SW)24is installed at an appropriate position of the generator10to be operated by the user for selecting one of a constant voltage operation mode and a constant frequency operation mode (explained later). The switch24is provided with a knob for setting required voltage as a desired voltage when the constant voltage operation mode is selected, and with a switch for selecting one of commercial power source frequencies 50 Hz or 60 Hz as a desired frequency when the constant frequency operation mode is selected. An output of the operation mode selector switch24is also sent to the ECU22.

FIG. 2is a block diagram functionally showing the operation of the ECU22shown inFIG. 1. As shown, the ECU22includes an operation mode determination unit22a, predetermined speed storing unit22b, output voltage detection unit22c, engine speed storing unit22d, PID control unit22eand engine speed calculation unit22f.

FIG. 3is a flowchart for showing the operation of the ECU22shown inFIG. 1andFIG. 2.

The operation of the ECU22will be explained mainly referring toFIG. 3.

In S10, it is determined whether the operation mode selected by the operation mode determination unit22ais the constant voltage operation mode, i.e., the operation mode selected by the user using the operation mode selector switch24is the constant voltage operation mode between the two operation modes (the constant voltage operation mode and constant frequency operation mode).

FIG. 4is an explanatory graph showing characteristics of the two operation modes.

In the generator10according to this embodiment, two types of operation modes are prepared which includes the constant voltage operation mode in which the engine speed NE is controlled to a desired speed such that the detected output voltage becomes the desired voltage, and the constant frequency operation mode in which the engine speed NE is controlled to a predetermined speed such that the frequency of the AC power outputted from the output winding14b1becomes a desired frequency.

This will be further explained. As mentioned in the foregoing, since the capacitor-compensation-type generator does not require a brush, slip ring etc., and the structure is simple, it is wide spread in the low-price range. However, in a prior art capacitor-compensation-type generator, as shown inFIG. 5, the output voltage increases/decreases as the engine speed NE increases/decreases and, as shown inFIG. 6, the output voltage also fluctuates as the load increases/decreases, disadvantageously resulting in unstable output voltage. As regards the frequency, it should preferably be constant for a certain load, but this type of generator is not fully satisfactory also on the frequency.

In view of the above, this embodiment is configured such that the speed NE of the engine12can be changed using the throttle motor12sand two types of operation modes are prepared to be selectable by the user.

Returning to the explanation ofFIG. 3, when the result in S10is No, meaning that the constant frequency operation mode is selected, the program proceeds to S12, in which it is determined whether the frequency of 50 Hz is selected as the desired frequency. When the result in S12is Yes, the program proceeds to S14, in which the above-mentioned predetermined speed is determined to be 3000 rpm, while, when the result is No, proceeding to S16, in which it is determined to be 3600 rpm.

In S18, the predetermined speed is set or stored, in S20, the present engine speed NE is detected and in S22, the operation of the throttle motor12sis PID-controlled.

Specifically, the ECU22controls the operation of the throttle motor12sin accordance with the constant frequency operation mode in which the engine speed NE is controlled to the predetermined speed (fixed value: 3000 or 3600 rpm) such that frequency of the AC power outputted from the output winding14b1becomes the desired frequency (50 or 60 Hz).

Explaining further with reference toFIG. 2, when the constant frequency operation mode is selected by the operation mode determination unit22abased on the user's selection, the ECU22selects or determines either one from two kinds of predetermined speed (fixed value) stored in the predetermined speed storing unit22band stores or sets the selected one in the engine speed storing unit22d.

The ECU22then calculates feedback control terms including a P (proportional) term, I (integral) term and D (derivative) term based on an error between the predetermined speed and the engine speed NE calculated or detected from the output of the generation coil12pby the engine speed calculation unit22f, thereby driving the throttle motor12sto open and close the throttle valve12dso as to decrease the error.

Since, as mentioned above, the output of the generation coil12pis synchronized with the engine speed NE, it becomes possible to detect the engine speed NE and to control frequency of the AC power outputted from the output winding14b1to be constant, i.e., 50 or 60 Hz regardless of variation in load, as shown inFIG. 4, by PID-controlling (feedback-controlling) the operation of the throttle motor12sso as to decrease the error between the predetermined speed and the detected engine speed NE.

When the result in S10is Yes, meaning that the constant voltage operation mode is selected, the program proceeds to S24, in which the output voltage is detected, to S26, in which the desired speed is calculated, and to S18onward, in which the throttle motor12sis driven in accordance with the constant voltage operation mode in which the engine speed NE is controlled to the desired engine speed such that the detected output voltage becomes the desired voltage.

Explaining further with reference toFIG. 2, when the constant voltage operation mode is selected by the operation mode determination unit22abased on the user's selection, the ECU22detects the output voltage in the output voltage detection unit22cto calculate the desired speed and stores or sets the calculated speed in the engine speed storing unit22d.

The desired voltage in the constant voltage operation mode is a value set by the user. When the constant voltage operation mode is selected and the desired voltage is set, the PID control unit22ecalculates the desired engine speed so that the detected output voltage converges to the desired voltage. Based on an error between the desired engine speed and the detected engine speed NE, the PID control unit22ecalculates the feedback control terms including the P (proportional) term, I (integral) term and D (derivative) term, thereby driving the throttle motor12sto open and close the throttle valve12dso as to decrease the error.

Thus, since the desired engine speed is calculated so as to converge the detected output voltage to the desired voltage and the feedback control terms including the P (proportional) term, I (integral) term and D (derivative) term are calculated based on the error between the desired engine speed and detected engine speed NE, for PID-controlling or feedback-controlling the throttle motor12sto decrease the error, as shown inFIG. 4, it becomes possible to control voltage of the AC power outputted from the output winding14b1to be constant regardless of variation in load.

As stated above, the embodiment is configured to have a capacitor-compensation-type generator (10) (or method to control the same) having a rotor (14a) wound with a field winding (14a2) that is short-circuited with a diode (14a1), a stator (14b) wound with an output winding (14b1) that is adapted to cross flux generated by the field winding to output AC power and with an exciting winding (14b3) that is disposed at predetermined phase angle with respect to the output winding and is short-circuited with a phase advance capacitor (14b2), and an internal combustion engine (12) that drives the rotor to rotate relative to the stator, comprising: an engine speed detector (power generation coil12p, ECU22, engine speed calculation unit22f, S20) that detects a speed of the engine (NE); an output voltage detector (voltage sensor20, ECU22, output voltage detection unit22c, S24) that detects output voltage of the AC power outputted from the output winding; an actuator (stepper motor12s) that changes the engine speed; and an actuator controller (ECU22, PID control unit22e, S22) that controls operation of the actuator in accordance with one of a constant voltage operation mode in which the detected engine speed NE is controlled to a desired speed such that the detected output voltage becomes a desired voltage (S10to S16), and a constant frequency operation mode in which the detected engine speed is controlled to a predetermined speed such that frequency of AC power outputted from the output winding becomes a desired frequency (S24to S26). With this, the voltage or frequency of the outputted AC power can be made constant.

Specifically, in the case of the constant voltage operation mode, the AC power at constant voltage which is required by the user can be outputted regardless of increase or decrease in load, and in the case of the constant frequency operation mode, the AC power at constant frequency can be outputted regardless of variation in load. Further, the engine speed NE is controlled to be low under low load in the constant voltage operation mode, thereby enhancing fuel efficiency and improving environmental friendliness due to lowered noise level.

The generator (or the method of controlling the same) further includes: an operation mode selector switch (24) adapted to be operated by an user for selecting one of the constant voltage operation mode and the constant frequency operation mode, and the actuator controller controls operation of the actuator in response to the operation mode selected through the operation mode selector switch by the user. With this, in addition to the above-mentioned effects, it becomes possible to follow the user's intention well.

In the generator (or the method of controlling the same), the desired voltage used in the constant voltage operation mode is set by the user and the actuator controller calculates the desired speed such that the detected output voltage converges to the desired voltage when the constant voltage operation mode is selected (S10, S24, S26). With this, in addition to the above-mentioned effects, it becomes possible to output the AC power at constant voltage which is required by the user regardless of increase or decrease in load, thereby enabling to follow the user's intention furthermore.

In the generator (or the method of controlling the same), the predetermined speed used in the constant frequency operation mode is a fixed value set based on the desired frequency and the actuator controller controls the detected speed to the fixed value when the constant frequency operation mode is selected (S10to S22). With this, in addition to the above-mentioned effects, it becomes possible to output the AC power at constant frequency further reliably.

Japanese Patent Application No. 2008-112,109 filed on Apr. 23, 2008, is incorporated herein in its entirety.

While the invention has thus been shown and described with reference to specific embodiments, it should be noted that the invention is in no way limited to the details of the described arrangements; changes and modifications may be made without departing from the scope of the appended claims.