JP2002084795A - Power generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power generator capable of preventing drop in DC output power of a rectifier by inserting a capacitor in series with the output line of a generator. SOLUTION: The power generator comprises a prime mover such as a gas turbine or the like rotating at a high speed, a synchronous generator coupled to the prime mover to generate a high-frequency power, the rectifier for rectifying the power to convert the rectified power into a DC power, and an inverter for converting the DC power into a power of a commercial power frequency to output the power. In this plant, the capacitor is inserted in series with the output line of the generator. A capacity value of the capacitor is that to be cancelled by the reactance voltage of the internal inductance of the generator by a reactance voltage of the capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a rectifier circuit for an output of a synchronous generator that operates using a high-speed gas turbine engine as a drive source.

[0002]

BACKGROUND OF THE INVENTION Relatively small gas turbine engines are:
The generator that rotates at a rotational speed of tens of thousands to several hundred thousand rpm and is directly connected to the gas turbine engine is a permanent magnet synchronous generator that can withstand ultra-high-speed rotation. The output frequency of this generator is a high frequency of about 1 kHz to 3 kHz even if the number of poles is two, and cannot be directly linked to the system of the commercial power supply. Therefore, as shown in FIG.
The generator output is once converted to DC power by a rectifier circuit,
Further, a method of converting the output into an AC output synchronized with the frequency of the commercial power supply of 50/60 Hz by an inverter and linking the AC output to the system is adopted. The filter is used to remove the switching ripple from the PWM waveform of the inverter and to output a sine waveform.

Further, a diesel engine or a reciprocating engine using gas as a fuel may be used as a prime mover instead of a gas turbine engine. In this case, the rotation speed of the prime mover is 1500 rpm to 1800 r for small and medium capacity models.
In general, medium-speed rotation of about pm is used, and lower-speed rotation is generally used for large-capacity models.

[0004]

However, when the output of the generator is rectified by the above-described method, there is a problem that a voltage drop occurs due to the reactance voltage of the internal inductance of the generator, and the DC output voltage of the rectifier circuit decreases. Was.

[0005] For example, in a permanent magnet type synchronous generator designed for a gas turbine engine, the reactance voltage of the internal inductance is 0.4 pu (per unit, a value with respect to a reference value of voltage, current or electric power), and each of the rated values is 1 pu. ), And the rated voltage drops by about 25% at the rated load. Further, in a synchronous generator used together with a low-medium-speed rotation prime mover, an IPM (Interior Perm) in which a permanent magnet is embedded inside the rotor.
In the synchronous magnet generator, the reactance voltage of the internal inductance is 0.5 pu or more, and in the wound field synchronous generator, the reactance voltage of the internal inductance is 1 pu or more. The DC voltage drops further than the generator.

As described above, when a shortage of the DC voltage occurs, the output voltage waveform is distorted. Therefore, it is necessary to set the DC voltage to be higher than the peak value of the output voltage.
For this reason, conventionally, the distortion of the output voltage waveform has been dealt with by increasing the open-circuit voltage of the generator and increasing the withstand voltage of the semiconductor element of the rectifier circuit or the inverter circuit by one rank. However, in order to increase the open-circuit voltage of the generator, it is necessary to increase the ratio of expensive permanent magnets, and there is a problem that the cost of the entire generator increases. In addition, when the ratio of the permanent magnet is increased, the size of the rotor must be increased, and not only does the strength withstanding the centrifugal force decrease, but also the maximum number of revolutions is limited. There was a problem that the purpose of reducing the size and weight could not be achieved.

In addition, it is necessary to increase the rated voltage of semiconductor elements and other main components of the rectifier circuit and the inverter circuit, and there is a problem that the cost of the apparatus increases.

The present invention has been made under such a background, and a rectifier circuit is provided by inserting a capacitor having a capacity for canceling a reactance voltage due to an internal inductance of the generator in series with an output line of the generator. It is an object of the present invention to provide a power generator capable of preventing a decrease in DC output voltage.

[0009]

In order to solve the above-mentioned problems, a prime mover, a generator directly connected to the prime mover to generate AC power, and a rectifier circuit for rectifying the AC power and converting the AC power to DC power are provided. In a power generator including an inverter that converts the DC power into AC power of a desired frequency and outputs the converted power, a capacitor is serially retrofitted on the output side of the generator.

In order to solve the problem, it is desirable to provide a prime mover rotating at high speed or a synchronous generator rotating at high speed.

The output of the inverter is AC power at the frequency of a commercial power supply, and it is desirable that the output of the inverter and the commercial power supply be system-linked.

The capacitance value of the capacitor may be equal to or smaller than the capacitance value at which the reactance voltage of the capacitor is canceled by the reactance voltage due to the internal impedance of the generator. desirable.

The generator can be used as a starting motor at the time of starting the prime mover by using the AC power supplied through the inverter, and the prime mover uses a gas turbine engine, a diesel engine, and gas as fuel. Desirably, one of the reciprocating engines.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a single-line diagram showing a configuration of a power generator according to an embodiment of the present invention.
FIG. 2 is an equivalent circuit diagram around the output of the generator. In FIG. 1, reference numeral 1 denotes a gas turbine engine, which drives a directly connected generator 2 to generate electric power. This gas turbine engine 1 has tens of thousands to several hundred thousand rpm.
Therefore, the frequency of the electric power generated by the generator 2 is 1 kHz to 3 kHz even if the number of poles is two.
The frequency is as high as z, and cannot be directly linked to the system of the commercial power supply.

Thus, a method is employed in which the generated high-frequency power is converted into commercial-frequency power by the power converter 3 and linked to a commercial power supply system. The power converter 3 has a capacitor C1 interposed in series with the output line of the generator 2, converts it into DC power by the rectifier circuit 4, smoothes it with the smoothing capacitor C, and then detects the DC component of the current. The current is detected by DCCT, converted into a commercial frequency power containing no DC component by the inverter 5, and output via the filter 6.

Next, a method of starting the gas turbine engine 1 of the power generator will be described. A starting power supply 12 prepared in advance is applied to the rectifier circuit 4 through a circuit breaker CB3 to be converted into a direct current, and AC power is applied to the generator 2 through a circuit breaker CB4 by an inverter 5. At this time, the generator 2 operates as a starting motor, and drives and starts the gas turbine engine 1. The control circuit 7 controls the voltage and frequency of the electric power applied to the generator 2 to desired values until the gas turbine engine 1 ignites and reaches a rotational speed at which the gas turbine engine 1 can operate independently. At this time, the circuit breakers CB1 and CB2 are turned off.

FIG. 2 is a diagram showing an equivalent circuit of the generator 2 and the rectifier circuit 4 of the power converter 3 of FIG. In this figure, E represents the open-circuit generated voltage of the generator 2, R1 represents the internal resistance, and L1 represents the internal inductance. Since the synchronous generator has a large internal inductance L1, when a current flows, the reactance voltage drop due to the inductance L1 increases, and the DC output voltage of the rectifier circuit 4 decreases.

Therefore, the capacitor C1 is inserted in series with the output line of the generator 2 to cancel the voltage drop due to the internal inductance L1. Internal inductance L1
When the power generation frequency of the generator is fHz, the combined impedance Z of the capacitor C1 becomes Z = 2πfL1− (1 / 2πfC1), and the impedance Z can be made zero by selecting the capacitance value of the capacitor C1. The decrease in the output DC voltage of the circuit 4 can be minimized.

In the actual machine, when the capacitance value of the capacitor C1 is smaller than the calculated value due to the characteristics of the rectifier circuit 4,
DC voltage drop is minimized. FIG. 3 shows an example of output power-DC voltage characteristics in an actual machine. Note that the unit pu (per unit) of the output voltage and the DC voltage in this figure represents a ratio to a rated value. In this figure, the DC voltage at the rated output is reduced by 25% in the circuit according to the prior art without the capacitor C1, but the DC voltage at the rated output is reduced in the circuit according to the embodiment of the present invention in which the capacitor C1 is inserted into the output line. The decrease is suppressed to 1%.

Focusing on the output current of the generator, in the circuit according to the embodiment of the present invention in which the capacitor C1 is inserted in the output line as shown in FIG. 4, the current of the generator at rated output is reduced by 30%. It represents what was done. For this reason, the efficiency of the device is improved, which can contribute to reduction in size and weight.

Next, another embodiment of the present invention will be described with reference to FIG. The basic operation of this embodiment is the same as that of the above-described embodiment, but the method of starting the gas turbine engine 1 is different. Instead of using a smoothing capacitor for smoothing the DC output of the rectifier circuit 4, a battery 8 is connected instead. When starting the gas turbine engine 1, the electric power of the battery 8 is converted into an alternating current by the inverter 5, and this electric power is applied to the generator 2 to start the gas turbine engine 1.

The operation of one embodiment of the present invention has been described above in detail with reference to the drawings. However, the present invention is not limited to this embodiment, and a design change or the like may be made without departing from the gist of the present invention. The present invention is also included in the present invention. For example, instead of a gas turbine engine mainly using a prime mover for driving a generator for high-speed rotation, a diesel engine mainly used for low-medium-speed rotation or a reciprocating engine using gas as fuel may be used.

[0023]

As described above, according to the present invention, the following effects can be obtained. a. Since the inductive reactance voltage drop generated by the internal inductance of the generator is offset by the capacitive reactance voltage of the capacitor inserted in the output line, it is possible to prevent a decrease in the DC voltage under load. b. Therefore, the circuit voltage of the generator can be designed low,
The amount of the field permanent magnet used can be reduced. c. For this reason, since the rotor of the generator can be downsized, the maximum rotation speed can be increased, and the generator can be reduced in size and weight. d. In addition, since the maximum value of the DC voltage can be designed to be low, a semiconductor or a smoothing capacitor having a low rated voltage can be selected. e. Furthermore, since the current of the generator can be reduced, the copper loss of the generator is reduced. Further, since the open circuit voltage of the generator can be reduced, iron loss of the generator is reduced. Therefore, the efficiency of the generator can be improved. f. There is no reactive power generated by the internal inductance of the generator, and the permanent magnet for the field is not demagnetized. Therefore, it is not necessary to take measures against demagnetization of the permanent magnet, and the thickness of the permanent magnet can be reduced. Therefore, the amount of the permanent magnet used can be reduced, and the cost of the generator can be reduced. g. When the prime mover is started, the configuration of the device can be simplified by using the generator as the starting motor.

[Brief description of the drawings]

FIG. 1 is a single-line diagram showing a configuration of a power generator according to an embodiment of the present invention.

FIG. 2 is a diagram showing an equivalent circuit up to a rectifier circuit of a generator and a power converter.

FIG. 3 is a diagram showing an example of output power-DC voltage characteristics in an actual device.

FIG. 4 is a diagram showing an example of output power-current characteristics of a generator.

FIG. 5 is a single-line diagram showing a configuration of a power generator according to another embodiment of the present invention.

FIG. 6 is a single-line diagram showing a configuration of a power generation device according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Gas turbine engine 2 ... Generator 3 ... Power converter 4 ... Rectifier circuit 5 ... Inverter 6 ... Filter 7 ... Control circuit 8 ... Battery 11 ... Angle sensor 12 ... Power supply for starting C ... Smoothing capacitor C1 ... Compensation capacitor CB1, CB2, CB3, CB4: Circuit breaker DCCT: Current transformer PT: Transformer

Claims (9)

[Claims] 1. A prime mover, a generator directly connected to the prime mover to generate AC power, a rectifier circuit for rectifying the AC power and converting the DC power to DC power, and converting the DC power to AC power of a desired frequency. A power generator, comprising: an inverter that outputs the power to the generator; and a capacitor is inserted in series on the output side of the generator. 2. The power generator according to claim 1, wherein the prime mover rotates at a high speed. 3. The power generator according to claim 1, wherein the generator is a synchronous generator that rotates at a high speed. 4. The inverter according to claim 1, wherein an output of said inverter is AC power of a commercial power supply frequency.
The power generator according to any one of the above. 5. The power generator according to claim 1, wherein the output of the inverter and a commercial power supply are linked to each other. 6. The capacitor according to claim 1, wherein the capacitance value of the capacitor is a capacitance value at which a reactance voltage by the capacitor is offset by a reactance voltage by an internal inductance of the generator. Power generator. 7. The capacitor according to claim 1, wherein a capacitance value of the capacitor is smaller than a capacitance value at which a reactance voltage due to the capacitor is offset by a reactance voltage due to an internal inductance of the generator. The power generator according to any one of the above. 8. The power generator according to claim 1, wherein the generator can be used as a starting motor at the time of starting the prime mover by AC power supplied through the inverter. apparatus. 9. The power generator according to claim 1, wherein the prime mover is any one of a gas turbine engine, a diesel engine, and a reciprocating engine using gas as fuel.