JP2008160980A - Induction generator start-up method - Google Patents

Description

  The present invention relates to a distributed power source that supplies power to an electric power system by driving the induction generator by wind power, thermal power, an engine, or the like, and in particular, an inrush current that occurs when the induction generator is connected to the electric power system. The present invention relates to an induction generator starting method that can be suppressed.

FIG. 4 shows a conventional example disclosed in Patent Document 1, for example.
That is, in FIG. 4, when the rotational speed of the induction generator 2 is made higher than the rated speed (corresponding to the frequency of the power system voltage), the active power can be supplied to the power system 1. On the other hand, if the rotational speed is lower than the rated rotational speed, the active power is supplied from the power system 1 to the induction generator 2.
In such a system, in order to start the induction generator 2, a circuit breaker 4 and a variable reactive power generator 3 are provided between the power system 1 and the induction generator 2. As the variable reactive power generator 3, a capacitor and a reactor are used, or an inverter is used.

Then, when starting the induction generator 2, with the circuit breaker 4 open, using an external means such as an engine (not shown), the induction generator 2 is rotated to the synchronous speed, and the voltage of the induction generator 2 is increased. When the reactive power generated by the variable reactive power generator 3 is adjusted so as to be equal to the voltage of the power system 1, and when the phase angle of the induction generator 2 and the phase angle of the voltage of the power system 1 substantially coincide, 4 is turned on to suppress the inrush current.
JP 2005-117879 A

  In the example of FIG. 4, in order to suppress the inrush current of the induction generator, it is necessary to generate a voltage having the same frequency and magnitude as the voltage of the power system before connecting to the power system. Is adjusted by external means such as an engine, and the size is adjusted by the reactive power from the reactive power generator from the variable reactive power generator. Since the variable reactive power generator 3 uses an inverter or a capacitor and a reactor, it is easy to control the reactive power. However, the external reactive means such as the engine controls the frequency to be the same as the power system voltage. It is difficult.

  For this reason, conventionally, the circuit breaker 4 is turned on when the phase angle of the voltage of the induction generator and the voltage of the power system substantially coincide. As a result, the phase angle shifts due to the delay time from when the closing command is given to the breaker until the breaker is actually turned on, and an excessive current flows due to the difference between the induction generator voltage and the power system voltage. May cause equipment damage. In addition, since the circuit breaker cannot be turned on until the phase angles are almost the same, it may take a long time for the induction generator to connect to the power system after the operation command is input. obtain.

  Accordingly, an object of the present invention is to prevent an excessive inrush current from flowing when the induction generator is connected to the power system, and to shorten the time required to reach the connection.

  In order to solve such a problem, in the invention of claim 1, a circuit breaker between the power system and the induction generator is provided for an induction generator that supplies power to a load connected to the power system. In parallel, when a rectifier that converts AC power on the power system side to DC power and an inverter that converts the DC power to AC power on the induction generator side are connected to the induction generator, Calculate the amount of current to make the induction generator voltage equal to the power system voltage with the generator rotating at the rated speed or less based on the power system voltage and the induction generator voltage. Is connected to the power system after flowing from the inverter.

  According to the present invention, when the induction generator is linked to the power system, the current calculated based on the difference between the power system voltage and the induction generator voltage in a state where the induction generator is rotated at the rated rotation speed or less. Is allowed to flow from the inverter to the induction generator to make the induction generator voltage the same as the power system voltage. As a result, the induction generator can be stably linked to the power system without causing an excessive inrush current.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, 5 and 6 are voltage detectors, 7, 8 and 11 are coordinate converters, 9 and 10 are voltage regulators, 12 is a current regulator, 13 is a ramp function generator, 14 is an oscillator, and 15 is a multiplier. , 16 is a rectifier, and the others are the same as in FIG. Hereinafter, the differences will be mainly described.
That is, the inverter 3 and the rectifier 16 are connected in parallel with the circuit breaker 4 inserted between the electric power system 1 and the induction generator 2. When the induction generator 2 is connected to the power system 1, the rectifier 16 supplies DC power to the inverter 3, and the inverter 3 converts the DC power into AC power.

  The voltage detector 6 detects the power system voltages Vsa, Vsb, Vsc, while the voltage detector 5 detects the induction generator voltages Vga, Vgb, Vgc. The system voltages Vsa, Vsb, Vsc are multiplied by the ramp function from the function generator 13 in the multiplier 15 to become outputs Vsa ', Vsb', Vsc 'as shown in FIG. This is because the power system voltage detection value is slowly changed from zero voltage to the rated voltage so as not to change the output voltage of the inverter 3 abruptly.

The coordinate converter 7 performs three-phase to two-phase conversion on the outputs Vsa ′, Vsb ′, and Vsc ′ of the multiplier 15 according to the following equation (1) expressed by Equation 1.

Next, from the obtained two-phase amount, coordinate axis conversion is performed by the following equation (2) expressed by Equation 2 to obtain Vsd and Vsq.

Similarly, the coordinate converter 8 performs three-phase to two-phase conversion on the output voltage detection values Vga, Vgb, and Vgc of the detector 5, and performs coordinate axis conversion from the obtained two-phase amount by the above equation (2). To obtain Vgd and Vgq.
Thereafter, the difference between Vsd and Vgd and the difference between Vsq and Vgq are respectively obtained and input to voltage regulators 9 and 10 each composed of a gain, an integral element, etc., so that current commands Id and Iq of inverter 3 are obtained. Get.

The coordinate converter 11 performs coordinate conversion of the following formula (3) shown in Equation 3.

Next, the coordinate converter 11 performs two-phase to three-phase conversion according to the following equation (4) expressed by Equation 4 to obtain three-phase current command values Ia, Ib, and Ic.

  Then, the current regulator 12 adjusts and calculates the three-phase current detection value separately detected through the current transformer so as to coincide with the three-phase current command value output from the coordinate converter 11, thereby the inverter. 3 is obtained, and a current according to the three-phase current command value is supplied to the induction generator 2. In the above equations (2) and (3), cos θ and sin θ are phase angles calculated by the oscillator 14 on the basis of the power system voltage, cos θ is a component in phase with the power system voltage, and sin θ is calculated from the power system voltage. Each component with a 90 ° phase delay is shown.

A function generator 13 provided between the power system voltage detector 6 and the coordinate converter 7 is a power system voltage that is an output of the detector 6 in the multiplier 15 so that the inverter 3 does not output a sudden voltage. By multiplying the detection value by the ramp function, for example, as shown in FIG. 2, it is provided to obtain a voltage that rises from 0 to 100% at a constant rate.
When the induction generator 2 is connected to the power system 1 with the above-described configuration, the rotation speed of the induction generator 2 is set to the electric power by an external means such as an engine (not shown) with the circuit breaker 4 in the “open” state. The frequency is controlled to be equal to or lower than the frequency of system 1.

  For example, as shown in FIG. 3A, the rotational speed of the induction generator 2 is controlled with the rated speed as a target. However, since external means such as an engine cannot be controlled at high speed, speed fluctuation occurs. Here, when the rated speed is exceeded, the effective power flows from the induction generator 2 into the inverter 3, thereby increasing the DC voltage of the inverter 3. Since the rectifier 16 cannot return the active power to the power system 1, as shown in FIG. 3B, the rotational speed of the induction generator 2 is kept below the rated rotational speed including fluctuations.

  Next, the inverter 3 is operated, and current is output to the induction generator 2 so that the difference between the power system voltage and the induction generator voltage becomes zero as described above. When 100% of the power system voltage is output from the multiplier 15, the induction generator voltage becomes the same as the power system voltage. After that, the circuit breaker 4 is “closed” so that it can be connected to the system. Here, since the rotational speed of the induction generator is lower than the power system voltage frequency, the active power is supplied from the inverter 3 to the induction generator 2 via the rectifier 16. This amount of active power is determined in relation to the difference between the rotational speed of the induction generator and the power system voltage frequency. However, since the rotational speed control error of the induction generator is about 1%, the capacity of the inverter 3 is significantly increased. It is not the amount to do.

  As described above, the magnitude and frequency of the induction generator can be controlled to be the same as the power system voltage, and then the inrush current can be suppressed by turning on the circuit breaker 4. It becomes possible. In FIG. 1, since the rectifier 16 can be a diode or a thyristor rectifier, it can be configured at a lower cost than an inverter using an IGBT or the like. That is, in consideration of the case where there is power regeneration from the induction generator to the power system due to fluctuations in the rotational speed of the induction generator, the present applicant has filed an application that uses an inverter instead of the rectifier of FIG. (Japanese Patent Application No. 2006-224004: Proposed Method) can provide a lower cost activation method than that of the proposed method.

Block diagram showing an embodiment of the present invention Waveform diagram showing an example of the multiplier output shown in FIG. Waveform diagram for explaining the operation of the present invention Block diagram showing a conventional example

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electric power system, 2 ... Induction generator, 3 ... Inverter, 4 ... Circuit breaker, 5, 6 ... Voltage detector, 7, 8, 11 ... Coordinate converter, 9, 10 ... Voltage regulator, 12 ... Current regulation 13 ... Ramp function generator, 14 ... Oscillator, 15 ... Multiplier, 16 ... Rectifier.

Claims (1)

  A rectifier that converts AC power on the power system side to DC power in parallel with a circuit breaker between the power system and the induction generator for an induction generator that supplies power to a load connected to the power system. And an inverter that converts the DC power into AC power on the induction generator side, and when the induction generator is connected to the power system, the induction generator is rotated with the induction generator rotating at a rated speed or less. A current amount for making the machine voltage equal to the power system voltage is calculated based on the power system voltage and the induction generator voltage, and the calculated current amount is supplied from the inverter and then linked to the power system. Induction generator starting method.

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