JP4271090B2 - Three-phase inverter for parallel generator operation - Google Patents

Description

  The present invention relates to a three-phase inverter device for parallel generator operation, which is connected to an output power source of a three-phase generator driven by a prime mover and performs parallel operation by controlling the balance of output active power between the generator and the inverter. Is.

  When DC active power is converted to AC power by a three-phase inverter and connected to another power source to control output active power in parallel operation, the inverter's three-phase output current is converted to active current and reactive current. A method of controlling active power by separating and controlling each is known.

However, it is completely independent of other systems, and in a power supply system with only a limited load, when the generator and inverter outputs are connected and operated in parallel, more power is output than the load. Then, the generator is driven by the electric power from the inverter. For this reason, there is a method in which a current detector is provided at the output of the generator to detect the effective current from the generator, and the output voltage of the inverter is controlled so that the effective current is positive and equal to or higher than a reference value. . (For example, refer to Patent Document 1).
However, in this method, it is necessary to provide a detection circuit for detecting the effective current of the generators that are operated in parallel, and there is a problem that the generator cannot be stopped and the inverter cannot be operated alone.

  As an improvement measure for the above problem, the inverter does not perform current control, the frequency command is increased / decreased by an external command, the inverter output active power is detected, and the frequency command is drooped by this active power, so that the inverter output power The method of controlling can be considered. FIG. 2 is an explanatory diagram of a method for controlling the output power of the inverter based on the above method. In FIG. 2, 1 is a DC power source, 2 is a three-phase inverter, 3 is a current detector, 4 is a three-phase reactor, 5 is a voltage detection transformer, 6 is a three-phase AC generator, 7 is a load, and 11 is a reference frequency adjustment. , 12 is an active power calculator, 13 is a droop amount calculator, and 14 is a subtractor.

When the active power output from the inverter is increased while the output inverter 2 and the generator 6 are operating in parallel, the reference frequency command is gradually increased by inputting the frequency increase command to the reference frequency adjuster 11. By making the output frequency of the three-phase inverter 2 larger than the frequency of the generator 6, the phase of the output voltage of the three-phase inverter 2 changes from the output voltage of the generator 6 toward the leading side. For this reason, the phase of the voltage applied to both ends of the three-phase inductance 4 changes toward the advance side with respect to the phase of the output voltage of the generator 6. On the other hand, since a current 90 degrees behind the voltage applied to both ends of the three-phase inductance 4 flows, the effective current component having the same phase as the output voltage of the generator 6 increases. . As the active current increases, the active power calculated by the active power calculator 14 also increases, and the droop rate calculated by the droop rate calculator 15 also increases, so the frequency command decreases by the droop rate. When the output frequency of the inverter coincides with the generator frequency due to the increase in the droop rate, the phase of the voltage applied to both ends of the inductance 4 with respect to the output voltage of the generator 7 does not change, and the active power does not increase any more. Therefore, the active power can be controlled by the difference between the reference frequency command and the output frequency of the generator 7, and the power sharing ratio between the three-phase inverter 2 and the generator 6 is adjusted by increasing or decreasing the reference frequency command. be able to.
However, in this method, when the output frequency of the generator 6 vibrates, there is a problem that the control of the active power cannot follow and the control of the active power cannot be performed.

Japanese Patent Laid-Open No. 5-130741

  The problem to be solved is that the active power cannot be controlled when the frequency of the connected generator fluctuates.

A three-phase inverter that converts a DC power source into a three-phase AC power source, a reference frequency adjuster that adjusts the reference frequency of the inverter with an increase signal and a decrease signal, a three-phase reactor attached to the output of the inverter, and the three-phase reactor An active power calculator that calculates the output active power of a phase inverter and a three-phase AC generator that is driven by a prime mover to generate a three-phase AC power source. The output of the three-phase reactor and the output of the three-phase AC generator In the three-phase inverter device for generator parallel operation, which is configured to be connected to the load together and perform parallel operation,
The frequency command of the inverter is a value obtained by subtracting a value proportional to the output active power of the inverter from the reference frequency, and the phase difference between the phase of the inverter and the phase of the generator is the value of the generator from the frequency command. It has a phase difference controller for controlling the output frequency of the inverter so as to become a phase difference command obtained by integrating a value obtained by subtracting the average frequency.

  By comprising like this invention, even when the output frequency of a generator fluctuates, it becomes possible to control the active power of a three-phase inverter stably.

  The purpose of stably controlling the active power of the three-phase inverter was realized simply by using a phase difference controller.

  FIG. 1 is a block diagram showing an embodiment of the apparatus of the present invention, wherein 1 to 7 and 11 to 14 are the same as FIG. Further, 15 is an average frequency calculator, 16 is a subtracter, 17 is an integrator, 18 is a phase detector, and 19 is a phase difference controller.

  The reference frequency adjuster 11 gradually increases or decreases the reference frequency based on the given frequency increase signal and frequency decrease signal. The active power calculator 12 calculates the output active power of the three-phase inverter 2 from the current detected by the current detector 3 and the voltage detected by the voltage detection transformer 5. The droop amount calculator 13 calculates a droop amount proportional to the calculated active power. The subtracter 14 calculates a frequency command by subtracting the amount of droop from the reference frequency. The average frequency calculator 15 calculates the average frequency of the generator 6 using the voltage detected by the voltage detection transformer 5 and a low-pass filter. The subtracter 16 calculates the difference between the frequency command and the average frequency by subtracting the average frequency from the frequency command. The integrator 17 calculates the phase difference command by integrating the difference between the frequency command and the average frequency. The phase detector 18 calculates the output voltage phase of the generator 6 from the voltage detected by the voltage detection transformer 5. The phase difference controller 19 multiplies the value obtained by subtracting the phase difference command from the difference between the output voltage phase of the three-phase inverter 2 and the output voltage phase of the generator 6 and adds the gain to the output frequency. Calculate the output frequency of the three-phase inverter.

When increasing the effective power of the three-phase inverter, the reference frequency is gradually increased by a frequency increase command. When the frequency command increases due to the increase of the reference frequency, the difference between the frequency command and the average frequency of the generator increases, and the phase difference command obtained by integrating this increases. Since the phase difference controller controls the phase difference between the output voltage phase of the three-phase inverter and the output phase of the generator, that is, the phase difference between both ends of the three-phase reactor 4, to follow the phase difference command. The phase difference of the reactor 4 advances and increases to the phase side. Since a three-phase reactor 4 has a 90-degree phase lag current with respect to the voltage applied across it, the active current component in the same phase increases with respect to the generator voltage, and the effective power of the three-phase inverter increases. . As the active power increases, the droop amount calculated by the droop amount calculator 13 increases and the frequency command is drooped. Therefore, when the active power increases and the frequency command matches the average frequency of the generator, the phase difference command Since the increase stops, the active power does not increase any more. Therefore, the active power can be controlled by the difference between the reference frequency command and the average frequency of the generator, and the power sharing ratio between the three-phase inverter 2 and the generator can be adjusted by increasing or decreasing the reference frequency command. it can.

  When there is a fluctuation in the frequency of the generator, the time constant of the low-pass filter of the average frequency calculator is made sufficiently longer than the fluctuation period, and the gain in the phase difference controller sufficiently follows the fluctuation. By setting to, active power can be controlled without being affected by frequency fluctuations.

  In addition, in order to increase the active power on the generator side, even when the generator frequency is controlled to increase, the difference between the reference frequency and the average frequency of the generator is small, so the phase difference command is As a result, the output active power of the three-phase inverter is reduced. Therefore, by setting the proportional amount in the droop amount calculator so that the drooping characteristic with respect to the active power is the same as that of the generator, the output active power of the three-phase inverter is increased according to the decrease in the output power of the generator. Therefore, balanced control is possible.

  By configuring in this way, even when performing parallel operation with a generator whose output frequency varies, a three-phase inverter for generator parallel operation that can easily perform active power balance control with a reference frequency increase / decrease command An apparatus can be realized.

It is the block diagram which showed the Example of this invention. Example 1 It is the block diagram which showed an example of background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply 2 Three-phase inverter 3 Current detector 4 Three-phase reactor 5 Voltage detection transformer 6 Three-phase AC generator 7 Load 11 Reference frequency adjustment part 12 Active power calculator 13 Droop amount calculator 14 Subtractor 15 Average frequency calculator 16 subtractor 17 integrator 18 phase detector 19 phase difference controller

Claims (1)

A three-phase inverter that converts a DC power source into a three-phase AC power source, a reference frequency adjuster that adjusts the reference frequency of the inverter with an increase signal and a decrease signal, a three-phase reactor attached to the output of the inverter, and the three-phase reactor An active power calculator that calculates the output active power of a phase inverter and a three-phase AC generator that is driven by a prime mover to generate a three-phase AC power source. The output of the three-phase reactor and the output of the three-phase AC generator In the three-phase inverter device for generator parallel operation, which is configured to be connected to the load together and perform parallel operation,
The frequency command of the inverter is a value obtained by subtracting a value proportional to the output active power of the inverter from the reference frequency, and the phase difference between the phase of the inverter and the phase of the generator is the value of the generator from the frequency command. A three-phase inverter device for generator parallel operation, comprising a phase difference controller for controlling an output frequency of the inverter so as to obtain a phase difference command obtained by integrating a value obtained by subtracting an average frequency.

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