JP4247835B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device that operates in conjunction with a grid.

  In recent years, applications such as a photovoltaic power generation system in which a power conversion device is installed in conjunction with an electric power system and control of reactive power and harmonics of the system as well as transmission and reception of active power with the system have been expanded.

When a power converter such as an inverter is operated in conjunction with the system, it is important to control the output voltage in balance with the system as well as to adjust the output frequency of the inverter to the frequency of the system.

  An ordinary commercial power system is often a stable and strong system with low system impedance. In this case, stable operation can be achieved if the power conversion device linked to the system performs operation following the frequency and voltage of the system. However, some contrivance is required when linking with an unstable system having a relatively high system impedance and a short-circuit capacity.

As a countermeasure, there has been proposed a control method that feeds back the output voltage of the power converter and supplies a stable voltage (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-146564 (page 2-5, FIG. 1)

  However, the control method proposed in Patent Document 1 may be effective in preventing overcurrent when the system voltage suddenly changes, but the system voltage and frequency are disturbed due to fluctuations in the system load. However, in order to follow the fluctuations, there was a problem of increasing instability.

  The present invention has been made in view of the above, and an object thereof is to appropriately convert system tracking and independent control from the system according to the strength of the system, and to perform power conversion that enables stable system linkage. To provide an apparatus.

  In order to achieve the above object, the power conversion device of the present invention is a power conversion device that is connected to a grid and exchanges at least one of active power, reactive power, and harmonics between the grids. A first voltage reference proportional to a system voltage to which the power conversion apparatus is connected, a second voltage reference having a constant amplitude generated in synchronization with the system voltage, and active power control. The control is performed in accordance with a combined voltage reference obtained by combining a third voltage reference that is at least one control output of reactive power control and harmonic control.

  In the present invention, the output voltage reference is determined by combining the system voltage, the reference voltage generated in synchronization with the system, and the control output. Therefore, stable operation is possible even in a so-called weak system with a small short-circuit capacity. The power converter device which can be continued can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  Embodiment 1 of the present invention will be described below with reference to FIG. FIG. 1 is a block diagram of a power converter according to the present invention.

  The AC output of the inverter 1 is connected to the transformer 3 via the current detector 12. The output of the transformer 3 is connected to the system 2. In order to realize grid connection, devices such as circuit breakers are usually connected, but the illustration is omitted here. Each signal line is usually composed of two phases (two lines) or three phases (three or four lines), but in FIG.

  The voltage detector 11 is connected to the output of the inverter 1 and detects the voltage of the system 2 at the point where the inverter 1 is connected. The output of the voltage detector 11 is connected to the synchronous detector 13 and the amplifier 14. The synchronization detector 13 detects the frequency and phase of the voltage of the system 2 at the point where the inverter 1 is connected, creates a synchronization phase signal, and supplies it to the reference generator 17 and the current controller 18 as a phase reference. The synchronization detector 13 generates a reference sine wave signal having a constant voltage amplitude in synchronization with the system 2, and supplies this to the amplifier 15.

  The output of the amplifier 15 and the output of the amplifier 14 are added by an adder 16 and used as one input of an inverter control device 19. The inverter control device 19 performs so-called pulse width modulation control and the like with the input signal as a reference, and generates a gate pulse for driving the inverter 1.

  On the other hand, the reference generator 17 generates a current reference signal that becomes a reference for outputs such as active power, reactive power, and harmonics, according to the purpose of use of the inverter 1. This signal generation is performed based on the synchronization phase signal given from the synchronization detector 13. A signal synthesized by the output of the reference generator 17 and the output of the current detector 12 is input to the current controller 18. Normally, the difference between the output of the reference generator 17 and the output of the current detector 12 is simply used. The current control device 18 converts the current signal of the above difference into a control voltage reference using the synchronous phase signal given from the synchronous detector 13 as a reference, and uses it as the other input of the inverter control device 19.

  The inverter 1 performs control such that the output voltage of the inverter 1 is equal to the voltage of the system 2 in the state where there is no output current in order to perform grid connection stably. By adding the output of the voltage detector 11 to the output of the current control device 18 and inputting it to the inverter control device 19, the output voltage of the inverter 1 is equal to that of the system 2 when the output of the current control device 18 is zero. It becomes possible to be.

  With the above configuration, the output voltage of the inverter 1 is obtained by multiplying the output of the voltage detector 11 (the voltage, phase, frequency, and voltage amplitude of the system 2 are equivalent) by the gain of the amplifier 14 and the output of the synchronous detector 13. Is controlled by a voltage reference obtained by adding a reference sine wave (having the same phase and frequency as system 2 and constant amplitude) to the gain of amplifier 15 and the output of current control device 18. Therefore, if the gains of the amplifier 14 and the amplifier 15 are appropriately selected according to the strength of the system, it is difficult to be affected by the distortion and disturbance of the system, and the operation is stable regardless of the resonance condition of the system. A configuration of a power conversion device that can do this is possible. For example, if the gain of the amplifier 14 is set to zero, the control element that follows the system voltage becomes zero.

  In addition, although the direct current circuit of the inverter 1 is described as a mere capacitor in FIG. 1, the configuration of various power sources, batteries, power generation devices, rotating devices / power generation devices with an AC → DC power conversion device, etc. You may have.

  As described above, according to the configuration of the present invention, a so-called grid interconnection inverter device can be stably operated even when it is connected to a weak system having severe resonance conditions.

  FIG. 2 is a block diagram showing a second embodiment of the power conversion apparatus according to the present invention. About each part of this Example 2, the same part as each part of the power converter device which concerns on Example 1 of FIG. 1 is shown with the same code | symbol, and the description is abbreviate | omitted. The second embodiment is different from the first embodiment in that a gain adjusting device 20 that receives the detection signal of the voltage detector 11 is added and its output is supplied to the amplifier 14 and the amplifier 15.

  According to the present embodiment, the constants of the amplifier 14 and the amplifier 15 are adjusted (mainly increased or decreased) by the output of the gain adjusting device 20. The gain adjusting device 20 adjusts the gains of the amplifier 14 and the amplifier 15 by a preset evaluation function according to the output of the voltage detector 11 reflecting the state of the system 2.

  The evaluation function of the gain adjusting device 20 is selected as follows, for example. That is, when the output of the voltage detector 11 is stable, the gain of the amplifier 14 is increased and the gain of the amplifier 15 is decreased to control the output voltage of the inverter 1 so as to follow the voltage of the system 2. . On the contrary, when the output of the voltage detector 11 becomes unstable, the gain of the amplifier 14 is lowered, the gain of the amplifier 15 is raised to follow the fluctuation of the system 2, and the original output voltage of the system 2 is maintained. To be controlled.

  The gain adjusting device does not necessarily need to be automatically operated by the output of the voltage detector 11, but detects the linkage status between the system 2 and the inverter 1 by another method, and changes the output according to the detection result. May be.

  As described above, according to the configuration of the present invention, it is always optimally adjusted according to the situation of the system, is hardly affected by distortion and disturbance of the system, and operates stably regardless of the resonance condition of the system. It is possible to configure a power conversion device that can Therefore, even when a so-called grid interconnection inverter device is connected to a weak system having severe resonance conditions or the like, the inverter device is always optimally adjusted according to the situation of the system and can be operated stably.

  FIG. 3 is a block diagram showing a third embodiment of the power conversion apparatus according to the present invention. About each part of this Example 3, the same part as each part of the power converter device which concerns on Example 2 of FIG. 2 is shown with the same code | symbol, and the description is abbreviate | omitted. The third embodiment is different from the second embodiment in that a waveform distortion detection device 21 that receives the detection signal of the voltage detector 11 is added and its output is given to the gain adjustment device 20.

  In the present embodiment, the waveform distortion status of the system 2 detected by the waveform distortion detection device 21 based on the output of the voltage detector 11 is input, and the output of the gain adjustment device 20 is determined. The gains of the amplifier 14 and the amplifier 15 are adjusted by the output of the gain adjusting device 20.

  What is detected by the waveform distortion detection device 20 is a waveform distortion component generated due to the resonance condition of the system 2, and corresponds to voltage distortion, current distortion, and the like. As the waveform distortion, not only a single harmonic but also a composite of each harmonic or a non-theoretical harmonic can be considered. If the gain adjusting device 20 outputs an appropriate command in response to these waveform distortions, the output voltage of the inverter 1 can automatically follow changes in the waveform distortion.

  For example, in a state where the output of the waveform distortion detector 21 is small and stable, the gain of the amplifier 14 is increased and the gain of the amplifier 15 is decreased to control the output voltage of the inverter 1 so as to follow the voltage of the system 2. To. Conversely, when the output of the waveform distortion detector 21 increases, the gain of the amplifier 14 is lowered and the gain of the amplifier 15 is raised so as not to follow the fluctuation of the system 2 so that the original output voltage of the system 2 is maintained. Try to control.

  As described above, according to the configuration of the present invention, it is always optimally adjusted according to the waveform distortion state of the system, is hardly affected by the distortion and disturbance of the system, and operates stably regardless of the resonance condition of the system. It is possible to configure a power conversion device that can do this. Therefore, even when a so-called grid interconnection inverter device is connected to a weak system having severe resonance conditions, the inverter device is always optimally adjusted according to the waveform distortion of the system and can be operated stably. .

  FIG. 4 is a block diagram showing a power converter according to a fourth embodiment of the present invention. About each part of this Example 4, the same part as each part of the power converter device which concerns on Example 2 of FIG. 2 is shown with the same code | symbol, and the description is abbreviate | omitted. The fourth embodiment is different from the second embodiment in that a voltage fluctuation detecting device 22 that receives the detection signal of the voltage detector 11 is added and its output is given to the gain adjusting device 20.

  In the present embodiment, the voltage fluctuation situation of the system 2 detected by the voltage fluctuation detection device 22 based on the output of the voltage detector 11 is input, and the output of the gain adjustment device 20 is determined. The gains of the amplifier 14 and the amplifier 15 are adjusted by the output of the gain adjusting device 20.

  The voltage fluctuation detection device 22 detects voltage fluctuations generated by the impedance of the system 2, other customer equipment, and other conditions, including any voltage of several tens of Hz to several Hz or less. There is upset. These voltage fluctuations are not limited to single harmonics but may be a combination of various fluctuations or fluctuations that occur suddenly in a short time. If the gain adjusting device 20 outputs an appropriate command in response to these voltage fluctuations, the output voltage of the inverter 1 can automatically follow changes in voltage fluctuations as in the third embodiment. It becomes.

  As described above, according to the configuration of the present invention, it is always optimally adjusted according to the voltage fluctuation situation of the system, hardly affected by the distortion and disturbance of the system, and stable regardless of the resonance condition of the system. A power converter that can be operated can be configured. Therefore, even when a so-called grid interconnection inverter device is connected to a weak system or the like where the resonance conditions are severe, it is always optimally adjusted according to the waveform fluctuation situation of the system and can be operated stably. .

The block block diagram of the power converter device which concerns on Example 1 of this invention. The block block diagram of the power converter device which concerns on Example 2 of this invention. The block block diagram of the power converter device which concerns on Example 3 of this invention. The block block diagram of the power converter device which concerns on Example 4 of this invention.

Explanation of symbols

1 Inverter 2 System 3 Transformer 11 Voltage detector 12 Current detector 13 Synchronization detector 14 Amplifier 15 Amplifier 16 Adder 17 Reference generator 18 Current controller 19 Inverter controller 20 Gain adjuster 21 Waveform distortion detector 22 Voltage fluctuation Detection device

Claims (5)

It is a power conversion device that is connected to the system and transfers at least one of active power, reactive power, and harmonics between the systems,
The output voltage of the power converter is
A first voltage reference proportional to the system voltage to which the power converter is connected;
A second voltage reference having a constant amplitude generated in synchronization with the system voltage;
A power conversion apparatus, wherein control is performed according to a combined voltage reference obtained by combining a third voltage reference that is at least one control output of active power control, reactive power control, and harmonic control. The power converter has an inverter connected to the system via a transformer,
The first voltage reference is a signal obtained by amplifying the output of a voltage detector for detecting a voltage of a system to which the output of the inverter is connected, by a first amplifier,
The second voltage reference is a signal obtained by amplifying the output of the synchronous detector that detects the phase and frequency of the system by the output of the voltage detector by the second amplifier,
The third voltage reference includes an output of a current detector that detects an output current of the inverter;
The output of a current control device that controls to match the output of a reference generator that provides at least one control reference among active power control, reactive power control, and harmonic control. Power conversion device.   The power conversion device according to claim 2, further comprising a gain adjustment device, wherein gains of the first amplifier and the second amplifier can be adjusted. Furthermore, it comprises a waveform distortion detection device that receives the output of the voltage detector,
4. The gain of the first amplifier and the second amplifier is automatically adjusted according to the degree of waveform distortion by inputting the output to the gain adjusting device. Power conversion device. Furthermore, it comprises a voltage fluctuation detection device that inputs the output of the voltage detector,
4. The gain of the first amplifier and the second amplifier is automatically adjusted according to the degree of voltage fluctuation by inputting the output to the gain adjusting device. Power conversion device.

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