JP6747756B2 - Power conversion system - Google Patents

Description

The present invention relates to a power conversion system capable of suppressing harmonics generated by a separately excited converter that is connected to an AC system.

BACKGROUND ART Conventionally, there is known an event (also called a harmonic instability phenomenon) in which a harmonic generated by a separately excited converter connected to an AC system continues after being gradually expanded. This phenomenon occurs when a parallel resonance point of a specific harmonic order exists in the AC system.

In order to avoid such a harmonic instability phenomenon, various solutions have been proposed. For example, it has been proposed to provide a phase-modulating equipment provided with a phase-modulating capacitor in an AC system and shift the parallel resonance point by turning on/off the phase-modulating equipment to suppress the generation of harmonics (for example, See Patent Document 1). In addition, it has been proposed to avoid a harmonic instability phenomenon by connecting a synchronous phase modulator to the AC system.

However, when the phase adjusting equipment is provided in the AC system, there may be restrictions on the operation of the phase adjusting equipment. For example, the phasing equipment is provided for reactive power compensation, but if this is used to suppress the generation of harmonics, reactive power compensation cannot be performed. Further, when the synchronous phase modulator is provided in the AC system, a loss occurs when the synchronous phase modulator is operated, and the maintenance thereof is required.

JP, 2001-37083, A

In view of such circumstances, the present invention provides a power conversion system capable of avoiding a harmonic instability phenomenon without causing operational restrictions on a phase-modulating capacitor and without using a synchronous phase modulator. With the goal.

A first aspect for achieving the above object is a separately excited converter connected between two alternating current systems, and a self-excited converter connected to one or both of the two alternating current systems , An AC filter and a phasing capacitor connected to each of the AC systems, wherein the self-excited converter is a self-excited power converter connected to the AC system, and a voltage value of the AC system. And a control unit that calculates a first current command value based on the reactive power value, and an active filter that outputs a second current command value whose amplitude is proportional to the harmonic voltage component of the AC system in phase. The controller outputs to the power converter such that the current output from the power converter to the AC system follows a value obtained by superimposing the second current command value on the first current command value. In the power conversion system, the voltage command value of is calculated .

In the first aspect, it is possible to suppress harmonics generated by the separately excited converter connected to the AC system, avoid harmonic instability phenomenon, and enable stable operation. Further, since the phase-modulating capacitor connected to the AC system is not applied to suppress harmonics, the operation of the phase-modulating capacitor is not restricted. Further, since the AC system does not need the synchronous phase shifter, it is possible to avoid the loss of operating the AC phase shifter and eliminate the need for maintenance.

A second aspect of the present invention is the power conversion system according to the first aspect, wherein the active filter includes a high-pass filter or a band-pass filter that detects a harmonic voltage component from the AC voltage of the AC system, The power conversion system is characterized in that the harmonic current component is multiplied by a predetermined gain to output the second current command value having the same phase as the harmonic voltage component but an amplitude proportional thereto.

In the second aspect, a harmonic voltage is extracted by a high-pass filter or a band-pass filter, and the harmonic voltage component is multiplied by a predetermined gain, so that a second phase whose amplitude is in phase with the harmonic voltage component is proportional. A current command value can be output.

A third aspect of the present invention is the power conversion system according to the second aspect, wherein the gain is set to a value that avoids a harmonic instability phenomenon. It is in.

In the third aspect, by setting the gain, the second current command value for avoiding the harmonic instability phenomenon can be calculated.

According to the present invention, a harmonic instability phenomenon of a separately excited converter can be avoided without causing operational restrictions on a phase-modulating capacitor, and without using a synchronous phase modulator, and a stable power conversion system can be provided. Can be realized

1 is a schematic diagram of a power conversion system according to a first embodiment. 3 is a block diagram of a self-excited converter according to Embodiment 1. FIG. Voltage _{V sys,} current _i lcc _{+ i acf,} is a graph showing the relationship between the output current _{i vsc.} Voltage _{V sys,} current _i lcc _{+ i acf,} is a graph showing the relationship between the output current _{i vsc.}

<Embodiment 1>
FIG. 1 is a schematic diagram of a power conversion system according to this embodiment. As shown in the figure, the power conversion system 10 includes a self-excited converter VSC and a separately excited converter LCC.

The separately-excited converter LCC is a general separately-excited power converter, and is interconnected between two AC systems (AC system A and AC system B). Further, the self-excited converter VSC is connected to the AC system A.

An AC filter ACF1 and a phasing capacitor C1 are connected to the AC system A, and an AC filter ACF2 and a phasing capacitor C2 are connected to the AC system B. The AC filters ACF1 and ACF2 and the phasing capacitors C1 and C2 are used to suppress the harmonic current generated by the separately excited converter LCC.

Further, the AC bus of the AC system A is connected to a voltage source and a short circuit reactance (AC Grid), and the AC bus of the AC system B is connected to a voltage source and a short circuit reactance (AC Grid). The voltage source and the short-circuit reactance simulate the short-circuit capacities of the AC buses of the AC system A and the AC system B, respectively.

The separately-excited converter LCC, the self-excited converter VSC, the phasing capacitor C1 and the phasing capacitor C2 are connected to the AC bus of the AC system A and the AC bus of the AC system B via a transformer (not shown). doing.

Further, the voltage of the AC bus of the AC system A is V _sys , the back voltage of the AC system A is V _s , the short circuit reactance of the AC bus of the AC system A is L _ac , and the separately excited converter LCC after passing through the AC filter ACF1. the output current _i lcc _{+ i acf,} self-commutated converter output current from VSC _{i vsc,} the power flow to the non-connecting end from the connecting end of the self-commutated converters VSC and _{P lcc.}

The detailed configuration of the self-excited converter VSC will be described with reference to FIG. FIG. 2 is a block diagram of the self-excited converter according to this embodiment.

The self-excited converter VSC of the present embodiment includes a self-excited power converter 20 connected to the AC system A, a control unit 30 that controls the power converter 20, and an active filter 40.

The power converter 20 is a voltage type self-excited converter. The power converter 20 is provided with voltage command values V _u ^* , V _v ^* , and V _w ^* from the control unit 30 for each of the three-phase alternating current, and outputs an alternating voltage corresponding to them to the alternating current system A. Then, the current i _vsc is output to the AC system A by the AC voltage based on the voltage command values V _u ^* , V _v ^* , and V _w ^* .

The control unit 30 performs reactive power control (AQR) and DC voltage control (DCAVR) so that the current output from the power converter 20 to the AC system A follows the current command values i _q ^* , i _d ^*. The voltage command value V _d ^* and the voltage command value V _q ^* to the power converter 20 are output. Specifically, the control unit 30 obtains the reactive power value q _ac from a detector (not shown) that detects the reactive power of the AC system A, and detects the reactive power value q _ac and the reactive power command value q _ac ^* . A control value with which the deviation becomes zero is obtained, and the current command value i _q ^* is _obtained by multiplying the control value by a predetermined gain K _aqr .

Further, the control unit 30 obtains the voltage value V _dc from a detector (not shown) that detects the voltage of the AC system A so that the deviation between the voltage value V _dc and the voltage command value V _dc ^* becomes zero. Current control value i _d ^* is _obtained by multiplying the control value by a predetermined gain K _dcavr . Note that these two current command values i _q ^* and i _d ^* correspond to the first current command value in the claims.

Further, the control unit 30 includes a non-interference current controller 31 (ACR). The non-interference current controller 31 obtains a d-axis current value i _d from a detector (not shown) that detects the current of the AC system A, and determines the deviation between the current value i _d and the current command value i _d ^*. The voltage command value V _d ^* which becomes zero is output. Similarly, the non-interference current controller 31 obtains a q-axis current value i _q from a detector (not shown) that detects the current of the AC system A, and obtains the current value i _q and the current command value i _q ^* . The voltage command value V _q ^* is output so that the deviation becomes zero.

The voltage command values V _d ^* , V _q ^* output by the non-interference current controller 31 are converted into voltage command values V _u ^* , V _v ^* , V _w ^* by the inverse dq converter 32, and the power converter It is output to 20.

When the active filter 40 is not operated, the self-excited converter VSC operates similarly to the conventional self-excited converter. That is, the control unit 30 outputs the current i _vsc corresponding to the voltage command value V _dc ^* and the reactive power command value q _ac ^* to the AC system A.

Active filter 40 of this embodiment includes a dq converter 41, and a 42d highpass filter, and 42q, and the gain _{K af.}

The dq converter 41 obtains voltage values V _u , V _v , and V _w from a detector (not shown) that detects the voltage of each phase of the AC system A, and dq-converts these values based on the fundamental wave phase. , And voltage values V _d and V _q are output. As a result, the fundamental wave frequency components of V _u , V _v , and V _w are converted into DC amounts at V _d and V _q .

42d pass filter extracts the harmonic voltage component from the voltage value V _d. Similarly the high pass filter 42q extracts harmonic voltage component from the voltage value V _q. Specifically, the high-pass filters 42d and 42q having a cutoff frequency of 5 Hz are used.

Instead of the high pass filter, a band pass filter that extracts a specific harmonic voltage may be used. For example, since the second harmonic voltage components of V _u , V _v , and V _w whose fundamental wave component is 50 Hz are converted to 50 Hz in V _d and V _q , specifically, the pass band is, for example, 45. A bandpass filter with a frequency of ˜55 Hz is used.

Harmonic voltage component output 42d highpass filter, from 42q is predetermined gain _{K af} is multiplied. The value obtained by multiplying the harmonic voltage components of the voltage command values V _d and V _q by the gain K _af corresponds to the second current command value of the claims in which the amplitude is proportional to the harmonic voltage component in phase.

The control unit 30 superimposes the second current command value obtained by multiplying the harmonic voltage component output from the voltage command value V _d by the gain K _af on the current command value i _d ^* . Similarly, the control unit 30 superimposes the second current command value obtained by multiplying the harmonic voltage component output from the voltage command value V _q by the gain K _af on the current command value i _q ^* .

1/K _af, which is the reciprocal of the gain K _af , corresponds to the resistance value. With such a control unit 30, the self-excited converter VSC does not respond to the fundamental frequency of the AC system A but acts as a resistance to the harmonic frequency. The gain _Kaf is set to a value that avoids the phenomenon of harmonic instability. Specifically, since the harmonic instability phenomenon occurs when the impedance at the parallel resonance frequency of the AC system A exceeds the equivalent impedance of the separately excited converter, a value lower than this is set. For example, when the equivalent impedance of the separately excited converter LCC is 500Ω, 1/K _af is set to 330Ω, that is, K _af is set to 0.003S. Alternatively, a value that avoids the harmonic instability phenomenon may be set by trial and error by experiment or computer simulation.

By connecting such a self-excited converter VSC to the AC system A, the impedance at the parallel resonance point of the AC system A is reduced. As a result, the current i _vsc output from the self- _exciting converter VSC to the AC system A has a waveform that cancels the harmonic component.

The parameters shown in Table 1 were applied to the power conversion system having the configuration shown in FIGS. 1 and 2, and the instantaneous value simulation was executed. FIG. 3 and FIG. 4 are graphs showing the relationship _among the voltage V _sys , the current i _lcc +i _acf , and the output current i _vsc from the self-excited converter VSC obtained from the simulation result. FIG. 3 is a case where the active filter of the self-excited converter is not operated, and FIG. 4 is a graph when the active filter of the self-excited converter is operated. The horizontal axis represents time, and the vertical axis represents voltage or current.

As shown in FIG. 3, when the self- _exciting converter VSC including the active filter 40 is not in operation, the current i _vsc is zero. At this time, as shown in the voltage V _sys and the current i _lcc +i _acf , it can be confirmed that the harmonic currents of 100 Hz and 320 Hz are flowing out from the separately excited converter LCC. In the actual power conversion system, the operation of the separately excited converter LCC is stopped in order to prevent damage to the equipment.

On the other hand, when the self-excited converter VSC including the active filter 40 is operating, the self-excited converter VSC does not respond to 45 to 55 Hz which is near the basic frequency of the AC system A, and other frequencies. Equivalently acts as a resistance of 1/K _af =330Ω.

Therefore, as shown in FIG. 4, the current i _vsc output from the self-excited converter VSC has a waveform that cancels the harmonic current. This significantly reduces the influence of the harmonic currents of 100 Hz and 320 Hz on the voltage V _sys and the current i _lcc +i _acf .

As described above, according to the power conversion system 10 of the present embodiment, it is possible to suppress the harmonic generated by the separately excited converter LCC and avoid the harmonic instability phenomenon. Further, in the power conversion system 10, since the phasing capacitor C2 is not applied to suppress harmonics, there is no restriction on the operation of the phasing capacitor. Furthermore, since the power conversion system 10 does not require the synchronous phase shifter, it is possible to avoid the loss of operating the synchronous phase shifter and eliminate the need for maintenance.

Further, in the example shown in FIG. 4, since the reactive power command value q _ac ^{* is set} to zero, the current i _vsc has a waveform based on the command value from the active filter 40. Not limited. For example, the self-excited converter VSC may operate in the same manner as the conventional fundamental wave reactive power compensator, and may further have a mode in which the current command value by the active filter 40 is superimposed. By connecting the self-excited converter VSC having such a mode to the existing power conversion system using the separately excited converter LCC, the harmonic instability phenomenon of the existing separately excited converter LCC is avoided, and stable. It is possible to do the required driving.

In addition, in the power conversion system 10 described above, the active filter 40 including the high-pass filter or the band-pass filter and the gain is used, but the configuration is not limited to such a configuration. The active filter 40 may have any configuration as long as it can output a second current command value that is in phase with the harmonic voltage component of the AC system A and whose amplitude is proportional. Since the active filter outputs such a second current command value, a current capable of avoiding the harmonic instability phenomenon can be output from the self-exciting converter VSC to the AC system.

Further, although the self-excited converter VSC is connected to one AC system A, it may be connected to two AC systems A and B.

10... Electric power conversion system, 20... Electric power converter, 30... Control part, 40... Active filter, 42d, 42q... High pass filter

Claims (3)

A separately excited converter connected between two AC systems,
A self-exciting converter connected to one or both of the two AC systems ;
An AC filter and a phasing capacitor connected to each of the two AC systems,
The self-exciting converter is
A self-excited power converter connected to the AC system,
A control unit that calculates a first current command value based on the voltage value and the reactive power value of the AC system ;
An active filter that outputs a second current command value that is in phase with the harmonic voltage component of the alternating current system and whose amplitude is proportional,
The control unit is
The voltage command value to the power converter is calculated so that the current output from the power converter to the AC system follows the value obtained by superimposing the second current command value on the first current command value. A power conversion system characterized by: The power conversion system according to claim 1,
The active filter includes a high-pass filter or a band-pass filter that detects a harmonic voltage component from the AC voltage of the AC system, and by multiplying the harmonic voltage component by a predetermined gain, the same phase as the harmonic voltage component is obtained. power conversion system and outputs the second current command value amplitude proportional in. The power conversion system according to claim 2,
The gain is set to a value that avoids a harmonic instability phenomenon.