JP2015230555A - Self-excited reactive power controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-excited reactive power controller capable of suppressing the voltage pulsation of a capacitor of a single phase power converter.SOLUTION: In a self-excited reactive power controller, AC sides of a plurality of single phase power converters are connected in cascade to each other, a capacitor connected to a DC side of the single phase power converter generates reactive power as a DC voltage source, and the single phase power converter whose AC sides are connected in cascade to each other is made to be equipped with for three phases is connected to a three phase AC system. In the self-excited reactive power controller, in each phase, a harmonic voltage having a multiple number of three is superimposed in the output voltage of each single phase power converter in the same phase. Accordingly, the voltage pulsation of the capacitor of the single phase power converter can be suppressed.

Description

  The present invention relates to a self-excited reactive power control apparatus.

  In recent years, the amount of distributed power sources such as photovoltaic power generation has increased. Since the amount of power generated by these distributed power sources changes due to changes in weather, the voltage of the distribution system is rapidly changed, causing a rapid change in the voltage of the distribution system. For this reason, it is necessary to control the voltage of the power distribution system within an appropriate range with respect to these voltage changes. Therefore, a reactive power control device that controls the reactive current of the distribution system and controls the voltage at high speed so as to be within an appropriate range has been proposed (see, for example, Patent Document 1). The reactive power control device includes a reactor connected to the AC side and a single-phase power converter. There is a cascade power converter in which modules are cascaded so that it can be used in a high-voltage power distribution system without a transformer. A capacitor is connected to the DC side of the single-phase power converter of each module. The reactive power control device generates reactive power using this capacitor as a DC voltage source.

JP 2007-280358 A

  By the way, in the above self-excited reactive power control device, since reactive current flows, instantaneous power pulsation of twice the power frequency occurs in each phase, and the voltage of the capacitor pulsates at twice the power frequency. If the voltage pulsation increases and the minimum value of the capacitor voltage becomes too low, the reactive current cannot be controlled.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a self-excited reactive power control device capable of suppressing voltage pulsation of a capacitor of a single-phase power converter.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
In a self-excited reactive power control device that solves the above problem, a capacitor connected to the DC side of a single-phase power converter generates reactive power as a DC voltage source, and the single-phase power converter includes three phases. The gist of the self-excited reactive power control apparatus directly connected to the phase AC system is to superimpose a harmonic voltage of a multiple of 3 in each homologous phase on the output voltage of each single-phase power converter.

  According to the above configuration, the single-phase power converter is provided for three phases, and each single-phase power converter is directly connected to the three-phase AC system. Then, reactive power is generated using a capacitor provided on the DC side of each single-phase power converter as a DC voltage source, and a harmonic voltage that is a multiple of 3 is output to the output voltage of each single-phase power converter in each homologous phase. Superimpose. That is, even if the capacitor voltage pulsates at twice the power supply frequency, the pulsation of the capacitor voltage is suppressed by superimposing the harmonic voltage that is a multiple of three. Therefore, the average value of the capacitor voltage can be lowered, the switching element can have a sufficient breakdown voltage, and the switching loss can be reduced. Further, if the average value of the capacitor voltage is the same, the capacitance of the capacitor can be reduced. Furthermore, since it is superimposed on each homologous phase, the harmonic voltage of each phase does not appear in the waveform of the line voltage, and the input current control is not affected.

In the self-excited reactive power control device, the harmonic voltage is preferably a third harmonic voltage.
According to the above configuration, since the harmonic voltage superimposed on the output voltage of each single-phase power converter is the third harmonic voltage, the pulsation of the capacitor voltage is the highest compared to the harmonic voltage of a multiple of 3 other than 3. Can be suppressed.

  In the self-excited reactive power control device, when both the power phase voltage and the harmonic voltage of the three-phase AC system are cosine waves, the phase angle of the harmonic voltage with respect to the power phase voltage is −π / 2. It is preferably a value that is larger than π / 2.

  According to the above configuration, the capacitor voltage is obtained by superimposing the harmonic voltage on the output voltage of each single-phase power converter by setting the phase angle of the harmonic voltage to a value larger than −π / 2 and smaller than π / 2. It is possible to effectively suppress pulsation.

In the self-excited reactive power control device, the phase angle between the power supply phase voltage and the harmonic voltage is preferably zero.
According to the above configuration, the pulsation of the capacitor voltage can be most effectively suppressed by superimposing the harmonic voltage on the output voltage of each single-phase power converter by setting the phase angle of the harmonic voltage to 0. it can.

  ADVANTAGE OF THE INVENTION According to this invention, the voltage pulsation of the capacitor | condenser of a single phase power converter can be suppressed.

(A) is a circuit diagram which shows schematic structure of one Embodiment of a self-excited reactive power control apparatus, (b) is a circuit diagram which shows the structure of the single phase power converter of a self-excited reactive power control apparatus. The u phase equivalent circuit diagram which shows the control principle of the reactive power by a self-excited reactive power control apparatus. The vector diagram of the advance reactive current in the equivalent circuit of u phase which shows the control principle of the reactive power by a self-excited reactive power control apparatus. The vector diagram of the delay reactive current in the equivalent circuit of u phase which shows the control principle of the reactive power by a self-excited reactive power control apparatus. The figure which shows the analysis model of a self-excited reactive power control apparatus. The figure which shows the structure of the current control system based on the dq axis | shaft model of a self-excited reactive power control apparatus. (A) is a figure which shows a module output phase voltage waveform when a 3rd harmonic is superimposed by a self-excited reactive power control device, (b) is a module when a 3rd harmonic is superimposed by a self-excited reactive power control device. The figure which shows an output line voltage waveform. The figure which shows the relationship between a power supply phase angle and the integral value of module instantaneous power in case the harmonic phase angle is 0 when a 3rd harmonic is superimposed by the self-excited reactive power control device. The relationship between the power supply phase angle when the third harmonic is superimposed by the self-excited reactive power controller, the relationship between the harmonic phase angle and the integrated value of the module instantaneous power, and the maximum and minimum values of the integrated value of the module instantaneous power FIG. The figure which shows the circuit of the self-excited reactive power control apparatus used for experiment. (A) is a figure which shows the waveform of the power supply phase voltage before pulsation suppression of a capacitor voltage when a delay current is sent in the experiment of the self-excited reactive power control device, (b) is a figure which shows the waveform of the power supply current, ) Is a diagram showing the waveform of the converter input current, (d) is a diagram showing the waveform of the load current, (e) is a diagram showing the waveform of the capacitor voltage at the first stage, and (f) is a capacitor voltage at the second stage. (G) is a diagram showing the waveform of the capacitor voltage at the third stage, (h) is a diagram showing the waveform of the module output phase voltage, and (i) is a diagram showing the waveform of the module output line voltage. . (A) is a figure which shows the waveform of the power supply phase voltage before the pulsation suppression of a capacitor voltage when an advance electric current is sent in the experiment of a self-excited reactive power control apparatus, (b) is a figure which shows the waveform of a power supply current, ) Is a diagram showing the waveform of the converter input current, (d) is a diagram showing the waveform of the load current, (e) is a diagram showing the waveform of the capacitor voltage at the first stage, and (f) is a capacitor voltage at the second stage. (G) is a diagram showing the waveform of the capacitor voltage at the third stage, (h) is a diagram showing the waveform of the module output phase voltage, and (i) is a diagram showing the waveform of the module output line voltage. . (A) is a figure which shows the waveform of the power supply phase voltage after suppressing the pulsation of a capacitor voltage when a lagging current is passed in the experiment of the self-excited reactive power control device, (b) is a figure which shows the waveform of the power supply current, ) Is a diagram showing the waveform of the converter input current, (d) is a diagram showing the waveform of the load current, (e) is a diagram showing the waveform of the capacitor voltage at the first stage, and (f) is a capacitor voltage at the second stage. (G) is a diagram showing the waveform of the capacitor voltage at the third stage, (h) is a diagram showing the waveform of the module output phase voltage, and (i) is a diagram showing the waveform of the module output line voltage. . (A) is a figure which shows the waveform of the power supply phase voltage after suppression of the pulsation of the capacitor voltage when conducting a forward current in the self-excited reactive power control device experiment, (b) is a figure showing the waveform of the power supply current, (c) ) Is a diagram showing the waveform of the converter input current, (d) is a diagram showing the waveform of the load current, (e) is a diagram showing the waveform of the capacitor voltage at the first stage, and (f) is a capacitor voltage at the second stage. (G) is a diagram showing the waveform of the capacitor voltage at the third stage, (h) is a diagram showing the waveform of the module output phase voltage, and (i) is a diagram showing the waveform of the module output line voltage. .

  Hereinafter, an embodiment of a self-excited reactive power control device will be described with reference to FIGS. The self-excited reactive power control device of this embodiment is a cascade power converter in which modules of single-phase power converters are cascade-connected in three stages.

[Configuration of cascade power converter]
As shown in FIG. 1 (a), the cascade power converter is connected to a three-phase AC power source (power supply phase voltages e _u , e _v , e _w ) through a three-series module (single phase) via an input reactor L _f. The power converter is star-connected. As shown in FIG. 1B, each module of the cascade power converter is configured by connecting a DC capacitor C and four insulated gate bipolar transistors (IGBTs) in an H-bridge connection. The capacitor voltage v _cjk and the module output voltage v _{mjk of} each module are distinguished from each other by adding a suffix of the phase and the number of series stages (j = u, v, w, k = 1, 2, 3). For example, the u-phase first-stage module is expressed as a capacitor voltage v _cu1 and a module output phase voltage v _mu1 . As shown in FIG. 1 (a), the module portion is kept constant by controlling the capacitor voltage v _c. Further, the output voltage of the u-phase series module is represented as a module output phase voltage v _mu . The input current i _u , i _v , i _w of the cascade power converter is controlled by the module output phase voltage v _mu .

[Reactive power control principle of cascade power converter]
Cascade power converter supplies by an amount equivalent to the transducer loss active power is controlled to maintain the capacitor voltage v _c of the module to a constant value. Further, the cascade power converter can control the reactive power to an arbitrary value.

FIG. 2 is a u-phase equivalent circuit, in which the module output phase voltage v _mu is represented by a voltage source. A steady-state u-phase voltage equation is obtained by the following equation (1) from the equivalent circuit using the power supply angular frequency ω.

FIG. 3 is a vector diagram when the input current i _u is set as a reactive current. As shown in FIG. 3, the cascade power converter module output phase voltage v _mu power supply phase voltage e _u and phase, by providing a voltage greater than the power supply phase voltage e _u, the processing proceeds input current i _u Can be controlled.

FIG. 4 is a vector diagram when the input current i _u is a delayed reactive current. As shown in FIG. 4, the cascade power converter module output phase voltage v _mu power supply phase voltage e _u and phase, by providing a voltage less than the power supply phase voltage e _u, delays the input current i _u Can be controlled.

The maximum voltage that can be output as the module output phase voltage v _mu is the sum of the three-stage u-phase module DC voltages, which must be higher than the module output phase voltage peak value during reactive current control. That is, the line voltage effective value E of the power source, the power source angular frequency omega, with the rated reactive current _{I n,} the capacitor voltage of each module (DC _{voltage) v cu1,} v _cu2, v following expression for _cu3 (2) It is necessary to satisfy.

[Control of cascade power converter]
As shown in FIG. 5, the module output phase voltages v _mu , v _mv , and v _mw connected in series for each phase are represented as voltage sources. Considering the resistance R _f of the input reactor L _f, the three-phase voltage equation for the instantaneous value is obtained by the following equation (3). Here, p is a differential operator.

The power supply phase voltages e _u , e _v , and e _w are given by the following equation (4) as a symmetric three-phase AC voltage having a line voltage effective value E and a power supply angular frequency ω.

The three-phase alternating current amount is expressed as a direct current amount, and is converted into rotational coordinates (dq coordinates) synchronized with the power supply phase angle θ in order to simplify the control. A transformation matrix C _{dq to dq} coordinates is obtained by the following equation (6).

Then, when the equations (3) and (4) are coordinate-transformed using the equation (6), the following equation (7) is obtained.

Substituting equation (8) into equation (7) and solving for i _d and i _q yields equation (9) below.

The block of the cascade power converter surrounded by a broken line in FIG. 6 is a dq axis model based on Expression (9). The block of the cascade power converter is represented as a block diagram from the module output voltages v _md and v _{mq on the} dq axis to the input currents i _d and i _q . In the block of the cascade power converter, there are interference terms between dq axes and disturbance of the power supply voltage E due to conversion of the AC amount to DC.

The d-axis control system for the effective current is used to control the average voltage v _cav of the module capacitor, performs PI control on the deviation between the DC voltage command value v _c ^* and the detected value v _c, and d-axis current The command value i _d ^* is given. In the reactive current q-axis control system, the reactive power command value Q ^* is divided by the line voltage effective value E of the power source to obtain the reactive current command value i _q ^* . In order to make the interference term between the dq axes and the disturbance of the power supply voltage E incoherent, the interference term and the disturbance term are compensated, respectively, and a current control system is configured by PI control.

[Module instantaneous power and DC voltage pulsation]
The cascade power converter controls the reactive power. For this reason, the converter input currents i _u , i _v , i _w of the lag current of the input current effective value I are obtained by the following equation (10).

Equation (10) is a lagging current, but in the case of advancing, the input current effective value I may be negative. Ignoring the voltage drop is small due to input reactor L _f. Further, assuming that each module performs the same operation, the u-phase module output phase voltage v _mu is obtained by the following equation (11) of the effective value V ₁ and the power supply phase angle θ.

Capacitor voltage v _c is the module pulsates by the instantaneous power p to absorb. Using the equations (10) and (11), the instantaneous power p of the u-phase module is obtained by the following equation (13).

Capacitor voltage _{v c} pulsating, using a DC average value _{V co,} represented by an approximate equation of equation (14).

Therefore, the pulsation width of the capacitor voltage v _c is proportional to the integral value of the instantaneous power p. The integral value W of the instantaneous power p in the equation (13) is obtained by the following equation (15).

Voltage ripple of the capacitor voltage v _c is proportional to the product V _{1 I} of the fundamental wave RMS value V ₁ and the input current effective value I, pulsates at twice the power supply frequency of the power supply. The difference ΔW between the maximum value V ₁ I / 2 and the minimum value −V ₁ I / 2 of the integral value W in the equation (15) is obtained by the following equation (16).

[Method of suppressing DC voltage pulsation]
In the present embodiment, in order to suppress the capacitor voltage pulsation, the third harmonic voltage v ₃ of the following equation (17) of the effective value V ₃ and the phase angle φ is superimposed on the module output phase voltage v _mu . The third harmonic voltage v ₃ is a cosine wave together with the power supply phase voltages e _u , e _v and e _w .

The module output phase voltage v _mu is the sum of the equations (11) and (17), and is obtained by the following equation (18).

FIG. 7A shows the waveforms of the module output phase voltages v _mu and v _mv when the third harmonic voltage is superimposed. FIG. 7B shows the waveform of the module output line voltage v _muv when the third harmonic voltage is superimposed. Since the third harmonic voltage is in each homologous phase, it does not appear in the waveform of the module output line voltage v _muv and does not affect the input current control system.

Equation (10), the instantaneous power _{p 3} u-phase module when superimposed third harmonic voltage from (18) is obtained by the following equation (19).

Integral value _{W 3} of the instantaneous power _{p 3} is obtained by the following equation (20).

By reducing the change in the integrated value W ₃ of the instantaneous power p _3, it can be suppressed capacitor voltage ripple. As the variation range of the integrated value W ₃ of the instantaneous power p ₃ of the formula (20) is minimized, by obtaining the phase angle φ of the third harmonic voltage v _3, you can minimize the pulsation of the capacitor voltage v _c . From the equation (20), the integral value W ₃ of the instantaneous power p ₃ is a function of 2θ, so it is considered in the range of 0 ≦ θ ≦ π. The effective value _{V 3} of the third harmonic voltage _{v 3} is the module output phase voltage _{v mu} of formula (18) becomes high, since it requires a voltage higher capacitor voltage _{v c,} 3 of the fundamental wave RMS value _{V 1} Less than 10%. The ratio of the fundamental wave RMS value V ₁ of the effective value V ₃ of the third harmonic voltage v ₃ can be arbitrarily set. For example, the effective value V _{3 of the third} harmonic voltage v ₃ can be made equal to or less than 100% of the fundamental wave effective value V ₁ .

[Minimum value and maximum value of integral value W of instantaneous power p]
The integral value W ₃ of the instantaneous power p ₃ of the formula (20), as a function W ₃ of the phase angle phi of the power supply phase angle theta and the third harmonic voltage v _{3 (theta,} phi), when the change width is minimized The minimum and maximum values of are derived. The integral value W ₃ (θ, 0) of the instantaneous power p ₃ when the phase angle φ = 0 of the _third harmonic voltage v ₃ is substituted into the equation (20) is obtained by the following equation (22).

FIG. 8 shows the integrated value W ₃ (θ of the instantaneous power p _{3 in which} the integrated value W of the instantaneous power p in Expression (15) and the third harmonic voltage v ₃ with the phase angle φ = 0 in Expression (22) are superimposed. , 0). The minimum value W _3min of the integral value W ₃ (θ, 0) of the instantaneous power p ₃ is obtained by the following equation (23) when the power supply phase angle θ = 0, π.

The minimum value W _3min is higher by V ₃ I / 4 than before the superposition of the third harmonic voltage in the equation (15). The maximum value W _3max of the integral value W ₃ (θ, 0) of the instantaneous power p ₃ is obtained by the following equation (24) when the power supply phase angle θ = π / 2.

The maximum value W _3max is lower by 3V ₃ I / 4 _than before the superposition of the third harmonic voltage in Expression (15). Therefore, the difference ΔW ₃ between the maximum value and the minimum value of the integral value W ₃ (θ, 0) of the instantaneous power p ₃ when the third harmonic voltage is superimposed is obtained by the following equation (25).

The reduction rate ε of the pulsation voltage when the third harmonic voltage is superimposed is obtained by the following equation (26).

The integral value W ₃ (θ, 0) of the instantaneous power p _{3 in} the equation (22) indicates that the capacitor voltage pulsation can be most suppressed. The minimum value _{W 3min} to confirm the integral value _{W 3} of the instantaneous power _{p 3} in the vicinity of the integral value _W 3 of the instantaneous power _{p 3} obtained by substituting the power phase angle theta = 0 in equation (20) in equation (23) ( 0, φ) is obtained by the following equation (27).

In FIG. 9, the integral value W ₃ (θ, 0) of the instantaneous power p _{3 in} the equation (22) and the integral value W ₃ (0, φ) of the instantaneous power p _{3 in} the vicinity of the minimum value W _{3min in} the equation (27). Is shown in a three-dimensional manner. Integral value _W 3 of the instantaneous power _{p 3} (0, phi) in, the third harmonic integration value of the instantaneous power _{p 3} in the phase angle phi = 0 of the voltage _{v 3 W 3min = W 3 (} 0,0) is the minimum value , The integral value W ₃ (θ, 0) of the instantaneous power p ₃ at the phase angle φ = 0 of the _third harmonic voltage v ₃ can be set to the highest value of the capacitor voltage pulsation.

In order to confirm the integral value W ₃ (θ, 0) of the instantaneous power p _{3 in} the vicinity of the maximum value W _3max of the equation (24), the instantaneous power p obtained by substituting the power supply phase angle θ = π / 2 into the equation (20). integral value of _{3 W 3 (π / 2,} φ) is obtained by the following equation (28).

FIG. 9 shows the integral value W ₃ (θ, 0) of the instantaneous power p ₃ in equation (22) and the integral value W ₃ (π / 2) of the instantaneous power p _{3 in} the vicinity of the maximum value W _{3max in} equation (28). The relationship of φ) is shown three-dimensionally. Integral value _{W 3 (π / 2, φ} ) of the instantaneous power _{p 3} in the integral value of the instantaneous power _{p 3} in the phase angle phi = 0 of the third harmonic voltage _{v 3 W 3max = W 3 (} π / 2,0 ) Is the lowest among the maximum values, and the integrated value W ₃ (θ, 0) of the instantaneous power p ₃ of the phase angle φ = 0 of the _third harmonic voltage v ₃ can make the maximum value of the capacitor voltage pulsation the lowest.

Therefore, the integral value W ₃ (θ, 0) of the instantaneous power p ₃ in the equation (22) in which the phase angle φ = 0 of the _third harmonic voltage v ₃ can suppress the capacitor voltage pulsation most.
[Experiment]
The effect of suppressing the pulsation of the capacitor voltage by the cascade power converter described above will be confirmed by experiments. That is, reactive power control is performed by a cascade power converter, and a difference due to the presence or absence of pulsation suppression control is confirmed.

[Experimental conditions]
FIG. 10 shows the experimental circuit configuration of the cascade power converter, and Table 1 shows the experimental conditions. The input line voltage effective value is 200 V, and the frequency is 60 Hz. The value of the input reactor _{L f} is 3mH, the capacity of the module capacitors is a 470 .mu.F. Further, the capacitor voltage command value v _c ^* of the module is 71V. The q-axis current command value i _q ^{* is set} to ± 13 A so that the effective line current value is 7.5 A. Further, the load capacity is 1.8 kVA and the control reactive power is 2.6 kvar.

[Experimental result]
By superimposing the _third harmonic voltage v3, the pulsation of the capacitor voltage is reduced by 30%. Third harmonic voltage v superimposed on the module output phase voltage ₃ is given by the following equation the effective value V ₃ as 0.3 of the power supply line voltage effective value E (29).

[No capacitor voltage pulsation suppression control]
11 and 12 show waveforms when the capacitor voltage pulsation suppression control is not performed. 11 and 12 show the power supply phase voltage e _u , power supply current i _su , converter input current i _u , load current i _lu , capacitor voltages v _{cu1 to} v _cw3 , module output phase voltage v _mu , module from the top. The output line voltage is v _muv . Except capacitor voltage _v cu1 _{to v CW3} is displayed only U-phase.

FIG. 11 shows a waveform when −13 A is passed through the module power converter along the q axis. Converter input current _{i u} shown in FIG. 11 (d), the phase has become a [pi / 2 delayed with respect to the power supply phase voltage _{e u} shown in FIG. 11 (a). Further, the module output phase voltage v _mu shown in FIG. 11 (h) is multi-level because the modules are connected in series in three stages. Capacitor voltages v _{cu1 to} v _cw3 shown in FIGS. 11 (e), 11 (f), and 11 (g) are 71 V at each stage, and the pulsation width is 25 _V.

FIG. 12 shows a waveform when +13 A is passed through the module power converter along the q axis. Figure 12 (d) to the transducer input current _{i u} indicating the phase has become a [pi / 2 proceeds to the power supply phase voltage _{e u} shown in Figure 12 (a). Further, the module output phase voltage v _mu shown in FIG. 12 (h) is multilevel because the modules are connected in series in three stages. The capacitor voltages v _{cu1 to} v _cw3 shown in FIGS. _12E , _12F , and _12G are 71V in each stage, and the pulsation width is 32V.

[With capacitor voltage pulsation suppression control]
13 and 14 show waveforms when the capacitor voltage pulsation suppression control is performed. FIG. 11 shows a waveform when −13 A is passed through the module power converter along the q axis. Converter input current _{i u} shown in FIG. 13 (d), the phase has a [pi / 2 delayed with respect to the power supply phase voltage _{e u} shown in FIG. 13 (a). Further, the module output phase voltage v _mu shown in FIG. 13 (h) is multilevel because the modules are connected in three stages in series.

Capacitor voltages v _{cu1 to} v _cw3 shown in FIGS. _13E , _13F , and _13G are 71V at each stage, and the pulsation width is 18V. Since the pulsation width 25V when the pulsation suppression control shown in FIGS. 11 (e), 11 (f), and 11 (g) is not performed is 0.7 times 17.5V, it can be said that the theoretical suppression effect is obtained. _Further , the third harmonic voltage does not appear in the module output line voltage v _muv1 shown in FIG. 13 (i), and the power supply current i _su shown in FIG. 13 (b) is not affected.

FIG. 14 shows a waveform when +13 A is passed through the module power converter along the q axis. Converter input current _{i u} shown in FIG. 14 (d), the phase has become a [pi / 2 proceeds to the power supply phase voltage _{e u} shown in FIG. 14 (a). Further, the module output phase voltage v _mu shown in FIG. 14 (h) is multilevel because the modules are connected in three stages in series.

Capacitor voltages v _{cu1 to} v _cw3 shown in FIGS. _14E , _14F , and _14G are 71V at each stage, and the pulsation width is 22V. When the pulsation width 32V when the pulsation suppression control shown in FIGS. 12 (e), 12 (f), and 12 (g) is not performed is 0.7 times 22.4V, it can be said that the theoretical suppression effect is obtained. _Further , the third harmonic voltage does not appear in the module output line voltage v _muv shown in FIG. 14 (i), and the power supply current i _su shown in FIG. 14 (b) is not affected.

  Thus, since the average value of the capacitor voltage can be lowered by the pulsation suppression control of the cascade power converter, the switching element withstand voltage can be afforded and the switching loss can be reduced. If the average value of the capacitor voltage is the same, the capacitor capacity can be reduced by pulsation suppression control.

As described above, according to this embodiment, the following effects can be obtained.
(1) Three-phase single-phase power converters in which AC sides of a plurality of single-phase power converters are cascade-connected to each other are provided, and each single-phase power converter is directly connected to a three-phase AC system. Then, reactive power is generated by using a capacitor provided on the DC side of each single-phase power converter as a DC voltage source, and third order is applied to the module output phase voltages v _mu , v _mv , and v _mw of each single-phase power converter. Harmonic voltages are superimposed on each homologous phase. That is, even the capacitor voltage v _c was pulsates at twice the power frequency, that is the third harmonic voltage is superimposed, the pulsation of the capacitor voltage v _c is suppressed. Therefore, it is possible to lower the average value of the capacitor voltage v _c, it is enough to withstand the switching element can be reduced switching loss. Further, if the same average value of the capacitor voltage v _c, it is possible to reduce the capacitance of the capacitor. Further, since the third harmonic voltage is superimposed on each homologous phase, the third harmonic voltage of each superimposed phase cancels each other in the waveforms of the module output line voltages v _muv , v _mvw , v _muw. It does not appear and does not affect the input current control.

(2) By setting the phase angle φ of the harmonic voltage to a value larger than −π / 2 and smaller than π / 2, harmonics are generated in the module output phase voltages v _mu , v _mv , and v _mw of each single-phase power converter. it is possible to perform pulsation suppression capacitor voltage v _c by superimposing the voltage effectively.

(3) the phase angle φ of the harmonic voltage by zero, of each single-phase power converter module output phase voltage _{v mu,} v _mv, v _mw capacitor voltage v _c by superimposing harmonic voltage Pulsation suppression can be most effectively performed.

  (4) Each phase is provided with a plurality of single-phase power converters, and the AC sides of the plurality of single-phase power converters in each phase are cascade-connected to each other. It is directly connected to each phase. Therefore, by connecting a plurality of single-phase power converters in each phase in cascade, it can be multi-staged (multi-level), and the current / voltage waveform can be improved and the capacity can be increased.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
In the above embodiment, the phase angle φ of the third harmonic voltage is set to 0, but a value larger than −π / 2 excluding 0 and smaller than π / 2 may be adopted.

In the above embodiment, the third harmonic voltage that can suppress the pulsation of the capacitor voltage vc is superimposed, but a harmonic voltage that is a multiple of 3 except 3 may be superimposed. Also in this manner, it is possible to suppress the pulsation of similarly capacitor voltage v _c in the case of superimposed third harmonic voltage.

  In the above embodiment, the capacity of the capacitor of each module (single phase power converter) can be arbitrarily selected according to the magnitude of reactive power to be controlled, and combinations of different capacities are also possible.

  -In the said embodiment, although it was multistaged as the structure provided with two or more single-phase power converters of each phase, if the capacity | capacitance of the capacitor | condenser was sufficient, each single-phase power converter was provided for each phase. It is good also as a structure.

  -In the said embodiment, you may employ | adopt a rectangular wave (square wave) and a triangular wave as a harmonic.

  C: DC capacitor.

Claims (4)

Self-excited reactive power control device in which a capacitor connected to the DC side of a single-phase power converter generates reactive power as a DC voltage source, and the single-phase power converter includes three phases and is directly connected to a three-phase AC system In
A self-excited reactive power control device, wherein a harmonic voltage of a multiple of 3 is superimposed on each homologous phase on the output voltage of each single-phase power converter. The self-excited reactive power control device according to claim 1, wherein the harmonic voltage is a third-order harmonic voltage. In the self-excited reactive power control device according to claim 1 or 2,
When both the power phase voltage and the harmonic voltage of the three-phase AC system are cosine waves, the phase angle of the harmonic voltage with respect to the power phase voltage is greater than −π / 2 and smaller than π / 2. A self-excited reactive power control device. The self-excited reactive power control device according to claim 3, wherein a phase angle between the power supply phase voltage and the harmonic voltage is zero.