JP7323499B2 - Controller for three-level power converter - Google Patents

Description

The present disclosure relates to a controller for a 3-level power converter.

2. Description of the Related Art Conventionally, a neutral-point-clamped (NPC) three-level power converter that converts DC power into AC power is known. In the NPC type 3-level power converter, the DC voltage is equally divided into the high potential side and the low potential side by a capacitor, and the neutral point potential that holds the high potential side DC voltage and the low potential side DC voltage equally. need control.

Japanese Patent Laying-Open No. 2013-255317 (Patent Document 1) discloses a control device that adds a sixth harmonic to an output voltage command to correct the output voltage command.

JP 2013-255317 A

The sixth harmonic can suppress imbalance between the high potential side DC voltage and the low potential side DC voltage when the output current of the three-level power converter is in positive phase. However, depending on the configuration of the loads connected to the tri-level power converter, the output currents of the tri-level power converter can become unbalanced. That is, the output current of the 3-level power converter may contain a negative-sequence current component. When the negative-sequence current component becomes large, the imbalance between the high-potential side DC voltage and the low-potential side DC voltage cannot be sufficiently suppressed in the sixth harmonic.

The present disclosure has been made to solve the above problems, and even if the output current is unbalanced, a three-level power conversion that can suppress the imbalance between the high potential side DC voltage and the low potential side DC voltage. It is an object of the present invention to provide a control device for an instrument.

A control device according to the present disclosure is a control device for a 3-level power converter including a plurality of switching elements for converting 3-level DC voltages into AC voltages. The control device includes a correction circuit that corrects an output voltage command of the 3-level power converter, and a control circuit that controls a plurality of switching elements according to the output voltage command corrected by the correction circuit. The correction circuit includes a first generator that generates a sixth harmonic of the fundamental of the three-level power converter and at least one second generator that generates even harmonics other than the sixth harmonic of the fundamental. , and an adder for adding the sixth and even harmonics to the output voltage command.

According to the present disclosure, even if the output current is unbalanced, it is possible to suppress the imbalance between the high potential side DC voltage and the low potential side DC voltage.

It is a figure showing the whole 3 level power converter composition concerning an embodiment. It is a figure which shows the structure of the control apparatus which concerns on a reference form. 4 is a diagram showing an example of output voltage commands Vu, Vv, Vw input to a control device and harmonics added to the output voltage commands Vu, Vv, Vw; FIG. 2 is a diagram showing simulation results using the models of the DC circuit and the switching circuit shown in FIG. 1 when a sixth harmonic is added to the output voltage commands Vu, Vv, Vw as harmonics; FIG. It is a figure which shows the internal structure of the control apparatus which concerns on this Embodiment. 2 is a diagram showing simulation results using the models of the DC circuit and the switching circuit shown in FIG. 1 when secondary harmonics are added as harmonics to output voltage commands Vu, Vv, and Vw; FIG. 2 is a diagram showing simulation results using the DC circuit and switching circuit models shown in FIG. 1 when adding a fourth harmonic as a harmonic to output voltage commands Vu, Vv, and Vw; FIG. 2 is a diagram showing simulation results using the models of the DC circuit and the switching circuit shown in FIG. 1 when eighth-order harmonics are added to output voltage commands Vu, Vv, and Vw as harmonics; FIG. It is a figure which shows the whole structure of the 3 level power converter which concerns on a modification.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated in principle. Note that the embodiments and modifications described below may be selectively combined as appropriate.

<Overall configuration of 3-level power converter>
FIG. 1 is a diagram showing the overall configuration of a 3-level power converter according to an embodiment. As shown in FIG. 1, the 3-level power converter 1 includes a control device 100, a DC circuit 200, a switching circuit 300, and current transformers 3U, 3V, 3W.

DC circuit 200 includes a high potential terminal P, a low potential terminal N, and capacitors C1 and C2.

The high potential terminal P is connected to the positive electrode of a DC power supply (not shown). The low potential terminal N is connected to the negative pole of the DC power supply. As a result, the potential of the low potential terminal N becomes lower than that of the high potential terminal P. As shown in FIG.

Capacitors C1 and C2 are connected in series between a high potential terminal P and a low potential terminal N. As shown in FIG. The capacitors C1 and C2 divide the DC voltage between the high potential terminal P and the low potential terminal N into a high potential side voltage Vpc and a low potential side voltage Vcn. Capacitor C1 and capacitor C2 are connected to each other at neutral point C.

The switching circuit 300 converts the three-level DC voltage in the DC circuit 200 into a three-phase (U-phase, V-phase, W-phase) AC voltage and supplies the three-phase AC voltage to the load 5 . Each of the three-phase AC voltages generated by the switching circuit 300 has the potential of the high potential terminal P, the potential of the neutral point C, the potential of the low potential terminal N, the potential of the neutral point C, the potential of the high potential terminal P, . . , three levels of AC voltage that change in the order of .

Switching circuit 300 includes switching elements S1U-S4U, S1V-S4V, and S1W-S4W. The switching elements S1U to S4U, S1V to S4V, S1W to S4W are switching devices composed of, for example, self arc-extinguishing semiconductor elements such as IGBTs that can be turned on and off by a gate signal, and anti-parallel connected diodes.

Switching elements S1U to S4U form a three-level inverter that converts a DC voltage into a U-phase AC voltage. The switching elements S1V to S4V form a three-level inverter that converts a DC voltage into a V-phase AC voltage. The switching elements S1W to S4W constitute a three-level inverter that converts a DC voltage into a W-phase AC voltage.

FIG. 1 shows a three-level inverter according to the T-type NPC (Advanced Neutral-Point-Clamped) system. That is, the switching elements S1U and S2U are connected in series between the high potential terminal P and the low potential terminal N. FIG. Between the connection point 2U of the switching elements S1U and S2U and the neutral point C, the switching elements S3U and S4U are connected in series in directions that can be controlled in opposite withstand voltage directions. Similarly, the switching elements S1V and S2V are connected in series between the high potential terminal P and the low potential terminal N. FIG. Between the connection point 2V of the switching elements S1V and S2V and the neutral point C, the switching elements S3V and S4V are connected in series in directions that can be controlled in opposite withstand voltage directions. The switching elements S1W and S2W are connected in series between the high potential terminal P and the low potential terminal N. As shown in FIG. Between the connection point 2V of the switching elements S1W and S2W and the neutral point C, the switching elements S3W and S4W are connected in series in directions that can be controlled in opposite withstand voltage directions.

U-phase, V-phase, and W-phase AC powers are output from the connection points 2U, 2V, and 2W to the load 5, respectively.

The potential of the connection point 2U is one of the potential of the high potential terminal P, the potential of the neutral point C, and the potential of the low potential terminal N depending on the states of the switching elements S1U to S4U. For example, the potential of the connection point 2U becomes the potential of the high potential terminal P when the switching elements S1U and S4U are on and the switching elements S2U and S3U are off. The potential of the connection point 2U becomes the potential of the low potential terminal N when the switching elements S1U and S4U are off and the switching elements S2U and S3U are on. The potential of the connection point 2U becomes the potential of the neutral point C when the switching elements S1U and S2U are off and the switching elements S3U and S4U are on.

Similarly, the potential of the connection point 2V is one of the potential of the high potential terminal P, the potential of the neutral point C, and the potential of the low potential terminal N depending on the states of the switching elements S1V to S4V. The potential of the connection point 2W is one of the potential of the high potential terminal P, the potential of the neutral point C, and the potential of the low potential terminal N depending on the states of the switching elements S1W to S4W.

Current transformers 3U, 3V, 3W are provided between connection points 2U, 2V, 2W and load 5, respectively. Current transformers 3U, 3V and 3W measure the values of output currents iu, iv and iw that flow out to load 5 from connection points 2U, 2V and 2W, respectively. Current transformers 3U, 3V, and 3W output values of measured output currents iu, iv, and iw to control device 100 .

Control device 100 controls each of switching elements S1U to S4U, S1V to S4V, and S1W to S4W by PWM (Pulse Width Modulation) to generate U-phase, V-phase, and W-phase alternating current from connection points 2U, 2V, and 2W. output power. As shown in FIG. 1, the control device 100 includes a correction circuit 10 and a PWM control circuit 40. As shown in FIG.

A correction circuit 10 corrects the output voltage commands Vu, Vv, Vw of the three-level power converter 1 . The output voltage command Vu is a U-phase output voltage command, and is a signal synchronized with the sine wave sin θ of the phase θ stored in the control device 100 . The output voltage command Vv is a V-phase output voltage command, and is a signal delayed by 120° with respect to the output voltage command Vu. The output voltage command Vw is a W-phase output voltage command, and is a signal that leads the output voltage command Vu by 120°.

The PWM control circuit 40 controls the switching elements S1U to S4U, S1V to S4V, S1W to S4W according to the output voltage commands Vu, Vv, Vw corrected by the correction circuit 10. FIG. Specifically, the PWM control circuit 40 turns on/off the switching elements S1U to S4U, S1V to S4V, and S1W to S4W by comparing the corrected output voltage commands Vu, Vv, and Vw with the carrier signal. Each is PWM-controlled.

<Control device according to reference form>
Before describing the internal configuration of the control device 100 according to the present embodiment, the configuration of the control device according to the reference embodiment will be described with reference to FIG.

FIG. 2 is a diagram showing the configuration of a control device 900 according to the reference embodiment. As shown in FIG. 2, the control device 900 includes a computing unit 91, a polarity determiner 92, a sine wave generator 93, a subtractor 94, an amplifier 95, a multiplier 96, adders 97 to 99. and a PWM control circuit 40 . Hereinafter, the operation of each component of the control device 900 will be described assuming that the control device 900 is applied instead of the control device 100 in the three-level power converter 1 shown in FIG.

The calculation unit 91 calculates reactive power output from the three-level power converter 1 based on the output voltage commands Vu, Vv, Vw and the output currents iu, iv, iw, and outputs the calculation result. The reactive power output from the computing unit 91 is obtained when the phases of the output currents iu, iv, and iw are delayed with respect to the output voltage commands Vu, Vv, and Vw (that is, the delayed reactive power is output according to the inductive load). is defined to be positive when The reactive power output from the computing unit 91 is determined when the phases of the output currents iu, iv, and iw lead the output voltage commands Vu, Vv, and Vw (that is, leading reactive power is output according to the capacity load). is defined to be negative when

The calculation unit 91 may calculate the reactive power based on the q-axis component obtained by dq-converting the output currents iu, iv, and iw using, for example, a reference sine wave having the same phase as the output voltage command. .

The polarity determiner 92 outputs the positive/negative determination result of the value of the reactive power output from the calculation unit 91 . The polarity determiner 92 outputs a determination result of "1" when the value of reactive power is positive (that is, when lagging reactive power is output according to the inductive load). The polarity determiner 92 outputs a determination result of "-1" when the value of the reactive power is negative (that is, when the leading reactive power is output according to the capacitive load).

A sine wave generator 93 generates a sixth harmonic having a frequency six times that of the fundamental wave of the three-level power converter 1 . The sine wave generator 93 multiplies the generated 6th harmonic by the determination result output from the polarity determiner 92, and outputs the 6th harmonic multiplied by the determination result.

Note that the fundamental wave of the three-level power converter 1 is synchronized with the sine wave sin θ of the phase θ stored in the control device 100 . That is, the fundamental wave is synchronized with the U-phase output voltage command Vu.

Subtractor 94 calculates the deviation (Vpc−Vcn) between voltage Vpc and voltage Vcn in three-level power converter 1 . The deviation calculated by subtractor 94 indicates the degree of imbalance between voltage Vpc and voltage Vcn.

The amplifier 95 multiplies the deviation calculated by the subtractor 94 by a predetermined gain K and outputs the multiplication result.

A multiplier 96 multiplies the sixth harmonic output from the sine wave generator 93 and the output of the amplifier 95 to adjust the amplitude of the sixth harmonic.

Multiplier 96 switches the sign of the sixth harmonic according to the magnitude relationship between voltage Vpc and voltage Vcn. The sign of the output of amplifier 95 changes according to the magnitude relationship between voltage Vpc and voltage Vcn. Specifically, when voltage Vpc>voltage Vcn, the output of amplifier 95 is positive. If voltage Vpc<voltage Vcn, the output of amplifier 95 is negative. Therefore, multiplier 96 does not invert the sign of the sixth harmonic output from sine wave generator 93 when voltage Vpc>voltage Vcn. Multiplier 96 inverts the sign of the sixth harmonic output from sine wave generator 93 when voltage Vpc<voltage Vcn.

The adders 97 to 99 add the output of the multiplier 96 to the U-phase, V-phase and W-phase output voltage commands Vu, Vv and Vw to correct the output voltage commands Vu, Vv and Vw.

PWM control circuit 40 controls switching elements S1U to S4U, S1V to S4V and S1W to S4W according to output voltage commands Vu, Vv and Vw corrected by adders 97 to 99, respectively.

When the control device 900 according to the reference embodiment is applied instead of the control device 100 in the three-level power converter 1, the sign of the sixth harmonic is determined according to whether it is the leading reactive power or the lagging reactive power, and the sixth harmonic is added to the output voltage commands Vu, Vv, Vw.

<Problems when applying the control device according to the reference form>
Next, problems when the control device 900 according to the reference embodiment shown in FIG. 2 is applied to the 3-level power converter 1 will be described.

Let Δh be the amplitude (magnitude) of the harmonic added to the output voltage commands Vu, Vv, and Vw, h be the order of the harmonic, and φh be the phase difference of the harmonic with respect to the fundamental wave. is represented by the formula

Equation (1) represents the U-phase output voltage ku. Equation (2) indicates the V-phase output voltage kv. Equation (3) represents the W-phase output voltage kw. The output voltages ku, kv, and kw correspond to corrected output voltage commands input to the PWM control circuit 40 .

Depending on the configuration of the load 5 connected to the 3-level power converter 1, the output current may become unbalanced and a reverse-phase current component may occur in the output current.

Ip is the amplitude (magnitude) of the positive-sequence current component included in the output current; φp is the phase of the positive-sequence current component; In is the amplitude (magnitude) of the negative-sequence current component included in the output current; Assuming that the phase is φn, the output current is expressed by the following equation.

Equation (4) represents the U-phase output current iu. Equation (5) represents the V-phase output current iv. Equation (6) represents the W-phase output current iw.

FIG. 3 is a diagram showing an example of output voltage commands Vu, Vv, Vw input to the control device and harmonics added to the output voltage commands Vu, Vv, Vw. In FIG. 3, solid lines 50U, 50V and 50W indicate output voltage commands Vu, Vv and Vw, respectively. A solid line 50H indicates a sixth harmonic, which is an example of harmonics. In the example shown in FIG. 3, the U-phase output voltage ku has a waveform obtained by adding the solid line 50U and the solid line 50H. The V-phase output voltage kv has a waveform obtained by adding the solid line 50V and the solid line 50H. The W-phase output voltage kw has a waveform obtained by adding the solid line 50W and the solid line 50H.

FIG. 4 shows a simulation using the models of the DC circuit 200 and switching circuit 300 shown in FIG. It is a figure which shows a result.

FIG. 4(a) shows the results of the ability to suppress the deviation between the voltage Vpc and the voltage Vcn when it is assumed that the output current is only the positive-sequence current component (that is, In=0). FIG. 4(b) shows the results of the ability to suppress the deviation between the voltage Vpc and the voltage Vcn when it is assumed that the output current is only the negative-sequence current component (that is, Ip=0). In the graphs shown in FIGS. 4A and 4B, the horizontal axis indicates the phase difference φh of the harmonic wave with respect to the fundamental wave, and the vertical axis indicates the ability to suppress the deviation between the voltage Vpc and the voltage Vcn. The larger the absolute value of the suppression capability, the more the deviation between the voltage Vpc and the voltage Vcn is suppressed.

As shown in FIG. 4, the sixth harmonic can suppress imbalance between the voltage Vpc and the voltage Vcn when only the positive-sequence current component is output. However, the sixth harmonic cannot suppress the imbalance between the voltage Vpc and the voltage Vcn regardless of the values of In and φh when only the reversed-phase current component is output.

Therefore, when the control device 900 shown in FIG. 2 is applied to the three-level power converter 1, the output current becomes unbalanced according to the configuration of the load 5, and if the negative-sequence current component in the output current increases, voltage Vpc and It becomes impossible to sufficiently suppress the imbalance with the voltage Vcn.

<Configuration of control device according to the present embodiment>
FIG. 5 is a diagram showing the internal configuration of control device 100 according to the present embodiment. As shown in FIG. 5, the correction circuit 10 includes a computing unit 11, polarity determiners 12 and 13, generators 14 to 17, adders 18 to 20, a subtractor 21, an adjuster 22, and adders 23-25.

Based on the values of the output currents iu, iv, and iw measured by the current transformers 3U, 3V, and 3W, the calculation unit 11 calculates reactive power due to positive-sequence current components contained in the output currents (hereinafter referred to as “positive-sequence reactive power ”) and the reactive power due to the negative-sequence current component contained in the output current (hereinafter referred to as “negative-sequence reactive power”).

The positive-sequence reactive power output from the calculation unit 11 is positive when the phase of the positive-sequence current component is delayed with respect to the positive-sequence voltage (that is, when the delayed reactive power is output according to the inductive load). is defined as The positive-sequence reactive power output from the calculation unit 11 is negative when the phase of the positive-sequence current component leads the positive-sequence voltage (that is, when the leading reactive power is output according to the capacity load). is defined as

Similarly, when the phase of the negative-sequence current component is delayed with respect to the negative-sequence voltage, the negative-sequence reactive power output from the calculation unit 11 is ), which is defined to be positive. The negative phase reactive power output from the calculation unit 11 is negative when the phase of the negative phase current component leads the phase of the negative phase voltage (that is, when the leading reactive power is output according to the capacity load). is defined as

The calculation unit 11 may calculate the positive phase reactive power and the negative phase reactive power from the output currents iu, iv and iw using a known calculation method such as three-phase two-phase conversion.

For example, the calculation unit 11 converts the output currents iu, iv, and iw into alternating currents iα and iβ in three-phase to two-phase mode according to the following equation (7).

Next, the alternating currents iα and iβ are dq-converted according to the following equation (8). A d-axis component id and a q-axis component iq obtained by the dq transform indicate active power and reactive power, respectively. In the dq conversion, by using the phase θ of the output voltage, the active power and reactive power (positive phase reactive power) due to the positive sequence current are calculated. In the dq transformation, the active power and reactive power (negative phase reactive power) due to the negative phase current are calculated by using the phase -θ.

The q-axis component is negative when the phase of the current component lags behind the voltage, and positive when the phase of the current component leads the voltage. Therefore, the calculation unit 11 may calculate the positive phase reactive power and the negative phase reactive power by multiplying the q-axis component by -1.

The calculation unit 11 outputs the calculated positive phase reactive power to the polarity determiner 12 and outputs the calculated negative phase reactive power to the polarity determiner 13 .

The polarity determiner 12 outputs a determination result of "1" when the positive phase reactive power is positive, and outputs a determination result of "-1" when the positive phase reactive power is negative.

The polarity determiner 13 outputs a determination result of "1" when the negative phase reactive power is positive, and outputs a determination result of "-1" when the negative phase reactive power is negative.

Generator 14 generates the sixth harmonic of the fundamental wave of three-level power converter 1 . The generator 14 has a sine wave generator 27 and an amplifier 28 .

A sine wave generator 27 generates a sixth harmonic having a frequency six times that of the fundamental wave. The sine wave generator 27 multiplies the generated 6th harmonic by the determination result output from the polarity determiner 12, and outputs the 6th harmonic multiplied by the determination result.

Amplifier 28 multiplies the sixth harmonic output from sine wave generator 27 by gain K2 predetermined according to the configuration of load 5, and outputs the multiplication result.

A generator 15 generates a second harmonic of the fundamental wave of the three-level power converter 1 . Generator 15 has a sine wave generator 29 and an amplifier 30 .

A sine wave generator 29 generates a second harmonic wave having twice the frequency of the fundamental wave. The sine wave generator 29 multiplies the generated secondary harmonic by the determination result output from the polarity determiner 13, and outputs the secondary harmonic multiplied by the determination result.

Amplifier 30 multiplies the second harmonic output from sine wave generator 29 by a gain K3 predetermined according to the configuration of load 5, and outputs the multiplication result.

A generator 16 generates a fourth harmonic of the fundamental wave of the three-level power converter 1 . The generator 16 has a sine wave generator 31 and an amplifier 32 .

A sine wave generator 31 generates a fourth harmonic having a frequency four times that of the fundamental wave. The sine wave generator 31 multiplies the generated fourth harmonic by the determination result output from the polarity determiner 13, and outputs the fourth harmonic multiplied by the determination result.

The amplifier 32 multiplies the fourth harmonic output from the sine wave generator 31 by a gain K4 predetermined according to the configuration of the load 5, and outputs the multiplication result.

Generator 17 generates the eighth harmonic of the fundamental wave of three-level power converter 1 . The generator 17 has a sine wave generator 33 and an amplifier 34 .

A sine wave generator 33 generates an eighth harmonic wave having a frequency eight times that of the fundamental wave. The sine wave generator 33 multiplies the generated eighth harmonic by the determination result output from the polarity determiner 13, and outputs the eighth harmonic multiplied by the determination result.

The amplifier 34 multiplies the eighth harmonic output from the sine wave generator 33 by a gain K5 predetermined according to the configuration of the load 5, and outputs the multiplication result.

The adder 18 adds the 8th harmonic output from the generator 17 to the 4th harmonic output from the generator 16 . Adder 19 adds the output of adder 18 to the second harmonic output from generator 15 . Adder 20 adds the output of adder 19 to the sixth harmonic output from generator 14 . The adder 20 outputs the sum of the 6th, 2nd, 4th and 8th harmonics respectively output from the generators 14-17.

Subtractor 21 calculates the deviation (Vpc−Vcn) between voltage Vpc and voltage Vcn in three-level power converter 1 . The deviation calculated by the subtractor 21 indicates the degree of imbalance between the voltage Vpc and the voltage Vcn.

The adjuster 22 adjusts the amplitudes of the 6th, 2nd, 4th and 8th harmonics output from the adder 20 based on the deviation calculated by the subtractor 21 .

Further, adjuster 22 switches the signs of the sixth harmonic, second harmonic, fourth harmonic, and eighth harmonic output from adder 20 according to the magnitude relationship between voltage Vpc and voltage Vcn. . Specifically, regulator 22 does not reverse the sign of the 6th, 2nd, 4th, and 8th harmonics when voltage Vpc>voltage Vcn. Regulator 22 inverts the signs of the sixth, second, fourth and eighth harmonics when voltage Vpc<voltage Vcn.

The adjuster 22 has an average calculator 35 , an amplifier 36 and a multiplier 37 . The average calculator 35 calculates a moving average of deviations in one cycle of the fundamental wave. The amplifier 36 multiplies the moving average calculated by the average calculator 35 by a predetermined gain K1. A multiplier 37 multiplies the output of the amplifier 36 and the output of the adder 20 . In this way, the adjuster 22 adjusts the product of the moving average of the deviation in one cycle of the fundamental wave and the predetermined gain K1 to the sixth, second, fourth and eighth harmonics. Multiply by .

The adders 23 to 25 add the output of the regulator 22 to the U-phase, V-phase and W-phase output voltage commands Vu, Vv and Vw to correct the output voltage commands Vu, Vv and Vw.

PWM control circuit 40 controls switching elements S1U-S4U, S1V-S4V, S1W-S4W according to output voltage commands Vu, Vv, Vw corrected by adders 23-25.

<Action/effect>
As described above, control device 100 according to the present embodiment includes correction circuit 10 and PWM control circuit 40 . A correction circuit 10 corrects the output voltage commands Vu, Vv, Vw of the three-level power converter 1 . The PWM control circuit 40 controls the switching elements S1U to S4U, S1V to S4V, S1W to S4W according to the output voltage command corrected by the correction circuit 10. FIG.

The correction circuit 10 includes a generator 14 that generates a sixth harmonic of the fundamental wave of the three-level power converter 1, generators 15 to 17 that generate even-order harmonics other than the sixth harmonic of the fundamental wave, It includes adders 23 to 25 for adding the sixth harmonic and the even harmonic to the output voltage command. Generator 15 generates the second harmonic of the fundamental wave. Generator 16 generates the fourth harmonic of the fundamental wave. Generator 17 generates the eighth harmonic of the fundamental wave.

As described above with reference to FIG. 4, the sixth harmonic can suppress imbalance between the voltage Vpc and the voltage Vcn when only the positive-sequence current component is output. Therefore, since correction circuit 10 includes generator 14 that generates the sixth harmonic, control device 100 can generate voltage Vpc and voltage Vcn even when the proportion of the positive-sequence current component in the output current is large. can suppress the imbalance of

FIG. 6 is a simulation using the models of the DC circuit 200 and the switching circuit 300 shown in FIG. It is a figure which shows a result. FIG. 7 shows a simulation using the models of the DC circuit 200 and the switching circuit 300 shown in FIG. 1 when the fourth harmonic (that is, h=4) is added to the output voltage commands Vu, Vv, and Vw as harmonics. It is a figure which shows a result. FIG. 8 shows a simulation using the models of the DC circuit 200 and switching circuit 300 shown in FIG. 1 when the eighth harmonic (that is, h=8) is added to the output voltage commands Vu, Vv, and Vw It is a figure which shows a result.

6 to 8, (a) shows the results of the ability to suppress the deviation between the voltage Vpc and the voltage Vcn when it is assumed that the output current is only the positive-sequence current component (that is, In=0). shown. (b) shows the result of the ability to suppress the deviation between the voltage Vpc and the voltage Vcn when it is assumed that the output current is only the negative-sequence current component (that is, Ip=0). In the graphs shown in FIGS. 6 to 8, the horizontal axis indicates the phase difference φh of the harmonic with respect to the fundamental wave, and the vertical axis indicates the ability to suppress the deviation between the voltage Vpc and the voltage Vcn. The larger the absolute value of the suppression capability, the more the deviation between the voltage Vpc and the voltage Vcn is suppressed.

As shown in FIGS. 6 to 8, the 2nd, 4th, and 8th harmonics are obtained regardless of the values of Ip and φh when only the positive sequence current component is output. However, the imbalance between the voltage Vpc and the voltage Vcn cannot be suppressed. However, the 2nd, 4th, and 8th harmonics can suppress the imbalance between the voltage Vpc and the voltage Vcn when only the reversed-phase current component is output. Therefore, by including the generators 15 to 17 for generating the second harmonic, the fourth harmonic, and the eighth harmonic in the correction circuit 10, even if the proportion of the negative-sequence current component in the output current is large, Also, the control device 100 can suppress the imbalance between the voltage Vpc and the voltage Vcn.

In this manner, the control device 100 suppresses the imbalance between the voltage Vpc and the voltage Vcn even when the output current becomes unbalanced according to the configuration of the load 5 and the negative-sequence current component of the output current is large. can.

The generator 14 generates a sixth harmonic having an amplitude equal to the gain K2, which is a constant predetermined according to the configuration of the load 5. FIG. Generator 15 generates a second harmonic having an amplitude of gain K3, which is a constant predetermined according to the configuration of load 5 . Generator 16 generates a fourth harmonic having an amplitude of gain K4, which is a constant predetermined according to the configuration of load 5 . The generator 17 generates an eighth harmonic having an amplitude equal to a gain K5, which is a constant predetermined according to the configuration of the load 5. FIG.

The ratio of the positive-sequence current component and the negative-sequence current component in the output current differs depending on the configuration of the load 5 . Therefore, by setting the magnitudes of gains K2 to K5 in advance according to the configuration of load 5 connected to three-level power converter 1, the imbalance between voltage Vpc and voltage Vcn can be efficiently suppressed.

Further, when the proportion of the negative-sequence current component in the output current is large, the effect of suppressing the imbalance between the voltage Vpc and the voltage Vcn due to each of the second, fourth, and eighth harmonics is Varies depending on configuration. Therefore, depending on the configuration of the load 5 connected to the three-level power converter 1, the magnitudes of the gains K3 to K5 are determined in advance. Also, the imbalance between the voltage Vpc and the voltage Vcn can be efficiently suppressed.

In this way, the amplitudes of the harmonics (that is, the gains K2-K5) generated by the generators 14-17 are predetermined according to the configuration of the load 5, so that three different types of load 5 can be applied. A level power converter 1 can be provided. In other words, the flexibility of load 5 connected to 3-level power converter 1 can be increased.

The generator 14 has a sine wave generator 27 which generates a sixth harmonic with a frequency six times that of the fundamental. The sine wave generator 27 multiplies the generated 6th harmonic by the determination result output from the polarity determiner 12, and outputs the 6th harmonic multiplied by the determination result. The polarity determiner 12 outputs a determination result of "1" when the positive phase reactive power is positive, and outputs a determination result of "-1" when the positive phase reactive power is negative. That is, generator 14 determines the sign of the sixth harmonic according to the sign of the phase angle between the positive-sequence voltage and the positive-sequence current component contained in the output current from 3-level power converter 1 .

Generators 15-17 have sine wave generators 29, 31 and 33, respectively, which generate 2nd, 4th and 8th harmonics having frequencies 2, 4 and 8 times the fundamental wave. The sine wave generators 29, 31, and 33 multiply the generated even-order harmonics by the determination result output from the polarity determiner 13, and output the even-order harmonics multiplied by the determination result. The polarity determiner 13 outputs a determination result of "1" when the negative phase reactive power is positive, and outputs a determination result of "-1" when the negative phase reactive power is negative. That is, the generators 15 to 17 determine the signs of even-order harmonics according to the sign of the phase angle between the negative-sequence voltage and the negative-sequence current component contained in the output current from the three-level power converter 1. do.

As described in Patent Document 1, it is necessary to switch the polarity of harmonics according to the lagging power factor or the leading power factor, that is, the lagging reactive power or the leading reactive power.

According to the present embodiment, the sign of the sixth harmonic that suppresses the imbalance between the voltage Vpc and the voltage Vcn when the proportion of the positive-sequence current component in the output current is large is included in the positive-sequence voltage and the output current. is determined according to the positive or negative phase angle with the positive-sequence current component. Thereby, the imbalance between the voltage Vpc and the voltage Vcn can be suppressed regardless of whether the positive phase reactive power is the lagging reactive power or the leading reactive power.

Similarly, the signs of the second harmonic, the fourth harmonic, and the eighth harmonic that suppress the imbalance between the voltage Vpc and the voltage Vcn when the proportion of the negative-sequence current component in the output current is large are the negative-sequence voltage and the negative phase current component included in the output current. Thereby, the imbalance between the voltage Vpc and the voltage Vcn can be suppressed regardless of whether the negative-phase reactive power is the lagging reactive power or the leading reactive power.

The correction circuit 10 adjusts the amplitudes of the 6th, 2nd, 4th and 8th harmonics respectively generated by the generators 14 to 17 based on the deviation between the voltage Vpc and the voltage Vcn. It further includes a regulator 22 for controlling. As a result, the amplitudes of the sixth harmonic, the second harmonic, the fourth harmonic and the eighth harmonic are adjusted to sizes suitable for suppressing the imbalance between the voltage Vpc and the voltage Vcn.

The adjuster 22 multiplies the 6th, 2nd, 4th and 8th harmonics by the product of the moving average of deviations in one cycle of the fundamental wave and a predetermined gain K1. This makes it possible to suppress the generation of new harmonics when adjusting the amplitudes of the 6th, 2nd, 4th and 8th harmonics. By suppressing the generation of new harmonics, the generation of noise in the output voltage is suppressed.

<Modification>
In the above description, correction circuit 10 of control device 100 includes three generators 15 to 17 as generators for generating even-order harmonics other than sixth-order harmonics. However, the correction circuit 10 may include only one or two of the generators 15-17. As shown in FIGS. 6 to 8, each of the 2nd, 4th and 8th harmonics other than the 6th harmonic has a large proportion of the negative-sequence current component in the output current. Even so, the imbalance between the voltage Vpc and the voltage Vcn can be efficiently suppressed. Therefore, by including only one or two of the generators 15 to 17, even if the proportion of the negative-sequence current component in the output current is large, the imbalance between the voltage Vpc and the voltage Vcn can be effectively suppressed.

In the above description, switching circuit 300 constitutes a three-level inverter according to the T-type NPC scheme. However, the configuration of the switching circuit 300 is not limited to this. For example, the switching circuit may constitute a three-level inverter according to the NPC scheme.

FIG. 9 is a diagram showing the overall configuration of a 3-level power converter according to a modification. A 3-level power converter 1A shown in FIG. 9 includes a switching circuit 300A instead of the switching circuit 300 as compared with the 3-level power converter 1 shown in FIG.

Switching circuit 300A includes switching elements S5U-S8U, S5V-S8V, S5W-S8W, and diodes D1U, D2U, D1V, D2V, D1W, D2W.

The switching elements S5U to S8U, S5V to S8V, and S5W to S8W are switching devices composed of, for example, self arc-extinguishing semiconductor elements such as IGBTs that can be turned on and off by a gate signal, and anti-parallel connected diodes.

Switching elements S5U to S8U constitute a three-level inverter that converts a DC voltage into a U-phase AC voltage. The switching elements S5V to S8V constitute a three-level inverter that converts a DC voltage into a V-phase AC voltage. The switching elements S5W to S8W constitute a three-level inverter that converts a DC voltage into a W-phase AC voltage.

FIG. 9 shows a three-level inverter according to the NPC scheme. That is, the switching elements S5U to S8U are connected in series between the high potential terminal P and the low potential terminal N. FIG. The cathode of diode D1U is connected to the connection point of switching elements S5U and S6U, and the anode of diode D1U is connected to neutral point C. The anode of diode D2U is connected to the connection point of switching elements S7U and S8U, and the cathode of diode D2U is connected to neutral point C.

Similarly, the switching elements S5V to S8V are connected in series between the high potential terminal P and the low potential terminal N. FIG. The cathode of the diode D1V is connected to the connection point of the switching elements S5V and S6V, and the anode of the diode D1V is connected to the neutral point C. The anode of the diode D2V is connected to the connection point of the switching elements S7V and S8V, and the cathode of the diode D2V is connected to the neutral point C.

The switching elements S5W to S8W are connected in series between the high potential terminal P and the low potential terminal N. As shown in FIG. The cathode of the diode D1W is connected to the connection point of the switching elements S5W and S6W, and the anode of the diode D1W is connected to the neutral point C. The anode of the diode D2W is connected to the connection point of the switching elements S7W and S8W, and the cathode of the diode D2W is connected to the neutral point C.

U-phase AC power is output to the load 5 from the connection point 4U of the switching elements S6U and S7U. V-phase AC power is output to the load 5 from the connection point 4V of the switching elements S6V and S7V. W-phase AC power is output to the load 5 from the connection point 4W of the switching elements S6W and S7W.

The potentials of the connection points 4U, 4V, and 4W vary depending on the states of the switching elements S5U to S8U, S5V to S8V, and S5W to S8W, respectively. Take any of the electric potentials.

Control device 100 is also applied to 3-level power converter 1A including switching circuit 300A shown in FIG. Thereby, even if the output current is unbalanced, the imbalance between the voltage Vpc and the voltage Vcn can be suppressed.

It should be considered that the embodiments disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the scope and meaning of equivalents of the scope of the claims.

1, 1A level power converter, 2U, 2V, 2W, 4U, 4V, 4W connection point, 3U, 3V, 3W current transformer, 10 correction circuit, 11, 91 calculation unit, 12, 13, 92 polarity determiner, 14-17 generator, 18-20, 23, 25, 97-99 adder, 21, 94 subtractor, 22 adjuster, 27, 29, 31, 33, 93 sine wave generator, 28, 30, 32, 34, 36, 95 amplifier, 35 average calculator, 37, 96 multiplier, 40 PWM control circuit, 100, 900 control device, 200 DC circuit, 300, 300A switching circuit, C neutral point, C1, C2 capacitor, D1U , D2U, D1V, D2V, D1W, D2W diode, N low potential terminal, P high potential terminal, S1U to S8U, S1V to S8V, S1W to S8W switching element.

Claims (6)

A control device for a 3-level power converter including a plurality of switching elements for converting 3-level DC voltage to AC voltage,
a correction circuit that corrects the output voltage command of the three-level power converter;
a control circuit that controls the plurality of switching elements according to the output voltage command corrected by the correction circuit;
The correction circuit is
a first generator that generates a sixth harmonic of the fundamental wave of the three-level power converter;
at least one second generator for generating even harmonics other than the sixth harmonic of the fundamental;
an adder that adds the sixth harmonic and the even harmonic to the output voltage command. The first generator determines the sign of the sixth harmonic according to the sign of the phase angle between the positive-sequence voltage and the positive-sequence current component included in the output current from the three-level power converter. ,
2. The at least one second generator determines the sign of the even-order harmonic according to whether the phase angle between the negative-sequence voltage and the negative-sequence current component included in the output current is positive or negative. The control device according to . The three-level power converter further includes a DC circuit having a first terminal, a second terminal having a lower potential than the first terminal, and an intermediate potential point between the first terminal and the second terminal,
The correction circuit is
the 6th harmonic generated by the first generator based on the deviation between the voltage between the first terminal and the intermediate potential point and the voltage between the intermediate potential point and the second terminal; 3. A controller according to claim 1 or 2, further comprising an adjuster for adjusting amplitudes of the waves and the even harmonics produced by the at least one second generator. 4. The adjuster according to claim 3, wherein said adjuster multiplies said sixth harmonic and said even harmonic by a product of a moving average of said deviation in one period of said fundamental wave and a predetermined first constant. controller. The at least one second generator includes a second harmonic generator that generates a second harmonic of the fundamental wave, a fourth harmonic generator that generates a fourth harmonic of the fundamental wave, and a second harmonic generator that generates a fourth harmonic of the fundamental wave. 5. A control device according to any preceding claim, comprising at least one of an 8th harmonic generator for generating the 8th harmonic of the wave. The first generator generates the sixth harmonic having an amplitude of a second constant predetermined according to the configuration of the load,
said at least one second generator comprises said second harmonic generator, said fourth harmonic generator and said eighth harmonic generator;
The secondary harmonic generator generates the secondary harmonic having an amplitude of a third constant predetermined according to the configuration of the load,
The fourth harmonic generator generates the fourth harmonic having an amplitude of a fourth constant predetermined according to the configuration of the load,
6. The control device according to claim 5, wherein said eighth harmonic generator generates said eighth harmonic having an amplitude of a fifth constant predetermined according to the configuration of said load.

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