JP2019187121A - Power conversion device and control method thereof - Google Patents

Abstract

To suppress an increase in capacitor capacity while suppressing a change in a neutral point potential in a wider operation region.SOLUTION: A power conversion device according to an embodiment includes a neutral point clamp type power converter, and control means for controlling the neutral point potential fluctuation of the power converter by calculating a zero phase voltage of the power converter by using a predetermined calculation formula, and superimposing the zero phase voltage on the voltage command value of each phase, and when there is a voltage command value whose sign changes due to the superposition of the zero phase voltage, the control means reverses the sign of the voltage command value and recalculates the zero phase voltage, and superimposes the zero phase voltage after recalculation on the voltage command value of each phase.SELECTED DRAWING: Figure 3

Description

  Embodiments described herein relate generally to a power conversion device and a method for controlling the power conversion device.

  Power converters that convert direct current to alternating current are also called inverters and converters, and are used in a wide range of fields in society. The most basic inverter is a two-level inverter composed of two semiconductor switching elements, and outputs two voltage levels in one leg.

  On the other hand, as shown in FIG. 12, each phase has four semiconductor switching elements and two diodes (semiconductor switching elements may be used) in one leg, and has a DC voltage dividing capacitor common to each phase. There is a point-clamped (Neutral-Point-Clamped) inverter. FIG. 12 shows an example of the power conversion device 1 including the three-phase NPC inverter 100. The NPC inverter 100 can output three voltage levels in one leg and contributes to high breakdown voltage, loss reduction, and harmonic reduction, and is used in various inverters.

Japanese Patent No. 5622437

IEEJ Transactions D, vol. 113, No. 1, 1993, Analysis of Neutral Potential Fluctuation of Neutral Clamp Voltage Type PWM Inverter

In the example of FIG. 12, NPC inverters 100, for each phase, comprises six semiconductor switching devices _S 1 to S ₆ in one leg, has a DC component voltage capacitor _C 1, _{C 2} for dividing the DC voltage _{v PN} . Here, the potential of the neutral point NP of the DC voltage _dividing capacitors C ₁ and C ₂ is assumed to be vn. The potential of the neutral point of the NPC inverter v _n has the property that varies at three times the fundamental wave in accordance with operation of the inverter. When the variation of the neutral point potential v _n is large, the voltage varies according to the semiconductor switching element, there is a possibility that the element in a pressure excess is broken when the voltage is high, when the voltage is low over not put out the desired voltage There is a possibility of modulation.

The size of the variation of the neutral point potential v _n, the modulation rate and power factor, capacitance, load current is concerned. The capacitance and the load current to a constant value, calculating the magnitude of the fluctuation of the neutral point potential v _n by the modulation rate and the power factor, is expressed as a graph 13. In FIG. 13, the power factor is expressed as a phase difference between voltage and current. Higher modulation rate is high, and (closer to the phase difference = π / 2) the lower the power factor, the variation of the neutral point potential v _n it can be seen larger.

The simplest method of suppressing the fluctuation of the neutral point potential v _n is to increase the capacitance. However, an increase in the capacitor capacity leads to an increase in the volume and cost of the inverter, and the energy at the time of the accident also increases.

On the other hand, the variation of the neutral point potential v _n can be suppressed to some extent by the control. Specifically By superimposing the zero-phase voltage v ₀ shown in equation (1) below each phase command value v _u, v _v, to v _w, can suppress variations in the neutral point potential v _n.

Here, v _u , v _v , and v _w represent leg voltage command values normalized by 1, and i _u , i _v , and i _w represent currents output from the leg of each phase. sign represents a sign function.

However, with these methods, there is an operation region where fluctuations cannot be suppressed. If the fluctuation of the neutral point potential v _n in the case of applying the control described in Non-Patent Document 1 or Patent Document 1 similarly computed is shown in Figure 14. In other words, the fluctuation can be greatly suppressed in the operation region where the modulation factor is low and the power factor is low (the operation region close to phase difference = π / 2), but the variation still exists in other regions.

  The problem to be solved by the present invention is to provide a power conversion device and a control method for the power conversion device that can suppress the fluctuation of the neutral point potential in a wider operating region and prevent the increase of the capacitor capacity. It is in.

  The power conversion device of the embodiment calculates a neutral point clamp type power converter and a zero-phase voltage of the power converter using a predetermined calculation formula, and converts the zero-phase voltage into a voltage command value for each phase. A control unit that performs control to suppress fluctuation of the neutral point potential of the power converter by superimposing, and the control unit has a voltage command value whose sign changes due to the superposition of the zero-phase voltage Then, the sign of the voltage command value is inverted and the zero phase voltage is recalculated, and the zero phase voltage after the recalculation is superimposed on the voltage command value of each phase.

  According to the present invention, it is possible to suppress the fluctuation of the neutral point potential in a wider operating region and prevent the increase in the capacitor capacity.

The figure which shows an example of the NPC inverter in 1st Embodiment. The figure which shows an example of the function structure of the neutral point electric potential fluctuation | variation suppression control in the same embodiment. The figure which shows an example of operation | movement of the neutral point electric potential fluctuation | variation suppression control in the same embodiment. The figure which shows an example of a function structure of the overmodulation limit control in the embodiment. The figure which shows an example of the fluctuation | variation of the neutral point electric potential in the same embodiment. The figure which shows an example of the function structure of the neutral point electric potential fluctuation | variation suppression control in 2nd Embodiment. The figure which shows an example of operation | movement of the neutral point electric potential fluctuation | variation suppression control in the same embodiment. The figure which shows an example of the fluctuation | variation of the neutral point potential in the same embodiment. The figure which shows an example of the NPC circuit of the inverter converter structure in 3rd Embodiment. The figure which shows an example of the function structure of the neutral point electric potential fluctuation | variation suppression control in the same embodiment. The figure which shows an example of the fluctuation | variation of the neutral point potential in the same embodiment. The figure which shows an example of the circuit of the NPC inverter in a prior art. The figure which shows an example of the fluctuation | variation of the neutral point electric potential in a prior art. The figure which shows an example of the fluctuation | variation of the neutral point electric potential at the time of applying the neutral point electric potential fluctuation | variation suppression control in a prior art.

  Hereinafter, embodiments will be described with reference to the drawings.

[First Embodiment]
First, the first embodiment will be described. In the following, description of portions common to the above-described conventional configuration will be omitted, and description will be made focusing on different portions.

  FIG. 1 is a diagram illustrating an example of the configuration of the power conversion device according to the first embodiment. In FIG. 1, the same reference numerals are given to the elements common to FIG. 12 described above.

  The NPC inverter 100 constituting the power conversion device 1 is a general three-phase NPC inverter similar to that shown in FIG. However, it is not limited to this example. For example, although an NPC inverter is illustrated as a neutral point clamp type power converter in this embodiment, this may be implemented in place of the NPC converter. Further, the neutral point clamp may be a T-type midpoint clamp or other types.

The power conversion apparatus 1, further, the normal control for suppressing control and variation of the neutral point potential v _n of the operation of the NPC inverter 100 (hereinafter, referred to as "neutral point potential fluctuation suppression control".) Control for A device 10 is provided.

Controller 10, a zero-phase voltage of the NPC inverter 100 is calculated by using a predetermined calculation formula, the NPC inverter 100 by superimposing the zero-phase voltage to each phase of the voltage command values of the neutral point potential v _n Control for suppressing fluctuation is performed. In particular, when there is a voltage command value whose sign changes due to the superposition of the zero-phase voltage, the control device 10 inverts the sign of the voltage command value and recalculates the zero-phase voltage, It has a function to superimpose the voltage on the voltage command value of each phase.

In general neutral point potential fluctuation suppression control, the zero-phase voltage v ₀ is obtained by Equation (1) and is superimposed on the voltage command values v _u , v _v , and v _w of each phase. Thus variation of the neutral point potential v _n is suppressed to some extent. However, each voltage command value in Equation (1) has a sign, and the sign may change by superimposing a zero-phase voltage. In that case, since would change calculation original condition of the zero-phase voltage, fluctuation suppressing effect of the neutral point potential v _n is not exhibited by the zero-phase voltage. Therefore, in this embodiment, when the sign is changed by superimposing the zero-phase voltage, the sign is inverted and the zero-phase voltage is _recalculated to obtain the zero-phase voltage v _0re . By _{superimposing the} zero-phase voltage v _0re on the voltage command values v _u , v _v , and v _w of each phase, the fluctuation suppressing effect is properly exhibited.

  FIG. 2 is a diagram illustrating an example of a functional configuration of neutral point potential fluctuation suppression control of the NPC inverter 100 by the control device 10 provided in the power conversion device 1 according to the present embodiment.

  As illustrated in FIG. 2, the control device 10 includes calculation units 11 to 17, a determination unit 18, calculation units 19 to 21, and a switching unit SW <b> 11 as various functions.

The arithmetic unit 11 inputs reference voltage command values v _u , v _v , v _w for the NPC inverter 100 and output currents i _u , i _v , i _w obtained from the NPC inverter 100, and uses the equation (1). Then, the zero phase voltage is calculated, and the calculation result is output as the zero phase voltage v ₀ .

The calculation unit 12 adds the zero-phase voltage v ₀ output from the calculation unit 11 to each of the voltage command values v _u , v _v , and v _w , and outputs the calculation result as the voltage command values v _u0 , v _v0 , v Output as _w0 .

The calculation unit 13 obtains and outputs an intermediate value among the voltage command values v _u0 , v _v0 , and v _w0 after the zero-phase voltage v ₀ addition output from the calculation unit 12. For example, when the voltage command values v _u0 , v _v0 , and v _w0 after addition of the zero-phase voltage v ₀ are arranged in order of increasing value (or decreasing order), the intermediate value here is the second highest value (or It refers to the voltage command value (low value).

  The calculation unit 14 determines the sign of the intermediate value output from the calculation unit 13 and outputs a value of “1” when the sign is positive, for example, while the sign is negative, for example. A value of “0” is output to.

The calculation unit 15 calculates and outputs an intermediate value among the voltage command values v _u , v _v , and v _w . For example, when the voltage command values v _u , v _v , and v _w are arranged in descending order of values (or in ascending order), the intermediate value here is the voltage command value having the second highest value (or the lowest value). Point to.

  The calculation unit 16 determines the sign of the intermediate value output from the calculation unit 15 and outputs a value of “1” when the sign is positive, for example, while the sign is negative, for example. A value of “0” is output to.

  The calculation unit 17 subtracts the value output from the calculation unit 16 from the value output from the calculation unit 14 and outputs the calculation result.

The determination unit 18 determines whether or not the value output from the calculation unit 17 is “0”. If the value is “0”, it is considered that the sign of the intermediate value has not changed. , Outputs a signal for operating the switching unit SW11 so that the voltage command value output from the calculation unit 12 is selected by the switching unit SW11 and output as voltage command values v _u0 , v _v0 , v _w0 , When the value is “1”, it is considered that the sign of the intermediate value has changed, and the voltage command value after addition of the zero-phase voltage v _0re output from the calculation unit 21 described later is selected by the switching unit SW11. A signal for operating the switching unit SW11 is output so that the voltage command values v _u0 , v _v0 , and v _w0 are output.

  The computing unit 19 inverts the sign of the value output from the computing unit 16 and outputs the result.

The calculation unit 20 inputs the voltage command values v _u , v _v , v _w and the intermediate value obtained by inverting the sign output from the calculation unit 19, and recalculates the zero-phase voltage using the formula (1) again. _And outputs the calculation result as a zero-phase voltage _v0re .

The calculation unit 21 adds the zero-phase voltage v _0re output from the calculation unit 20 to each of the voltage command values v _u , v _v , v _w and outputs the calculation result.

  Here, an example of an operation based on the neutral point potential fluctuation suppression control shown in FIG. 2 will be described with reference to FIG.

The control device 10 uses the arithmetic unit 11 to calculate zero based on the voltage command values v _u , v _v , v _w and the output currents i _u , i _v , i _w obtained from the NPC inverter 100 using equation (1). The phase voltage is calculated to obtain the zero phase voltage v ₀ (S11). The voltage command values v _u , v _v , and v _w may be used for the recalculation of the zero-phase voltage v _{0re in} addition to the calculation of the intermediate value, and therefore are temporarily stored in a predetermined storage area. (S12).

Further, the control unit 10, the calculating section 15 calculates an intermediate value of the voltage command values _{v u, v v, v w} (S13).

On the other hand, the control device 10 adds the zero-phase voltage v ₀ obtained by the computing unit 11 to the voltage command values v _u , v _v , and v _w by the computing unit 12, and the voltage command values v _u0 , v _v0 and _vw0 are obtained (S14). For these voltage command values v _u0 , v _v0 , and v _w0 , the arithmetic unit 13 obtains intermediate values of the voltage command values v _u0 , v _v0 , and v _w0 .

Next, the control device 10 determines whether or not the intermediate value has changed before and after the addition of the zero-phase voltage v ₀ (S15). That is, it is determined through the calculation units 14, 16, 17 and the determination unit 18 whether or not the sign of the intermediate value obtained by the calculation unit 15 matches the sign of the intermediate value obtained by the calculation unit 13. When the determination result in the determination unit 18 is “0”, it is considered that the signs are the same between the two, and the sign of the intermediate value is not changed before and after the zero-phase voltage v ₀ is added. (No in S15). On the other hand, when the determination result in the determination unit 18 is not “0”, the sign does not match between the two, and the sign of the intermediate value changes before and after the zero-phase voltage v ₀ is added. Can be considered (Yes in S15).

If the intermediate value has not changed (No in S15), the control device 10 causes the voltage command values v _u0 , v _v0 , and v _w0 obtained by the calculation unit 12 to be output through the switching unit SW11.

On the other hand, if the intermediate value has changed (Yes in S15), the control device 10 uses the arithmetic unit 16, 19 to indicate the sign of the intermediate value of the voltage command values v _u , v _v , v _w obtained by the arithmetic unit 15. Then, the calculation unit 20 recalculates the zero-phase voltage to obtain the zero-phase voltage v _0re (S16), and the calculation unit 21 _obtains the calculated zero-phase voltage v _0re by the voltage command value v _u , The voltage command values v _u0 , v _v0 , and v _w0 are obtained by adding to each of v _v and v _w (S17). The voltage command values v _u0 , v _v0 , and v _w0 obtained by the calculation unit 21 are output through the switching unit SW11.

As described above, when the sign of the intermediate value is changed by superimposing the zero phase voltage, the sign is inverted and the zero phase voltage is _recalculated to obtain the zero phase voltage v _{0re. 0re} is _superimposed on the voltage command values v _u , v _v and v _w of each phase. Thereby, the fluctuation suppression effect is exhibited appropriately.

Next, an example of overmodulation limit control that suppresses overmodulation of the voltage command value will be described in preparation for the case where the voltage command values v _u , v _v , and v _w exceed the modulation factor 1 and become overmodulated. However, this overmodulation limit control is not necessarily required, and its implementation may be omitted.

FIG. 4 is a diagram illustrating an example of a functional configuration of overmodulation limit control performed on the voltage command values v _u0 , v _v0 , and v _w0 generated by the control in FIG. 2. Here, an example is given in which the modulation of the voltage command value is limited by the modulation factor 1 so that the voltage command values v _u , v _v , and v _w do not exceed the modulation factor 1 and become overmodulated.

In the example of FIG. 4, voltage command values v _u0 , v _v0 , v _w0 are input, and a corrected zero-phase voltage v _0mod is obtained. The corrected zero phase voltage v _{0 mod} is a correction value of the zero phase voltage v ₀ and is used to prevent overmodulation. By superimposing the corrected zero-phase voltage _{v 0Mod} on voltage command value _{v u0, v v0, v w0} , while preventing over-modulation, the fluctuation suppression effect can be maximized.

  As illustrated in FIG. 4, the control device 10 includes calculation units 31 to 39 and switching units SW <b> 21 and SW <b> 22.

The calculation unit 31 calculates and outputs the maximum value of the voltage command values v _u0 , v _v0 , and v _w0 .

The calculation unit 32 calculates and outputs the minimum value of the voltage command values v _u0 , v _v0 , and v _w0 .

  The computing unit 33 outputs a difference value obtained by subtracting the maximum value of the voltage command value from the upper limit threshold “1” of the modulation rate.

  The computing unit 34 outputs a difference value obtained by subtracting the minimum value of the voltage command value from the lower limit threshold value “−1” of the modulation rate.

  The calculation unit 35 calculates and outputs the absolute value of the minimum value of the voltage command value output from the calculation unit 32.

  The calculation unit 36 includes a maximum voltage command value output from the calculation unit 31 (hereinafter “A”) and a minimum voltage command value output from the calculation unit 35 (hereinafter “B”). ) And if A is greater than or equal to B, a signal for operating the switching unit SW21 is output so that the difference value output from the calculation unit 33 is selected, while A is less than B In this case, a signal for operating the switching unit SW21 is output so that the difference value output from the calculation unit 34 is selected.

The calculating part 37 calculates _| requires and outputs each absolute value of voltage command value _vu0 , _vv0 , _vw0 .

  The calculation unit 38 determines whether each value output from the calculation unit 37 exceeds the threshold “1”, and outputs each determination result.

The calculation unit 39 determines whether any of the determination results output from the calculation unit 38 has exceeded the threshold value “1”, and indicates that the threshold value “1” has been exceeded. In this case, a signal for operating the switching unit SW22 is output so that the value output from the SW21 is selected by the switching unit SW22 and output as the corrected zero-phase voltage v 0 _mod , while the threshold value “1” is exceeded. If this is not indicated, a signal for operating the switching unit SW22 is output so that the fixed value “0” is selected by the switching unit SW22 and output as the corrected zero-phase voltage v 0 _mod .

In such a configuration, when all of the voltage command values v _u0 , v _v0 , and v _w0 are within the upper limit threshold “1” of the modulation rate and the lower limit threshold “1” of the modulation rate, the calculation unit 37 None of the absolute values output from “1” exceeds the threshold “1”, and the determination results output from the calculation unit 38 do not indicate that any of the absolute values exceeds “1”.

At this time, the calculation unit 39 operates the switching unit SW22 so that the fixed value “0” is selected. As a result, the fixed value “0” passes through the switching unit SW22 and is output as the corrected zero-phase voltage v 0 _mod . By _{setting the} correction amount to 0 with this corrected zero-phase voltage v _0mod (= 0), the occurrence of overmodulation is prevented.

On the other hand, when any one of the voltage command values v _u0 , v _v0 , and v _w0 exceeds the upper limit threshold “1” of the modulation factor or falls below the lower limit threshold “−1”, the absolute value output from the computing unit 37 Any one of them exceeds the threshold “1”, and any of the determination results output from the calculation unit 38 indicates that the threshold “1” has been exceeded.

At this time, the calculation unit 39 operates the switching unit SW22 so that the value output from the SW21 is selected. Further, the calculation units 31 to 36 make the larger one of the maximum value “A” and the minimum value (absolute value) “B” of the voltage command value (that is, the upper limit threshold “1” or the lower limit threshold “ 1 ”) is selected, and the difference value between the selected value“ A ”or“ B ”and the corresponding threshold value passes through the switching unit SW21 and further through the switching unit SW22 to _obtain a corrected zero-phase voltage v 0 _mod. Is output. The corrected zero-phase voltage _{v 0Mod} will be added to the voltage command value _{v u0, v v0, v w0} . Thus, while suppressing the overmodulation, it is possible to maximize the variation suppression effect of the neutral point potential v _n.

The control device 10 obtains final voltage command values v _u ^* , v _v ^* , v _w ^* from the corrected zero-phase voltage v 0 _mod obtained by the control of FIG. 4 using the following equation (2). .

The zero-phase voltage superimposed on the voltage command values v _u , v _v , v _w to obtain the voltage command values v _u ^* , v _v ^* , v _w ^* is as shown in the following equation (3): _This is a zero-phase voltage v _o ′ obtained by _{adding the} zero-phase voltage v ₀ and the corrected zero-phase voltage v _{0 mod} .

The control device 10 controls the NPC inverter 100 by giving the voltage command values v _u ^* , v _v ^* , and v _w ^* to the NPC inverter 100.

The variation of the neutral point potential v _n in the case of applying the present embodiment, the modulation rate, calculated for each power factor (phase difference between voltage and current), when graphed, is as shown in FIG.

  Compared with the fluctuations of the prior art shown in FIG. 14, it can be seen that fluctuations in the operating region where the modulation factor is low and the power factor is low (region close to phase difference = π / 2) are suppressed in FIG. .

According to the first embodiment, it is possible to suppress the fluctuation of the neutral point potential v _n in a wider operation region prevents an increase in capacitance, it is possible to provide a safe electric power conversion device is compact and low-cost.

In the present embodiment, since the sign of the intermediate value of the voltage command values v _u , v _v , and v _w changes when the zero-phase voltage is superimposed, the change of the sign is determined for the intermediate value. Although the case was illustrated, it is not limited to this example. For example, the voltage command values _{v u,} v v, _v without performing processing for determining the intermediate values of _w, each phase voltage command values _{v u,} v v, for each _{v w,} to determine a change of sign It may be. Moreover, you may make it determine the voltage command value from which a code | symbol changes with methods other than the above.

  Further, the presence or absence of a change in the sign of the voltage command value before and after superimposing the zero-phase voltage may be determined based on the subtraction result of the two voltage command values before and after superimposing the zero-phase voltage. However, the determination may be made using another method (for example, another type of logic circuit).

[Second Embodiment]
Next, a second embodiment will be described. Below, description of the part which is common in 1st Embodiment is abbreviate | omitted, and it demonstrates centering on a different part.

  The configuration of the power conversion device according to the second embodiment is the same as that shown in FIG. However, the control device 10 according to the second embodiment has a case where the denominator of the above-described equation (1) changes across 0 even when there is no voltage command value whose sign is changed due to the superposition of the zero-phase voltage. Has a function of recalculating the zero-phase voltage by inverting the sign of the intermediate voltage command value. Thereby, it is prevented that an excessive zero-phase voltage is generated when the denominator of the expression (1) crosses 0, and the fluctuation suppression control is normally operated.

  FIG. 6 is a diagram illustrating an example of a functional configuration of neutral point potential fluctuation suppression control of the NPC inverter 100 by the control device 10 provided in the power conversion device 1 according to the present embodiment. In FIG. 6, the same reference numerals are given to the elements common to FIG. 2 described above.

  As shown in FIG. 6, the basic configuration is the same as the configuration of FIG. 2 described in the first embodiment, except that a determination unit 18 ′ is provided instead of the determination unit 18.

The above-described equation (1) has a denominator, and when the denominator is close to 0, the zero-phase voltage v ₀ takes an excessive value. Then, the voltage command value is overmodulated and correct control cannot be performed. Thus, in the present embodiment, the denominator of equation (1) is prevented from becoming an excessive zero-phase voltage across 0, and fluctuation suppression control is normally operated. Whether the denominator is a positive value or a negative value differs depending on the power factor. Therefore, the determination unit 18 ′ determines whether the stride is zero or not by determining whether the power factor is positive or negative.

  Similar to the determination unit 18 described above, the determination unit 18 ′ determines whether or not the value output from the calculation unit 17 is “0”, and if the value is “0”, the intermediate value However, the subsequent processing is different from that of the determination unit 18.

When the value output from the calculation unit 17 is “0”, the determination unit 18 ′ switches the switching unit SW11 so that the voltage command values v _u0 , v _v0 , and v _w0 output from the calculation unit 12 are selected. It does not necessarily output a signal to operate. If the denominator of equation (1) changes across 0, the voltage command after adding the zero-phase voltage _v0re obtained by recalculating the zero-phase voltage based on the intermediate value with the sign inverted. The values are output as voltage command values v _u0 , v _v0 , v _w0 . That is, when the denominator of the expression (1) changes across 0, the determination unit 18 ′ _selects the voltage command value after addition of the zero-phase voltage v _0re output from the calculation unit 21 by the switching unit SW11 and _sets the voltage A signal for operating the switching unit SW11 is output so as to be output as the command values v _u0 , v _v0 , and v _w0 .

When the denominator of Expression (1) does not change across 0, the voltage command value output from the calculation unit 12 is selected by the switching unit SW11 and output as the voltage command values v _u0 , v _v0 , and v _w0. As a result, a signal for operating the switching unit SW11 is output.

  Here, an example of the operation based on the neutral point potential fluctuation suppression control shown in FIG. 6 will be described with reference to FIG. In FIG. 7, the same reference numerals are given to elements common to FIG. 3 described above.

  A frame A in FIG. 7 represents determination processing by the determination unit 18 ′.

  The processes in steps S11 to S14 and S16 to S17 are as described in FIG.

In step S15, the control unit 10 determines whether or not the intermediate value has changed before and after the adding the zero-phase voltage v ₀ (S15). That is, it is determined through the calculation units 14, 16, 17 and the determination unit 18 ′ whether or not the sign of the intermediate value obtained by the calculation unit 15 matches the sign of the intermediate value obtained by the calculation unit 13. When the determination result in the determination unit 18 ′ is “0”, the signs are the same between the two, and the sign of the intermediate value is not changed before and after the addition of the zero-phase voltage v _0. Can be considered (No in S15).

  In step S15, if the intermediate value has not changed (No in S15), the control device 10 determines whether or not the denominator of Equation (1) has changed across 0 (S21 to S23).

Here, if the power factor is greater than 0 and the denominator is not less than 0 (Yes in S21, No in S22), the control device 10 assumes that the denominator does not change across 0, and calculates the calculation unit. The voltage command values v _u0 , v _v0 , and v _w0 obtained by 12 are output through the switching unit SW11. On the other hand, if the power factor is greater than 0 and the denominator is 0 or less (Yes in S21, Yes in S22), the control device 10 regards that the denominator has crossed 0 and proceeds to the processing in step S16. Proceed with

If the power factor is not greater than 0 and the denominator is not greater than 0 (No in S21, No in S23), the control device 10 assumes that the denominator does not change across 0, and calculates the calculation unit. The voltage command values v _u0 , v _v0 , and v _w0 obtained by 12 are output through the switching unit SW11. On the other hand, if the power factor is not greater than 0 and the denominator is greater than or equal to 0 (No in S21, Yes in S23), the control device 10 assumes that the denominator has crossed 0 and the process of step S16. Proceed to

  On the other hand, if the intermediate value has changed in step S15, the process proceeds to step S16 as in the case of FIG.

The variation of the neutral point potential v _n in the case of applying the present embodiment, the modulation rate, calculated for each power factor (phase difference between voltage and current), when graphed, is as shown in FIG.

  Compared with the variation according to the first embodiment shown in FIG. 5, in FIG. 8, the variation in the operating region where the modulation factor is low and the power factor is low (region close to phase difference = π / 2) is completely suppressed. I understand that.

According to the second embodiment, in addition to the effects obtained in the first embodiment, an excessive zero-phase voltage is prevented from being generated when the denominator of Expression (1) crosses 0, and fluctuation suppression control is normally performed. it is possible to act, it is possible to suppress the fluctuation of the neutral point potential v _n in a wider operation region.

[Third Embodiment]
Next, a third embodiment will be described. In the third embodiment, a part of the technique described in each embodiment described above is used.

  FIG. 9 is a diagram illustrating an example of the configuration of the power conversion device according to the third embodiment.

  The power conversion device 1 of the present embodiment includes an NPC converter having an inverter / converter configuration in which a DC voltage unit is common for each phase.

In the example of FIG. 9, each phase of the converter 101 and the inverter 102 constituting the NPC converter, respectively, with six semiconductor switching elements _S 1 to S ₆ in one leg, divide the DC voltage _{v PN} DC The voltage dividing capacitors C ₁ and C ₂ are shared. Here, the potential of the neutral point NP of the DC voltage _dividing capacitors C ₁ and C ₂ is assumed to be vn.

The power conversion apparatus 1 further control apparatus 10 which performs control to suppress fluctuation of the control and the neutral point potential v _n in the normal operation of two of the NPC converter 'is provided.

The control device 10 ′ obtains the zero-phase voltage v ₀ ⁱ of the inverter 102 using the above-described equation (1), and obtains the current of the neutral point NP obtained by measurement or obtained by calculation and the equation (1). (Or using a mathematical expression similar to Equation (1)) to obtain the zero-phase voltage v ₀ ^c of the converter 101 and superimpose the obtained zero-phase voltage of the converter 101 on the voltage command value of each phase of the converter 101. The function of performing control to superimpose the obtained zero-phase voltage of the inverter 102 on the voltage command value of each phase of the inverter 102 is provided.

The neutral point potential _{v n,} and the neutral point current _i ^{n c} flowing from the neutral point current _i ^{n i} and converter 101 flowing from the inverter 102 is affected. I _n ⁱ and i _n ^c are represented by the following formulas (4) and (5), respectively.

  Here, the superscript i represents the inverter 102, and the subscript c represents the converter 101.

The sum of the two neutral current, since the current _{i n} flows into the capacitor _C 1, _{C 2,} is expressed by the following equation (6).

Since the equation (6) is not neutral potential v _n if zero fluctuates, may be established Equation (7) below.

  Here, when the formula (5) is substituted into the formula (7), the following formula (8) is obtained.

  When this equation (8) is transformed, the following equation (9) is obtained.

Thereby, the zero-phase voltage v ₀ ^{c of} converter 101 is obtained.

Incidentally, after obtaining the zero-phase voltage _v ^{0 i} of the inverter 102, and the sought after zero-phase voltage _v ^{0 c} of the converter _101, the first embodiment described above respectively _v ^{0 i} and _v ^{0 c} The overmodulation limit control process described with reference to FIG. 4 may be performed. However, the overmodulation limit control process is not necessarily required.

By superimposing the zero-phase voltage v ₀ ^c to the voltage command value of each phase of the converter 101, the variation of the neutral point potential v _n of the inverter 102 generates the converter 101 can be suppressed in concert.

Equation (9) includes the neutral point current i _n ⁱ of the inverter 102. This i _n ⁱ is obtained by the calculation of Expression (4). The zero-phase voltage v ₀ ⁱ of the inverter 102 used for the calculation of the equation (4) is a zero-phase voltage that is actually superimposed on the voltage command value of each phase of the inverter 102. This corresponds to the value v ₀ obtained by the zero-phase voltage calculation of the NPC inverter in the first and second embodiments described above. That is, the zero phase voltage v ₀ ^c of the converter 101 is calculated after obtaining the zero phase voltage v ₀ ⁱ by the zero phase voltage calculation of the inverter 102.

Such as when the frequency of the converter 101 from the frequency of the inverter 102 is fast, the inverter 102 is dominantly cause variations neutral point potential v _n. If the frequency of the converter 101 is sufficiently high, the influence on the neutral point potential fluctuation is small. Therefore, the neutral point is obtained by superimposing the zero-phase voltage v ₀ ^c shown in Expression (9) on the voltage command value of each phase of the converter 101. effectively suppress the fluctuation of the potential v _n.

  FIG. 10 is a diagram illustrating an example of a functional configuration of neutral point potential fluctuation suppression control of the NPC converter by the control device 10 ′ provided in the power conversion device 1 according to the present embodiment.

  As illustrated in FIG. 10, the control device 10 ′ includes calculation units 41 to 45 as various functions.

The calculation unit 41 includes reference voltage command values v _u ⁱ , v _v ⁱ , and v _w ⁱ (herein abbreviated as “v _x ⁱ ”) for the inverter 102 and output currents i _u ⁱ and i _v ⁱ obtained from the inverter 102. , I _w ⁱ (here, abbreviated as “i _x ⁱ ”), and the same processing as the zero-phase voltage calculation described in the first and second embodiments, that is, the expression (1) is used. This is a function for outputting the zero-phase voltage v ₀ ⁱ of the inverter 102 by performing the zero-phase voltage calculation of the inverter 102 and performing re-calculation with the sign of the voltage command value reversed.

The calculation unit 42 receives the zero-phase voltage v ₀ ⁱ of the inverter 102 calculated by the calculation unit 41, performs the same process as the overmodulation limit control described in the first embodiment, and corrects the inverter 102. This is a function for outputting the zero-phase voltage v ₀ ^{i ′} . However, this is not an essential element.

The calculation unit 43 is a function for inputting the zero-phase voltage v ₀ ⁱ or the corrected zero-phase voltage v ₀ ^{i ′} of the inverter 102 and calculating the neutral point current i _n ⁱ of the inverter 102 using the equation (4). .

The calculation unit 44 inputs the neutral point current i _n ⁱ of the inverter 102 calculated by the calculation unit 43 and uses reference voltage command values v _u ^c , v _v ^c , and v _w ^c (here “ v _x ^c "and abbreviation) and obtained from the converter 101 output current ^{_{i u c, i v c,}} i w c ( here enter the abbreviation) and" _i ^{x c} ", using equation (1) converter 101. Zero-phase voltage calculation of 101 and re-calculation with the sign of the voltage command value reversed. More specifically, the zero-phase voltage calculation using the equation (9) including the variable i _n ⁱ and the sign of the voltage command value are reversed. This is a function of performing the recalculation and outputting the zero-phase voltage v ₀ ⁱ of the inverter 102.

The calculation unit 45 receives the zero-phase voltage v ₀ ^c of the converter 101 calculated by the calculation unit 44, performs the same processing as the overmodulation limit control described in the first embodiment, and corrects the converter 101. This is a function for outputting the zero-phase voltage v ₀ ^{c ′} . However, this is not an essential element.

In such a functional configuration, the control device 10 ′ is an inverter that uses Equation (1) or the like from the voltage command value v _x ⁱ of the inverter 102 and the output current i _x ⁱ of the inverter 102 by the calculation units 41 to 43. The zero-phase voltage calculation of 102 and the re-calculation with the sign of the voltage command value reversed are performed to obtain the zero-phase voltage v ₀ ⁱ and the corrected zero-phase voltage v ₀ ^{i ′} of the inverter 102, and the neutral point current of the inverter 102 Find i _n ⁱ .

Next, the control device 10 ′ uses the arithmetic units 44 and 45 to calculate the equation (2) from the neutral point current i _n ⁱ of the inverter 102, the voltage command value v _x ^c of the converter 101, and the output current i _x ^{c of the} converter 101. 1) The zero-phase voltage calculation of the converter 101 using the above and the re-calculation with the sign of the voltage command value inverted are performed to obtain the zero-phase voltage v ₀ ^c and the corrected zero-phase voltage v ₀ ^{c ′} of the converter 101.

Then, the control device 10 ′ superimposes the obtained zero-phase voltage v ₀ ⁱ or the corrected zero-phase voltage v ₀ ^{i ′} of the inverter 102 on the voltage command value v _x ⁱ of the inverter 102 and obtains it. The zero-phase voltage v ₀ ^{c of the} converter 101 and the corrected zero-phase voltage v ₀ ^{c ′} are superimposed on the voltage command value v _x ^c of the converter 101 and given to the converter 101.

The variation of the neutral point potential v _n in the case of applying the present embodiment, the modulation rate, when the calculated graph for each power factor is shown in Figure 11. Comparing FIG. 11 with FIG. 8, it can be seen that the fluctuation in the operation region (region close to π / 2) where the modulation factor is high and the power factor is low is generally reduced. The degree to which the fluctuation decreases depends on the operating conditions of the inverter 102 and the converter 101, but the tendency of the fluctuation to remain unchanged.

According to this embodiment, in a broader operation region can suppress the fluctuation of the neutral point potential v _n, it is possible to provide a safe electric power conversion device is compact, low-cost prevents an increase in capacitance.

In this embodiment, the neutral point current i _n ⁱ of the inverter 102 is obtained by calculation. However, using the value obtained by measuring the neutral point current of the actual inverter 102 using a current sensor or the like, the equation (9) You may calculate.

  As described above in detail, according to each embodiment, it is possible to suppress the fluctuation of the neutral point potential in a wider operation region and prevent the increase in the capacitor capacity.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10, 10 '... Control apparatus, 11-17, 19-21, 41-45 ... Operation part, 18, 18' ... Determination part, 100 ... NPC inverter, 101 ... Converter, 102 ... Inverter.
31-39 ... arithmetic unit, SW11, SW21, SW22 ... switching unit.

Claims (7)

Neutral point clamp type power converter,
Control that suppresses fluctuations in the neutral point potential of the power converter by calculating the zero-phase voltage of the power converter using a predetermined calculation formula and superimposing the zero-phase voltage on the voltage command value of each phase And a control means for performing
When there is a voltage command value whose sign changes due to the superposition of the zero-phase voltage, the control means reverses the sign of the voltage command value and recalculates the zero-phase voltage, and the zero-phase voltage after recalculation Is superimposed on the voltage command value of each phase,
Power conversion device. The control means obtains an intermediate value among the voltage command values of each phase, and when the sign of the intermediate value changes due to the superposition of the zero-phase voltage, the sign of the intermediate value is inverted and the zero-phase voltage Recalculate
The power conversion device according to claim 1. Even if there is no voltage command value whose sign changes due to the superposition of the zero-phase voltage, the control means may change the sign of the voltage command value if the sign changes across 0 in the denominator of the calculation formula. And the zero-phase voltage is recalculated.
The power converter according to claim 1 or 2. A first power converter and a second power converter sharing a neutral point;
The zero-phase voltage of the second power converter is obtained using a predetermined calculation formula, and the neutral point current obtained by measurement or obtained by calculation and the first calculation formula are used. The zero-phase voltage of the power converter is obtained, the obtained zero-phase voltage of the first power converter is superimposed on the voltage command value of each phase of the first power converter, and the obtained second power is obtained. A control device that performs control to superimpose a zero-phase voltage of the converter on a voltage command value of each phase of the second power converter;
A power conversion device comprising: The control device limits the zero-phase voltage so that the modulation rate for the voltage command value of each phase does not exceed a predetermined value.
The power converter device of any one of Claims 1 thru | or 4. A control method for a power converter having a neutral point clamp type power converter,
The control means calculates the zero-phase voltage of the power converter using a predetermined calculation formula, and superimposes the zero-phase voltage on the voltage command value of each phase to change the neutral point potential of the power converter. Including controlling to suppress
In the control, when there is a voltage command value whose sign changes due to the superposition of the zero-phase voltage, the sign of the voltage command value is inverted, the zero-phase voltage is recalculated, and the zero-phase voltage after recalculation is A method for controlling a power converter, comprising superimposing on a voltage command value for each phase. A method for controlling a power conversion device having a first power converter and a second power converter sharing a neutral point,
The control means obtains the zero-phase voltage of the second power converter using a predetermined calculation formula and uses the neutral point current obtained by measurement or obtained by calculation and the predetermined calculation formula. The zero phase voltage of the first power converter is obtained, the obtained zero phase voltage of the first power converter is superimposed on the voltage command value of each phase of the first power converter, and the obtained Performing control to superimpose the zero-phase voltage of the second power converter on the voltage command value of each phase of the second power converter;
A method for controlling the power conversion device.