JP2019187135A - Power conversion device and control method thereof - Google Patents

Abstract

To suppress an increase in switching loss 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 applying a first voltage command value and a second voltage command value generated using a voltage command value of each phase of the power converter to a first switching element group and a second switching element group of each of the phases constituting the power converter, respectively. The control means includes means for performing a first control mode for generating the first voltage command value and the second voltage command value from a new voltage command value of each phase obtained by superimposing the zero phase voltage of the power converter on the voltage command value of each phase of the power converter, and a second control mode for generating the first voltage command value and the second voltage command value on the basis of a voltage command value of each phase of the power converter and the maximum and minimum values so as to switch the modes.SELECTED DRAWING: Figure 2

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. 7, 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. In FIG. 7, the example of the power converter device 1 which consists of a three-phase NPC inverter 100 is shown. 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.

J. Pou, et al., “Fast-Processing Modulation Strategy for the Neutral-Point-Clamped Converter With Total Elimination of Low-Frequency Voltage Oscillations in the Neutral Point”, IEEE Transactions on Industrial Electronics, vol. 54, no. 4 , 2007

In the example of FIG. 7, the NPC inverter 100 includes six semiconductor switching elements S _{1 to} S ₆ in one leg for each phase, and includes DC voltage dividing capacitors C ₁ and C ₂ that divide 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 100 v _n has the property that varies at three times the fundamental wave in accordance with inverter operation. 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 represented as shown in the graph of FIG. In FIG. 8, 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.

This variation in the neutral point potential v _n can be suppressed by a control (for example, Non-Patent Document 1). Generally, there is one command value for each phase of the NPC inverter, but there is a method of using two commands, ie, an upper arm voltage command value v _up and a lower arm voltage command value v _un as shown in FIG. The upper arm voltage command value v _up is a command value given to the semiconductor switching elements S ₁ , S ₂ , S ₅ located in the upper half of each arm in FIG. 7, and the lower arm voltage command value v _un This is a command value given to the semiconductor switching elements S ₃ , S ₄ , S ₆ located in the lower half of each arm in FIG.

FIG. 9 shows an example of the u-phase command value. The upper arm voltage command value v _up is compared with the upper carrier car _p to obtain a gate signal to be given to the upper arm semiconductor switching elements S ₁ , S ₂ , S ₅ . On the other hand, the lower arm voltage command value v _un is compared with the lower carrier car _n to obtain a gate signal to be given to the lower arm semiconductor switching elements S ₃ , S ₄ , and S ₆ . The upper carrier car _p changes between modulation factors 0 and 1, and the lower carrier car _n changes between modulation factors −1 and 0.

The upper arm voltage command value v _ip and the lower arm voltage command value v _in (where i = u, v, w) for three phases are obtained by the following equation (1).

  Here, min is a function for obtaining the minimum value in the argument, and max is a function for obtaining the maximum value.

For example, when there are three-phase voltage command values v _u , v _v , and v _w shown in FIG. 10A, the u-phase voltage command values v _u are as shown in FIG. Converted. Further, the comparison process between the upper carrier car _p and the upper arm voltage command value v _up and the comparison process between the lower carrier car _n and the lower arm voltage command value v _un shown in FIG. A PWM-like u-phase output voltage v _uout as shown in (d) is obtained.

  When the modulation method by this control is applied and the magnitude of the fluctuation of the neutral point potential due to the modulation factor and the power factor is calculated, it is expressed as a graph in FIG. That is, it can be seen that the fluctuation of the neutral point potential can be completely suppressed in a certain operation region.

  However, looking at the PWM waveform in FIG. 10D, there is a section in which the switching element group of the upper arm and the switching element group of the lower arm are switched. In the normal modulation method, the NPC inverter switches only one of the upper arm switching element group and the lower arm switching element group. However, since both switches in this section, the switching frequency is doubled. Since this section is 1/3 of one cycle, on average, the switching frequency of the inverter increases 1.33 times. Then, an increase in switching loss is caused. In order to solve this problem, the inverter cooling device becomes larger and the cost becomes higher. In addition, the running cost of the inverter increases.

  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 an increase in switching loss while suppressing fluctuations in neutral point potential in a wider operating region. There is to do.

  The power conversion device according to the embodiment includes a neutral point clamp type power converter and the first switching element group and the second switching element group of each phase constituting the power converter. Control is performed to suppress fluctuations in the neutral point potential of the power converter by giving a first voltage command value and a second voltage command value generated using the voltage command value of each phase of the converter. Control means, the control means from the new voltage command value of each phase obtained by superimposing the zero phase voltage of the power converter on the voltage command value of each phase of the power converter. Based on the first control mode for generating the voltage command value and the second voltage command value, the voltage command value of each phase of the power converter, and the maximum value and the minimum value thereof. And a second control mode for generating a command value and the second voltage command value. Ete has means to implement.

  According to the present invention, it is possible to suppress an increase in switching loss while suppressing a change in neutral point potential in a wider operating region.

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 the operation | movement of the neutral point electric potential fluctuation | variation suppression control by the zero phase voltage superimposition in the same embodiment. The figure which shows an example of the fluctuation | variation of the neutral point electric potential by the zero phase voltage superimposition in the embodiment. The block diagram which shows an example of a function structure of the carrier comparison process in 3rd Embodiment. The figure which shows an example of the waveform of the carrier comparison process in the 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 modulation method by neutral point potential fluctuation | variation suppression control of a prior art. The figure which shows an example of the modulation | alteration waveform by neutral point potential fluctuation | variation suppression control of a prior art. The figure which shows an example of the neutral point electric potential fluctuation | variation by the neutral point electric potential fluctuation suppression control of 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. 7 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.

The control device 10 includes semiconductor switching elements S ₁ , S ₂ , S ₅ (first switching element group located in the upper half of each arm) and semiconductor switching elements S ₃ , S ₄ constituting the NPC inverter 100. , S ₆ (second switching element group located in the lower half of each arm) and the second voltage elements generated using the voltage command values v _u , v _v , v _w of each phase of the NPC inverter 100, respectively. voltage command value of 1 and performs a normal control for suppressing control and variation of the neutral point potential v _n of the operation of the NPC inverter 100 by giving a second voltage command value.

In particular, the control device 10 uses the voltage command values v _u , v _v , v _w of each phase of the NPC inverter 100 to superimpose the zero phase voltage of the NPC inverter 100 on the new voltage command values of each phase. The upper arm voltage command value (first voltage command value) v _up , v _vp , v _wp and the lower arm voltage command value (second voltage command value) v _un , v _vn , v _wn are generated. The upper arm voltage command value using the above-described equation (1) based on the control mode 1 and the voltage command values v _u , v _v , v _w of each phase of the NPC inverter 100 and the maximum and minimum values thereof. It has a function of switching and executing the second control mode for generating v _up , v _vp , v _wp and lower arm voltage command values v _un , v _vn , v _wn .

  For example, in the first control mode, the control device 10 determines that the modulation rate of any voltage command value of each phase on which the zero-phase voltage is superimposed is within a predetermined range (for example, the modulation rate is less than 1 and less than −1). When exceeding the large range), switching to the second control mode is performed. On the other hand, in the second control mode, when all the modulation factors of the voltage command values of the respective phases on which the zero-phase voltage is superimposed are within a predetermined range, switching to the first control mode is performed.

In the neutral point potential fluctuation suppression control in the second control mode using Equation (1), as described above, fluctuations in the neutral point potential can be completely suppressed in a certain operating region. Since the switching frequency increases in a section in which the arm switching element groups S ₁ , S ₂ , S ₅ and the lower arm switching element groups S ₃ , S ₄ , S ₆ are both switched, the switching loss increases. . Therefore, in the present embodiment, a period during which the modulation rate of the voltage command value of each phase on which the zero-phase voltage is superimposed is within a predetermined range (a period that is not overmodulation) is a neutral point according to the first control mode. Controls potential fluctuation suppression. In the first control mode, there is no section in which the upper arm switching element groups S ₁ , S ₂ , S ₅ and the lower arm switching element groups S ₃ , S ₄ , S ₆ are both switched. As a result, it is possible to suppress an increase in loss to a minimum while suppressing a neutral point potential fluctuation in a wider operating region.

  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. However, this configuration example is an example, and the present invention is not limited to this example.

  As illustrated in FIG. 2, the control device 10 includes a zero-phase voltage superimposition processing unit 11, determination units 12 and 13, calculation units 14 to 17, and switching units SW <b> 11, SW <b> 12, SW <b> 21, and SW <b> 22 as various functions.

  Among these elements, the switching units SW21 and SW22 perform switching so that one of the first control mode and the second control mode is selected.

  The neutral point potential fluctuation suppression control in the first control mode is realized using the zero-phase voltage superimposition processing unit 11, the determination units 12 and 13, the switching units SW11 and SW12, and the switching units SW21 and SW22. On the other hand, neutral point potential fluctuation suppression control in the second control mode is realized using the calculation units 14 to 18 and the switching units SW21 and SW22.

The zero-phase voltage superimposing unit 11 calculates the zero-phase voltage of the NPC inverter 100 using the following equation (2), and converts the zero-phase voltage into the voltage command values v _u , v _v , and v _w for each phase. It has a function of superposing and outputting as voltage command values v _u0 , v _v0 , v _w0 . 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, recalculates the zero-phase voltage, and calculates the zero-phase voltage after the recalculation. It also has a function of outputting the voltage command values v _u0 , v _v0 , and v _w0 superimposed on the voltage command values of each phase. This makes it possible to suppress the fluctuation of the neutral point potential v _n in a wider operation region. Further, even when there is no voltage command value whose sign has been changed due to the superposition of the zero-phase voltage, the control device 10 is an intermediate value when the denominator of the above-described equation (2) changes across 0. The function of recalculating the zero-phase voltage by inverting the sign of the voltage command value is also provided. This prevents an excessive zero-phase voltage from being generated when the denominator of Equation (2) crosses 0, and allows the fluctuation suppression control to operate normally.

  In the zero phase voltage superimposing processing unit 11, the following equation (2) is used.

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

  Here, an example of the operation of the zero-phase voltage superimposition processing unit 11 will be described with reference to FIG.

The zero-phase voltage superimposing processing unit 11 uses the equation (2) to calculate the zero-phase 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. performing calculations of the voltage determining 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 zero-phase voltage superimposition processing unit 11 obtains an intermediate value of the voltage command values v _u , v _v , and v _w (S13).

On the other hand, the zero-phase voltage superimposing processing unit 11 adds the obtained zero-phase voltage v ₀ to each of the voltage command values v _u , v _v , and v _w to obtain the voltage command values v _u0 , v _v0 , and v _w0 . Obtain (S14). These voltage command value _{v u0,} v _{v0, v} for _w0 also previously obtained intermediate values of the voltage command values _{v u0, v v0, v w0} .

Next, the zero phase voltage superimposition processing unit 11 determines whether or not the sign of the intermediate value has changed before and after the addition of the zero phase voltage v ₀ (S15). That is, it is determined whether or not the signs of the intermediate values match before and after the zero-phase voltage v ₀ is added. If the signs match, it can be considered that the sign of the intermediate value has not changed before and after the zero-phase voltage v ₀ is added (No in S15). On the other hand, if the signs do not match between the two, it can be considered that the sign of the intermediate value has changed before and after the addition of the zero-phase voltage v ₀ (Yes in S15).

  If the intermediate value has changed in step S15 (Yes in S15), the process proceeds to step S16.

  On the other hand, if the intermediate value has not changed in step S15 (No in S15), the zero-phase voltage superimposition processing unit 11 determines whether or not the denominator of the expression (2) has changed across 0. (S21-S23).

Here, if the power factor is greater than 0 and the denominator is not 0 or less (Yes in S21, No in S22), the zero-phase voltage superimposing processing unit 11 indicates that the denominator does not change across 0. The voltage command values v _u0 , v _v0 , v _w0 obtained in step S14 are output. 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 zero-phase voltage superimposing processing unit 11 regards that the denominator has crossed 0, and the step The process proceeds to S16.

In addition, if the power factor is not greater than 0 and the denominator is not greater than or equal to 0 (No in S21, No in S23), the zero-phase voltage superimposing processing unit 11 indicates that the denominator does not change across 0. The voltage command values v _u0 , v _v0 , v _w0 obtained in step S14 are output. 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 zero-phase voltage superimposing processing unit 11 regards that the denominator has crossed 0, The process proceeds to step S16.

In step S16, the zero-phase voltage superimposition processing unit 11 performs recalculation of the zero-phase voltage after inverting the sign of the intermediate value of the voltage command values v _u , v _v and v _w obtained in step S13. The zero-phase voltage v _0re is obtained (S16), and the obtained zero-phase voltage v _0re is added to each of the voltage command values v _u , v _v , v _w stored in step S12 to obtain a voltage command value v _u0 , _vv0 , and _vw0 are obtained (S17), and the obtained voltage command values _vu0 , _vv0 , and _vw0 are output.

In addition, the process of S21-S23 mentioned above is not necessarily required, and you may abbreviate | omit the implementation. In this case, if the intermediate value does not change in step S15 (No in S15), the zero-phase voltage superimposition processing unit 11 does not recalculate the zero-phase voltage, and the voltage command value v _u0 obtained in step S14. , V _v0 , v _w0 are output.

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.

Since the voltage command values v _u0 , v _v0 and v _w0 output from the zero-phase voltage superimposing processing unit 11 are command values for one leg of each phase, the voltage command values are determined by the determination units 12, SW 11 and SW 12. _Are divided into upper arm voltage command values v _up , v _vp , v _wp and lower arm voltage command values v _un , v _vn , v _wn .

Specifically, the determination unit 12 determines whether the modulation rate is positive or negative. If the modulation rate is positive, the voltage command values v _u0 , v _v0 , and v _w0 are the upper arm voltage command values. The switching units SW11 and SW12 are respectively operated so that the output values v _up , v _vp , and v _wp are output, and the fixed value “0” is output as the lower arm voltage command values v _un , v _vn , and v _wn . On the other hand, if the modulation factor is not positive (if negative), the fixed value “0” is output as the upper arm voltage command values v _up , v _vp , v _wp , and the voltage command values v _u0 , v _v0 , v _w0 to ensure output voltage command value _v un lower _arm, v _vn, as _{v wn,} operating switch unit SW11, SW12, respectively.

Also, the modulation units 13, SW 21, and SW 22 cause the modulation rate of any one of the voltage command values v _u0 , v _v0 , and v _w0 output from the zero-phase voltage superimposing unit 11 to be smaller than 1 and larger than −1, for example. The first control mode or the second control mode is selected depending on whether or not the range is exceeded.

Specifically, the determination unit 13 determines whether all of the voltage command values v _u0 , v _v0 , and v _w0 have an absolute value of the modulation factor smaller than 1, and if it is smaller, it is output from the switching unit SW11. The values are output as upper arm voltage command values v _up , v _vp , v _wp through the switching unit SW21, and the values output from the switching unit SW12 are output through the switching unit SW22 as lower arm voltage command values v _un , v _vn , v _The switching units SW21 and SW22 are each operated so as to be output as _wn . In this case, the first control mode is set.

On the other hand, if the absolute value of the modulation rate of any one of the voltage command values v _u0 , v _v0 , and v _w0 is not smaller than 1, the value output from the calculation unit 16 becomes the voltage command value v for the upper arm through the switching unit SW21. _The switching units SW21, SW22 are output so as to be output as _up , v _vp , v _wp and output as the lower arm voltage command values v _un , v _vn , v _wn through the switching unit SW22. To operate each. In this case, the second control mode is set.

The calculation units 14 to 18 are elements that perform the calculation of the above-described equation (1). Calculate “(v _i / 2) − (min (v _u , v _v , v _w ) / 2)” (where i = u, v, w) by the calculation units 14, 15, and 16 While _calculating the voltage command value v _ip (i.e., v _up , v _vp , v _wp ), the calculation units 14, 17, and 18 perform “(v _i / 2) − (max (v _u , v _v , v _w )”. / 2) "is calculated, and the lower arm voltage command value _{v in (i.e.,} v _un, v _vn, seek _{v wn).}

The variation of the neutral point potential v _n in the case of applying the neutral point potential fluctuation suppression control by the zero-phase voltage, the modulation ratio was calculated for each power factor (phase difference between voltage and current), when graphed, As shown in FIG. That is, it can be seen that in the operation region where the modulation factor is low and the power factor is low (phase difference = near π / 2), the neutral point potential fluctuation can be completely suppressed.

In the neutral point potential fluctuation suppression control by the zero-phase voltage, the upper arm switching element groups S ₁ , S ₂ , S ₅ and the lower arm switching element groups S ₃ , S ₄ , S ₆ are both switched. Since there is no section and the switching frequency does not increase, the loss can be reduced as compared with the control using only the equation (1). Further, by applying this embodiment, the control using the equation (1) is applied in the operation region where the fluctuation occurs in FIG. 4, so that the fluctuation of the neutral point potential is suppressed in a wider operation region. be able to. In this case, the graph of the variation of the neutral point potential v _n is similar to FIG 11.

  As described above, according to the second embodiment, it is possible to suppress an increase in loss to a minimum while suppressing a neutral point potential fluctuation in a wider operation region. In addition, it is possible to provide a small-sized and low-cost power conversion device by suppressing an increase in switching loss while preventing an increase in capacitor capacity.

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 in the second embodiment includes a determination unit (not shown) different from the determination unit 13 illustrated in FIG. 2 of the first embodiment, and is controlled with a determination criterion different from that of the first embodiment. Switch the mode.

  The control device 10 according to the second embodiment switches from the second control mode to the first control mode (or switches from the first control mode to the second control mode) according to the operating conditions of the NPC inverter 100. Do. The operating condition for applying the first control mode or the operating condition for applying the second control mode is determined in advance using, for example, a modulation factor and a power factor. In addition, you may determine using not only this but an active power command, a reactive power command, etc. Information indicating the operation condition is stored in a predetermined storage area, and is used as a criterion for switching the control mode during operation of the NPC inverter 100.

  For example, a boundary between a first operation range in the first control mode and a second operation range in the second control mode is determined in advance using, for example, a modulation factor and a power factor, and the first operation region The first control mode is applied to the operation in, and the second control mode is applied to the operation in the second operation region.

  According to the second embodiment, the determination criterion for switching the control mode can be set more finely than in the first embodiment, so that the balance between loss suppression and neutral point potential fluctuation suppression is improved. The operation in a more appropriate control mode according to the driving situation can be realized.

[Third Embodiment]
Next, a third 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, in the second control mode, the control device 10 in the second embodiment further includes an NPC inverter 100 according to the states of the upper arm voltage command value v _up and the lower arm voltage command value v _un. It has a function to change the carrier frequency.

For example, the control device 10 has a function of reducing the carrier frequency to, for example, a half of the normal frequency when both the upper arm voltage command value _vup and the lower arm voltage command value _vun are not 0, or During the period when the switching frequency of the element group including the semiconductor switching elements S ₁ , S ₂ , S ₅ of the upper arm and the semiconductor switching elements S ₃ , S ₄ , S _{6 of} the lower arm increases more than a certain value, For example, it has a function of lowering the carrier frequency to, for example, a normal frequency.

  FIG. 5 is a diagram illustrating an example of a functional configuration of carrier frequency switching control provided in the control device 10 provided in the power conversion device 1 according to the present embodiment. However, this configuration example is an example, and the present invention is not limited to this example.

  There are two types of carriers, car1 and car2, where car1 is a normal carrier and car2 is a switching carrier. Here, car2 is, for example, a frequency that is ½ of the frequency of car1, but is not limited thereto. For example, car2 may be 1/3 of the frequency of car1.

  The control device 10 includes comparison units 31 and 32, calculation units 33 and 34, determination units 35 and 36, a calculation unit 37, and switching units SW31 and SW32.

The comparison unit 31 uses the comparison result between the upper arm voltage command value v _up and the normal carrier car1 or the comparison result between the upper arm voltage command value v _up and the switching carrier car2 as the gate signal g for the upper arm element. Output as _up .

Comparing unit 32 includes a voltage command value v _un the lower arm, the result of comparison between the difference between the normal carrier car1 value "1" which is calculated by the arithmetic unit 33, or the voltage command value v _un lower arm, the comparison result of the difference between the switching carrier car2 value "1" which is calculated by the arithmetic unit 34, and outputs a gate signal g _un the lower arm device.

The determination unit 35 determines whether or not the upper arm voltage command value v _up is 0. If it is 0, 1 is output, and if it is not 0, 0 is output.

The determination unit 36 determines whether or not the lower arm voltage command value _vun is 0. If it is 0, 1 is output, and if it is not 0, 0 is output.

If at least one of the outputs of the determination units 35 and 36 is not 0 (that is, if at least one of the upper arm voltage command value v _up and the lower arm voltage command value v _un is 0), the calculation unit 37 The switching units SW31 and SW32 are operated so as to select the contact 0, respectively. On the other hand, if both the outputs of the determination units 35 and 36 are 0 (that is, if both the upper arm voltage command value v _up and the lower arm voltage command value v _un are not 0), the switching units SW31, Each SW 32 is operated so as to select one contact.

In such a configuration, for the upper arm voltage command value v _{Stay up-and} lower arm voltage command value v _un is in a period of at least one of which is 0, it is applied normal carrier car1. On the other hand, in the period for the upper arm voltage command value v _{Stay up-and} lower arm voltage command value v _un is not both 0, the switching carrier car2 is applied. This is shown in a waveform diagram as shown in FIG.

The period for the upper arm voltage command value v _{Stay up-and} lower arm voltage command value v _un is not both 0, when provisionally applying ordinary carrier car1, total number of switching times of the upper and lower arms is doubled, In the present embodiment, since the carrier car2 is applied, the carrier frequency is halved, and the total number of times of switching does not change compared to before switching. That is, an increase in switching loss is suppressed.

  According to the third embodiment, an increase in switching loss can be further suppressed as compared with the first embodiment.

  As described above in detail, according to each embodiment, an increase in switching loss can be suppressed while suppressing a change in neutral point potential in a wider operation region.

  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 ... Control apparatus, 11 ... Zero phase voltage superimposition process part, 12, 13 ... Determination part, 14-17 ... Calculation part, 31, 32 ... Comparison part, 33, 34 ... Calculation part, 35, 36 ... Determination part, 37 ... arithmetic unit, 100 ... NPC inverter, SW11, SW12, SW21, SW22, SW31, SW32 ... switching part.

Claims (6)

Neutral point clamp type power converter,
The first voltage generated using the voltage command value of each phase of the power converter for the first switching element group and the second switching element group of each phase constituting the power converter, respectively. Control means for performing control for suppressing fluctuations in the neutral point potential of the power converter by giving a command value and a second voltage command value;
The control means includes
The first voltage command value and the second voltage command value from the new voltage command value of each phase obtained by superimposing the zero phase voltage of the power converter on the voltage command value of each phase of the power converter. A first control mode for generating
A second control mode for generating the first voltage command value and the second voltage command value based on the voltage command value of each phase of the power converter and its maximum and minimum values;
A power conversion device having means for switching and implementing. The control means includes
In the first control mode, when any modulation rate of the voltage command value of each phase on which the zero-phase voltage is superimposed exceeds a predetermined range, switching to the second control mode is performed.
The power conversion device according to claim 1. The control means includes
Depending on the operating conditions of the power converter, switching between the first control mode and the second control mode is performed.
The power conversion device according to claim 1. The control means includes
In the second control mode, the carrier frequency of the power converter is changed according to the respective states of the first voltage command value and the second voltage command value.
The power conversion device according to claim 1. The control means includes
In the second control mode, the carrier frequency of the power converter is reduced during a period in which the switching frequency of the element group including the first switching element group and the second switching element group increases more than a certain value.
The power conversion device according to claim 4. A control method for a power converter having a neutral point clamp type power converter,
The control means generates the first switching element group and the second switching element group of each phase constituting the power converter using the voltage command value of each phase of the power converter, respectively. Performing control to suppress fluctuations in the neutral point potential of the power converter by giving a first voltage command value and a second voltage command value,
The first voltage command value and the second voltage command value from the new voltage command value of each phase obtained by superimposing the zero phase voltage of the power converter on the voltage command value of each phase of the power converter. A first control mode for generating
A second control mode for generating the first voltage command value and the second voltage command value based on the voltage command value of each phase of the power converter and its maximum and minimum values;
The control method of a power converter device including switching and implementing.