CN110380636B - Power conversion device and control method for power conversion device - Google Patents
Power conversion device and control method for power conversion device Download PDFInfo
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- CN110380636B CN110380636B CN201910292624.8A CN201910292624A CN110380636B CN 110380636 B CN110380636 B CN 110380636B CN 201910292624 A CN201910292624 A CN 201910292624A CN 110380636 B CN110380636 B CN 110380636B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/4833—Capacitor voltage balancing
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0025—Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
Abstract
A power converter according to an embodiment is provided with a control device (10), wherein the control device (10) has a mechanism for switching between a 1 st control mode and a 2 nd control mode, wherein in the 1 st control mode, the 1 st voltage command value and the 2 nd voltage command value are generated from a new voltage command value of each phase obtained by superimposing a zero-phase voltage of a power converter (100) on a voltage command value of each phase of the power converter (100), and in the 2 nd control mode, the 1 st voltage command value and the 2 nd voltage command value are generated based on the voltage command value of each phase of the power converter (100) and a maximum value and a minimum value thereof.
Description
Priority is claimed based on japanese patent application No. 2018-076721 (application date: 2018, 4/12), which is incorporated by reference in its entirety.
Technical Field
Embodiments of the present invention relate to a power conversion device and a method of controlling the power conversion device.
Background
A power converter that converts direct current and alternating current is also called an inverter or a converter, and is used in a wide range of fields in society. The most basic inverter is a 2-level (level) inverter formed of 2 semiconductor switching elements, and outputs 2 voltage levels with 1 pin.
On the other hand, there is a Neutral-Point Clamped (NPC) inverter as follows: as shown in fig. 7, 4 semiconductor switching elements and 2 diodes (semiconductor switching elements may be used) are provided for 1 pin for each phase, and a dc voltage dividing capacitor common to the phases is provided. Fig. 7 shows an example of a power conversion device 1 including a three-phase NPC inverter 100. The NPC inverter 100 can output 3 voltage levels with 1 pin, and is advantageous for high withstand voltage, loss reduction, and high frequency reduction, and therefore is used in various inverters.
In the example of fig. 7, NPC inverter 100 includes 6 semiconductor switches at 1 pin for each phaseComponent S1～S6Having a DC voltage vPNDivided DC voltage dividing capacitor C1、C2. Here, a DC voltage-dividing capacitor C is provided1、C2Has a potential v of neutral point NP ofn. Neutral point potential v of NPC inverter 100nThe inverter has a property of varying by 3 times the fundamental wave according to the operation of the inverter. If the neutral point potential vnIf the variation of (3) is large, the voltage applied to the semiconductor switching element varies, and when the voltage is high, the element may be broken due to exceeding the withstand voltage, and when the voltage is low, a desired voltage may not be obtained, and overmodulation may be caused.
Potential v of neutral pointnThe magnitude of the variation in (c) is related to the modulation rate and power factor, capacitor capacitance, load current. The neutral point potential v caused by the modulation factor and the power factor is calculated while the capacitor capacitance and the load current are set to constant valuesnThe magnitude of the fluctuation of (a) is shown as a graph in fig. 8. In fig. 8, the power factor is represented as a phase difference of voltage and current. It is found that the neutral point potential v is higher in the modulation factor and lower in the power factor (closer to the phase difference pi/2)nThe larger the variation in.
Suppression of neutral point potential vnThe simplest way of varying (c) is to increase the capacitor capacitance. However, the increase in the capacitor capacitance increases the size and cost of the inverter, and the energy during an accident also increases.
The neutral point potential vnThe variation of (2) can be suppressed by the control. Normally, the command value for each phase of the NPC inverter is 1, but as shown in fig. 9, there is a voltage command value v for using an upper arm (arm)upAnd a voltage command value v for the lower branchunThe method of these 2. Voltage command value v for upper circuitupFor the semiconductor switching element S in fig. 7 located in the upper half of each branch1、S2、S5Assigned command value, lower branch voltage command value vunFor the semiconductor switching element S located at the lower half of each branch in fig. 73、S4、S6Given the value of the instruction.
In FIG. 9 with uThe instruction values of the phases are shown as examples. By setting the upper branch voltage command value vupAnd upper carrier carpThe comparison process is performed to obtain the semiconductor switching element S for the upper branch1、S2、S5The gate signal given. On the other hand, the lower branch voltage command value v is set tounAnd a download cardnThe comparison process is performed to obtain the semiconductor switching element S for the lower branch3、S4、S6The gate signal given. Upper carrier carpThe carrier car is changed between modulation rates 0-1nThe modulation rate is varied from-1 to 0.
Three-phase upper branch voltage command value vipAnd a voltage command value v for the lower branchin(i ═ u, v, and w) is determined by the following formula (1).
Here, min is a function for obtaining the minimum value among the independent variables, and max is a function for obtaining the maximum value.
For example, there are three-phase voltage command values v shown in fig. 10Au、vv、vwIn the case of (1), the u-phase voltage command value v is setuThe conversion is performed by equation (1) as shown in fig. 10B. Further, the upper carrier car shown in fig. 10C passes throughpVoltage command value v for upper branchupAnd the lower carrier carnVoltage command value v for lower branch circuitunThe comparison processing of (3) gives a PWM-waveform u-phase output voltage v as shown in FIG. 10Duout。
The magnitude of the fluctuation of the neutral point potential due to the modulation factor and the power factor in the case of the modulation method to which this control is applied is calculated and expressed as shown in the graph of fig. 11. That is, it is found that the fluctuation of the neutral point potential can be completely suppressed in a certain operation region.
However, if the PWM waveform of fig. 10D is observed, there is a section in which both the switching element group of the upper arm and the switching element group of the lower arm are switched. In a typical modulation method, the NPC inverter switches only one of the switching element group of the upper arm and the switching element group of the lower arm, but both of them are switched in this interval, and therefore the switching frequency is doubled. Since the interval is 1/3 of 1 cycle, the switching frequency of the inverter is increased to 1.33 times on average. Thus, an increase in switching loss results. In order to solve this problem, the cooling device for the inverter is increased in size and cost. In addition, the operating cost of the inverter also increases.
In view of the above, it is desirable to provide a technique capable of suppressing the fluctuation of the neutral point potential and suppressing the increase of the switching loss in a larger operation region.
Disclosure of Invention
The power conversion device according to the present invention includes: a neutral point clamped power converter; and a control device that performs control for suppressing a variation in a neutral point potential of the power converter by applying a 1 st voltage command value and a 2 nd voltage command value generated using a voltage command value of each phase of the power converter to a 1 st switching element group and a 2 nd switching element group that constitute each phase of the power converter, respectively, the control device including means for switching and executing: a 1 st control mode for generating the 1 st voltage command value and the 2 nd voltage command value based on a new voltage command value for each phase obtained by superimposing a zero-phase voltage of the power converter on a voltage command value for each phase of the power converter; and a 2 nd control mode for generating the 1 st voltage command value and the 2 nd voltage command value based on the voltage command value of each phase of the power converter and the maximum value and the minimum value thereof.
Drawings
Fig. 1 is a diagram showing an example of an NPC inverter according to embodiment 1.
Fig. 2 is a diagram showing an example of a functional configuration of the neutral point potential variation suppression control according to the present embodiment.
Fig. 3 is a diagram showing an example of the operation of the neutral point potential variation suppression control based on the zero-phase voltage superposition according to the present embodiment.
Fig. 4 is a diagram showing an example of the variation of the neutral point potential due to the zero-phase voltage superposition according to the embodiment.
Fig. 5 is a block diagram showing an example of a functional configuration of the carrier comparison processing according to embodiment 3.
Fig. 6 is a diagram showing an example of a waveform of the carrier comparison processing according to this embodiment.
Fig. 7 is a diagram showing an example of a circuit of a conventional NPC inverter.
Fig. 8 is a diagram showing an example of a variation in the neutral point potential in the conventional art.
Fig. 9 is a diagram showing an example of a modulation method based on the neutral point potential variation suppression control of the related art.
Fig. 10A, 10B, 10C, and 10D are diagrams showing an example of a modulation waveform based on the neutral point potential variation suppression control according to the related art.
Fig. 11 is a diagram showing an example of neutral point potential variation based on the neutral point potential variation suppression control of the related art.
Detailed Description
Hereinafter, embodiments will be described with reference to the drawings.
[ embodiment 1 ]
First, embodiment 1 will be explained. In the following, a description of a portion common to the above-described conventional structure is omitted, and a description of a different portion is mainly given.
Fig. 1 is a diagram showing an example of the configuration of a power conversion device according to embodiment 1. In fig. 1, the same elements as those in fig. 7 are denoted by the same reference numerals.
The NPC inverter 100 constituting the power conversion device 1 is a normal three-phase NPC inverter similar to that shown in fig. 7. However, the present invention is not limited to this example. For example, although the NPC inverter is exemplified as the neutral point clamped power converter in the present embodiment, the NPC inverter may be implemented as a substitute for the NPC converter. The neutral point clamp may be a T-type neutral point clamp or may be a type other than the T-type neutral point clamp.
The power conversion device 1 further includes a control device for controlling the normal operation of the NPC inverter 100, and a control program for controlling the normal operation of the NPC inverter 100Suppression of neutral point potential vnAnd a control device 10 for controlling the fluctuation of (a) the voltage (a) to be measured (hereinafter referred to as "neutral point potential fluctuation suppression control").
The control device 10 controls the semiconductor switching elements S of the respective phases constituting the NPC inverter 1001、S2、S5(the 1 st switching element group located in the upper half of each branch) and a semiconductor switching element S3、S4、S6(the 2 nd switching element group located in the lower half of each branch) is given a voltage command value v for each phase using the NPC inverter 100u、vv、vwThe 1 st voltage command value and the 2 nd voltage command value are generated to control the normal operation of the NPC inverter 100 and suppress the neutral point potential vnControl of the variation of (2).
In particular, the control device 10 has a function of switching between a 1 st control mode and a 2 nd control mode, and the 1 st control mode is executed in accordance with a voltage command value v for each phase of the NPC inverter 100u、vv、vwA new voltage command value for each phase obtained by superimposing the zero-phase voltage of the NPC inverter 100 is generated as an upper-branch voltage command value (1 st voltage command value) vup、vvp、vwpAnd a lower branch voltage command value (2 nd voltage command value) vun、vvn、vwnThe 2 nd control mode is based on the voltage command value v of each phase of the NPC inverter 100u、vv、vwAnd the maximum value and the minimum value thereof, and generating an upper-branch voltage command value v using the above equation (1)up、vvp、vwpAnd a voltage command value v for the lower branchun、vvn、vwn。
For example, in the 1 st control mode, when any one of the modulation factors of the voltage command values of the phases to which the zero-phase voltage is superimposed exceeds a predetermined range (for example, a range in which the modulation factor is smaller than 1 and larger than-1), the control device 10 performs switching to the 2 nd control mode. On the other hand, in the 2 nd control mode, if all the modulation ratios of the voltage command values of the respective phases to which the zero-phase voltage is superimposed are within a predetermined range, switching to the 1 st control mode is performed.
In the neutral point potential variation suppression control based on the 2 nd control mode using the expression (1), the variation of the neutral point potential can be completely suppressed in the certain operation region as described above, but only by this control, the switching element group S in the upper arm is controlled1、S2、S5And a switching element group S of the lower branch3、S4、S6In the section where both of these sections are switched, the switching frequency increases, and therefore the switching loss increases. Therefore, in the present embodiment, the neutral point potential variation suppression control in the 1 st control mode is performed during a period (period other than the overmodulation period) in which the modulation factor of the voltage command value of each phase to which the zero-phase voltage is superimposed falls within a predetermined range. In the 1 st control mode, the group S of switching elements without upper branch1、S2、S5And a switching element group S of the lower branch3、S4、S6Both switched on and off. This can suppress the fluctuation of the neutral point potential in a larger operation region and can suppress the increase of the loss to the minimum.
Fig. 2 is a diagram showing an example of a functional configuration of the neutral point potential variation 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 is not limited to this example.
As shown in fig. 2, the control device 10 includes, as various functions, a zero-phase voltage superposition processing unit 11, determination units 12 and 13, operation units 14 to 18, and switching units SW11, SW12, SW21, and SW 22.
The switching units SW21 and SW22 of these elements switch to select one of the 1 st control mode and the 2 nd control mode.
Neutral point potential variation suppression control in the 1 st 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 SW 22. On the other hand, the neutral point potential variation suppression control in the 2 nd control mode is realized by using the computing units 14 to 18 and the switching units SW21 and SW 22.
Zero-phase voltage superposition processing unitThe NPC inverter 100 calculates the zero-phase voltage using the following expression (2), and outputs the zero-phase voltage to the voltage command value v of each phaseu、vv、vwSuperimposed as a voltage command value vu0、vv0、vw0And (4) an output function. The control device 10 further includes a voltage command value that changes in sign by superimposing the zero-phase voltage, a recalculation of the zero-phase voltage by inverting the sign of the voltage command value, and a voltage command value v obtained by superimposing the recalculated zero-phase voltage on the voltage command value of each phaseu0、vv0、vw0And (4) an output function. This makes it possible to suppress the neutral point potential v in a larger operating regionnA variation of (c). Further, the control device 10 has a function of performing recalculation of the zero-phase voltage by inverting the sign of the voltage command value of the intermediate value when the denominator of the above equation (2) changes across 0 even when there is no voltage command value whose sign changes by superposition of the zero-phase voltage. This prevents the generation of an excessive zero-phase voltage due to the denominator of equation (2) crossing 0, and allows the fluctuation suppression control to function normally.
The zero-phase voltage superimposition processing unit 11 uses the following expression (2).
Wherein v isu、vv、vwIndicates the voltage command value i of each phase pin normalized by 1u、iv、iwRepresenting the current output from the pin of each phase. sign denotes 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. 3.
The zero-phase voltage superposition processing unit 11 bases on the voltage command value vu、vv、vwAnd the output current i derived from the NPC inverter 100u、iv、iwThe zero-phase voltage v is obtained by calculating the zero-phase voltage using the equation (2)0(S11). In addition, the voltage command value vu、vv、vwWith subsequent calculation, in addition to the intermediate value, also for the zero-phase voltage v0reThe above calculation is temporarily stored in a predetermined storage area (S12).
The zero-phase voltage superposition processing unit 11 obtains the voltage command value vu、vv、vwThe intermediate value of (S13).
On the other hand, the zero-phase voltage superposition processing unit 11 adds the voltage command value v to the voltage command value vu、vv、vwRespectively adding the obtained zero-phase voltages v0To obtain a voltage command value vu0、vv0、vw0(S14). Regarding these voltage command values vu0、vv0、vw0Also, a voltage command value v is obtainedu0、vv0、vw0To the median value of (c).
Subsequently, the zero-phase voltage superposition processing unit 11 determines that the zero-phase voltage v is added0Whether the signs of the preceding and following intermediate values have changed (S15). That is, it is determined that the zero-phase voltage v is applied0Whether the signs of the preceding and following intermediate values coincide. When the sign of the voltage v is identical to that of the zero-phase voltage v, the voltage v can be regarded as being applied0The sign of the intermediate value between before and after has not changed (No of S15). On the other hand, when the sign of the voltage v is not the same, it can be regarded that the zero-phase voltage v is applied0The sign of the intermediate values before and after has changed (Yes of S15).
In step S15, if the sign of the intermediate value has changed (Yes in S15), the process proceeds to step S16.
On the other hand, in step S15, if the sign of the intermediate value has not changed (No in S15), the zero-phase voltage superimposition processing unit 11 performs determination as to whether or not the denominator of expression (2) has changed across 0 (S21 to S23).
Here, if the power factor is larger than 0 and the denominator is not less than 0 (Yes in S21, No in S22), the zero-phase voltage superposition processing unit 11 regards that the denominator does not change across 0, and sets the voltage command value v obtained in step S14 to be equal to or less than 0u0、vv0、vw0And (6) outputting. On the other hand, if the power factor is larger than 0 and the denominator is 0 or less (Yes in S21, Yes in S22), the zero-phase voltage superposition processing unit 11 assumes that the denominator changes over 0, and proceeds to the processing in step S16.
Further, if the power factor is larger than 0 and the denominator is not equal to or larger than 0 (No in S21, No in S23), the zero-phase voltage superposition processing unit 11 regards the denominator as not changing across 0, and sets the voltage command value v obtained in step S14 to be equal to or larger than 0u0、vv0、vw0And (6) outputting. On the other hand, if the power factor is larger than 0 and the denominator is 0 or more (No in S21, Yes in S23), the zero-phase voltage superimposition processing unit 11 assumes that the denominator changes over 0, and proceeds to the processing in step S16.
In step S16, the zero-phase voltage superimposition processing unit 11 sets the voltage command value v obtained in step S13 to the valueu、vv、vwAfter the sign of the intermediate value of (3) is inverted, the zero-phase voltage is recalculated to obtain the zero-phase voltage v0re(S16), the zero-phase voltage v is calculated0reRespectively corresponding to the voltage command value v stored in step S12u、vv、vwAdding the voltage command value v to obtain a voltage command value vu0、vv0、vw0(S17) and comparing the obtained voltage command value vu0、vv0、vw0And (6) outputting.
The above-described processing of S21 to S23 is not necessarily required, and may be omitted. 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 sets the voltage command value v obtained in step S14 to the value of "No (No)" in step S3526u0、vv0、vw0And (6) outputting.
In this way, when the sign of the intermediate value changes by superimposing the zero-phase voltage, the sign is inverted and the zero-phase voltage is recalculated to obtain the zero-phase voltage v0reThe zero-phase voltage v is set0reVoltage command value v to each phaseu、vv、vwAnd (6) superposing. This appropriately exerts the fluctuation suppression effect.
Due to the voltage command value v outputted from the zero-phase voltage superposition processing unit 11u0、vv0、vw0Is a command value for 1 pin of each phase, and the judgment unit 12, SW11 and SW12 divide the voltage command value into an upper-branch voltage command value vup、vvp、vwpAnd a voltage command value v for the lower branchun、vvn、vwn。
Specifically, the determination unit 12 determines whether the modulation factor is positive or negative, and if the modulation factor is positive, the switching units SW11 and SW12 are operated so that the voltage command value v is set to be positiveu0、vv0、vw0As a voltage command value v for an upper circuitup、vvp、vwpOutputting the fixed value '0' as the lower branch voltage command value vun、vvn、vwnAnd (6) outputting. On the other hand, if the modulation factor is not positive (if negative), the switching units SW11 and SW12 are operated so that the fixed value "0" becomes the upper-branch-use voltage command value vup、vvp、vwpOutput and voltage command value vu0、vv0、vw0As a lower branch voltage command value vun、vvn、vwnAnd (6) outputting.
The judgment unit 13, SW21, and SW22 output the voltage command value v from the zero-phase voltage superposition processing unit 11u0、vv0、vw0Is larger than a range of, for example, smaller than 1 and larger than-1, the 1 st control mode or the 2 nd control mode is selected.
Specifically, the determination unit 13 determines whether or not the voltage command value v is presentu0、vv0、vw0The absolute value of which modulation factor is smaller than 1, and if smaller, switching units SW21 and SW22 are operated so that the value output from switching unit SW11 passes through switching unit SW21 as upper-branch voltage command value vup、vvp、vwpThe value outputted from the switching unit SW12 is used as the lower arm voltage command value v via the switching unit SW22un、vvn、vwnAnd (6) outputting. In this case, the 1 st control mode is set.
On the other hand, if the voltage command value vu0、vv0、vw0When the absolute value of any of the modulation ratios is not more than 1, the switching units SW21 and SW22 are operated so that the value output from the arithmetic unit 16 is made to be the upper-branch voltage command value v via the switching unit SW21up、vvp、vwpThe value outputted from the arithmetic unit 18 is passed through the switching unit SW22 as the lower arm voltage command value vun、vvn、vwnAnd (6) outputting. In this case, the 2 nd control mode is set.
The operation units 14 to 18 are elements for performing the operation of the above formula (1). Calculating "(v) by the calculating units 14, 15, 16i/2)－(min(vu，vv，vw) (where i is u, v, and w), the upper-branch voltage command value v is obtainedip(i.e., v)up、vvp、vwp) On the other hand, "(v) is calculated by the calculation units 14, 17, and 18i/2)－(max(vu，vv，vw) /2) ", and the lower arm voltage command value v is obtainedin(i.e., v)un、vvn、vwn)。
If the neutral point potential v is calculated according to the modulation factor and the power factor (the phase difference between the voltage and the current) when the neutral point potential variation suppression control based on the zero-phase voltage is appliednThe change in the image is patterned as shown in FIG. 4. That is, it is found that in an operating region where the modulation factor is low and the power factor is low (close to the phase difference of pi/2), the fluctuation of the neutral point potential can be completely suppressed.
In the neutral point potential variation suppression control based on the zero-phase voltage, the switching element group S having no upper arm is used1、S2、S5And a switching element group S of the lower branch3、S4、S6In both the switching intervals, the switching frequency is not increased, and therefore, the loss can be reduced as compared with the control using only expression (1). In addition, by applying the present embodiment,since the control using the equation (1) is applied to the operating region in which the fluctuation appears in fig. 4, the fluctuation of the neutral point potential can be suppressed in a larger operating region. In this case, the neutral point potential vnThe graph of variation of (a) is the same as that of fig. 11.
As described above, according to embodiment 1, it is possible to suppress the fluctuation of the neutral point potential in a larger operation region and to suppress the increase of the loss to the minimum. Further, it is possible to provide a small-sized and low-cost power conversion device in which an increase in switching loss is suppressed while preventing an increase in capacitor capacitance.
In the present embodiment, the voltage command value v is obtained when the zero-phase voltage is superimposedu、vv、vwIn the above, the sign of the intermediate value is changed, and thus, the change of the sign is determined for the intermediate value, but the present invention is not limited to this example. For example, the voltage command value v may not be determinedu、vv、vwFor the voltage command value v of each phaseu、vv、vwThe change of the sign is determined separately. The voltage command value having a changed sign may be determined by a method other than the above method.
The presence or absence of a change in the sign of the voltage command value before and after the zero-phase voltage is superimposed may be determined based on the subtraction result of 2 voltage command values before and after the zero-phase voltage is superimposed, but the determination is not limited to this, and may be performed by another method (for example, another type of logic circuit).
[ 2 nd embodiment ]
Next, embodiment 2 will be explained. Hereinafter, the description of the portions common to embodiment 1 will be omitted, and the description will be given centering on the different portions.
The power conversion device according to embodiment 2 has the same configuration as that shown in fig. 1. However, the control device 10 according to embodiment 2 includes a determination unit (not shown) different from the determination unit 13 shown in fig. 2 of embodiment 1, and switches the control mode based on a determination criterion different from that of embodiment 1.
The control device 10 according to embodiment 2 switches from the 2 nd control mode to the 1 st control mode (or switches from the 1 st control mode to the 2 nd control mode) in accordance with the operating conditions of the NPC inverter 100. The operating conditions to which the 1 st control mode is applied or the operating conditions to which the 2 nd control mode is applied are set in advance using, for example, a modulation factor and a power factor. The present invention is not limited to this, and may be set using an active power command, an inactive power command, or the like. The information indicating the operating conditions is stored in a predetermined storage area and used as a criterion for determining switching of the control mode during operation of the NPC inverter 100.
For example, the boundary between the 1 st operation range of the 1 st control mode and the 2 nd operation range of the 2 nd control mode is set in advance using, for example, the modulation factor and the power factor, the 1 st control mode is applied to the operation in the 1 st operation range, and the 2 nd control mode is applied to the operation in the 2 nd operation range.
According to embodiment 2, since the criterion for switching the control mode can be set more finely than in embodiment 1, the balance between the loss suppression and the neutral point potential variation suppression can be made better, and the operation in the appropriate control mode can be realized in accordance with the operating conditions.
[ embodiment 3 ]
Next, embodiment 3 will be explained. Hereinafter, the description of the portions common to embodiment 1 will be omitted, and the description will be given centering on the different portions.
The power conversion device according to embodiment 3 has the same configuration as that shown in fig. 1. However, the control device 10 according to embodiment 3 further has functions of: in the 2 nd control mode, the upper-branch voltage command value v is usedupAnd a voltage command value v for the lower branchunThe respective states change the carrier frequency of the NPC inverter 100.
For example, the control device 10 has functions of: voltage command value v for upper branchupAnd a voltage command value v for the lower branchunWhen the carrier frequency is not 0, for example, the carrier frequency is lowered to a normal 1/2 frequency, or the semiconductor switching element S of the upper branch is connected1、S2、S5With the semiconductor switching element S of the lower branch3、S4、S6The carrier frequency of the NPC inverter 100 is lowered to, for example, a normal 1/2 frequency while the switching frequency of the grouped element groups is increased by a predetermined time or more.
Fig. 5 is a diagram showing 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 is not limited to this example.
The carriers include 2 types of car1 and car2, car1 is a normal carrier, and car2 is a handover carrier. Here, car2 is, for example, a 1/2 frequency that is the frequency of car1, but is not limited thereto. car2 may also be, for example, the 1/3 frequency of the frequency of car 1.
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 SW 32.
The comparison unit 31 compares the upper-branch-use voltage command value vupComparison result with normal carrier car1 or upper-branch-use voltage command value vupThe result of comparison with the switching carrier car2 is used as the gate signal g for the upper branch elementupAnd (6) outputting.
The comparison unit 32 compares the lower arm voltage command value vunThe comparison result with the difference between the normal carrier car1 and the value "1" calculated by the arithmetic unit 33, or the lower arm voltage command value vunThe result of comparison with the difference between the switching carrier car2 calculated by the arithmetic section 34 and the value "1" is taken as the gate signal g of the lower arm elementunAnd (6) outputting.
The determination unit 35 determines the upper-branch voltage command value vupAnd whether the signal is 0 or not, and if the signal is 0, 1 is output, and if the signal is not 0, 0 is output.
The judgment unit 36 judges the lower arm voltage command value vunAnd whether the signal is 0 or not, and if the signal is 0, 1 is output, and if the signal is not 0, 0 is output.
If at least one of the outputs of the judgment parts 35 and 36 is not 0 (i.e., if the upper-branch voltage command value v is set to be equal toupAnd a voltage command value v for the lower branchunAt least one is 0), then operation is performedThe section 37 operates so that the switching sections SW31, SW32 select the contact 0, respectively. On the other hand, if both of the outputs of the determination units 35, 36 are 0 (i.e., if the upper-branch-use voltage command value v is set to 0upAnd a voltage command value v for the lower branchunNeither is 0), the arithmetic section 37 operates so that the switching sections SW31, SW32 select the 1-contact, respectively.
In such a configuration, the voltage command value v is applied to the upper branchupAnd a voltage command value v for the lower branchunWhile at least one is 0, normal carrier car1 is applied. On the other hand, the voltage command value v for the upper branchupAnd a voltage command value v for the lower branchunDuring the period when neither of these is 0, the handover carrier car2 is applied. This is shown in fig. 6 if the waveform diagram is used.
Suppose that the voltage command value v is used for the upper branchupAnd a voltage command value v for the lower branchunIn the period in which neither of the carriers is 0, the total number of switching times of the upper arm and the lower arm is doubled by applying the normal carrier car1, but in the present embodiment, since the carrier car2 is applied, the carrier frequency is 1/2, and the total number of switching times is unchanged from before switching. That is, an increase in switching loss is suppressed.
According to embodiment 3, an increase in switching loss can be further suppressed as compared with embodiment 1.
As described above in detail, according to each embodiment, it is possible to suppress the fluctuation of the neutral point potential and suppress the increase of the switching loss in a larger operation region.
Several embodiments of the present invention have been described, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments may be implemented in other various forms, and various omissions, substitutions, and changes may be made without departing from the spirit 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 equivalent scope thereof.
Claims (5)
1. A power conversion device is provided with:
a neutral point clamped power converter (100); and
a control device (10) which performs control for suppressing variation in the neutral point potential of the power converter (100) by applying a 1 st voltage command value and a 2 nd voltage command value generated using voltage command values of the phases of the power converter (100) to a 1 st switching element group located in the upper half of each branch and a 2 nd switching element group located in the lower half of each branch which constitute each phase of the power converter (100),
the control device (10) has a mechanism for switching and implementing the following control modes:
a 1 st control mode for generating the 1 st voltage command value and the 2 nd voltage command value based on a new voltage command value for each phase obtained by superimposing a zero-phase voltage of the power converter (100) on a voltage command value for each phase of the power converter (100); and
a 2 nd control mode for generating the 1 st voltage command value by subtracting the minimum value of the voltage command values of the phases of the power converter (100) and dividing the same by 2, and for generating the 2 nd voltage command value by subtracting the maximum value of the voltage command values of the phases of the power converter (100) and dividing the same by 2,
the control device (10) lowers the carrier frequency of the power converter (100) in the 2 nd control mode, based on the respective values of the 1 st voltage command value and the 2 nd voltage command value, when the respective values are not 0.
2. The power conversion apparatus according to claim 1,
the control device (10) switches to the 2 nd control mode when a modulation factor of a voltage command value of each phase, on which the zero-phase voltage is superimposed, exceeds a predetermined range in the 1 st control mode.
3. The power conversion apparatus according to claim 1,
the control device (10) switches between the 1 st control mode and the 2 nd control mode according to the operating conditions of the power converter (100).
4. The power conversion apparatus according to claim 1,
in the 2 nd control mode, the control device (10) decreases the carrier frequency of the power converter (100) while the switching frequency of the element group in which the 1 st switching element group and the 2 nd switching element group are combined is increased.
5. A method for controlling a power converter having a neutral point clamped power converter (100),
the method comprises the following steps: a control device (10) that performs control for suppressing fluctuations in the neutral point potential of the power converter (100) by assigning a 1 st voltage command value and a 2 nd voltage command value generated using voltage command values of the phases of the power converter (100) to a 1 st switching element group located in the upper half of each branch and a 2 nd switching element group located in the lower half of each branch that constitute each phase of the power converter (100), respectively;
the above control includes the steps of switching and implementing the 1 st control mode and the 2 nd control mode,
generating the 1 st voltage command value and the 2 nd voltage command value based on a new voltage command value of each phase obtained by superimposing a zero-phase voltage of the power converter (100) on a voltage command value of each phase of the power converter (100) in the 1 st control mode; and
in the 2 nd control mode, the 1 st voltage command value is generated by subtracting the minimum value of the voltage command values of the phases of the power converter (100) by 2, and the 2 nd voltage command value is generated by subtracting the maximum value of the voltage command values of the phases of the power converter (100) by 2,
the control device (10) lowers the carrier frequency of the power converter (100) in the 2 nd control mode, based on the respective values of the 1 st voltage command value and the 2 nd voltage command value, when the respective values are not 0.
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| JP2018076721A JP7002985B2 (en) | 2018-04-12 | 2018-04-12 | Power converter and control method of power converter |
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| JP2019187135A (en) | 2019-10-24 |
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| DE102019002715A1 (en) | 2019-10-17 |
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