KR20220061570A - Switching control apparatus of three-phase PWM inverter for reducing switching loss - Google Patents

Abstract

The present invention relates to a switching control apparatus of a three-phase pulse width modulation (PWM) inverter. According to the present invention, the switching control apparatus of the three-phase PWM inverter for reducing a switching loss includes: a reference frequency setting unit for setting a fixed switching frequency applied to a continuous conduction mode (CCM) switching scheme as a reference switching frequency; and an inductance determination unit for determining an inductance value of an inductor inside the three-phase PWM inverter, which allows a maximum switching frequency value within a variable switching frequency range applied to a discontinuous conduction mode (DCM) switching scheme to be the reference switching frequency, wherein the three-phase PWM inverter is controlled by the DCM switching scheme, in which an inductance value greater than or equal to the determined value is applied to the inductor. According to the present invention, when the three-phase PWM inverter is driven by the DCM switching scheme, an inductance value that ensures a lower switching loss than a switching loss of the CCM switching scheme is selected and applied, so that a switching loss is reduced as compared with the CCM switching scheme under the same condition.

Description

Switching control apparatus of three-phase PWM inverter for reducing switching loss

The present invention relates to a switching control device for a three-phase PWM inverter, and more particularly, to a switching control device for a three-phase PWM inverter for reducing switching loss.

With the recent development of wide bandgap devices such as SiC and GaN, the switching frequency applied to the DC/AC inverter has reached 100 kHz or more, and thus the volume of passive elements required in the power conversion device can be reduced, thereby increasing the power density. There was an increasing advantage. However, as the switching frequency increases, the switching loss also increases, which is a factor impairing the efficiency of the power conversion device.

1 is a diagram schematically showing the structure of a three-phase PWM inverter. This three-phase PWM inverter 1 (10) is applicable to a three-phase motor (Moter) 20 or a grid-connected type (Grid), and is used for controlling the motor or supplying power to the grid. Hereinafter, a three-phase motor is mainly exemplified.

The 3-phase PWM inverter 10 converts the input DC voltage (V _IN ) into a 3-phase AC voltage through PWM (Pulse Width Modulation) switching and applies (supply) it to the 3-phase motor. This PWM inverter is configured to include a total of six switches, that is, three switch pairs (S1 and S2, S3 and S4, S5 and S6) corresponding to each of the three phases (R, S, T).

Each contact of the three switch pairs is connected to each phase end of the motor. That is, the AC output of each phase (R, S, W) is applied to each phase of the 3-phase motor after passing through the LC filter stage.

The existing three-phase PWM inverter operates in CCM (Continuous Conduction Mode), in which current continuously flows through the inductor of the LC filter, and supplies a sine wave current of each phase to the motor or system.

FIG. 2 is a diagram illustrating a current waveform flowing through an inductor when the three-phase PWM inverter of FIG. 1 is driven by the CCM technique and the switching frequency is constant. Here, the horizontal axis represents time and the vertical axis represents current values.

2 shows the waveform of the current flowing in the R phase, which is one of the three phases, when operating in the CCM method. Although not shown, the S-phase waveform has a phase difference of 120 degrees with respect to the R phase, and the T-phase waveform has a phase difference of 240 degrees with respect to the R phase.

However, when the inverter operates as a CCM, the switch always operates at the same switching frequency regardless of the magnitude of the average current flowing through the inductor, so that a switching loss proportional to the switching frequency is continuously generated. In addition, as the switching frequency of the inverter is increased to 100 kHz or more in order to reduce the power density according to the development of a wide bandgap device, in the case of the CCM technique, there is a problem in that the ratio of the switching loss increases in proportion to the increased switching frequency.

In order to solve this problem, there is a DCM (Discontinuous Conduction Mode) switching technique in which the current flowing through the inductor flows discontinuously. The DCM technique discontinuously controls the current of each phase flowing through the output inductor of a three-phase inverter.

FIG. 3 is a diagram illustrating a current waveform flowing through an inductor when the inverter of FIG. 1 is driven by the DCM switching technique to change the switching frequency.

In the case of the CCM technique shown in FIG. 2, the current flowing through the inductor is continuously controlled according to the reference current of a sine wave in the controller, but the DCM operation shown in FIG. It operates in a hysteresis technique that limits and controls.

Through this, the switching frequency is increased in the section where the average current of the inductor is low and the switching frequency is decreased in the section where the average current of the inductor is high, thereby reducing the overall switching loss.

However, the variable frequency variation range of DCM may vary depending on how the inductance value of the inductor is selected, and if the frequency variation range becomes too large, loss rather than CCM increases.

The technology that is the background of the present invention is disclosed in Korean Patent Application Laid-Open No. 10-1766433 (published on August 8, 2017).

The present invention provides a switching control device of a three-phase PWM inverter to have a lower loss than the CCM switching method by selecting and applying an inductance value to have a lower switching loss than the CCM switching method in driving the three-phase PWM inverter by the DCM switching method. It is intended to provide

The present invention, in a switching control device of a three-phase PWM inverter for reducing switching loss, a reference frequency setting unit for setting a fixed switching frequency applied to the CCM switching technique as a reference switching frequency, and a variable applied to the DCM switching technique and an inductance determining unit that determines an inductance value of an inductor in a three-phase PWM inverter for a maximum switching frequency value in a switching frequency range to become the reference switching frequency, wherein the three-phase PWM inverter is controlled by the DCM switching technique, but the determined To provide a switching control device for a three-phase PWM inverter in which an inductance value greater than or equal to the value is applied to the inductor.

Also, the inductance determining unit may determine the inductance value by substituting the input voltage of the three-phase PWM inverter, the rms AC voltage applied to the motor, the peak current flowing through the inductor, and the reference switching frequency into a setting function.

In addition, the setting function may be expressed by the following equation.

Here, L _R is the determined inductance value, F _sw is the reference switching frequency, V _IN is the input voltage, V _R(AC) is the rms AC voltage, and I _ref is the peak current.

In addition, it further includes a dead time setting unit for setting a dead time for the switching frequency, the three-phase PWM inverter, the dead time may be reflected in the DCM switching control.

In addition, the inductance value is determined differently according to the reference switching frequency, which is a switching frequency applied to the CCM switching technique, and the higher the reference switching frequency, the lower the inductance value may be determined.

The present invention can reduce switching loss by applying a DCM switching technique to which a change in a switching frequency is applied in driving a three-phase PWM inverter.

In particular, the present invention reduces the switching loss compared to the CCM switching technique in a circuit under the same condition by selecting an inductance value to have a lower switching loss than the CCM switching technique in driving a three-phase PWM inverter using the DCM switching technique and reflecting it in the inductor. There are advantages to being able to

1 is a diagram schematically showing the structure of a three-phase PWM inverter.
FIG. 2 is a diagram illustrating a current waveform flowing through an inductor when the inverter of FIG. 1 is driven by the CCM technique and the switching frequency is constant.
FIG. 3 is a diagram illustrating a current waveform flowing through an inductor when the inverter of FIG. 1 is driven by the DCM switching technique to change the switching frequency.
4 is a diagram showing the configuration of a switching control device of a three-phase PWM inverter for reducing switching loss according to an embodiment of the present invention.
FIG. 5 is a diagram illustrating a variable frequency control technique using FIG. 4 .
FIG. 6 is a schematic diagram of switching for supplying current to R phase in the three-phase inverter of FIG. 1 .
7 is a switching schematic diagram for current control in R phase in FIG. 6 .
8 is a diagram illustrating a switching frequency variation according to a L _R value in a half cycle.
9 is a diagram illustrating a method for implementing a variable switching scheme in an embodiment of the present invention.
10 is a diagram for explaining a switching loss.
11 is a diagram comparing instantaneous and average switching losses according to modes for a half cycle when DCM and CCM are used when L _R = 500 uH.
12 is a diagram comparing instantaneous and average switching losses according to modes for a half cycle when DCM and CCM are used when L _R = 100 uH.

Then, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. However, the present invention may be implemented in several different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part is "connected" with another part, this includes not only the case of being "directly connected" but also the case of being "electrically connected" with another element interposed therebetween. . Also, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

The present invention proposes a technique for reducing switching loss during high-frequency driving of a three-phase inverter by varying the switching frequency according to the average output current of the three-phase inverter. In particular, the present invention can reduce switching losses compared to the CCM technique under the same conditions by selecting the optimal inductor value and dead time in driving a three-phase PWM inverter with DCM.

The present invention can be applied to motor and grid-connected applications, but if it is a low-frequency AC field, the application field is not limited, and the present invention takes the motor field as a main example. For the basic structure and principle of a three-phase PWM inverter, refer to the background of the invention and FIG. 1 .

4 is a diagram illustrating the configuration of a switching control device of a three-phase PWM inverter for reducing switching loss according to an embodiment of the present invention, and FIG. 5 is a diagram illustrating a variable frequency control technique using FIG. 4 .

4 and 5 , the switching control device 100 of a three-phase PWM inverter according to an embodiment of the present invention includes a reference frequency setting unit 110 , an inductance determining unit 120 , and a dead time setting unit 130 . includes

First, the reference frequency setting unit 110 sets a fixed switching frequency (eg, 100 kHz) applied to the CCM switching technique as the reference switching frequency for optimal inductor design ( S510 ).

In the case of the CCM switching technique, since it always operates at the same switching frequency as described in the background art, a switching loss proportional to the corresponding switching frequency is continuously generated.

Unlike the CCM, the DCM switching technique discontinuously controls each phase current flowing through the output inductor of the 3-phase PWM inverter, and uses a time-varying switching frequency instead of a fixed switching frequency.

Therefore, when DCM is used, the switching frequency varies between the minimum switching frequency (fmin) and the maximum switching frequency (fmax). At this time, when the maximum value of the variable switching frequency range of the DCM, that is, the maximum switching frequency value fmax, is equal to the switching frequency applied to the CCM, the switching loss is lower than that of the CCM technique.

However, the switching frequency range (switching frequency range) of DCM operation varies according to the inductor value of the LC filter at the output stage of the 3-phase PWM inverter. That is, the output inductor value of each phase of the inverter affects the switching frequency fluctuation range of the DCM. This will be described later with reference to FIG. 8 .

Therefore, if the optimal inductor value is determined to make the maximum switching frequency of DCM operation the switching frequency of CCM (reference switching frequency) and this is applied as the output eductor value of the inverter, it can operate with lower switching loss than CCM under the same conditions. be able to

To this end, the inductance determiner 120 determines the inductance value (L _R ) of the inductor so that the maximum switching frequency value (fmax) within the variable switching frequency range (fmin to fmax) applied to the DCM switching technique becomes the reference switching frequency value. It is decided (S520).

Specifically, the inductance determiner 120 substitutes the input voltage of the three-phase PWM inverter, the rms AC voltage applied to the motor, the peak current flowing through the inductor, and the reference switching frequency (F _sw ) into the setting function to substitute the inductance value L _R ) to determine

In this case, the setting function may be expressed as in Equation 1 below.

Here, L _R is the inductance value, F _sw is the reference switching frequency, V _IN is the input voltage of the inverter, V _R(AC) is the rms AC voltage applied to the motor, and I _ref is the peak current flowing through the inductor. Also, in sin(ωt), t denotes time and ω denotes angular velocity.

For example, if the reference switching frequency, which is the switching frequency of the CCM, is 100 kHz, the maximum frequency that can be varied in order for the DCM to have a switching loss lower than this is set to 100 kHz. And by applying the reference switching frequency F _sw and inverter design specifications V _IN , V _R(AC) , I _ref to Equation 1, the inductance value L _R of the inductor is calculated.

The reason for determining the inductance value using Equation 1 will be described later in detail.

Next, the dead time setting unit 130 sets a dead time (Dead Time) to have a lower switching loss than the CCM switching technique (S530).

Accordingly, the output-side inductor of the 3-phase PWM inverter may be applied with the previously determined inductance value or a larger value, and may be controlled by the DCM switching method with the dead time reflected in each switch of the inverter.

Here, the dead time may be applied before and after the time when the sign of the inverter output current is inverted from positive to negative or from negative to positive. For example, in FIG. 3 , the dead time is set so that switching is not performed in the section before and after the point in time when the current is 0. If the dead time = 570 us, switching is not performed during the 570 us period (t1-570 us ~ t1+570 us) before and after the time when the current is 0 (assuming t1).

This dead time has the purpose of preventing this because, when the current becomes 0, the theoretical switching frequency of the DCM technique approaches infinity and the switching loss increases as the switching frequency increases.

Thereafter, in the three-phase PWM inverter, a value greater than or equal to the previously determined inductance value is applied to the output inductor, and the inductance value and the dead time are applied to control using the DCM technique (S540).

For example, if the inductance value is determined to be 500 uH, the three-phase PWM inverter with this 500 uH applied to the output inductor has a switching frequency of up to 100 kHz when the DCM technique of varying the switching frequency is applied, which is The circuit has a lower switching loss than the case of using the CCM technique driven at a constant switching frequency of 100 kHz.

As a result, the 3-phase PWM inverter is controlled by the DCM switching technique, but an inductance value greater than or equal to the value determined in Equation 1 is applied to the inductor and the corresponding dead time is reflected in DCM switching control, thereby reducing switching loss than the CCM technique can do. If an inductance value smaller than the determined value is used, the frequency fluctuation width increases, the maximum frequency exceeds 100 kHz, and the switching loss also increases.

Next, the reason for determining the inductance value through Equation 1 will be described.

First, in the embodiment of the present invention, the switching loss is reduced while the switching frequency is varied through DCM for discontinuously controlling the current of each phase flowing through the three-phase inverter output inductor. The principle of DCM is explained as follows.

FIG. 6 is a schematic diagram of switching for supplying current to R phase in the three-phase inverter of FIG. 1 .

FIG. 6 shows only the circuit for the R phase related to the switches S1 and S2 among all three phases (R, S, T) for convenience of explanation. The remaining phases contain the same circuit.

Here, a DC voltage (V _IN ) is applied to both ends of S1 and S2, and an LC filter composed of an inductor and a capacitor is connected through a contact point between S1 and S2. At this time, an alternating voltage (V _R(AC) ) is output through both ends of the capacitor and applied to the R phase of the motor.

In the case of FIG. 6 , it is assumed that the current flowing through the motor is positive. FIG. 6A shows a section in which energy is charged in the inductor L _R and FIG. 6B shows a section in which energy is discharged.

7 is a switching schematic diagram for current control in R phase in FIG. 6 .

As shown in FIG. 7 , in the case of the DCM technique, upper/lower bands for the hysteresis operation are selected by Equations 2 and 3, and a triangular-shaped discontinuous current is finally controlled to flow through the inductor L _R .

Equation 2 is a current value according to time t of the upper band, and Equation 3 represents a different current value with time of the lower band.

In Equations 2 and 3, ω of sin(ωt) is the angular velocity, and I _ref is the peak current flowing through the inductor (L _R ).

When the current flowing through the inductor is calculated based on this, the condition (charge) of FIG. 6 (a) can be expressed by Equation 4, and the condition (discharge) of (b) can be expressed as Equation 5.

Here, V _IN is an input voltage, V _R(AC) is an AC voltage output from the R phase of the inverter 10 and applied to the motor, and L _R is an inductance value for the R phase inductor.

The ON/OFF times of each of the switches S1 and S2 are expressed by Equations 6 and 7, and finally expressed as a frequency-related expression as in Equation 8.

In Equation 8, F _SW represents a switching frequency at time t in the DCM switching technique. The switching frequency of DCM is affected by the input voltage (V _IN ) of the inverter, the output voltage (V _R(AC) ), the inductance of the inductor (L _R ), and the peak current (I _ref ) flowing through the inductor.

When Equation 8 is changed to a formula for L _R , the form of Equation 1 is derived. The embodiment of the present invention selects the inductance ( _LR ) through which the DCM has a lower loss than the CCM under the same conditions.

In Equation 8, F _sw means a value that changes with time, but F _sw substituted when calculating L _R in Equation 1 becomes the switching frequency of CCM and the maximum switching frequency for DCM (eg, 100 kHz). This is to determine the inductance value for making the variable maximum frequency value of the DCM equal to the switching frequency of the CCM. Using this, DCM has lower loss than CCM.

8 is a diagram illustrating a switching frequency variation according to a L _R value in a half cycle. At this time, the vertical axis is the switching frequency and the unit is 10 ⁵ Hz, so a value of 1 means 100 kHz and a value of 5 means 500 kHz.

For example, power 400W, V _IN =450V, V _{R(AC)_RMS} =110V (60Hz), Deadband = 570 us, under the condition of unit power factor, when L _R =100 uH, the maximum switching frequency (when the average current flowing through the inductor is minimum) = 500 kHz, the minimum switching frequency (when the average current flowing through the inductor is maximum) = 60 kHz, and when L _R =500 uH, the maximum switching frequency = 100 kHz and the minimum switching frequency = 10 kHz. At this time, since the switching frequency becomes infinite at the point of time t=0 in Equation 8, the maximum switching frequency is limited to 100 kHz under the condition of 500 uH by applying the deadband.

As shown in FIG. 8 , it can be seen that the switching frequency range (switching frequency range) of the DCM varies according to the inductance value, and it is necessary to select the dead time so that the switching frequency does not become infinite.

Considering that the switching loss is calculated by multiplying the product of voltage and current at the time of switching by the switching frequency, if the switching frequency of CCM operates at 100 kHz, the maximum that can be varied for DCM to have lower switching loss than CCM By determining the frequency to be 100 kHz (f _sw = 100 kHz), L _R =500 uH can be calculated from Equation (1).

In this embodiment, assuming that the switching frequency of the CCM is 100 kHz, the maximum switching frequency of the DCM is selected as 100 kHz to obtain a low switching loss. Therefore, since the maximum switching frequency of the DCM may vary according to the switching frequency of the CCM, the maximum switching frequency in the present invention is not limited to a specific frequency.

9 is a diagram illustrating a method for implementing a variable switching scheme in an embodiment of the present invention.

The controller measures the current flowing through the inductor of each phase and compares the measured value with the determined upper/lower band. Until the upper band is reached, the controller turns on the upper switch of each phase and turns off the lower switch to charge the inductor, but reaches the upper band. Repeat the operation to discharge the inductor by turning off the upper switch and turning on the lower switch. Finally, the discontinuous current is filtered by the output stage LC filter to supply the current to each phase of the motor. Both S-phase and T-phase are the same as the principle of R-phase, but the phase of the upper band is controlled to have a phase difference of 120 degrees for S-phase and 240 degrees for T-phase based on R-phase, and the motor is driven.

Hereinafter, the verification result in which the present invention has a lower switching loss than the CCM will be described in detail.

As in the previous example, the inductor is 500 uH, output 400 W, V _IN =450 V, V _{R(AC)_RMS} = 110 V (60 Hz), Deadband = 570 us, under the condition of having a unit power factor, in the case of CCM, the switching operation is performed at a fixed frequency of 100 kHz, and the present invention is variable between 10 kHz and 100 kHz The frequency is switched, and the switching loss is calculated based on this.

In the case of DCM used in the present invention from the above conditions, from Equation 9, the rms current flowing through the inductor is 3.636 [Arms] and the peak current 5.143 [A] is calculated, and Equations 2 and 3 are respectively Equations 10 and 11 , and the switching frequency is expressed by Equation 12 as in the case of 500 uH of FIG. 8 .

However, in the case of CCM, due to the ripple (10%) of the current flowing in the inductor along the reference current as shown in FIG. 2, it is expressed as Equations 13 and 14.

10 is a diagram for explaining a switching loss. The switching loss is expressed by the product of the voltage and current applied to the switch at the moment when the switch is turned on or off, as shown in FIG. 10, and is calculated as the area of the triangle.

The switching loss of the present invention and the CCM was compared through the calculation of the switching loss occurring in the No. 1 switch S1 of FIG. 1, and the switch ON and OFF times for the present invention (DCM) and the CCM were 40 ns using the same switch. was assumed to be the same.

In the present invention, it can be seen from FIGS. 6 and 7 that the No. 1 switch S1 is turned off when the current flowing through the inductor reaches the upper band and is turned on when the lower band is reached. From this, instantaneous switching loss is calculated as in Equations 15 and 16.

Here, t _off and t _off represent an off time and an on time of the switch. For reference, this is an approximate expression because the switching frequency (10~100 kHz) is very fast compared to the output voltage and current frequency (60Hz).

However, in the case of CCM, since the frequency is constant at 100 kHz, the switching loss is expressed as Equations 17 and 18 below.

By summing the results of Equations 15 and 16, the instantaneous switching loss of the DCM according to the present invention is calculated. Similarly, by summing the results of Equations 17 and 18, the instantaneous switching loss in the CCM technique can be calculated.

11 is a diagram comparing instantaneous and average switching losses according to modes for a half cycle when DCM and CCM are used when L _R = 500 uH.

11 shows the instantaneous and average switching loss according to the mode for a half cycle when the inductor is 500uH, the blue line is the instantaneous switching loss of the present invention, the red line is the instantaneous switching loss of the CCM, and the light blue line is the instantaneous switching loss of the present invention Average switching loss, the pink line shows the average switching loss of CCM.

Here, the instantaneous switching loss of DCM is the sum of Equations 15 and 16, and the instantaneous switching loss of CCM is the sum of Equations 17 and 18. The average switching loss for each case is the average value of the instantaneous switching loss over time.

In the case of the present invention (DCM) in the section where the current flowing through the inductor is the largest, the switching frequency varies from a maximum of 100 KHz to a minimum of 10 kHz, and has a lower instantaneous switching loss compared to a CCM that always switches at 100 kHz. Finally, the half-cycle average switching loss of the present invention is 6.67 [W], and the CCM is 1.47 [W], confirming that the switching loss is reduced through the variable frequency switching technique of the present invention.

12 is a diagram comparing instantaneous and average switching losses according to modes for a half cycle when DCM and CCM are used when L _R = 100 uH. 12 shows the instantaneous and average switching losses according to the mode for a half period when the inductor is 100 uH.

Unlike FIG. 11 , when the inductor has a value of 100 uH as shown in FIG. 12 , the switching frequency varies between a maximum of about 500 kHz and a minimum of 60 kHz. As a result of calculating the switching loss from this, the average switching loss of the present invention is 7.34 [W] and 6.67 [W] in the case of CCM, indicating that the switching loss is rather increased than that of CCM.

That is, the switching loss and frequency variation range are affected by the size of the inductor, and it can be seen that the DCM loss is larger than the CCM when the inductor is 100 uH, unlike the 500 uH, as shown in FIG. 12 .

Therefore, in order for the present invention to have lower switching loss than the conventional CCM, it can be seen from Equation 1 that the inductor and deadband for the switching frequency of the CCM to be the maximum variable frequency (100 kHz in this embodiment) in the present invention must be selected. can

Here, when comparing FIGS. 2 and 3 and Equations 10 and 13, in the case of the present invention, the peak current is greater than that of the CCM due to the DCM operation. Accordingly, as the load increases, the peak current increases, which increases the RMS current flowing through the inductor, thereby increasing the conduction loss of the switch. That is, when applied to high current applications, the increase in conduction loss is larger than the decrease in switching loss according to the present invention, thereby reducing overall efficiency. Therefore, the present invention can be mainly applied to low current applications.

According to the present invention as described above, it is possible to reduce the switching loss by applying the DCM switching technique in which the switching frequency varies, and in particular, it is possible to reduce the switching loss than the CCM switching technique under the same condition through the optimal inductor and dead time design. .

Although the present invention has been described with reference to the embodiment shown in the drawings, which is only exemplary, those of ordinary skill in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Accordingly, the true technical protection scope of the present invention should be determined by the technical spirit of the appended claims.

100: 3-phase PWM inverter switching control device
110: reference frequency setting unit 120: inductance determining unit
130: dead time setting unit

Claims (5)

In the switching control device of a 3-phase PWM inverter for reducing switching loss,
a reference frequency setting unit for setting a fixed switching frequency applied to the CCM switching technique as a reference switching frequency; and
Including an inductance determining unit that determines the inductance value of the inductor in the three-phase PWM inverter for the maximum switching frequency value in the variable switching frequency range applied to the DCM switching technique to become the reference switching frequency,
The three-phase PWM inverter,
A switching control device of a three-phase PWM inverter controlled by the DCM switching technique and wherein an inductance value greater than or equal to the determined value is applied to the inductor. The method according to claim 1,
The inductance determining unit,
A switching control device for a 3-phase PWM inverter that determines the inductance value by substituting the input voltage of the 3-phase PWM inverter, the rms AC voltage applied to the motor, the peak current flowing through the inductor, and the reference switching frequency into a setting function. 3. The method according to claim 2,
The setting function is a variable frequency switching device of a three-phase PWM inverter expressed by the following equation:

Here, L _R is the determined inductance value, F _sw is the reference switching frequency, V _IN is the input voltage, V _R(AC) is the rms AC voltage, and I _ref is the peak current. The method according to claim 1,
Further comprising a dead time setting unit for setting a dead time for the switching frequency,
The three-phase PWM inverter,
A switching control device of a three-phase PWM inverter in which the dead time is reflected in the DCM switching control. The method according to claim 1,
The inductance value is determined differently according to the reference switching frequency, which is a switching frequency applied to the CCM switching technique,
A switching control device for a three-phase PWM inverter in which the inductance value is determined to be a lower value as the reference switching frequency is higher.

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