KR19990039712A - Inverter and its control method - Google Patents

Abstract

The present invention relates to an inverter for generating a three-phase load voltage and supplying the load to the load by switching the DC power from the DC power supply and a control method thereof. An inverter according to the present invention includes a DC power supply unit, a pulse width modulator for receiving a voltage control signal of a three-phase AC power and pulse width modulation to generate a switching control signal, and a direct current from the DC power supply unit according to the switching control signal. An inverter comprising an inverting portion having at least three pairs of switching elements for switching a power supply and generating a three-phase load voltage and supplying the load, wherein the load current of each phase changes from negative to positive and from positive to negative A zero detection unit for detecting a changing zero crossing point; In a predetermined region including the zero crossing point that changes from negative to positive, the magnitude of the three-phase AC power supply is not smaller than the maximum value of the modulation wave, and in the predetermined region including the zero crossing point that changes from positive to negative, the three-phase AC power supply And a control signal adjusting unit for adjusting the three-phase alternating current power by adding a predetermined control voltage such that the magnitude of? Is not greater than the minimum value of the modulation wave. As a result, it is possible to prevent distortion of the load current in a region where the magnitude of the load current is small regardless of the power factor angle of the load current.

Description

Inverter and its control method

The present invention relates to an inverter, and more particularly, a DC power supply unit, a pulse width modulator for receiving a voltage control signal of a three-phase AC power and pulse width modulating to generate a switching control signal, and the DC control unit according to the switching control signal. The present invention relates to an inverter including at least three pairs of switching elements for switching a DC power supply from a power supply unit and an inverting unit for generating a three-phase load voltage and supplying the load to a load and a control method thereof.

A pulse width modulated inverter is a device that converts a DC power source into a plurality of pulsed AC voltages having different widths by alternately turning on switching elements. It is widely used in industrial sites because it can supply a load voltage having a voltage and a power loss.

By the way, in the pulse width modulation inverter, switching elements should be turned on alternately in order to generate an alternating voltage in the form of a pulse. At the same time, if the switching elements are in the on state, the DC power is applied only to the switching elements and the switching elements are damaged. There is a problem, and a number of methods have been devised and applied to solve this problem.

One such method applies a dead time when the switching device is turned on.

1 is a configuration diagram of an inverter applying a conventional dead time. The inverter that applies only the dead time has three comparators (COM, 8), three inverting inverters (INV, 9), and a dead time applying unit (7) and six switching control signals (C ₁ ^* , C ₂ ^* ,). C ₃ ^* , C ₄ ^* , C ₅ ^* , C ₆ ^* ) and a pulse width modulator 6.

Three-phase sine wave AC power supplies Va, Vb, and Vc are supplied from a three-phase AC power supply source (not shown), and a triangular wave is supplied from a modulation wave supply source (not shown). Using a Modulation Index (M) defined as the ratio of the maximum value of the AC power source to the maximum value of the modulated wave, the three-phase sinusoidal AC power source can be represented by Equation 1. This expression will be used later.

Va = Msinθ

Vb = Msin (θ-120˚)

Vc = Msin (θ + 120˚)

here, θ Is the phase angle of the three-phase AC power supply, and M is the modulation index.

Here, FIG. 2 shows a phase sine wave AC power supply and a triangular wave together with a phase load current having power factor angles of 30 ° and 90 °. 2 represents the phase angle of the control voltage, and the vertical axis represents the magnitude of the triangular wave. Meanwhile, when the three-phase AC power source is represented by Equation 1, the three-phase load current may be represented by Equation 2.

here, θ Is the phase angle of the three-phase AC power supply, M is the modulation index, and Z is the load impedance.

The three comparators (COM, 8) connected to the three-phase AC power supply and the modulated wave supply source compare the three-phase sine wave AC power (Va, Vb, Vc) and the triangular wave by phase, and the magnitude of the sine wave AC power is larger than that of the triangular wave. If it is large, a high voltage is output, and if it is small, a zero pulse is output. At this time, the output of the comparator 8 is divided into two, and the inverting inverter 9 connected to the comparator 8 inverts one of the outputs of the comparator 8. This produces three uninverted pulse trains (C ₁ , C ₃ , C ₅ ) and three inverted pulse trains (C ₂ , C ₄ , C ₆ ), and C ₁ and C ₂ and C ₃ and C ₄ It has a phase difference of 120 degrees, and C ₃ and C ₄ and C ₅ and C ₆ have a phase difference of 120 degrees. FIG. 3 shows the a-phase pulse train generated at this time, that is, C ₁ and C ₂ . 3, the horizontal axis represents phase angles, and the vertical axis represents pulse amplitudes.

The dead time applying unit 7 connected to the comparator 8 and the inverter 9 for inversion has six pulse strings C._One, C₂, C₃, C₄, C₅, C₆Is the dead time Δt, that is, the switching element Q._One, Q₂, Q₃, Q₄, Q₅, Q₆) 6 switching control signals (C) by delaying the accumulated charge by a time sufficient to discharge_One ^*, C₂ ^*, C₃ ^*, C₄ ^*, C₅ ^*, C₆ ^*) Where C_One ^*And C₂ ^*Is a sine wave ac power from a₃ ^*And C₄ ^*Is a sine wave ac power from b,₅ ^*And C₆ ^*Is It is generated from sinusoidal AC power in phase c. The a-phase switching control signal generated at this time, that is, C_One ^*And C₂ ^*4 is shown. 4, the horizontal axis represents the phase angle, the vertical axis represents the amplitude of the pulse, C_One ^*There are six places, C₂ ^*Dead time is authorized in five places.

DC voltage supply (4) supplies a direct current power source, an inverting unit (2) is connected to the DC voltage supply 4 and the pulse width modulation unit 6, as shown in Fig. _1, C 1 ^*, DC power supply unit using C ₂ ^* , C ₃ ^* , C ₄ ^* , C ₅ ^* and C ₆ ^* as switching control signals of Q ₁ , Q ₄ , Q ₂ ^* , Q ₅ , Q ₃ and Q ₆ switching elements, respectively The DC power supply Ed of (4) is converted into a pulsed AC voltage and supplied to the load. At this time, the Q ₁ , Q ₂ , and Q ₃ switching elements in the upper arm and the Q ₄ , Q ₅ and Q ₆ switching elements in the lower arm are turned on when the switching control signal is high.

The diodes D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , and D ₆ connected in parallel with the switching elements Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ and Q ₆ It protects the switching elements (Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ ) from the self-induction action by the inductance component of.

Here, comparing FIG. 2 and FIG. 4, the dead time is applied in the vicinity of the power factor angle of the load current is 30 ° and 75 °, the distortion of the load current occurs.

In general, when the dead time is applied, the load current is distorted and the normal operation of the load is disturbed. Therefore, a means for compensating for the variation of the load current due to such distortion must be taken.

However, in order to compensate for the variation of the load current due to distortion, accurate detection of the load current should be premised.However, when the load current is small, in particular, in the region near the zero crossing point of the load current, the detection of the load current is accurate. Due to this difficulty, there was a problem that accurate compensation of the load current due to distortion was impossible.

In order to solve this problem, a method of applying a regulated voltage within a predetermined phase range of a three-phase AC power supply has been devised and applied. This method is based on the fact that applying the same voltage to the three-phase AC power supply does not affect the operation of the load.

5 is a configuration diagram of an inverter applying a conventional dead time and a control voltage.

Inverter for applying the dead time and the control voltage has three adders (ADD, 33) and the control voltage generation unit 32, the control signal control unit 31 for adjusting the three-phase AC power by adding a predetermined control voltage, Six switching control signals (C ₁ ^* , C ₂ ^* , C ₃ ^* , C ₄ ^* ) with three comparators (COM, 28), three inverting inverters (INV, 29) and a dead time application section 27 , C ₅ ^* , C ₆ ^* ) has a pulse width modulator 26.

Three-phase sine wave AC power supplies Va, Vb, and Vc are supplied from a triangular wave supply source (not shown) from a supply source (not shown) of the three-phase AC power source.

The regulation voltage generation unit 32 connected to the supply source of the three-phase AC power source generates the regulation voltage V ₀ given by Equation (3).

When 0˚ <θ≤60˚, Vo = -1-Msin (θ-120˚)

60˚ <θ≤120˚ when, Vo = 1-Msinθ

120˚ <θ≤180˚ when, Vo = -1-Msin (θ + 120˚)

180˚ <θ≤240˚ when, Vo = 1-Msin (θ-120˚)

240˚ <θ≤300˚ when, Vo = -1-Msinθ

300˚ <θ≤360˚ when, Vo = 1-Msin (θ + 120˚)

This regulating voltage is shown in FIG. 6 represents the phase angle of the control voltage, and the vertical axis represents the magnitude. As shown in FIG. 6, 30˚ <θ≤90˚ The center of the regulation voltage in the interval is 90 ° phase angle.

The adder 33 connected to the regulating voltage generator 32 and the supply source of the three-phase AC power source is a three-phase sinusoidal alternating current power source given by Equation 4 by adding a control voltage given by Equation 3 to the three-phase sinusoidal AC power source ( Va ^* , Vb ^* , Vc ^* ).

60˚ <θ≤120˚ when, Va ^* = 1

120˚ <θ≤180˚ when,

180˚ <θ≤240˚ when,

240˚ <θ≤300˚ when, Va ^* = -1

300˚ <θ≤360˚ when,

In this case, FIG. 7 shows the adjusted a-phase sine wave AC power supply Va ^* together with the triangular wave. The horizontal axis of FIG. 7 represents a phase angle, and the vertical axis represents a magnitude. As shown in FIG. 7, the magnitude of Va ^* is equal to the maximum value of the triangular wave between the phase angles of 60 ° and 120 °, and the same as the minimum value of the triangular wave between the phase angles of 240 ° and 300 °.

The three comparators (COM, 28) connected to the adder 33 and the triangular wave source (not shown) compare the regulated three-phase alternating current power supply (Va ^* , Vb ^* , Vc ^* ) and the triangular wave for each phase to perform a sine wave alternating current. If the size of the power supply is larger than the triangular wave, a high voltage is output, and if it is small, a zero voltage is output. At this time, the output of the comparator 28 is divided into two, and the inverting inverter 29 connected to the comparator 28 inverts one of the outputs of the comparator 28. This produces three uninverted pulse trains (C ₁ , C ₃ , C ₅ ) and three inverted pulse trains (C ₂ , C ₄ , C ₆ ), and C ₁ and C ₂ and C ₃ and C ₄ It has a phase difference of 120 degrees, and C ₃ and C ₄ and C ₅ and C ₆ have a phase difference of 120 degrees. FIG. 8 shows the a-phase pulse train generated at this time, that is, C ₁ and C ₂ . 8, the horizontal axis represents phase angles, and the vertical axis represents pulse amplitudes.

The dead time applying unit 27 connected to the comparator 28 and the inverting inverter 29 has six pulse strings C._One, C₂, C₃, C₄, C₅, C₆The six switching control signals (C) by delaying the time from zero to high by the dead time (Δt)._One ^*, C₂ ^*, C₃ ^*, C₄ ^*, C₅ ^*, C₆ ^*) Where C_One ^*And C₂ ^*Is a phase sine wave ac power, C₃ ^*And C₄ ^*Is b phase sine wave ac power, C₅ ^*And C₆ ^*Is It is generated from c phase sine wave AC power. The a-phase switching control signal generated at this time, that is, C_One ^*And C₂ ^*9 is shown. 9, the horizontal axis represents phase angles, and the vertical axis represents pulse amplitudes._One ^*There are five places, C₂ ^*It can be seen that dead time is authorized at four places.

A direct current voltage supply 24 supplies a direct current power source, an inverting unit 22 connected to the DC voltage supply 24 and the pulse width modulation unit 26 as shown in Fig. 5, C ₁ ^*, DC power supply unit using C ₂ ^* , C ₃ ^* , C ₄ ^* , C ₅ ^* and C ₆ ^* as switching control signals of Q ₁ , Q ₄ , Q ₂ ^* , Q ₅ , Q ₃ and Q ₆ switching elements, respectively The DC power supply Ed of 24 is converted into a pulsed AC voltage and supplied to the load. At this time, as shown in FIG. 9, C ₁ ^* maintains a high voltage and C ₂ ^* maintains a zero voltage between the phase angles of 60 ° to 120 °, and the phase angle of 240 ° to 300 ° according to the adjustment voltage. It can be seen that C ₁ ^* maintains zero voltage and C ₂ ^* maintains high voltage, so that switching of Q ₁ and Q ₄ switching devices does not occur. Therefore, it is not necessary to apply dead time in this phase angle region, and distortion of the load current can be avoided.

By the way, comparing FIG. 2 and FIG. 9, when the power factor angle of the AC power supply and the load current is 30 degrees, C is near the zero crossing point of the load current._One ^*on Dead time is applied and distortion occurs in the load current.

Configuration and role of diodes D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , D ₆ , and operation of switching elements Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ are conventional It is the same as the inverter to apply only dead time of.

As described above, when the predetermined region to which the adjustment voltage is added is determined based on only the three-phase AC power supply, switching of the switching element may occur in the region where the load current is small depending on the power factor angle of the load current. The same problem as in the case of the inverter applying only the dead time conventionally occurs.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter and a control method thereof in which switching of a switching element does not occur in a region where the magnitude of the load current is small regardless of the power factor angle of the load current.

1 is a configuration diagram of an inverter applying a conventional dead time,

2 is a waveform diagram of a triangular wave, a phase sine wave AC power source and a phase load current having power factor angles of 30 ° and 90 °,

3 is a waveform diagram of a phase pulse train input to a dead time applying unit in the inverter shown in FIG. 1;

4 is a waveform diagram of a phase switching control signal in the inverter shown in FIG. 1;

5 is a configuration diagram of an inverter applying a conventional dead time and a control voltage;

6 is a waveform diagram of a control voltage in the inverter shown in FIG. 5;

7 is a waveform diagram of a phase sine wave AC power source adjusted in the inverter shown in FIG. 5;

8 is a waveform diagram of a phase pulse train input to a dead time applying unit in the inverter shown in FIG. 5;

9 is a waveform diagram of a phase switching control signal in the inverter shown in FIG. 5;

10 is a configuration diagram of an inverter according to the present invention;

11 is a waveform diagram of a triangular wave, a sine wave AC power supply and a phase load current having a power factor of 66 °;

12 is a waveform diagram of a control voltage according to the present invention;

13 is a waveform diagram of a phase sinusoidal AC power source adjusted according to the present invention;

14 is a waveform diagram of a phase pulse train input to a dead time applying unit according to the present invention;

15 is a waveform diagram of a phase switching control signal according to the present invention.

<Description of Symbols for Main Parts of Drawings>

2, 22, 42: inverting section 4, 24, 44: DC power supply section

6, 26, 46: pulse width modulator 7, 27, 47: dead time

8, 28, 48: comparators 9, 29, 49: inverting inverter

31, 51: control signal control unit 32, 52: control voltage generation unit

33, 53: adder 61: zero detection unit

The purpose of the present invention is to provide a DC power supply unit, a pulse width modulator for receiving a voltage control signal of a three-phase AC power source and generating a switching control signal by modulating a pulse width thereof, An inverter comprising an inverting unit having at least three pairs of switching elements for switching and generating a three-phase load voltage and supplying the load, wherein the load current of each phase changes from negative to positive and zero from negative to negative. A zero detection unit for detecting a crossing point; In a predetermined region including the zero crossing point that changes from negative to positive, the magnitude of the three-phase AC power supply is not smaller than the maximum value of the modulation wave, and in the predetermined region including the zero crossing point that changes from positive to negative, the three-phase AC power supply Is achieved by an inverter further comprising a control signal adjusting unit for adjusting the three-phase alternating current power by adding a predetermined control voltage such that the magnitude of?

Here, by calculating the power factor angle of the load current of each phase and the three-phase AC power supply of each phase, the zero crossing point of the load current can be detected, and the power factor angle is preferably calculated by the following equation (5). .

here, Va, Vb, Vc Are the sinusoidal AC power in each phase, Ia, Ib, Ic Is the load current of each phase.

On the other hand, the predetermined region is in the left and right 30 ° range around the zero crossing point of the load current, it is possible to apply the control voltage without overlapping over one cycle of the three-phase AC power supply. At this time, the control voltage is preferably determined according to Equation 6 so that the maximum value or minimum value of the three-phase AC power source adjusted in the predetermined region is equal to the maximum value or minimum value of the modulated wave.

When 0˚ <θ + (90˚-ψ) ≤60˚, Vo = -1-Msin (θ-120˚)

60˚ <θ + (90˚-ψ) ≤120˚ when, Vo = 1-Msinθ

120˚ <θ + (90˚-ψ) ≤180˚ when, Vo = -1-Msin (θ + 120˚)

180˚ <θ + (90˚-ψ) ≤240˚ when, Vo = 1-Msin (θ-120˚)

240˚ <θ + (90˚-ψ) ≤300˚ when, Vo = -1-Msinθ

300˚ <θ + (90˚-ψ) ≤360˚ when, Vo = 1-Msin (θ + 120˚)

here, θ Is the phase angle of the three-phase AC power supply, M is the ratio of the maximum value of the three-phase AC power supply to the modulated wave, and ψ is the power factor angle of the load current.

In addition, an object of the present invention is to provide a control method for an inverter including at least three pairs of switching elements and switching a DC power source in accordance with a switching control signal to generate a three-phase load voltage and supply the load to the load. Detecting a zero crossing point that changes from negative to positive and a zero crossing point that changes from positive to negative; In a predetermined region including the zero crossing point that changes from negative to positive, the magnitude of the three-phase AC power supply is not smaller than the maximum value of the modulation wave, and in the predetermined region including the zero crossing point that changes from positive to negative, the three-phase AC power supply Adjusting a three-phase AC power source by adding a predetermined control voltage such that the magnitude of? Is not greater than the minimum value of the modulated wave; It is achieved by the control method of the inverter comprising the step of generating a switching control signal of the switching device from the regulated three-phase AC power supply.

In the detecting of the zero crossing of the load current, the zero crossing point of the load current may be detected by calculating the power factor angle of the load current of each phase and the three-phase AC power supply of each phase. Is preferably based on equation (5).

In addition, the predetermined region is within a range of 30 ° to the left and right around the zero crossing point of the load current, so that the control voltage can be applied without overlapping over one cycle of the three-phase AC power supply. At this time, the control voltage is preferably determined according to Equation 6 so that the maximum value or minimum value of the three-phase AC power source adjusted in the predetermined region is equal to the maximum value or minimum value of the modulated wave.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

10 is a configuration diagram of an inverter according to the present invention. The inverter according to the present invention includes a zero detector 61 for detecting a zero crossing point of a load current, three adders ADD, 53 and a regulated voltage generator 52. Control signal adjusting unit 51 for adjusting a three-phase AC power by adding a predetermined control voltage, three comparators (COM, 48), three inverting inverters (INV, 53), and a dead time applying unit ( And a pulse width modulator 46 for generating _six switching control signals C ₁ ^* , C ₂ ^* , C ₃ ^* , C ₄ ^* , C ₅ ^* , C ₆ ^* .

Three-phase sine wave AC power supplies Va, Vb, and Vc are supplied from a triangular wave supply source (not shown) from a supply source (not shown) of the three-phase AC power source. FIG. 11 illustrates the a-phase sine wave AC power and the triangular wave according to the load current of the a-phase having a power factor of 66 °. Here, the load current is given by the equation (2), the horizontal axis of Fig. 11 represents the phase angle, the vertical axis represents the magnitude.

The zero detection unit 61 connected to the load calculates the power factor angle of the load current by Equation 5 and detects a zero crossing point that changes from negative to positive and a zero crossing point that changes from positive to negative. That is, in Equation 5, ,

, Since the power factor angle of the load current can be obtained, and the zero crossing point of the load current can be obtained by comparing it with the three-phase AC power supply.

The regulated voltage generation unit 52 connected to the three-phase AC power supply unit (not shown) and the zero detection unit 61 generates the control voltage V ₀ given by Equation 6, and shows the control voltage. 12. The horizontal axis of FIG. 12 represents the phase angle of the adjustment voltage, and the vertical axis represents the magnitude. As shown in FIG. 12, 60˚ <θ + (90˚-66˚) ≤120˚ In other words, 36˚ <θ≤96˚ The center of the regulation voltage in the section is the phase angle of 66 °, which is equal to the power factor angle of the load current.

The adder 53 connected to the regulating voltage generation unit 52 and the supply source of the three-phase AC power supplies a three-phase sinusoidal AC power source provided by Equation 7 by adding a control voltage given by Equation 6 to the three-phase sinusoidal AC power source ( Va ^* , Vb ^* , Vc ^* ).

36˚ <θ≤96˚ when, Va ^* = 1

96˚ <θ≤156˚ when,

156˚ <θ≤216˚ when,

216˚ <θ≤276˚ when, Va ^* = -1

276˚ <θ≤336˚ when,

At this time, FIG. 13 shows the adjusted a-phase sine wave AC power supply Va ^* together with the triangular wave. 13, the horizontal axis represents phase angle and the vertical axis represents magnitude. As shown in FIG. 13, the magnitude of Va ^* is equal to the maximum value of the triangular wave between the phase angles of 36 ° and 96 °, and the same as the minimum value of the triangular wave between the phase angles of 216 ° and 276 °.

The three comparators (COM, 48) connected to the adder 53 and the triangular wave source (not shown) compare the regulated three-phase alternating current power supply (Va ^* , Vb ^* , Vc ^* ) with the triangular wave for each phase to perform a sine wave alternating current. If the size of the power supply is larger than the triangular wave, a high voltage is output, and if it is small, a zero voltage is output. At this time, the output of the comparator 48 is divided into two, and the inverting inverter 49 connected to the comparator 53 inverts one of the outputs of the comparator 48. This produces three uninverted pulse trains (C ₁ , C ₃ , C ₅ ) and three inverted pulse trains (C ₂ , C ₄ , C ₆ ), and C ₁ and C ₂ and C ₃ and C ₄ It has a phase difference of 120 degrees, and C ₃ and C ₄ and C ₅ and C ₆ have a phase difference of 120 degrees. FIG. 14 shows the a-phase pulse train generated at this time, that is, C ₁ and C ₂ . In Fig. 14, the horizontal axis represents phase angle, and the vertical axis represents pulse amplitude.

The dead time applying unit 47 connected to the comparator 48 and the inverting inverter 49 has six pulse strings (C)._One, C₂, C₃, C₄, C₅, C₆The six switching control signals (C) by delaying the time from zero to high by the dead time (Δt)._One ^*, C₂ ^*, C₃ ^*, C₄ ^*, C₅ ^*, C₆ ^*) Where C_One ^*And C₂ ^*Is a sine wave ac power from a₃ ^*And C₄ ^*Is a sine wave ac power from b,₅ ^*And C₆ ^*Is It is generated from sinusoidal AC power in phase c. The a-phase switching control signal generated at this time, that is, C_One ^*And C₂ ^*Figure 15 shows. 15, the horizontal axis represents phase angles, and the vertical axis represents pulse amplitudes._One ^*There are five places, C₂ ^*It can be seen that dead time is authorized at four places.

A direct current voltage supply 44 supplies a direct-current power supply, direct-current voltage supply 44, and the pulse width modulator 46, an inverting unit 42 that is connected to, as shown in FIG. 10, C ₁ ^*, DC power supply using C ₂ ^* , C ₃ ^* , C ₄ ^* , C ₅ ^* and C ₆ ^* as switching control signal of Q ₁ , Q ₄ , Q ₂ ^* , Q ₅ , Q ₃ , Q ₆ switching elements respectively The DC power supply Ed of the supply unit 44 is converted into a pulsed AC voltage and supplied to the load. At this time, as shown in FIG. 15, C ₁ ^* maintains a high voltage and C ₂ ^* maintains a zero voltage between the phase angles 36 ° to 96 ° according to the control voltage intended by the present invention, and the phase angle 216 °. It can be seen that between ₁ to 276 ° C ₁ ^* maintains zero voltage and C ₂ ^* maintains high voltage so that switching of Q ₁ and Q ₄ switching devices does not occur. Therefore, it is not necessary to apply dead time in this phase angle region, and distortion of the load current can be avoided.

Configuration and role of diodes D ₁ , D ₂ , D ₃ , D ₄ , D ₅ , D ₆ , and operation of switching elements Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ are conventional It is the same as the inverter that applies only dead time of.

Although the case where the power factor angle of the load current is 66 ° has been described above, as the power factor angle of the load current changes, as shown in Equation 6, the switching element is in the left and right 30 ° ranges around the power factor angle of the load current. The regulation voltage is also changed so that no switching occurs. Thus, the distortion can be avoided even for a load current having an arbitrary power factor angle.

In the present description, the maximum value of the three-phase AC power supply and the load current is represented by the modulation index, but the same result can be obtained even if the maximum value is displayed in a different form. In the case of the sinusoidal AC power supply of the phase, the phase difference of 120 degrees is delayed from that of the a phase, and the sinusoidal AC power supply of the phase c is delayed by the phase difference of 240 degrees of the phase of the a phase.

According to the inverter and the control method as described above, the zero crossing point of the load current is detected, and the voltage control signal is adjusted so that switching of the switching element does not occur by adding a predetermined regulating voltage in a predetermined region centered on the zero crossing point. By doing so, it is possible to prevent distortion of the load current in a region where the magnitude of the load current is small regardless of the zero crossing point of the load current.

Claims (10)

A DC power supply, a pulse width modulator for receiving a voltage control signal of a three-phase AC power and pulse width modulating to generate a switching control signal, and at least three switching DC power from the DC power supply according to the switching control signal. In the inverter having a switching device for generating a load voltage of the three-phase with a pair of switching elements, A zero detection unit for detecting a zero crossing point in which the load current of each phase changes from negative to positive and a zero crossing point in which the load current changes from positive to negative; In a predetermined region including the zero crossing point that changes from negative to positive, the magnitude of the three-phase AC power supply is not smaller than the maximum value of the modulation wave, and in the predetermined region including the zero crossing point that changes from positive to negative, the three-phase AC power supply And a control signal adjusting unit configured to adjust the three-phase AC power supply by adding a predetermined control voltage such that the magnitude of V is not greater than the minimum value of the modulation wave. The method according to claim 1, And the zero detection unit detects a zero crossing point of each phase load current by calculating a load current of each phase and a power factor angle of the three-phase AC power supply of each phase. The method according to claim 2, The power factor angle is calculated according to the inverter: here, Va, Vb, Vc Each phase is sinusoidal AC power, Ia, Ib, Ic Is the load current of each phase. The method according to any one of claims 1 to 3, And the predetermined area is in a range of 30 ° to the left and right of the zero crossing point of the load current. The method according to claim 4, The control voltage is determined according to the following equation: 0˚ <θ + (90˚-ψ) ≤60˚ when, Vo = -1-Msin (θ-120˚) 60˚ <θ + (90˚-ψ) ≤120˚ when, Vo = 1-Msinθ 120˚ <θ + (90˚-ψ) ≤180˚ when, Vo = -1-Msin (θ + 120˚) 180˚ <θ + (90˚-ψ) ≤240˚ when, Vo = 1-Msin (θ-120˚) 240˚ <θ + (90˚-ψ) ≤300˚ when, Vo = -1-Msinθ 300˚ <θ + (90˚-ψ) ≤360˚ when, Vo = 1-Msin (θ + 120˚) here, θ Is the phase angle of the three-phase AC power supply, M is the ratio of the maximum value of the three-phase AC power supply to the modulated wave, and ψ is the power factor angle of the load current. A control method of an inverter having at least three pairs of switching elements and switching a direct current power source in accordance with a switching control signal to generate a three-phase load voltage and supply the load to the load. Detecting a zero crossing point that changes from negative to positive and a zero crossing point that changes from positive to negative of the load current of each phase; In a predetermined region including the zero crossing point that changes from negative to positive, the magnitude of the three-phase AC power supply is not smaller than the maximum value of the modulation wave, and in the predetermined region including the zero crossing point that changes from positive to negative, the three-phase AC power supply Adjusting a three-phase AC power source by adding a predetermined control voltage such that the magnitude of? Is not greater than the minimum value of the modulated wave; And generating a switching control signal of the switching element from the regulated three-phase AC power supply. The method according to claim 6, Detecting the zero crossing point, The control method of the inverter, characterized in that the zero crossing point is detected by calculating the load current of each phase and the power factor angle of the three-phase AC power supply of each phase. The method according to claim 7, The control method of the inverter, characterized in that the power factor is calculated by the following equation: here, Va, Vb, Vc Each of each phase is AC power, Ia, Ib, Ic Is the load current of each phase. The method according to any one of claims 6 to 8, wherein The predetermined area is a control method of the inverter, characterized in that the left and right 30 ° range around the zero crossing point of the load current. The method according to claim 9, The control voltage of the inverter, characterized in that determined according to the following equation: 0˚ <θ + (90˚-ψ) ≤60˚ when, Vo = -1-Msin (θ-120˚) 60˚ <θ + (90˚-ψ) ≤120˚ when, Vo = 1-Msinθ 120˚ <θ + (90˚-ψ) ≤180˚ when, Vo = -1-Msin (θ + 120˚) 180˚ <θ + (90˚-ψ) ≤240˚ when, Vo = 1-Msin (θ-120˚) 240˚ <θ + (90˚-ψ) ≤300˚ when, Vo = -1-Msinθ 300˚ <θ + (90˚-ψ) ≤360˚ when, Vo = 1-Msin (θ + 120˚) here, θ Is the phase angle of the three-phase AC power supply, M is the ratio of the maximum value of the three-phase AC power supply to the modulated wave, and ψ is the power factor angle of the load current.