JPH0720373B2 - 3-phase static power converter - Google Patents

Description

TECHNICAL FIELD The present invention can obtain an approximate sine wave by using a pulse width modulation (PWM) type three-phase bridge type inverter or the like.
The present invention relates to a phase static power converter.

2. Description of the Related Art A method of obtaining an output voltage approximate to a sine wave by a pulse width modulation type inverter or cycloconverter is already known. However, conventionally, since the switching element is controlled to be turned on and off so that the target phase voltage of the sine wave can be obtained,
Inevitably, the number of times of switching increases and the switching loss increases.

Therefore, an object of the present invention is to provide a three-phase static power converter that can easily reduce the switching loss while securing an approximate sine wave.

The present invention for achieving the above object will be described with reference to the reference numerals of the drawings showing an embodiment. A switching element for replacement for converting a DC voltage of a DC power supply 1 into a three-phase AC voltage.
S1 to S6 three-phase bridge circuit, forming first, second and third target phase voltage waveforms in order to obtain a three-phase approximate sinusoidal line voltage from the three-phase bridge circuit. Three-phase static power comprising a control circuit for controlling the conversion switching elements S1 to S6 so as to obtain a three-phase voltage waveform which is averagely approximated to the second and third target phase voltage waveforms. In the converter, target phase voltage waveform forming means for forming the first, second and third target phase voltage waveforms included in the control circuit has three-phase sine wave voltages ea, eb, ec.
And a three-phase half-wave rectified voltage forming means 24 for obtaining a positive three-phase half-wave rectified voltage e ₃ of the three-phase sine wave voltages ea, eb, and ec. , A voltage generating means 1a for generating a voltage E / 2 that is 1/2 of the voltage E of the DC power supply 1, and subtracting the three-phase half-wave rectified voltage e ₃ from the voltage E / 2 that is 1/2 of the voltage E Then, the subtracting means 25 for forming the inverted waveform voltage e ₄ of the three-phase half-wave rectified voltage and the inverted waveform voltage e of the first phase sine wave voltage ea generated from the three-phase sine wave voltage generation circuit 7 _Four
Is added to output a voltage waveform e ₀ a that becomes flat only in the section of π / 6 to 5π / 6 as the target phase voltage waveform of the first phase, and the three-phase sine wave voltage Generation circuit 7
From the first target phase voltage waveform by adding the inverted waveform voltage e ₄ to the second phase sine wave voltage eb generated from And a third sine generated from the three-phase sine wave voltage generation circuit 7 and a second adding means 26b for outputting a voltage waveform e ₀ b having a phase difference of 2π / 3 as the second target phase voltage waveform. The inverted waveform voltage e ₄ is added to the wave voltage ec, and the waveform has the same waveform as the first target phase voltage waveform and has a phase difference of 4π / 3 with respect to the first target phase voltage waveform. The present invention relates to a three-phase static power converter, which comprises a third adding means 26c which outputs a voltage waveform e ₀ c as the third target phase voltage waveform.

Note that the target voltage waveform can be formed to have a flat portion in the interval of 7π / 6 to 11π6 as described in the second aspect of the claims.

The three-phase half-wave rectified voltage forming means in the present invention corresponds to the rectifying circuit 24 or 24a of the embodiment, the E / 2 or −E / 2 voltage generating means corresponds to the power supply 1a or 1b of the embodiment, and the subtraction is performed. The means corresponds to the subtracting circuit 25 or 25a, and the first, second and third adding means correspond to the adders 26a, 26b and 26c.

Effect of the Invention The present invention has the following effects.

(A) Target phase voltage waveform in the first invention of the present application
e ₀ a, e ₀ b, e ₀ c are 4π / 6 or 120 only within the positive half-wave interval.
It has a flat portion with a width of degrees and no flat portion in the negative half-wave section. The target phase voltage waveform in the second aspect of the invention has a flat portion of 4π / 6, that is, a width of 120 degrees only in the negative half-wave section, and does not have a flat portion in the positive half-wave section. This flat portion is a period in which it is unnecessary to turn on / off the switching elements S1 to S6. In the conventional method, since the flat portions are provided on both the positive half-wave and the negative half-wave, switching from the flat portion to the non-flat portion (sine wave portion) occurs four times during the 2π section. On the other hand, in the present invention, since the flat portions are collectively provided in the positive or negative half-wave, the switching from the flat portion to the non-flat portion occurs only twice, and the switching elements S1 to S6 in the 2π section are generated. It is possible to reduce the number of times of switching than in the conventional case, and it is possible to reduce power loss. Even if the positive half wave and the negative half wave of the target phase voltage waveform are different from each other, an approximate sine wave line voltage can be obtained with the waveform specified in the present invention.

(B) When the target phase voltage waveform is formed according to the first and second inventions of the present application, a waveform having a flat portion only in the positive or negative half wave can be easily obtained.

First Embodiment FIG. 1 shows a pulse width modulation type three-phase inverter according to a first embodiment of the present invention. This three-phase inverter consists of a DC power supply (1), six switching transistors S ₁ ,
It is composed of an inverse converter (2) in which S ₂ , S ₃ , S ₄ , S ₅ , and S ₆ are connected in a 3-phase bridge, and control circuits (3), (4), and (5) for each phase. The inverse converter (2) converts the voltage of (1) into a sine wave that is approximate to the average value and supplies the sine wave to a load (6) such as a three-phase AC motor.

Since the pulse width modulation control circuits (3), (4) and (5) have substantially the same configuration, the first phase control circuit (3) will be described. (7a) is a target sine wave voltage generating circuit, which generates a sine wave ea shown in FIG. 3 (a) as a target output line voltage waveform by the inverse converter (2).

(9) is a target phase voltage waveform generating circuit, which is shown in FIG.
3 is a circuit for forming the target phase voltage e ₀ a shown in FIG. 3 (d) based on the target sine wave ea. The waveform e in FIG. 3 (d)
₀ a is the PWM of the first-phase switching transistors S ₁ and S ₂ .
This is a target signal for controlling, and the switching transistors S ₁ and S ₂ are on / off controlled so as to obtain the waveform of FIG. 3 (d). Details of the method of forming the waveform of FIG. 3D will be described later.

(10) is a triangular wave voltage generating circuit, which generates the triangular wave voltage (10a) shown in FIG. 7 (a). (11) is a comparison circuit, which compares the target phase voltage waveform e ₀ a of FIG. 7 (a) with the triangular wave voltage (10a) and forms the pulse width modulation control signal of FIG. 7 (b). It consists of a comparator. The pulse width modulation control signal of FIG. 7 (b) obtained from the comparison circuit (11) is supplied to the base of the transistor S ₁ by the line (12) and is inverted by the NOT circuit (13). Is supplied by line (14) to the base of transistor S ₂ . Similar pulse width modulation control signals are formed in the second and third phase control circuits (4) and (5), and the line (1
5) (16) (17) (18) is supplied to the base of the Yotsute transistor S ₃ to S ₆ in.

The control signals pulse-width modulated so as to obtain the target phase voltage waveforms e ₀ a, e ₀ b, and e ₀ c of the first, second, and third phases shown in FIG. If the switching transistors S _{1 to} S ₆ are added from (3), (4) and (5), the inverse converter (2)
A waveform whose average value approximates to a sine wave is obtained between the output lines (19), (20) and (21) of. For example, between the first phase line (19) and the second phase line (20), as shown in FIG.
Waveform of ea Just advance the phase and A pulse-width-modulated output voltage approximating the waveform is obtained.

FIG. 2 shows a circuit for forming the target phase voltage waveforms e ₀ a, e ₀ b, e ₀ c of FIG. (7a), (7b) and (7c) are target sine wave voltage generation circuits for the first, second and third phases, and ea = Asinωt, Generates a three-phase sine wave. The amplitude A takes various values based on voltage control.

(22a), (22b), (22c) are half-wave rectification circuits for each phase consisting of diodes. Target sine wave voltage generation circuit (7a)
Half-wave rectification is performed on each of the sine waves obtained from (7b) and (7c). (23) is an adder circuit, which is a half-wave rectifier circuit (22
Add the outputs of (a), (22b) and (22c) to add 3 in Fig. 3 (b).
Rectifier circuit (22a) (22b) to obtain the half-wave rectified waveform e ₃
This is the part where the output line of (22c) is OR-connected with a wire. Therefore, the portion surrounded by the dotted line, which is composed of the rectifier circuits (22a) (22b) (22c) and the adder circuit (23), is the three-phase half-wave rectifier circuit (24). Since e ₃ is a three-phase half-wave rectified output, it contains three times the frequency component of the sine wave ea.

(25) is a subtraction circuit, which is the voltage of the DC power supply (1) shown in FIG. Voltage supplied from the power supply (1a) corresponding to Is a circuit that obtains the voltage waveform e ₄ shown in FIG. 3C by subtracting the three-phase half-wave rectified voltage e ₃ from. Incidentally, e _4, because then corresponds to the three-phase half-wave rectified waveform e _3, including three times the frequency components of the fundamental sine wave ea.

(26a) (26b) (26c) is the target sine wave voltage ea, eb, ec
The waveform e ₄ obtained from the subtraction circuit (25) is superimposed on
It is a circuit that forms the target phase voltage waveforms e ₀ a, e ₀ b, and e ₀ c shown in FIG. The sine wave ea, eb, ec in Fig. 3 (a)
If the waveform e ₄ of FIG. 3C is superposed, as is apparent from FIG. 3D, in the waveform e ₀ a of the first phase, But Leveling and flattening. Also in the waveforms e ₀ b and e ₀ c, It has a flat portion in the shifted region. As a result, the waveform
When obtaining a phase voltage that approximates e ₀ a, e ₀ b, and e ₀ c on average by pulse width modulation, the waveform of each phase Therefore, it becomes unnecessary to turn the switching element on and off, and the switching loss is reduced.

Next, the relationship between the sine wave ea shown in FIG. 3 (a) and the target phase voltage waveform e ₀ a of FIG. 3 (d) will be described. The waveform e _{4 in} FIG. 3 (c) is expressed by the following equation.

However, ω is 2πf, f is the frequency of sine waves ea, eb, ec, Is the DC component of the waveform e ₄ , n is an integer, and An is the amplitude of each harmonic component. As is clear from this equation, the waveform e ₄ does not include the f component and is composed of only the triple frequency component (3f).

Waveform e ₀ a obtained by combining sine wave ea and waveform e _{4 in} FIG. 3 (c)
Is expressed by the following equation.

Based on this formula, The voltage value in the section is Becomes That is, a flat portion occurs in 1/3 of one cycle (2π) of the waveform.

Even if the target phase voltage waveforms e ₀ a, e ₀ b, and e ₀ c are distorted waves as shown in FIG. 3 (d), the voltage waveform of each phase is a symmetrical wave due to the characteristics of the three-phase AC. Yes, 1/3 cycle When the waveforms have exactly the same waveform with a delay, the harmonics of the multiple of 3 series are not included in the line voltage waveform. Similarly, since the DC component has the same value for each phase, it cannot be represented in the line voltage. That is, the target phase voltage waveform e shown in FIG.
_Even if the inverse converter (2) is subjected to pulse width modulation control so that ₀ a, e ₀ b, and e ₀ c are obtained, the line voltage waveform applied to the load is
The sine waves ea, eb, and ec in Fig. 3 (a) are What you did It is equivalent to the phase-shifted one by the average value.

Fig. 3 shows the amplitude A of the sine waves ea, eb, ec However, even if the amplitude A is set to a different value, the same effect can be obtained. Fourth
The figure shows the amplitude A Fig. 5 shows the amplitude A And the amplitude A is shown in FIG. Is shown. Although only the target phase voltage waveform e ₀ a of the first phase is shown and the waveforms of the second and third phases are not shown in (d) of FIGS. 4 to 6, It also appears in the shifted position.

As is clear from FIG. 6 (a), according to this method, the amplitude A of the sine waves ea, eb, and ec indicating the virtual phase voltage is set to the power supply voltage. More than Can be Virtual phase voltage is power supply voltage of If this can be achieved, the line voltage will increase accordingly. That is, when a sine wave output is obtained by the conventional control method, the amplitude of the phase voltage is shown in Fig. 4 (a). However, according to the method of the present invention, the phase voltage is higher than that in the case of FIG. It is possible to increase the maximum output voltage by about 15%.

Thus the amplitude A Even so, since the waveform e ₀ a of FIG. 6 (d) satisfies the same conditions as the waveform e ₀ a of FIG. 3 (d), the harmonic component does not increase. Also, the flat part Can be obtained.

Next, FIG. 8 showing the second embodiment of the present invention will be described. However, the same parts as those in the first embodiment shown in FIGS. 1 to 7 are designated by the same reference numerals, and the description thereof will be omitted. 8th
Also in the system shown in the figure, the target sine wave voltage generation circuit (7a) generates the waveform ea of FIG. 3 (a), and the target phase voltage waveform generation circuit (9) generates the waveform e ₀ a of FIG. 3 (d). Generate.

On the other hand, the pulse width modulation phase voltage e _A is detected from the line (19) and is input to the filter (30). Filter (3
0) constitutes an average value voltage generation circuit, and is an average value voltage _A (FIG. 7) of the pulse width modulation output voltage e _A obtained from the line (19) in the same state as in FIG. 7 (b). Waveform
waveform that almost matches e ₀ a). Reference numeral (31) denotes a voltage comparison circuit, which has an average value voltage a obtained from the filter (30) and a target phase voltage waveform e ₀ a shown in FIG. 3 (d) obtained from the target phase voltage waveform generation circuit (9). Compare
The output corresponding to the difference is obtained.

Reference numeral (31a) is a short-circuit trigger circuit, which obtains an output voltage with a hysteresis characteristic of an upper trigger level V _T1 and a lower trigger level V _T2 . That is, the comparison circuit (3
The low level output occurs when _A -e ₀ a obtained from 1) has come larger than the upper trigger level V _{T1, A} -e ₀
This is a circuit that generates a high level output when a becomes smaller than the lower trigger level V _T2 . The comparison circuit (31 and the shift trigger circuit (31a) may be integrated into an IC.

(32) is a transistor base drive circuit, which controls the transistor S ₁ to turn off based on the high level output of the shift trigger circuit (31a), and reversely controls the transistor S ₂ to turn on. It is a circuit that generates a pulse that controls the transistor S ₁ to turn on based on the level output and conversely turns off the transistor S ₂ .

If a pulse width modulation output voltage e _A as shown in FIG. 7 (b) is detected from the first phase output line (19) of the inverse converter (2) in the circuit of FIG. 8, this is the filter ( In 30), the average value is obtained and the average value voltage _A becomes close to the waveform e ₀ a. The comparison circuit (31) compares the average value voltage _A with the target phase voltage waveform e ₀ a and generates a voltage corresponding to the difference.
When the voltage of this difference exceeds the hysteresis value of the shift trigger circuit (31a), the output state is inverted. If the detected average value voltage _A is higher than the target phase voltage waveform e ₀ a, the transistor S ₁ is turned off to reduce the output amplitude. Conversely, the average value voltage _A is the target phase voltage waveform e ₀ a
If it is lower than that, the transistor S ₁ is turned on to increase the output amplitude.

The control based on the first-phase control circuit (3) has been described above, but the same control is performed in the second-phase and third-phase control circuits (4) and (5). Now, the detected voltage of the second phase is e _B , the average value voltage thereof is _{B 0} , the target phase voltage thereof is e ₀ b, the detected voltage of the third phase is ec, the average value voltage thereof is _{C 2} , and the target phase voltage thereof is e ₀
With c, the control is as follows. Under the condition of _B -e ₀ b> V _T1, the transistor S ₃ is turned off, S ₄ is turned on, the conditions of _B -e ₀ b <V _T2, the transistor S ₃
Is on and S ₄ is off.

On the other hand, under the condition of _C− e ₀ c> V _T1 , the transistor S ₅ is turned off,
S ₆ turns on, and under the condition of _C− e ₀ c <V _T2 , the transistor S ₅ turns on and S ₆ turns off.

When also the first phase indicated with the same form, under the conditions of _A -e ₀ a> V _T1, the transistor S ₁ is turned off, S ₂ is turned on, _A
Under the condition of −e ₀ a <V _T2 , the transistor S ₁ is turned on and S ₂ is turned off.

With the circuit shown in FIG. 8, even if the output phase voltage of the inverse converter (2) is controlled so as to have the target phase voltage waveform e ₀ a shown in FIG. It can be a sine wave. Moreover, since the waveforms e ₀ a, e ₀ b, and e ₀ c have flat portions, the number of times of switching can be reduced.

9 and 10 show a third embodiment of the present invention. The basic circuit of this embodiment is the same as that of FIG.
Only the method of forming the target phase voltage waveforms e ₀ a, e ₀ b, e ₀ c shown in the figure is different. In FIG. 9, a negative three-phase half-wave rectification circuit (24a) is provided to obtain the negative three-phase half-wave rectification waveform e ₅ shown in FIG. 3 (b). Then, in the subtraction circuit (25a), the negative voltage obtained from the power supply (1b) And the waveform e _{5 in} Fig. 3 (b) Is performed, and the waveform e ₆ of FIG. 3 (c) is formed. That is,
Similar to the case of e _4, the waveform according to the following equation is formed.

Then, this waveform e ₆ is the addition circuit (26a) (26b) (26c)
Then, it is added to the sine waves ea, eb, and ec of each phase. As a result,
The target phase voltage waveform e ₀ a shown in FIG. 10 is obtained. The waveform e ₀ a is expressed by the following equation as in the case of FIG.

The waveform shown in FIG. 10 is a waveform obtained by inverting the polarity of the waveform shown in FIG. 3 (d), and therefore the same effect can be obtained. When the amplitudes A of the sine waves ea, eb, and ec change as shown in FIGS. 4, 5, and 6, e ₅ and e ₆ change as shown in each figure, and A target phase-phase voltage waveform in which the polarities of the waveform e ₀ a in FIGS. 4 to 6D are reversed is obtained. Also,
The circuit of FIG. 9 is also applicable to the target phase voltage generating circuit (9) of FIG.

Modifications The present invention is not limited to the above-described embodiments, and the following modifications are possible, for example.

(A) Target phase voltage waveforms e ₀ a, e shown in FIG.
₀ b, the e ₀ c without analog form, may be formed by using a digital circuit.

(B) The filter (30) shown in FIG. 8 is used as a circuit for generating a digital signal indicating an average value, and the target phase voltage waveform generation circuit (9) is also configured to generate a digital signal, so that both are digitally compared. You may

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a three-phase inverter according to a first embodiment of the present invention, and FIG. 2 is a block diagram showing a target phase voltage waveform generating circuit, FIG. 3, FIG. 4, FIG. FIG. 6 and FIG. 7 are waveform charts showing the state of each part of FIG. 1 and FIG. FIG. 8 is a circuit diagram showing a three-phase inverter according to the second embodiment of the present invention. FIG. 9 is a block diagram showing a target phase voltage waveform generating circuit according to the third embodiment of the present invention, and FIG. 10 is a waveform diagram showing a target phase voltage waveform formed by the circuit of FIG. (1) …… DC power supply, (2) …… Inverse converter, (3)
(4) (5) ... Control circuit, (7) ... Target sine wave voltage generation circuit, (9) ... Target phase voltage waveform generation circuit.

Claims (2)

[Claims] 1. A three-phase bridge circuit of exchange switching elements (S1 to S6) for converting a DC voltage of a DC power supply (1) into a three-phase AC voltage, and an approximate sine of three phases from the three-phase bridge circuit. In order to obtain the voltage between the wavy lines, the first, second and third target phase voltage waveforms are formed, and the three phases of the three phases which are averagely approximated to the first, second and third target phase voltage waveforms are formed. In order to obtain a phase voltage waveform, the conversion switching element (S1
~ S6) control circuit for controlling the target phase voltage for forming the first, second and third target phase voltage waveforms included in the control circuit. The waveform forming means generates a three-phase sine wave voltage (ea, eb, ec) for generating a three-phase sine wave voltage (7), and a positive voltage of the three-phase sine wave voltage (ea, eb, ec). A three-phase half-wave rectified voltage forming means (24) for obtaining a three-phase half-wave rectified voltage (e ₃ ), and a voltage generation for generating a voltage E / 2 that is half the voltage E of the DC power supply (1) and means (1a), the inverted waveform voltage of 1/2 of the voltage E / 2 from the three-phase half-wave rectified voltage (e ₃₎ the subtraction to the 3-phase half-wave rectified voltage of the voltage E a (e ₄₎ Π / 6 is obtained by adding the inverted waveform voltage (e ₄ ) to the subtraction means (25) to be formed and the sine wave voltage (ea) of the first phase generated from the three-phase sine wave voltage generation circuit (7). From 5π / 6 A first addition means (26a) for outputting a voltage waveform (e ₀ a) in which only a section is flat as the first target phase voltage waveform; and a third phase sine wave voltage generation circuit (7) The inverted waveform voltage (e ₄ ) is added to the sine wave voltage (eb) of the second phase to have the same waveform as the first target phase voltage waveform with respect to the first target phase voltage waveform. From a second adding means (26b) for outputting a voltage waveform (e ₀ b) having a phase difference of 2π / 3 as the second target phase voltage waveform, and the three-phase sine wave voltage generating circuit (7). The inverted waveform voltage (e ₄ ) is added to the generated sine wave voltage (ec) of the third phase, and the first target phase voltage has the same waveform as the first target phase voltage waveform. or a third adding means for outputting a voltage waveform (e ₀ c) as the third target phase voltage waveform (26c) having a phase difference of 4 [pi] / 3 with respect to the waveform 3-phase static power converter, characterized by comprising. 2. A 3-phase bridge circuit of switching elements (S1 to S6) for exchange for converting a DC voltage of a DC power supply (1) into a 3-phase AC voltage, and a 3-phase approximate sine from the 3-phase bridge circuit. In order to obtain the voltage between the wavy lines, the first, second and third target phase voltage waveforms are formed, and the three phases of the three phases which are averagely approximated to the first, second and third target phase voltage waveforms are formed. In order to obtain a phase voltage waveform, the conversion switching element (S1
~ S6) control circuit for controlling the target phase voltage for forming the first, second and third target phase voltage waveforms included in the control circuit. The waveform forming means generates a three-phase sine wave voltage (ea, eb, ec) for generating three-phase sine wave voltage (ea, eb, ec), and a negative voltage of the three-phase sine wave voltage (ea, eb, ec). A three-phase half-wave rectified voltage forming means (24a) for obtaining a three-phase half-wave rectified voltage (e ₅ ) and a negative voltage −E / 2 which is half the voltage E of the DC power supply (1). a voltage generating means (1b), the inverted waveform of the half of the negative voltage -E / 2 from the negative of the three-phase half-wave rectified voltage (e ₅₎ the subtraction to the 3-phase half-wave rectified voltage of the voltage E The inversion waveform voltage (e ₆ ) is applied to the subtracting means (25a) that forms the voltage (e ₆ ) and the first-phase sine wave voltage (ea) generated from the three-phase sine wave voltage generating circuit (7). Add A first adding means (26a) for outputting as the first target phase voltage waveform having a voltage waveform (e ₀ a) that is flat only in the section from 7π / 6 to 11π / 6; and the three-phase sine wave voltage generation The inverted waveform voltage (e ₆ ) is added to the sine wave voltage (eb) of the second phase generated from the circuit (7) to have the same waveform as the first target phase voltage waveform. Second adding means (26b) for outputting a voltage waveform (e ₀ b) having a phase difference of 2π / 3 with respect to the target phase voltage waveform of 1 as the second target phase voltage waveform; The inverted waveform voltage (e ₆ ) is added to the sine wave voltage (ec) of the third phase generated from the wave voltage generation circuit (7) to have the same waveform as the first target phase voltage waveform. third adding of the output voltage waveform (e ₀ c) having a phase difference of 4 [pi] / 3 with respect to the first target phase voltage waveform as the third target phase voltage waveform of Te 3-phase static power converter, characterized in that consists of the stages (26c).