JP3483769B2 - Cycloconverter control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a cycloconverter which performs asymmetrical control.

[0002]

2. Description of the Related Art In a cycloconverter in which each phase power converter has a two-stage configuration, the output voltage of the first-stage power converter and the output voltage of the second-stage power converter are set to different values, and The asymmetrical control method for improving the side power factor has been widely used from the past.

FIG. 7 is a block diagram showing a conventional cycloconverter controller, which is an example of controlling a three-phase induction motor as a load. As shown in the figure, the main circuit of the cycloconverter includes power supply transformers 2 ₁ and 2 ₂ connected to a three-phase AC power supply 1 and secondary windings 2a _{1 of} the power supply transformers 2 ₁ and 2 ₂ . 2b ₁ , 2c ₁ , 2a ₂ , 2b ₂ , 2c ₂
-Phase Graetz-connected converter (power converter) 3a ₁ , 3b ₁ , 3c ₁ , 3a ₂ , 3b ₂ , 3c _{2 connected to}
And supplies electric power to the three-phase induction motor 4 connected to the output side thereof. The 3-phase Graetz connected converter _{3a 1, 3b 1, 3c 1} , 3a 2, 3b 2, 3c
₂ , the thyristors are connected in anti-parallel, respectively, and currents in both forward and reverse directions can flow. Further, current detectors 5a, 5b, 5c for detecting a load current are provided on the output side of the three-phase Graet's connection converters 3a, 3b, 3c.
The phase induction motor 4 has a speed detector 6 for detecting its speed.
Is attached. The control circuit is a three-phase induction motor 4
A speed setting device 10 for setting the speed is provided, and the speed reference signal set by the speed setting device 10 and the speed feedback signal detected by the speed detector 6 are input to the speed control circuit 11. The speed control circuit 11 performs a proportional integration operation so that the speed feedback signal follows the speed reference signal and outputs a torque reference signal.
Further, the velocity feedback signal obtained from the velocity detector 6 is input to the magnetic flux weakening control circuit 12, and a secondary magnetic flux reference signal is obtained as its output. Vector operation circuit 1
The torque reference signal from the speed control circuit 11 and the secondary magnetic flux reference signal from the magnetic flux weakening control circuit 12 are input to 3, and based on preset constants of the three-phase induction motor 4,
A torque current reference signal, a magnetic flux current reference signal and a slip angular frequency signal are calculated. In addition, the current detectors 5a, 5b,
The load current of each phase detected from 5c is converted into two phases by the three-phase / two-phase converter 14, separated into the torque current feedback signal and the magnetic flux current feedback signal, and input to the current control circuits 15 and 16. There is. Current control circuit 15,
The torque current reference signal and the magnetic flux current reference signal, which are the outputs of the vector calculation circuit 13, are input to the other inputs of 16 respectively, and the proportional-integral operation is performed so that each current feedback signal follows each current reference signal. That is, the torque axis voltage signal Vq and the magnetic flux axis voltage signal Vd are output. In the voltage command circuit 17, the torque axis voltage signal Vq and the magnetic flux axis voltage signal Vd output from the current control circuits 15 and 16, and the slip angular frequency signal ωs output from the vector calculation circuit 13
And the speed feedback signal detected by the speed detector 6 are input, the output voltage of each phase is calculated, and the three-phase Graetz-connected converter 3 is adjusted so as to obtain the calculated output voltage.
It controls a ₁ , 3b ₁ , 3c ₁ , 3a ₂ , 3b ₂ , 3c ₂ . The control described above is widely known as vector control of an induction motor.

Next, the details of the voltage command circuit 17 will be described with reference to FIG. As shown in the figure, in the voltage command circuit 17, the input torque axis voltage signal Vq and magnetic flux axis voltage signal Vd are input to the voltage vector calculation circuit 21 to calculate the voltage amplitude command value V and the phase signal θ. Further, the slip angular frequency signal ωs and the velocity feedback signal ωr are added by the adder 22, and then the magnetic flux angle signal θ by the integrator 23.
Converted to 0. This converted magnetic flux angle signal θ 0 is added by the adder 24 with the phase signal θ from the voltage vector calculation circuit 21, and the voltage phase command value θ v is added to the voltage of each phase along with the voltage amplitude command value V from the voltage vector calculation circuit 21. It is input to the command devices 25, 26 and 27. The voltage commander 25, 26, 27 for each phase outputs the output voltage command value Vu ₁ ,
Vu ₂ , Vv ₁ , Vv ₂ , Vw ₁ and Vw ₂ are calculated by the following equations.

[0005]

## EQU1 ## Vu ₁ , Vu ₂ = f (V.sin θv, Iu) Vv ₁ , Vv ₂ = f (V ・ sin (θv −120 °), Iv) Vw ₁ , Vw ₂ = f (V ・ sin (Θv −240 °), Iw) (1) In the above equation, f is a two-output function and has the characteristics shown in FIG. As shown in FIG. 9, V ₁ or V depending on the polarity of the current
Either of the _two outputs the maximum voltage or the minimum voltage. Such a control method of the voltage command value of each converter is called asymmetric control. When asymmetrical control is performed, a voltage having a waveform as shown in FIG. 10 is output from each phase converter.

[0006]

In such an asymmetrical control type cycloconverter, the firing phase of either the first-stage power converter or the second-stage power converter is the output limit, and therefore the one-stage The average input power factor is improved as compared with the symmetrical control system in which the output voltages of the second and second stage power converters have the same value. However, such an asymmetrical control system is not necessarily a system that optimizes the input power factor of a cycloconverter that combines three phases. Further, in the asymmetric control method, the ignition phase is the first stage, 2
The two power converters in the second stage are asynchronous with each other, and as shown in FIG. 11, the current is likely to be intermittent and control instability is likely to occur. In addition, the amount of generated harmonics also increases.

The present invention has been made in view of the above,
An object of the present invention is to provide a cycloconverter control device capable of increasing the input power factor of the cycloconverter, reducing the amount of generated harmonics, and avoiding intermittent output current.

[0008]

In order to solve the above-mentioned problems, the invention according to claim 1 relates to a three-phase load line-to-line output voltage while maintaining the line-to-line output waveform as a sine wave. In a control device for a cycloconverter of a voltage control system that varies the output voltage waveform of each phase, the reactive power generated by the cycloconverter is calculated based on each phase output voltage and each phase output current of the cycloconverter, and each phase output voltage is calculated. Evaluate the generated harmonic of the cycloconverter based on the ignition timing determined by, the output voltage of each phase so that the evaluation function value obtained from the evaluation result of the generated reactive power and the generated harmonic becomes the minimum. have a evaluation means for determining, firing Thailand
Ignition of each phase as an evaluation of the generated harmonic
Find the phase difference between the timing and the firing timing of the other phase,
The gist is to use the reciprocal value of the sum of squares of this phase difference.
It With this configuration, the output voltage of each phase is determined so that the reactive power generated and the generated harmonics of the cycloconverter are reduced among the possible combinations of the output voltages of each phase. Also, the ignition timings of the power converters for each phase must match.
Then, does each power converter perform commutation every 60 °?
The fifth and seventh harmonics increase. Therefore, each phase
If the ignition timing of the power converter of
Is good. Therefore, the ignition timing of each phase and the ignition of other phases
Calculate the phase difference of the timing and reciprocal the sum of squares of this phase difference
Evaluate generated harmonics with a simplified method of using values
It becomes possible to do .

According to a second aspect of the present invention, in the control device for a cycloconverter according to the first aspect, the power converter of each phase of the cycloconverter has a two-stage configuration, and the evaluation means includes the evaluation function. The gist is to determine the output voltage of the first-stage power converter and the output voltage of the second-stage power converter for each phase so that the value becomes minimum.
With this configuration, when the power converter of each phase has a two-stage configuration, the sum of the output voltage of the first-stage power converter of each phase and the output voltage of the second-stage power converter is the output of each phase. It becomes a voltage. Therefore, by determining the output voltage of the first-stage power converter and the output voltage of the second-stage power converter of each phase so that the evaluation function value becomes the minimum, the action of the invention according to claim 1 above. Similarly, the reactive power and harmonics generated by the cycloconverter are reduced.

[0010]

According to a third aspect of the present invention, in the control device for a cycloconverter according to the first aspect, the evaluation means ensures a certain phase difference with a firing timing determined by the output voltage of each phase. As a constraint,
The gist is to determine the output voltage of each phase so that the generated reactive power is minimized. With this configuration, securing a certain phase difference between the firing timings of the respective phases is equivalent to evaluating the generated harmonics to be small. Even if the output voltage of each phase is determined so that the generated reactive power is minimized under this condition, an action equivalent to the action of the invention described in claim 1 is obtained, and the generated reactive power of the cycloconverter is obtained. And less harmonics are generated.

According to a fourth aspect of the present invention, in the control device for a cycloconverter according to the first aspect, the cycloconverter has a two-stage power converter for each phase, and the evaluation means is for each phase. The output voltage of the first stage power converter and the second stage of each phase so that the generated reactive power is minimized, with the constraint that a certain phase difference with a firing timing determined by the output voltage of The gist is to determine the output voltage of the eye power converter. With this configuration, when the power converter of each phase has a two-stage configuration,
The output voltage of the first-stage power converter and the second-stage power converter of each phase are minimized so that the generated reactive power is minimized, provided that the ignition timing of each phase is ensured to have a certain phase difference. By determining the output voltage of, the generated reactive power and generated harmonics of the cycloconverter are reduced as in the case of the operation of the invention described in claim 4.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 to 4 are views showing a first embodiment of the present invention. The overall control block diagram shown in FIG. 1 is almost the same as that in FIG. 7, but for convenience of explanation, the power converter of each phase (three-phase Graet's connection converter) is one stage. In FIGS. 1 and 2 and a diagram showing a second embodiment to be described later, the same or equivalent parts as the circuits and devices in FIGS. 7 and 8 are represented by the same reference numerals as those described above, A duplicate description will be omitted. First, Fig. 1
The configuration of the control device for the cycloconverter according to the present embodiment will be described with reference to FIG. 1. In the present embodiment, a voltage command circuit 30 that calculates a voltage command for each phase is provided. FIG. 2 shows a detailed configuration of the voltage command circuit 30. The generated reactive power / generated harmonics evaluation circuit 31 as an evaluation unit of the cycloconverter is provided. The generated reactive power / generated harmonic evaluation circuit 31 generates the generated reactive power Q.
Then, the evaluation function value V is calculated from the generated harmonic evaluation value H by the weighting factors w ₁ and w ₂ , and the output voltage of each phase is determined so that this V becomes minimum.

V = w ₁ × Q ² + w ₂ × H ² (2) Here, a method of calculating the generated reactive power Q will be described. The required voltage must be applied to the electric motor, but in the configuration shown in FIG. 1, a predetermined voltage may be applied to the line voltage of the induction motor 4. On the other hand, each power converter 3
Since the output voltages of a, 3b, and 3c are phase voltages, there is a degree of freedom in their determination. Line voltage Euv, E of the induction motor 4
vw and Ewu are given by the following equations.

Eu = E ₁ × sin (θ) Ev = E ₁ × sin (θ-120 °) Ew = E ₁ × sin (θ-240 °) Euv = Eu -Ev Evw = Ev -Ew Ewu = Ew- Eu (3) The output voltage of each phase power converter 3a, 3b, 3c is Vu,
Given that Vv and Vw, the following relationships must be satisfied.

Vu-Vv = Euv Vv-Vw = Evw Vw-Vu = Ewu (4) Next, the output voltage of each phase is usually the power converter 3a,
There is an upper limit value and a lower limit value according to the firing timing of 3b and 3c. In particular, since the lower limit value is determined by the margin angle in the inverse conversion operation, the upper limit value and the lower limit value have different sizes. Further, since the relationship between the conversion operation and the voltage polarity differs depending on the polarity of the output current of the power converter, that is, when the current in the positive direction, the positive side of the output voltage becomes the forward conversion operation, whereas when the current in the negative direction, Since the negative side of the output voltage is the reverse conversion operation,
It is necessary to switch the upper limit value ULMT and the lower limit value LLMT of the output voltage depending on the polarity of the output current. The current of each phase is Iu
, Iv, Iw,

[Equation 2]     LLMT≤Vu≤ULMT (when Iu≥0)     -ULMT≤Vu≤-LLMT (when Iu <0)     LLMT≤Vv≤ULMT (when Iv≥0)     -ULMT≤Vv≤-LLMT (when Iv <0)     LLMT ≦ Vw ≦ ULMT (when Iw ≧ 0)     -ULMT≤Vw≤-LLMT (when Iw <0) (5) There are restrictions. Here, from equation (4), Vv = Vu-Evu Vw = Vu + Ewu (6) Since there is a relationship of

LLMT ≤ Vu -Euv ≤ ULMT (when Iv ≥ 0) -ULMT ≤ Vu -Euv ≤ -LLMT (when Iv <0) LLMT ≤ Vu + Ewu ≤ ULMT (when Iw ≥ 0) -ULMT ≤ Vu + Ewu ≦ −LLMT (when Iw <0) (7) These can be summarized as follows with respect to Vu.

[0018]

LLMT≤Vu≤ULMT (when Iu≥0) -ULMT≤Vu≤-LLMT (when Iu <0) LLMT + Euv≤Vu≤ULMT + Evu (when Iv≥0) -ULMT + Euv≤Vu≤-LLMT + Euv ( Iv <0) LLMT-Ewu ≤ Vu ≤ ULMT-Ewu (when Iw ≥ 0) -ULMT-Ewu ≤ Vu ≤ -LLMT-Ewu (when Iw <0) (8) On the other hand, generation of cycloconverter The reactive power Q is related to the firing angle α of the thyristor power converter and is given by the following equation.

[0019]

## EQU00005 ## As Vu = k.times.cos .alpha.u, Q = sin .alpha.u * | Iu | + sin .alpha.v * | Iv | + sin .alpha.w * | Iw | = √ (1- (Vu / k) ² ) * | Iu | + √ (1- (Vv / k) ² ) × | Iv | + √ (1- (Vw / k) ² ) × | Iw | (9) Substituting equation (6),

[Equation 6] Q = √ (1- (Vu / k) ² ) × | Iu | + √ (1-((Vu −Euv) / k) ² ) × | Iv | + √ (1-((Vu + Ewu ) / K) ² ) × | Iw | ... (10)

Next, the method of evaluating the generated harmonics will be described. The generated harmonics are related to ignition timing, load current, input impedance, etc. Although the calculation may be performed strictly, in consideration of the feasibility, the calculation should be simplified. When the ignition timings of the respective phases match, the power converters 3a, 3b, 3c commutate every 60 °, so that the 5th and 7th harmonics increase. Therefore, it is preferable that the firing timings of the respective phases be shifted as much as possible. Therefore, as the evaluation of the generated harmonics by the ignition timing, the phase difference between the ignition timing of each phase and the ignition timings of other phases is obtained, and the reciprocal of the sum of squares of this phase difference is evaluated value H of the generated harmonics. Used as. Let the firing angles of each phase be αu, αv, and αw.

[0021]

[Formula 7] H = 1 / [((αu −αv) MOD60) ² + ((αv −αw) MOD60) ² + ((αw −αu) MOD60) ² ] (11). Here, the above MOD60 is the remainder operation of 60 degrees,
As shown in FIG. 3, the phase difference of the firing angle is converted into the range of ± 30 °. As the evaluation function of the whole, the above formula (2) is used.
As shown in. Therefore, equation (2) should be minimized under the condition of equation (8). The voltage waveform actually obtained by this method is shown in FIG.

According to the present embodiment described above, the output voltage is determined so that the reactive power and harmonics generated by the cycloconverter are reduced, so that an economical cycloconverter control device can be provided. .

5 and 6 show a second embodiment of the present invention. The overall control block diagram shown in FIG. 5 is substantially the same as that of FIG. 1 except that the power converter of each phase has a two-stage configuration. The configuration of the cycloconverter control device according to the present embodiment will be described with reference to FIG.
In the present embodiment, a voltage command circuit 40 that calculates a voltage command for each phase is provided. FIG. 6 shows a detailed configuration of the voltage command circuit 40, in which a generated reactive power / generated harmonics evaluation circuit 41 is provided as an evaluation means of the cycloconverter. The generated reactive power / generated harmonic evaluation circuit 41 inputs the output voltage of each phase and the output current of each phase of the cycloconverter, calculates the generated reactive power of the cycloconverter, and inputs the output voltage of each phase to set the ignition timing. Calculate and evaluate the generated harmonics. Then, the evaluation function value V is calculated from the generated reactive power Q and the generated harmonic evaluation value H by the weighting factors w ₁ and w ₂ , so that this V becomes minimum.
Determine the output voltage for each phase. In this case, the power converter of each phase has a two-stage configuration, and the power converter 3 of the first stage is used.
a ₁ , 3b ₁ , 3c ₁ and the second-stage power converters 3a ₂ , 3
Each output voltage of b ₂ and 3c ₂ can be individually determined. Power converters 3a ₁ , 3b ₁ , 3c ₁ , 3a ₂ , 3b ₂ , for each phase
The output voltage of 3c ₂ is Vu, Vv, Vw, the first stage, 2
Power converters 3a ₁ , 3b ₁ , 3c ₁ , 3a ₂ ,
The output voltages of 3b ₂ and 3c ₂ are Vu ₁ , Vu ₂ , and
If Vv ₁ , Vv ₂ , Vw ₁ and Vw ₂ are set, the following relationships are established.

Vu = Vu ₁ + Vu ₂ Vv = Vv ₁ + Vv ₂ Vw = Vw ₁ + Vw ₂ (12) Further, the upper limit value ULMT and the lower limit value LLMT are respectively given by the following equations.

[0025]

LLMT / 2 ≦ Vu ₁ , Vu ₂ ≦ ULMT / 2 (when Iu ≧ 0) −ULMT / 2 ≦ Vu ₁ , Vu ₂ ≦ −LLMT / 2 (when Iu <0) LLMT / 2 ≦ Vv ₁ , Vv ₂ ≤ ULMT / 2 (when Iv ≥ 0) -ULMT / 2 ≤ Vv ₁ , Vv ₂ ≤ -LLMT / 2 (when Iv <0) LLMT / 2 ≤ Vw ₁ , Vw ₂ ≤ ULMT / 2 (when Iw ≧ 0) −ULMT / 2 ≦ Vw ₁ , Vw ₂ ≦ −LLMT / 2 (when Iw <0) (13) On the other hand, the reactive power Q generated by the cycloconverter is given by the following equation. .

[0026]

[Equation 9] Q = √ (1- (Vu ₁ / k) ² ) × | Iu | + √ (1- (Vu ₂ / k) ² ) × | Iu | + √ (1- (Vv ₁ / k) ² ) × | Iv | + √ (1- (Vv ₂ / k) ² ) × | Iv ｜ + √ (1- (Vw ₁ / k) ² ) × | Iw | + √ (1- (Vw ₂ / k) ) ² ) × | Iw | (14) Next, regarding the harmonic evaluation value H,

[Equation 10] H = 1 / [((αu ₁ −αu ₂ +30) MOD60) ² + ((αu ₁ −αv ₁ ) MOD60) ² + ((αu ₁ −αv ₂ +30) MOD60) ² + ((αu ₁₋ αw ₁ ) MOD60) ² + ((αu ₁₋ αw ₂ + 30) MOD60) ² + ((αu ₂ −αv ₁ + 30) MOD60) ² + ((αu ₂ −αv ₂ ) MOD60) ² + ((αu ₂ −αw ₁ +30) MOD60) ² + ((αu ₂ −αw ₂ ) MOD60) ² + ((αv ₁ −αv ₂ +30) MOD60) ² + ((αv ₁ −αw ₁ ) MOD 60) ² + ((αv ₁ −αw ₂ +30) MOD60) ² + ((αv ₂ −αw ₁ +30) MOD60) ² + ((αv ₂ −αw ₂ ) MOD60) ² + ((αw ₁ −αw ₂ +30) MOD60) ² ]… ( 15) Here, the first-stage power converters 3a ₁ , 3b ₁ ,
3c ₁ and the second stage power converters 3a ₂ , 3b ₂ , 3c
_{In the case of 2} , the phase difference is usually 30 ° due to the input transformer, so this phase difference is considered in the evaluation of H. The overall evaluation function is as shown in the above equation (2). Therefore, equation (2) should be minimized under the conditions of equations (8), (12), and (13).

In the first and second embodiments, the generated reactive power / generated harmonics evaluation circuits 31 and 41, which are evaluation means, are based on the phase output voltage and the phase output current of the cycloconverter. The generated reactive power Q of the cycloconverter was calculated, and the evaluation value H of the generated harmonic was calculated based on the ignition timing determined by the output voltage of each phase, and was calculated from the generated reactive power Q and the generated harmonic evaluation value H. The output voltage of each phase or each output voltage of the first-stage power converter and the second-stage power converter is determined so that the evaluation function value V is minimized. Wave evaluation circuit 31, 4
1 is the output voltage of each phase or 1 so that the generated reactive power Q is minimized under the constraint that a certain phase difference with a firing timing determined by the output voltage of each phase is secured.
Each output voltage of the power converter of the second stage and the power converter of the second stage may be determined. Securing a certain phase difference between the ignition timings of the respective phases is equivalent to evaluating that the generated harmonics are reduced, and the generated reactive power Q is minimized under this condition. Even if the output voltage of each phase or each output voltage of the first-stage power converter and the second-stage power converter is determined, the amount of reactive power Q and harmonics generated by the cycloconverter can be reduced. .

[0028]

As described above, according to the first aspect of the present invention, the reactive power generated by the cycloconverter is calculated based on the output voltage and the output current of each phase of the cycloconverter, and each phase is calculated. Evaluate the generated harmonics of the cycloconverter based on the ignition timing determined by the output voltage, and output of each phase so that the evaluation function value obtained from the evaluation result of the generated reactive power and the generated harmonics is minimized. Since the evaluation means for determining the voltage is provided, the output voltage of each phase is determined so that the reactive power generated and the generated harmonics of the cycloconverter are reduced among the possible combinations of the output voltages of the respective phases, and the cycloconverter is determined. Input power factor is high and the amount of generated harmonics can be reduced.
Further, since the ignition timing of each phase varies when the amount of generated harmonics is small, the problem of current interruption can be avoided. In addition, the generated harmonics due to the ignition timing
As an evaluation of, the ignition timing of each phase and the ignition timing of other phases
Find the phase difference of the imming and calculate the reciprocal of the sum of squares of this phase difference.
Is used, so the generated harmonics can be
Appropriate wave evaluation .

According to a second aspect of the present invention, the cycloconverter has a two-stage power converter for each phase, and the evaluation means is arranged so as to minimize the evaluation function value of each phase. Since the output voltage of the first-stage power converter and the output voltage of the second-stage power converter are determined, even when the power converter of each phase has a two-stage configuration, the reactive power generated by the cycloconverter is generated. Also, the output voltage of each phase can be determined so that the generated harmonics are reduced, and the same effect as the effect of the invention described in claim 1 can be obtained.

[0030]

According to the third aspect of the invention, the evaluation means has a constraint condition that the ignition timing determined by the output voltage of each phase has a certain phase difference.
Since the output voltage of each phase is determined so that the generated reactive power is minimized, ensuring a certain phase difference with the ignition timing of each phase is evaluated so that generated harmonics are reduced. This is equivalent to what has been done, and even if the output voltage of each phase is determined so that the generated reactive power is minimized under this condition, the same effect as the effect of the invention described in claim 1 can be obtained.

According to a fourth aspect of the present invention, the cycloconverter has a two-stage power converter for each phase, and the evaluation means has a constant ignition timing determined by the output voltage of each phase. The output voltage of the first-stage power converter and the output voltage of the second-stage power converter for each phase are determined so that the generated reactive power is minimized, with the constraint of ensuring the phase difference of Therefore, even when the power converter of each phase has a two-stage configuration, the same effect as the effect of the invention described in claim 1 can be obtained by the same operation as the effect of the invention described in claim 4. can get.

[Brief description of drawings]

FIG. 1 is a block diagram of a control device for a cycloconverter that is a first embodiment of the present invention.

FIG. 2 is a block diagram showing an internal configuration of the voltage command circuit in FIG.

FIG. 3 is a diagram for explaining a phase difference calculation of firing timing of each phase in the first embodiment.

FIG. 4 is a diagram showing an example of an output voltage waveform of each phase in the first embodiment.

FIG. 5 is a block diagram of a second embodiment of the present invention.

FIG. 6 is a block diagram showing an internal configuration of the voltage command circuit in FIG.

FIG. 7 is a block diagram of a conventional cycloconverter control device.

8 is a block diagram showing an internal configuration of the voltage command circuit in FIG.

FIG. 9 is a diagram showing an output function characteristic of asymmetric control in the above-mentioned conventional technique.

FIG. 10 is a diagram showing an output voltage waveform when asymmetrical control is performed in the above conventional technique.

FIG. 11 is a diagram for explaining a problem of intermittent output current in the above conventional technique.

[Explanation of symbols]

1 3-phase AC power supply 3a, 3b, 3c 3-phase Graetz connection converter (power converter) 4 3-phase induction motor (3-phase load) 30, 40 Voltage command circuit 31, 41 Generated reactive power / generated harmonics evaluation circuit (evaluation means)

Claims (4)

(57) [Claims] 1. A control device for a cycloconverter of a voltage control system which varies the output voltage waveform of each phase while maintaining the sine wave of the line output waveform with respect to the line output voltage of a three-phase load. The generated reactive power of the cycloconverter is calculated based on each phase output voltage and each phase output current of the converter, and the generated harmonic of the cycloconverter is evaluated based on the ignition timing determined by the output voltage of each phase. It has a rating means the evaluation function value obtained from the evaluation results of generating reactive power and the generated harmonics to determine the phase of the output voltage so as to minimize, by firing timing
As an evaluation of the generated harmonics, the ignition timing of each phase and
Obtain the phase difference of the ignition timing of the other phase,
A control device for a cycloconverter, which uses the reciprocal value of the sum of squares . 2. The cycloconverter has a two-stage power converter for each phase, and the evaluation means includes a first-stage power converter for each phase so that the evaluation function value is minimized. The control device for the cycloconverter according to claim 1, wherein the output voltage and the output voltage of the second-stage power converter are determined. 3. The evaluation means is configured so that the generated reactive power of each phase is minimized under the constraint that the ignition timing determined by the output voltage of each phase has a certain phase difference. The control device for a cycloconverter according to claim 1, wherein the output voltage is determined. 4. The cycloconverter has a two-stage power converter for each phase, and the evaluation means ensures a certain phase difference with a firing timing determined by the output voltage of each phase. The constraint condition is that the output voltage of the first-stage power converter and the output voltage of the second-stage power converter of each phase are determined so that the generated reactive power is minimized. Cycloconverter control device described.