JP3207275B2 - Power converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for controlling a plurality of converters operated by commonly connecting AC terminals so that the average values of DC voltages are equal.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram of a main circuit of a conventional power converter. In the figure, 1 is an AC power supply, and 2 to 4 are capacitors connected between the phases of the AC power supply 1. Converters 5 and 6 for converting AC power and DC power are connected to the AC power supply 1 with their AC terminals in common, and perform parallel operation. The capacitors 2 to 4 are used to absorb switching surges of the converters 5 and 6. Reference numerals 7 to 18 are self-extinguishing type switching elements constituting the converters 5 and 6. Hereafter, the gate is used as a self-extinguishing type switching element.
A case where an on-off thyristor (GTO) is used will be described. Reference numerals 19 to 22 denote DC reactors for smoothing a DC current, and reference numerals 23 and 24 denote loads.

FIG. 5 is a block diagram of a conventional control circuit for controlling the power converter of FIG. In the figure, 25 is a phase reference of the alternating current of the converters 5 and 6, 26 is a comparator, 27
Is a logic circuit for generating a signal for firing the GTO of the converter 5, and 28 to 33 are firing signals of the GTOs 7 to 12 of the converter 5. 34 is a phase shift circuit for operating the converter 5 and the converter 6 in different phases. 35 is a comparator, 36 is a logic circuit for generating a signal for firing the GTO of the converter 6, 37
Reference numerals to 42 denote firing signals of the GTPs 13 to 18 of the converter 6.

FIG. 6 is an operation waveform diagram when the power converter of FIG. 4 is controlled by the conventional control circuit shown in FIG. The operation in the case where the control is performed by the conventional control circuit will be described below with reference to FIGS. In FIG. 6, (1) indicates an AC current phase reference, and the output of 25 indicates 0 ° of the current phase.
A value proportional to 360 ° is generated.

[0005] (2) is the output of the comparator 26, for example, (1)
Is "1" when the phase is in the range of 0 ° to 60 °, and 60 ° to 1
“2” when in the range of 20 °, “3” in the range of 120 ° to 180 °, “4” in the range of 180 ° to 240 °,
"5" in the range of 240 ° to 300 °, 300 ° to 36
It is assumed that a value of “6” is generated in the range of 0 °. Next, the logic circuit 27 sets the G of the converter 5 according to the value of (2).
Control of the energization state of the TO will be described. That is, (2) is "1"
GTO7 and GTO11 by the ignition signals 28 and 32
Is turned on. When (2) is "2", the firing signal 28
GTO7 and GTO12 are turned on by means of and 33. When (2) is "3", GT
O8 and GTO12 are turned on. When (2) is "4", the GTOs 8 and 10 are turned on by the firing signals 29 and 31. When (2) is "5", GTO9 and GTO10 are turned on by firing signals 30 and 31.
When (2) is "6", the GTO 9
And the GTO 11 are turned on.

By controlling the GTO of the converter 5 as described above, a current as shown in (3) flows through the U phase of the converter 5. In the V phase, a current delayed by 120 ° from (3) flows, and in the W phase, a current delayed by 240 ° from (3) flows. (4) is a voltage generated on the DC side of the converter 5 at this time.

On the other hand, the output (1) of the AC current phase shift reference 25 is converted by the phase shift circuit 34 into a value delayed by 30 °,
5 given. The comparator 35 and the logic circuit 36 are the comparator 2
6 and the logic circuit 27 operate in exactly the same way
The energized state of O is controlled. Therefore, the GTO of the converter 6 operates in exactly the same manner with the phase of the GTO of the converter 5 delayed by 30 °. Therefore, (5)
As shown in FIG.
A current with a delayed phase flows. In the V-phase, a current delayed by 120 ° with respect to (5) is applied.
A current with a phase delay of 40 ° flows. (6) is a voltage generated on the DC side of the converter 6 at this time. (7) is the sum of the U-phase current (3) of the converter 5 and the U-phase current (5) of the converter 6,
This is a current flowing through the AC power supply 1.

[0008]

As described above, by connecting the converter 5 and the converter 6 in parallel and operating the GTO by shifting the conduction phase of the GTO by 30 °, the AC current is represented by (7). Thus, a trapezoidal wave is formed, and harmonics can be reduced. However, the DC voltage of converter 5 and converter 6 is (4)
As shown in (6), since the average values are not equal, the DC side cannot be connected in parallel.

In order to eliminate the above-mentioned drawbacks of the conventional device, the present invention controls the current supply state of the GTO so that the average values of the DC voltages of the converter 5 and the converter 6 become equal, thereby controlling the DC side. It is an object to provide a power converter that can be connected in parallel.

[0010]

In order to achieve the above object, the present invention provides a first converter in which a self-extinguishing type switching element is bridge-connected and a self-extinguishing type switching element which is bridge-connected. A load connected in common via a DC reactor between the DC side terminals of the first and second converters, respectively;
In the power converter, the AC terminals of the converter and the second converter are connected in common and connected to an AC power supply, according to the phase reference of the AC current of the first converter and the second converter. Each of the first converter and the second converter
A logic circuit for controlling an energization state of a function generator for generating a cosine function based on the phase reference of the alternating current, the
The value of the cosine function is the control delay of the AC current with respect to the AC voltage.
The value of the cosine function at the first timing according to the angle and this control
30 ° phase delay with respect to the timing according to the delay angle
The average of the values of the cosine function at the second timing
The first converter and the second converter
And a logic circuit for switching the energization state between the devices.
It is characterized by having done .

[0011]

In the operation waveform diagram of the conventional power converter shown in FIG. 6, the DC voltage (4) of the converter 5 and the DC voltage of the converter 6 are different.
The difference between the average values of (6) and (8) indicated by hatching
It is equal to the difference between the parts of (9). (10) is a sine function whose shape is the same as that of (8) and (9), indicated by hatching (11)
Is equal to the difference between (8) and (9). (12) is the integral of the sine function (10), (8), (9) and (11)
Is a cosine function representing the area of the portion. That is, the value of (12) at time t1 is equal to the area of (8), the value of (12) at time t2 is equal to the area of (9), and (1) at time t1.
The difference between the value of (2) and the value of (12) at time t2 is equal to the area of (11). In the conventional control shown in FIG. 6, during the period from time t1 to t2, the U-phase current (3) of the converter 5 flows and the U-phase current (5) of the converter 6 does not flow. Therefore, in the present invention,
At time t3 when the area indicated by (11) becomes １ ／, the energization state of the U-phase current (3) of the converter 5 and the U-phase current (5) of the converter 6 are switched, so that the DC voltage (4 ) And the average value of DC voltage (6) are controlled.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a main circuit according to the present invention. In FIG. 1, reference numerals 1 to 23 are the same as those described in the description of the prior art in FIG. FIG. 2 is a block diagram of a control circuit showing one embodiment of the present invention for controlling the power converter of FIG. In the figure, reference numerals 25 to 42 are the same as those in the configuration diagram of the conventional embodiment described with reference to FIG. 43 is a function generator which generates a sine function corresponding to the output of the AC current phase reference 25;
Is an integrator, which integrates the output of the function generator 43 to generate a cosine function. 45 is a comparator, which compares the output of the integrator 44 with the firing tamping 46 of the converters 5 and 6, and And a signal for switching the energization state of the converter 6 is generated. A knot circuit 47 inverts an output signal of the comparator 45. 4
Reference numerals 8 and 50 denote AND circuits, and reference numerals 49 and 51 denote OR circuits. The switching between the output of the logic circuit 27 and the output of the logic circuit 36 switches the conduction state of the converter 5 and the converter 6. FIG. 3 is an operation waveform diagram when the power converter of FIG. 1 is controlled by the control circuit of FIG. Hereinafter, the operation of the present invention will be described with reference to FIG. 1, FIG. 2, and FIG. In FIG. 3, (1)
Is the output of the AC current phase reference 25, and the current phase is 0 ° to 36 °.
Generates a value proportional to 0 °.

(2) is the output of the comparator 26. For example, (1)
Is "1" when the phase is in the range of 0 ° to 60 °, and 60 ° to 1
“2” when in the range of 20 °, “3” in the range of 120 ° to 180 °, “4” in the range of 180 ° to 240 °,
“5” when in the range of 240 ° to 300 °, 300 ° to 3
A value of "6" is generated in the range of 60 degrees.

Next, the control of the conduction state of the GTO of the converter 5 or 6 by the logic circuit 27 according to the value of (2) will be described. That is, when the output signal of the comparator 45 is “0”, the output signal of the knot circuit 47 becomes “1”, and the AND circuit 4
The output of the logic circuit 27 and the firing signals 28 to 33 are connected by the OR 8 and the OR circuit 49 to control the converter 5. In this operation, when (2) is "1", the GTOs 7 and 11 are turned on by the firing signals 28 and 32. When (2) is "2", GTO7 and GT
O12 is turned on. When (2) is "3", GTO8 and GTO12 are turned on by the firing signals 29 and 33. When (2) is "4", the GTOs 8 and 10 are turned on by the firing signals 29 and 31. When (2) is "5", GTO9 and GT
O10 is turned on. When (2) is "6", GTO9 and GTO11 are turned on by the firing signals 30 and 32.

On the other hand, the output (1) of the AC current phase reference 25 is converted into a value delayed by 30 ° by the phase shift circuit 34,
5 given. The comparator 35 and the logic circuit 36 operate in exactly the same way as the comparator 26 and the logic circuit 27 to control the GTO conduction state of the converter 6 or the converter 5.

That is, when the output signal of the comparator 45 is "0", the output signal of the knot circuit 47 becomes "1", and the output of the logic circuit 36 and the firing signals 37 to 42 are output by the AND circuit 50 and the OR circuit 51. Connected and converter 6 is controlled. Therefore, the GTO of the converter 6 operates in exactly the same manner with the phase of the GTO of the converter 5 delayed by 30 °.

When the output signal of the comparator 45 becomes "1", the output signal of the knot circuit 47 becomes "0" and the AND circuit 4
8 and the OR circuit 49, the output of the logic circuit 36 and the ignition signals 28 to 33 are connected, and the AND circuit 50 and the OR circuit 51 are connected.
Connects the output of the logic circuit 27 to the firing signals 37 to 42. Thus, the energization state of converter 5 and converter 6 can be switched.

(3) is a current flowing in the U phase of the converter 5. In the V phase, a current delayed by 120 ° with respect to (3) flows, and in the W phase, a current delayed by 240 ° with respect to (3) flows. (4) is a voltage generated on the DC side of the converter 5 at this time. (5) is the U-phase current of the converter 6. In the V phase
The current delayed by 120 ° phase with respect to (5)
A current with a phase delay of 240 ° flows with respect to (5). (6)
Is a voltage generated on the DC side of the converter 6 at this time.

(7) is the U-phase current (3) of the converter 5 and the converter 6
The current is the sum of the U-phase current (5) of FIG. (10) is the same sine function as that described in FIG. This is obtained by inputting the output (1) of the AC current phase reference 25 to the function generator 43, adding the control delay angle α of the AC current to the AC voltage, and converting it into a sine function that repeats every 60 °. By inputting the output (10) of the function generator 43 to the integrator 44 for integration and resetting it to zero every 60 °, a cosine function represented by (12) can be obtained at the output.

Next, the operation of the comparator 45 will be described. The ignition timing 46 gives a timing of t1 according to the control delay angle α of the AC current with respect to the AC voltage. t
Timing 2 is a point delayed by 30 ° from the timing of t1. Let A be the value of the cosine function (12) at the timing of t1. Let B be the value of the cosine function (12) at the timing of t2. Since the cosine function (12) is a function uniquely determined with respect to the output (1) of the AC current phase reference 25, A and B can be obtained when the control delay angle α of the AC current with respect to the AC voltage is determined. The average value of A and B is C
And The timing when the value of the cosine function (12) matches C is defined as t3. The comparator 45 generates a "1" signal at its output during the period from t1 to t3. (1
3) is an output signal of the comparator 45. When the output of the comparator 45 becomes "1", the conduction state of the converters 5 and 6 is switched by the AND circuit 48, the OR circuit 49, the AND circuit 50, and the OR circuit 51 as described above. 6 and FIG. 3, it can be seen that the U-phase currents (3) and (5) and the DC voltages (4) and (6) are switched during the period from t1 to t3. Shown here by hatching (8)
Area is equal to the above-mentioned CA. The area of the portion (9) indicated by hatching is equal to the above-mentioned BC. Here, it is the average value of C, A and B, so that CA and B
-C is equal. That is, the area of the portion (8) indicated by hatching is equal to the area of the portion (9) indicated by hatching. Therefore, the average value of DC voltage (4) and DC voltage (6) are equal. As described above, the case where the energization state of the converter 5 and the converter 6 is switched during the period from t1 to t3 in the period from t1 to t2, but the period from t3 to t2 in the period from t1 to t2, Converter 5 and converter 6
DC voltage (4) and DC voltage
The average value of (6) can be made equal. In addition, for the sake of simplicity, the case where the cosine function (12) is generated using the integrator 44 that obtains a value corresponding to the area of the sine function (11) has been described. The cosine function (12) may be directly generated from the output (1) of the AC current phase reference 25, and therefore the integrator 44 may not be used. Further, in the above description, the case where two converters are operated in parallel has been described, but two or more converters can be operated in parallel in the same manner.

[0022]

As described above, according to the present invention, the average value of the DC voltage is controlled to be equal when the AC currents of a plurality of converters having AC terminals connected in common are operated at different phases. Since the DC side of a plurality of converters can be connected in common and operated in parallel to obtain an AC current with a small number of harmonics, a great effect can be obtained particularly when large-capacity power conversion is performed. can get.

[Brief description of the drawings]

FIG. 1 is a main circuit configuration diagram showing an example of a power converter to which the present invention is applied.

FIG. 2 is a block diagram of a control circuit showing one embodiment of the present invention.

FIG. 3 is an operation waveform diagram when the power converter of FIG. 1 is controlled by the control circuit of FIG. 2;

FIG. 4 is a main circuit configuration diagram of a conventional power converter.

FIG. 5 is a block diagram of a conventional control circuit for controlling a conventional power converter.

FIG. 6 is an operation waveform diagram when the power converter of FIG. 4 is controlled by the conventional control circuit of FIG. 5;

[Explanation of symbols]

1 ... AC power supply 2-4 ...
Capacitors 5,6 ... Converters 7-18 ...
GTO 19-22 DC reactors 23, 24
Load 25 ... AC current phase reference 26 ...
Comparator 27… Logic circuit 28-33 ……
Firing signal 34 …… Phase shift circuit 35 ……
Comparator 36 ...... Logic circuit 37-42 ......
Firing signal 43 ... Function generator 44 ...
Integrator 45 ...... Comparator 46 ......
Firing timing 47 …… Not circuit 48 ……
AND circuit 49 ... OR circuit 50 ...
AND circuit 51 …… OR circuit

Claims (1)

(57) [Claims] 1. A first converter having a self-extinguishing type switching element connected in a bridge, a second converter having a self-extinguishing type switching element connected in a bridge, and the first converter and a second converter. A load connected in common between the DC-side terminals of the second converter via a DC reactor;
And an AC power supply connected to an AC power supply by connecting the AC terminals of the converter and the second converter in common, according to the phase reference of the AC current of the first converter and the second converter. wherein the first transducer second transducer of that
A logic circuit for controlling the respective energization states, a function generator for generating a cosine function based on the phase reference of the AC current, and a value of the cosine function for controlling the AC current with respect to the AC voltage.
The value of the cosine function at the first timing according to the delay angle
30 ° phase with respect to the timing corresponding to the control delay angle
The average of the values of the cosine function at the second delayed timing
The first converter and the second converter
Power conversion apparatus characterized by and comprising: a logic circuit, a for switching current supply state between the mutual transducer.