JPH1094262A - Voltage-type self-excited converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a converter that does not contain higher harmonic components other than integral multiples of the voltage fundamental frequency of an alternatingcurrent system. SOLUTION: When a voltage source 3 is connected between the direct current terminals on a voltage-type self-excited converter 4 and its alternating current terminals are connected with an alternating-current system 1 through an impedance element 2, a digital current control means 14A calculates an output current command to the converter 4 with specified timing based on the deviation between a detected value of the output current of the converter 4 and a preset value. Further, a pulse pattern determining means 17 compares the current command from the digital current controlling means 14A and a triangular wave from a triangular wave generating means, and determines an on/off pattern of a self-extinguishing switching element. At this time the digital current controlling means 14A calculates the output current command to the converter 4 with timing synchronized with the triangular-wave signals from the triangular wave generating means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage-type inverter used as an inverter for converting direct current to alternating current, a reactive power compensator for compensating for reactive power, an active filter for suppressing harmonics of alternating current, and the like. The present invention relates to a self-excited converter.

[0002]

2. Description of the Related Art FIG. 9 is a circuit diagram showing a configuration of a voltage type self-excited converter. In the figure, a voltage type self-excited converter (hereinafter simply referred to as a converter) 4 is a self-extinguishing type switching element, for example, a gate turn-off thyristor 4A to 4A to 4C.
It is composed of a circuit in which 4F is connected in a three-phase bridge. Then, the AC system 1 is connected via the impedance element 2
The converter 4 is connected to an AC terminal, and a DC power supply or a voltage source 3 composed of a capacitor is connected between the DC terminals of the converter 4.

FIG. 10 is a block diagram showing the configuration of the entire conversion device including the control device of the converter 4. Here, the current of the AC system is detected by the current detector 10 and the voltage is detected by the voltage detector 11. These detected values are stored in the power detector 1
Added to 2. The power detector 12 is a calculator that calculates the state quantities of the active power and the reactive power based on the detected values of the current and the voltage, respectively. The power control circuit 13 compares the state quantity calculated by the power detector 12 with a command value which is a reference of the state quantity controlled by the converter 4, and makes the difference zero.
Calculates the current command value of the phase and calculates the digital current control circuit 14
Add to The digital current control circuit 14 compares the current command value calculated by the power control circuit 13 with the AC system current detected by the current detector 10, and outputs an output voltage command to make the difference zero to the cross point detector 16. Add to Also,
When viewed from the phase of the AC system, the output voltage of the triangular wave generator 15 in which the 0-degree position and the 360-degree position are each a zero cross point is applied to the cross point detector 16. The cross point detector 16 detects an intersection between the three-phase output voltage command and the triangular wave voltage. The pulse pattern determination circuit 17 outputs a gate pulse for turning on and off the self-extinguishing type switching elements 4A to 4F based on the detection signal at the intersection and applies the gate pulse to the converter 4.

FIG. 11 shows the operation execution timing of the control operation of the digital current control circuit 14. In the figure, reference numeral 20 denotes a voltage waveform for one phase of the AC system 1 and reference numeral 21 denotes a triangular wave generator 15.
6 is a triangular-wave voltage waveform output from. Here, as an example, a case is shown in which a triangular wave voltage having a frequency three times that of the AC system 1 is output. Reference numeral 22 denotes the operation execution timing of the digital current control circuit 14. In this case, the digital current control circuit 14 is a digital operation circuit configured using a digital operation device such as a CPU (Central Processing Unit). The digital current control circuit 14 calculates the command value of the output current of the converter 4 at intervals of the calculation execution timing 22. FIG. 12 is an explanatory diagram illustrating the detailed configuration and operation of the digital current control circuit 14. Here, first, as shown in (a), the digital current control circuit 14 includes a pulse generator 30 for generating a pulse of a predetermined frequency, and a pulse counter 31 for counting the pulses and outputting pulses at regular intervals. It is composed of Then, the pulse generator 30 outputs the pulse 3 shown in FIG.
When 2 is output, the pulse counter 31 counts this and outputs an operation execution timing pulse 33 shown in (c). Therefore, the period indicated by the diagonal lines in (d) is the execution time 34 of the current command. FIG. 13 shows the digital current control circuit 14.
1 shows a voltage command 23 for one phase of the converter 4 output together with the AC system 20 and the triangular waveform 21.

[0005]

The digital current control circuit 14 using the above-described digital arithmetic unit executes the control operation at a fixed time interval set by the pulse counter 31, so that the following inconveniences occur. there were.

The AC output voltage waveform of the converter 4 shown in FIG. 9 is a rectangular wave having a DC voltage as a peak value. Therefore,
The AC output voltage contains many harmonic components with respect to the fundamental frequency of the AC system 1. The order and magnitude of the generated harmonic component are determined by the number of parallel connected swing elements of the converter 4 and the triangular wave frequency output from the triangular wave generator 15, that is, the triangular wave included in one cycle of the voltage of the AC system 1. Calculated theoretically by number. Further, similarly to the harmonic component of the voltage of the AC system 1, the system current of the AC system 1 also includes a harmonic component. Furthermore, the number of triangular waves is an odd multiple (frequency) of the voltage fundamental frequency of the AC system 1.

When a digital arithmetic unit is used for the digital current control circuit 14, the digital current control circuit 14
At the same time interval (constant frequency) as the calculation execution timing 22, a state quantity is read from the current detector 10 and the like, and a command value is read from the power control circuit 13 to execute the control calculation. Therefore, the AC voltage harmonic component included in the AC system 1 or the AC current harmonic component included in the AC system 1 interferes with the frequency of the arithmetic execution timing of the digital current control circuit 14, and the magnitude of the harmonic component Occurs. When the harmonics increase, there is a problem that the AC system 1 is damaged or the control stability of the converter 4 is adversely affected.

The harmonic component obtained from the frequency of the triangular wave generated from the triangular wave generator 15 and the fundamental frequency of the AC system 1 is expressed by the following equation (1). _{f b = n · f c ±} k · f s ... (1) However, f _b: the harmonic component f _c: triangular wave frequency f _s: AC system fundamental frequency n = 1,3,5, when the ... When k = 0, 2, 4,..., n = 1, 3, 5,.

The harmonic component generated by the equation (1) and the frequency component of the operation execution timing 22 of the digital current control circuit 14 that interfere with each other are expressed by the following equation (2). f _h = f _b −f _a (2) where f _{h is} a harmonic component due to interference f _{a is a} current control calculation execution timing frequency.

The harmonic component of the equation (1) is calculated by the triangular wave generator 1
5 is a theoretical harmonic generated by the triangular wave frequency generated, and this equation (1) is a well-known calculation equation. The harmonic component calculated by the equation (2) is superimposed on the harmonic component generated by the relation of the equation (1) to increase the harmonic component, causing damage to the AC system 1 or adversely affecting the control stability. Or give. Examples of these problems are shown below.

Problem example (a) Basic frequency of AC system 1 = 50 Hz (primary) Triangular wave frequency generated by triangular wave generator 15 = 150 Hz
(Tertiary) Calculation execution timing 22 of the digital current control circuit 14
Frequency = 210 Hz (4.2 order) n = 2 The harmonic generated under the condition of k = 1 is calculated by the following equation (3). f _b = 2 × 150 + 1 × 50 = 350 Hz (7th order) (3) The harmonic component obtained by the equation (3) and the harmonic component due to the interference at the operation execution timing 22 are shown in the following equation (4). Value. f _h = 650 Hz−210 Hz = 140 Hz (2.8 order) (4) That is, a harmonic component (2.8 order) that is an integral multiple or less of the voltage fundamental frequency of the AC system 1 is generated, and the AC system 1 Adversely affect

Inconvenience example (b) The operation execution timing 22 of the digital current control circuit 14 is changed to 450 under the condition of the equation (3).
When the frequency is set to Hz, the harmonic component caused by the interference becomes f _h = 450 Hz−350 Hz = 100 Hz (second order) (5) as shown in the following equation (5), and has an even order, which adversely affects the AC system. .

In addition to the above-mentioned problems, the phase of the triangular waveform 21 output from the triangular wave generator 15 shown in FIG. 9 and the output voltage command 23 of the converter 4 output from the digital current control circuit 14 When a phase difference occurs, the AC voltage waveform output from the converter 4 is
At 7, the polarity of the voltage becomes asymmetric, and the harmonic component further increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a first object of the present invention is to provide a voltage-type self-excited converter which does not include a harmonic component other than an integral multiple of a voltage fundamental frequency of an AC system. Is to provide.

A second object of the present invention is to provide a voltage-type self-excited converter that does not include even-order harmonic components.

[0016]

According to a first aspect of the present invention, there is provided a voltage-type self-excited converter having a self-extinguishing type switching element connected in a bridge, a voltage source connected between DC terminals, and an AC source. A voltage-type self-excited converter whose terminal is connected to an AC system via an impedance element, power detection means for detecting the output power of the converter, and a triangular wave generating means for generating a triangular wave signal, at a predetermined timing, A digital current control means for calculating an output current command of the converter based on a deviation between a detected value of the output power of the converter and a preset value; a current command of the digital current control means and a triangular wave of the triangular wave generating means; And a pulse pattern determining means for determining the ON / OFF pattern of the self-extinguishing type switching element by comparing the digital current control means with the triangular wave generating means. At a timing synchronized with the item, but which is adapted to calculate the output current command converter, thereby, it is unnecessary to include a harmonic component other than an integer times the voltage fundamental frequency of the AC system.

In the voltage-type self-excited converter according to the second aspect of the present invention, the digital current control means further calculates an output current command of the converter at a timing obtained by dividing the triangular wave by an even value. This eliminates the inclusion of harmonic components other than integral multiples of the voltage fundamental frequency of the AC system, and also eliminates the inclusion of even-order harmonic components.

According to a third aspect of the present invention, in the voltage-type self-excited converter, the triangular wave generating means generates a triangular wave synchronized with an output of the digital current control means.
As a result, harmonic components other than integral multiples of the voltage fundamental frequency of the AC system are not included, and even harmonic components are not included.

The voltage-type self-excited converter according to a fourth aspect of the present invention further comprises voltage phase detection means for detecting a voltage phase of the AC system, and the digital current control means comprises one cycle of the AC system voltage. The output current command of the converter is calculated at a timing obtained by dividing the triangular wave by an integer multiple, whereby a harmonic component other than an integer multiple of the voltage fundamental frequency of the AC system may be included. Disappears.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on preferred embodiments. FIG. 1 is a block diagram showing the configuration of the first embodiment of the present invention. In the figure, the same elements as those of FIG. This uses a digital current control circuit 14A instead of the digital current control circuit 14,
The digital current control circuit 14A includes a triangular wave generator 1
5, the output current command of the converter is calculated at a timing synchronized with the triangular wave signal.

The operation of the first embodiment configured as described above will be described below with reference to the waveform diagram of FIG.

In FIG. 2, reference numeral 20 denotes a voltage waveform for one phase of the AC system 1, and reference numeral 21 denotes a triangular waveform output from the triangular wave generator 15. Here, the position of 0 degree in the phase of the AC system is shown. Each of the 360-degree positions is a zero-cross point, and has a frequency three times as high as the frequency of the AC system.
Reference numeral 22 denotes an operation execution timing of the digital current control circuit 14, which is synchronized with the triangular waveform 21 here. The calculation execution timing 22 shows a case where the frequency has three times the frequency of the triangular waveform 21. Incidentally, the frequency of the operation execution timing 22 synchronized with the triangular waveform 21 is as follows (6)
It is expressed by an equation. f _a = m · fc _c (6) m = 1,2,3,... Accordingly, the harmonic component due to the interference is _calculated by the following equation (7) according to the equations (1), (2) and (6). It is expressed by an equation. _{f h = (n-m)} · f c ± k · f s ... (7) (7) equation in n, m, k because the integer, integer multiples shown in malfunction example (a) the harmonic component generated Other harmonic components do not occur.

Thus, according to the first embodiment, harmonics other than integral multiples of the voltage fundamental frequency of the AC system are not included.

FIG. 3 is a block diagram showing the configuration of the second embodiment of the present invention. In the figure, the same elements as those in FIG. .
This uses a digital current control circuit 14B in place of the digital current control circuit 14. This digital current control circuit 14B outputs an output current command of the converter at a timing synchronized with the triangular wave signal of the triangular wave generating means. In addition to the calculation, the output current command of the converter is calculated at the timing at which the triangular wave is divided into even values.

The operation of the second embodiment configured as described above will be described below with reference to the waveform diagram of FIG. Here, the calculation execution timing 22 is the triangular waveform 21
Are synchronized with the timing obtained by dividing one cycle of the above into an even number. At this time, the frequency of the operation execution timing 22 is represented by the following equation. f _a = 2 · m · fc _c (8) m = 1,2,3,.
It is expressed by the following equation (9) according to the equations (2) and (8). _{f h = (n-2m)} · f c as _{± k · f s ... (9} ) (9) is clear from the equation, the harmonic components other than the integer times the fundamental wave of the AC system 1 is generated And no even-order harmonic components are generated.

FIG. 5 is a block diagram showing the configuration of the second embodiment of the present invention. In the figure, the same elements as those in FIG. .
This means that instead of the triangular wave generator 15,
This triangular wave generator 15A generates a triangular wave synchronized with the output of the digital current control circuit 14.

The operation of the third embodiment configured as described above will be described below with reference to the waveform diagram of FIG. Here, the zero cross point of the triangular waveform 21 is synchronized with the zero cross point of the output voltage command 23 of the converter 4 output from the digital current control circuit 14. Thus, even if the phase of the output voltage command 23 changes, the triangular waveform 2
1 is synchronized without generating a phase difference. According to the third embodiment, since the voltage output from the converter 4 is symmetrical in the positive and negative directions, the harmonic of the AC system 1 does not increase. Further, similarly to the first and second embodiments, the calculation execution timing of the digital current control circuit 14 is changed to the triangular waveform 21.
In this case, there is no harmonic component other than an integral multiple of the voltage fundamental frequency of the AC system or an even harmonic component.

FIG. 7 is a block diagram showing the configuration of the fourth embodiment of the present invention. In the figure, the same elements as those in FIG. .
In this device, a voltage phase detector 19 for detecting the voltage phase of the AC system 1 is newly provided.
4C calculates the output current command of the converter 4 at a timing obtained by dividing one cycle of the voltage of the AC system by an integral multiple of a triangular wave.

The operation of the fourth embodiment configured as described above will be described below with reference to the waveform diagram of FIG. The operation of the digital current control circuit 14 is performed by the AC system 20.
Is executed at an operation execution timing 22 obtained by dividing one cycle into integers. In this case, the frequency of the operation execution timing 22 is represented by the following equation. f _a = m · fs _s (10) m = 1,2,3,... Accordingly, the harmonic component due to the interference is calculated from the following equations (11) from the equations (1), (2) and (10). It is represented by the equation. _{f h = n · f c ±} (k-m) · f s ... (11) Thus, according to the embodiment shown in FIG. 4, the AC system 1
Generates only integer multiples of theoretical harmonics and does not include harmonics other than integer multiples of the voltage fundamental frequency.

According to each of the above embodiments, the cross point between the output voltage of the digital current control circuit and the output voltage of the triangular wave generator is detected by the cross point detector 16, and a pulse is generated based on the detected signal. Pattern determination circuit 1
7 is a self-extinguishing type switching element 4 constituting the converter 4
Although the on / off control patterns of A to 4F are generated, the cross point detector 16 and the pulse pattern determination circuit 17
May be provided in the voltage comparator, or the same operation as described above can be performed by providing the microcomputer with these functions.

[0031]

As apparent from the above description, according to the voltage-type self-excited converter according to the first and fourth aspects, harmonics other than integral multiples of the voltage fundamental frequency of the AC system are included. Never.

According to the voltage-type self-excited converter of the second and third aspects, harmonic components other than integral multiples of the fundamental wave of the AC system 1 are not generated. No even-order harmonic components are generated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the embodiment shown in FIG. 1;

FIG. 3 is a block diagram showing a configuration of a second embodiment of the present invention.

FIG. 4 is a waveform chart for explaining the operation of the embodiment shown in FIG. 3;

FIG. 5 is a block diagram showing a configuration of a third embodiment of the present invention.

FIG. 6 is a waveform chart for explaining the operation of the embodiment shown in FIG. 5;

FIG. 7 is a block diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 8 is a waveform chart for explaining the operation of the embodiment shown in FIG. 7;

FIG. 9 is a general circuit diagram of a converter constituting the voltage-type self-excited converter.

FIG. 10 is a block diagram showing a configuration of a conventional voltage-type self-excited converter.

11 is a waveform chart for explaining the operation of the voltage-type self-excited conversion device shown in FIG.

FIG. 12 is an explanatory diagram of a detailed configuration and operation of main components of the voltage-type self-excited conversion device shown in FIG. 10;

FIG. 13 is a waveform chart for explaining the operation of the voltage-type self-excited conversion device shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 AC system 2 Impedance element 3 Voltage source 4 Voltage type self-excited converter 4A-4F Self-extinguishing type switching element 10 Current detector 11 Voltage detector 12 Power detector 13 Power control circuit 14, 14A, 14B, 14C Digital current Control circuit 15, 15A Triangular wave generator 16 Cross point detector 17 Pulse pattern determination circuit 18 Voltage phase detection circuit

Claims (4)

[Claims] 1. A voltage-type self-excited converter comprising a self-extinguishing type switching element bridge-connected, a voltage source connected between DC terminals, and an AC terminal connected to an AC system via an impedance element. Power detecting means for detecting the output power of the converter, triangular wave generating means for generating a triangular wave signal, and at a predetermined timing, a deviation between the detected value of the output power of the converter and a preset value. Digital current control means for calculating the output current command of the converter based on the current command of the digital current control means and the triangular wave of the triangular wave generating means, and comparing the ON / OFF pattern of the self-turn-off type switching element. And a pulse pattern determining means for determining the triangular wave signal of the triangular wave generating means. Voltage type self-commutated converter, characterized in that at the timing, and calculates the output current command of the transducer. 2. The voltage-type self-excited converter according to claim 1, wherein said digital current control means calculates an output current command of said converter at a timing obtained by dividing said triangular wave by an even value. 3. The voltage-type self-excited converter according to claim 1, wherein said triangular wave generating means generates a triangular wave synchronized with an output of said digital current control means. 4. The apparatus according to claim 1, further comprising voltage phase detection means for detecting a voltage phase of the AC system, wherein the digital current control means divides one cycle of the voltage of the AC system into timing obtained by dividing the triangular wave by an integral multiple. The voltage-type self-excited converter according to claim 1, wherein an output current command of the converter is calculated.