JPH08228488A - Method of correcting dead time of high frquency link dc/ac converter - Google Patents

Abstract

PURPOSE: To suppress the distortion of output voltage waveform of a high frequency transformer by quickening the timing of the switching operation of two switching elements, which perform switching with their phases slid from a group of switches, by the period equivalent to the dead time. CONSTITUTION: In a switching sequence which generates high-frequency power by alternately turning on and off switching elements 11 and 12 constituting an inverter part, and alternately turning on and off, switching elements 13 and 14 performing switching, with their phases slid from this switching element group, the switching operation of the switching elements 13 and 14 are quickened by the period equivalent to the dead time Td. For this account, the output voltage er of a high frequency transformer is corrected into waveform where the low-order high frequency is reduced. Hereby, the distortion of the output voltage waveform of the high frequency transformer can be suppressed.

Description

Detailed Description of the Invention

[0001]

This invention relates to a motor drive, U
The present invention relates to a control method of a high frequency link DC / AC converter by a cycloconverter used for PS (Uninterruptible Power Supply) or the like.

[0002]

2. Description of the Related Art The circuit configuration of a high frequency link DC / AC converter using a cycloconverter is shown in the block diagram of FIG. In FIG. 8, the direct current from the direct current power source 1 is connected to the four switching elements 1 via the parallel capacitor 2.
1 and 12 and 13 and 14 are input to the inverter unit 3 configured by a single-phase bridge connection and converted into high frequency power. The high frequency power output from the inverter unit 3 is input to the high frequency transformer 4, is transformed, and is input to the cycloconverter unit 5. The cycloconverter unit 5, which is configured by connecting the bidirectional switching elements 21, 22, 23, 24, 25, and 26 in a three-phase bridge, converts the high frequency power input via the high frequency transformer 4 into commercial frequency power, and the reactor and the capacitor. The AC power having the commercial frequency is output through the AC filter 6 composed of.

High frequency link D by cycloconverter
The C / AC converter has a feature that it can be easily miniaturized, but has a drawback that it is low in efficiency because it has a large number of power conversion stages. Therefore, the inverter unit 3
In order to reduce the switching loss of the cycloconverter unit 5, the method of (3) is operated at three levels, and the cycloconverter unit 5 is commutated when the secondary voltage of the high frequency transformer 4 is zero. That is, the inverter unit 3
The operation sequence of each switching element that constitutes the cycloconverter unit 5 is an application of the concept of instantaneous space vector control for the purpose of reducing the number of switching times, and is based on the output waveforms of the output voltage and the output current. It is divided into 18 operation modes, as shown in FIG. Of the above operation modes, operation modes 1 and 2
Taking the operation sequence in the case of as an example, the operation sequence is as shown in FIG. 3, and the phase voltage output from the cycloconverter unit 5 in this operation mode is e
_w > _eu > 0 and _ev <0. Depending on the magnitude of the phase voltage to be output, the maximum phase voltage e _w and the minimum phase voltage e _w
The switching sequence of the inverter unit 3 is provided based on the gate signal determined by comparing _v with the sawtooth carrier. That is, the switching element 1
The switching elements 1 and 12 and the switching elements 13 and 14 are alternately turned on / off by different switching sequences. Further, the arms V phase and W phase of the cycloconverter unit 5 corresponding to the respective phases perform switching in synchronization with the carrier, and the remaining arms U phase perform switching as the result of comparison with the carrier.
Bidirectional switching element 2 of cycloconverter unit 5
1, 23 and 25, the upper switching elements S _u ,
The switching sequence of S _v and S _w is as shown in FIG. 3, and it can be seen that the line voltages e _uv , e _vw , and _{ew v} have three levels of voltage. At this time, the operating states of the converter unit 3 and the cycloconverter unit 5 are divided into eight states, and the equivalent circuit diagrams in each state are as shown in FIGS. 5 and 6.

[0004]

As shown in FIG. 2, the switching element 11 in each arm of the inverter unit 3 is as follows.
12 and 13 and 14 and 14 are alternately turned on and off by different switching sequences. That is, the switching operation of ON / OFF in the switching elements 11 and 12 is performed in the operating states 3 and 4 and 7 and 8, and is performed in the operating states 1 and 2 and 5 and 6 in the case of the switching elements 13 and 14. There is. As is clear from FIG. 5 and FIG. 6, since the parallel loop of the switching element 13 is included in the closed loop of the inverter unit 3 in the operating state 1, there is a time lag in switching to the operating state 2. On the other hand, since the closed loop of the inverter unit 3 in the operating state 3 is due to the switching elements 11 and 14 being turned on, there is no time lag in switching to the operating state 4. Similarly, there is no time lag in switching from operating states 7 to 8, and there is a time lag in switching between operating states 5 and 6. As a result, the output voltage e of the high frequency transformer 4
_T becomes a voltage lacking the dead time T _d , as shown in FIG. Therefore, the output voltage waveform is as shown in FIG.
Waveform distortion occurs as shown in.

[0005]

The dead time correction method for a high frequency link DC / AC converter according to the present invention is made to solve the above-mentioned drawbacks of the gate signal generation method according to the prior art. The timings of the switching operations of the switching elements 13 and 14 that form part 3 are each advanced by the dead time T _d .

[0006]

As shown in FIG. 1, the switching elements 13 and 1
If the ON / OFF operation of the switch 4 is advanced by the dead time T _d , the waveform of the output voltage e _T of the high frequency transformer 4 becomes as shown in FIG. 1, and the output voltage waveform is distorted as shown in FIG. 7B. Is reduced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS High frequency link DC / A according to the present invention
An embodiment of the dead time correction method of the C converter will be described with reference to the drawings. FIG. 8 is a block diagram showing the circuit configuration of a high-frequency link DC / AC converter using a cycloconverter.
It is composed of the cycloconverter unit 5 and the AC filter 6, and since it is the same as that of the conventional technique, its explanation is omitted.

Next, the operation sequence of the switching elements forming the inverter section 3 and the cycloconverter section 5 will be described. 3, the output voltage e _u of cycloconverter unit, e _v, e _w and output current i _u,
i _v, of the 18 modes of operation determined by i _w, taking the case of the operation modes 1 and 2 as an example, a e _w> e _u> 0 and _{e v> 0, i w>} 0 and i _v < It is 0. The sawtooth carrier is compared with the maximum value e _w and the minimum value e _{v of the} output voltage to generate the gate signals of the switching elements 11 and 12 and 13 and 14 of the inverter unit 3, and the switching is shown in FIG. A switching sequence is obtained.

In the operating state 2, the switching element 11
An output voltage e _T of the high-frequency transformer 4 is generated by forming a closed loop including and 14, and is continued during the operating state 3. Further, in the operating state 6, the closed loop including the switching elements 12 and 13 is formed, so that the output voltage of the high-frequency transformer 4 becomes −e _T , which is continued during the operating state 7. In addition, the cycloconverter unit 5
The switching sequence of the upper switching elements S _u , S _v , and S _w in the bidirectional switching elements 21, 23, and 25 that configure the above is as shown in FIG. 3, and the two phase arms of the V phase and the W phase have zero voltage. Switching (ZV
S). Therefore, the switching loss occurs only in the U-phase arm, so that the switching loss is reduced.

FIG. 2 shows the sequence of gate signals for the switching elements 11 and 12 and 13 and 14 in the inverter section 3 and the voltage applied to each switching element. The voltages applied to the switching elements 13 and 14 are shown in FIGS. As described with reference to the equivalent circuit diagram shown in FIG. 6, the dead time T _d is delayed. Therefore, the output voltage e _T of the high frequency transformer 4 also has a waveform lacking by the dead time T _d . In order to improve this waveform, it is advisable to advance the switching operations of the switching elements 13 and 14 respectively by the dead time T _d , and the output voltage e _T of the high frequency transformer 4 is corrected as shown in FIG.
As a result, the output voltage waveform becomes a waveform in which low-order harmonics are reduced as shown in FIG.

As a method of generating a gate signal for on / off controlling the switching elements 11 and 12 and 13 and 14 which form the inverter section 3, a gate signal generating circuit may be formed by a discrete IC or the like. The gate signal generation program may be stored in the CPU configuring the system, and the description thereof will be omitted because it can be easily realized by using a known technique.

[0012]

As described above, according to the dead time correction method for the high frequency link DC / AC converter of the present invention, the timing of the switching operation of the switching elements 13 and 14 among the switching elements constituting the inverter section is set to the dead time. It is designed to be advanced by a corresponding period. This dead time correction method can suppress the distortion of the output voltage waveform of the high frequency transformer.

[Brief description of drawings]

FIG. 1 is a switching sequence of an inverter unit according to the present invention.

FIG. 2 is a switching sequence of a conventional inverter unit.

FIG. 3 is a switching sequence of a conventional inverter unit and converter unit.

FIG. 4 is an operation mode of the cycloconverter unit.

FIG. 5 is an equivalent circuit diagram.

FIG. 6 is an equivalent circuit diagram.

FIG. 7 is a waveform diagram of an output voltage.

FIG. 8 is a block diagram of a high frequency link DC / AC converter.

[Explanation of symbols]

1 DC power supply 2 Capacitor 3 Inverter section 4 High frequency transformer 5 Cycloconverter section 6 AC filter 11, 12, 13, 14 Switching element 21, 22, 23, 24, 25, 26 Bidirectional switching element

Claims (1)

[Claims] 1. An inverter section comprising a single-phase bridge-connected switching element for inputting direct-current power and converting it to high-frequency power, and a high-frequency transformer for transforming the high-frequency power input from the inverter section and outputting it to a cycloconverter section. A cycloconverter unit in which bidirectional switching elements for converting high-frequency power input via the high-frequency transformer into commercial-frequency power are connected in a three-phase bridge, and an AC filter including a reactor and a capacitor provided in an output circuit of the cycloconverter unit. A high-frequency link DC / AC converter constituted by a switching element (11) constituting the inverter section
And (12) are alternately turned on and off, and switching elements (13) and (14) that perform switching by shifting the phase from the switching element group are alternately turned on and off to generate high frequency power. -In the sequence, the switching elements (13) and (1
A dead time correction method for a high frequency link DC / AC converter, characterized in that the switching operation of 4) is controlled so as to advance the timing by a period corresponding to the dead time.