JPH077944A - Controlling method for electric-power converter apparatus - Google Patents

Abstract

PURPOSE:To perform the switching operation of a cycloconverter only during the zero period of the output voltage of an inverter. CONSTITUTION:An electric-power converter 1 is constituted in such a way that DC electric power 6 is converted, by an inverter 2, into AC electric power whose frequency is higher than a prescribed frequency and that the AC electric power is converted into three-phase AC electric power at a prescribed frequency by a three-phase cycloconverter 4 which is controlled by a switching operation interlocked with the switching operation of the inverter 2. In addition, the length and the direction of the voltage vector of a voltage which is to be output as the three-phase AC electric power by a control device 6 are computed, the output width of the inverter 2 is controlled by the length of the voltage vector, and the switching timing of the three-phase cycloconverter 4 is controlled by the direction of the voltage vector.

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 converting DC power into three-phase AC power, and more particularly to a power converter for use in an uninterruptible power supply or the like which requires insulation between input and output. Regarding control method.

[0002]

2. Description of the Related Art In a power converter for converting DC power into three-phase AC power, a configuration as shown in FIG. 9 is known as a conventional technique in the case where insulation is required between input and output. That is, the DC power from the DC power supply 60 is supplied to the control circuit 63.
Is converted into three-phase AC power by a three-phase inverter 61 controlled by and is output via an insulation transformer 62. However, in such a configuration, the isolation transformer 6
Since 2 is used at the same low frequency as the output frequency (eg 50Hz or 60Hz), a large and heavy insulation transformer is required. A power conversion device that solves this problem is disclosed in Japanese Patent Application Laid-Open No. 4- 197078. The configuration of the power conversion device disclosed in the above publication is shown in FIG. Figure 1
At 0, the power converter 50 includes a single-phase inverter 52 that converts DC power from the DC power supply 51 into single-phase AC power having a frequency higher than the frequency of the three-phase AC power output by the power converter 50, and the single-phase inverter 52. A single-phase transformer 53 for insulatingly transmitting the output power of the phase inverter 52, a cycloconverter 54 for converting the single-phase AC power transmitted through the single-phase transformer 53 into a three-phase AC power, and the single-phase inverter 52. And a control circuit 55 for controlling the switching operation of the switching element of the cycloconverter 54 with the PWM signal generated in association with the operation of the single-phase inverter 52. In the above structure, the DC power from the DC power supply 51 is converted into the single-phase AC power having a frequency higher than the output power frequency by the single-phase inverter 52, and is transmitted to the cycloconverter 54 by the single-phase transformer 53. The cycloconverter 54 is controlled by the control circuit 55 with a PWM signal associated with the operation of the inverter 52, and converts the high frequency single-phase AC power from the single-phase inverter 52 into a three-phase AC power of a predetermined frequency. With this configuration, the single-phase transformer 53, which is an insulation transformer, can be made smaller and lighter because it is used at a frequency higher than a predetermined output frequency.
The power converter can be remarkably downsized. In the power converter 50, the control circuit 55 is provided with means for generating the inverter output width signal Swi.
As shown in the operation signal diagram of FIG. 3, since the single-phase inverter 52 is driven by the inverter output width signal Swi shown in the operation signal (h) and the level inversion signal Sp shown in FIG. ), The period when the inverter output becomes zero is provided. By performing the switching operation of the cycloconverter 54 during the period when the inverter output is zero, the energy loss due to the switching operation is reduced, and a power conversion device with a small power loss is realized.

[0003]

However, in the control method having the above-described conventional configuration, when all switching operations of the cycloconverter are performed in the period when the inverter output is zero, the output voltage waveform distortion is large and a good quality is obtained. I can't get power. Therefore, in order to obtain the desired output voltage, the cycloconverter must be switched even during the period when the output voltage of the inverter exists, and the effect of reducing the energy loss due to this switching operation cannot be fully exerted. was there. The present invention has been made in view of the above problems, and an object thereof is to provide a control method for a power conversion device that can perform a switching operation of a cycloconverter only during a zero period of an output voltage of an inverter.

[0004]

In order to achieve the above object, a method adopted by the present invention is to convert DC power into AC power having a frequency higher than a predetermined frequency by an inverter, and the AC power is subjected to a switching operation of the inverter. In a control method of a power converter that converts a three-phase AC power of a predetermined frequency by a three-phase cycloconverter controlled by a switching operation linked to the above, the length and direction of the voltage vector of the voltage to be output as the above-mentioned three-phase AC power Is calculated, the output width of the inverter is controlled by the length of the voltage vector, and the switching timing of the three-phase cycloconverter is controlled by the direction of the voltage vector. is there.

[0005]

According to the present invention, the length and direction of the voltage vector of the voltage to be output as the three-phase AC power is calculated, and the output width of the inverter is set by the length of this voltage vector. The switching timing of the three-phase cycloconverter is set according to the direction. By controlling the switching of the three-phase cycloconverter at the switching timing determined by the direction of the voltage vector, the three-phase AC state can be obtained. However, this alone is not sufficient to obtain the voltage amplitude as three-phase AC, so the pulse width output from the inverter is controlled by the length of the voltage vector. By the control described above, the switching operation of the three-phase cycloconverter can be performed while the inverter output is zero voltage, and the energy loss due to the switching operation can be reduced.

[0006]

Embodiments of the present invention will be described below with reference to the accompanying drawings for the understanding of the present invention. The following embodiments are examples of embodying the present invention and do not limit the technical scope of the present invention. Here, FIG. 1 is a block diagram showing the configuration of a power converter for implementing the control method according to the present invention, FIG. 2 is a voltage vector diagram showing an example of an instruction voltage vector, and FIG. 3 is a three-phase cycloconverter for each voltage vector. Pattern diagram showing the switching timing of
4 is a voltage vector diagram that can be output in one sampling cycle, FIG. 5 is a diagram showing an example of voltage vector area division, FIG. 6 is a diagram of output voltage vector for each voltage vector area division, and FIG. 7 is a command voltage vector FIG. 8 is a voltage vector diagram showing an example, and FIG. 8 is a switching pattern diagram showing switching timing according to the command voltage vector shown in FIG.
In FIG. 1, a power converter 1 includes a single-phase inverter 2 that converts DC power from a DC power supply 6 into single-phase AC power having a frequency higher than a predetermined frequency output by the power converter 1.
And a single-phase transformer 3 that insulates between the input and output and transmits the output power of the single-phase inverter 2 to the next stage, and converts the single-phase AC power from the single-phase inverter 2 into three-phase AC power of a predetermined frequency. Switching elements S1, S2, S3, S constituting the three-phase cycloconverter 4 and the single-phase inverter 2
The switching elements S5 and S that constitute the three-phase cycloconverter 4 while controlling the switching operation of
PWM generated by interlocking the switching operations of S6, S7, S8, S9, and S10 with the operation of the single-phase inverter 2
And a control circuit 5 which is controlled by a signal. The control circuit 5 includes a single-phase inverter control signal generator 7, a cycloconverter control signal generator 8, and a digital controller 9. The digital controller 9 calculates the direction and length of the voltage vector from the three-phase AC power to be output from the three-phase cycloconverter 4 by a vector control method, and uses this as a command voltage to generate a single-phase inverter control signal. To the converter 7 and the cycloconverter control signal generator 8. The command voltage vector is expressed as shown in FIG.
V6 represents each phase of the voltage vector output by the three-phase cycloconverter 4, and the switching timings of the switching elements S5 to S10 for outputting each of the voltage vectors V1 to V6 are set as shown as a specific example in FIG. To be done.

A control method of the power converter configured as above will be described below. For example, assuming that the number of switching times within one sampling period is four, the voltage vector equivalently output in one sampling period is as shown in FIG.
There are 24 types as shown in. Therefore, as shown in FIG. 5, in the range surrounded by the vectors V1 and V3, V1
And V3 can be divided into five areas 1-5. When the command voltage Vref is included in these areas, the command voltage Vref is represented by one voltage vector in the area and output. In this way, the output voltage vector when one sampling cycle is divided into four can be determined as a switching pattern as shown in FIG. However, this alone is the length of the vector (voltage amplitude)
Since it is not sufficient to express, it is compensated by controlling the pulse width of the single-phase inverter 2. The above control will be described with reference to specific switching patterns. For example, when the command voltage vector Vref (1) as shown in FIG. 7 is given, the digital controller 9 first calculates the vector length, and outputs it as the output width command of the single-phase inverter 2 as shown in FIG. The inverter output width signal shown in a-1) is output to the single-phase inverter control signal generator 7. The single-phase inverter control signal generator 7 follows the output width command signal in FIG.
As shown in (b-1), the switching elements S1, S2,
ON / OFF control of S3 and S4. As a result, the single-phase inverter 2 outputs the inverter output voltage (Vinv) as shown in FIG. 8 (c-1). In the present embodiment, the number of divisions in one sampling period is 4, so that there are four pulses of the inverter output voltage within one sampling period as shown in the figure. Next, the digital controller 9 calculates the switching timing of the three-phase cycloconverter 4 from the command voltage vector. From the area where the command voltage vector Vref-1 is present, one pulse of the vector V1 and three pulses of V3 are output as shown in FIG. 6 (FIG. 8d-1). The cycloconverter control signal generator 8 controls the switching of the three-phase cycloconverter 4 as shown in FIG. 8E-1 according to the switching pattern for each voltage vector shown in FIG. As a result of this switching control,
From the three-phase cycloconverter 4, three-phase output voltages Vuv, Vvw, Vwu as shown in FIG. 8 (f-1) are obtained.

The command voltage vector Vref-2 shown in FIG.
Is given, the digital controller 9
Outputs the inverter output width signal shown in FIG. 8A-2 to the single-phase inverter control signal generator 7 as the output width command of the single-phase inverter 2 from the vector length. According to this output width command signal, the single-phase inverter control signal generator 7 switches the switching element S as shown in FIG. 8 (b-2).
ON / OFF control of 1, S2, S3 and S4. As a result, the single-phase inverter 2 outputs the inverter output voltage (Vinv) as shown in FIG. 8C-2. Next, the digital controller 9 calculates the switching timing of the three-phase cycloconverter 4 from the command voltage vector. From the area where the command voltage vector Vref (-1) exists, as shown in FIG. 6, the vector V1 is 2 pulses and V5 is 2 pulses.
Pulse output (FIG. 8d-2). The cycloconverter control signal generator 8 controls the switching of the three-phase cycloconverter 4 as shown in FIG. 8 (e-2) according to the switching pattern for each voltage vector shown in FIG. As a result of this switching control, the three-phase cycloconverter 4 outputs the three-phase output voltage V as shown in FIG.
uv, Vvw, Vwu are obtained. As described above, the single-phase inverter 2 and the three-phase cycloconverter 4 can be controlled in association with each other by the voltage vector of the voltage desired to be output from the power converter 1, so that the three-phase cycloconverter can be controlled during the zero voltage period of the single-phase inverter 2. 4 can be switched, and the power conversion device with less energy loss can be controlled.

[0009]

As described above, according to the present invention, the length and direction of the voltage vector of the voltage to be output as the three-phase AC power is calculated, and the output width of the inverter is determined by the length of the voltage vector. Set the switching timing of the three-phase cycloconverter according to the direction of the voltage vector. By controlling the switching of the three-phase cycloconverter at the switching timing determined by the direction of the voltage vector, the three-phase AC state can be obtained. However, this alone is not sufficient to obtain the voltage amplitude as three-phase AC, so the pulse width output from the inverter is controlled by the length of the voltage vector.
By the control described above, the switching operation of the three-phase cycloconverter can be performed while the inverter output is zero voltage, and the energy loss due to the switching operation can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a power converter that implements a control method according to the present invention.

FIG. 2 is a voltage vector diagram showing an example of an instruction voltage vector according to the embodiment.

FIG. 3 is a pattern diagram showing switching timing of the three-phase cycloconverter for each voltage vector according to the embodiment.

FIG. 4 is a voltage vector diagram that can be output in one sampling cycle according to the embodiment.

FIG. 5 is a diagram showing an example of area division of a voltage vector according to the embodiment.

FIG. 6 is a diagram of an output voltage vector for each area division of the voltage vector according to the embodiment.

FIG. 7 is a voltage vector diagram showing an example of a command voltage vector according to the embodiment.

FIG. 8 is a switching pattern diagram showing switching timing according to the above example.

FIG. 9 is a circuit diagram showing a configuration of a power conversion device according to a conventional example.

FIG. 10 is a circuit diagram showing a configuration of a power conversion device according to a conventional example.

FIG. 11 is a switching pattern diagram for explaining the operation of the above power converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Power converter 2 ... Single-phase inverter 3 ... Single-phase transformer 4 ... Three-phase cycloconverter 5 ... Control circuit 6 ... DC power supply 7 ... Inverter control signal generator 8 ... Converter control signal generator 9 ... Digital controller

Claims (1)

[Claims] 1. A three-phase cycloconverter that converts direct-current power into alternating-current power having a frequency higher than a predetermined frequency by an inverter, and controls the alternating-current power by a switching operation linked to the switching operation of the inverter. In a method of controlling a power conversion device for converting into three-phase AC power, the length and direction of the voltage vector of the voltage to be output as the three-phase AC power is calculated, and the output width of the inverter is controlled by the length of the voltage vector. A control method of the power converter, wherein the switching timing of the three-phase cycloconverter is controlled according to the direction of the voltage vector.