JPH1189242A - Power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a single phase power converter which can reduce higher harmonic. SOLUTION: In a power converter of series n-stage single phase output, n-number of single phase output inverter bridges 1-4 capable of three-level output are installed, and output terminals of the inverter bridges 1-4 are connected in series. The power converter consists of the following; voltage amplitude ratio distributing means 10, 15 for making the amplitude ratio of amplitudes V1, V2, V3 and Vn of the respective output voltages of the inverter bridges 1-4 be V1:V2:V3:Vn=1:2:4: 2(<n-1> ), command voltage generating means 10, 15 which generate a voltage most approximate to an output voltage command to be applied to the power converter by combination of output voltages of the inverter bridges 1-4, and output voltage adjusting means 10, 15 which so adjust the generation voltage that the average value of output voltages of the whole power converter is made equal to the voltage command by pulse-width modulating the inverter bridge 1.

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 AC power.

[0002]

2. Description of the Related Art Conventionally, a single-phase power converter of a multi-pulse width modulation type is well known as an inverter having relatively little voltage distortion. A conventional single-phase power conversion device of a multiplex pulse width modulation method using a battery as a power source has a configuration as shown in FIG. 7 and includes a power cell 70, 71, 72, 73 composed of a single-phase output inverter bridge. The input voltages are substantially equal, and when a sine wave is given as a voltage command, the output voltage of the single-phase power conversion device of the multiple pulse width modulation method is a staircase wave having the same step width as shown in FIG.

[0003]

However, in the above-described conventional example, the FFT analysis of the output voltage waveform in the single-phase power converter of the multiple pulse width modulation system as shown in FIG.
The spectrum is as shown in FIG. FIG. 9 shows a spectrum in the case of a four-stage power cell having an output frequency of 100 Hz and a triangular carrier frequency of 10 KHz. In the case of a multiplex inverter composed of such four-stage power cells, a carrier frequency × 8 × m ( m = 1,2,3, ...
・) There is a problem that harmonics are generated. In view of the above, according to the present invention, the single-phase power conversion device of the multi-pulse width modulation system originally has a lower harmonic of the output voltage than a general power conversion device. Therefore, it is an object of the present invention to provide a power converter that can further reduce harmonics compared to a conventional power converter using a multiple pulse width modulation method.

[0004]

In order to achieve the above object, the invention according to claim 1 comprises n single-phase output inverter bridges each capable of three-level output having insulated inputs. In an n-stage single-phase output power converter in which the output terminals of an inverter bridge are connected in series, the amplitude ratio of the output voltages V1, V2, V3 and Vn of the n single-phase output inverter bridges is represented by V1 : V2: V3:...: Vn = 1: 2: 4:...: 2 ^(n-1) ... (1) A command voltage generating means for generating a voltage closest to the output voltage command given by the combination of the output voltages of the single-phase output inverter bridges having the output voltage amplitudes of V2 to Vn, and a single-phase output voltage having the output voltage amplitude of V1. Output inverter Output voltage adjusting means for adjusting the voltage generated by the command voltage generating means so that the average value of the output voltages of the entire series of n-stage power converters becomes equal to the voltage command by pulse width modulation of the pulse width. It is characterized by that. According to a second aspect of the present invention, the single-phase output inverter bridge having the output voltage amplitude of V1 is pulse-width-modulated so that the average value of the output voltage of the entire series n-stage power converter is equal to the voltage command. An output voltage adjusting means for finely adjusting the voltage generated by the command voltage generating means is provided. According to a third aspect of the present invention, a plurality of sets of the single-phase output power converters according to the first or second aspect are provided, and one end of an output terminal of each set of the single-phase output power converters is connected. The output of the power converter of each single-phase output is a star connection, and the output of the power converter of each single-phase output is an output voltage adjusted to be equal to the voltage command by the command voltage generating means and the output voltage adjusting means. And a multi-phase voltage output means for controlling the electrical angles of the output voltages so as to be shifted by equal intervals, and outputting as a multi-phase voltage from each of the unconnected terminals of the power converter. According to this configuration, the voltage amplitude of each single-phase output inverter bridge (V
1: V2: V3: ...: Vn) is 1: 2: 4:
・: Since the output is distributed at a distribution ratio of 2 ^(n-1) , in a power converter having a configuration in which four single-phase output inverters are connected in series, each single-phase output inverter bridge has a positive voltage, From a three-level output of negative voltage and zero voltage, the entire power converter connected with a four-stage single-phase output inverter bridge can generate (2 ⁵ -1 = 31) stages of voltages with V1 as a unit step, which is optimal. A desired output voltage can be obtained by various combinations. Further, by making V1 PWM adjustable, fine adjustment becomes possible, and the voltage command Vre
A sine wave output faithful to f is obtained, and harmonics can be reduced.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. 1 to 5 are views according to a first embodiment of the present invention. FIG. 1 shows the first embodiment of the present invention.
1 is a configuration diagram of a single-phase power conversion device according to an embodiment.
FIG. 2 is a diagram showing steps of the output voltage of the single-phase power cell shown in FIG. FIG. 3 is a diagram showing steps of the output voltage of the single-phase power converter shown in FIG. FIG. 4 is an output voltage waveform diagram of the single-phase power converter shown in FIG. FIG. 5 is FIG.
FIG. 6 is a diagram showing an FFT analysis spectrum of the output voltage waveform shown in FIG. In FIG. 1, n = 4 here, and 4
A single-phase power converter is constituted by single-phase power cells 1 to 4 connected in stages, and battery power supplies 5, 6, 7, and 8 are connected to the single-phase power cells 1 to 4, respectively. The configuration of the power cell itself is the same as that of the conventional example. The single-phase power cell 1 internally has a single-phase inverter bridge composed of semiconductor switches 11 to 14, and the power cell controller 10 controls a capacitor 9 based on a command from a voltage command generator 15.
Switch 11 to which DC voltage V1 is applied via
To 14 are turned ON / OFF to perform PWM control. Since the following single-phase power cells 2, 3, and 4 have the same configuration, the single-phase power cell 1 will be described below as a representative. The voltage amplitude ratio allocating means, the command voltage generating means, and the output voltage adjusting means presented in the claims are software parts that function on the voltage command generator 15 and the power cell controller 10. The single-phase power cell 1 can output three levels of voltages of 0 voltage, positive voltage, and negative voltage as the amplitude value on the vertical axis, as in the PWM output waveform shown in FIG. The horizontal axis shows one cycle of 0 to 10 ms, which is an example corresponding to 100 Hz in terms of frequency. Generally, the amplitude of the output voltage of a power cell is proportional to the input voltage of the power cell, and becomes equal to the input voltage of the power cell if voltage loss in the power cell is ignored. Here, in general, when the n-stage power cells have the following voltage amplitudes (where n is an integer of 2 or more in the following equation), V1: V2: V3:...: Vn = 1: 2: 4: ...: 2 ^(n-1) ... (1) The voltages that can be output by the entire power cells connected in series in n stages are three levels, zero voltage, positive voltage, By combination with the negative voltage, V1 is set to the positive side and the negative side as a unit step, respectively.

[0006]

(Equation 1)

Step. It becomes 0 voltage. Therefore,
The output is a step of V1, 2 to the power of n + 1, and
, And a voltage of {2 ^{(n + 1)} -1} stages can be output. In FIG. 1, the voltages of the batteries 5 to 8 are represented by V1 and V2.
, V3, V4, the voltages V1, V2, V3, V4
Is a ratio as shown in equation (3). V1: V2: V3: V4 = 1: 2: 4: 8 (3) In FIG. 1, batteries 5 to 8 are used as input power supplies for the power cells 1 to 4, An input form from a DC-AC inverter or the like insulated by a transformer, or a solar cell or the like may be used as an input power supply. As shown in FIG. 1, when four stages of single-phase power cells having a voltage ratio as shown in the equation (3) are combined in series, as shown in FIG. 3, 15 stages on the positive side and 1 stage on the negative side.
5 stages, therewith enabling total (2 ⁵ -1 = 31) voltage generating stage at zero voltage, based on the sine wave voltage command of the voltage command generator 15 as a whole, a sine wave as shown in FIG. 3 is generated Will do. Assuming that the voltage command of the sine wave is Vref, the voltage command generator 15 outputs the voltage command Vref, and the sine wave output shown in FIG. In this case, a voltage smaller than V1 in the step cannot be output. In this case, the following may be further performed. That is, if the amplitude of the voltage command Vref is as small as V1
It is not possible to generate an appropriate output voltage corresponding to the power cell 1 having a voltage amplitude equivalent to V1 as a single-phase inverter of a pulse width modulation type in the voltage command generator 15 in particular. Is defined as the following equation (4). Vref1 = Vref-a1.times. (2.times.a2 + 4.times.a3 + 8.times.a4) .times.V1 (4) However, each control ratio a4 to a1 takes the following value. a4 is 1 when | Vref |> 8 × V1, 0 otherwise, a3 is 1 when | Vref | −8 × a4> 4 × V1,
Otherwise, 0 and a2 are | Vref | -8 * a4-4 * a3> 2 * V1
In this case, 1 is set, 0 is set otherwise, and a1 is set to 1 when Vref ≧ 0, and -1 is set otherwise. Further, V1, V2, V3, V
Power cell 4 outputs a voltage of 8 × a1 × a4 × V1; power cell 3 outputs a voltage of 4 × a1 × a3 × V1; Outputs a voltage of 2 × a1 × a2 × V1, and the power cell 1 is controlled by the controller so as to perform PWM output using Vref1 as a voltage command. That is, in the power cell 1, the voltage P is set to Vref1 as the voltage command.
As shown in FIG. 4, the WM output is performed, and the average value of the entire output voltage becomes equal to the sine wave voltage command Vref.
PWM is performed in each V1 step to perform fine adjustment of output, thereby enabling fine adjustment of the entire output voltage and making the average value of the entire output voltage equal to the sine wave voltage command Vref. Thereby, the fidelity can be improved. As a result, as shown in FIG. 4, the voltage command is a sine wave of 100 Hz and the carrier frequency of the triangular wave is 10 Hz.
FIG. 5 shows the spectrum of the FFT analysis result of the output voltage waveform of the power conversion device of KHz, and FIG. 9 shows the spectrum of the conventional multi-pulse width modulation type single-phase power conversion device shown in FIG.
As compared with the FT analysis result, it can be seen that the peak level of the harmonic is reduced to about 1/6 (-15 dB).

(Second Embodiment) Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to the drawings. FIG. 6 is a configuration diagram of a power conversion device according to the second embodiment of the present invention. In FIG. 6, three sets of single-phase power converters 16, 17, and 18 each configured by four-stage series-connected power cells include:
Each is the same as the single-phase power conversion device described in the first embodiment. One terminal s of each of the single-phase power converters 16, 17, 18 is Y-connected to the neutral point b, and each single-phase power converter 16, 17, 18 is controlled based on the control of the three-phase voltage output means 20 including a control mechanism such as a voltage command generator. If the electrical angles of the voltage commands of the phase power converters 16, 17, and 18 are controlled so as to be shifted by 120 °, output voltages with less harmonics faithful to the three-phase voltage commands are obtained from the output terminals U, V, and W. be able to. Each power cell has the same configuration as the power cell 1 of FIG. That is, a PWM control is performed by internally turning on and off a semiconductor switch to which a DC voltage is applied via a capacitor by a power cell controller based on a command from a voltage command generator. Then, as shown in the PWM output waveform shown in FIG. 2, each power cell has three amplitudes of 0 voltage, positive voltage, and negative voltage as the amplitude value on the vertical axis.
A level voltage can be output. Therefore, as shown in the figure, when the five-stage power cells have the following voltage amplitudes, V1: V2: V3: V4: V5 = 1: 2: 4: 8: 16 These five-stage power cells are connected in series. The voltage that can be output by the entire power cell is 31 steps on the positive side and the negative side, respectively, with V1 as a unit step, in combination with the three levels of each power cell, 0 voltage, positive voltage, and negative voltage.
Voltage. Therefore, it is possible to output 63-stage voltages obtained by subtracting 1 from 2 (5 + 1) (= 64). In this way, the voltage of each power cell is appropriately combined and roughly variably controlled so as to approximate a sine wave voltage command.
By performing M output and performing fine-adjustment output adjustment so that the average value of the entire output voltage becomes equal to the sine wave voltage command, fine adjustment of the entire output voltage becomes possible. As described above, according to the first and second embodiments, harmonics output from the power converter can be effectively reduced, so that a filter necessary for an output stage can be omitted or downsized. In particular, in cogeneration systems and uninterruptible power supply facilities, regenerative devices that link to system power, and solar power converters that link solar cells to system power via boost choppers, inverters, etc. If applied, high-quality power can be output without disturbing the system power supply.

(Third Embodiment) As described above, in FIG. 6, a three-phase power system is formed by using three sets (16, 17, 18) of the single-phase power converters described in the first embodiment. Although configured, the present invention is not limited to this,
It is also possible to configure a polyphase power system such as a six-phase or a twelve-phase. In FIG. 6, each single-phase power converter is connected to 5
Although the power cells are constituted by power cells connected in series, the present invention is not limited to this, and a multi-stage structure of six or more stages is also possible.

[0010]

As described above, according to the present invention,
Since a single-phase power converter or a multi-phase power converter with less generation of harmonics can be provided, it is possible to reduce the size of the filter required for the output part, and to connect a regenerative converter or a photovoltaic power inverter connected to the grid. By applying the present invention to a power converter, it is possible to configure a power converter that does not disturb the system power supply.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a single-phase power conversion device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing steps of an output voltage of the single-phase power cell shown in FIG. 1;

FIG. 3 is a diagram showing steps of an output voltage of the single-phase power converter shown in FIG. 1;

4 is an output voltage waveform diagram of the single-phase power converter shown in FIG.

5 is a diagram showing an FFT analysis spectrum of the output voltage waveform shown in FIG.

FIG. 6 is a configuration diagram of a power conversion device according to a second embodiment of the present invention.

FIG. 7 is a configuration diagram of a conventional single-phase power converter.

8 is a diagram showing an output voltage waveform of the single-phase power converter shown in FIG.

9 is a diagram showing an FFT analysis spectrum of the output voltage waveform shown in FIG.

[Explanation of symbols]

 1-4 single-phase power cell 5-8 battery 9 capacitor 10 power cell controller 11-14 semiconductor switch 15 voltage command generator 16-18 single-phase power converter 20 three-phase voltage output means

Claims (3)

[Claims] 1. An n-stage single-phase output power converter comprising n single-phase output inverter bridges capable of three-level output having insulated inputs and connected in series with output terminals of the single-phase output inverter bridge. In the apparatus, the amplitude ratios of the output voltages V1, V2, V3 and Vn of the n single-phase output inverter bridges are expressed as follows: V1: V2: V3:...: Vn = 1: 2: 4:. ..: 2 ^(n-1) (1) and a voltage closest to an output voltage command to be given to the n-stage series power converters is an output voltage amplitude of V2 to Vn. And a command voltage generation means for generating a command voltage generated by a combination of output voltages of the single-phase output inverter bridge. 2. The power converter, wherein a single-phase output inverter bridge having an output voltage amplitude of V1 is pulse width-modulated, and an average value of output voltages of the whole series n-stage power converters is determined by the voltage command. A power conversion device comprising output voltage adjusting means for finely adjusting the voltage generated by the command voltage generating means so as to be equal. 3. A plurality of single-phase output power converters according to claim 1 or 2, wherein one end of each output terminal of each set of the single-phase output power converters is connected to form a star connection,
The output of each single-phase output power converter is output as an output voltage adjusted to be equal to the voltage command by the command voltage generating means and the output voltage adjusting means. A power converter, comprising: a multi-phase voltage output means for controlling the angles so as to be shifted by equal intervals, and outputting a multi-phase voltage from each of the unconnected terminals of the power converter.