JPH05328731A - Multilevel inverter - Google Patents

Abstract

PURPOSE:To permit applications over wider range for a power converter and making it possible to uniform the switching frequency or switching loss for switching elements forming a multilevel inverter. CONSTITUTION:Among DC power supplies E0 to E4 having a plurality of or several pairs of voltage levels in a multilevel inverter, a DC power supply E0 or E1 and E2 are used as main power supplies and DC power supplies E3 and E4 of other levels are formed as DC-DC converters CNV1 and CNV2 which have the main DC power supply as input and have the adjustable output voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-level inverter for converting a DC power supply having a plurality or a plurality of pairs of voltage levels into an AC voltage having a plurality of instantaneous voltage levels associated with the plurality or the plurality of pairs, and more particularly to a multi-level inverter. Provided is a multi-level inverter which enables equalization of switching frequencies or switching losses of switching elements constituting a level inverter and enables wide-range application as a power converter.

[0002]

2. Description of the Related Art FIG. 5 shows a configuration example of one phase of a 5-level multi-level inverter. E _{1 to} E ₄ are DC power supplies,
E1, E2 and E3, E4 form a pair of DC power supplies, respectively. S _{0 to} S ₄ are switching circuits, D ₁ and D ₂ are diodes, and L is a load.

The DC power sources E _{1 to} E ₄ are generally formed by transforming and rectifying a commercial power source, but details thereof will be omitted.

FIG. 6 (a) shows a concrete configuration example of the switching circuits S _{1 to} S ₄ when a GTO (gate turn-off thyristor) is used as a switching element. It is configured.
6 (b) to 6 (d) are concrete configuration examples of the switching circuit S ₀ when the GTO is also used. In FIG. 6 (b), the diode connected in the full bridge and the DC terminal are connected. GTO, in Fig. 6 (c) the same switching circuit as Fig. 6 (a) in anti-series connection, and in Fig. 6 (d) GTO.
And a diode are connected in series and connected in anti-parallel.

In FIG. 5, the voltages of the DC power supplies E1 and E2 are set to E /
2, the voltage of the DC power supplies E3, E4 is E / 4, and the switching states of the switching circuits S _{0 to} S ₄ are 1,
When 0 is displayed when the switch is off, each switching circuit S ₀ ~
Output point U for switching state of S ₄ and power supply midpoint 0
, The output voltage V _U is as follows.

[Table 1]

FIG. 7 shows an output voltage waveform when the inverter shown in FIG. 5 is sine wave modulated by pulse width control (PWM) with a constant carrier frequency.

That is, the inverter of FIG. 5 is capable of generating a voltage having five levels, and by switching between these levels, the load L has a lower switching frequency and a better quality with less distortion. It is possible to supply the voltage or current of.

[0008]

However, in such a multi-level inverter, each switching circuit has a relation between the modulation voltage (the sine wave voltage shown by the dotted line in FIG. 7) and the DC voltage. The switching frequency allotment fluctuates greatly. For example, FIG. 7 (a) shows a waveform when the difference between the modulation voltage and the DC power supply voltage E / 2 is small,
As is clear from this, when the difference between the modulation voltage and the DC power supply voltage is small, the number of times of switching of the switching circuits S ₁ and S ₄ increases, and conversely, FIG. 7 (b) shows the modulation voltage and the DC power supply voltage. This is an example of the waveform in the case where the difference between and is relatively large. In this case, the number of switching times of the switching circuits S ₂ , S ₃ , and S ₀ increases.

This switching frequency greatly changes depending on not only the relative relationship between the modulation voltage and the DC power supply voltage as described above but also the waveform of the modulation voltage, and the switching is concentrated in a specific switching circuit to increase the switching loss. The switching element will be destroyed due to the above.

[0010]

In order to solve the above problems of the conventional multi-level inverter, in the multi-level inverter according to the present invention, one or more of a plurality of or a plurality of pairs of DC power supplies of the multi-level inverter are used. A pair of voltage level DC power supplies is a main DC power supply, and another voltage level DC power supply is a DC / DC converter which receives the main DC power supply as an input and whose output voltage is adjustable.

[0011]

In this structure, the switching frequency or switching loss of the switching circuit can be equalized by adjusting the output voltage of the DC / DC converter, and in general, commercial power supply is formed by transformer rectification. Since the number of main DC power supplies to be used is one or a pair, the range of application as a power converter can be expanded.

[0012]

1 is a circuit diagram of an embodiment of a multilevel inverter according to the present invention. In FIG. 1, the same reference numerals as those in FIG. 5 denote the same elements. E ₁ and E ₂ are a pair of main DC power supplies, CN, which are generally obtained by rectifying commercial power supplies.
V _1, CNV ₂ are each an input of the main DC power source E _1, E _2, a controllable output voltage E _3, E ₄ DC-DC converter for generating, another pair by E _3, E ₄ Configure a DC power supply. When the voltage of the main DC power supplies E ₁ and E ₂ is E / 2, the DC / DC converter
The output voltages E ₃ and E ₄ of CNV ₁ and CNV ₂ are controlled around E / 4.

The DC / DC converters CNV ₁ and CNV ₂ can take various forms, but since they have a well-known structure, detailed description thereof will be omitted.

FIG. 2 shows an example of the output voltage waveform in the present invention when the modulation wave is a sine wave as in FIG. Figure 2 (a)
Is the case where the difference between the modulation voltage and the main DC power supply voltage is small, and the output voltages E ₃ and E ₄ of the DC / DC converters CNV ₁ and CNV ₂ are E / 4.
Fig. 2 (b) shows an example of waveforms when the voltage is increased further, and the difference between the modulation voltage and the main DC power supply voltage is large, and the output voltages E ₃ and E _{4 of the} DC / DC converters CNV ₁ and CNV ₂ are large. It is an example of the waveform when is reduced from E / 4.

As is clear from a comparison between FIG. 2 (a) and FIG. 7 (a), when the difference between the modulation voltage and the DC power supply voltage is small,
In the present invention, by causing the output voltage E _3, E ₄ DC-DC converter CNV _1, CNV ₂ increases from E / 4, with increasing switching path of the switching circuit S _2, S _3, the switching circuit The switching section of S ₁ and S ₄ is reduced. As a result, the number of times of switching of the switching circuits S ₂ and S ₃ increases, and the number of times of switching of the switching circuits S ₁ and S ₄ decreases, so that the difference between the switching frequencies of both switching circuit groups is reduced. Further, the switching circuits S ₂ and S ₃ not only increase the number of times of switching, but also change the output voltage E ₃ and E ₄ of the DC / DC converters CNV ₁ and CNV _2.
Since the switching voltage is increased by increasing from E / 4, the switching loss increases more than the rate of increase in the number of times of switching. On the contrary, since the switching frequency of the switching circuits S ₁ and S ₄ is reduced and the switching voltage is also reduced, the switching loss is reduced more than the reduction rate of the switching number, and the switching loss of both switching circuit groups is equalized.

FIG. 2 (b) is an example of the output voltage waveform when the difference between the modulation voltage and the DC power supply voltage is large. The output voltages E ₃ and E ₄ of the DC / DC converters CNV ₁ and CNV ₂ are E / E. By decreasing from 4, the difference between the switching frequencies of both switching circuit groups is reduced by the action opposite to the above, and the switching loss is equalized.

The main DC power sources E ₁ and E ₂ in FIG. 1 are generally obtained by rectifying a commercial power source as described above.
At that time, it is more preferable to reduce the harmonic current of the commercial input by using a 12-phase configuration including the input transformer.

FIG. 3 is a circuit diagram of another embodiment of the multi-level inverter according to the present invention, showing only the DC power supply portion of the multi-level inverter. In the figure, E ₀ is generally one main DC power source obtained by rectifying a commercial power source, C ₁ and C ₂ are voltage divisions of this one main DC power source, and a pair of main DC power sources E ₁ and E ₂ CNV ₁ and CNV ₂ are DC / DC converters capable of controlling output voltage similar to those in FIG. 1, and are a pair of main DC power supplies.
It inputs E ₁ and E ₂ and outputs a pair of DC voltages E ₃ and E ₄ .

The operation of the multi-level inverter according to FIG. 3 is similar to that of FIG. 1, and detailed description thereof will be omitted.

In FIG. 3, there is only one main DC power source made by rectification such as a commercial power source, and therefore an input transformer is not required, so that the size and weight can be reduced, and an uninterruptible power supply requires a battery for the DC stage. The application range as a power converter can be expanded, such as application to a power supply device.

The DC / DC converter CNV ₁ ,
Although CNV ₂ is illustrated as a pair of main DC power supplies E ₁ and E ₂ as an input power supply, it may be one main DC power supply E ₀ . The DC power source E ₁ made by dividing by the capacitor C _1, C _2,
E ₂ can also be configured by another DC / DC converter that receives one main DC power supply E ₀ .

FIG. 4 shows another embodiment of the present invention.
An embodiment in which the present invention is applied to a five-level three-phase multi-level inverter will be described. S _{11 to} S ₃₄ are switching circuits similar to S _{1 to} S ₄ in FIG. 5, and S _{10 to} S ₃₀ are S ₀ in FIG.
The switching circuit is the same as the above, and is the same as that of FIG. 3 except that it has a three-phase configuration.

The embodiments of FIGS. 1 to 4 exemplify the case where GTO is used as the switching element and the number of levels of the multi-level inverter is 5, but the present invention determines the type of switching element and the number of levels. It is clear from the above description that it is not limiting.

[0024]

As described above, according to the present invention,
The switching frequency or the switching loss of the switching elements forming the multilevel inverter is equalized, and the destruction of the elements due to the uneven weight of the switching loss can be prevented. Further, according to the present invention, even a multi-level inverter can be applied to an uninterruptible power supply device having a battery in a DC stage, and the application range as a power converter can be expanded.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of a multilevel inverter according to the present invention.

FIG. 2 is an output voltage waveform diagram of the multilevel inverter shown in FIG. 1, where (a) shows a case where the difference between the modulation voltage and the main DC power supply voltage is small, and the DC / DC converters CNV ₁ and CNV ₂ This is a waveform example when the output voltages E ₃ and E ₄ are increased from E / 4, and (b) shows a large difference between the modulation voltage and the main DC power supply voltage.
And the output voltage E ₃ and E ₄ of the DC / DC converters CNV ₁ and CNV ₂ to E / 4
It is a waveform example when it is further reduced.

FIG. 3 is a circuit diagram of another embodiment of the multi-level inverter according to the present invention.

FIG. 4 is a circuit diagram of a multi-level inverter according to another embodiment of the present invention.

FIG. 5 is a circuit diagram of an example of a conventional multilevel inverter.

FIG. 6 is a circuit diagram showing a specific configuration example of a switching circuit.

FIG. 7 is an output voltage waveform diagram of the multilevel inverter shown in FIG. 5, where (a) is a waveform when the difference between the modulation voltage and the DC power supply voltage E / 2 is small, and (b) is the modulation voltage. It is a waveform example when the difference from the DC power supply voltage is relatively large.

[Explanation of symbols]

E ₀ ~ E ₄ DC power supply S ₀ ~ S ₄ Switching circuit D ₁ , D ₂ , D diode GTO Gate turn-off thyristor L load CNV ₁ , CNV ₂ DC / DC voltage converter

Claims (1)

[Claims] 1. A multilevel inverter for converting a DC power supply having a plurality or pairs of voltage levels into an AC voltage having a plurality of instantaneous levels associated with the plurality or pairs, wherein one or a pair of voltage levels is provided. A multilevel inverter characterized in that a DC power supply is a main DC power supply, and a DC power supply of another voltage level is constituted by a DC / DC converter whose input voltage is the main DC power supply and whose output voltage can be adjusted.