TECHNICAL FIELD

The invention disclosed in this specification relates to an AC power supply device.

BACKGROUND ART

Switching power supply devices including switch elements and filters such as a DC/DC converter and a DC/AC converter, are currently used in very wide fields such as consumer products, industrial equipment, and in-vehicle products. For these switching power supply devices, small size, light weight and high efficiency are regarded as important, and are demanded more for larger power devices.

Among them, as a high voltage inverter having a high input voltage, a multilevel inverter is used in many cases, in which switching output levels of a bridge unit are not two values of high and low (+E and −E) but can be more values (e.g. a three-level inverter (+E, 0, −E), a five-level inverter (+E, +E/2, −E), and the like).

This reduces voltage applied to an output filter reactor so that the output filter reactor can be downsized or reduced in loss or noise, a reduces voltage applied to each of switch elements so as to adopt a low withstand voltage element that is abundant in the market or reduce switching loss.

As such a multilevel inverter, for example, a neutral point clamped (NPC) type is used, such as a diode clamp inverter (Patent Documents 1 and 2 and Non-Patent Document 1), or a living capacitor inverter (Patent Documents 3 and 4 and Non-Patent Document 2).

LIST OF CITATIONS

Patent Literature

Patent Document 1: JP-A-1-47277

Patent Document 2: JP-A-5-146160

Patent Document 3: JP-A-2008-92651

Patent Document 4: JP-A-2016-59132

Patent Document 5. JP-A-10-308510

Patent Document 6: JP-A-2014-3051

Non-Patent Literature

Non-Patent Document 1:A. Nabae et. al., IEEE Trans. Ind. Appl., vol. 17, No. 5, pp. 518-523, 1981.

Non-Patent Document 2: T. A. Meynard et al., in Conf. Rec. IEEE PESC, vol. 1, pp. 397-403, June 1992.

SUMMARY OF THE INVENTION

Technical Problem

As a switch element in the multilevel inverter described above, a silicon isolated gate bipolar transistor (Si-IGBT) is basically used, and operating conditions such as circuit constants and an operating frequency are adjusted for Si-IGBT.

Note that a basic concept of the multilevel inverter may be considered as reduction of load on the output filter side by adopting multiple steps of the switch element. However, in these methods, two switch elements are connected in series in a current path, and hence a conduction loss of a switch element is apt to occur.

In contrast, research and commercialization of a silicon carbide metal-oxide-semiconductor field effect transistor (SiC-MOSFET), which is a wide bandgap semiconductor and has a high dielectric breakdown strength, have proceeded recently, and higher withstand voltage and lower on-resistance thereof have also proceeded further (see, for example, Patent Documents 5 and 6).

The emergence of this high withstand voltage transistor enables high frequency operation, which is difficult for Si-IGBT, and has made opportunities of reviewing a circuit type for forming the high voltage inverter.

In view of the above-mentioned problem found by the inventors of the present invention, an object of the invention disclosed in this specification is to provide an AC power supply device that can reduce switching loss and total loss (e.g. a high voltage inverter that outputs 400 V AC in three phases and four lines (U, V, and W phases plus a neutral point X)).

Means for Solving the Problem

An AC power supply device disclosed in this specification includes at least two input capacitors connected in series between a first power supply node and a second power supply node, so that a connection node thereof is a neutral point of a three-phase output; three phases of transistor bridges each consisting of first and second PWM control bridges each including two switch elements connected in series between the first power supply node and the second power supply node; three phases of transformers connected to output terminals of the three phases of transistor bridges, respectively; three phases of reactors connected to the three phases of transformers respectively; and three phases of smoothing capacitors connected to the three phases of reactors, respectively. The three phases of transformers are single coil autotransformers, each including a core and first and second windings coupled with each other via the core, one ends thereof being connected to output terminals of the first and second PWM control bridges, respectively, while the other terminals being connected to the smoothing reactors on opposite sides to the smoothing capacitors. The first and second windings are wound in such directions that magnetic fluxes generated in the core are cancelled with each other (first structure).

Note that in the AC power supply device having the first structure, the first and second PWM control bridges turn on and off the switch elements with a phase difference of ½ period therebetween (second structure).

Further, in the AC power supply device having the first or second structure, it is preferred to adopt a structure in which the three phrases of transformers and the three phases of smoothing reactors are formed as three phases of transformer-coupled reactors having both functions (third structure).

Further, in the AC power supply device having the third structure, it is preferred to adopt a structure in which the core is constituted of a combination of at least a first core section and a second core section, and the first and second windings are wound on the first core section in such directions that magnetic fluxes generated in the first core section are cancelled with each other (fourth structure).

Further, in the AC power supply device having the fourth structure, it is preferred to adopt a structure in which the first core section is made of a material having anisotropy in loss due to high frequency magnetic field, the second core section covers at least a part of a side surface of the first core section and is disposed so that magnetic flux passing through the same causes leakage inductance of the transformer-coupled reactor, and the core further includes a magnetic shielding part arranged to limit a path of magnetic flux passing between the first core section and the second core section to a side surface direction of the first core section (fifth structure).

Further in the AC power supply device having the third structure, it is preferred to adopt a structure in which the core further includes a third core section, the first and second core sections ore made of a material having anisotropy in loss due to high frequency magnetic field and are molded so that the loss due to high frequency magnetic field does not chance along a direction of magnetic flux passing the same, the second core section is disposed so that magnetic flux passing the same causes leakage inductance of the transformer-coupled reactor, and the third core section covers at least a part of side surfaces of the first end second core sections and is disposed so that magnetic flux passing the same enables magnetic fluxes generated in the first and second core sections to cook and go each other (sixth structure).

Further, in the AC power supply device having any one of the first to sixth structure, it is preferred to adopt a structure in which according to an output power, an operation of one of the first and second PWM control bridges is stopped, and an operating frequency of the switch element is changed (seventh structure).

Further in the AC power supply device having any one of the first to seventh structures, it is preferred to adopt a structure in which according to an output voltage, an on-duty of the switch element is limited (eighth structure).

Further, an the AC power supply device having any one of the first to eighth structures, it is preferred to adopt a structure in which the switch element is made of a wide bandgap semiconductor (ninth structure).

Further, an AC power supply device disclosed in this specification includes two input capacitors connected in series between a first power supply node and a second power supply node; first and second PWM control bridges each including two switch elements connected in series between the first power supply node and the second power supply node; and a transformer having one end connected to output terminals of the first and second PWM control bridges and the other end connected to one end of a load, in which the other end of the load is connected to a connection node of the two input capacitors (tenth structure).

Note that in the AC power supply device having the tenth structure, it is preferred to adopt a structure further including a smoothing capacitor connected in parallel to the load (eleventh structure).

Further, in the AC power supply device having the first structure, it is preferred to adopt a structure further including three phases of load circuits having a neutral point connected to the other ends of the three phases of reactors, in which the neutral point is connected to the connection node of the two input capacitors (twelfth structure).

Further, a transformer-coupled reactor disclosed in this specification, which is used for a power supply device, includes a first core section formed in an annular shape; a second core section disposed inside the annular shape of the first core section so that a part of the second core section has intimate contact with the first core section and that a first winding is wound on the first core section and the second core section; a third core section disposed inside the annular shape of the first core section so that a part of the third core section has intimate contact with the first core section and that a second winding is wound on the first core section and the third core section; a fourth core disposed to cover at least a part of side surfaces of the first core section and the second core section, so that magnetic flux passing the same enables magnetic fluxes generated in the first core section and the second core section to come and go each other; and a fifth core disposed to cover at least a part of side surfaces of the first core section and the third core section, so that magnetic flux passing the same enables magnetic fluxes generated in the first core section and the third core section to come and go each other (thirteenth structure).

Advantageous Effects of the Invention

According to the invention disclosed in this specification, it is possible to provide an AC power supply device (such as a high voltage inserter) that can reduce switching loss and total loss.

