JP5958904B2 - Multi-step inverter - Google Patents

Description

  The present invention relates to a multi-step inverter such as a three-phase 24 step inverter.

  Conventionally, a three-phase voltage type 24-step inverter disclosed in Non-Patent Document 1 is known as a multi-step inverter. In this conventional multi-step inverter, in order to obtain a 24-step waveform for one cycle, the winding of each three-phase transformer must be devised to give a phase difference to the output voltage of each phase unit.・ A three-phase transformer with a delta connection was installed.

  However, in such a conventional multi-step inverter, a three-phase transformer is provided on the three-phase output side so that the load current flows, so that the winding becomes larger and the entire inverter system becomes larger. There was a point.

  In particular, when used in applications such as mounting on an aircraft, rotating the generator with the rotation of the engine, and converting the AC power to convert three-phase AC power of a predetermined voltage, miniaturization of the multi-step inverter is strongly demanded. It was done. For example, in the case of a conventional multi-step inverter that extracts electric power of several tens of kPa to 100 kPa, the peak current of the output current of the main inverter composed of six switching elements flows 1.5 times as large as the normal current. A normal load current flows through a delta-connected three-phase transformer. For this reason, each phase coil requires a large winding that can withstand this load current, and as a result, the entire multi-step inverter is enlarged.

JP 2009-171807 A

Sasakawa and Iida, “Harmonic Injection Three-Phase Voltage-Type 24-Step Inverter”, 2008, IEEJ National Conference Paper, No. 4-080

  The present invention has been made in view of the above-described problems of the prior art, and provides a multi-step inverter that does not require a large star-delta connection three-phase transformer on the output side of the inverter circuit and can be reduced in size. For the purpose.

  In the present invention, the DC side of a main inverter that converts a DC voltage into a three-phase voltage is connected to the highest voltage point and the lowest voltage point of four different constant voltage sources, and each phase AC output terminal of the main inverter is connected. , Connect each phase output of the three-phase autotransformer, connect the secondary winding of the single-phase transformer to the neutral point of the three-phase autotransformer, the highest voltage of the constant voltage source of the four voltages The input side of the NPC inverter is connected to the point, the lowest voltage point, the second voltage point, and the fourth voltage point, and the voltage middle point of the four voltage constant voltage source is the secondary winding of the single-phase transformer. And connect the neutral winding of the three-phase autotransformer via a wire between the voltage midpoint of the four voltage constant voltage source and the output of the NPC inverter. And a multi-step inverter that injects the output voltage of the NPC inverter into the neutral point of the three-phase auto-transformer. The features.

  In the above invention, the different four voltage constant voltage sources can be constituted by four capacitors that divide the DC voltage source into two sets of voltages and a chopper that adjusts the two sets of voltages.

  According to the present invention, it is composed of a three-phase main inverter, an NPC inverter, four different voltage constant voltage sources, a three-phase auto-transformer and a single-phase transformer, and a three-phase star-delta connection on the output side of the main inverter. Since a transformer is not required, it is possible to avoid an increase in the size of the entire inverter device due to a three-phase transformer having a complicated winding and a large capacity, and a small multi-step inverter can be provided.

  In addition, according to the present invention, by configuring the four voltage constant voltage source with four voltage dividing capacitors and a chopper, the voltage of the DC voltage source can be stably divided into four voltages and maintained. The output waveform of the multi-step inverter can be stabilized.

The circuit diagram of the 24 step inverter of the 1st Embodiment of this invention. The wave form diagram of the pulse pattern of the switching element of the 24 step inverter of the said embodiment, U phase output terminal voltage _vUN , the secondary winding voltage va of _a single phase transformer, and output phase voltage _vUO . The wave form diagram of U phase output terminal voltage _vUN in the simulation result of the 24 step inverter of the said embodiment, the secondary winding voltage va of _a single phase transformer, and output phase voltage _vUO . The circuit diagram of the DC voltage source of the 24 step inverter of the said embodiment. The circuit diagram of the 24 step inverter of the 2nd Embodiment of this invention. Explanatory drawing of how the electric current flows in the operation state (1) of the chopper in the said embodiment. Explanatory drawing of how the electric current flows in the operation state (2) of the chopper in the said embodiment. The output waveform figure of the simulation result of a prior art example and 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment]
A three-phase voltage type 24-step inverter will be described as a first embodiment of the present invention with reference to FIGS. The 24-step inverter of this embodiment is provided with a zigzag-connected three-phase single-turn transformer at the output end of a six-level output three-phase main inverter, and injects four-level harmonics, thereby increasing the output voltage to 24 steps. It is characterized by a waveform.

As shown in FIG. 1, the 24-step inverter of the present embodiment includes a DC voltage source E _d , a main inverter INV-M including switching elements S _{1 to} S _6, and an auxiliary circuit AUX in a broken line portion.

The main inverter INV-M includes U-phase upper and lower switching elements S ₁ and S ₄ , V-phase switching elements S ₂ and S ₅ , and W-phase switching elements S ₃ and S _6, as will be described later. Six levels of voltage are output by a combination of on / off operations of the switching elements of each phase.

The auxiliary circuit AUX includes an output transformer T composed of a three-phase single-turn transformer with zigzag connection, a DC voltage dividing circuit E _s that divides a DC voltage source E _d into two sets of voltages E ₁ and E ₂ , and a switching element S ₇ to S _12, the diode _D 1, consisting of _{D 2} NPC inverters INV-HF, and an auxiliary transformer _{T a} further comprising a single-phase transformer. Further, the neutral point O of the two pairs of DC voltages E _1, E ₂ of the connecting point N and the output transformer T, are connected via the secondary winding of the auxiliary transformer T _a. In the figure, k is the turns ratio of the auxiliary transformer T _a, in the following description the number of turns of the primary winding and the secondary winding and N _1, N _2, is defined as k = N 2 _/ N _1.

Figure 4 is shows a detailed circuit example of the DC voltage source E _d, the AC power source A which is generated by the generator driven by an engine, three mutually insulated with the primary winding W ₁ of the two is stepped down by winding _{W 21,} W _{22, W 23} in configured transformer _{T b,} are respectively rectified by full wave rectifier _{RE 1, RE 2, RE 3} , further DC-DC converter D-CON _{1 , D-CON 2, D-} CON respective voltages _E 2 through _3, 2E 1, the _{E 2} stable into a DC DC voltage dividing circuit _{E s} (1) terminal, (2) terminal, (3 ) Is supplied to each terminal. Note that the DC voltage source E _d, but is not limited to this circuit configuration.

The NPC inverter INV-HF causes the switching elements S _{7 to} S ₁₂ to be turned on / off by the gate control circuit G-CNT, and the voltage of the four levels for each phase is supplied to the auxiliary transformer T _a by a combination of the on / off operations. To the neutral point of the output transformer T, and the voltage at that point is changed. The NPC inverter INV-HF, the auxiliary transformer _{T a} of the secondary winding voltage _{v a} is _k 1 _E d symmetric three times the frequency of the output phase _voltage, and convex waveform consisting of the voltage of the k 2 _{E d} It is controlled to become.

Next, the operation of the 24-step inverter of the present embodiment will be described. 2A shows a pulse pattern of switching elements S _{1 to} S ₆ of the main inverter IVN-M and switching elements S _{7 to} S ₁₂ of the NPC inverter INV-HF, and FIG. 2B shows an output of the main inverter INV-M. The end voltage v _UN , (c) shows the secondary winding voltage v _a of the auxiliary transformer T _a , and (d) shows the final output phase voltage v _UO of the main inverter INV-M. Note that the switching elements S _{1 to} S ₁₂ are driven and controlled by the gate control circuit G-CNT and operate with the illustrated pulse pattern. At the same time, FIG. 2 shows the waveform of each part related to the U phase, but the V waveform and the W phase are obtained by shifting the phase by 120 °.

Although the switching element of a normal voltage source inverter conducts for 180 ° period, in this method, the switching elements S _{1 to} S ₆ of the main inverter INV-M are conducted for 120 ° period. Accordingly, the output terminal voltage v _UN in the on periods A and B of the U-phase switching elements S ₁ and S ₄ is expressed by the following equation (1).

In the periods C, D, E, and F in which the switching elements S ₁ and S ₄ are turned off, the phase voltages v _VO and v _WO are given by the following formula (2).

The total winding voltage of the output transformer T is expressed by the following equation (3).

The output phase voltage v _UO is obtained from the above equations (2) and (3).

become. Therefore, the output terminal voltage v _UN during the period when the U-phase switching elements S ₁ and S ₄ are off is given by the following equation (5) from the circuit configuration and the above equation.

On the other hand, the auxiliary circuit switching element _S 7 _{to S 12} of the AUX, the auxiliary transformer Ta of the secondary winding voltage _{v a} is 3 times symmetric in frequency _k 1 _E d of the output phase _voltage, k 2 voltage _{E d} It is controlled to have a convex waveform consisting of By turning on and off the switching element _S 7 _{to S 12,} the secondary winding voltage _{v a} take the following values.

Here, k ₁ and k ₂ are voltage ratios, and k ₁ / k = E ₁ / E _d and k ₂ / k = 1/2.

From the circuit configuration of FIG. 1, the output phase voltage v _UO is expressed by the following equation (7).

As a result, when the equations (1), (5), and (6) are substituted into the above equation (7), the U-phase output phase voltage v _UO is composed of 24 steps in one cycle as shown in FIG. The staircase waveform is improved. Further, the V-phase output voltage v _VO and the W-phase output voltage v _WO have waveforms obtained by delaying the U-phase output voltage v _UO by 120 °.

  Note that the output of the 24-step voltage of each phase of the main inverter INV-M is extracted as an AC power source through a filter in a smooth sine waveform.

The result of having performed simulation calculation about the 24 step inverter of 1st Embodiment of the said structure is demonstrated. Waveform improving effect of the present method, either to any convex voltage waveform of the secondary winding voltage v _a of the auxiliary transformer Ta, also depends on the k _1, k ₂ for forming a v _a. Therefore, when the total distortion rate μ of the output phase voltage defined by the following expression is minimized, k ₁ = 0.040 and k ₂ = 0.115 are obtained as the optimum values of this method.

Here, V _UO and V _UO1 are the total effective value and the fundamental effective value of the output phase voltage v _UO .

The total distortion rate μ at the optimum value is 8.3%. Although the distortion rate is increased by about 0.8% compared to the conventional 24-step method with a distortion rate of 7.5%, it can be said that the waveform improvement effect is substantially equivalent to 24 steps. Further, k, E ₁ , E _{2 at} the minimum value of the total distortion rate μ are expressed by the following equation (9).

FIG. 3 shows a U-phase simulation waveform at E _d = 200 V and a resistive load of 5Ω. Output voltage of the U-phase v _UN as with diagrammatically analysis becomes a 6-level step waveform, the secondary winding voltage v _a of the auxiliary transformer Ta is a convex-shaped voltage waveform composed of 3 times the frequency of the output phase voltage ing. The output phase voltage v _UO is improved to a 24-step waveform for one cycle by the function of the auxiliary circuit AUX.

  As described above, according to the 24-step inverter of the present embodiment, a three-phase single-turn transformer is used as an output transformer in place of the three-phase transformer of the star delta connection that has been the cause of the conventional increase in size. By adopting it, it is possible to reduce the size, and for example, it is suitable for use in a field that requires weight reduction, such as an AC power supply device mounted on an aircraft.

[Second Embodiment]
The 24-step inverter according to the second embodiment of the present invention will be described with reference to FIGS. Second embodiment, the feature that the first embodiment, DC voltage dividing circuit E _s of the DC voltage source E _d, was composed of the chopper CH and the voltage dividing capacitor C ₁ -C ₄ To do. Other configurations are the same as those of the first embodiment, and therefore circuit elements common to the first embodiment will be described using common reference numerals.

The 24-step inverter of the second embodiment shown in FIG. 5 includes a DC voltage E _d , a main inverter INV-M including switching elements S _{1 to} S _6, and an auxiliary circuit AUX in a broken line portion. The auxiliary circuit AUX is an NPC inverter comprising _a zigzag output transformer T, four voltage dividing capacitors C _{1 to} C ₄ , switching elements S _{7 to} S ₁₂ , diodes D ₁ and D ₂ , and an auxiliary transformer Ta. It is composed of an INV-HF, _a chopper CH including switching elements S _a1 and S _a2 , reactors L _a1 and L _a2 , and a diode _Da . Further, the neutral point O of the connection point N to the output transformer T of the capacitor is connected through a secondary winding of the single-phase transformer T _a. Due to the need for switching control of the increased switching elements S _a1 and S _a2 of the chopper CH, the gate control circuit G-CNT ₂ controls on / off of the switching elements S _{1 to} S ₁₂ , and the switching elements of the chopper CH On / off control of S _a1 and S _a2 is also performed.

Also in this method, the switching elements S _{1 to} S ₆ of the main inverter INV-M are made conductive for the same 120 ° period as the three-phase current source inverter. On the other hand, the switching element _S 7 _{to S 12} of the auxiliary circuit AUX is three times the frequency of the secondary winding voltage _{v a} is the output phase voltage of the single-phase transformer _{T a,} the voltage amplitude _k 1 _{E d, k} 2 _E Control is performed so as to obtain a symmetrical convex voltage waveform that becomes _d .

6 and 7 show the operation of the chopper CH. As indicated by an arrow I ₁ in FIG. 6, when the switching elements S _a1 and S _a2 are turned on, the current I ₁ flows through C ₁ −S _a1 −L _a1 and C ₄ −L _a2 −S _a2, and the respective capacitors C ₁ , C ₄ charges are discharged through the reactors L _a1 and L _a2 . As shown by the arrow _{I 2} in FIG. 7, when off the switching element _{S a1, S a2,} energy _{I 2} stored in the reactor _{L a1, L a2} to charge capacitor _C 2, _{C 3} through the diode _{D a.} The capacitor voltage is kept at a desired predetermined voltage by repeating the above operation and adjusting the on-time of the switching elements S _a1 and S _a2 .

FIG. 8 shows a simulation result when the DC voltage source E _d = 450 V and the power factor is 80%. When there is no chopper CH, the voltages of E ₁ and E ₂ cannot be maintained at appropriate values. The output phase voltage v _UO has a distorted voltage waveform as shown in FIG. On the other hand, by providing the chopper CH as in the present embodiment, the voltages of E ₁ and E ₂ are appropriately maintained, and the output phase voltage v _UO is from 24 steps in one cycle as shown in FIG. It was confirmed that the voltage waveform was as follows.

_{S 1 ~S 12, Sa 1,} Sa 2 switching elements E _{1, E 2} voltage _{C 1} ~C _4, C _d capacitor _{D 1,} D 2, D _a diode INV-M main inverter AUX auxiliary circuit T output transformer T _a auxiliary transformer T _b transformer G-CNT, G-CNT ₂ gate control circuit E _d DC voltage source Es voltage dividing circuit N voltage middle point IVN-HF NPC inverter CH chopper _{RE 1,} RE 2, RE ₃ full wave Rectifier D-CON ₁ , D-CON ₂ , D-CON ₃ DC-DC converter

Claims (2)

Connect the DC side of the main inverter that converts DC voltage to three-phase voltage to the highest voltage point and the lowest voltage point of different four voltage constant voltage sources,
Connect each phase output of the three-phase auto-transformer to each phase AC output terminal of the main inverter,
Connect the secondary winding side of the single-phase transformer to the neutral point of the three-phase single-turn transformer,
The input side of the NPC inverter is connected to the highest voltage point, lowest voltage point, second voltage point, and fourth voltage point of the four voltage constant voltage source,
A third voltage point in the middle of the voltage of the four-voltage constant voltage source is connected to a neutral point of the three-phase autotransformer via a secondary winding of the single-phase transformer;
A primary winding of the single-phase transformer is connected between a voltage midpoint of the four voltage constant voltage source and an output of the NPC inverter;
A multi-step inverter characterized in that the output voltage of the NPC inverter is injected into a neutral point of the three-phase auto-transformer.   2. The different four voltage constant voltage sources are configured by four capacitors that divide a DC voltage source into two sets of voltages and a chopper that adjusts the two sets of voltages. Multi-step inverter.

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