WO2015141681A1 - Multilevel power converter and method for controlling multilevel power converter - Google Patents

Abstract

A multilevel power converter (1) provided with a transformer (14) having AC input/output terminals (T1-1, 2) on a primary side and an intermediate terminal (T2-3) on a secondary-side coil, a first and a second arm (12-P, N) being connected to both ends (T2-1, 2) on the secondary side and being provided with a plurality of cascade-connected unit cells (11-1, ...M) having a semiconductor switch, a DC capacitor (C), and an input/output terminal for a charge/discharge current, and a DC power supply (Vdc) being connected to the intermediate terminal (T2-3), the free end of the DC power supply (Vdc) and the first and second arms (12-P, N) being connected at an arm joint part (13); wherein circulation currents (iZP, iZN) flowing through the first arm (12-P) and the second arm (12-N) are separately defined, and the average DC voltage value in each arm is independently controlled, whereby the need for arm balance control is obviated.

Description

Multilevel power converter and control method of multilevel power converter

The present invention relates to a single-phase power converter and a three-phase power converter that convert direct current and alternating current bidirectionally, and a multi-phase power converter that includes a three-phase two-phase power converter that bidirectionally converts three-phase alternating current and two-phase alternating current. The present invention relates to a level power converter and a control method for a multi-level power converter.

The importance of battery power storage devices is increasing with increasing opportunities for introducing wind power and solar power. FIG. 20 is a diagram illustrating a general configuration of the battery power storage device. The battery power storage device 1000 includes a battery 100 such as a NAS battery (registered trademark) or a lithium ion battery, a grid converter 200 that converts a DC voltage of the battery 100 into an AC voltage, a grid converter 200, and a power system 400. And an interconnecting transformer 300 that interconnects. In the battery power storage device 1000, the DC voltage of the battery 100 is relatively low with respect to the effective voltage value of the power system 400, so that a high step-up ratio is required for the interconnection converter 200. For this reason, conventionally, high voltage and large capacity have been realized by using a transformer for a converter in an interconnection converter of several megawatts. However, the use of such a transformer for a converter is a factor that leads to an increase in size and weight of the device.

In order to solve such problems, a modular multilevel converter (MMC) has been proposed as a next-generation transformerless power converter that is easy to mount and suitable for large capacity and high voltage applications.

The modular multi-level converter is characterized in that the arm is composed of a module in which a plurality of bidirectional chopper cells or full-bridge converter cells are connected in series. Excluding problems such as insulation, it is possible to increase the AC output voltage and suppress voltage and current ripple without increasing the breakdown voltage of the semiconductor switch by increasing the number of series cells. It is also expected as a large capacity power converter. The modular multi-level converter is easy to mount, rich in redundancy, and can be reduced in size and weight, so that it can be applied to a power converter for grid interconnection, a motor drive device for an induction motor, and the like.

As a modular multilevel converter, for example, a cascading modular multilevel converter (Modular Multilevel Cascade Converter: MMCC) has been proposed (for example, see Patent Document 1 and Non-Patent Documents 1 to 4).

However, if the high step-up ratio of the interconnection converter that converts the DC voltage of the battery power storage device into the AC voltage is realized by the transformer for the converter, the size and weight of the device are increased. That is, even if a modular multi-level converter that is easy to mount and suitable for high-capacity and high-voltage applications is used, the transformer for the converter can be removed, but it is connected from the viewpoint of voltage matching and electrical insulation. There is a problem that the transformer cannot be removed.

In the future, wind power generation and solar power generation are expected to spread not only to the industrial world but also to general households, and further demands for further downsizing, lowering price and higher efficiency of battery power storage devices are required. Is done. Further, there is a need for a power converter that is smaller, lower in price, and more efficient than the cascade-type modular multilevel converter (MMCC) described in Patent Document 1 and Non-Patent Documents 1 to 4.

Therefore, the inventors of the present invention have a modular multi-level single-phase power converter and a three-phase power converter, which are simple in structure, small in size, low in cost, and high in efficiency, which convert DC and AC bidirectionally. A three-phase two-phase power converter has been devised that converts a phase alternating current and a two-phase alternating current in both directions, has a simple structure, is small, is inexpensive, and is highly efficient (see Patent Document 2). Hereinafter, the modular multilevel single-phase power converter, the three-phase power converter, and the three-phase two-phase power converter are collectively referred to as a multilevel power converter.

The multi-level power converter described in Patent Document 2 uses a modular push-pull converter (MPC) with a circuit configuration in which each arm of a push-pull inverter is modularized using cells. Is done. The modular push-pull converter is hereinafter referred to as MPC.

In order to realize normal operation of MPC, Patent Document 2 discloses average value control, arm balance control, circulating current control, and individual balance control as control for making the DC capacitor voltage used in each cell constant. The following four controls are disclosed.

JP 2011-182517 A International Application PCT / JP2012 / 079668

However, in the arm balance control disclosed in Patent Document 2 in which the DC capacitor voltage in each cell is constant, DC voltage information is communicated between the arms at a high speed, and the high speed communication is performed between the arms. Each arm must be installed close to each other, and there were design restrictions.

Therefore, in view of the above problems, an object of the present invention is to independently control the average DC voltage value of each arm, thereby eliminating arm balance control that keeps the DC capacitor voltage in each cell constant, and the DC voltage between the arms. It is necessary to eliminate the high-speed communication of the information, and to eliminate the restrictions on the MPC design.

According to the first aspect of the present invention for realizing the above object,
Two semiconductor switches connected in series, a DC capacitor connected in parallel to the two semiconductor switches, and an input / output terminal for current discharged from the DC capacitor or charged to the DC capacitor in accordance with the switching operation of the semiconductor switch A unit cell;
1st and 2nd arm which consists of one unit cell or a plurality of unit cells cascade-connected to each other via input / output terminals, wherein the first and second arms have the same number of unit cells. And a second arm;
An arm coupling portion having a first terminal to which one end of the first arm is connected, a second terminal to which one end of the second arm is connected, and a third terminal to which one end of the DC power supply is connected When,
A transformer having an AC input / output terminal on the primary side and an intermediate terminal on the secondary side winding, and two terminal terminals of the secondary side winding are connected to the first arm of the first arm coupling portion. And the terminal of the second arm to which the second terminal of the arm coupling portion is not connected are connected to each other, and the intermediate terminal is connected to the terminal of the arm coupling portion of the DC power source. A transformer to which the terminal on the side to which the terminal of 3 is not connected is connected;
Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulating current command value of the second arm are created. Command value creation means for
AC in consideration of the current flowing through the first and second arms and the winding ratio of the transformer and the AC current applied to the AC input / output terminal with respect to the circulating current command values of the first and second arms. There is provided a multi-level power converter comprising control means for controlling the circulating currents flowing through the first and second arms, respectively, to add or subtract, respectively.

According to the second aspect of the present invention for realizing the above object,
Two semiconductor switches connected in series, a DC capacitor connected in parallel to the two semiconductor switches, and an input / output terminal for current discharged from the DC capacitor or charged to the DC capacitor in accordance with the switching operation of the semiconductor switch A unit cell;
1st and 2nd arm which consists of one unit cell or a plurality of unit cells cascade-connected to each other via input / output terminals, wherein the first and second arms have the same number of unit cells. And a second arm;
A first terminal to which a DC power source is connected between one end of the first arm, a second terminal to which another DC power source is connected between one end of the second arm, An arm coupling portion having a terminal and a third terminal connected to the second terminal;
A transformer having an AC input / output terminal on the primary side and a three-terminal coupling reactor on the secondary winding, and the DC power supply of the first arm is connected to the two terminal terminals of the secondary winding The intermediate terminal located on the winding between the two terminals of the three-terminal coupling reactor is connected to the terminal on the side that is not connected to the terminal on the side of the second arm that is not connected to the other DC power source. A transformer to which three terminals are connected;
Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulating current command value of the second arm are created. Command value creation means for
AC in consideration of the current flowing through the first and second arms and the winding ratio of the transformer and the AC current applied to the AC input / output terminal with respect to the circulating current command values of the first and second arms. There is provided a multi-level power converter comprising control means for controlling the circulating currents flowing through the first and second arms, respectively, to add or subtract, respectively.

According to the third aspect of the present invention for realizing the above object,
Two semiconductor switches connected in series, a DC capacitor connected in parallel to the two semiconductor switches, and an input / output terminal for current discharged from the DC capacitor or charged to the DC capacitor in accordance with the switching operation of the semiconductor switch A unit cell;
1st and 2nd arm which consists of one unit cell or a plurality of unit cells cascade-connected to each other via input / output terminals, wherein the first and second arms have the same number of unit cells. And a second arm;
A first capacitor connected to a terminal on the side of the first arm to which the DC power supply is connected;
A second capacitor connected to a terminal of the second arm on the side to which the DC power supply is connected;
A first terminal to which a terminal on the side of the first capacitor not connected to the first arm is connected, and a second terminal to which a terminal on the side of the front capacitor not connected to the second arm is connected And an arm coupling portion having a first terminal and a third terminal connected to the second terminal,
A transformer having an AC input / output terminal on the primary side and a three-terminal coupling reactor on the secondary side winding, the first capacitor of the first arm being connected to the two terminal terminals of the secondary side winding Is connected to the terminal on the side where the second capacitor is not connected, and the intermediate terminal located on the winding between the two terminals of the three-terminal coupling reactor is connected to the second terminal of the second arm. A transformer to which three terminals are connected;
Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulating current command value of the second arm are created. Command value creation means for
AC in consideration of the current flowing through the first and second arms and the winding ratio of the transformer and the AC current applied to the AC input / output terminal with respect to the circulating current command values of the first and second arms. There is provided a multi-level power converter comprising control means for controlling the circulating currents flowing through the first and second arms, respectively, to add or subtract, respectively.

A fourth aspect of the present invention that achieves the above object is a method for controlling the multilevel power converters according to the first to third aspects, comprising:
In the multilevel power converter according to any one of the first to third aspects,
When the winding ratio of the primary side and the secondary side of the transformer is N ₁ / N ₂ and the current input to the AC input terminal of the transformer is i _ac , the circulating current of the first arm and the second current Arm circulating current
i _ZP = i _P + (N ₁ / N ₂ ) × i _ac
i _ZN = i _N- (N ₁ / N ₂ ) × i _ac
Defined in
Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulating current command value of the second arm are created. And
AC in consideration of the current flowing through the first and second arms and the winding ratio of the transformer and the AC current applied to the AC input / output terminal with respect to the circulating current command values of the first and second arms. Provided is a control method for a multilevel power converter, characterized in that control is performed so that the circulating currents flowing through the first and second arms are added or added.

According to the present invention, by independently controlling the DC voltage average value of each arm, arm balance control for making the DC capacitor voltage in each cell constant is eliminated, and high-speed communication of DC voltage information between arms is eliminated. Unnecessary restrictions on MPC design can be eliminated.

It is a circuit diagram which shows the single phase power converter by a 1st Example. FIG. 6 is a circuit diagram showing a chopper cell which is a unit cell in the single-phase power converter according to the first to fifth embodiments. FIG. 6 is a circuit diagram showing a bridge cell which is a unit cell in a single-phase power converter according to first to fifth embodiments. It is a circuit diagram which shows the single phase power converter by a 2nd Example. It is a circuit diagram which shows the circuit structure of the arm in the single phase power converter by a 3rd Example. It is a circuit diagram which shows the circuit structure of the arm in the single phase power converter by a 3rd Example. It is a circuit diagram which shows the circuit structure of the arm in the single phase power converter by a 3rd Example. It is a circuit diagram which shows the single phase power converter by a 4th Example. It is a circuit diagram which shows the single phase power converter by a 5th Example. It is a circuit diagram which shows the three-phase power converter by a 6th Example. It is a circuit diagram which shows the transformer in the three-phase power converter shown in FIG. It is a circuit diagram which shows the transformer in the three-phase power converter shown in FIG. It is the control block diagram (the 1) about the direct-current capacitor control of the three-phase power converter by a 6th example. It is a control block diagram (the 2) about the direct-current capacitor control of the three phase power converter by a 6th example. It is a control block diagram (the 3) about direct-current capacitor control of the three phase power converter by a 6th example. It is a block diagram which shows the direct-current capacitor | condenser control apparatus of the three-phase power converter by a 6th Example. It is a block diagram which shows the instantaneous active power control and the instantaneous reactive power control in the experiment of the three-phase power converter by a 6th Example. It is a figure which shows the experimental waveform about the steady-state characteristic when carrying out the inverter operation | movement of the three-phase power converter by a 6th Example. It is a figure which shows the experimental waveform about the steady-state characteristic when carrying out the rectifier operation | movement of the three-phase power converter by a 6th Example. It is a figure which shows the experimental waveform in start-up operation | movement when operating the three-phase power converter by a 6th Example on predetermined operating conditions. It is a figure which shows an experimental waveform when the instantaneous active power command value is changed in steps from -4 kW to -5 kW in the three-phase power converter according to the sixth embodiment. It is a circuit diagram which shows the three-phase power converter by a 7th Example. It is a circuit diagram which shows the Scott transformer used by this invention. It is the instantaneous voltage vector figure (the 1) of the Scott transformer shown in FIG. It is the instantaneous voltage vector figure (the 2) of the Scott transformer shown in FIG. It is a circuit diagram which shows the three-phase two-phase power converter by an 8th Example. It is a figure which shows the general structure of a battery power storage apparatus.

FIG. 1 shows a first embodiment of a multilevel power converter according to the present invention, and shows a circuit diagram of a single-phase power converter 1. Hereinafter, components having the same reference numerals in different drawings mean components having the same functions. FIG. 2A is a circuit diagram showing a chopper cell CC which is a unit cell in the single-phase power converter in the first embodiment and the following embodiments. FIG. 2B is a circuit diagram showing a bridge cell BC that is a unit cell that can be used in the single-phase power converter 1 of the first embodiment and the following embodiments.

The single-phase power converter 1 according to the first embodiment includes unit cells 11-1 to 11-M (where M is a natural number), a first arm 12-P and a second arm 12-N, A coupling unit 13 and a transformer 14 are provided. The unit cells 11-1 to 11-M include two semiconductor switches SW connected in series, a DC capacitor C connected in parallel to the two semiconductor switches SW, and a DC capacitor C according to the switching operation of the semiconductor switch SW. It has input / output terminals T1 and T2 for discharging or charging the DC capacitor C.

In the following, the DC capacitors C in the unit cells 11-1 to 11-M are described outside the unit cells 11-1 to 11-M for easy understanding. The unit cells 11-1 to 11-M may be either the chopper cell CC shown in FIG. 2A or the bridge cell BC shown in FIG. 2B.

The chopper cell CC shown in FIG. 2A includes two semiconductor switches SW connected in series, a DC capacitor C connected in parallel to the two semiconductor switches SW, and a discharge or DC from the DC capacitor C according to the switching operation of the semiconductor switch SW. This is a bidirectional chopper cell having input / output terminals T1 and T2 for current charged in the capacitor C. The two terminals of one of the two semiconductor switches SW are the input / output terminals T1 and T2 of the chopper cell CC.

The bridge cell BC shown in FIG. 2B is configured by connecting two sets of two semiconductor switches SW connected in series in parallel and connecting a DC capacitor C in parallel thereto. The series connection point of each set of two semiconductor switches SW connected in series is defined as input / output terminals T1 and T2 for discharging current from the DC capacitor C or charging the DC capacitor C. The chopper cell CC and the bridge cell BC are also called unit cells.

In any of the unit cells shown in FIGS. 2A and 2B, each semiconductor switch SW includes a semiconductor switching element S that passes a current in one direction when turned on, and a feedback diode D connected in antiparallel to the semiconductor switching element S. Have A voltage output from one unit cell appears between the input / output terminals T1 and T2 of the unit cell.

As shown in FIG. 1, the first arm 12-P and the second arm 12-N have the same number of unit cells or a plurality of unit cells cascaded to each other via the input / output terminals T1 and T2. To have. In FIG. 1 and the following embodiments, the unit cells arranged in the first arm 12-P and the second arm 12-N are denoted by reference numerals 11-1 to 11-M (where M is a natural number. The same applies to the above.

The arm coupling unit 13 includes a first terminal a to which the lower terminal 1ab of the first arm 12-P is connected and a second terminal b to which the lower terminal 2ab of the second arm 12-N is connected. And a third terminal c positioned between the first terminal a and the second terminal b. The negative terminal of the DC power source V _dc is connected to the third terminal c.

In the first embodiment, the arm coupling portion 13 includes a first terminal a, a second terminal b, and between the first terminal a and the second terminal b, as shown in FIG. It consists of a three-terminal coupling reactor L having a third terminal c which is an intermediate tap located on the winding. In FIG. 1, the polarity of the three-terminal coupling reactor L is represented by a black circle (•). The polarity of the winding between the first terminal a and the third terminal c and the polarity of the winding between the third terminal c and the second terminal b are opposite to each other (in the example shown in FIG. To face the direction you want to).

The transformer 14 has AC input / output terminals T1-1 and T1-2 on the primary side, and centered on the secondary winding between the two terminal terminals T2-1 and T2-2 on the secondary side. It has an intermediate terminal T2-3 which is a tap. Between the AC input and output terminal of the primary T1-1 and T1-2 of the transformer 14, an AC output voltage v _ac single-phase power converter 1 appears. Here, the number of turns of the primary winding of the transformer 14 and N _1, the number of turns of the secondary winding and N _2. Therefore, on the secondary side, the number of turns of the winding between the end terminal T2-1 and the intermediate terminal T2-3 and the number of turns of the winding between the intermediate terminal T2-3 and the end terminal T2-2 are both the N _2/2.

In FIG. 1, the polarities of the primary side winding and the secondary side winding of the transformer 14 are represented by black circles (•). In the secondary winding, the polarity of the winding between the end terminal T2-1 and the intermediate terminal T2-3 and the polarity of the winding between the intermediate terminal T2-3 and the end terminal T2-2 are: The same direction (aligned to the left in the illustrated example). On the other hand, the polarity direction of the primary winding does not necessarily have to be the same as the polarity direction of the secondary winding.

The terminal T2-1 of the secondary winding of the transformer 14 is the terminal on the side of the first arm 12-P to which the first terminal a of the arm coupling portion 13 is not connected, that is, the first arm 12 The upper terminal 1at of −P is connected, and the second terminal b of the arm coupling portion 13 of the second arm 12-N is not connected to the terminal T2-2 of the secondary winding of the transformer 14 Side terminal, that is, the upper terminal 2at of the second arm 12-N is connected. Further, the intermediate terminal T2-3 of the transformer 14, the DC power source V _dc, the terminal of the third side of the terminal c is not connected, that is the positive terminal of the DC power source V _dc is connected to the arm coupling portion 13 .

The operation of the single-phase power converter 1 according to the first embodiment is analyzed using mathematical formulas as follows.

Between transformer 14 AC input and output terminals of the primary side T1-1 and T1-2, AC voltage v _ac single-phase power converter 1 appears. _{Let ac} be the _ac current. Further, the arm current flowing through the first arm 12-P is i _P, and the arm current flowing through the second arm 12-N is i _N. A voltage appearing between input / output terminals (T1 and T2 in FIGS. 2A and 2B) of each unit cell 11-j (where j = 1 to M) in the first arm 12-P is represented by v _Pj , When the voltage appearing between the input / output terminals (T1 and T2 in FIGS. 2A and 2B) of each unit cell 11-j (where j = 1 to M) in the arm 12-N is _1N the output voltage sum v _N of the output voltages of the arm 12-P total v _P and the second arm 12-N is represented by the respective formulas 1 and 2.

On the other hand, when the modulation degree is m (0 ≦ m ≦ 1) and the angular frequency is ω, the total output voltage v _P of the first arm 12- _P and the total output voltage v _N of the second arm 12- _N are They are represented by Formula 3 and Formula 4, respectively.

Here, the circulating current i _Z is defined as shown in Equation 5.

Since the three-terminal coupling reactor in the arm coupling unit 13 has an inductance of L only for the circulating current i _Z , the voltage equations shown in Equations 6 and 7 are established.

Equation 8 and Equation 9 are obtained from Equation 3, Equation 4, Equation 6, and Equation 7.

As can be seen from Equation 9, the circulating current i _Z is a direct current amount. That is, the arm current i _N flowing through the arm current i _P and the second arm 12-N through the first arm 12-P is that both contain a DC component. In the transformer 14, the magnetic flux due to the direct current cancels each other, so no direct-current magnetic flux is generated. Note that the relationship of v _P + v _N = 2V _dc is used in the derivation of the above-described Expression 9. However, in actuality, v _P + v _N ≠ 2V _dc due to the influence of the harmonic voltage, dead time, and the like, so that the AC component is superimposed on the circulating current i _Z.

On the other hand, when the first arm 12-P arm flowing in the current i _P and the second arm 12-N to flow through the AC component contained in the arm current i _N, respectively (i _{P) ac} and (i _{N) ac,} Equation 10 is obtained from the relationship of the magnetomotive force of the transformer.

Assuming that the relationship of (i _P ) _ac = − (i _N ) _ac holds in Equation 10, Equations 11 and 12 are obtained.

In the present invention, the circulating current i _ZP flowing through the first arm 12-P and the circulating current i _ZN flowing through the second arm 12-N are defined separately. Then, in FIG. 1, the circulating current i _ZP is given by the following equations A and B.
i _ZP = i _P + (i _P ) _ac = i _P + (N ₁ / N ₂ ) i _ac (A)
i _ZN = i _N- (i _N ) _ac = i _N- (N ₁ / N ₂ ) i _ac (B)

The second term on the right side of Formula A and Formula B corresponds to the AC component included in circulating current i _ZP and circulating current i _ZN . Therefore, the circulating current i _ZP and the circulating current i _ZN are ideally only a direct current component. In the present invention, the DC voltage average values v _aveCP and v _aveCN of the first arm 12-P and the second arm 12-N are independently controlled by using the circulating current i _ZP and the circulating current i _ZN. Can do.

FIG. 3 shows a second embodiment of the multilevel power converter according to the present invention, and shows a circuit diagram of the single-phase power converter 1. In the single-phase power converter 1 according to the second embodiment, the arm coupling portion 13 in the first embodiment described with reference to FIGS. 1, 2A and 2B is not a three-terminal coupling reactor L but a normal one. The reactor is constituted by uncoupled reactors L1 and L2. For other circuit components, the unit cells 11-1 to 11-M, the first arm 12-P, the second arm 12-N and the transformer 14 shown in FIG. 1, as well as FIG. 2A and FIG. Since it is the same as that of the unit cell shown in 2B, the same reference numerals are given to the same circuit components, and detailed description thereof will be omitted.

In the second embodiment, as shown in FIG. 3, the arm coupling portion 13 includes two reactors L1 and L2 connected in series with each other. The first terminal a which is one terminal of the reactor L1, and the reactor It has the 2nd terminal b which is one terminal of L2, and the 3rd terminal c which is a series connection point of the two reactors L1 and L2 connected in series. Reactors L1 and L2 may be substituted with the leakage inductance of transformer 14.

4A to 4C show a third embodiment of the multilevel power converter of the present invention, and are circuit diagrams showing the circuit configuration of the arm in the single-phase power converter 1. FIG. The single-phase power converter 1 according to the third embodiment is obtained by changing the positions of the reactors L1 and L2 constituting the arm coupling portion 13 in the second embodiment described with reference to FIG. 4A to 4C show only the first or second arm including the reactor L and the unit cells 11-1 to 11-M among the reactors L1 and L2 constituting the arm in the single-phase power converter 1. Yes. In the third embodiment, as shown in FIGS. 4A to 4C, each of the first arm and the second arm is connected to an arbitrary position between the unit cells 11-1 to 11-M cascade-connected to each other. Therefore, the first terminal a, the second terminal b, and the third terminal c of the arm coupling portion 13 shown in FIG. 3 are changed so as to be connected to each other. Other circuit components are the same as those in the second embodiment. The reactor L may be replaced with the leakage inductance of the transformer 14.

FIG. 5 shows a fourth embodiment of the multi-level power converter of the present invention, and shows a circuit diagram of the single-phase power converter 1. The single-phase power converter 1 according to the fourth embodiment is obtained by changing the arm coupling portion 13 and the transformer 14 in the first embodiment described with reference to FIGS. 1, 2A, and 2B.

The unit cells 11-1 to 11-M, the first arm 12-P, and the second arm 12-N are the same as those in the first embodiment described with reference to FIGS. 1, 2A, and 2B. Since there is, detailed description is omitted. As in the first embodiment, each of the unit cells 11-1 to 11-M can use either the chopper cell CC shown in FIG. 2A or the bridge cell BC shown in FIG. 2B, and includes two semiconductor switches SW connected in series. A DC capacitor C connected in parallel to the two semiconductor switches SW, and input / output terminals T1 and T2 for discharging current from the DC capacitor C or charging to the DC capacitor in accordance with the switching operation of the semiconductor switch SW. As in the first embodiment, the first arm 12-P and the second arm 12-N include a plurality of units connected in cascade through one unit cell 11-1 or input / output terminals T1 and T2. The same number of unit cells 11-1 to 11-M is provided.

The arm coupling unit 13 includes a first terminal a to which the other end of the DC power source V _dc whose one end is connected to the lower terminal 1ab of the first arm 12-P and the second arm 12-N A third terminal connected to the second terminal b connected to the other end of another DC power source V _dc whose one end is connected to the lower terminal 2ab, and the first terminal a and the second terminal b. Terminal c.

As shown in FIG. 5, the transformer 14 ′ in the fourth embodiment is located at the intermediate terminal of the transformer 14 in the single-phase power converter 1 according to the first embodiment described with reference to FIG. 1. Further, a three-terminal coupling reactor 15 is provided. That is, the three-terminal coupling reactor 15 is provided on the secondary winding of the transformer 14 ′. Between transformer 14 AC input and output terminals of the primary 'T1-1 and T1-2, AC output voltage v _ac single-phase power converter 1 appears. Here, the number of turns of the primary side winding of the transformer 14 ′ is N _1, and the number of turns of the secondary side winding is N ₂ . Therefore, on the secondary side, the number of windings between the terminal terminal T2-1 and the three-terminal coupling reactor 15 and the number of windings between the three-terminal coupling reactor 15 and the terminal T2-2 are: both the N _2/2.

The terminal T2-1 of the secondary winding of the transformer 14 'is connected to the terminal of the first arm 12-P on which the DC power source _Vdc is not connected, that is, the upper terminal of the first arm 12-P. 1at is connected. Further, the terminal T2-2 of the secondary winding of the transformer 14 ′ is a terminal on the side of the second arm 12-N to which no further DC power source V _dc is connected, that is, the second arm 12. -N upper terminal 2at is connected. The third terminal c of the arm coupling portion 13 is connected to the intermediate terminal T2-3 located on the winding between the both terminals of the three-terminal coupling reactor 15.

In FIG. 5, the polarity of the primary side winding and the secondary side winding of the transformer 14 ′ is represented by black circles (•). In the secondary winding, the polarity of the winding between the end terminal T2-1 and the intermediate terminal T2-3 and the polarity of the winding between the intermediate terminal T2-3 and the end terminal T2-2 are: The directions are opposite (facing each other in the illustrated example). On the other hand, the polarity direction of the primary winding does not necessarily have to be the same as the polarity direction of the secondary winding. Further, regarding the polarity direction of the three-terminal coupling reactor 15, the polarities of the two windings between the two end terminals of the three-terminal coupling reactor 15 and the intermediate terminal T2-3 are the same direction (in the illustrated example, the left direction). To match). The direction of the polarity of the three-terminal coupling reactor 15 can be aligned on the right side in the illustrated example.

FIG. 6 is a circuit diagram of a single-phase power converter 1, showing a fifth embodiment of the multilevel power converter of the present invention. The single-phase power converter 1 according to the fifth embodiment changes the connection relationship between the arm coupling portion 13 and the DC power source v _dc in the fourth embodiment described with reference to FIG. Accordingly, a new capacitor is provided.

The unit cells 11-1 to 11-M, the first arm 12-P, and the second arm 12-N are the same as those in the first embodiment described with reference to FIGS. 1, 2A, and 2B. . That is, the unit cells 11-1 to 11-M can use either the chopper cell CC shown in FIG. 2A or the bridge cell shown in FIG. 2B as in the first embodiment. A DC capacitor C connected in parallel to the two semiconductor switches SW, and input / output terminals T1 and T2 for discharging current from the DC capacitor C or charging to the DC capacitor C according to the switching operation of the semiconductor switch SW. As in the first embodiment, the first arm 12-P and the second arm 12-N include a plurality of units connected in cascade through one unit cell 11-1 or input / output terminals T1 and T2. The same number of unit cells 11-1 to 11-M is provided. The DC power source V _dc is connected between the lower terminal 1ab of the first arm 12-P and the lower terminal 2ab of the second arm 12-N.

The first capacitor C _dc1 has one end connected to the lower terminal 1ab of the first arm 12-P and the other end connected to the first terminal a. The second capacitor C _dc2 has one end connected to the lower terminal 2ab of the second arm 12-N and the other end connected to the second terminal b. A first capacitor C _dc1 and the second capacitor C _dc2 connected in series, a first capacitor C _dc1 and a second capacitor C _dc2, which is the series connection is connected in parallel to the DC power source V _dc. At this time, the polarity directions of the first capacitor C _dc1 and the second capacitor C _dc2 are matched with the polarity direction of the DC power source V _dc .

The arm coupling unit 13 includes a first terminal a connected to the first capacitor C _dc1 , a second terminal b connected to the second capacitor C _dc2 , and an intermediate terminal T2 of the three-terminal coupling reactor 15. And a third terminal c connected to -3.

As in the case of the fourth embodiment, the transformer 14 'in the fifth embodiment has an intermediate terminal of the transformer 14 in the single-phase power converter 1 according to the first embodiment described with reference to FIG. A three-terminal coupling reactor 15 is provided at the same position. That is, the three-terminal coupling reactor 15 is provided on the secondary winding of the transformer 14 ′. Between transformer 14 AC input and output terminals of the primary 'T1-1 and T1-2, AC output voltage v _ac single-phase power converter 1 appears. Here, the number of turns of the primary side winding of the transformer 14 ′ is N _1, and the number of turns of the secondary side winding is N ₂ . Therefore, on the secondary side, the number of windings between the terminal T2-1 and the three-terminal coupling reactor 15 and the number of windings between the three-terminal coupling reactor 15 and the terminal T2-2 are: both the N _2/2.

The upper terminal 1at of the first arm 12-P is connected to the terminal T2-1 of the secondary winding of the transformer 14 ′, and the terminal T2-2 of the secondary winding of the transformer 14 ′. Is connected to the upper terminal 2at of the second arm 12-N. Further, the third terminal c of the arm coupling portion 13 is connected to the intermediate terminal T2-3 located on the winding between the two end terminals T2-1 and T2-2 of the three-terminal coupling reactor 15.

Also in FIG. 6, the polarities of the primary side winding and the secondary side winding of the transformer 14 ′ are represented by black circles (•). In the secondary winding, the polarity of the winding between the end terminal T2-1 and the intermediate terminal T2-3 and the polarity of the winding between the intermediate terminal T2-3 and the end terminal T2-2 are: The directions are opposite (in the illustrated example, they face each other). On the other hand, the polarity direction of the primary winding is not necessarily the same as the polarity direction of the secondary winding. Regarding the polarity of the three-terminal coupling reactor, the two windings between the two terminals T2-1 and T2-2 and the intermediate terminal T2-3 of the three-terminal coupling reactor 15 have the same polarity (not shown) In the example, it is aligned to the left). The direction of the polarity of the three-terminal coupling reactor can be aligned on the right side in the illustrated example.

A three-phase power converter can be configured using the single-phase power converter 1 according to the first to fifth embodiments described above for three phases. In addition, a three-phase two-phase power converter can be configured by using two phases of the single-phase power converter 1 according to the first to fifth embodiments. Next, a three-phase power converter will be described as a sixth embodiment and a seventh embodiment. A three-phase two-phase power converter will be described later as an eighth embodiment.

FIG. 7 shows a sixth embodiment of the multilevel power converter according to the present invention, and is a circuit diagram showing a three-phase power converter 2. 8A and 8B are circuit diagrams showing transformers in the three-phase power converter 2 shown in FIG. In the sixth embodiment, the case where the three-phase power converter 2 is configured using the single-phase power converter 1 according to the first embodiment will be described as an example. The single-phase power according to the second to fifth embodiments will be described. Even when the power converter 1 is used, the same configuration can be adopted. The case where the three-phase power converter 2 is configured using the single-phase power converter 1 according to the fifth embodiment will be described as a seventh embodiment described later.

In the sixth embodiment shown in FIG. 7, three single-phase power converters 1 are used for u-phase, v-phase, and w-phase, and these single- phase power converters 1u, 1v, and Indicated by 1w. And the three phase power converter 2 is formed using these single phase power converters 1u, 1v, and 1w. In FIG. 7, the single-phase power converters 1v and 1w have the same circuit configuration as that of the single-phase power converter 1u, and therefore a detailed description of the circuit configuration is omitted. Hereinafter, although the u-phase single-phase power converter 1u will be mainly described, the same applies to the v-phase and w-phase single-phase power converters 1v and 1w. In this embodiment, the number of unit cells is 4 per arm as an example, 8 per 1 phase, and thus 24 in the three-phase power converter 2. However, this value is only an example, It is not limited to this.

In the three-phase power converter 2 according to the sixth embodiment, using the transformers 14 in the single- phase power converters 1u, 1v, and 1w provided in the u-phase, v-phase, and w-phase, Each phase in the three-phase transformer 24 having a star connection on the secondary side and an open star connection on the secondary side is configured. As an example, the turns ratio N ₁ : N ₂ of the primary winding and the secondary winding is 1: 1. FIG. 8A shows the star connection on the primary side of the three-phase transformer 24, and FIG. 8B shows the open star connection on the secondary side of the three-phase transformer 24. As shown in FIG. 8B, the number of terminals of the secondary side winding that is an open star connection is originally nine, but in the sixth embodiment, each phase of u, v, and w is shown in FIG. By configuring the third terminal c, which is an intermediate terminal in the three-terminal coupling reactor L of the arm coupling portion 13, as one common terminal, the number of necessary terminals can be reduced to seven.

As described with reference to FIG. 1, in the single-phase power converter 1, the negative terminal of the DC power source V _dc is connected to the third terminal c of the arm coupling portion 13, and the intermediate terminal of the transformer 14. T2-3 is connected to the positive terminal of the DC power source _Vdc . On the other hand, in the sixth embodiment, the DC power supply V _dc connected to the single-phase power converter 1 in FIG. 1 as described above is _replaced with each phase of u, v, and w as shown in FIG. Common.

Next, control of a DC capacitor in each unit cell of the three-phase power converter 2 according to the sixth embodiment will be described below with reference to FIGS. 9A to 9C, FIG. 10 and FIG. 9A to 9C are control block diagrams for DC capacitor control of the three-phase power converter 2 according to the sixth embodiment. FIG. 10 is a block diagram showing a DC capacitor control device 50 of the three-phase power converter 2 according to the sixth embodiment. As described above, the three-phase power converter 2 according to the sixth embodiment includes the single-phase power converter 1 according to the first embodiment for three phases. The block diagrams shown in FIGS. 9A to 9C and FIG. 10 are for the u-phase single-phase power converter 1u (that is, the single-phase power converter 1 according to the first embodiment) of the three-phase power converters. Although direct current capacitor control is shown, the present invention can also be applied to the v-phase and w-phase single-phase power converters 1v and 1w, and the three-phase power converter 2 in the single-phase power converter 1 according to the second to fifth embodiments. It is the same even if it comprises. For the same reason, the DC capacitor control of the three-phase power converter 2 described below can be applied as it is as the single DC capacitor control of the single-phase power converter 1 according to the first to fifth embodiments. .

According to the sixth embodiment, as shown in FIGS. 9A to 9C, the DC capacitor control of the three-phase power converter 2 is roughly divided into the following three controls. The three controls are called average value control, circulating current control, and individual balance control. Hereinafter, these three controls will be described individually.

Average value control is control in which the value obtained by averaging the voltage average value of all DC capacitors in each arm follows the DC voltage command value. The circulating current control is control that causes the circulating current flowing through the first arm and the circulating current flowing through the second arm to follow the circulating current command value created in the average value control. The individual balance control is a control in which the voltage value of each DC capacitor in the arm follows the value obtained by averaging the voltage values of all DC capacitors in the same arm, and is executed for each arm. Control.

The above three controls are executed by a DC capacitor control device 50 of the three-phase power converter 2 as shown in FIG. The DC capacitor control device 50 includes a command value creating means 51 and a control means 52. The command value creating means 51 circulates the first arm 12-P based on the voltage value of the DC capacitor in the first arm 12-P and the voltage value of the DC capacitor in the second arm 12-N. A current command value i _ZP ^* and a circulating current command value i _ZN ^{* of} the second arm 12 -N are created. The control means 52 controls the circulating currents i _ZP and i _ZN flowing through the first and second arms to follow the circulating current command values i _ZP ^* and i _ZN ^* of the first and second arms, respectively. To do. The circulating currents i _ZP and i _ZN of the first and second arms are converted into the current ratios i _P and i _N flowing through the first and second arms by the turns ratio N ₁ / N ₂ of the transformer 14 and AC input. This is obtained by adding or subtracting an AC component (N ₁ / N ₂ ) × (I _ac ) in consideration of the AC current i _ac applied to the output terminals T1-1 and T1-2.

Also, the control means 52 has a switching command means 63 for switching the semiconductor switch in response to the control to be followed. Each of these means is realized using an arithmetic processing device such as a DSP or FPGA.

Hereinafter, each of the three controls shown in FIGS. 9A to 9C will be described with reference to FIG. The command value is described with a symbol *, but in the present specification, it is described as a circulating current command value i _ZP ^* , whereas in the drawing, the circulating current command value is i ^* _ZP . The positions of the symbols * are different. However, here, i _ZP ^* and i ^* _ZP are assumed to be the same. The same applies to other codes.

FIG. 9A is a block diagram showing average value control in which a value obtained by averaging the voltage average value of all the DC capacitors in each arm follows the DC voltage command value. The average value control shown in FIG. 9A is performed by the command value creating means 51 in the DC capacitor control device 50 shown in FIG. The command value creating means 51 creates a circulating current command value i _ZP ^* for the first arm 12-P and a circulating current command value i _ZN ^* for the second arm 12-N. The values V _aveCP and V _aveCN obtained by averaging the voltage values of all DC capacitors in the first arm 12-P and the second arm 12-N follow a predetermined DC voltage command value V _C ^* . A feedback loop is configured.

That is, the command value creating means 51 shown in FIG. 10 obtains a value v _aveCP obtained by averaging the voltage values of all the DC capacitors in the first arm 12-P shown in FIG. for controlling so as to follow the command value V _C ^*, to generate a first circulating current command value i _ZP of arm 12-P ^*. Similarly, the command value creating means 51 has a value v _aveCN obtained by averaging the voltage values of all the DC capacitors in the second arm 12-N, following a predetermined DC voltage command value V _C ^* . The circulating current command value i _ZN ^* for the second arm 12-N is generated to control the second arm 12-N.

Subsequently, FIG. 9B shows that the circulating current i _ZP flowing through the first arm and the circulating current i _ZN flowing through the second arm follow the circulating current command values i _ZP ^* and i _ZN ^* created in the average value control. It is a block diagram which shows circulating current control made to do. The circulating current control is executed for each arm. In FIG. 9B, the individual balance control for the first arm 12-P is mainly described, but the circulating current control for the second arm 12-N is described. It is written in parentheses "()".

In the circulating current control shown in FIG. 9B, the circulating current command value i _ZP ^{* of the} circulating current i _ZP flowing through the first arm, created by the command value creating means 51 in the DC capacitor control device 50 shown in FIG. to the circulating current command value i _ZN ^* of the circulating current i _ZN through the second arm, so that the circulating current i _ZP and circulating current i _ZN flowing through the second arm through the first arm to follow, the control unit 52 It is something to control.

The circulating current i _ZP flowing through the first arm and the circulating current i _ZN flowing through the second arm are the current i _P flowing through the first and second arms, as shown in Equations 13 and 14 and FIG. 9B. and i _N, and the turns ratio N ₁ / N ₂ of the transformer 14, AC output terminals T1-1, AC component in consideration of the alternating current i _ac applied to T1-2 (N ₁ / N ₂ ) × (i _ac ) added or subtracted. Then, the control means 52 constitutes a feedback loop for causing the circulating current i _ZP flowing through the first arm and the circulating current i _ZN flowing through the second arm to follow the circulating current command values i _ZP ^* and i _ZN ^*. The voltage command values v _AP ^* and v _AN ^* are generated.

FIG. 9C is a block diagram showing individual balance control in which the voltage value of each DC capacitor in the arm follows the value obtained by averaging the voltage values of all DC capacitors in the same arm. . The individual balance control is executed for each arm, and in FIG. 9C, the individual balance control for the first arm 12-P is mainly described, but the individual balance control for the second arm 12-N is described. It is written in parentheses "()".

The control means 52 _adds the voltage value v _CPj of each DC capacitor in the first arm 12-P to the value v _aveCP obtained by averaging the voltage values of all DC capacitors in the first arm 12-P. , And the voltage v _aveCN obtained by averaging the voltage values of all the DC capacitors in the second arm 12-N to the voltage of each DC capacitor in the second arm 12-N. Control is performed to follow each value v _CNj . A voltage command value for this purpose is created for each unit cell 11-j in each arm 12-P and 12-N. For the first arm 12-P, v _BPj ^* and the second arm 12-N Is represented by v _BNj ^* . Here, j is 1 to M, where M is the number of unit cells in the arm.

The voltage control value for controlling the DC capacitor in the unit cell 11-j in each of the arms 12-P and 12-N is created by the above three controls, and this is equivalent to one phase of the three-phase power converter 2 (ie, The final output voltage command for each unit cell 11-j in each arm 12-P and 12-N is combined with the voltage command value v _ac ^* for the AC voltage to be output by the single-phase power converter 1). Values are created as in Equation 15 and Equation 16.

Here, the DC voltage V _dc is used as a feedforward term in order to stabilize the control.

The switching operation of the semiconductor switch SW in each unit cell 11-j in the three-phase power converter 2 is controlled using the output voltage command values v _Pj ^* and v _Nj ^* shown in the above formulas 15 and 16. The As described above, the control means 52 has the switching command means 63 for switching the semiconductor switch SW. The output voltage command values v _Pj ^* and v _Nj ^* generated for the arms 12-P and 12-N are normalized by the voltages V _CPj and V _CNj of the DC capacitors, respectively, and then a triangular wave with a carrier frequency f _c The PWM signal is compared with the carrier signal (maximum value: 1, minimum value: 0), and a PWM switching signal is generated. The generated switching signal (described as a switching command value in FIG. 10) is used by the switching command means 63 for switching control of the semiconductor switch SW (see FIGS. 2A and 2B) in the corresponding unit cell 11-j. .

When the three-phase power converter 2 according to the sixth embodiment uses eight unit cells per phase (four in each arm), a PWM waveform having a phase voltage of 9 levels and a line voltage of 17 levels is obtained. Become. The generation of the switching signal is realized by using an arithmetic processing device such as a DSP or FPGA.

Next, experimental results using the three-phase voltage converter 2 according to the sixth embodiment will be described. The circuit parameters shown below were used for the experiment.
Rated capacity 5kVA
Rated line voltage effective value V _S 200V
Rated current effective value I 15A
System frequency f 50Hz
Transformer turns ratio N ₂ / N ₁ 1.5
DC link voltage V _dc 140V
Coupling inductor L 4mH
DC voltage command value V _C ^* 75V
DC capacitor C 3.3mF
Unit capacitance constant H 45ms
The carrier frequency f _c 2kHz
AC side reactor L _S 2.75mH

In the experiment, since the number M of chopper cells of each arm 12-P and 12-N is 4, the three-phase voltage converter 2 has 24 chopper cells. The MPC on the AC side was connected to a three-phase AC of 200V through the AC reactor Ls, and the DC side was connected to a DC power source having a DC voltage _Vdc of 140V.

FIG. 11 is a block diagram showing instantaneous active power control and instantaneous reactive power control in the experiment of the three-phase power converter 2 according to the sixth embodiment. There can be any number of cells in each arm. Here, the instantaneous active power command value is represented by p ^* and the instantaneous reactive power command value is represented by q ^* . The phase voltage command values v ^{u *} , v ^{v *} and v ^{w *} of each phase of the three-phase power converter 2 in the sixth embodiment are the non-interfering currents of the power source currents i ^u , i ^v and i ^w of each phase. Determined by control.

The three-phase power converter 2 according to the sixth embodiment includes a DC capacitor voltage control means 71 and an output voltage command value creation means 72 for each unit cell. The DC capacitor voltage control means 71 includes a DC voltage command value V _C ^* , voltage values v ^u _CP1 , v ^u _{CP2 ˜v} ^w _CNM of each DC capacitor of each arm of three phases, arm current i of each arm of each phase ^u _P , i ^u _N ,..., i ^w _N and AC currents i _ac ^u , i _ac ^v , i _ac ^w of each phase are input, and voltage command values v ^u _AP ^* , v ^u _AN ^* to v ^{w of} each phase are input. _BN ^* and voltage command values v ^u _BPj ^* to v ^w _BPj ^* of each DC capacitor of each phase are output.

The voltage command values v ^u _AP ^* and v ^u _AN ^* to v ^w _BN ^* of each phase output from the DC capacitor voltage control means 71 and the voltage command values v ^u _BPj ^* to v ^w _BPj of each DC capacitor of each phase ^* And the DC power supply voltage value V _dc and the phase voltage command values v ^{u *} , v ^{v *} and v ^{w *} of each phase are input to the output voltage command value creating means 72 of each unit cell. The voltage command values v ^u _Pj ^* , v ^u _Nj ^* , .about.v ^w _Nj ^* of the chopper cells of each arm of each phase are output from the output voltage command value creating means 72 of each unit cell.

FIG. 12 shows experimental waveforms using the three-phase power converter 2 according to the sixth embodiment. The MPC operates as an inverter, the instantaneous active power command value p ^* is −5 kW, and the instantaneous reactive power command. The value q ^* is 0 kVA. The voltages on the secondary side of the transformer 14 are v ₂ ^u , v ₂ ^v and v ₂ ^w are 9-step PWM waveforms. total harmonic distortion THD of i ^u was reduced to 1.9%. The arm currents i ^u _P and i ^u _N include both a DC component and a 50 Hz AC component, and the DC component is 6.3 A. On the other hand, the amplitude of the AC component at 50 Hz is 2/3 (= N ₁ / N ₂ ) of the supply current, and the circulating current i ^u _ZP is DC component I ^u _ZP = 6.3 A due to the effect of the transformer 14. In addition to a fundamental frequency component of 50 Hz. However, the 50 Hz component is negligible compared to the DC component. From a substantial viewpoint, the u-phase current i ^u _ZPN defined by the formula (i _ZPN = i _ZP −i _ZN ) does not include a DC component. The DC capacitor voltages v ^u _CP1 and v ^u _CN1 both contain a DC component and an AC component, and the DC component is regulated to 75V by voltage control. The DC component I _dc of the DC power supply current is 39 A, which is 6 times higher than the current I ^u _Z.

FIG. 13 shows an experimental waveform using the three-phase power converter 2 according to the sixth embodiment. The MPC operates as a rectifier, the instantaneous active power command value p ^* is 5 kW, and the instantaneous reactive power command value. q ^* is 0 kVA. Compared with the experimental waveform of FIG. 12 the experiment waveform shown in FIG. 13, the amplitude ^{v u} _2, v v ₂ and v ^w ₂ shown in FIG. 13, the amplitude v ^u ₂ shown in FIG. 12, v ^v ₂ and It is smaller than v ^w ₂ . This is due to the influence of the resistance value of the power circuit. Depending on the resistance value, the amplitude thereof decreases during the rectification operation, but in the case of reverse conversion, the amplitude increases in the opposite manner. This is because the polarities of the currents i ^u _ZP and i _dc change to negative due to the rectification operation. The amplitudes of the currents i ^u _ZP and i _dc shown in FIG. 13 are smaller than those shown in FIG. 12 due to the power loss of the converter. The other waveforms shown in FIG. 13 are the same as the waveforms shown in FIG.

FIG. 14 shows experimental waveforms using the three-phase power converter 2 according to the sixth embodiment. V _dc is 140 V, the instantaneous active power command value p ^* is −5 kW, and the instantaneous reactive power command value q ^* is It is a waveform during the start-up operation at 0 kVA. In the period from time t1 to time t2, vC * increases from 70V to 75V at a slope change rate of 5V / 0.1 s. In the period from time t3 to time t4, the instantaneous reactive power command value q ^* is 0 kW, whereas the instantaneous active power command value p ^* is 0 kW to -5 kW at a slope change rate of -5 kW / 0.1 s. is decreasing. The amplitudes of the supply current and arm current increase without overcurrent flowing. Further, the average value of the DC voltages v ^u _CP1 and v ^u _CN1 is regulated by the command voltage value 75V without a steady error. The DC component contained in the current i ^u _ZPN is suppressed to zero even during the transient state.

FIG. 15 shows an experimental waveform using the three-phase power converter 2 according to the sixth embodiment, and is a waveform when the instantaneous active power command value p ^* changes stepwise from −4 kW to −5 kW. . According to the experimental waveform, the DC link current idc shows a primary response to a change in the instantaneous active power command value p ^*, in which the time constant estimated from the experimental waveform is as short as 1.5 ms. Even in a state where the instantaneous active power command value p ^* changes stepwise, no direct current is generated in i ^u _ZPN .

The modular push-pull PWM converter (MPC) of the present invention can be applied to a battery power storage system. The present invention proposes a new control method for MPC and can achieve 6 degrees of freedom in the circulating current for 3-phase MPC. As a result, the average voltage in the first arm and the second arm can be regulated independently without interference, and a simple and reliable system can be provided. Experimental results obtained from a practical three-phase 200 V, 5 kW system show that the importance and efficiency of the converter is guaranteed.

FIG. 16 is a circuit diagram showing a three-phase power converter according to the seventh embodiment. In the seventh embodiment, a three-phase power converter is configured by using the single-phase power converter according to the fifth embodiment described with reference to FIG. In FIG. 16, single-phase power converters provided in the u-phase, v-phase, and w-phase, respectively, are denoted by reference numerals 1u, 1v, and 1w, and three-phase power configured by these single- phase power converters 1u, 1v, and 1w. The converter is denoted by reference numeral 2. In FIG. 16, the single-phase power converters 1v and 1w have the same circuit configuration as that of the single-phase power converter 1u, and therefore a detailed description of the circuit configuration is omitted. Hereinafter, although mainly the u phase will be described, the same applies to the v phase and the w phase. In this embodiment, the number of unit cells is 4 per arm as an example, 8 per phase, and thus 24 in the three-phase power converter 2. However, this numerical value is merely an example, It is not limited to this.

As described with reference to FIG. 6, the transformer 14 ′ in the fifth embodiment has an intermediate terminal of the transformer 14 in the single-phase power converter 1 according to the first embodiment described with reference to FIG. 1. A three-terminal coupling reactor 15 is provided at the position. That is, the three-terminal coupling reactor 15 is provided on the secondary winding of the transformer 14 '. In the three-phase power converter 2 according to the seventh embodiment, each phase in the three-phase transformer 24 is configured by using this transformer 14 '.

As described with reference to FIG. 6, the DC power source V _dc in the fifth embodiment is between the lower terminal 1ab of the first arm 12-P and the lower terminal 2ab of the second arm 12-N. Connected to. In the seventh embodiment, the DC power supply V _dc connected as described above to the single-phase power converter 1 in FIG. 6 is common to the phases u, v, and w as shown in FIG. The voltage value is twice that of the fifth embodiment shown in FIG. Here, by connecting the intermediate terminal (center tap) of the three-terminal coupling reactor 15 with Y, the voltage dividing capacitor that existed in the fifth embodiment shown in FIG. 6 can be removed.

In the eighth embodiment, a three-phase two-phase power converter is configured by providing two phases of the single-phase power converter 1 according to the first to fifth embodiments. A Scott transformer is used to provide two-phase single-phase power converters 1 according to the first to fifth embodiments and connect them to the system side.

FIG. 17 is a circuit diagram showing a Scott transformer used in the present invention. The Scott transformer 25 is composed of two single-phase transformers, an M seat transformer Tm and a T seat transformer Tt. Let N _{1 be} the number of turns of the primary winding of the M-seat transformer Tm, and N ₂ be the number of turns of the secondary winding. At this time, the intermediate terminal (center tap) of the primary side winding of the M seat transformer Tm is connected to the primary side winding of the T seat transformer Tt. The number of turns of the primary winding of the T-seat transformer Tt is √3N _1/2 . 18A and 18B are instantaneous voltage vector diagrams of the Scott transformer shown in FIG. As shown in FIG. 18A, when three-phase balanced sine wave voltages v ^u , v ^v and v ^w are applied to the primary winding of the Scott transformer, a two-phase sine wave having a phase difference of 90 degrees is applied to the secondary winding. Voltages v ^α and v ^β appear.

FIG. 19 is a circuit diagram showing a three-phase two-phase power converter according to the eighth embodiment. In the eighth embodiment shown in FIG. 19, a case where a three-phase two-phase power converter is configured using the single-phase power converter according to the first embodiment will be described as an example. The same configuration can be achieved using a single-phase power converter according to the example. In FIG. 19, single-phase power converters provided in the α-phase and β-phase are denoted by reference numerals 1α and 1β, respectively, and a three-phase two-phase power converter configured by the single-phase power converters 1α and 1β is denoted by the reference numerals This is represented by 3. In FIG. 19, the circuit configuration of the single-phase power converter 1β is the same as that of the single-phase power converter 1β, and therefore a specific description of the circuit configuration is omitted. Hereinafter, the α phase will be mainly described, but the same applies to the β phase. In this embodiment, the number of unit cells is set to 4 per arm as an example, 8 per 1 phase, and thus 16 in the three-phase power converter 2. However, this value is only an example. However, the present invention is not limited to this.

In the three-phase two-phase power converter 3 according to the eighth embodiment, the Scott transformer 25 is used by using the transformers 14 in the single-phase power converters 1α and 1β provided in the α-phase and β-phase. Each phase in is constituted. As an example, the turn ratio N ₁ : N ₂ between the primary winding and the secondary winding is √3: 1. In the secondary side α phase of the three-phase two-phase power converter 3 according to the eighth embodiment, the Scott transformer 25 described with reference to FIG. 17 has an intermediate on the secondary side winding of the M seat transformer Tm. A terminal (center tap) α ₁ is provided. Further, in the secondary β phase of the three-phase two-phase power converter 3, an intermediate terminal (center tap) is placed on the secondary winding of the T-seat transformer Tt of the Scott transformer 25 described with reference to FIG. ) Β ₁ is provided. As described with reference to FIG. 1, in the single-phase power converter 1, the negative terminal of the DC power source V _dc is connected to the third terminal c of the arm coupling portion 13, and the intermediate terminal of the transformer 14. The positive terminal of the DC power source V _dc is connected to T2-3. In the sixth embodiment, by connecting these intermediate terminals α ₁ and β ₁ to the positive terminal of the DC power source V _dc , As shown in FIG. 19, the α phase and the β phase are common.

Further, in the secondary side α-phase of the three-phase two-phase power converter 3, both terminals α0 and α1 of the secondary side winding of the M seat transformer Tm of the Scott transformer 25 are connected to the first arm 12-P. And the upper terminal of 12-N are connected. A three-terminal coupling reactor that is an arm coupling portion 13 is connected to the lower terminals of the first arms 12-P and 12-N. The negative terminal of the DC power source _Vdc is connected to the intermediate terminal of the three-terminal coupling reactor. The secondary side β phase of the three-phase to two-phase power converter 3 has the same configuration as the α phase.

As described above, in the multilevel power converter and the control method of the multilevel power converter of the present invention, the arm balance is compared with the conventional control method by independently controlling the DC voltage average value of each arm. Since the control could be eliminated, high-speed communication of DC voltage information between the arms became unnecessary, and restrictions on the MPC design could be eliminated.

1, 1u, 1v, 1w Single-phase power converter (multi-level power converter)
2 Three-phase power converter (multi-level power converter)
3 Three-phase two-phase power converter (multi-level power converter)
11-1,..., 11-M unit cell 12-P first arm 12-N second arm 13 arm coupling portion 14, 14 ′ transformer 15 three-terminal coupling reactor 24 three-phase transformer 25 Scott transformer 50 DC capacitor control device 51 Command value creation means 52 Control means 63 Switching control means 71 DC capacitor voltage control means 72 Output voltage command value creation means for each unit cell a first terminal b second terminal c third terminal BC bridge Cell CC Chopper cell D Free-wheeling diode S Semiconductor switching element SW Semiconductor switch T1-1, T1-2 AC input / output terminal T2-1, T2-2 Terminal terminal of secondary winding T2-3 Intermediate terminal V _dc DC power supply

Claims (13)

1. Two semiconductor switches connected in series, a DC capacitor connected in parallel to the two semiconductor switches, and an input / output of a current discharged from the DC capacitor or charged to the DC capacitor according to the switching operation of the semiconductor switch A unit cell having a terminal;
   The first and second arms comprising one unit cell or a plurality of unit cells cascaded to each other via the input / output terminals, wherein the first and second arms are the same number of the units. First and second arms having cells;
   An arm having a first terminal to which one end of the first arm is connected, a second terminal to which one end of the second arm is connected, and a third terminal to which one end of a DC power supply is connected A coupling part;
   A transformer having an AC input / output terminal on the primary side and an intermediate terminal on the secondary winding, wherein the first terminal of the first arm is connected to two terminal terminals of the secondary winding. A terminal to which the terminal is not connected and a terminal of the second arm to which the second terminal is not connected are respectively connected, and the intermediate terminal is connected to the third terminal of the DC power source. A transformer to which the unconnected terminal is connected;
   Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulation of the second arm Command value creating means for creating a current command value;
   With respect to the circulating current command values of the first and second arms, the current flowing through the first and second arms, the winding ratio of the transformer, and the alternating current applied to the alternating current input / output terminal A multi-level power converter comprising: control means for controlling so that circulating currents flowing through the first and second arms follow, respectively, with or without an AC component taking into account
2. The arm coupling portion includes the first terminal, the second terminal, and the third terminal that is an intermediate tap located on a winding between the first terminal and the second terminal. The multi-level power converter according to claim 1, comprising a three-terminal coupled reactor having the following.
3. The arm coupling portion includes two reactors connected in series to each other, the first terminal being one terminal of the two reactors connected in series and the other of the two reactors connected in series. The multilevel power converter according to claim 1, comprising two reactors including the second terminal that is a terminal and the third terminal that is a series connection point of the two reactors connected in series.
4. In each of the first arm and the second arm, a reactor connected to an arbitrary position between the unit cells cascade-connected to each other,
   The multilevel power converter according to claim 1, wherein in the arm coupling portion, the first terminal, the second terminal, and the third terminal are connected to each other.
5. Two semiconductor switches connected in series, a DC capacitor connected in parallel to the two semiconductor switches, and an input / output of a current discharged from the DC capacitor or charged to the DC capacitor according to the switching operation of the semiconductor switch A unit cell having a terminal;
   The first and second arms comprising one unit cell or a plurality of unit cells cascaded to each other via the input / output terminals, wherein the first and second arms are the same number of the units. First and second arms having cells;
   A first terminal to which a DC power source is connected between one end of the first arm, a second terminal to which another DC power source is connected between one end of the second arm, An arm coupling portion having a first terminal and a third terminal connected to the second terminal;
   A transformer having an AC input / output terminal on the primary side and a three-terminal coupling reactor on the secondary winding, wherein the DC terminal of the first arm is connected to two terminal terminals of the secondary winding. A terminal that is not connected to a power source and a terminal of the second arm that is not connected to the further DC power source are connected to each other, and is located on the winding between the terminals of the three-terminal coupling reactor. A terminal having a transformer connected to the third terminal;
   Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulation of the second arm Command value creating means for creating a current command value;
   With respect to the circulating current command values of the first and second arms, the current flowing through the first and second arms, the winding ratio of the transformer, and the alternating current applied to the alternating current input / output terminal A multi-level power converter comprising: control means for controlling so that circulating currents flowing through the first and second arms follow, respectively, with or without an AC component taking into account
6. Two semiconductor switches connected in series, a DC capacitor connected in parallel to the two semiconductor switches, and an input / output of a current discharged from the DC capacitor or charged to the DC capacitor according to the switching operation of the semiconductor switch A unit cell having a terminal;
   The first and second arms comprising one unit cell or a plurality of unit cells cascaded to each other via the input / output terminals, wherein the first and second arms are the same number of the units. A first arm and a second arm having a cell and connected to a DC power source between one end of the first arm and the second arm;
   A first capacitor connected to a terminal of the first arm to which the DC power supply is connected;
   A second capacitor connected to a terminal of the second arm to which the DC power supply is connected;
   A first terminal to which a terminal of the first capacitor to which the first arm is not connected is connected, and a terminal of the second capacitor to which the second arm is not connected are connected. An arm coupling portion having a second terminal and a third terminal connected to the first terminal and the second terminal;
   A transformer having an AC input / output terminal on the primary side and a three-terminal coupling reactor on the secondary winding, the two end terminals of the secondary winding having the first arm of the first arm 1 is connected to the terminal on the side where the capacitor is not connected, and the terminal on the side where the second capacitor is not connected to the second arm, and is positioned on the winding between the terminals of the three-terminal coupling reactor. The intermediate terminal to be connected to the transformer to which the third terminal is connected;
   Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulation of the second arm Command value creating means for creating a current command value;
   With respect to the circulating current command values of the first and second arms, the current flowing through the first and second arms, the winding ratio of the transformer, and the alternating current applied to the alternating current input / output terminal A multi-level power converter comprising: control means for controlling so that circulating currents flowing through the first and second arms follow, respectively, with or without an AC component taking into account
7. The command value generation means controls so that a value obtained by averaging the voltage values of all the DC capacitors in the first arm and the second arm follows a predetermined DC voltage command value. The multilevel power converter according to any one of claims 1, 5, and 6, wherein a circulating current command value is generated for each of the first and second arms.
8. The control means controls the voltage values of the DC capacitors in the first arm to follow the values obtained by averaging the voltage values of all the DC capacitors in the first arm, Further, control is further performed for causing the voltage values of the DC capacitors in the second arm to follow the values obtained by averaging the voltage values of all the DC capacitors in the second arm. The multi-level power converter according to claim 7.
9. The multi-level power converter according to claim 8, wherein the control means includes switching command means for switching the semiconductor switch in response to the follow-up control.
10. Each of the semiconductor switches is
    A semiconductor switching element that allows current to flow in one direction when on,
    A feedback diode connected in antiparallel to the semiconductor switching element;
    The multilevel power converter according to any one of claims 1 to 9, wherein
11. A three-phase multilevel power converter comprising three phases of the multilevel power converter according to any one of claims 1 to 10,
    The transformer in each multi-level power converter constitutes each phase in a three-phase transformer having a star connection on the primary side and an open star connection on the secondary side,
    The multi-level power converter is connected to the common DC power source,
    A three-phase multi-level power converter characterized by that.
12. A three-phase two-phase multilevel power converter comprising two phases of the multilevel power converter according to any one of claims 1 to 10,
    The secondary winding of the transformer in each multilevel power converter constitutes a winding of each phase on the secondary side of the Scott transformer,
    The multi-level power converter is connected to the common DC power source,
    A three-phase two-phase multilevel power converter characterized by that.
13. The multilevel power converter according to any one of claims 1, 5 and 6,
    When the winding ratio of the primary side and the secondary side of the transformer is N ₁ / N ₂ and the current input to the AC input terminal of the transformer is i _ac , the circulating current of the first arm and the second The circulating current of the arm
    i _ZP = i _P + (N ₁ / N ₂ ) × i _ac
    i _ZN = i _N- (N ₁ / N ₂ ) × i _ac
    Defined in
    Based on the voltage value of the DC capacitor in the first arm and the voltage value of the DC capacitor in the second arm, the circulating current command value of the first arm and the circulation of the second arm Create a current command value and
    With respect to the circulating current command values of the first and second arms, the current flowing through the first and second arms, the winding ratio of the transformer, and the alternating current applied to the alternating current input / output terminal A control method for a multi-level power converter, characterized in that control is performed so that circulating currents flowing through the first and second arms follow, with or without an AC component taking into account

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