JP2000037078A - Multilevel power converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To balance the voltage of respective capacitors quickly while reducing the facility capacity by providing a plurality of auxiliary AC/DC power converters having DC side connected between the terminals of each capacitor and a transformer having a plurality of windings coupled magnetically each other and connected with AC side of the auxiliary AC/DC power converters. SOLUTION: Auxiliary AC/DC power converters CONVj, CONVk are switched while shifting the phase by an angle α. A trapezoidal AC current flows because of the leakage inductance between the windings Wj, Wk of the transformer TR. Power is conducted between the phase lead side and the phase lag side and a DC current produced through synchronous rectification of the trapezoidal current is fed from the auxiliary AC/DC power converters CONVj, CONVk. Consequently, power can be interchanged between arbitrary DC stages and the DC voltage can be balanced quickly. Furthermore, capacity of the transformer TR can be reduced by a factor (Ip/ΔI) in the formula representing the size of transformer, or the like, Φm (number of crossing flux of winding).Irms (effective current value of winding)=(E.Irms/(4/f))/(Ip/ΔI).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a multi-level AC / DC power converter for interchanging power between a DC power supply and an AC power supply.

[0002]

2. Description of the Related Art A conventional multi-level AC / DC of this kind is used.
FIG. 10 shows a generalized circuit diagram of the inter-power converter. In the figure, E ₁ to En are DC power supplies, C ₁ to Cn are n DC capacitors (hereinafter simply referred to as capacitors) connected in series between the total terminals PP and NN of the n DC power supplies,
S _P1 to S _P n and S _N1 through S _N n is the total DC terminals P
A solid state switch which is n switching elements respectively connected in series between P and NN and an AC terminal AC
(Hereinafter simply referred to as a switch), D _1P , D _1N to D ₍ n
_{-1) P, D (n -1} ) N is the series connection point of the switch P ₁ to Pn
_-1 and a clamp diode (hereinafter simply referred to as a diode) connected to N ₁ to Nn _-1 .

In the above-mentioned conventional circuit, out of a total of 2n switches, n switches connected in series with each other are turned on, and the other switches are turned off. When the series switch group to be turned on is sequentially changed from the positive potential side to the negative potential side, the potential of the AC terminal AC changes to n + 1 levels. For this reason, it is called a multi (n + 1) level converter. In the multi-level AC / DC power converter (hereinafter simply referred to as a converter), the current flowing into and out of the AC terminal AC changes to bipolar, and the output terminal is connected to the total DC terminals PP and NN. Not exclusively. Therefore, the DC current flowing through each DC power supply is not uniform. If the associated switch is not conducting, the DC current will be negative due to zero or current returning from the diode. That is, the power and DC current between the DC stages become uneven. Therefore, each DC
There is no independent DC power supply E ₁ to En in the stage, and the operation cannot be performed by sharing the voltage only by the capacitor. Normally, DC power is supplied collectively by two terminals or two lines, and a three-wire power supply method having a neutral line is also limited to a case where DC power transmission or a multi-voltage power supply is required. Even in DC transmission, it is necessary that one pole side can operate independently. For this reason, the usage has been extremely limited.

FIG. 11 shows a countermeasure circuit for improving the problem of the basic circuit shown in FIG. This circuit is provided to not the capacitor C ₁ separately from the converter circuit of FIG. 10 corresponding to Cn. In FIG. 11, the converter circuit is omitted. In the figure, to no San and Sb ₁ to no Sa ₁ Sb _{(n -1)} is a chopper switch, to no L ₁ L _(n
-1) is a DC reactor. If the DC stage number n is an even number, termination is performed at the switch San of the group a, and if the DC stage number n is odd, the termination is performed at the switch Sb ₍ n− ₁₎ of the group b.

FIG. 12 is a principle diagram for explaining the operation of the countermeasure circuit according to the prior art. In FIG. 12A, the switches S ₁ and S ₂ are alternately turned on and off at the same time ratio in a steady state. If the transient or reactor loss is not negligible, control can be performed with the time changed by ± Δt. Voltage V _L applied to the reactor L is expressed by a waveform shown in FIG. (B). Here, t ₁ and t ₂ are the conduction times of the switches S ₁ and S ₂ , E ₁ and E ₂ are the voltages of the capacitors C ₁ and C ₂ , and T is the switching period. Here, when the DC voltage becomes unbalanced, a DC voltage component appears in the reactor L, and the DC current Idc flows. Now, E ₁ > E ₂
Then, the DC current Idc flows in the direction of the arrow shown in the figure, and the current waveform of the reactor L at this time is shown in FIG. Thus, the capacitor C ₁ is the average current I ₁ of the switch S ₁
(About Idc / 2) by discharging, the capacitor C ₂ is (are charged the polarity becomes negative) is discharged by the average current I ₂ of the switch S ₂ (about -Idc / 2). With the above operation, the DC voltage is balanced. When E ₁ <E ₂ , the polarity of the current flowing through the reactor L changes, and the DC voltage is similarly balanced. In other words, if the converter requires an unbalanced DC current Idc 'for the series connection of the capacitors, the necessary DC current Idc is supplied via a chopper and a DC reactor.

[0006]

In this conventional countermeasure circuit, since a DC voltage balancing operation is performed between adjacent capacitors, when an imbalance occurs between capacitors at distant potentials, the power is immediately reduced. Cannot be exchanged, and balancing is effected through the action of multiple stages of choppers, which may result in poor response speed. In particular, there is a problem that the response speed for balancing the capacitor close to the positive total terminal PP and the capacitor close to the negative total terminal NN is low. Further, there is a problem that the required DC reactor under the same operating frequency condition increases, and the required capacity of the switch also increases. The specific calculation contents of this capacity will be described later for convenience of explanation.

In addition, in order to simplify the operation by omitting the transformer, if it is directly connected to an AC power system, DC transmission and B
There is a problem that a zero-phase current is generated in an AC / DC-DC / AC conversion system such as a TB. This problem will not be described in detail because no prior art can be found, but in short, three-phase converters have often used the action of eliminating harmonics between lines, but the AC system is grounded. If this is the case, a problem arises in that a failure occurs in the grounding system. Due to the above problems, the range of application has been limited despite the good output voltage waveform of the multilevel AC / DC power converter.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The voltage of each DC stage can be quickly balanced, and the capacity of a reactor and a switch can be reduced. It is an object of the present invention to obtain a multilevel power converter capable of expanding a range.

[0009]

SUMMARY OF THE INVENTION A multi-level power converter according to the present invention is connected to positive and negative terminals connected to a first power supply of a DC system, and to a second power supply of an AC or DC system. An output terminal, a series-connected body of a plurality of switching elements connected between the positive terminal and the output terminal and between the output terminal and the negative terminal, connected between the positive terminal and the negative terminal A series connection of a plurality of capacitors, and a clamp diode connected between the series connection point of the switching element and the series connection point of the capacitor, by turning on and off the switching element, from the output terminal, In a multi-level power conversion device configured to obtain a plurality of levels of potential output between the potential of the positive terminal and the potential of the negative terminal, A plurality of auxiliary AC / DC power converters connected between terminals of each capacitor; and a plurality of windings magnetically coupled to each other and connected to the AC side of each of the auxiliary AC / DC power converters. It is equipped with a transformer.

The transformer of the multi-level power converter according to the present invention includes a plurality of primary windings connected to the AC side of the auxiliary AC / DC power converter, and a plurality of primary windings connected to the plurality of primary windings. Each of the groups is provided with a plurality of secondary windings which are magnetically coupled to the primary windings of these groups and connected to each other.

Further, the multi-level power converter according to the present invention comprises: means for detecting the voltage of each capacitor and calculating a DC voltage command value for each capacitor from the sum thereof; Means are provided for shifting the operation phase of each auxiliary AC / DC power converter with respect to a predetermined reference phase so that the command value matches.

Further, the multi-level power converter according to the present invention comprises: a positive terminal and a negative terminal connected to a first DC power supply; an output terminal connected to a second AC or DC power supply; A serially connected body of a plurality of switching elements connected between the positive terminal and the output terminal and between the output terminal and the negative terminal, four or more connected between the positive terminal and the negative terminal A series connected body of capacitors, and a clamp diode connected between the series connection point of the switching element and the series connection point of the capacitor, and by controlling the on / off of the switching element, from the output terminal, In a multi-level power converter configured to obtain a plurality of levels of potential output between the potential of the positive terminal and the potential of the negative terminal, adjacent to each other A plurality of auxiliary AC / DC power converters each including a pair of switching elements connected in series with each other and having a DC side connected between both terminals of each of the capacitor pairs; A transformer having a plurality of windings that are magnetically coupled and connected between an intermediate connection point of each of the capacitor pairs and an AC terminal of the intermediate connection point of each of the switching element pairs.

Further, in the multilevel power conversion device according to the present invention, when the number of series of the capacitors is an odd number, a capacitor pair is constituted by one of the capacitors and a capacitor adjacent to one of the capacitors, and 1
In this configuration, a capacitor pair is constituted by the capacitors and the capacitor adjacent to the other of the capacitors.

Further, the multi-level power converter according to the present invention comprises: a positive terminal and a negative terminal connected to a first DC power supply; an output terminal connected to a second AC or DC power supply; A series connection of a plurality of switching elements connected between the positive terminal and the output terminal and between the output terminal and the negative terminal, and an odd number of 5 or more connected between the positive terminal and the negative terminal A series connection of the capacitors, and a clamp diode connected between the series connection point of the switching element and the series connection point of the capacitor, and by controlling the switching element on and off, from the output terminal, In a multi-level power conversion device configured to obtain a plurality of levels of potential output between the potential of the positive terminal and the potential of the negative terminal, The capacitors except for the one at the center in the connection direction of the capacitors are formed by a pair of capacitors adjacent to each other and a pair of switching elements connected in series, and the DC side thereof is connected between both terminals of each of the capacitor pairs. A plurality of connected first auxiliary AC / DC power converters, a second auxiliary AC / DC power converter whose DC side is connected between terminals of the one capacitor, and magnetically coupled to each other And a plurality of windings connected between the intermediate connection point of each of the capacitor pairs and the AC terminal of the intermediate connection point of each of the switching element pairs and on the AC side of the second AC / DC power converter. It is equipped with a transformer.

Further, in the multilevel power converter according to the present invention, a gap is provided in a magnetic path constituting the transformer.

Further, the multi-level power converter according to the present invention detects the voltage of each capacitor pair (including individual capacitors other than the capacitor pair, including the capacitor, the same applies hereinafter) and detects each voltage from the sum thereof. Means for calculating the DC voltage command value of the capacitor pair, and the operation phase of each auxiliary AC / DC power converter is set to a predetermined reference phase so that the detected voltage value of each capacitor pair matches the DC voltage command value. Means for shifting with respect to.

Further, the multi-level power converter according to the present invention includes a plurality of multi-level power converters, and uses a common DC system first power source to interconnect a plurality of different AC system second power sources. In the multi-level power converter that performs power interchange in the above, the auxiliary AC / DC power converter and the transformer are shared by each of the multi-level power converters.

Further, in the multilevel power converter according to the present invention, the auxiliary AC / DC power converter is operated in a square wave mode.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a circuit diagram of a multilevel AC / DC power converter according to Embodiment 1 of the present invention. Note that multi-level AC / DC
Since the general form of the inter-power conversion device has been described in detail in FIG. 10, the main conversion circuit portion is omitted from the description. In FIG. 1, Cj and Ck are arbitrary j-th and k
The capacitor connected to the DC stage, CONV
j and CONVk are auxiliary AC / DC power converters (hereinafter simply referred to as auxiliary converters) in which DC terminals are connected to capacitors Cj and Ck, and TR is connected to an AC terminal of the auxiliary converter and magnetically coupled to each other. A transformer having windings Wj and Wk. _{Incidentally, S 11, S 12, S} 21, S 22 is a switch of the auxiliary transformer.

The auxiliary converters CONVj and CONVk are well-known single-phase bridge-type square-wave inverter converters. In order to exchange power between the DC stages, switching is performed by shifting the phase by a slight angle α, and the waveform at this time is shown in FIG. The voltage V of the j-th auxiliary converter CONVj
j is the angle α from the voltage Vk of the kth auxiliary converter CONVk.
Only the case where the phase is advanced is shown. Since there is leakage inductance between the windings Wj and Wk of the transformer TR, the AC current changes due to the voltage difference during the phase shift period, and the trapezoidal AC current flows. The phase leading side supplies power and the phase lagging side receives power, and the DC current of the auxiliary converter is a current obtained by synchronously rectifying the trapezoidal wave current. Its value is approximately equal to the peak value of the alternating current. As described above, power can be interchanged between arbitrary DC stages, and DC voltage can be quickly balanced.

Next, the transformer TR required for the present invention
(Conventionally, DC reactor L is equivalent) and switch S ₁₁
And the like will be described in comparison with the conventional case. First, in the conventional case (see FIG. 12), the size of the DC reactor and the equivalent k
VA is the maximum number of flux linkages of the winding Δm and the winding current effective value Ir
ms. The former is represented by the product of the inductance L and the current peak value Ip. That is, Фm · Irms = L · Ip · Irms (1) The required inductance L is a pulsating component of the reactor current ± △ I
And the operating frequency f and the DC voltage E per DC stage, and are expressed by the following equation. L △ I = (T / 4) ・ E = E / (4 ・ f) ∴L = E / (4 ・ f △△ I) (2) Equation (1) From (2), it is possible to express the size of transformers,
rms is represented by the following equation. Фm · Irms = (E · Irms / (4 · f)) · (Ip / △ I) (3)

On the other hand, according to the present invention, the product of the flux linkage number Δm related to the size of the transformer and the effective current Irms is calculated as follows. Note that ΔP is electric power transferred between DC stages. Number of magnetic flux linkages of winding Фm = (T / 4)） E = E / (4 ・ f) Effective value of winding current Irms = △ P / E = I Accordingly, ФmФIrms is given by the following equation. Фm · Irms = E · Irms / (4 · f) (4) Therefore, in the method of the related art, it was multiplied by (Ip / △ I) (Equation (3)). , This magnification is not applied. Therefore, in the conventional method, ΔI / Idc is 20%
If you try to make it about, it will take 6 times the coefficient,
In the present invention, only one time is required. That is, the transformer of the present invention has a remarkable effect of being reduced to a fraction of that of the DC reactor of the prior art.

On the other hand, in the conventional case, the voltage Voff applied to the switch and the half-period average value (approximate peak value) I of the current I
In order to evaluate the required capacity of the switch with the capacity VAs obtained by multiplying the required number by s, the following calculation is made. At this time, the power supplied from one DC stage is ΔP, the power required by the other DC stage is ΔP, and the DC voltage of each stage is E. DC 1-stage DC current I = △ P / E Reactor current average value Idc = 2 ・ I Switch current half-cycle average value Is = Idc = 2 △△ P / E switch off state voltage Voff = 2 ・ E switch required Number (n: even number) Ns = n + (n−2) Accordingly, the required switch capacitance VAs is given by the following equation. VAs = {n + (n−2)} · 2 · E · 2 · △ P / E = 8 · (n−1) · △ P ················ (5)

On the other hand, according to the present invention, the required capacity of the switch is calculated as follows. Switch average half-cycle average value Is = I = △ P / E Switch off voltage Vs = E Required number of switches Ns = 4n Accordingly, required capacitance VAs is given by the following equation. VAs = 4 · n · ΔP (6) That is, when the number of stages n is large, the switch capacity is reduced to about half of the case of the conventional technology (Equation (5)). A very remarkable effect of being reduced is obtained. Further, by operating the auxiliary converter in the square wave mode without using the PWM control sine wave output converter, pulsation of the DC side current is reduced, and an effect of reducing switching loss is obtained.

Embodiment 2 FIG. 2 is a circuit diagram of a second embodiment according to the present invention. Note that multi-level AC / D
The general form of the C-to-C power converter has been described in detail with reference to FIG. In the figure, CONVj and CONVk are three-phase auxiliary converters. Transformer as shown in FIG. (C), divided into a primary winding _{W 1, W 2, W 3} , W 4 ·· into a plurality of groups, where, W ₁ and W _2, W ₃ and W ₄ Are defined as one group, and the secondary windings W ₁₁ , W ₁₂ ,.
.. May be constituted by a plurality of transformers TR1, TR2,... And the respective secondary windings may be connected to each other. The method of coupling between the windings via the secondary winding shown in FIG. (C) can also be implemented with a single-phase auxiliary converter. This makes it easier to adjust the leakage inductance when a large number of windings are used.

When the three-phase auxiliary converter is operated with a square wave, the Y-phase voltage is as shown in the upper waveform of FIG. The voltage Vj of the j-th auxiliary converter is the voltage Vk of the k-th auxiliary converter
The case where the phase is further advanced by the angle α is shown. Since there is leakage inductance between the windings Wj and Wk of the transformer, the alternating current changes due to the voltage difference during the phase shift period, and a two-step trapezoidal alternating current flows. The phase leading side supplies power and the phase lagging side receives power, and the DC current of the auxiliary converter is a current obtained by synchronously rectifying the trapezoidal wave current. At this time, since the DC current is synchronously rectified for three phases, the pulsation of the DC current is extremely small even if the AC current for one phase pulsates.
As described above, power can be interchanged between arbitrary DC stages and DC voltage can be quickly balanced as in the first embodiment. Also, if the three-phase converter has the same VA capacity as the single-phase converter, the switch capacity is also the same. If the transformers have the same capacity, the sum of Δm · Irms will be the same. Therefore, the same effect as described above can be obtained.

Embodiment 3 Third Embodiment FIG. 3 shows a circuit diagram of a third embodiment according to the present invention. Note that multi-level AC / D
The general form of the C-to-C power converter has been described in detail with reference to FIG. 3, the capacitor C ₁ -C ₄ is a pair of capacitors C ₁ and each capacitor pair C ₂ and C ₃ and C ₄ adjacent to each other. And CONV ₂₁ and CO
The NV ₄₃ has an auxiliary AC / DC power converter (hereinafter simply referred to as an auxiliary converter) whose DC side is connected between both terminals of each of the capacitor pairs (C ₁ , C ₂ ) and (C ₃ , C ₄ ). ) To form a so-called half-bridge comprising _two switches S ₁ and S ₂ and _two switches S ₃ and S ₄ connected in series. TR is an intermediate connection point between each pair of capacitors (C ₁ , C ₂ ) and (C ₃ , C ₄ ) and an intermediate connection between the switch pair (S ₁ , S ₂ ) and (S ₃ , S ₄ ) of the auxiliary converter. a transformer having a winding W ₁ and W ₂ which are connected magnetically coupled to each other between the AC end of the point. As described above, a half-bridge type auxiliary converter is provided for every two DC stages. In the conventional case, as shown in FIG. 11, the switch of the group b on the left side is necessary, but it is not necessary in the present invention. Further, the windings are connected via a magnetic core.

Next, the operation will be described. The switch pairs (S _1, S ₂₎ and the winding W _1, direct current component Idc ₁ flows through the windings W ₁ when the difference is generated in the DC voltage E _1, E _2.
Similarly, by the switch pair (S ₃ , S ₄ ) and the winding W ₂ , D
When a difference occurs between the C voltages E ₄ and E ₃ , a DC current component Idc ₂ flows through the winding W ₂ . Thus, DC voltage E ₁ of the example of the prior art and also the capacitor C _1, C _2, E ₂ is equilibrated. Similarly, the DC voltage E ₄ of the capacitors C ₄ and C ₃ ,
E _{3 is} also equilibrated. At this time, multi-level AC / DC
The operation principle of the power converter between
In a winding having a symmetrical positional relationship with respect to the intermediate potential point C ₀ (or the intermediate DC stage) of the entire DC voltage, the DC current component Idc ₁
And Idc ₂ flow in opposite directions. That is, in the case of the operation of sending power to the AC side, it is necessary to send power from the positive and negative ends where surplus power is supplied to the central portion where power is insufficient, and in the case of regenerative operation, power is insufficient from the central portion where power is excessive. Must be sent to the positive and negative ends. Therefore, the power interchange by chopper operation as the positive side half and the negative half acts symmetrically, a switch S ₁ and switch S ₄ is operated in phase, in phase with the switch S ₂ and the switch S ₃ Make it work.
Accordingly, the windings W ₁ and W ₂ of the transformer also are the polarity reversed and the negative half positive half.

[0029] On the other hand, as the auxiliary converter operation coupled with the AC through a winding W _1, W _2, by operating with a phase difference alpha, alternating current component Iac _1, Iac ₂ each winding W ₁ , it flows through the winding W _2. By this AC conversion operation, a group of the capacitor pair (C ₁ , C ₂ ) and the capacitor pair (C
Electricity can be exchanged between the groups ₃ and C ₄ ). As a result, power interchange and DC voltage balancing between the four DC stages are realized with the two auxiliary converters.

Next, the above operation will be described based on switch currents (corresponding to capacitor currents) Is ₁ to Is ₄ determined by the following equation by introducing a switch function. This relationship is to no current Is ₁ of the switch become known from Is _4.
This equation is shown below. Is ₁ = St ₁ Idc ₁ + St ₁ Iac ₁ Is ₂ = -St ₂ Idc ₁ -St ₂ Iac ₁ Is ₃ = -St ₃ Idc ₂ -St ₃ Iac ₂ Is ₄ = St ₄ Idc ₂ + St ₄ Iac ₂ , St ₁ to St ₄ are switch functions that become “1” when the respective switches S ₁ to S ₄ are turned on. Further, Idc ₁ and Idc ₂ are the windings W ₁ and W _{2 as described above.}
And contributes to voltage balancing between the capacitors C ₁ and C _{2 and} between C ₃ and C ₄ . Iac ₁ , Iac
Reference numeral ₂ denotes the same alternating current component, which contributes to voltage balancing between the pair of capacitors (C ₁ , C ₂ ) and (C ₃ , C ₄ ).

First, referring to FIG. 4, capacitors C ₁ and C ₂
The operation of voltage balancing with the above will be described. Both switches S
_{When the operation} is performed with the energization time of ₁ and S ₂ equal (t ₁ = t ₂ ), the operation is substantially the same as that described in the related art, so that the constraint of t ₁ = t ₂ is released here. The description will be made on the assumption that the conduction time ratio is actively changed for control. As shown in FIG. 4 (c), when the _{t 1 E 1> t 2 E} 2, the windings W _1, the direct current component Idc ₁ flows in the direction shown in FIG. 3, the switch current Is ₁ capacitor C ₁ is discharged, the capacitor C ₂ is charged by the switch current is _2. Thereby, the voltages E ₁ and E _{2 of} the capacitors C ₁ and C ₂ are obtained.
Equilibrates. It should be noted here that the voltage balancing response can be enhanced by actively changing the ratios t ₁ and t ₂ . FIG. 4D shows the switch currents Is ₁ and Is ₂ when t ₁ E ₁ <t ₂ E _{2. In} this case,
The capacitor C ₁ is charged, the capacitor C ₂ is discharged,
The two voltages E ₁ and E ₂ equilibrate rapidly.

Next, the operation of voltage balancing between the capacitor pair (C ₁ , C ₂ ) and the capacitor pair (C ₃ , C ₄ ) will be described with reference to FIG. The figure shows (E ₁
+ E ₂ )> (E ₃ + E ₄ ) and the auxiliary converter CO
The NV ₄₃ is operated with the phase delayed by α with respect to the CONV ₂₁ so that Iac ₁ > 0 and Iac ₂ <0. Accordingly, as shown in FIG. (G), the capacitor C ₁ is discharged by the switch current Is _1, capacitor C ₂ by the switch current Is ₂ discharges. That is, the capacitors C ₁ and C ₂ are both discharged, and the voltage drops. Further, as shown in FIG. (H), the capacitor C ₄ by the switch current Is ₄ is charged, the capacitor C ₃ by the switch current Is ₃ is charged. That is, the capacitors C ₃ and C ₄ are both charged, and their voltages rise. Therefore, the voltages of both capacitor pairs are balanced.

When (E ₁ + E ₂ ) <(E ₃ + E ₄ ), the operation phase of the auxiliary converter CONV ₄₃ is changed to CON.
By going beyond that of V ₂₁ , the capacitors C ₁ ,
Both were charged C _2, thereby balancing the voltages of both capacitors pairs by which both discharge the capacitor C _3, C _4.

As described above, it is understood that the on / off control of each of the switches S _{1 to} S ₄ allows the DC current and thus the power to be interchanged between the four DC stages. Since both power exchange through AC and power exchange through chopper action can be performed, the effect of simplifying the auxiliary converter circuit can be obtained. In consideration of the power interchange by the DC current component Idc, it is better that the magnetic core can intentionally increase the exciting current to store the magnetic energy, and the power interchange ability by the chopper effect and the power interchange ability by the AC operation can be safely achieved. Can be maintained. Specifically, a structure in which a gap is provided in the magnetic path of the iron core forming the transformer TR is adopted.

Embodiment 4 FIG. FIG. 6 is a circuit diagram of a fourth embodiment according to the present invention. Note that multi-level AC / D
The general form of the C-to-C power converter has been described in detail with reference to FIG. Embodiment 4 shows an embodiment in which DC is generally divided into n stages. One switch per stage
And one winding W of the transformer TR is provided for every two stages, and they are all coupled. At this time, the arrangement is made so that the positive and negative halves are symmetrical. When the number of stages n is an odd number (5 or more), a bridge-type auxiliary converter CONVc is provided in the DC stage to which the central capacitor Cc is connected in order to achieve power interchange by the AC coupling of the first and second embodiments. To couple the transformer winding Wc with other windings. As a result, power interchange in the central stage that handles large power can be executed with all DC stages. When the number of stages n is an even number, the symmetry can be made in positive and negative half-minutes as in FIG.

As a configuration different from that in FIG. 6 when the number of stages n is an odd number, for example, a capacitor pair (Cc _-1 , Cc _-1) is composed of a capacitor Cc in the center stage and a capacitor Cc _-1 one stage above it
c), and the capacitor Cc in the center stage and the capacitor Cc ₊ 1 one stage below it form a capacitor pair (C
c, Cc ₊₁ ), and these two capacitor pairs (C
The half-bridge type auxiliary converter and the winding according to the third embodiment may be provided for each of (c ₋₁ , Cc) and (Cc, Cc ₊₁ ).

In addition, it is possible to control the power interchange by the chopper operation by actively changing the conduction time ratio of the switches S ₁ to Sn.

The operation is the same as that of the third embodiment, and electric power can be exchanged between multiple stages. Naturally, the same effect is obtained, and an effect that can cope with an arbitrary number n of DC stages is obtained.

Embodiment 5 Next, a DC voltage balancing control device in a multi-level AC / DC power converter generally including an n-stage capacitor will be described as a fifth embodiment with reference to FIG. Since the general form of the multilevel AC / DC power converter has been described in detail in FIG. 10 and the above-described embodiment, the main conversion circuit portion and the auxiliary converter will be omitted with reference to them. Embodiment 5
FIG. 9 is a DC voltage balancing control block diagram suitable for a case where an auxiliary converter CONV is provided for each DC stage as in the first and second embodiments. In the figure, Vc ₁ , V
c _2, Vck, ·· Vcn the voltage of each DC stage, REF voltage Vc _1, Vc ₂ of the DC stage, Vck, a sum from · · Vcn example by summation means SUM, for example, an average value in the division unit DIV And outputs a DC voltage command value Vcr of each DC stage. AVR ₁ , A
VR _2, AVRk, ·· AVRn comparison adjustment means for comparing each DC voltage of the DC voltage command value Vcr and the DC _{stage, δ 1, δ 2, δk} , ·· δn is the output of the comparison adjusting means, each It is a phase adjustment signal (change from the reference phase θ) of the auxiliary converter. A ₁ , A ₂ , Ak,... An are auxiliary converters CONV ₁ , CONV ₂ , CONVk,.
n (not shown) is a reference phase θ operating at a predetermined frequency
... Δn with respect to the phase adjustment signals δ ₁ , δ ₂ , δk,.

With the above configuration, the DC voltages of the respective stages are compared by using the average value of the DC voltages of the respective stages as a command, and the phase adjustment signals δ ₁ , δ ₂ , δk corresponding to the unbalance of the DC voltages of the respective stages are obtained. ,
・ Δn is obtained. These are adjusted by A ₁ , A ₂ , Ak,
··· Input to An and add or subtract based on the reference phase θ,
The above-mentioned auxiliary converters are operated at the phases of δ ₁ , θ + δ ₂ , θ + δk,. As a result, the interchange power between the auxiliary converters is adjusted, and the DC voltage at each stage can be averaged. That is, it can be balanced.

Although the DC voltage is balanced in the above description, the total sum of the DC voltages has a degree of freedom as an independently controllable amount. Therefore, there is obtained an effect that the main control (for example, total DC voltage control) of the converter which is performed separately does not interfere with the main control and the main control can be freely performed separately.

Embodiment 6 FIG. A circuit diagram of a sixth embodiment according to the present invention is shown in FIG. Note that multi-level AC / DC
Since the general form of the inter-power converter has been described in detail in FIG. 10 and the above-described embodiment, the main conversion circuit portion and the auxiliary converter will be omitted by quoting them. The sixth embodiment shows a DC voltage balancing control block diagram suitable for a case where a half-bridge type auxiliary converter CONV is provided for each adjacent DC stage as in the third and fourth embodiments. In the drawing, A ₂₁ , A ₄₃ ,..., An ₍ n ₋₁₎ are means for calculating the sum of the voltages of the capacitors of adjacent DC stages (for example, means for detecting the voltage between both ends of a capacitor pair, or each capacitor). Means for adding the voltage detection value of
F is the sum of the outputs of the voltage detecting means A ₂₁ , A ₄₃ ,... An ₍ n _-1) by the summing means SUM, calculates the average value by the dividing means DIV, and calculates the DC voltage command value Vc of each capacitor pair.
Command value generating means for outputting r. AVR ₂₁ , AVR
_{A 43, ··· AVRn (n -1} ) is comparable means for comparing each of the sums of voltages of the DC stage capacitor and the DC voltage command value Vcr _{adjacent, δ 21, δ 43, ··} δn (n -1 ₎ Is the output of the comparison and adjustment means, which is the phase adjustment signal (change from the reference phase θ) of each auxiliary converter. A _21b , A _43b , A
n _{(n -1) b} auxiliary converter CONV _21, CONV _43, ··
CONVn ₍ n ₋₁₎ (not shown) is operated at a predetermined frequency with respect to a reference phase θ, and the phase adjustment signals δ ₂₁ , δ ₄₃ ,
... An adjusting means for adjusting by .delta.n ₍ n- ₁₎ .

In the summation means SUM and the dividing means DIV for calculating the average value in the command value generation means REF, when the number of DC stages n is even, the denominator is used because the number of DC stages for voltage balancing is n. M is n. When n is an odd number, it is often unnecessary to balance the intermediate stage. In this case, the number M of DC stages to be balanced may be n-1.

With the above configuration, the DC voltages of the two stages are compared using the average value of the DC voltages of the two stages (corresponding to one capacitor pair) as a command, and the unbalanced DC voltage of each stage is determined. The phase adjustment signals δ ₂₁ , δ ₄₃ ,... Δn ₍ n ₋₁₎ are obtained. These are added and subtracted by A _21b , A _43b ,... An ₍ n _{-1) b}
And add or subtract based on the reference phase θ, θ + δ ₂₁ , θ
The respective auxiliary converters are operated at a phase of + δ ₄₃ ,... Θ + δn ₍ n _-1) . As a result, the interchange power between the auxiliary converters is adjusted, and the DC voltage at each stage can be averaged.
That is, it can be balanced. Note that the voltage balancing in the adjacent DC stages is performed by the change in the DC current flowing through the transformer winding W itself as described above, so that the feedback control is unnecessary. Of course, active feedback control may be performed.

In the above description, the DC voltages are balanced, but the total sum of the DC voltages has a degree of freedom as an independently controllable amount. Therefore, the same effect as in the sixth embodiment can be obtained in that the main control (for example, total DC voltage control) of the present converter which is performed separately does not interfere with the main control and the main control can be performed freely.

Embodiment 7 FIG. FIG. 9 shows a circuit diagram of a seventh embodiment according to the present invention. Note that multi-level AC / D
Since the general form of the C-to-C power converter has been described in detail in FIG. 10 and the above-described embodiment, the main conversion circuit portion and the auxiliary converter are omitted or conceptually shown with reference to them. In the seventh embodiment, a load Loa such as drive control of an AC motor is used.
9 shows an example of application to an AC / DC-DC / AC conversion system for supplying power to a power supply d. In the drawing, Vs is an AC power supply system, Xs is a reactance or AC reactor of a transformer not shown, MLC ₁ is a first multi-level AC / DC power converter in which an AC terminal is connected to the AC power supply system Vs, In the MLC _2, the DC line of each stage has the converter MLC _1.
Second multilevel AC / DC between the power converter, C ₁ to Cn are DC each stage to be used in common to both converter MLC _1, MLC ₂ capacitors connected in parallel to the DC line of each stage of the, CONV ₁ to CONVn the above auxiliary converter, AVR equilibration control means of the DC voltage of each stage by the auxiliary transducer, PT ₁ to PTn is DC voltage detection means for each stage, Load AC of the second converter MLC ₂ This is an AC load connected to the terminal.

The capacitor and the auxiliary converter for balancing the DC voltage of each stage and its control can be shared by both converters. Since the DC lines of each stage are connected in parallel, the power interchange capacity of the auxiliary converter for voltage balancing can be reduced because power can be interchanged directly between the two converters for each stage. Second converter M
The LC ₂ can output a good output voltage waveform to an AC load, and is suitable for supplying power to a high-voltage load where insulation is a problem.
Further, since the first converter MLC ₁ also maintaining good voltage waveform to the AC power supply system easy, harmonic failure is reduced. The load AC system is a second AC power supply system Vs indicated by a dotted line.
_In the case of ₂ , it is suitable for providing power interchange between both AC systems and adjusting reactive power for the AC system.

In this case, as described above, the distribution of the power distribution unevenly appearing in the capacitors in the series stage has the opposite symmetry depending on the direction of the power flow. Therefore, as shown in FIG. 9, by sharing the DC system of the two multi-level AC / DC power converters in which the power flow between AC / DC is in the opposite direction, the voltage balancing of each capacitor is achieved. Becomes easier.

FIG. 9 shows two multi-level AC / D units.
It is provided with inter-C power converters MLC ₁ and MLC ₂ , and the DC system is shared, and power is exchanged between two AC systems.
/ DC power converter, and the DC system can be shared, and power can be interchanged in a plurality of different AC systems.

In each of the above embodiments, the multi-level AC / DC power converter for performing power conversion between the first power supply of the DC system and the second power supply of the AC system has been described. Although the present invention no longer has the symmetry with respect to the center stage described above, the present invention can be applied to the case where power conversion is performed between the first power supply of the DC system and the second power supply of the DC system. It works.

As described above, by applying the present invention, it is possible to efficiently balance the DC voltage of each stage by accommodating the power between the DC stages, so that it is easy to increase the number of divisions of the DC voltage. As a result, the output voltage level of the converter can be easily increased, and a good AC output waveform or a multilevel good DC output waveform can be obtained. For these reasons, the effect that the applicable range of the multilevel power converter can be expanded is obtained.

[0052]

As described above, the multi-level power converter according to the present invention is connected to the positive and negative terminals connected to the first power supply of the DC system, and to the second power supply of the AC or DC system. An output terminal, a series connection of a plurality of switching elements respectively connected between the positive terminal and the output terminal and between the output terminal and the negative terminal, and connected between the positive terminal and the negative terminal. A series connection of a plurality of capacitors, and a clamp diode connected between a series connection point of the switching element and a series connection point of the capacitor, and by controlling on / off of the switching element, from the output terminal. A multi-level power converter configured to obtain a plurality of levels of potential output between the potential of the positive terminal and the potential of the negative terminal; A plurality of auxiliary AC / DC power converters connected between terminals of each capacitor; and a plurality of windings magnetically coupled to each other and connected to the AC side of each of the auxiliary AC / DC power converters. Since the transformer is provided, the voltage of each capacitor is quickly balanced, and the required capacity of the switching element and the transformer as a whole can be reduced.

Further, the transformer of the multilevel power converter according to the present invention includes a plurality of primary windings connected to the AC side of the auxiliary AC / DC power converter, and a plurality of the primary windings connected to the plurality of primary windings. Divided into groups, each group has a plurality of secondary windings that are magnetically coupled to and connected to the primary windings, making it easy to adjust the leakage inductance when a transformer uses many windings. Become.

Further, the multi-level power converter according to the present invention includes means for detecting the voltage of each capacitor and calculating a DC voltage command value for each capacitor from the sum thereof, and detecting the voltage detection value of each capacitor and the DC voltage. Means for shifting the operation phase of each auxiliary AC / DC power converter with respect to a predetermined reference phase so that the command value coincides with the reference value is provided, so that the voltages of the capacitors in a plurality of stages can be quickly balanced. And the sum of the DC voltages can be separately and independently controlled.

Further, the multi-level power converter according to the present invention comprises: a positive terminal and a negative terminal connected to a first DC power supply; an output terminal connected to an AC or DC second power supply; A serially connected body of a plurality of switching elements connected between the positive terminal and the output terminal and between the output terminal and the negative terminal, four or more connected between the positive terminal and the negative terminal A series connected body of capacitors, and a clamp diode connected between the series connection point of the switching element and the series connection point of the capacitor, and by controlling the on / off of the switching element, from the output terminal, In a multi-level power converter configured to obtain a plurality of levels of potential output between the potential of the positive terminal and the potential of the negative terminal, adjacent to each other A plurality of auxiliary AC / DC power converters each including a pair of switching elements connected in series with each other and having a DC side connected between both terminals of each of the capacitor pairs; A transformer having a plurality of windings that are magnetically coupled and connected between an intermediate connection point of each of the capacitor pairs and an AC terminal of the intermediate connection point of each of the switching element pairs; Balancing is quickly performed, and the required capacity of switching elements and transformers as a whole can be reduced.

Further, in the multilevel power converter according to the present invention, when the number of series of the capacitors is odd, one of the capacitors and a capacitor adjacent to one of the capacitors form a capacitor pair, and 1
Since a capacitor pair is formed by the number of capacitors and a capacitor adjacent to the other of the capacitors, even when the number of series of capacitors is an odd number, all of them can be configured as a capacitor pair. A multi-level power converter can be reliably realized.

Further, the multi-level power converter according to the present invention comprises: a positive terminal and a negative terminal connected to a first DC power supply; an output terminal connected to a second AC or DC power supply; A series connection of a plurality of switching elements connected between the positive terminal and the output terminal and between the output terminal and the negative terminal, and an odd number of 5 or more connected between the positive terminal and the negative terminal A series connection of the capacitors, and a clamp diode connected between the series connection point of the switching element and the series connection point of the capacitor, and by controlling the switching element on and off, from the output terminal, In a multi-level power conversion device configured to obtain a plurality of levels of potential output between the potential of the positive terminal and the potential of the negative terminal, The capacitors except for the one at the center in the connection direction of the capacitors are formed by a pair of capacitors adjacent to each other and a pair of switching elements connected in series, and the DC side thereof is connected between both terminals of each of the capacitor pairs. A plurality of connected first auxiliary AC / DC power converters, a second auxiliary AC / DC power converter whose DC side is connected between terminals of the one capacitor, and magnetically coupled to each other And a plurality of windings connected between the intermediate connection point of each of the capacitor pairs and the AC terminal of the intermediate connection point of each of the switching element pairs and on the AC side of the second AC / DC power converter. Since the transformer is provided, the voltage of each capacitor is quickly balanced, and the required capacity of the switching element and the transformer as a whole can be reduced.

Further, in the multi-level power converter according to the present invention, since a gap is provided in the magnetic path constituting the transformer, the power can be more smoothly exchanged by the DC current component flowing through each winding.

Further, the multi-level power converter according to the present invention detects the voltage of each capacitor pair (including individual capacitors other than the capacitor pair, including the capacitor, the same applies hereinafter) and detects each voltage from the sum thereof. Means for calculating the DC voltage command value of the capacitor pair, and the operation phase of each auxiliary AC / DC power converter is set to a predetermined reference phase so that the detected voltage value of each capacitor pair matches the DC voltage command value. With means for shifting
The voltages of the capacitors in the plurality of stages can be quickly balanced, and the sum of the DC voltages can be separately and independently controlled.

Further, the multi-level power converter according to the present invention includes a plurality of multi-level power converters, and uses a common first power supply of the DC system to interconnect a plurality of different second power supplies of the AC system. In the multi-level power converter that exchanges power in the above-described manner, the auxiliary AC / DC power converter and the transformer are shared by each of the above-mentioned multi-level power converters. Power interchange can be performed.

In the multi-level power converter according to the present invention, the auxiliary AC / DC power converter is operated in the square wave mode, so that the pulsation of the DC current is reduced and the switching loss is also reduced. Is done.

[Brief description of the drawings]

FIG. 1 shows a multilevel AC according to a first embodiment of the present invention.
FIG. 3 is a circuit diagram and an operation waveform diagram showing a main part of the / DC power converter.

FIG. 2 shows a multilevel AC according to a second embodiment of the present invention.
FIG. 3 is a circuit diagram and an operation waveform diagram showing a main part of the / DC power converter.

FIG. 3 shows a multi-level AC according to Embodiment 3 of the present invention.
FIG. 2 is a circuit diagram showing a main part of the / DC power converter.

FIG. 4 is a diagram for explaining the operation of FIG. 3;

FIG. 5 is a diagram for explaining the operation of FIG. 3;

FIG. 6 shows a multilevel AC according to a fourth embodiment of the present invention.
FIG. 2 is a circuit diagram showing a main part of the / DC power converter.

FIG. 7 shows a multilevel AC according to a fifth embodiment of the present invention.
FIG. 2 is a circuit diagram showing a main part of the / DC power converter.

FIG. 8 shows a multilevel AC according to Embodiment 6 of the present invention.
FIG. 2 is a circuit diagram showing a main part of the / DC power converter.

FIG. 9 shows a multilevel AC according to a seventh embodiment of the present invention.
FIG. 3 is a circuit diagram showing a power converter between / DC.

FIG. 10 is a circuit diagram for explaining the operation principle of the multilevel AC / DC power converter.

FIG. 11 is a circuit diagram showing a main part of a conventional multilevel AC / DC power converter.

FIG. 12 is a diagram for explaining the operation of FIG. 11;

[Explanation of symbols]

Cj, Ck capacitor, TR a transformer, S ₁₁ to S ₂₂ and the like switches, CONVj, CONVk like auxiliary AC / D
Inter-C power converter.

Claims (10)

[Claims] A positive terminal and a negative terminal connected to a first power supply of a DC system; an output terminal connected to a second power supply of an AC or DC system; a portion between the positive terminal and the output terminal and the output; A series connection of a plurality of switching elements connected to each between a terminal and a negative terminal, a series connection of a plurality of capacitors connected between the positive terminal and the negative terminal, and a series connection of the switching elements A clamp diode connected between a point and a series connection point of the capacitor is provided, and by controlling the switching element to be turned on and off, a voltage between the potential of the positive terminal and the potential of the negative terminal is output from the output terminal. In a multi-level power converter configured to obtain a plurality of levels of potential outputs, a DC side is connected between a plurality of auxiliary AC / DCs connected between terminals of the capacitors. Force transducer, and a multi-level power converting apparatus characterized by comprising a transformer having a plurality of windings magnetically coupled connected to the AC side of each of the auxiliary AC / DC between the power converter to each other. 2. The transformer comprises a plurality of primary windings connected to the AC side of the auxiliary AC / DC power converter, and the plurality of primary windings divided into a plurality of groups. The multi-level power converter according to claim 1, further comprising a plurality of secondary windings magnetically coupled to each other and connected to each other. 3. A means for detecting the voltage of each capacitor and calculating a DC voltage command value of each capacitor from the sum thereof, and each auxiliary AC voltage so that the detected voltage value of each capacitor coincides with the DC voltage command value. 3. The multi-level power converter according to claim 1, further comprising means for shifting an operation phase of the / DC power converter with respect to a predetermined reference phase. 4. A positive and negative terminal connected to a first power supply of a DC system, an output terminal connected to a second power supply of an AC or DC system, between the positive terminal and the output terminal, and the output. A series connection of a plurality of switching elements connected to each of a terminal and a negative terminal, a series connection of four or more capacitors connected between the positive terminal and the negative terminal, and the switching element By providing a clamp diode connected between the series connection point of the capacitor and the series connection point of the capacitor, and by controlling the switching element on and off, from the output terminal, the potential of the positive terminal and the potential of the negative terminal A multi-level power conversion device configured to obtain a plurality of levels of potential output between a pair of capacitors adjacent to each other as a capacitor pair, A plurality of auxiliary AC / DC power converters, each comprising a pair of switching elements connected in a row, the DC side of which is connected between both terminals of each of the capacitor pairs; A multi-level power converter, comprising: a transformer having a plurality of windings connected between an intermediate connection point and an AC terminal of the intermediate connection point of each of the switching element pairs. 5. When the number of series capacitors is odd, one of the capacitors and a capacitor adjacent to one of the capacitors form a capacitor pair, and
5. The multi-level power conversion device according to claim 4, wherein a capacitor pair is formed by a plurality of capacitors and a capacitor adjacent to the other of the capacitors. 6. A positive terminal and a negative terminal connected to a first power source of a DC system, an output terminal connected to a second power source of an AC system or a DC system, between the positive terminal and the output terminal, and the output. A series connection of a plurality of switching elements respectively connected between a terminal and a negative terminal, a series connection of five or more odd-numbered capacitors connected between the positive terminal and the negative terminal, and the switching A clamp diode connected between the series connection point of the element and the series connection point of the capacitor, and controlling the on / off of the switching element so that the potential of the positive terminal and the potential of the negative terminal are output from the output terminal. And a multi-level power converter configured to obtain a plurality of levels of potential outputs between the capacitor and a capacitor other than the one at the center in the connection direction. A plurality of first auxiliary AC / DC powers, each of which includes a pair of switching elements connected in series with each other and having a DC side connected between both terminals of each of the capacitor pairs. A converter, a second auxiliary AC / DC power converter having a DC side connected between terminals of the one capacitor, and an intermediate connection point of each of the capacitor pairs magnetically coupled to each other and each of the switching elements A multi-level power converter comprising a transformer having a plurality of windings connected between an AC terminal of a pair of intermediate connection points and an AC side of the second AC / DC power converter. apparatus. 7. The multi-level power conversion device according to claim 4, wherein a gap is provided in a magnetic path constituting the transformer. 8. A means for detecting a voltage of each capacitor pair (including an individual capacitor other than the capacitor pair, including the capacitor, the same applies hereinafter) and calculating a DC voltage command value of each capacitor pair from the sum of the voltages. And means for shifting the operation phase of each auxiliary AC / DC power converter with respect to a predetermined reference phase so that the detected voltage value of each capacitor pair and the DC voltage command value match. The multi-level power converter according to any one of claims 4 to 7. 9. A plurality of multilevel power converters according to claim 1, wherein a plurality of different second AC power supplies share a common DC first power supply. In the multi-level power converter that exchanges power in the above, the auxiliary AC / DC power converter and the transformer are shared by the respective multi-level power converters. 10. The auxiliary AC / DC power converter is operated in a square wave mode.
10. The multilevel power converter according to any one of claims 9 to 9.