JP2019187151A - Power conversion device - Google Patents

Abstract

To provide a power conversion device capable of stably performing neutral point potential control.SOLUTION: A power conversion device 10 comprises: converters 23u to 23w of a neutral point clamp system having a full-bridge configuration that are provided correspondingly to respective phases of an AC circuit; transformers 22u to 22w that are connected between the AC circuit and the converters 23u to 23w and transform AC voltage of the converters 23u to 23w to supply the transformed voltage to the AC circuit; and a control device 50 for controlling operation of the converters 23u to 23w. The transformers 22u to 22w are delta-connected on the side of the AC circuit. The control device 50 controls the converters 23u to 23w so as to supply current flowing back into the delta-connection of the transformers 22u to 22w.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a power conversion apparatus.

  In power converters that convert DC power into AC power or convert AC power into DC power, attempts have been made to increase the voltage. The neutral point clamp type power converter is one of the types of power converters that can output a three-level phase voltage and can handle a high voltage.

  In the neutral point clamp type power converter, a neutral point that divides the DC voltage equally between the high-potential side and the low-potential side by the capacitor and holds the high-potential side DC voltage and the low-potential side DC voltage evenly. Potential control is required.

  Various neutral point potential control methods have been proposed, but neutral point potential control requires detection of the current flowing through the converter, so in the state of no load or light load on the AC side, It is difficult to stably execute neutral point potential control. Therefore, neutral point potential control may be stabilized by forcibly supplying an alternating current to the alternating current side and flowing the current through the converter. However, there is a concern that an AC current supplied to the AC side may affect an AC circuit such as a power system.

JP-A-11-113263

  Embodiments provide a power conversion device capable of stably controlling a neutral point potential.

  The power conversion device according to the embodiment is connected between a neutral-point-clamped converter having a full-bridge configuration provided in accordance with each phase of the AC circuit, the AC circuit and the converter, and the conversion A transformer for transforming the AC voltage of the transformer and supplying the AC circuit to the AC circuit, and a control device for controlling the operation of the converter. The transformer is delta-connected on the AC circuit side. The controller controls the converter to supply a current that circulates in the delta connection of the transformer.

  In this embodiment, a full-bridge converter is provided for each phase, so that a transformer that can be Δ-connected on the primary side can be provided, and zero-phase current can be recirculated into the Δ-connection. Therefore, the neutral potential can be stably controlled without affecting the AC circuit side.

It is a block diagram which illustrates the power converter concerning an embodiment. It is a block diagram which illustrates a part of power converter device of FIG. It is a block diagram which illustrates a part of power converter device of FIG. It is a block diagram which illustrates a part of power converter device of FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
In the present specification and drawings, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

FIG. 1 is a block diagram illustrating a power conversion apparatus according to the embodiment.
As shown in FIG. 1, the power conversion device 10 of this embodiment includes a power converter 20 and a control device 50. The power converter device 10 is connected to an AC circuit via AC terminals 21u to 21w. For example, the AC circuit can be configured to include a three-phase or single-phase 50 Hz or 60 Hz AC power supply 1 or a transformer 2. The AC circuit may include an AC load such as an induction motor, an AC power transmission line, and the like. The power conversion apparatus 10 is connected to the DC circuit 3 through DC terminals 21p and 21n. The DC circuit 3 includes, for example, a DC power transmission line, a storage battery, a solar battery, and the like. The DC circuit 3 may include a DC power source or the like generated by another power conversion device.

  The power conversion device 10 converts an AC voltage into a DC voltage, or converts a DC voltage into an AC voltage. The power converter 10 may perform such bidirectional power conversion, or may perform unidirectional power conversion.

  The power converter 20 includes AC terminals 21u to 21w and DC terminals 21p and 21n. Between the AC terminals 21u to 21w and the DC terminals 21p and 21n, converters 23u to 23w are connected corresponding to each phase of the AC circuit. Transformers 22u-22w are connected between AC terminals 21u-21w and converters 23u-23w, respectively. The transformers 22u to 22w are Δ (delta) connected on the side of the AC terminals 21u to 21w. In the present specification, for the transformers 22u to 22w, the winding connected to the AC circuit is called a primary winding, and the winding connected to the converters 23u to 23w is called a secondary winding. . The primary winding side is simply referred to as a primary side, and the secondary winding side is also simply referred to as a secondary side.

  More specifically, a transformer 22u and a converter 23u are provided corresponding to the U phase of the AC circuit, a transformer 22v and a converter 23v are provided corresponding to the V phase, and a W phase is supported. A transformer 22w and a converter 23w are provided.

  Converter 23u includes AC terminals 24ua and 24ub, DC terminals 24up and 24un, and a neutral point terminal 24uo. The AC terminals 24ua and 24ub are connected to the secondary winding of the transformer 22u. The DC terminals 24up and 24un are connected to DC terminals 21p and 21n of the power converter 20. A capacitor 25p is connected between the DC terminal 24up and the neutral point terminal 24uo. A capacitor 25n is connected between the neutral point terminal 24uo and the DC terminal 24un.

  The converter 23v is configured in the same manner as the converter 23u described above, is connected to the secondary winding of the transformer 22v by AC terminals 24va and 24vb, and is connected to the DC of the power converter 20 by DC terminals 24vp and 24vn. It is connected to terminals 21p and 21n.

  The converter 23w is also configured similarly to the converters 23u and 23v described above, and is connected to the secondary winding of the transformer 22w by the AC terminals 24wa and 24wb, and is connected to the power converter 20 by the DC terminals 24wp and 24wn. DC terminals 21p and 21n.

  The DC sides of all the converters 23u to 23w are connected in parallel. That is, the DC terminals 24 up, 24 vp, and 24 wp are connected to the DC terminal 21 p of the power converter 20. The DC terminals 24un, 24vn, 24wn are connected to the DC terminal 21n of the power converter 20. The neutral point terminals 24uo, 24vo, and 24wo are connected to each other.

  The voltage between the DC terminal 21p and the neutral point O is VPO, and the voltage between the neutral point O and the DC terminal 21n is VON. Note that the potential of the DC terminal 21p is set to a value higher than the potential of the DC terminal 21n. The potential of the DC terminal 21p is positive when viewed from the potential of the neutral point O, and the potential of the DC terminal 21n is negative when viewed from the neutral point O.

  The controller 50 receives the DC voltages VPO and VON, the phase currents iu to iw, and the voltages vu to vw corresponding to the AC phases, and drives the switching elements that constitute the converters 23u to 23w. ˜vgw is generated and supplied to each of the converters 23u to 23w. As will be described in detail later, the control device 50 generates various command values based on the input DC voltages VPO and VON, the currents iu to iw of each phase, and the AC voltages vu to vw, and is preset. Drive signals vgu to vgw are generated based on the command value.

FIG. 2 is a block diagram illustrating a part of the power conversion apparatus of FIG.
FIG. 2 shows a simplified circuit configuration of the converter 23u. In this example, a diode clamp type neutral point clamp circuit is shown.

  As shown in FIG. 2, the converter 23 u includes switching elements 31 to 38 and diodes 39 to 42. The switching element 31 is, for example, an IGBT (Insulated Gate Bipolar Transistor), and a diode is connected in antiparallel.

  The switching elements 31 and 32 are connected in series at the connection node n1. The switching elements 33 and 34 are connected in series at the connection node n2. The switching elements 35 and 36 are connected in series at a connection node n3. The switching elements 37 and 38 are connected in series at a connection node n4. The series connection circuits of the switching elements 31 and 32, the switching elements 33 and 34, the switching elements 35 and 36, and the switching elements 37 and 38 are called arms.

  The arms formed by the switching elements 31 and 32 are connected in series with the arms formed by the switching elements 33 and 34. The connection node between the arm formed by the switching elements 31 and 32 and the arm formed by the switching elements 33 and 34 is connected to the AC terminal 24ua.

  Between the connection nodes n1 and n2, diodes 39 and 40 connected in series are connected. The connection node of the series connection circuit of the diodes 39 and 40 is connected to the neutral point terminal 24uo.

  The arms formed by the switching elements 35 and 36 are connected in series with the arms formed by the switching elements 37 and 38. The connection node between the arm formed by the switching elements 35 and 36 and the arm formed by the switching elements 37 and 38 is connected to the AC terminal 24ub.

  Between the connection nodes n3 and n4, diodes 41 and 42 connected in series are connected. The connection node of the series connection circuit of the diodes 41 and 42 is connected to the neutral point terminal 24uo.

  The series circuit of the switching elements 31 to 34 and the series circuit of the switching elements 35 to 38 are connected in parallel between the DC terminals 24up and 24un. The arm formed by the switching elements 31 and 32, the arm formed by the switching elements 33 and 34, the arm formed by the switching elements 35 and 36, and the arm formed by the switching elements 37 and 38 have a full bridge circuit having AC terminals 24ua and 24ub and DC terminals 24up and 24un. It is. This full bridge circuit is clamped to the potential of the neutral point terminal 24uo (neutral point potential) by the diodes 39 to 42.

  The potentials Vu (A) and Vu (B) of the AC terminals 24ua and 24ub with respect to the neutral point potential are potentials controlled for each converter for neutral point potential control, which will be described in detail later.

  In a neutral point clamp type converter, a zero-phase voltage command value is generated based on a deviation between positive and negative DC voltages VPO and VON with respect to a neutral point voltage, and the neutral point potential is controlled. In the power conversion device 10 of the present embodiment, transformers 22u to 22w are connected between the converters 23u to 23w and the AC circuit. The primary side of the transformers 22u to 22w is Δ-connected.

  Even when there is no load or light load on the AC circuit side, the power converter 10 generates a zero-phase voltage according to the command value. Phase current flows. By flowing a zero-phase current to the primary side of the transformers 22u to 22w, a current flows through each of the converters 23u to 23w, so that the converter operation can be continued stably. In addition, since the zero-phase current flowing on the primary side of the transformers 22u to 22w circulates in the Δ connection, the current can be prevented from flowing out to the AC circuit side such as the power system.

In the power conversion device 10 of the present embodiment, a voltage command value for controlling the neutral point potential is generated for each AC phase separately from the generation of the zero-phase voltage command value.
FIG. 3 is a block diagram illustrating a part of the power conversion apparatus in FIG. 1.
FIG. 3 shows a configuration example for controlling the neutral point potential for the U-phase converter 23u. The control device 50 also has the same configuration for the V-phase and W-phase converters 23v and 23w, and a detailed description thereof will be omitted.

  As shown in FIG. 3, the control device 50 includes an adder / subtractor 51, coefficient multipliers 52 and 59, a PI controller 53, multipliers 54 and 57, encoders 55 and 56, and adders 58 and 60. ,including. The control device 50 generates a control output (neutral point potential control output) for neutral point potential control by the adder / subtractor 51, the coefficient unit 52, and the PI controller 53. A deviation between the DC voltages VPO and VON is calculated by an adder / subtractor 51 and a coefficient unit 52, and a neutral point potential control output is generated by a PI controller 53.

  The control device 50 sets the neutral point potential control direction by the multiplier 54 and the encoders 55 and 56. The encoders 55 and 56 output “+1” when the sign of the input signal is positive, and output “−1” when the sign of the input signal is negative. The multiplier 54 receives the output from the converter 23 u or the current iu input to the converter 23 u and the output of the encoder 55. The encoder 55 receives a U-phase voltage command value vu *. The encoder 56 determines the direction of controlling the neutral point potential in consideration of the signs of the line current iu of the converter 23u and the U-phase voltage command value vu *.

  The multiplier 57 adds a sign to the neutral point potential control output v0 and adds it to the voltage command value vu *. The positive voltage command value Vu (A) * is generated by being added to the output of the multiplier 57 by the adder 58. The negative voltage command value Vu (B) * is generated by being inverted by the coefficient unit 59 and then added to the output of the multiplier by the adder 60.

  In the above description, the case of the diode clamp system has been described as the circuit configuration of the neutral point clamp system. However, any neutral circuit clamp type converter that performs neutral point potential control can be applied to other circuit systems. be able to. For example, a part of the switching element of the converter and the diode may be replaced with a bidirectional switch, and the configuration of the converter may be a T-type neutral point clamping method.

  In the above example, the AC circuit has been described as having three phases. However, the number of phases of the AC circuit is not limited to this, and may be four or more.

The effect of the power converter device 10 of this embodiment is demonstrated.
The power conversion apparatus 10 according to the present embodiment includes a full bridge circuit corresponding to each phase of the AC circuit, and a transformer Δ-connected between the AC circuit and the full bridge circuit. Even if the AC circuit side is in a no-load or light-load state, the control device 50 generates a zero-phase voltage command value and continues the converter current by flowing the zero-phase current to the primary side of the transformer. It can flow. Therefore, the power conversion device 10 can stably perform neutral point potential control output even in the case of no load or light load.

  Since the primary side of the transformer is Δ-connected, the zero-phase current output by the converter does not flow back through the Δ-connection and flow out to the AC circuit side. Therefore, the power conversion device 10 can stably perform neutral point potential control without affecting the AC circuit side.

  The AC circuit is not limited to an AC power source such as a power system, and may be an AC load such as an electric motor. In the power converter 10 of this embodiment, when the AC circuit is an AC load, the neutral point potential can be stably controlled even when it is necessary to cut off the power supply to the AC load. Therefore, the operation can be continued without stopping the power conversion device 10.

  It is known that the response of neutral point potential control changes according to the direct current output from the converter or the direct current input to the converter. The response of neutral point potential control is expressed as the following equation (1).

Neutral point potential control response ∝ DC neutral point current change
= ± (v0 × converter current) / DC voltage between PN (1)
Here, v0 is a neutral point potential control output (FIG. 3), and the converter current is iu to iw.

  As shown in Expression (1), the amount of change in the neutral point potential of the direct current is proportional to the magnitudes of the currents iu to iw of the converters 23 u to 23 w corresponding to the respective phases. Therefore, the control response of the neutral point potential can also be improved by setting the current flowing through each phase to return the zero-phase current on the primary side of the transformer to an appropriate value. That is, in the power conversion device 10 of the present embodiment, by performing the neutral point potential control corresponding to each phase, the neutral point potential control is stably performed and the response of the neutral point potential control is accelerated. be able to.

(Modification)
In the above-described embodiment, neutral point potential control is stably performed by flowing a zero-phase current constantly to the primary side of the transformer, including cases where the AC circuit side is unloaded or lightly loaded. On the other hand, by constantly recirculating the zero-phase current, a loss always occurs in the transformer and the converter, and noise or the like due to the operation of the converter occurs. Therefore, in the present modification, when a preset condition is satisfied, the power conversion device 10 causes the zero-phase current to flow through the primary side of the transformer, and there is no need for stabilization by the zero-phase current. Prevents a zero-phase current from flowing.

FIG. 4 is a block diagram illustrating a part of the power conversion apparatus in FIG. 1.
FIG. 4 shows a zero-phase current conduction circuit 70. Zero-phase current conduction circuit 70 is provided in control device 50, for example.

  As shown in FIG. 4, the zero-phase current conducting circuit 70 includes comparators 71 and 75, an adder / subtractor 72, a coefficient unit 73, an arithmetic unit 74, AND circuits 76 and 80, an off-delay circuit 77, An inverting circuit 78 and a one-shot circuit 79 are included. The zero-phase current energizing circuit 70, when the alternating current of the converter falls below a predetermined drop level and the deviation of the DC voltages VPO, VON with respect to the neutral point potential exceeds a predetermined unbalance level, A zero-phase current command value is supplied to the control device so that the zero-phase current is supplied to the primary side of the transformer.

  Hereinafter, a case will be described in which any one of the currents iu to iw of the converters 23u to 23w of each phase is detected to be below a predetermined drop level, but the current detection condition is not limited thereto. Any appropriate condition may be used. For example, it may be detected that the average value of the effective values of the currents iu to iw has fallen below a predetermined decrease level, or other appropriate conditions.

  When the deviation between the DC voltages VPO and VON exceeds a predetermined unbalance level, a zero-phase current command value is supplied so as to energize the zero-phase current for a certain period. When the imbalance between the DC voltages VPO and VON is resolved, the zero-phase current is cut off.

  The comparator 71 receives a preset converter current drop level iT1. The comparator 71 compares the current iu of the converter 23u with the converter current drop level iT1. The comparator 71 supplies an H level signal to the AND circuit 80 when the current iu is lower than the converter current decrease level iT1.

  The DC voltages VPO and VON are input to the adder / subtractor 72 and the coefficient unit 73, and the deviation (the arithmetic average of the voltage from the neutral point potential) is calculated. The output of the coefficient unit 73 is input to an arithmetic unit 74 that calculates an absolute value, and is compared with a DC voltage unbalance level VUB by a comparator 75. When the absolute value of the deviation between the DC voltages VPO and VON is equal to or greater than the DC voltage unbalance level VUB, an H level signal can be supplied to the AND circuit 76.

  The other input of the AND circuit 76 is supplied with the output of the off delay circuit 77 connected to the output of the AND circuit 76 being inverted by the inverting circuit 78. The off-delay circuit 77 has a preset off-delay time. The off-delay circuit 77 becomes L level after the set off-delay time elapses even if the output of the AND circuit 76 becomes L level (off). That is, the AND circuit 76 allows the AND circuit 76 to output the H level when the deviation between the DC voltages VPO and VON instantaneously exceeds the unbalance level VUB.

  The one-shot circuit 79 is connected to the output of the AND circuit 76. When the H-level signal is input, the one-shot circuit 79 supplies an H-level one-shot signal having a preset pulse width to the AND circuit.

The operation of the zero-phase current energizing circuit 70 will be described.
The zero-phase current conducting circuit 70 becomes operable when the converter outputs or the alternating current input to the converter falls below the converter current drop level iT1.

  The pulse width set by the one-shot circuit 79 when the deviation between the DC voltages VPO and VON of the power converter 20 becomes equal to or greater than the DC voltage unbalance level VUB while the zero-phase current conducting circuit 70 is operable. The zero-phase current for the period determined by is supplied to the primary side of the transformer.

  In this modification, it is detected that the current flowing through the converter has decreased, and the zero-phase current is forced to flow through the transformer, so even if the AC circuit side is unloaded, etc., the neutral point is stable. Potential control can be performed.

  Further, in this modified example, in addition to the decrease in the current of the converter, when the deviation of the DC voltages VPO and VON is large, the zero-phase current is flown, so that neutral point potential control should be actively performed. Can only be in the state. If the imbalance between the deviations of the DC voltages VPO and VON is large, the voltage applied to the switching element in the converter becomes excessive, and the switching element may be damaged. Therefore, by appropriately setting the DC voltage unbalance level VUV, in the modified example, it is possible to prevent accidents such as breakage of the switching element without frequently flowing a zero-phase current and reducing conversion efficiency. .

  Thus, in this modification, when a predetermined condition is not satisfied, no zero-phase current flows through the transformer, so that the efficiency of the converter does not decrease.

  Since the zero-phase current is supplied when neutral point potential control is required, it is not necessary to supply the zero-phase current when other factors or the DC voltage is not unbalanced.

  As described above, in this modification, the zero-phase current of the transformer is supplied or stopped depending on the state of the current on the AC side and the state of the unbalance on the DC side. Can be operated under optimum operating conditions.

  According to the embodiment described above, it is possible to realize a power conversion device that can accurately calculate the sign of the zero-phase voltage and output the command value of the zero-phase voltage.

  As mentioned above, although several embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and the equivalents thereof. Further, the above-described embodiments can be implemented in combination with each other.

  1 AC power supply, 2 transformer, 3 DC circuit, 10 power converter, 20 power converter, 22u to 22w transformer, 23u to 23w converter, 25p, 25n capacitor, 31 to 38 switching element, 39 to 42 diode, 50 controller, 51 adder / subtractor, 52, 59 coefficient unit, 53 PI controller, 54, 57 multiplier, 55, 56 encoder, 58, 60 adder, 70 zero-phase current conduction circuit, 71, 75 comparator, 72 adder / subtractor, 73 coefficient unit, 74 arithmetic unit, 76, 80 AND circuit, 77 off-delay circuit, 78 inversion circuit, 79 one-shot circuit

Claims (5)

Neutral point clamp type converter with full bridge configuration provided according to each phase of AC circuit,
A transformer connected between the AC circuit and the converter and transforming an AC voltage of the converter to supply the AC circuit;
A control device for controlling the operation of the converter;
With
The transformer is delta-connected on the AC circuit side,
The said control apparatus is a power converter device which controls the said converter so that the electric current which circulates in the delta connection of the said transformer may be supplied. The converter is
Neutral point,
A first DC terminal having a higher potential than the neutral point;
A second DC terminal having a lower potential than the neutral point;
Including
The controller is
Based on the deviation between the first DC voltage between the first DC terminal and the neutral point and the second DC voltage between the neutral point and the second DC terminal, Generate a neutral point potential control output to control the potential,
The first DC voltage command value for the first DC voltage and the second DC voltage command value for the second DC voltage are generated based on the direction of the AC line current flowing through the converter. Power converter.   The control device forcibly sets a zero-phase current command value when the AC line current is lower than a predetermined threshold current, and sets the zero-phase voltage command value based on the zero-phase current command value. The power converter of Claim 2 which produces | generates.   The power converter according to claim 3, wherein the zero-phase current command value is forcibly set when a deviation between the first DC voltage and the second DC voltage is equal to or greater than a predetermined threshold voltage.   The power converter according to any one of claims 1 to 4, wherein the neutral point clamp method of the converter is either a diode clamp method or a T-type clamp method.

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