CN110380635B - Power conversion device and control method for power conversion device - Google Patents
Power conversion device and control method for power conversion device Download PDFInfo
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- CN110380635B CN110380635B CN201910289169.6A CN201910289169A CN110380635B CN 110380635 B CN110380635 B CN 110380635B CN 201910289169 A CN201910289169 A CN 201910289169A CN 110380635 B CN110380635 B CN 110380635B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/18—Arrangements for adjusting, eliminating or compensating reactive power in networks
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
- H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
- H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/453—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/458—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M5/4585—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only having a rectifier with controlled elements
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/30—Reactive power compensation
Abstract
A power conversion device and a control method for the power conversion device, the power conversion device of the embodiment comprises: an inverter (3) and a converter (5) each having a DC-side terminal and an AC-side terminal, the DC-side terminals being connected to common DC link sections (4a, 4b), and the AC-side terminals being connected to a common power system; and a control device that controls reactive power output to the power system so as to be a sum of the reactive power output from the inverter (3) via the generator (1) and the reactive power output from the converter (5).
Description
The present application is based on Japanese laid-open application 2018-077718 (application date: 2018, 4/13), and benefits are granted to the user on the basis of the application. The present application includes the entire contents of the aforementioned prior application by reference to the aforementioned prior application.
Technical Field
Embodiments of the present invention relate to a power conversion apparatus and a method of controlling the power conversion apparatus.
Background
A power conversion device that converts direct current and alternating current to each other includes an Inverter (Inverter) and a Converter (Converter), and is applied to a wide area in society.
The most basic inverter is a 2-level inverter composed of 2 semiconductor switching elements. The 2-level inverter outputs 2 voltage levels at 1 leg (leg).
Fig. 6 is a diagram showing an example of a circuit configuration of an NPC (Neutral-Point-Clamped) inverter.
As shown in fig. 6, there is a neutral-point clamped inverter using 4 semiconductor switching elements (hereinafter, sometimes referred to as switching elements), 2 semiconductor switching elements (which may be diodes) for clamping, and a dc voltage dividing capacitor for 1 arm.
Fig. 6 illustrates a three-phase NPC inverter/converter circuit by way of example. The NPC inverter can output 3 voltage levels at 1 arm, and contributes to high withstand voltage, reduction in loss, and reduction in harmonics. Therefore, the NPC inverter is applied to various inverters.
The structure of the circuit shown in fig. 6 will be explained. First, in the dc link section, the capacitor C1 on the high potential side is connected in series with the capacitor C2 on the low potential side. An ac-side terminal of the UVW-phase converter including the U-phase converter 101 is connected to the ac power supply. The ac-side terminal of the uvw-phase inverter including the u-phase inverter 102 is connected to the load.
The converter 101 has: 4 switching elements SW _ C1, SW _ C2, SW _ C3 and SW _ C4 connected in series from a high potential side to a low potential side to form an arm; and 4 free wheel diodes D _ C1, D _ C2, D _ C3 and D _ C4 connected in reverse parallel to each switching element in a 1-to-1 manner.
The converter 101 further has: 2 switching elements SW _ C5 and SW _ C6 connected in series from a connection point of the switching elements SW _ C1 and SW _ C2 to a connection point of the switching elements SW _ C3 and SW _ C4; and 2 diodes D _ C5 and D _ C6 connected in reverse parallel to the switching elements SW _ C5 and SW _ C6 in a 1-to-1 manner.
Capacitor C1 holds DC voltage vdc1. Capacitor C2 holds DC voltage vdc2. In each switching element, the collector is on the high potential side and the emitter is on the low potential side. In each diode, the negative electrode side is a high potential side, and the positive electrode side is a low potential side.
Further, a current i is output from the interconnection point of the switching elements SW _ C2 and SW _ C3 to the outside of the converter 101u c. A neutral point NP (potential v) which is a point of interconnection between the switching elements SW _ C5 and SW _ C6 and a point of interconnection between the capacitors C1 and C2n) And (4) connecting. A current i flows through a point of interconnection between the capacitors C1 and C2n c. Rotation of V phase and W phaseThe converter has the same structure as the converter 101 of the U-phase.
The u-phase inverter 102 includes: 4 switching elements SW _ I1, SW _ I2, SW _ I3 and SW _ I4 connected in series from a high potential side to a low potential side to constitute an arm; and 4 free-wheeling diodes D _ I1, D _ I2, D _ I3, D _ I4 connected in reverse parallel to each switching element in a 1-to-1 manner.
The u-phase inverter 102 further includes: 2 switching elements SW _ I5 and SW _ I6 connected in series from a connection point of the switching elements SW _ I1 and SW _ I2 to a connection point of the switching elements SW _ I3 and SW _ I4; and 2 diodes D _ I5 and D _ I6 connected in reverse parallel to each other in a 1-to-1 manner with respect to the switching elements SW _ I5 and SW _ I6.
Further, a current I is output from the interconnection point of the switching elements SW _ I2 and SW _ I3 to the outside of the inverter 102u i. The interconnection point of the switching elements SW _ I5 and SW _ I6 is connected to the neutral point NP. A current i flows through the interconnection pointn i. The v-phase and w-phase inverters have the same configuration as the u-phase inverter 102.
Fig. 7 is a diagram showing an example of a circuit configuration of a secondary field converter of the induction generator.
As shown in fig. 7, the secondary excitation converter of the induction generator 111, which is an alternator, includes an inverter 112, a dc link unit, a converter 114, and a transformer 115. The dc link section is a dc link section common to the inverter 112 and the converter 114, and is a series circuit of a high-potential-side capacitor 113a and a low-potential-side capacitor 113 b.
The inverter 112 excites the secondary field winding of the induction generator 111. The reactive power Q is output from the induction generator 111 to the transformer 116 on the power system side. Effective power P required for excitation of secondary excitation windingcThe voltage is supplied from the transformer 116 to the converter 114 via the secondary excitation converter-side transformer 115. The converter 114 converts the active power PcAnd is supplied to a dc link portion between the inverter 112 and the converter 114. The power generation system is constituted by such a secondary excitation converter and the induction generator 111.The power generation system is used, for example, in a wind turbine generator and a variable speed generator.
The NPC inverter has a DC voltage v between PN pairspnA capacitor for voltage division. Potential v of neutral point NP of NPC inverternThe inverter has a property of varying at a frequency 3 times as high as the fundamental wave in accordance with the operation of the inverter. If the fluctuation (Ripple of neutral point potential) of the neutral point potential is large, the voltage applied to the switching element fluctuates. When the voltage is high, there is a risk that the element is broken due to the excess of the withstand voltage. If the voltage is low, a desired voltage may not be output, and overshoot may occur.
The magnitude of the fluctuation of the neutral point potential is related to the Modulation index (Modulation index), the power factor, the capacitor capacity, and the load current. Fig. 8 is a diagram showing an example of the magnitude of the variation in the neutral point potential due to the modulation factor and the power factor in the NPC inverter. Fig. 8 shows an example in which the capacitor capacity and the load current are set to constant values, and the magnitude of the fluctuation of the neutral point potential due to the modulation factor and the power factor is calculated.
Here, the power factor is shown as a Phase difference (Phase difference) between a voltage and a current. In fig. 8, it is understood that the higher the modulation factor or the lower the power factor, the larger the variation in the neutral point potential.
The simplest method of suppressing the variation in the neutral point potential is to increase the capacitor capacity. However, the increase in the capacitor capacity increases the size and cost of the inverter, and the energy at the time of failure also increases.
On the other hand, the variation of the neutral point potential can be suppressed to some extent by the control of the NPC inverter. By applying a zero-phase voltage v represented by the following formula (1)0With a voltage command value v of each phaseu、vv、vwBy addition, the neutral point potential variation can be suppressed.
Here, formula (II)(1) V isu、vv、vwI of equation (1) is a voltage command value for each phase (U-phase, V-phase, W-phase or U-phase, V-phase, W-phase) arm normalized by 1u、iv、iwIs the current output from the arm of each phase. Sign in expression (1) represents a sign function.
However, there is an operating region in which fluctuation of the neutral point potential cannot be sufficiently suppressed by the above control. Fig. 9 is a diagram showing an example of the magnitude of the fluctuation of the neutral point potential when the fluctuation suppression control is performed in the NPC inverter. Fig. 9 shows the same calculation result as the variation of the neutral point potential in the case where the control disclosed in japanese patent No. 5622437 is applied, for example. Fig. 9 shows that the lower the power factor, the larger the variation in the neutral point potential. In the power generation system shown in fig. 7, when the reactive power Q is mainly output to the power system, the power factor of the inverter is low, and the neutral point potential of the capacitor fluctuates greatly.
Disclosure of Invention
The present invention addresses the problem of providing a power conversion device and a method for controlling the power conversion device, which are capable of suppressing the variation in the neutral point potential of an inverter and preventing the increase in the capacitor capacity.
The power conversion device of the embodiment includes: an inverter and a converter each having a dc-side terminal and an ac-side terminal, the dc-side terminals being connected to a common dc link section, and the ac-side terminals being connected to a common power system; and a control device that controls reactive power output to the power grid so as to be a total of reactive power output from the inverter via the generator and reactive power output from the converter.
According to the present invention, the fluctuation of the neutral point potential of the inverter can be suppressed, and the increase of the capacitor capacity can be prevented.
Drawings
Fig. 1 is a diagram showing an example of a configuration of a system to which a power conversion device according to a first embodiment is applied.
Fig. 2 is a block diagram showing an example of a control circuit for the reactive power command value according to the first embodiment.
Fig. 3 is a diagram showing an example of an output range of a current from the converter.
Fig. 4 is a diagram showing an example of a configuration of a system to which the power conversion device according to the second embodiment is applied.
Fig. 5 is a diagram showing an example of a configuration of a system to which the power conversion device according to the third embodiment is applied.
Fig. 6 is a diagram showing an example of a circuit configuration of the neutral point clamped inverter.
Fig. 7 is a diagram showing an example of a circuit configuration of a secondary field converter of the induction generator.
Fig. 8 is a diagram showing an example of the magnitude of the variation in the neutral point potential due to the modulation factor and the power factor in the NPC inverter.
Fig. 9 is a diagram showing an example of the magnitude of the fluctuation of the neutral point potential when the fluctuation suppression control is performed in the NPC inverter.
Detailed Description
Hereinafter, embodiments will be described with reference to the drawings.
(first embodiment)
Fig. 1 is a diagram showing an example of a configuration of a system to which a power conversion device according to a first embodiment is applied. In the following, the same reference numerals as those used in fig. 1 are given to the same or equivalent components as those of the power converter shown in fig. 1, and the description is given.
In fig. 1, a secondary excitation converter of a three-phase induction generator (hereinafter referred to as an induction generator) 1 of a variable speed water-lifting power generation system (hereinafter referred to as a power generation system) includes an NPC inverter (hereinafter referred to as an inverter) 3, an NPC converter (hereinafter referred to as a converter) 5, and a Transformer (Transformer) 6. The secondary excitation converter and the control device 10 constitute a power conversion device. The power conversion device and the induction generator 1 constitute a power generation system. The induction generator 1 is connected with a water turbine 2 for pumping water and generating electricity.
The ac-side terminal of the inverter 3 is connected to the secondary field winding of the induction generator 1. The ac-side terminal of the converter 5 is connected to the power system via a transformer 6. The inverter 3 and the converter 5 have a dc-side terminal and an ac-side terminal, respectively. The dc-side terminals of the inverter 3 and the converter 5 are connected to a common dc link (link) unit. The dc link unit is a dc link unit shared by the inverter 3 and the converter 5, and is a series circuit of a high-potential-side capacitor 4a and a low-potential-side capacitor 4 b. The ac-side terminal of the inverter 3 and the ac-side terminal of the converter 5 are connected to a common power system. The ac-side terminal of the inverter 3 and the ac-side terminal of the converter 5 can be connected to a common power system via the induction generator 1 and the transformer 6, respectively.
The inverter 3 supplies electric power to the secondary field winding of the induction generator 1 to excite the induction generator 1. The stator windings of the induction generator 1 are connected to the power system via a transformer 7.
When the induction generator 1 outputs the active power to the power system, the inverter 3 also outputs the active power to the induction generator 1. When the induction generator 1 outputs reactive power to the power system, the inverter 3 outputs reactive power to the induction generator 1.
The converter 5 obtains the active power P required for the operation of the inverter 3 from the utility grid via the utility grid-side transformer 7 and the converter-side transformer 6cAnd applying the effective power PcIs supplied to the dc link section between the converter 5 and the inverter 3.
A case where the power generation system outputs the reactive power Q to the power grid will be described. In the first embodiment, the induction generator 1 outputs the reactive power Q to the power systemgThe converter 5 will not output the reactive power QcThe reactive power Q is directly output to the power grid via the transformer 6, and the power generation system outputs the reactive power Q to the power grid. Here, the direct output to the power system means that the output is performed without passing through the induction generator 1. That is, the following formula (2) is established.
Q＝Qg+Qc… type (2)
Here, QgThe superscript g of (a) denotes the induction generator 1, QcThe superscript c of (a) denotes the converter 5. Here, the power generation end effective power of the induction generator 1 is arbitrary and is not described.
The converter 5 functions to maintain the dc voltage, but if the converter 5 has an extra capacity for power output, the converter 5 can output reactive power.
Fig. 2 is a block diagram showing an example of a control circuit for the reactive power command value according to the first embodiment.
As shown in fig. 2, the control device 10 gives the reactive power command value Q to the converter 5c＊. Here, the reactive power command value Q for the induction generator 1 is setg＊The operation of (2) will be further described.
Fig. 3 is a diagram showing an example of the output range of the current from the converter 5.
As shown in fig. 3, the range in which the converter 5 can output electric power can be represented by a rotating coordinate system using a d-axis and a q-axis (an axis orthogonal to the d-axis). Output current I of the converter 5cIs the maximum value of the output current I corresponding to the circle indicated by the dotted line in FIG. 3max cThe range of (1). When the effective current I is required for maintaining the DC voltaged cRepresented by a vector on the d-axis shown in FIG. 3, the reactive current I that can be outputq cBy a vector I parallel to the q-axis in FIG. 3q cAnd (4) showing. Based on this relationship, the reactive current command value I for the converter 5 can be obtained by the following expression (3)q c＊。
Here, based on the effective current command value I for the converter 5d c＊An invalid current command value I for the converter 5q c＊Effective voltage command value V for converter 5d c＊And an invalid voltage command value V for the converter 5q c＊To aim atReactive power command value Q of converter 5c＊Can be obtained by the following formula (4).
Qc＊＝Vq c＊Id c＊－Vd c＊Iq c＊… type (4)
The reactive power command value Qc＊Cannot exceed the reactive power command value Q for the power generation system＊That is, a total command value of reactive power output from the induction generator 1 to the power grid and reactive power output from the converter 5 to the power grid. Therefore, limiter 18 invalidates power command value Qc＊Limited to-Q＊～Q＊The range of (1).
Here, the reactive power command value Q for the induction generator 1g＊Can be set from the reactive power command value Q for the power generation system＊Subtracting the reactive power command value Q for the converter 5c＊And the resulting value. Thus, the following formula (5) is established. That is, in the first embodiment, the power conversion device outputs the reactive power command value output from the power generation system to the power system as the sum of the reactive power command value for the converter 5 and the reactive power command value for the induction generator 1. The controller 10 of the power converter controls the reactive power command value output from the power generation system to the power system so as to be the sum of the reactive power command value for the converter 5 and the reactive power command value for the induction generator 1.
Qg＊＝Q＊－Qc＊… type (5)
In this way, the controller 10 controls the reactive power command value Q for the induction generator 1g＊A reactive power command value Q for a converter 5 is given to an induction generator 1 via an inverter 3c＊A converter 5 for outputting a reactive power command value Q for the power generation system＊。
As shown in fig. 2, the control device 10 includes arithmetic units 11 and 12, a subtractor 13, an arithmetic unit 14, multipliers 15 and 16, a subtractor 17, a limiter 18, and a subtractor 19 as an arithmetic circuit. The arithmetic circuit can be realized by a computer device including a storage device such as a cpu (central Processing unit), a ram (random Access memory), and a rom (read Only memory) that executes a program.
Next, a specific example of the output of the reactive power command value using the arithmetic circuit will be described.
The arithmetic unit 11 outputs the maximum value I of the output current of the converter 5max cSquare of (d). The operator 12 outputs an effective current instruction value I for the converter 5d c＊Square of (d). Maximum value of output current Imax cIs an arbitrary value in design.
The subtractor 13 outputs a deviation obtained by subtracting the output value from the operator 12 from the output value from the operator 11. The arithmetic unit 14 takes the square root of the deviation from the subtracter 13 as the reactive current instruction value I for the converter 5q c＊And (6) outputting.
The operation using the above-described operators 11 and 12, subtractor 13, and operator 14 corresponds to the operation based on the above-described equation (3).
The multiplier 15 outputs a reactive current instruction value I from the arithmetic unit 14 to the converter 5q c＊Multiplied by the effective voltage command value V for the converter 5d c＊And the resulting value. The multiplier 16 outputs a command value I of effective current passing through the converter 5d c＊Multiplied by an invalid voltage command value V for the converter 5q c＊And the resulting value.
The subtractor 17 outputs a deviation obtained by subtracting the output value of the multiplier 15 from the output value of the multiplier 16. The operation using the multipliers 15 and 16 and the subtractor 17 corresponds to the operation based on the above expression (4).
The limiter 18 will be at-Q by subtracting the deviation from the subtractor 17＊～Q＊Is limited as the reactive power command value Q for the converter 5c＊And (6) outputting.
The subtractor 19 obtains the command value Q of reactive power from the power generation system＊Subtracting the reactive power command value Q for the converter 5 from the limiter 18c＊The obtained deviation is used as the reactive power command value Q for the induction generator 1g＊And (6) outputting. The operation using the subtractor 19 corresponds to the operation based on the above expression (5).
Here, a conventional example will be explained. In the conventional example, as shown in fig. 7 described above, the reactive power Q is output only from the induction generator 111 to the power system. That is, the following formula (6) is established.
Q＝Qg… type (6)
The converter 114 shown in fig. 7 converts the active power PcSupplied to the DC link section. On the other hand, reactive power QcAnd is not output from the converter 114. That is, the reactive power command value Q for the induction generator 111g＊The reactive power command value Q for the converter 114 is expressed by the following equation (7)c＊Represented by the following formula (8).
Qg＊＝Q＊… type (7)
As described above, the lower the power factor, the larger the neutral point potential variation of the NPC inverter. In the present embodiment, when the induction generator 1 outputs reactive power to the power system, the inverter 3 also outputs reactive power.
The description of the present embodiment is returned. In the present embodiment, the reactive power Q output from the induction generator 1 to the power gridgIs (a) or (b) (see formula (5)) below.
(a) By subtracting the reactive power output value Q output from the converter 5 to the power system from the reactive power output value Q, which is the actual output value of the power generation systemcThe obtained electric power
(b) By deriving the reactive power command value Q for the power generation system＊Subtracting the reactive power command value Q to the converter 5c＊And the resulting power.
Thus, the power factor of the inverter 3 is improved. As a result, the neutral point potential variation of the NPC inverter can be reduced.
According to the present embodiment, in the NPC inverter/converter, it is possible to suppress the variation in the neutral point potential of the NPC inverter and prevent the increase in the capacitor capacity. As a result, a small, low-cost, and safe power conversion device can be realized.
Common matters of the respective embodiments including the first embodiment will be described below.
The NPC converter may also be a T-type NPC converter. In addition, in the calculation circuit of the control device 10, the effective voltage command value V for the converter 5 is replacedd c＊And an invalid voltage command value V for the converter 5q c＊The effective voltage output value V of the converter 5 may also be usedd cAnd the invalid voltage output value V of the converter 5q c。
In addition, in the calculation circuit of the control device 10, the effective current command value I for the converter 5 is replacedd c＊The effective current output value I of the converter 5 may also be usedd c。
(second embodiment)
Fig. 4 is a diagram showing an example of a configuration of a system to which the power conversion device according to the second embodiment is applied.
The basic configuration of a system to which the power conversion device according to the present embodiment is applied is the same as that of the first embodiment. However, instead of the water turbine 2 of the first embodiment, the windmill 30 rotates the induction generator 1. That is, the induction generator 1 is used as a wind power generator.
In the present embodiment, the secondary excitation converter of the induction-type wind turbine generator is constituted by the NPC inverter/converter similar to that of the first embodiment, and the output of the reactive power is performed in the same manner as that of the first embodiment. Reactive power Q output by induction generator 1 to power systemgIs (c) or (d) (see formula (5)) below.
(c) By subtracting the reactive power output from the converter 5 to the power system from the actual output value Q of the reactive power output value as the actual output value of the power generation systemForce output value QcThe obtained electric power
(d) By deriving the reactive power command value Q for the power generation system＊Subtracting the reactive power command value Q to the converter 5c＊The obtained electric power
Thus, the power factor of the inverter 3 is improved. As a result, the neutral point potential variation of the NPC inverter can be reduced.
According to the present embodiment, similarly to the first embodiment, in the NPC inverter/converter, it is possible to suppress the variation in the neutral point potential of the NPC inverter and prevent the increase in the capacitor capacity. As a result, a small, low-cost, and safe power conversion device can be realized.
(third embodiment)
Fig. 5 is a diagram showing an example of a configuration of a system to which the power conversion device according to the third embodiment is applied.
In the present embodiment, the induction generator 1 described in the first embodiment is not provided. The system to which the power conversion device according to the present embodiment is applied can be applied to, for example, a voltage compensator or a power flow (power flow) controller of a power system. In the third embodiment, a converter-side parallel transformer 41 and a power system-side series transformer 42 are provided instead of the transformers 6 and 7 described in the first embodiment. The ac-side terminal of the inverter 3 is connected to the power system via a series transformer 42, the ac-side terminal of the converter 5 is connected to the power system via a shunt transformer 41, and the dc link section is common to the inverter 3 and the converter 5.
Normally, the inverter 3 outputs a compensation voltage or a voltage for controlling a power flow to the power grid, and the converter 5 obtains only the effective power necessary for the operation of the inverter 3 from the power grid. In the present embodiment, reactive power to the power system is output in the same manner as in the first embodiment. However, the reactive power command value for the induction generator 1 described in the first embodiment is the reactive power command value Q for the inverteri＊Is output towards the power system.
From inverter 3 toDerived reactive power QiIs (e) or (f) below.
(e) By subtracting the reactive power output value Q output from the converter 5 to the power system from the reactive power output value Q, which is the actual output value of the power generation systemcThe obtained electric power
(f) By deriving the reactive power command value Q for the power generation system＊Subtracting the reactive power command value Q to the converter 5c＊The obtained electric power
Therefore, the power factor of the inverter 3 is improved, and the neutral point potential variation can be reduced.
According to the present embodiment, similarly to the first embodiment, in the NPC inverter/converter, it is possible to suppress the variation in the neutral point potential of the NPC inverter and prevent the increase in the capacitor capacity. As a result, a small, low-cost, and safe power conversion device can be realized.
While several embodiments of the present invention have been described, the above embodiments are merely presented as examples and are not intended to limit the scope of the invention. The above-described new embodiment can be implemented in various other embodiments, and various omissions, substitutions, and changes can be made without departing from the spirit of the invention. The above-described embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.
Claims (7)
1. A power conversion device is provided with:
an inverter (3) and a converter (5) each having a DC-side terminal and an AC-side terminal, the DC-side terminals being connected to common DC link sections (4a, 4b), and the AC-side terminals being connected to a common power system; and
and a control device (10) that controls reactive power output to the power grid so that the reactive power is the sum of reactive power output from the inverter (3) via the generator (1) and reactive power output directly from the converter (5) via the transformer to the power grid.
2. The power conversion apparatus according to claim 1,
the control device (10) is provided,
calculating a reactive power command value for the converter (5) based on the output current of the converter (5) and the output voltage of the converter (5),
and a control unit configured to control a deviation between a command value of a total of reactive power output from the generator (1) to the power system and reactive power output from the converter (5) to the power system and the calculated reactive power command value for the converter (5) to be output as a reactive power command value for the generator (1).
3. The power conversion apparatus according to claim 2,
the converter (5) is provided with a plurality of switches,
and outputting reactive power corresponding to the reactive power command value for the converter (5) calculated by the control device (10) to the power system within the range of output power capacity.
4. The power conversion apparatus according to claim 2,
the control device (10) is provided,
calculating an invalid current command value for the converter (5) based on a maximum value of the output current of the converter (5) and an effective current command value for the converter (5),
a reactive power command value for the converter (5) is calculated based on the reactive current command value and the output voltage of the converter (5).
5. The power conversion device according to any one of claims 1 to 4,
the inverter (3) supplies electric power to a secondary field winding of the generator (1) whose stator winding is connected to the power system.
6. A power conversion device is provided with:
an inverter (3) and a converter (5), wherein the DC-side terminals are connected to the common DC link sections (4a, 4b), and the AC-side terminals are connected to the common power system; and
and a control device (10) that controls reactive power output to the power grid so that the reactive power is the sum of the reactive power output from the inverter (3) and the reactive power directly output from the converter (5) to the power grid via the transformer.
7. A method for controlling a power conversion device, which is a method for controlling a power conversion device,
the power conversion device comprises an inverter (3) and a converter (5), wherein the inverter (3) and the converter (5) respectively comprise a DC-side terminal and an AC-side terminal, the DC-side terminals are respectively connected to common DC link parts (4a, 4b), the AC-side terminals are respectively connected to a common power system,
in the above-described control method of the power conversion apparatus,
the reactive power output to the power grid is controlled so as to be the sum of the reactive power output from the inverter (3) via the generator (1) and the reactive power output directly from the converter (5) via the transformer to the power grid.
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| JP2018077718A JP7005417B2 (en) | 2018-04-13 | 2018-04-13 | Power converter and control method of power converter |
| JP2018-077718 | 2018-04-13 |
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| Publication number | Publication date |
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| CN110380635A (en) | 2019-10-25 |
| DE102019002713A1 (en) | 2019-10-17 |
| JP7005417B2 (en) | 2022-01-21 |
| JP2019187156A (en) | 2019-10-24 |
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