JP6730946B2 - Power converter controller - Google Patents

Description

Embodiments of the present invention relate to a control device for a power converter.

In recent years, high-voltage DC power transmission (hereinafter, HVDC) is expected to be a means for realizing long-distance power transmission and interconnection between different systems. In HVDC, reduction of power transmission loss and reduction of power transmission line equipment cost can be realized. For example, long-distance power transmission has a cost advantage over AC power transmission. For this reason, HVDC is rapidly becoming popular both at home and abroad.

The HVDC employs a power converter for converting the power of the AC system into DC or converting the DC flowing in the DC system into AC. Conventionally, a separately excited power converter to which a thyristor is applied has been used as the power converter. The self-excited power converter can reduce the dependency on the AC system and the installation area as compared with the separately excited power converter. Therefore, in recent years, application of a self-excited power converter has been promoted.

The self-excited power converter also has an advantage that black start is easy. The black start is to start up the AC system from the power converter when the AC side does not have a power source such as a generator and is composed of only a load. For example, at the time of a power failure, a black start occurs. During black start, the self-excited power converter operates as a voltage source. Therefore, the power converter must supply an inrush current or an unbalanced current to the transformer when the transformer is turned on or the power is supplied to the unbalanced load.

Such inrush current and unbalanced current are often not intended for the DC transmission system. At the time of black start, an inrush current or an unbalanced current flows to the transformer, which may cause an overcurrent or overvoltage state in the power converter, and the protection function may stop the power converter.

Japanese Patent No. 4673328

Embodiments of the present invention provide a controller for a power converter that can continue operation of the power converter during a black start.

In order to solve the above problems, the embodiment is generated based on the deviation between the alternating current command value set according to the line current of the alternating current system and the alternating current measured value measured according to the line current. An AC current control unit that outputs a first voltage command value related to the voltage to be output based on the first command value that has been generated and the AC voltage measurement value that is measured according to the phase voltage of the AC system. The alternating current control unit, in response to the input of a black start command to operate in the absence of the power supply of the alternating current system , the alternating current measured value, extracted from the alternating current measured value, harmonics other than the fundamental wave. A first switching unit for setting the component , a second switching unit for setting the AC current command value to 0 in response to the input of the black start command, and the AC for the input of the black start command. A third switching unit that sets the voltage measurement value to a preset AC voltage command value.

1 is a block diagram illustrating a power converter, a control device, and a DC power transmission system to which these are applied, according to a first embodiment. It is a circuit diagram which illustrates the power converter of 1st Embodiment. It is a block diagram which illustrates the control device of a 1st embodiment. It is a block diagram which illustrates a part of control device of FIG. It is a block diagram which illustrates a part of control device of FIG. It is a block diagram which illustrates a part of control device of a power converter of a modification of a 1st embodiment. It is a block diagram which illustrates the electric power converter which concerns on 2nd Embodiment, a control apparatus, and the DC power transmission system to which these are applied. FIG. 8A is a block diagram illustrating the power converter according to the second embodiment. FIG.8(b) is a block diagram which illustrates a part of power converter of FIG.8(a). It is a block diagram which illustrates the control device of a 2nd embodiment. It is a block diagram which illustrates a part of control device of FIG. It is a block diagram which illustrates a part of control device of FIG.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each portion, the size ratio between the portions, and the like are not necessarily the same as the actual ones. Even if the same portion is shown, the dimensions and ratios may be different depending on the drawings.
In the specification and the drawings of the application, components similar to those described in regard to a drawing thereinabove are marked with like reference numerals, and a detailed description is omitted as appropriate.

FIG. 1 is a block diagram illustrating a power converter, a control device, and a DC power transmission system to which these are applied, according to the present embodiment.
As shown in FIG. 1, the DC power transmission system 100 includes an AC system AS1, an AC system AS2, and a DC system DS1. In the DC power transmission system 100, DC and AC are mutually converted among the AC system AS1, the AC system AS2, and the DC system DS1 to supply electric power. The AC systems AS1 and AS2 are systems that supply AC power. Both the AC system AS1 and the AC system AS2 can be a power transmission side and a power reception side. Elements constituting the AC systems AS1 and AS2 include a power supply, a load, an AC transmission line, and the like. For example, the AC systems AS1 and AS2 can be configured to include a three-phase or single-phase 50 Hz or 60 Hz power supply, a load, and an AC transmission line. The DC system DS1 is a power system that supplies DC power with the AC systems AS1 and AS2.

DC power transmission system 100 includes power converters 1a and 1b and control devices 2a and 2b. The power converters 1a and 1b mutually convert AC power and DC power. The power converters 1a and 1b are connected to the AC system AS1, the DC system DS1, and the AC system AS2 under the control of the control devices 2a and 2b, respectively.

The power converter 1a is connected between the AC system AS1 and the DC system DS1. The power converter 1b is connected between the DC system DS1 and the AC system AS2. The power converters 1a and 1b function as both a forward converter and an inverse converter. That is, in the DC power transmission system 100, the power can be bidirectionally exchanged between the AC system AS1 and the AC system AS2.

The forward converter is a power converter that converts AC power into DC power. The inverse converter is a power converter that converts DC power into AC power. For example, when the AC system AS1 functions as the power transmission side and the power converter 1a functions as a forward converter, the power converter 1a converts the AC power from the AC system AS1 into DC power and supplies the DC power to the DC system DS1. When the AC system AS2 functions as a power receiving side and the power converter 1b functions as an inverse converter, the power converter 1b converts the DC power from the DC system DS1 into AC power and supplies the AC power to the AC system AS2.

FIG. 2 is a circuit diagram illustrating the power converter of this embodiment.
The power converters 1a and 1b have the same configuration, and may be hereinafter referred to as the power converter 1. As shown in FIG. 2, the power converter 1 includes a three-phase bridge circuit 11 and a capacitor 12. The three-phase bridge circuit 11 includes three legs 13 connected in parallel corresponding to the three phases. Each leg 13 includes a unit arm 14 connected in series to the positive side and the negative side. The power converter 1 converts direct current into three-phase alternating current, or converts three-phase alternating current into direct current. The power converter 1 divides the level of the input DC voltage into two and outputs it.

The unit arm 14 includes a switching element 14a and a diode 14b. The switching element 14a is a self-extinguishing element such as an IGBT (Insulated Gate Bipolar Transistor), an IEGT (Injection Enhanced Gate Transistor), and a GTO (Gate Turn-Off thyristor). The diode 14b is connected in antiparallel to the switching element 14a. The diode 14b is a freewheeling diode that allows a current in the direction opposite to the applied voltage to flow to prevent the switching element 14a from being destroyed. Although not shown, each switching element 14a is connected to a drive circuit for turning on and off the self-extinguishing element and a power supply for the drive circuit.

Positive side and negative side DC terminals 15p and 15n of the legs 13 connected in parallel are connected to the DC system DS1. The AC terminals 16u, 16v, 16w of the respective phases are drawn out from the connection nodes of the unit arms 14 on the positive side and the negative side of each leg 13.

A transformer 17 is connected between the connection node of the unit arm 14 on the positive side and the negative side and the AC terminals 16u, 16v, 16w of each phase. The AC system AS1 or the AC system AS2 is connected to the primary side of the transformer 17 via the AC terminals 16u, 16v, 16w. A connection node of the unit arms 14 on the positive side and the negative side is connected to the secondary side of the transformer 17.

A voltage sensor 18a is provided for each phase on the primary side of the transformer 17. The voltage sensor 18a detects the AC voltage of each phase of the AC system and supplies the data of the AC voltage of each phase to the control devices 2a and 2b.

A current sensor 19 is provided in each phase on the secondary side of the transformer 17. The current sensor 19 detects the line current of each phase flowing through the power converters 1a and 1b and supplies the data of the line current of each phase to the control devices 2a and 2b.

The capacitor 12 is connected between the DC terminals 15p and 15n and connected in parallel with each leg 13. The capacitor 12 is a voltage source that supplies the stored energy as a voltage. That is, the three-phase bridge circuit 11 can output the voltage of the capacitor 12 as a pseudo AC voltage by turning on and off the self-extinguishing element.

The DC voltage across the capacitor 12 is detected by the voltage sensor 18b and is supplied to the control devices 2a and 2b as a DC voltage detection value.

FIG. 3 is a block diagram illustrating the control device of the present embodiment.
The control devices 2a and 2b have the same configuration, and hereinafter may be simply referred to as the control device 2. The control device 2 inputs a DC voltage, an AC voltage of each phase, an AC current, or the like, generates a gate signal Vg so as to output desired AC power or DC power, and supplies the gate signal Vg to the power converter 1.

As shown in FIG. 3, the control device 2 includes a DC voltage control unit 21, an AC current control unit 22, a dq coordinate conversion unit 23, an inverse dq coordinate conversion unit 24, and a gate signal generation unit 25. ..

The DC voltage control unit 21 receives the DC voltage command value Vdc* and the DC voltage detection value Vdc. DC voltage command value Vdc* is set, for example, by a higher-level management system (not shown). The DC voltage detection value Vdc is a DC voltage between the DC terminals 15p and 15n. The DC voltage detection value Vdc is detected by the voltage sensor 18b provided in the power converter 1.

The DC voltage control unit 21 performs feedback control or the like so that the detected DC voltage value Vdc matches the desired DC voltage command value Vdc*, and generates the AC active current command value Id*.

Here, the AC effective current means a current having the same phase as the AC system voltage. The AC reactive current means a current having a phase (90° advanced phase) orthogonal to the phase of the AC system voltage. Similarly, the AC effective voltage refers to a voltage having the same phase as the AC system voltage, and the AC reactive voltage refers to a voltage having a phase (90° advanced phase) orthogonal to the phase of the AC system voltage. To do. The same applies to these command values, measured values, and detected values.

The AC current control unit 22 inputs the AC active current command value (first command value) Id* and the AC reactive current command value Iq*. The AC current control unit 22 controls the AC active current measurement value Id to match the AC current measurement value with the AC current command value Id* generated by the DC voltage control unit 21. The AC active current measurement value Id is a d-axis output obtained by performing dq coordinate conversion on the line currents Iu, Iv, and Iw of each phase. As will be described later, the AC current control unit 22 uses non-interference feedback control utilizing rotational coordinate conversion such as dq coordinate conversion.

A black start command BS is input to the AC current control unit 22. As described later in detail, the AC current control unit 22 operates differently from the normal time based on the input of the black start command BS. By performing different operations, the control device 2 generates the command value of the output voltage so as to suppress unintended inrush current and unbalanced current.

The dq coordinate conversion unit 23 inputs the detected values of the line currents Iu, Iv, Iw of the AC system. The detected value is detected by the current sensor 19 provided in the power converter 1 and supplied to the dq coordinate conversion unit 23. The dq coordinate conversion unit 23 performs dq coordinate conversion on the current of each phase in synchronization with the phase of the power system and outputs the AC active current measurement value Id and the AC reactive current measurement value Iq. The dq coordinate conversion unit 23 supplies the AC active current measurement value Id and the AC reactive current measurement value Iq to the AC current control unit 22.

The inverse dq coordinate conversion unit 24 is connected to the output of the alternating current control unit 22. The inverse dq coordinate conversion unit 24 corresponds the d-axis output voltage command value Vd and the q-axis output voltage command value Vq output from the AC current control unit 22 to each phase of the system in synchronization with the phase of the power system. Convert to voltage command value.

The gate signal generator 25 is connected to the output of the inverse dq coordinate converter 24. The gate signal generator 25 includes, for example, a PWM control circuit. The gate signal generation unit 25 outputs the gate signal Vg in which the duty and the like are set according to the voltage command value corresponding to each phase output from the inverse dq coordinate conversion unit 24.

4 and 5 are block diagrams illustrating a part of the control device of FIG.
In FIG. 4, a configuration example of the AC current control unit 22 of the control device 2 is shown as a block diagram. FIG. 5 shows a configuration example of high-pass filters that are filters 35d and 35q for removing the DC component.

As shown in FIGS. 1 and 4, the alternating current control unit 22 includes a first switching unit 31, a second switching unit 32, and a third switching unit 33. The first switching unit 31, the second switching unit 32, and the third switching unit 33 each include two switches. The AC current control unit 22 includes a portion related to the AC active current and a portion related to the AC reactive current. The portion related to the AC active current includes a switch 31d (first switching unit 31), a switch 32d (second switching unit 32), and a switch 33d (third switching unit 33). The portion related to the AC reactive current includes a switch 31q (first switching unit 31), a switch 32q (second switching unit 32), and a switch 33q (third switching unit 33).

The switch 31d of the first switching unit 31 inputs one of the two inputs to the adder/subtractor 34d. The two inputs are the AC active current measurement value Id and the signal Id(h) obtained by removing the DC component from the AC active current measurement value Id.

The switch 31d switches the AC active current measurement value Id subtracted from the AC active current command value Id* for feedback control to the signal Id(h) passing through the filter 35d in response to the input of the black start command BS. As a result, the DC component can be removed from the AC active current measurement value Id to be fed back.

As shown in FIG. 5, the filters 35d and 35q are composed of, for example, first-order delay elements 35d1 and 35q1 and adder/subtractors 35d2 and 35q2. Removing the direct current component on the dq rotation coordinates is equivalent to removing the fundamental wave frequency (for example, 50 Hz or 60 Hz) of the alternating current system. When the rotational coordinate conversion is not used for AC current control, the filter may be a band elimination filter that passes frequencies other than the fundamental frequency of the AC system.

The switch 32d of the second switching unit 32 connects one of the two inputs to the adder/subtractor 34d. The two inputs are the AC active current command value Id* and the AC active current command value set to 0 (zero).

The switch 32d switches the AC active current command value Id* to 0 (zero) in response to the input of the black start command BS.

The adder/subtractor 34d calculates a deviation from each output of the switches 31d and 32d, outputs the deviation, and inputs the deviation to the proportional controller 36d. The proportional controller 36d generates a feedback amount so that the deviation approaches zero.

The proportional controller 36d is, for example, a controller having a proportional control gain Kp. The proportional controller 36d may be a proportional-plus-integral controller having a gain (Kp+Ki/s). The controller may of course be a PID controller.

The switch 33d of the third switching unit 33 switches between the AC effective voltage measurement value Vdac and the AC effective voltage command value Vdac*. Here, the AC effective voltage command value Vdac* is a preset voltage command value, and has a predetermined amplitude and frequency. The AC effective voltage measurement value Vdac is a d-axis voltage obtained by measuring the voltage of each phase of the power system and converting the dq coordinate.

The AC effective voltage, the AC reactive voltage, the AC effective current, and the AC reactive current are based on the phase of the AC effective voltage command value Vdac* at the time of black start. That is, the AC reactive voltage and the AC reactive current have a phase (a phase advanced by 90°) orthogonal to the phase of the AC valid voltage command value Vdac*. The AC active current has the same phase as the AC active voltage command value Vdac*. The dq coordinate conversion unit 23 and the inverse dq coordinate conversion unit 24 operate in synchronization with the phase of the AC effective voltage command value Vdac* at the time of black start.

The switch 33d switches the AC valid voltage measurement value Vdac to the AC valid voltage command value Vdac* in response to the input of the black start command BS, and supplies the AC valid voltage command value Vdac* to the adder 37d. The adder 37d adds the feedback amount output from the proportional controller 36d and the output of the switch 33d, and outputs it as a d-axis output voltage Vd for a command value for setting the output voltage.

The portion related to the AC reactive current is also configured similarly to the portion related to the AC active current. That is, the switch 31q of the first switching unit 31 switches the AC reactive current command value Iq* between 0 and a non-zero command value and outputs it. The switch 32q of the second switching unit 32 switches and outputs the AC reactive current measurement value Iq and the signal Iq(h) of the harmonic component of the AC reactive current measurement value Iq output from the filter 35q. The switches 31q and 32q are input to the adder/subtractor 34q. The adder/subtractor 34q supplies the calculated deviation to the proportional controller 36q. The switch 33q switches one of the two inputs from the AC reactive voltage measured value Vqac to the AC reactive voltage command value Vqac*. The output of the proportional controller 36q and the output of the switch 33q are added by the adder 37q and output as the q-axis output voltage Vq for setting the output voltage.

The feedback amount output from the proportional controller 36d of the AC active current portion is multiplied by -1, and the subtracter 38d further subtracts the non-interference amount obtained by multiplying the AC reactive current measurement value by ω×L.

The feedback amount output from the proportional controller 36q for the AC reactive current portion is also multiplied by -1, and the non-interference amount obtained by multiplying the AC active current measurement value by (ω×L) is added by the adder/subtractor 38q.

In this way, mutual interference can be eliminated by adding a non-interference amount to each of the active current side and the reactive current side. Therefore, the control device 2 can independently perform the operation on the active current side and the reactive current side. Note that the proportional controllers 36d and 36q and the non-interference amount calculation are components that are also used during normal operation. In the control device 2 of the present embodiment, by adding the first to third switching units 31 to 33, it is possible to divert and use the AC current control unit that is normally used.

The operation of the control device 2 of this embodiment will be described in detail. As described above, since the AC active current and the AC reactive current can be operated independently, the AC active current will be described here. The same applies to the AC reactive current.

First, the case where there is no black start command BS will be described. The switch 31d of the first switching unit 31 supplies the AC active current measurement value Id to the adder/subtractor 34d without passing through the filter 35d. The switch 32d of the second switching unit 32 supplies a non-zero AC active current command value Id* to the adder/subtractor 34d.

The deviation between the AC active current command value Id* and the AC active current measurement value Id is obtained by the adder/subtractor 34d, and the deviation is input to the proportional controller 36d. The proportional controller 36d multiplies the deviation by the gain and calculates the feedback amount.

Further, the proportional controller 36d multiplies the above feedback amount by -1 and outputs the result. The non-interference amount obtained by multiplying the AC reactive current measurement value by (ω×L) is subtracted from the output from the proportional controller 36d. ω is the angular frequency of the AC system, and L is the interconnection inductance.

The switch 33d of the third switching unit 33 supplies the AC effective voltage measurement value to the adder 37d. The adder 37d adds the AC effective voltage measurement value Vdac to the decoupling feedback amount, and outputs the command value of the voltage that the power converter 1 should output. By the above calculation, the AC active current measurement value Id is controlled so as to match the AC active current command value Id*.

Next, the operation when the black start command BS is input will be described. When the black start command BS is input, the switch 31d of the first switching unit 31 switches the input to the adder/subtractor 34d to the signal Id(h) via the filter 35d. The switch 32d of the second switching unit 32 switches the input to the adder/subtractor 34d to zero. Since the filter 35d is a high-pass filter, the signal Id(h) has a DC component removed, and includes a harmonic component other than the fundamental component of the AC system. The proportional controller 36d calculates the feedback amount so that the harmonic component of the AC system becomes zero.

The switch 33d of the third switching unit 33 switches the input to the adder 37d from the AC effective voltage measured value Vdac to the AC effective voltage command value Vdac*. At the time of black start, the AC system is cut off, and the control device 2 cannot obtain the system voltage. Therefore, the control device 2 internally generates a command value corresponding to the voltage of the normal AC system and uses it as the fixed AC voltage command value Vdac*.

In this way, the control device 2 can suppress the inrush current of the transformer and the unbalanced current due to the unbalanced load by controlling the components of the alternating current system other than the fundamental wave component to zero.

The AC effective voltage command value Vdac* may be a waveform that rises with time from a low value such as zero in response to the input of the black start command BS. By setting the AC effective voltage command value Vdac* to have such a time-varying waveform, the output can be soft-started and the influence on the load can be reduced.

The effects of the control device 2 of the present embodiment will be described.
In the control device 2 of the present embodiment, the AC current control unit 22 includes a first switching unit 31, a second switching unit 32, and a third switching unit 33. The 1st switching part 31, the 2nd switching part 32, and the 3rd switching part 33 switch an input according to the input of the black start command BS. When the black start command BS is input, the first switching unit 31 removes the fundamental wave component of the AC active current measurement value Id and the AC reactive current measurement value Iq to remove the harmonic component signal Id(h). , Iq(h). The second switching unit 32 switches the AC active current command value Id* and the AC reactive current command value Iq* to zero. The control device 2 generates a command value of the output voltage so that the signals Id(h) and Iq(h) including the harmonic components of the AC active current measurement value Id and the AC reactive current measurement value Iq are set to zero, The gate signal is supplied to the power converter 1 based on this.

The third switching unit 33 switches the AC valid voltage measurement value Vdac and the AC reactive voltage measurement value Vqac to the AC valid voltage command value Vdac and the AC reactive voltage command value Vqac, respectively, in response to the input of the black start command BS. Therefore, the controller 2 can continue to operate even during black start when the system voltage does not exist.

The inrush current flowing in the transformer during black start and the like, the unbalanced current flowing due to the unbalanced load, and the like are extracted as harmonic components of the AC active current measurement value Id and the AC reactive current measurement value Iq. As described above, the control device 2 of the present embodiment controls these harmonic components to zero, so that inrush current, unbalanced current, etc. can be suppressed. Therefore, the control device 2 can prevent the inrush current, the unbalanced current, or the like from unintentionally operating the current protection function or the like of the power converter 1 to stop the power transmission operation.

In the control device 2 of the present embodiment, even if the voltage phase of the AC system necessary for black start does not exist, in the control device 2 of the present embodiment, the AC effective voltage command value generated inside the control device 2 or the like. Can be used, so that the operation can be stably continued.

[Modification]
FIG. 6 is a block diagram illustrating a part of the control device of this modification.
In the case of the above embodiment, when the black start command BS is input, the third switching unit 33 inputs the fixed AC voltage command value Vdac* after the soft start has elapsed. Since the power system is connected to the load of the power converter, the load variation may be large. Therefore, an overload state or the like may occur in the case of setting to supply a constant voltage regardless of the impedance of the load.

In this modification, the AC effective voltage command value Vdac* at the black start is corrected according to the current flowing according to the load. As shown in FIG. 6, in the present modification, the AC current control unit 122 further includes a slope gain unit 131 and an adder/subtractor 132.

The AC gain measurement value Id is input to the slope gain unit 131. The slope gain unit 131 outputs a voltage correction value Vcor according to the AC active current measurement value Id. For example, the slope gain unit 131 is a coefficient unit having the slope gain Gslope set to a constant value. Therefore, the slope gain unit 131 outputs Gslope×AC active current measurement value Id as the voltage correction value Vcor of the voltage command value.

The correction value output from the slope gain unit 131 is subtracted from the AC effective voltage command value Vdac* by the adder/subtractor 132. The AC effective voltage command value Vdac(cor) thus corrected is added to the feedback amount.

If the AC voltage command value is simply a fixed value, the electric power changes depending on the load. Therefore, when the load is heavy, a larger current than necessary may flow. Therefore, in the present modification, the slope gain is used to adjust the AC voltage command value in which the current is suppressed according to the current measured by the current sensor. Even if the load is heavy, the current can be suppressed by subtracting the amount of excess current from the voltage command value by applying the applied gain and impedance.

The block diagrams, block diagrams, and the like of the above-described modified examples of the embodiments are examples, and the present invention is not limited to the illustrated cases. For example, the control device 2 may be realized by controlling a computer including a CPU (Central Processing Unit) with a predetermined program. The program in this case can implement the processing of each unit as described above by physically utilizing the hardware of the computer. How to set the range processed by hardware and the range processed by software including a program is not limited to a particular mode. A part or all of the block diagram may be replaced with a program. The control devices 2a and 2b may be configured as a system realized by a common computer.

Further, although not shown, the control device 2 includes a storage unit that stores information necessary for the processing of each unit described above, such as a measured value and a command value. A storage area for information that is input from the outside and temporarily stored and information that is exchanged by absorbing the difference in processing timing between the respective units can also be regarded as the storage unit. These circumstances also apply to the case of other embodiments described later.

[Second Embodiment]
In the above-described embodiment, the example in which the three-phase/two-level converter is used as the power converter has been described. The configuration of the power converter is not limited to this. As another example, a case where an MMC (Modular Multilevel Converter) is used as a power converter will be described.

FIG. 7 is a block diagram illustrating a power converter, a control device, and a DC power transmission system to which these are applied, according to the present embodiment.
FIG. 8A is a block diagram illustrating the power converter of this embodiment. FIG.8(b) is a block diagram which illustrates a part of power converter of FIG.8(a).
As shown in FIG. 7, the control devices 202a and 202b are connected to the power converters 201a and 201b, respectively. The power converters 201a and 201b have the same configuration, and may be described as the power converter 201 below. Further, the control devices 202a and 202b also have the same configuration, and may be hereinafter described as the control device 202.

As shown in FIG. 8A, the power converter 201 has legs 261 connected in parallel corresponding to the three phases. Each leg 261 has unit arms 262a and 262b connected in series on the positive side and the negative side.

The unit arms 262a and 262b are configured by connecting unit cells 263 in multiple stages in series. The unit cell 263 is a unit converter called a chopper cell.

A current sensor 266 is provided on each of the unit arms 262a and 262b. The current sensor 266 detects the current of each of the unit arms 262a and 262b and supplies current data to the control device 202.

As shown in FIG. 8B, the unit cell 263 includes a switching element 263a, a diode 263b, and a capacitor 263c. The switching element 263a is a self-extinguishing type semiconductor element. Two switching elements 263a are connected in series. Although not shown, each switching element 263a is connected to a drive circuit and a power supply for turning on/off the self-turn-off element.

The diode 263b is a free wheeling diode. The two diodes 263b are respectively connected in antiparallel to the switching elements 263a connected in series.

The capacitor 263c is connected in parallel to the two switching elements 263a connected in series.

The unit cell 263 is cascode-connected to another unit cell 263 or the like by the two terminals T1 and T2. In order to connect the plurality of unit cells 263 to the cascode, the terminal T1 of one unit cell 263 is connected to the terminal T2 of the other unit cell 263.

The positive and negative terminals of the legs 261 connected in parallel are DC terminals 215p and 215n connected to the DC system DS1. The positive and negative unit arms 262a and 262b in each leg 261 are connected via a buffer reactor 264. The AC terminals 216u to 216w of the respective phases are drawn out from the midpoint of the positive and negative side buffer reactors 264 via the transformer 265.

The power converter 201 can output a stepwise multilevel waveform by shifting the operation timing of the unit cell 263. Therefore, the power converter 201 can make the output waveform approximate to a sine wave. In the power converter 201 using MMC, it is possible to reduce or eliminate the capacity of the AC filter, which was necessary in the three-phase two-level converter. The power converter 201 does not require a high withstand voltage capacitor such as a three-phase two-level converter.

The unit arms 262a and 262b may be formed by connecting n unit cells 263 in series. Although n=2 in the above description, it is sufficient if n≧1. In addition, the reactance component of the transformer 265 may be used to reduce the buffer reactor 264.

Although not shown, a voltage sensor is provided for each unit cell 263. This voltage sensor detects the voltage across the capacitor 263c and supplies voltage data to the control device 202.

The power converter 201 as described above operates by turning on/off each switching element 263a in accordance with the gate signal output from the control device 202.

As shown in FIG. 9, the control device 202 includes a capacitor voltage control unit 221, an alternating current control unit 22, a circulating current control unit 223, a fourth switching unit 224, and a fifth switching unit 225. Including. The alternating current control unit 22 has the same configuration as in the other embodiments described above. The same components are assigned the same reference numerals and detailed description thereof will be appropriately omitted.

The capacitor voltage control unit 221 inputs the cell capacitor voltage command value Vc* and the average voltage Vc of all cell capacitors. The capacitor voltage control unit 221 outputs a command value requesting a required voltage for the capacitor 263c of the unit cell.

The alternating current control unit 22 is connected to the output of the adder 226 via the switch 224a of the fourth switching unit 224. The adder 226 adds the output of the capacitor voltage control unit 221 and the output of the fifth switching unit 225 and outputs the result. The AC current control unit 22 determines the power based on the AC active current command value (second command value) Id* to which the command value from the capacitor voltage control unit 221 is added and the preset AC reactive current command value Iq*. It outputs a voltage command value that requests the required voltage on the AC side of converter 201.

The circulating current control unit 223 inputs the zero-phase circulating current command value Ic0* and the circulating current command values Icα*, Icβ*. The circulating current control unit 223 stores the internal power converter 201 based on the zero-phase circulating current command value Idc0* to which the DC current command value Idc* is added by the adder 227 and the circulating current command values Icα* and Icβ*. It outputs a command value that requests the voltage required for the circulating current to flow. This command value is added to the voltage command value output from the AC current control unit 22 by the adder 228. The circulating current is a current that circulates through the legs 261 mainly for equalizing the capacitor voltage. The circulating current referred to here includes a component that remains without going out of the power converter 201 and a component that goes out toward the DC side.

The fourth switching unit 224 includes two switches 224a and 224b. One switch 224a switches one input to one of two outputs according to the black start command BS. The input of the switch 224a is connected to the output of the adder 226. The adder 226 adds the output of the capacitor voltage control unit 221 and the output of the fifth switching unit 225 and outputs the result.

The other switch 224b switches between two inputs and connects them to one output according to the black start command BS. The output of the switch 224a is connected to one input of the switch 224b. The DC current command value Idc* is supplied to the other input of the switch 224b. The output of the switch 224b is supplied to the circulating current control unit 223 via the adder 227.

The fourth switching unit 224 outputs the DC current command value Idc* added to the zero-phase circulating current command value Ic0* according to the input of the black start command BS, and the AC active current output from the capacitor voltage control unit 221. Switch to the command value Id*.

The fifth switching unit 225 switches one of the two inputs to one output. The value of the DC power based on the measured value is supplied to one input of the fifth switching unit 225. The value of the AC power based on the measured value is supplied to the other input of the fifth switching unit 225. In this example, the DC power based on the measured value is calculated by the multiplier 229. The measured value Idc of the DC current and the DC voltage command value Vdc* are input to the multiplier 229. The AC power based on the measured value is calculated by the multiplier 230. The AC active current measurement value Id detected by the current sensor 266 and the AC active voltage command value Vdac* preset by the host system or the like are input to the multiplier 230.

The fifth switching unit 225 switches the power added to the command value from the capacitor voltage control unit 221 from DC power to AC power according to the input of the black start command BS. That is, the fifth switching unit 225 switches the power to be fed forward to the output from the capacitor voltage control unit 221 between the DC power and the AC power.

Hereinafter, the details of each of the above units will be described. The gain in each of the following sections is a control block that performs PID control on the deviation and performs mutual conversion of the current command value and the voltage command value. Further, various measured values input to the control device 202 are obtained by voltage values and current values from the current sensor 266, the voltage sensor of the capacitor 263c, sensors installed in the system, and the like, and calculations from these values. Furthermore, a higher-level management system that determines various command values and inputs them to the control device 2 is called a higher-level system. The calculation of the measurement value or the calculation of the command value based on the measurement value may be performed outside the control device 202 or may be performed by a calculation unit inside the control device 202. That is, it is free to use a value calculated outside the upper system or the like or a value calculated inside the control device 202.

As shown in FIG. 10, the capacitor voltage controller 221 includes an adder/subtractor 211a and a proportional controller 221b. The capacitor voltage controller 221 uses the adder/subtractor 211a to calculate the deviation between the capacitor voltage command value Vc* of each cell and the capacitor average voltage Vc of all cells. The deviation output from the adder/subtractor 221a is input to the proportional controller 221b, and the proportional controller 221b generates a current command value according to the deviation by, for example, PID control. The capacitor voltage command value Vc* is input from the upper system. The capacitor average voltage Vc is calculated based on the measured value of the capacitor 263c from the voltage sensor.

Normally, in order to include the energy corresponding to the power output from the power converter 201 on the DC side in the AC command value, the DC command value obtained by converting the power into the current command value from the capacitor voltage control unit 221. Is added to feed forward. That is, the electric power supplied in the DC power transmission is the electric power that the power converter 201 is accommodating separately from the energy of the capacitor 263c. The current command value including the interchanged power is the AC active current command value Id* described below.

As shown in FIG. 11, the circulating current control unit 223 includes an adder/subtractor 223a, a proportional controller 223b, a limiter 223c, a setting unit 223d, and an adder 223e. Regarding the zero-phase component of the circulating current controller 223, the circulating current controller 223 uses the adder/subtractor 223a to obtain the deviation between the DC current command value Idc0* and the DC current measured value Idc. Then, the proportional controller 223b generates a voltage command value according to the deviation. Further, a DC voltage command value Vdc* is added to this voltage command value. The DC voltage command value Vdc* is a command value input from the host system. As will be described later, a zero-phase circulating current command value Ic0* is added to the DC current command value Idc0*. The zero-phase circulating current command value Ic0* is a command value corresponding to the zero-phase component obtained by the αβ0 converter 231 from the measured value. The DC current command value Idc* is a command value input from the upper system. The output of the circulating current controller 223 is added to the output of the alternating current controller 22.

Further, the circulating current control unit 223 includes a limiter 223c and a setting unit 223d. The limiter 223c defines the fluctuation range of the zero-phase circulating current command value Ic0*. As the upper and lower limit values of the limiter 223c, the limit values input from the upper system are set by the setting unit 223d. In this example, the limit values are set to positive and negative values with the same absolute value.

The limit value is set such that, of the pair of power converters 201a, 201b installed at both ends of the DC system DS1, the power converter 201a on the side receiving the black start command BS is the current control end. .. The limit value of the other power converter 201b is set so as to be the voltage control end.

The limit value for the current control end is a value other than 0, and the limit value for the voltage control end is 0. When the limit value is not 0, the input value is allowed to change, and the upper and lower limits of the change are defined. When the limit value is 0, the DC voltage command value is output as it is. The current control end and the voltage control end will be described later.

The circulating current command value is a zero phase component of the circulating current obtained by αβ0 conversion based on the interphase balance control operation amount and the PN balance control operation amount. The inter-phase balance control operation amount is a current value corresponding to a voltage that balances the three-phase capacitor voltages. The PN balance control operation amount is a current value corresponding to a voltage for balancing the capacitor voltages of the positive and negative unit arms 262a and 262b. The inter-phase balance control operation amount and the inter-PN balance control operation amount are obtained by calculation from the measurement value of the capacitor 263c from the voltage sensor.

The αβ0 conversion unit 231 converts the α-phase and β-phase two-phase components (three-phase two-phase conversion) into zero-phase components. This zero-phase component is added to the DC current command value Idc* as the zero-phase circulating current command value Ic0*. Note that the α-phase component and the β-phase component may also be used for the calculation, but since they are not always necessary for the principle description of the present embodiment, the description of the calculation is omitted.

The fourth switching unit 224 includes switches 224a and 224b. The switch 224a switches the output destination of the current command value from the capacitor voltage control unit 221 from the AC current control unit 22 to the circulating current control unit 223 based on the black start command BS from the upper system. The switch 224b switches the DC current command value Idc* input to the circulating current control unit 223 to the current command value from the capacitor voltage control unit 221 together with the switching of the switch 224a.

The fifth switching unit 225 is a switch that switches the power to be fed forward to the output from the capacitor voltage control unit 221 from the DC power to the AC power according to the input of the black start command BS. This DC power is obtained from the measured value from the current sensor 266 and the DC voltage command value Vdc* from the host system. The DC voltage command value Vdc* is the same as the DC voltage command value Vdc* input to the circulating current control unit 223. The AC power is obtained from the measured value from the current sensor 19 and the command value of the AC voltage from the host system. The electric power to be fed forward is a value obtained by converting the electric power into the dimension of the current.

The operation of the control device 202 of this embodiment will be described. In the following description, an example in which the power converter 201a functions as a forward converter on the power transmitting side and the power converter 201b functions as an inverse converter on the power receiving side is described as an example of controlling the power converter 201a that is the forward converter. To do. In the normal state, the AC power from the power source in the AC system AS1 is converted into DC power by the power converter 201a and supplied to the DC system DS1, and this DC power is converted into AC power by the power converter 201b. It refers to the state of being supplied to the AC system AS2.

First, the normal operation when the black start command BS is not input will be described. The capacitor voltage control unit 221 obtains a voltage required as the current capacitor voltage from the deviation between the capacitor average voltage Vc of all cells and the capacitor voltage command value Vc* of each cell, and converts it into a current command value and outputs it. For example, when the average capacitor voltage Vc is lower than the capacitor voltage command value Vc*, the voltage is increased, and when it is higher than the capacitor voltage command value Vc*, the current command value is output so as to decrease the voltage.

A current value converted from DC power is fed forward to this current command value, and is input to the AC current control unit 22 as an AC active current command value Id*. That is, the effective power on the AC side is determined by the sum of the control current of the capacitor 263c and the energy on the DC side, which is the interchange power.

The AC current control unit 22 outputs the command value of the AC voltage corresponding to the active current and the reactive current required of the power converter 201, based on the AC active current command value Id* and the AC reactive current command value Iq*. An AC voltage measurement value obtained from the grid is added to this command value, and a voltage command value from a circulating current control unit 223 described later is added to the command value, which is output as a voltage command value to the power converter 201. That is, a command value requesting the voltage required for the capacitor 263c and the voltage required for the circulating current is added to the system voltage to obtain the voltage command value.

The circulating current control unit 223 obtains a required voltage command value from the deviation between the DC current command value Idc0* to which the zero-phase circulating current command value Ic0* is added and the measured DC current Idc as described above, Further, it outputs a voltage command value that is a combination of the DC voltage command value Vdc* from the host system.

Here, the power converters 201a and 201b used in the power transmitting end and the power receiving end in the HVDC are either voltage control terminals that determine the voltage or current control terminals that determine the current. Normally, the power transmission end serves as a voltage control end, which performs constant voltage control. Then, the power receiving end becomes a current control end, and the current is controlled by changing the voltage. As a result, the power receiving end can generate a command value that allows the current to flow and can freely move the voltage within a certain range. The operating points of the two power converters 201a and 201b of the voltage control end and the current control end are the intersections of the constant voltage at the voltage control end and the fluctuating voltage at the current control end. This is because the operating point cannot be determined if any of the voltages fluctuates freely.

For example, as described above, it is assumed that the power converter 201a is a power converter end forward converter and the power converter 201b is a power receiver end inverse converter. The limiter 223c of the control device 202a at the power transmission end is set to 0 as the upper and lower limit values. Therefore, the DC voltage command value Vdc* is output as it is, and the voltage becomes constant. As a result, the power converter 201a functions as a voltage control terminal that fixes the voltage.

On the other hand, the limiter 223c of the control device 202b at the power receiving end is set to a value other than 0 as the upper and lower limit values. Therefore, the DC voltage command value is allowed to change. When the DC voltage command value changes within the range of fluctuation according to the situation, the power converter 201b functions as a current control end that changes the current.

In this way, the control device 202b supplies the gate signal Vg to the power converter 201b based on the command value of the generated AC voltage.

Next, the case where the black start command BS is input will be described. At the black start, the switch 224a of the fourth switching unit 224 disconnects the output destination of the capacitor voltage control unit 221 from the AC current control unit 22. At the same time, the switch 224b switches the DC current command value Idc* input to the circulating current control unit 223 to the command value output from the capacitor voltage control unit 221.

Since the system voltage normally exists, power can be generated and output from the system voltage and the current output from the power converter as described above. However, at the time of black start, there is no power supply on the AC side, and a current flows depending on the load.

Therefore, control device 202 switches the output destination of capacitor voltage control unit 221 to set the command value added to zero-phase circulating current command value Ic0* as the current command value output from capacitor voltage control unit 221. .. In other words, the voltage required by the capacitor 263c is not included in the AC active current command value Id* on the AC side by request from the AC current control unit 22, but is changed to the zero-phase circulating current command value Ic0* on the DC side. It is changed so as to request from the circulating current control unit 223.

Further, in response to the black start command BS, the fifth switching unit 225 switches the current value added to the current command value output from the capacitor voltage control unit 221 to the current value converted from AC power. That is, at the time of black start, the command value is controlled on the DC side, so this time, AC power is added in advance to feed forward.

The AC voltage in this AC power is the AC effective voltage command value Vdac. The AC current in this AC power is an AC active current measurement value Id detected by the current sensor 266. In this example, the AC power is obtained by inputting the AC active voltage command value Vdac* and the AC active current measurement value Id to the multiplier 230.

When the AC system AS1 is in black start, the limit value setting of the limiter 223c of the circulating current control unit 223 is changed. For example, when the power supply of the AC system AS1 is turned off and the power converter 201a at the power transmission end is black-started, the limiter 223c of the control device 202a receiving the black start command BS is set to 0 as the limit value from the upper system. Set a value that is not. Thereby, unlike the normal time, the power converter 201a can function as a current control end that changes the current.

On the other hand, in the control device 202b of the power converter 201b at the power receiving end, the limiter 223c sets 0 as the limit value from the upper system. Thereby, unlike the normal time, the power converter 201b functions as a voltage control terminal that fixes the voltage.

By the above switching operation, the circulating current control unit 223 determines the required voltage command from the deviation between the measured DC current and the DC current command value obtained by adding the circulating current command value to the command value from the capacitor voltage control unit 221. The value is obtained, and the voltage command value including the direct current voltage command value from the host system is output.

A value obtained by adding a fixed AC voltage command value to this voltage command value is output as a voltage command value to the power converter 201a.

The effects of the control device 202 of this embodiment will be described. The control device 202 of the present embodiment supplies a gate signal to the power converter 201, which is an MMC, to control it. The control device 202 includes a fourth switching unit 224. The fourth switching unit 224 changes the DC current command value Idc* added to the zero-phase circulating current command value Ic0* to the capacitor according to the input of the black start command BS that operates in a state where the AC system AS1 is not powered. Switching to the command value from the voltage control unit 221.

Therefore, during black start, the capacitor voltage can be maintained by switching the control on the AC side to the control on the DC side.

Moreover, the control device 202 of the present embodiment includes a fifth switching unit 225. The fifth switching unit 225 adds the power to be added to the command value from the capacitor voltage control unit 221 to obtain the power output from the power converter 201, from the DC power to the AC power according to the input of the black start command BS. Switch to power.

Therefore, it is possible to request the circulating current control unit 223 to include the AC power to be obtained by the power converter 201 in the command value from the capacitor voltage control unit 221.

The circulating current control unit 223 has a setting unit 223d that defines the fluctuation range of the zero-phase circulating current command value Ic0* and sets the limit value. The limiter 223c sets a limit value of the power converter 201a on the side receiving the black start command BS among the pair of power converters 201a and 201b installed at both ends of the DC system DS1 as a current control end. , The other power converter 201b is used as a voltage control terminal to set a limit value.

In a situation where there is no power supply for the AC system AS1, it is not possible to freely supply the power required at the power receiving end side. Therefore, by setting the power receiving end side as the voltage control end and the power transmission end side as the current control end, it is possible to control the current at the black start power transmission end side. Moreover, the switching between the voltage control end and the current control end can be performed only by the information on the DC side.

According to the embodiment described above, it is possible to realize a power converter control device that can continue the operation of the power converter at the time of black start.

Although some embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalents thereof. Further, the above-described respective embodiments can be implemented in combination with each other.

1,1a,1b power converter, 2,2a,2b control device, 11 three-phase bridge circuit, 12 capacitor, 13 leg, 14 unit arm, 17 transformer, 21 DC voltage control unit, 22,122 AC current control unit , 23 dq coordinate conversion unit, 24 inverse dq coordinate conversion unit, 25 gate signal generation unit, 31 first switching unit, 32 second switching unit, 33 third switching unit, 35d, 35q filter, 201, 201a, 201b Power converter, 202, 202a, 202b Control device, 221 Capacitor voltage control unit, 223 Circulating current control unit, 224 Fourth switching unit, 225 Fifth switching unit, 261 legs, 262a, 262b Unit arm, 263 unit Cell, 264 buffer reactor, 265 transformer, 266 current sensor

Claims (7)

A controller for a power converter that controls a power converter that interconnects an AC power system and a DC power system,
A first command value generated based on a deviation between an AC current command value set according to the line current of the AC system and an AC current measurement value measured according to the line current, and a phase voltage of the AC system And an AC current control unit that outputs a first voltage command value related to the voltage to be output based on the measured AC voltage value according to
The alternating current control unit,
According to the input of the black start command which operates in the absence of the power supply of the AC system, the AC current measurement value is set to a harmonic component other than the fundamental wave extracted from the AC current measurement value . Switching part,
A second switching unit that sets the alternating current command value to 0 in response to the input of the black start command;
A third switching unit that sets the AC voltage measurement value to a preset AC voltage command value in response to the input of the black start command;
Of the power converter including the. Further comprising a rotating coordinate conversion unit for converting the alternating current measured value into a rotating coordinate,
The AC current control unit includes a filter that is connected between the rotary coordinate conversion unit and the first switching unit and that removes a DC component from the AC current measurement value to extract an AC component. Power converter controller. A capacitor voltage control unit that outputs a second command value that requests a voltage required for a capacitor of a unit cell connected to a cascode in the power converter;
A command value requesting a voltage required for a circulating current inside the power converter based on the circulating current command value to which the second command value is added, and the command value being added to the first voltage command value. A circulating current controller that outputs a two-voltage command value;
A fourth switching unit that switches a second command value added to the circulating current command value to a preset direct current command value in response to the input of the black start command;
Further equipped with,
The control device for a power converter according to claim 1, wherein the alternating current control unit outputs the first voltage command value based on the second command value. To obtain the power the power converter output, the power to be added to the second command value, in accordance with the input of the black start command, further comprising a fifth switching section for switching the AC power from the DC power The control device for the power converter according to claim 3. The circulating current control unit,
A limiter that defines the fluctuation range of the circulating current command value,
A setting unit for setting a limit value to the limiter,
Including
The setting unit of the pair of power converters installed on both ends of the DC system, the power converter on the side receiving the black start command sets the limit value to a current control terminal and the other power The control device for a power converter according to claim 3 or 4, wherein a limit value for setting the converter as a voltage control end is set. The control device for a power converter according to claim 1, wherein the AC voltage command value changes at a predetermined time change rate in response to the input of the black start command. The control device for a power converter according to any one of claims 1 to 6, wherein the AC voltage command value is corrected by subtracting a voltage obtained by multiplying the AC current measurement value by a predetermined slope gain.

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