JP2013051798A - Converter, and control method and control program therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform DC control between Y-connection sections.SOLUTION: Voltages and currents in individual phases of a dual Y-connection circuit 23 of a power converter section 20 are detected. A switching element 25 of a power converter section 20 is controlled so that at least one of the voltage and current in a DC circuit derived from the detection result is constant, based on relevant information showing relationship between voltages and currents in individual phases of the dual Y-connection circuit 23 of the power converter section 20 and voltages and currents in the DC circuit. The DC circuit is that contained in an equivalent circuit of the dual Y-connection circuit.

Description

  The present invention relates to a converter, a converter control method, and a converter control program.

  In recent years, performance of self-excited elements has been rapidly improved, and self-excited converters using self-excited switching elements have been proposed. This self-excited converter is capable of supplying any active / reactive power without depending on the AC system to be linked, and has many advantages over other-excited converters using other-excited switching elements such as thyristors. Have

  As a self-excited converter, a so-called MMC (Modular Multilevel Converter) circuit configuration in which a circuit module called a chopper or a single-phase inverter cell is connected to each phase of the electric power system in multiple stages is put into practical use. Has been. The MMC converter can output a high AC voltage while reducing the number of switching elements connected in series because the combined voltage for the number of cell stages is output as an AC voltage. Among the MMC systems, there is a double Y-connection MMC system in which Y-connection circuits in which Y-connections are made for circuits of each phase in which cells are connected in multiple stages are provided as circuit systems capable of handling active power. In Non-Patent Document 1, a DC power source is connected to two Y connection portions of a double Y connection MMC, and in a motor drive circuit, a current flowing through each phase circuit of the double Y connection MMC is converted into a circulating current and an AC current. Describes the technology to disassemble and handle.

Hideaki Fujita et al., “Analysis and Control of DC Capacitor Voltage of MMCC-DSCC”, Proceedings of 2010 IEEJ Industrial Applications Conference, August 2010, P259-264

  However, in the above-described prior art, a direct current power source is provided between the Y connection portions of the double Y connection MMC, and the direct current between the Y connection portions is not controlled. For this reason, it could not be used for a DC system such as a BTB (Back To Back) system or a DC power transmission without a device (DC power supply, capacitor, etc.) for stabilizing the DC voltage.

  The present invention has been made in view of the above, and an object thereof is to provide a converter, a converter control method, and a converter control program capable of controlling the voltage or current of a DC line. To do.

  In order to solve the above-described problems and achieve the object, a converter according to the present invention includes a self-excited switching element and a capacitor that stores and discharges electric power according to on and off of the switching element. A Y-connection circuit that Y-connects the circuits provided for each phase of the power system is provided in duplicate, and a power conversion unit that performs power conversion, and a voltage of each phase of the double Y-connection circuit of the power conversion unit And the detection unit for detecting current, the voltage and current of each phase of the double Y connection circuit of the power conversion unit, and the double Y connection circuit when the double Y connection circuit is represented by an equivalent circuit including a DC circuit A storage unit storing relationship information indicating a relationship between the voltage and current of the DC circuit, and the voltage and current of the DC circuit derived from the detection result of the detection unit based on the relationship information stored in the storage unit. At least one is one And having a control means for controlling the switching elements of the power conversion unit such that.

  According to the present invention, the switching element of the power conversion unit is controlled so that at least one of the voltage and current of the DC circuit in which the double Y-connection circuit of the power conversion unit is shown as an equivalent circuit is constant. The voltage or current of the line can be controlled.

FIG. 1 is a diagram illustrating an example of a conceptual configuration of a power system including a converter according to the present embodiment. FIG. 2 is a diagram illustrating an example of a carrier wave and a modulated wave. FIG. 3 is a diagram illustrating an example of an equivalent circuit of a power system including a converter. FIG. 4 is a diagram illustrating each arm current and arm voltage of each arm of the equivalent circuit. FIG. 5A is a diagram illustrating current and voltage of an AC circuit. FIG. 5B is a diagram showing the current and voltage of the interphase circulation circuit. FIG. 5C is a diagram showing the current and voltage of the DC circuit. FIG. 5D is a diagram illustrating a current and a voltage of the circulation circuit. FIG. 6 is a diagram illustrating paths (A) and (B) of the AC circuit. FIG. 7 is a diagram illustrating paths (C) and (D) of the circulation circuit. FIG. 8 is a diagram illustrating paths (E), (F), and (G) of the DC circuit. FIG. 9A is a diagram illustrating an AC circuit. FIG. 9B is a diagram illustrating a circulation circuit. FIG. 9C is a diagram illustrating a DC circuit. FIG. 10 is a diagram illustrating an example of a schematic configuration of a control system that controls the converter. FIG. 11 is a flowchart showing the procedure of the control process. FIG. 12 is a diagram showing a schematic configuration of the BTB system used for the simulation. FIG. 13 is a diagram showing main specifications of a BTB system for which simulation has been performed. FIG. 14A is a diagram showing current waveforms of the upper and lower arms of the R phase. FIG. 14B is a diagram illustrating a current waveform of a three-phase alternating current. FIG. 14C is a diagram illustrating voltage waveforms in the circuit modules of the upper arm and the lower arm. FIG. 14D is a diagram illustrating a voltage waveform of each phase of the converter. FIG. 14E is a diagram showing a current waveform of a direct current. FIG. 14F is a diagram illustrating a current waveform of a three-phase circulating current. FIG. 15 is a diagram illustrating a computer that executes a control program.

  Hereinafter, embodiments of a converter according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating an example of a conceptual configuration of a power system including a converter according to the present embodiment. In the example shown in FIG. 1, the converter 10 is connected to the end of the power system 12. In this embodiment, it is assumed that the converter 10 is connected to the power system 12 via the Y-Δ transformer 13. The converter 10 should just be provided in either of the electric power grid | systems 12, and does not necessarily need to be provided in the terminal.

  The power system 12 is supplied with three-phase AC power from the host system. The converter 10 is a device that can exchange active power and reactive power at high speed and continuously with the power system 12 using a self-excited semiconductor element.

  The converter 10 includes a power conversion unit 20. The power conversion unit 20 exchanges power with the power system 12. The power conversion unit 20 is provided with a double Y-connection circuit 23 in which Y circuits are connected to a series circuit 22 in which circuit modules 21 called cells are connected in series in three stages for each phase of the power system 12. The circuit configuration is a double Y-connection MMC. Hereinafter, the series circuit 22 of each phase of the Y connection circuit 23 is also referred to as an arm. Hereinafter, the arm of the upper Y connection circuit 23 in FIG. 1 is also referred to as an upper arm, and the arm of the lower Y connection circuit 23 in FIG. 1 is also referred to as a lower arm. For example, the circuit module 21 may have a so-called inverter cell type circuit configuration in which two series circuits 26 in which two switching elements 25 are connected in series are connected in parallel to the capacitor 24. Further, for example, a so-called chopper cell type circuit configuration in which two switching elements 25 are connected in series to the capacitor 24 may be employed. Each switching element 25 of the circuit module 21 is provided with a diode 27 that connects both ends.

  Each circuit module 21 performs PWM (pulse width modulation) control for turning on and off the switching element 25 by comparing an input carrier wave and a modulated wave. FIG. 2 is a diagram illustrating an example of a carrier wave and a modulated wave. In order to effectively use the element, the waveform of the modulated wave is usually determined so that the peak is around 1. However, when the power conversion unit 20 determines the waveform of the modulated wave so that the peak is near 1, the magnitude of the modulated wave exceeds 1 by increasing the voltage level of the entire modulated wave as will be described later. When this happens, normal PWM control cannot be performed. For this reason, the modulated wave according to the present embodiment is suppressed to a certain level.

Here, control of the converter 10 according to the present embodiment will be described. The circuit configuration of the double Y connection MMC can be ideally replaced with an equivalent circuit as shown in FIG. In the equivalent circuit shown in FIG. 3, three circuit modules 21 of each arm of the double Y connection MMC are shown as the AC voltage source 30. Each arm has an impedance L. Each arm of the double Y connection MMC is connected to a voltage source 31 simulating the electric power system 12 via the leakage impedance L _TF of the Y-Δ transformer 13. In the equivalent circuit shown in FIG. 3, the DC voltage source of the DC voltage Vdc is shown to exist on the DC circuit side connecting the two Y connection portions of the double Y connection MMC. This DC voltage Vdc represents a DC voltage to be output in a DC system such as a BTB system or DC power transmission.

The voltage and current of the double Y connection MMC are analyzed using the equivalent circuit shown in FIG. In the equivalent circuit shown in FIG. 3, the Δ connection of the Y-Δ transformer 13 is replaced with a Y connection on the equivalent circuit. In the equivalent circuit shown in FIG. 3, a point that satisfies the following expression (1) is defined as a virtual neutral point 32.
_{e r + e S + e t} = 0 (1)

Also, as shown in FIG. 4, currents flowing through the upper arms of the RST phase are represented as i _pr , i _ps , and i _pt, and voltages of the upper arms of the RST phase are represented as v _pr , v _ps , and v _pt . Further, currents flowing through the lower arms of the RST phase are represented as i _nr , i _ns , i _nt, and voltages of the lower arms of the RST phase are represented as v _nr , v _ns , and v _nt , respectively. Called voltage.

Here, each variable shown in the following formulas (2-1) to (2-6) is defined as a current state quantity representing the state of the converter 10.
i _r = i _pr −i _nr (2-1)
i _s = i _ps −i _ns (2-2)
i _t = i _pt −i _nt (2-3)
i _d = 1/2 × (i _pr + i _ps + i _pt + i _nrr + i _ns + i _nt ) (2-4)
_{i Crs = 1/3 × (} i pr + i nr) -1/6
X (i _ps + i _pt + i _ns + i _nt ) (2-5)
i _Cst = −1 / 3 × (i _pt + i _nt ) −1/6
X (i _pr + i _ps + i _nr + i _ns ) (2-6)

Then, as shown in FIG. 5A, defined _i r shown in equation _{(2-1) ~ (2-3),} i s, and the AC current RST phase output a _{i t} to the AC circuit. Further, as shown in FIG. 5B, the formula (2-5), is defined as _{i Crs,} RS phase _{i Cst,} phase circulating current flowing phase circulation circuit between the ST phase shown in (2-6). Further, as shown in FIG. 5C, defined as DC current output a i _d shown in Formula (2-4) to a DC circuit. Here, in this embodiment, since the AC side is not grounded, the relationship shown in the following formula (3) is established. i _d is consistent with the current flowing in the actual direct current line.
i _r + i _s + i _t = 0 (3)

Similarly to the current, each variable shown in the following equations (4-1) to (4-6) is defined as a voltage state quantity representing the state of the converter 10.
v _r = 1/2 × (−v _pr + v _nr ) (4-1)
v _s = 1/2 × (−v _ps + v _ns ) (4-2)
v _t = 1/2 × (−v _pt + v _nt ) (4-3)
v _d = 1/3 × (v _pr + v _ps + v _pt + v _nr + v _ns + v _nt ) (4-4)
_{v Crs = 2/3 × (} v pr + v nr) -1/3
× (v _ps + v _pt + v _ns + v _nt ) (4-5)
v _Cst = −2 / 3 × (v _pt + v _nt ) +1/3
× (v _pr + v _ps + v _nr + v _ns ) (4-6)

Then, as shown in FIG. 5A, v _r , v _s , and v _t shown in equations (4-1) to (4-3) are defined as AC voltages of the RST phase that are output to the AC circuit. Further, as shown in FIG. 5B, v _Crs and v _Cst shown in equations (4-5) and (4-6) are defined as interphase circulation voltages of the interphase circuit between the RS phase and the ST phase. Further, as shown in FIG. 5C, v _d shown in Expression (4-4) is defined as a DC current output to the DC circuit.

In the above definition, the interphase circulating currents i _Crs and i _Cst and the interphase circulating voltages v _Crs and v _Cst are not three-phase symmetrical. In order to provide symmetry, i _Lr , i _Ls , i _Lt , v _Lr , v _Ls , and v _Lt shown in FIG. 5D are _{expressed as follows} using four variables i _Crs , i _Cst , v _Crs , and v _Cst . It is defined as equations (5) to (10).
i _Lr = i _Crs
= 1/3 x (i _pr + i _nr ) -1/6
X (i _ps + i _pt + i _ns + i _nt ) (5)
i _Ls = −i _Crs + i _Cst
= 1/3 x (i _ps + i _ns ) -1/6
X (i _pt + i _pr + i _nt + i _nr ) (6)
i _Lt = −i _Cst
= 1/3 × (i _pt + i _nt ) −1/6
X (i _pr + i _ps + i _nr + i _ns ) (7)
_vLr = 2/3 * ( _vpr + _vnr ) -1/3
× (v _ps + v _pt + v _ns + v _nt ) (8)
v _Ls = 2/3 × (v _ps + v _ns ) −1/3
× (v _pt + v _pr + v _nt + v _nr ) (9)
v _Lt = 2/3 × (v _pt + v _nt ) −1/3
× (v _pr + v _ps + v _nr + v _ns ) (10)

Then, i _Lr , i _Ls , and i _Lt shown in the equations (5) to (7) are defined as circulating current. Further, v _Lr , v _Ls , and v _Lt shown in equations (8) to (10) are defined as circulating voltages. The relationship shown in the following formulas (11) and (12) holds for this circulating current and interphase circulating voltage.
_iLr + _iLs + _iLt = 0 (11)
_vLr + _vLs + _vLt = 0 (12)

From the above, the equations for deriving each variable can be expressed as the following equations (13) and (14) using the transformation matrix.

Therefore, the state quantities of the AC circuit, the circulation circuit, and the DC circuit are expressed by the respective arm currents i _pr , i _ps , i _pt , and the arm voltages v _pr of the upper arm as shown in the following equations (15) and (16). , V _ps , v _pt , and arm currents i _nr , i _ns , i _nt , and arm voltages v _nr , v _ns , v _nt of the lower arm.

Here, in Expression (13), six variables are converted into seven using a 6 × 7 matrix, and the order increases before and after the conversion. In order to maintain the symmetry of the three phases, the two variables of the interphase circulating currents i _Crs and i _Cst are changed to the three variables of the circulating currents i _Lr , i _Ls and i _Lt under the constraint condition of the equation (11). This is due to the development. The circulating currents i _Lr , i _Ls , and i _Lt can be expressed by the following equation (17) by performing three-phase to two-phase conversion.

  In the case of this equation (17), the order does not increase before and after conversion, but the matrix is not three-phase symmetric. Similarly, the matrix shown in Expression (14) can be expressed by performing three-phase to two-phase conversion.

Next, the state equation of the AC circuit will be described. As shown in FIG. 6, in the equivalent circuit, when Kirchhoff's law is applied to the paths (A) and (B) constituting the AC circuit, the relationships shown in the following equations (18) and (19) are established.

When the difference between Expression (18) and Expression (19) is obtained, it is expressed as the following Expression (20).

Further, the following formulas (21) and (22) are obtained from the formula (20) by the symmetry of the three phases.

And the following formula | equation (23) is also calculated | required from Formula (1), (3), (20), (22).

Here, when L _ac = L / 2 + L _TF and v _r + v _s + v _t = 3V ₀ , the following expression (24) is obtained.

Further, the following formulas (25) and (26) are also obtained from the formula (24) by the symmetry of the three phases.

  These formulas (24) to (26) are general formulas for a three-phase inverter in a non-grounded system, and show that non-interference control by DQ conversion can be performed even with a double Y-connection MMC. In addition, the above is a case where the converter 10 is connected to the system by the Y-Δ transformer 13 as shown in FIG. 1 and is not grounded. When grounded, it can be handled in the same manner by taking into account the influence of grounding.

Next, the state equation of the circulation circuit will be described. As shown in FIG. 7, in the equivalent circuit, when Kirchhoff's law is applied to the paths (C) and (D) constituting the circulation circuit, the relationships shown in the following equations (27) and (28) are established.

When the difference between Expression (27) and Expression (28) is obtained, it is expressed as the following Expression (29).

Here, when a 2 · _L = L L, is represented by the following formula (30).

Further, from the equation (30), the S phase and the T phase can be obtained as in the following equations (31) and (32) due to the symmetry of the three phases.

Next, a state equation of the DC circuit will be described. As shown in FIG. 8, when Kirchhoff's law is applied to the paths (E), (F), and (G) constituting the DC circuit in the equivalent circuit, the relationship shown in the following equation (33) is established.

When the three equations shown in equation (33) are added and arranged, the following equation (34) is obtained.

Here, when L _d = 2/3 × L, the following expression (35) is obtained.

  Thus, the state equation of the double Y-connection MMC can be expressed by the equations (24) to (26), (30) to (32), and (35). This is because the circuit configuration of the double Y-connection MMC is obtained by performing the variable conversion of the equations (13) and (14), so that the state equation of the circuit is changed to one DC circuit as shown in FIGS. 9A to 9C. It can be divided into a total of seven circuits of three circulation circuits and three AC circuits, and shows that the DC circuit, the circulation circuit, and the AC circuit can be controlled independently. Since the AC circuit, the circulation circuit, and the DC circuit are independent, the control of the AC circuit and the circulation circuit does not affect the DC circuit. When performing a DC system such as a DC power transmission or a BTB system, the converter 10 needs to keep the current and voltage of the DC circuit constant, but the DC current and voltage are controlled while performing various controls of the AC circuit and the circulation circuit. It is possible to keep it constant.

  Next, the configuration of the control system that controls the converter 10 according to the present embodiment will be described. FIG. 10 is a diagram illustrating an example of a schematic configuration of a control system that controls the converter. In the example illustrated in FIG. 10, the converter 10 includes a detection unit 41, a storage unit 42, a control unit 43, and a signal generation unit 44.

  The detection unit 41 detects the current of each phase of the power conversion unit 20 and the capacitor voltage across the circuit module 21 connected for each phase.

  The storage unit 42, when the circuit configuration of the power conversion unit 20 is divided into a DC circuit, a circulation circuit, and an AC circuit and shown as an equivalent circuit, the voltage and current of the DC circuit, the circulation circuit, and the AC circuit, and the power conversion unit 20. The relationship information indicating the relationship between the voltage and current of each phase of the double Y connection circuit 23 is stored. For example, the storage unit 42 stores information represented by the equations (13) and (14) and information represented by the equations (15) and (16) as the relationship information.

  Based on the relationship information stored in the storage unit 42 based on the detection result of the detection unit 41, the control unit 43 converts the power conversion unit so that the voltage and current of the DC circuit, the circulation circuit, and the AC circuit satisfy predetermined conditions. The switching elements of the 20 circuit modules 21 are controlled. Specifically, the control unit 43 obtains an arm current and an arm voltage for each arm of each phase of the power conversion unit 20 from the detection result of the detection unit 41, and uses equations (13) and (14) for each phase. AC current and AC voltage, phase-by-phase circulating current and circulating voltage, DC voltage and DC current are derived. The control unit 43 determines whether the derived AC current and AC voltage for each phase, circulating current and voltage for each phase, DC voltage, and DC current satisfy predetermined conditions. When there is a voltage or current that does not satisfy the condition, the control unit 43 uses the equations (15) and (16) to specify the arm voltage that does not satisfy the condition and affects the current, and specifies that the condition is satisfied. Instructed to change the arm voltage. For example, when the DC voltage is lower than the voltage set as the predetermined condition, the control unit 43 gives an instruction to increase all arm voltages or one of the arm voltages by a predetermined amount, and the DC voltage is set as the predetermined condition. If it is higher than the voltage, an instruction is given to reduce all arm voltages or any of the arm voltages by a predetermined amount. In addition, when any one of the alternating current and the alternating voltage for each phase, the circulating current and the circulating voltage for each phase, the direct current voltage, and the direct current satisfy the condition, the control unit 43 generates the voltage and current that satisfy the condition as much as possible. Change the arm voltage so that it does not fluctuate. For example, when an alternating current or an alternating voltage satisfies a predetermined condition in any phase and the direct current voltage is increased, the alternating current or the alternating voltage is changed to a phase that satisfies the condition using Equations (15) and (16). An arm voltage that has an effect and an arm voltage that has no effect are specified, and an instruction to increase the arm voltage that has no effect is given. In addition, for example, when the circulating current or the circulating voltage satisfies a predetermined condition in any phase and the DC voltage is increased, the circulating current or the current due to the change in each arm voltage is calculated using the equations (15) and (16). The degree of change of the circulating voltage and the degree of increase of the DC voltage are obtained, and an instruction to change the arm voltage so that the change of the circulating current and the circulating voltage is canceled and the DC voltage rises is issued. In addition, for example, when the DC voltage satisfies the condition and the AC current, AC voltage, circulating current, or circulating voltage is changed, the change in DC voltage is canceled, and the AC current, AC voltage, circulating current, or circulating voltage changes. To change the arm voltage.

  The signal generator 44 supplies a carrier wave and a modulated wave to the circuit module 21 of each arm of each phase of the power converter 20 and superimposes it on the supplied modulated wave according to an instruction from the controller 43. Change the voltage level of the constant voltage to raise or lower the voltage level of the entire modulated wave. Thereby, in the power converter 20, the arm voltage changes for each arm of each phase by changing the ON / OFF period of the switching element 25 of the circuit module 21 for each arm of each phase.

  For example, the control unit 43 may realize control by a circuit configuration using an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). Further, an electronic circuit such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit) and a storage unit that stores the program may be provided, and control may be realized by executing processing of the program by the electronic circuit.

  Next, the flow of control processing by the control unit 43 according to the present embodiment will be described. FIG. 11 is a flowchart showing the procedure of the control process. This control process is always executed after the control unit 43 is activated.

  As shown in FIG. 11, the control unit 43 obtains an arm current and an arm voltage for each arm of each phase of the power conversion unit 20 from the detection result by the detection unit 41, and obtains an AC current and AC voltage for each phase, The circulating current, circulating voltage, direct current voltage and direct current are derived (step S100). The control unit 43 instructs to change the arm voltage so that the derived AC current and AC voltage for each phase, circulating current and voltage for each phase, DC voltage, and DC current satisfy predetermined conditions ( Step S101). For example, when there is a voltage or current that does not satisfy a predetermined condition, the control unit 43 does not fluctuate the voltage or current that satisfies the condition as much as possible, and the voltage or current that does not satisfy the condition satisfies the predetermined condition. Gives instructions to change the voltage.

  As a result, the signal generation unit 44 changes the voltage level of the constant voltage to be superimposed on the modulated wave in accordance with an instruction from the control unit 43, and modulates the carrier wave and the modulation to the circuit module 21 of each phase arm of the power conversion unit 20. Supply waves. Thereby, in power converter 20, arm voltage changes for every arm of each phase.

  The control unit 43 determines whether or not an operation stop is instructed by another control unit that controls the entire converter 10 (step S102). When the operation stop is instructed (Yes at Step S102), the control unit 43 ends the process. On the other hand, when the operation stop is not instructed (No at Step S102), the control unit 43 proceeds to Step S100.

  Next, the result of simulating the operation when the BTB system 50 is constructed using the converter 10 according to the present embodiment will be described. FIG. 12 is a diagram showing a schematic configuration of the BTB system used for the simulation. FIG. 13 shows the main specifications of the BTB system on which the simulation was performed.

  The BTB system 50 shown in FIG. 12 has the same circuit configuration on the power transmission side and the power reception side, and the converter 10 is provided at each of the power reception end and the power transmission end. The converters 10 are respectively connected to different AC systems by Y-Δ transformers 13. It is assumed that the converter 10 has three circuit modules 21 per arm and employs an inverter cell type circuit module 21.

  One of the DC circuits between the two converters 10 is directly grounded, and it is assumed that there are no circuit elements such as a power supply and a capacitor that fix the DC voltage.

In the simulation, the converter 10 of the power receiving side performs a certain control of the DC voltage v _d, converter 10 of the power transmission performs constant control of the DC current i _d. 14A to 14F show waveforms of the converter on the power transmission side.

  FIG. 14A shows the current waveform of the upper and lower arms of the R phase, and FIG. 14B shows the current waveform of the AC current of the three phases. Moreover, FIG. 14C has shown the voltage waveform in the circuit module 21 of an upper arm and a lower arm, and FIG. 14D has shown the voltage waveform of each phase of a converter. Simulation results show that the BTB system 50 can operate stably.

  FIG. 14E shows a current waveform of a direct current, and FIG. 14F shows a current waveform of a three-phase circulating current. As a result of the simulation, the BTB system 50 has a DC voltage and a DC current of 1.0 p. It is u and power is transmitted normally. In the steady state, the circulating current is set to 0, and the circulating current does not flow.

[Effect of Example 1]
As described above, the converter 10 according to the present embodiment includes the self-excited switching element 23 and the capacitor 24 that stores and discharges power according to the on / off of the switching element 23. The Y connection circuit 23 obtained by Y-connecting the circuits provided for each phase is provided in the power conversion unit 20 in a double manner, and the power conversion unit 20 performs power conversion. Moreover, the converter 10 detects the voltage and current of each phase of the double Y connection circuit 23 of the power conversion unit 20 by the detection unit 41. The converter 10 includes the voltage and current of each phase of the double Y connection circuit 23 of the power converter 20 and the DC circuit when the double Y connection circuit is represented by an equivalent circuit including a DC circuit. Relation information indicating the relation between the voltage and the current is stored in the storage unit 42. Then, the converter 10 uses the power so that at least one of the voltage and current of the DC circuit derived from the detection result by the detection unit 41 based on the relationship information stored in the storage unit 42 is constant by the control unit 43. The switching element 25 of the conversion unit 20 is controlled. Thereby, the converter 10 which concerns on a present Example can perform direct current | flow control between Y connection parts. Thereby, the converter 10 which concerns on a present Example can perform direct current | flow control using for direct current systems, such as a BTB system and direct current power transmission.

  In this embodiment, the theory of handling the current and voltage of each arm of the double Y-connection MMC by breaking it into an AC component, a DC component, and a circulation component is disclosed. According to this theory, the AC circuit, the DC circuit, and the circulation circuit can be controlled independently. Thereby, in the converter 10 according to the present embodiment, each circuit can be controlled independently, so that the DC voltage and the DC current can be kept constant while controlling the AC current and the circulating current, and the double Y-connection MMC. DC power transmission and BTB system control can be easily performed. For example, in the converter 10 according to the present embodiment, the relationship information includes AC and voltage of each phase of the double Y connection circuit 23 of the power conversion unit 20, and alternating current using the double Y connection circuit 23 as an equivalent circuit. It further includes information indicating the relationship between the voltage and current of the AC circuit and the voltage and current of the circulation circuit in the case of the circuit and the circulation circuit. Then, the converter 10 allows the control means to maintain the voltage and current of the AC circuit and the circulation circuit while maintaining at least one of the voltage and current of the DC circuit constant based on the relationship information stored in the storage unit 42. The switching elements 25 of the power converter 20 are controlled so as to satisfy predetermined conditions. Thereby, the converter 10 which concerns on a present Example can perform direct current | flow control between Y connection parts, controlling alternating voltage, alternating current, circulating voltage, and circulating current.

  Although the embodiments related to the disclosed apparatus have been described above, the present invention may be implemented in various different forms other than the above-described embodiments. Therefore, another embodiment included in the present invention will be described below.

  In the above embodiment, the power converter 20 is illustrated as having a circuit configuration in which the circuit modules 21 are connected in three stages in series for each phase of the power system 12, as shown in FIG. The apparatus is not limited to this. For example, a circuit configuration in which one circuit module 21 is provided for each phase may be employed. Moreover, it is good also as a circuit structure which connected the circuit module 21 for each phase 2 steps | paragraphs or 4 steps | paragraphs or more in series. Moreover, although the converter 10 was illustrated as what is connected with the electric power grid | system 12 via the Y-delta transformer 13, the apparatus of an indication is not limited to this. For example, it is possible to connect to the power system 12 via a YY transformer or to connect directly to the power system 12 by performing appropriate control.

  Further, depending on various loads, usage conditions, and the like, the processing in each step of each processing described in the embodiment may be arbitrarily finely divided or combined, or the processing order may be changed.

  Further, each component of each illustrated apparatus is functionally conceptual, and does not necessarily need to be physically configured as illustrated. In other words, the specific state of distribution / integration of each device is not limited to the one shown in the figure, and all or a part thereof may be functionally or physically distributed or arbitrarily distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. For example, the control unit 43 shown in FIG. 10 may be divided into finer processing units.

[Control program]
Various processes of the control unit 43 described in the above embodiment can also be realized by executing a program prepared in advance by a computer system. Therefore, in the following, an example of a computer that executes a control program having the same function as the control unit 43 described in the above embodiment will be described with reference to FIG. FIG. 15 is a diagram illustrating a computer that executes a control program.

  As shown in FIG. 15, the computer 300 includes a CPU (Central Processing Unit) 310, a ROM (Read Only Memory) 320, and a RAM (Random Access Memory) 340. These units 300 to 340 are connected via a bus 400.

  The ROM 320 stores in advance a control program 320a that exhibits the same function as the control unit 43 shown in the first embodiment. That is, the ROM 320 stores a control program 320a as shown in FIG. Note that the control program 320a may be separated as appropriate.

  Various related information is stored in the HDD 330. The relationship information corresponds to the relationship information stored in the storage unit 42 illustrated in FIG.

  Then, the CPU 310 reads the related information and stores it in the RAM 340. The CPU 310 executes the control program 320a using the relationship information stored in the RAM 340. Each data stored in the RAM 340 does not always need to be stored in the RAM 340, and only the data necessary for the process may be stored in the RAM 340.

  Note that the above-described control program 320a is not necessarily stored in the ROM 320 from the beginning.

  For example, the program is stored in a “portable physical medium” such as a flexible disk (FD), a CD-ROM, a DVD disk, a magneto-optical disk, or an IC card inserted into the computer 300. Then, the computer 300 may read and execute the program from these.

  Furthermore, the program is stored in “another computer (or server)” connected to the computer 300 via a public line, the Internet, a LAN, a WAN, or the like. Then, the computer 300 may read and execute the program from these.

DESCRIPTION OF SYMBOLS 10 Converter 12 Power system 20 Power conversion part 21 Circuit module 23 Y connection circuit 24 Capacitor 25 Switching element 41 Detection part 42 Storage part 43 Control part 44 Signal generation part

Claims (4)

Double Y-connection circuit that Y-connects a circuit provided for each phase of a three-phase AC power system, including a self-excited switching element and a capacitor that stores and discharges power according to ON / OFF of the switching element. A power conversion unit that performs power conversion, and
A detection unit for detecting a voltage and a current of each phase of the double Y-connection circuit of the power conversion unit;
The relationship between the voltage and current of each phase of the double Y-connection circuit of the power converter and the voltage and current of the DC circuit when the double Y-connection circuit is represented by an equivalent circuit including a DC circuit A storage unit storing relationship information indicating
Control for controlling the switching element of the power converter so that at least one of the voltage and current of the DC circuit derived from the detection result by the detector based on the relation information stored in the storage is constant Means,
A converter characterized by comprising: The relation information includes the voltage and current of each phase of the double Y-connection circuit of the power converter, and the AC circuit when the double Y-connection circuit is represented as an equivalent circuit by an AC circuit and a circulation circuit. And information indicating the relationship between the voltage and current of the circuit and the voltage and current of the circulation circuit,
Based on the relation information stored in the storage unit, the control means maintains at least one of the voltage and current of the DC circuit constant, and the voltage and current of the AC circuit and the circulation circuit satisfy predetermined conditions, respectively. The converter according to claim 1, wherein the switching element of the power conversion unit is controlled so as to satisfy the condition. Double Y-connection circuit that Y-connects a circuit provided for each phase of a three-phase AC power system, including a self-excited switching element and a capacitor that stores and discharges power according to ON / OFF of the switching element. A method of controlling a converter having a power conversion unit that performs power conversion,
Detecting the voltage and current of each phase of the double Y-connection circuit of the power converter,
The relationship between the voltage and current of each phase of the double Y-connection circuit of the power converter and the voltage and current of the DC circuit when the double Y-connection circuit is represented by an equivalent circuit including a DC circuit The switching element of the power conversion unit is set so that at least one of the voltage and current of the DC circuit derived from the detection result is constant based on the relationship information stored in the storage unit that stores the relationship information indicating A control method of a converter characterized by controlling. Double Y-connection circuit that Y-connects a circuit provided for each phase of a three-phase AC power system, including a self-excited switching element and a capacitor that stores and discharges power according to ON / OFF of the switching element. A control program for a converter having a power conversion unit for performing power conversion,
By detecting the voltage and current of each phase of the double Y-connection circuit of the power converter, the voltage and current of each phase are detected,
The relationship between the voltage and current of each phase of the double Y-connection circuit of the power converter and the voltage and current of the DC circuit when the double Y-connection circuit is represented by an equivalent circuit including a DC circuit The power conversion unit is configured so that at least one of the voltage and current of the DC circuit derived from the detection result of the detection unit is constant based on the relationship information stored in the storage unit that stores the relationship information indicating A control program for a converter, characterized by causing each process to control a switching element.

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