Control device, power converter, control method

Abstract

This technology provides a way to suppress reactive power from generators when a new power source is connected to an AC bus. [Solution] A control device 90 according to one embodiment of the present disclosure includes an AC bus 10 that receives power from an AC power source 30, an AC power source 40 that can be switched between a connected state where it is connected to the AC bus 10 and a disconnected state where it is disconnected from the AC bus 10, and a power converter 50 that performs power conversion between AC at one end connected to the AC bus 10 and DC at the other end, wherein at least one of the AC power source 30 and the AC power source 40 is a generator, and the control device 90 for a power system 1 is configured to output reactive power QCNV from the power converter 50 to the AC bus 10, corresponding to the q-axis voltage of the AC power source 40, with reference to the phase θ of the voltage VPS0 of the AC bus 10.

Description

Technical Field

[0004] ,

[0006] , , , , , ,

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[0001] The present disclosure relates to a control device and the like.

Background Art

[0002] For example, techniques for controlling the reactive power of a generator are disclosed (see Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, for example, when a second power source is connected to an AC bus to which power from an existing first power source is supplied, the phases of the first power source and the second power source may be shifted. As a result, when at least one of the first power source and the second power source is a generator, a large instantaneous reactive current may be generated at the time of connection of the second power source, and the reactive power of the generator may exceed the allowable range. As a result, system instability, damage to the generator, damage to the load, etc. may be caused.

[0005] Therefore, in view of the above problems, an object is to provide a technique capable of suppressing the reactive power of a generator when a new power source is connected to an AC bus.

Means for Solving the Problems

[0006] To achieve the above object, in one embodiment of the present disclosure, A control device for a power system, comprising: an AC bus that receives power from a first power source; a second power source that can switch between a connected state and a disconnected state connected to the AC bus; and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, wherein at least one of the first power source and the second power source is a generator, The power converter outputs reactive power to the AC bus corresponding to the q-axis voltage of the second power supply, with the phase of the voltage of the AC bus as the reference. A control device is provided.

[0007] In other embodiments of this disclosure, A power system comprising an AC bus receiving power from a first power source, and a second power source that can be switched between a connected state, where it is connected to the AC bus, and a disconnected state, where it is disconnected from the AC bus, wherein at least one of the first power source and the second power source is a generator, and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, The system outputs reactive power to the AC bus corresponding to the q-axis voltage of the second power supply, with the phase of the voltage of the AC bus as the reference. A power converter is provided.

[0008] Furthermore, in yet another embodiment of this disclosure, A control method for a power system comprising: an AC bus receiving power from a first power source; a second power source that can switch between a connected state and a disconnected state, where it is disconnected from the AC bus; and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, wherein at least one of the first power source and the second power source is a generator, The power converter outputs reactive power to the AC bus corresponding to the q-axis voltage of the second power supply, with the phase of the voltage of the AC bus as the reference. A control method is provided. [Effects of the Invention]

[0009] According to the above embodiment, reactive power of the generator can be suppressed when a new power source is connected to the AC bus. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram illustrating an example of a power system. [Figure 2] This figure shows the first specific example of a power system. [Figure 3] This figure shows a second specific example of a power supply system. [Figure 4] This is a time chart diagram showing an example of the time evolution of phase voltage and reactive power in a power system relating to a general comparative example, when a new power source is connected to an AC bus that receives power from an existing power source. [Figure 5] This is a time chart diagram illustrating another example of the time evolution of phase voltage and reactive power in a power system relating to a general comparative example, where a new power source is connected to an AC bus that receives power from an existing power source. [Figure 6] This figure shows an example of the relationship between the voltage of the AC bus and the voltage of the new power supply. [Figure 7] This diagram illustrates the operating range of a generator in terms of active and reactive power. [Figure 8] This figure shows an example of power flow in an AC bus. [Figure 9] This is a functional block diagram showing an example of a control device. [Figure 10] This flowchart provides a schematic example of the processing performed by a control device. [Figure 11] This figure shows a first example of reactive power when a new power source is connected to an AC bus that receives power from an existing power source, for both the power system relating to a schematic comparative example and the power system according to the embodiment. [Figure 12] This figure shows a second example of reactive power when a new power source is connected to an AC bus that receives power from an existing power source, for both the power system relating to a schematic comparative example and the power system according to the embodiment. [Figure 13]FIG. is a diagram showing a third example of reactive power when a new power source is connected to an AC bus receiving power supply from an existing power source for each of the power systems according to a schematic comparative example and the power system according to an embodiment. [Figure 14] FIG. is a diagram showing a fourth example of reactive power when a new power source is connected to an AC bus receiving power supply from an existing power source for each of the power systems according to a schematic comparative example and the power system according to an embodiment. [Figure 15] FIG. is a time chart diagram of simulation results showing an example of the operation when a new power source is connected to an AC bus receiving power supply from an existing power source for the power system according to the first comparative example. [Figure 16] FIG. is a time chart diagram of simulation results showing an example of the operation when a new power source is connected to an AC bus receiving power supply from an existing power source for the first specific example of the power system. [Figure 17] FIG. is a time chart diagram of simulation results showing an example of the operation when a new power source is connected to an AC bus receiving power supply from an existing power source for the power system according to the second comparative example. [Figure 18] FIG. is a time chart diagram of simulation results showing an example of the operation when a new power source is connected to an AC bus receiving power supply from an existing power source for the second specific example of the power system. [Figure 19] FIG. is a time chart diagram of simulation results showing another example of the operation when a new power source is connected to an AC bus receiving power supply from an existing power source for the second specific example of the power system. DETAILED DESCRIPTION OF THE INVENTION [[ID=​​​​​​​​​​​​Figure 1 is a schematic diagram showing an example of power system 1. Figure 2 is a diagram showing a first specific example of power system 1. Figure 3 is a diagram showing a second specific example of power system 1.

[0014] As shown in Figure 1, the power system 1 includes an AC bus 10, an AC load 20, an AC power source 30, an AC power source 40, a power converter 50, a DC bus 60, a DC power source 70, a DC load 80, and a control device 90.

[0015] The AC bus (also called an "AC bus") 10 supplies AC power to the AC load 20. For example, the AC bus 10 supplies three-phase AC to the AC load 20. The AC bus 10 may also supply power to the DC bus 60 through the power converter 50.

[0016] The AC load 20 is an electrical load that operates using the AC power supplied from the AC bus 10.

[0017] The AC load 20 that operates using AC power supplied from the AC bus 10 is, for example, one, as shown in Figure 1. Alternatively, there may be multiple AC loads 20 that operate using AC power supplied from the AC bus 10.

[0018] Furthermore, a switch for switching between connecting and disconnecting the power path between the AC load 20 and the AC busbar 10 may be provided.

[0019] The AC power supply 30 supplies AC power to the AC bus 10. For example, the AC power supply 30 supplies three-phase AC to the AC bus 10.

[0020] A switch 30S is provided in the power path between the AC power source 30 and the AC busbar 10 to switch between connecting and disconnecting the power path. This allows the switch 30S to switch between a connected state, where power is supplied from the AC power source 30 to the AC busbar 10, and a disconnected state, where power supply from the AC power source 30 to the AC busbar 10 is interrupted. The switch 30S is, for example, a Molded Case Circuit Breaker (MCCB).

[0021] The AC power supply 30 is, for example, one, as shown in Figure 1. Alternatively, there may be multiple AC power supplies 30.

[0022] The switching operation of the switch 30S is performed under the control of another control device (hereinafter, for convenience, referred to as the "AC bus control device") which is provided separately from the control device 90 and performs control related to the AC bus 10. Alternatively, the switching operation of the switch 30S may be performed under the control of the control device 90.

[0023] For example, AC power supply 30 functions as the main power source for AC busbar 10. The following explanation assumes that the switch 30S will remain closed unless there is any abnormality in the AC power supply 30.

[0024] The AC power supply 40 supplies AC power to the AC bus 10. For example, the AC power supply 40 supplies three-phase AC to the AC bus 10.

[0025] The AC power supply 40 is, for example, one, as shown in Figure 1. Alternatively, there may be multiple AC power supplies 40.

[0026] A switch 40S is provided in the power path between the AC power source 40 and the AC busbar 10 to switch between connecting and disconnecting the power path. As a result, the switch 40S can switch between a connected state in which power is supplied from the AC power source 40 to the AC busbar 10 and a disconnected state in which the power supply from the AC power source 30 to the AC busbar 10 is cut off.

[0027] The switching operation of the switch 40S is performed, for example, under the control of the AC bus control device. Alternatively, the switching operation of the switch 40S may be performed under the control of the control device 90.

[0028] For example, AC power supply 40 functions as an auxiliary power source for AC bus 10. The following explanation assumes that the switch 40S can be switched between open and closed states according to predetermined conditions when AC power supply 30 is connected to AC bus 10 (specifically, when switch 30S is closed).

[0029] The following explanation will focus on the case where AC power source 40 connects to AC bus 10 from a disconnected state, under the assumption that AC power source 30 supplies power to AC bus 10. In this case, AC power source 30 may be conveniently referred to as the "existing power source," and AC power source 40 may be conveniently referred to as the "new power source."

[0030] At least one of the AC power sources 30 and 40 is a generator (specifically, an AC generator).

[0031] For example, as shown in Figure 2, the power system 1 includes an AC grid 30A as an example of an AC power source 30, and a generator 40A as an example of an AC power source 40.

[0032] AC system 30A is a power system that distributes AC power to AC busbar 10. AC system 30A is, for example, a commercial power system (also referred to as a "commercial system" or "commercial power system").

[0033] A transformer 30T for interconnection is provided in the power path between the AC system 30A and the switch 30S. As a result, AC power whose voltage has been adjusted by the transformer 30T is supplied to the AC bus 10.

[0034] The generator 40A is an AC generator that includes a rotor and a stator, and generates AC power by the rotation of the rotor by a predetermined power. For example, the generator 40A is a wind turbine. Alternatively, the generator 40A may be a generator powered by a thermal power generator or an internal combustion engine (for example, a diesel engine).

[0035] Furthermore, as shown in Figure 3, for example, the power system 1 includes a generator 30B as an example of an AC power source 30 and a generator 40A as an example of an AC power source 40.

[0036] The generator 30B is an AC generator that includes a rotor and a stator, and generates AC power by the rotation of the rotor by a predetermined power. For example, the generator 30B is a generator powered by a thermal power generator or an internal combustion engine. Alternatively, the generator 30B may be a wind turbine.

[0037] The power converter 50 has one end connected to the AC bus 10 and the other end connected to the DC bus 60, and performs power conversion between the AC on one end and the DC on the other end.

[0038] For example, the power converter 50 converts the AC power from the AC bus 10 into DC power and supplies it to the DC bus 60. Also, for example, the power converter 50 converts the DC power from the DC bus 60 into AC power and supplies it to the AC bus 10.

[0039] The power converter 50 is, for example, a bidirectional AC / DC converter (also referred to as an "AC (Alternating Current) / DC (Direct Current) converter"). The bidirectional AC / DC converter includes, for example, an inverter circuit. In addition to the inverter circuit, the bidirectional AC / DC converter may also include a DC / DC converter circuit for adjusting the DC voltage.

[0040] The inverter circuit includes, for example, a full-bridge circuit with multiple semiconductor switches. This allows the inverter circuit to convert DC power into AC power through the switching action of the multiple semiconductor switches. Furthermore, the inverter circuit includes a recirculation diode connected in parallel to each of the multiple semiconductor switches. This allows the inverter circuit to function as a rectifier for AC input, converting AC power into DC power.

[0041] A transformer 50T for grid connection is provided in the power path between the power converter 50 and the AC bus 10.

[0042] Furthermore, a switch for switching between connecting and disconnecting the power path between the power converter 50 and the AC bus 10 (for example, the power path between the transformer 50T and the AC bus 10) may be provided.

[0043] The DC bus 60 supplies DC power to the DC load 80.

[0044] The DC power supply 70, for example, supplies DC power to the DC bus 60. The DC power supply 70 may also be capable of storing energy by receiving DC power from the DC bus 60. The DC power supply 70 is, for example, a battery. Alternatively, the DC power supply 70 may be a capacitor. Furthermore, the DC power supply 70 may be a solar power generation system, a wind power generation system, or the like.

[0045] The DC power supply 70 is, for example, one, as shown in Figure 1. Alternatively, there may be multiple DC power supplies 70.

[0046] DC load 80 is an electrical load that operates using DC power supplied from DC bus 60.

[0047] The control device 90 performs control related to the power system 1. For example, the control device 90 controls the power converter 50 while monitoring various states of the AC bus 10.

[0048] For example, the control device 90 acquires a detected value (also referred to as "measured value" or "measured value") of the voltage of the AC bus 10 (hereinafter referred to as "AC bus voltage") VPS0 from a voltage sensor (not shown). This allows the control device 90 to monitor the AC bus voltage VPS0. Also, for example, the control device 90 acquires a detected value of the voltage of the AC power supply 40 (hereinafter referred to as "new power supply voltage") VPS1 from a voltage sensor (not shown). This allows the control device 90 to monitor the new power supply voltage VPS1. The control device 90 may also acquire information representing the open / closed state of the switch 30S. For example, the control device 90 acquires information representing the open / closed state of the switch 30S. Also, when the control device 90 controls the open / closed state of the switch 30S, it acquires information representing the open / closed state of the switch 30S during the process of controlling the open / closed state of the switch 30S. The information representing the open / closed state of the switch 30S represents the current open / closed state of the switch 30S. Furthermore, the information representing the open / closed state of the switch 30S may also be information that provides prior notification indicating a transition of the switch 30S to an open or closed state.

[0049] For example, the control device 90 is provided separately from the power converter 50. Specifically, for example, the control device 90 may be a PLC (Programmable Logic Controller), edge controller, edge server, etc., installed in the same facility as the power converter 50. Alternatively, the control device 90 may be a server device (for example, an on-premise server or a cloud server) installed in a different location from the facility where the power converter 50 is installed. Furthermore, the functions of the control device 90 may be built into the power converter 50.

[0050] Some or all of the functions of the control device 90 may be realized solely by hardware, such as electrical circuits or electronic circuits. Alternatively, some or all of the functions of the control device 90 may be realized by a combination of hardware and software, such as a program, and auxiliary storage devices, memory devices, and processors that correspond to the installation destination, loading destination, and execution unit of the program. Examples of auxiliary storage devices include HDDs (Hard Disk Drives), SSDs (Solid State Drives), EEPROMs (Electrically Erasable Programmable Read Only Memory), and flash memory. Examples of memory devices include SRAMs (Static Random Access Memory) and DRAMs (Dynamic Random Access Memory). The processor may include, for example, a CPU (Central Processing Unit). The processor may also include, for example, a GPU (Graphics Processing Unit), an FPGA (Field Programmable Gate Array), and an ASIC (Application Specific Integrated Circuit).

[0051] [Reactive power during grid connection of new power sources] Referring to Figures 4 to 6, we will explain the reactive power generated when AC power source 40 (new power source) is connected to AC bus 10 from a disconnected state while AC power source 30 (existing power source) is supplying power to AC bus 10.

[0052] Figure 4 is a time chart diagram showing an example of the time changes in phase voltage and reactive power when a new power source is connected to an AC bus 10 that receives power from an existing power source, for a power system relating to a schematic comparative example. Figure 5 is a time chart diagram showing another example of the time changes in phase voltage and reactive power when a new power source is connected to an AC bus 10 that receives power from an existing power source, for a power system relating to a schematic comparative example. Figure 6 is a diagram showing an example of the relationship between the voltage of the AC bus 10 (AC bus voltage) VPS0 and the voltage of the new power source (new power source voltage) VPS1.

[0053] Specifically, Figure 6 shows the relationship between the voltage of AC bus 10 (AC bus voltage) VPS0 and the new power supply voltage VPS1 on a rotating coordinate system with the d-axis and q-axis as reference to the phase of the voltage of AC bus 10 (AC bus voltage) VPS0.

[0054] The schematic comparative example is a comparative example of power system 1 shown in Figure 1. In the following description of the schematic comparative example, the same reference numerals are used for components that are the same as those in power system 1 in Figure 1.

[0055] Specifically, the power system relating to the schematic comparative example differs from power system 1 in Figure 1 in that, when a new power source (AC power source 40) is connected to the AC bus 10 which receives power from an existing power source (AC power source 30), the power converter 50 does not output the reactive power QCNV described later to the AC bus 10, but in other respects it is the same as power system 1 in Figure 1.

[0056] As shown in Figure 4A, in the example in Figure 4, the new power supply is connected to the AC bus 10 at time t01, with a relatively large phase difference between the U-phase voltage of the AC bus 10 (hereinafter referred to as "AC bus U-phase voltage") VPS0_U and the U-phase voltage of the new power supply (hereinafter referred to as "new power supply U-phase voltage") VPS1_U.

[0057] As shown in Figure 4B, in the example in Figure 4, when a new power source is connected to the AC bus 10 at time t01, the reactive power QPS0 of the existing power source and the reactive power QPS1 of the new power source change rapidly in opposite directions, taking a very large absolute value, then decreasing in absolute value, and then undershooting significantly before finally converging to near zero.

[0058] Furthermore, as shown in Figure 5A, in another example in Figure 5, at time t02, the new power supply is connected to the AC bus 10 while the phase difference between the AC bus U-phase voltage VPS0_U and the new power supply U-phase voltage VPS1_U is relatively small.

[0059] As shown in Figure 5B, in another example in Figure 5, when a new power source is connected to the AC bus 10 at time t02, the reactive power QPS0 of the existing power source and the reactive power QPS1 of the new power source change rapidly in opposite directions, taking a maximum value with a relatively large absolute value, then decreasing in absolute value, and then undershooting significantly before finally converging to near zero.

[0060] Thus, in the power system of the schematic comparative example, when a new power source is connected to the AC bus 10 that receives power from an existing power source in the comparative example, reactive power is generated in both the existing and new power sources due to the phase difference between the voltage of the AC bus 10 (hereinafter, "AC bus voltage") VPS0 and the voltage of the new power source (hereinafter, "new power source voltage") VPS1. Furthermore, in the power system of the schematic comparative example, even when the phase difference between the AC bus voltage VPS0 and the new power source voltage VPS1 is relatively small, relatively large reactive power is generated in both the existing and new power sources.

[0061] When a new power source is connected to an AC bus 10 that receives power from an existing power source, the reactive power Qgap flowing between the AC bus 10 and the new power source is expressed by the following equation (1), using the reactive current Igap flowing between the AC bus 10 and the new power source.

[0062]

number

[0063] Here, the difference ΔV between the AC bus voltage VPS0 and the new power supply voltage VPS1 (see Figure 6) can be approximated by the following equation (2), using the admittance Y from the existing power supply to the new power supply, assuming that the phase difference δ between the AC bus voltage VPS0 and the new power supply voltage VPS1 is very small.

[0064]

number

[0065] Therefore, when a new power source is connected to an AC bus 10 that receives power from an existing power source, the reactive power Qgap flowing between the AC bus 10 and the new power source is approximated by equations (1) and (2), and then by equation (3) below.

[0066]

number

[0067] Typically, the admittance Y from the existing power source to the new power source is very large (i.e., the loss is very small). Therefore, even when the phase difference δ between the AC bus voltage VPS0 and the new power source voltage VPS1 is very small, i.e., when the difference ΔV between the AC bus voltage VPS0 and the new power source voltage VPS1 is very small, the reactive power Qgap flowing between the AC bus 10 and the new power source will be a relatively large value. As a result, as described above, in the power system relating to the schematic comparative example, even when the phase difference between the AC bus voltage VPS0 and the new power source voltage VPS1 is relatively small, relatively large reactive power is generated in both the existing and new power sources.

[0068] [Operating range for reactive power of generators] Referring to Figure 7, the operable range with respect to the reactive power of a generator adopted as at least one of the AC power sources 30 and 40 will be explained.

[0069] Figure 7 illustrates the operating range of the generator in terms of active power P and reactive power Q.

[0070] Specifically, Figure 7 includes Figures 7A to 7C. Figure 7A is a vector diagram showing an example of the relationship between the internal induced voltage E, terminal voltage VDG, and armature current IDG of a motor in advanced-angle operation (also called "advancing-phase operation") where the phase of the armature current IDG of the generator leads the phase of the internal induced voltage E. Figure 7B is a vector diagram showing an example of the relationship between the internal induced voltage E, terminal voltage VDG, and armature current IDG of a motor in retarded-angle operation (also called "retarded-phase operation") where the phase of the armature current IDG of the generator lags behind the phase of the internal induced voltage E. Figure 7C is a diagram showing an example of the operable range for the active power P and reactive power Q of the generator.

[0071] When the generator is operating at a retarded frequency (see Figure 7B), if the reactive power Q (i.e., lagging reactive power) increases, the current flowing through the rotor field winding increases, resulting in a rise in the temperature of the field winding. Therefore, as shown in Figure 7C, the generator has an operating limit (i.e., an upper limit) set for the positive reactive power Q corresponding to retarded frequency operation, based on the allowable temperature rise of the field winding.

[0072] Furthermore, when the generator is operating at an advanced ignition timing (see Figure 7A), if the reactive power Q (i.e., leading reactive power) increases, the current flowing through the ends of the stator core increases, resulting in a rise in the temperature of the stator core. Therefore, as shown in Figure 7C, the generator has an operating limit (i.e., an upper limit) set for the reactive power Q in the direction corresponding to advanced ignition timing, based on the allowable limit of the temperature rise of the stator core.

[0073] Thus, if the absolute value of the generator's reactive power Q becomes large, it may exceed the operating range of the generator and potentially exceed the permissible limits for temperature rise of the field windings and stator core. Therefore, even if the apparent power of the generator is within the rated range, it is desirable to avoid operating conditions that result in an excessively large absolute value of the reactive power Q. Accordingly, when a new power source is connected to the AC bus 10 while an existing power source is supplying power to the AC bus 10, it is desirable to suppress the reactive power of the generators corresponding to at least one of the existing power source and the new power source.

[0074] [Overview of methods for suppressing reactive power in generators] Referring to Figure 8, an overview of the method for suppressing reactive power in generators adopted as at least one of the existing power source and the new power source will be described when a new power source is connected while the existing power source is supplying power to the AC bus 10.

[0075] Figure 8 shows an example of power flow related to the AC bus 10. Specifically, Figure 8 shows the power flow of the AC bus 10, including active power PAL and reactive power QAL supplied to the AC load 20, active power PPS0 and reactive power QPS0 output from the existing power source (AC power source 30), active power PPS1 and reactive power QPS1 output from the new power source (AC power source 40), and active power PCNV and reactive power QCNV output from the power converter 50.

[0076] As shown in Figure 8, the following power equation (4) holds true for the power flow between the AC load 20, the existing power source, the new power source, and the power converter 50.

[0077]

number

[0078] Therefore, the following equations (5.1) and (5.2) hold between the reactive power QAL supplied to the AC load 20, the reactive power QPS0 output from the existing power source, the reactive power QPS1 output from the new power source, and the reactive power QCNV output from the power converter 50.

[0079]

number

[0080] Therefore, for example, when a new power source is connected to an AC bus 10 that receives power from an existing power source, the power converter 50 can suppress the reactive power QPS0 of the generator as the existing power source and the reactive power QPS1 of the generator as the new power source by outputting a desired reactive power QCNV.

[0081] [Control device function configuration] The functional configuration of the control device 90 will be described with reference to Figure 9.

[0082] Figure 9 is a functional block diagram showing an example of the control device 90.

[0083] As shown in Figure 9, the control device 90 includes, as functional units, a phase detection unit 901, a conversion unit 902, a conversion unit 903, and a reactive power command generation unit 904.

[0084] The phase detection unit 901 detects the phase θ of the AC bus voltage VPS0 based on the detected value (also referred to as "measured value" or "measured value") of the AC bus voltage VPS0, and obtains the cosine cosθ and sine sinθ of the phase θ. For example, the phase detection unit 901 is a PLL (Phase Locked Loop).

[0085] The conversion unit 902 performs calculations to convert the detected value of the AC bus voltage VPS0, which is represented as a three-phase AC, into the detected values ​​of the d-axis component (hereinafter, "AC bus d-axis voltage") VPS0_d and the q-axis component (hereinafter, "AC bus q-axis voltage") VPS0_q of the AC bus voltage VPS0 on a rotating coordinate system with respect to the phase θ of the AC bus voltage VPS0.

[0086] The conversion unit 902 includes an αβ conversion unit 902A and a dq conversion unit 902B.

[0087] The αβ conversion unit 902A performs calculations to convert the AC bus voltage VPS0, which is represented as three-phase AC, into α-axis and β-axis components on a fixed coordinate system, using known conversion formulas.

[0088] The dq conversion unit 902B performs calculations to convert the α-axis and β-axis components of the AC bus voltage VPS0 into detected values ​​of the d-axis component (AC bus d-axis voltage) VPS0_d and the q-axis component (AC bus q-axis voltage) VPS0_q on a rotating coordinate system with respect to the phase θ of the AC bus voltage VPS0 as the reference, using known conversion formulas. Specifically, the dq conversion unit 902B calculates the AC bus d-axis voltage VPS0_d and the AC bus q-axis voltage VPS0_q using known conversion formulas based on the cosine cosθ and sine sinθ of the phase θ of the AC bus voltage VPS0 output from the phase detection unit 901.

[0089] The conversion unit 903 performs calculations to convert the detected value of the new power supply voltage VPS1, which is represented by three-phase AC, into the d-axis component (hereinafter referred to as "new power supply d-axis voltage") VPS1_d and the q-axis component (hereinafter referred to as "new power supply q-axis voltage") VPS1_q of the new power supply voltage VPS1 on a rotating coordinate system with respect to the phase θ of the AC bus voltage VPS0.

[0090] The αβ conversion unit 903A performs calculations to convert the new power supply voltage VPS1, which is represented as three-phase AC, into α-axis and β-axis components on a fixed coordinate system, using known conversion formulas.

[0091] The dq conversion unit 903B performs calculations to convert the α-axis and β-axis components of the new power supply voltage VPS1 into the d-axis component (hereinafter, "new power supply d-axis voltage") VPS1_d and the q-axis component (hereinafter, "new power supply q-axis voltage") of the new power supply voltage VPS1 on a rotating coordinate system with respect to the phase θ of the AC bus voltage VPS0, using known conversion formulas. Specifically, the dq conversion unit 903B calculates the new power supply d-axis voltage VPS1_d and the new power supply q-axis voltage VPS1_q using known conversion formulas based on the cosine cosθ and sine sinθ of the phase θ of the AC bus voltage VPS0 output from the phase detection unit 901.

[0092] The reactive power command generation unit 904 generates a reactive power command QCNV* based on the detected value of the AC bus d-axis voltage VPS0_d output from the conversion unit 902 and the detected value of the new power supply q-axis voltage VPS1_q output from the conversion unit 903.

[0093] The reactive power command generation unit 904 includes a multiplication unit 904A, a proportional control unit 904B, and a bandwidth limiting unit 904C.

[0094] The multiplication unit 904A multiplies the AC bus d-axis voltage VPS0_d and the new power supply q-axis voltage VPS1_q, and outputs the multiplied value.

[0095] The proportional control unit 904B takes the product of the detected value of the AC bus d-axis voltage VPS0_d and the detected value of the new power supply q-axis voltage VPS1_q as input, applies proportional control (P control), and outputs a reactive power command QCNV** for the reactive power QCNV output from the power converter 50. Specifically, the proportional control unit 904B generates the reactive power command QCNV** by multiplying the product of the detected value of the AC bus d-axis voltage VPS0_d and the detected value of the new power supply q-axis voltage VPS1_q by a proportional gain Kp.

[0096] The proportional gain Kp is determined, for example, according to the capacity of the motor whose reactive power is to be suppressed. Specifically, for example, the proportional gain Kp is set so that its absolute value increases as the capacity of the target motor decreases. Also, as described later, the sign of the proportional gain Kp is switched depending on whether the target motor is an existing power source or a new power source.

[0097] The band limiting unit 904C generates and outputs the reactive power command QCNV* by applying a filter F(s) that limits the frequency band of the reactive power command QCNV** to a range controllable by the power converter 50. For example, filter F(s) is a bandpass filter. Specifically, filter F(s) is expressed by the following equation (6), for example, a low-pass filter with time constant T1 and a high-pass filter with time constant T2.

[0098]

number

[0099] The control device 90 outputs a reactive power command QCNV* to the power converter 50. As a result, the power converter 50, under the control of its own control circuit, performs the switching operation of the main circuit and outputs reactive power QCNV, which corresponds to the reactive power command QCNV*, to the AC bus 10.

[0100] The reactive power command QCNV* generated by the reactive power command generation unit 904 is expressed by the following equation (7).

[0101]

number

[0102] Here, as shown in Figure 6 above, the AC bus d-axis voltage VPS0_d can be considered as the AC bus voltage VPS0 itself. Also, as shown in Figure 6, the new power supply q-axis voltage VPS1_q can be considered equivalent to the difference ΔV (=VPS1-VPS0) between the AC bus voltage VPS0 and the new power supply voltage VPS1. Therefore, by substituting equation (3) into equation (7), the reactive power command QCNV* can be expressed by the following equations (8.1) and (8.2) using the reactive power QPS1 of the new power supply.

[0103]

number

[0104] Therefore, as can be seen from equations (5.1) and (5.2) above, by appropriately setting the proportional gain Kp, the reactive power QPS1 of the motor as a new power source and the reactive power QPS0 of the motor as an existing power source can be suppressed when a new power source is connected to the AC bus 10 that receives power from an existing power source.

[0105] Furthermore, the reactive power command generation unit 904 may generate the reactive power command QCNV* by employing a control method other than proportional control. For example, the reactive power command generation unit 904 may generate the reactive power command QCNV* by applying proportional-integral control (PI control) or proportional-integral-derivative control (PID control).

[0106] [Control device processing] Referring to Figure 10, an example of the processing performed by the control device 90 will be described.

[0107] Figure 10 is a flowchart illustrating a schematic example of the processing performed by the control device 90.

[0108] Specifically, Figure 10 includes Figure 10A, which is a main flowchart diagram schematically showing an example of the processing of the control device 90, and Figure 10B, which is a subflowchart diagram schematically showing an example of the processing of the control device 90.

[0109] The main flowchart in Figure 10A is executed repeatedly at predetermined processing cycles, for example, when the power converter 50 is in operation. The subflowchart in Figure 10B shows the details of the process in step S40 of the main flowchart in Figure 10A.

[0110] In Figure 10, the switch 40S corresponding to the new power supply (AC power supply 40) is conveniently referred to as the "interconnection switch."

[0111] As shown in Figure 10A, the control device 90 acquires the latest state representing the open / closed state of the switch 40S (step S10).

[0112] Once the process in step S10 is complete, the control device 90 proceeds to step S20.

[0113] The control device 90 determines whether the switch 40S has transitioned from the open state to the closed state (step S20).

[0114] If the control device 90 determines that the switch 40S has not transitioned from the open state to the closed state, it can determine that the new power supply has not transitioned from the disconnected state to the connected state, and proceeds to step S30. On the other hand, if the control device 90 determines that the switch 40S has transitioned from the open state to the closed state, it can determine that the new power supply has transitioned from the disconnected state to the connected state, and proceeds to step S40.

[0115] Furthermore, the control device 90 may be capable of acquiring information corresponding to prior notification of the transition of the switch 40S from the open state to the closed state. In this case, in step S20, the control device 90 may determine whether or not it has detected in advance the transition of the switch 40S from the open state to the closed state.

[0116] The control device 90 causes the power converter 50 to operate in normal mode (step S30).

[0117] The normal mode is an operating mode that represents the normal operation of the power converter 50. For example, the normal operation of the power converter 50 is the operation of supplying active power from the AC bus 10 to the DC bus 60, or the operation of supplying active power from the DC bus 60 to the AC bus 10.

[0118] Once the processing in step S30 is complete, the control device 90 terminates the processing of this main flowchart.

[0119] Meanwhile, the control device 90 proceeds to the flowchart shown in Figure 10B, causing the power converter 50 to operate in reactive power output mode (step S40).

[0120] The reactive power output mode is an operating mode in which the power converter 50 outputs reactive power to the AC bus 10.

[0121] As shown in Figure 10B, the phase detection unit 901 of the control device 90 obtains the sine sinθ and cosine cosθ of the phase θ of the AC bus voltage VPS0 (step S401).

[0122] Once the processing in step S401 is complete, the control device 90 proceeds to step S402.

[0123] The conversion unit 902 of the control device 90 calculates the detected values ​​of the AC bus d-axis voltage VPS0_d and the AC bus q-axis voltage VPS0_q based on the sine sinθ and cosine cosθ obtained in step S401 (step S402).

[0124] Once the process in step S402 is complete, the control device 90 proceeds to step S403.

[0125] The conversion unit 903 of the control device 90 calculates the detected values ​​of the new power supply d-axis voltage VPS1_d and the new power supply q-axis voltage VPS1_q based on the sine sinθ and cosine cosθ obtained in step S401 (step S403).

[0126] Once the processing in step S403 is complete, the control device 90 proceeds to step S404.

[0127] The reactive power command generation unit 904 of the control device 90 generates a reactive power command QCNV* based on the detected value of the AC bus d-axis voltage VPS0_d acquired in step S402 and the detected value of the new power supply q-axis voltage VPS1_q acquired in step S403 (step S404).

[0128] Once step S404 is completed, the control device 90 terminates the processing of this subflowchart and returns to the main flowchart.

[0129] Once the process in step S40 is complete, the control device 90 terminates the process of this main flowchart.

[0130] [Specific examples of the reactive power suppression effect of new power sources] Referring to Figures 11 and 12, a specific example of the suppression effect of reactive power QPS1 of a new power source when a new power source is connected to an AC bus 10 that receives power from an existing power source from a disconnected state will be explained.

[0131] Figure 11 shows a first example of reactive power when a new power source is connected to an AC bus that receives power from an existing power source, for both the power system according to the schematic comparative example and power system 1 according to the embodiment. Figure 12 shows a second example of reactive power when a new power source is connected to an AC bus that receives power from an existing power source, for both the power system according to the schematic comparative example and power system according to the embodiment.

[0132] Specifically, Figure 11 includes Figure 11A, which shows a first example of reactive power in a power system relating to a schematic comparative example when a new power source is connected to an AC bus that receives power from an existing power source, and Figure 11B, which shows a first example of reactive power in a power system 1 according to the embodiment when a new power source is connected to an AC bus that receives power from an existing power source. Furthermore, Figure 12 includes Figure 12A, which shows a second example of reactive power in a power system relating to a power system relating to a schematic comparative example when a new power source is connected to an AC bus that receives power from an existing power source, and Figure 12B, which shows a second example of reactive power in a power system 1 according to the embodiment when a new power source is connected to an AC bus that receives power from an existing power source.

[0133] Figures 11 and 12 show the simulation results under the assumption that the capacity of the existing power source is very large, such as AC system 30A as AC power source 30, that the reactive power QPS0 of the existing power source does not change due to the reactive power output from the power converter 50, and that the absolute value of the reactive power QAL of the AC load 20 is sufficiently small.

[0134] Figure 11 shows the simulation results when the reactive power QPS0 of the existing power supply is a positive value.

[0135] As shown in Figure 11A, in the power system of the schematic comparative example, the reactive power QCNV output from the power converter 50 is zero, and the reactive power QPS1 of the new power source is a relatively large negative absolute value.

[0136] In contrast, as shown in Figure 11B, in the power system 1 according to this embodiment, a negative reactive power QCNV is output from the power converter 50, and as a result, the magnitude (absolute value) of the negative reactive power QPS1 of the new power source is almost halved.

[0137] Figure 12 shows the simulation results when the reactive power QPS0 of the existing power supply is a negative value.

[0138] As shown in Figure 12A, in the power system of the schematic comparative example, the reactive power QCNV output from the power converter 50 is zero, and the reactive power QPS1 of the new power source is a relatively large positive absolute value.

[0139] In contrast, as shown in Figure 12B, in the power system 1 according to this embodiment, a positive reactive power QCNV is output from the power converter 50, and as a result, the magnitude (absolute value) of the positive reactive power QPS1 of the new power source is almost halved.

[0140] Thus, in the power system 1 according to this embodiment, the control device 90 can suppress the reactive power QPS1 of the new power source when the new power source is connected to the AC bus 10 from a disconnected state, regardless of the sign of the reactive power QPS0 of the existing power source. Therefore, when the new power source is a generator, it is possible to suppress situations in which the reactive power QPS1 of the generator deviates from the operating range.

[0141] [Specific examples of the reactive power suppression effect of existing power sources] Referring to Figures 13 and 14, a specific example of the suppression effect of the reactive power QPS0 of an existing power source when a new power source is connected to an AC bus 10 that receives power from an existing power source from a disconnected state will be explained.

[0142] Specifically, Figure 13 includes Figure 13A, which shows a third example of reactive power in a power system relating to a schematic comparative example when a new power source is connected to an AC bus that receives power from an existing power source, and Figure 13B, which shows a third example of reactive power in a power system 1 according to the embodiment when a new power source is connected to an AC bus that receives power from an existing power source. Furthermore, Figure 14 includes Figure 14A, which shows a fourth example of reactive power in a power system relating to a schematic comparative example when a new power source is connected to an AC bus that receives power from an existing power source, and Figure 14B, which shows a fourth example of reactive power in a power system 1 according to the embodiment when a new power source is connected to an AC bus that receives power from an existing power source.

[0143] Figures 13 and 14 show simulation results based on the assumption that, for example, the capacity of the new power supply is very large, the reactive power QPS1 of the new power supply does not change due to the reactive power output from the power converter 50, and the absolute value of the reactive power QAL of the AC load 20 is sufficiently small. In other words, Figures 13 and 14 show simulation results assuming that the existing power supply is more susceptible to fluctuations than the new power supply.

[0144] Figure 13 shows the simulation results when the reactive power QPS1 of the new power supply is a positive value.

[0145] As shown in Figure 13A, in the power system of the schematic comparative example, the reactive power QCNV output from the power converter 50 is zero, and the reactive power QPS0 of the existing power supply is a relatively large negative absolute value.

[0146] In contrast, as shown in Figure 13B, in the power system 1 according to this embodiment, a negative reactive power QCNV is output from the power converter 50, and as a result, the magnitude (absolute value) of the negative reactive power QPS0 of the existing power supply is almost halved.

[0147] Figure 14 shows the simulation results when the reactive power QPS1 of the new power supply is a negative value.

[0148] As shown in Figure 14A, in the power system of the schematic comparative example, the reactive power QCNV output from the power converter 50 is zero, and the reactive power QPS0 of the existing power supply is a relatively large positive absolute value.

[0149] In contrast, as shown in Figure 14B, in the power system 1 according to this embodiment, a positive reactive power QCNV is output from the power converter 50, and as a result, the magnitude (absolute value) of the positive reactive power QPS0 of the existing power supply is almost halved.

[0150] Thus, in the power system 1 according to this embodiment, the control device 90 can suppress the reactive power QPS0 of the existing power source when the new power source is connected to the AC bus 10 from a disconnected state, regardless of the sign of the reactive power QPS1 of the new power source. Therefore, when the existing power source is a generator, it is possible to suppress situations in which the reactive power QPS0 of the generator deviates from the operating range.

[0151] [Operation of the first specific example of a power system] Referring to Figures 15 and 16, the operation of a first specific example of power system 1 (see Figure 2) when a new power source is connected to an AC bus 10 that receives power from an existing power source from a disconnected state will be explained.

[0152] Figure 15 is a time chart of simulation results showing an example of operation when a new power source is connected to an AC bus that receives power from an existing power source, for the power system relating to the first comparative example. Figure 16 is a time chart of simulation results showing an example of operation when a new power source is connected to an AC bus that receives power from an existing power source, for the first specific example of power system 1.

[0153] Specifically, Figure 15 includes Figure 15A, which shows the time chart of the change in active power; Figure 15B, which shows the time chart of the change in reactive power; Figure 15C, which shows the time chart of the change in phase voltage; and Figure 15D, which shows the time chart of the change in phase current. Similarly, Figure 16 includes Figure 16A, which shows the time chart of the change in active power; Figure 16B, which shows the time chart of the change in reactive power; Figure 16C, which shows the time chart of the change in phase voltage; and Figure 16D, which shows the time chart of the change in phase current.

[0154] The first comparative example is a comparative example of the first specific example of power system 1 shown in Figure 2. In the following description of the first comparative example, the same reference numerals are used for components that are the same as those in the first specific example of power system 1.

[0155] Specifically, the power system relating to the first comparative example differs from the first specific example of power system 1 in that it does not output reactive power QCNV from the power converter 50 to the AC bus 10 when a new power source is connected to the AC bus 10 which receives power from an existing power source, but is otherwise the same as the first specific example of power system 1.

[0156] In the example shown in Figure 15, at time t10, generator 40A is connected to AC bus 10, which is supplied with power by AC system 30A, from a disconnected state.

[0157] In the example shown in Figure 16, the proportional gain Kp is set to a predetermined positive value, and at time t11, the generator 40A is connected to the AC bus 10, which is supplied with power by the AC system 30A, from a disconnected state.

[0158] As shown in Figure 16C, in the first specific example of power system 1, starting at time t11, the power converter 50 outputs a positive reactive power QCNV to the AC bus 10 that is the same as the reactive power QPS1 of generator 40A. Therefore, in the first specific example of power system 1, the magnitude (absolute value) of the first peak of the reactive power QPS1 of generator 40A is kept smaller than in the case of the first comparative example (see the first peak after time t10 in Figure 15C).

[0159] In this way, by setting the proportional gain Kp to a desired positive value, the control device 90 can suppress the reactive power of the generator 40A, which is used as a new power source.

[0160] [Operation of a second specific example of a power system] Referring to Figures 17 to 19, the operation of a second specific example of power system 1 (see Figure 3) when a new power source is connected to an AC bus 10 that receives power from an existing power source from a disconnected state will be explained.

[0161] Figure 17 is a time chart diagram showing an example of operation when a new power source is connected to an AC bus that receives power from an existing power source, for the power system relating to the second comparative example. Figure 18 is a time chart diagram showing an example of operation when a new power source is connected to an AC bus that receives power from an existing power source, for the second specific example of power system 1. Figure 19 is a time chart diagram showing another example of operation when a new power source is connected to an AC bus that receives power from an existing power source, for the second specific example of power system 1.

[0162] Specifically, Figure 17 includes Figure 17A, which shows the time chart of the change in active power; Figure 17B, which shows the time chart of the change in reactive power; Figure 17C, which shows the time chart of the change in phase voltage; and Figure 17D, which shows the time chart of the change in phase current. Similarly, Figure 18 includes Figure 18A, which shows the time chart of the change in active power; Figure 18B, which shows the time chart of the change in reactive power; Figure 18C, which shows the time chart of the change in phase voltage; and Figure 18D, which shows the time chart of the change in phase current. Similarly, Figure 19 includes Figure 19A, which shows the time chart of the change in active power; Figure 19B, which shows the time chart of the change in reactive power; Figure 19C, which shows the time chart of the change in phase voltage; and Figure 19D, which shows the time chart of the change in phase current.

[0163] The second comparative example is a comparative example of the second specific example of power system 1 shown in Figure 3. Hereafter, the second comparative example will be described using the same reference numerals for components that are the same as those in the second specific example of power system 1.

[0164] Specifically, the power system relating to the second comparative example differs from the second specific example of power system 1 in that it does not output reactive power QCNV from the power converter 50 to the AC bus 10 when a new power source is connected to the AC bus 10 which receives power from an existing power source, but is otherwise the same as the first specific example of power system 1.

[0165] In the example shown in Figure 17, at time t20, generator 40A is connected to the AC bus 10, which is supplied with power by generator 30B, from a disconnected state.

[0166] In the example shown in Figure 18, the capacities and characteristics of generators 30B and 40A are set to be exactly the same, and the proportional gain Kp is set to a predetermined negative value. At time t21, generator 40A is connected to the AC bus 10, which is supplied by generator 30B, from a disconnected state.

[0167] In another example shown in Figure 19, the capacities and characteristics of generators 30B and 40A are set to be exactly the same, and the proportional gain Kp is set to a predetermined positive value. At time t22, generator 40A is connected to the AC bus 10, which is supplied by generator 30B, from a disconnected state.

[0168] As shown in Figure 18C, in one example of the operation of the second specific example of power system 1, starting at time t21, the same positive reactive power QCNV as that of the existing power source generator 30B is output to the AC bus 10 from the power converter 50. Therefore, in one example of the operation of the second specific example of power system 1, the magnitude (absolute value) of the first peak of the reactive power QPS0 of the existing power source generator 30B is kept smaller than in the second comparative example (see the first peak after time t20 in Figure 17C).

[0169] Furthermore, as shown in Figure 19C, in other examples of the operation of the second specific example of power system 1, starting at time t22, the same negative reactive power QCNV as that of the generator 40A as a new power source is output to the AC bus 10 from the power converter 50. Therefore, in other examples of the second specific example of power system 1, the magnitude (absolute value) of the first peak of the reactive power QPS1 of the generator 40A as a new power source is kept smaller than in the second comparative example (see the first peak after time t20 in Figure 17C).

[0170] In this way, by appropriately selecting the positive or negative sign of the proportional gain Kp, the control device 90 can suppress the reactive power of the generator 30B as an existing power source or the reactive power of the generator 40A as a new power source.

[0171] Furthermore, the sign of the proportional gain Kp may be set automatically. For example, the sign of the proportional gain Kp may be set automatically to suppress the reactive power of the generator with the smaller capacity, or the generator that is operated with an advanced timing, between the existing generator 30B and the new generator 40A.

[0172] [Other embodiments] Other embodiments will be described.

[0173] The embodiments described above may be modified or altered as appropriate. Hereinafter, examples of modifications or alterations to the embodiments described above will be referred to as "modified examples" for convenience.

[0174] For example, in the above embodiment, the existing power source may be an AC power source 40 and the new power source may be an AC power source 30. Specifically, for example, in the event of a power outage in the AC system 30A, which is the AC power source 30, the switch 30S may be switched to the open state, and the generator 40A, which is the AC power source 40, may perform independent operation by supplying power to the AC bus 10. After the AC system 30A is restored, the AC system 30A may be connected to the AC bus 10 as the new power source from a disconnected state.

[0175] [Effect] The control device, power converter, and control method according to this embodiment will be described below.

[0176] In a first aspect of this embodiment, a control device for a power system is provided, which includes an AC bus that receives power from a first power source, a second power source that can switch between a connected state and a disconnected state connected to the AC bus, and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, wherein at least one of the first power source and the second power source is a generator. The control device is, for example, the control device 90 described above. The first power source is, for example, the existing power source (AC power source 30) described above. The AC bus is, for example, the AC bus 10 described above. The second power source is, for example, the new power source (AC power source 40) described above. The power converter is, for example, the power converter 50 described above. The generator is, for example, the generator 30B or generator 40A described above. The power system is, for example, the power system 1 described above. Specifically, the control device causes the power converter to output reactive power to the AC bus corresponding to the q-axis voltage of the second power supply, with reference to the phase of the AC bus voltage. The AC bus voltage is, for example, the AC bus voltage VPS0 described above. The phase of the AC bus voltage is, for example, the phase θ described above. The q-axis voltage of the second power supply is, for example, the new power supply q-axis voltage VPS1_q described above. The reactive power corresponding to the q-axis voltage of the second power supply is, for example, the reactive power QCNV corresponding to the reactive power command QCNV* described above.

[0177] As a result, the control device can suppress the reactive power of the generator, whether it be the first or second power source, when a second power source in a disconnected state is connected to an AC bus receiving power from the first power source. Therefore, the control device can prevent situations in which the reactive power of the generator exceeds the operating range.

[0178] Furthermore, in a second aspect of this embodiment, based on the first aspect described above, the first power source may be an external AC system. The second power source may be a generator.

[0179] As a result, the control device can suppress the reactive power of the generator acting as the second power source when a second power source in a disconnected state is connected to an AC bus receiving power from the first power source.

[0180] Furthermore, in a third aspect of this embodiment, based on the first aspect described above, both the first power source and the second power source may be generators.

[0181] As a result, the control device can suppress the reactive power of the generator as the first power source or the generator as the second power source when a second power source in a disconnected state is connected to an AC bus receiving power from the first power source.

[0182] Furthermore, in a fourth aspect of this embodiment, assuming any one of the first to third aspects described above, the control device may output reactive power corresponding to the q-axis voltage of the second power supply, with reference to the phase of the voltage of the AC bus, from the power converter to the AC bus in conjunction with the timing when the second power supply transitions from a disconnected state to a connected state.

[0183] This allows the control device to output reactive power from the power converter to the AC bus in accordance with the timing when the second power source, which is disconnected, is connected to the AC bus that receives power from the first power source.

[0184] Furthermore, in a fifth aspect of this embodiment, based on any one of the first to fourth aspects described above, the control device may generate a command value for reactive power to be output from the power converter to the AC bus based on the q-axis voltage of the second power supply and the d-axis voltage of the AC bus, with the phase of the AC bus voltage as the reference. The command value is, for example, the reactive power command QCNV* described above.

[0185] As a result, the control device can appropriately suppress the reactive power of the generator, either the first or second power source, when a second power source in a disconnected state is connected to an AC bus receiving power from the first power source.

[0186] Furthermore, in a sixth aspect of this embodiment, based on the fifth aspect described above, the control device may use a phase-locking loop to obtain the sine and cosine of the phase of the AC bus voltage, convert the voltage of the second power supply into voltages on a fixed coordinate system of the α and β axes, and calculate the q-axis voltage of the second power supply by converting the converted voltages on the fixed coordinate system into voltages on a rotating coordinate system of the d and q axes based on the sine and cosine.

[0187] This allows the control device to appropriately generate commands for the reactive power of the power converter.

[0188] Furthermore, in the seventh aspect of this embodiment, based on the fifth or sixth aspect described above, the control device may generate the command value by performing a bandwidth limit on the multiplication value of the q-axis voltage of the second power supply and the d-axis voltage of the AC bus, with respect to the phase of the AC bus voltage.

[0189] This allows the control device to generate command values ​​that are limited to a frequency band controllable by the power converter, for example. Therefore, when a second power source is connected to an AC bus receiving power from a first power source in a disconnected state, the control device can cause the power converter to output the desired reactive power to the AC bus.

[0190] Furthermore, in the eighth aspect of this embodiment, based on the seventh aspect described above, the control device may perform the bandwidth limiting by applying a bandpass filter.

[0191] This allows the control device to appropriately generate command values ​​limited to the frequency band that the power converter can control.

[0192] Furthermore, in the ninth aspect of this embodiment, assuming any one of the fifth to eighth aspects described above, the control device may generate the command value by applying a control gain to the multiplicative value of the q-axis voltage of the second power supply and the d-axis voltage of the AC bus, with respect to the phase of the AC bus voltage. The control gain may be determined according to the capacity of the generator. The control gain is the proportional gain Kp described above.

[0193] As a result, the control device can more appropriately suppress the reactive power of the generator, whether it be the first or second power source, when a second power source in a disconnected state is connected to an AC bus receiving power from the first power source.

[0194] Furthermore, in the tenth aspect of this embodiment, assuming any one of the first to ninth aspects described above, a storage battery or capacitor may be connected to the other end of the power converter. The storage battery or capacitor is, for example, the storage battery or capacitor as the DC power supply 70 described above.

[0195] This allows the control device to output reactive power from the power converter to the AC bus using a battery or capacitor.

[0196] Furthermore, in an eleventh aspect of this embodiment, a power converter is provided for a power system that includes an AC bus receiving power from a first power source and a second power source that switches between a connected state where it is connected to the AC bus and a disconnected state where it is disconnected from the AC bus, wherein at least one of the first power source and the second power source is a generator, and the power converter performs power conversion between AC at one end connected to the AC bus and DC at the other end. The power converter is, for example, the power converter 50 described above. The first power source is, for example, the existing power source (AC power source 30) described above. The AC bus is, for example, the AC bus 10 described above. The second power source is, for example, the new power source (AC power source 40) described above. The generator is, for example, the generator 30B or generator 40A described above. The power system is, for example, the power system 1 described above. Specifically, the power converter outputs reactive power to the AC bus corresponding to the q-axis voltage of the second power source, with reference to the phase of the voltage of the AC bus. The voltage of the AC bus is, for example, the AC bus voltage VPS0 described above. The phase of the AC bus voltage is, for example, the phase θ described above. The q-axis voltage of the second power supply is, for example, the new power supply q-axis voltage VPS1_q described above. The reactive power corresponding to the q-axis voltage of the second power supply is, for example, the reactive power QCNV corresponding to the reactive power command QCNV* described above.

[0197] As a result, the power conversion device performs the same functions and effects as the control device in the first example described above.

[0198] Furthermore, with respect to the power conversion device, an embodiment similar to the second to tenth embodiments of the control device can be realized, based on the eleventh embodiment.

[0199] As a result, the power conversion device performs the same functions and effects as the control devices of the second to tenth embodiments described above.

[0200] Furthermore, in a twelfth aspect of this embodiment, a control method for a power system is provided, which includes an AC bus that receives power from a first power source, a second power source that can switch between a connected state and a disconnected state, and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, wherein at least one of the first power source and the second power source is a generator. The first power source is, for example, the existing power source (AC power source 30) described above. The AC bus is, for example, the AC bus 10 described above. The second power source is, for example, the new power source (AC power source 40) described above. The power converter is, for example, the power converter 50 described above. The generator is, for example, the generator 30B or generator 40A described above. The power system is, for example, the power system 1 described above. Specifically, in this control method, reactive power corresponding to the q-axis voltage of the second power source, with reference to the phase of the voltage of the AC bus, is output from the power converter to the AC bus. The voltage of the AC bus is, for example, the AC bus voltage VPS0 described above. The phase of the AC bus voltage is, for example, the phase θ described above. The q-axis voltage of the second power supply is, for example, the new power supply q-axis voltage VPS1_q described above. The reactive power corresponding to the q-axis voltage of the second power supply is, for example, the reactive power QCNV corresponding to the reactive power command QCNV* described above.

[0201] As a result, this control method produces the same functions and effects as the control device of the first embodiment described above.

[0202] Furthermore, regarding the control method, based on the twelfth embodiment described above, an embodiment similar to the second to tenth embodiments for the control device can be realized.

[0203] As a result, this control method produces the same functions and effects as the control devices of the second to tenth embodiments described above.

[0204] Although embodiments have been described in detail above, this disclosure is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist described in the claims. [Explanation of symbols]

[0205] 1. Power Systems 10 AC busbar 20 AC load 30 AC power supply 30A AC system 30B Generator 30S switch 30T Transformer 40 AC power supply 40A Generator 40S switch 50 Power converter 50T Transformer 60 DC bus 70 DC power supply 80 DC load 90 Control device 901 Phase detection unit 902 Conversion Unit 902A Conversion Unit 902B dq conversion unit 903 Conversion Unit 903A Conversion Unit 903B dq conversion unit 904 Reactive Power Command Generation Unit 904A Multiplication section 904B Proportional Control Unit 904C Bandwidth Limiting Unit

Claims

1. A control device for a power system, comprising: an AC bus that receives power from a first power source; a second power source that can switch between a connected state and a disconnected state connected to the AC bus; and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, wherein at least one of the first power source and the second power source is a generator, The power converter outputs reactive power to the AC bus corresponding to the q-axis voltage of the second power supply, with the phase of the voltage of the AC bus as the reference. Control device.

2. The first power source is an external AC system. The second power source is a generator. The control device according to claim 1.

3. The first power source and the second power source are both generators. The control device according to claim 1.

4. In conjunction with the timing when the second power supply transitions from a disconnected state to a connected state, the power converter outputs reactive power corresponding to the q-axis voltage of the second power supply, with the phase of the AC bus voltage as a reference, to the AC bus. The control device according to any one of claims 1 to 3.

5. Based on the q-axis voltage of the second power supply and the d-axis voltage of the AC bus, with respect to the phase of the voltage of the AC bus, a command value for reactive power to be output from the power converter to the AC bus is generated. The control device according to any one of claims 1 to 3.

6. Using a phase-locked loop, the sine and cosine of the phase of the AC bus voltage are obtained. The voltage of the second power supply is converted into a voltage on a fixed coordinate system of the α and β axes, Based on the sine and cosine, the voltage on the fixed coordinate system after the transformation is converted to a voltage on the d-axis and q-axis rotating coordinate system, The q-axis voltage of the second power supply is calculated as follows: The control device according to claim 5.

7. The command value is generated by applying a bandwidth limit to the multiplicative value of the q-axis voltage of the second power supply and the d-axis voltage of the AC bus, with the phase of the AC bus voltage as the reference. The control device according to claim 5.

8. The bandwidth limit is performed by applying a bandpass filter. The control device according to claim 7.

9. The command value is generated by applying a control gain to the product of the q-axis voltage of the second power supply and the d-axis voltage of the AC bus, with the phase of the AC bus voltage as the reference. The control gain is determined according to the capacity of the generator. The control device according to claim 5.

10. A battery or capacitor is connected to the other end of the power converter. The control device according to any one of claims 1 to 3.

11. A power system comprising an AC bus receiving power from a first power source, and a second power source that can be switched between a connected state, where it is connected to the AC bus, and a disconnected state, where it is disconnected from the AC bus, wherein at least one of the first power source and the second power source is a generator, and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, The system outputs reactive power to the AC bus corresponding to the q-axis voltage of the second power supply, with the phase of the voltage of the AC bus as the reference. Power converter.

12. A control method for a power system comprising: an AC bus that receives power from a first power source; a second power source that can switch between a connected state and a disconnected state connected to the AC bus; and a power converter that performs power conversion between AC at one end connected to the AC bus and DC at the other end, wherein at least one of the first power source and the second power source is a generator, The power converter outputs reactive power to the AC bus corresponding to the q-axis voltage of the second power supply, with the phase of the voltage of the AC bus as the reference. Control method.

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