JP7475773B2 - Power Conversion Equipment - Google Patents

Description

An embodiment of the present invention relates to a power conversion device.

In a distributed power system using distributed power sources such as solar power generators, wind power generators, and batteries connected to a power grid, reactive power is injected from the distributed power sources to the interconnection point to compensate for voltage fluctuations at the interconnection point of the distributed power sources. The injection of reactive power is controlled by a power conversion device that converts the power of the distributed power sources into power that corresponds to the power grid.

For example, it is known to control the reactive power injected into the interconnection point so that the power factor at the output end of the power conversion device is constant. This makes it possible to suppress voltage fluctuations at the interconnection point caused by active power injected from distributed power sources.

However, in control that keeps the power factor constant at the output end of the power conversion device, the amount of reactive power at the interconnection point can change due to the influence of components such as transformers and cables, resulting in a difference between the power factor at the output end of the power conversion device and the power factor at the interconnection point. Such a difference in power factor can lead to overcompensation at the interconnection point.

In response to this, a countermeasure has been proposed to keep the power factor at the interconnection point constant by providing a control controller and constantly monitoring the power factor at the interconnection point. However, using a control controller increases the cost of introducing the control controller. For this reason, in distributed power systems, it is desirable to be able to suppress changes in the power factor at the interconnection point more effectively by simply adjusting the output of the power conversion device, without using a control controller.

Patent No. 6384426 Patent No. 6384439

An embodiment of the present invention provides a power conversion device that can further suppress changes in the power factor at the interconnection point.

According to an embodiment of the present invention, there is provided a power conversion device that converts power of a distributed power source into AC power compatible with a power system connected to an infinite bus power system and supplies the converted AC power to the power system, thereby connecting the distributed power source to the power system, the power conversion device including: a main circuit unit that converts the power of the distributed power source into AC power compatible with the power system; and a control unit that controls an operation of the main circuit unit, the control unit including a reference data storage unit that stores reference data representing a relationship between a magnitude of active power of the main circuit unit and a magnitude of reactive power or a power factor of the main circuit unit for achieving a target power factor at a point of interconnection with the power system, and ... that corresponds to the magnitude of the active power by referring to the reference data stored in the reference data storage unit based on the magnitude of the active power of the main circuit unit, and an output value setting unit that controls the main circuit unit so as to determine the magnitude of the reactive power of the main circuit unit based on the magnitude or power factor of the reactive power determined from data and output reactive power of the determined magnitude, and a reference data calculation unit that calculates the reference data, wherein the control unit operates the main circuit unit at a fixed power factor and inputs to the reference data calculation unit the active power value, reactive power value, voltage value, and power factor of the interconnection point and the active power value, reactive power value, voltage value, and power factor of an output terminal of the main circuit unit when the magnitude of the active power is changed between 0% and 100%, and the reference data calculation unit calculates the reference data based on the input active power value, reactive power value, voltage value, and power factor of the interconnection point and the active power value, reactive power value, voltage value, and power factor of the output terminal of the main circuit unit, and stores the calculated reference data in the reference data storage unit .

A power conversion device is provided that can further suppress changes in the power factor at the interconnection point.

1 is a block diagram illustrating a distributed power supply system according to an embodiment of the present invention; 1 is a block diagram illustrating a power conversion device of a distributed power supply system according to an embodiment. 11 is a graph illustrating an example of a relationship between active power and reactive power in a reference data acquisition operation. 10 is a flowchart illustrating an example of an operation of a control unit. 10 is a flowchart illustrating an example of an operation of a control unit.

Each embodiment will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as in reality. Even when the same part is shown, the dimensions and ratios of each part may be different depending on the drawing.
In this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals and detailed descriptions thereof will be omitted as appropriate.

FIG. 1 is a block diagram that illustrates a distributed power supply system according to an embodiment.
1, the distributed power system 2 includes a power system 4 connected to an infinite bus power system 3, a distributed power source 6, and a power conversion device 10. The power of the power system 4 is AC power. The power of the power system 4 is, for example, three-phase AC power.

The distributed power source 6 is, for example, a solar panel. The power of the distributed power source 6 is DC power. The power conversion device 10 is connected to the distributed power source 6 and is also connected to the power grid 4 via transformers 12, 14, etc. The power conversion device 10 converts the power of the distributed power source 6 into AC power compatible with the power grid 4 and supplies the converted AC power to the power grid 4, thereby connecting the distributed power source 6 to the power grid 4.

The distributed power source 6 is not limited to a solar panel, but may be other generators such as a wind power generator or a gas turbine generator. The distributed power source 6 may also be a charge storage element such as a storage battery or a capacitor. The power of the distributed power source 6 is not limited to DC power, but may be AC power, etc.

The power conversion device 10 supplies active power to the power grid 4 based on the output of the distributed power source 6, and also supplies optimal reactive power to the power grid 4. This allows the power conversion device 10 to suppress fluctuations in the voltage at the interconnection point LP with the power grid 4 due to the influence of its own active power supply.

FIG. 2 is a block diagram that illustrates a power conversion device of the distributed power supply system according to the embodiment.
2 , the power conversion device 10 has a main circuit unit 40, a control unit 42, and an output measurement unit 44. The main circuit unit 40 converts DC power or AC power supplied from the distributed power source 6 into AC power compatible with the power grid 4. The control unit 42 controls the operation of the main circuit unit 40.

The main circuit section 40 has, for example, multiple switching elements, and performs power conversion by turning the multiple switching elements on and off. The control section 42 controls the power conversion by the main circuit section 40 by controlling the on/off switching of the multiple switching elements of the main circuit section 40. For example, a well-known inverter circuit is used for the main circuit section 40. The configuration of the main circuit section 40 may be any configuration that can perform the above-mentioned power conversion.

The output measurement unit 44 detects the active power value, reactive power value, voltage value, and power factor at the output end of the main circuit unit 40 of the AC power output from the main circuit unit 40, and inputs the detected active power value, reactive power value, voltage value, and power factor to the control unit 42.

The distributed power system 2 further includes, for example, measuring devices 20 and 22. The measuring device 20 detects the voltage value Vdc of the DC voltage input from the distributed power source 6 to the power conversion device 10 and the current value Idc of the DC current input from the distributed power source 6 to the power conversion device 10, and inputs the detected voltage value Vdc and current value Idc to the control unit 42.

The control unit 42, for example, performs control of the MPPT (Maximum Power Point Tracking) method, which makes the DC power track the maximum power point of the distributed power source 6. The control unit 42, for example, extracts the maximum power point (optimum operating point) of the distributed power source 6 based on the voltage value Vdc and current value Idc detected by the measurement device 20, and controls the operation of the main circuit unit 40 so as to supply active power corresponding to the extracted maximum power point to the power system 4.

However, the method of determining the active power supplied from the power conversion device 10 to the power system 4 is not limited to the MPPT method. The active power supplied from the power conversion device 10 to the power system 4 may be determined based on an active power command value input from a higher-level controller, for example. The control unit 42 may control the operation of the main circuit unit 40 so as to supply the active power corresponding to the input active power command value to the power system 4. The control unit 42 may control the operation of the main circuit unit 40 so as to supply the active power corresponding to the amount of power generated by the distributed power source 6 to the power system 4, for example.

The measuring device 22 detects the active power value P of the interconnection point LP of the power conversion device 10 with the power system 4, the reactive power value Q of the interconnection point LP, the voltage value Vs of the interconnection point LP, and the power factor at the interconnection point LP, and inputs the detected active power value P, reactive power value Q, voltage value Vs, and power factor to the control unit 42.

The control unit 42 has a reference data storage unit 50, an output value setting unit 52, and a reference data calculation unit 54.

The reference data storage unit 50 stores reference data 60. The reference data 60 represents the relationship between the magnitude of the active power of the main circuit unit 40 and the magnitude or power factor of the reactive power of the main circuit unit 40 to achieve a target power factor at the interconnection point LP.

The reference data 60 represents the magnitude of reactive power of the main circuit unit 40 required to bring the interconnection point LP to the target power factor when a predetermined amount of active power is output from the main circuit unit 40 to the power system 4. Alternatively, the reference data 60 represents the power factor of the main circuit unit 40 required to bring the interconnection point LP to the target power factor when a predetermined amount of active power is output from the main circuit unit 40 to the power system 4.

The reference data 60 represents, for example, the relationship between the magnitude of active power and the magnitude or power factor of reactive power in the form of a table or an approximate formula. As a result, when the control unit 42 outputs a predetermined amount of active power from the main circuit unit 40 to the power system 4, it can refer to the reference data 60 to determine the magnitude or power factor of the reactive power of the main circuit unit 40 required to set the interconnection point LP to the target power factor.

The output value setting unit 52 receives the voltage value Vdc and current value Idc of the distributed power source 6 measured by the measuring device 20. The output value setting unit 52 determines the magnitude of the active power of the main circuit unit 40, for example, by MPPT control based on the voltage value Vdc and current value Idc. After determining the magnitude of the active power of the main circuit unit 40, the output value setting unit 52 refers to the reference data 60 stored in the reference data storage unit 50 based on the determined magnitude of the active power, and obtains the magnitude of the reactive power or the power factor of the main circuit unit 40 corresponding to the determined magnitude of the active power from the reference data 60.

The method of determining the magnitude of the active power based on the voltage value Vdc and the current value Idc is not limited to the MPPT method, and other methods may be used. For example, the output value setting unit 52 may determine the magnitude of the active power based on an active power command value input from outside, or may determine the magnitude of the active power based on the current active power value of the main circuit unit 40 measured by the output measurement unit 44.

The output value setting unit 52, for example, determines the magnitude of reactive power or power factor corresponding to the magnitude of active power by referring to reference data 60, which is table data, based on the magnitude of active power. Alternatively, the output value setting unit 52 determines the magnitude of reactive power or power factor corresponding to the magnitude of active power by substituting the magnitude of active power into reference data 60, which is an approximation formula.

The output value setting unit 52 determines the magnitude of the reactive power of the main circuit unit 40 based on the magnitude of the reactive power or the power factor calculated from the reference data 60, and controls the main circuit unit 40 to output active power and reactive power of the determined magnitude. The output value setting unit 52 switches on and off a plurality of switching elements of the main circuit unit 40, thereby supplying active power and reactive power of the determined magnitude from the main circuit unit 40 to the power system 4.

The measuring device 20, for example, periodically detects the voltage value Vdc of the DC voltage input from the distributed power source 6 to the power conversion device 10, and the current value Idc of the DC current input from the distributed power source 6 to the power conversion device 10, and periodically inputs the voltage value Vdc and the current value Idc to the output value setting unit 52.

The output value setting unit 52 determines the magnitude of the active power and reactive power of the main circuit unit 40 each time the voltage value Vdc and the current value Idc are input, and supplies the determined active power and reactive power from the main circuit unit 40 to the power system 4. By repeating the above process, the output value setting unit 52 supplies active power of a magnitude corresponding to the distributed power source 6 to the power system 4, and also supplies reactive power of a magnitude corresponding to the active power to the power system 4 at any time.

In this way, by supplying active power and reactive power to the power system 4, it is possible to suppress fluctuations in the voltage at the interconnection point LP caused by the supply of active power from the power conversion device 10 to the power system 4. For example, it is possible to suppress fluctuations in the voltage value Vs at the interconnection point LP to within ±2%.

The control unit 42 performs a reference data acquisition operation to acquire reference data 60 at a predetermined timing, such as at the start of operation when the power conversion device 10 is connected to the interconnection point LP. The control unit 42 has, for example, an operation unit (not shown), and performs the reference data acquisition operation based on the operation of the operation unit by an operator or the like. The control unit 42 may, for example, communicate with an external device such as a higher-level controller, and perform the reference data acquisition operation based on a control signal input from outside.

In the reference data acquisition operation, the control unit 42, for example, operates the main circuit unit 40 with a fixed power factor and changes the magnitude of the active power between 0% and 100%. In other words, the control unit 42 changes the magnitude of the active power from 0% to 100% or from 100% to 0% with a fixed power factor. The fixed power factor in the reference data acquisition operation is the target power factor at the interconnection point LP. In other words, 100% of the magnitude of the active power of the main circuit unit 40 is the rated output of the main circuit unit 40.

When the magnitude of the active power is changed between 0% and 100% with a fixed power factor, the control unit 42 inputs to the reference data calculation unit 54 the active power value P, reactive power value Q, voltage value Vs, and power factor of the interconnection point LP detected by the measurement device 22, and the active power value, reactive power value, voltage value, and power factor of the output end of the main circuit unit 40 detected by the output measurement unit 44.

During the reference data acquisition operation, the reference data calculation unit 54 calculates the reference data 60 based on the input active power value P, reactive power value Q, voltage value Vs, and power factor of the interconnection point LP, and the active power value, reactive power value, voltage value, and power factor of the output end of the main circuit unit 40.

FIG. 3 is a graph showing an example of the relationship between active power and reactive power in the reference data acquisition operation.
FIG. 3 shows an example of reactive power at the output end of the main circuit unit 40 and an example of reactive power at the interconnection point LP when the reference data acquisition operation is performed with the fixed power factor set to approximately 100% and the magnitude of the active power at the output end of the main circuit unit 40 changed from 0% to 100%.

As shown in FIG. 3, the reactive power at the output end of the main circuit unit 40 is controlled to a constant value of approximately 0 Mvar in the range of active power magnitude from 0% to 100% in order to achieve a power factor of approximately 100%.

In contrast, the reactive power at the interconnection point LP changes compared to the reactive power at the output end of the main circuit unit 40 due to the influence of the impedance of the transformers 12, 14 and the cables. In other words, even when the power factor at the output end of the main circuit unit 40 is controlled to be constant, the power factor at the interconnection point LP changes.

The reference data calculation unit 54, for example, calculates the difference between the reactive power at the output end of the main circuit unit 40 and the reactive power at the interconnection point LP for each magnitude of the active power at the output end of the main circuit unit 40, and links the calculated difference to the magnitude of the active power at the output end of the main circuit unit 40 and creates a table to calculate the reference data 60.

For example, in the example of Figure 3, when the magnitude of the active power is 100%, the difference between the reactive power at the output end of the main circuit unit 40 and the reactive power at the interconnection point LP is approximately -7 Mvar. In this case, by setting the magnitude of the reactive power at the output end of the main circuit unit 40 to +7 Mvar, it is possible to suppress changes in the reactive power at the interconnection point LP. In other words, it is possible to suppress changes in the power factor at the interconnection point LP and bring the power factor at the interconnection point LP closer to the target power factor.

The reference data calculation unit 54 may, for example, calculate the difference between the reactive power at the output end of the main circuit unit 40 and the reactive power at the interconnection point LP for each magnitude of the active power at the output end of the main circuit unit 40, and calculate the reference data 60 by determining the relationship between the calculated difference and the magnitude of the active power at the output end of the main circuit unit 40 as an approximation equation.

The reference data calculation unit 54 inputs the calculated reference data 60 to the reference data storage unit 50, and stores the reference data 60 in the reference data storage unit 50. As a result, after the reference data 60 is stored in the reference data storage unit 50, as described above, when a predetermined amount of active power is output from the main circuit unit 40 to the power system 4, the reference data 60 is referenced, and the amount or power factor of the reactive power of the main circuit unit 40 required to make the interconnection point LP a target power factor can be found from the reference data 60.

When multiple power conversion devices 10 are connected to the interconnection point LP, the reference data acquisition operation is performed individually for each of the multiple power conversion devices 10. When performing the reference data acquisition operation for one power conversion device 10, the other power conversion devices 10 are stopped. This makes it possible to appropriately calculate the reference data 60 by reflecting the influence of the components on the path between the interconnection point LP and one power conversion device 10 while suppressing the influence of the active power and reactive power output from the other power conversion devices 10.

FIG. 4 is a flowchart illustrating an example of the operation of the control unit.
FIG. 4 shows an example of a reference data acquisition operation of the control unit 42. In FIG.
4, in the reference data acquisition operation, the control unit 42 operates the main circuit unit 40 at a fixed power factor, changes the magnitude of the active power between 0% and 100%, and acquires, as measurement information, the active power value P, reactive power value Q, voltage value Vs, and power factor of the interconnection point LP detected by the measurement device 22, and the active power value, reactive power value, voltage value, and power factor of the output end of the main circuit unit 40 detected by the output measurement unit 44 (step S101 in FIG. 4). The control unit 42 inputs the acquired measurement information to the reference data calculation unit 54.

For example, the reference data calculation unit 54 calculates the difference between the reactive power at the output end of the main circuit unit 40 and the reactive power at the interconnection point LP for each magnitude of the active power at the output end of the main circuit unit 40, and links the calculated difference to the magnitude of the active power at the output end of the main circuit unit 40 and tabulates the reference data 60. Alternatively, the reference data calculation unit 54 calculates the difference between the reactive power at the output end of the main circuit unit 40 and the reactive power at the interconnection point LP for each magnitude of the active power at the output end of the main circuit unit 40, and calculates the reference data 60 by obtaining an approximation of the relationship between the calculated difference and the magnitude of the active power at the output end of the main circuit unit 40 (step S102 in FIG. 4).

The reference data calculation unit 54 inputs the calculated reference data 60 to the reference data storage unit 50, and stores the reference data 60 in the reference data storage unit 50.

FIG. 5 is a flowchart illustrating an example of the operation of the control unit.
FIG. 5 illustrates an example of a normal operation of the control unit 42. As shown in FIG.
5, in normal operation, the output value setting unit 52 of the control unit 42 first determines the magnitude of the current active power of the main circuit unit 40 by MPPT control based on the voltage value Vdc and the current value Idc. After determining the magnitude of the active power of the main circuit unit 40, the output value setting unit 52 refers to reference data 60 stored in the reference data storage unit 50 to obtain the magnitude of the reactive power or the power factor of the main circuit unit 40 corresponding to the determined magnitude of the active power from the reference data 60 (step S201 in FIG. 5).

The output value setting unit 52 determines the magnitude of the reactive power of the main circuit unit 40 based on the magnitude of the reactive power or the power factor obtained from the reference data 60, and controls the main circuit unit 40 to output active power and reactive power of the determined magnitude, thereby supplying active power and reactive power of the determined magnitude from the main circuit unit 40 to the power system 4 (step S202 in FIG. 5).

The output value setting unit 52 repeats the processes of steps S201 and S202, for example, each time the voltage value Vdc and the current value Idc are input. This makes it possible to suppress fluctuations in the voltage at the interconnection point LP caused by the supply of active power from the power conversion device 10 to the power system 4.

In this way, according to the power conversion device 10 of this embodiment, the control unit 42 has a reference data storage unit 50, and by referring to the reference data 60 stored in the reference data storage unit 50, it is possible to determine from the reference data 60 the magnitude of the reactive power or power factor of the main circuit unit 40 that corresponds to the magnitude of the active power output from the main circuit unit 40 and is necessary to make the interconnection point LP a target power factor.

As a result, the power conversion device 10 according to this embodiment does not require a control controller or the like that constantly monitors the power factor of the interconnection point LP, and can further suppress changes in the power factor of the interconnection point LP by simply adjusting the output of the power conversion device 10. For example, it is possible to suppress the occurrence of flicker due to overcompensation of reactive power at the interconnection point LP, thereby contributing to maintaining power quality. In addition, because the power conversion device 10 according to this embodiment does not require a control controller or the like, it is also possible to reduce the cost of the distributed power system 2.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

2... Distributed power system, 3... Infinite bus power system, 4... Power system, 5... Power supply equipment, 6... Distributed power source, 10... Power conversion device, 12, 14... Transformer, 20, 22... Measurement device, 40... Main circuit section, 42... Control section, 44... Output measurement section, 50... Reference data storage section, 52... Output value setting section, 54... Reference data calculation section, 60... Reference data

Claims (3)

A power conversion device that converts power from a distributed power source into AC power compatible with a power system connected to an infinite bus power system and supplies the converted AC power to the power system, thereby interconnecting the distributed power source with the power system,
a main circuit unit that converts the power of the distributed power source into the AC power corresponding to the power grid;
A control unit that controls the operation of the main circuit unit;
Equipped with
The control unit is
a reference data storage unit that stores reference data that indicates a relationship between the magnitude of active power of the main circuit unit and the magnitude or power factor of reactive power of the main circuit unit for achieving a target power factor at a connection point with the power grid;
an output value setting unit that refers to the reference data stored in the reference data storage unit based on the magnitude of the active power of the main circuit unit, determines from the reference data the magnitude or power factor of the reactive power of the main circuit unit corresponding to the magnitude of the active power, determines the magnitude of the reactive power of the main circuit unit based on the magnitude or power factor of the reactive power determined from the reference data, and controls the main circuit unit so as to output reactive power of the determined magnitude;
a reference data calculation unit that calculates the reference data;
having
the control unit inputs to the reference data calculation unit the active power value, reactive power value, voltage value, and power factor of the interconnection point and the active power value, reactive power value, voltage value, and power factor of an output terminal of the main circuit unit when the main circuit unit is operated at a fixed power factor and the magnitude of the active power is changed between 0% and 100%,
The reference data calculation unit calculates the reference data based on the input active power value, reactive power value, voltage value, and power factor of the interconnection point and the active power value, reactive power value, voltage value, and power factor of the output terminal of the main circuit unit, and stores the calculated reference data in the reference data storage unit . 2. The power conversion device according to claim 1, wherein the reference data calculation unit calculates the difference between the reactive power at the output end of the main circuit unit and the reactive power at the interconnection point for each magnitude of the active power at the output end of the main circuit unit, and links the calculated difference to the magnitude of the active power at the output end of the main circuit unit in a table to calculate the reference data. 2. The power conversion device according to claim 1, wherein the reference data calculation unit calculates the difference between the reactive power at the output end of the main circuit unit and the reactive power at the interconnection point for each magnitude of the active power at the output end of the main circuit unit, and calculates the reference data by obtaining an approximation of the relationship between the calculated difference and the magnitude of the active power at the output end of the main circuit unit.

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