Patent ID: 12218577

DESCRIPTION OF EMBODIMENTS

Embodiments will now be described with reference to the drawings.

The drawings are schematic and conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values. Also, the dimensions and proportions may be illustrated differently among drawings, even for identical portions.

In the specification and drawings, components similar to those described previously or illustrated in an antecedent drawing are marked with the same reference numerals; and a detailed description is omitted as appropriate.

FIG.1is a block diagram schematically illustrating a power conversion device according to an embodiment.

As illustrated inFIG.1, the power conversion device10includes a major circuit part12, a control device14, a first measurement device16, and a second measurement device18. The major circuit part12performs power conversion. The control device14controls the power conversion by the major circuit part12.

The major circuit part12is connected with a power system2and a power supply device4. The power system2is a power system of alternating current. The AC power of the power system2is, for example, three-phase AC power. However, the AC power of the power system2may be single-phase AC power, etc. The power supply device4is, for example, a power storage device that uses a storage battery, etc. The power supply device4outputs DC power to the major circuit part12.

For example, the major circuit part12converts the DC power input from the power supply device4into AC power corresponding to the power system2and outputs the AC power after the conversion to the power system2, and charges the power supply device4by converting AC power input from the power system2into DC power. Thereby, the major circuit part12connects the power supply device4with the power system2.

The power supply device4is not limited to a power storage device and may be, for example, a solar cell panel, etc. In such a case, the major circuit part12may not have the function of converting the AC power input from the power system2into DC power.

Also, the power supply device4may be, for example, another generator such as a wind power generator, a gas turbine generator, etc. The power that is input from the power supply device4to the major circuit part12is not limited to DC power and may be AC power. The major circuit part12may be configured to convert the AC power input from the power supply device4to other AC power corresponding to the power system2. The power supply device4may be, for example, a different power system from the power system2. The major circuit part12may be, for example, a frequency conversion device that connects two power systems of different frequencies, etc.

Thus, the power conversion by the major circuit part12is not limited to a conversion from direct current to alternating current and may be any conversion that converts the power of the power supply device4into AC power corresponding to the power system2.

The major circuit part12includes a power conversion part20and a filter circuit22. The power conversion part20converts power. The power conversion part20includes, for example, multiple switching elements and converts power by switching the multiple switching elements. The power conversion part20includes, for example, multiple switching elements having a three-phase bridge connection. The configuration of the power conversion part20may be any configuration that can convert the input power into AC power corresponding to the power system2by the switching of multiple switching elements, etc.

The filter circuit22is located at the alternating current side of the power conversion part20. In other words, the filter circuit22is located between the power conversion part20and the power system2. The filter circuit22causes the AC power output from the power conversion part20to approach a sine wave. For example, the filter circuit22causes the AC power output from the power conversion part20to approach a sine wave by suppressing high-frequency components included in the AC power output from the power conversion part20.

The filter circuit22includes, for example, a reactor24connected in series to the AC output point of the power conversion part20, and a capacitor26connected in parallel with the AC output point of the power conversion part20. The reactor24and the capacitor26are provided for each phase of the AC power output from the power conversion part20. However, the configuration of the filter circuit22is not limited thereto; any configuration that can cause the AC power output from the power conversion part20to approach a sine wave may be used.

The first measurement device16measures phase voltages Va(INV), Vb(INV), and Vc(INV) of the phases and line currents Ia(INV), Ib(INV), and Ic(INV) of the phases of the AC power output from the power conversion part20and inputs the measurement results to the control device14.

The second measurement device18measures phase voltages Va(PCS), Vb(PCS), and Vc(PCS) of the phases and line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases of the AC power output from the major circuit part12(the filter circuit22), an active power P(PCS) at the output end of the major circuit part12, and a reactive power Q(PCS) at the output end of the major circuit part12and inputs the measurement results to the control device14.

The control device14controls the power conversion by the major circuit part12by controlling the operation of the power conversion part20. In other words, the control device14controls the switching of the multiple switching elements of the power conversion part20.

The control device14receives the input of the measurement results of the first measurement device16and the second measurement device18and receives the input of an active power command value and a reactive power command value of the AC power output from the major circuit part12from a higher-level controller, etc.

The control device14controls the operation of the power conversion part20based on the measurement results input from the first measurement device16and the second measurement device18and the active power command value and the reactive power command value input from the higher-level controller, etc.

More specifically, the control device14calculates instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases of the AC power output from the power conversion part20based on the reactive power command value, the active power command value, and the measurement results that are input, and controls the operation of the power conversion part20so that voltages corresponding to the calculated instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) are output from the power conversion part20.

Thus, the control device14controls the output voltage of the major circuit part12. The control device14performs a voltage-controlled operation of the major circuit part12. The measurement results are not limited to being directly input to the control device14from the first measurement device16and the second measurement device18and may be input to the control device14via, for example, a higher-level controller, etc.

Also, the measured value of the active power P(PCS) at the output end of the major circuit part12and the measured value of the reactive power Q(PCS) at the output end of the major circuit part12are not limited to being input to the control device14from the second measurement device18and may be determined by, for example, calculating in the control device14based on the measured values of the phase voltages Va(PCS), Vb(PCS), and Vc(PCS) of the phases and the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases. The second measurement device18may not always measure the active power P(PCS) and the reactive power Q(PCS).

The control device14includes a command value calculation part30and an overcurrent suppression controller32. The command value calculation part30receives the input of an active power command value and a reactive power command value input from a higher-level controller or the like and receives the input of the measured values of the active power P(PCS) and the reactive power Q(PCS) measured by the second measurement device18.

The command value calculation part30calculates a phase voltage phase command value θ of the AC power output from the major circuit part12based on the active power command value and the measured value of the active power P(PCS). Also, the command value calculation part30calculates a phase voltage amplitude command value |V| of the AC power output from the major circuit part12based on the reactive power command value and the measured value of the reactive power Q(PCS). The command value calculation part30inputs the calculated phase voltage phase command value θ and phase voltage amplitude command value |V| to the overcurrent suppression controller32. It is sufficient to use a well-known calculation method to calculate the phase voltage phase command value θ and the phase voltage amplitude command value |V|.

The overcurrent suppression controller32receives the input of the phase voltage phase command value θ and the phase voltage amplitude command value |V| from the command value calculation part30and receives the input of the phase voltages Va(INV), Vb(INV), and Vc(INV) and the line currents Ia(INV), Ib(INV), and Ic(INV) measured by the first measurement device16and the measured values of the phase voltages Va(PCS), Vb(PCS), and Vc(PCS) and the line currents Ia(PCS), Ib(PCS), and Ic(PCS) measured by the second measurement device18.

The overcurrent suppression controller32calculates the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) to suppress the overcurrent at the output end of the major circuit part12by using all of the input information of the phase voltage phase command value θ, the phase voltage amplitude command value |V|, the phase voltages Va(INV), Vb(INV), and Vc(INV), the line currents Ia(INV), Ib(INV), and Ic(INV), the phase voltages Va(PCS), Vb(PCS), and Vc(PCS), and the line currents Ia(PCS), Ib(PCS), and Ic(PCS).

FIG.2is a block diagram schematically illustrating the overcurrent suppression controller according to the embodiment.

As illustrated inFIG.2, the overcurrent suppression controller32includes a dq inverse transformation part40, the first subtractors41ato41c, the first arithmetic units42ato42c, the first adders43ato43c, the limiters44ato44c, the second subtractors45ato45c, the second arithmetic units46ato46c, the second adders47ato47c, and the control signal generator48.

The phase voltage phase command value θ and the phase voltage amplitude command value |V| are input to the dq inverse transformation part40. The phase voltage amplitude command value |V| is input to the dq inverse transformation part40as a voltage signal of the d-axis component. Also, “0” is input as a voltage signal of the q-axis component to the dq inverse transformation part40. The dq inverse transformation part40performs a dq inverse transformation (an inverse park transform) of the phase voltage phase command value θ, the phase voltage amplitude command value |V|, and the voltage signal of the q-axis component that are input. Thereby, the dq inverse transformation part40calculates command values of the instantaneous value voltages of the phases of the AC power output from the major circuit part12based on the phase voltage phase command value θ and the phase voltage amplitude command value |V|. Then, the dq inverse transformation part40inputs the calculated command values of the instantaneous value voltages to the first subtractors41ato41c.

The first subtractors41ato41creceive the input of the command values of the instantaneous value voltages of the phases from the dq inverse transformation part40and receive the input of the measured values of the phase voltages Va(PCS), Vb(PCS), and Vc(PCS) of the phases measured by the second measurement device18.

The first subtractors41ato41ccalculate the differences between the command values of the instantaneous value voltages of the phases and the measured values of the phase voltages Va(PCS), Vb(PCS), and Vc(PCS) of the phases by subtracting the measured values of the phase voltages Va(PCS), Vb(PCS), and Vc(PCS) of the phases from the command values of the instantaneous value voltages of the phases.

The first arithmetic units42ato42ccalculate correction values to cause the phase voltages Va(PCS), Vb(PCS), and Vc(PCS) of the phases to approach the command values of the instantaneous value voltages of the phases by multiplying the differences calculated by the first subtractors41ato41cby a first proportionality constant K1. More specifically, the correction values are correction values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases of the AC power output from the major circuit part12. The first arithmetic units42ato42cinput the calculated correction values to the first adders43ato43c.

The first adders43ato43creceive the input of the correction values from the first arithmetic units42ato42cand receive the input of the measured values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases measured by the second measurement device18.

The first adders43ato43cadd the correction values to the measured values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases. Thereby, the first adders43ato43ccalculate command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases of the major circuit part12necessary to cause the phase voltages Va(PCS), Vb(PCS), and Vc(PCS) of the phases of the AC power output from the major circuit part12to approach the instantaneous value voltage output command values of the phases. The first adders43ato43cinput the calculated command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases to the limiters44ato44c.

When the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases that are input are not less than an upper limit, the limiters44ato44climit the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases to the upper limit; and when the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases that are input are not more than a lower limit, the limiters44ato44climit the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases to the lower limit.

When the command values that are input are greater than the lower limit and less than the upper limit, the limiters44ato44cinput the command values that are input as-is to the second subtractors45ato45c. When the command values that are input are not more than the lower limit, the limiters44ato44climit the command values to the lower limit and input the command values after the limiting to the second subtractors45ato45c. Also, when the command values that are input are not less than the upper limit, the limiters44ato44climit the command values to the upper limit and input the command values after the limiting to the second subtractors45ato45c. Thereby, the limiters44ato44csuppress the undesirable generation of an overcurrent in the major circuit part12due to an instantaneous potential difference occurring due to an abrupt change of the system voltage of the power system2, etc.

The second subtractors45ato45creceive the input of the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases from the limiters44ato44cand receive the input of the measured values of the line currents Ia(INV), Ib(INV), and Ic(INV) of the phases of the power conversion part20measured by the first measurement device16.

The second subtractors45ato45ccalculate the differences between the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases and the measured values of the line currents Ia(INV), Ib(INV), and Ic(INV) of the phases by subtracting the measured values of the line currents Ia(INV), Ib(INV), and Ic(INV) of the phases from the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases.

The second arithmetic units46ato46ccalculate the correction values for outputting currents corresponding to the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases from the power conversion part20by multiplying the differences calculated by the second subtractors45ato45cby a second proportionality constant K2. More specifically, the correction values are correction values of the phase voltages Va(INV), Vb(INV), and Vc(INV) of the phases of the AC power output from the power conversion part20. The second arithmetic units46ato46cinput the calculated correction values to the second adders47ato47c.

The second adders47ato47creceive the input of the correction values from the second arithmetic units46ato46cand receive the input of the measured values of the phase voltages Va(INV), Vb(INV), and Vc(INV) of the phases of the power conversion part20measured by the first measurement device16.

The second adders47ato47cadd the correction values to the measured values of the phase voltages Va(INV), Vb(INV), and Vc(INV) of the phases. Thereby, the second adders47ato47ccalculate the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases of the AC power output from the power conversion part20.

Thereby, in the overcurrent suppression controller32, the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) can be calculated to suppress the overcurrent at the output end of the major circuit part12by using all of the input information of the phase voltage phase command value θ, the phase voltage amplitude command value |V|, the phase voltages Va(INV), Vb(INV), and Vc(INV), the line currents Ia(INV), Ib(INV), and Ic(INV), the phase voltages Va(PCS), Vb(PCS), and Vc(PCS), and the line currents Ia(PCS), Ib(PCS), and Ic(PCS).

In the overcurrent suppression controller32, the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) can be calculated to suppress the overcurrent at the output end of the major circuit part12by the limiters44ato44climiting the command values of the line currents Ia(PCS), Ib(PCS), and Ic(PCS) of the phases of the AC power output from the major circuit part12to be between the lower limit and the upper limit.

The second adders47ato47cinput the calculated instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases to the control signal generator48.

The control signal generator48generates a control signal for outputting, from the power conversion part20, voltages corresponding to the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases input from the second adders47ato47cand inputs the generated control signal to the power conversion part20. Thereby, the control signal generator48outputs the voltages corresponding to the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases to the power conversion part20.

For example, the control signal generator48generates the control signal for controlling the switching of the switching elements of the power conversion part20by performing sine wave pulse width modulation control based on the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases. However, the configuration of the control signal generator48is not limited thereto and may be any configuration that can generate the control signal for outputting the voltages corresponding to the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases from the power conversion part20.

For example, a configuration may be used in which the control signal generator48is located at the major circuit part12side; the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) of the phases are input to the major circuit part12from the control device14(the overcurrent suppression controller32); and the control signal is generated at the major circuit part12side. The overcurrent suppression controller32may not always include the control signal generator48. The configuration of the overcurrent suppression controller32is not limited to the configuration described above and may be any configuration that can calculate the instantaneous value voltage output command values Va(ref), Vb(ref), and Vc(ref) to suppress the overcurrent at the output end of the major circuit part12by using all of the input information.

FIG.3is a graph schematically illustrating an example of the operation of the power conversion device according to the embodiment.

FIG.4is a graph schematically illustrating an example of the operation of a reference power conversion device.

FIG.4schematically illustrates an example of the operation of the reference power conversion device in which the control device14does not include the overcurrent suppression controller32.

InFIGS.3and4, the horizontal axis is the time (seconds), and the vertical axis is the output current (pu: per unit) referenced to the rated output of the major circuit part12.

FIG.3illustrates an example of the operation of the power conversion device10when a three-wire ground fault having a fault point residual voltage of about 50% occurred from time t1to t2.FIG.4illustrates an example of the operation of the reference power conversion device for a similar case.

As illustrated inFIG.4, in the reference power conversion device that does not include the overcurrent suppression controller32, the output current of the major circuit part12exceeded±2 (pu) when the fault occurred.

In contrast, in the power conversion device10according to the embodiment, the upper limit is set to +1.2 (pu) and the lower limit is set to −1.2 (pu) in the limiters44ato44cof the overcurrent suppression controller32. Thereby, in the power conversion device10according to the embodiment as illustrated inFIG.3, the output current of the major circuit part12was suppressed to about ±1.2 (pu) even when the fault occurred. Compared to the reference power conversion device that does not include the overcurrent suppression controller32, the generation of the overcurrent can be suppressed in the power conversion device10even when the fault occurs.

In the power conversion device10according to the embodiment as described above, the control device14includes the overcurrent suppression controller32. Thereby, the generation of the overcurrent can be suppressed even when a voltage-controlled operation is performed. For example, the generation of the overcurrent in the major circuit part12and the undesirable failure of components inside the major circuit part12such as the switching elements of the power conversion part20, etc., can be suppressed even when an instantaneous potential difference is generated by an abrupt change of the system voltage, etc.

Although several embodiments of the invention are described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments may be carried out in other various forms; and various omissions, substitutions, and modifications can be performed without departing from the spirit of the invention. Such embodiments and their modifications are within the scope and spirit of the invention and are included in the invention described in the claims and their equivalents.