US-12627244-B2 - Power conversion device and control device

US12627244B2US 12627244 B2US12627244 B2US 12627244B2US-12627244-B2

Abstract

A current suppression control unit calculates a correction amount of a reference voltage command value for operating a power converter as a voltage source, and sets an amplitude value of a voltage command value by reflecting the correction amount in an amplitude value of the reference voltage command value. The correction amount is set to make the amplitude value of the voltage command value smaller than the amplitude value of the reference voltage command value, in response to a decrease in an AC voltage at an interconnection point.

Inventors

Kaho MUKUNOKI
Toshiyuki Fujii
Ryosuke UDA
Kota HAMANAKA
Shuhei Fujiwara

Assignees

MITSUBISHI ELECTRIC CORPORATION

Dates

Publication Date: 20260512
Application Date: 20211007

Claims (15)

1 . A power conversion device comprising: at least one power converter configured to include switching elements, for converting DC power from a DC power source into AC power and outputting the AC power to a power system; and a control device to control power conversion in the power converter, the control device including a voltage control unit to generate a reference voltage command value for operating the power converter as a voltage source that outputs an AC voltage having a frequency and a phase which are different from those in the power system, a current suppression control unit to generate a voltage command value for the power converter using an AC voltage at an interconnection point of the power converter with respect to the power system and the reference voltage command value, and a switching control unit to control turning on/off of the switching elements of the power converter according to the voltage command value, the current suppression control unit having a first correction computation unit to compute a first correction amount for making an amplitude value of the voltage command value smaller than an amplitude value of the reference voltage command value, in response to a decrease in the AC voltage at the interconnection point, using an amplitude value of the AC voltage at the interconnection point, and an amplitude correction unit to set the amplitude value of the voltage command value by reflecting the first correction amount in the amplitude value of the reference voltage command value.
2 . The power conversion device according to claim 1 , wherein, when the amplitude value of the AC voltage at the interconnection point is more than a predefined determination value, the first correction computation unit sets the first correction amount to zero.
3 . The power conversion device according to claim 1 , wherein, when the amplitude value of the AC voltage at the interconnection point is less than or equal to a predefined determination value, the first correction computation unit sets the first correction amount according to a difference between the amplitude value of the reference voltage command value and the amplitude value of the AC voltage at the interconnection point.
4 . The power conversion device according to claim 1 , wherein, when the amplitude value of the AC voltage at the interconnection point is more than a predefined determination value, the first correction computation unit computes the first correction amount so as to set the amplitude value of the voltage command value according to the amplitude value of the reference voltage command value, and when the amplitude value of the AC voltage at the interconnection point is less than or equal to the predefined determination value, the first correction computation unit computes the first correction amount so as to set the amplitude value of the voltage command value according to the amplitude value of the AC voltage at the interconnection point.
5 . The power conversion device according to claim 1 , wherein the current suppression control unit further includes a second correction computation unit to compute a second correction amount according to the amplitude value of the AC voltage at the interconnection point when the amplitude value of the voltage command value is set substantially equal to the amplitude value of the reference voltage command value, and the amplitude correction unit sets the amplitude value of the voltage command value by reflecting the first and second correction amounts in the amplitude value of the reference voltage command value.
6 . The power conversion device according to claim 5 , wherein the second correction computation unit computes the second correction amount to compensate for a deviation of the amplitude value of the AC voltage at the interconnection point with respect to the amplitude value of the reference voltage command value.
7 . The power conversion device according to claim 1 , wherein a phase of the voltage command value is set according to a phase of the reference voltage command value.
8 . The power conversion device according to claim 1 , wherein a plurality of the power converters are arranged, the plurality of power converters are connected to the power system in parallel via a multiple voltage transformer, and the control device operates the plurality of power converters in parallel, according to the voltage command value that is common generated by the current suppression control unit.
9 . A control device for a power converter configured to include switching elements, for converting DC power from a DC power source into AC power and outputting the AC power to a power system, the control device comprising: a voltage control unit to generate a reference voltage command value for operating the power converter as a voltage source that outputs an AC voltage having a frequency and a phase which are different from those in the power system, a current suppression control unit to generate a voltage command value for the power converter using an AC voltage at an interconnection point of the power converter with respect to the power system and the reference voltage command value, and a switching control unit to control turning on/off of the switching elements of the power converter according to the voltage command value, the current suppression control unit including a first correction computation unit to compute a first correction amount for making an amplitude value of the voltage command value smaller than an amplitude value of the reference voltage command value, in response to a decrease in the AC voltage at the interconnection point, using an amplitude value of the AC voltage at the interconnection point, and an amplitude correction unit to set the amplitude value of the voltage command value by reflecting the first correction amount in the amplitude value of the reference voltage command value.
10 . The control device according to claim 9 , wherein, when the amplitude value of the AC voltage at the interconnection point is more than a predefined determination value, the first correction computation unit sets the first correction amount to zero.
11 . The control device according to claim 9 , wherein, when the amplitude value of the AC voltage at the interconnection point is less than or equal to a predefined determination value, the first correction computation unit sets the first correction amount according to a difference between the amplitude value of the reference voltage command value and the amplitude value of the AC voltage at the interconnection point.
12 . The control device according to claim 9 , wherein, when the amplitude value of the AC voltage at the interconnection point is more than a predefined determination value, the first correction computation unit computes the first correction amount so as to set the amplitude value of the voltage command value according to the amplitude value of the reference voltage command value, and when the amplitude value of the AC voltage at the interconnection point is less than or equal to the predefined determination value, the first correction computation unit computes the first correction amount so as to set the amplitude value of the voltage command value according to the amplitude value of the AC voltage at the interconnection point.
13 . The control device according to claim 9 , wherein the current suppression control unit further includes a second correction computation unit to compute a second correction amount according to the amplitude value of the AC voltage at the interconnection point when the amplitude value of the voltage command value is set substantially equal to the amplitude value of the reference voltage command value, and the amplitude correction unit sets the amplitude value of the voltage command value by reflecting the first and second correction amounts in the amplitude value of the reference voltage command value.
14 . The control device according to claim 13 , wherein the second correction computation unit computes the second correction amount to compensate for a deviation of the amplitude value of the AC voltage at the interconnection point with respect to the amplitude value of the reference voltage command value.
15 . The control device according to claim 9 , wherein a phase of the voltage command value is set according to a phase of the reference voltage command value.

Description

TECHNICAL FIELD The present disclosure relates to a power conversion device and a control device. BACKGROUND ART In recent years, renewable energy generated by dispersed-type power sources such as solar power generation facilities have been introduced into power systems. Since a dispersed-type power source is connected to a power system via a power converter, if the amount of introduced renewable energy increases, the ratio of synchronous generators connected to the power system decreases, and thereby there is a concern that an inertia force of the power system with respect to frequency change may decrease. Thus, there has been proposed virtual synchronous generator control that compensates for a decreased inertia force by causing a power conversion device interconnected to a system to perform a behavior similar to that of a synchronous generator. Specifically, a power converter having a voltage control-type virtual synchronous generator control function (hereinafter also referred to as a “virtual synchronous generator”) is controlled to simulate a behavior in a case where a synchronous power generator to be simulated is connected to a power system. For example, Japanese Patent Laying-Open No. 2019-80476 (PTL 1) describes that, in computing a voltage command value for an alternating current (AC)/direct current (DC) converter according to an output command value for virtual synchronous generator control, if a short circuit accident occurs in a power system, an output current suppression unit performs control to change an internal impedance of a virtual synchronous generator such that an output current of the AC/DC converter may not exceed a current limit value. CITATION LIST Patent Literature PTL 1: Japanese Patent Laying-Open No. 2019-80476 SUMMARY OF INVENTION Technical Problem Since a virtual synchronous generator operates as a voltage source, if a short circuit accident occurs in a power system and a voltage at an interconnection point decreases, a voltage difference between an output voltage of the virtual synchronous generator and the voltage at the interconnection point increases. Thus, an output current of a power converter becomes excessive, and thereby the power converter is stopped for protection, which poses a problem. To deal with this problem, in PTL 1, if a short circuit accident occurs in the power system, control is performed to change the internal impedance of the virtual synchronous generator and compute the voltage command value as a voltage source, to thereby decrease the voltage difference such that an excess current may not occur. Therefore, in the technique of PTL 1, in order to obtain an appropriate current suppression effect in case of a system accident, it is necessary to set the amount of change of the internal impedance of the virtual synchronous generator as appropriate. However, since a system impedance changes depending on a load state and the like, and also changes depending on the manner of a short circuit accident, it becomes difficult to make the amount of change (the increased amount) of the internal impedance of the virtual synchronous generator in the output current suppression unit of PTL 1 appropriate to correspond to the system impedance. As a result, there is a concern that the effect of suppressing an excess current may not be stably obtained. An object in an aspect of the present disclosure is to provide a power conversion device and a control device capable of stably performing control that operates a power converter interconnected to a power system as a voltage source and suppresses occurrence of an excess current. Solution to Problem According to an embodiment of the present disclosure, a power conversion device is provided. The power conversion device includes at least one power converter configured to include switching elements, and a control device to control power conversion in the power converter. The power converter converts DC power from a DC power source into AC power and outputs the AC power to a power system. The control device includes a voltage control unit, a current suppression control unit, and a switching control unit. The voltage control unit generates a reference voltage command value for operating the power converter as a voltage source that outputs an AC voltage having a frequency and a phase which are different from those in the power system. The current suppression control unit generates a voltage command value for the power converter using an AC voltage at an interconnection point of the power converter with respect to the power system and the reference voltage command value. The switching control unit controls turning on/off of the switching elements of the power converter according to the voltage command value. The current suppression control unit has a first correction computation unit and an amplitude correction unit. The first correction computation unit computes a first correction amount for making an amplitude value of the voltage