US-12627144-B2 - Voltage control apparatus and voltage control method

US12627144B2US 12627144 B2US12627144 B2US 12627144B2US-12627144-B2

Abstract

A voltage control apparatus, when a voltage drop of an output voltage of an inverter is equal to or larger than a threshold, calculates first virtual impedance using various variables, calculates, such that an output current of the inverter does not exceed a rated value, second virtual impedance to be temporarily added to the first virtual impedance, calculates a virtual active voltage and a virtual reactive voltage by multiplying each of an active current and a reactive current calculated by the output current, by virtual impedance obtained by adding up the first virtual impedance and the second virtual impedance, and performs voltage control based on the virtual active voltage and the virtual reactive voltage such that each of the active current and the reactive current can approach each of an active current command value and a reactive current command value required of a power grid.

Inventors

Mohammad BANI SHAMSEH
Haiqing Li

Assignees

TMEIC CORPORATION

Dates

Publication Date: 20260512
Application Date: 20230630

Claims (14)

1 . A voltage control apparatus comprising: an inverter that converts DC power output from a battery into AC power and supplies the AC power to a power grid; and circuitry connected to the inverter, wherein the circuitry is configured to execute: when a voltage drop of an output voltage of the inverter is equal to or larger than a threshold because of fluctuation in an AC voltage of the power grid, processing for calculating first virtual impedance using variables including an active voltage command value and a reactive voltage command value calculated by a voltage command value, and an active current command value and a reactive current command value calculated by the output voltage and the voltage command value; processing for calculating, such that an output current of the inverter does not exceed a rated value, second virtual impedance to be temporarily added to the first virtual impedance; processing for calculating a virtual active voltage and a virtual reactive voltage by multiplying each of an active current and a reactive current calculated by the output current, by virtual impedance obtained by adding up the first virtual impedance and the second virtual impedance; and processing for performing voltage control based on the virtual active voltage and the virtual reactive voltage such that each of the active current and the reactive current is able to approach each of the active current command value and the reactive current command value required of the power grid.
2 . The voltage control apparatus according to claim 1 , wherein the circuitry is configured to, in the processing for calculating the second virtual impedance, when the voltage drop of the output voltage is equal to or larger than the threshold, set the second virtual impedance to a value corresponding to the output voltage, and when the voltage drop of the output voltage is smaller than the threshold, set the second virtual impedance to zero.
3 . The voltage control apparatus according to claim 2 , wherein the second virtual impedance is reactance consisting of amplitude set by a first variable and a frequency set by a second variable, and the circuitry is configured to, when the voltage drop of the output voltage is equal to or larger than the threshold, set a value of the first variable to be larger and set a value of the second variable to be smaller as the output voltage is smaller, and set the value of the first variable to be smaller and set the value of the second variable to be larger as the output voltage is larger.
4 . The voltage control apparatus according to claim 2 , wherein the variables further include an active voltage and a reactive voltage calculated by the output voltage, and the circuitry is configured to, in the processing for calculating the virtual impedance, calculate the virtual impedance based on a condition that the reactive voltage is zero, the reactive voltage command value is zero, a voltage value obtained by subtracting the virtual active voltage and the active voltage from the active voltage command value is zero, and a voltage value obtained by subtracting the virtual reactive voltage and the reactive voltage from the reactive voltage command value is zero.
5 . The voltage control apparatus according to claim 2 , wherein the first virtual impedance includes resistance and reactance, and the circuitry is configured to, in the processing for calculating the first virtual impedance, calculate each of the resistance and the reactance corresponding to the output voltage.
6 . The voltage control apparatus according to claim 2 , wherein the active current command value is calculated by multiplying a differential voltage obtained by calculating a difference between the voltage command value and the output voltage, by a constant value, and the reactive current command value is calculated such that a sum obtained by adding up a square value of the active current command value and a square value of the reactive current command value is 1.
7 . The voltage control apparatus according to claim 3 , wherein the variables further include an active voltage and a reactive voltage calculated by the output voltage, and the circuitry is configured to, in the processing for calculating the virtual impedance, calculate the virtual impedance based on a condition that the reactive voltage is zero, the reactive voltage command value is zero, a voltage value obtained by subtracting the virtual active voltage and the active voltage from the active voltage command value is zero, and a voltage value obtained by subtracting the virtual reactive voltage and the reactive voltage from the reactive voltage command value is zero.
8 . The voltage control apparatus according to claim 3 , wherein the first virtual impedance includes resistance and reactance, and the circuitry is configured to, in the processing for calculating the first virtual impedance, calculate each of the resistance and the reactance corresponding to the output voltage.
9 . The voltage control apparatus according to claim 3 , wherein the active current command value is calculated by multiplying a differential voltage obtained by calculating a difference between the voltage command value and the output voltage, by a constant value, and the reactive current command value is calculated such that a sum obtained by adding up a square value of the active current command value and a square value of the reactive current command value is 1.
10 . The voltage control apparatus according to claim 1 , wherein the variables further include an active voltage and a reactive voltage calculated by the output voltage, and the circuitry is configured to, in the processing for calculating the virtual impedance, calculate the virtual impedance based on a condition that the reactive voltage is zero, the reactive voltage command value is zero, a voltage value obtained by subtracting the virtual active voltage and the active voltage from the active voltage command value is zero, and a voltage value obtained by subtracting the virtual reactive voltage and the reactive voltage from the reactive voltage command value is zero.
11 . The voltage control apparatus according to claim 1 , wherein the first virtual impedance includes resistance and reactance, and the circuitry is configured to, in the processing for calculating the first virtual impedance, calculate each of the resistance and the reactance corresponding to the output voltage.
12 . The voltage control apparatus according to claim 1 , wherein the active current command value is calculated by multiplying a differential voltage obtained by calculating a difference between the voltage command value and the output voltage, by a constant value, and the reactive current command value is calculated such that a sum obtained by adding up a square value of the active current command value and a square value of the reactive current command value is 1.
13 . The voltage control apparatus according to claim 12 , wherein the active current command value is represented by a percentage, and when a calculation result of the active current command value exceeds 100%, the circuitry sets the active current command value to 100%.
14 . A voltage control method comprising: converting, using an inverter, DC power output from a battery into AC power and supplying the AC power to a power grid; when a voltage drop of an output voltage of the inverter is equal to or larger than a threshold because of fluctuation in an AC voltage of the power grid, calculating first virtual impedance using variables including an active voltage command value and a reactive voltage command value calculated by a voltage command value, and an active current command value and a reactive current command value calculated by the output voltage and the voltage command value; calculating, such that an output current of the inverter does not exceed a rated value, second virtual impedance to be temporarily added to the first virtual impedance; calculating a virtual active voltage and a virtual reactive voltage by multiplying each of an active current and a reactive current calculated by the output current, by virtual impedance obtained by adding up the first virtual impedance and the second virtual impedance; and performing voltage control based on the virtual active voltage and the virtual reactive voltage such that each of the active current and the reactive current is able to approach each of the active current command value and the reactive current command value required of the power grid.

Description

TECHNICAL FIELD The present disclosure relates to a technique for controlling an output voltage of an inverter. BACKGROUND ART Patent Literature 1 discloses a technique that can stably continue operation in a power converter (that is, an inverter) that executes control simulating a synchronous generator. In this related art, when an AC voltage of a power grid fluctuates, voltage control is performed such that active power input and output between the power grid and the power converter decreases. CITATION LIST Patent Literature [PTL 1] JP 7183486 B SUMMARY OF THE INVENTION Problems to be Solved by the Invention A case is assumed in which a voltage control-type GFM (Grid Forming) inverter is used as an inverter that supplies an AC voltage to a power grid. In this case, as explained in Patent Literature 1, when the AC voltage of the power grid fluctuates, voltage control is performed to reduce a difference in active power input and output between the power grid and the power converter. However, even if the voltage control for stabilizing the active power is performed, it is likely that an output current of the inverter cannot reach a reference current required of the power grid and the power grid becomes unstable. Therefore, in order to supply stable active power to the power grid, it is necessary to perform the voltage control to output an active current and a reactive current required of the power grid. One object of the present disclosure is to provide a technique that, when an AC voltage of a power grid fluctuates, can perform voltage control to output an active current and a reactive current required of the power grid. Means for Solving the Problems A first aspect of the present disclosure relates to a voltage control apparatus. The voltage control apparatus includes an inverter that converts DC power output from a battery into AC power and supplies the AC power to a power grid. The voltage control apparatus further includes a controller connected to the inverter. The controller executes: processing for, when a voltage drop of an output voltage of the inverter is equal to or larger than a threshold because of fluctuation in an AC voltage of the power grid, calculating first virtual impedance using variables including an active voltage command value and a reactive voltage command value calculated by a voltage command value and an active current command value and a reactive current command value calculated by the output voltage of the inverter and the voltage command value; processing for calculating, such that an output current of the inverter does not exceed a rated value, second virtual impedance to be temporarily added to the first virtual impedance; processing for calculating a virtual active voltage and a virtual reactive voltage by multiplying each of an active current and a reactive current calculated by the output current, by virtual impedance obtained by adding up the first virtual impedance and the second virtual impedance; and processing for performing voltage control based on the virtual active voltage and the virtual reactive voltage such that each of the active current and the reactive current can approach each of the active current command value and the reactive current command value required of the power grid. A second aspect of the present disclosure further includes the following characteristics in addition to the first aspect. In the processing for calculating the second virtual impedance, when the voltage drop of the output voltage of the inverter is equal to or larger than the threshold, the controller sets the second virtual impedance to a value corresponding to the output voltage. In the processing for calculating the second virtual impedance, when the voltage drop of the output voltage of the inverter is smaller than the threshold, the controller sets the second virtual impedance to zero. A third aspect of the present disclosure further includes the following characteristics in addition to the second aspect. The second virtual impedance is reactance consisting of amplitude set by a first variable and a frequency set by a second variable. When the voltage drop of the output voltage of the inverter is equal to or larger than the threshold, the controller sets a value of the first variable to be larger and sets a value of the second variable to be smaller as the output voltage of the inverter is smaller. Further, when the voltage drop of the output voltage of the inverter is equal to or larger than the threshold, the controller sets the value of the first variable to be smaller and sets the value of the second variable to be larger as the output voltage of the inverter is larger. A fourth aspect of the present disclosure further includes the following characteristics in addition to any one aspect of the first aspect to the third aspect. The variables further include an active voltage and a reactive voltage calculated by the output voltage. In the processing for calculating the virtual