# US 2026/0085656 A1 · Synthetic inertia control method and system of a wind turbine generator > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2026/0085656 A1 - Document ID: US20260085656A1 - Status: Published application - Kind: A1 - Application number: 18/892,813 - Filed: 2024-09-23 - Published: 2026-03-26 - Earliest claimed: 2024-09-23 - Assignees: Korea Renewable Energy Institute Inc. - Applicants: Korea Renewable Energy Institute Inc. - Inventors: Yong Cheol KANG - Web page: https://patentgrep.com/patent/US20260085656A1 ## CPC - F03D 7/028: {controlling wind motor output power} - F03D 7/0284: {in relation to the state of the electric grid} - F03D 7/043: {characterised by the type of control logic} - F05B 2270/327: Rotor or generator speeds - F05B 2270/337: Electrical grid status parameters, e.g. voltage, frequency or power demand - F03D: WIND MOTORS - F05B: INDEXING SCHEME RELATING TO WIND, SPRING, WEIGHT, INERTIA OR LIKE MOTORS, TO MACHINES OR ENGINES FOR LIQUIDS COVERED BY SUBCLASSES F03B, F03D AND F03G ## Abstract The present invention relates to a synthetic inertia control method that includes performing maximum power point tracking control, detecting a frequency deviation in a power system, and switching, when the frequency deviation is greater than a predetermined value, the maximum power point tracking control to temporary frequency support control, wherein the temporary frequency support control includes a first stage of calculating and controlling, for a predetermined first time period from a time point (conversion time point) at which the maximum power point tracking control is converted to the temporary frequency support control, an active power reference value that is increased from an original reference value according to the maximum power point tracking control at the conversion time point, and the increased active power reference value according to the temporary frequency support control is calculated as a function of the frequency deviation and a rotor speed of the wind turbine generator. ## Claims ### Claim 1 A synthetic inertia control method by a control system of a wind turbine generator, the method comprising: performing maximum power point tracking (MPPT) control; detecting a frequency deviation in a power system; and switching, when the frequency deviation is greater than a predetermined value, the maximum power point tracking (MPPT) control to temporary frequency support (TFS) control; wherein the temporary frequency support (TFS) control comprises: a first stage of calculating and controlling, for a predetermined first time period from a time point (conversion time point) at which the maximum power point tracking (MPPT) control is converted to the temporary frequency support (TFS) control, an active power reference value that is increased from an original reference value according to the maximum power point tracking (MPPT) control at the conversion time point, and wherein the increased active power reference value according to the temporary frequency support (TFS) control is calculated as a function of the frequency deviation and a rotor speed of the wind turbine generator. ### Claim 2 (depends on 1) The method of claim 1, further comprising: a second stage of continuously reducing the active power reference value to converge a speed of the rotor; a third stage of reducing the active power reference value for a second time period to allow the speed of the rotor to reach a rotor speed on the maximum power point tracking (MPPT) control curve; and a stage of terminating the temporary frequency support (TFS) control and switching back to the MPPT control when the speed of the rotor reaches a rotor speed on the MPPT control curve, wherein the active power reference value in the second stage is calculated as a function of the rotor speed, and wherein the active power reference value in the third stage is calculated as a function of the rotor speed and a time. ### Claim 3 (depends on 1) The method of claim 1, wherein an equation for calculating the active power reference value of the first stage comprises: a value obtained by multiplying the frequency deviation by a control gain that varies according to the speed of the rotor. ### Claim 4 (depends on 3) The method of claim 3, wherein the active power reference value of the first stage is calculated by the following equation: P ref ( ω r , Δ ⁢ f ) = k * F ⁡ ( ω r ) + a ⁡ ( ω r ) * Δ ⁢ f , for ⁢ t 0 < t ≤ t 0 + T set where the k * F ⁡ ( ω r ) = k g ⁢ ω r 3 (kg is a constant for an MPPT operation), and wherein k is an arbitrary constant, ωr is a speed of a rotor, F(ωr) is a function of w that varies with a rotor speed, α(ωr) is a control gain that varies with the rotor speed, Δf is a deviation of a reference frequency and a measured system frequency, and Tset is the first time period. ### Claim 5 (depends on 4) The method of claim 4, wherein the F(ωr)=ωrn (n is 0 or a natural number). ### Claim 6 (depends on 4) The method of claim 4, wherein the control gain α(ωr) that varies with the rotor speed is expressed by the following equation: a ⁡ ( ω r ) = G max 2 ω max - ω min ⁢ ( ω r - ω min ) where ωmax is a maximum rotor speed of the wind turbine generator, ωmin is a minimum rotor speed, and Gmax is a control gain of ωmax. ### Claim 7 (depends on 2) The method of claim 2, wherein in the second stage, the reference value of the active power is reduced along a line connecting one of points under a Pm curve as well as within a region where ωr<ωTset from a point in the first time period in an active power-rotor speed plane. ### Claim 8 (depends on 2) The method of claim 2, wherein the active power reference value of the second stage is calculated by the following equation: P ref ( ω r ) = P ref ( T set ) ω Tset - ω min ⁢ ( ω r - ω min ) where Pref (Tset) and ωTset are an active power reference value and a rotor speed, respectively, at a time point after the first time period has passed, ωr is a speed of a rotor, and ωmin is a minimum rotor speed. ### Claim 9 (depends on 2) The method of claim 2, wherein the active power reference value of the third stage is calculated by the following equation: P ref ( ω r , t ) = k g ⁢ ω r 3 + Δ ⁢ P C [ - 1 Δ ⁢ T ⁢ ( t - t C ) + 1 ] , for ⁢ t C < t ≤ t C + Δ ⁢ T where ωr is a speed of a rotor, kg is a constant for an MPPT operation, ΔPc is a difference between active power and kgωc3 at a rotor speed point (point C in FIG. 5) converged in the second stage, tc is a time point at point C, and ΔT is a second time period set to reach a rotor speed on the MPPT control curve at point C. ### Claim 10 (depends on 1) The method of claim 1, wherein the first time period is a time period during which the system frequency deviation falls within a predetermined reference value after the system frequency has rebounded beyond the lowest frequency. ### Claim 11 A synthetic inertial control system of a wind turbine generator, the system comprising: a frequency deviation detection unit that detects a frequency deviation of a power system from a reference frequency and a measured system frequency; a rotor speed detection unit that detects a rotor speed of a wind turbine generator; a switching unit that switches between maximum power point tracking (MPPT) control and temporary frequency support (TFS) control; an active power reference value calculation unit that calculates an active power reference value for wind turbine generator output control using the frequency deviation and the rotor speed; and a control unit that controls a wind turbine generator according to the calculated active power reference value, wherein when switched to the temporary frequency support (TFS) control by the switching unit, the active power reference value calculation unit calculates an active power reference value that is increased from an original reference value according to the maximum power point tracking (MPPT) control at a time point (conversion time point) converted to the temporary frequency support (TFS) control, the increased active power reference value is calculated as a function of the frequency deviation and the rotor speed, and the control unit performs a first stage control according to an active power reference value calculated as a function of the frequency deviation and the rotor speed for a predetermined first time period from the conversion time point. ### Claim 12 (depends on 11) The system of claim 11, wherein the active power reference value calculation unit calculates an active power reference value of the second stage that continuously decreases as a function of the rotor speed, and an active power reference value of the third stage as a function of the rotor speed and a time, wherein the control unit performs a second stage control that continuously reduces active power according to the active power reference value of the second stage to converge a speed of the rotor, and a third stage control for a second time period to allow the speed of the rotor to reach a rotor speed on the MPPT control curve according to the active power reference value of the third stage, and wherein the switching unit terminates the temporary frequency support (TFS) control and switches back to the MPPT control when the speed of the rotor reaches a rotor speed on the MPPT control curve. ### Claim 13 (depends on 11) The system of claim 11, wherein an equation for calculating the active power reference value of the first stage comprises: a value obtained by multiplying the frequency deviation by a control gain that varies according to a speed of the rotor. ### Claim 14 (depends on 13) The system of claim 13, wherein the active power reference value for the first stage control is calculated by the following equation: P ref ( ω r , Δ ⁢ f ) = k * F ⁡ ( ω r ) + a ⁡ ( ω r ) * Δ ⁢ f , for ⁢ t 0 < t ≤ t 0 + T set where k * F ⁡ ( ω r ) = k g ⁢ ω r 3 (kg is a constant for an MPPT operation), and wherein k is an arbitrary constant, ωr is a speed of a rotor, F(ωr) is a function of ωr that varies with a rotor speed, α(ωr) is a control gain that varies with the rotor speed, Δf is a deviation of a reference frequency and a measured system frequency, and Tset is a first time period. ### Claim 15 (depends on 14) The system of claim 14, wherein F(ωr)=ωrn (n is 0 or a natural number). ### Claim 16 (depends on 14) The system of claim 14, wherein the control gain α(ωr) that varies with the rotor speed is expressed by the following equation: a ⁡ ( ω r ) = G max 2 ω max - ω min ⁢ ( ω r - ω min ) where ωmax is a maximum rotor speed of the wind turbine generator, ωmin is a minimum rotor speed, and Gmax is a control gain of ωmax. ### Claim 17 (depends on 12) The system of claim 12, wherein the second stage control is a control that reduces a reference value of the active power along a line connecting one of points under a Pm curve as well as within a region where ωr<ωTset from a point in the first time period in an active power-rotor speed plane. ### Claim 18 (depends on 12) The system of claim 12, wherein the active power reference value for the second stage control is calculated by the following equation: P ref ( ω r ) = P ref ( T set ) ω Tset - ω min ⁢ ( ω r - ω min ) where Pref (Tset) and ωTset are an active power reference value and a rotor speed, respectively, at a time point after the first time period has passed, ωr is a speed of a rotor, and ωmin is a minimum rotor speed. ### Claim 19 (depends on 12) The system of claim 12, wherein the active power reference value for the third stage control is calculated by the following equation: P ref ( ω r , t ) = k g ⁢ ω r 3 + Δ ⁢ P C [ - 1 Δ ⁢ T ⁢ ( t - t C ) + 1 ] , for ⁢ t C < t ≤ t C + Δ ⁢ T where ωr is a speed of a rotor, kg is a constant for an MPPT operation, ΔPc is a difference between active power and kgωc3 at a rotor speed point (point C in FIG. 5) converged in the second stage, tc is a time point at point C, and ΔT is a second time period set to reach a rotor speed on the MPPT control curve at point C. ### Claim 20 (depends on 11) The system of claim 11, wherein the first time period is a time period during which the system frequency deviation falls within a predetermined reference value after the system frequency has rebounded beyond the lowest frequency.