CN-122000998-A - Cascade multi-level converter inertia support control method and device

CN122000998ACN 122000998 ACN122000998 ACN 122000998ACN-122000998-A

Abstract

The invention discloses a cascade multilevel converter inertia support control method and device, the method comprises the steps of establishing a mathematical model of a cascade multilevel converter, calculating submodule capacitor voltage fluctuation components under different working conditions, detecting frequency change rates in frequency events of a power system, determining a safety regulation domain of the submodule capacitor voltage of the cascade multilevel converter according to the submodule capacitor voltage fluctuation components under different working conditions, determining the maximum regulating quantity of the submodule capacitor voltage, establishing a droop control link, multiplying the frequency deviation of the power system by the droop coefficient to serve as a submodule capacitor voltage change reference value, predicting the load change quantity of the power system by combining the inertia identification result of the power system, solving the optimal droop coefficient by taking the submodule capacitor voltage change reference value equal to the maximum regulating quantity of the submodule capacitor voltage as a constraint condition, and regulating the submodule capacitor voltage of the cascade multilevel converter by the droop control link, the voltage control link and the current control link to provide inertia support for the power system. The device comprises a frequency change rate calculation module, a load prediction module, a sagging control module, a voltage control module, a current control module and a modulation module. According to the inertia supporting control method and device for the cascade multilevel converter, disclosed by the invention, the capacitance voltage out-of-limit caused by capacitance voltage double frequency fluctuation during inertia supporting can be avoided, and the inertia supporting capacity of the cascade multilevel converter is improved through the selection of the optimal sagging coefficient.

Inventors

XIAO QIAN
ZHAO YANSONG
JIN YU
YU HAOLIN
LU WENBIAO
LI TIANXIANG
MU YUNFEI
JIA HONGJIE

Assignees

天津大学
东北电力大学

Dates

Publication Date: 20260508
Application Date: 20251020

Claims (7)

1. A method for controlling inertia support of a cascaded multilevel converter, the method comprising: Establishing a mathematical model of the cascade multilevel converter, and calculating submodule capacitance voltage fluctuation components under different working conditions; Detecting the frequency change rate in a frequency event of the power system, determining a safe regulation domain of the capacitance voltage of a submodule of the cascaded multilevel converter according to the fluctuation components of the capacitance voltage of the submodule under different working conditions, and determining the maximum regulation quantity of the capacitance voltage of the submodule; constructing a droop control link, and multiplying the frequency deviation of the power system by a droop coefficient to be used as a sub-module capacitance voltage change reference value; the load variation of the power system is predicted by combining the power system inertia identification result, and the optimal sagging coefficient is solved by taking the constraint condition that the sub-module capacitance voltage variation reference value is equal to the maximum adjustment quantity of the sub-module capacitance voltage; and the capacitor voltage of the submodule of the cascading multilevel converter is regulated through droop control, voltage control, current control and modulation links, so that inertia support is provided for the power system.
2. The method for controlling the inertia support of the cascaded multilevel converter according to claim 1, wherein the establishing a mathematical model of the cascaded multilevel converter, calculating the capacitance-voltage fluctuation components of the submodules under different working conditions of the cascaded multilevel converter comprises the following specific steps: The cascading multilevel converter comprises 3 bridge arms, each bridge arm is formed by cascading N sub-modules, the bridge arms are connected with a power grid through a filter inductor, when the filter inductor inductance value is L, and the three-phase power grid phase voltage v sj is symmetric, j represents a phase sequence, and a, b and c and the three-phase power grid phase voltage v sj can be respectively expressed as follows: wherein V m is the amplitude of the grid phase voltage, and ω is the angular frequency; During normal operation, the three phases are symmetrical, and the three-phase output phase voltage expression of the cascading multi-level converter is as follows: wherein v dc is the average value of the capacitance voltage of the submodule, m is the modulation ratio, and the size is the ratio of the amplitude of the output phase voltage to Nv dc ; The three-phase output current i j of the cascaded multilevel converter is expressed as follows: Where I m is the magnitude of the output current, Is the power factor angle; the three-phase instantaneous power expression of the cascaded multilevel converter is as follows: The expression of the relationship between the three-phase instantaneous power p j of the cascaded multilevel converter and the capacitance voltage of the submodule is as follows: Wherein E C is the energy stored by the capacitors of the submodules of each phase, v dc0 is the rated value of the capacitor voltage of the submodules, and C dc is the capacitance value of the capacitors of the submodules; The instantaneous value expression of the capacitance voltage of the submodule is obtained as follows: Wherein Deltav dc2 is the voltage double frequency fluctuation component of the sub-module capacitor during normal operation.
3. The cascaded multilevel converter inertia support control method according to claim 1, wherein the detecting the frequency change rate in the frequency event of the power system, determining the safe adjustment domain of the capacitor voltage of the submodule of the cascaded multilevel converter according to the fluctuation components of the capacitor voltage of the submodule under different working conditions, and determining the maximum adjustment amount of the capacitor voltage of the submodule specifically comprises: the frequency change rate RoCoF in detecting a power system frequency event is expressed as follows: wherein f is the power system frequency; According to the fluctuation components of the capacitance and voltage of the submodule under different working conditions, determining the safety regulation domain of the capacitance and voltage of the submodule of the cascaded multilevel converter, and determining the expression of the maximum regulation amount of the capacitance and voltage of the submodule as follows Wherein v dcmax is the upper limit of the capacitance voltage of the submodule, v dcmin is the lower limit of the capacitance voltage of the submodule, deltav dcmax is the maximum adjustment quantity of the capacitance voltage of the submodule, and Deltav dc2m is the amplitude of the double frequency fluctuation component of the capacitance voltage of the submodule in normal operation.
4. The inertia support control method of the cascaded multilevel converter according to claim 1, wherein the step of constructing a droop control step, the step of multiplying the power system frequency deviation by a droop coefficient as a sub-module capacitor voltage variation reference value is specifically: constructing a droop control link, and multiplying the frequency deviation of the power system by a droop coefficient to be used as a reference value of capacitance-voltage variation of the submodule The expression is: Wherein k is a droop coefficient, v dcmin is a lower limit of a submodule capacitor voltage, delta omega pu is a per unit value of power system frequency deviation, and the expression is as follows: Where ω 0 is the nominal angular frequency and f 0 is the nominal frequency.
5. The method for controlling the inertia support of the cascaded multilevel converter according to claim 1, wherein the method for predicting the load variation of the power system by combining the inertia identification result of the power system uses the sub-module capacitor voltage variation reference value equal to the maximum adjustment amount of the sub-module capacitor voltage as a constraint condition, and the method for solving the optimal droop coefficient is as follows: according to the inertia identification result of the power system and the frequency change rate RoCoF, the load change of the power system can be predicted, and the per unit value is recorded as ; Considering the role of the droop control loop, the frequency extremum f ext and the frequency extremum f ext of the power system in a frequency event And k is related, and can be expressed as Taking the constraint condition that the reference value of the capacitance voltage change of the submodule is equal to the maximum adjustment quantity of the capacitance voltage of the submodule, the expression of the per unit value Deltav dcmaxpu of the maximum adjustment quantity of the capacitance voltage of the submodule can be obtained as follows: based on the above, the optimal sag factor can be solved, which can be expressed as: Where Δf maxpu is the per unit value of the maximum frequency deviation, the value can be expressed as: And the optimal droop coefficient is selected, so that the inertia supporting capacity of the cascaded multilevel converter is maximized within the range of allowing the capacitance-voltage conversion of the submodule.
6. The method for controlling the inertia support of the cascaded multilevel converter according to claim 1, wherein the step of adjusting the capacitor voltage of the submodule of the cascaded multilevel converter through droop control, voltage control, current control and modulation links is specifically to provide the inertia support for the power system: obtaining a capacitor voltage change reference value of a submodule of the cascaded multilevel converter through a droop control link ; The voltage control link is used for controlling the capacitor voltage of the submodule of the cascaded multilevel converter to track the reference value of the submodule so as to obtain the reference value of the d-axis component of the current; The current q-axis component reference value is given by the control system; controlling the dq axis component of the current by using a current control link to enable the dq axis component to track respective reference values; and the switching signals of all the switching devices of the cascade multilevel converter are obtained through the modulation link, the conduction of the switching devices is controlled, and the inertia supporting control of the cascade multilevel converter is realized.
7. A cascaded multilevel converter inertia support control device, the device comprising: the frequency change rate calculation module is used for calculating state variables such as frequency deviation, frequency change rate and the like of the power system; The load prediction module is used for predicting load change in the frequency event according to the system inertia identification result and the frequency change rate; the droop control module is used for selecting an optimal droop coefficient, and multiplying the frequency deviation of the power system by the droop coefficient to be used as a capacitance-voltage variation reference value of the submodule; The voltage control module is used for controlling the capacitor voltage of the submodule of the cascaded multilevel converter to track the reference value of the submodule to obtain the reference value of the d-axis component of the current; the current control module is used for controlling the current dq axis component of the cascaded multilevel converter; The modulation module converts the control signal obtained by the current control module into a modulation signal, and obtains the switching signal of each switching device of the cascade multilevel converter by using a modulation algorithm to control the conduction of the switching device.

Description

Cascade multi-level converter inertia support control method and device Technical Field The invention relates to the technical field of control of multilevel converters, in particular to a cascade multilevel converter inertia supporting control method and device. Background The cascade multilevel converter can provide reactive compensation for the power system through cascade of a plurality of submodules, and has wide application prospect in the power electronic power system. The number of submodules of the cascaded multilevel converter is large, the energy stored by the capacitors of each submodule is considerable, and short-time inertia support can be provided in the frequency event of the power system by adjusting the voltage of the capacitors of the submodules. The existing inertia support control is mainly controlled by a virtual synchronous machine and sagging. The virtual synchronous machine control is realized by constructing a rotor motion equation, so that the converter simulates rotor characteristics of the synchronous machine and provides indirect inertia support for the power system. Droop control provides direct inertial support for the power system by multiplying the frequency deviation by a droop coefficient as a reference for the amount of capacitance voltage change, and the level of inertia provided can be quantitatively calculated. However, the conventional droop control considers the frequency doubling fluctuation component of the capacitance voltage of the submodule of the cascaded multilevel converter when the multilevel converter operates at multiple times, and the capacitance voltage is easy to be out of limit when inertia support is provided. In addition, the existing droop control method lacks of development of maximizing the inertia supporting capability of the cascaded multilevel converter, and is difficult to maximally utilize the inertia supporting capability of the cascaded multilevel converter. Therefore, according to the actual operation characteristics of the cascaded multilevel converter, an inertia support control method suitable for the cascaded multilevel converter needs to be developed, so that the safe operation of the cascaded multilevel converter is ensured, and the maximized inertia support is provided. Disclosure of Invention The invention provides a control method and a device for cascade multilevel converter inertia support, which can solve the problem of capacitor voltage out-of-limit caused by factor module capacitor voltage doubling fluctuation of the cascade multilevel converter in the inertia support process, ensure the safety of the inertia support of the cascade multilevel converter, and maximally utilize the inertia support potential of the cascade multilevel converter, and are described in detail below: In a first aspect, a cascaded multilevel converter inertia support control method includes: Establishing a mathematical model of the cascade multilevel converter, and calculating submodule capacitance voltage fluctuation components under different working conditions; Detecting the frequency change rate in a frequency event of the power system, determining a safe regulation domain of the capacitance voltage of a submodule of the cascaded multilevel converter according to the fluctuation components of the capacitance voltage of the submodule under different working conditions, and determining the maximum regulation quantity of the capacitance voltage of the submodule; constructing a droop control link, and multiplying the frequency deviation of the power system by a droop coefficient to be used as a sub-module capacitance voltage change reference value; the load variation of the power system is predicted by combining the power system inertia identification result, and the optimal sagging coefficient is solved by taking the constraint condition that the sub-module capacitance voltage variation reference value is equal to the maximum adjustment quantity of the sub-module capacitance voltage; and the capacitor voltage of the submodule of the cascading multilevel converter is regulated through droop control, voltage control, current control and modulation links, so that inertia support is provided for the power system. The method for calculating the capacitance and voltage fluctuation components of the submodules under different working conditions of the cascaded multilevel converter comprises the following steps of: The cascading multilevel converter comprises 3 bridge arms, each bridge arm is formed by cascading N sub-modules, the bridge arms are connected with a power grid through a filter inductor, the inductance value of the filter inductor is L, during normal grid-connected operation, three-phase power grid phase voltages v sj are symmetrical, j represents phase sequences, and a, b and c and three-phase power grid phase voltages v sj can be respectively expressed as follows: wherein V m is the amplitude of the grid phase voltage, and ω is the angular fre