CN-122026689-A - LCL type three-level converter event triggering prediction control method, device and medium

CN122026689ACN 122026689 ACN122026689 ACN 122026689ACN-122026689-A

Abstract

The invention discloses an event triggering prediction control method, an event triggering prediction control device and a medium for an LCL-type three-level converter, wherein the method comprises the steps of constructing a first cost function of only a current control target and a second cost function of only a direct-current side midpoint voltage control target of the three-level converter; the method comprises the steps of obtaining the maximum error allowed by a system variable on the premise of ensuring the stability of the system, setting a current trigger interval and a midpoint voltage trigger interval by combining current and midpoint voltage performance indexes, judging the current working condition of the system according to the actual current, midpoint voltage, the current trigger interval and the midpoint voltage trigger interval, determining candidate voltage vectors based on a voltage vector conversion rule according to the working condition of the system, selecting an optimal voltage vector from the determined candidate voltage vectors, and applying a gate driving signal corresponding to the optimal voltage vector to a power electronic semiconductor device of the three-level converter. The invention can obviously reduce the switching frequency of the system, thereby effectively reducing the system loss, improving the operation efficiency and prolonging the service life of the equipment.

Inventors

TAN GUOJUN
GUO ZHIKANG
WANG ANDONG
LI ZHAOXUN
ZHANG JINGWEI
YANG BO

Assignees

江苏国传电气有限公司

Dates

Publication Date: 20260512
Application Date: 20251230

Claims (10)

1. An event-triggered predictive control method for an LCL-type three-level converter, which is characterized by comprising the following steps: Acquisition of The state variables comprise current at the converter side, power grid voltage, filter capacitor voltage and upper and lower bus capacitor voltages at the direct current side; Extracting high-frequency components of the filter capacitor voltage, correcting a current reference value of the converter side without considering resonance suppression based on an active damping strategy fed back by the high-frequency components of the filter capacitor voltage, and calculating to obtain A moment converter resonance suppression current reference value; according to the discrete mathematical model of the three-level converter under the two-phase static coordinate system, combining State variable of time three-level converter Constructing a first cost function of only a current control target and a second cost function of only a direct-current side midpoint voltage control target of the three-level converter according to the resonance suppression current reference value of the moment converter; acquiring the maximum error allowed by the system variable on the premise of ensuring the stability of the system, and setting a current trigger interval and a midpoint voltage trigger interval by combining the current and midpoint voltage performance indexes; judging the current working condition of the system according to the actual current, the midpoint voltage, the current trigger interval and the midpoint voltage trigger interval, wherein the working conditions comprise: The working condition 1 is that the current and the midpoint voltage do not reach the triggering condition, and the voltage vector of the previous control period is maintained unchanged; Working condition 2, that is, current reaches a trigger condition and midpoint voltage does not reach, a first layer of a control target of event trigger prediction control is current tracking, and a second layer of the control target is midpoint voltage balancing; The working condition 3 is that the midpoint voltage reaches a trigger condition, the first layer of a control target of event trigger prediction control is midpoint voltage balance, and the second layer is current tracking; for the working condition 2 or the working condition 3 of the system, determining candidate voltage vectors based on a voltage vector conversion rule; Selecting an optimal voltage vector from the determined candidate voltage vectors; and applying a gate driving signal corresponding to the optimal voltage vector to the power electronic semiconductor device of the three-level converter.
2. The method for event-triggered predictive control of an LCL three-level converter according to claim 1, wherein the extracting the high-frequency component of the filter capacitor voltage corrects the current reference value on the converter side without considering resonance suppression based on an active damping strategy of feedback of the high-frequency component of the filter capacitor voltage, and calculates the corrected current reference value A time converter resonance suppression current reference value comprising: For a pair of Performing coordinate transformation on the filter capacitor voltage acquired at the moment to obtain capacitor voltage components in a two-phase rotating coordinate system; Separating out the high-frequency component of the capacitor voltage through a low-pass filter to obtain the high-frequency component of the capacitor voltage in the two-phase rotating coordinate system; setting a damping coefficient zeta, and calculating a feedback proportion coefficient according to the resonant angular frequency of the LCL filter and the side inductance of the converter ; In the two-phase rotating coordinate system, correcting a current reference value of the converter side without considering resonance suppression by using a high-frequency component of the capacitor voltage to obtain a resonance suppression current reference value in the two-phase rotating coordinate system; Converting the resonance suppression current reference value in the two-phase rotating coordinate system into the two-phase stationary coordinate system through inverse Park transformation to obtain Time of day converter resonance suppression current reference.
3. The LCL three-level converter event-triggered predictive control method according to claim 2, wherein the following is performed The reference value of the resonance suppression current of the time converter is as follows: , In the formula, 、 In a two-phase stationary coordinate system The time of day converter resonance suppression current reference value, 、 In a two-phase rotating coordinate system Time of day converter resonance suppression current reference.
4. The LCL three-level converter event-triggered predictive control method according to claim 1, wherein the first cost function including only current control targets is: , In the formula, As a function of the first cost of the product, 、 In a two-phase stationary coordinate system The current transformer resonance suppression current reference value at the moment, 、 The current prediction value is the current prediction value of the converter side under a two-phase static coordinate system; The second cost function including only the midpoint voltage control target is: , In the formula, As a function of the second cost of the product, Is the predicted value of the midpoint voltage.
5. The method for controlling event triggering prediction of LCL three-level converter according to claim 1, wherein obtaining maximum error allowed by system variables under the premise of ensuring system stability, and setting a current triggering interval and a midpoint voltage triggering interval by combining current and midpoint voltage performance indexes comprises: starting from the most strict condition of system stability, constructing a Lyapunov function of the system; obtaining the maximum error allowed by the system variable on the premise of guaranteeing the stability of the system; the optimal trigger interval is determined according to the performance indexes of current and midpoint voltage, wherein the current performance index is that the total harmonic distortion rate is not more than 5%, the midpoint voltage performance index is determined by the tolerance of the system to the secondary ripple voltage of the direct current side, and the midpoint voltage fluctuation is limited to +/-3% of the direct current voltage.
6. The LCL-type three-level converter event-triggered predictive control method according to claim 5, wherein the predicted values of the current and the midpoint voltage at time k+1 are predicted assuming that the converter switching state remains unchanged, and the current trigger interval and the midpoint voltage trigger interval are expressed as: , , In the formula, 、 In order to trigger the condition of the trigger, In order to be a current trigger interval, The midpoint voltage triggers the interval.
7. The event-triggered predictive control method for an LCL-type three-level converter according to claim 1, wherein said voltage vector conversion rule is to select only the voltage vector adjacent to the optimum voltage vector at the previous time and satisfy that the phase voltage and line voltage of the three-level converter cannot be changed more than As candidate voltage vectors, the zero voltage vector considers only the "000" state.
8. The LCL-type three-level converter event-triggered predictive control method according to claim 1, wherein the selecting an optimal voltage vector from the determined candidate voltage vectors comprises: When the system is in the working condition 2, the candidate voltage vector set is screened to enable The predicted value of the current of the converter side at the moment falls into the voltage vector in the current trigger interval, and the voltage vector with the minimum second cost function value is selected as the optimal voltage vector; when the system is in the working condition 3, the candidate voltage vector set is screened to enable The predicted value of the midpoint voltage at the moment falls into the voltage vector in the midpoint voltage trigger interval, and the voltage vector with the minimum first cost function value is selected as the optimal voltage vector.
9. An LCL-type three-level converter event-triggered predictive control device, the device comprising: The acquisition module is used for acquiring The state variables of the three-level converter at the moment comprise converter side current, grid voltage, filter capacitor voltage and direct-current side upper and lower bus capacitor voltage; The resonance suppression current reference value calculation module is used for extracting the high-frequency component of the filter capacitor voltage, correcting the current reference value of the converter side without considering resonance suppression based on an active damping strategy fed back by the high-frequency component of the filter capacitor voltage, and calculating to obtain A moment converter resonance suppression current reference value; the cost function construction module is used for combining according to a discrete mathematical model of the three-level converter under a two-phase static coordinate system State variable of time three-level converter Constructing a first cost function of only a current control target and a second cost function of only a direct-current side midpoint voltage control target of the three-level converter according to the resonance suppression current reference value of the moment converter; The trigger interval setting module is used for acquiring the maximum error allowed by the system variable on the premise of ensuring the stability of the system, and setting a current trigger interval and a midpoint voltage trigger interval by combining the current and midpoint voltage performance indexes; The working condition judging module is used for judging the current working condition of the system according to the actual current, the midpoint voltage, the current triggering interval and the midpoint voltage triggering interval; The working conditions comprise working condition 1, wherein the current and the midpoint voltage do not reach the triggering conditions; working condition 2, that is, current reaches a trigger condition and midpoint voltage does not reach, a first layer of a control target of event trigger prediction control is current tracking, and a second layer of the control target is midpoint voltage balancing; the working condition 3 is that the midpoint voltage reaches a trigger condition, the first layer of a control target of event trigger prediction control is midpoint voltage balance, and the second layer is current tracking; The candidate voltage vector determining module is used for determining candidate voltage vectors based on a voltage vector conversion rule under the working condition 2 or the working condition 3 of the system; The optimal voltage vector selection module is used for selecting an optimal voltage vector from the determined candidate voltage vectors; And the driving module is used for applying the gate driving signal corresponding to the optimal voltage vector to the power electronic semiconductor device of the three-level converter.
10. A computer readable storage medium having stored thereon computer executable instructions, which when executed by a processor implement the LCL-type three-level converter event-triggered predictive control method of any one of claims 1 to 8.

Description

LCL type three-level converter event triggering prediction control method, device and medium Technical Field The invention belongs to the field of three-level converter control, and particularly relates to an event triggering prediction control method, device and medium for an LCL (LCL-type three-level converter). Background In order to cope with climate change, a sustainable energy system mainly comprising photovoltaic and wind power is established as a global consensus. In the process, the three-level converter plays an indispensable key role as a core interface for connecting high-power generation equipment with a power grid. In such a system, which usually employs an LCL-type filter to achieve high quality control of the grid-connected current, the selection and optimization of the switching frequency is critical, which directly determines the stability, power quality and operating life of the system. The operating life of a power semiconductor device is closely related to its temperature. For silicon-based power semiconductor devices, the device burn-in rate doubles for every 10 ℃ increase after operating temperatures exceeding 50 ℃. Therefore, limiting the device temperature rise is critical to improving the long-term reliability of the device. Reducing the switching frequency is a straightforward and efficient measure from the point of view of reducing switching losses to control the temperature rise. However, in converters employing LCL filters, a reduction in switching frequency presents a serious challenge in terms of increased resonant risk. LCL filters are a three-order system with resonance problems and their controller design is severely dependent on accurate system discrete models. Modeling methods based on traditional PWM carrier modulation generally equivalent the modulation link to a first order inertial link, but this requires a switching frequency much higher than the fundamental and resonant characteristic frequencies of the system. When the switching frequency is greatly reduced, this precondition is no longer true. Excessive delay of the PWM link can lead to rapid decline of discrete model precision, thereby leading to resonance instability of the LCL filter and threatening system safety. Therefore, research on a high-performance control strategy that is stable and can realize low-switching-frequency operation of the system has become a key problem to be solved in the current LCL type three-level converter system. Disclosure of Invention In order to solve the technical problems in the background technology, the invention provides an event triggering prediction control method, an event triggering prediction control device and a medium for an LCL type three-level converter. The method combines an event triggering mechanism with model predictive control, dynamically judges the update moment of the switch state through the real-time state of the system, and drives the switch state not in a fixed period. On the premise of ensuring that the network side current harmonic wave and the direct current side midpoint voltage fluctuation are maintained in a strictly set trigger interval, the switching frequency of the system can be obviously reduced, thereby effectively reducing the system loss, and improving the operation efficiency and the service life of equipment. In order to achieve the above object, the embodiment of the present invention provides the following technical solutions: In a first aspect, the present invention provides an LCL three-level converter event-triggered predictive control method, where the method includes: Acquisition of The state variables comprise current at the converter side, power grid voltage, filter capacitor voltage and upper and lower bus capacitor voltages at the direct current side; Extracting high-frequency components of the filter capacitor voltage, correcting a current reference value of the converter side without considering resonance suppression based on an active damping strategy fed back by the high-frequency components of the filter capacitor voltage, and calculating to obtain A moment converter resonance suppression current reference value; According to a discrete mathematical model of the three-level converter under a two-phase static coordinate system, combining the state variables and the state variables of the three-level converter at the k moment Constructing a first cost function of only a current control target and a second cost function of only a direct-current side midpoint voltage control target of the three-level converter according to the resonance suppression current reference value of the moment converter; acquiring the maximum error allowed by the system variable on the premise of ensuring the stability of the system, and setting a current trigger interval and a midpoint voltage trigger interval by combining the current and midpoint voltage performance indexes; judging the current working condition of the system according to the actual