CN-115566915-B - Cascaded multi-level rectifier topology and control method thereof

CN115566915BCN 115566915 BCN115566915 BCN 115566915BCN-115566915-B

Abstract

The invention provides a cascade multilevel rectifier topology and a control method thereof, wherein a data model is built based on the topology, discretization is carried out, a prediction model is formed, a reference voltage vector at the next moment is predicted, two basic voltage vectors closest to the reference voltage vector are selected by using a first valence function, the action time of the two basic voltage vectors is calculated respectively, and the action time is distributed to the corresponding basic voltage vectors, so that double-vector control is realized. The invention has the advantages of multiple topologies, less current ripple and good control effect.

Inventors

XING XIANGYANG
HU ZUOHANG
LIU HAO

Assignees

山东大学

Dates

Publication Date: 20260508
Application Date: 20221021

Claims (8)

1. A control method of cascade multilevel rectifier topology is characterized in that a data model is built based on topology, discretization is carried out, a prediction model is formed, a reference voltage vector at the next moment is predicted, two basic voltage vectors closest to the reference voltage vector are selected by using a first valence function, the acting time of the two basic voltage vectors is calculated respectively, and the acting time is distributed to the corresponding basic voltage vectors to realize double-vector control; The method further comprises the steps of constructing a second value function, controlling the midpoint and flying capacitor voltage, and applying a switching state with the minimum second value function to control; wherein the second value function is defined as: Wherein m is the weight coefficient of the H bridge flying capacitor, H is the weight coefficient of the DC side capacitor, In order to sample the period of time, Is a capacitor at the direct current side, Current in x phase, where x = a, b, c; the voltage across the capacitor for the x-phase H-bridge, where x=a, b, c, 、 The voltages of the upper capacitor and the lower capacitor at the direct current side are respectively; and (3) with Status flags for fly capacitor voltage and DC side capacitor voltage, respectively When the voltage vector state is-3, 1 or-1.5, the current flowing through the flying capacitor is At this time take = -1, When the voltage vector state is-1, 1.5 or 3, the current flowing through the flying capacitor is + Taking out When the voltage vector states are-2, 0 and 2, the current does not pass through the flying capacitor and is taken For (E) =0 When the voltage vector states are-1.5, 0 and 1.5, the DC side capacitance is affected, and then the voltage vector is taken When the voltage vector is in other state, the capacitor on the DC side is not affected =0; Wherein, a cascaded multi-level rectifier topology includes: each phase of bridge arm comprises a cascade H-bridge unit and a Vienna rectifier; The H bridge unit comprises two-level half bridge units formed by four switching tubes in a head-tail phase string, the upper middle point and the lower middle point of the H bridge circuit are connected with two ends of a flying capacitor, the middle points of the two half bridge units are respectively connected with a power grid and a Vienna rectifier of a rear stage, the Vienna rectifier comprises two diodes which are connected in series, one side of the middle point of each diode is connected with two switching tubes which are connected in anti-series, and the other side of the middle point of each diode is connected with the H bridge unit of a front stage; the parallel three-phase bridge arm DC output end is connected with two capacitors with the same capacitance value in series.
2. The control method of claim 1, further comprising direct current side voltage control using a PI controller.
3. The control method of claim 1, wherein creating a data model based on topology and discretizing, the specific process of forming a predictive model comprises: According to kirchhoff voltage law, a data model of a topological structure is constructed, a Clarke transformation is utilized to convert a mathematical model in an abc coordinate system into an alpha-beta coordinate system, a backward difference is adopted to discretize the model, and a discrete time equation of the discretized model is pushed forward for one period.
4. A control method as claimed in claim 1,2 or 3, wherein the first cost function is a cost function for controlling the phase voltage at the input of the rectifier.
5. The control method of claim 4, wherein a seven-level space voltage vector diagram is created, and the sector division is performed according to the direction of the three-phase current.
6. The control method of a cascaded multi-level rectifier topology of claim 1, wherein switching tubes at different positions of each phase leg employ power devices of different voltage classes or types.
7. A control device comprising a processor for implementing instructions and a computer-readable storage medium for storing instructions adapted to be loaded by the processor and to perform the steps of a method of controlling a cascaded multi-level rectifier topology according to any one of claims 1-6.
8. A control system of a cascade type multilevel rectifier topology employing a control method of a cascade type multilevel rectifier topology according to any one of claims 1 to 6, comprising: a direct-current-side voltage control module configured to perform direct-current-side voltage control; The alternating-current side current control module is configured to establish a data model based on topology, discretize the data model to form a prediction model, predict a reference voltage vector at the next moment, select two basic voltage vectors closest to the reference voltage vector by using a first valence function, respectively calculate the acting time of the two basic voltage vectors, and allocate the acting time to the corresponding basic voltage vectors to realize double-vector control; and a capacitance-voltage balance control module configured to perform capacitance-voltage balance control.

Description

Cascaded multi-level rectifier topology and control method thereof Technical Field The invention belongs to the technical field of power electronics, and particularly relates to a cascaded multi-level rectifier topology and a control method thereof. Background The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art. In recent years, with the development of fields such as solar energy, wind energy and new energy automobiles, as a bridge between a power grid and equipment, a power electronic converter has also been put on higher demands. Due to the limitation of the IGBT voltage level, the traditional two-level rectifier cannot meet the requirements of modern power electronic devices in the aspects of voltage level, current harmonic wave and the like. It is therefore of great importance to develop a high performance rectifier that can withstand higher voltages and has smaller harmonics. In order to overcome the disadvantages of the conventional two-level rectifier, a learner proposed a multi-level rectifier. Compared with the traditional two-level rectifier, the multi-electric rectifier has the obvious advantages of small volume, low output voltage and current harmonic, high working voltage and power, high switching frequency of devices, low voltage stress and the like, and therefore, the multi-electric rectifier is widely applied. However, the multi-level rectifier circuit structure is complex, the power switch devices are more, and certain difficulty exists in control. For multi-level rectifiers, the control strategies commonly used are SPWM control, SVPWM control, and model predictive control. The model predictive control is used as an advanced control method, can quickly track current change, and has the advantages of good dynamic performance, high robustness and the like. However, in order to achieve fast tracking of the current, the harmonic wave of the ac current measured by the rectifier is increased, which results in an undesirable control effect. Disclosure of Invention In order to solve the problems, the invention provides a cascaded multi-level rectifier topology and a control method thereof, and the cascaded multi-level rectifier topology has the advantages of multiple topologies, and has the advantages of less current ripple and good control effect. According to some embodiments, the present invention employs the following technical solutions: A cascading type multilevel rectifier topology comprises three-phase bridge arms which are connected in parallel, wherein each phase of bridge arm comprises a cascading H-bridge unit and a Vienna rectifier; The H bridge unit comprises two-level half bridge units formed by four switching tubes in a head-tail phase string, the upper middle point and the lower middle point of the H bridge circuit are connected with two ends of a flying capacitor, the middle points of the two half bridge units are respectively connected with a power grid and a Vienna rectifier of a rear stage, the Vienna rectifier comprises two diodes which are connected in series, one side of the middle point of each diode is connected with two switching tubes which are connected in anti-series, and the other side of the middle point of each diode is connected with the H bridge unit of a front stage; the parallel three-phase bridge arm DC output end is connected with two capacitors with the same capacitance value in series. As an alternative embodiment, the switching tubes at different positions of each phase bridge arm adopt power devices with different voltage classes or types. According to the control method based on the topology, a data model is built based on the topology, discretization is carried out, a prediction model is formed, a reference voltage vector at the next moment is predicted, two basic voltage vectors closest to the reference voltage vector are selected by using a first valence function, the acting time of the two basic voltage vectors is calculated respectively, and the acting time is distributed to the corresponding basic voltage vectors, so that double-vector control is realized. As an alternative embodiment, the method further comprises constructing a second value function, controlling the midpoint and flying capacitor voltage, and applying a switching state at which the second value function is minimal to the control. As an alternative embodiment, the method further comprises using a PI controller for dc-side voltage control. As an alternative embodiment, the data model is built based on topology and discretized, and the specific process of forming the prediction model includes: According to kirchhoff voltage law, a data model of a topological structure is constructed, a Clarke transformation is utilized to convert a mathematical model in an abc coordinate system into an alpha-beta coordinate system, a backward difference is adopted to discretize the model, and a discrete time