Parallel control method for three-phase inverters without output isolation transformer

Abstract

The invention discloses a three-phase inverter parallel-connection control method without an output isolation transformer. The method comprises the following steps: an output end of each three-phase inverter is connected with an LCL filter, and a filtering capacitor of each LCL filter is connected with a dumping resistor in series, so that the stability is improved, the harmonic wave of a harmonic point is limited, and stability range of control parameters is increased. By means of pre-synchronization before parallel connection and carrier synchronization in the process of parallel connection operation, the phases among the three-phase inverters and parallel-connected communication buses are synchronized, carriers among the three-phase inverters connected in parallel are synchronized, and stability of parallel connection is guaranteed. By means of the algorithms combining pole assignment capacitor voltage control and virtual resistance matching control, the response speed of the inverters is improved, the control performance is improved, and the influence on parallel-connection current sharing by circuit resistance is lowered. By means of seamless mode switching and alternative current over-current and short-circuit failure protection base on three-ring control, under the condition of absence of the output isolation transformer, the three-phase inverter parallel-connection control method is used for independently resolving short-circuit failures of a parallel-connection micro power grid.

Description

technical field [0001] The invention relates to a control method of a converter device, in particular to a three-phase inverter parallel control method without an output isolation transformer, and belongs to the application field of special power supply and distributed power supply control technology. Background technique [0002] The parallel operation of inverters can effectively expand the capacity of the power system and improve the reliability of the system. It is the basis for realizing power modularization and distributed power systems, and has been widely used in large-scale ship power transformation and distribution and land micro-grid systems. In the above transformation and distribution systems, the high-power three-phase inverter is the main interface module, but due to the consideration of system volume, weight and cost constraints, it is usually required to cancel the isolation transformer on the output side of the inverter, but this Independent and parallel op...

AI Technical Summary

Problems solved by technology

[0004] (2) Since there is no isolation on the output side, there is inevitably a path between the parallel inverters that directly short-circuits the DC input power supply of each inverter through the switching power device and the output filter reactor, resulting in a large switching frequency characteristic current Harmonics, which lead to unreliable and unstable parallel inputs, need to be addressed

[0005] (3) Since there is no isolation on the output side, there will be large current harmonics at the LCL resonance frequency point that does not exist during independent operation in parallel connection, resulting in system instability, which needs to be resolved

[0006] (4) Since there is no isolation on the output side, when the DC side of the inverter is also connected in parallel, the circulating current generated during parallel connection will cause the DC bus voltage to rise and affect the safe operation of the inverter, so a good circulating current control algorithm is more needed

[0007] (5) Even for inverters with the same hardware architecture, due to the differences in device parameters and control system parameters and the length of the output cables of each inverter, there will be differences in the output impedance and resistance and inductance characteristics of each inverter. It makes it difficult for the traditional classic non-interconnection line drooping parallel algorithm to guarantee the effect of parallel power sharing

Images