A Negative Sequence Unbalance Compensation Method Applied in VV Traction Power Supply System

Abstract

The invention relates to the power quality technology of electrified railways, in particular to a negative sequence unbalance compensation method applied to a VV traction power supply system. The compensation current is input by judging the magnitude of the load current in real time, and the negative sequence unbalance of the VV traction power supply system is corrected locally. Comprehensive compensation; including the following steps: step 1. Detect the load current of the power supply arms on both sides of the VV traction power supply system; Compensation currents with equal values ​​and opposite phases; step 3, inject the compensation current from the secondary side of the traction transformer into the VV traction power supply system through the three-phase converter described in step 2 to offset the negative sequence current in the VV traction power supply system to complete the negative sequence imbalance compensation. This method makes the negative sequence unbalance compensation idea simpler and more direct, the control strategy of the three-phase converter is simpler, and the cost, capacity and floor space of the three-phase converter are reduced.

Description

technical field [0001] The invention belongs to the technical field of electrified railway power quality, in particular to a negative sequence unbalance compensation method applied to a VV traction power supply system. Background technique [0002] High-speed railway electric locomotive load causes three-phase current imbalance, resulting in negative sequence current. The negative sequence current brings additional losses to the generator, causing rotor heating, additional vibration, etc., which seriously affects the safe and stable operation of the power system. The locomotive harmonics bring extra power loss to the power equipment, causing the relay protection device to malfunction or refuse to operate, reducing the reliability of the power system. Therefore, the negative sequence and harmonic power quality problems of high-speed railway power supply systems have received extensive attention. [0003] The magnitude of the negative sequence current is related to the tract...

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Problems solved by technology

However, this compensation method adopts the form of capacitance compensation. When a capacitive load is connected to the system, although the capacitive load itself does not generate power harmonics, the capacitive load will amplify the harmonics existing in the power system. If the capacitive load and the power system The oscillation frequency of the inductive load in the system is close to the natural frequency of the system, which will cause infinite amplification of the harmonics of the power system, resulting in blackout accidents; Composed of transformers and common DC capacitors, this compensation method uses RPC to transmit active power, the transmitted active current value is half of the load current, and the transmission direction is from the side with a small load to the side with a large load. In this way, the two side traction load power is equal, thereby eliminating negative sequence current

When this method is used for negative sequence compensation, since the voltage and current level that the RPC can withstand is low and the reliability is not strong, it is necessary to connect the circuit through a transformer at both ends of the RPC, which not only greatly increases the cost of the device, but also makes the active Increased compensation capacity and device footprint, leading to application limitations

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