| Electrified railway plays a crucial role in national economy and bringsconveniences to people’s life. However, due to its characteristics of traction loads ofnonlinear, asymmetry and fluctuation, there are also current and voltage waveformsasymmetry in three phases, mainly the current asymmetry and huge harmonicinjection, as in the public electric network of electrified railway. Especially, with therapid development of electrified railway, power quality problems of harmonic andnegative sequence caused by traction loads have affected the safe and stable operationof power system and the electric railway power supply system. Thus it is necessary totake reasonable and effective means to improve the power quality of electrifiedrailway, so as to ensure the safety and stability of these two systems.Based on analyzing of three kinds of traction transformers’ negative sequencecurrent and unbalanced degree, this paper choosed the impedance-matching tractiontransformer for good quality of negative sequence current decreasing. According to itselectrical characteristics, this paper proposed a negative sequence and harmoniccomprehensive compensation scheme, analyzed the principles and presented thecompensation current expression for different compensation occasions.It also analyzed the reactive and harmonic current detection method. Thedetection diagram of negative sequence and harmonic real time compensation currentdetection technique of the comprehensive compensation device was proposed basedon FBD and the characteristic of electrified railway.Then, this paper studied the control of comprehensive compensation device.Through discussing the existing current compensation tracking control methods, andthe advantages and disadvantages of DC voltage control as well as the control basedon the position of compensation point and check point, a control strategy suitable forthe comprehensive compensation device is presented, which is based on the loadcurrent feedback of voltage outer loop, current inner loop and double closed loophysteresis.At last, simulations of compensation effect based on the negative sequence andharmonic comprehensive compensation device are conduced, to verify the ability ofharmonic suppression, power balance and comprehensive compensation. Thesimulation results indicated that the device can adjust the two unbalanced traction loads to balance, eliminate the negative sequence current in three-phase powernetwork, and meanwhile, effective filtering harmonic current on traction powersupply system, to achieve comprehensive compensation. |
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