Solid-state transformer-based new traction drive system and control

doi:10.1007/s11465-018-0467-0

Front. Mech. Eng.

2018, Vol. 13

Issue (3) : 411-426 https://doi.org/10.1007/s11465-018-0467-0

RESEARCH ARTICLE

Solid-state transformer-based new traction drive system and control

Jianghua FENG, Jing SHANG, Zhixue ZHANG, Huadong LIU(

), Zihao HUANG

CRRC Zhuzhou Institute Co., Ltd., Zhuzhou 412001, China

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Abstract

A new type of traction drive system consisting of solid-state traction transformer (SSTT), inverter unit, auxiliary inverter, traction motor and other key components is built in order to suit the demand of developing the next-generation electric traction system which will be efficient and lightweight, with high power density. For the purpose of reducing system volume and weight and improving efficiency and grid-side power quality, an efficient SSTT optimized topology combining high-voltage cascaded rectifiers with high-power high-frequency LLC resonant converter is proposed. On this basis, an integrated control strategy built upon synchronous rotating reference frame is presented to achieve unified control over fundamental active, reactive and harmonic components. The carrier-interleaving phase shift modulation strategy is proposed to improve the harmonic performance of cascaded rectifiers. In view of the secondary pulsating existing in a single-phase system, the mathematical model of secondary power transfer is built, and the mechanism of pulsating voltage resulting in beat frequency of LLC resonant converter is revealed, so as to design optimum matching of system parameters. Simulation and experimental results have verified that the traction system and control scheme mentioned in this paper are reasonable and superior and that they meet the future application requirements for rail transit.

Keywords solid-state traction transformer high-voltage cascaded rectifier LLC resonant converter synchronous rotating reference frame carrier-interleaving phase shift control secondary pulsating voltage beat frequency

Corresponding Author(s): Huadong LIU

Just Accepted Date: 30 October 2017 Online First Date: 29 November 2017 Issue Date: 11 June 2018

Cite this article:

Jianghua FENG,Jing SHANG,Zhixue ZHANG, et al. Solid-state transformer-based new traction drive system and control[J]. Front. Mech. Eng., 2018, 13(3): 411-426.

URL:

https://academic.hep.com.cn/fme/EN/10.1007/s11465-018-0467-0
https://academic.hep.com.cn/fme/EN/Y2018/V13/I3/411

Fig.1 New traction drive system

Fig.2 Fundamental current control principle based on synchronous rotating reference frame. BPF: Band pass filter; PLL: Phase-locked loop

Fig.3 Equivalent circuit diagram of SSTT cascaded rectifier

Fig.4 Voltage loop based on instantaneous power balance

Fig.5 Equivalent circuit diagrams of cascaded rectifier on d and q planes

Fig.6 Certain-order harmonic current detection and control

Fig.7 Current harmonics control principle

Fig.8 Schematics of the LLC resonant converter

Fig.9 Vector diagram of difference frequency components

Parameters	Value
Grid voltage, $U s$ /kV	25
Rated power/(kV?A)	1800
Cells of cascaded	13
HV-CHB cell switch frequency/Hz	450
Carrier phase-shift angle	$π / 13$

Tab.1 Parameters of the simulation model

Fig.10 Voltage of the H-bridge unit adopting (a) the carrier phase shift control strategy and (b) the carrier inter-leaving phase shift control strategy

Parameters	Value
Grid voltage, $U s$ /kV	3.5?7.0
Rated power/(kV?A)	600
DC voltage, $U dref$ /V	3600
Cells of cascaded, $N$	2?4
HV-CHB cell switch frequency/Hz	450
Input Choke, $L s$ /mH	20
IGBT voltage grade of HV-parts/V	6500
IGBT voltage grade of LV-parts/V	3300
Ratio of transformer, $M$	2
Magnetic inductance, $L m$ /mH	10
Leakage inductance, $L r$ /μH	500?700
Resonance capacitance, $C r$ /μF	7?14
Output voltage, $U o$ /V	1800
Intermediate capacitance, $C in$ /μF	2000
Output capacitance, $C o$ /μF	1000?4000

Tab.2 Parameters of the experimental prototype

Fig.11 Waveform of rated-load (a) input response and (b) cut-off response of the cascaded rectifier

Fig.12 Response waveform when grid voltage fluctuates by (a) 10% and (b) 20%

Fig.13 (a) Current waveforms without the harmonic suppression strategy; (b) current waveforms with the 3rd-, the 5th-, and the 7th-order harmonics being filtered; (c) steady-operation waveforms with the harmonic suppression strategy

Fig.14 Beat frequency of the LLC resonant converter

Fig.15 Reduced current fluctuation of the LLC resonant converter

Parameters	Value
Grid voltage, $U s$ /kV	25
Rated power/(kV?A)	1800
Max grid voltage/kV	31
Min grid voltage/kV	17.5
Rated frequency/Hz	50
DC voltage, $U dref$ /V	3600
Cells of cascaded, $N$	13
Cells of redundancy	1
HV-CHB cell switch frequency/Hz	450
Input choke, $L s$ /mH	20
IGBT voltage grade of HV-parts/V	6500
IGBT voltage grade of LV-parts/V	3300
Ratio of transformer, $M$	2
Magnetic inductance, $L m$ /mH	12.5
Leakage inductance, $L r$ /μH	700
Resonance capacitance, $C r$ /μF	7
Output voltage, $U o$ /V	1800
LLC switch frequency, $f s$ /Hz	1800?2200

Tab.3 Parameters of the full-scale prototype

Fig.16 SSTT prototype for 25 kV 50 Hz railway grid

Fig.17 The SSTT prototype is being tested

Fig.18 Measured key waveforms of the 25 kV SSTT prototype with different loads: (a) Less than 50 kV?A; (b) 200 kV?A; (c) and (d) rated power 1800 kW

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