Qingguang Yu

A neutral-point potential balancing algorithm for three-level NPC inverters using analytically injected zero-sequence voltage

Based on the zero-sequence component of the reference voltages, this paper comprehensively analyzes the neutral-point variation and balancing control for three-level neutral-point-clamped inverter. An analytical method is proposed to accurately calculate the injected zero-sequence voltage for NP balancing. Based on the analytical analysis, the limitation of NP balancing control is revealed and the NP-fully-controllable region is presented. A real-time NP balancing algorithm is proposed as well. The feasibility of the proposed method is verified using simulation results for a 6 kV/1800 kVA medium voltage drive.

Overview of STATCOM technologies

Abstract: /spl plusmn/20Mvar STATCOM indicates that China is the 4/sup th/ country to develop STATCOM in the world. This paper introduces the development of STATCOM particularly in China. Topologies of STATCOM are discussed, and the cascade multilevel configuration is given in details. Power valves such as GTO, IGBT, IGCT, IEGT used in STATCOM are also mentioned for competence. Shanghai /spl plusmn/50 Mvar STATCOM is introduced to illustrate the state-of-art of STATCOM in China.

Nonlinear Controller for Cascade H-Bridge Inverter-Based STATCOM

Cascade H-bridge multilevel inverter technique brings a lot of advantages to static synchronous compensator over conventional multi-pulse STATCOM. Based on the theory of the exact linearization via feedback, a MIMO nonlinear controller is proposed. The averaged model of STATCOM based on cascade multilevel inverter is established and the nonlinear control law is analyzed. Simulation results show, under this controller, STATCOM can achieve fast dynamic control of reactive power, with dc link voltage controlled at almost a constant value. Experimental results of a prototype STATCOM based on 17-level cascade H-bridges inverter are also shown to verify the control law

Analysis of high di/dt current pulses in three-level NPC inverters using series connected IGCTs and RC snubbers

High di/dt current pulses are harmful to the safety of IGCTs, especially to the low current conducting or freewheeling conducting IGCTs. This paper comprehensively analyzes the current pulses that flow through the inner switch of a three-level NPC inverter with series connected IGCTs and RC-snubbers. Four cases of high di/dt current pulses are addressed. The moments at which the high di/dt current pulses occur are clearly demonstrated. The value of the corresponding di/dt is estimated as well. The analysis is verified through simulation results using PSCAD/EMTDC. Based on the comprehensive analysis, the methods to handle these high di/dt current pulses are given respectively. An external re-trigger system is designed for a 6 kV/1800 kA three-level NPC inverter-fed medium voltage drive using series connected IGCTs. A more safe and reliable operation is reached for the series connected IGCTs in the three-level NPC inverter.

DSP LF2407 in NPC three-level inverter using constant V/f principle and SHE-PWM method

In this paper, a DSP TMS320LF2407 control system in a neutral-point-clamped (NPC) three-level inverter using constant V/f principle and SHE-PWM method is developed. Results of PSCAD simulation and experiments show that the designed system has high performance.

Research of LTCC NiCuZn Transformer Prototype

In this paper, based on the primary principle of transformers, designs the devices structure and the mathematic circuit model of the low profile planar transformers with LTCC (low temperature co-fired ceramic) NiCuZn. FEA (finite element analysis) for the electromagnetic analysis is used to calculate electromagnetic parameters of planar transformers with different winding structures. At last, low profile transformer prototype is made and tested

High power electronic device measurements of four IGCTs (4.5 kV/4.0 kA) in series connection

In this paper, high power electronics device measurements of four IGCTs (4.5 kV/4.0 kA) in series connection are put forward, which are used to investigate IGCTs in high power circuits with or without using RC-snubbers, or at least operation with small snubbers. The series connection of IGCTs is commonly applied in the high power inverter field, where expensive and space-consuming snubbers are adopted, to overcome the problems of asymmetric distribution of the blocking voltage among the IGCTs. Reasons of an asymmetric distribution of the blocking voltage during and after IGCTs turn off process are analyzed. The first phase of the experimental results are presented and discussed.

Three-level AC-DC-AC VSI with IGCTs used in P&F

In this paper, a three-level AC-DC-AC VSI (Voltage Source Inverter) with IGCTs (Integrated Gate Communicated Thyristors) used in pumps and fans was developed. The inverter structure has an uncontrolled rectifier with 24-pulse DC voltage output, and has a diode NPC (Neutral Point Clamped) three-level inverter with an LC filter to maintain a 6 kV sine wave voltage output. Results of simulation and experiment show that the designed system has high performance, reliability and availability.

High power induction motor VVVF drives system with IGCTs in thermal power plant

In this paper, a variable voltage variable frequency (VVVF) drive system with IGCTs (integrated gate commutated thyristors) for a high power induction motor (IM) has been developed. The designed VVVF system includes a 24-pulse rectifier and a three-level neutral point clamped (NPC) voltage source inverter (VSI). The three-level inverter with two IGCTs in series connection in each cell with an output LC- filter was used to obtain a 6 kV high voltage output. The digital signal processor (DSP) with field programmable gate array (FPGA) controller is adopted to fulfill an optimized constant V/Hz control strategy. According to the pumps and fans load, an optimized constant V/Hz control strategy is adopted. The pulse width modulation-selective harmonic elimination (PWM-SHE) pattern is carried out to keep sine wave output with minimal harmonics and minimal torque ripple.

Accomplishment of low profile planar transformer prototype with NiCuZn

In this paper, the primary principle of low profile planar trasnsformers was introduced, its different structures was discussed. The mathematic model of the circuit and the magnetism of the low profile planar transformers were put forward. FEA (Finite Element Analysis) method for the electromagnetic analysis is used to obtain the electromagnetic parameters of the low profile planar transformers according to its different winding structures. Finally, low profile planar transformer prototype is developed and its basic performances were tested.