Zhongchao Zhang

A Generalized Three-Phase Multilevel Current Source Inverter with Carrier Phase-Shifted SPWM

A Generalized three-phase multilevel current source inverter (CSI) structure is proposed in this paper. The novel multilevel CSI topology consists of n modules of current-source, three-phase six-valve converters and 2(n-1) sharing-current inductors. These inductors divide the dc link current into n-l different current ratings, and these current ratings are used to make up of 2n+1 current levels at the output of the CSI. In this structure, the bulky transformers in the ac side of the conventional CSI are eliminated, and current equilibrium problem of sharing-current inductors can be solved by redundant switching combination states. The operation principle and control strategy of the five-level inverter are analyzed in detail. The implementation of carrier phase-shifted SPWM scheme is investigated for digital control of the novel multi-module CSI structure. Simulated and experimental results demonstrate the proposition.

LCC Resonant Converter Operating under Discontinuous Resonant Current Mode in High Voltage, High Power and High Frequency Applications

The full-bridge series-parallel resonant converters (also known as LCC resonant converters) with capacitive output filter is evaluated in high output voltage (≫50kV), high power (≫50kW) and high frequency (20 kHz) ESP (Electrostatic Precipitator) power supply applications. By using the leakage inductance and the winding capacitance of the transformer as the resonant elements only an additional series resonant capacitor is needed to form the LCC topology. ZCS turn-on and ZVZCS turn-off of the power switches are achieved by adopting the DCM (discontinuous current mode) control method. The concept of critical load is introduced as a key parameter to aid the circuit design. A prototype has been built to verify the operation principle of the circuit. Experimental results are given.

PWM control of a 5-level single-phase current-source inverter with controlled intermediate DC-link current

Multilevel converters offer benefits of reduced harmonics and increased power ratings compared to their two level counterparts, but to date most of the research in this area has been directed towards voltage source inverters rather than current source inverters. Partly, this is because DC link capacitors are a more effective energy storage medium than link inductors, with less losses and easier operating requirements. However, for higher power applications, and with improvements in inductors using superconducting magnetic energy storage systems (SMES), current source inverters can have particular advantages in some circumstances. Hence it is useful to explore how a multilevel CSI system might be managed. This paper presents a 6-switch single-phase 5-level current source inverter, and compares its topology to a previously reported 8-switch system. For both converter topologies, it is identified that control of the intermediate 1/2-level DC link current is a major challenge, and a closed loop strategy is proposed to control this current under varying load conditions. Simulation and experimental results are presented to confirm the operation of the new 6-switch topology under PWM control, and to verify that the 1/2-level link current can be maintained at half of the total DC current with very little current ripple under differing load conditions.

Design of High Voltage, High Power and High Frequency Transformer in LCC Resonant Converter

The design of a high voltage, high power and high frequency transformer is introduced considering its operation in the LCC resonant converter. The leakage inductance and winding capacitance of the transformer are used as the resonant elements. An additional series resonant capacitor is added to form the LCC topology. The discontinuous current mode (DCM) is adopted to achieve the ZCS turn-on and ZVZCS turn-off of the power switches. Smaller value of the winding capacitance is preferred because it has the effect of decreasing the peak value of the resonant current at almost the same output voltage. The theoretic calculation of the winding capacitance and leakage inductance of the transformer is given. The error between the theoretical calculation and practical measurement is within 15%. So optimization design of the parasitic resonant elements can be achieved to meet requirement of the circuit. A prototype of LCC resonant converter with 60kW and 60kV output is built based on the designed transformer. Experiment results are given.

A new single-phase multilevel current-source inverter

A new single-phase multilevel current-source inverter (CSI) topology is proposed. The structure of this new topology is very simple. The switching strategy that can ensure equal current division among the branches and current harmonics reduction is presented. Simulations as well as practical experiments analyze the characteristics of this new topology.

Analysis and experimentation of a new three-phase multilevel current-source inverter

Multilevel converter technology has been mainly used for voltage-source inverters (VSI) by now. But with the development of the superconducting magnetic energy storage (SMES) technology, superconducting inductors can be used as higher efficiency energy storage elements, the application of current source multilevel inverters (CSIs) in power systems will be more and more popular. A new kind of three-phase multilevel CSI topology is presented in this paper. The new multilevel CSIs synthesize the staircase current wave from several levels of balance inductor currents. The switching strategy that can ensure equal current division among the branches and current harmonics reduction is presented. A three-phase 6-level CSI and a three-phase CSI using the new topology are discussed by the simulations. An experimental prototype of a three-phase 6-level CSI has been built to practise the proposition in the paper.

Generalized multilevel current source inverter topology with self-balancing current

A generalized single-phase multilevel current source inverter (MCSI) topology with self-balancing current is proposed, which uses the duality transformation from the generalized multilevel voltage source inverter (MVSI) topology. The existing single-phase 8- and 6-switch 5-level current source inverters (CSIs) can be derived from this generalized MCSI topology. In the proposed topology, each intermediate DC-link current level can be balanced automatically without adding any external circuits; thus, a true multilevel structure is provided. Moreover, owing to the dual relationship, many research results relating to the operation, modulation, and control strategies of MVSIs can be applied directly to the MCSIs. Some simulation results are presented to verify the proposed MCSI topology.

HID lamps with electronic ballast

In this paper, the start-up characteristics of automotive HID lamps with electronic ballast is investigated. In order to prevent the lamp from extinguish immediately after break-over, auxiliary current circuit is proposed to provide additional current to lamp. During warm-up or run-up phase, DC lighting period also is needed to light a discharge lamp more reliably at the starting time of the discharge lamp. Experiments have been carried out to verify the function of these two proposed solution.

Multilevel current source inverter topologies based on the duality principle

This paper explores the issue of constructing multi-level current source inverter (MCSI) topologies using the duality principle. In order to extend the application of duality to the three-phase power electronic circuits which are non-planar, two methods for planar treatment with three-phase voltage source inverter (VSI) are presented. Based on such equivalent transformation, an improved topology of three-phase flying-capacitor multi-level voltage source inverter (MVSI) is obtained, then a new kind of three-phase MCSI topology is derived from the application of the duality on such MVSI topology. This allows the wealth of existing knowledge relating to modulation of multilevel VSI to be immediately mapped to the multilevel CSI. Analytical results show that the derived MCSI and its corresponding MVSI present dual features such as operations, modulations and control strategies, etc. Some simulation results are given to verify the proposed MCSI structure.

Development of a three-phase high power factor Multilevel Current-Source Rectifier

In this paper, a three-phase high power factor Multilevel Current-Source Rectifier (MCSR) is developed. The structure of the given MCSR consists of three modules of current-source, three-phase six-valve converters and some sharing-current inductors. The operation characteristics of the MCSR are investigated. In the MCSR, Carrier Phase-Shifted SPWM is used. Harmonic characteristics of the ac input current and the dc output voltage and current are analyzed in detail. It is shown that, many good features can be achieved such as equivalent higher carrier frequency at the ac side of the MCSR even with lower switching frequency. Furthermore, dc output voltage has no low harmonic components, and the power factor of the ac side is easy to control to be unit. A fully digital solution of tri-logic SPWM gating signals for the MCSR is studied based on the DSP and FPGA platform. At last, simulated and experimental results are given to demonstrate the proposition.