Showing papers by "Min Chen published in 2015"

A Novel Control Strategy of Suppressing DC Current Injection to the Grid for Single-Phase PV Inverter

Abstract: Photovoltaic (PV) inverters without the isolation transformer become more attractive due to higher efficiency and lower weight. However, it may have dc offset current problem and is critical to the power system. In this paper, a novel control strategy of suppressing dc current injection to the grid for PV inverters is investigated. It is based on the idea of accurately sensing the dc offset voltage of PV inverter output. Since dc component of the inverter output can be eliminated, dc injection to the grid can be effectively suppressed. Finally, the control scheme is verified by the experiment.

A High Step-Up DC to DC Converter Under Alternating Phase Shift Control for Fuel Cell Power System

Abstract: This paper investigates a novel pulse width modulation (PWM) scheme for two-phase interleaved boost converter with voltage multiplier for fuel cell power system by combining alternating phase shift (APS) control and traditional interleaving PWM control. The APS control is used to reduce the voltage stress on switches in light load while the traditional interleaving control is used to keep better performance in heavy load. The boundary condition for swapping between APS and traditional interleaving PWM control is derived. Based on the aforementioned analysis, a full power range control combining APS and traditional interleaving control is proposed. Loss breakdown analysis is also given to explore the efficiency of the converter. Finally, it is verified by experimental results.

A high power density and efficiency bi-directional DC/DC converter for electric vehicles

Abstract: In electric vehicle systems, bi-directional DC/DC converters are used to interface the battery bank with the high voltage DC bus of the inverter The high power density and high efficiency are required for bidirectional DC/DC converters This paper discusses the relationship between switching frequency, inductor value and passive components volume First, the topologies of the system and the converter are presented Then, the loss breakdown model is provided A selection for the switching frequency is presented and an option of inductor value is provided to reduce the converter size and to keep the converter efficient Then the converter layout which further enhances the power density is discussed Finally, a high power density and high efficiency converter prototype is built, and the efficiency and thermal performance evaluation of the converter at different operating conditions is given

DC-link voltage control strategy of a bi-directional DC/DC converter for electric vehicles

Abstract: In electric vehicle (EV) systems, bi-directional DC/DC converters are applied to interface the battery bank with the high voltage DC-link of the inverter. The control of the DC-link voltage is important for the high performance of the system. A DC-link voltage control strategy for the bidirectional DC/DC converter is proposed, which eliminates the need for detecting the operating mode and do not need to change the control loop when the modes transfer between the motor driving mode and the regenerative braking mode. The dynamic model of the bi-directional DC/DC converter with the constant power load is built. Afterward design of the proposed control is presented. Finally, a prototype is built to validate the proposed DC-link voltage control strategy and evaluate the dynamic performance.

Simplified PWM for fault tolerant control of open winding PMSM fed by hybrid inverter

Abstract: This paper proposes a simplified PWM strategy for fault tolerant control of an open winding permanent magnet synchronous motor (OW-PMSM) fed by hybrid inverter (HI). The HI usually consists of two six-switch three-phase inverters (SSTPIs), the inverter powered by a DC source is named as main inverter (MI) and the inverter powered by a capacitor is named as compensation inverter (CI). When a power switch or a leg of CI fails, the CI can be reconfigured to a four-switch three-phase inverter (FSTPI). Since the phase current flows through the two capacitors in the FSTPI, it would introduce the neutral-point voltage fluctuation. By taking the unexpected neutral-point voltage fluctuation into account, a simplified PWM strategy is designed for the FSTPI, which can guarantee the high-quality voltages and currents even at the low speed states, it can also reduce the computation time of the system. Simulation studies have been carried out to verify the effectiveness and superiorities of the proposed strategy.

Design of hybrid AC-DC-AC topology for Uninterruptible Power Supply

Abstract: A hybrid AC-DC-AC topology for Uninterruptible Power Supply (UPS) is investigated, which is composed of a two level three-phase four-wire rectifier and a three level T-type inverter. It has distinct advantages for the applications of on line UPS. The grid side power quality can be easily satisfied with the front-end two level three-phase rectifier. Since output voltage's THD is challenge to UPS with sever nonlinear load, the T-type inverter is used to enhance the load power quality with higher conversion efficiency. The rectifier is transformed into step-up converter for the battery during the grid faults. The efficiency optimization of the proposed UPS with the hybrid AC-DC-AC topology is studied. The control strategies for the UPS are investigated. At last, the UPS prototype with 200kVA is designed and tested to validate the performance of the proposed UPS.

A self-adaptive blanking circuit for IGBT short-circuit protection based on V CE measurement

Abstract: In order to determine whether the IGBT short-circuit fault occurs, the collector-emitter voltage V CE of an IGBT has been detected in the IGBT gate drivers. The blanking circuit is needed in this kind of protection method to avoid the malfunction of the short-circuit protection during IGBT turn-on transient. However, this blanking circuit should be carefully designed for different types of IGBT modules. In order to make the IGBT short-circuit protection circuit suitable for the tolerance of IGBT modules, a self-adaptive blanking circuit combined with the aforementioned short-circuit protection method based on V CE measurement is proposed. The analysis of the proposed circuit is given, and the experimental results are included to prove the effectiveness of the proposed circuit.

Peak-buck peak-boost current-mode control for switched step-up step-down regulators

Abstract: A peak-buck peak-boost current mode control structure and scheme for a synchronous four-switch and non-synchronous two-switch buck-boost regulators sense input and output voltages to smoothly transition between buck mode, buck-boost mode, and boost mode for high power efficiency and low output ripples. With the inductor current sensing, the control scheme achieves the best performance in continuous conduction and discontinuous condition mode operations.

An accurate power-sharing control method based on circulating-current power model for voltage-source-inverter parallel system

Abstract: This paper analyzes the voltage-source-inverter parallel system as a multi-input & multi-output system, and proposes the circulating-current mathematical model, the steady-state model and small-signal model of parallel system. Then the phasor models of the circulating-current and the circulating-current power are proposed. Subsequently, the mathematical model of traditional droop control is built and analyzed based on the circulating-current power model. According to the analysis of droop control, this paper proposes an accurate parallel control strategy (ω-P cir and V-Q cir control), which can eliminate the circulating-current power and the bias of output voltage frequency and amplitude. Finally, simulation and experiment result are presented, which validates the performance of the proposed method.

Three-phase interleaved high step-up boost converter with voltage multiplier for fuel cell power system

Abstract: Three-phase interleaved boost converter with voltage multiplier has higher voltage gain, lower input current ripple and output voltage ripple compared with legacy boost converter. In addition, the voltage stress on switches of the converter is only half of the output voltage. However, the converter will have a higher voltage stress on the switches if it operates in light load. A novel PWM control scheme is proposed to solve the higher voltage stress problem in light load. The proposed PWM control method is integrated with the traditional interleaving PWM method in higher load in order to keep low voltage stress on the switches over full power range. Finally, the control scheme is verified by the experiment.

Switching noise suppression for hybrid IGBT modules

Abstract: In a hybrid IGBT module with SiC diodes as free-wheeling diodes, high frequency oscillation occurs during turn-on, which will cause higher EMI noise due to the larger capacitance of SiC diode To evaluate the influence of gate drive parameters on turn-on oscillation, different gate voltages and gate charge currents are used It is found that by changing gate drive parameters alone cannot reduce the settling time of the oscillation significantly Then an oscillation suppression method with damping circuits is proposed According to the analytical and experimental results, the damping circuits are able to effectively accelerate the damping of turn-on oscillation without significant increase in current overshoot and turn-on energy loss Finally to suppress the turn-on current overshoot, active gate driver method is also used without large increase in the turn-on energy loss The combination of damping circuit and active gate driver may be an optimized choice to achieve the lowest EMI noise

An accurate power flow control strategy based on voltage-based power flow control in Microgrid

Abstract: In microgrid, distributed generation (DG) unit should control the output active and reactive power to main grid accurately in the grid-connected mode. The traditional voltage-based power flow control method has the limitation in power control that the steady-state error of output power may exist which usually caused by the frequency and amplitude fluctuation in grid voltage. In many references, the steady-state error of output reactive power has been eliminated by amplitude compensation, while the steady-state error of output active power has been seldom analyzed. This paper analyzed the steady-state error of active power and proposed an accurate power flow control strategy based on output voltage frequency reference compensation in order to eliminate the steady-state error of output active power. Simulation and experiment results are both presented, which validate the performance of proposed method.

A startup scheme for zero-voltage-switching PV inverter

Abstract: In order to guarantee all the switching devices of the inverter working in the safe operation area, zero voltage switching (ZVS) operation is needed even at the startup stage. To help the ZVS inverter achieving completely soft switching at the startup stage, a startup scheme is proposed. The startup scheme adds a pre-charge stage before the general startup stage. The pre-charge stage is realized by a simple pre-charge circuit and a ZVS pre-charge pulse sequence. The pre-charge circuit works before the general startup stage only and is guaranteed by principle to be deactivated during the normal operation stage. The pre-charge pulse sequence is designed to achieve ZVS operation in the pre-charge stage. The experiment on a 3kW prototype shows the startup scheme realizes ZVS operation at the startup stage and the voltage stress on the power devices is minimized.

ZVS PWM scheme to suppress ground leakage currentof full-bridge grid inverter

Abstract: The common mode (CM) model of the full-bridge inverter with active-clamping technique is derived and the ground leakage current of the existing Zero-Voltage-Switching (ZVS) PWM scheme is analyzed. In order to minimize the ground leakage current of the ZVS inverter, a novel ZVS PWM scheme is proposed. Firstly, the ZVS condition is analyzed and then the ZVS PWM scheme is designed to realize the zero voltage switching for both main switches and auxiliary switch in a large power range. After that, the CM characteristic of the proposed PWM scheme is analyzed. The experiment on a 3kW prototype shows the realization of ZVS operation and the significant reduction of the ground leakage current.

Flyback converter, method for operating the same and method for operating a flyback converter at load currents below a threshold current

Abstract: In a flyback converter (20 using primary side sensing to sense the output voltage for regulation feedback a comparator (36) on the primary side detects whether the output voltage has exceeded a predetermined regulated voltage by a first threshold to detect an over-voltage condition, resulting from a current generated by the converter exceeding the load current Triggering of the comparator causes the converter to enter a non-switching sleep mode, whereby the output voltage droops over a period of time When the output voltage has drooped below the predetermined regulated voltage by a second threshold, a synchronous rectifier is controlled (28) to turn on, then off, to generate a pulse in the primary winding Upon detection of the pulse, the sleep mode is terminated, and normal operation resumes until a regulated voltage is achieved or until the first threshold is again exceeded by the output voltage