Wu Weiyang

A Multi-Directional Power Converter for a Hybrid Renewable Energy Distributed Generation System with Battery Storage

Power electronics is the key technology for enabling renewable power generation and dispatching distributed generation (DG) with improved load-side efficiency. This paper presents a multi-directional power converter with a high-frequency isolation transformer for a stand-alone hybrid renewable energy DG system with battery storage. Full-bridge power converters are employed to realize bi-directional power flow among renewable generator, battery storage and load. Detailed analysis is provided for a four-directional power converter in a wind-photovoltaic distributed generation system. In addition, a two loop PI control scheme is proposed to achieve constant output voltage and exact power flow management. Theoretical analyses are verified by simulations in PSPICE and MATLAB

An improved droop controller for grid-connected voltage source inverter in microgrid

This paper addresses the low-frequency relative stability problem of the grid-connected voltage source inverter (VSI) based distributed generation (DG) unit in microgrid, in which the conventional active power-frequency (P-ω) and reactive power-voltage (Q-E) droop controllers are commonly used to share the loads. In the sense of the characteristic equation and eigenvalues, the relative stability and the transient response are remarkably affected by the change of the droop gains and/or stable operating points, resulting in the poor damping and eventually instability. An improved P-ω and Q-E droop scheme based on the static droop characteristics combined with a derivative term is presented to preserve the system stability and obtain an improved damping performance. Subsequently, the dynamic performance of the system can be adjusted without affecting the static droop gains to damp the oscillatory modes of the power sharing controllers. Finally, the desired transient and steady-state responses can be obtained.

A Single-Phase Grid-Connected Inverter System With Zero Steady-State Error

A single-phase grid-connected inverter system with a novel current control strategy is presented in this paper. The controller consists of a proportional regulator and a new type of resonant regulator. Compared with traditional PI control methods, the P+resonant (PR) control can introduce an infinite gain at the fundamental frequency and hence can achieve zero steady-state error. A more practical quasi-PR controller is used based on theoretical analysis. In this paper, a step by step procedure for designing the quasi-PR controller is proposed and verified by experiments. Theoretical analysis and experimental results of an experimental prototype verified the high performance of the proposed system in both the sinusoidal reference tracking and the disturbance rejection

A Single-stage Boost-Flyback PFC Converter

This paper presents a novel single-stage single-switch power factor correction (PFC) converter. The proposed topology is derived by combining a boost cell and a flyback cell into one power stage. In this converter, the transformer in the flyback cell has two-coupling primary windings, which have the same turns. Two bulk storage capacitors are used to store the power energy from the input source, and then feed one primary winding of the transformer respectively. In addition, the two capacitors can absorb the leakage inductances energy and clamp the voltage of power switch. Compared with using one bulk capacitor, the voltage across each capacitor here is lower, only half of the line voltage. This converter will potentially have low switch voltage stress, good regulation capability and high efficiency. To verify the performance of the proposed converter, a design example is given with its experimental results

Phase Multilevel Inverter Fault Diagnosis and Tolerant Control Technique

This paper gives a solution to implement a self-diagnosis and tolerant control for a 3-level neutral point clamped inverter. Redundancies in semiconductor configurations are used to enable a continuous operation with a faulty power switch. The fault tolerance is obtained by using a SCR to substitute faulty switch. In case of failure events, the on-line diagnosis technique can fix faulty switch and take relevant tolerance measures. Through simulations and experiments, this diagnosis technique is validated

An Alternating-master-salve Parallel Control Research for Single Phase Paralleled Inverters Based on CAN Bus

A novel alternating-master-salve control strategy for paralleling inverter is proposed, which merely make use of CAN bus to achieve the high precision of synchronization and fast current-sharing control. Only single interconnection bus is requires and simple arithmetic is used by the proposed scheme. Moreover, the paralleled inverters act as master in turn during each cycle of the output voltage and the paralleled modules are identical. There are not difference between master and slave and the parallel system will still operate normally under either paralleled module fault, so N+1 redundancy can be achieved. The experimental results verify good static and dynamic current-sharing performance by adopting the parallel strategy. And the parallel system also has a good parallel performance under the linear and nonlinear load

Improved Control for Parallel Inverter with Current-Sharing Control Scheme

A novel current-sharing control scheme is presented for redundant parallel inverters. The control scheme employs the share bus which interconnects all the parallel inverters to transfer synchronous signal and average current signal. Current-sharing of all the parallel modules is realized through distributed average circuit. Average current is subtracted from the output current of each parallel inverter module and the subtraction result provides the instantaneous current deviation. The average current deviation of half line cycle is used to revise the voltage reference of next line cycle, which can achieve current-sharing and improve overall reliability. The instantaneous current deviation of switching period is fed back to the current-loop to improve the system dynamic response. Theoretical analysis and experimental results indicate that the control scheme performs a precise current sharing in dynamic state and steady state

The studies of Single-phase Inverter Fault Diagnosis Based on D-S Evidential Theory and Fuzzy Logical Theory

A data fusion method for single-phase inverter fault diagnosis based on D-S evidential theory and fuzzy logical theory is presented. By measuring the output voltage the two bridge-arms voltage and the temperature of MOSFET, the belief function assignment is obtained, and the fusion belief function assignment is obtained by using D-S rule and fuzzy logic, and fault component is found. By comparing the diagnosis results based on separate original data and fused data respectively, it is shown that the latter is more accurate than the former in the fault recognition

Resonant tank and transformer design in series resonant converter

The objective of this paper is to establish the industrial design procedure of the resonant tank components and HF transformer in series-resonant converter or inverter. Based on the analysis of the main operation principles of the resonant tank and HF transformer, an industrial design process of these components is given by considering the design requirements which is acquired via the simulation; utilizing the aforementioned components, a 1 KW series-resonant inverter prototype has been constructed, and the validity of the design procedure has been proved via the experimental results.

DSP-based closed-loop control of bi-directional voltage mode high frequency link inverter with active clamp

This paper presents a novel modulation and digital controller based on a bi-directional voltage mode high frequency link inverter with active clamp to achieve fast dynamic response and high static performance. The inverter consists of a full-bridge converter, a bi-directional active rectifier, an active clamp branch and a pulse width modulation (SPWM) inverter bridge. A novel modulation strategy is applied by modulating the triangle carrier wave and two inverse sinusoidal modulation waves, it is no need of checking the pole of the output voltage to switch the modulated signals, and it is able to weaken the distortion of the output waveform on zero passage. Double closed-loop digital control with load current feed-forward is applied to achieve good dynamic response. The modulation and control strategy is realized by using the TMS320LF2407A DSP and EPM7128 CPLD. Theoretical analysis and experimental results referring to a laboratory prototype (3 KVA) indicate that the proposed modulation and control scheme are promising for the applications of DC/AC power supply.