Zhang Chunjiang

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

Comparison of duty ratio perturbation & observation and reference voltage perturbation & observation methods applied in MPPT

Aimed to duty radio P&O (Perturbation and Observation) method which is the most widely applied in MPPT (Maximum Power Point Tracking) control for PV (Photovoltaic) generation, steady-state characteristic is analyzed, and the relationship between output power fluctuation of solar cell and disturbance quantity is deduced. On this basis a reference voltage P&O method for maximum power point tracking is proposed and control algorithm is given in this paper. Simulations and experiments prove that MPPT method based on reference voltage P&O is better evidently than that based on duty radio P&O in the field of improving response speed and reducing power fluctuation, and tracking effect is satisfied.

The islanding start and operation control of doubly-fed wind generation system

Firstly, this paper studies the meaning of doubly-fed wind generation system in islanding operation. The mathematical model of DFIG(Doubly Fed Induction Generator) is deduced. With the use of storage system, this paper researches the control strategy of doubly-fed wind power systems islanding start and operation which include idle-load start and load start based on stator flux oriented, and compares the advantages and disadvantages of the two starting methods. Secondly, in order to improve the utilization of wind energy, this paper study the control strategy of the load-side converter and the rotor-side converter when the doubly-fed wind power system is in islanding operation, which achieve the decoupling control of stator active and reactive power independently and ensure voltage amplitude and frequencys stability of the load. Finally, simulation platform is built with the MATLAB software, which completes the simulation of the above-mentioned control strategy, and the experiment is done. It promotes the application of double-fed generation in micro-grid and improves wind energy utilization

Grid-connected inverters interface control with unified constant-frequency integration control

A new control approach based on unified constant-frequency integration control (UCI) for current tracing is presented for photovoltaic grid-connected inverters. The working theory is analyzed and the control equation is deduced. The control approach is realized by a digital controller DSP. Different from the normal SPWM and PLL (phase locked loop) control approach in grid-connected inverters interface control, this control approach has the merit of automatic phase tracking capability, simplified control and high output power factor. And it can regulate the output in accordance with the dc voltage and grid voltage automatically

Analysis of the conflict between close-loop control and the current-sharing of ac parallel inverters and parallel control strategy

On the basis of the developed mathematic model of one phase inverter, the paper analyzed the conflict between the closed-loop control and the current-sharing of the parallel inverters. The compound control combining open loop with closed loop was presented based on the reference voltage feed-forward to relieve the conflict. The current-sharing control strategy based on interactive-tracking synchronization (ITS) and the adjustment of reference voltage amplitude was proposed, and two parallel-connected inverters controlled by DSP were implemented. The experiments indicate that the good static and dynamic current-sharing performance of the parallel system can be gained by the proposed method and N+1 parallel redundancy can be realized.

An interactive following current-sharing control strategy for paralleled inverters in full digital

This paper analyzes the influence of the amplitude and phase of the inverters output voltage on the power of the parallel system. A no-master-slave control strategy for paralleling inverter based on an interactive following method is proposed, which controls the amplitude of reference voltage and synchronize the phase of the reference voltage to share the active and reactive power by synchronization bus and CAN bus. The DSP (TMS320LF2407) is adopted to realize full digital control in this system. The experimental results demonstrate that the function of N+1 redundancy can be realized and the active and reactive powers are greatly shared

Three phase three level inverter digital control based on over sample and multi-time calculation

The principle of a diode neutral point clamped three-phase three-level inverter with neutral line was analyzed, and the mathematical model of the main circuit is established on the basis of the operation principle. The oversample and multi-time calculation control strategy was proposed to reduce the typical delay in digital control and improve the system calculation accuracy, lower the inverter output voltage THD. In order to further improve the inverter output voltage waveform, the logic external execution was also proposed. The proposed control method was verified on a 20kVA inverter controlled by microchip processor IC30F5015 DSP. The experiment results indicated that the THD of the inverter output voltage is decreased considerably.

A new balance control method of three-level converter NPP

With the NPC converter widely applied to distributed generation system, the ability to ensure the DC bus neutral-point potential (NPP) balance has a crucial impact on the system. Research on grid-connected NPC three-level converter, in this paper, mathematical model of NPP fluctuation is established firstly, the mechanism of NPP ac-dc fluctuations is analyzed, the relationship between NPP error calculation and system operation mode (rectifier-mode or inverter-mode) is deduced, NPP control model based on equalizing loop is established. Secondly, the inherent relationship for NPP balancing control and controller parameter tuning method are given by theoretical analysis. In order to maximize suppress NPP AC fluctuations, the paper proposes a method that controller parameters is designed according to the largest open-loop shear frequency by system frequency characteristic analysis. The NPP Control method has the following advantages: effectively suppressing of NPP ac/dc fluctuations at the same time, positive and negative DC bus voltage fast dynamic response, high utilization rate of dc voltage. Finally, the correctness of the theoretical analysis is verified by MATLAB simulation.

Analysis of a new type islanding detection method for micro-grid based on the calculation of variance

UL1741 rules that to realize the islanding detection, the inverter must stop running within 2s after the main grid failure occurs. However, with the increasing of the capacity of distributed generation system, in order to guarantee the stability and reliability of power supply simultaneously, IEEE Std.1547 proposed the concept that DG runs off-grid after islanding occurs. The concepts of the traditional islanding protection were attacked, the original islanding detection methods are no longer suitable for the flexible micro power grid operation system. This paper presents a new active islanding detection method which could suitable for micro-grid operation and control. The method, which under the premise of without destroying islanding operation conditions, fine-tunes the PWM modulation wave, real-time acquisition the voltage of point of common coupling, using the mathematical statistics method to extract the quadratic differential of the output voltage, according to the changes of the mathematical characteristic value in the grid connected mode and the islanding mode to judge if there was islanding occurred, and the theory basis of quantitative analysis of the disturbance quantity selection. Simulation and experiment results verify the correctness and feasibility of the proposed method.

Research on off-grid control strategy of micro-grid based on current compensation

Micro-grid can operate in both the grid-connected mode and stand-alone mode. Seamless transfer is required in micro-grid switching progress based on IEEE1547.4. The key technology is to reduce the impact of current and voltage to load or grid during the mode transfer. A practical grid-connected switch is a physical switch and the switching delay exists. The paper analyzes the influence of the switching delay in detail, that is, there is a uncontrollable intermediate state in the transfer process of off-grid, which will cause voltage and current overshoot. This paper presents a current compensation control strategies without increasing system complexity. Detailed analysis of the parameters affect on the system and the design basis are obtained. Simulation and experiment results verify the correctness and feasibility of the proposed method.