Yuan Liqiang

Design and control of a three-phase grid-connected photovoltaic system with developed maximum power point tracking

In this paper an optimum design and control of three-phase grid-connected PV system has been proposed and analyzed. Also, a developed maximum power point tracking (MPPT) controller that uses the PV array differential power to voltage (dP/dV) as an index to provide the reference voltage of maximum power point (MPP) quickly and accurately is presented. The control scheme of a three phase current-controlled space vector pulse-width modulation (SVPWM) inverter in rotating synchronous coordinate d-q with the proposed MPPT algorithm and feed-forward compensation is discussed. The PV grid-connected system controller employs multi-loop control with the filter inductor current of the inverter in the inner loop to achieve fast dynamic response and the outer loop to control dc bus voltage for MPPT. The design method provided in the paper for the controller parameters and filter proved to be very practical and effective. Both the power quality into the grid and power factor correction comply with standards IEEE 929-2000. Good agreement is obtained between simulation and experimental results which illustrated the high performance of the proposed approach.

Performance evaluation of three control strategies for three-level neutral point clamped PWM rectifier

This paper presents the performance evaluation and comparisons of three typical control strategies for three-level neutral point clamped (NPC) rectifier with pulse width modulation (PWM). These are voltage oriented control (VOC), direct power control (DPC) and direct power control based on space vector modulation (DPC-SVM). The theoretical background is described, and the advantages and disadvantages of each scheme are studied through analyses and a series of experiments. A comprehensive comparison and evaluation are implemented for the three methods from several aspects such as algorithm complexity, steady state and dynamic performances, current THD with unbalanced power source voltage, and startup current which is important for the high power applications. The results show that all the three schemes can provide good abilities; and VOC and DPC-SVM possess better steady state performance while DPC is provided with best dynamic performance.

A High Voltage and High Power Adjustable Speed Drive System Using the Integrated

A filter device is indispensable in most ac adjustable speed drive systems to eliminate the high-frequency components in the output voltage of an inverter, which could protect the insulation of the ac motor and reduce electromagnetic interference. Additionally, due to the restraints of power electronic devices, especially in the high voltage and high power systems with neutral point clamped (NPC) three-level structure, the step-up transformer is usually applied to ascend the output voltage. Thus, the system would be bulky when both of the components, filter and transformer, are adopted simultaneously. This paper efficiently utilizes the leakage inductance of the transformer and effectively integrates the filter and step-up transformer to achieve boosting and filtering simultaneously, and economizes on cost and volume. Besides, some relevant dynamic processes, like dc pre-excitation at the starting process, the self-excitation in the pulse-blocking process, and the response to load variation are discussed, respectively. This integrated configuration is validated by corresponding simulations and experiments, and has also been successfully applied in the three-level NPC 6000V/1MVA system. The other relevant factors in this device are discussed in detail

LC

Single-stage grid-connected photovoltaic (PV) system has advantages such as simple topology, low cost, etc. However, since this kind of system has only one stage of power conversion, all the control objectives need to be considered simultaneously, such as maximum power point tracking (MPPT), synchronization with the utility voltage and harmonics reduction for output current, so that the complexity of control scheme is much increased. This paper presents a modified MPPT strategy, which can remarkably improve the stability of the single-stage grid-connected PV system during rapidly changing process of light intensity, besides realizing the control objectives above. Comparing it with traditional constant-step MPPT strategy, this paper illustrates the improvement of the novel strategy based on PSIM simulation platform. A 300 Wp grid-connected PV system is also established in laboratory to verify the stability of this modified MPPT strategy, in which DSP (TMS320F2407) is employed to implement the proposed MPPT controller. Simulation and experimental results show the high stability and high efficiency of this modified strategy applied in single-stage grid-connected PV system

and Step-Up Transforming Filter

This paper presents a novel control scheme for three-level neutral point clamped (NPC) back-to-back converter. The distribution and balance of instantaneous energy for the converter is analyzed, and the direct power control with space vector modulation (DPC_SVM) for front-end rectifier and rotor field oriented control (FOC) for back-end inverter-fed induction motor are adopted respectively. A power feed-forward control loop from inverter to rectifier side is introduced to obtain better dynamic performance for the DC-link. Experimental results show that with the proposed control scheme, the three-level NPC back-to-back converter exhibits excellent dynamic performance, and can minimize DC-bus voltage fluctuations with low size of DC-bus capacitors.

Modified MPPT strategy applied in single-stage grid-connected photovoltaic system

Various failures and destructions occur in the applications of the power electronic converter. The real practice shows that these failures are connected with the concentration of the transient power pulse. In allusion to the physical characteristics of power electronic converters, this paper proposed that the power pulse and its sequence are the basis for power electronics in the perspective of electromagnetic energy. The authors analyzed the transient processes in the power semiconductors, electric conduction loops and controller system and illustrated the power pulse phenomena in high voltage and high power inverters. This investigation on the power pulse sequence is very meaningful for the failure analysis and device protection and has become an important topic in power electronics.

A novel control scheme for three-level NPC back-to-back converter

This paper presents the design, simulation and implementation of circuit for IGCT (integrated gate commutated thyristor) test platform, which is an equivalent circuit for the common commutation types occurring in the 2-or 3-level VSI (voltage source inverter) circuits. Based on the equivalence, the design of the test circuit for 5SHX08F4502 without switching-off snubber, including the topology and the element parameters, especially the ones of stray inductors, is described in detail. The test circuit is simulated with the package PSIM, and the IGCT model is functional level. The simulation and experiment results are both given in the paper.

Transient of power pulse and its sequence in power electronics

Applying co-simulation technology is a very important trend in power electronics simulation, which can make full use of the merits of different software to improve the efficiency of building up a system. In this paper, a simulation platform for three-level adjustable speed drive (ASD) based on co-simulation of PSIM and SIMULINK is presented, which includes the interface between PSIM and SIMULINK, main circuit in PSIM, space vector pulse width modulation (SVPWM), dead time and minimum pulse width, view of output voltage and its Fourier analysis in SIMULINK. Based on this platform, the cause of large current when motor starts is studied. Simulation and experimental results show that the minimum pulse width contributes a lot for the large starting current of the ASD. In conclusion, applying the simulation platform introduced in this paper, the dynamic behavior of the three-level ASD can be easily studied, which reduces the cost and improves efficiency at the same time compared to hardware investments, and may help to realize the optimal design of the ASD in practice

The IGCT test platform for voltage source inverters

In order to ensure the reliability and dynamic characters of IGCTs equipped in MV (medium voltage) three-level inverter, the switching experiments for single IGCT in the inverter are proposed in this paper. The experiment scheme is described in detail, including the topology, key parameters and the control method. Based on the experiment results, the switching behavior for every IGCT in the inverter is compared, and the influence factors to the behavior are analyzed, such as the inverters structure, topology position of IGCTs, the stray inductance in commutating loop, etc Finally, the advantages of the experiment are summarized in the conclusions.

PSIM and SIMULINK Co-simulation for Three-level Adjustable Speed Drive Systems

The converter is an EMI emissions source to the grid and loaders. Moreover, it is interfered by the elements of itself. Therefore, particular attention should be paid to EMI for converter design. Based on a 55kW two-level converter prototype, the analysis of a switching power supply which is an important EMI emissions source in converter is performed. Furthermore, the DC bus bar can also produce EMI noises, and it is carefully analyzed in this paper. Two versions of converter prototypes are used to study the switching power supply and DC bus-bar structure. Comprehensively comparative experiments are performed. The experiment results show that the conducted EMI in IGBT-based converters can be reduced through improving the switching power supply and the structure of DC bus bar.