Conference Paper: Hybrid power control of cascaded STATCOM/BESS for wind farm integration[Show abstract] [Hide abstract] ABSTRACT: Static synchronous compensator combined with battery energy storage system-STATCOM/BESS, can regulate four-quadrant active and reactive power, which is an ideal scheme to solve problems of wind farm integration. Multilevel converter is the key technology for STATCOM/BESS. The advantages of cascaded multilevel converter are analyzed and the structure of cascaded STATCOM/BESS is described. Hybrid power control strategy is proposed to compensate active and reactive power of wind farm comprehensively. The reference current of STATCOM/BESS is determined according to the requirements of active power smoothness and voltage control. The control strategy can coordinate charge or discharge of batteries with reactive power compensation of STATCOM, and balance the batteries capacity of H-bridges. The proposed control strategy is validated by simulation on the wind power system using cascaded STATCOM/BESS as the compensation device. Simulation results show that the cascaded STATCOM/BESS can effectively improve the characteristics of wind farm integration and provide dynamic support to the grid.
- [Show abstract] [Hide abstract] ABSTRACT: The power system frequency stability depends on system power balance, and the required active power for the power balance can be quickly obtained from the kinetic energy stored in the rotating mass. A power control strategy of the permanent magnet synchronous generator (PMSG) is presented for the system dynamic frequency support. On the one hand, a supplemental active power control loop is added in the maximum power extraction controller of the grid side inverter. It is used to modify the controller to achieve effective network inertia response because the power system inertia reflects the system property of resisting frequency changes. On the other hand, a supplemental reactive power control loop is added to reactive power controller to improve the system damping characteristics. Finally, the dynamic performances of a typical network containing PMSG-based wind farms are tested using MATLAB/Simulink. The simulation studies illustrate that the network dynamic frequency stability can be improved using the proposed control strategy.
Conference Paper: Comparison of inertia control methods for DFIG-based wind turbines[Show abstract] [Hide abstract] ABSTRACT: Doubly fed induction generator (DFIG)-based wind turbines are nowadays used widely in large wind farms. Due to the fact the control system of DFIG is not based on the power system frequency, the whole inertia of the power system is reducing rapidly with the penetration of wind generation increasing. This is extremely bad for the stability of the system frequency. Thence, ancillary inertia control strategies of DFIG need to be developed to compensate for this deficiency. At the beginning of this article, the vector control system of DFIG-based wind turbines is described briefly. The inertia control methods making use of that model could later be designed out. Then, a concept called controllable virtual inertia is put out and the derivation of its formula is given in details. After the two inertia control strategies of DFIG are described fully, the mechanism that how the virtual inertia of DFIG can be manipulated is revealed: the parameters (K1, K2and K3) contained in the inertia control schemes determine proportionally the virtual inertia level of DFIG. Finally, through the simulations in Matlab/Simulink, the two strategies of inertia control for DFIG-based wind turbines which have been utilized in this work are effective for the system frequency support and the concept named as controllable virtual inertia has theory worth for further research.
Conference Paper: Interconnection of wind farms with grid using a MTDC network[Show abstract] [Hide abstract] ABSTRACT: In the light of the practical project experience, the multi-terminal DC (MTDC) is regarded as one of the preferable solutions to solve the grid interconnection issue of wind generation. This paper mainly focuses on the application of the voltage source converter(VSC) based MTDC technology to integrate large scale wind farms to the electric power grid. A radial MTDC system is explored as the best choice for wind power integration, due to that it can mitigate the fluctuation of the aggregated wind power. Based on the analysis of the VSC model and control, the coordinated control strategy for the proposed MTDC system is designed. The operation performance of a four-terminal MTDC system connecting two DFIG-based wind farms, the local and remote grids is also studied, and the proposed control strategy is adopted to achieve a constant power for long distant transmission to the load center under wind speed variations and faults on DC line.
Conference Paper: Hierarchical coordinated control of DC microgrid with wind turbines[Show abstract] [Hide abstract] ABSTRACT: Control and operation of a DC microgrid under various operating conditions are investigated in this paper. A wind turbines based DC microgrid configuration is used to accurately describe different operation modes firstly. For a DC mcrogrid system, an abnormal DC voltage caused by power fluctuations can disrupt normal operation or even cause the whole system to collapse. Therefore, to improve the system stability, this paper proposes a hierarchical coordinated control strategy according to the DC voltage variation range. Under any condition, there must be at least one DC terminal being responsible for DC voltage control. On this basis, the control method for each power electronic converter is described under different control levels. Finally, the validity of the proposed hierarchical control strategy is demonstrated by simulations on a DC microgrid with wind turbines using MATLAB/Simulink in different operation modes, considering various operating conditions, such as variations of wind speed and load, AC grid fault, and load shedding.
- [Show abstract] [Hide abstract] ABSTRACT: In some control strategies of the direct-rive permanent magnet generator (DDPMG), the mathematics model is excessively simplified and some complex nonlinear characteristics, such as core saturation and cross-saturation, are generally neglected. To solve this problem, this paper utilizes the frozen element permeability method to compute the armature self- and mutual-inductance, permanent magnet d- and q-axis flux varying with d-axis and q-axis current, then an improved model is presented in which the core saturation and cross-saturation between d-axis and q-axis are considered effectively. Based on this model, the method for computing the performance of the generators is also proposed. Taking a 1.5-MW DDPMG as an example, the time-stepping finite element method (T-S FEM) is adopted to analyze the performance with no-load and loaded conditions, the results show a good agreement with the ones obtained by the improved model. Compared with the simplified model, it is demonstrated that the presented model has the high efficiency and reliability and can provide a good reference for optimization design of DDPMG and other PM motors.
- [Show abstract] [Hide abstract] ABSTRACT: 1 Abstract-A DC microgrid using multi-terminal DC system (MTDC) is an effective solution to integrate wind turbines with distribution network, due to the lower investment and the flexible system power flow distribution. A four-terminal DC microgrid composed of permanent magnet synchronous wind generators, power distribution grid, energy storage battery, and passive loads is used to validate the reasonability of the system configuration firstly. And then a power management scheme based on the above configuration is proposed to keep the power balance and stable operation. In addition, based on the analysis of the voltage source converter (VSC) model, the control strategies of constant DC voltage for coordinating various side converters are studied. Finally, simulation results show that the MTDC-based microgrid power balance is maintained automatically in grid integration and islanding modes under different conditions such as variations of wind speed and loads. The effectiveness and feasibility of the control strategies for the proposed four-terminal DC microgrid with turbines are verified.
- [Show abstract] [Hide abstract] ABSTRACT: This paper investigates the control and operation of permanent magnet synchronous generator (PMSG)-based wind generation systems employing the full-scale frequency converter under network fault conditions. The factors inducing the oscillations of DC-link voltage of the full-scale frequency converter during grid voltage dips are analyzed. A novel control strategy is proposed to suppresses the DC-link voltage oscillations and enhance the low voltage ride-through (LVRT) capability of PMSG-based wind turbine. The generator-side converter is controlled to maintain a stable DC-link voltage, while the grid-side converter is controlled to provide a dynamic coordinated control for the active and reactive power output according to the grid voltage amplitude variations during grid faults. The simulation results implemented in Matlab/Simulink show that the proposed control strategy not only improves the stability of PMSG by means of suppressing the DC-link voltage oscillation, but also provides a dynamic reactive power support to restraint the disturbance of the grid voltage.
- [Show abstract] [Hide abstract] ABSTRACT: In order to enhance the low voltage ride-through (LVRT) and grid support capabilities of a multi-pole permanent magnet synchronous generator (PMSG) using full-scale frequency converter, this paper presents a coordinated control strategy for the active and reactive power output of the grid-side converter. When a voltage dip occurs in the grid, the generator-side converter of PMSG is used to rapidly regulate the active power output of the generator to eliminate the unbalanced power in the DC-link side and maintain a stable DC-link voltage, while the grid-side converter of PMSG is employed to realize a coordinated control for active and reactive power output according to the grid voltage change range. The simulation results implemented in Matlab/Simulink show that the proposed control strategy not only realizes the LVRT of PMSG but also provides a dynamic reactive power support to recover the grid voltage.
- [Show abstract] [Hide abstract] ABSTRACT: A flexible LCCL load matching electrostatic coupling approach for SRI (series resonant inverters) of induction heating is proposed. It enables more flexible and convenient load matching through the multiple configurations of the matching series capacitors in the LCCL circuit. The LCCL resonant circuit topology and electrical characteristics are analyzed. The LCCL multiple capacitor configurations principle is given. The single phase full-bridge SRI for induction heating power supply prototype and SRI with output transformer are designed and tested by using an FPGA as the main controller. The experimental results validate the proposed approach and confirmed that the proposed approach can reach higher efficiency in contrast with the SRI with output transformer.
- [Show abstract] [Hide abstract] ABSTRACT: This paper investigates virtual inertia control of doubly fed induction generator (DFIG)-based wind turbines to provide dynamic frequency support in the event of abrupt power change. The model and control scheme of the DFIG is analysed. The relationships among the virtual inertia, the rotor speed and the network frequency variation are then investigated. The "hidden" kinetic energy that can be released to contribute to the grid inertia by means of shifting the operating point from the maximum power tracking curve to a virtual inertia control curve is investigated. The virtual inertia control strategy based on shifting power tracking curves of the DFIG is proposed and the calculation method for determining these virtual inertia control curves is presented. A three-machine system with 20 percent of wind penetration is used to validate the proposed control strategy. Simulation results show that by the proposed control strategy, DFIG based wind farms have the capability of providing dynamic frequency support to frequency deviation, and thus improving the dynamic frequency performance of the grid with high wind power penetration. (6 pages)
Conference Paper: Control of DFIG-based wind farms for power network frequency support[Show abstract] [Hide abstract] ABSTRACT: This paper investigates the frequency control scheme of a doubly fed induction generator (DFIG)-based wind farms to provide frequency support for the power system steady operation. Due to the decoupling of the rotor speed and the grid frequency by the connected converters, the DFIG-based wind farm rarely contributes to the network effective inertia. This is particularly true in the small isolated power system with lower system inertia. A novel method of controlling the DFIG active power and rotor speed is proposed to enable the DFIG-based wind farms participate in the network frequency support. A typical network that combines synchronous generator-based power plants and DFIG-based wind farms is modeled by MATLAB/Simulink to assess the system dynamic performance. The control strategy of the DFIG-based wind farm for the power network frequency regulation is validated by the simulation studies. With the proposed strategy, the DFIG-based wind farm system can provide useful network support as a conventional power plant. Thereby the power network operation and reliability can be improved.
- [Show abstract] [Hide abstract] ABSTRACT: This paper investigates the grid support strategy of a VSC-HVDC link for the DFIG-based wind farm integration, including grid frequency regulation and power oscillation damping. The VSC-connected configuration may reduce the power system inertia with fast power control. In order to improve the power system stability with fast penetration of wind power generation, the control strategy of the VSC-HVDC and DFIG for the transmission network frequency regulation and power oscillation damping is proposed. In the event of sudden generation loss or large load demand, the system frequency variation can be reduced by active power modulation of the DFIG-based wind farms and the power oscillations can be damped by reactive power modulation of the grid side VSC. This coordinated control strategy is validated by the simulation studies using MATLAB/Simulink. With the proposed strategy, the VSC-HVDC connected wind farms can provide useful network support similar to a conventional power plant, thereby improving the power system operation and reliability.
- [Show abstract] [Hide abstract] ABSTRACT: Performance investigations and drive designs of an interior permanent magnet (PM) machine, in both the constant torque and the flux-weakening operating regions, are generally conducted based on the machine parameters that are calculated from finite element analysis (FEA). To properly select the optimal current control angles for maximum torque generations at various speeds, this paper presents thorough assessments of the magnetic cross-coupling impacts of the interior PM machine from different calculation schemes. In addition, analytical models based on direct and indirect finite element calculations of the machine characteristics at those severe magnetic saturation conditions will be devised to provide a reliable on-line operational control reference.
- [Show abstract] [Hide abstract] ABSTRACT: The paper presents impacts of the stator slot with skew and segment magnet rotor on the performance of interior permanent magnet (IPM) machine for an electric traction. Comparisons of the average torque, torque ripples, cogging torque and no-load back EMF with skew and un-skew are given and how suitable a segmented rotor IPM machine and its torque characteristic and the field weakening capability are investigated. The results of the machine performance comparisons are based on comprehensive use of finite element analysis tools (Ansoft Maxwell 2D).One of the machine designs with one stator slot-pitch skew and no-segment magnet rotor for electric traction has been manufactured as prototype. From the FEA results, it shows that the IPM synchronous machine with two-teeth stator slots skewed and two-segmented magnet rotor has better performance than the conventional IPM synchronous machine.
- [Show abstract] [Hide abstract] ABSTRACT: This paper presents impacts of different permanent magnet materials and operational temperatures on the performance of interior permanent magnet (IPM) machines for electric vehicle applications. Variations of the average torque, torque ripple, cogging torque, and no-load EMF with different neodymium-iron-boron (NdFeB) permanent magnet materials and operational temperatures are investigated. Based on finite-element method (FEM), performance about the ripple and cogging torques of the IPM machine will be analyzed and some useful conclusions can be provided for researchers and engineers in the related traction motor industries.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper CCL static electricity coupling load matching method using in induction heating power is described. The characteristics of CCL resonant circuit and output maximum power is discussed in detail. Under the condition of output rated load power, give the current and voltage peculiarity curves for different parameters. Finally give the calculation of matching component Lp, C and Cs. Because CCL static electricity coupling load matching method could calculate the complementary capacitance easily at the time of output maximum power, another thought of induction heating load matching is put forward to use in the future.
- [Show abstract] [Hide abstract] ABSTRACT: In this paper, a new voltage unbalance correction scheme for the pulse-width modulation current-source rectifier is presented. By regulating the instantaneous active/reactive power, a constant dc-current without 100 Hz ripple together with sinusoidal input current at controllable power factor are achieved. A current controller based on sliding-mode variable structure control in stationary frame is proposed, which achieves high performance current tracking in the fact of system uncertainties and disturbances. The existence and stability of sliding-mode is ensured by using a proper reaching law. The effectiveness of the proposed scheme is validated by simulation results.
- [Show abstract] [Hide abstract] ABSTRACT: Power transformer is very important in power system. In this paper, according to complementary strategy, a new transformer fault diagnosis method based on rough sets theory (RST) and Bayesian network (BN) is present. Through reduction approach of RST information table to simplify expert knowledge and to reduce fault symptoms, the minimal diagnostic rules can be mined. According to the minimal rules, complexity of BN structure and difficulties of fault symptom acquisition are largely decreased. At the same time, probability reasoning can be realized by BN, which can be used to describe changes of fault symptoms and analyze fault reasons of transformer. Finally, the correctness and effectiveness of this method are validated by the result of practical fault diagnosis examples.
North China Electric Power University
Peping, Beijing, China
- School of Electrical Engineering