Lu Jiahao

Bio: Lu Jiahao is an academic researcher from Guangdong University of Technology. The author has contributed to research in topics: Variable-frequency transformer & Voltage. The author has an hindex of 3, co-authored 11 publications receiving 22 citations.

Immunizing Variable Frequency Transformer From Dual-Side Asymmetrical Grid Faults via a Single-Converter-Based Novel Control Strategy

Abstract: Both variable frequency transformer (VFT) and high voltage direct current converter are feasible solutions for asynchronous interconnection of different power grids. The VFT possesses inherent natural damping and high overloading capability, which is important for stability and reliability of power grids. The VFT, however, has not been widely used, since it cannot well solve some grid faults like asymmetrical grid faults. In this paper, a novel control strategy is designed on a single series compensation converter (SCC) of traditional VFT. With only replacement of this proposed strategy, the traditional VFT is immune to dual-side asymmetrical grid faults. In detail, three controllers are designed and implemented in a single SCC, i.e., two negative sequence controllers are designed to deal with asymmetrical grid faults at stator and rotor sides of the VFT, respectively; A positive sequence controller is adopted to control the reactive power flowing through the VFT, which reserves the original function of the SCC. Detailed theoretical analysis and hardware-in-loop experiments are carried out to verify the proposed control strategy.

Microgrid for direct load control by frequency-variable transformer and operation method of microgrid

Abstract: The invention discloses a microgrid for direct load control by a frequency-variable transformer, and an operation method of the microgrid. The microgrid comprises a cooperative control system, the frequency-variable transformer, a wind turbine generator set, a wind power fling-cut switch and a load-adjustable fling-cut switch, wherein the cooperative control system is used for acquiring wind speed parameters of the wind turbine generator set, controlling a pitch angle and a fling-cut state of the wind turbine generator set and the rotating speed of the frequency-variable transformer according to the wind speed parameters, and further controlling the voltage and the frequency of a voltage-variable and frequency-variable alternating current bus; self-adaption between output power of the wind turbine generator set and input power of an adjustable load is realized while the wind turbine generator set is controlled to provide maximum electric energy for the microgrid. According to the microgrid disclosed by the invention, a self-adaptive linking mechanism is established between the output power of the wind turbine generator set and the input power of the adjustable load, so that an effect of balancing the power fluctuation of wind power is realized by direct load control. Besides, the wind turbine generator set is connected with the voltage-variable and current-variable alternating current bus by the wind power fling-cut switch; independent arrangement of a power electronic converter is not needed, so that the cost is low.

Control method for variable frequency transformer fault ride through circuit and related circuit

Abstract: The invention discloses a control method of variable frequency transformer fault ride-through circuit, and the related circuit. The control method of variable frequency transformer fault ride-throughcircuit includes the steps: preprocessing the acquired power grid voltage, the stator interface voltage and the rotor interface voltage to obtain the stator voltage direct current component and the rotor voltage direct current component, and obtaining the first power grid voltage frequency and the second power grid voltage frequency through detection and processing by means of a digital phase-locked loop; performing reference voltage calculation processing on the stator voltage direct current component, the rotor voltage direct current component, the first power grid voltage frequency and thesecond power grid voltage frequency to obtain the voltage reference value of a first PWM transformer and the voltage reference value of a second PWM transformer; and performing control signal acquisition processing on the voltage reference values to obtain switch signals of controlling the first PWM transformer and the second PWM transformer. When the asymmetric fault of the power grid voltage occurs, the control method of variable frequency transformer fault ride-through circuit performs voltage compensation to solve the asymmetric fault of power grid voltage so as to prevent propagating of the asymmetric fault of voltage.

Fault ride-through control method for variable-frequency transformer and related device

Abstract: The application discloses a fault ride-through control method for a variable-frequency transformer, which comprises the following steps: first, obtaining the voltage of a first grid, the voltage of asecond grid, the voltage of a stator and the current of the stator; then, calculating the voltage reference value corresponding to a single series three-phase converter after preprocessing; and finally, converting the voltage reference value into a control signal to control the series three-phase converter. The negative sequence voltage and negative sequence current of the stator caused by the negative sequence voltage of the first grid can be restrained, and the torque and power fluctuation of double rotor angular speed and double stator synchronization speed can be eliminated. The negative sequence current of the stator caused by the negative sequence voltage of the second grid can be restrained, and the electromagnetic torque and power fluctuation of double rotor synchronization speed can be greatly reduced. That is to say, the voltage imbalance problems of the left and right grids are solved at the same time by using a single series three-phase converter. Moreover, the grid cost isreduced. The application also discloses a fault ride-through control device, a circuit controller and a computer readable storage medium, which have the same beneficial effects.

Cascade converter of variable frequency transformer circuit and related circuit

Abstract: The application discloses a cascade converter of a variable frequency transformer circuit. An H-bridge converter and a three-phase converter can be equivalently obtained through eight switches of thecascade converter so as to realize the function of the original circuit, namely, the equivalent H-bridge converter can control the variable-frequency transformer, the three-phase converter can regulate the DC-side voltage, the functions of ten switches are realized by only using eight switches, the cost of the converter is reduced, and the total cost for constructing an asynchronous power grid isfurther reduced, and the resource utilization rate is improved. The application further discloses a variable frequency transformer circuit and a wind power unit with the above advantages.

Reliability Modeling and Assessment of Cyber Space in Cyber-Physical Power Systems

Abstract: The information technology in a cyber-physical power system plays a significant role in quickly regulating the energy flow that can cope with the complexity of power system operation and control. The energy processing capability of power systems depends heavily on the reliability of information systems. The reliability model of cyber space includes not only the binary-state operation-failure representation of physical devices, but also the multi-state representation of information flow in corresponding networks. This paper proposes a reliability modeling and assessment method for the power information system (i.e., cyber space in power system). The proposed composite Markov model would couple physical characteristics and information flow performances in a two-layer model. The proposed reliability methods combine the sequential Monte-Carlo simulation with the linear programming model to acquire maximum flows that would supply power demands. The proposed methodology is applied to the reliability analyses of the power information system in the IEEE 14-bus system in which the performances of the proposed indices are evaluated.

Self-Learning Robust Control Synthesis and Trajectory Tracking of Uncertain Dynamics

Abstract: In this article, we investigate the self-learning robust control synthesis and tracking design of general uncertain dynamical systems. Based on the adaptive critic learning, the robust stabilization method is developed with the help of conducting problem transformation. In addition, by considering the optimal control solution with a discounted cost function, the established method is extended to address the robust trajectory tracking design problem. The Lyapunov stability analysis is also conducted for proving the robustness of the related control plants. Finally, the simulation verification with the three case studies is provided in terms of robust stabilization and trajectory tracking, respectively.

Microgrid for direct load control by frequency-variable transformer and operation method of microgrid

Abstract: The invention discloses a microgrid for direct load control by a frequency-variable transformer, and an operation method of the microgrid. The microgrid comprises a cooperative control system, the frequency-variable transformer, a wind turbine generator set, a wind power fling-cut switch and a load-adjustable fling-cut switch, wherein the cooperative control system is used for acquiring wind speed parameters of the wind turbine generator set, controlling a pitch angle and a fling-cut state of the wind turbine generator set and the rotating speed of the frequency-variable transformer according to the wind speed parameters, and further controlling the voltage and the frequency of a voltage-variable and frequency-variable alternating current bus; self-adaption between output power of the wind turbine generator set and input power of an adjustable load is realized while the wind turbine generator set is controlled to provide maximum electric energy for the microgrid. According to the microgrid disclosed by the invention, a self-adaptive linking mechanism is established between the output power of the wind turbine generator set and the input power of the adjustable load, so that an effect of balancing the power fluctuation of wind power is realized by direct load control. Besides, the wind turbine generator set is connected with the voltage-variable and current-variable alternating current bus by the wind power fling-cut switch; independent arrangement of a power electronic converter is not needed, so that the cost is low.