The traditional linear control method for a Boost converter has a poor dynamic performance and weak robustness to load disturbance. To solve this problem, a fixed-frequency sliding mode current control method based on power balance is proposed. First, the observed value of load current is used to calculate the input power, which is required to maintain the stability of output voltage. Then, the input power of the converter is adjusted by controlling the inductor current, so that the system's state trajectory is restrained on the sliding mode surface that possesses invariance to load disturbance, thus ensuring the system's large signal stability and improving its dynamic performance. Finally, based on the equivalent control principle, the equivalent sliding mode control is achieved through the PWM technique to avoid problems of chattering and unstable switch frequency. Simulations of the Boost converter under the condition of step load change are carried out in Simulink, and the proposed method is compared with the traditional linear control method. Results show that when using the proposed method, the system's dynamic performance is better and its large signal stability under large load disturbances is guaranteed.

With a substantial increase in the proportion of power electronic grid-connected devices in a power system, the output characteristics on the power supply side are obviously different from the output characteristics of traditional power supply represented by synchronous generators. The fault analysis of power electronics dominated power systems, especially the network asymmetrical fault analysis, faces new challenges. However, the existing fault analysis methods basically do not realize the time-varying amplitude/frequency characteristics of the devices' internal voltage, and the available time-varying amplitude/frequency symmetrical components method based on time-varying amplitude/frequency signals is just a set of mathematical decomposition formulas without explicit physical connotation as a support. Under this background, the characteristics of the relationship between the three-phase instantaneous values formed by the positive-and negative-sequence time-varying amplitude/frequency rotating vector are analyzed, and the

The grid-forming(GFM) converter is one of the main components of high-permeability power electronic equipment, and its fault ride-through(FRT) capability is an important basis for ensuring the stable operation of a power system with a high degree of power electronics. On this basis, an FRT strategy for GFM converter is proposed, which not only considers the hardware constraints(i.e., current constraints) of the converter, but also can keep it running in protected mode under symmetric and asymmetric faults. First, the FRT-related problem of the GFM converter is analyzed in detail. Then, an appropriate FRT model and the corresponding control method are established. Finally, the effectiveness of the proposed method was verified by power-hardware-in-the-loop simulation and experiment. Results show that compared with a grid-following converter, the proposed control method can guarantee the instantaneous injection of reactive current when the GFM converter fails to prevent the overcurrent problem, and the GFM converter can still operate fault-tolerant under serious fault conditions.

Aimed at the problem that the traditional virtual inertia control method cannot restore the DC bus voltage to its rated value at the frequency recovery stage, a virtual inertia control method using a high-pass filter is proposed. MATLAB/Simulink simulation results show that the changes in DC bus voltage can reflect the microgrid frequency in real-time, and the novel virtual inertia control strategy can ensure the frequency stability in the entire changing process. At the frequency recovery stage, the virtual inertia is reduced to accelerate the frequency recovery, providing sufficient time margin for subsequent frequency adjustment. The high-pass filter virtual inertia control method can restore the DC bus voltage to its initial value and maintain the DC bus voltage stability of the new energy storage microgrid without changing the inertia support of the super capacitor energy storage.

Under the background of energy crisis and environmental issues, the high-gain DC-DC converter is indispensable in renewable energy applications. A dual-switch quadratic structure is proposed to enhance the voltage gain of the traditional quadratic boost converter while reducing the current stress of switches. On this basis, by combining the switched capacitors and a coupled inductor, a dual-switch quadratic high-gain DC-DC converter with a couple inductor is put forward. This converter has advantages such as a very high voltage gain, a pair of switches with the same phase, low voltage stress of switches and output diode, and zero-current switching off in many diodes. The operating principle and steady-state performance of the converter are analyzed in detail, including the voltage gain derivation and the voltage and current stresses of components. Finally, a 120 W prototype was fabricated to verify the theoretical analysis and the feasibility of the converter.

Affected by factors such as wind speed and light intensity, wind power generation has characteristics of randomness, intermittence and large fluctuation, so its direct grid connection will cause damage to power grid. To realize a smooth grid connection of wind power and provide safe and reliable power supply to an urban rail transit system, a hybrid energy storage system composed of super capacitors and lithium batteries is proposed as a stabilizing measure. As the traction load of urban rail transit also fluctuates greatly, the hybrid energy storage system not only stabilizes the output of wind and photovoltaic (PV), but also stabilizes the traction load. The wavelet packet decomposition technology is used to decompose and reconstruct the traction load and wind and PV output power signals on multiple scales, the low-frequency wind and PV grid-connected power and medium-and high-frequency components are obtained, and batteries and super capacitors are used to absorb the medium-and high-frequency components, respectively. Aimed at the minimum comprehensive cost of hybrid energy storage system, the state-of-charge and power limit of the hybrid energy storage system are taken as constraints. The differential evolution particle swarm optimization algorithm with shrinkage factor is used to minimize the annual comprehensive cost of

In a closed-loop control system, the aging monitoring method for power devices based on electrical parameters is one of the difficulties in the field of power electronics reliability. The direct torque control (DTC) system of a permanent magnet synchronous motor (PMSM) is taken as an example, and an on-line monitoring method for the aged state of power devices in a power inverter is studied based on the phase diagram of flux linkage and current. First, the aged characteristics of power devices are analyzed, and it is concluded that the on-state resistance will increase due to the aging of bond wires. Second, the relationship between power device bond wires aging and the phase diagram of flux linkage and the relationship between aging and direct axis current and three-phase current peak value are studied, and the aging monitoring methods are proposed accordingly. Finally, through several groups of simulation experiments, it is verified that both the monitoring method based on the phase diagram of flux linkage and the monitoring method based on current can realize on-line monitoring of the aged state of power device bond wires in the power inverter. The monitoring method based on the phase diagram of flux linkage is easy to observe when there are some fluctuations in the system flux, so it is not desirable considering that the power device has already been in a failure state at the same time. In comparison, the monitoring method based on three-phase current can more accurately monitor the aged state of power devices, and its effect is more advantageous.

Compared with the traditional plug-in charging method, it is safer and more convenient to employ an inductive power transfer (IPT) system to charge autonomous underwater vehicles (AUVs). To alleviate the strong magnetic field inside the AUV hull and the dramatic power fluctuation caused by the rotation misalignment of the AUV under the turbulent water, a three-phase IPT system with a novel coupling structure is proposed. The coupler is composed of three transmitting coils and four receiving coils connected in alternating reverse series, which can suppress the central magnetic field and improve the anti-rotation misalignment performance simultaneously. The Maxwell simulation results show that when the AUV hull rotates, the equivalent mutual inductance Meq fluctuation is less than 2%, and the magnetic field of the AUV center always maintains a low level. In addition, to simplify the system analysis, a decoupling method based on a passive component is adopted to decouple the three transmitting coils. A laboratory-scale prototype based on an LCC-S compensation topology was built to verify the feasibility of the system. Experimental results show that when AUV rotated, the output power varied from 536 W to 595 W with a maximum fluctuation of 9.91%. The maximum DC-DC efficiency of the system was 86.28%.

Aimed at the disadvantages of a traditional AC-AC variable frequency converter such as too many power devices, complex control and low power factor, a control method for an AC-AC variable frequency circuit with continuous output frequency based on the plugged pulse AC-AC variable frequency circuit control principle is proposed. The circuit topologies and working principle of a three-phase to three-phase converter and a six-phase to three-phase converter are presented in detail. The simulation models of these two variable frequency speed control systems are established in a MATLAB/Simulink simulation environment, and the simulation results are consistent with the theoretical analysis. Finally, prototypes were fabricated, and the effectiveness and feasibility of the proposed novel control method for variable frequency speed control system were verified by simulation and experimental results.

Although the LCL filter has a good performance of suppressing high-frequency harmonics, it may cause problems such as resonance oscillation and instability. For an LCL grid-connected inverter, the conventional capacitor-current-feedback type active damping method can suppress the resonant peak effectively, at the cost of additional current sensors. Under this background, a novel active damping control strategy based on an H∞ filter is proposed. The state space model and process noise model of the LCL filter are derived to solve the H∞ filter. The filter capacitor current can be estimated according to the information about grid current and the voltage at a point of common coupling, and feedback is further completed. The system damping is improved, and the estimation accuracy can be guaranteed even if parameter perturbations exist in the LCL filter. Simulation and experimental results show that the proposed method was insensitive to changes in the parameters of the LCL filter and the grid impedance, thereby verifying its feasibility and superiority.