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As common submodule (SM) capacitor voltage measuring method of modular multilevel converter(MMC) requiring large number of voltage sensors, submodule voltage measuring technique based on observation is then introduced to reduce voltage sensors. However, observed submodule capacitor voltage has a strong dependence on the parameters, which will reduce the robustness of MMC control system. In this paper, a deadbeat control method for MMC with reduced sensors is proposed to enhance the robustness, which is just uses the arm bridge current and the load current reference value as the control input to improve the robustness of the operation performance. Simulation and experimental results have proven the effectiveness of the proposed control method.

Modular Multilevel Converter (MMC) has proven to be the most viable and promising candidates for high power applications. However, half bridge submodule, the most commonly used cells in MMC, possess limited two-level output voltage and inability to block dc fault current, consequently restricting the application of MMC in high power situations. A novel structure of submodule with threelevel output voltage and dc fault blocking capability relying on antiparallel insulated-gate bipolar transistors used in MMC is presented in this paper. Compared with other submodules with the same function, the new-model submodule has additional benefits of less diodes and semiconductor switching devices, lower conducting losses, and faster speed of dc fault current blocking. To stabilize the capacitors voltage, a control method based on neighboring number sorting is proposed according to the structure characteristics of this new-model three-level MMC (3LMMC). The feasibility and validity of the proposed converter under the fault condition is demonstrated by simulations in MATLAB/Simulink.

For a disk-type contra-rotating permanent magnet synchronous motor (CR-PMSM), when the dynamic master-slave control method with sliding mode speed control is employed, the robustness of the rotor in the case of large sudden load variation is poor, speed and torque pulsation of slave rotor under the conditions of heave unbalanced load torque are great. Aiming at these problems, an optimized vector control strategy adopting load torque compensation is proposed in the paper. The strategy realizes the torque current control of dual rotor. Meanwhile, two sliding mode observers are applied to observe load torque of dual rotor, and the observed values are made feedforward compensation to the system. The experimental results show that, by adopting the proposed strategy, the robustness of the rotor is improved when sudden load changes are large, and the dual rotor of CR- PMSM could synchronously track for a given speed with no pulsation in the situation of heavy unbalanced load torque.

In this paper, a footprint determination algorithm for entry vehicles based on three-dimensional acceleration profile is proposed, which solves the problem of fast determination of the entry coverage with complex multi-constraints. The aerodynamic adjustment capability is greatly improved since both the angle of attack and bank are regarded as primary variables, and in this way larger entry footprint is achieved. Furthermore, due to the introduction of quasi-equilibrium glide condition (QEGC), the altitude of the entry trajectory changes smoothly without jumping. Firstly, based on the QEGC, a new type of longitudinal acceleration corridor and lateral lift to drag corridor are designed, and the profiles are chose as the interpolation results of the upper and lower boundaries. Secondly, based on PID theory, a three-dimensional profile tracker is designed to realize the corresponding entry trajectories. Finally, the traversal of the interpolation parameters in the corridors is carried out, and the entry footprint satisfying various complex constraints is obtained. The approach is tested using Common Aero Vehicle-H model, and the results demonstrate that the proposed algorithm can determinate the footprint of entry vehicles rapidly while satisfying all the path and terminal constraints.

A rapid boost trajectory generation algorithm is presented in this paper, considering the new requirements of hypersonic boost-glide missiles, such as the low terminal altitude, high velocity, and wide range coverage. The algorithm divides the boost trajectory into the longitudinal and lateral sub-planes. In the longitudinal sub-plane, the angle of pitch is designed as the time segment function. The maximum angle of attack and the pitch rate are selected as the key parameters to be determined. Newton iteration scheme is used to calculate the key parameters, according to the strict terminal altitude and velocity constraints. In the lateral sub-plane, an analytical calculation of the azimuth angle is proposed based on the theory of spherical triangle, which guarantees an initial aiming at the preselected target. Furthermore, new boost modes, such as intermittent boost mode and low altitude direct boost mode, are proposed. The trajectory characteristics and the application prospect are deeply analyzed. Finally, a three-stage solid rocket is used in the simulation. The results demonstrate that the algorithm can rapidly generate the boost trajectory for hypersonic boost-glide missile and achieve complex flight missions.

In this paper, a planning approach of maneuver trajectory based on dynamic inversion is proposed, which can greatly improve the penetrability of hypersonic glide vehicles in dive phase. Maeuvering and guiding overloads are combined using a weight coefficient, which is designed as the function of altitude. Enough adjust ability is guranteed at the end of dive phase, and more complex maneuver trajectories are achieved. Firstly, four different modes of maneuver trajectories are realized by coordinating the maneuver in longitudinal and lateral sub-planes, respectively. Dynamic inversion is employed to establish the relationship between the designed trajectory and the needed overload. Secondly, the minimum energy loss is selected as the optimization index, and the optimal overload is obtained based on the maximum principle. the final path angle constraint is also considered in this algorithm. Finally, the maneuvering and guiding overloads are combined using a weight coefficient, and the corresponding angle of attack and bank are obtained. The approach is tested using common aero vehicle-H (CAV-H) model, and the results demonstrate that the method proposed in this paper can realize the maneuver trajectory in dive phase with high terminal accuracy and strong penetration ability.

A direct optimization algorithm, which satisfies multiple path and terminal constraints, is proposed to generate the optimal trajectories for the single-stage-to-orbit space planes. Minimum fuel cost is selected as the optimality criterion in this method, and a segment strategy of the ascent trajectory is proposed according to the characteristics of the combined engines. The optimal control problem is transformed into a multi-stage optimal control problem, and a Gauss pseudo-spectral method is used to solve the parameterized control variables. Both the numerical simulations and simplified calculation based on the Gauss pseudospectral method are carried out to test the effectiveness and robustness of the proposed algorithm. Results demonstrate that the algorithm can rapidly generate the optimal ascent trajectory for single-stage-to-orbit space planes and achieve complex flight missions.

An entry trajectory planning algorithm that generates multi-target trajectories satisfying path and terminal constraints is investigated in this paper. The entry trajectory is divided into the initial and glide phase, and a switch condition is used to ensure a smooth connection of these two phases. A nominal angle of attack is used in the whole trajectory and then the bank angle is the main control variable which is under design. In the initial phase, a constant bank angle is used to generate the trajectory to match a fix terminal height of transition condition. In the glide phase, a planner consists of the longitudinal and lateral sub-planner is developed based on the drag acceleration guidance logic. The drag acceleration profile is designed as a second order curve of velocity, its initial and terminal points are fixed and the middle value of the drag acceleration is calculated onboard according to the distance to go. The magnitude of the bank angle is solved from the longitudinal sub-planner, whereas the sign of the bank angle is determines by the lateral sub-planner. Then, a tracker is employed to follow the reference drag acceleration profile. The algorithm converts the highly constrained multi-target entry trajectory planning problem into a two parameters searching problem. Finally, the approach is tested using Common Aero Vehicle-H model, and the results demonstrate that the algorithm can generate multi-target entry trajectories rapidly while satisfying all the path and terminal constraints.