A Control Parameters Design Method With Multi-Constrains for an LCL-Filtered Grid-Connected Inverter in a Weak Grid

Under weak grid conditions, the variation of the grid impedance will affect the steady-state and dynamic performance of the LCL-filtered grid-connected inverter and even make the inverter unstable. To ensure the system stability and further improve the dynamic performance in a weak grid, a control parameter design method with multi-constrains considering the system bandwidth for the current controller and active damping is proposed in this paper. First, based on the current controller and active damping with only grid current feedback, the effects of control parameters and grid impedance on the LCL resonant suppression and the performance of the inverter are analyzed. Moreover, the parameter constraints of the controllers are derived considering the grid impedance, including stability, resonance suppression, and margin constraints. Furthermore, as the system bandwidth affects the dynamic performance of the inverter, combined with the obtained multi-constraints, the optimal control parameters are determined by achieving the maximum bandwidth of the system against the impedance variation. Compared with other two methods, when the proposed method is applied, the system can operate with a better dynamic and steady-state performance. Finally, experiments are performed on a 2 kW three-phase grid-connected inverter in the weak grid, which verify the effectiveness of the parameter design method proposed in this paper.

Virtual Energy Management for Physical Energy Savings in a Legged Robot Hopping on Granular Media

We discuss an active damping controller to reduce the energetic cost of a single step or jump of dynamic locomotion without changing the morphology of the robot. The active damping controller adds virtual damping to a virtual leg spring created by direct-drive motors through the robot’s leg linkage. The virtual damping added is proportional to the intrusion velocity of the robot’s foot, slowing the foot’s intrusion, and thus the rate at which energy is transferred to and dissipated by the ground. In this work, we use a combination of simulations and physical experiments in a controlled granular media bed with a single-leg robot to show that the active damping controller reduces the cost of transport compared with a naive compression-extension controller under various conditions.

Adaptive control to actively damp bistabilities in highly interrupted turning processes using a hardware-in-the-loop simulator

Interruptions in turning make the process forces non-smooth and nonlinear. Smooth nonlinear cutting forces result in the process of being stable for small perturbations and unstable for larger ones. Re-entry after interruptions acts as perturbations making the process exhibit bistabilities. Stability for such processes is characterized by Hopf bifurcations resulting in lobes and period-doubling bifurcations resulting in narrow unstable lenses. Interrupted turning remains an important technological problem, and since experimentation to investigate and mitigate instabilities are difficult, this paper instead emulates these phenomena on a controlled hardware-in-the-loop simulator. Emulated cutting on the simulator confirms that bistabilities persist with lobes and lenses. Cutting in bistable regimes should be avoided due to conditional stability. Hence, we demonstrate the use of active damping to stabilize cutting with interruptions/perturbations. To stabilize cutting with small/large perturbations, we successfully implement an adaptive gain tuning scheme that adapts the gain to the level of interruption/perturbation. To facilitate real-time detection of instabilities and their control, we characterize the efficacy of the updating scheme for its dependence on the time required to update the gain and for its dependence on the levels of gain increments. We observe that higher gain increments with shorter updating times result in the process being stabilized quicker. Such results are instructive for active damping of real processes exhibiting conditional instabilities prone to perturbations.

Enhancing the Shock Response Performance of Micromachined Silicon Resonant Accelerometers by Electrostatic Active Damping Control

This paper presents a micromachined silicon resonant accelerometer based on electrostatic active damping control, which can improve the shock response performance of the accelerometer. In the accelerometer, an electrostatic active damping structure and damping control circuit are designed to improve the equivalent damping coefficient of the system. System-level Simulink modeling and simulation of the accelerometer with an electrostatic active damping closed-loop control link were carried out. The simulation results indicate that the system can quickly return to normal output without an obvious vibration process after the shock. The fabricated and packaged accelerometer was connected to an external test circuit for shock performance testing. The stabilization time of the accelerometer after a 100 g, 3–5 ms half-sine shock was reduced from 19.8 to 5.6 s through use of the damping control. Furthermore, the change in deviation before and after the shock without damping control was 0.8197 mg, whereas it was 0.1715 mg with damping control. The experimental results demonstrate that the electrostatic active damping control can effectively improve the dynamic performance of the micromachined silicon resonant accelerometer.

Thermo-elastostatic analyzes of new dampers made of polymer springs with negative thermal expansion

The article presents original results of research of the dampers with passive and semi-active damping using polymer springs (also artificial muscles or nylon springs) with negative thermal expansion. Passive damping can be ensured by the strong damping effects of polymer springs. Semi-active damping can be provided by heating the springs from an additional heat source. According to design such dampers, mathematical models for analytical elastostatic and thermoelastostatic analyzes of dampers for selected load cases are processed in the paper. The permissible values of mechanical and thermal load of the dampers are determined. The obtained results are verified by numerical analysis using the finite element method. The elastostatics of the passive damper and its damping functionality have been verified on a real model of the damper. The compiled mathematical models can be used in the design of polymer dampers as well as in their automatic control. Designed and analysed dampers can be used in smaller mobile or stationary systems such as scooters, small car kits and the like. The elastodynamic functionality of the dampers with passive and semiactive damping will be presented and discussed in our further paper.

Active Damping Injection Output Voltage Control with Dynamic Current Cut-off Frequency for DC/DC Buck Converters

With regard to DC/DC buck converter applications, the objective of this study is to expand the admissible range of the output voltage cut-off frequency while lowering the steady-state current cut-off frequency as possible. This study fortifies the inner loop by incorporating the novel subsystems such as an auto-tuner (for the dynamic current cut-off frequency) and active damping injection invoking the pole-zero cancellation nature with the particular designed feedback gain structure. The outer loop active damping control renders the closed-loop speed transfer function to be a first-order low-pass filter with the cooperation of the specially structured design parameters; in addition, it provides time-varying disturbance attenuation. The experimental results obtained for a 3-kW buck converter validate the feasibility of the proposed technique by showing a 34% performance enhancement (at least) compared with the recent active damping controller.