Research on Governor Parameter Optimization to Suppress Ultra-Low Frequency Oscillation of Power System Caused by Hydropower Unit

In the actual power system with hydropower, long-time and ultra-low frequency oscillation events occur many times. It is found that the unreasonable setting of governor parameters is an important reason for the oscillation. Firstly, the single machine on load system model is used to analyse the relationship between the PID parameters of the governor and the system stability, then the relationship between oscillation mode and PID parameters of governor is analyzed by eigenvalue analysis method, and the negative damping provided by speed regulation system is analyzed by damping torque method, and then the particle swarm optimization algorithm is used to optimize the PID parameters. Through the analysis of the step response of the single machine system before and after the optimization and the damping torque coefficient provided by the speed regulation system, it shows the effectiveness of the optimization algorithm. Finally, in the simulation platform MATLAB/SIMULINK, a single machine load system model which is closer to the actual power grid is built. The governor parameters of the generator are simulated and verified, and the PID parameters are adjusted by using the parameters obtained by the optimization algorithm. The results show that the optimized parameters have a good suppression for the ultra-low frequency oscillation.

Low Frequency Damping Control for Power Electronics-Based AC Grid Using Inverters with Built-In PSS

Low frequency oscillations are the most easily occurring dynamic stability problem in the power system. With the increasing capacity of power electronic equipment, the coupling coordination of a synchronous generator and inverter in a low frequency range is worth to be studied further. This paper analyzes the mechanism of the interaction between a normal active/reactive power control grid-connected inverters and power regulation of a synchronous generator. Based on the mechanism, the power system stabilizer built in the inverter is used to increase damping in low frequency range. The small-signal model for electromagnetic torque interaction between the grid-connected inverters and the generator is analyzed first. The small-signal model is the basis for the inverters to provide damping with specific amplitude and phase. The additional damping torque control of the inverters is realized through a built-in power system stabilizer. The fundamentals and the structure of a built-in power system stabilizer are illustrated. The built-in power system stabilizer can be realized through the active or reactive power control loop. The parameter design method is also proposed. With the proposed model and suppression method, the inverters can provide a certain damping torque to improve system stability. Finally, detailed system damping simulation results of the universal step test verify that the analysis is valid and effective.

Theoretical investigations on the linear and nonlinear damping force for an eddy current damper combining with rack and gear

To study the damping characteristics of a new type of eddy current damper with rack and gear recently proposed by the authors, the damping torque for the eddy current damper with rack and gear was theoretically investigated based on some fundamental assumptions, including evenly distributed magnetic field on a conductor plate and no magnetic leakage. A linear relationship between damping torque and velocity was obtained. Numerical simulations by using COMSOL Multiphysics were conducted to evaluate the accuracy of the linear theoretical formula. When angular velocity is less than 30 rad/s, it seems that the linear theoretical results agree well with the numerical results, and maximum relative error between them is about 6.58%. Then, by using COMSOL Multiphysics, a series of parametric studies on damping torque, including the effects of the air gap, the thickness of a back iron plate, the location and number of permanent magnets, and the thickness of a conductor plate, were carried out to further examine the linear theoretical formula. The results show the effects of the air gap and back iron plate on the relative error between linear theoretical and numerical results can be ignored, whereas the location and number of permanent magnets and the thickness of the conductor plate have significant influences on the relative error. Finally, a nonlinear theoretical formula was obtained by introducing three modified coefficients into the linear theoretical formula, and its accuracy was verified in some typical cases. It is proved that there is sufficient accuracy to adopt the nonlinear theoretical formula in preliminary design of the eddy current damper with rack and gear to determine the main structural parameters.

Design and evaluation of a hybrid passive–active knee prosthesis on energy consumption

The existing lower limb prostheses with passive knees have disadvantages, causing an asymmetric gait and higher metabolic cost during level walking which is in contrast with a normal gait. However, most existing active knee prostheses need a significant amount of energy. In this paper, a novel hybrid passive–active knee prosthesis (HPAK) that allows passive and active operating modes is proposed, which contains an active motor unit and a novel hydraulic damper with an electrically controlled valve that adjusts the damping torque dynamically during each gait cycle. An energy consumption model was built to evaluate the energy consumption when walking on level ground in three different simulation conditions to, respectively, simulate the complete HPAK, an ordinary active prosthesis (AKP) and an ordinary passive prosthesis (PKP). The results show that, in a cycle, the HPAK consumes only 16.19 J, which is 3.6 times lower than the AKP (58.95 J), and the PKP consumes only 1.24 J due to the novel spring–hydraulic damper structure designed and presented in this paper. These results indicate that the proposed novel hybrid passive–active knee prosthesis can have a positive effect on reducing energy consumption and improving the approximation of healthy gait characteristics when walking on level ground, contrasting with active or passive knee prostheses.

Analytical Approach of a Pure Flow Mode Serpentine Path Rotary Magnetorheological Damper

This paper has two main goals in the development of a novel flow-mode magnetorheological brake (MRB): (1) produce a mathematical model of a flow-mode MRB and (2) predict the torque density of the proposed MRB compared to the other type of MRB. In this design, the flow mode MRB is made by screw pump to make the Magnetorheological Fluid (MRF) flow through the radial and annular channel. The serpentine path flux is developed in the proposed MRB to make the annular channel an active region as well. With the proposed design concept, the work of a pure flow-mode serpentine path MRB can be accomplished. In this study, Finite Element Method Magnetics (FEMM) is used to calculate the magnetic field applied to the active regions and analytical approach used to obtain the output damping torque. The simulation results show that the magnetic fluxes flow through the radial channel and annular channel as well. The radial and annular channel is activated, which led to higher output damping torque. The mathematical modelling shows that the helical angle of the screw pump significantly affects the damping torque. The results show that the output damping torque density can be adjusted from 42.18 N/mm2 in the off-state with 0 rpm to around 40,518.96 N/mm2 at 20 rpm. The torque density of the proposed MRB is higher than the shear mode MRB.

Improvement of Small Signal Stability of SMIB System with Optimized Power System Stabilizer

As electrical power system is a complex system, there are more chances of stability issues may arise. One of the stability issues is Low Frequency Oscillations (LFOs) which makes the system unstable. As these oscillations are having low frequency i.e. large time constant with slowly increasing magnitude, they are referred to small signal stability. The main reason of these oscillations is due to lack of sufficient damping torque. Automatic Voltage Regulator (AVR) action in generator is providing sufficient synchronizing torque for system stability. This is possible with high gain and low time constant AVR which results in reduction of damping torque. Power System Stabilizer (PSS) is used together with AVR for providing necessary damping torque to minimize the LFOs. For effective damping, the PSS performance is improved by optimizing its parameters. In this paper, Single Machine Infinite Bus (SMIB) system is considered for studying the effect of LFOs. The SMIB system is simulated for a step disturbance in reference voltage and the results are carried out for different optimizing techniques Particle Swarm Optimization (PSO), Cat Swarm Optimization (CSO), Teaching and Learning based Optimization (TLBO)

Design of a Motorcycle Steering Damper for a Safer Ride

Powered-two-wheelers (PTWs) are increasingly popular because of their lower cost compared to cars, and therefore the riders’ exposure risk is increasing. Due to their complex dynamics characterized by high non-linearity and inherent instability, PTWs are more difficult to control compared to four-wheeled vehicles. Wobble is a high-frequency instability mode affecting the steering assembly of the PTW, and which often causes the rider to lose control and crash when it occurs. In this paper, we present the design of a new motorcycle semi-active steering damper integrated into the steering column and utilizing a magnetorheological fluid (MRF) for variable damping torque. An analytical model of the concept was first used to perform the preliminary sizing, followed by concept validation using a 3D FE multiphysics magnetic-fluid analysis. The final innovative design offers several advantages compared to traditional steering dampers: (i) a wide range of adjustable damping torque values, with a multiplication factor up to 10 with a maximum electrical current of 2 A; (ii) total integration into the motorcycle steering column enabled by its axial design and limited radius; (iii) a simple chamber geometry that allows for easy manufacture; (iv) longer seal life due to the absence of direct contact between seals and the MRF.

Velocity Planning for Astronaut Virtual Training Robot with High-Order Dynamic Constraints

SUMMARYIn order to improve the training efficiency and establish a multi-person cooperative training simulation system, including “virtual human,” in the process of virtual reality-based astronaut training, it is necessary to plan the velocity at which astronauts carry the target object. A velocity planning algorithm, combining a traditional six-stage acceleration/deceleration algorithm, based on a time-discrete model with high-order dynamic constraints, considering the elastic damping torque of the space suit, is proposed. The described algorithm is verified on MATLAB to prove its feasibility. Compared to other algorithms, the planning time of the proposed algorithm is significantly reduced.