Soft machines typically exhibit slow locomotion speed and low manipulation strength because of intrinsic limitations of soft materials. Here, we present a generic design principle that harnesses mechanical instability for a variety of spine-inspired fast and strong soft machines. Unlike most current soft robots that are designed as inherently and unimodally stable, our design leverages tunable snap-through bistability to fully explore the ability of soft robots to rapidly store and release energy within tens of milliseconds. We demonstrate this generic design principle with three high-performance soft machines: High-speed cheetah-like galloping crawlers with locomotion speeds of 2.68 body length/s, high-speed underwater swimmers (0.78 body length/s), and tunable low-to-high-force soft grippers with over 1 to 103 stiffness modulation (maximum load capacity is 11.4 kg). Our study establishes a new generic design paradigm of next-generation high-performance soft robots that are applicable for multifunctionality, different actuation methods, and materials at multiscales.

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Similar to other major electrical apparatuses, the reliability and stability of the DC network is becoming the most important issue when using voltage source converter based multi-terminal DC (VSC-MTDC) system for offshore wind power integration. A coordinated control strategy of VSC-MTDC named master-auxiliary is proposed by combining the advantages of the voltage margin and voltage droop control. This strategy has three advantages: the master converter station with the constant DC voltage control can provide reference to the system DC voltage and is helpful for the stabilization of DC voltage; the integrated control of the DC voltage in both master and auxiliary converter stations are helpful for providing adequate active power control and restrain large power variation; the active power control (APC) converter station can serve as a backup for the DC voltage control in abnormal conditions. In order to guarantee the reliability and stability of the system under various operating conditions, this paper introduces the priority of DC voltage control to the coordination control strategy. Moreover, a parameter optimizing method of controllers for this strategy is also proposed. Finally, the effectiveness of the master-auxiliary control is verified by simulations under normal and abnormal conditions. Index Terms-voltage source converter (VSC), DC transmission, multi-terminal DC (MTDC), coordination control, master-auxiliary control. His researchinterests include the control strategy of multi-terminal dc transmission and the control strategy of HVDC system etc. Ke-jun Li(Corresponding author) (M'07 )received the B.S. and M.S. degrees from Lee has been involved in research on renewable energy, power flow, transient and dynamic stability, voltage stability, short circuits, relay coordination, power quality analysis, demand response, on-line equipment protection, monitoring, and control system, and utility deregulation. He has served as the primary investigator (PI) or Co-PI of over seventy funded research projects. He has published more than one hundred sixty (160) journal papers and conference proceedings. He has provided on-site training courses for power engineers in Panama, China, Taiwan, Korea, Saudi Arabia, Thailand, and Singapore. He has refereed numerous technical papers for IEEE, IET, and other professional organizations. Prof. Lee is a Fellow of IEEE and registered Professional Engineer in the State of Texas. Zhao-hao Ding (S'11) received his Bachelor of Science degree in 2010 from Shandong University, Jinan, China. He is currently pursuing his Ph.D. degree at University of Texas at Arlington (UTA). He is also a research member of Energy Systems Research Center (ESRC). His area of interest includes renewable energy integration, bulk power system planning and operation, microgrid operation and control, power market and stochastic optimization.