The concept of electric springs (ESs) has been proposed as a new solution for stabilizing power grid fed by intermittent renewable energy sources. With a battery or active power source (DC, on the inside), the ESs can provide both active and reactive power compensations. So far, three typical topologies of single-phase ESs have been reported. Unlike traditional devices where power generation follows the load demand, the ESs are associated with non-critical loads form the so-called smart loads that transfer the fluctuated power to the non-critical loads, adaptively, according to the intermittent nature of power generation. After reviewing the main control strategies of single-phase ESs, the paper analyzes their advantages and disadvantages as well as their suitable applications. Comparisons among different control strategies on a specific topology version are implemented. Finally, conclusions and possible future trends are pointed out.

The conventional space vector pulse width modulation (SVPWM) algorithm is mature and widely used in the control of three-phase inverters. As we know, the position of the voltage vectors can be seen directly by human eyes, which can be used to replace the existing way for sector selection in the conventional SVPWM algorithm. Based on the fact, a novel method simulating human eye recognition for sector selection of SVPWM is proposed in this paper. In the real application, machine can replace human eyes, and it can 'see' the sector step by step in which the voltage vector is located, and immediately give the switching time of the two non-zero voltage vectors. Theoretically, it can save the running time and complexity of the SVPWM algorithm reflected in the situation that multiple inverters are connected in parallel with the number of voltage vectors being increased. The feasibility of the proposed SVPWM algorithm has been validated by both simulation and experiments, which offers the possibility of the application in the multiple or multilevel converters. INDEX TERMS SVPWM, machine vision, voltage vector, multiple inverters.