Design Of A Kind Of DC Energy-feedback Electric Load Based On Phase-shifted Full Bridge

With the current global energy crisis, shortage of energy resources is the primary factor that hampers the development of Chinese economy. The only way to solve this problem is to explore and recycle new energy source. With the advantages like small volume, light weight, energy saving, less installation space and high test performance, DC energy-feedback electric load is widely used in testing and aging of DC power supply products. It can save and recycle electric energy by converting DC electric power into AC electric power which can be sent back to the grid. This paper mainly analyses the structure of system topology, the working principle and the controlling strategy. It also explains the design of DC feedback electric load based on the phase-shifted full bridge.Firstly, this paper analyses the working principle of DC feedback electric load and gives the method of this system by comparing various design proposals. The system topology is mainly composed of a DC/DC converter and DC/AC converter. Both the converters adopt single phase full bridge. Because hard switch has the disadvantages like huge switching loss, serious EMI and weakness in realizing high frequency DC/DC converter adopts a Zero voltage switch control method of phase-shifted full bridge with a clamp diode in the primary side. DC/AC converter adopts a method of single polarity SPWM modulation. Based on the traditional double closed-loop control method, which means that the variable of outer loop is voltage and that of inner loop is current, DC/AC converter adopts a new control technology that combines grid voltage as the feed-forward method and zero current tracking control method. By this control strategy, the system has quick transient response and is more stable.Secondly, this paper introduces the hardware circuit and software design of DC feedback electric load in detail. The hardware concludes the design process of main power circuit and the types of selection parameters, the diver circuit, the detection circuit, the control and displayer circuit. The core chip of control system is TMS320F28335which is the mainstream DSP of TI. Auxiliary logic control unit uses EPM3604A which is the CPLD chip of Altera. TMS320F28335has a strong enhanced PWM, enhanced CAP module and high-speed floating-point arithmetic functions, with that, we can compile software program more convinces and reduce the development cycle. The design of software gives the whole system control process, it focus on the digital implementation of phase-shifted PWM, single polarity SPWM and PLL technology of grid-connected.Finally, it gives the result of simulation model by the Simulink module of Matlab. Then it analyses the experimental waveforms based on the experimental prototype of a3.5KW DC feedback electric load. It demonstrates the efficiency of design. The DC feedback electric load can simulate the real load. Its output current is approximately sinusoidal, has small harmonic content and can connect to the grid reliably. The power factor is close to1.0that basically meets the requirement of design and the system can operate stably and reliably.