On fig1. the basic circuitry of the new converter displayed. There are three sub-converters (cells) in the circuit each represented by a low frequency bridge rectifier and a full bridge high frequency inverter made by four power switches. One leg of the bridge has a pair of GaN FETs while the other leg consists two fast IGBTs. The inverter drives a transformer across serial-parallel resonant network which shapes the magnetizing current to the ideal waveform for maximum power transfer across the transformer and provides low loss commutation of active switching devices. Since this resonant LLCC2 converter is a strongly nonlinear system therefore it is pretty difficult to control and no control devices available on the market. We have developed a DSP based digital control for maintain the operational parameters of the converter and regulating charge characteristics.
Even with the fastest state-of-the-art power semiconductor devices the losses would be pretty high due to the operational frequency of the converter. Only in case of full soft ZV/ZC switching across the whole operational range it can match to the target conversion efficiency otherwise bulky heatsink would be required affects the power density. Another advantage of the soft switching is that the dV/dt stresses of the components greatly reduced which lowers the electro-magnetic interference issues. DSP has information about the input Voltages, input Currents, resonant tank parameters and charging rates as well as actual load balance of the charging cells. Implemented complex nonlinear digital control changes the operational frequency, pulse width with dead-times and phase shift of each individual cells maintains the best conversion point of the converter. Three individual cells have interleaved high-frequency operation by proper timings of switch drive pulses which fact becomes important when all cells connected in parallel mode (single phase operation).
         A very unique feature of the proposed converter is that the AC Powering method could be selected easily by changing only the AC line cable (fig2.). Actual configuration of individual cells determined by the power plug arrangement. The input power socket is fixed while two types of power cables can be used for AC connection, one type with four wires (L1, L2, L3, PE) for the three phase operation and another type with three wires (L, N, PE) for the single phase operation. Probably it is the easiest and most failure-proof way of 3/1 phase operational selection by the end user without the risk of misconfiguration risks (fig3.).

        True Three Phase powering: 3 X 200V – 3 X 480V (nominal 400V) provided by the proper AC line cable to the L1, L2, L3 inputs. All of three converters work in actively balanced “Y” configuration. Neutral connector is not used so the “stair point in the Y circuit” is not exposed outside. The control circuitry recognizes the actual type of connection (3/1 phase) and automatically reconfigures the converters for the optimal operation modes. Separated high-speed current and voltage feedback loops by individual cells of the control DSP maintain the best balancing of load between the line conductors. Due to the high voltage operation a relative small size power cable is required which
could mean much less copper cross-section area requirement and a better cost-effective power distribution. Three phase operation with high power factor and low line current shape distortion has the advantage of best interfacing to power sources, AC distribution lines or diesel generators. The converter is able to handle the worst voltage balance problems across the line conductors and even remains operational with two phases*.