Soft Switched Interleaved DC/DC Converter as front-end of Multi Inverter Structure for Micro Grid Applications

ABSTRACT:

An isolated four channel DC/ DC converter with zero voltage switching (ZVS) is proposed as front-end of multiple inverter structures to integrate renewable and other low voltage energy sources to micro grid. Interleaving technique is adopted to connect each module of proposed converter to a common dc source. This dc source can be a fuel cell stack, PV panels,  battery or any other low voltage dc source. All four channels are interleaved and phase shift of 90o is provided between the gate signals of each channels which reduces the input current ripple.Output port of the proposed converter provide four isolated and regulated dc voltages. These isolated dc sources can be connected in series or parallel or series-parallel manner to obtain required dc link voltage of various inverter structure. Issues like capacitor voltage balancing of diode clamped multilevel inverters can overcome through proposed converter. By incorporating coupled inductor for isolation and energy storage along with voltage multiplier circuit, proposed converter can achieve higher voltage step up with lower turns ratio and lower voltage stress at moderate duty ratio. Hence MOSFETs of low voltage rating (low RDS(ON)) can be utilized to reduce conduction loss. A 2kW prototype of proposed interleaved DC/DC converter is developed and tested with diode clamped three level inverter, five level inverter and three phase two level inverter to verify the design.

 

KEYWORDS:

  1. DC-DC Converter
  2. Zero voltage switching
  3. Active clamp
  4. Interleaving
  5. Coupled inductor
  6. High voltage gain

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Proposed Interleaved DC/DC Converter.

 

EXPECTED SIMULATION RESULTS

 Fig. 2. Experimental results at full load for Vin = 55V, (a) Gate signals for main switches of all four channels which are phase shifted by 90o (b) Gate signals for main and clamp switches of channel-a and channel-b. (c) Input current drawn by individual channels at full load (d) Resultant input current drawn from the input source at full load by interleaving operation of all four channels (e) Voltage stress across the main switches of all four channels at full load (f) Soft turn on (ZVS) of main and clamp switches of channel-a, ZVS turn on region is highlighted (g) Voltage stress across the voltage multiplier diodes Da1 and Da2 of channel-a along with input current of same channel (h) Voltage stress across the output diode Dao of channel-a along with voltage stress of diode Da1.

Fig. 3. Experimental results: (a) Phase voltage and current of three level inverter feeding R-L load of 0.85 power factor (b) Regulated and balanced dc link voltage of 3 level diode clamped inverter (c) Phase voltage and current of 5 level diode clamped inverter feeding to R-L load of 0.85 power factor (d) Balanced DC link voltage of five level diode clamped inverter which is regulated by proposed converter (e) Line voltage and current of 2 level full bridge inverter feeding R-L load of 0.85 power Factor.

 

CONCLUSION:

An isolated 4-channel interleaved dc/dc converter with soft switching and high voltage step up gain is proposed as a front end of multiple inverter structures. Proposed converter makes use of isolated coupled inductor and dual voltage multiplier circuit to achieve voltage step up with lower voltage stress on devices. Active clamp circuit is used to clamp the voltage spike on MOSFETs and also to provide soft turn on for MOSFET switches. Interleaved operation enhanced the power output and reduces the input current ripple. Modularity of proposed converter is an added advantage. Four isolated output port of proposed converter can be connected in series, parallel or series-parallel combination to obtain required dc link voltages of multiple commonly used inverter structures like three phase two level inverter, three level NPC and five level NPC inverter structures. Proposed converter can overcome the capacitor voltage balancing issues of five level and three level NPC inverters without any additional voltage balancing circuits. Feasibility of same is experimentally verified and results are shown. By using MOSFETs of low on state resistance, conduction losses are reduced in proposed converter. A 2kW prototype of proposed converter is build and results are verified. Maximum efficiency of proposed converter is found to be 95.83%.

 

REFERENCES:

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