Michael Frisch, Technical Marketing Manager, Vincotech GmbH (Germany)
Temesi Ernö, Manager Application Engineering, Vincotech Kft. (Hungary)
Vincotech is able to offer a wide spectrum of power modules for solar applications. The following paper provides application support information for transformer-less single phase solar inverter based on the Vincotech power module: FZ06BIA045FH-P897E. The module is able to carry an output power of 6kW but for efficiency optimization a nominal power of 3KW is recommended.
The topology is supporting the following required functions:
The booster is active when the solar voltage is below the peak of the power grid voltage.
In this case the booster (T5, D8,9) sets the MPP for the photo voltaic solar cell (PV). When the PV MPP voltage reaches the peak of the line, the bypass diode (D7) cuts boost stage losses. The adjustment of the MPP has to be controlled by the output H-bridge inverter. The output of the booster is the DC link voltage, filtered by a capacitor (C4). This capacitor should be a parallel composition of a high tangent delta film capacitor and an electrolytic capacitor. The high frequency capacitor have to be placed close to the module pins to limit overvoltage shoots at turn off of the MOS-FET (T2 and T4), while the electrolytic capacitor should be sized for the 100Hz power fluctuation of the 50Hz mains.
The H-bridge works by asymmetric unipolar modulation. The high side of the asymmetric H-bridge should be driven by 50Hz half-wave dependent on the polarity of the mains while the opposite low side is PWM modulated to form the mains sinusoidal shape.
The 10nF ceramic capacitor (C5) should be placed close to the gate-emitter pins of the high side transistors to eliminate cross through conduction due to fast switching of the low side transistors. A negative gate turn off voltage on the high side gate may also improve switching performance. The low side gate drive resistor should be selected to adjust the speed of MOSFET switching.
However one of the inductors is connected with opposite winding direction in one phase connection. In this manner the utilization of the inductor becomes more effective (Fig. 3) than with single winding (Fig. 4) inductors and delta capacitors, while still keeping the common mode voltage noise between line and DC link to an even lower level.(Vcmd).
If the output current sense is put before the inductor (L1), the test current will be the sum of output current to grid and CM (common-mode) current to C1 and C2. So two current senses have to be used and put on the output line before L1. The output current to grid is determined by the sum of the two currents.
For a conclusive module design the following issues are a must:
Fig. 6 shows the Vincotech standard module flowSOL0-BI (P896-E01) which incorporates the advantages listed previously:
A simulation based on measured values of this circuit shows the following results (here are only the semiconductor losses considered!):
The total EE for the module (booster + inverter) is 98,8%. This shows that a total efficiency, including the passive components, of 98% is reachable. Fig. 8 also shows that the efficiency of the alternative full IGBT solution drops significantly at partial load.