12
main SPS. They are all flyback converter. However, the grid SPS includes a rectifier to
convert grid AC voltage to a DC voltage but the main SPS is multiple output circuits.
Taking main SPS to explain the operation of flyback converter as a example. When Q13 is
on, all rectifier diodes are on “open” status and all output capacitors supply currents to the
load. The primary coil of the transformer will become a pure inductor and the primary
current will linearly increase to store energy in the coil. When Q13 is off, primary current
will stop and all rectifier diodes will turn to “close” status. It will release the stored energy
from the primary coil of the transformer to the secondary coil to supply loads. At the same
time, it will charge output capacitors in15V_DRV,
12V, +5V.
The +15V_DRV,
12V, +5V power supplies stable voltage to all kinds of ICs and other
devices such as HCT. The +12V_RLY is supplied to fans and relays.
4.2 Boost circuit
Figure 4.4 Boost circuit
As shown in the Figure 4.4, when Q1 is on, the current will increase to store energy in
choke(L2) and capacitor C7 will supply power to the load. When the Q1 is off, the choke
will release energy to BUS. Therefore, we can control the current in chokes (input current)
by regulating the time of Q1 on and off. In this way, we can control the input PV voltage by
regulating the cycle of the Q1 and
executive
MPPT function.
4.3 Inverter
The input of the full bridge inverter topology is DC voltage,
the DC BUS
, and the output is
an AC voltage, as shown in the Figure 4.5. When Q3 and Q4 are on while Q2 and Q5 are
off, the voltage of the bridge midpoint is +BUS. When Q3 and Q4 are off and Q2 and Q5
are on, the voltage of the midpoint bridge is –BUS. We can get any voltage waveform
bBUS and –BUS voltage and any frequency from π filter output by regulating the
cycle of Q2/Q3/ Q4/Q5, including sine wave form.
L5,C10,C11,C12 consists of a inverter filter to eliminate the EMI of the power to load.