Page 88 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

Three-Phase Photovoltaic Systems: Structures, Topologies, and Control 75

Ref.
1 PR Sampled ref.
Comp.
Internally µC IO
0.5 Carr. generated
Carrier

PWM
0 t 0 t
PWM
t t
T T
(a) (b)

FIGURE 4.5 PWM pulse train generation: (a) implementation with analog comparator, (b) implementation
using a PWM unit in the microcontroller (μC).

Carrier Zero-order
hold
Scope
<=
+ +
Ref_U RO
<=
+ +
RO1
Ref_V

<=
+ +
RO2
Ref_W

Carr_max + – 0

max
ST-PWM
3rd harmonic THI-PWM
SVM
min – + + + 0.5 DPWM-Min
DPWM-Max
Selector1
Carr_min

®
FIGURE 4.6 Simulink model of different modulation techniques.
quantization should be equal to the counter time base. The reference signals are generated as three
sinusoidal waveforms where the peak-to-peak amplitude can vary between 0 and 1 or −1 and 1,
depending on the settings of the carrier wave. In closed-loop application, the control algorithm gen-
erates these reference signals. The three comparator blocks are generating the PWM output signal of
the modulator. In order to simulate the behavior of the improved modulation techniques, the injec-
tion of zero-sequence voltage has to be performed. For the THI-PWM method, a sinusoidal with
triple frequency has to be added to the three reference waveforms, as illustrated in Figure 4.6. In case
of closed-loop application, this zero-sequence waveform should be generated based on the phase/
frequency of the grid voltage, which is supplied by the grid synchronization block. For simulation
of the SVM and DPWM methods, a “min” and “max” block can be used. These blocks have as input