{blockLibraryPP_blocksPP_FF_PhysicalSS_ModelingFF_ElectricalFF_ControlFF_GeneralSS_ControlFF_PWMSS_GeneratorSS_OO_2-LevelLL_PP_label}

Block {blockLibraryPP_blocksPP_FF_PhysicalSS_ModelingFF_ElectricalFF_ControlFF_GeneralSS_ControlFF_PWMSS_GeneratorSS_OO_2-LevelLL_PP_label} generates pulses for a pulse width modulation (PWM) converter using a two-level topology. The unit can control switching devices (FET, GTO or IGBT) of three different types of converters: single-phase half-bridge (1 arm), single-phase full-bridge (2 arms) or three-phase bridge (3 arms).

The reference signal (U_ref), also called the modulating signal, is associated with a symmetrical triangular carrier. When the reference signal is larger than the carrier, the pulse for the upper switching device has a high level (1), and the pulse for the lower one has a low level (0).

To control a single-phase full-bridge device, you can select unipolar or bipolar PWM modulation. With unipolar modulation, each arm is independently controlled. The second reference signal is generated inside the converter by shifting the phase of the original reference signal by 180 degrees. When using bipolar modulation, the state of the lower switch of the second arm is the same as the state of the upper switch of the first arm, and the state of the upper switch of the second arm is the same as the state of the lower switch of the first arm. Unipolar modulation provides the best quality of the AC waveform, but bipolar modulation creates a very slightly varying common-mode voltage.

The figure shows three sampling methods for the reference signal U_ref. The natural sampling method simulates the behavior of an analog implementation of a PWM oscillator. Using two uniform sampling methods, U_ref can be sampled twice at both the minimum and peak of the carrier, or only once at the minimum of the carrier. The first method is called asymmetric sampling or the double-edge method. The second method is called symmetric sampling or the single edge method.

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