The error is compensated by a Pi-integrator to achieve stable output voltage under steady-state operation. The outer control loop uses the output voltage as a feedback signal, which is compared with a reference signal. 24.14, there are two control loops: an outer and an inner. In an instantaneous voltage feedback SPWM control, the output voltage is continuously compared with the reference signal improving the dynamic performance of the UPS inverter.īetter performance even with non-linear and step-changing loads can be achieved by multiple control loop strategies. These approaches control only the amplitude of the output voltage and are good only at high frequencies. The average approach is basically the same but, the sensed voltage is converted to an average value and after that, is compared with a reference signal. In natural sampling type, the peak value of the output voltage is detected and compared with a reference voltage in order to obtain the error, which is used to control the reference to the modulator. The sinusoidal PWM (SPWM) can be of natural sampling type, average type, or instantaneous type. Analog techniques are used in continuous approach. The feedback control can be continuous or discontinuous. This strategy uses a single feedback loop to provide well-regulated output voltage with low THD.
The advantage of this method is low output voltage harmonic and robustness.
This method can be utilized for both single-phase and three-phase systems.
The most common switching technique is Sinusoidal PWM. Other factors considered for a good control technique are nearly zero steady-state inverter output voltage error, good voltage regulation, robustness, fast transient response, and protection of the inverter against overload under linear/non-linear loads. In addition, it should provide the proper mechanism to recharge the battery set and maintain high input power factor and low total input current harmonic distortion. The main task of the control system in a UPS unit is to minimize the output voltage total harmonic distortion in different loading profiles. Adel Nasiri Ph.D., in Power Electronics Handbook (Third Edition), 2011 24.5 Control Techniques
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