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Nt1310 Unit 5 Lab Report

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Modelling of the series transformer, VSC and LC filter is presented in this section. A time-varying threephase utility voltage is inconvenient for controller implementation. Therefore, all the ac parameters were converted into synchronous reference frame using the park transformation [12]. The open loop plant model was derived and a relationship between Vinv and Vc was obtained (see Fig. 2). Applying voltage balance equation to loop 1 of Fig. 2 and current balance equation to node 1, the state space equations (1) and (2) were obtained: Considering the above governing equations of the plant model ((3), (4) and (5)), the open loop state space representation was obtained and is given in Fig. 3. Notations are as same as that is give in Table 1 …show more content…

The respective Kp_outer and KI_outer of the outer loop were calculated using the characteristic equation of the outer loop given below: Phase Detection A phase-locked loop (PLL) generates a signal that has a fixed relation to the phase of a reference signal and is given in Fig. 4. A phase locked loop responds to both the frequency and the phase of the input signals, automatically raising or lowering the frequency of the controlled oscillator until it is matched to the reference in both frequency and phase. Here three phase PLL was implemented with three basic functional blocks: the phase detector, a PI controller and a voltage controlled oscillator. The phase detector is a circuit capable of delivering an output signal that is proportional to the phase difference between its two input signals. The PI controller is a low pass filter and used to suppress high frequency component and provide dc controlled signal to voltage controlled oscillator which acts as an integrator. The output of the PI controller is the inverter output frequency that is integrated to obtain inverter phase angle θ. When the difference between grid phase angle and inverter phase angle is equal, Vq = …show more content…

Simulation Study The smart distribution transformer and its controllers were evaluated through simulations using PLECS simulation platform. The system specifications used to design the simulation model are given in Table 3. Controller Results Considering a specific transformer loading condition, simulation results were taken for four different voltage injections from (230 V-6%) to (230 V-3%), (230 V-3%) to 230 V, 230 V to (230 V+3%) and (230 V+3%) to (230 V+6%). Fig. 6 shows the variation of V* 2_d and V2_d for all the above mentioned voltage injections. Similarly Fig. 7 shows the R.M.S. voltage of the modified transformer secondary terminal, Va_2 for a voltage step from 230 V to (230 V+3%). The inner and outer controller behavior for the above transient condition is given in Fig. 8, it can be seen that the output voltage takes nearly one cycle to settle whereas the inner loop is much faster than the outer loop and it settles before the outer loop. Case

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