Control and Performance Analysis of a Single-Stage Utility-Scale Grid-Connected PV System

IEEE SYSTEMS JOURNAL, VOL. 11, NO. 3, SEPTEMBER 2017

ABSTRACT:

For utility-scale photovoltaic (PV) systems, the control objectives, such as maximum power point tracking, synchronization with grid, current control, and harmonic reduction in output current, are realized in single stage for high efficiency and simple power converter topology. This paper considers a highpower three-phase single-stage PV system, which is connected to a distribution network, with a modified control strategy, which includes compensation for grid voltage dip and reactive power injection capability. To regulate the dc-link voltage, a modified voltage controller using feedback linearization scheme with feedforward PV current signal is presented. The real and reactive powers are controlled by using dq components of the grid current. A small-signal stability/eigenvalue analysis of a grid-connected PV system with the complete linearized model is performed to assess the robustness of the controller and the decoupling character of the grid-connected PV system. The dynamic performance is evaluated on a real-time digital simulator.

 

KEYWORDS:

  1. DC-link voltage control
  2. Feedback linearization (FBL)
  3. Photovoltaic (PV) systems
  4. Reactive power control
  5. Small signal stability analysis
  6. Voltage dip.

SOFTWARE: MATLAB/SIMULINK

 

BLOCK DIAGRAM:

One of the four 375-kW subsystems.

Fig. 1. One of the four 375-kW subsystems.

  

EXPECTED SIMULATION RESULTS:

(a) PV array voltage for MPPT. (b) PV array (PPV) and grid injected real power (Pg). (c) Grid injected reactive power (Qg).

Fig. 2. (a) PV array voltage for MPPT. (b) PV array (PPV) and grid injected real power (Pg). (c) Grid injected reactive power (Qg).

Grid injected currents and THD.

Fig. 3. Grid injected currents and THD.

PV system response to voltage dip in grid.

Fig. 4 PV system response to voltage dip in grid.

PV system response to a three-phase fault at bus 3.

Fig. 5. PV system response to a three-phase fault at bus 3.

PV system response to an LG fault.

Fig. 6. PV system response to an LG fault.

Pg  response of the whole 1.5-MW PV system.

Fig. 7. Pg  response of the whole 1.5-MW PV system.

 

CONCLUSION:

The proposed modified dc-link voltage controller with FBL technique, using INC MPPT, and real and reactive power controls with enhanced filter for compensation for grid voltage dips has been tested at different insolation levels on a real-time digital simulator (RTDS). Small-signal analysis of a PV system connected to an IEEE 33-bus distributed system is performed. The results from simulation and eigenvalue analysis demonstrate the effectiveness of the FBL controller compared with the controller without FBL. It is found that the FBL controller  outperforms the controllerwithout FBL, as the FBL controller’s  performance is linear at different operating conditions. With grid voltage dip compensator filter, the dynamic performance is much improved in terms of less oscillations and distortion in waveforms. In addition, the eigenvalue analysis shows that the effect of the disturbance in distribution system is negligible on PV system stability as the eigenmodes of the PV system are almost independent of the distribution system. This has been also confirmed by three-phase fault analysis of distribution system in RTDS model. The controller performance is also validated on 4×375 kW PV units connected to the distribution system.

 

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