DVR Sliding mode control strategy of dynamic voltage restorer
The dynamic voltage restorer (DVR) plays a crucial role in enhancing power quality, particularly for sensitive loads that are vulnerable to voltage sags. This blog will explore the sliding mode control (SMC) method applied in the DVR voltage control strategy. We will delve into the operational principles of DVR, its components, and the implementation of SMC within a MATLAB simulation environment.
Understanding Dynamic Voltage Restorer (DVR)
The dynamic voltage restorer is a power electronics device designed to protect sensitive loads from voltage sags that can occur in electrical distribution systems. Voltage sags are temporary reductions in voltage, which can adversely impact sensitive electronic equipment. A typical scenario involves a distribution feeder with two lines: one serving domestic loads and the other catering to sensitive loads like computers and servers.
When a fault occurs in the distribution system, it can lead to voltage sags that affect the sensitive loads. To mitigate this, it is essential to maintain the voltage at the load side at a nominal level, typically one per unit. The DVR is utilized to inject the necessary voltage during these disturbances, ensuring that sensitive loads remain unaffected.
Components of a Dynamic Voltage Restorer
The DVR consists of several key components that work together to maintain voltage stability:
DC Energy Storage: This component provides the necessary energy for voltage injection during faults.
IGBT Converter: The Insulated Gate Bipolar Transistor (IGBT) converter is crucial for converting the DC energy into the required AC voltage.
Control System: The control system continuously monitors the distribution feeder voltage and determines the amount of voltage to inject to maintain stability.
The Need for Sliding Mode Control
Sliding mode control is a robust control strategy that is particularly effective in dealing with system uncertainties and non-linearities. In the context of a DVR, SMC ensures that the voltage injected during sags is precisely controlled, thus maintaining the load voltage at the desired level.
The SMC method operates by defining a sliding surface that the system states should converge to. Once the states reach this surface, they are maintained on it, ensuring stable operation despite disturbances.
Implementing DVR in MATLAB
To implement the DVR system using MATLAB, we first need to define the parameters of our electrical system. This includes specifying the grid voltage, load characteristics, and the fault conditions.
In our simulation, we consider a scenario where a fault occurs, leading to a voltage sag. During this period, the DVR is activated to inject voltage. The process involves several steps:
Voltage Measurement: The load voltage is continuously monitored and measured.
Conversion to Per Unit: The measured voltage is converted into per unit values to facilitate control.
ABC to DQ Conversion: The three-phase voltage (ABC) is transformed into a two-coordinate system (DQ) for easier control.
Sliding Mode Control Application: The control algorithm compares the reference voltage with the actual measured voltage and adjusts the injected voltage accordingly.
Conversion Back to ABC: The control output is converted back from DQ to ABC to be injected into the system.
Simulation Results
The simulation provides valuable insights into the performance of the DVR with the sliding mode control strategy. During the simulation, we observe the grid voltage, load voltage, and the injected voltage over time.
Upon introducing a fault at 0.1 seconds, the system experiences a voltage sag. However, the DVR promptly injects the required voltage, maintaining the load voltage at one per unit. This demonstrates the effectiveness of the DVR in mitigating voltage sags.
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