⚡ Dynamic Voltage Restorer (DVR): DVR Sliding Mode Control Strategy of Dynamic Voltage Restorer
- lms editor
- 12 hours ago
- 3 min read
A Dynamic Voltage Restorer (DVR) is one of the most effective custom power devices used in power distribution systems to protect sensitive loads from voltage disturbances such as voltage sags, swells, and harmonics. It operates by injecting a compensating voltage in series with the supply to maintain a constant load voltage, typically at 1 per unit (pu).
🔍 Why Do We Need a DVR?
⚠️ Voltage sags commonly occur due to:
Short-circuit faults
Sudden connection of large loads
Motor starting
Grid disturbances
📉 Even a short-duration sag can:
Trip sensitive equipment
Damage power electronic devices
Interrupt industrial processes
✅ The DVR acts as a fast-acting voltage compensator, ensuring uninterrupted and high-quality power supply.
🏗️ Basic Operating Principle of DVR
🔌 The DVR is connected in series between the supply and the sensitive load.
🧠 Working concept:
Continuously monitors grid voltage
Detects voltage sag/swell or harmonics
Injects an appropriate compensating voltage
Maintains load voltage at rated value (1 pu)
📌 The load never “sees” the disturbance.
🧩 Key Components of a DVR System
🔋 DC Energy Storage
Stores energy required during voltage sag
Can be:
Batteries
Supercapacitors
DC-link capacitors
⚙️ Voltage Source Converter (IGBT-Based)
Converts DC power to AC
Injects required compensating voltage
High switching frequency ensures fast response
🌀 Series Injection Transformer
Injects DVR voltage into the distribution line
Provides isolation and voltage matching
🎛️ Series Filter (LC Filter)
Smoothens inverter output
Reduces switching harmonics
📐 Step 1: Per-Unit (PU) Conversion
🔢 Measured load voltage is converted into per-unit values✔️ Simplifies controller design✔️ Improves numerical stability
🔄 Step 2: ABC → DQ Transformation
🧭 Three-phase voltages (ABC) are transformed into:
VD (Direct-axis voltage)
VQ (Quadrature-axis voltage)
📌 Advantages:
Decoupled control
Easier regulation
Reduced complexity
🎯 Step 3: Reference Comparison
⚖️ VD → compared with 1 pu reference
⚖️ VQ → compared with zero
This ensures:
Correct voltage magnitude
Proper phase alignment
🛠️ Sliding Mode Control (SMC) in DVR
🧲 Why Sliding Mode Control?
✔️ Robust against parameter variations✔️ High disturbance rejection✔️ Fast dynamic response
⚙️ How SMC Works
Defines sliding surfaces for VD and VQ
Forces system states to converge to reference
Maintains stability even during faults and harmonics
📌 Ideal for nonlinear power electronic systems like DVRs.
🔁 Step 4: DQ → ABC Conversion
🔄 Controlled VD and VQ are transformed back into three-phase reference voltages
⚡ These references are:
Compared with actual load voltage
Used to generate PWM pulses
🎚️ Voltage Injection Process
🧩 The series inverter injects:
Missing voltage during sag
Opposite voltage during harmonic distortion
🎯 Result:
Load voltage remains constant at 1 pu
⚠️ Case 1: Voltage Sag Condition
Grid voltage drops suddenly
DVR detects sag within milliseconds
Injects compensating voltage
Load voltage stays constant
✔️ No interruption to sensitive load
🎼 Case 2: Harmonic Injection
Nonlinear loads introduce harmonics
DVR injects opposing harmonic voltage
Cancels distortion
📉 THD is significantly reduced📈 Power quality is improved
📊 Performance Highlights of DVR with SMC
✅ Fast dynamic response✅ Accurate voltage regulation✅ Strong harmonic mitigation✅ Robust under grid faults✅ Suitable for real-time implementation
🏁 Conclusion
🚀 The Dynamic Voltage Restorer with Sliding Mode Control is a powerful solution for modern power distribution systems. By combining:
Real-time voltage sensing
Per-unit normalization
DQ-frame control
Sliding Mode Control
Series voltage injection
…the DVR ensures that sensitive loads always receive a clean, stable, and uninterrupted voltage supply, even under severe grid disturbances.
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