Dynamic Voltage Restorer (DVR)

Overview

At present, among various power quality problem, voltage sag is the problem with the highest frequency and the most serious harm.

The most common causes of voltage sag are as follows:

1）Cause by fault current

When a short-circuit fault occurs in the transmission network or the distribution network, the current increases sharply, causing a voltage sag at the public voltage connection point, and the voltage sag spreads along the gird to cause disturbance to a large number of users.

2）Caused by induction motor starting

When the induction motor is started at full voltage, the voltage value that needs to be drawn from the system is 5-10 times that of the full load operation, this large current will cause a voltage sag when it flows through the system impedance.

3）Caused by lightning strike

Insulator flashover and line-to-ground discharge caused by lightning strikes are the main causes of system line voltage drop. In the rainy season or in thunderous areas, operating equipment exposed to the open air is easily disturbed by lightning

4）Unpredictable accidental events: road construction, traffic accidents, human misoperation, etc.

DVR is currently recognized as an effective series compensation device for keeping the supply voltage of sensitive loads stable. When the system voltage sags or rises suddenly, it uses its own energy storage and inverter devices to output voltages with adjustable phase and amplitude to ensure that the voltage of sensitive loads is still within an acceptable range when disturbed by the system voltage

Working Principle

If the power grid is in a stable state and runs in thermal backup mode, the bidirectional DC/AC inverter controls the charging current through a control algorithm to keep the system in a floating charge state, while the DVR continuously detects the grid voltage. When the voltage drops, the algorithm can detect it within 500us, and quickly control the switch to shut off, cut off the input grid voltage, make the DVR to operate in the compensation output mode, absorb the energy stored in its own super capacitor, inject the AC voltage into the system through the inverter which is consistent with the phase and amplitude of the grid voltage before the drop, and provide high-quality power for sensitive loads in a short time. After the grid voltage recovers, the DVR controls the conduction of the bidirectional thyristor through the control algorithm to realize seamless switching to the grid voltage.

Compensation Effect Diagram

a.The three-phase drop to 0%, the overall waveform of the grid voltage and load voltage, the upper part of the picture is load voltage, and the lower part is gird voltage.

b.The three-phase drop to 0%, the waveform of the grid voltage

c.The three-phase drop to 0%, the waveform of the load voltage

d.The instantaneous detailed waveform of entering voltage compensation, and the time is within 2ms.

Applications

1.Automobile manufacturing, painting, etc.  flexible automatic control and chain supply line management

2.Polymerization processing industry of plastic products, paper industry, glass manufacturing industry, chemical industry-big power consumers

3.IT and Communication Industry-High-value end customers need ultra-high reliability

4.Medical equipment—the sag causes the equipment to work abnormally, affecting the diagnosis, treatment, operation, and even endangering the life of the patient  

5.In the semiconductor manufacturing industry, a short-term voltage sag will cause the produced chips to become defective products, resulting in huge losses

6.Widely used in the precision processing industry, the microprocessor of the control system of the equipment is particularly sensitive to voltage sags

7.Most contactor and relay manufacturers specify a loss of voltage protection of 0.5p.u., which will exit and disconnect if the duration exceeds 1 cycle

8.When the voltage drop depth supplied to the induction motor is greater than 30%, the electromagnetic torque will be smaller than the mechanical torque, the motor speed will decrease, and the current drawn will increase

Technical Parameters

Model Descriptioon

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