What is Grid Synchronization?

Synchronization is the process of matching the voltage and frequency of a generator or other source to a running network. An AC generator cannot deliver power to an electrical grid unless it is running at the same frequency as the network. If two segments of a grid are disconnected, they cannot exchange AC power again until they are brought back into exact synchronization.

A direct current (DC) generator can be connected to a power network by adjusting its open-circuit terminal voltage to match the network voltage, by either adjusting its speed or its field excitation. The exact engine speed is not critical. However, an AC generator must match both the amplitude and the timing of the network voltage, which requires both speed and excitation to be systematically controlled for synchronization.

In modern grids, synchronization of generators is carried out by automatic systems.


Problems in India?

In India, the need for a good grid synchronization is even more than countries like the US because of the following reasons –

  1. Varying voltage – The voltage in India is one of the most unstable in the world which is ranging from 110V to 270V. This variance adversely affects the inverter and can cause damage to its internal components.
  2. Frequency – Frequency variance(40-60Hz) is as extreme as voltage variance and can also affect the inverter performance adversely.
  3. Power Cuts  – In India the power cut problems are not new. The power cuts can vary from 2 to many times a day depending upon the area one is living and can again hinder the performance of the inverter.


Why is Grid Synchronization necessary is necessary and which scheme to choose?

Now, this is where Grid synchronization come into the picture. The purpose of synchronization is to monitor, access, enable, and automatically take the control action to prevent the abnormalities of voltage and frequency by the minimization of difference in voltage, frequency, and phase angle between the corresponding phases of the generator output and grid supply.

India has unstable grid. It keeps varying in different regions and states of India. The voltage varies from 110 to 270V(already stated),  because of that grid feed is affected by unstable voltage which directly affects the inverters.

A good synchronization scheme must:

  1. Proficiently detect the phase angle of the utility signal
  2. Track the phase and frequency variations smoothly
  3. Forcefully reject disturbances and harmonics.

These factors, together with the implementation simplicity and the cost are all important when examining the credibility of a synchronization scheme.