What is a grid-connected PV system?

1. Introduction

Distributed grid-connected PV system is a power generation method that uses PV modules to directly convert solar energy into electrical energy, and can guarantee the stability and reliability of power generation and the quality of power supplied to the distribution network to a certain extent. It is a new, environmentally friendly power generation system with long-term development prospects.

The system is built and operated at or near the user's site. It is a PV power generation facility characterized by self-generation and self-use on the user side, excess electricity connected to the grid, and balanced regulation in the distribution network system. It can gradually solve the user's electricity consumption problem nearby, and realize the compensation and external transmission of power supply difference through grid connection. Distributed PV power generation system is small in scale and can be constructed according to actual requirements. It has a large selection of construction areas and has great development space in the future development of comprehensive energy utilization.

The grid-connected cabinet is mainly composed of knife switches, circuit breakers and related control components. It is called "grid-connected cabinet" because it connects the generator system and the power grid system and is equipped with a complete grid-connected protection device, which plays the role of generator grid connection. PV grid-connected cabinet exists in the PV system as the total outlet of the PV power station. It is a distribution device connecting the PV power station and the power grid. It can protect and measure the total amount of PV power generation, facilitate fault inspection and management, and improve the economic benefits of the power generation system.

2. Solution

During the operation of PV grid-connected cabinets, fluctuations in voltage and frequency on the grid side may cause shocks to the station and overload, which will not only damage the grid equipment but also threaten the lives of maintenance personnel. Harmonic problems are the main problems of PV power generation. PV power generation uses AC and DC inverters. Since the inverter converts DC power into AC power by turning on and off semiconductor power switches, harmonic problems will occur in this link. In addition, due to the uncertainty of PV projects, the output power fluctuates randomly, resulting in grid frequency deviation, voltage fluctuations and flicker.

In view of the above situation, this solution uses anti-islanding protection devices to collect grid-connected voltage, frequency, grid incoming current and other signals. When an islanding phenomenon occurs, the grid connection point is quickly cut off to quickly disconnect the station from the grid side. At the same time, an online power quality monitoring device is configured to conduct real-time monitoring of voltage harmonics, voltage fluctuations and flicker, frequency deviation, voltage imbalance, voltage sag/surge/short-term interruption, etc. The use of these two devices in photovoltaic grid-connected cabinets provides a guarantee for the reliable operation of the power grid. The equipment configuration scheme of this solution is shown in Table 1.

Device NameProduct TypeFunction
Anti-islanding protection deviceAM5SE-ISInverter power protection, frequency mutation tripping, automatic closing under pressure and other protection functions
Power quality online monitoring deviceAPView500Power quality monitoring of grid-connected cabinets, including voltage harmonics, voltage fluctuation and flicker, frequency deviation, voltage imbalance, voltage sag/swell/short-term interruption

3. Product Selection

AM5SE-IS anti-islanding protection device is mainly suitable for 35kV, 10kV and low voltage 380V photovoltaic power generation, gas power generation and other new energy grid-connected power supply systems. When an islanding phenomenon occurs, the grid connection point can be quickly cut off to quickly disconnect the station from the grid side, thus protecting the lives of the entire power station and related maintenance personnel.


Technical parameters

Power supply

Rated input

AC/DC220V,or AC/DC110V


Rated Voltage×(1±20%)



Rated Voltage

Rated input

AC 100V/100/ √3y






≤0.5VA (single phase)

Rated Current

Rated input

AC 5A/1A






≤0.5VA (single phase)


Rated frequency

50Hz or 60Hz






Rated Voltage

AC/DC220V,or AC/DC110V


Rated Voltage×(1±20%)


≤1W(DC220V)(single channel)


Mechanical life


Switching capacity


On current

continuous  ≥5A,  short time

Interrupting capacity






5%~95%(No condensation and
freeze inside)



Optional Functions


-F-T-M-B-C-MD-D2-D3-TB-IS  -K-UB
Over-current (with compound voltage
dependant,3 stages)

Directional over-current (with voltage
dependant,3 stages)

Differential with Ratio restraining

Instantaneous Differential

CT supervision

Over-current (2 stages)

Directional earth fault (I01,2 stages)

Directional earth fault (I02,2 stages)

2 stages earth fault (I01)

2 stages earth fault (I02)

Over-current IDMT(Normal inverse,Very
inverse,Extremely inverse)

Earth fault IDMT (I01)

Earth fault IDMT (I02)

Clearance zero sequence protection(2 stages)

Positive sequence over-current (2 stages)

Positive sequence over-current IDMT

Negative sequence over-current (2 stages)

Negative sequence over-current IDMT


Starting air-cooled water chiller

On-load tap changer lock out

Trip and close circuit supervision (alarm)

Under-voltage (trip)

Under-voltage (alarm)

PT supervision

Three phase auto-re close

Under frequency

Over frequency

Post-accelerated over-current

Over-voltage protection

Blocking rotor

Unbalance voltage

Unbalance current

Residual over-voltage protection

Residual over-voltage (alarm)

Positive sequence over-voltage protection

Negative sequence over-voltage protection


Starting time-out

Directional power

Thermal overload

Incorrect phase sequence

Voltage Phase loss

BUS tie protection and standby power
automatic switch

FC block

PT supervision and parallel connection

Self-produced zero over current protection


Rate of change of-frequency

Auto-close with voltage recovery

Over haul-lockout                                                              √

Recommended Acrel Energy Meter and Related Products
+8618795636361 michelle.zhou@email.acrel.cn
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