Micro-gird For Hybrid Inverter+On-grid Inverter System

Introduction

There is a large number of traditional on-grid inverters on the market. Due to islanding effect, on-grid inverters are unable to work during off-grid. This characteristic makes users lose the on-grid inverter PV energy when off-grid.

Micro-grid is the function that making hybrid inverter simulates the grid to activate on-grid inverter during off-grid. By connecting on-grid inverter to hybrid inverter’s EPS port, hybrid inverter can use PV or battery energy to activate on-grid inverter during off-grid.

Diagram 1

Advantages

Cost-saving

Wasted on-grid inverter PV energy been saved, lower electricity bill

Eco-friendly

No extra devices needed

Simple and worry-free

No complicated configuration required, enable and forget

Configuration

1. Strictly follow the wiring diagram on Diagram 1.

2. Enable “Settings→Advanced Settings→Micro-grid”.

3. Set “Settings→Advanced Settings→Micro-grid→PV INV Max Power”

Compatibility

Hardware version:

Hybrid inverter	X1-Hybrid/Fit G4	X1-IES	X3-IES	X3-ULTRA	X1-SPT 6.0
On-grid inverter	Single-phase	Single-phase	Single &Three-phase	Single &Three-phase	Single split-phase
Battery	TB-AT-SYS-HV-5.8、 T-BAT-SYS-HV-3.0、 T-BAT-SYS-HV-R2.5/3.6 T-BAT-SYS-HV-S2.5/3.6	T-BAT-SYS-HV-S50E	T-BAT-SYS-HV-S50E	T-BAT-SYS-HV-S2.5/3.6 T-BAT-SYS-HV-5.8	TB-AT-SYS-HV-5.8 T-BAT-SYS-HV-S3.6

Note:

On-grid inverters can be any brand which supports “power response to overfrequency”

Compatible batteries may be adjusted, please contact service support for the latest battery compatibility file.

Software version:

Hybrid inverter	X1-Hybrid/Fit G4	X1-IES	X3-IES	X3-ULTRA	X1-SPT
Software version	ARM≥1.43 DSP≥1.46	ARM≥5.07 DSP≥10.01	ARM≥8.03 DSP≥11.00	ARM≥14.08 DSP≥13.02	ARM≥1.11 DSP≥1.11

Note:

1. X1-Fit G4 cannot be used in pure off-grid environment

2. The maximum output power of the On-grid inverter must meet the following two points at the same time:

1) On-grid inverter output power≤Max. hybrid inverter EPS output power

2) On-grid inverter output power≤Max. battery charging power

3. EPS Max. single-phase output power of the Hybrid inverter：

X3-IES	EPS Max. single-phase output power
5K	2.5kW
6K	3kW
8K	4kW
10K	5.5kW
12K	5.5kW
15K	5.5kW

X3-ULTRA	EPS Max. single-phase output power
15K	6.7kW
20K	6.7kW
25K	10kW
30K	10kW

Case study:

The following is an example of a micro-grid system:

Inverter Model & Quantity	Inverter Rated Power	Photovoltaic Panel	Battery
X3-Ultra*1	30kW	30kWp	/
T-BAT-SYS-HV-S3.6*13	/	/	47.8kWh
X1-Smart G2	10kW	12kWp	/

X3-Ultra in this system is paired with the following batteries system: the batteries are in a tower connected to two battery ports, charging capacity of the batteries is 39.9kW(13*51.2V*30A*2). Compared to X3-Ultra 30K EPS rated power, 30K is the batteries’s Max. charging power (whichever is the lesser). Therefore, this system satisfies Pon-grid INV<Pultra max. Bat charging and Pon-grid INV = Pultra EPS Max. single-phase output power. This is a successful micro-grid system.

4. Active response to frequency deviation with micro-grid function

In order to improve the stability of the micro-grid function, the logic of micro-grid frequency rise has been optimized^③, as follows:

1) When the micro-grid function is not enabled, the default frequency of the output voltage in off-grid mode is 50Hz/60Hz;

2) When the micro-grid mode is enabled and the battery does not limit the charging current (Taking 50Hz as an example, see Diagram 2):

• When the SOC is less than 80%, the frequency of the output voltage in off-grid mode is 50Hz;
• When the SOC is greater than 80%, then a frequency boost process is initiated;
• When the SOC exceeds 90%, the frequency boost process is accelerated at a higher rate; (Increasing the output voltage frequency to trigger the on-grid inverter's over-frequency load shedding logic)

（When the off-grid frequency is 60Hz, the corresponding node on Diagram 2 is 61Hz/63Hz）

Diagram 2: The relationship between the battery's SOC and the frequency boost

3) When the micro-grid mode is enabled, if the maximum charging power limit of the battery is still greater than the maximum output power of the externally connected on-grid inverter, the output voltage in off-grid mode is 50Hz/60Hz;

4) When the micro-grid mode is enabled, if the maximum charging power limit of the battery is less than the maximum output power of the externally connected on-grid inverter, the frequency of the output voltage in off-grid mode is 53Hz/63Hz, which will limit the operating power of the on-grid inverter^④;

Note:

③This micro-grid logic has been implemented on software version X1-Hybrid/Fit G4/X1-IES/X3-IES/X3-ULTRA mentioned above.

④In a micro-grid system, the hybrid inverter is unable to ascertain the actual output power of the on-grid inverter. If the maximum output power of the on-grid inverter is close to the maximum charging power of the battery, and when the battery's charging current is limited due to factors such as temperature, the micro-grid function will not be able to operate normally in order to ensure system safety.