Power Solution 1500VDC photovoltaic power generation system

MORNSUN is proud to introduce a new DC/DC converter, PVxx-29Bxx series, to address the needs of 1500 VDC Photovoltaic systems. This series of DC/DC converters accepts a wide input range from 200 – 1500 VDC providing standard output voltages of 24V, 12V and 5V to power monitoring and control circuits in systems.

The PVxx-29Bxx simplifies the wiring design reducing cost of system manufacturing and maintenance when compared with AC power or battery power. This converter also features multiple protection functions that improve system safety when a breakdown occurs.

1. Basic structure and request of the PV power generation system

A PV power generation system contains:

• solar panel
• combiner box
• DC power distribution cabinet
• inverter and boosting transformer (Diagram 1: PV Power generation System)

In this system, in order to reduce the wiring between solar panel arrays and the inverters, the arrays are built by group, and connected in parallel to get electric combination into the solar combiner, and then the DC will be provided through DC cabinet to the solar inverter and then into the power grid.

The output voltage of solar panel arrays varies significantly for sun light from different regions, seasons and time. And the solar combiner needs to detect every group of the solar panel array’s voltage, current, power and anti-thunder condition, and realize the functions of failure warning, locating and communication. The solar inverter needs to detect the voltage, current and drive the control board while converting the DC to AC. Because the solar panel arrays output is normally higher than 1kv, conventional power module cannot accept the voltage from the high-voltage line as input, if adopting the solution of external power for driving multiple detection units for solar combiners and inverters, unstable operating voltage, wiring and single shorted circuit problems may occur and cause power failure of the whole detection system.

Therefore, these factors of a power supply should be considered for PV power system equipment,

• Input voltage and output voltage : e.g. 200-1500VDC input and standard output of 12V/15V/24V
• Isolation between primary side and secondary side: 4000VAC
• Multiple Protections: input under-voltage protection, reverse input protection, output overcurrent protection, short-circuit protection and output over-voltage protection, etc.
• High Reliability in harsh environments
• Output voltage:12V/15V/24V available

To meet the PV power generation application requirement, MORNSUN released a series of DC-DC converters with 200 – 1500 VDC input and 4000 VAC isolation. Additionally, MORNSUN has a pack of DC-DC solutions which can ensure the safety isolation in different units of the circuit.

2. Power Solution for Monitoring Unit of PV Combiner Box

In order to enhance the reliability and practicality, the PV combiner box is equipped with DC Anti-thunder protection module, DC fuse, circuit breaker and some functional circuits, such as Control and Processing, Working State Monitoring and Communication circuits, etc.

Diagram 2 shows a typical monitoring unit solar combiner box with the following MORNSUN parts:

• With the feature of 200 – 1500 VDC input, 4000 VAC isolation of the PVxx-29B24, it becomes much simpler to get the power source from the solar panel array and convert it to the 24VDC for the monitoring unit.
• DC-DC converter F0505S-1WR2 is used to drive the hall sensor with isolation between high and low voltage.
• The DC/DC converter B0503XT-2WR2 provides the 3.3V isolated DC for the MCU.
• The transceiver TD501D485H integrates the isolated serial communication signal and isolated power, which can impede electromagnetic interference and avoid ground loop interference.

This solution is functionally meets the requirements and also provides safety isolation, which is simple and reliable.

3. Power Solution for Monitoring Unit of Photovoltaic Inverter

At the front end, the combiner box is used to combine the current, and after the DC cabinet monitoring, the DC voltage will be converted into AC through the inverter. The converting process of the inverter is also needed to be monitored, controlled and communicated to ensure the inverted voltage can meet the requirement. This monitoring unit can accept the wide input range of 200-1500VDC from the bus.

As Diagram 3 shows:

• The PVxx-29B24 gets the power source from high-voltage bus and step down to 24VDC
• The low-drop regulator K7805-500R3 and K7815-500R3 can provide the right voltage with high efficiency for the circuit behind it.
• The B0503XT-2WR2 provides the 3.3V isolated DC for MCU.
• The transceiver TD501D485H integrates the isolated serial communication signal and isolated power, which can impede electromagnetic interference and avoid ground loop interference.
• The QP12W08S-37 is isolation DC-DC integrated IGBT driver, which can simplify the design and improve reliability.