150-1500VDC Input Voltage DC/DC Converter PV Series Designed for 1500V PV Power System


Morgan Shao, Field Application Engineer at Mornsun

With global non-renewable resources are increasingly scarce, the renewable energy is called upon to increase in all major electricity markets. As a cost-competitive, reliable and sustainable electricity source, Solar PV power has emerged as the dominant alternative energy source.

International Energy Agency (IEA) forecasts the share of renewable energy in global power generation is expected to be over 30% before 2030, with solar PV power generation accounting for 10% of it. By 2040 it will be over 50% (solar PV: 20% ) will and grow to over 80% (solar PV: 60%) at the end of this century. Meanwhile, according to a study by Solar Power Europe (SPE), Global solar power capacity is growing sharply and could reach 540 gigawatts (GW) by 2020, according to a study by Solar Power Europe (SPE). As a cost-competitive, reliable and sustainable electricity source, Solar PV is blossoming around the world. Europe is the biggest solar market with a sum of 157GW (reference: 89GW), in which the UK was the fastest growing market. China is the fastest growing market globally, which is expected to add 86 GW (reference: 28GW) by 2020. India´s market is predicted to rank in third place with 54GW (reference: 3GW), followed by Japan and the United States, with 59GW (reference: Japan 23GW, the United States 19GW), respectively.

This article will show the advantages and challenges of 1500V PV power system from three aspects and introduce a solution from MORNSUN with 1500V input PVxx-29Bxx series power supply.

 

Advantages of 1500V PV Power System

What’s 1500V system? It simply defines that the withstand voltages of cables, converters, inverters and other components used in PV systems. PV system voltages are increasing from 1000V to 1500V. The main advantages of 1500V systems is less costs saving and higher efficiency over 1000V system.

Boosting voltage to reduce line losses is an effective measure for design cost reduction. Higher input voltages reduce wire losses of AC-side and DC-side as well as winding losses in the low-voltage side of the transformer and improve by 1.5-2% of the power plant system’s efficiency. Calculated by P= UI, given that the power is constant, the current will drop to 1/1.5 when the voltage increases 1.5 times. Similarly, assuming the length and diameter of the cables are confirmed and the resistance R is constant, the cable loss will be 1/2.25 when the current lowers 1.5 times, as Ohm’s Law P=I2R. To sum up, equipment losses are reduced and power generation is increased when DC-side voltage increases from 1000V to 1500V.

A complete PV power generation system design should have PV array, combiner, DC cabinet, inverter and step-up transformer as shown in diagram 1. Compared with traditional 1000V DC voltage system, 1500V system has less connections between sting arrays and inverter. The PV arrays are constructed in series and then connect with the combiners in parallel, DC cabinet, inverter and power grid in sequence.

 

PV Power Generation System

Figure 1: PV Power Generation System

 

Another measure for design cost reduction comes from less components. 1500V system expands single-string components from 22 in a 1000V system to 32 in a 155V system, thereby reducing the quantities of strings and inverter, combiners and DC-side cables. Besides, less volumes of equipment such as inverter or transformer due to higher power density is also beneficial to reducing the costs of transportation and maintenance. Take 10MW PV power plant as an example, 1500V system could reduce 568 strings and 38 PV combiners, with a cost reduction of $77,390. With less equipment, costs of post-operation and maintenance will be reduced accordingly.

 

Design Comparison between 1000V System and 1500VSystem

Table 1: Design Comparison between 1000V System and 1500VSystem

 

Challenges of 1500V System

Although increasing the voltage from 1000V to 1500V benefits the system significantly, it faces challenges from three aspects, PV module and related components technology, raw material and certification. Therefore, a friendly collaboration across the industry and new standards meeting the requirements of 1500V system are needed.

 

PV module and related components technology.

Seen from the PV module itself, the main challenges are electrical safety and potential performance degradation. Seen from the system design, it causes a stricter product selection, better-matched components and higher risk of Potential Induced Degradation (PID).

 

Raw material.

The insulation and the electric clearance count most when the voltage rises to 1500V, for higher voltage may cause disruptive discharge. So, it will have higher requirements for the reliability of raw materials in terms of the layout of backboard, electrical connectors and electrical insulation. This technology overcomes and needs cooperation of other circuit breakers, fuses, lightning protection devices and switching power supply owing to higher requirements of withstand voltage and the reliability when compared to a 1000V system.

 

Certification.

1500V system requires a full range of certification standards for production components. Since 2013, multiple component groups have been certified with TUV for 1500V but very few ones for special devices such as high-voltage power supply and others meet the standard.

 

1500V PV Power System Solution

As PV combiner and PV inverter are key components of the PV system, the power solution have been challenged with 1500VDC voltage. Most manufacturers directly use power products on the market because there’re lots of difficulties when converting the 1000V DC high-voltage into 24V low-voltage, and certain ones choose to self-design power solution to save costs. It cannot be denied that there are certain advantages for self-design, however, solutions provided by professional power manufacturers are far superior to it in terms of reliability and performance (e.g.: high temperature, life, altitude, etc.).

Besides, using power module greatly simplifies the system design and avoid the risks of system failure caused by supply. Moreover, certification is the greatest challenge for power products. 1500VDC high voltage should meet the relevant standards for higher safety distance and creepage distance (see Table 2), which self-design solution is difficult to meet. High altitude also exacerbate the technical difficulty for PV module design.

 

Minimum creepage distances

Table 2: Minimum creepage distances

 

In a word, high-voltage PV module from professional manufacturers could solve the above-mentioned problems and provide a more reliable and longer life-cycle power solution, which usually has CE certification meeting different requirements for PV module in different countries.

 

PV15/PV40-29Bxx for 1500V System / DC/DC Converter PV Series for 1500V System

To address the need of 1500V system, MORNSUN released 15W/40W 1500VDC input PV15/PV40-29Bxx. They have four main features as follows:

  1. 200-1500VDC ultra-wide input voltage A trend of PV industry is that 1500VDC system will be in place of today´s standard 1000VDC system, which enables 50% longer strings and lowers the costs with fewer combiner boxes, less wiring and trenching, and less labor.
  2. CE/CSA approval The PV series with 1500VDC input voltage pass EN62109 standards, which greatly improve the reliability of the converter itself and the system.
  3. Built-in input under-voltage protection ensuring system stability A PV system converts the sun’s radiation into usable electricity and also powers itself. As sunlight intensity varies, so too can the voltage to the control system vary. This voltage variation may lead to frequent system restarts.PV15/PV40-29Bxx series are designed with input under-voltage protection which protect system stability from frequent restart.
  4. Suitable for high-altitude applications (up to 5000 meters) Most of the PV systems are installed in harsh environments or at high altitude fields. PV15/PV40-29Bxx are designed to meet the application requirement to ensure the systems’ reliability and safety, taking the customer environment and altitude into account and passing reliability tests. They are suitable for high altitude applications up to 5000m, safe and reliable. Features:
  1. Ultra-wide input voltage: 200-1500VDC
  2. Operating temperature: -40°C to +70°C
  3. Isolation: 4000VAC
  4. High efficiency, low ripple & noise
  5. UL 1741/CSA-C22.2 No.107.1, EN62109 approval
  6. Suitable for high-altitude applications (up to 5000 meters)
  7. Protections: UVP, RVP, SCP, OCP, OVP

 

PV Inverter

Figure 2: PV Inverter

 

Application 1: Monitoring Unit of PV Combiner Box

In order to enhance the reliability and practicality, 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.

 

Application 1: Monitoring Unit of PV Combiner Box

Figure 3: Application 1: Monitoring Unit of PV Combiner Box

 

Figure 3: Shows a typical monitoring unit solar combiner box. With the feature of 200- 1500VDC input, 4000VAC isolation of PVxx29B24, it becomes much simpler to get the power source from the solar panel array and convert it to 24VDC for the monitoring unit. DCDC converter F0505S-1WR2 is used to drive the hall sensor with isolation between high and low voltage. DC-DC converter 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. This solution functionally meets the requirements and also provides safety isolation, which is simple and reliable.

 

Application 2: Monitoring Unit of PV Inverter

In 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 also needs 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.

 

Application 2: Monitoring Unit of PV Inverter

Figure 4: Application 2: Monitoring Unit of PV Inverter

 

As Figure 4 shows, PVxx-29B24 gets the power source from high-voltage bus and step down to 24VDC, and the low-drop regulator K7805-500R3 and K7815-500R3 can provide the right voltage with high efficiency for the circuit behind it. 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. QP12W08S-37 is isolation DC-DC integrated IGBT driver, which can simplify the design and improve reliability.

 

Conclusion

The gradual large-scale popularity of PV energy is the rational development trend of global energy. MORNSUN actively participates in the development of green energy technology and develops 1500V high-voltage PV power module PVxx-29Bxx series to address the needs of control monitoring units in 1500VDC PV power system. PV power itself does simplify the circuit solutions, reduce the cost of building and maintenance and comprehensively enhance the stability, security and reliability of the system.

 

About the Author

Morgan Shao works as a Field Application Engineer at Mornsun Guangzhou Science & Technology Co., a China-based national high-tech enterprises. With 16 years of development, Mornsun has grown to become one of the biggest, full-range industrial power module manufacturers in domestic China.

 

References

  1. Grid integration oflarge-capacityRenewable Energy sources and use of largecapacity Electrical Energy Storage
  2. Global Market Outlook for Solar Power 2015-2019
  3. PV industry to pick only a matter of time in the first three quarters of the amount of an additional installed capacity of 161%
  4. Renewable Energy Markets and Prospects by Technology
  5. Renewable Energy Medium-Term Market Report 2015
  6. Study on 1500V Photovoltaic Components and its Systems

More information: MORNSUN    Source: Bodo's Power Systems, January 2017