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Sungrow’s SG125HV: the World’s Most Powerful 1500Vdc String Inverter

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Sungrow’s SG125HV: the World’s Most Powerful 1500Vdc String Inverter
 
 
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Fig-1: SG125HV Appearance (left) and the Virtual Central Solution (right)
 
The SG125HV is the world’s highest power inverter in the string category.  Weighing in at 72kg, so it stays in the two-man installation category.  The key specifications for the SG125HV are listed below.  The following paragraphs will describe the system design parameters that utilize these specs to connect them with utility scale system design and ultimately, the Virtual Central Solution.
 
High Efficiency
 
Sungrow’s SG125HV was designed to have a power converter platform that was more efficient than previous generations of products. Utilizing 5-level converter bridge, the SG125HV provides extraordinary best-in-class efficiency, further increasing project ROI by maximizing input vs output power conversion efficiency and minimizing loss. The maximum efficiency of SG125HV can reach 98.9%, and the Euro. efficiency is 98.7%. Greater efficiency equals to greater AC power yield.
 
Wide Operating temperature range
 
Sungrow’s SG125HV has one of the widest operating temperature ranges available in the industry, with full power available from -25°C to 50°C and operation in power de-rate mode available up to 60°C.
 
The SG125HV is rated for 125,000W at ambient temperatures up to 50°C. At temperatures above 50°C the inverter will ramp down power or ‘de-rate’ in order to maintain control of internal temperature and losses.  The de-rated operation will continue until the ambient temperature exceeds 60°C.
 
Less cable cost, save Capex
 
Sungrow’s in-depth project design analysis and Capex economics reviews have determined that in most cases it is overall more cost-effective to have the 1500V DC SG125HV inverter located nearer the AC POC than the PV array field. As previously explained, utility-scale project cabling costs are dominated by voltage drop concerns and longer runs of two cables (DC+/DC-) at 1500V are simply less expensive than running three cables (A, B and C phases) at 600V AC. In order to facilitate the recommended design scheme that uses external (i.e. mounted within or immediately peripheral to the PV array) combiner boxes with longer DC+/DC- ‘homeruns’ back to the inverter located near the POC, the Sungrow SG125HV inverter utilizes a single DC input architecture that allows larger homerun cables or even trunk bus cables to be connected directly to the inverter without the need for fusing or other maintenance-intensive components within the inverter. 
 
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Fig-2: DC input cable vs. AC output cable
AC output configuration
 
In an effort to further reduce project Capex and push the inverter’s efficiency to the highest levels, a voltage level higher than 480V AC was required. The SG125HV outputs a nominal 600V AC output voltage which reduces AC output current by 25% when compared to the same amount of power at standard 480V AC. Lower current yields smaller cable costs by the same percentage and greatly benefits project Capex. 
 
In addition, the inverter does not require a neutral connection from the primary transformer, so only 3 phases plus a PE ground are connected to each inverter, further reducing cabling costs vs competitors which require a neutral conductor in addition to the three phases cables and PE ground.   
 
Small and light to bring the simple installation
 
The SG125HV is comparably sized to inverters with half the power rating and was designed to be simple to install. A metal backplate is provided, along with fastening hardware, which gives installers flexibility with mounting options. The inverter can be hung on appropriately-rated strut supports, on concrete walls, or virtually anywhere the mounting bracket can be installed. 
 
A comparison of the cost to install central inverters with the costs of installing string inverters brings up some significant differences. Aside from the MV transformer, installing the string inverters and related BOS does not involve anything more than just manpower.  There is no need for wide access paths or bringing heavy lifting equipment to the site.
 
For string inverters, especially the SG125HV at 72kg, there is no need for massive concrete structures or skid platforms. The inverters can be mounted to existing solar array structures or a relatively simple rack made of Uni-strut.  Some shading should be considered as good engineering practice to reduce the thermal load and to reduce the overall weather impact on the units.
 
To create the Virtual Central Solution, it is not absolutely necessary for all the SG125HV inverters to be mounted right next to each other although it can save in integration costs in the long run.  The inverters can be spread out individually or located in groups.  This approach can reduce the DC wiring lengths without creating unreasonably long AC wire runs. However, the closer the groups are to each other, the easier it will be to integrate the communication and control system.
It is best to parallel the several SG125HV inverters via one or more AC breaker panels.  Fused disconnect switches can be used as well.  This helps in both circuit protection as well as in providing electrical isolation on the AC side which will facilitate the removal and replacement of individual inverters.
 
Stable display and communications
 
For user convenience, the SG125HV includes an LED HMI display panel to indicate inverter operating status and other system parameters such as Bluetooth connectivity, serial communications status, and fault and ground impedance status.
 
Customer communications to the SG125HV inverter are done through the serial RS485. Additionally, the inverter allows Bluetooth connection to smart devices enabling the Sun Access App to communicate with the inverter wirelessly to set parameters, check fault codes, etc.
 

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