“In line with local conditions and design”-PV Inverter selection guide

Polaris solar PV net news: objective: PV inverters are one of the two major components of photovoltaic power generation system, PV inverter’s core mission is to track the maximum power output of the photovoltaic array, and energy with a minimum of conversion loss, best quality of electricity fed into the grid. Due to inverse variable device is series in PV square and grid Zhijian, inverse variable device of select will became PV station can long-term reliable run and achieved expected returns of key, paper proposed has “suit measures to local conditions, science design”–that according to PV station installed scale, and by at environment and grid access requirements, reasonable select inverse variable device type, makes station construction party, and investment party, and operations party and grid, related multi in security, and stable and proceeds Shang of common interests maximize, promoting PV industry health, and ordered development.

1, PV plant taxonomy and plant characteristics

PV installations in accordance with different, PV power station, power station and the roof is generally divided into desertification Hill station three.

Desert power plant: broad flat desert land resources development of photovoltaic power plant. This type of power station is large in scale, generally greater than 5MW, currently a single power station 50MW or more scale is remarkably common; power inverter output after booster directly fed into the 110KV, 330KV or more high voltage grids; environment in which flat, PV module, no shelter. The station is the main photovoltaic power plant in China, mostly in the West.

Hill Station: mountains, hills, and other resources to develop photovoltaic power plant. This kind of power stations vary in size, ranging from a few MW to hundreds of MW; mainly generating electricity into the grid; under the influence of topography and many components are inconsistent or occlusion sooner or later. This type of power plant is mainly used in mountainous areas, mining wasteland and plenty cannot grow.

Rooftop power station: the use of plants, public buildings, residential roof PV power station in resource development. Size limited by effective roof area of this type of power station, installed capacity in thousands of Watts into dozens of megawatts; power generation to encourage local absorptive, directly fed into the low-voltage distribution networks or 35KV and below high voltage power component orientation, inclination and shadows of diversification. The station is the current main forms of distributed PV applications, mainly in the Department of Middle East and southern regions of China.

2, inverter classification and characteristics

Photovoltaic inverter based on their power ratings, internal circuit configuration and application is different, and can generally be divided into centralized inverters, string inverters and micro-inverters are three types.

Centralized inverters: the main feature is the single power, maximum power tracking (MPPT) small size, low cost per watt. Currently the mainstream model of 500KW, 630KW, European and North American mainstream single 800KW of power is even higher, power rating and level of integration is also constantly improving, Germany this year SMA introduced a stand-alone power 2.5MW inverter. According to the inverter main circuit structure, centralized inverter can be divided into the following two types:

Centralized inverters are most preferred for large photovoltaic power plant, in 5MW’s photovoltaic power stations around the world, and its selection of more than 98%.

String inverter: single power between 3-60KW. Mainstream single power 30-40KW, single or multiple MPPT and generally 6-15KW along the MPPT. This type of inverter high cost per watt, mainly used in small and medium power stations, selected in the global capacity of 1MW power station exceeds 50%.

Micro-inverters: stand-alone power 1KW, MPPT used mostly in 0.25-1KW along the MPPT, its advantage is that it can on each block, or some independent MPPT control panels, but the cost per watt inverter is very high. Currently below 10KW household PV power plant in North America had more applications.

Several inverters are typically used as shown in the figure.

As figure by shows, PV component through series formed group series, multiple group series Zhijian parallel formed square, concentrated type will a square of all group series DC side access 1 Taiwan or 2 Taiwan inverse variable device, MPPT number relative less; group series type will along or several road group series access to a Taiwan inverse variable device, a square in the has more road MPPT, micro inverse variable device is on each block battery Board for MPPT track. When individual components due to shadows or inconsistent, serial and parallel mismatch occurs. Multi MPPT of string type string can be solved in parallel mismatch problems, micro-inverter can solve the parallel between string mismatch can also resolve the series mismatch between components. Therefore, from a technical perspective, the essential difference between several inverters for components mismatch problems.

Based on the inverter type selection to PV system lifetime find the balance between total and the total cost, also the grid access, such as fault-crossing ability, power quality, network adaptation requirements. According to various characteristics of the inverter, combined with the application of PV power plant to the actual situation, friendly, convenient, high return on investment from the grid selection of scientific and rational aspects of building maintenance.

3, different power Inverter selection guide

3.1, desert power plant–set-advantages

Centralized inverter has the following advantages, a desert plant of choice.

Lower initial investment. Based on comparative analysis, integrated programme-programme at the beginning of a string inverter per megawatt-hour vote to save investment of about 260,000 yuan.

Electricity type and string balance: in desert power plants focused on essentially flat type and string-generating capacity, General concentrated in the most efficient and overload capacity, such as the advantages of centralized capacity slightly higher than the string type. Few power stations sooner or later rows before and after the block, using string type cannot be overcome, need to avoid through optimized component layout.

Operation more convenient and economical. Through comparison between centralized and string-type mainstream programmes of 100MW power station operation and maintenance data, generating losses both; as a group is the serial device is a machine maintenance, and set device is a device to maintain, maintenance cost, centralized advantage is obvious. Meanwhile, in the hundreds of thousands of acres of MW-class large-scale power station, to completely replace the scattered arrangement of string inverters, maintenance personnel spent more time on the road will be much higher than the time for replacement of equipment, this is the string of large utility scale one of the negative factors.

Integrated programme more in line with the grid-access requirements. Grid for grid-connected photovoltaic power generation scheduling response, faults cross, limit, extra hair, smooth, harmonic limits, power rates, emergency stop has strict requirements. Fault through is refers to grid appeared short-circuit, and waves Chung, and deficiency phase situation Xia, inverse variable device must can in 625 milliseconds to several seconds of time within still output must capacity of active and reactive power, ensure power system following electric protection can normal action, due to concentrated type inverse variable device in station middle number less, single function powerful, communications control simple, fault during can through fault of probability great Yu group series inverse variable device. June 2013 mid-country network organization of field low voltage through test, multiple models concentrated inverse variable device also different degree appeared de network situation, envisaged if has thousands of Taiwan small inverse variable device in large station in the run, once grid appeared fault, due to equipment many control complex, grid coupled, and resonant probability spurt, group series type inverse variable device must will appeared large de network, and even equipment itself damaged of situation, endanger grid security run. Because of too many inverter to ensure within 30ms response requirements of power system reactive power scheduling instructions.

3.2, Hill Station–multiple MPPT concentrated solutions can also be considered string type.

Hills desert plants can be seen as the terrain is not flat power plant is also fed into the electricity grid, scale for more than 5MW. Hill power station project, usually a coordinate system is about more than more than 100 KW capacity for planning component (125KW components laying into the same direction), and achieve the optimal proportion of investment in power generation and maintenance costs. For this application development of more MPPT module mode of concentrated type inverse variable device, each road MPPT track more than 100 more KW component, will same towards component of design accounted for to area units narrowed to about 1000 square meters, greatly upgrade has construction convenience sex and effective solution towards and block problem, while total Exchange bus output, has concentrated type inverse variable device grid friendly sex features, is Hills station of preferred programme.

Selected Hill power station, if the terrain is complex, achieving more than 100 KW components the same toward laying is very difficult, string inverter can be considered as a supplement.

3.3 type, roof power station–recommended string, also can choose intensive programme

Relatively complex roof design of power station, roof-top size, layout, texture loading, and effects such as shadows and components laying and Inverter selection plan is required to achieve maximum benefits. And the component installed on the roof, fire prevention and other security issues need to be considered. Access to distribution networks, directly adjacent to the customers ‘ demands, you need to consider consumer electricity safety, power quality to meet the requirements, and for relay protection coordination with the original distribution and so on. Access after distribution network, power factor effect on users is clear, except for output power of the inverter, but also need to quickly spot power of the PV system, user, real-time load data and distribution previous SVC-integrated SVG into the calculation to determine real-time reactive power output inverter capacity. Therefore, selection of rooftop PV system needs to be secure and network-friendly, investment returns, maintain balance, and many other factors.

Complex roof structures, occlusion or inconsistent, recommend using string inverter. Complex roof structures, in order to simplify design, string inverter is recommended, and depending on where the actual roof and outlets and network voltage, select the inverter. String inverter need arc monitoring and shutdown capabilities to effectively prevent the occurrence of fires, eliminate PID function, have high-accuracy leakage protection and protection functions.

A large plant, taking into account the roof bearing and maintaining convenience, optional centralized programmes. Flat, large scale industrial building roofs, fewer shadows, towards simple, mostly 10KV medium-voltage distribution grid. Taking into account the plant mostly for color steel roof, loading capacity is limited to install string inverter, and routine maintenance, does not affect the normal operation, the actual situation, can choose a centralized inverter.

Summary: the inverter as a bridge between the component and the power grid, is a core component of photovoltaic systems. Depending on plant size, and different applications, select the appropriate inverter, cost and capacity are highly beneficial to the system. In large, flat desert, beaches, suitable for use centralized inverters; large, rugged hills power plant, suitable for using centralized inverter of MPPT; diversified roofing plant is relatively small in scale, layout, selection for string inverter. According to local conditions, select PV inverter, ensures that the PV power station in investment decision phase and avoid detours, in advanced stage of operation and maintenance is more reliable and efficient operation. 

Original title: “according to local conditions, scientific design,” PV Inverter selection guide

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