This article describes the construction of transformerless inverters used in today's commercial and public PV installations. It analyzes how power integrators and utilities can exert new capabilities by integrating multiple inverters directly into the grid or only with a medium voltage transformer. Finally, the paper also details the many benefits of reducing system complexity and maximizing power generation efficiency. The new generation of transformerless technology reduces the system complexity of power integrators and utilities, targeting two of the most common large-scale PV installations—building inverter direct-connect projects and power grid-connected power transmission. Public installation projects, this technology maximizes its power transmission capabilities.
Although the price of solar photovoltaic power is becoming more and more competitive, it is crucial for the entire industry to continue to enhance performance, increase efficiency, and reduce costs. Increasing the quality and performance of large-scale investment equipment is one way to increase revenues. In addition, the performance and efficiency of inverters are just as important as photovoltaic modules and arrays. In the design of large-scale photovoltaic systems, power integrators and utility utilities are abandoning the traditional inverter equipment and instead begin to select the most advanced transformerless inverter technology in order to reduce system complexity and maximize Power transmission. It is indeed necessary to take a closer look at how transformerless inverter technology can help change the competitive landscape by affecting system design, efficiency, and system balance (BoS) costs. The new technology of direct conversion using a separable bipolar +600 and -600 VDC battery array eliminates the need for transformers on low-voltage three-phase grids. This configuration not only improves power generation efficiency, but also eliminates the need for conventionally used inverter transformers, reduces associated system balancing (BoS) costs, and avoids unnecessary line attenuation associated with unipolar configurations. This technology also brings more benefits to large-scale commercial or public installation projects for power integrators and utility utilities. For example, commercial projects that typically scale between 1 and 2 MW require one to eight inverters at the low voltage side of the building's entrance transformers at the point of connection, and each inverter must be equipped with a separate, custom isolation transformer. - Even if the transformer is integrated with the inverter. The true transformerless design of the inverter can support direct connections, does not require any additional transformer equipment and custom modifications, and will not produce system balancing costs. For common installations where the MV transformer connection point is between 5 and 12.7 kV, multiple transformerless inverters can be integrated into a properly sized standard MV transformer. The transformer can be placed anywhere in the electric field to be close to the inverter. Transformer-less inverter technology and two-pole array configuration Solar photovoltaic systems using transformerless inverter technology When generating electricity, no transformers are needed between the photovoltaic modules and the load – usually high voltage alternating current (HVAC) equipment and commercial fluorescent lighting .
Although some manufacturers claim to have transformerless technology, in fact, their products still require an isolation transformer between the inverter and the load. They simply integrate the inverters into an inverter box or sell them separately. A true transformerless inverter converts power directly from the inverter and transmits it to the attached load. This is due to the use of a bipolar ±600 VDC array configuration. Power integrators and utility utilities can benefit from system performance improvements and system balance cost reductions: Higher efficiency Reduced equipment and wire size and quantity Reduced materials and installation construction costs To illustrate these advantages, let's look at both The framework of the most common large-scale PV installations is the U.S. local grid inverter direct connection project and the utility installation of grid-connected power transmission. Direct Grid-Connected PV Inverters Used in Commercial Roof Installation Projects A 1 MW commercial rooftop system with connection points at the low pressure end of the facility entrance requires one to four grid-connected PV inverters. When using conventional inverters, each must be paired with a separate or custom isolation transformer—regardless of whether or not the transformer is integrated with the inverter. As a result, the power supply is immediately attenuated, because isolation transformers are usually only 98% to 99% efficient, and they can degrade performance by up to 2%. Due to its bulkiness and heavy weight, conventional inverters limit the design of photovoltaic inverter systems. System designs using two 500-kilowatt inverters require the installation of an inverter on the ground because of the large size and weight of the inverter/transformer. Even if the isolation transformer can be separated from the inverter, the lower output voltage and multi-winding required for each inverter will be limited due to the high cost of the wire due to the lower voltage and higher current. Separate distances. The stability problem when integrating inverters also needs attention. Traditional inverter design usually uses undamped large triangular filters. When many devices are placed in parallel or the inverter is set on a long transmission line, these filters may cause the system to run unstable.
Moreover, if the inverters are placed in parallel in the same box and each 500-kw inverter is driven by four smaller 125-kilowatt units, then the system is susceptible to electrical interference, and will bring the entire photovoltaic system with Multiple failure points. In contrast, the true transformerless inverter is directly fixed at the entrance of the building, even fixed on a large-scale distribution installation board. With no isolating transformer, the additional 1% to 2% of the energy efficiency obtained from the PV module power supply goes directly to the load. At a power of 500 kW, this means that a minimum of 5 kW of additional output is provided free of charge. In addition, the direct conversion to a usable voltage, rather than the lower unipolar inverter AC voltage, reduces the AC current by more than half, thereby reducing the cost of the wires at the end of the AC. Without a transformer, the inverter's smaller size and lighter weight give power integrators greater freedom in installation and overall system design. Due to weight limitations and necessary reinforcement measures, installing a conventional inverter on the roof of a five-story building may be prohibitive in terms of cost, but designers can install transformerless inverters in commercial buildings. On the roof (not in the basement), it is connected directly to the mounting plate on the fifth floor. This design can not only avoid the expensive up to five floors of DC wiring, but also shorten the length of AC power lines and reduce the associated costs.