Transformerless inverter construction used in solar photovoltaic projects - News - Global IC Trade Starts Here.
A 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 connection projects and grid-connected power generation A public installation project that maximizes its power transmission capabilities.
While the price of solar photovoltaic power supplies is becoming more competitive, it is critical for the industry to continue to enhance performance, increase efficiency and reduce costs. Increasing the quality and performance of large investment equipment is one way to increase revenue. In addition, the performance and efficiency of inverters are as important as photovoltaic modules and arrays. In the design of large-scale photovoltaic systems, power integrators and utility companies are turning away from traditional inverter equipment and instead choosing the most advanced transformerless inverter technology 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 with detachable two-pole +600 and -600 VDC battery arrays eliminates the need for transformers on low-voltage three-phase networks. This configuration not only increases power generation efficiency, but also eliminates the traditionally required inverter transformers, reduces associated system balance (BoS) costs, and avoids unnecessary line attenuation associated with unipolar configurations. The technology also brings additional benefits to large commercial or utility installations for power integrators and utilities. For example, commercial projects typically ranging in size from 1 to 2 megawatts require one to eight inverters at the connection point on the low-voltage side of the building's inlet transformer, and each inverter is equipped with a separate, custom isolation transformer. - Even if the transformer is integrated with the inverter. A true transformerless inverter can support direct connections without any additional transformer equipment and custom modifications, and it does not create system balancing costs. For common installations where the medium voltage transformer connection point is between 5 and 12.7 kV, multiple transformerless inverters can be integrated into a standard medium voltage transformer of appropriate size. The transformer can be placed anywhere in the electric field to be close to the inverter.
Transformerless inverter technology and two-pole array configuration
Solar PV systems with transformerless inverter technology do not require any transformers between the PV modules and the load during power generation – typically high voltage alternating current (HVAC) equipment and commercial fluorescent lighting. Although some manufacturers claim to have transformerless technology, in reality, their products still need to have 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 bipolar ±600 VDC array configuration. Power integrators and utility companies can benefit from improved system performance and reduced system cost savings:
Higher efficiency, reduced equipment and wire size and quantity, reduced material and installation costs
To illustrate these advantages, let's look at the architecture of the two most common large-scale PV installations, the inverter connection project for the US local grid and the public installation for grid-connected power generation.
Direct grid-connected PV inverters used in commercial roof installation projects
A 1 MW commercial roof system with a connection point at the low-voltage end of the facility requires 1 to 4 grid-connected PV inverters. With conventional inverters, each must be paired with a separate or custom isolation transformer – regardless of whether the transformer is integrated with the inverter. As a result, power supply is immediately diminished because isolation transformers are typically only 98% to 99% efficient, and they can reduce performance by up to 2%.
Due to their size and weight, traditional inverters limit the design of photovoltaic inverter systems. System design with two 500 kW inverters requires the installation of an inverter on the ground because of the size and weight of this inverter/transformer. Even if the isolation transformer can be separated from the inverter, the lower output voltage and multiple windings required for each inverter will be limited due to the expensive lead cost due to the lower voltage and higher current. The distance separating each other.
Stability issues when integrating inverters are also of concern. Traditional inverter designs typically use an undamped large triangular filter. These filters can cause system instability when many devices are placed in parallel or when the inverter is placed on a long transmission line. Moreover, if the inverters are placed in the same box in parallel, each 500 kW
The inverter is driven by four smaller 125 kW units, which are susceptible to electrical interference and can present multiple points of failure for the entire PV system.
In contrast, true transformerless inverters are fixed directly at the entrance of a building, even on a power distribution mounting board of sufficient size. Since there is no isolation transformer, the extra 1% to 2% energy efficiency obtained from the PV module power supply goes directly into the load. At a power of 500 kW, this means a minimum free additional 5 kW output. In addition, the direct conversion to a usable voltage, rather than a lower unipolar inverter AC voltage, while the AC current is reduced by more than half, thereby reducing the cost of the wires at the AC side.
Without a transformer, the inverter is smaller and lighter, giving power integrators greater freedom in installation and overall system design. Due to weight limitations and necessary reinforcement measures, installing a conventional inverter on a five-story building roof can be prohibitively cost-effective, but designers can install transformerless inverters in commercial buildings. On the roof (instead of being installed in the basement), it is directly connected to the mounting plate on the fifth floor. This design not only eliminates expensive up to five floors of DC wiring, but also shortens the length of the AC wires and reduces associated costs.
Finally, multiple inverters can be connected in parallel without a transformer, while the power supply can be used directly for stable performance. Transformerless inverter technology uses a much larger Line Reactor and smaller triangular filter capacitors. These smaller triangular filter capacitors are also buffered by a series resistor to improve the stability of the control system and reduce the interaction between the parallel inverters. A 500 kW inverter with a single engine design also reduces the number of components, thereby increasing the reliability of the entire system.
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