Increasing demands from electric cars, renewable energy, and the smart grid are driving more and more demand in the solar energy market. As the market skyrockets, the focus is on the increased efficiency, reliability and safety of high performance inverters.
“Addressing the challenges of effective power management in grid-level solar power integration cannot be underestimated,” notes Power Electronics News. “According to Precedence Research, the global solar inverter market was $8.12 billion in 2021 and is expected to exceed $16.88 billion by 2030. The growing demand for green energy is driving the global solar inverter market to curb the impact of carbon dioxide and other greenhouse gas emissions.”
To accomplish this, photovoltaic (PV) solar-cell systems convert light into DC power which then is converted into AC power. This conversion is critical, as is the application of maximum power-point tracking (MPPT), which maximizes energy extraction from the solar cells. DC intermediate power is sent to an inverter for AC power generation before entering the grid. MPPT on the DC input side and inverter-side anti-islanding protection (a safety feature that prevents grid-tied inverters from continuing to feed power into the grid after a power outage) are key functions.
Solar Inverters
Today, these PV systems often employ solar inverters, which are quickly becoming the preferred choice for many solar panel system owners. These inverters employ pulse width modulation (PWM), which uses pulses of varying width to control the output voltage of the inverter. The width of these pulses is determined by the desired output voltage, while the frequency is determined by the desired output frequency. Solar inverters are efficient, using much less energy than other types of inverters. They also produce clean, sinusoidal AC waveforms, are more reliable and less expensive. There are multiple solar inverter topologies:- Central inverters are the simplest, with all panels are connected to a single inverter.
- String inverters are the most common, converting from a string of solar panels. • Microinverters are smaller inverters installed at each solar panel. These
- increasingly popular inverters allow each panel to operate independently, improving performance and efficiency.
Current Sensors
Accurate MPPT readings are critical in PV systems, and that job falls on current sensors. Not only do sensors need to accurately measure current flowing through the panels, they also need to be stable over temperature changes, especially because these systems are designed to face extreme weather types, so that the inverter can adjust the voltage to maximize MPPT. Sensors are also responsible for fault detection, such as short or open circuits, and protect against overcurrent conditions. Finally, sensors enable proper use of advanced circuit management so systems perform at an optimum level. All of this must be tightly monitored and controlled, as each part of a power conversion circuit impacts the other. There are several ways to monitor the current in a circuit. Legacy approaches include shunt-based solutions, which offer dynamic performance and linearity, but struggle with high currents, leading to thermal issues. Shunts are not isolated, contact-based systems, leading to potential failures. Hall sensors are more sophisticated, but lack accuracy and bandwidth – both critical factors in the inverter system. In addition, their physical size and weight make them problematic in any situation where space is at a premium. Today, superior-performing Tunnel Magneto Resistance (TMR) sensors are replacing both Shunt and Hall. Their accuracy, bandwidth and price are ideal for solar inverter topologies, including micro-inverters and DC-DC optimizers. In micro-inverters, the current sensor is typically located on the same PCB as the inverter’s power electronics, allowing the sensor to measure the current directly from the solar panels. In DC-DC optimizers for string inverters, the sensor is typically located on a separate PCB, so it can measure multiple solar panels. In both cases, Crocus Technology’s current sensors are well-suited, as they offer multiple advantages, including:- High accuracy: Crocus Technology’s current sensors are accurate to within 1%FS over temperature -40 to 125degree C, essential for ensuring that panels are operating efficiently under all conditions.
- High bandwidth: Crocus Technology’s current sensors have a bandwidth of up to 1 MHz, enabling them to accurately measure the high frequency currents of fastest-changing solar panels.
- Low noise: Crocus Technology’s current sensors feature 10x lower noise than Hall, ensuring accurate measurement in the mA range maximizing MPPT.
- Isolation: Crocus Technology’s current sensors provide galvanic isolation between the high-voltage current sensing circuit and the low-voltage control circuit, which protects inverter and optimizer damage in the event of a fault in the high-voltage circuit.
