I. Key points to improve conversion efficiency
1. Optimize control algorithms
-Advanced control algorithms are of great significance to improving the efficiency of off-grid solar inverters. Adopt optimization strategies of maximum power point tracking (MPPT) algorithms, such as fuzzy logic controlled MPPT algorithms. Traditional MPPT algorithms may have difficulty in accurately tracking the maximum power point under complex light and temperature change environments. The fuzzy logic controlled MPPT algorithm can dynamically adjust the working point of the photovoltaic array through fuzzy rule reasoning based on multiple input variables such as light intensity and temperature. For example, in the morning when the light intensity gradually increases and the temperature is low, the algorithm can quickly adjust the working voltage of the photovoltaic array to the optimal value, so that the solar panel always generates electricity close to the maximum power point, improving the power generation efficiency.
-In addition, using the space vector pulse width modulation (SVPWM) algorithm instead of the traditional sinusoidal pulse width modulation (SPWM) algorithm can also improve efficiency. The SVPWM algorithm can make the voltage waveform output by the inverter closer to a sine wave, reduce the harmonic content, reduce the loss of loads such as motors, and improve the utilization rate of the DC bus voltage, so that more effective power can be output at the same input power, and the overall efficiency of the off-grid solar inverter can be improved.
2. Strategies to enhance stability and reliability
1. Optimization of heat dissipation design
-Good heat dissipation design is the key to ensuring stable and reliable operation of off-grid solar inverters. First, choose the material and size of the heat sink reasonably. For example, an aluminum alloy heat sink is used, which has good thermal conductivity and light weight. According to the power size and heating of the inverter, calculate the area and thickness of the required heat sink. For a 10kW off-grid solar inverter, an aluminum alloy heat sink with an area of 1-2 square meters and a thickness of 3-5 mm may be required to ensure that the power device is within the normal operating temperature range.
-Adding a cooling fan or using a liquid cooling system is also an effective heat dissipation method. In high temperature environments or high power operation, the cooling fan can accelerate air flow and take away the heat from the heat sink. The liquid cooling system has a higher cooling efficiency. The coolant circulates in the heat dissipation pipe to transfer the heat to the radiator for dissipation. For example, in some large off-grid solar power station inverters, the liquid cooling system can control the temperature of the power device at a lower level than air cooling, extend the service life of the power device, and improve the reliability of the inverter.
2. Circuit protection and redundancy design
-A perfect circuit protection mechanism is essential. Overvoltage, undervoltage, overcurrent and short-circuit protection circuits are set at the input and output of the inverter. When the input voltage is too high or too low, the overvoltage and undervoltage protection circuits can act in time to cut off the circuit to prevent the power device from breaking down due to excessive voltage or failing to work properly due to too low voltage. The overcurrent and short-circuit protection circuits respond quickly when the load current is too large or a short circuit occurs to protect the internal circuit of the inverter. For example, by combining fast fuses and electronic protection circuits, the fast fuses can quickly blow at the moment of short circuit, serving as the first line of defense for short circuit protection. The electronic protection circuit can accurately monitor the current size, and timely adjust or cut off the circuit when overcurrent occurs to ensure the safety of the inverter.
-Redundant design can improve the reliability of the inverter. For example, redundant power units are used in the power module design. When a power unit fails, the redundant power unit can automatically take over the work to ensure the continuous operation of the inverter. In some off-grid application scenarios with extremely high requirements for power supply reliability, such as communication base station power supply systems in remote areas, this redundant design can greatly reduce the risk of power outages caused by inverter failures and improve the stability and reliability of the entire system.
III. Measures to improve power quality
1. Harmonic suppression technology
-Off-grid solar inverters may generate harmonics during operation, affecting the power quality. The use of active power filter (APF) technology can effectively suppress harmonics. APF detects the harmonic components in the load current, generates a compensation current of equal magnitude and opposite phase, and injects it into the grid to offset the harmonic current. For example, in an off-grid solar power supply system containing a large number of nonlinear loads (such as electronic equipment, fluorescent lamps, etc.), APF can reduce the total harmonic distortion (THD) from 20%-30% to less than 5%, so that the output power quality meets the relevant standards, reduce the damage of harmonics to electrical equipment, and improve the stability of the system.
-Optimizing the output filter design of the inverter can also reduce harmonics. For example, an LCL filter is used, which consists of an inductor, a capacitor, and a resistor. By reasonably selecting the inductor, capacitor, and damping resistor values of the LCL filter, the high-order harmonics output by the inverter can be effectively filtered out within a wider frequency range, making the output voltage waveform closer to a sine wave, improving the power quality, and avoiding the resonance problem of the filter itself, ensuring the safe and stable operation of the system.
2. Voltage regulation and frequency stability
-In order to ensure the stability of the output voltage of the off-grid solar inverter, a voltage closed-loop control strategy can be adopted. By monitoring the output voltage in real time, comparing it with the set voltage value, and then adjusting the output voltage of the inverter. For example, when the load changes and the output voltage drops, the voltage closed-loop control circuit will increase the output voltage amplitude of the inverter to restore the output voltage to the set value. In some applications with high voltage stability requirements, such as power supply for precision instruments and equipment, this voltage regulation function can ensure the normal operation of the equipment and avoid measurement errors or equipment damage caused by voltage fluctuations.
-For frequency stability, in off-grid solar power supply systems, since there is no grid frequency benchmark, the inverter itself needs to have a frequency stabilization function. Crystal oscillator or digital phase-locked loop (PLL) technology is used to generate a stable frequency benchmark. For example, the digital phase-locked loop can accurately lock and control the output frequency of the inverter according to the set frequency value, so that the output frequency is stable at 50Hz or 60Hz (according to the standards of different regions). Even in the case of changes in solar input power or load fluctuations, the frequency stability can be guaranteed, meeting the requirements of AC load for frequency stability and ensuring the normal operation of electrical equipment.
Through optimization measures in conversion efficiency, stability and reliability, and power quality, off-grid solar inverters can play a better role in off-grid solar power generation systems, improve the performance and practicality of the entire system, and provide better quality and more reliable power supply for off-grid areas.