The control strategy for small household solar inverters needs to balance efficiency, cost, stability, and safety. The core is to achieve maximum utilization of solar energy, meet output waveform standards, and operate reliably under limited power. Here are several more suitable control strategies and their practical value.
1、 Maximum Power Point Tracking (MPPT): The Core to Improve Power Generation Efficiency
MPPT is a "standard configuration" for household inverters, which tracks the maximum power point (MPP) of solar panels in real time to ensure that the maximum power output is always maintained during changes in lighting and temperature, resulting in a 15% -30% increase in efficiency compared to systems without MPPT.
Comparison of Common MPPT Algorithms (Optimal Selection for Household Scenarios)
Advantages and disadvantages of algorithm principles, applicable scenarios
The perturbation observation method adjusts the voltage/current slightly to observe power changes. The structure is simple, low-cost, and easy to achieve sudden changes in lighting, which may lead to misjudgment. There may be power fluctuations and stable lighting on household roofs
The incremental conductance method determines that MPP tracking speed is fast and has strong anti-interference ability by comparing conductance increment with instantaneous conductance. The algorithm is slightly more complex and requires slight hardware computing power. Frequent changes in lighting (such as tree shade obstruction) are also necessary
Fuzzy control method dynamically adjusts tracking strategy based on empirical rules to adapt to nonlinear characteristics. It requires a large amount of experimental data to optimize rules for good stability and high cost. It is a high-end household system with extremely high efficiency requirements
Household preference suggestion: Prioritize the disturbance observation method (low cost, high reliability). If the roof lighting is unstable (such as with trees around), it can be upgraded to the incremental conductivity method.
2、 Waveform generation and control: ensuring output power quality
Home inverters need to convert DC power into 220V/50Hz sine AC power, and the waveform quality directly affects the lifespan and grid compatibility of household appliances. Common strategies are as follows:
1. Sinusoidal Pulse Width Modulation (SPWM)
The most commonly used waveform control method for household inverters is to generate a pulse sequence equivalent to a sine wave (with a duty cycle that varies sinusoidally), filter it to obtain a sine wave.
Advantages: Low waveform distortion rate (total harmonic distortion THD ≤ 5%), in line with grid standards, suitable for grid connection or driving precision household appliances (such as computers and air conditioners).
Applicable scenarios: All household scenarios, especially those that require grid connection or sensitive loads (such as smart home devices).
2. Simplify SPWM (suitable for low-cost off grid systems)
Simplify the SPWM algorithm, reduce computational complexity, and generate approximate sine waves (THD ≤ 8%). Although the efficiency is slightly reduced, the cost is reduced by 20%, making it suitable for off grid households with only simple loads such as lighting and fans (such as rural areas without power grids).
3、 Output voltage/current control: ensuring electrical stability
The power fluctuation of household loads (such as refrigerators and televisions) is significant, and stable output needs to be achieved through control strategies to avoid damage to equipment caused by sudden voltage/current changes.
1. Voltage and current dual closed-loop control
Principle: The inner loop controls the current (quickly responds to load changes), and the outer loop controls the voltage (maintains the output voltage stable at 220V ± 5%), forming a "voltage current" dual feedback.
Advantage: Strong ability to resist load disturbances. When the load suddenly starts (such as an air conditioning compressor), voltage fluctuations can be controlled within ± 3%.
Applicable scenarios: Backup loads that require independent power supply in off grid systems (without grid support) or grid connected systems.
2. Single voltage closed-loop control (simplified solution)
Only stable output through voltage feedback, simple structure, low cost, suitable for grid connected systems (the power grid itself can provide voltage support), or load stable scenarios (such as only supplying power to mobile phones and routers).
4、 Dedicated control for grid connection: key to safety and compliance
If the inverter is connected to the power grid, it must meet the requirements of same frequency, same phase, and same amplitude, and also have safety protection functions.
1. Phase synchronization control
Real time detection of grid voltage phase through phase-locked loop (PLL), adjustment of inverter output phase, ensuring that the difference between the two is ≤ 1 °, and avoiding equipment damage caused by circulating current during grid connection.
2. Island effect detection
When the power grid suddenly loses power, the inverter needs to stop outputting within 0.5-2 seconds (i.e. "islanding protection") to prevent the inverter from supplying power to the power grid and endangering the safety of maintenance personnel. The commonly used passive detection method for household use (such as detecting voltage/frequency mutations) has low cost and meets reliability requirements.
Summary: The core logic of home inverter control strategy
The control strategy for small household solar inverters should prioritize efficiency while balancing simplicity and safety
Basic configuration: disturbance observation method MPPT+SPWM waveform control+single voltage closed-loop (grid connected scenario);
Advanced configuration: incremental conductance MPPT+voltage and current dual loop+phase-locked loop synchronization+islanding detection (for off grid or complex load scenarios).
These strategies balance cost and performance, maximizing the use of solar energy while ensuring the safe operation of household appliances, making them the optimal choice for home use scenarios.
