The complete system of off-grid inverter consists of several sub-modules working together, and its detailed architecture is as follows:

1. DC input and pre-processing unit
Input filtering: Filter out the high frequency noise of DC power source (e.g. battery pack, PV panel) through capacitors and inductors to avoid interference to the inverter circuit.
DC-DC converter (optional): If the input voltage fluctuates greatly (e.g., the output of PV panels varying with light), Boost or Buck topology is used to adjust the voltage to a stable value. For example, Boost circuits are commonly used in PV systems to step up the 12-48V input to the 300-400V high-voltage DC bus to improve inverter efficiency.
2.MPPT controller (special for PV system)
Working Principle: MPPT (Maximum Power Point Tracking) calculates the current power by sampling the voltage and current of the PV panels in real time and adjusts the duty cycle of the DC-DC converter so that the PV panels always work at the maximum power point (Vmp, Imp). Commonly used algorithms include Perturbation and Observation (P&O) and Incremental Conductance (INC).
Efficiency Impact: MPPT can increase the power generation efficiency of PV system by 10%-30%, especially effective under cloudy or low light conditions.
3. Energy storage battery management system (BMS)
Charge and Discharge Control: Multi-stage charging strategy (e.g. constant current→constant voltage→float charging) is used to prevent the battery from being over-charged or over-discharged. Lithium batteries require precise voltage monitoring (e.g., single-unit voltage difference ≤50mV), while lead-acid batteries focus on temperature compensation.
SOC estimation: Estimate the remaining capacity (SOC) of the battery by Coulomb counting or open circuit voltage (OCV) method to ensure that the inverter distributes energy reasonably.
4. Inverter circuit core topology
Full-bridge inverter circuit: 4 power switches (e.g. MOSFETs or IGBTs) form an H-bridge, which generates an AC waveform by alternating conduction. The advantages are high output power and low harmonic distortion, but the control complexity is high.
Half-bridge inverter circuit: Only 2 switching devices are required, which is lower cost, but the output voltage amplitude is half of the input voltage, which is suitable for low power scenarios.
High-frequency and industrial frequency design:
High Frequency Inverter: Uses a high frequency transformer (above 20kHz), small size and light weight, but requires complex filtering circuits.
Industrial frequency inverter: using 50/60Hz transformer, high reliability but bulky, suitable for industrial scenarios.
5. Filtering and waveform optimization
LC low-pass filtering: composed of inductors and capacitors, the cut-off frequency is set slightly higher than the output AC frequency (e.g. 50Hz), filtering out the high-frequency harmonics in the PWM square wave.
LCL filtering (advanced design): more common in grid-connected inverters, can further suppress high-frequency noise, but need damping resistors to avoid resonance.
6. Core functions of the control unit
SPWM modulation (Sinusoidal Pulse Width Modulation): Compare the reference sinusoidal waveform with the high-frequency triangular carrier waveform to generate the PWM signal to drive the switching device and control the amplitude and frequency of the output voltage.
Closed-loop feedback control: real-time acquisition of output voltage and current through Hall sensors, using PID algorithm to dynamically adjust the PWM duty cycle, to ensure that the voltage is stabilized at 220V ± 5%, frequency 50Hz ± 0.5Hz.
Protection mechanism:
Overload protection: when the load current exceeds the rated value (e.g. 120% for 10 seconds), the output is cut off immediately.
Short-circuit protection: use hardware comparator to quickly detect short-circuit (response time <10μs), shut down the switching tube.
Reverse connection protection: When the input DC polarity is reversed, blow the fuse or trigger the MOSFET reverse cutoff.