The loss of solar inverters is an important factor affecting their efficiency and performance, and its magnitude is related to various factors. The following provides a detailed analysis from the aspects of devices, operating conditions, and system design:
1、 Device and Circuit Design Factors
Characteristics of power devices
Switching losses: IGBT, MOSFET and other power devices experience losses during the switching process due to voltage and current overlap. The higher the switching frequency, the greater the losses (such as high-frequency inverters usually have higher losses than low-frequency inverters).
Conduction loss: When a device is turned on, there is a conduction resistance (such as Rds (on) of a MOSFET), which generates thermal loss when current passes through, proportional to the square of the current and the conduction resistance.
Diode losses: The forward voltage drop and reverse recovery characteristics of freewheeling diodes can cause losses, while fast recovery diodes can reduce reverse recovery losses.
Loss of magnetic components
Transformers and inductors: hysteresis loss and eddy current loss of the iron core (related to the iron core material, operating frequency, and magnetic flux density), as well as copper loss of the winding (related to current and wire resistance).
High frequency transformer: Skin effect and proximity effect intensify at high frequencies, leading to a significant increase in copper loss.
Drive circuit loss
The power consumption of the driving signal and the device switching delay caused by unreasonable driving parameters (such as driving voltage and current) indirectly increase the switching loss.
2、 Operating conditions and load factors
Load rate (output power)
Inverters have different efficiencies under different loads, usually with the highest efficiency at 50% to 80% of rated load. The proportion of losses increases under light or overload conditions (such as high fixed loss ratio under light load and intensified device heating under overload).
Input voltage fluctuation
The output voltage of solar panels varies with light and temperature, and the inverter may experience increased losses due to frequent MPPT (Maximum Power Point Tracking) adjustments or efficiency curve deviations when operating at non optimal points.
operation temperature
An increase in device temperature can lead to an increase in on resistance (such as MOSFET), a decrease in switching speed, and thus an increase in losses. At the same time, high temperatures can also affect the lifespan and performance of capacitors and other components.
Output waveform and harmonics
Compared to square wave/modified sine wave inverters, sine wave inverters have higher switching losses but lower harmonic losses; If the output harmonic content is high, it will cause additional losses on the load side (such as motor heating).
3、 System design and topology factors
Topology structure type
Single stage inverters (such as full bridge topologies) have a simple structure, but their MPPT and inverter functions are integrated, resulting in a more concentrated loss distribution;
Multi level inverters (such as DC-DC+DC-AC) optimize efficiency through hierarchical conversion, but the circuit complexity increases and may introduce more device losses.
The topological differences between grid connected inverters and off grid inverters (such as whether they include power frequency transformers) can affect the distribution of losses (copper and iron losses are more pronounced in power frequency transformers).
Thermal Design
Poor heat dissipation leads to excessive device temperature, which in turn increases losses (such as high thermal resistance of heat sinks or fan failures that can reduce heat dissipation efficiency).
Control Strategy
The accuracy and response speed of MPPT algorithm: Large tracking errors or frequent oscillations can lead to input power loss;
The optimization level of PWM modulation strategies (such as SVPWM, SPWM) affects switch losses and output harmonics.
4、 External environment and installation factors
Environmental temperature and ventilation
In high temperature environments, the cooling efficiency of inverters decreases, device temperatures rise, and losses intensify; Sealed installation or poor ventilation will further deteriorate the heat dissipation conditions.
Grid quality (grid connected inverters)
Voltage fluctuations, harmonic interference, or frequency offset in the power grid may cause inverter overload, protection actions, or additional losses (such as increased copper losses due to current distortion).
Connecting wires and contact resistance
Thin, long, or poorly connected input and output cables can increase line resistance and cause heat loss when current flows through (especially in high current scenarios).
5、 Other factors
Component aging and reliability
Drying up of capacitor electrolyte and degradation of power device parameters (such as increased on resistance) will lead to an increasing loss year by year.
Protection and filtering circuit
The inductance, capacitance and other components in lightning protection circuits and EMI filtering circuits may introduce additional losses (although the proportion is usually low, it cannot be ignored).
Summary: Loss optimization direction
Device selection: Use power devices with low on resistance and fast switching speed (such as SiC and GaN devices), and low loss iron core materials (such as nanocrystals and ferrites).
Topology and control optimization: High frequency soft switching technology (such as LLC resonant topology) reduces switching losses, and efficient MPPT algorithm reduces tracking errors.
Heat dissipation and layout: Optimize heat dissipation structure, shorten high current path, and reduce contact resistance.
Operation management: dynamically adjust the working mode according to the load to avoid long-term overload or light load operation.
By comprehensively considering the above factors, the losses of solar inverters can be effectively reduced, and system efficiency and reliability can be improved.
