How to solve the harmonic of switching power supply
In modern electronic equipment, switching power supply is a widely used form of power supply, which has the characteristics of small size and high efficiency. However, switching power supply will also produce harmonics, which will affect the quality of power supply and the stability of power grid to a certain extent, and even cause harm to circuits and devices. Therefore, it is imperative to solve the harmonic problem of switching power supply.
Causes of harmonics in switching power supply
Harmonic wave refers to a kind of electric waveform with higher frequency than fundamental wave, and its source generally comes from factors such as nonlinear load, non-sinusoidal voltage and electromagnetic interference. The working principle of switching power supply determines that it is easy to produce harmonics.
1. Short-circuit effect of capacitor filter circuit
In switching power supply, the capacitor filter circuit mainly reduces the pulsating voltage on the output of power supply, but at high frequency, the capacitor is also a short circuit. However, short circuit will make harmonic current flow into the power supply, produce oscillation in the conductor, and cause noise and thermal effect.
2. Resonance effect of inductance filter circuit
In the switching power supply, the inductance filter circuit is mainly used to prevent the high-frequency pulsation of the power supply output. When the load current is very low, the inductance is in a resonant state, which will produce high-frequency harmonic current. The generated high-frequency harmonic current will resonate in the power supply capacitor and line inductance, and generate high-frequency oscillation when the current flows.
3. Resonance influence of inductance feedback circuit
Resonant feedback circuit is an important performance characteristic of switching power supply. The feedback controller is used to continuously monitor the load and power supply, so as to adjust the power supply output in time and improve the efficiency of the whole circuit. However, the inductive feedback circuit will reduce the output voltage of the power supply through the resonant circuit, which will increase the generation of harmonic current.
4. The influence of working frequency
The higher the working frequency of switching power supply, the higher the harmonics and the richer the harmonic current. The high-frequency current will generate relatively large electromagnetic waves on the coil, which will also lead to the phenomenon that the electrical appliance itself and electromagnetic waves are full of interaction in the air.
Harm of switching power supply harmonics
Harmonic of switching power supply will do harm to equipment and system, and the specific harm is as follows:
1. Harm to the switching power supply itself.
The harmonic generated by switching power supply at high frequency will increase the internal heat consumption of switching tube and increase the risk of its damage.
2. Harm to the load
The output harmonics of switching power supply will affect the load, which is easy to damage the components in the circuit, especially for precision instruments and medical equipment.
3. Harm to the power grid
After the switching power supply outputs harmonics, it will spread through the power grid and increase the harmonic current of the power grid, which will lead to problems such as overload of the power grid, temperature rise of cables, damage of the power transformer core and so on, thus affecting the stability.
Solutions to harmonics of switching power supply
In order to better solve the harmonic problem of switching power supply, the following solutions are usually adopted:
1. Adopt harmonic suppression circuit.
Using harmonic suppression circuit can limit the generation of high frequency current and effectively reduce the influence of harmonic current on switching power supply.
2. Adopt a new filter
The new filter has a good solution to the harmonic problem of switching power supply, such as using non-inductive topology circuit, multi-capacitor-multi-parameter filter and so on.
3. Improve the design of switching power supply.
In the design of switching power supply, we should optimize its electronic components, wiring forms and composite materials, so as to minimize its internal energy loss and energy degradation and reduce the generation of harmonics.
4. Install energy-saving appliances or increase the output voltage.
By installing energy-saving appliances or increasing the output voltage of switching power supply, the generation and influence of harmonic current can be effectively reduced.
