The difference between electromagnetic induction heater half bridge and full bridge

To understand and answer this question about half-bridge and full-bridge battles, we must first understand what the law of electromagnetic induction is? The law of electromagnetic induction originated from the Danish scientist Oersted’s discovery of the electromagnetic effect in 1820. Many physicists tried to find the inverse effect of the electromagnetic effect, that is, can magnetism produce electricity? Later, many scientists tried to find the answer to this question, but they were unsuccessful.

Until 1831, the British physicist Faraday wound two coils on both sides of the soft iron ring. One was a closed loop. A magnetic needle was placed in parallel near the lower end of the wire. The other was connected to the battery pack and connected to the switch to form a power supply. Close the loop. Experiments have found that when the switch is turned on, the magnetic needle deflects; when the switch is turned off, the magnetic needle deflects in the reverse direction, which indicates that there is an induced current in the coil without a battery pack. Faraday immediately realized that this is a non-constant transient effect. Then he did dozens of experiments, and summarized the situation of induced current into 5 categories: changing current, changing magnetic field, moving constant current, moving magnet, conductor moving in the magnetic field, and formalized these phenomena. Named electromagnetic induction.

The law of electromagnetic induction, the condition of production: the circuit is closed and circulating. The magnetic flux passing through the closed circuit changes. A part of the circuit cuts the magnetic induction line movement in the magnetic field (cutting the magnetic induction line movement is to ensure that the magnetic flux of the closed circuit changes) (only partial cutting can be done, all cutting is invalid) (if one condition is missing, there will be no induced current produce).

The microscopic explanation of the induced current: when a part of the circuit is cutting the magnetic line of induction, it is equivalent to that the free electrons in a part of the circuit do not move along the direction of the magnetic line of induction in the magnetic field, so the free electrons will be affected by the Lorentz force. The function of the directional movement in the conductor, if a part of the circuit is in a closed loop, it will form an induced current, if it is not a closed loop, the two ends will accumulate charge to generate an induced electromotive force.

The reason why the electromagnetic induction phenomenon emphasizes the "part of the conductor" of the closed circuit is that when the entire closed circuit cuts the magnetic induction line, the induced currents on the left and right sides are counterclockwise and clockwise, which cancels out the current for the entire circuit. Energy relationship in electromagnetic induction: electromagnetic induction is an energy conversion process, for example, gravitational potential energy, kinetic energy, etc. can be converted into electrical energy, thermal energy, etc.

The main circuit method to realize induction heating: According to the main circuit of induction heating, it can be divided into two different structures, half bridge and full bridge. Some people think that the half bridge is worse than the full bridge. This is caused by the different understanding of the circuit. Half bridge and full bridge refer to the structure of the main circuit, not the quality. It is like a motorcycle and a car. A motorcycle has 2 wheels and a car has 4 wheels. This is just the difference in the structure of the two cars. All cars Not all are better than motorcycles, and there are many motorcycles that are much better than cars! The realization method of the half bridge is as follows:

Explain the difference between electromagnetic induction heater half bridge and full bridge in detail

The lower structure of C1 and C2 on the left forms a "resonant capacitor", and the T1 and T2 on the right are IGBT high-speed switching tubes. L is the coil, R is the internal resistance of the coil, and the current passes through C1, L, and T2 in the upper half of the cycle. The current direction of L is from left to right; the current passes through T1, L, C2 in the second half of the cycle. The current direction of L is from right to left; under the action of turning on the upper and lower bridges of the IGBT in turn, the coil passes through two back and forth within one cycle to become alternating current, and L produces an alternating magnetic field. The two IGBT switch tubes work in turn at high speed and cannot work at the same time, otherwise the main circuit will be directly short-circuited. This method is called "half bridge structure". Generally used in some low-power induction heating products with low current. For example, it is safer within 15kW, and the control method used to realize the half bridge is generally frequency modulation or width modulation.

If you want to make the power larger, obviously, the structure of the half-bridge is no longer appropriate, and the current of the IGBT must be reduced to increase the power. Change the resonant capacitor on the left side of the half-bridge to an IGBT switch, and connect this resonant capacitor in series with L to form a full-bridge circuit structure, as shown in the figure below:

Explain the difference between electromagnetic induction heater half bridge and full bridge in detail

Working table analysis: the first half cycle T1——L——C——T3; the second half cycle: T4——C——L——T2. The voltage across L is twice that of the half bridge, so the power obtained is 4 times that of the same voltage. so. This is why the full bridge structure is used for high power. Circuit methods for realizing full-bridge control usually include phase shift, frequency modulation, width modulation, pulse density adjustment and other control methods.

Comparison of induction plus effect of full bridge and half bridge: half bridge has smaller inductance and smaller heating area, but the power density for heating the same area is larger; full bridge has larger inductance and larger heating area, but heating the same area The power density is relatively small. The specific selection of heating structure depends on the user's heating load area and the size of the ether heating power density to determine.