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18650 rechargeable battery lithium 3.7v 3500mah
18650 rechargeable battery lithium 3.7v 3500mah
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  Induction heating power control circuit

  The composition of the power electronic control circuit in the induction heating power supply shows diversified composition methods. The control scheme is mainly based on the power adjustment method of the induction power supply and the heating load characteristic requirements. The structure of the control circuit will be different.

  The power control and adjustment methods of induction heating power supplies can generally be divided into two types: DC side power adjustment and inverter side power adjustment. DC side power regulation is divided into three-phase fully controlled rectifier power regulation and DC chopper voltage regulation and power regulation. The control circuit scheme for power regulation on the inverter side is based on the requirements of the heating process characteristics. The control methods that can be used are more flexible. Commonly used ones include frequency modulation (pFM), phase-shift power modulation (pSM), and pulse width modulation constant frequency power modulation (pWM). , pulse density modulation power modulation (pDM), width modulation plus frequency modulation power modulation (pWM+pFM), pulse width modulation plus pulse density modulation power modulation (pWM+pDM) and other power modulation methods.

  Induction heating power supplies have the highest heating efficiency and fastest speed for metal materials, and are low consumption and environmentally friendly. It has been widely used in thermal processing, heat treatment, thermal assembly, welding, smelting and other processes of metal materials in various industries. Induction heating power supply consists of two parts. One part is the AC power supply that provides energy, also called variable frequency power supply; the other part is the induction coil that completes the electromagnetic induction energy conversion, called the inductor.

  Basic composition and principles of induction heating power supply control circuit

  (1) The control method depends on the load characteristics of the induction heating power supply and the power adjustment method. Generally, voltage feedback control and current feedback control can be used.

  1) Using voltage control, the purpose is to ensure that the output DC bus voltage is constant, that is to say, the terminal voltage applied to the induction heating winding is constant. The control sample can be taken from the DC bus voltage or the voltage on the inverter inductor winding or resonant compensation capacitor. An isolated voltage sensor (TV) is generally used for sampling. After calculation and comparison processing, the conduction angle of the thyristor or the phase shift or pulse width of the pWM drive pulse of the inverter switch tube is controlled to change the DC output to the inverter. The voltage on the DC bus may change the average (or effective value) of the inverter output voltage, and ultimately the output voltage is maintained constant due to the effect of closed-loop negative feedback. The fluctuation of the input voltage has a great impact on the output power of the heating power supply, that is, on the heating temperature of the workpiece, and will directly affect the product process quality requirements of the heated workpiece.

  The output power of the heating power supply is p=u2/Z. Under the condition of unchanged load, the power p is related to the voltage group or the voltage on the resonance compensation capacitor. Proportional to the square of u. That is, the heating temperature is proportional to the square of the voltage. If the voltage is unstable, the heating temperature will be uneven. For occasions where high temperature stability is required for heating and quenching of blank workpieces, automatic voltage stabilization function must be provided, otherwise product quality will not be guaranteed.

  2) Using current control, the purpose is to ensure constant output DC or high-frequency output current. The control sample can be taken from the DC bus current or the current in the inverter induction heating winding. Sampling generally uses an isolated current sensor (TA). The object controlled by the current feedback signal is the same as the voltage control. The purpose is to achieve changes in the output current, that is, changes in the output power p and heating temperature. This is because p=IUuzuzu, so it can be seen that changes in voltage U or load impedance Z will cause changes in current I, that is, changes in power or heating temperature.

  3) Power control is used to ensure constant power output of the induction heating power supply. The sampling signal simultaneously samples voltage and current signals. After being processed by the multiplier, the output of the pI regulator is compared with the power given to control the conduction angle of the thyristor or the width and phase shift of the inverter drive pulse signal, or use dynamic impedance. The matching method controls the equivalent impedance on the power supply side to be equal to the load to achieve constant power, ensure that the heating temperature is constant at a given power, and meet the workpiece heating process characteristics and quality requirements.

  (2) The control circuit of an induction heating power supply that adopts the DC side power adjustment scheme requires a phase-locked frequency automatic tracking system. none. Whether the inverter uses pulse width modulation (pwM) control technology to adjust power, or uses phase shifting (pSM) to adjust power, if the inverter side does not perform automatic frequency adjustment, two major problems will occur: ① Inverter The switching power device cannot work well in the soft switching state. The switching device is subject to large voltage and current stress. In addition to endangering the safety of the device, the switching loss also increases; ② Because the operating frequency of the inverter is different from the inherent resonant frequency of the resonant circuit. Not equal, a large reactive current flows through the inverter circuit or switching device, and the power factor drops, the maximum power output cannot be reached, and the efficiency of the inverter drops. The purpose of frequency tracking is to ensure that the switching frequency fs of the inverter is equal to the natural resonant frequency of of the resonant circuit, and that the voltage and current are consistent in phase. Because there is no phase difference between voltage and current, the power factor cos=1 and maximum power output is obtained.

  The phase-locked frequency automatic tracking control circuit can be implemented using analog circuits, for example: ① Through inverter output current detection sampling, zero-crossing detection, shaping, etc., it is processed into a square wave signal to control a dedicated pulse width modulator (pWM) integrated circuit The synchronization terminal; ② After the current signal is sampled, it is rectified and calculated by the pI regulator. To control the frequency setting end of the pWM integrated circuit. The commonly used SG3525pWM integrated circuit with more complete functions uses an analog control circuit to realize automatic frequency tracking, which is more convenient to use. Terminal 6 of SG3525 is the frequency resistor setting pT terminal. Changing the voltage (or current) of this terminal can change the frequency of the pWM output pulse. By adding the square wave pulse processed after current sampling to the synchronization terminal 3 of the pWM modulator SG3525, the frequency of the pWM output pulse can be synchronized with the frequency of the current.

  Phase-locked frequency automatic tracking control circuits are currently more commonly used dedicated phase-locked loop integrated circuits, such as general-purpose CD4046, high-speed phase-locked loop MM74HC4046, and digital phase-locked frequency tracker control using microcontrollers and digital signal processors DSp. Systems, etc., digital phase-locked loops and analog phase-locked processors, DSp digital phase-locked frequency tracker control systems, etc., digital phase-locked loops and analog phase-locked.

  (3) Load matching control is also a key control technology for induction heating power supplies. According to electrical engineering principles, when the output impedance of the power supply is equal to the load impedance, the maximum power can be obtained from the load. The load impedance will change during the induction heating process. If the output impedance of the power supply cannot be adjusted in time to match the load impedance, it will be impossible to obtain the maximum rated output power on the load, and the efficiency of the heating power supply will decrease. In addition, if the same induction heating power supply is used to heat workpieces with different load characteristics, and for the convenience of operation and cost savings, the parameters or characteristic impedance of the heating power supply load resonant circuit are not changed, which is common in practical applications. If you adjust the output impedance of the heating power supply in a timely manner for different heating loads to match it, you can also obtain maximum power and efficiency on the load for different heating loads.

  The commonly used method for load impedance matching is to use a matching transformer between the heating power supply and the load, and adjust the change of the transformer to achieve the purpose of equalizing the equivalent impedance on the power supply side and the load impedance. Secondly, electronic circuit control methods can be used to achieve load impedance matching. For example: by adjusting the pulse density of the inverter switch tube drive signal, the equivalent impedance on the power supply side is adjusted to match the load impedance; by adjusting the phase shift of the inverter switch tube drive signal pulse, the equivalent impedance on the power supply side is adjusted. Match it to the load impedance. Matching impedance actually means matching power so that the power supply reaches maximum efficiency.

  (4) The control system of induction heating power supply should also include inevitable failures. Therefore, the heat-sensing power supply, like other electronic equipment, may also experience occasional malfunctions: In order to ensure that the power supply meets the requirements for use under the condition that the electrical performance parameters and technical indicators meet the requirements, in order to ensure that the power supply operates in harsh environments and sudden failures. To ensure the safety and reliability of the power supply device, multiple fault protection functional circuits must be designed. Once a fault occurs, the power supply device is safe and reliable. Multiple fault protection circuits must be designed to function so that the power supply automatically enters the protective working state, or automatically shuts down and stops working. , or automatically correct the parameters to operate under a normal and reasonable working condition. It should be said that among the many quality indicators of induction heating power supply, safety and reliability are the primary principles.

  What should the induction heating power supply protection and control function circuit include?

  1) Overcurrent detection and protection. This includes over-current detection and protection of input current and inverter output current.

  When overcurrent occurs, the protection control circuit should promptly correct parameters to make the power supply operate in a current-limiting state and ensure that the power supply operates within the rated input or output current. Only in the event of severe overcurrent or short circuit failure, shutdown protection measures can be taken.

  2) Input voltage overvoltage and undervoltage protection. If the input voltage is too high or too low, the main hazards caused to the heating power supply are:

  The voltage or current stress endured by the power device will exceed the normal rating, causing the possibility of device damage. Moreover, when the input voltage is too low, the operating DC voltage of the control circuit exceeds the minimum voltage or even if it does not exceed the minimum voltage, it will cause the control circuit to operate unstable and cause the heating power supply to malfunction.

  Technology Zone Typical voltage topology applications in automotive systems How to convert an adjustable DC-DC into a numerically controllable switching regulated power supply How to wire a three-terminal voltage regulator tube and its method Description Three-terminal voltage regulator tube model Voltage stabilization value and detailed information ADI The LT8603 with powerbyLinear™ can accept 42V input voltage


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