dielectric barrier strong ionization discharge -Lithium - Ion Battery Equipment

Research and manufacture of inverter power supply for dielectric barrier strong ionization discharge -Lithium - Ion Battery Equipment

Dielectric barrier strong ionization discharge technology is an important emerging aspect of plasma application technology. It covers a thin dielectric layer on both sides or one side of the gas discharge gap by using methods such as sticking. When a high-voltage alternating current of a certain frequency is applied between the two electrodes, the gas in the gap will be ionized, forming a strong The gas discharges, thereby creating a high concentration plasma. The discharge intensity of the gas in the gap is a quantity related to frequency, voltage, material and structure. Due to the limitation of high-power frequency converter devices and technologies, the traditional power supply device for dielectric barrier discharge can only be realized in two ways: one is to use a transformer to directly boost the power frequency AC to the required voltage; the other is to use devices such as thyristors Modulates power frequency alternating current to a relatively high frequency alternating current. Using these two methods of power supply, although a high voltage can be applied between the two poles of the discharge device, and the inverter power supply of devices such as thyristors or GTRs can also increase the operating frequency of the discharge device, it still cannot meet the requirements of high-performance gas discharge. In order to meet the needs of the project, release the fund project: an engineer funded by the National Natural Science Foundation of China (69871002), and his research direction is the application of power electronics technology in plasma engineering.(Lithium - Ion Battery Equipment)

The gas discharge in the electrical gap is not strong enough. The discharge device and the inverter power device are bulky, and the structure of the inverter power supply is complex and unstable, which cannot meet the needs of practical applications, and limits the development of the application technology of dielectric barrier strong ionization discharge.

The emergence of high-frequency and high-power power electronic devices such as IGBT and the development of related frequency conversion technology provide a reliable premise and guarantee for the development of dielectric barrier strong ionization discharge, an emerging technology. We know that IGBT is a composite device of MOSFET and GTR, which has the dual advantages of MOSFET and GTR. Applying IGBT to the inverter power supply for dielectric barrier strong ionization discharge not only doubles the performance of the dielectric barrier discharge device, but also doubles the volume of the discharge device and power supply device, further simplifies the inverter power supply, and makes the dielectric barrier discharge device double. The application range of strong ionization discharge technology is getting wider and wider.

2 Equivalent circuit of dielectric barrier discharge The principle structure of dielectric barrier discharge is shown in a, 1 is the high voltage electrode; it is the dielectric layer; 3 is the discharge gap; 4 is the ground electrode; 5 is the power supply. According to the physical structure analysis, the dielectric barrier discharge is actually a lossy capacitor composed of discharge electrodes, dielectric layers, and discharge air gaps, which can be equivalent to a resistive capacitive load for the power supply. b is the equivalent circuit diagram of dielectric barrier discharge. Among them, Cg is the capacitance of the discharge air gap; Rg is the equivalent resistance of the discharge gap, which changes with the voltage applied between the electrodes and has a strong nonlinearity; Cs is the capacitance of the dielectric. The insertion of the dielectric layer effectively suppresses the unlimited increase of the discharge current, prevents spark discharge or arc discharge in the discharge gap, and makes the gas discharge formed in the gap more intense, and thus adds some new features: ① Dielectric barrier The discharge device has high initial voltage and working voltage. When the voltage applied between the two electrodes of the dielectric barrier discharge device is lower than the initial voltage, no gas discharge will be formed in the gap, and the current passing through the load is very small. When the voltage in the gap is higher than the initial voltage of the discharge gap, gas discharge begins to occur in the gap, and the intensity of the discharge is proportional to the voltage. The higher the voltage, the stronger the discharge; ② To achieve dielectric barrier strong ionization discharge, the power supply must be With a higher operating frequency, the intensity of the dielectric barrier discharge is proportional to the frequency of the power supply voltage. The higher the voltage frequency applied to both ends of the electrodes, the stronger the gas discharge in the gap, and the greater the loss of the dielectric, the more serious the heat generation; ③In order to achieve the best discharge effect, the dielectric layer in the dielectric barrier discharge device is generally made very large Thin, the applied voltage often works close to the critical breakdown voltage value, and the overvoltage capability of the discharge device is very low; ④The dielectric barrier discharge device is a resistive and capacitive load, and the circuit may form with the leakage inductance of the transformer and the circuit when it is working. LC oscillation, so that overvoltage is formed at both ends of the load, especially when starting, it is easier to form a resonant overvoltage, which endangers the safety of the discharge device and the power supply itself. Therefore, the design of the circuit must ensure that the voltage applied to the load can quickly exceed the starting voltage The initial voltage will not form overvoltage.

3 Basic structure of IGBT inverter power supply for dielectric barrier discharge The block diagram of the IGBT inverter power supply designed according to the technical requirements of dielectric barrier discharge is shown in the figure. The three-phase alternating current is rectified into a smooth direct current by the rectification filter circuit after being filtered by EMC. The IGBT full-bridge inverter converts this DC power into a single-phase AC power with a uniformly adjustable duty ratio within a certain range, and then outputs it to a dielectric barrier discharge device after being boosted by a high-frequency and high-voltage transformer. All regulation of the system is realized by IGBT full-bridge inverter. The purpose of using the EMC filter circuit in the power system is to effectively suppress the electromagnetic noise and conduction noise generated by the inverter circuit and high-frequency and high-voltage gas discharge, so as to prevent the inverter power supply and high-frequency and high-voltage gas discharge from affecting the mains network and the power system itself. and other equipment around it. The rectification and filtering part of the system adopts three-phase full-bridge uncontrollable rectification and LC filtering, which can simplify the circuit and reduce the cost. The IGBT inverter adopts the full-bridge PWM technology, which not only meets the requirements of the dielectric barrier discharge technology, but also simplifies the structure of the inverter power system. The high-frequency high-voltage transformer uses a ferrite core suitable for high-frequency work. When winding the winding, try to use a thinner insulating material with good insulation performance, and at the same time wind the primary coil with a small number of turns in the middle of the secondary coil. , to reduce leakage inductance.

4 Control circuit The control circuit is a very important aspect in the dielectric barrier discharge power supply system. All functions of the dielectric barrier discharge are realized by the control circuit controlling the IGBT inverter. The control circuit of the power supply is composed of signal detection circuit, PWM control circuit, drive and protection circuit and other parts.

4.1 Signal detection The power supply is equipped with input voltage signal detection, IGBT over-current signal detection, output voltage signal detection, load current signal detection and so on. The input voltage signal is obtained by the auxiliary transformer; the IGBT overcurrent detection is obtained from the source of the IGBT through the diode; the output voltage detection is obtained through the voltage divider; the load current detection is to connect a measuring capacitor C in series to the dielectric barrier obtained from the low voltage side of the discharge device (see). Because: out), and because: C detects the capacitance of the capacitor. It can be seen that as long as the voltage on the capacitor is detected, the current flowing through the load can be known. The purpose of using a measuring capacitor to measure the load current: on the one hand, the dielectric barrier discharge device itself is a capacitive load, and using the measuring capacitor to detect the load current will simplify the circuit while ensuring the measurement accuracy; on the other hand, it will not cause the circuit loss.

42PWM control circuit The core component used by the PWM control circuit is the SG3524 pulse width modulation component. As shown, the system soft-start circuit is composed of an adder and an integrator composed of operational amplifiers, and is connected to pin 9 of the SG3524. When the system is powered on, the soft start circuit controls the level of pin 9 of SG3524 so that the output voltage is just at the initial voltage of discharge and maintains it for a period of time, and then the integrator gradually increases the level of pin 9 according to a certain slope to make the output voltage rise to the discharge voltage. voltage setting. This avoids impacting the load when starting. The stability of the output voltage is realized by the error amplifier (pin 1, pin 2) of SG3524 and peripheral circuits. When faults such as overvoltage, overcurrent, overload, and undervoltage occur in the power supply system, after processing by the signal processing circuit, the trigger sends a high level to pin 10 of the SG3524 and locks the output voltage for 20ms, and then repeats the soft start process. If the fault phenomenon persists within a certain period of time, the power supply output will be completely interrupted and a fault alarm will be issued.

The output PWM modulation wave can directly drive the isolated optocoupler.

PWM control circuit 4.3 Improvement of the drive circuit EXB841 is a special IGBT drive module produced by Fuji Corporation of Japan. Due to the structure and use, some problems often occur, so some improvements have been made to the drive circuit in the application: ① The EXB841 drive module uses a single +20V For power supply, the negative bias voltage is formed by using a 5V voltage regulator tube. Because of its small power, it cannot suppress the fluctuation of the grid voltage well, and it is easy to cause damage to the IGBT. Therefore, a 6V regulator tube with a power of 1W is connected outside the circuit, and the power supply voltage is slightly increased. In this way, the damage of the drive module can be effectively prevented, and at the same time, the IGBT can be driven and turned off more reliably; ②The fast recovery rectifier diode connected in series between the over-current detection terminal of the EXB841 drive circuit and the drain of the IGBT protects the IGBT from over-current It has a very important impact, and the forward voltage drop is generally required to be 3V. However, the fast recovery 5 conclusions that can be purchased in the domestic market have been successful in the dielectric barrier discharge technology. Applications. Practice has proved that the design of the inverter power supply system fully meets the needs of dielectric barrier discharge technology. The power supply not only has a simple circuit structure, doubles the volume, and has stable and reliable performance, but also greatly reduces the volume of a dielectric barrier discharge device using the power supply, and greatly improves the performance. The application results of the power supply unit with an output power of 20kW and a working frequency of 20kHz in a high-yield, high-concentration ozone generator show that the volume of the power supply unit is only one-fifth of the original volume, and the volume of the ozone generator is only one-sixth of the original volume First, under the same production conditions, the concentration of O3 increases several times, the highest concentration can reach 200g/m3, and the consumption of raw gas is also reduced. The problem brought about by the inverter power supply is that the increase in frequency increases the energy consumption of the discharge device and decreases the efficiency. The next development goal is to improve the control method and try to improve the efficiency of the device while maintaining high concentration and high output of the ozone generating device.



Contact Us

24 hours online service