The circuit was compared and analyzed.
The coal mine underground electric motor lighting power supply is a device that inverts a 550V or 250V DC power supply into a 24V AC or DC output. In the early 1990s, China has developed and developed a "directed lighting transformer for thyristor mines" and promoted it in coal mines. With the rapid development of integrated circuit technology at home and abroad and the continuous development and application of new power electronic devices, the requirements for small size, light weight, high efficiency and high performance have also been put forward for the inverter power supply. Therefore, the relevant departments have developed a new type of "mineral inverter lighting power supply" and promoted it in coal mines. The principle of the new mine lighting power supply is briefly introduced and compared with the thyristor inverter power supply.
Working principle of thyristor DC lighting transformer The principle of mining DC lighting transformer is shown in After the power is turned on, the diode is isolated! i. The filter inductor “0” and the filter capacitor 0 form a filter circuit, and then the transformer 1 is charged. At the same time, the voltage is stabilized by the commutation line “1, the step-down resistor %3 is established in the control circuit. At this time, a relaxation oscillator composed of a single junction transistor or the like operates, and a pulse signal is emitted, and after being shaped and amplified by power, the pulse transformer MB is coupled to output a pulse to trigger the thyristor SCR to be turned on. SCR- is turned on, then the "11-constituted oscillating circuit works. When the vibration is reversed, the thyristor SCR is forcibly turned off. After the next pulse arrives, the above process is repeated. Since the transformer is subjected to voltage during the above work, in its The output stage couples and outputs an alternating voltage for the illumination lamp, and the alternating voltage is further used by the rectifier filter circuit composed of the diode capacitor 3 for the DC speaker.
Low, high output harmonic components, poor operational reliability and relatively large noise, severely restrict its promotion and application in coal mines. The new "mineral inverter lighting power supply" completely replaces the original thyristor power supply with a switching power supply.
The working principle of the new mine inverter lighting power supply 2.1 The design idea is to use S5920MOS high-power switch tube instead of the original thyristor tube to improve the switching speed and working frequency, the design frequency is 50kHz. The second is the high-frequency transformer using %25B material. Instead of the original ordinary power frequency transformer, not only the frequency is increased, but the volume is reduced by 3/4. Third, the TL494PWM pulse width modulation integrated circuit is used instead of the voltage modulation circuit of the original discrete component to improve the stability and reliability of the circuit.
Design a new generation of products based on the replacement of main components. Components should be integrated and miniaturized as much as possible. The circuit design strives to reduce its own losses and optimize the circuit layout. After many times of debugging and strict screening, the product structure is very compact, the volume is reduced to 1/2 of the original, the output DC is stable, and the protection action is sensitive. The field test confirmed the original design features and met the original design requirements.
2.2 Working principle The principle of the new mine inverter lighting power supply is shown in When the high voltage direct current is input, the voltage is sent to the main switch circuit by the filter isolation circuit, and the other is used as the turn-on voltage of the control circuit through the start circuit to the core control circuit PWM pulse generator. DWM output switching pulse, the main switching circuit is driven by the pulse amplifying circuit (as shown), the main switching circuit adopts a half bridge conversion circuit, Mi and '2 are alternately turned on, and the high frequency voltage is generated under the transformer. Filter circuit, output 24V DC.
The output voltage is on the one hand the PWM DC power supply, and on the other hand, as the output sampling signal, the PWM is sent through the feedback link. When the load and the high voltage DC are small fluctuations or changes within a certain range under different loads, the sampling signal is compared with the reference signal voltage. Input and output according to Table 1. The original thyristor power supply inverter voltage output waveform is asymmetrical (see above). The power utilization rate is low, and the general thyristor power conversion rate is about 30+.
In the experiment, the input voltage to the switching power supply is 600V. When the load is different, the measured power conversion rate does not change much. The experimental data is shown in Table 1. It is known from Table 1. When the load is different, the conversion rates are: It can be considered that the switching power supply conversion efficiency is about 55+. It is nearly double the thyristor type.
High output stability. The task of the output circuit is to rectify and filter the square wave voltage of the secondary of the high frequency transformer. In the middle, the series coupling capacitor 3 is coupled to form a series resonant circuit on the other hand. The resonant frequency /R is: and Lr in order to make the coupling capacitance charging curve change linearly, the resonant frequency /R must be lower than the switching frequency / s of the power supply. According to the above conditions, the filter selects the filter inductance %, 3 and 0 parameters. The rectifier circuit with LC filter is suitable for occasions with large power, large current and small output pulse, especially for high frequency effect. When the high frequency square wave (see) is rectified and filtered, the output is stable 24V. DC, under the condition of load change or high voltage power supply fluctuation, the PWM circuit modulates the voltage regulation, and the output curve is almost horizontal.
Because of the asymmetry of the inverter voltage waveform (see), the thyristor power supply has high harmonic components, low power supply operating frequency, and soft output characteristics. Especially when the high-voltage power supply fluctuates greatly, the feedback link is nonlinear and the output is jittery.
High reliability. When the original thyristor power supply is working, because it has no self-shutdown capability, it must add a shutdown circuit. The turn-off speed and the energy required to turn off depend on factors such as the parameters of the shutdown circuit and the magnitude of the load. Once the parameters are determined, the shutdown capability is also a fixed value parameter, so that when the DC power supply fluctuations in the well are large, there may be an "out of control" unstoppable phenomenon. According to the usage statistics of a mine in Xishan Mining Bureau, overcurrent protection When the action is not timely, the current limiting resistor and the thyristor tube are often burnt. In the new inverter, the main power device adopts MOS power tube, which is characterized in that when the gate and source voltages are zero, the drain and source are in a high-resistance state, that is, the self-shutdown capability, thus eliminating the additional off. Break the circuit. Secondly, the middle Fm and the 8 are respectively connected across the drain and the source of the two power tubes, and have a dual function. When the power tube is turned off, it controls the leakage inductance energy of the high-frequency transformer to return to the DC level, and On the one hand, due to the sudden increase of the magnetic flux in the transformer, when the drain voltage is instantaneously negative, the damper diode can bypass the power tube until the drain becomes a positive voltage, which can effectively prevent the reverse conduction of the power tube and cause damage to the device. .
Theoretical analysis, the failure of the new generation of inverter power supply should be significantly reduced. The mine of Xishan Mining Bureau uses switch-type inverter power supply for more than one year, the power tube has not been burned, and if there is an unexpected load short circuit, the bow is removed. After that, the power supply can automatically resume normal operation, greatly reducing the amount of on-site maintenance. In addition, the original thyristor power supply is basically a discrete component, and the working speed, reliability and stability of each link of the circuit cannot be compared with the new integrated circuit.
Low noise. The original thyristor inverter, due to its operation in the low frequency range, produces an oscillating sound during operation. The M74 FET has a relatively high operating frequency (5*9:; <609:;). When working, no noise is heard, which greatly improves the working environment.
Conclusion In recent years, the power supply has been used in Jincheng, Longxi and Xishan bureaus, which proves that it has high conversion efficiency, no noise, small volume, stable output and high reliability. Switching inverter power supply must replace controllable. Silicon-type inverter power supply, because of the high efficiency, low failure rate and simple maintenance operation of the new inverter power supply, has been greatly welcomed after being put on the market.
First: Zhao Guangli, born in March 1966, Yingxian County, Shanxi Province, graduated from the Electrical Engineering Department of Shanxi Mining Institute in 1989, engineer, Special Equipment Inspection Institute of Shanxi Provincial Bureau of Quality and Technical Supervision, No. 8 Guoshi Street, Taiyuan City, Shanxi Province , 030001.
