阅读说明：本技术 一种隔离式灯丝电源控制系统 (Isolated filament power control system ) 是由 曲延滨 宋蕙慧 其他发明人请求不公开姓名 于 2019-03-19 设计创作，主要内容包括：本发明涉及一种隔离式的灯丝电源控制系统,属于电源领域,特别是为了保持变压器原边低压和副边高压的完全隔离,实现对灯丝电流的稳定控制。为了能够实现高压隔离,通常采用变压器进行隔离,而为了实现完全的高压隔离,区别于以往的灯丝电源变压器副边采样控制系统的设计,本系统采用原边采样进行灯丝电源稳定性的控制。充分考虑乐变压器分布参数和灯丝电阻随温度变化而变化的情况,具有1.完全隔离性2.鲁棒性3.灵活性4.简约性5.体积小等优点,可以很好的替换以往的老式灯丝电源控制系统,并且具有良好的安全性、稳定性和可靠性。(The invention relates to an isolated filament power supply control system, belongs to the field of power supplies, and particularly aims to keep the primary side low voltage and the secondary side high voltage of a transformer completely isolated and realize stable control of filament current. In order to realize high-voltage isolation, a transformer is generally adopted for isolation, and in order to realize complete high-voltage isolation, the system is different from the design of a secondary sampling control system of a conventional filament power supply transformer, and primary sampling is adopted for controlling the stability of a filament power supply. The method fully considers the condition that distribution parameters of the transformer and the resistance of the filament change along with the temperature change, has the advantages of 1, complete isolation, 2, robustness, 3, flexibility, 4, simplicity, 5, small volume and the like, can well replace the prior old filament power supply control system, and has good safety, stability and reliability.)

1. An isolated filament power supply control system is characterized in that in order to achieve complete isolation of a primary side and a secondary side of a transformer and stable control of filament current, the isolated filament power supply control system comprises a direct current power supply, a full-bridge inverter, an LC filter, a transformer, a filament resistor, a sampling circuit and a control circuit, wherein the direct current power supply is connected with the full-bridge inverter to provide a 48V direct current power supply for the whole system, current after inversion is isolated by an LC filter network and a transformer with a transformation ratio of 1:1 (the primary side and the secondary side are 15 turns of coils), and then the isolated filament resistor is added to the filament resistor.

2. The isolated filament power supply control system according to claim 1, wherein the LC filtering link fully considers the distribution parameters of the transformer, and the transformer equivalent model is used for designing, so that the relation between the inverter output voltage Vab and the filament resistor Vout voltage is approximately 10 times.

3. The isolated filament power control system according to claim 1, wherein the voltage is sampled at the output end of the inverter, thereby avoiding the physical connection problem caused by the secondary side sampling of the transformer and realizing the stable control of the filament current.

Technical Field

The invention relates to an isolated filament power supply control system, belongs to the field of power supplies, and particularly aims to realize complete isolation of a primary side and a secondary side of a transformer and stable control of filament current.

Background

The welding technique is known as "sewing machine" in modern industry, and the electron beam welding technique is widely used in various industrial environments due to its extremely high energy density, and it is essentially to convert the kinetic energy of high-speed moving electrons into heat energy. The electron beam welding machine mainly depends on filament power supply, high voltage power supply and focusing power supply to effectively cooperate, firstly, the filament power supply generates electrons by heating cathode filament. Secondly, the high voltage power supply accelerates the electrons through an accelerating electric field, so that the electrons carry larger energy. And finally, the focusing power supply collects the dispersed electrons into an electron beam, and after the electron beam impacts the surface of the workpiece, the kinetic energy of the electron beam is converted into heat energy, so that the workpiece is rapidly melted.

The filament power supply in the electron beam welding machine device is used as an electron emission device, the performance of stable and continuous electron emission directly relates to whether the whole device can work normally, so the stability of the filament power supply is a key factor for determining the stability of the emitted electrons, and one pole of the filament power supply is usually connected with one pole of a high-voltage power supply due to the influence of a floating reference potential. However, since the resistance of the filament increases with the increase in temperature and the current flowing through the filament is maintained within a certain range, exceeding the maximum operating current may reduce the life of the filament, even melting in a short time. It is very necessary to further consider the control of the stability of the filament power supply.

An electron beam welding machine filament power supply device for welding steel rails (application number 201520166323.8) is disclosed, which is characterized in that an LLC resonant converter is introduced to improve the working frequency of a power supply, reduce switching loss and noise waves, and enable a switching device to conveniently realize soft switching, but the problems of high-voltage isolation, filament resistance change along with temperature and the like are not fully considered.

A grid-control electron gun power supply (application No. 201710949894.2) discloses a grid-control electron gun power supply with an anti-sparking function, wherein a high-voltage output end is the output of a transformer, high-voltage end equipment and elements are few, the anti-sparking capability is strong, and the reliability is high; the filament power supply and the grid control power supply work on the ground potential, the control and the installation are convenient, but the influence of the distribution parameters of the transformer is not fully considered.

Disclosed in the patent application No. 201720322612.1 is a lamp filament power supply circuit, which mainly comprises a reference comparison circuit, a differential sampling circuit, a transformer circuit, an output rectifying filter circuit and a protection circuit, and controls the circuit through a PWM generating circuit without considering high voltage isolation.

Therefore, the current filament power supply in China mainly has the following defects.

Firstly, distribution parameters of a high-frequency transformer are not fully considered, in order to completely isolate a low-voltage primary side and a high-voltage secondary side of the transformer, the distance between coils of the transformer is generally increased, and the isolation effect is further enhanced by adopting insulating oil, but the increase of the distance between the coils leads to the increase of leakage inductance, because flux linkage generated by the primary side cannot be completely absorbed on the secondary side coil, the leakage inductance can be reduced by increasing the coils or optimizing the selection of core materials of the transformer, but the size of the transformer is increased, and how to balance the leakage inductance and the size is a key problem.

Secondly, high-voltage isolation is not fully considered, because one end of the filament power supply is connected with one end of the high-voltage power supply, the high-voltage isolation is required from the aspects of safety and operation stability, the isolation is generally only used by a transformer, the signal sampling of the feedback link still needs to be carried out from the secondary side of the transformer, the isolation is not complete enough, if an accident happens, the high-voltage side of the secondary side still has a path to be transmitted to the front end, the loss which is difficult to recover is possibly caused, and therefore the signal sampling of the feedback link can only be carried out from the front stage of the transformer.

And thirdly, the condition that the resistance of the filament changes along with the temperature change is not fully considered, the temperature of the resistance of the filament also rises along with the rise of heating time, the resistivity also changes, and in addition, the current of the filament cannot exceed the maximum working current, and the filament can be damaged in an unrecoverable manner after the current exceeds the maximum working current. In order to maintain stability of electron beam emission, stability of current passing through the filament must be maintained, and thus the stability of the filament current needs to be achieved by negative feedback control.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide an isolated filament power supply control system, which adopts primary side negative feedback control of a transformer and can realize complete isolation of a filament power supply and a high-voltage power supply and maintain the stability of filament current.

In order to achieve the purpose, the invention adopts the technical scheme that.

The isolated filament power supply control system comprises a direct current power supply, a full-bridge inverter, an LC filter, a transformer, a filament resistor, a sampling circuit and a control circuit.

The direct current power supply is provided with 48V direct current power supply by the storage battery.

The full-bridge inversion is a single-phase full-bridge inversion circuit, and consists of four MOSFET-type switching tubes.

The LC filtering is a filtering network formed by combining an inductor and a capacitor with distribution parameters of a transformer.

The transformer adopts a high-frequency transformer.

The filament resistor adopts a tungsten filament which is long and used as a filament, and electrons can overflow when the filament reaches a certain temperature.

The sampling circuit directly collects the output voltage of the inverter by adopting a differential operational amplifier principle.

The control circuit is characterized in that a voltage signal acquired by the sampling circuit is transmitted to the control circuit, the control circuit adopts a basic operational amplifier circuit to realize PID control, a sinusoidal signal is output to the PWM chip, and the PWM chip outputs a PWM control signal through signal comparison to control the duty ratio of the switching tube so as to control the output voltage.

Due to the adoption of the technical scheme, compared with the prior art, the invention has the following beneficial effects.

1. And the distribution parameters of the transformer are considered, and the distribution parameters of the transformer are fully utilized in the process of designing the filter.

2. Because the control circuit samples from the primary side of the transformer, the primary side and the secondary side of the transformer are not physically connected, and complete high-voltage isolation is realized.

3. Considering the change of filament resistance with temperature, the filament resistance at normal temperature is smaller than that of hot filament, and the change of filament resistance rises with the rise of temperature.

4. Robustness, because the loss is distributed to four switching tubes, the stability of the switching tubes is enhanced.

5. Flexibility, voltage amplitude (from 0 to maximum) and frequency can be easily varied using full-bridge inversion.

6. And the method is simple, and does not need any additional sampling circuit or other devices on the secondary side.

7. The size is reduced, the inverter can work under the high-frequency condition, and the size of inductance, electric capacity and transformer can be reduced to further reduce the volume of whole device.

Drawings

Fig. 1 is a schematic structural diagram of an isolated filament power supply control system.

Fig. 2 is a circuit diagram of an isolated filament power supply control system.

Detailed Description

In order to better understand the technical solution of the present invention, the following further describes the working principle and the implementation mode of the present invention with reference to the attached drawings.

As shown in fig. 1, which is a schematic structural diagram of an isolated filament power supply control system, the isolated filament power supply control system of the invention includes a dc power supply, a full-bridge inverter, an LC filter, a transformer, a filament resistor, a sampling circuit, and a control circuit. The direct current power supply is connected with a full-bridge inverter to provide a 48V direct current power supply for the whole system, the current after inversion passes through an LC filter network, fundamental waves can be transmitted into a transformer, the fundamental waves are isolated by a transformer with a transformation ratio of 1:1 (the primary side and the secondary side are 15 turns of coils) and then are added to a filament resistor, the filament resistor is pure resistive, the voltage of the primary side of the transformer is approximately equal to the voltage of the filament resistor, and the fundamental waves are inverted from the full-bridge inverter to the secondary side of the transformer to realize impedance matching, so that the fundamental wave voltage inverted from the full-bridge inverter is approximately in direct proportion to the voltage of the filament resistor. The experimental measurement data are shown in table 1, wherein each symbol represents:

vc: PWM reference control voltage

Vab: output voltage of inverter

Ip: output current of inverter

Vout: filament resistance upper voltage

Iout: current on filament resistance

TABLE 1 Vc, Vab/10, Ip, Vout, Iout measurements.

。

It can be seen from table 1 that as the PWM reference control voltage increases, the inverter output voltage Vab and the filament resistor Vout voltage increase, and the ratio of Vout/Vab to Iout/Ip indicates that the inverter output voltage Vab and the filament resistor Vout voltage are approximately 10 times in relation to each other, so that the inverter output voltage Vab can be directly collected from the front end to be used as the control target of the feedback system, thereby achieving the control of the stability of the filament resistor Vout.

The design of the whole control system always surrounds the aim of complete isolation, firstly, the distribution parameters of a transformer are considered in the design of an LC filter network, secondly, the voltage of a filament resistor is controlled by directly sampling from the primary side of the transformer, and finally, the voltage is adjusted in control by considering the condition that the filament resistor changes along with the temperature change so as to keep the stability of current.

Fig. 2 shows a circuit diagram of an isolated filament power supply control system, where the input is 48V dc, VMLSCCM is a MOSFET half-bridge module of an internal integrated PWM driving circuit, ends a and p are respectively connected to the positive and negative poles at fixed distance from dc, end c is an output end, and vc is an input end of a PWM reference control voltage. Lf and Ld are inductors for realizing filter series connection, Cf and Cs are capacitors for realizing filter parallel connection, Cp and Lm are stray capacitors and leakage inductors parasitic to the transformer, Np = Ns =15 is the number of turns of primary and secondary side coils of the transformer, Rload is load resistance, voltage output by full-bridge inversion is sampled and sent to a PI controller through differential operational amplifier, a control signal is further converted into reference voltage of a 0-10V PWM driving chip, and then output voltage of the inverter is controlled, and negative feedback closed-loop control is realized.

In summary, the present invention has: 1. the lamp filament power supply control system has the advantages of complete isolation 2, robustness 3, flexibility 4, simplicity 5, small size and the like, can well replace the prior old lamp filament power supply control system, and has good safety, stability and reliability.