Complaint
Besides the traditional solid state high frequency welder, our company has successfully developed new type of high power factor rectification technique for new generation solid state HF welder. The three-phase full-bridge rectifier circuit composed of six thyristors is stable and reliable. Most of the existing solid-state high-frequency circuits in China adopt this technology, and it is widely used in the welding of steel pipes and aluminum bars. However, there are also disadvantages of low power factor and serious harmonic pollution.
Because of silicon controlled rectifier device adopts the phase shifting control, power regulation is by changing the trigger angle and voltage regulation, circuit from the grid to absorb the sine wave is lack of angle, and leave the grid is also part of the sine wave, obviously in the left part contains a large number of harmonics, at the same time because of different voltage and current phase, resulting in low power factor, the lower the DC output voltage, The lower the power factor).
The theoretical calculation and test show that when the trigger Angle of the three-phase fully controlled rectifier bridge is 0, or the uncontrollable bridge composed of diodes is used for rectifier, the harmonic generated by the bridge is very small and the power factor is very high (more than 0.9). However, in practice, continuous DC voltage regulation (that is, output power regulation) is required, and the HF welder cannot always be working at full voltage condition. In order to make the induction welder have the minimum harmonic, the highest power factor, and the output power adjustable function, we must add additional voltage regulating device behind the uncontrollable rectifier bridge, that is, separate the rectifier and voltage regulating.
Three-phase power frequency of the three-phase uncontrolled consisting of alternating current (AC)through the diode bridge rectifier bridge into DC, and flat DC voltage generated by the large capacitor filter group, theh adopt high power switch module IGBT to realize on-off control. In the case of constant switch frequency, by adjusting the percentage of time of on-off, we can control the output DC voltage average value. This is pulse width modulation technology (for short as PWM or chopper technology). PWM chopper modulation generated width variable pulse DC, through reactance or capacitor filtering, can provide to the load with fast, stable and adjustable DC voltage and current.
Comparison of SCR HF welder & high power factor HF welder
| Comparison parameters | Silicon controlled rectifier | High power factor HF welder |
| Controlled device | Controlled SCR | IGBT |
| Working frequency | 300HZ | 12~14KHZ |
| Control mode | Phase shift trigger | PWM modulation |
| The output DC | Lack of angle, half wave | High density DC square wave |
| 300HZ voltage ripple component | 8%~30% | <2% |
| Control time constant and control effect | 3.3 milliseconds,control effect not smooth | 75 microsecond, control effect is smooth and stable |
| Voltage regulation accuracy | <5% | <1% |
| Accuracy of steady flow | <5% | <1% |
| Cooling way | Water cooled | Water cooled |
| Efficiency of AC-DC | <90%,reactive power loss is big | 93% |
| Power factor | Change between0~0.9,usually around 0.75~0.8 | The range can reach 0.92 |
| Non work current on the net side | Big | small |
| Capacity utilization of user power supply | 70%~80% | 90% |
| The user's power factor compensation capacitor | Need to be | Don't need |
| Welding temperature control & effect | The temperature fluctuates greatly, the weld quality is slightly worse | The temperature fluctuation is small, the weld quality is pefect |
| The input voltage allows the range of fluctuation | ±10% | ±20% |
| Power grid interference | Big , not easy to eliminate | Small, easy to eliminate |
| Failure protection speed | Slower, milliseconds | Extremely fast, microseconds |
| Energy saving effect | Good | Better |
The advantages of the solid state high frequency welder using PWM technology:
1. High power factor: If the power factor is greater than or equal to 0.92, no power compensation device is required.One set complete of solid state hf welder is generally composed of the following parts: power distribution cabinet, step-down tranformer, rectifying cabinet, inverter cabinet, water cooling system, DC speed control cabinet, operation table. The site layout can be referenced as follows:
