MEDIUM (MFDC) FREQUENCY INVERTER

Three Phase Inverter DC

Three Phase Inverter DC utilizes three-phase balanced input. Current is in full wave form rectified to DC and switch to 1000Hz or higher to produce AC supply to primary transformer. The current is rectified into DC for welding afterwards.

Medium (till 1000Hz) Frequency Inverter Welders use millisecond pulse width modulation (switching) technology with closed-loop feedback to control the weld energy in sub-millisecond increments. Three phase input current is full wave rectified to DC and switched at 1kHz to produce an AC current at the primary of the welding transformer. The secondary current is then rectified to produce DC welding current with an imposed, low-level, AC ripple. The high-speed feedback circuitry enables the inverter power supply to adapt to changes in the secondary loop resistance and the dynamics of the welding process. For example, a 1 kHz inverter power supply adjusts the output current every 0.5 miliseconds after rectification, which also allows the weld time (duration of current) to be controlled accurately in increments as small as 1 milliseconds.  The high frequency closed loop feedback can be used to control (maintain constant) either current, voltage, or power while also monitoring another of the same three parameters.
Additional benefits of high frequency switching technology include reduced power consumption, smaller welding transformers, and the use of a very short pre-weld “check pulse” to test electrode and parts positioning prior to executing a weld. The result of this pre-weld check can be used to inhibit the weld by setting check limits.

CONSTANT CURRENT can be used for 65% of all welding applications including those that exhibit low contact resistance, small variability in contact resistance, flat parts, and multiple part “sandwiches.”
CONSTANT VOLTAGE can be used for applications where the workpieces do not have flat surfaces, e.g. crossed wires, and where the resistance varies significantly, and for extremely short welds (less than 1 millisecond).
CONSTANT POWER can be used for applications with significant variations in electrical resistance from weld to weld, including applications where the plating erodes and builds-up on the face of the welding electrodes.
Due to their extensive programmability, small transformer size, and robustness, high frequency inverter power supplies are generally the best choice for automation applications.

Three Phase Inverter DC solution has the following advantages:

  1. It does not have blank period in the current wave form. Heat produced is continuous and efficient. The fast feedback control (roughly 1 millisecond) ensures stable welding quality and controls welding splash.
  2. High frequency means high current density. It easily generates the required welding heat in the shortest time interval. Thus, welding is completed in a faster approach with minimum power consumption.
  3. High-frequency switching technology also reduces power consumption to 60-70% comparing with Single Phase AC solution.
  4. High-frequency transformer makes wide-range welding possible. Traditional AC transformer may induce insufficient current disperse with poor welding quality.
 
 

Compared with the normal AC controller, MF controller has the following advantages:

  1. The current in secondary welding loop is DC. Dramatically reduce the impact to the welding current due to the inductive reactance in secondary loop when conducting welding to the work piece.
  2. The weight of transformer is reduced greatly. It is light and convenient. The weight and size of the MF transformer is only 1/3 of the AC type transformer. Suitable for robot welding system.
  3. Prolong the service life of electrode
  4. Be able to weld material like aluminum, galvanized steel, etc. with good welding performance.
  5. Especially suitable for three-layer plate welding, ultrathin material welding and precision welding.
  6. Less splashes.
  7. Increase control of current and welding quality.