The digital series inverter IF power supply is the sixth generation product introduced by our company. In addition to the conventional main circuit, the control circuit only needs two transformers and one control circuit board. The contactor, intermediate relay, and other auxiliary circuits are completely removed, so that the whole set of equipment is rarely connected. Moreover, since the three-phase AC input does not have to distinguish the phase sequence, the intermediate frequency output line does not have to distinguish the phase, which makes the user's on-site debugging more convenient. 

Technical features of induction melting furnace: Our company's series inverter thyristor intermediate frequency power supply has the following advantages.

 The whole machine can realize fool-like operation to avoid accidents caused by operational errors.

 The rectification inverter is completed by a power potentiometer and buffers the soft start. Self-judgment of the load state, if the load is short-circuited or open circuit, the zero-impact, micro-current lock-controlled inverter output can be used to avoid further expansion of the fault.

High power factor, low harmonic interference. The power factor of the whole machine is comφ≥0.95. It is not necessary to configure reactive power compensation and harmonic elimination devices to reduce the investment in construction.

 Inverter pulse width and commutation dead time can be flexibly adjusted to suit various load frequencies.

 High reliability: As we all know, the most troublesome problem of series inverter is that the through-pass protection is difficult, and the cause of the through-through is 80% from the sudden change of the load, and the control circuit is capable of timely adapting or external magnetic field clutter, etc., causing the inverter pulse to be misaligned. This line uses the voltage and current double lock pulse position, which fundamentally solves the factor of generating through.

High start-up success rate: 100% start-up in any load state, with extremely high load adaptability: high power factor full load output even in the cold furnace (cold) state.

Extremely high power saving effect: the relative parallel resonance rate is 20~30%, the reason is as follows:

The turn-off loss is small. Since the series resonance is a natural commutation, there is no commutation overlap angle, so there is no turn-off loss;

High-voltage characteristic series resonance belongs to voltage resonance, the inductor voltage is Q times of the output voltage, and 1500V~4000V high voltage can be obtained without double voltage or transformer boosting. Each current of the inverter output flows through the inductive load, and is connected in parallel. Resonance, the tank current is 2 to 3 times smaller. This high voltage, low current characteristic results in a significant reduction in tank losses.

 Low reactive loss Series resonance is a voltage resonance, DC filtering uses capacitive filtering, and the rectifier bridge is in full operation during normal operation. In the open state, the power factor of the grid reaches cosφ≥0.96 or more, and the low harmonic loss, the electrical efficiency is much higher than the parallel resonance.

High compatibility: The board reserves IGBT drive interface, temperature control interface, remote control interface and online blocking protection interface. The IGBT driver board can directly drive the IGBT module; the temperature controller (or computer) can realize programmable temperature control. 

Good environmental performance: Relative to parallel resonance, the sound of the whole machine is smooth and brittle, no clutter noise, and the IF harmonics of the power grid are extremely small.

High frequency characteristics: With ordinary KK inverter silicon (off time 20uS), the working frequency can reach 4KHz. If KA or KG thyristor is used, the frequency can reach 18KHz, achieving super-audio induction heating effect. This enables the production of high-power super-audio power supplies. The cost is much lower than the IGBT power supply of the same power, but its stability is much higher than the IGBT power supply.

The IF power supply uses a 6-pulse rectification line. This kind of circuit has three advantages: (1) the harmonic interference is small, (2) the rectifier works in the all-on state, and the voltage and current are always in phase, so the power factor of the grid side of the intermediate frequency power supply is always greater than 0.96 regardless of the output power.  

Constant power digital serial inverter power cabinet

The power cabinet is made of high-strength cold-rolled steel with a thickness of 1.5 mm. Open the door to easily access the various parts such as rectification and inverter. The top of the power cabinet has hooks for transportation and installation.

The copper platoon and copper tube in the power cabinet use domestic well-known brands (Lotus Copper), the power cabinet components are arranged reasonably, easy to maintain, routing, wiring specifications. Maintenance personnel can easily access all service points.

Isolation control room

Main control room: a closed isolation control room is arranged in the upper part of the front door, and the control parts such as the main control board and the control power supply are installed, so that the signal of the main control board can be conveniently observed. Since the main power electronic components in the power cabinet are equipped with a water cooling system, the temperature rise during the operation will not affect the temperature of the main control room, so the main control room does not need an additional cooling system, and the circuit in the main control room. All electronic components on the board are selected from internationally renowned brands and are selected according to high temperature grades. Therefore, the circuit board running in the main control room has very high stability.

The IF power supply is also equipped with a PLC-assisted smelting management system. The color screen touch can not only display the real-time data and information of the power supply operation, but also display the operating status and information of the entire system, and has automatic oven, cold furnace start, fault diagnosis and fault. Information display and storage, operation information display, system status display and other functions.

Incoming air switch protection system

The fast-acting DW breaker isolates the power supply line from the transformer and the power cabinet. When a fault occurs, it trips immediately to protect the power cabinet from further damage. It is operated by an electric operating mechanism and has a 24V loss-proof coil for interlock protection.

With overcurrent protection, when an overcurrent occurs, it trips to protect the action and cuts off the power supply to the power cabinet.

The lower part of the air switch is mounted to protect the semiconductor from rapid melting.

AC-DC rectification section and circuit protection

The bridge rectifier section converts the alternating current into direct current to provide a stable DC platform for the inverter section. In normal operation, ensure minimal impact on plant power harmonics. In addition, in the event of a fault, the rectified thyristor acts as a fast action switch, disconnecting the power supply from the inverter and protecting the power cabinet.

When the inverter is started, the rectification link can monitor the DC current and voltage, and provide a step that the power supply rises steadily to prevent the impact on the power supply.

The RC absorption branch at both ends of the thyristor can act as a buffer current sudden change when the thyristor switch is used.

Filter link (DC filter capacitor in the intermediate frequency power cabinet)

Reactor, leveling DC current, removing current ripple, preventing high frequency signals from entering the factory power supply line.

Filter capacitor. Filter capacitor is water cooled

The filter capacitor has an external discharge resistor that can be discharged within 5 minutes after the power is turned off.

The reactor is air-core, water-cooled, vacuum-cast with epoxy resin, solid-sealed, and protected by a temperature switch. When the temperature is too high, the power is turned off.

DC-AC IF inverter circuit source.

The inverter circuit includes the following parts:

The high-power inverter thyristor forms a full-bridge inverter circuit that converts direct current into intermediate-frequency alternating current.

The series RC absorption circuit is connected across the thyristor to buffer the thyristor switch.

Inverter capacitor bank (separate capacitor cabinet can also be installed in the intermediate frequency power cabinet)

The compensation capacitor cabinet has a solid overall structure and beautiful appearance. The double-layer mica insulation technology is used for the insulation treatment of the capacitor. Even if water is sprayed on the capacitor accidentally, the insulation strength of the cabinet can be ensured.

In order to reduce the loss of the high current loop, the compensating capacitor bank is installed in the basement as close as possible to the electric furnace. All capacitors adopt new high-capacity non-toxic medium water-cooled RFM series electric heating capacitors, which have the advantages of large single capacity, low dielectric loss and small floor space.

The capacitor cabinet is installed near the furnace body, which can reduce the loss of the tank and improve the efficiency. A temperature monitoring point is installed in the capacitor cabinet to ensure stable operation of the power supply.

The compensation capacitor configuration is optimal. The inside of the capacitor does not contain toxic substances. The newly adopted materials are non-toxic and flame-retardant, and even if arcing and short-circuiting occur inside, even when the capacitor casing is broken, it will not harm the human body.

Each capacitor has a safety release port that automatically opens to relieve internal pressure when the capacitor pressure is slightly below the burst pressure.

Control System

Single main control board installed in the locking door

 Power output accuracy is less than 1%

Power rise time from 0 to 100% less than 200 milliseconds

Minimum power less than 10%

The control operation is simple, only the move/stop button and a power dial together, there is no other adjustment.

Internal closed circuit water cooling system

On the water inlet device, a temperature switch is installed, and when the temperature exceeds 45 ° C, the power supply is cut off;

On the water inlet, a pressure gauge is installed;

A differential pressure switch is installed between the inlet water separator and the return water collector, and when the pressure difference is less than 200KPA (certain value), the power supply is cut off.

Install a pressure gauge on the return water collector;

Each of the internal water flow branches is equipped with a temperature switch. When the temperature exceeds 65 ° C, the power supply is cut off and indicated.

In summary, our company's constant power digital power supply and other control mode power supply have:

Effectively suppress interference measures on the power grid, so that any powered equipment in the power grid is not affected. The role of the impedance regulator allows the device to always operate at its optimum.

Compared with the old-fashioned line, the power saving effect is obvious, and the power saving can be about 10-20%.

The power factor is up to 0.93.

The startup success rate of the power supply can reach 100%;

Due to the low number of connections, the failure rate can be reduced by 90%.

Commissioning and maintenance is simple.