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Induction Heating Since 2000

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Basic test of IGBT intermediate frequency induction heating system & Limit test

1). The basic test of low-voltage resonance what can we see from low-voltage resonance:

1. Resonant unobvious, resonant locking, resonant controlled, control system accuracy

2. Output voltage waveform, ZVS waveform

3. Grid waveform of high and medium frequency current

4. Conduction voltage drop and saturation conduction waveform of the module under high and medium frequency current

5. Limit frequency, the limit operating frequency that can be locked

6. Conduction loss, radiator temperature, main generating hot spots

7. The heating of the resonant capacitor and filter capacitor. The heating of the resonant capacitor is only related to the intermediate frequency current

8. Set the current boundary of the control system

9. Whether the design of the main structure is reasonable or not and the current intensity of copper parts

10. Mean current problem of parallel structure, an actual mean current ratio

11. Partial protection functions can be tested

2). The basic test of HV resonance what can we see from hV resonance:

1. Output voltage waveform, ZVS waveform, breakpoint waveform

2. Turn off the break phase

3. Open locking phenomenon, tube explosion phenomenon

4. Stable operation of the current envelope, frequency envelope, and module stability

5. Cut off a loss, conduction loss

6. Observe abnormal waveforms everywhere and find out the cause of tube explosion quickly once it occurs

7. ZVS capacitance, resonant capacitance, filter capacitance heating phenomenon

8. Radiator temperature rise

3) Test the output current limit of the host

According to the output capacity of the module, a safety boundary of the output current is determined, and the X2 potentiometer is adjusted in the low-voltage resonance to make the host reach this current boundary. This is the most commonly used method for mass production of mature products (for example, the FF150RKE3G output current is fixed at MF90A, which is relatively safe); It is not the input current, but the output current of the module, that determines the safety of the host.

4) Overvoltage limit test of IGBT switch of the host

Enter the low-voltage resonance mode and let the host output with the maximum rated current. The voltage waveform of the bus on the test module will see a sharp pulse shock as IGBT is turned off. This is the phenomenon of switch overvoltage, which is caused by the inductive reactance distribution between the absorption capacitance and the lead wire between the modules. This is an unfavorable factor, which will cause the module to overpressure and increase the loss. Therefore, the bus bar should be shortened as much as possible to suppress this high-frequency oscillation phenomenon. The amplitude of the pulse overvoltage must be carefully observed and measured. The height of the pulse overvoltage should not exceed 100V.

5) No-load test/core saturation limit test (transformer output)

Under the condition of not feeding the induction coil, the opening resonant current (≤1.5 times rated intermediate frequency current) shall not be saturated. The saturation margin of the magnetic core is very important. Without sufficient margin, saturation will occur when the magnetic core continues to work, which will bring many adverse effects. Observe the current waveform, output voltage, and resonance frequency. When there is a sign of saturation, there is a sharp waveform on the current, and the resonance frequency will significantly climb (normally, the current changes from small to large, with the frequency changing very little, generally no more than 1KHZ).In the no-load test, once the sign of saturation is found, the test should be stopped immediately for rectification. Transformer saturation is a serious quality event, which will cause the main engine tube explosion, magnetic core overheating, rapid decline in heating efficiency, and other problems.No-load test is also a great test for the resonant capacitor, which may cause capacitor overheating, breakdown discharge, and other phenomena, sometimes causing the host super frequency but can not find the reason; Running at the rated current for 15-30 minutes, the accumulated heat shows some problems and is easily exposed; The convenience of the no-load test compared with load test is that the current can be adjusted at will. Once the loading impedance of the induction coil increases, the intermediate frequency current may not be adjusted at will.

Elements related to core saturation:

1. Insufficient material selection and too light weight of the magnetic core

2. Too high output turn voltage

3. No air gap (1mm-2mm) in the magnetic circuit of the magnetic core

4. Poor initial coupling, high leakage sensitivity, and poor manufacturing process of copper parts

5. The frequency is too low

6) Load input power limit test

Induction coil into work after testing, load testing main active power, heating speed, heating uniformity, such as performance, mainly for impedance matching time, under the condition of the induction coil, the same did not move, change different have different impedance, the diameter of the iron bars with large diameter and high impedance only impedance of the optimal point, will be the largest active current input, small big will reduce the active power;

Common problems in host design:

1. Core saturation problem (transformer output)

2. Power capacitor heating and internal discharge problems

3. IGBT parallel operation, current sharing problem

4. IGBT shut off the overpressure problem

5. Cooling of IGBT, copper bar, capacitance, and other high temperature points

6. Problem of filter capacitance to IGBT non-inductive loop

7. Oxidation of copper parts and problems of contact point resistance

8. Circuit protection, overcurrent protection, short circuit protection, zero sequence protection, frequency protection, magnetic core saturation protection

9. Power harmonic pollution and magnetic field radiation

10. Synthesis of soft switch technology ZCS_ZVS

11. Field manual and field data are insufficient

Substructure design, routine data, limit data, symptom manifestation, adjustment method, adjustment sequence, measurement points, measurement tools, dependent data

12. Control system problem summary, control board, transformer, shielding line, and other accessories, current precision, phase precision

13. Common application problems, such as frequency problems, impedance problems, power problems, etc

14. Grid waveform, low voltage resonance, high voltage resonance, no-load test, load test.

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