Reliability Test Methods in Power Module Testing

 

　　1. Repeated power on and off test

 

　　Test instruction:

 

　　When the power module output is at maximum load, the input voltage is 220V, (input overvoltage point -5V) and (input undervoltage point +5V) respectively, and the input is repeatedly turned on and off to test the performance of the power module being repeatedly turned on and off.

 

　　Test Methods:

 

　　A. The input voltage is 220V, the power module is fast with the maximum load, the voltage input is controlled by the contactor, it is closed for 15s and disconnected for 5s (or it can be simulated by AC SOURCE), and it runs continuously for 2 hours. The power module should be able to work normally;

 

　　B. The input voltage is -5V, the power module is at the maximum load, and the voltage input is controlled by a contactor. It is closed for 15s and disconnected for 5s (or can be simulated by using AC SOURCE). The power module should be able to work normally after running continuously for 2 hours.

 

　　C. The input voltage is the undervoltage point -5V, the power module is at maximum load, and the voltage input is controlled by a contactor. It is closed for 15s and disconnected for 5s (or AC SOURCE can be used for simulation). After running continuously for 2 hours, the power module should be able to work normally.

 

　　Judging criteria:

 

　　In the above tests, the power module works normally. After the test, the power module can work normally without obvious changes in performance, and it is qualified; otherwise, it is unqualified.

 

   2 Repeated short circuit test

 

　　Test instruction

 

　　When the module output is short-circuited under various input and output states, the module should be able to achieve protection or retraction. After repeated short-circuits and fault elimination, the module should be able to automatically resume normal operation.

 

　　Test Methods:

 

　　A. No-load to short-circuit: Within the full range of input voltage, the module should be able to achieve output current limiting or retraction normally when it is switched from no-load to short-circuit. After the short-circuit is eliminated, the module should be able to resume normal operation. The module should be repeatedly operated from no-load to short-circuit, with a short-circuit time of 1s, a release time of 1s, and a duration of 2 hours. After that, release the short-circuit to determine whether the module can work normally.

 

　　B. Full load to short circuit: Within the full range of input voltage, the module should be able to achieve output current limiting or retraction normally when it is fully loaded to short circuit. After the short circuit is eliminated, the module should be able to resume normal operation. Let the module go from full load to short circuit and keep the short circuit state for 2 hours. Then release the short circuit to determine whether the module can work normally.

 

　　C. Short-circuit startup: Short-circuit the module output first, then connect to the mains, and then power on within the module's input voltage range. The module should be able to achieve normal current limiting or retraction. After the short-circuit fault is eliminated, the module should be able to resume normal operation. Repeat the above test 10 times, release the short circuit, and determine whether the module can work normally.

 

　　judgement standard:

 

　　After the above tests, if the power module can work normally when turned on; if the casing is opened for inspection, and there is no abnormality in the circuit board and other parts (such as whether the input relay is stuck during the short circuit process, etc.), it is qualified; otherwise, it is unqualified.

 

 

　　3 Input low voltage point cycle test

 

　　Test instruction:

 

　　The setting hysteresis of the input undervoltage point protection of the primary power module often causes the following situations: the input voltage is low, close to the undervoltage point of the primary power module to shut down, undervoltage when loaded, and after the cut-off, due to the internal resistance of the power supply, the voltage will rise after the load is removed, which may cause the primary power module to be in a state of repeated development at low voltage.

 

　　Test Methods:

 

　　The power module is running at full load, and the input voltage changes slowly from (input undervoltage point -3V) to (input undervoltage point +3V). The time is set to 5 to 8 minutes. The cycle is repeated and the power module should be able to work normally and stably, and run continuously for at least 0.5 hours without obvious changes in the performance of the power module.

 

　　judgement standard:

 

　　The primary power module operates normally and continuously, and there is no obvious change in performance after at least 0.5 hours, which is qualified; otherwise, it is unqualified.

 

　　4 Input transient high voltage test

 

　　Test instruction:

 

　　The PFC circuit uses an average value circuit for over-voltage and under-voltage protection. Therefore, when a transient high voltage is input, the PFC circuit may quickly implement protection, causing damage. The stable operation capability of the primary power module under transient conditions is tested to evaluate reliability.

 

　　Test Methods:

 

　　A. Rated voltage input, use a dual-trace oscilloscope to test the input voltage waveform and overvoltage protection signal. The input voltage jumps from the power limit point plus 5V to 300V. Read the number of cycles N of 300V before overvoltage protection from the oscilloscope as the basis for the following tests.

 

　　B. Rated input voltage, the power module runs at full load, a 300V voltage jump is superimposed on the input, the number of superimposed cycles is (N-1), the superimposed frequency is 1 time/30s, and the total operation time is 3 hours.

 

　　judgement standard:

 

　　If the primary power module can operate stably under the above conditions without damage or other abnormal phenomena, it is qualified; otherwise, it is unqualified.

 

　　5 Input voltage drop and output dynamic load

 

　　Test instruction:

 

　　During the actual use of the primary module, when the input voltage drops, the extreme situation of sudden load on the power module may occur. At this time, the power devices and magnetic components operate in the maximum transient current state. The test can verify the rationality of the circuit and software design of control timing, current limiting protection, etc.

 

　　Test Methods:

 

　　A. Adjust the input voltage to jump between the undervoltage point +5V (duration is 5s) and the overvoltage point -5V (duration is 5s), and adjust the output to jump between the maximum load (maximum rated capacity, duration is 500ms) and no-load (duration is 500ms), and run for 1 hour;

 

　　B. Adjust the input voltage to jump between the undervoltage point of +5V (duration of 5s) and the overvoltage point of -5V (duration of 5s), and adjust the output to jump between the maximum load (maximum rated capacity, duration of 1s) and no-load (duration of 500ms), and run for 1 hour.

 

　　judgement standard:

 

　　Under the above conditions, it should be able to run stably without damage or other abnormal phenomena, and it is qualified; otherwise, it is unqualified. If damage occurs, record the fault problem to provide a basis for analyzing the cause of the damage. [page]

　　6 High-pressure no-load and low-pressure limited-current operation test

 

　　Test instruction:

 

　　High-voltage no-load operation is to test the loss of the module, especially the module with soft switching technology. Under no-load conditions, the soft switch becomes a hard switch, and the loss of the module increases accordingly. Low-voltage full-load operation is to test the loss of the module at the maximum input current. Under normal conditions, the module has the lowest efficiency when it is at low voltage input and full load output, and the heating of the module is the most serious at this time.

 

　　Test Methods:

 

　　A. Adjust the module's input voltage to the input overvoltage protection point -3V. The module's output is the lowest output voltage and runs at no load. At this time, the module's duty cycle is the minimum.

 

　　The module should not be damaged after running continuously for 2 hours;

 

　　B. Adjust the input voltage of the module to the undervoltage point +3V. The output of the module is at the inflection point of the highest output voltage. At this time, the duty cycle of the module is the largest. The module should not be damaged after running continuously for 2 hours.

 

　　C. Adjust the module input voltage to the input voltage at the lowest efficiency point, and the module output is at the inflection point of the highest output voltage. The module should not be damaged after running continuously for 2 hours.

 

　　D. Adjust the input voltage of the module to the overvoltage point of -3V. The output of the module is at the inflection point of the highest output voltage. At this time, the duty cycle of the module is the largest. The module should not be damaged after running continuously for 2 hours.

 

　　E. Adjust the module input voltage to the input voltage at the lowest efficiency point, and the module output is at the inflection point of the highest output voltage. The module should not be damaged if it runs continuously for 2 hours.

 

　　Note: The above tests must be performed at the maximum operating temperature specified in the specification.

 

　　judgement standard:

 

　　If the module is not damaged when working under the above conditions, it is qualified; otherwise, it is unqualified.

 

　　7 Power supply special waveform test

 

　　Test instruction:

 

　　Verify the power module's ability to operate stably under spikes, glitches and harmonics that may be caused by grid waveform distortion. The following waveforms must be input for testing:

 

　　(1) Glitch input test waveform

 

　　The glitch of the power grid is the most common waveform in the power grid. There is no limit on the size and amplitude of the glitch. In general, the glitch input in the power grid can be basically simulated through the oscillation wave input test and the ringing input waveform, but the following glitch input test is also required

 

　　Features: The power grid has an overshoot and drops to 0V. The overshoot and drop pulse widths are very narrow, generally not greater than 100ms, and the overshoot amplitude generally does not exceed 100V. The drop phase is not limited to the peak point, and it may occur at any phase. This waveform is very common in actual power grids, and turning on any switch will cause this phenomenon.

 

　　(2) Voltage clipping waveform input

 

　　This waveform is also very common in the power grid, and its characteristics are: the power grid suddenly drops to 0V from an uncertain phase, and then does not recover until the next half wave begins. In IEC1004-4-11, the waveform drop starts from more than half a cycle, but there are still many similar waveforms with a drop time of less than half a cycle in the actual power grid. The test requires that the input voltage waveform drops from 90 degrees, drops 1/4 cycle, and works for a long time of 2 hours.

 

　　(3) The half wave head of the power grid rises to double the voltage. This waveform is mainly used to simulate the resonant overvoltage that will suddenly appear in the actual power grid. In this case, the input overvoltage protection circuit of the module does not work. This impact is dangerous for the circuit with PFC. Test content: A. When the input voltage is 180V and the output is fully loaded, use AC SOURCE to simulate this waveform. It is required to work at 180V for 3 minutes, then the voltage suddenly increases to 380V for 100ms, and then returns to 180V. Let the module work for a long time for 1 hour in this case, and it should not be damaged; B. Set AC SOURCE so that the input voltage is 0V for 5 minutes, then the voltage suddenly increases to 380V for 100ms, and then returns to 0V. Let the module work for a long time for 1 hour in this case, and it should not be damaged.

 

　　The specific waveform (the waveform in case A) is as follows:

 

　　Test Methods:

 

　　Use AC SOURCE to power the module, and the module outputs at full load; use AC SOURCE to simulate spikes, glitches and harmonic voltage inputs, work for 2 hours for each special voltage input, and measure the input current and output voltage. The module should be able to operate stably, and pay attention to other possible problems such as X capacitors , auxiliary power supplies, and soft start resistors during the test.

 

　　Measure to judge:

 

　　If it can operate stably and without damage under the conditions of spikes, burrs and harmonic voltages that may occur in practice, it is qualified; otherwise, it is unqualified.

 

　　8 Operating voltage test

 

　　Test instruction:

 

　　There are various operating overvoltages in the power grid, the most common of which is the overvoltage caused by closing the unloaded line. This overvoltage also poses a greater threat to the module. This test is to verify the module's ability to resist operating overvoltages.

 

　　Test Methods:

 

　　The simulation of overvoltage line is very simple, the principle is as follows:

 

　　The inductor parameter is 10mH (for reference: in the EES module test method, there is no grounding capacitor, the input resistor is connected in series with the inductor, and the resistance value is 0 ohm, the inductor is 8mH and the resistance is 79 ohm, the inductor is 10mH), the capacitor is 16.7uF, and the test waveform is as follows (not shown).

 

　　The device under test is connected to both ends of the capacitor. At the moment of K closing, overvoltage will be generated at both ends of the capacitor to simulate the degree of damage to the device caused by overvoltage during the power-on process. As an extreme test item, the input is connected to the L and N lines, the device under test is connected to both ends of the capacitor, and the machine is frequently turned on and off, with a repetition frequency of 1 time/5 minutes, and the test is continuous for 5 hours. For three-phase input devices, the input is connected to the L and L lines, the device under test is connected to both ends of the capacitor, with a repetition frequency of 1 time/5 minutes, and the test is continuous for 2 hours.

 

　　judgement standard:

 

　　If there is a short-term functional decline or performance degradation during the test but it can recover automatically, it is qualified; however, if there is a permanent performance degradation or manual intervention is required to recover, it is unqualified.

 

　　9 Active PFC performance test

 

　　Test instruction:

 

　　Power modules with active PFC are sensitive to grid spikes, glitches and harmonics and should be tested thoroughly and carefully.

 

　　Test Methods:

 

　　Use AC SOURCE as the input voltage source, and output with half load and full load respectively, test the input current waveform and voltage waveform, and monitor the voltage after PFC at the same time; test the phase and amplitude relationship of the input voltage and current of the power grid under spikes, glitches and harmonics; measure the current and voltage of the PFC switch tube, and verify the safety of the switch tube and other power devices and the ability of current to track voltage changes under the full voltage range and glitches, spikes, harmonics, etc.

 

　　judgement standard:

 

　　PFC testing can be used as a reliability reference, and when serious problems occur, they should be resolved in a timely manner.