Application Note - how to use

Transcription

1 How to use a SKiiP - Tester Application note Bild 1: Bedienungsanleitung Application - how to use type: L23005 version: 1.1_eng document: 1.1 date: Ing. Büro M.Billmann 08/2013 Lerchensteige 10 D Emskirchen Telefon +49-(0) Fax +49-(0) M.Billmann@ib-billmann.de L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 1/16

2 ING. BÜRO M.BILLMANN Semikron SKiiP Tester Manual Control Unit E: secondary side celvin measurement F: 4 1/2 digit voltmeter, ext A: 24V DC supply input B: SKiiP I / II / III supply select +24V; +15V; ±15V C: V CE up to 170V V F at 1.3A DC G: primary side SKiiP interface, wired or optical H: digital I/O status, LED I: pri analog signal monitor K: pri/sek monitor 4 5 D: PWM signal generation L: PWM input signal matrix sketch: front panel elements technical details may change without notice! L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 2/16

3 Functional description Front side elements and connectors A: Supply input for auxiliary power supply 24V DC B: Selector for SKiiP supply C: Selector for V CE (IGBT) V F (Diode) measurement D: PWM signal generator, 10 khz or permanent (CW) signal E: Interface for SKiiP secondary side power terminals F: Connector for external DVM G: primary side SKiiP interface GB/GH/GD, wired or optical H: Digital I/O status PWM SKiiP input signals I: Selector for monitoring analog primary side SKiiP signals K: Selector monitoring primary / secondary signal monitoring L: PWM signal matrix 2 PWM into 6 SKiiP inputs L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 3/16

4 Contens 1. About this document 2. Used symbols and shortcuts 3. How to prepare a SKiiP tester 4. How to use 5. Test setup SkiiPs with DC link attached 6. How to proceed on site to test a SKiiP 7. Primary side standby current consumption 8. Status LEDs 9. Primary side 10kHz PWM current consumption 10. Primary side steady ON current consumption 11. Primary side analog signals 12. Summary - Primary side monitoring 13. Secondary side monitoring - SKiiP as standalone unit 14. Summary - Secondary side monitoring 15. Additional hints - Calibration 16. Service L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 4/16

5 1. About this document This application note describes - a practical example - how to use the SKiiP Tester - how to identify weak SKiiPs with the SKiiP Tester L23005 This document is targeting at the following persons: - Professionals in power electronics - Electronic field engineers involved in finding and replacing SKiiPs on site. 2. Used symbols and shortcuts note warning s will highlight advantages of certain operation modes to bring out the maximum efficiency of the unit. Warning notes: Read them carefully and follow those instructions. Warning notes shall prevent danger and will help to prevent damage of the unit or the device under test. 3. How to prepare a SKiiP tester There are many different types of SKiiPs in the field, worldwide. Wired signal, fiber optical signal, 14-/20/26-pin DIN primary interface, D- SUB interface and customized units. Therefore the standard delivery of a SKiiP tester is completely functional, including a power supply, but without the connection cable from tester to SKiiP primary side. A separate voltmeter has to be attached as well. note Service personal needs to assemble an adapter cable from the SKiiP tester to the SKiiP variants used in their applications. The SKiiP tester provides DIN41651 pinout for flat cable in 14- pin, 20-pin, and 26pin referring to the SKiiP datasheets. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 5/16

6 4. How to use The SKiiP Tester L23005 is a manually operated, handheld unit designed for electrical implementation between a power supply, a digital voltmeter and a SKiiPpack to be tested. It enables fast and easy access to monitor the SKiiP behaviour under various conditions applied. The SKiiP tester can be operated at two levels of inspection severity: 4.1 SKiiP with DC Link and AC attached [SKiiP to be tested is not removed from the system and still part of the inverter] No access to power terminals, only monitoring of primary side is possible. From our experience this provides an 85% chance to detect a SKiiP malfunction in very fast time. No removal from the inverter is needed. Just disconnect the primary side interface towards the inverter and connect the primary side cable from the SKiiP Tester. warning Never connect a SKiiP Tester to a SKiiP while DC link voltage is present! Never connect a SKiiP Tester to an inverter system that is not completely shut down, disabled and discharged! Remove the AC power terminal connection! Use qualified personnel only! 4.2 SKiiP as standalone unit [SKiiP is removed from inverter and access to all, even power terminals, is possible]. Monitoring of primary side and power terminals possible. From our experience this provides a >95% chance to detect a SKiiP malfunction in reasonable time. After removal from the inverter many companies collect their possibly faulty SKiiPs in repair centres. In addition to the fast test of the primary interface described above now the secondary power silicon can be tested for parameters as: - Breakdown voltage (per IGBT and freewheeling diode) - IGBT ON Switching (by pressing the permanent ON A or B buttons. - Vce_ON (IGBT) at roughly 1.5Adc - Vf at roughly 1.5Adc (diode conduction) From our experience even slightly damaged breakdown voltage curves of silicon chips can be detected with the internal source of 170V/50µA. Once the voltage drops below 150Vdc there probably is a problem inside the SKiiP. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 6/16

7 Some SKiiP sections have the U-option with DC-link voltage measurement (mostly located parallel to the DC power terminals of HB2 of a SKiiP). As this is an additional load to the tester s internal 50µA source some 5-10 volts lower are expected. Those sections are non-faulty, please double check a possible DC-link measurement option before thinking of this SKiiP as faulty. If the SKiiP to be tested is standalone just connect the primary side interface with cable from the SKiiP Tester and attach DC & AC power terminals with the cables that are inside the standard Tester delivery. Repeat secondary side tests with every SKiiP section (2-/3-/4-fold SKiiP BG, GD, GH). 5. Test setup SkiiPs with DC link attached Much time is needed to replace a suspicious SKiiP with a new one on site. If the original unit is not faulty lot of time is wasted and unnecessary rejects towards the SKiiP supplier are the consequence. warning Never connect a SKiiP Tester to a SKiiP while DC link voltage is present! Never connect a SKiiP Tester to an inverter system that is not completely shut down, disabled and discharged! Remove the AC power terminal connection! Use qualified personnel only! First of all - always perform a visual inspection of the suspicious SKiiP. If mechanical damage, debris, or traces of explosion are visible an electrical check is not needed to identify the SKiiP as broken. 6. How to proceed on site to test a SKiiP 1.) Make sure the inverter is completely powered down, discharged and accessible safe (same procedure as if you wish to change a SKiiP). 2.) Unplug the primary side wiring from the d.u.t. SKiiP (device under test) 3.) Power up the SKiiP Tester with its power supply (or with any 24Vdc supply that is current limited to <3A) 4.) Connect a digital voltmeter in auto range voltage mode (200.0mV to V should be within the auto range option) L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 7/16

8 Spare cables are standard computer LAN cables. Spare parts can be found everywhere in the world. Cable length is a minor issue, due to Kelvin measurement. The position of the cables towards the SKiiP tester is not relevant. Any 8-pin cable will operate in any of the three positions in the SKiiP Tester. The functions DC terminal, AC terminal or voltmeter output is chosen automatically. The SKiiP tester will work with any 24V DC supply of 1.2A or more, center pin positive. If a SKiiP is in primary side short circuit, the 24V supply will feed this short circuit through the SKiiP tester. The tester s internal 100mOhm shunt will be damaged if your 24Vdc supply exceeds 3Adc. 7. Primary side standby current consumption All knob / button numbers in the following parts refer to the sketch front panel elements on page 2. 5.) Turn the supply knob [1] towards the SKiiP in OFF position (left turn knob in upper row facing downwards). 6.) Power up your digital multimeter, (set to voltage auto range mode) 7.) Connect the primary side cable from the SKiiP Tester to the d.u.t. SKiiP, use a type of cable & fiber optics that meets your SKiiP version Some SKiiPs use a D-SUB connector instead of a DIN pin or 26-pin connector. You may get an easy adaption by using a press-fit D-SUB connector and attach it on the flat cable. 8.) Turn the right turn knob of the lower row [5] into position primary signals. note Always start with the primary side power consumption in standby and under input signals ON & 10kHz. There is a chance of > 80% to detect a fault. If a fault is identified there is no need to complete the test matrix and additional time is saved. 9.) Turn the middle turn knob of the upper row [2] in position 24V path 10.) Turn the turn knob of the upper row [3] into position I_supply. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 8/16

9 Now the tester is ready to monitor SKiiP current consumption under various input command conditions. 11.) Power up the d.u.t. SKiiP by turning the left turn knob [1] of the upper row into position 24V. Now you see the power consumption of the SKiiP under test at 24Vdc supply in standby condition. No PWM signals are applied; all IGBTs are in OFF status. If the value indicates good or bad must be decided by a reference value from a good sample, or in comparism to a neighbour SKiiP s value. The internal shunt has a value of 100mOhm. Thus a current consumption of e.g ma will display in 18.73mV. Allow a settling time of some seconds and expect a little change in consumption due to the circuit heating up. There are many variants of SKiiP in the field. Their power consumption varies from some possible minor changes within date-code, component variance and mostly ambient temperature. Please note that it is not possible to hand out a cross reference list with all expected SKiiP currents. A relative measurement and decision will always be much more accurate, faster and less confusing. All SKiiPs allow feeding 15Vdc into 24V. Modern SKiiP-III will take more current at 15V due to lower input voltage. Elder SKiiP II will go into under voltage error and display this by the HB1 error LED. Those have an internal shut down below 18V, the 24V supply is disabled. 12.) Turn the supply knob into position 15V into 24V and observe error LEDs and supply consumption. Does your SKiiP only take 15Vdc supply (former versions of SKiiP)? Or does your SKiiP use +/-15V supply (some special types)? Just supply accordingly and monitor supply current in standby state. If your SKiiP is powered through the 15V supply please put the knob [2] into the monitor supply path 15V position. There is another, similar 100mOhm shunt and the voltmeter will measure the voltage drop due to current consumption in the 15V path. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 9/16

10 8. Status LEDs 13.) Monitor the ERROR LED indicators. Not all LEDs are relevant for all types of SKiiP. A SKiiP GB has only one half bridge inside, thus the status of the HB2 and HB3 LEDs must stay red. Do all relevant LEDs turn green or stay red? In case of testing a SKiiP GD all three HB errors should turn to green. Check the temperature error LED status. A functional cold SKiiP must show temp_error as green. For fibre optical linked SKiiPs refer to the LED at the fibre optical input. Green refers to no error. No light, or red light are suspicious. 9. Primary side 10kHz PWM current consumption As mentioned above roughly 80% of faulty SKiiPs are identified by the standby current consumption and status of error LEDs. The SKiiP tester L23005 provides pulse patterns and steady ON commands for a more detailed primary side examination. The chance to identify more hidden problems will increase from roughly 80% to >85% by performing the following additional functional tests of SKiiP Power Modules. Supply the SKiiP to be tested in a convenient way and apply standby condition. Start with the IGBT selection matrix switches [10] and [11] all in upper positions (=default). For SKiiP GB only the HB1 switches are relevant, the SKiiP interface of GB types does not use HB2 or HB3. 14.) Push the supply knob [6] and apply 10kHz of 50% duty cycle PWM commands to all TOP IGBT switches inside the SKiiP. Monitor and write down the current consumption. 15.) Push the supply knob [7] and apply 10kHz of 50% duty cycle PWM commands to all BOT IGBT switches inside the SKiiP. Monitor and write down the current consumption. Both values should be close together, one side tends to always need a little more. The delta in current consumption BOT=ON compared to TOP=ON is never identical; it always shows a slight mismatch of a few ma. 16.) Push the supply knob [6] AND [7] simultaneously. Apply 10kHz of 50% duty cycle alternating PWM commands to all IGBT switches inside the SKiiP. Monitor and note down current consumption. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 10/16

11 If your SKiiP does not tolerate 10kHz (part of self-protection of some big modern SKiiPs) refer to the next test step, only. If you insist on this measurement contact us to modify your SKiiP tester to lower frequencies (e.g. 5kHz). We refuse to generally do this change on all our testers, because the signal ratio will decrease linear and a fast identification needs time and more accuracy on the voltmeter. 10. Primary side steady ON current consumption The last test procedure described above will only work on SKiiPs that tolerate 10kHz. In addition it will deliver an indication of the average current consumption. For a SKiiP with slacked joints a test procedure with steady signals instead of PWM commands provides more stable fault identification. To identify the exact position of the weak IGBT-driver channel use the knobs [7] and [9] in combination with the position of the switching matrix [10], [11], HB1,HB2, HB3. Always bring only one of the possible 6 IGBT channels into a steady ON condition. Allow a little settling time and write down the current consumption. Some SKiiPs GD have only one IGBT driver path broken. By using the selection matrix you may identify the exact channel and write it down. Compare the relative change in current through all TOP and through all BOT switches. A notable change in current consumption (e.g. from HB2 TOP to HB3 TOP) indicates a SKiiP problem. 11. Primary side analog signals If the suspicious SKiiP passed all primary side tests so far return into standby consumption. The position of knob [3] will give the output voltages of the analog pins of the SKiiP interface. 17.) I_HB 1, HB2, HB3 will show the offset of the SKiiP internal current sensor. It should be within several mv positive or negative. From our experience faulty current sensors deliver 25% to 50% of the maximum output rail as offset. This should lead to much higher steady state amplitudes than +/- 50mV to locate the fault. The steady state current consumption can already identify, but not exactly locate the problem. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 11/16

12 A SKiiP GB only connects I_HB1. Any measurements on HB2 or HB3 will just collect noise due to open end cables in the mv range. 18.) The U_dc analog output should display zero with an offset of several mvs. As your DC-link must be fully discharged due to safety instructions, please double check the DC-link voltage (some SKiiPs recharge even big capacitor banks due to Vce desaturation monitoring up to 30Vdc). 19.) The Temp_analog signal gives the heatsink temperature according to the SKiiP datasheet curve. At moderate (cold) temperatures most SKiiPs display 0.3V 0.9V. If the SKiiP is still warm/hot from operation values up to several volts can be monitored and the SKiiP is not weak here. A broken sensor or a slack joint brings a voltage of >8Vdc. There are special types of SKiiP in the field that can accurately measure & display very low temperatures. Please refer to their characteristic curve in their datasheet. 12. Summary - Primary side monitoring If the SKiiP under test has successfully passed all tests mentioned above and is still considered to be faulty, it must be removed from the inverter to check power terminal behaviour. From our experience we recommend to double check all other components first. As mentioned, the chance that it is not this SKiiP causing trouble is better than 85% after successful passing all tests described above. 13. Secondary side monitoring - SKiiP as standalone unit After the SKiiP has been removed from the application, access to the power terminals for measurements is possible. The SKiiP tester has a built-in, current-limited voltage source that provides roughly 170Vdc with >100kOhm impedance. Decoupled from this high voltage and connected in parallel is a 15V source limited to roughly 1.5A. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 12/16

13 This source provides power silicon measurements at higher voltage level as well as forward voltage measurements of silicon devices in ON state at low currents (1.5A). We are aware that 170V and 1.5 A do not test the limits of the SKiiP silicon power capabilities. But from our experience a damaged characteristic semiconductor curve can be detected in most cases with this kind of source. If the removed SKiiP arrives from the field as a standalone unit we recommend performing the primary side tests in the new location. The SKiiP tester provides best results by comparing relative readings. Deciding the status of a SKiiP by its absolute readings always needs the consideration of possible deviation from the test setup. Deviation from test setups on site and in a in a repair centre may occur from: - different ambient temperature - testing time (heating up of SKiiP circuit during measurement) - power supply tolerance - cable length and condition (supply voltage drop) - shunt tolerance inside SKiiP tester - voltage/current source tolerance inside SKiiP tester - PWM frequency tolerance - voltmeter calibration and accuracy The SKiiP tester is designed as a lower cost device and usually is profitable by reduced maintenance and shut down time the first few usages. We do not intend to narrow the tester-internal tolerances. This would increase cost and still cannot provide much better measurement accuracy, as some external test conditions still can neither be considered, nor covered. 20.) Perform primary side measurements as described in the chapters above. 21.) Fill out or complete the test protocol. Find a suggestion of a test protocol at the end of this application note. Always prefer your company s guidelines for reports. Consider that most faulty SKiiPs are returned to the supplier. If your test protocol contains the relevant data that led to the decision this device is faulty, you safe a lot of time & money at L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 13/16

14 the suppliers incoming inspection. So your company will additionally benefit from this records. 22.) Turn the SKiiP supply knob [1] into OFF position. 23.) Attach the AC and DC cables to the first section of the SKiiP under test. Some SKiiP testers need a cross tip screw driver, modern editions use hand operated knurled screws. The orientation of the cable-pcbs is failsafe. 24.) Turn knob [5] from primary signal into TOP position to monitor the upper silicon of the attached halfbridge. 25.) Re-power the primary side of the SKiiP with knob [1] in standby state. 26.) Turn the knob [4] from off into Vce(IGBT). 27.) Monitor the OFF state voltage drop of the TOP IGBT and its freewheeling diode in section one of the SKiiP. It should be around 170V, not below 150V.If in doubt, compare to other sections of the same SKiiP or to other SKiiPs. 28.) Push and hold button [7] with switch [10] in upper (=default) position. Monitor and write down forward voltage drop of IGBT silicon at roughly 1.5A. It should read <600mV and be in the same range of all other sections in ON mode. 29.) By releasing button [7] the readout must return to the 170V level. 30.) Turn knob [4] into Vf (diode) position. 31.) Monitor and note the forward voltage drop of the free-wheeling diode. It should be in the same range as the ON state IGBT (<600mV) but usually is different from the IGBT curve. 32.) Switch knob [4] into off postion. 33.) Switch knob [5] into position BOT. 34.) Repeat the measurements performed in position TOP now focusing the BOT section. 35.) Write down the results. The use of the PWM generator knob [6] or [8] is not recommended while testing power terminals. We do not expect comparable results, the test setup starts to act as a tiny buck or boost converter and the displayed values are not stable. The use of PWM signals does not make sense here. 36.) Power down the SKiiP supply with knob [1] into OFF position. 37.) Remove AC and DC cables from the section that has been tested. 38.) Attach AC and DC cables to the next remaining section of the SKiiP under test. 2-fold, 3-fold, or 4-fold SKiiPs need repetition accordingly. 39.) Repeat the measurements for TOP and BOT in steady ON and OFF state of the IGBT. 40.) Repeat the forward voltage of the free-wheeling diode. L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 14/16

15 As mentioned above some sections of some SKiiP types have DC-link measurement installed. These sections bring out an additional load [10 MegOhm range] to the tester s internal 170V source. Double check for such types and consider such section as non-faulty, even if the 170V voltage drops lower than in the other sections of such SKiiP types. For example a normal readout for a 3-fold Udc SKiiP can be: open -HB1-HB2-HB3 : 172V-163V-150V-162V. With DC-Link option on position HB2 this readout is not suspicious. Without the DC-Link option HB2 it is suspicious. 14. Summary - Secondary side monitoring If the SKiiP under test has successfully passed all tests primary and secondary side (=power terminals) there is a >95% chance that this SKiiP does not have a problem and is worth to be tested/used in a high power application. From our experience many SKiiPs are returned without having internal trouble. This creates more down time because the real reason for malfunction is not identified. 15. Additional hints - Calibration For further details refer to the manual of the SKiiP tester. Do only operate the unit in dry areas. Intended usage: - Saving time while troubleshooting in applications - Decision assistant for SKiiP is definitely faulty or probably well - Test cycle time < 5min including test setup time - No dismounting of SKiiP into subcomponents - Less unsubstantiated rejects to Semikron What is NOT covered? - NO 100% substitute for inhouse Semikron functional test - NO breakdown voltage measurement (only 170V max ) - NO gate leakage current measurement - NO R th -measurement, - NO measurement with rated current (only 1,3A DC,max ),... L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 15/16

16 Calibration As the SKiiP tester is optimized for relative measurements the readouts of the absolute values are less important. We do not recommend a scheduled return to our company for calibration. In some countries shipping twice exceeds the cost for a new tester. A qualified operator can easily check the SKiiP tester for internal malfunction: - Mechanical damage (drop from wind turbine is a popular issue) - Mechanically overstressed switches - Current values not as expected from experience: Measure current consumption of SKiiP under test with a calibrated meter Compare to the SKiiP tester s readout. If readout is faulty, return for repair to replace the 100mOhm shunt. - Voltage values Vce and Vf not as expected from experience: Measure 170V and no SKiiP attached with a calibrated meter (but with the AC and DC cables mounted) Measure short circuit current in the 170V position (should be in the range of 1.2 2A) If considered faulty, return for repair of the internal source. - Broken power supply; replace with any 24V supply in the suitable range - Overstressed cables; replace with LAN cable from any computer store 16. Service Never carry out repair on your own, please contact: Ing.-Büro M.Billmann Lerchensteige 10 D Emskirchen Phone: +49-(0) Fax: +49-(0) M.Billmann@ ib-billmann.de L23005_SKiiP-Tester_Appnote_HTU_ENG_v1.1.doc; ; M.Billmann; 16/16