Editing Overvoltage and undervoltage faults
Your changes will be displayed to readers once an authorized user accepts them. (help) |
Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.
The edit can be undone.
Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision | Your text | ||
Line 1: | Line 1: | ||
− | Drive faulting due to voltage fluctuations in [[HV DC bus]] are commonly experienced with servo systems. These faults occur when drive measures a HV DC bus supply voltage that is not within the range defined by | + | Drive faulting due to voltage fluctuations in [[HV DC bus]] are commonly experienced with servo systems. These faults occur when drive measures a HV DC bus supply voltage that is not within the range defined by [[FUV]] and [[FOV]] parameters. The deviation of voltage may be impossible to notice with multimeter as length of these voltage surges can be in millisecond range. |
==Overvoltage faults== | ==Overvoltage faults== | ||
− | Servo drive attached to a motor can act two ways: energy supply and energy consumer. The energy consumer behavior occurs during decelerations and during fast torque reversals, and this causes current flow from motor to drive power supply capacitors. If the generated energy is not absorbed anywhere, the voltage of HV DC bus capacitors will rise above overvoltage threshold ( | + | Servo drive attached to a motor can act two ways: energy supply and energy consumer. The energy consumer behavior occurs during decelerations and during fast torque reversals, and this causes current flow from motor to drive power supply capacitors. If the generated energy is not absorbed anywhere, the voltage of HV DC bus capacitors will rise above overvoltage threshold ([[FOV]]) and trigger an software cleanable overvoltage fault. Overvoltage faults that are caused by returned energy from motor, can be dealt with a [[regenerative resistor]] and with optional extra capacitance in HV DC bus. |
Scenarios where returned energy is causing the rise of HV DC bus voltage: | Scenarios where returned energy is causing the rise of HV DC bus voltage: | ||
*Deceleration of motor speed when there is significant amount of energy stored in mechanical motion (rotating inertia or moving mass). This typically occurs with spindles and linear axes. | *Deceleration of motor speed when there is significant amount of energy stored in mechanical motion (rotating inertia or moving mass). This typically occurs with spindles and linear axes. | ||
− | *Sudden reversal of torque [[setpoint]]. This can generate voltage spike even when motor is standing still. This typically occurs in high bandwidth torque control applications (such as | + | *Sudden reversal of torque [[setpoint]]. This can generate voltage spike even when motor is standing still. This typically occurs in high bandwidth torque control applications (such as racing simulators). These spikes are very short and an added capacitor to HV DC bus and/or low resistance regenerative resistor might provide a solution. |
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
===Sizing regenerative resistor=== | ===Sizing regenerative resistor=== | ||
− | + | The needed regenerative resistor value can be calculated by equation: | |
− | + | :R=nominal_supply_voltage/peak_motor_current [Ohms] | |
I.e. if supply voltage is 48VDC and peak current is 10A, then a resistor of 4.8 ohms may be needed to consume all current that is returning from the motor. However, in most practical cases the regenerative current is less than the motor peak current, which allows using higher resistance thus reducing risk of overloading the MOSFET switch operating the resistor. It is recommended to experiment with higher resistor values first, and gradually move to lower resistances if problem persists. | I.e. if supply voltage is 48VDC and peak current is 10A, then a resistor of 4.8 ohms may be needed to consume all current that is returning from the motor. However, in most practical cases the regenerative current is less than the motor peak current, which allows using higher resistance thus reducing risk of overloading the MOSFET switch operating the resistor. It is recommended to experiment with higher resistor values first, and gradually move to lower resistances if problem persists. | ||
Line 23: | Line 17: | ||
{{damage|Before connecting a resistor to drive or drive's motherboard, check from user guides and/or electrical specifications the minimum allowed resistance. Specifications (list may be partial): [[Argon specifications]], [[IONICUBE electrical specifications]], [[IONICUBE 1X electrical specifications]]. | {{damage|Before connecting a resistor to drive or drive's motherboard, check from user guides and/or electrical specifications the minimum allowed resistance. Specifications (list may be partial): [[Argon specifications]], [[IONICUBE electrical specifications]], [[IONICUBE 1X electrical specifications]]. | ||
}} | }} | ||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
==Undervoltage faults== | ==Undervoltage faults== | ||
Line 43: | Line 22: | ||
==Using additional capacitor in HV DC bus== | ==Using additional capacitor in HV DC bus== | ||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
===Surge duration based method=== | ===Surge duration based method=== | ||
For short current surges/spikes, a capacitor added to HV DC bus might provide a solution for filtering out the spikes. Capacitor can be sized by equation: | For short current surges/spikes, a capacitor added to HV DC bus might provide a solution for filtering out the spikes. Capacitor can be sized by equation: | ||
− | + | :C=peak_motor_current*surge_duration/max_voltage_change [Farads] | |
− | I.e. if current is 20A, surge duration 0.005 seconds and maximum allowed voltage change (increase or drop) during that surge/spike is 10 VDC, then capacitance becomes | + | I.e. if current is 20A, surge duration 0.005 seconds and maximum allowed voltage change (increase or drop) during that surge/spike is 10 VDC, then capacitance becomes C=20A*0.005s/10V=0.01F which equals 10000 µF. |
===Motor inductance based method=== | ===Motor inductance based method=== | ||
If the duration is unknown, and we're dealing with fast reversing torque setpoint on a relatively large motor, the capacitor size may be calculated based on the stored energy inside motor inductance: | If the duration is unknown, and we're dealing with fast reversing torque setpoint on a relatively large motor, the capacitor size may be calculated based on the stored energy inside motor inductance: | ||
− | + | :C=motor_inductance*peak_motor_current^2/max_voltage_change^2 [Farads] | |
− | I.e. if current is 20A, motor inductance 5 mH (0.005 H) and maximum allowed voltage change in capacitor | + | I.e. if current is 20A, motor inductance 5 mH (0.005 H) and maximum allowed voltage change in capacitor, then capacitance becomes C=0.005H*20A^2/10V^2=0.02F or 20000 uF. |
===Keeping it practical=== | ===Keeping it practical=== | ||
− | Targeting low value in max voltage change will increase capacitor size significantly, and may become unpractical. I.e. if supply voltage is 48V and max voltage is | + | Targeting low value in max voltage change will increase capacitor size significantly, and may become unpractical. I.e. if supply voltage is 48V and max voltage is 55V, the max voltage change would be only 7V. Reducing supply voltage by few volts, say 44V, the allowed voltage change becomes 11V which yields much smaller required capacitance. |
− | {{tip|Operating drive near maximum supply voltage limit may cause high requirements for overvoltage prevention. Sometimes it may be easier to reduce supply voltage little bit to make more headroom for voltage increase. Many switching power supplies have a trimpot allowing to adjust voltage | + | {{tip|Operating drive near maximum supply voltage limit may cause high requirements for overvoltage prevention. Sometimes it may be easier to reduce supply voltage little bit to make more headroom for voltage increase. Many switching power supplies have a trimpot allowing to adjust voltage by few volts.}} |
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + | ||
− | + |