How to dimension a power supply for an Ingenia drive

How to dimension a power supply for an Ingenia drive

In this How-to guide we will show you how to properly dimension the power supply that you need in your system. Choosing an appropriate power supply is an important step for a successful motion control system solution. The choice of a power supply is mainly determined by voltage, current and power supply type.

Following are shown some guidelines to properly dimension the power supply for an Ingenia drive:

Voltage

The power supply voltage should be the targeted for the motor requirements, without exceeding the nominal ratings of the Ingenia drive. For example, up to 48 V for the NIX-X/48 and up to 170 V for the NIX-5/170. Make sure that the voltage rating of the power supply does not exceed the voltage rating of the motor, otherwise it could be damaged in the long run.

To calculate your power supply voltage needs use the motor specifications or curves and the following formula for a DC brushed:


For brushless motors when you know the phase to neutral values (for stator star connection):

  • Trapezoidal commutation (BLDC): 
  • Sinusoidal commutation (BLAC, PMSM): 

For brushless motors when you know the phase to phase values (terminal to terminal):

  • Trapezoidal commutation (BLAC): 
  • Sinusoidal commutation (BLAC, PMSM): 

Where:

  • VDCbus is the power supply voltage (for a DC driver).
  • VBEMF is the motor back-EMF voltage at the maximum operating speed. This can be calculated from the motor datasheet. 
  • Rphase is the resistance of the motor coils.
  • IMax is the maximum operating current of the motor.

Take extra care with triangle-star connections and the datasheets provided by the motor manufacturers. It is a typical source of error when calculating the real back-EMF.

It is not always necessary to operate the system at the maximum driver/motor voltage!
In many applications it is just not necessary to go to the maximum driver or motor voltage. Higher voltages mean:
  • Higher EMI (Electromagnetic interference) problems.
  • More switching losses (heat).
  • Higher current ripple to the motor (di/dt).
  • An oversized power supply (cost).
  • Lower power stage PWM resolution resulting to lower control performance. Since motor applied voltage is DC bus * PWMduty, the higher the voltage, the higher the steps.
There is no problem in operating a motor in a voltage lower than the nominal.

Nominal current

The nominal current of the power supply should be calculated from the maximum output power of the motor. Since a drive is a power converter, input DC current does not have the same value than output phase current. Further information can be found here.

Output power is calculated as the product between mechanical speed and power, or in electrical parameters, the product between output voltage and current (RMS). In a three-phase system, the product of phase-to-neutral voltage and phase current has to be multiplied by the number of phases. 

The worst case situation is when a maximum torque (and therefore maximum current) is required at maximum speed. In this situation .  However, in most cases maximum torque is only required during start-ups, so the requirements of the power supply can be reduced.

The required input current for a brushed DC motor can be calculated as:


For brushless motors, it can be calculated as:

  • Trapezoidal commutation (BLDC):
  • Sinusoidal commutation (BLAC, PMSM): 

Where:

  • IDC in is the power supply nominal current (for a DC driver).
  • ωmax is the no-load maximum speed achievable with this power supply voltage.
  • ωmax torque is the speed where maximum torque is applied. 
  • Iphase max is the maximum phase current provided by the drive. 
For multi axis systems, share the DC supply between all the drivers
If you can, use a single power supply for as many axis as possible. This will reduce the cost and increase the efficiency of your system as the braking energy of one of the axis can be used for the others.

Power supply type 

The power supply type should be chosen according to cost, efficiency, EMI and feedback requirements of our system. 

  • Non-regulated rectified power supplies, based on a rectifier and a passive filter are cheap and efficient. Although the voltage is not regulated, low-frequency input voltage ripple is not a problem in closed-loop operation. If an input EMI filter is not included, low-frequency harmonics are injected to the grid. Always use an isolation transformer if not included in the power supply. 

  • Switched power supplies are more expensive, but they offer high efficiency and regulated output voltage. Usually they include power factor corrector (PFC), which reduce the grid harmonic distortion and improve the power factor. Use good quality switched power supplies that will withstand the varying loads of driving a servo drive.

Isolated power supplies

For safety reasons, it is important to use isolated power supplies.

Overvoltage / overcurrent protection

There is a special consideration if the power supply will be working at or near the maximum voltage rating of the drive. If the motor will be rapidly decelerating a large inertial load from a high speed, care has to be taken to absorb the returned energy. In this case, a Shunt braking resistor should be used.

Some power supplies (mainly switched power supplies) include active protections. It is important to choose a power supply with wide overcurrent and overvoltage margins since current pulses can be common in high torque applications and overvoltages can appear during regenerative braking. If active protections are included, we highly recommend to choose a power supply with auto-restart function in order to not stop the application during transients. Ensure you do not exceed the OVP (over-voltage protection) during operation.

Power dissipation

Referring to power dissipation, we recommend power supplies with convection dissipation for cabinet mounted applications, where a fan can be added if required. For applications with limited space, conduction dissipated power supplies can be used. 


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