Question:
Can ECS axis modules be supplied by an EME 9360 DC power supply unit and, if so, what must be observed?
Answer:
Instead of using an ECS power supply module, you can also use an EME 9360 (9364, 9365) DC power supply unit to supply ECS axis modules.
In this case, the following must be observed:
• DC fuses are required between the individual ECS axis modules and the DC bus.
• In the ECS axis modules, the existing mains voltage must be set under C0173 to adapt the switching thresholds for over and undervoltage.
• The charging current limitation of the ECS axis modules must be activated (setting C0175 = 1).
• For operation in generator-mode, a brake chopper must be used, if necessary.
Information about the charging current limitation:
The ECS axis modules are provided with a charging current limitation to limit the charging current at mains connection by means of charge resistors. The 9360 DC power supply unit is not equipped with a charging current limitation. Therefore, the charging current limitation of the ECS axis modules must be active (C0175 = 1) for operation on the 9360 DC power supply unit.
Initial charging current:
After switching on the power supply, the DC-bus capacitors will be charged first. For all ECS axis modules, the initial charging current arising here will be 5.6 A per ECS axis (identical charge resistor).
The charging time constant (tau = RxC) for the ECS axis modules is (48 A and 64 A) 33 ms. For the smaller device sizes (4 A, 8 A, 16 A, 32 A), it is with 16.5 ms half as long.
In applications with a larger number of ECS axis modules in the DC-bus connection, the initial charging current will quickly reach significant dimensions. This current peak must be considered when dimensioning the mains and DC fuses, and, if necessary, the cables and the power supply unit.
The 9360 power supply unit can cope with the charging current peak of 50 ECS axis modules.
Technical data of the 9364/9365 power supply units according to the documentation:
• Continuous power: 50 kW / 100 kW,
• DC-bus current: 90 A / 180 A,
• Max. DC-bus current for 1 minute: 135 A / 270 A.
In practical operation, applications with up to 50 ECS axis modules on a 9360 power supply unit will be a maximum case. For 50 ECS axis modules, the initial charging current would have to be estimated at 50 x 5.6 A = 280 A. The initial charging current would thus be higher than the maximum DC-bus current specified for the 9364/9365 power supply units. The high current load of the mains rectifiers will only be active for a short time because the charging current decreases with the charging time constant of max. 33 ms. The rectifier diodes can, however, for a short time cope with very high overcurrent values. E.g. for the 9364, 2400 A for 10 ms are specified in the diode data sheet. For lower current values, the permissible current flow time will be longer.
By means of the above parameters it can be estimated that the short-term charging current peak of 50 ECS axis modules constitutes no problem for the 9360 power supply units.
Notes for dimensioning the mains and DC fuses:
The mains fuses mainly serve to protect the cables from thermal overload during operation. They feature a 'slow' tripping characteristic and the rated current of the fuses is close to the permissible current limit.
The DC fuses, however, mainly serve as 'emergency protection' in the event of short circuits in the DC-bus connection. In the DC-bus connection, many capacitors (energy storage devices) are interconnected in parallel in a low-resistance manner. In the case of a short circuit, the short-circuit current will rise very quickly because of the low limiting impedances. Therefore, the DC fuses used here must feature a very 'fast' tripping characteristic.
Contrary to the slow mains fuses, the rated current of the fast DC fuses must usually be significantly overdimensioned to ensure that the DC fuses will not respond to every current peak occurring during operation. An addition for the rated DC fuse current must be considered because all fuses are subject to ageing in the event of current peaks and, as a result, will already respond earlier.
