Siemens SINAMICS S120 Function Manual page 549

Overload responses
The power unit responds with alarm A07805. The Control Unit initiates the parameterized
responses via p0290 at the same time that the alarm is issued. Possible responses include:
● Reducing the pulse frequency (p0290 = 2, 3)
● Reducing the output frequency (p0290 = 0, 2)
● No reduction (p0290 = 1)
Function diagrams (see SINAMICS S120/S150 List Manual)
• 8014
Overview of important parameters (see SINAMICS S120/S150 List Manual)
• r0036
• r0037[0...19] CO: Power unit temperatures
• p0290
• p0294
Drive functions
Function Manual, (FH1), 04/2014, 6SL3097-4AB00-0BP4
T his is a highly effective method of reducing losses in the power unit, since switching
losses account for a high proportion of the total losses. In many applications, a temporary
reduction in pulse frequency is tolerable in order to maintain the process.
Disadvantage:
Reducing the pulse frequency increases the current ripple which, in turn, can increase the
torque ripple on the motor shaft (with low inertia load), thereby increasing the noise level.
Reducing the pulse frequency does not affect the dynamic response of the current control
circuit, since the sampling time for the current control circuit remains constant.
This variant is recommended when you do not need to reduce the pulse frequency or the
pulse frequency has already been set to the lowest level. Further, the load should also
have a characteristic similar to the fan, that is, a quadratic torque characteristic with
falling speed. Reducing the output frequency significantly reduces the converter output
current which, in turn, reduces the losses in the power unit.
You should choose this option if it is neither possible to reduce the pulse frequency nor
reduce the output current. The converter does not change its operating point once an
alarm threshold has been overshot, which means that the drive can be operated until it
reaches its shutdown values. Once it reaches its shutdown threshold, the converter
switches itself off with alarm A05000 (power unit: Overtemperature inverter heat sink),
A05001 (power unit: Overtemperature chip) or A07805 (drive: Power unit overload I2t).
The time until shutdown, however, is not defined and depends on the degree of overload.
Signals and monitoring functions - thermal monitoring power unit
CO: Power unit overload I2t
Power unit overload response
Power Module warning I2t overload
Monitoring and protective functions
9.2 Thermal monitoring and overload responses
549