High demands are placed on the dynamics of feed drives in today's tooling machines. In order to maintain the required product quality and low path deviations even under the influence of disturbance forces, the drives must have good dynamic behavior. High PWM frequencies in the drive inverter contribute to this, keeping the dead times in the system low and thus maximizing the bandwidth. Based on the characteristics of the machines and the requirements of the processes, the control parameters and PWM frequencies are usually set to fixed values.
However, high PWM frequencies, which are necessary for high drive dynamics, cause significant switching losses in the power semiconductors. This reduces the energy efficiency, leads to additional expenditure for the corresponding heat dissipation and reduces the service life. Studies show that maximum dynamics are not necessary for many manufacturing steps, since high accuracies are not required. These include, for example roughing processes but also traverses to the tool changer or a standstill of the axis.
In order to further increase energy efficiency in tooling machines, the PWM frequency shall be reduced during runtime in those manufacturing steps in which lower requirements are placed on accuracy and dynamics. This results in a reduction of the switching frequency of the power semiconductors and consequently lower switching losses.
For the procedure of the adaptive PWM, the control cascade consisting of current, velocity and position controller is extended by a switching frequency controller. The switching frequency controller implements different algorithms to change the PWM frequency at runtime. For example, the PWM frequency can be switched depending on internal drive data or by external data. Furthermore, the parameters of the control cascade are adapted to the respective PWM frequency by the switching frequency controller. The integration of the method requires modifications of the switching signal generation, as well as in all cascades of the control system. The FPGA-based Open Automation Platform (OAP), developed at the ISW fulfills the basic requirements. Within the scope of the project, the adaptive PWM will be integrated in an industrial tooling machine. The procedure will be analyzed and evaluated with respect to all relevant aspects such as dynamics, accuracy, manufacturing process and energy consumption.