Induction Machine (IM) and Variable Frecuency Driver (V/f type) starting from the DC bus feeding the power mosfets, which are driven using PWM.

For a given motor the DC power supply or battery must be adjusted to the rms line voltage times square root of 2. and the V_to_f gain must also be adjusted to Vrms/nominal freq.

After that, only the frequency imput needs to be changed according to the desired speed or operating point

Induction Machine (IM) and PWM Drive circuit, with mechanical fan load.

Induction Machine (IM) and PWM Drive circuit, with mechanical fan load.

Induction Machine (IM) and PWM Drive circuit, with mechanical fan load.

This example shows a more detailed circuit- and logic-level implementation of the PID Control Loop shown in the companion example, “PID Speed Control Loop – Continuous”. The ideal motor drive block of the “Continuous” version is expanded here, to include both a H-bridge motor drive, and also the digital logic necessary for converting the continuous PID controller output into the desired PWM signals that are distributed to drive the gates of the power MOSFET switches. The MOSFET model was calibrated to represent an IRF3710, using only information published on the manufacturer’s datasheet.

The rest of the system, including the PID block-diagram controller, the mechanical fan load and the DC Motor characterized to represent an FRC CIM Motor, are the same as in the Continuous version. While the simulation time for this switching version is significantly longer, more detailed information about practical circuit performance and component sizing is available. For example, the fan speed step response is somewhat different from the conceptual design, because of the losses in the MOSFETs under high current conditions, as well as voltage drop in the battery. Also, information regarding component stress levels within the “datasheet specified” MOSFETs and Diodes is provided.

This Electric Power Steering (EPS) System design includes a PWM Switching Inverter circuit that uses Toshiba TPHR7904PB Power MOSFETs. The drive includes a D-Q control algorithm, and uses space-vector modulation (SVM) to generate digital PWM signals. These control the ON/OFF state of the switches.

The mechanical load model includes static and kinetic friction, a steering force that varies with rack displacement, as well as various mass, inertia, damping and spring/stiffness elements of the steering system. The steering torque, applied by the vehicle's driver, is assisted by torque from the motor scaled by the gear ratio. For the control, the first gain/pole-zero block (far left) specifies the amount of "torque_assist" gain (assist torque as a multiple of the vehicle operator's torque applied to the steering wheel), as well as providing compensation to improve system stability.

This design focuses on the performance of the switches in the inverter circuit, including tracking of the thermal characteristics of one representative switch. In a companion version of this design, "EPS System with PMSM - Pre-Circuit Design for Toshiba Drive", Clarke and Park Transform models are used with a continuous ideal voltage drive, and provides much faster simulation results with a focus on overall system dynamic performance.

This design is similar to the design "Ideal Switching Design for Moog PMSM - BLDC Motor Use-Case", but the ideal switches in the inverter are replaced with "Datasheet" Power MOSFET models. These models are calibrated to match the datasheet specified characteristics of an STW45NM50 device. This replacement required the conversion to the digital signals used to control the switch states, to actual gate voltages. So representative models of the necessary gate drivers were also added.

In addition, a "hot part monitor" model was added to one of the Power MOSFETs. This models the datasheet specified "Rthj_amb" (0.32 degrees C per Watt), in order to predict the internal junction temperature during different phases of inverter operation. A thermal time-constant of 1 ms was assumed, which may be quite unrealistic. It is possible to add much higher fidelity thermal network models of the heat transfer path if valid parameters are given.

Finally, one of the low-pass filters used in the current sense path was changed to reflect a possible circuit implementation using op-amps. This is to show the ability to move seamlessly between ideal signal-flow (or continuous transfer function block) modeling to circuit implementation modeling, anywhere in a system design.

You can also see a version of this design that uses the manufacturer provided SPICE model for the Power MOSFET: "STW45NM50 MOSFET Switching Design for Moog PMSM - BLDC Motor Use-Case"

This example shows a more detailed circuit- and logic-level implementation of the PID Control Loop shown in the companion example, “PID Speed Control Loop – Continuous”. The ideal motor drive block of the “Continuous” version is expanded here, to include both a H-bridge motor drive, and also the digital logic necessary for converting the continuous PID controller output into the desired PWM signals that are distributed to drive the gates of the power MOSFET switches. The MOSFET model was calibrated to represent an IRF3710, using only information published on the manufacturer’s datasheet.

The rest of the system, including the PID block-diagram controller, the mechanical fan load and the DC Motor characterized to represent an FRC (First Robotics Competition) CIM Motor, are the same as in the Continuous version. While the simulation time for this switching version is significantly longer, more detailed information about practical circuit performance and component sizing is available. For example, the fan speed step response is somewhat different from the conceptual design, because of the losses in the MOSFETs under high current conditions, as well as voltage drop in the battery. Also, information regarding component stress levels within the “datasheet specified” MOSFETs and Diodes is provided.

This example shows a more detailed circuit- and logic-level implementation of the PID Control Loop shown in the companion example, “PID Speed Control Loop – Continuous”. The ideal motor drive block of the “Continuous” version is expanded here, to include both a H-bridge motor drive, and also the digital logic necessary for converting the continuous PID controller output into the desired PWM signals that are distributed to drive the gates of the power MOSFET switches. The MOSFET model was calibrated to represent an IRF3710, using only information published on the manufacturer’s datasheet.

The rest of the system, including the PID block-diagram controller, the mechanical fan load and the DC Motor characterized to represent an FRC (First Robotics Competition) CIM Motor, are the same as in the Continuous version. While the simulation time for this switching version is significantly longer, more detailed information about practical circuit performance and component sizing is available. For example, the fan speed step response is somewhat different from the conceptual design, because of the losses in the MOSFETs under high current conditions, as well as voltage drop in the battery. Also, information regarding component stress levels within the “datasheet specified” MOSFETs and Diodes is provided.