**3.1 Power comparison (PC) technique**

To calculate the absolute value of output power of MC drive to achieve power comparison (PC) technique, the torque producing current (i\*sq) and measured rotor speed (ωre) are sensed. **Figure 7** shows the gate drive signal, which is generated for RCC of input power clamp (IPC) method. Here power dissipation through a resistor in the regeneration control circuit (RCC) is directly proportional to the duty cycle of unidirectional switch (UDS), as in Eq. (1),

$$\mathbf{P}\_{\text{dis}} \propto \mathbf{D} \tag{1}$$

where D = duty cycle of the unidirectional switch and Pdis = power dissipation through the resistor.

The duty cycle calculation requires the maximum electrical braking power (Pmb) to be calculated, as shown in Eq. (2). The duty cycle of the switches is then less than or equal to unity under all operating conditions.

$$\mathbf{P\_{mb}} = \mathbf{T\_{me}} \,\mathrm{co\_{mre}}\tag{2}$$

where Tme = electromagnetic torque and ωmre = speed of MC drive.

The gate drive signals for RCC switches are generated by using field programmable gate array (FPGA) with digital signal processor (DSP). Here FPGA that receives input parameters (ωre, Te, i\*sq) from sensors is fed into DSP, which does all mathematical calculations to generate gate drive signal as shown in **Figure 7**, and again fed back to FPGA that is sending gate drive signal to the gate drive of UDS. The duty of UDS/BDS is linearly varying with respect to output negative

**Figure 7.** *Block diagram of the power comparison (PC) technique for IPC method.*

power. The MC drive is not capable to output whole of regenerated power because of it losses such as friction, windage, iron, switching and conduction losses. Because of above reason, the braking resistor dissipates less than the actually regenerated power. As written in Eqs. (3) and (4), the design of braking resistor (Rb) relies on maximum regenerative power during regeneration.

$$\mathbf{P}\_{\rm in,max} = \left| \mathbf{V}\_{\rm in} \right|^2 / \mathbf{R}\_{\rm b} \tag{3}$$

$$\mathbf{I}\_{\mathbf{b}} = \mathbf{V}\_{\text{in}} / \mathbf{R}\_{\mathbf{b}} \tag{4}$$

where the braking current (Ib) and input power (Pin,max) are directly proportional to the input voltage. The braking resistor design also depends on the braking time, thermal capacity of the resistor, and heat sink. And the current rating of UDS/ BDS in RCC must be higher than the braking current.
