Power Electronics Module
The Power Electronics Module (PEM) is located in the rear of the vehicle secured to the rear subframe and battery.
The PEM has connections for:
A ground strap is fitted between the PEM and the battery enclosure which is grounded through the chassis.
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WARNING: The PEM is a high voltage system and should not be opened. Failure to comply could result in serious injury or death. |
NOTE: There are no serviceable components in the PEM. It is to be replaced as a complete unit in the event of malfunction; all repairs are to be completed by the original manufacturer.
| Description | Specification |
| PEM Input Operating Voltage | Nominal 12.5V +/-2%, transient 11.5V Direct Current (DC) to 14V (DC) |
| PEM Input Operating Current | 15A (Typ.)/35A (Max.) |
| PEM Standby Current | 1A (Typ.) |
| Motor Blower Output Voltage | 12V (DC) PWM at 0% to 100% duty cycle |
| Maximum Motor Blower Output Current | 13A |
| Battery Heater Output Voltage | 90V (AC) to 250V Alternating Current (AC) with PWM current regulation |
| Battery Heater Output Current | 7.5A (Typ.) |
| Typical Power Dissipation | 800W - Charging at 240V (AC) at 70A 500W - Driving at 40kW 15 W - Idle |
| Maximum Power Dissipation | 6kW - Driving at 218kW for 30 seconds |
| Description | Specification |
| DC Input/Output Operating Voltage | 280V (DC) to 415V (DC) (typ.) 250V (DC) to 420V (DC) (max.) |
| Maximum DC Current Input | 650A for 10 seconds |
| Continuous DC Input Current | 144A at 77°F (25°C) Ambient |
| Maximum DC Output Current | 175A rms continuous, 640A rms peak |
| Minimum Isolation (chassis to high voltage DC) | 2000V (DC) |
| Peak Regen Current | 75A for 30 seconds |
| Description | Specification |
| Output Voltage | 0 to 250V (AC) rms 3-phase, |
| Output Frequency | 0 to 450Hz |
| Continuous Output Current | 144A rms |
| Maximum Output Current | 850A rms |
| Maximum Ripple Current | 100A peak at 10kHz |
| Continuous Delivered Power | 75kW at 77°F (25°C) ambient |
| Maximum Delivered Power (5 seconds) | 218kW at 383V (DC) for 10 seconds |
The PEM contains five functional boards:
The human interface function contains all the controls and indicators that allow the driver to interact with the vehicle and receive information back. These include the gear selector, accelerator pedal, touch screen and charge port illumination.
The battery is charged by configuring the PEM and motor as a switching regulator in a boost configuration. In this configuration the PEM accepts AC power and converts it to DC current at battery voltage.
The following measurement and management features are used to achieve its objective of controlling the charging procedure:
The motor receives power from the battery via the motor drive electronics and has the following functions:
This module uses sensors located around the vehicle to monitor the temperature of various components and control the cooling fans. These include motor stator, MegaPoles and LCMC inductor.
This function provides logistical support for the previously described function. This includes the following:
The Transmission Control Module (TCM) is located on the underside of the trunk assembly communicates to the PEM over the CAN 1 connection.
The Power Electronics Module (PEM) has three main functions:
The PEM responds to the gear selector and accelerator inputs to transfer DC power from the battery which is converted to 3-phase AC for the motor. During normal operation, the PEM monitors parameters such as the voltage delivered by the battery and the rotation speed of the motor. The PEM also monitors temperatures of the motor and power electronics; cooling fans for the motor and internal PEM electronics are driven at speeds in proportion to measured temperatures. The PEM uses the Digital Motor Controller (DMC) to translate driver commands from the gear selector and accelerator pedal into precisely-timed AC power signals applied to the motor to generate the correct speed and direction of rotation to move the vehicle.
Circuits within the PEM monitor temperatures, voltages, and currents for maximum or minimum limits using a combination of hardware and firmware adjustable values. These circuits prevent damage to the PEM, battery or motor when a variance from nominal operating conditions is detected. For example, exceeding a limit of one or more of the monitored values can cause a reduction or cessation in power delivered to the motor until the out of specification value returns to normal. The PEM controls the speed of the motor blower and PEM blower to manage subsystem temperatures.
Line current supplied to the PEM is measured via a current sensor inside the PEM in the CIC (Charge Input Circuit) on one side of the AC line. This sensor is used to regulate the line current, but it is also compared to the PCS (Phase Current Sensor) currents to ensure that the value is within an expected range.
AC line voltage is measured across the charge port cable by the DMC board.
The PEM supports bi-directional CAN bus communication. PEM internal nodes that are accessible via the CAN bus include the DFC (Dual Fan Controller), pedal monitor and the DMC. CAN communication between the Vehicle Management System (VMS) and the Transmission Control Module (TCM) is passed through the PEM. A 500 Kbps CAN bus is used to transfer control and status information between processors of the PEM controller, the VMS and the ABS ECU. In normal operation the bus termination occurs in the TCM.
The PEM controls the electrical supply to the battery during charging. The PEM also monitors charging from the motor during regen. A number of factors are monitored and can be changed by the PEM within preset limits:
'Charge current handshaking' is the mechanism that determines the charge rate is a variable width pulse on the HPC pilot signal. The pilot signal uses the AC ground pin as a signal return. A fixed load resistance and diode on the DMC board interacts with a source impedance in the HPC to produce a specific amplitude for the pilot signal inside the PEM. A relay closure on the DMC signals that the PEM has detected a valid pilot signal and is ready to charge. The width of the pilot signal pulses is related to the charge rate allowed.
Regen operates on the principle that the electric motor can also operate as an electrical generator during the braking process. This places a load on the motor which in turn provides an additional braking effect.
The amount of torque generated in either gear is proportional to the accelerator pedal position – full torque when the pedal is fully released; less as the pedal is depressed, reaching zero torque when the pedal reaches its neutral torque position although the neutral torque position is speed dependant.
The motor controller converts this torque command into the appropriate 3-phase voltage and current waveforms to produce the commanded torque in the motor in the most efficient way. The torque command can be positive or negative. When the torque serves to slow the vehicle then energy is returned to the battery creating regenerative braking.
The maximum regen deceleration varies depending on vehicle speed. The maximum regen braking profiles are defined as a target total deceleration rate (including drag) as a function of vehicle speed. The maximum regen braking profiles are tailored to everyday driving conditions, which typically exhibit higher deceleration rates at lower speeds. This is different from a gasoline vehicle where, in any given gear, the engine braking torque falls as the speed falls.
NOTE: A failure of the ABS system disables regen braking. A notification will be displayed on the touch screen.
The ammeter within the instrument pack is operational whenever the key is in the ON position:
The PEM translates driver commands from the gear selector and the accelerator pedal into precisely timed AC power that is applied to the motor to generate the correct speed and direction of rotation to move the vehicle.
Shift requests from the driver are encoded by optical switches that are interrupted by an opaque flag attached to the selector lever. The selector lever incorporates mechanical detents for each gear. Each gear has a separate optical switch that drives a separate line to the PEM controller. Power for the optical switches is obtained from the 12V distribution lug in the front of the vehicle.
This module controls the current supplied to the motor and the level of power derived from regenerative braking.
Three MegaPoles act as electronic switches to connect the battery bus to the 3-phase windings of the motor. The switching follows a set of three Pulse Width Modulation (PWM) signals generated by the PWM generator.
Maintenance of constant vehicle speed is the function of the cruise control hardware and firmware in the PEM controller. User input from momentary switch actuators invoke various cruise control states while feedback from motor RPM or the foot-operated brake maintains or cancels the selected state. The accelerator pedal can override cruise control settings to increase vehicle speed but does not cancel cruise control mode.
Three momentary contact switches on a stalk on the steering column are used to select the various cruise control functions. The switches, labeled ‘O’, ‘I’, and ‘R’, are sampled by the PEM controller, debounced, and used to select the operating state. The ‘O’ switch is normally closed while the others are normally open.
Motor RPM is monitored once the desired cruise speed has been selected. Motor phase current frequency and amplitude are commanded to maintain the selected speed.
Application of the foot-operated brake pedal overrides the selected cruise control function and rescinds the existing state. Pressing the ‘O’ switch will also cancel the cruise control function.
The TCM is responsible for engaging and disengaging the parking pawl. The parking pawl is engaged when the key is turned from ON to ACC and the vehicle is stationary and disengaged when the key is inserted. The parking pawl is disengaged when the vehicle is started.
The thermal control module monitors and controls the temperature of both the motor and the PEM itself. Dual fans are employed to reduce the working temperature of these components using temperature sensors within the motor, MegaPoles and the charge component. The cooling fan speed is variable to enable control of the temperature.
Several types of thermal sensors are used in the PEM to monitor operating temperatures of internal components. The sensor outputs eventually end up on the DFC board to control fan speeds and torque limits. The internal components monitored are:
Motor RPM is sensed via two Hall effect sensors and a 64 tooth gear mounted on the end of the motor. Power for the sensors is supplied through the motor encoder interface cable from a 5V linear regulator. The output of the Hall sensors is open drain so pull-up resistors are used on the DMC to create logic level signals.
Two of the three MegaPoles in the PEM are fitted with Pole Current Sensors (PCS) that convert current to voltage using a precision current shunt resistor.
The PEM incorporates many built-in safety circuits to protect both the vehicle occupants and the power train. These are:
This module includes all the controls and indicators on the vehicle. The following components are under control of the PEM:
The PEM contains several features designed to promote the safety of service technicians when working on the PEM in a vehicle. Three components associated with PEM safety are:
The Controller Area Network (CAN) bus is used to transfer control and status information between processors of the PEM controller, the Vehicle Management System (VMS).