The increasing technical demands on the power electronics of modern electric (EV) and hybrid (HEV) vehicles increasingly present designers with an almost insurmountable task. Increasing the energy efficiency and power density of power transmission and conversion systems requires more complex control electronics incorporating efficient Gallium Nitride (GaN) and Silicon Carbide (SiC) technology operating at high temperatures. switching frequencies. In addition to functional safety, connected vehicles also operate under IT-level security requirements and apply system interventions, such as firmware updates over the air (FOTA).
Faced with tight development budgets and competitive prices for end products, power electronics designers are forced to look for ways to simplify system design, including implementing more integrated control solutions.
To help overcome these challenges, this article discusses some of the advantages of Texas Instruments' C2000 series automotive-compatible real-time microcontrollers (MCUs), which are suitable for drive controls and power converters. EV and HEV power. After a brief description of the operation and interface of the F28003x family of controllers, the article provides an overview of the implementation of Field Oriented Control (FOC) in the traction inverter, and hysteretic current control in the charger. on board.
More efficiency for controlled drives and power converters
The remarkable performance of today's high-speed and electric vehicles is due in large part to the electronic control of drives and power converters. The real-time MCUs used in these subsystems use complex control algorithms and precise motor models to respond extremely quickly, with a control delay of just a few microseconds (µs). If the real-time closed-loop control is too slow and does not meet the defined time window, the control loop stability, accuracy, and efficiency are degraded.
To enable the use of proportional-integral-derivative (PID) controllers from standard libraries, vector controllers transform the three-phase stator current system into a two-dimensional current space vector to control magnetic flux density and rotor torque. . A fast current loop (blue arrow in figure 1) should achieve a control delay of less than 1 µs.
Figure 1: To achieve stable control, a real-time MCU must complete all arithmetic operations per loop step (blue arrow) in less than 1 µs. (Image source: Texas Instruments)
Combining fast vector control such as FOC and a highly efficient Permanent Magnet Synchronous Reluctance Motor (IPM-SynRM), the motor drives achieve high torques and up to 96% efficiency compared to classic DC motors ( i.e., the permanent magnet synchronous motor, or PMSM). Designers can implement the variable torque control between Lorentz force and reluctance force of the IPM-SynRM using a C2000 series real-time MCU and C2000WARE-MOTORCONTROL-SDK software in a time and cost efficient manner. The FOC also allows SynRMs to be controlled with great precision - even without magnets or position sensors - saving system weight and cost and making the motor more resistant to overloads.
For AC-DC power converters that function as On-Board Chargers for Electric Vehicles (OBCs) or conversely as PV inverters, it is important to keep the power grid free from harmonic distortions. This unclean Zero Voltage Switching (ZVS) can be counteracted with Hybrid Hysteretic Control (HHC) of the current. In this case, developers can also rely on C2000 MCUs to speed up circuit design by applying high-performance control algorithms from the C2000WARE-DIGITALPOWER-SDK software repository.
Simplify EV System Design with C2000 MCUs
To simplify power system design, Texas Instruments offers the C2000 series real-time MCU for rapid implementation of complex power controls, facilitating the design of a variety of flexible controls through a comprehensive hardware and software development environment. A single C2000 MCU enables vehicle designers to implement smaller, more affordable electric vehicle powertrains at half the cost, as they are designed to simultaneously drive on-board chargers, DC-DC converters, and traction inverters. Applications such as climate control, driver assistance systems and fuel cell control are also conceivable.
System designers can use a single, powerful MCU to control multiple power electronics and system components distributed throughout the vehicle. The TI website, especially the Resource Explorer and C2000 Academy, offers designers a great deal of help in the form of data sheets, application notes, evaluation boards, reference designs, training videos, and a forum. of developers.
TI has optimized the F28003x family of real-time controllers specifically for use in electric vehicles in terms of performance, integration, and cost. By offering 240 MIPS of processing power and integrated real-time control peripherals, circuit designers can improve the accuracy and power efficiency of their F280039CSPZ MCU-based power conversion and motor control systems, without the need for a FPGA. In addition, the easy-to-apply GaN and SiC technology reduces switching losses and increases power density thanks to higher switching frequencies, smaller magnetic components, and less cooling surface area.
The F28003x series supports Full Duplex Controller Area Network (FD CAN) communications, as well as various fast serial interfaces. An onboard 384 kilobyte (Kbyte) flash memory provides ample reserves for performing networked Internet of Things (IoT) functions. On-chip security features such as Secure Boot, an AES encryption engine, JTAG locking, and Hardware Embedded Self-Test (HWBIST) ensure that networked system interventions such as live firmware updates and by air (FOTA), are protected against tampering. The MCUs meet ASIL B requirements and have functional safety built in, speeding both application development time and the certification required for market release. Figure 2 provides an overview of the essential functions and interfaces.
Figure 2: Function block diagram of the F280039C MCU showing highlights such as fast processing, flexible communications and detection options, as well as security support features such as secure boot. (Image source: Texas-instruments)
Ideal for testing and prototyping, the TMDSCNCD280039C is a suitable evaluation board for the F280039C. To operate this controlCARD equipped with an HSEC180 (180-pin High Speed Edge Connector) header, a 180-pin TMDSHSECDOCK docking station is required.
Configurable Logic Blocks (CLBs) for custom logic
Innovative configurable logic blocks (CLBs) allow programmers to integrate custom logic into the C2000 real-time control system, eliminating external logic, FPGAs, CPLDs, or ASICs. By adding a CLB, existing C2000 peripheral modules such as Enhanced Pulse Width Modulator (ePWM), Enhanced Capture (eCAP) or Enhanced Quadrature Pulse Encoder (eQEP) can be extended with specific signals and functions the client's.
Logic blocks are configured via C2000 SysConfig, which is available in C2000Ware. It requires the SysConfig tool, which is part of TI's Code Composer Studio (CCS) integrated development environment (IDE) or is available as a stand-alone tool for use with other IDEs (Figure 3).
Figure 3: CLBs make it easy to implement custom logic into the C2000 real-time control system, eliminating the need for external logic and FPGAs. (Image source: Texas Instruments)
The C2000Ware software and documentation package minimizes development time by providing extensive device-specific drivers, libraries, and application examples, as well as by extending peripheral devices via CLB.
The basis for code development and debugging of C2000 embedded applications is the CCS IDE. The collection of tools includes an optimized C/C++ compiler, source code editor, project build environment, debugger, profiler, and many other features. The intuitive IDE offers a single user interface that guides users through every step of application development. Familiar tools and interfaces based on the Eclipse software framework help users get up and running quickly.
watch and tests
Instead of working on the complex periphery of the watch using CLB, programmers can use the built-in pattern generator (EPG) to perform simple test scenarios during programming or validation. The standalone EPG module makes it easy to generate custom pulse patterns (SIGGEN) and clock signals (CLOCKGEN), but can also capture and reshape an incoming serial data stream or synchronize with generated clock signals.
For debugging and non-intrusive monitoring and profiling of critical CPU buses and device events in a C2000 real-time system, Embedded Real-Time Analysis and Diagnostics (ERAD) is used. The hardware module offers extended bus comparators and system event counters located within the bus architecture of the MCU (Figure 4).
Figure 4 – ERAD provides advanced bus comparators and system event counters for interrupt generation, resides within the MCU bus architecture, and enables non-intrusive real-time system debugging. (Image source: Texas Instruments)
ERAD can independently generate system level interrupts and flags and feed them to other peripherals such as the CLB.
Faster implementation of FOC motor controls using C2000 MCUs
The implementation of variable torque control of an IPM-SynRM using vector control is complex. Depending on the speed and torque of the load, the algorithm must control the offset angle between two rotating coordinate systems. Thus, the rotor can electrically lead or retard the magnetic field of the rotating stator by up to ±90° using phase shift control, allowing variable operation between the RM and PMSM. Complex control of rotor torque and magnetic flux density can be quickly implemented using TI's Motor Control Software Development Kit.
The software, based on decades of combined experience, includes firmware that runs on C2000 motor control evaluation modules (EVMs) and TI designs (TIDs). Two key function libraries for vector control are InstaSPIN-FOC (FOC motor controls without encoders) and DesignDRIVE (FOC motor controls that require encoders).
Main features of InstaSPIN-FOC:
- Torque or speed without FOC sensor
- Flux, Angle, Speed and Torque (FAST) software observer for rotor estimates
- Identification of motor parameters
- Automatic adjustment of the observer and the torque control loop
- Superior performance for low speed and highly dynamic applications
A special feature of the FOC control loop is the FAST adaptive algorithm. This automatically determines the flux density, current angle, speed and torque from the phase currents and voltages (Figure 5). Thanks to the automatic identification of motor parameters, designers can quickly commission a new motor and rely on the automatic system for fine-tuning of the control loop.
Figure 5: A special feature of the FOC control loop is the FAST adaptive algorithm, which automatically detects flux density, current angle, speed and torque. (Image source: Texas Instruments)
DesignDRIVE main features:
- Speed or position sensed FOC
- Position Feedback: Incremental and Absolute Encoders
- Current detection techniques: Low-side shunt, line current sampling, and demodulation with sigma-delta filter
- Fast Current Loop (FCL): Optimized software library that takes full advantage of hardware resources to speed up system sampling, processing, and actuation to achieve the highest control bandwidth for a given PWM frequency in servo control applications
- Examples of real-time connectivity
Application example 1: An MCU controls the traction inverter and the DC-DC converter
Automakers tend to merge all three distributed system components into one chassis and minimize the number of MCUs to reduce system cost and complexity. However, this requires an MCU with high real-time control performance to manage all three. To address this, TI's Design Reference TIDM-02009 demonstrates the combined design of an EV/HEV drive inverter and a bi-directional DC-DC converter controlled by a single F28388DPTPS real-time MCU (Figure 6).
Figure 6: A single C2000 MCU board on the control board (bottom left) controls the traction inverter (top left) and the DC-DC converter (right). (Image source: Texas Instruments)
The drive inverter uses a software-based resolution-to-digital converter (RDC) to drive the motor at a high speed of up to 20.000 revolutions per minute (rpm). Its power stage consists of Wolfspeed's CCS050M12CM2 six-way power module, based on SiC FETs, driven by a TI UCC5870QDWJRQ1 smart gate driver. A state-of-the-art PWM module with integrated slope compensation in comparator subsystem (CMPSS) generates the PCMC waveform. The voltage sense path uses TI's AMC1311QDWVRQ1 extra-high isolation amplifiers with 2 volt inputs, and the current sense path uses TI's AMC1302QDWVRQ1 extra-high isolation precision amplifiers with ±50 millivolt inputs ( mV).
The DC-DC converter uses Peak Current Mode Control (PCMC) technology with phase-shifted full bridge (PSFB) topology and synchronous rectification (SR). Its bidirectionality has the advantage that the converter pre-charges the DC bus capacitor, eliminating the need for current limiting relays and series resistors. The integrated TCAN4550RGYTQ1 controller transceiver module provides interference resistant communication based on CAN FD.
Application Example 2: Efficient 6.6 kW Bi-Directional AC-DC Converter
For relatively high power outputs, the PMP22650 represents a GaN FET-based reference design for a single-phase, bi-directional AC-DC converter handling 6.6 kilowatts (kW) of power. The OBC charger can charge the traction battery with power from the grid and conversely pre-charge the DC link capacitors. The device converts 240 volts AC at 28 amps (A) on the primary side to 350 volts DC at 19 A on the secondary side.
A single F28388DPTPS MCU controls the power factor corrected (PFC) two-phase totem-pole link operating at a switching frequency of 120 kilohertz (kHz), and a full-bridge CLLLC topology (C = capacitor, L = inductor) followed synchronous rectification. The CLLLC converter uses both frequency and phase modulation for output regulation, operating at a variable frequency from 200 kHz to 800 kHz.
In Figure 7, the TMDSCNCD28388D controller card (middle) controls the primary side PFC intermediate circuit (left) and the secondary side full bridge CLLLC converter with synchronous rectification (right). The schematic of this design is shown in Figure 8.
Figure 7: The TMDSCNCD28388D controller card (middle) controls the primary side PFC link (left) and the secondary side full bridge CLLLC converter with synchronous rectification (right). (Image source: Texas Instruments)
The use of the newly developed LMG3522R030-Q1 high-speed GaN FETs enables an efficiency of up to 96% at full power and an open power density of 3,8 kW/litre. The power factor is 0,999 with less than 2% total harmonic distortion (THD). An alternative to the LMG3522 is the LMG3422R030RQZT GaN FET, also automotive rated, with a switching voltage of 600 volts and a Rds(ON) 30 milliohms (mΩ). It also integrates the door controller, overload protection and temperature control.
Figure 8: Circuit topology of the OBC consisting of the PFC intermediate circuit (left) and the secondary side full-bridge CLLLC converters with synchronous rectification (right). (Image source: Texas Instruments)
A special feature of this AC-DC converter is the HHC, which significantly reduces zero crossing distortion by emulating the voltage across the resonant capacitor. Test results also show better transient response, and this control loop design is also simpler than single-loop voltage control.
The example of a PV inverter shows how effectively the HHC reduces the distortion of the bridge switching transistors at zero crossing (figure 9, left), thus eliminating emission and distortions in the power grid. The high THD of 7.8% of the third harmonic on the sinusoidal mains voltage (figure 9, top right) is reduced to 0.9% using the HHC (figure 9, bottom right).
Figure 9: The HHC can significantly reduce the distortion of the bridge switching transistors at zero crossing (left) and thus eliminate THD. The high THD of 7.8% of the third harmonic on the sinusoidal line voltage (top right) is reduced to 0.9% (bottom right) using the HHC. (Image source: ietresearch.onlinelibrary.wiley.com)
By the way, the circuit design of this 6.6 kW DC-DC converter is based on TI's TIDA-010062 reference design, while the aforementioned C2000WARE-DIGITALPOWER-SDK makes it easy to design these power converters.
Conclusion:
Texas Instruments' C2000 series real-time MCUs can tackle almost any control task in automotive power electronics. The application of these MCU ecosystems enables system design in a time and cost efficient manner, aggregating and co-controlling what would normally be distributed system electronics using powerful MCUs in real time.
As demonstrated, GaN and SiC smart power controllers are relatively easy to implement. The library's extensive functionality and fully documented and pre-certified reference designs make it easy to implement more efficient FOC motor control and HHC control of drives.
