Control software targets for three-phase BLDC motor drives
Control software for three-phase BLDC motor drives has been unveiled by Power Integrations. Combined with Power Integrations’ BridgeSwitch integrated half-bridge motor driver and its Motor- Expert configuration and diagnostics tool, the hardware-software enables 98.2 per cent efficiency, reduces board space by more than 70 per cent and requires just three components for current feedback circuitry, compared to 30 components in a discrete design, said Power Integrations. The control software is suitable for residential and commercial appliances with three-phase motors, such as air conditioner fans, high speed hair dryers, refrigerator compressors, range hood fans and water pumps.
“Traditional three-shunt field-oriented control (FOC) solutions require expensive and bulky operational amplifiers (op-amps) and matching circuity for motor-current signal conditioning,” stated Cristian Ionescu-Catrina, senior product marketing manager for Power Integrations.
The BridgeSwitch integrated half-bridge ICs provide lossless current feedback for the positive half cycle, and the three-phase FOC software reconstructs the negative half-cycle current information from data present in the other phase current signals. This eliminates the need for costly and inefficient external current sense resistors, op-amps and matching circuitry and the associated complexity, claimed the company.
The software adds three-phase FOC to the company’s existing library of single-phase code. It allows real-time adjustment of motor speed and torque via the Motor-Expert graphical user interface (GUI). The code runs on any Arm Cortex-M0 at 48MHz and does not require a hardware accelerator block. It can also be ported to other equivalent MCUs.
The current modelling algorithm has passed static and dynamic test conditions, including low latency response to real-time events, claimed the company. The high degree of current accuracy ensures low jitter operation, it added. The new code is MISRA (Motor Industry Software Reliability Association) C-compliant, portable, modular and allows the user to modify any of the software layers.
Power Integrations’ BridgeSwitch ICs provide a motor current output signal that maps the current passing through the low-side FredFET. An internal sense-FET provides lossless current sensing. The sense circuit cannot provide current information when the anti-parallel body diode is conducting during commutation. Built-in gain amplification allows direct connection of the current phase signal to the microcontroller ADC input. The local sense circuit provides an accurate analogue of current with a high signal-to-noise ratio and a correspondingly high degree of accuracy, it claimed. The software includes a reconstruction algorithm that uses the phase-shifted trigonometric relationship between current signals of all three phases to deduce negative phase-current information.
Motor-Expert 2.0 is Power Integrations’ motor control configuration and diagnostics tool for the BridgeSwitch IC family. It provides a GUI allowing easy manipulation of input parameters, as well as a terminal emulator for interacting with the motor controller in serial mode. In addition, a motion scope feature displays linear graphs of important controller variables that can be viewed in real time.
The company claimed the tool reduces the cost and complexity of BLDC drive design and works with the newly released three-phase motor control software and reference design DER-964 to offer a complete tool for motor drive development.
Motor and application tuning is performed through the Motor-Expert 2.0 GUI with control loop co-efficients being updated in real-time without having to recompile code. The interface also enables users to visualise system operation, displaying the status of data, including current, speed, status, current error and speed error. A diagnostics field within the software interface provides insight into inverter and motor operation.
Motor-Expert 2.0 supports three-phase and single-phase motor drive design and replaces the previous version of Motor-Expert.
A new three-phase inverter reference design employing three BridgeSwitch integrated half-bridge ICs, DER-964, provides up to 300W output power without requiring a heatsink. It removes the shunts and op-amps seen in conventional feedback measurement and is suitable for a wide range of applications, such as compressors, range hoods, residential and commercial fans and pumps. The design is 98.2 per cent efficient, occupies a 65 x 50mm PCB and can be used with any Cortex-M0 or equivalent microcontroller.
The complete BridgeSwitch, Motor-Expert 2.0 and three-phase motor control software solution includes a downloadable manual for the software architecture, APIs, functions, calls and variables used in the code.
The new three-phase motor control code and Motor-Expert 2.0 tool are offered as part of the Motor-Expert Suite under a free licence for use with BridgeSwitch ICs.