PI control software for three-phase BLDC motor drives

Combined with Power Integrations’ BridgeSwitch integrated half-bridge motor driver and Motor- Expert configuration and diagnostics tool, this hardware-software solution claims to enable 98.2% efficiency, reduce board space by more than 70% and requires on,y three components for current feedback circuitry, compared to 30 components in a discrete solution.

The solution 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 operational amplifiers (op-amps) and matching circuity for motor- current signal conditioning,” states PI’s Cristian Ionescu-Catrina, “our BridgeSwitch integrated half- bridge ICs provide lossless current feedback for the positive half cycle, and our 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 external current sense resistors, op-amps and matching circuitry.”

The software adds three-phase FOC to the 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 48 MHz and does not require a hardware accelerator block. It can also be ported to other equivalent MCUs.

The current modeling algorithm is robust and reliable and has passed extensive static and dynamic test conditions, including low latency response to real-time events. The high degree of current accuracy ensures low jitter operation. The new code is MISRA C-compliant (Motor Industry Software Reliability Association), portable, modular and allows the user to modify any of the software layers.

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 analog of current with a high signal-to-noise ratio and a correspondingly high degree of accuracy. The new software includes a reconstruction algorithm that uses the phase-shifted trigonometric relationship between current signals of all three phases to accurately deduce negative phase-current information.

Motor-Expert 2.0 is Power Integrations’ easy-to-use 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.

Motor and application tuning is performed through the Motor-Expert 2.0 GUI with control loop coefficients being updated in real-time without having to recompile code. The interface also enables users to visualize 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 300 W 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% efficient, occupies a 65 mm x 50 mm 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 is available today and 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 license for use with BridgeSwitch ICs. BridgeSwitch ICs are priced starting at $1.69 in 10,000-unit quantities of the chipset. For further information, contact a Power Integrations sales representative.