Diagnostics of system faults with embedded motor drive integrated circuits

BridgeSwitch combines high efficiency, design flexibility, improved safety, IEC 60335-1 and IEC 60730-1 compliance with fault diagnostics.

Designers are increasingly challenged by the demands to continuously improve the efficiency and reliability of motor drives in consumer appliances. From the European Union to China, higher efficiency is being demanded for a growing range of consumer appliances, including dishwashers, refrigerators and heating, ventilation and air conditioning (HVAC) systems.^1,2 The designs must also meet the safety requirements of IEC 60335-1 and IEC 60730-1.

At the same time, consumers and manufacturers alike are demanding higher levels of reliability—less field service and fewer returns. According to a recent industry study, misdiagnosis results in 30% of “no fault found” compressor returns.³ adding costs and inefficiencies along the supply chain and resulting in dissatisfied consumers. The use of IoT can enable remote monitoring of consumer appliances, but the design must support meaningful and cost-effective fault diagnosis systems and protection functions.

To address these challenges, designers can turn to Power Integrations’ BridgeSwitch family of high-voltage, self-powered, half-bridge driver ICs with integrated protection, system monitoring and reporting that provide higher efficiency, increased design flexibility, and improved inverter and system reliability (Figure 1).

High efficiency simplifies heat management

BridgeSwitch’s integrated half-bridges simplify the design and manufacture of high-voltage, inverter-driven, single-phase or three-phase permanent magnet or brushless DC motor drives. BridgeSwitch ICs include a proprietary instantaneous phase current output signal that facilitates the design of sensorless control circuits. These integrated circuits include two 600-V, N-channel power FREDFETs, with high- and low-side drivers, in a small surface-mount package (13.6 × 9.4 × 1.35 mm) that offers extended distances of creep and allows cooling of both power the FREDFET through the PCB (Figure 2).

The ultra-soft and ultra-fast diodes in FREDFETs are optimized for hard-switching inverter drives. The high- and low-side controls and drivers are self-powered, eliminating the need for an external auxiliary power supply. The distributed thermal footprint combined with up to 99.2% efficiency eliminates the need for an external heatsink at rated continuous RMS current, reducing system cost, size and weight. BridgeSwitch ICs can deliver up to 400W of output power and are well suited for use in inverters in appliances such as dishwashers and refrigerators and for condenser fans in high efficiency air conditioners.

Hardware-based error protection saves certification costs and time

The microcontroller (MCU) in most inverter designs is used to monitor and respond to fault conditions as well as to control the motor. Motor control is easy and relatively quick to implement using standard software packages. Fault diagnosis and protection are more challenging and can vary greatly from application to application because they rely on many different sensors to monitor phase currents, system overheating conditions, vibration and other system parameters. It is difficult to program the MCU to interpret the sensor inputs and apply protection in the appropriate manner required to obtain certification to international standards.

Certification of monitoring and control software is a time-consuming and expensive process that often delays time to market. On the other hand, the hardware-based motor fault protection in BridgeSwitch ICs is compliant with IEC 60335-1 and IEC 60730-1 motor abnormality requirements without relying on control software, reducing costs and speeding up time for marketing.⁴ The resulting ability to use Class A software designation according to IEC 60730-1 can save two months of certification time, and the use of BridgeSwitch ICs also simplifies the safety approval process for product software updates.

BridgeSwitch combines comprehensive internal fault protection features with external system-level monitoring and reporting via a bidirectional fault bus (Figure 3). Internal fault protection includes two-stage thermal overload protection and hardware-programmable cycle-by-cycle overcurrent protection for both FREDFETs. System-level monitoring includes four levels of undervoltage and one level of overvoltage on the high-voltage DC bus and external sensors such as a temperature sensor with a negative temperature coefficient, a vibration sensor, and the ability to detect a stalled motor, a motor phase out, or a current overload.

The single-wire fault bus is based on an open architecture and allows BridgeSwitch ICs to send status updates using an 8-bit word, with the eighth bit providing odd parity to ensure signal integrity. Also used by the MCU to send:

• Commands to BridgeSwitch ICs
• Queries the BridgeSwitch IC for status updates
• Reset commands to ICs that are blocked for overheating damage

The ID pin is used at power-up to set a unique IHB identification for each BridgeSwitch IC, allowing the MCU to identify which IC provided a given fault warning: IHB1 has an ID pin connected to BPL, the ID pin is floating for IHB2, and the ID pin is linked to SG for IHB3 (Figure 4). In addition, the IHB ID setting of each IC supports single-wire bus arbitration using the device ID time period (t_ID). HB1 has at_ID of 40 µs, t_ID for HB2 is 60 µs, and t_ID for HB3 it is 80 µs. The system MCU is assigned t by default_ID of 160 µs, which ensures that it always wins bus arbitration.

The Motor-Expert package accelerates time to market

Power Integrations’ Motor-Expert software package includes speed and current functions for circuit control and includes a built-in C code application, library, and graphical control interface that supports single-phase and three-phase designs using BridgeSwitch ICs.⁵It accelerates time to market by providing a graphical interface for all parameters and commands, as well as a terminal emulator to interface with the motor controller in serial mode. The Motion Scope window displays real-time line graphs of controller variables. New features and use cases can be added and users can easily port software to the MCU. The software only needs 14 kB of code memory and 5 kB of SRAM, making it suitable for operation on MCUs with limited memory resources. Software developed using Motor-Expert meets static (MISRA) and dynamic performance requirements for latency, jitter and runtime.

Conclusion

Designers can turn to BridgeSwitch ICs with built-in system error diagnostics to reduce field returns and speed time to market. These self-powered half-bridge motor driver ICs provide the high efficiency, design flexibility, and improved inverter and system reliability required in today’s consumer appliances. Extensive hardware-based security features save certification time and cost. These ICs are compliant with IEC 60335-1– and 60730-1– as confirmed by UL report 4788685352. The identification pin allows the MCU to pinpoint the location of faults. Finally, the use of Motor-Expert design software further accelerates time to market for single-phase and three-phase BridgeSwitch IC applications.

References

¹Revised Chinese British Standard for Air Conditioners

²New energy labeling in Europe for refrigerators and dishwashers

³Understanding compressor electronics, Emerson Climate; Chapter 2, page 3

⁴UL report 4788685352UL Information Report IEC 60335-1 Safety of household and similar electrical appliances

⁵BridgeSwitch Motor-Expert Motor control configuration and diagnostics toolEnergy integrations

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Cristian Ionescu-Catrina is a Senior Product Marketing Manager at Power Integrations.