Jeffrey McGuire

Analysis of PWM Frequency Control to Improve the Lifetime of PWM Inverter

Studies show that the power cycling mean time to failure (MTTF) of the insulated-gate bipolar transistor (IGBT) bond wire in an adjustable speed drive may be very short under some very common conditions. This paper proposes a switching frequency reduction method based on the junction temperature variation (ΔTj) of an inverter IGBT. It has the following advantages. First, it reduces the pulsewidth-modulation frequency under low-speed higher torque condition. Second, the inverter is started more smoothly and safely under higher command switching frequency and high-torque condition. Third, the overall MTTF of the inverter IGBT can be improved. The theory analysis, simulation, and experimental result are provided to show these advantages.

Analysis of PWM frequency control to improve the lifetime of PWM inverter

Studies have shown that the power cycling Mean Time to Failure (MTTF) of the IGBT bond wire in an adjustable speed drive (ASD) may be very short under some very common conditions. This paper proposes a switching frequency reduction method based on junction temperature variation (ΔTj) of the inverter IGBT. It has the following advantages. Firstly, it only reduces the PWM frequency under low speed higher torque condition; secondly, the inverter can be started more smoothly and safely under higher command switching frequency and high torque condition. Thirdly, the overall MTTF of the inverter IGBT can be improved dramatically. Theory analysis, simulation and experimental result will be provided to show these advantages.

Ground fault location identification for multiple drive high resistance grounding systems

One of the more difficult problems to solve in industrial plants is to locate and eliminate a ground fault in High Resistance Grounding (HRG) system. This is because ground fault conditions in these systems do not draw enough current to reliably trip the ground fault current detector in the drive. This paper studied the ground fault identification (GFI) using voltage measuring method for multiple-drive HRG systems. The character of the voltage signals at different stages of the drive operating condition is studied. It is demonstrated that the location of the ground fault can be identified much easier if the appropriate operating conditions can be combined in the system level.

Ground fault location self-diagnosis in high resistance grounding drive systems

In industrial plants with High Resistance Grounding (HRG) configuration, one of the most difficult problems is to accurately detect and locate a ground fault in Adjustable Speed Drive (ASD) systems. This is because: (1) HRG ground fault current (1-10A) cannot reliably trip the over current protection function in drives; (2) In modern industrial plants, the existing methods are hard to detect and locate low voltage/low frequency ground faults; (3) With the existing methods, the fault location will be manually checked one by one using an ammeter. This paper will present a HRG ground fault self-diagnosis method for multi-ASD systems. The proposed method can solve the issues mentioned above: (1) Reliable HRG ground fault detection with wide motor speed range; (2) The HRG ground fault can be easily identified in multi-ASD systems; (3) The identification process is performed by the proposed self-diagnosis method, no trained technician is required during the identification process.

Study of PWM frequency and its impact to adjustable speed drive reliability

Pulse Width Modulation (PWM) control method has been widely studied and applied in the industrial area. For majority of the conditions, the PWM frequency is fixed to guarantee easier control implementation. However, the time constant of the IGBT thermal system is much lower than that of the inverter fundamental frequency at low speed. The lifetime of the inverter are severely reduced under low speed and high output conditions. To improve the lifetime of the inverter at lower speed without reduce the output current, a natural way is to reduce the PWM frequency under this condition. This paper evaluated the inverter performance under different PWM frequencies. After that, it studies the impact of PWM frequency to inverter losses, inverter reliability and system performance. It is concluded that operating the inverter at low switching frequencies may not sacrifice the output current waveform quality. Moreover, the inverter lifetime can be significantly increased. Analytical, simulation and experimental results will be presented to show its effectiveness.

Faulted phase location identification for adjustable speed drives in high resistance grounding system

High Resistance Grounding is preferred in many industrial applications. However, there are some drawbacks for the traditional HRG detection methods to locate a ground fault in Adjustable Speed Drive systems. The existing methods cannot detect or identify which phase faulted once the drive has HRG fault. This paper will present a leakage flux linkage detection based HRG fault identification method to identify the faulted phase of the drive.