Cascaded H-Bridge Using Selective Harmonic Current Mitigation-PWM Technique

Meets High Efficiency and Power Quality Requirements for Grid Tied Cascaded H-Bridge Multilevel Active Rectifiers

This grid tied cascaded H-bridge (CHB) multilevel AC/DC rectifier (converter) uses selective harmonic current mitigation pulse width modulation (SHCM-PWM) technique to meet the harmonic standards for high power devices. Multilevel converters are used to give a high output power for medium voltage sources such as batteries or solar panels. In the industrial setting, CHB multilevel rectifiers are used in both motor and electric vehicle drives since they reduce stress and do not damage the motor, promoting longer life-times for motors. Currently, selective harmonic elimination-PWM (SHE-PWM) or selective harmonic mitigation-PWM (SHM-PWM) are the techniques used in CHB multilevel rectifiers to reduce harmonics, the frequent cause of power quality (e.g. overheating or misfiring) problems. The number of harmonics these techniques can eliminate is dependent on the switching frequency.

Researchers at the University of Florida have proposed the SHCM-PWM technique that can eliminate more orders of harmonics than SHE or SHM using the same number of switching frequencies. Doing this, the SHCM-PWM technique can meet the current harmonic requirements.

Application

Selective harmonic current mitigation pulse width modulation (SHCM-PWM) technique to optimize cascaded H-bridge multilevel rectifiers

Advantages

• Mitigates current harmonics resulting from grid voltage harmonics, unlike SHM-PWM or SHE PWM techniques
• Mitigates higher orders of current harmonics than existing SHM-PWM or SHE-PWM techniques with the same number of switching frequencies
• Can meet both harmonic and TDD limits with smaller coupling inductance, reducing the cost and size of passive filters

Technology

Multilevel rectifiers are being increasingly used in electrical applications. This selective harmonic current mitigation pulse width modulation (SHCM-PWM) technique optimizes their performance. It uses low switching frequencies for grid connected cascaded H-bridge multilevel rectifiers to meet harmonic requirements within an extended harmonic spectrum. Instead of using voltage references to calculate switching angles for rectifiers as in conventional SHE-PWM and SHM-PWM, current references can be used to compensate the current harmonics due to both grid voltage harmonics and rectifier input voltage harmonics. This technique can meet both harmonic and TDD limits with smaller coupling inductance compared to SHE-PWM and SHM-PWM, therefore reducing the cost and size of passive filters.