Motorola Corporation

Kenneth A Berringer

Robert Bruce Davies

Brent W Pinder

The present invention relates generally to the reduction of odd harmonics of phase angle controlled loads. One embodiment relates to an apparatus for reducing odd harmonic currents introduced into an alternating current (AC) supply by a load having a zero crossing detector and a processor coupled to the zero crossing detector. The zero crossing detector is coupled to the AC current supply for measuring voltage zero crossings of the AC current supply. The processor receives a user control signal for controlling the load, such as, for example, a speed control, determines phase angles required at the voltage zero crossings of the AC current supply to implement the user control signal, and selectively modulating the phase angles when they are in a predetermined range of undesired phase angles in order to selectively reduce odd harmonics within the AC current supply.

Odd harmonics reduction of phase angle controlled loads

A phase current reconstruction circuit (10) senses and reconstructs a phase current in a phase bridges (12A). An amplifier (32) in a phase current reconstruction element (22) amplifies a voltage signal across a sensing resistor (18). The amplified voltage signal is transmitted to a sample and hold circuit (34), which reconstructs the phase current in the phase bridge (12A). An over-current comparator (36) compares the amplified voltage signal with a predetermined reference voltage to detect an over-current in the phase bridge(12A). If the over-current in the phase bridge (12A) is detected, an over-current latch (38) interrupts the pulse width modulation signal from a microcontroller (26) to a power switch (16A) in the phase bridge (12A), thereby switching off and protecting the power switch (16A) from damage that may be caused by the over-current.

Circuit and method for reconstructing a phase current

A power transistor (11) having a control electrode (16), a first electrode (17), a second electrode (181), and a kelvin electrode (19) is provided. The power transistor (11) comprises a plurality of transistors (12-15) coupled in parallel. Each transistor having a control electrode, a first electrode, and a second electrode coupled respectively to the control electrode (16) , first electrode (17) , and second electrode (18) of the power transistor (11). A plurality of first resistors (26-29) reduce oscillation and ringing, each first resistor is coupled between the kelvin electrode (19) and a second electrode of a transistor of the plurality of transistors (12-15). A plurality of second resistors (21-24) also reduces oscillation and ringing, each second resistor is coupled between the control electrode (16) and a control electrode of a transistor of the plurality of transistors (12-15).

Power transistor

A low voltage circuit is used to control a high voltage transistor which operates a high voltage motor. A blocking diode and a bootstrap capacitor are used to shift the voltage of the circuit between two levels. The circuit is enabled by inducing a current flow through an input terminal. The current is amplified and applied to a high voltage transistor. The circuit is disabled by termination of the current flow through the input terminal which causes the circuit to rapidly disable current flow through the high voltage transistor. The circuit also disables current flow through the high voltage transistor during voltage transients to prevent erroneous operation during the transients.

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Scottsdale, AZ, United States of America

Kenneth A Berringer