Waveform shaping circuit for spurious harmonic suppression

A lighting system waveform shaping circuit (WSC) includes a line voltage input, a line voltage output connectable to an input voltage port of a control unit, a neutral line input connectable to a neutral line of a voltage power source, and the WSC including an impedance matching network (IMN) configured to alter an input impedance of the lighting control circuit. In one embodiment, the IMN can include a resistor in series with the line voltage input, and an actively-controlled bypass switch in parallel with the resistor. In another embodiment, the IMN can include respective ferrite chokes surrounding the input and the output voltage lines, a capacitor between the line voltage input and the neutral line input, a capacitor between the neutral line input and a protected earth ground, and a resistor in series between the neutral line input and the lighting control unit neutral line input port.

BACKGROUND

A Digital Addressable Lighting Interface (DALI) is a data and protocol standard for lighting and/or related equipment (e.g., ballasts, dimmers, photoelectric cells, transformers, motion detectors, etc.). DALI compatible equipment can be interconnected on a DALI bus, even if from different manufactures and of different lighting technologies. DALI requires a single pair of wires as the communication bus to all devices on the same DALI network. All devices connected to the network can be addressed by a broadcast message, or individual devices can be controlled with a unique bus address.

A DALI network can include a controller and one or more lighting and/or related equipment devices having DALI interfaces. In some implementations, a DALI system can include a luminaire control unit (LCU), a luminaire (which can include a control unit and a LED light engine), and a data concentrator unit (DCU).

The LCU can wirelessly communicate with the DCU via radio frequency transmissions (e.g., typically in the range 869.4-869.65 MHz, at 500 mW). The LCU can be series connected via wires/cables between a line voltage power source and the luminaire control unit. The LCU can switch off the luminaire by interrupting the line voltage power to the luminaire control unit. Additionally, the LCU could also include connections to the luminaire control unit via the DALI network.

Individually, a conventional luminaire and a conventional LCU can each fulfill typical electromagnetic compatibility (EMC) requirements for spurious harmonic generation/suppression. However, when integrated at a system level this conventional equipment fails to meet specified EMC standards. When the LCU is active, RF communication with the DCU is non-predictable. The RF communication from the LCU to the DCU can cause generation of the unwanted harmonics. Further, the LCU's control of line voltage power to the luminaire control unit can result in high peak-current spikes, which themselves can generate unwanted harmonics. Thus, at a system level EMC standards are not often met by a DALI network containing an LCU, a DCU, and a luminaire.

DETAILED DESCRIPTION

Embodying systems include a waveform shaping circuit between the line voltage power and a LCU and a luminaire associated with the LCU (a single LCU can provide independent control to one or more luminaires). In accordance with an embodiment, the waveform shaping circuit can be a series resistance (e.g., in the range of about 200-980 Ohm) and a bypass switch connected in parallel between the line voltage source and the LCU input. In accordance with some embodiments, the waveform shaping circuit can include ferrite line elements in conjunction with discrete circuit components.

Embodying systems include the waveform shaping circuit to suppress unwanted spurious harmonics generated by operation of a conventional LCU in the control of a luminaire. These spurious harmonics can be caused due to the LCU having a high peak input current coincident with about the maximum swing (i.e., peak and valley) of each half period cycle of the AC input line voltage. The high peak input current can cause high total harmonic distortion (THD) on the line voltage, where one or more of the harmonics can have a high current. In contrast to conventional line filters that passively dissipate noise, embodying waveform shaping circuits decrease the generation of noise at its source by affecting the impedance match of the LCU to the input line voltage. Embodying devices do not merely dissipate noise, but rather eliminate the root cause of the noise generation. Accordingly, each embodiment of the waveform shaping circuit includes an impedance matching network that alters the input impedance of the LCU to minimize harmonic generation by the LCU.

FIG. 1depicts system100that includes waveform shaping circuit110in accordance with embodiments. Waveform shaping circuit110is external to LCU120, which communicates with DCU130via RF signals. System100includes at least one luminaire140controlled by the LCU. The luminaire can internally include control unit142, driver electronics144, and lighting source146.

RF communication by LCU120to DCU130can generate spurious harmonics on the line (L) and neutral (N) voltage lines150. Waveform shaping circuit110alters the input impedance of LCU120as seen by the voltage lines to affect a better impedance match to reduce these spurious harmonics. In accordance with embodiments, waveform shaping circuit can be in series with the LCU input terminals and the line and the neutral voltage lines.

FIG. 2depicts system200that includes waveform shaping circuit210in accordance with embodiments. Waveform shaping circuit210can be in series with the LCU voltage input terminal and the line voltage power source. In accordance with embodiments, waveform shaping circuit210can include series resistor212(e.g., having a resistance in the range of about 200-980 Ohms). Placement of a resistor of this value can generate an additional power consumption of up to about 0.5 W. This power consumption can be decreased by including bypass switch214, which can be controlled by the LCU to bypass series resistor212with an about zero, or low, resistance circuit when the current limitation is not needed (i.e., when the LCU is not active). Bypass switch214can be implemented by a semiconductor switch (e.g., transistor, MOSFET, JFET, TRIAC, etc.), a relay, and the like.

FIG. 3depicts system300that includes waveform shaping circuit310in accordance with embodiments. Waveform shaping circuit310can include input ferrite choke311, and output ferrite choke312, each of which can suppress high frequency spurious harmonics present on the line and the neutral voltage lines. Across the input line voltage (between the line and the neutral lines), waveform shaping circuit can include capacitor C1314(having a capacitance of about 47 nF). Capacitor C1can filter noise on the input voltages to suppress the spurious harmonics. Resistor R1316(having a resistance of about 470 Ohms), can be in series with the neutral line input to LCU120. Capacitor C2(having a capacitance of about 47 nF) is connected from the neutral line voltage to protected earth (PE) ground319. Capacitor C2can bypass spurious harmonics to the earth ground.

FIG. 4depicts an illustration of diagnostic modeling display400of a conventional system that does not include an embodying waveform shaping circuit. Harmonic pane410depicts harmonic distribution across a frequency band of about 50-2500 Hz. It should be readily understood that in the frequency band of about 400-1200 Hz, there are multiple harmonics412that are above an acceptable threshold.

Waveform pane420depicts models of ideal input current waveform422, and impacted input current waveform424. As can be observed, impacted waveform424includes perturbations at about voltage crossover points426,427. Similarly, high peak noise can be seen at input current peak428, and input current valley429.

FIG. 5depicts an illustration of diagnostic modeling results500of an embodying system that includes a waveform shaping circuit in accordance with embodiments. Harmonic pane510depicts that an embodying system that includes a waveform shaping circuit generates harmonics512that are below predetermined threshold level515. Waveform pane520depicts models of ideal input current waveform522, and impacted input current waveform524. As can be observed, impacted waveform524includes minimal perturbations at about current crossover points526,527. Similarly, waveform perturbations at input current peak528, and input current valley529are no longer present. The model impacted waveform524indicates that instead of high spikes at the input waveform peak and valleys (as present in the conventional systems), the excursion of the peak and valley is reduced and smoothed by an embodying system that includes a waveform shaping circuit.

Although specific hardware and methods have been described herein, note that any number of other configurations may be provided in accordance with embodiments of the invention. Thus, while there have been shown, described, and pointed out fundamental novel features of the invention, it will be understood that various omissions, substitutions, and changes in the form and details of the illustrated embodiments, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. Substitutions of elements from one embodiment to another are also fully intended and contemplated. The invention is defined solely with regard to the claims appended hereto, and equivalents of the recitations therein.