Harmonic Limiting Standards

22.5.1 Harmonic Limiting Standards

9 The standards IEC 1000-3-2 and EN 61000-3-2 [19] are the 5

11 ≤n≤39

most popular regulations regarding the harmonic pollution (odd harmonics produced by electronic equipment connected to the mains.

only)

These standards are a new version of the previous IEC 555-2 ∗ λ is the circuit power factor. regulation, and they are applicable to the equipment with less than 16 A/phase and supplied from low voltage lines of 220/380 V, 230/400 V, and 240/415 V at 50 or 60 Hz. Limits for equipment supplied from voltages lower than 220 V have

22.5.2 Passive Solutions

not yet been established. This regulation divides the electrical equipment in several

A first possibility to increase the ballast power factor and to classes from class A to class D. Class C is especially for lighting decrease the harmonic content of the input current is the use of

equipment, including dimming devices; the harmonic limits passive solutions. Figure 22.30 shows two typical passive solu- for this class are shown in Table 22.4. As shown in Table 22.4, tions, which can be used to improve the input power factor of this regulation establishes a maximum amplitude for each electronic ballasts. input harmonic as a percentage of the fundamental harmonic

Figure 22.30a shows the most common passive solution component. The harmonic content established in Table 22.4 is based on a filter inductor L. Using a large inductance L a square

quite restrictive, which means that the input current wave must input current can be obtained, with an input power factor of

0.9 and a THD of about 48%. However a square input wave- cal input power factor equal to 0.9, the THD calculated from form does not satisfy the IEC 1000-3-2 requirements and then Table 22.1 is only 32%.

be quite similar to a pure sine wave. For example, for a typi-

it is not a suitable solution. The addition of capacitor C across

FIGURE 22.30 Passive circuits to improve input power factor (a) LC filter and (b) tuned LC filter.

596 J. M. Alonso

400 V

1.0 A

Output voltage

200 V

0.5 A

Input current

−0.5 A AC

Input voltage

FIGURE 22.31 Valley-fill circuit: (a) electric diagram and (b) waveforms.

the ac terminals can increase the power factor up to 0.95, but to fulfill the IEC 1000-3-2 requirements is usually difficult. still the standard requirements are difficult to fulfill.

Therefore, they are normally applied in the lower power range.

A simple variation of this circuit is shown in Fig. 22.30b, where a parallel circuit tuned to the third harmonic of the line

22.5.3 Active Solutions

frequency is used to improve the shape of the line current. The input power factor obtained with this circuit can be close to Active circuits are most popular solutions to implement high- unity.

power-factor electronic ballasts. They use controlled switches

A third possible solution, known as valley-fill circuit, is to correct the input power factor and in some cases to include shown in Fig. 22.31a. The typical filter capacitor following the galvanic isolation via high-frequency transformers. Active cir- diode rectifier is split into two different capacitors that are alter- cuits normally used in electronic ballasts operate at a switching nately charged using three extra diodes. The addition of a small frequency well above the line frequency and over the audible series resistor improves the power factor by about two points, range. maintaining a low cost for the circuit. An inductor in place

Some typical active circuits used in electronic ballasts are of the resistor can also be used to improve the power factor shown in Fig. 22.32. Buck–boost and flyback converters shown but with a higher cost penalty. Figure 22.31b shows the out- in Figs. 22.32a and 22.32b, respectively, can be operated in dis- put voltage and input current of the valley-fill circuit. The main continuous conduction mode (DCM) with constant frequency disadvantage of this circuit is the high ripple of the output volt- and constant duty cycle in order to obtain an input power age, which produces lamp power and luminous flux fluctuation factor close to unity [20]. and high lamp current crest factor.

Figure 22.32c shows the boost converter, which is one of the Passive solutions are reliable, rugged, and cheap. However, most popular active circuits used to correct the input power the size and weight of these solutions are high and their design factor of electronic ballasts [21–23]. If the boost converter

FIGURE 22.32 Power factor correction circuits for ballasts: (a) buck–boost; (b) flyback; and (c) boost.

22 Electronic Ballasts 597 is operated in DCM, an input power factor close to unity either in the DCM–CCM borderline or in CCM can be as high

is obtained, provided that the output voltage is about twice as 95%. the peak input voltage [21]. The main disadvantage of DCM operation, when compared with the CCM mode, is the high distortion of the input current (due to the discontinuous high-

22.6 Applications

frequency current) and the higher current and voltage stresses in the switches. Therefore, the DCM operation is only used for Electronic ballasts are widely used in lighting applications, such the lower power range.

as portable lighting, emergency lighting, automotive appli- For the medium power range, the operation of the boost cations, home lighting, industrial lighting, and so on. They converter at the DCM–CCM borderline is preferred. In this provide low volume and size, making it possible to reduce the solution, the on-time of the controlled switch is maintained luminaire size as well, which is a very interesting new trend in constant within the whole line period and the switching fre- lighting design. quency is adjusted to allow the input current to reach zero at the end of the switching period. The typical control circuit

22.6.1 Portable Lighting

used and the input current waveform are shown in Figs. 22.33a and 22.33b, respectively. The inductor current is sensed using a In this application, a battery is used as power source and then a resistor in series with the switch, and the peak inductor current low input voltage is available to supply the lamp. Examples are is programmed to follow a sine wave using a multiplier. A com- hand lanterns and backlightings for laptop computers. Typi- parator is employed to detect the zero-crossing of the inductor cal input voltages in these applications range from 1.5 to 48 V. current in order to activate the switch. Most IC manufactur- Therefore, a step-up converter is necessary to supply the dis- ers provide a commercial version of this circuit to be used for charge lamp, and then electronic ballasts are the only suitable electronic ballast applications.

solution. Since the converter is supplied from a battery, the The boost circuit operating with borderline control provides efficiency of the ballast should be as high as possible in order

a continuous input current, which is easier to filter. Besides, to optimize the use of the battery energy, thus increasing the it presents low switch turn-on losses and low recovery losses operation time of the portable lighting. Typical topologies used in the output diode. The main disadvantages are the variable are the class E inverter and the push–pull resonant inverter, switching frequency and the high output voltage, which must obtaining efficiencies up to 95%.

be higher than the peak line voltage. For the higher power range, the boost converter can be

22.6.2 Emergency Lighting

operated in continuous conduction mode (CCM) to correct the input power factor. The input current in this scheme is Emergency lightings are used to provide a minimum lighting continuous with very low distortion and easy to filter. The level in case of a main supply cut-off. Batteries are employed current stress in the switch is also lower, which means that to store energy from the mains and to supply the lamp in more power can be handled maintaining a good efficiency. case of a main supply failure. A typical block diagram is The normal efficiency obtained with a boost circuit operating shown in Fig. 22.34. An ac–dc converter is used as a battery

C Q1 Control signal

Verr R

R V ref

(a)

(b)

FIGURE 22.33 (a) Boost power factor corrector with borderline control and (b) input current waveform.

598 J. M. Alonso

Battery

Lamp 1

Resonant Battery

PFC

DC/AC

charger stage Lamp 2

AC inverter

Lamp

stage

Power line

Microprocessor

Control circuit control

communication

stage FIGURE 22.35 Block diagram of a microprocessor-based lighting.

stage

FIGURE 22.34 Block diagram of an emergency lighting.

charger to store energy during normal line operation. A con- Other applications for higher power include more developed trol circuit continuously measures the line voltage and acti- ballasts based on a power factor correction stage followed by

vates the inverter in case of a main supply failure. Normally

a resonant inverter. Hot-cathode fluorescent lamps are mostly

a minimum operating time of one hour is required for the used in these electronic ballasts. Also, with the development system in emergency state. Thus, the use of high efficient elec- of modern HID lamps such as metal halide lamps and very tronic ballasts is mandatory to reduce the battery size and high-pressure sodium lamps (both showing very good color cost. Typical topologies used include class E inverters, push– rendition), the use of HID lamps is being more and more pull resonant inverters, and half-bridge resonant inverters. frequent in home, commercial, and industrial lighting. Fluorescent lamps are mainly used in emergency ballasts, but high intensity discharge lamps, such as metal-halide lamps or high-pressure sodium lamps, are also used in some special

22.6.5 Microprocessor-Based Lighting

applications. The use of microprocessors in combination with electronic ballasts is very interesting from the point of view of energy sav-