16-09-2016, 04:07 PM
A NOVEL SINGLE STAGE AC/DC CONVERTER BASED ON AN INTERLEAVED BUCK-BOOST CIRCUIT AND LLC RESONANT CONVERTER FOR STREET LIGHTING SYSTEM
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Abstract – In this paper, a novel single-stage AC/DC converter based on an interleaved Buck-boost circuit and LLC resonant converter for street lighting system. The buck-boost circuit and LLC resonant converter are integrated by sharing switches, which can decrease the system cost and improve system efficiency. The input voltage of the buck-boost circuit is half of the rectified voltage, and two buck-boost circuits are formed with the two half-bridge switches and corresponding diodes. The two buck-boost circuit’s work in interleaved mode and the inductor current is in discontinuous conduction mode. The half bridge LLC resonant converter is adopted here, and the soft switching characteristics of the LLC resonant converter is not changed by the switch integration. The primary-side switches still work in zero voltage switching (ZVS) mode, and the secondary diodes still work in zero current switching (ZCS) mode, which both reduce the switching losses and improve the efficiency of the system. The detailed design process of LED street lighting prototype is proposed with an efficiency of 94.8% at full load.
I.INTRODUCTION
LEDs are wide employed in many lighting systems such as street lighting, automobile headlights, and backlit screens as a result of their high efficiency, long lifespan, and good color-rending properties. Moreover, with the event of LED packing and coating technology, the price of LEDs has been decreasing. Within the future, LEDs will gradually become a replacement light, replacement gas discharge lamps.
For achieving constant current driving, the standard semiconductor diode driver contains the power-factor correction (PFC) stage, DC/DC device stage, and constant-current stage. This three-stage structure will alter the planning method and facilitate obtain a high power issue (PF) and low total harmonic distortion (THD). However, the three stage drive has low efficiency and poor responsible in conjunction with slow output dynamics. To solve this the traditional driver and to minimize system price, several researches conducted studies on a single-stage crystal rectifier driver, which might help to minimize prices and size, whereas making certain high potency, high reliability, and quick output dynamics.
Single-stage AC/DC converters have their own disadvantages. First, the bus voltage is high for light-weight load and the high input voltage state. Second, although the integration decreases the elements of the converter, it adds further current or voltages stress to the switches. However, though the PF for the two-stage converters are often terribly high and also the THD can be terribly low, they have their own issues. For example, the cost is high, and also the reliability is low. Therefore, in sensible use, we have a tendency to should balance the price and performance of the converter, and then create an acceptable selection between the single-stage and two-stage converters.
Nowadays, most single-stage converters supported the integration of the flyback circuit and different discontinuous conduction mode (DCM) DC/DC converters, that square measure wide used thanks to their low price and quick dynamics. Reference [11] projected a single-stage converter supported buck and flyback circuits. However, for this converter, when the input voltage was under the output voltage, the input current was zero, the crystal rectifier to a low PF and high THD. Reference [12] projected a single-stage crystal rectifier driver supported buck-boost and flyback circuits, and though the PF and THD were higher and lower, severally, compared to PF and THD in [11], the efficiency remained low. Further, [13] proposed a single-stage crystal rectifier driver supported buck-boost and flyback circuits, and whereas the system PF was improved and transformer leakage-inductance energy was fed back, the system switch losses remained high and also the efficiency was low thanks to switches still being in a very hard-switching mode. Reference [14] projected a single-stage AC/DC converter primarily based on a single-ended primary-inductor converter and flyback circuits. As a result of the flyback circuit worked in a very quasi-resonance stage, the switch losses decreased; but, the switch still didn’t add a true zero-voltage-switching (ZVS) stage, and also the switch loses remained high at a light-load state. Though several single-stage topologies primarily based on the flyback circuit are projected, no technique has been devised to more decrease the switch losses and improve system efficiency [15]-[18].
To decrease the switch losses of LED drivers, increasing varieties of researchers have centered on LLC resonant converter with a soft-switching property. The system efficiency increased significantly with the employment of LLC resonant converter [19]-[21]. However, the normal crystal rectifier driver primarily based on an LLC resonant converter is pricey as a result of an addition PFC circuit is needed. Reference [22] planned a single stage AC/DC device supported a DCM boost circuit and a half bridge LLC circuit. The soft-switching characteristics of the LLC electric circuit weren’t tormented by the integration of the switches for the single stage AC/DC device is 0.5, the bus voltage should be over double the input peak voltage; therefore, the device isn’t appropriate for high-input voltage conditions. Reference [23] optimized the parameter style of the device planned in [22] to decrease the bus voltage; but, the device still didn’t perform well beneath a high input voltage. Additionally, for the standard ac/dc device given in [2]-[23], the integrated switch was subjected to high voltage or current stress, that raised the power losses and reduced the reliableness of the system. Reference [24] planned a single-stage AC/DC device based mostly on associate interleaved boost circuit and a half bridge LLC resonant converter. The input voltage was divided into two elements in which two DCM boost circuits were formed; high PF and low THD were achieved. However, the topology contained two inductors that raised the entire value of the system. Moreover, the two inductors ought to have constant price to obtain a high PF and low THD. In sensible applications, the inductor sometimes contains a deviation, considering the value and production technology. Though a very high PF and low THD can be obtained by the model developed within the laboratory, obtaining a high PF and low THD in observe is troublesome. In addition, since the topology planned in [24] had an interchangeable structure and therefore the input voltage was divided into two elements, the two switches may share the voltage and currents stress resulting from switch integration which is incredibly advantageous. However, in sensible use, deviations within the inductance values inevitably occur as a result of one boost circuit needs one individual inductor, therefore, the two boost circuits cannot equally share the input power.
In this paper, a single-stage AC/DC device supported the boundary conduction mode (BCM) boost circuit and LLC resonant device is projected, associated it’s applied to a light-emitting diode street lighting system. Within the projected single-stage AC/DC converter, two BCM boost circuits square measure obtained by desegregation the switches of the half-bridge LLC resonant device, which realizes a PFC operate. As a result of the input voltage is split by two capacitors, the bus voltage is significantly reduced approximately to the worth of just about the input peak voltage, rendering the projected single-stage driver to approximately work under high input-voltage conditions. The soft-switching characteristics of the half-bridge LLC resonant converter area unit not affected. Compared with the traditional single-stage AC/DC converter projected in [2]-[23], two integrated switches area unit obtainable, and also the AC/DC converter options a symmetrical structure. Therefore, the integrated switches equally share the current and voltage stresses of the system caused by the switch integration, which improves the dependableness of the system. Additionally compared to the converter projected in [24], the two switches will equally share the current and voltage stresses as a result of the two boost circuits continually work under constant condition as they share one electrical device, which makes the novel converter applicable for sensible use.