Motor sin escobillas DC (BLDCM) ha sido ampliamente utilizado en los sistemas de accionamiento y control servo debido a su rápida respuesta, alta densidad de potencia y alta eficiencia y así sucesivamente. Por lo general, es impulsado por un inversor de PWM de conmutación dura, que tiene una baja frecuencia de conmutación, la pérdida de conmutación alta, la interferencia de alta electro magnética (EMI) y el ruido acústico, etc. Para resolver los inconvenientes de la fuente de tensión Tipo de conmutación dura inversor, muchos tipos de resonancia del circuito intermedio inversores se han estudiado ampliamente. Sin embargo, estos inversores tienen inconvenientes tales como el estrés de alto voltaje de los dispositivos, la modulación delta, límite umbral de la corriente del inductor o tensión del condensador y el control sofisticado. En este trabajo se propone una novela voltaje cero transición paralela inversor resonante fuente de tensión del circuito intermedio (ZVT-PRDCL-VSI) para sistemas de accionamiento BLDCM. El inversor posee ventajas de bajas pérdidas de conmutación de potencia, baja pérdida de potencia del inductor, pequeña tensión de voltaje del dispositivo, esquema de control simple y no hay problema de desequilibrio de la tensión del punto neutro. El principio de funcionamiento y el control de esquema del inversor se analizan. La validez del circuito se verifica mediante simulación y los resultados experimentales.

Keywords—Brushless DC motor, zero soltage switching, voltage source inverter, pulse width modulation.

I. INTRODUCTION

The brushless direct current motor (BLDCM) has high torque. compact size. and high efficiency. Therefore, BLDCM is widely used in computers, household and industrial products, and automobiles NI It is usually driven by a hard-switching PWNI inverter, which has low switching frequency, high switching loss, high EMI and acoustic noise. etc. To overcome the limitation of voltage source-type hard switching inverter, many resonant DC-link soft-switching inverter technologies have been well developed and studied [2-10]. The resonant DC-link (RDCL) technique was proposed [3]. With appropriate control of the bridge switches, the resonance can bring the DC-link voltage down to zero periodically and this zero interval is used to accomplish lossless switching of the bridge devices. The major problem with RDCL inverters is the high voltage stress of the devices. which is 2-3 times the DC-source voltage. Other problems include the sub-harmonics due to the delta modulation and the sophisticated control to assure proper energy in the resonant components. To overcome the RDCL drawbacks, the actively clamped resonant DC-link (ACRDCL) technique was introduced [4]. The ACRDCL technique reduces the device voltage stress down to 1.2-1.4 times. However, it is still higher than the input DC voltage. Furthermore, the resonance still occurs during the whole operating state, and the control used to balance the clamp capacitor voltage is also complicated. To generate notches of the DC link at require time. the parallel resonant DC link (PRDCL) technique. also named the quasi-resonant DC link (QRDCL) technique, was proposed thereafter [5-7] The resonant components were shifted to a path in parallel with the DC link. And auxiliary

switches were used to control the resonance. so that it would only occur during the short switching transients. However PRDCL required selling threshold of inductor current or capacitor voltage. it had caused complex control A novel DC-rail parallel resonant zero voltage transition (ZVT) voltage source inverter is introduced [8] it overcomes many drawbacks mentioned above. However it had the problem of the unbalancing problem of neutral-point voltage with light load soft-switching inverter [9]. The majority of soft-switching inverters proposed in the recent 1 years have been aimed at the induction motor drive applications. So it is necessary to research on the novel topology of soft-switching in crier and special control circuit for BLDCM drive stems [10]. This paper proposed a novel zero voltage transition parallel resonant DC link voltage source inverter (ZVT-PRDCL-VSI) for BLDCM. The topology of the soft-switching inverter for BLDCM is shown in Fig. 1. The topology of Fig. 1 has the ability to provide zero-voltage switching (ZVS) for all inverter switches independent of the direction of the DC link current. The drives, sytem contains DC voltage source. resonant circuit, conventional voltage source inverter, control circuit and BLDCM. The resonant circuit consists of three auxiliary switches, one resonant inductor, one resonant capacitor and several diodes and capacitors. The auxiliary switches are controlled at certain instant to obtain the resonance between inductor and capacitor. Thus the DC link voltage reaches zero temporaly (voltage notch) and the main switches of the inverter get ZVS condition. The conventional inverter is controlled by proper commutations such that of the three phases are with on states and the remaining one is with floating state.

II. OPERATION PRINCIPLE AND ANALYSIS

In the following discussion it is assumed that load current is ripple-free in a switching cycle and is denoted as I0. Transition of CI and C2 (ZVS shut-off for V2 and V3) is negligible due to less charging time and energy. The equivalent ZVT-PRDCL-VSI circuit is shown in Fig.2. The corresponding waveforms of gate signal of auxiliary switches, resonant capacitor voltage ( Uc ) and inductor current ( icr) are illustrated in Fig. 3. During soft switching of inverter devices, the circuit of Fig. 2 goes through various modes of operation, as shown in Fig. 4.

The process that DC link voltage reduces to zero and then rises to dc supply voltage again is called one zero voltage transition or one DC link voltage notch, shortened for ZVT. The operation of the ZVT can be divided into eight modes. Mathematical analysis of soft switching operation can be performed based on the equivalent circuits shown in Fig.2. Mode 0 [shown in Fig 4 (a)] t0< t<t1 Current flows from DC power supply through VI to the load. The voltage across Cr is equal to the supply voltage E The auxiliary switches V2 and 3 are in of state.

Mode l [shalt n in Fig 4(b)] t0< t<t2. This mode stars IA hen V I is turned of ZVS s off due to Cr) and SVo itch V3 is turned on t Zero Current Switch (ZCS) turns on due to Lr at t ti as shown 17-- Fie_ 3. Capacitor Cr resonates with inductor Lr. The inductorr current i is increased and capacitor voltage ucr is decreased. The equations as be written as the following di (t) di dt; (I)

I ig 4 Operating modes

Mode 2 [shown in Fig4 (c)] t2<t<t3. When t=t2, capacitor voltage U, is zero and load current /0 flows through the freewheeling diode Di. At same time, resonance between C, and L, is aborted because inductor current i 1, flows through V3 and DI. When V3 is turned off (ZVS turns off due to C2), inductor current it., is shifted to diode D2 and energy stored in inductor is recovered to power, so inductor current quickly decreases. When t--13. and i jT =0, get

Mode 3 [shown in Fig 4(d)] NV 13<i<t4. The voltage of DC link is zero. The main switches of the inverter can be either turned on or turned off under ZVS condition during the interval. Load current flows through the freewheeling

diode Di. Mode 4 [shown in Fig-I (e)] 1-1<t<1.5 The auxiliary switch V2 is turned on (ZCS turns on due to Lr). The

current through the resonant inductor Lr increases linearly from zero while the current through the freewheeling diode Di in the inverter decreases. The load current is slowly diverted from the freewheeling diodes to the resonant branch. This mode ends when the current through resonant inductor is equal to the link current and the current through the freewheeling diodes becomes zero. But U( is still zero. We have ii,(15)=10 (8) T4=15-14=-1.'1" (9)

Mode 5 [shown in Fig 4 „0] i5.--1<to This mode starts with the charging of capacitor Cr due to resonance between Lr and Cr. The inductor current is equal to the sum of the charging current of capacitor Cr and the link current /0 . The voltage across the DC link gradually builds up from zero to the source voltage E. The equations can be written as the following: dig r (t) LJ (t)+ L,. (.r= E (10) dU, (t) i 4(0= 10 + C,. ' (11) dr With initial condition U( (1) = 0 , iL,(1)= 1 solve equations ( 1 0 ), ( 1 1 ), Ucr(t)= E[1—cos(cort)1 (11) it,(t)= I ,+—Esin(o),1) (13) Further increase in the link voltage causes the anti-parallel diode of VI to be forward-biased. When the link voltage equals to the source voltage, the auxiliary switch V2 (ZVS turns off due to CI) is turned off and the main switch VI is turned on. Let Ur (1) = E , get

With initial condition Ucr (t) = 0 , it (t) = Io , r solve equations (10), (11), (t) = E[1 — cos(coo] E (1)=1„+ sin(cort) (13) Xr Further increase in the link voltage causes the anti-parallel diode of V1 to be forward-biased. When the link voltage equals to the source voltage, the auxiliary switch V2 (ZVS turns off due to C1) is turned off and the main switch V1 is turned on. Let tic, (t) = E, get (12) 7T 1r T5 = to—t5 2a), 4 I1 - (16)=I„+ X„ where, T. =

Mode 6 [shown in Fig 4 (g)] t6<t<t7. The auxiliary switch V2 is turned off and the main switch V1 is turned on at t6. The resonant inductor current is more than load current. The excess current over the load current flows through the anti-parallel diode of V1 and D3. This mode ends when the inductor current equals to the load current. Get (14) (15) 1 T6 = t7 —t6 r =— Xr co, (16) 18

Mode 7 Nolo n in Fig 4 (17)] t7-= i< a This mode fl starts ith the turn-off of the anti-parallel diode of V 1 at 17 and at the same time the main switch V1 starts conducting. The load current is now the sum of the resonant inductor current and the main switch VI current. This mode ends at t8 when all energy stored in the a resonant inductor is recovered. Get T7 =18-17 = E Now the circuit topology changes to the initial circuit of Fig. 4 and the next cycle of operation is prepared.

III. CONTROL SCHEME

For three phases BLDCM, six-step commutation with 4 120' conduction time, it allows current to flow in only two phases at any time. The inverter is controlled by the PWM technique to give proper commutations such that two of the three phases are with on states and the remaining one is with floating state. Moreover, the sequence of commutations is retained in proper order by use the rotor position signals. The speed of BLDCM is controlled by PW\ I duty ratio regulation of the inverter. When the dui) of PWM is 1, i.e., full duty circle, the main switches of the inverter work under the commutation frequency. When the phase current of the BLDCM needs commutation. the auxiliary switches V1 . V2, V3 are controlled. and resonant occurs between inductor and capacitor .The DC link voltage drops to zero, so ZVS condition of the main switches is obtained. The whole ZVT process occurs during phase current commutation. The control method is shown in Fig. 5(a). While the duty of PWM is less than 1, the auxiliary switch V1 works as a chop circuit. The switches of the conventional inverter do not operate within a PWM cycle when the phase current need not commutate. The current of inverter switch is shifted to freewheeling diode during the DC link voltage becomes zero. The control method is shown in Fig. 5(b). When PWM signal is flopped down, mode 1 begins, and DC link voltage is slowly dropped to zero. The voltage of DC link does not increase until P\VM signal is flipped up. When PWM signal is flipped up, mode 4 begins, inductor current increases and freewheeling, diode slowly turns off. At last, the voltage of DC link does not increase until PWM signal is flipped up. when PWM signal is flippedup, mode 4 begins inductor current increases and diode slowly turns off. At last. the ti voltage &the DC link is increased to supply voltage. Thus, only one ZVT occurs per PWM cycle. When PWM signal is flipped up, mode 4,5,6,7 are taken. So the switching frecuency of auxiliary switches would be not greater than PWM frecuency

SIMULATION AND EXPERIMENT

The proposed resonant DC link inverter for brushless DC motor drive system is modeled and verified simulation sofware. The DC link voltage is 24V, the switching frequency is 15 kHz. the resonant inductor is 20 uH and the resonant capacitance is 0.022uF The

simulation waveforms are shown in fig 6. The Fig.6 shows that the simulation result are consistent with the theoretical analysis in section 2 and 3 .The DC link voltage drops to zero when PWM signal is flopped down and increased to suppl voltage while PWM signal is flipped up. The DC link voltage is clamped to the source ()Rage, so voltage stress on all switches would be not greater than DC supply voltage. A laboratory-sized model has been constructed and an experiment was conducted to verify the theoretical analysis and simulation results of the proposed ZVT-RDCL soft switch inverter. The experiment system includes PWM circuit, timing sequence circuit based on complex programmable logic device (CPLD), inverter and its driver. The DC link voltage is 24V. PWM frequency is 15 kHz, the resonant inductor is 20 uH , the resonant capacitance is 0.022 uF , rated current of BLDCM is 2.3A, rated mechanical speed of BLDCM is 4000rpm. and No. of poles of BLDCM

the experiment waveforms are shown in fig7 the figures show that the experiment result are consistent with the theoretical analysis and simulation . the gate signal of switching V1 ,V2 and V3 are shown in fig 7 (a) and (b). from the figures we can see that the experiment logic waveforms of auxiliary switches match the control scheme in section 3, and operating time of V2 and V3 is short. Thus, the inductor power loss is low. 1 he DC link voltage (ic and inductor current i1 are shown in Fig.7 (e) and (d). From the waveforms, we can observe ZVT-R DCL inverter proposed performed well and device voltage stress is small. The phase voltage and current of BLDCM is shown in (e). The figure demonstrates that the BLDCM worked well under novel soft-switching inverter.

(e) Fig 7 Experiment waveforms (a) Gate signal of auxiliary V1 and V2, (h)Ciate signal of auxiliary VI and V3. (c) The DC link voltage and inductor current, (d) The dc link voltage and I nduCtor current (zoom out), (e) The phase voltage and phase current of BLIJCM V.

( ONCLUSIONS

A novel zero voltage transition parallel resonant DC link voltage source inverter is presented for BLDCM_ The proposed soft-switching inverter is constructed from the conventional one by simply augmenting auxiliary resonant DC link, and the soft switching is easily achieved by suitable switching of the auxiliary switch. Control of resonance is based on time sequence without testing any current or voltage, so control scheme is simple. The soft-switching operation of zero voltage transition parallel resonant DC link inverter is explained in terms of modes. The simulation and experimental results demonstrate good performances of inverter. [I]

REFERENCES

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