Starting Strategy

In this study, the proposed starting strategy of BDCM is divided into alignment mode and synchronization mode. The rotor is forced to locate in a given position in alignment mode. In synchronizing mode, the six switching signals start changing to generate a synchronous rotating magnet field with increasing rotating speed. When the standstill characteristics are known, an optimal accelerating speed rate and the accompanying voltage (PWM duty) can be obtained to lead the rotor rotating in specified speed synchronously to some speed where the sensorless circuits are able to function well.

5.4 Simulation Results

In this section, some simulation results are provided to evaluate the performance of six-step BDCM sensorless control (

120

^o SWPWM) and twelve-step BDCM sensorless control (

150

^o SWPWM). The configuration of sensorless control had been plotted in Fig. 4.1 and the simulated program in PSIM software is plotted in Fig. 5.5.

As shown in Fig. 5.5, the PSIM program involves four parts: three phase inverter which is fed by dc voltage 300V, BEDC-II, DLL block which involves the sensorless function of commutation signal generator, speed estimator, switching signal generator, and two coupled motors where one is called motor and the other is seen as a generator connected to Y-connected resistances

R .

_g

According to the BEDC-II analysis in (4.9)~(4.11), the simulated parameters for BEDC-II are listed as (4.12) and BEDC-II obtains the position signals

H ,

_a

H and

_b

H from the

_c inverter and motor terminal voltages V_P,

V ,

_a

V and

_b

V . By inputting the above position

_c signals

H , H and H into the DLL block, commutation signal H and the estimated

speed ω can be obtained from (5.1). Then, the speed controller tunes the PWM duty ratio _r adequately according to the speed difference between speed command

ω

^*_r and the estimated speed ω . At the same time, the switching signal generator yields the six gate signals _r according to the commutation signal

H and PWM duty ratio to yield square-wave currents

adequately.

The parameters of motor and inverter have been listed in Table 3.5, and those of generator are tabulated in Table 5.3.

Table 5.3. Simulated generator parameters Stator resistance

2 . 2 Ω

Stator inductance L_q

= 3 . 43

mH,

L

_d =2.73

mH

Voltage constant (Line-to-Line) 65

Vp / krpm

Pole number 4 pole

Motor inertia 1.92

kg

−

cm

²

With speed command ω_r^∗

= 3000

rpm, the simulated BDCM current waveforms

i and

_a the corresponding back-EMFs

e under various SWPWM for

_a

R

_g =100Ω and

R

_g = 20Ω are plotted in Fig. 5.6 and Fig. 5.7, respectively. We can find that both six-step and twelve-step sensorless controls work stably. In addition, it is noted that current harmonics in motor windings would not only result in the excess copper loss, but also contribute to the torque ripple at the shaft, the vibration and acoustic noise. It follows that current harmonics should be reduced as far as possible.

As shown in Fig. 5.6, when the yielding motor current is small (i.e. light load), the listed

THD and WTHD values show that six-step sensorless control is preferred. On the other hand,

when the yielding current becomes large (i.e. heavy load), the listed THD and WTHD values in Fig. 5.7 implies that twelve-step sensorless control is better than six-step sensorless control.

Ha

Hb

Hc

Fig. 5.5. Simulated model in PSIM.

2A

2A

5.5 Experimental Results

With

R

_g =100Ω and six-step 120^o SWPWM type-01_01, the measured gate signals

1

GT and G_T4, position sensing signal

H and motor winding current

_a

i under various

_a speed are plotted in Fig. 5.8. Likewise, the measured waveforms for

R

_g =100Ω and twelve-step 10Modified150^o SWPWM type-00110_001 are plotted in Fig. 5.9. The calculated THD and WTHD values are tabulated in Table 5.4 and plotted in Fig. 5.10.

Obviously, due to the current harmonics, sensorless BDCM control with six-step 01

_ 01 type SWPWM

120^o is better than that with Modified

150

^o SWPWM

10 1 0 0 _ 0 1 01 0

type with

R

_g =100Ω (i.e. light load).

Table 5.4.

THD and

_i

WTHD of experimented current waveform with

_i

R

_g =100Ω

SWPWM

120

^o

type-01_01

Modified

150

^o SWPWM type-00110_00110 SWPWM

ω (rpm) r

THD (%)

_i

WTHD (%)

_i

THD (%)

_i

WTHD (%)

_i

1000 65.66 20.43 85.75 34.04 1500 56.79 16.30 79.83 30.00 2000 48.81 15.94 78.94 27.29 2500 43.60 13.10 69.63 25.41 3000 41.67 13.03 51.51 20.69

A

speed ω equal to: (a)_r 1000

rpm

; (b)1500rpm; (c)2000rpm; (d)2500rpm; (e)3000rpm.

A Fig. 5.9. Experimental waveforms of Modified

150

^o SWPWM type-00110_00110 with

Ω 00

=1

R

g and speed ω equal to: (a)_r 1000

rpm

; (b)1500rpm; (c)2000rpm; (d)2500rpm;

(e)3000rpm.

1000 2000 3000

1000 2000 3000

)

With

R

_g = 20Ω, the measured gate signals G_T1 and G_T4, position sensing signal

H

_a and motor winding current

i with six-step

_a 120^o SWPWM type-01_01 and twelve-step

10 1 0 0 _ 0 1 01 0 type SWPWM 150

Modified ^o are plotted in Fig. 5.11 and Fig. 5.12,

respectively. The calculated THD and WTHD values are tabulated in Table 5.5 and plotted in Fig. 5.10.

From Table 5.5, we can find that the current harmonics of six-step sensorless control is less than that of twelve-step sensorless control when the motor speed ω is smaller than _r 1500rpm. However, when the speed becomes higher than 1500rpm, the current harmonics of six-step sensorless control is larger than that of twelve-step sensorless control.

Consequently, it is preferred to use twelve-step sensorless control at those conditions closed to the rated condition.

Table 5.5.

THD and

_i

WTHD of experimented current waveform with

_i

R

_g =20Ω

SWPWM

120

^o

type-01_01

Modified

150

^o SWPWM type-00110_00110 SWPWM

ω (rpm) r

THD (%)

_i

WTHD (%)

_i

THD (%)

_i

WTHD (%)

_i

1000 38.94 13.82 46.69 17.86 1500 37.01 13.77 36.47 13.81 2000 36.58 13.69 33.85 12.67 2500 33.78 12.84 30.21 11.69 3000 31.83 11.98 26.05 10.23

A

speed ω equal to: (a)_r 1000

rpm

; (b)1500rpm; (c)2000rpm; (d)2500rpm; (e)3000rpm.

ms Fig. 5.12. Experimental waveforms of Modified

150

^o SWPWM type-00110_00110 with

Ω 0

=2

R

g and speed ω equal to: (a)_r 1000

rpm

; (b)1500rpm; (c)2000rpm; (d)2500rpm;

(e)3000rpm.

CHAPTER 6

CONCLUSION

In order to integrate the small-sized motor drivers into SOC design, we should minimize the power consumption due to gate driving circuit, reduce temperature rise and eliminate possible hot spot in the PWM motor driver. With the common six-switch circuit topology, best selection of SWPWM scheme is an effective way to overcome the SOC challenges – power consumption and thermal balance. After the classification of linear modulation, effective PWM transition rate

α

_PWM , power loss unbalanced ratio and experimental demonstration, this thesis recommends the following best SWPWM schemes for SOC design type 01_01 and 10_10 for

120

^° SWPWM and type 010_010 for

180

^° SWPWM. The results are very important for small-sized motor drivers in some portable and electric equipment powered by batteries.

In addition, the low-speed performances and comparisons of two BEDCs and their sensorless controls are studied under position-dependent load torque. The implementation of commutation signal generation is the only difference between the sensorless control of BEDC-I and BEDC-II. From the analysis, the implementation of sensorless control for BEDC-I is simpler than that for BEDC-II. However, BEDC-II yields less position detecting error than BEDC-I especially at low speed. The simulation and experimental results also demonstrate the analysis result. It follows that BEDC-II is suitable in low-speed application of BDCMs.

Based on the study of SWPWM and BEDC, the proposed twelve-step BDCM sensorless control had been designed and implemented. The result shows that twelve-step BDCM sensorless control is better than six-step BDCM sensorless control at those conditions close to the rated condition. The performance evaluation of position-dependent load torque will be the

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A ^PPENDIX A

The Fig. A.1 and Fig. A.2 shows the experimental environment which we used in chapter 5

Fig. A.1. MCU and BDEC-II.

Fig. A.2. Structure of BDCM sensorless control.

在文檔中 方波脈寬調變及其於直流無刷馬達無感測控制之應用 (頁 99-0)