Power Electronics No. 11: Chopper circuit with

a braking function

Takeshi Furuhashi Furuhashi_at_cse.nagoya-u.ac.jp

1

Control circuit of a DC motor using a step-down chopper

Motor speed and armature current

1

2

3

2 4 6 0

0

vω

t [s]

vωcom

0

100

200

300

4 6

[V]

t [s]

ia [mA]

Tdec

ω

Tr

D E R3

ia

ia

Acceleration

Is the brake applied?

2

ω

Tr

D E R3

ia Motor torque Thus, to apply the brake, armature current ia should be

3

Control circuit of a DC motor using a step-down chopper

(7.12) aiKττ =

0 <ai

ωD E R3

No route to make ia reverse

Braking Driving

4

Control circuit of a DC motor using a step-down chopper

ω

Tr

D E R3

ia

Control circuit of a DC motor using a step-down chopper

ia

×

×

Ra

La

Ea

Equivalent circuit of a DC motoer

For applying a brake to an old train

This switch is turned on for braking

5

Thermal energy Kinetic energy Electric energy

ia

In the case of a chopper train

6

Note: VE > Vω 　　　　

Ra

La

Tr drive circuit

Tr E

D

ia

DC motor

Tr:ON D:OFF

Vω Vω

Ra

La

Tr drive circuit

Tr

D

ia

DC motor

D:ON Tr:OFF

E + C

R

LED

VE Tr

L D

Step-up chopper

Vo

Ra

La

Vω

Tr E

D

DCモータ Braking circuit for a DC motor

VE

Exchanging the output and the input

VE < Vo

VE > Vω

Output Power source

Output Power source

La

Ea

E

D

La

Ea

E

D

La

Ea

E

Dia

DC motor

La

Ea

E

D

ia

DC motor

Flow of current

Flow of energy

Flow of current

Flow of energy

＋

－ ＋

－

＋

－

＋

－

＋

－

＋ －

＋

－

＋ －

8

Loss in Tr

Discharging in the form of electric energy Storing in the form

of magnetic energy

Loss in D

Discharge of electric energy converted from kinetic energy

Operating modes of a DC motor braking circuit

Regeneration of energy

Tr

Tr: OFF Tr: ON

D1

D2

E

9

Incorporation of step-down and step-up choppers

Tr1 + D2 = step-down chopper Tr2 + D1 = step-up chopper

Tr1 Tr2

10

(a) ia > 0, Tr1: ON, Tr2 : OFF (b) ia > 0, Tr1: OFF， Tr2: ON

(c) ia < 0, Tr1: ON, Tr2: OFF (d) ia < 0, Tr1: OFF, Tr2: ON

ia flows through D2, though Tr2 is ready to be ON.

ON/OFF of transistors and operating modes of the new chopper circuit

D1

Tr1 Tr2

D2

ia

D1

Tr1 Tr2

D2 ia

E E

D1

Tr1 Tr2

D2

ia

D1

Tr1 Tr2

D2

ia

E E

ia flows through D1, though Tr1 is ready to be ON.

D1

Tr1 Tr2

D2

E

11

Simultaneously turned on

Prohibited switching Short circuit of power supply

D1

Tr1

E

Tr2 D2

RB RB

-

+

VE

vPWM

[V]

0 0.7

VE - 0.7

Tr2 OFF

ON

t [s]

ON

Tr1 ON

Short circuit of power supply

OFF

ON

vPWM

PWM controller

In the case when vPWM increases

Tr1 : PNP-type transistor Tr2: NPN-type transistor

[V]

0

-0.7

0.7 vBE

t [s]

vBE

D1

Tr1

E Tr2 D2

RB

VE

vref

三角波生成回路

- +

vtri

OP

vPWM

Tr2 ON OFF OFF

13

PWM controller

Tr1 : NPN-type transistor Tr2: PNP-type transistor

OFF Tr1 OFF ON

Power supply is not short circuited.

vωcom vω

t [s]

ia [mA]

t [s]

vωt [s]

[V]

(a) with the brake

(b) without the brake

0 1 2 3

0 1 2 3

0 1 2 3

0 1 2 3

[V]

vωcom

1 3

14

ia < 0

The deceleration time is made shorter.

ω

-

+

0.1µF100k

VR2 C1

OP1

D DCM1

DCM2

STEP 8. Circuit construction practice Design the circuit that satisfies the following. P gain Kp and I gain KI of the PI controller are 5 and

1000, respectively. If SW1 is turned on, the motor stops. If SW2 is turned on, a brake can be applied to DCM1. If SW2 is turned off, the brake is not available.

6V

3V

vPWM

510R4

LED1

（A1 A0 = 10）

3V PIC16F615 PIC12F615 PIC12F615

P1B

A2 A1 A0 1µFCS

-vωcom vcom

vω510 RB

Tr1 Tr2

D1

2SC2120 2SA950

10k

10k

R2

R1

2kR6

SW1

SW2

50Rs