This is the presentation on Dynamic breaking. in this presentation give the basic information about the dynamic breaking

1. Karansinh M. Parmar
Dynamic Breaking

2. What is dynamic braking and
when is it used?
 When a motor is in an overhauling
condition —that is, the load is moving
faster than the
designated motor speed
—the motor acts as a generator and
produces
electrical energy from mechanical
energy.
 This electrical energy, however, needs
somewhere to go, and the most common
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3. How dynamic braking works
 With dynamic braking, the electrical energy
generated during stopping is released as heat
through a voltage regulated transistor and
resistor.
 There are actually two versions of a dynamic
braking circuit:
1) a chopper
2) a dynamic brake
 The dynamic brake circuit includes the switching
device (an insulated-gate bipolar transistor, or
IGBT), the control circuit, and the resistor.3 Karansinh Parmar

4. Simplified schematic of a dynamic
braking circuit.
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5. Cont….
 A chopper, on the other hand, only includes the
regulatory circuit and switching device, with the
resistors being separate components.
 This allows the resistors to be appropriately sized
and mounted remotely, which can be important,
since the resistors generate a significant amount of
heat.
 The combination of switching device and control
circuit is generally referred to as the “chopper
module,” while the resistor is referred to as a
“dynamic brake resistor.”
 Dynamic brakes are typically rated for duty cycles in5 Karansinh Parmar

6. Cont….
 There are two types of control for dynamic braking:
a) Hysteresis control and
b) PWM (pulse-width modulation) control.
 With hysteresis control, the control circuit keeps
track of the DC bus voltage level and turns the
transistor on when the voltage reaches a
predetermined level, in order to avoid an
overvoltage fault in the drive.
 When current is flowing to the resistor, the energy is
turned into heat, which causes the DC voltage to
decrease. As the voltage drops to a preset
“low” level, the transistor is turned off.
 Where hysteresis control turns on the transistor and
leaves it on until the voltage drops to a
predetermined level,
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7. Cont…
 PWM control turns the resistor on and off
according to the level of the DC bus voltage.
 In general, hysteresis and PWM control methods
are equivalent in function, but PWM control is
preferred for applications with a common DC bus
because it helps avoid a situation where one
drive does a disproportion at share of the
dynamic braking work.
 In a common dc bus, a single rectifier supplies
power to the DC bus for all the DC-AC inverters,
rather than an individual rectifier in each AC drive.
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8. Linking the dc bus together between two VFDs through
fused connections makes one simple form of a common
bus. An oversized drive then supplies ac-to-dc
rectification.
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9. Dynamic braking or
regeneration?
 Dynamic braking is used when energy needs to be
dissipated periodically, and regeneration is generally
preferred when the motor is frequently acting as a
generator.
 From an application standpoint, overhauling loads (a
condition where the load is moving faster than the
designated motor speed), such as conveyors and cranes,
cause energy to be generated continuously and make
recovery and reuse more cost-effective.
 But applications where the deceleration speed varies, such
as fans, are suitable for dynamic braking.
 While regeneration lowers energy usage, dynamic braking
reduces wear on braking components that rely on friction.
 And although energy is wasted as heat in dynamic braking,
its upfront cost is significantly less than that of regenerative
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