The design of modern motor control systems
is quite complex and requires a deep understanding of control
system algorithms, microcontroller and digital signal processors,
sensor signal measurement and analog-to-digital converters, high
voltage interface and gate drivers, and the output inverter power
Traditional methodologies do not efficiently partition the
design tasks into well-defined architectural elements with
standardized interface protocols. This results in complex and
customized designs, high initial product cost, as well as high
lifetime ownership cost.
International Rectifier is introducing Accelerator, a new
architecture for motor-drive inverters. This power management
architecture uses a new chipset positioned between the
microcontroller or DSP (digital signal processor) and the motor and
high-level, a well-defined protocol for communicating with the
The guiding principles behind this design are:
- Intelligent partitioning
- Standardized interface protocol
- Performance enhancement of the power management functions.
The fundamental concept behind the Accelerator is to treat the
inverter as an intelligent power management peripheral for the
microcontroller or DSP. With the Accelerator architecture, control
system software can be written at a higher hierarchical level (for
example in C) without the need to program motor control power
management functions at the bit level.
Motor control power management functions might include
pulse-width modulation (PWM), dead-time generation and
compensation, diagnostic and protection, or voltage and current
measurement interfaces. Accelerator integrates the high-voltage
analog and power circuits required to turn the software algorithms
into motor-drive waveforms into the chipset in concert with the
other power management functions.
A suite of technologies is used to implement the chipset,
including mixed signal 0.5-µm CMOS and high-voltage integrated
circuits (HVIC) with ratings from 600 V to 1200 V. The intelligent
power management peripheral can be applied to a variety of
- Driving AC or brushless DC motors for industrial AC drives
- Industrial servo drives
- Appliance drives (air conditioners, washing machines,
- Electronic power steering (12 V, 42 V)
- Integrated starter alternator (42 V)
- High reliability drives (aviation, space).
Figure 1: A simplified block diagram for the Accelerator
intelligent power management peripheral.
Intelligent Power Management Peripheral
Accelerator lets you take advantage of the latest motor-drive
techniques without having to write cryptic code for microcontroller
or DSP in order to interface with Power Management Peripheral IC.
The dedicated communication driver software will be provided so
that you can link with your motion control algorithm code.
You can program the PWM waveform generator by sending input
coordinates via a serial interface.
Figure 2: A simplified circuit schematic for the first
series in the Accelerator chipset family.
Sampling frequencies, including high frequencies capable of
replacing analog PWM generators, range between 3.6-kHz and 58.6-kHz
with 12 bit to 8 bit voltage command resolution. The main timer
maintains the same pulse resolution at all frequencies.
The dead time generator's resolution is 266 ns and the maximum
dead time is about 4.2µs. The fault diagnostic-snapshot
feature uses four FIFO registers. These registers capture and store
the voltage vector, the fault-pin status, and two phases'
current-feedback readingsup to the last four consecutive PWM
statesas a fault history.
Figure 3: The overall block diagram. Programming of the
space vector modulator, dead time generator, and current sensing
interface is done through a dual-port memory. The memory is
periodically read or written by the controller at a high level
through a well-defined serial interface.
High Voltage Gate Drive
A three-phase inverter power stage usually consists of three
high-side and three low-side IGBTs or MOSFETs operating from a
high-voltage DC bus. The bus voltage varies depending on
applications, but can range from 12 V for automotive to 600 V for
230 VAC and 1200 V for 460 VAC industrial drives. Previous methods
use discrete opto-couplers to provide the high voltage gate drives
to the IGBTs or MOSFETs.
High voltage IC technology integrates a 3-phase gate driver in a
single chip such as the 600 V IR213x and 1200 V IR223x product
Figure 4: The first series of the International Rectifier
motor control chipsets integrates the 600 V IR2137 or 1200 V IR2237
in the gate driver. Added features include IGBT de-saturation
protection and synchronized soft shutdown. The protection against
short circuit conditions, such as line-to-line short, ground fault
and shoot through, results in controlled di/dt and no voltage spike
across the IGBT during short circuit turn-off as shown.
Phase Current Measurement
Motor phase current is difficult to measure accurately or with
precise linearity over wide current and temperature ranges. Hall
effect sensors can be used but are inherently bulky and costly.
Alternatively, you can use current sense resistors to measure the
differential voltage drop across each output phase. An opto-coupler
or high voltage IC is then used to translate the differential
voltage to a usable level.
Linear opto-couplers suffer from linearity drift over
temperature range and operating life because of current transfer
ratio (CTR) degradation over time. The International Rectifier
motor control chipset uses high voltage ICs such as the 600-V
IR217x and 1200-V IR227x product family. Differential voltage in
the range of ±200-mV, that sits on top of fast switching common
mode voltage up to 600 V or 1200 V, is converted to a ground-based
PWM output from the IR217x chip.
The PWM signal is then processed using a 12-bit counter with a
clock frequency of 120-MHz. The function also contains auto-offset
cancellation with initial offset calibration capability. A fast
13-bit hardware division block calculates the duty ratio of the
incoming PWM signal, canceling any temperature dependence of the
slope, and canceling the temperature drift to enable
temperature-independent data acquisition.
Overall, the motor current sensing interface provides a
high-speed, high-resolution measurement system whose performance
cannot be attained by the conventional capture/compare unit found
in the motion control DSP or microcontroller.
Figure 5a: A linearity plot of the direct and compensated
current measurement outputs from the IR2171 or IR2172 compared to
open loop and closed loop Hall effect sensors over the temperature
Figure 5b: The 1-kHz sinusoidal current waveform is shown
in the top trace. The processed waveform (after hardware divide to
eliminate temperature drift) is shown in the bottom trace to
indicate resulting minimal phase shift (less than 10( phase shift).
The middle trace shows the direct output from the IR2171."
Figure 5c: The Bode plot data supports the 10( phase
shift at 1 kHz which implies that any closed current control with
the IR2171 can achieve a total bandwidth of 1 kHz without any
Versatile Power Diagnostics
Drive systems often need to report to a centralized
diagnostic-information handling system, particularly in factory
automation because the cost of the system downtime is prohibitive
and fast problem resolution is mandatory. Traditionally, the
conventional microcontroller, or DSP, provides only scalar
information of whether or not a fault has occurred, without
providing any further intelligent information.
International Rectifier's new power management system provides
versatile, "intelligent" diagnostics. A fault condition in the
power circuit might include:
- IGBT line-to-line short
- IGBT ground fault
- Over-current indication from the IR2172 OC (over-current)
- Over-temperature of the IGBT module.
In the event of any fault in the power circuit, the system
latches the last moment of PWM pattern as a complete switching
state and reports back to the host system through the fast serial
interface communication. This snapshot of the IGBT switching state,
along with OC status of the motor current, allows motor drive
engineers to easily analyze the failure. When used with the IR2172,
the drive engineer can also implement the fast current control
through the OC status bit without tripping the motor because of an
International Rectifier Motor Control Roadmap
The concept of the International Rectifier Accelerator motor
control architecture is rooted in the idea of considering the
inverter as an intelligent power management peripheral to the
microcontroller or DSP. It is not just a replacement of the motion
control peripheral function, but a new definition of power
intelligence between switching events.
All the detailed power management functions are performed within
the chipset and the results are presented in memory locations that
are updated periodically. The upper level control software is
greatly simplified compared to motor-control DSP programs because
it requires only the high-level data updates to and from the
The intelligent power management peripheral roadmap is
evolutionary, allowing performance enhancements to be added in each
new generation while maintaining the standard interface protocol to
the system controller. The first series in the chipset family
includes robust power stage protection, linear current measurement,
SVPWM, dead time generation and system monitoring functions.
System performance is enhanced by the temperature-compensated
current measurement technique such that torque precision can reach
±1% vs. the ±2 to 3% in existing motor drives. Another benefit
of the intelligent power management peripheral is its relatively
small sizeit uses integrated technologies in mixed-mode CMOS
Mechanical integration of the power management peripheral with
the power stage is greatly simplified. When comparing the
intelligent power management peripheral approach to the older and
bulkier method of using discrete opto-couplers, Hall-effect sensors
and additional glue circuit components, typical reduction in PCB
size can reach up to 55% and component count reduction can reach
The entire chipset and its support components fit easily within
the dimensions of an industrystandard outline Econo2 package.
Further developments will couple new functions in the chipset with
the additional integration of sensor components inside the power
module, while maintaining a well defined pin-out standard for the
The second stage of development will focus on the advanced dead
time compensation, ripplefree motor current sensing, IGBT
temperature sensing, tripfree overcurrent limit control, and
histogrambased power diagnostics. Performance enhancements include
up to a 10 times improvements in usable speed ranges because of
accurate dead time compensation using voltage feedback. The
additional intelligence in the power management peripheral feature
set will allow applications to be extended to sensorless vector
control of industrial drive and precision control of brushless DC
Voltage feedback-based dead time compensation itself is not
unique, with many attempts recorded in the industry over the years.
However, because the implementation limit, they did not succeed.
The traditional approach of sensing the motor phase voltage was
based on either optically-isolated coupling devices or a high
resistor divider network. Both methods suffer from inaccurate
measurement because of a large time constant and accuracy limit
associated with the hybrid component structure of opto-coupling
devices. Using HVIC technology enables the accurate voltage
feedback to solve the traditional problem.
The new motor current sensing IC will have a unique feature to
eliminate erroneous sampling arising from motor ripple current
caused by the fast PWM switching. The current-sensing IC is able to
synchronize the sampling event relative to the motor PWM switching.
Therefore the effect of motor current ripple, which varies
depending on the motor inductance, will be eliminated to achieve
the stable current feedback system to the closed loop motor
IGBT module temperature feedback and DC bus voltage feedback
will be added to the next generation of the power management
peripheral IC to facilitate the torque foldback control and current
limit control which achieve a new level of trip-free operation.
New power diagnostics will have FIFO memory to store all IGBT
switching states of the last ten consecutive PWM switching periods
in the event of the drive fault condition (in other words, overcurrent and
overtemperature). This will help to more effectively guide the
application user to the root cause of the motor drive system fault
and shorten the downtime on the factory floor.
Other applications will also benefit from the development of the
Intelligent Power Management Peripheral Roadmap. Appliance drives
will become lower cost and easier to design with application
specific feature sets for compressors and for direct drive washers.
Automotive drives for electric power steering (EPS) and for
integrated starter alternators (ISA) will have higher torque and
speed performance. High-Reliability drives for space applications
will have robust protection and complete diagnostics.