How to cost-effectively transition to brushless DC motors for your applications

How to cost-effectively transition to brushless DC motors for your applications

Technology News |
By eeNews Europe

The various options of semiconductor integration are opening up an ever-growing array of applications for distributed intelligent small drive solutions based on synchronous motors. These include brushless DC motors (BLDC), permanent magnet synchronous motors (PMSM) and stepper motors. Because of their technical advantages and increased efficiency, these types of motors are replacing brush-type motors in many existing applications. Automobiles are a great example.

Typically automotive components must support low system cost, small, light and reliable, and show a high degree of efficiency. It is also important to reduce exhaust emissions and lower the fuel consumption. The need for drive concepts that work with a wide range of motors, and the extreme demands made on efficiency, system design and network ing options have major impact upon the actuator electronics.
The BLDC motor market

There are plenty of BLDC manufacturers in the US. Most companies are still focused on motor technology like brush- type  DC  motors,  stepper  motors,  etc. But many of them are establishing the BLDC  motor  as  a  basis  for  new  product  developments.  Even  though  there are  many  BLDC  motor  manufacturers in place, especially for the tiny BLDC motors, there are not so many integrated control electronic solutions on the market. Companies capable to manufacture BLDC motors with integrated intelligent electronics inside, together with a low cost approach are still not easy to find.
The level of adoption of BLDC motor technology is increasing. Many auto- motive functions such as fuel or water pumps,  HVAC  (Heating  Ventilation  and Air Conditioning), curve light, head-lamp levelling,  and  many  others,  are  converting  from  brush-type  DC  motor  or  step- per motor technology to BLDC motor technology.  Yes,  this  is  not  a  general proof that all brush DC or stepper motors will  convert  to  BLDC  motor  technology. But  the  main  argument  that  the  electronic to control the motor is too expensive compared to the price of the motor itself is becoming less valid every day. Furthermore, the BLDC motor advantages can significantly enhance other system properties (refer to the Table 1). Hence it can be foreseen an evolution to intelligent motion control.
Brushless DC motor advantage
BLDC   motors   have   several   advantages over competing motor technologies, summarized in Table 1.

Table 1: Summary of brushless DC motor advantages

Problems of the transition from brush- type DC motors towards BLDC motors?
When looking at motion control systems including brush-type DC motors (BDC), it is obvious, that control is less complex compared to a BLDC motor. In simple words: you have only to apply a voltage to the motor and it starts to move. Engineers with little experience in BLDC motor  control  system  design  often  fear that  they  will  have  difficulty  converting to BLDC motor technology, even though they know about the advantages. Complex electronics and the programming of such a system are thought to be a barrier. Also the higher system cost due to the electronic commutation is often considered as a showstopper.

However,  the  transition  from  BDC  to BLDC is not necessarily difficult. By using the   Micronas HVC 4223F   single-chip solution the electronic circuit can be quite simple.

In the example below, a solution is out- lined that requires only 13 components, including  the  HVC 4223F  itself.  E.g.  if the system includes already a PCB, the impact to the BOM is moderate. In many cases,  a  smaller  motor  can  be  utilized due to the better efficiency. The actuators can also be smaller further reducing material cost (motor, case, gear, etc.). Furthermore, the BLDC control system with the HVC 4223F can be programmed in a way that it behaves like a BDC motor from outside, comprising only a VBAT and ground supply as connections. Hence, existing motion control systems can be upgraded without changing the complete system design. And in the long term the system can be improved, e.g. with net- working and/or diagnostic functions etc. Customers do not have to start from scratch with software development since the existing application notes and demo software can provide an adequate level of functionality.
A single-chip architecture for maximum system integration and flexible drive systems
The new Micronas High-Voltage Controllers (HVC) allow systems with highly  integrated  motor  drive  electronics to achieve the performance potential of modern permanently excited DC motors. The  HVC 4223F  is  an  integrated  micro- computer system with all necessary peripheral modules for directly driving PMSM/BLDC  motors  and  bipolar  step- per  motors. The  programming  capability of the peripheral modules and the user defined software allow the best possible adaptation to the properties and attributes of different drive systems.
The   increasing   integration   density   in drive  solutions,  made  possible  by  the low power/weight ratio (W/kg) of the PMSM/BLDC motors, affects the power dissipation (power/thermal management), the flexibility of driving circuit and the selected  drive,  and  also  the  options  for diagnosis. The high integration density of the electronics requires adapting the thermal operating conditions by means of a target-specified power management. The new HVC family provides many functions which precisely allow this adaptation.

Adjusted motor activation for different applications and operating modes

The use of different drive concepts in automotive actuators requires the easy adaptation   of   the motor  power-bridge and  how  the  bridge  is  activated.  The HVC 4223F precisely addresses this issue with a configurable final output stage, fully integrated and programmable peripheral module, and  a  powerful  ARM  Cortex®-M3® Core. Six n/n half-bridges (incl. charging  pumps)  are integrated.  These can be adapted to the type of motor by the appropriate wiring circuit of the output pin and by the configuration of the software.
The EPWM-Module (Enhanced Pulse- Width   Modulation)   supports   passive and  active  free-wheeling  current patterns (“Asynchronous/Synchronous Rectification“) for different operating modes and types of motor (see Table 2). The integrated current measurement and the  D/A  converters  allow  the  programming of nominal current values (e.g. for current-controlled    micro-stepping).    In the PMSM/BLDC motor, without using sensors,   the   feedback   signal   of   the rotor  position  can  be  sent  via  comparators  and  integrated  star-point  references, or alternatively by means of Hall-effect sensors/encoders. Also, the commuted mode  of  operation  for  stepper  motors can be selected, e.g. for accomplishing higher rotational speeds. Adapting stepper motors  to  different  modes  of  operation (full / semi-step, wave drive, micro-step, commuted operations) is also possible or programmable.


Table 2: Overview of motor types and modes of operation with the new HVC

Algorithms for speed and current control can be quickly executed with the ARM Cortex-M3 CPU – supported by the high- speed A/D converter and adjustable signal paths for voltage and current measurements.  The  output  stage  includes  over- load protection (overvoltage / excess cur- rent) and diagnosis functions. The integrated peripheral modules for the motor activation  (EPWM,  comparators,  star point reference, D/A converter, diagnosis and overvoltage / excess current protection, temperature monitoring) can be programmed for the operating modes listed in the table.

Efficient system with ARM Cortex-M3 CPU
CPU and flash memory allow extremely high system flexibility by means of soft- ware,   e.g.   for   real-time   requirements for rotational speed and current control, communication in distributed actuator systems (e.g. in LIN clusters) and diagnosis functions. The main oscillator is already  integrated.  The  CPU  cycle  can be stepped down to reduce power consumption or power dissipation without affecting peripheral functions. To reduce electromagnetic emission, an EMI reduction module (ERM) is included. All peripheral  modules  can  be  programmed  via the AHB/APB bus system and are so adapted to the system requirements. The integrated NVRAM allows the storage of diagnostic and application data.
For power, the HVC family is supplied directly via the 12-volt on-board electrical system and complies with the ISO 7337 test pulses. Start-stop systems are sup- ported by a special “retention mode“. Compared with conventional linear regulators, the integrated switching regulator (buck converter) minimizes power losses. Energy-saving modes provide low power consumption, e.g. for Kl.30 applications. External loads (e.g. Hall sensors) can be supplied via a programmable high-side switch.
For communication in distributed small drive  systems  (e.g.  HVAC  systems),  a LIN-UART and the LIN Physical Layer are integrated  in  the  HVC.  Also,  a  second LIN  pin  is  available  for  use  in  LIN  clusters with auto-addressing as, for example, in HVAC valve applications. The described system integration and network capability is  an  important  step  on  the  way  to further miniaturization and integration in small and micro-motors.
The  reliability  of  a  drive  system  is  crucially influenced by the drive electronics used. The architecture of the new HVC includes extensive diagnosis and protective functions with an SPFM greater than 60% (“ASIL ready“). This is important for the  decomposition  in  accordance  with ISO 26262 at system level, i.e., also for the  assignment  of  the  safety  and  security requirements to individual and independent system elements, and can be carried out at system, hardware, and software level.
The  high  system  integration  has  a  positive  effect  on  the  required  system  FIT (FIT = Failure in Time) rates since the number of components is reduced.
A  good  example  for  the  flexible  diagnosis  is  the  implementation  of  a  “thermal   managements“   in   the   software.

Figure 1: Electronics integration in the BLDC motor

By evaluating current and temperature, measures can be taken to adapt to the operating profile, e.g. reducing the CPU cycle, restricting the motor current, adapt- ing  the  free-wheeling  current  pattern  in the motor bridge, etc.

The  small  40-pin  QFN  6×6 mm  package of  the  new  HVC 4223F  is  well  suited for  the  miniaturization  and  the  integration  of  the  electronics  into  the  motor or into the actuator. Also, the “exposed pad“ (ePAD) guarantees a good thermal connection. A junction temperature range of –40 °C to +150 °C and the integrated over-temperature monitoring allow the use in temperature-critical applications.
Application example for positioning actuator with BLDC motor
Mechanical actuators for positioning applications usually have to provide a high torque (e.g. in valves, flaps, etc.). Typically a gear is used to obtain low rpm at the load, introducing considerable losses due to  friction.  In  many  cases  the  actuator must  apply  a  stable  holding  torque  and the  actuator  shall  not  lose  its  last  position to avoid calibration runs. Due to weight  reduction  and  space  constraints the motor and electronic geometry plays an important role. The example describes a solution for a single-chip motor actuator with   the   HVC 4223F   driving   a   BLDC motor  in  sensor-less  six-step  commutation with a LIN communication interface. Figure 2  shows  the  principle  system  for a valve actuator integrating the complete electronic by the HVC 4223F single-chip solution.


Table 3: Overview of the used peripheral function with the HVC 4223F
Hardware – Software interaction and circuit solution
The efficient interaction of HW and SW inside a motion control system depends on the distribution of the particular functions  of  the  available  chip  peripherals. Table 3  summarizes  a  possible  approach for  the  system  in  Figure 2  with  sensor- less six-step commutation including rpm and current control, functions for diagnosis and communication stack. The soft- ware architecture can be e.g. a simple round-robin with interrupts.


Figure 2: Example system with BLDC-motor
A basic circuit solution for the system  is outlined in Figure 3. The number of external components for the motor can be reduced to a minimum of 12 components (refer  to  the  table  in  Figure 3).  In  case  of special system ESD and/or EMC requirements, some additional components like ferrite beads etc. might be required, e.g. in the DC supply link or LIN signal path.


Figure 3: Principle Circuit Solution
The number of small motor driving solutions   using   BLDC   motor   technology will  grow  because  of  the  declining  cost of electronics. The highly integrated single-chip   HVC 4223F   solution   from Micronas is an enabler for this development.

The diversity and functionality of motors will increase, including networking between intelligent drives. Furthermore, the  requirements  for  lower  weight, smaller size, higher power density, and lower   cost   must   be   met.  The   used motors  need  to  be  small,  light  and  are used in distributed LIN bus networks.
The design-in time can be reduced because complete platforms of tiny motors  can  be  developed  using  a single-chip solution. Tailoring to different motor types and properties can be achieved by means of adapting the soft- ware. Today’s brush-type DC motor solutions  can  be  replaced  1:1  by  a  BLDC motor system, that on the outside, look like a conventional motor but inside pro- vide all advantages needed to realize intelligent motion control.

Self-diagnosis and functional safety increasingly play an important role. Drives with  “integrated intelligence”  by  means of electronics can provide this diagnostic feature.  E.g.  the  properties  of  a  motor might change over life-time. These effects can be tracked and stored by the electronics and adjusted to a certain extent.
Adapting the software allows a large number   of   functions   and   applications to   be   addressed. The   customer can efficiently equip a complete platform of actuators  with  just  one  type  of  controller. The small number of discrete components and the high integration provide a high degree of miniaturization and allow economic solutions with the advantages and benefits of modern types of motors. The high level of reusability of hardware and software permits quick responses to changes in customer requirements.

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