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Technology Database
Technology Database    Electrical engineer DRIVE SYSTEM FOR ELECTRICAL VEHICLE

DRIVE SYSTEM FOR ELECTRICAL VEHICLE

Contact: Alexandr Sutormin

President SibECA Co., Ltd.

sam@mail.tomsknet.ru

http://www.sibeca.tomsk.net

Full Development of the LSV’s Drive System must be divided into the three stages (steps) like these:

Subject of the present proposal - is a both of the Draft & Complete Design and preparing to finalization of the full development project. First stage will be competed by manufacturing two samples of the Servo System GDS8-4000 according to the following technical requirements:

  • Power supply voltage - 72VDC (50…90)VDC
  • Maximum input power - 15kW
  • Recuperation - full recuperation
  • Back rotation with maximum speed - 2,000RPM
  • Operating conditions:
  • Temperature range - from –10C to +50C
  • Humidity level - less than 90%
  • Rated parameters:
  • Rated torque - 20 Nm
  • Rated Speed - 4,000 rpm
  • Rated output Power - 8.0 KW
  • Rated motor / total efficiency - 0.94 / 0.89
  • Controlled speed range - 1 : 100
  • Torque nonlinearity (torque mode) - less than 10%
  • Unloaded operating stage:
  • Maximum speed - 6,000 rpm
  • Maximum acceleration - 5× 103 S-2
  • Loaded operating stage:

Continuous mode:

A lot of allowed operating points for this mode must be turned up inside green area of the shown mechanical curve.

Overloaded mode:

A lot of allowed operating points for this mode must be turned up inside red area of the shown mechanical curve and must has limited duration. Duty cycle of the each overload mode must be chosen to prevent overheating of the motor (or will be limited by temperature feedback inside power controller).

Note. Mechanical curve shown for rated system voltage and rated temperature stage.

  • Continuous stall torque - 23 Nm
  • Peak stall torque - 57 Nm
  • Dimensions:
  • Motor - ø160x200mm (14kg)
  • Power control unit - volume maximum 10 liters

Drive System consists from BLDC motor and power control unit – High Frequency Power Converter HFPC.

General description of the BLDC motor structure

Nowadays there are next main parameters for electrical motors:

  • maximum power efficiency and recuperation capability;
  • compact, low weight construction (high power density);
  • low cost and good reliability;
  • good dynamical properties;

According to analysis of the known different kinds of the motors had shown just two kinds suitable motors –BrushLess Direct Current Motor (synchronous motor with permanent magnets on the rotor) and Induction Motor. From the first draft view Induction Motors look more attractive, because they didn’t include permanent magnets (which is relatively high expensive). But from other hand by using Induction Motor is not easy to provide efficient full-range recuperation stage (which is very needed to provide good efficiency for total EV’s cycle – acceleration~motion~break with recuperation). So, Induction motor will lost for EV’s application. From basically point of view permanent magnets – it’s additional energy built-in motor structure and by using this energy it’s not problem to organize generator mode of the operating and by using this energy possible to improve motor efficiency (to approach it to 100%). 

Remark to support superiority of the SibECA's BLDC motors

BLDC Compressor Motor designed by SibECA company has some features, which allow to improve main motor’s parameters comparing with competitor’s ones:

  • decreased to minimum outer diameter of the stator pack (according to increased numbers of the poles), which will allow to reduce total mass and dimensions of the assembled motor;
  • designed special winding will reduce cost of the winding process (by simplify technology) and will increase coefficient of the using slot’s areas by real copper section (It will allow to put inside slot more copper and reduce phase resistance and phase copper loss from it);
  • by using winding “turn to turn” and high thermoconductivity compound for encapsulation of the assembled stator will be improved heat transmission from “inside to outside motor”, so it’s looks possible to apply for efficient cooling just outer surface of the motor and to keep close own motor’s area.

Results of torque and reliability test

Reliability of the electrical machine – this is capability to operate according to requested functions and to keep all specified parameters during long operating time. Reliability is complex property of machine and finally can be confirmed just by real suitable tests.

Reliability of the BLDC motor will be defined by:

  • reliability of the stator :
    • stator pack, assembled from silicon steel sheet is a very readability unit, which without great overheating overheating will keep magnetical properties safety;
    • winding reliability – most frequently winding damages related with vibration separate copper wires inside stator’s slots – from this vibration wire insulation will be destroyed and will be short circuit between turns or between motor’s phases. Other reason for damaging of winding is overheating. Both designed motors have encapsulated winding. There are three advantages from it – all separate wires are solid (connected strongly by compound), so vibration excluded and stator’s noise reduced also. High thermocondactive compound helps to transmit heat loss from copper to outer cooling surface, so temperature gradient (especially important for overload stage) will be lower comparing with other construction and conditions for operating winding long time will be more lighter. Additionally – applied compound has very nice insulation properties, which will be guarantee isolation and protect contact of copper with air aerosol.
  • reliability of the rotor :
    • reliability of the permanent magnets provided by optimal magnetical load and limited reaction from stator side to remagnitizate rotor. Assembled rotor will be pass thermostabilization (in heater chamber to +150C) – it’ll guarantee saving of magnetical properties for any operating temperature less +150C;
    • reliability of the bondage of magnets – composite sleeve will guarantee suitable strength with safety factor 1,5 at maximum overspeed 9Krpm.
  • reliability of the bearings. Bearings are standard component and in motor will be applied suitable ones.
    • In designed structure of the motors rotor’s mass reduced as much as possible – load conditions from it and total motor’s weigh will be more good.

    • motor construction is fully closed, so no dust and other negative part there
    • operating motor temperature will be controlled by electrical driven fan and by intelligent control of the Inverter-Motor system

Reliability of the designed motors was confirmed by several tests. Were tested similar motors with power 1.5KW and 8KW (tested motors had same structure). Was tested torque of motors and defined process, which allow stabilizing it (by treating assembled rotors at temperature over than real operating). Torque test results have maximum error comparing with calculated value less 10%. During mentioned tests was checked and improved magnet’s bondage. Was measured also temperature gradient between winding and outer case surface during worst condition (temperature at outer surf of motor was measured by sensor and winding temperature was measured by increasing phase resistance). Results had confirmed properly operation of the winding without overheating even with outer temperature over +120C. Also were measured total stator’s losses with target to correct calculation of the efficiency. Samples of motors with same construction working properly.

Power control unit solution

Power control unit, referred to as hereinafter HFPC, presents from it three-phase pulse current inverter with PWM to 20KHz and controller. Inverter can be based on the modern power modules, which nowadays widely manufacturing almost all of the power units mass-makers (IXYS, Semikron, PowerRex, SunRex, International Rectifier and other). These power modules allow making very compact and efficient controller for Motor. Signal controller part includes speed regulator and looks like standard type. Current feedback (from current sensors) allows to have maximum efficiency of the motor for all range of the operating speed (600 ~ 6,000RPM).

Estimated Budget

Listed above stages of the Development Drive System GDS8-4000 for Electrical Vehicle can be completed by manufacturing and testing two samples (prototypes) within 25 weeks per ~ 60,000USD.

Notes:

  1. Shown expenses suitable to produce two sets of the servo system into Russia.
  2. To plan finalization stage of Development and to start serial production preparing we need to know real manufacture, especially to make motor. Because final complete drawings must satisfy real technology.
Source: SciTecLibrary.ru
Publishing date: August 12, 2003

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