Direct torque control of four-switch brushless dc motor with non-sinusoidal back emf

Salih Baris Ozturk, William C. Alexander, Hamid A. Toliyat

Research output: Contribution to journalArticlepeer-review

122 Citations (Scopus)


This paper presents a direct torque control (DTC) technique for brushless dc (BLDC) motors with non-sinusoidal back electromotive force (EMF) using a four-switch inverter in the constant torque region. This approach introduces a two-phase conduction mode as opposed to the conventional three-phase DTC drives. Unlike conventional six-step current and voltage control schemes, by properly selecting the inverter voltage space vectors from a simple look-up table at a predefined sampling time, the desired quasi-square wave current is obtained. Therefore, a much faster torque response is achieved compared to conventional current and voltage control schemes. In addition, for effective torque control, a novel switching pattern incorporating the voltage vector look-up table is designed and implemented for a four-switch inverter to produce the desired torque characteristics. Furthermore, to eliminate the low-frequency torque oscillations, pre-stored back EMF constant versus position look-up tables are designed and used in the torque estimation. As a result, it is possible to achieve two-phase conduction DTC of a BLDC motor drive with faster torque response due to the fact that the voltage space vectors are directly controlled. A theoretical concept is developed and the validity and effectiveness of the proposed DTC scheme are verified through the simulations and experimental results.

Original languageEnglish
Article number5204142
Pages (from-to)263-271
Number of pages9
JournalIEEE Transactions on Power Electronics
Issue number2
Publication statusPublished - 2010
Externally publishedYes


  • Brushless dc motor drives
  • Direct torque control
  • Fast torque response
  • Four switch inverter
  • Low-frequency torque ripples
  • Non-sinusoidal back EMF
  • Two-phase conduction


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