Je-Wook Park

Sensorless Control of Brushless DC Motors With Torque Constant Estimation for Home Appliances

A new sensorless control algorithm for brushless dc motors (BLDCMs) is proposed in this paper. The torque constant of a BLDCM is used as a reference signal for position detection because it is constant during the entire speed range and can be estimated by calculating the ratio of the back electromotive force (EMF) to the rotor speed. By using both a disturbance observer and the torque constant estimation error, the rotor speed can be obtained. The back EMF can be easily obtained from the voltage equation of the BLDCM. The estimated back EMF decreases simultaneously with the estimated torque constant at the commutation point. By using this phenomenon, the commutation of the phase currents can be done automatically at the drop point of the estimated torque constant. Unlike conventional back-EMF-based methods, the proposed method provides highly accurate sensorless operation even under low speeds because only the drop of the torque constant is used for position detection and current commutation. Therefore, the position accuracy is not affected by the electric parameter errors of the BLDCM. Also, this algorithm does not require an additional hardware circuit for position detection. The validity of the proposed algorithm is verified through several experiments.

A Dead Time Compensation Algorithm of Independent Multi-Phase PMSM with Three-Dimensional Space Vector Control

This paper proposes a new dead time compensation method of independent six-phase permanent magnet synchronous motors (IS-PMSM). The current of the independent phase machines contains odd-numbered harmonics because of the dead time and the nonlinear characteristics of the switching devices. By using the d-q-n three-dimensional vector analysis, these harmonics can be extracted at the n-axis current. Thus, the current distortion can be compensated by controlling the n-axis current of the IS-PMSM to zero. The proposed method is simple and can be easily implemented without additional hardware setup. The validity of the proposed compensation method is verified with simulations and several experiments.

An Optimal Current Distribution Method of Dual-Rotor BLDC Machines

This paper proposes an optimal current distribution method of dual-rotor brushless DC machines (DR-BLDCMs) which have inner and outer surface-mounted permanent-magnet rotors. The DR-BLDCM has high power density and high torque density compare to the conventional single rotor BLDCM. To drive the DR-BLDCM, dual 3-phase PWM inverters are required to excite the currents of a dual stator of the DR-BLDCM and an optimal current distribution algorithm is also needed to enhance the system efficiency. In this paper, the copper loss and the switching loss of a DR-BLDCM drive system are analyzed according to the motor parameters and the switching frequency. Moreover, the optimal current distribution method is proposed to minimize the total electrical loss. The validity of the proposed method was verified through several experiments.

Phase current estimation of BLDC motor drive system by using source side current of DC-link

This paper proposes an estimation algorithm of phase currents of inverter systems with the planar bus bars for brushless DC motors (BLDCM). In these inverters, a DC-link single current sensor measures the sum of a smooth capacitor current and phase currents of BLDCM. It is essential to extract phase currents from the measured single current to control BLDCM. Therefore, in this paper, the phase current is estimated by analyzing equivalent circuits of BLDCM in ON and OFF periods of switching elements. The usefulness of the proposed algorithm is verified through simulation and experimental results.

Vector control of multiple-module transverse flux PM generator for large-scale direct-drive wind turbines

This paper proposes an efficient current control algorithm and a suitable power conversion system of a multiple-module transverse flux permanent magnet generator (MM-TFPMG) for large-scale direct-drive wind turbines. The MM-TFPMG is composed of multiple-module structures based on an independent three-phase configuration. In this paper, the single-phase current control applying the d-q transformation and the independent three-phase dqn-axes current control are proposed for the generator-side control of the MM-TFPMG. The control performance and characteristics of the single-phase dq-axes current control with a variable cutoff frequency and the independent three-phase dqn-axes current control using a concept of vector control are analyzed. As a result, the independent three-phase dqn-axes current control by using the vector control is an appropriate method to efficiently control the generator-side of the MM-TFPMG. The proposed algorithm is easily implemented and has less computation resource. Moreover, the control performance is better than the independent single-phase dq-axes current control despite the change of wind speed. The validity and usefulness of the proposed independent three-phase dqn-axes current control algorithm are verified and compared through several experimental results.

Sensorless control algorithm of BLDC motors with current model

This paper proposes a new sensorless control algorithm of BLDC(Brushless DC) motors with current model based on the 120 degree conduction mode. The rotor speed and the position can be estimated by using the current model of BLDC motor which is modified version of the conventional current model of PMSM(Permanent Magnet Synchronous Motor) sensorless method. The rotor position and the speed can be obtained by using the difference of the actual current and the model current. The position error caused by the parameter errors of the current model, current distortion at commutation points and nonideal trapezoidal shape of back-EMF is also compensated by using simple PI controller and the feedback loop of the real current. The validity of the proposed sensorless control algorithm is verified through several experiments.

DC voltage balancing control of half-bridge PWM inverter for linear compressor

This paper proposes a new single phase back-to-back PWM converter for the power supply of the single phase by using both a full-bridge PWM rectifier and a half-bridge PWM inverter. In addition, the balancing control algorithm of DC voltage for this topology is also proposed by controlling the current of the half-bridge inverter. With the full-bridge PWM rectifier and the half-bridge PWM inverter, AC/DC/AC operation can be carried out by using only a six-pack power module and two series DC capacitors. Since two series connected capacitors are installed at the DC link, each capacitor voltage must be balanced for the safe operation. Using a IP(Integral-Proportional) controller, the DC voltage can be balanced without the current distortion. The proposed algorithm can be easily implemented without much computation and additional hardware circuit. The validity of the proposed algorithm is verified through simulations.

Position Correction Method for Misaligned Hall-Effect Sensor of BLDC Motor using BACK-EMF Estimation

This paper proposes a new position compensation method for misaligned Hall-effect sensors of BLDCM(Brushless DC Motor). If the Hall-effect sensors are installed at wrong position, the exact rotor position cannot be obtained. Therefore, when the BLDCM is controlled with this wrong position, the torque ripple can be increased and the average torque also decreases. The back-EMF of BLDCM can be obtained by using the voltage equation and by multiplying the back-EMF constant and rotor speed. At a constant speed, the estimated back-EMF by using the multiplication of the back-EMF constant and rotor speed is constant, but the estimated back-EMF from the voltage equation decreases at the commutation point because the line-to-line back-EMF of two conducting phases is start to decrease at this point. Therefore, by using the difference between these two estimated back-EMFs, the commutation point of the phase current can be determined and position compensation can be carried out. The proposed position correction method doesn`t require additional hardware circuit and can be easily implemented. The validity of the proposed position compensation method is verified through several experiments.

Minimum copper loss drive method of three-phase dual-rotor BLDC machines

Three-phase dual-rotor brushless DC machine (DR-BLDCM) is constructed with two concentric machines which have inner and outer surface-mounted permanent-magnet rotors. Dual-stator is located between the dual-rotor. The machines have advantages such as high power density and high torque due to the structural characteristic in the restricted circle space. However, the system with DR-BLDCM requires double 3-phase PWM inverters. In this system, the current division control of the torque command into the inner and the outer machine should be determined to satisfy the maximum torque and the system efficiency because the entire torque is the sum of the inner and the outer torque. If current is divided without considering the features of the inside and the outside machine, the efficiency can be lower because of the copper loss increase. Therefore, this paper proposes the current distribution method to increase the produce of the torque, and minimize the copper loss in the DR-BLDCM control system.

Fault Diagnosis for 3-Phase Diode Rectifier using Harmonic Ripples of DC Link Voltage

The fault analysis and detecting algorithm for a 3 phase diode rectifier is proposed. The 3 phase dioderectifier is used for the AC power rectifier of the PWM inverter. The input power or diode faults cause theripples of the DC voltage, degradation of the control performance and life shortening of the DC link capacitor.In this paper, the ripple of the DC voltage is mathematically analyzed for the earth fault of input power andopen circuit fault of the diode, respectively. The fault detection and type of fault can be obtained by comparingthe average DC voltage and the instant DC voltage which is sampled with 6 times of grid frequency. Theproposed method can be easily applicable and doesn`t require additional circuit. The experimental and simulationresults are presented to verify the validity of the proposed method.