Chan-Hee Choi

Deadbeat-Direct Torque and Flux Control of Interior Permanent Magnet Synchronous Machines With Discrete Time Stator Current and Stator Flux Linkage Observer

This paper presents a discrete time deadbeat-direct torque and flux controller (DB-DTFC) for interior permanent magnet synchronous machines (IPMSMs). A Gopinath-style discrete time flux linkage observer is developed which contains two different flux estimation methods based on current and voltage models for flux linkage. This observer produces correctly estimated flux linkages needed for accurate DB-DTFC implementation. In order to eliminate the sampling delay due to a characteristic of digital control computation, a complex vector model-based rotor reference frame current observer is also developed. Combining the discrete time current and flux linkage observers, the correct single time step (deadbeat) air-gap torque and stator flux linkage control at the (constant) switching frequency is achieved and experimentally evaluated.

Wide-Speed Direct Torque and Flux Control for Interior PM Synchronous Motors Operating at Voltage and Current Limits

This paper proposes a wide-speed direct torque and flux control method associated with the inverter voltage and current constraints of interior permanent-magnet synchronous motors. The proposed approach has potential advantages controlling torque and flux linkage at the voltage and current limits, since no integrators are employed for torque control or flux weakening. The transition between the non-limited operation and maximum voltage modulation can be achieved automatically without modifying the control law. To confirm this, we provide a graphical and analytical analysis that naturally leads to a unique stator voltage vector selection on the hexagon. The proposed controller can maximize the available inverter voltage and generate a higher output torque than conventional current vector controllers at high speeds. The method developed in this paper also retains the beneficial features of classical direct torque control, such as its fast dynamics and direct manipulation of the stator flux linkage for flux weakening.

Pulsating Signal Injection-Based Axis Switching Sensorless Control of Surface-Mounted Permanent-Magnet Motors for Minimal Zero-Current Clamping Effects

In this paper, we propose an injection-based axis switching (IAS) sensorless control scheme using a pulsating high-frequency (HF) signal to minimize position detection error and velocity estimation ripple resulting from the zero-current-clamping (ZCC) effect for surface-mounted permanent-magnet motors. When a pulsating carrier-signal voltage is injected in an estimated synchronous frame, the envelope of the resulting HF current measured in the stationary reference frame follows an amplitude-modulated pattern. Using this information, the IAS technique allows one to avoid multiple zero crossings of HF currents by adjusting the current phase angle according to the load condition. At no-load condition, the pulsating voltage is injected only on the d-axis, while the d-axis current is controlled to a certain nonzero value. Under a load condition, the injection voltage is switched to the q-axis, while the d -axis current drops back to zero. Thus, the proposed sensorless control enforces a much better estimation performance in a region of ZCC without a predefined offline commissioning test than the standard pulsating injection scheme. Experiments illustrate the effectiveness of the proposed method in suppressing the estimation error caused by the ZCC disturbance and in extending the system bandwidth.

Compensation of Zero-Current Clamping Effects in High-Frequency-Signal-Injection-Based Sensorless PM Motor Drives

This paper proposes an online compensation strategy for the unwanted disturbance voltage resulting from the zero- current clamping effect for high-frequency-signal-injection-based sensorless control schemes. We derive an analytical model that reveals intrinsic characteristics of the zero clamping effect for high- frequency signal injection. The model in this form is subsequently incorporated into the development of a specialized offline commissioning test to find motor inductances and a voltage distortion factor. From the sensitivity analysis of the effect on magnetic saturation, we confirm that the compensation error due to saturation has little negative impact on the proposed compensation method. The compensation result leads to an accurate position estimate in the zero-current clamping region. The proposed scheme does not rely on a complicated lookup table. Experiments demonstrate the superiority of the proposed method in suppressing the voltage distortions caused by the zero-current clamping effect.

Deadbeat direct torque and flux control of interior permanent magnet machines with discrete time stator current and stator flux linkage observer

This paper presents a discrete time deadbeat-direct torque and flux controller (DB-DTFC) for interior permanent magnet synchronous machines (IPMSMs). A Gopinath-style discrete time flux linkage observer is developed which contains two different flux estimation methods based on current and voltage models for flux linkage. This observer produces correctly estimated flux linkages needed for accurate DB-DTFC implementation. In order to eliminate the sampling delay due to a characteristic of digital control computation, a complex vector model-based rotor reference frame current observer is also developed. Combining the discrete time current and flux linkage observers, the correct single time step (deadbeat) air-gap torque and stator flux linkage control at the (constant) switching frequency is achieved and experimentally evaluated.

Voltage disturbance state-filter design for precise torque-controlled interior permanent magnet synchronous motors

This paper presents the development and implementation of an online voltage disturbance estimator to achieve the precise torque control of interior permanent magnet synchronous motors (IPMSMs) over a wide operating region. Different design methodologies for disturbance extraction are analyzed using a complex vector frequency-response function (FRF) and evaluated in terms of estimation accuracy. The proposed design has a form of the state-filter based on a Luenburger-style closed-loop stator current vector observer. We provide an accurate torque control strategy with the estimated disturbance, which is based on a torque command manipulation. In addition, the developed estimator is proven to work with any torque control schemes incorporating even with numerous lookup tables. The proposed disturbance estimation scheme has the advantage of being general and readily applicable to a wide range of other systems, such as PWM converters and symmetric machines.

Deadbeat-direct torque and flux control for interior PM synchronous motors operating at voltage and current limits

This paper proposes a wide-speed deadbeat-direct torque and flux control (DB-DTFC) method associated with inverter voltage and current constraints of interior permanent-magnet synchronous motors (IPMSMs). The proposed approach has potential advantages controlling torque and flux linkage at voltage and current limits since integrators are not involved for torque control or flux weakening. An automatic transition between non-limited operation and six-step modulation can be achieved without modifying the control law. To support this, we provide a graphical and analytic analysis that naturally leads to a unique stator voltage vector selection on the hexagon. The proposed controller can maximize the available inverter voltage and generate higher output torque than conventional current vector controllers at high speeds. The method developed in this paper also maintains beneficial DTC features, such as fast dynamics and direct manipulation of the stator flux linkage for flux weakening.

Compensation of Zero-Current Clamping Effects for Sensorless Drives Based on High-Frequency Signal Injection

This paper proposes an on-line compensation strategy of the unwanted disturbance voltage due to the zero current clamping effect for high-frequency-signal-injection based sensorless control schemes. An analytical model is derived which reveals intrinsic characteristics of the zero clamping effect for the high frequency signal injection. The model in this form is subsequently incorporated into the development of a specialized off-line commissioning test to find motor inductances and a voltage distortion factor. From the sensitivity analysis of the effect on the magnetic saturation, it is confirmed that the compensation error due to saturation has little negative impact on the proposed compensation method. The compensation result leads to an accurate position estimate during zero-current clamping region and the proposed scheme does not rely on a complicated look-up table. Experiments demonstrate the superiority of the proposed method in suppressing the voltage distortions caused by the zero-current clamping effect

Pulsating Signal Injection-Based Sensorless Control of PMSM Using Injection Axis Switching Scheme without Additional Offline Commissioning Test

In this paper, we propose an injection axis switching (IAS) sensorless control scheme using a pulsating high-frequency (HF) signal to minimize the position detection error and the velocity estimation ripple due to the zero current clamping (ZCC) effect for permanent magnet synchronous motors (PMSMs). When a pulsating carrier-signal voltage is injected in an estimated synchronous frame, the envelope of the resulting HF current measured in the stationary reference frame follows an amplitude-modulated pattern. Using this information, the IAS technique allows avoiding multiple zero-crossings of HF currents by adjusting the current phase angle according to the load condition. At no-load, the pulsating voltage is injected only on the d-axis while the d-axis current is controlled to a certain nonzero value. Under the loaded condition, the injection voltage is switched to the q-axis and the d-axis current drops back to zero. Thus, the proposed sensorless control enforces a much better estimation performance during ZCC region without a predefined offline commissioning test than the standard pulsating injection scheme. The performance of the proposed approach is demonstrated by experimental results.

Pulsating Signal Injection-Based Axis Switching Sensorless Control of PMSM for Minimal Zero Current Clamping Effects

This paper proposes an injection axis switching (IAS) sensorless control using a pulsating HF signal to minimize ZCC effect for permanent magnet synchronous motors (PMSM). When a pulsating carrier-signal voltage is injected in a synchronous frame, the envelope of the resulting HF current measured in the stationary reference frame follows an oscillating pattern with a maximum to zero magnitude. Taking this effect into account, multiple zero-crossings of HF currents around the zero-crossing region can be avoided by adjusting the current phase angle according to the load condition. For this purpose, we develop an injection axis switching scheme according to the load condition. At no-load, the pulsating voltage is injected only on the d-axis while the d-axis current is controlled to a certain nonzero value. Under the load condition, the injection voltage is switched to the q-axis and the d-axis current drops back to zero. Thus, the proposed sensorless control permits the HF current magnitude to be zero at every zero-crossing point. The minimization result leads to an accurate position estimate during ZCC region and the proposed scheme does not require any additional test prior to start-up. Experiments demonstrate the superiority of the proposed method in suppressing the voltage distortions caused by ZCC effect.