Daniel Fernandez

Permanent-Magnet Temperature Estimation in PMSMs Using Pulsating High-Frequency Current Injection

The injection of a high-frequency signal in the stator via inverter has been shown to be a viable option to estimate the magnet temperature in permanent-magnet synchronous machines (PMSMs). The variation of the magnet resistance with temperature is reflected in the stator high-frequency resistance, which can be measured from the resulting current when a high-frequency voltage is injected. However, this method is sensitive to d- and q-axis inductance (Ld and Lq) variations, as well as to the machine speed. In addition, it is only suitable for surface PMSMs (SPMSMs) and inadequate for interior PMSMs (IPMSMs). In this paper, the use of a pulsating high-frequency current injection in the d-axis of the machine for temperature estimation purposes is proposed. The proposed method will be shown to be insensitive to the speed, Lq, and Ld variations. Furthermore, it can be used with both SPMSMs and IPMSMs.

PMSM Magnetization State Estimation Based on Stator-Reflected PM Resistance Using High-Frequency Signal Injection

Permanent-magnet (PM) magnetization state estimation in PM synchronous machines (PMSMs) is of great importance for torque control and monitoring purposes. The magnetization state of a PMSM can change due to several reasons, injection of stator current (d-axis or q-axis) and variation of magnet temperature being the primary reasons. PM magnetization state estimation is not easy once the machine is assembled. Methods based on the back electromotive force can be used, but they require that the machine is rotating. This paper analyzes the use of high-frequency signal injection for PM magnetization state estimation in PMSMs. The magnetization state of the PMs in PMSMs affects the stator-reflected PM high-frequency resistance. The stator-reflected PM high-frequency resistance can be estimated by injecting a high-frequency voltage/current using the inverter. The high-frequency signal is superposed on the fundamental excitation used to produce torque, meaning that the method can operate at any speed, including zero speed, and without interfering with the normal operation of the machine.

Wireless permanent magnet temperature & field distribution measurement system for IPMSMs

Permanent magnet (PM) temperature measurement/estimation in permanent magnet synchronous machines (PMSMs) is of great importance for torque control and to prevent PM demagnetization. PM temperature estimation methods can be divided into thermal models, BEMF and pulse/high-frequency signal injection based methods. All of them provide a lumped PM temperature estimation. However, the temperature distribution along the magnet is not uniform, also asymmetries among poles can exist. Analyzing the impact of the temperature variations on the magnet field distribution requires simultaneous measurement of the PM temperature and field distributions. However, this is not easy due to the large amount of temperature and field sensors required, which places significant challenges regarding the sensors integration as well as the signal acquisition and transmission. Most of temperature measurement systems using contact type sensors that have been reported use a reduced amount of sensors and relatively low sampling rates. Furthermore, they do not include field sensors. This significantly limits the analysis that can be realized. This paper presents a wireless PM temperature and field measurement system for PMSMs. The developed system provides PM temperature and field distribution maps for all the poles with high spatial resolution and bandwidth. Uses of the developed system include analysis of the surface and internal PM temperature distribution, PM field distribution, assessment of local demagnetization risks due to hot spots in PMs, as well as development and assessment of new temperature and field distribution estimation methods for PMSMs.

Permanent-Magnet Temperature Distribution Estimation in Permanent-Magnet Synchronous Machines Using Back Electromotive Force Harmonics

Permanent magnet (PM) temperature measurement/estimation in permanent-magnet synchronous machines (PMSMs) is convenient for both torque control and monitoring purposes. Most of the existing methods provide an averaged/punctual temperature. However, PM temperature distribution is not uniform, which can have unexpected adverse effects such as reduced accuracy estimating the torque produced by the machine or local demagnetization e.g., due to hot spots. PM temperature distribution can be measured or estimated. Inner and outer PM surfaces are not visible once the machine is assembled. Therefore, measurement of the PM temperature distribution cannot be realized by visual means. An array of temperature sensors attached to the PM can be used in this case. While this is technically feasible, it is unaffordable in commercial products due to cost and robustness issues. Alternatively, the PM temperature distribution can be estimated. This paper analyzes the use of back electromotive force (BEMF) harmonics to estimate the differential temperature in the PM of a PMSM, i.e., the temperature difference between the hottest and coldest parts of the magnets. Combined with average PM temperature estimation methods, this information can be used to estimate the PM temperature spatial distribution. The proposed method has been developed on an empirical basis.

Comparative Analysis of BEMF and Pulsating High-Frequency Current Injection Methods for PM Temperature Estimation in PMSMs

Permanent magnet synchronous machines performance is highly dependent on the permanent magnets (PMs) temperature. However, PM temperature measurement is not easy and is not normally implemented in standard machines. Alternatively, PM temperature can be estimated. PM temperature estimation methods can be divided into three major groups: thermal model-based methods, BEMF-based methods, and methods based on the injection of some form of high-frequency signal into the stator terminals of the machine. One concern for thermal model-based methods is that the model often needs to be adjusted for each machine design and application, knowledge of the machine geometry, materials, and cooling system being, therefore, required. On the contrary, BEMF methods and methods based on high-frequency signal injection estimate the magnet temperature from measurable electrical variables, knowledge of the geometry or cooling system not being required. Though they use the same type of signals, BEMF and high-frequency signal injection methods present relevant differences. This paper realizes a comparative analysis of both methods. Physical principles, performance, and implementation will be addressed.

Permanent magnet temperature distribution estimation in PMSMs using BEMF harmonics

PM temperature measurement/estimation in permanent magnet synchronous machines (PMSMs) is convenient both for torque control and monitoring purposes. Most of existing methods provide and averaged/punctual temperature. However, PM temperature distribution is not uniform, which can have unexpected adverse effects like reduced accuracy estimating the torque produced by the machine or local demagnetization e.g. due to hot spots. PM temperature distribution can be measured or estimated. Since the PMs are not visible, measuring the PM temperature distribution would require an array of temperature sensors attached to the PM. While this is technically feasible, it is unaffordable in commercial products due to cost and robustness issues. Alternatively, the PM temperature distribution can be estimated. The paper analyzes the use of BEMF harmonics to estimate the differential temperature in the PM, i.e. the temperature difference between the hottest and coldest parts of the magnets. Combined with average PM temperature estimation methods, this information can be used to estimate the PM temperature spatial distribution.

PMSM magnetization state estimation based on stator-reflected PM resistance using high frequency signal injection

Permanent magnet (PM) magnetization state estimation in Permanent Magnet Synchronous Machines (PMSM) is of great importance for torque control and monitoring purposes. The magnetization state of a PMSM can change due to several reasons, injection of stator current (d or q-axis) and variation of magnet temperature being the primary reasons. PM magnetization state estimation is not easy once the machine is assembled. Methods based on the back-EMF (BEMF) can be used, but they require that the machine is rotating. This paper analyzes the use of high frequency signal injection for PM magnetization state estimation in PMSMs. The magnetization state of the PMs in PMSMs affects the stator-reflected PM high frequency resistance. The stator-reflected PM high frequency resistance can be estimated by injecting a high frequency voltage/current using the inverter. The high frequency signal is superposed on the fundamental excitation used to produce torque, meaning that the method can operate at any speed, including zero speed, and without interfering with the normal operation of the machine.1.

Permanent magnet temperature estimation in PM synchronous motors using low cost hall effect sensors

Knowledge of the permanent magnet (PM) temperature in PM synchronous machines (PMSMs) is of great importance both for control and monitoring purposes. Increase in PM temperature during motor operation can degrade the magnetic flux strength and consequently the machines torque production capability, also can cause irreversible demagnetization of the PM. Direct measurement of the PM temperature is not viable in practice, due to both cost and reliability issues. Indirect PM temperature estimation methods recently studied can require knowledge of thermal or electrical model parameters or can have undesired effects on motor operation. In this paper, the feasibility of using low cost hall-effect sensors for PM temperature estimation is investigated. Hall sensors are present for detecting the initial position of the rotor in majority of PMSM applications for which incremental encoders are used for control. The proposed method can therefore be implemented with low or no additional cost. Experimental results on two IPMSMs show that the method is capable of providing non-invasive estimation of the PM temperature without a priori motor parameter information for monitoring and protection against excessive increase in temperature.1

Permanent Magnet Temperature Estimation in PM Synchronous Motors Using Low-Cost Hall Effect Sensors

Knowledge of the permanent magnet (PM) temperature in PM synchronous machines (PMSMs) is of great importance both for control and monitoring purposes. Increase in PM temperature during motor operation can degrade the magnetic flux strength and consequently the machines torque production capability, and can also cause irreversible demagnetization of the PM. Direct measurement of the PM temperature is not viable in practice due to both cost and reliability issues. Indirect PM temperature estimation methods recently studied require knowledge of thermal or electrical model parameters or can have undesired effects on motor operation. In this paper, the feasibility of using low-cost Hall-effect sensors for PM temperature estimation is investigated. Hall sensors are present for detecting the initial position of the rotor in majority of PMSM applications for which incremental encoders are used for control. The proposed method can, therefore, be implemented with low or no additional cost. Experimental results on two interior PMSMs show that the method is capable of providing noninvasive estimation of the PM temperature without a priori motor parameter information for monitoring and protection against excessive increase in temperature.

Sensitivity Analysis of High-Frequency Signal Injection-Based Temperature Estimation Methods to Machine Assembling Tolerances

The injection of a high frequency signal in the stator via inverter has been proven to be a viable option to estimate the magnet temperature in permanent magnet synchronous machines (PMSMs). Injection of a pulsating d-axis current is especially appealing, as it is insensitive to the speed, Ld and Lq inductance variations. Furthermore, it is suitable both for interior PMSMs (IPMSMs) and surface PMSMs (SPMSMs). Regardless of its promising characteristics, there is a number of issues which can reduce its accuracy, including machine assembling tolerances and rotor lamination grain orientation, which might need to be considered. This paper analyzes the sensitivity of temperature estimation using pulsating d-axis high frequency current injection to rotor eccentricities, PM assembling tolerances and lamination grain orientation. Preliminary results indicate that these issues can have a non-negligible impact on the accuracy of the method1.