Measurement Of Current Derivative Research Articles

Fundamental PWM Excitation Based Rotor Position Estimation for a Dual Three-Phase Permanent Magnet Synchronous Machine

Two rotor position estimation methods for a dual three-phase (DTP) permanent magnet synchronous machine (PMSM) are investigated in this article, where the rotor position is estimated by exploiting the saliency of the motor through the phase current derivative measurement during the fundamental PWM excitation of a standard six-phase two-level inverter. It is found that in a DTP PMSM, the wide speed range rotor position estimation is possible not only in the torque-producing subspace, but also in the harmonic subspace. The principle and practical implementation of the methods are explained in details. The experimental results verify the effectiveness of the proposed rotor position estimation methods.

Synchronous Reluctance Motor Parameter and State Estimation Using Extended Kalman Filter and Current Derivative Measurement

The synchronous reluctance motor is becoming a very attractive alternative to the ac induction machine. This is due to the lack of rare-earth metals in their construction and a higher efficiency, which was brought about by recent progress in rotor design. However, in order to achieve an efficient and low-cost operation of the synchronous reluctance motor drive, an adaptive sensorless algorithm should be utilized to cope with machine nonlinearities. This article describes an adaptive observer, which can provide an estimation of rotor position and speed, as well as core loss and inductance parameters. A modified pulsewidth modulation (PWM) switching scheme and a current derivative measurement method are proposed, together with an extended Kalman Filter design. Experimental results are shown to demonstrate the method performance and feasibility.

A Hybrid Sensorless Controller of an Interior Permanent Magnet Synchronous Machine Using Current Derivative Measurements and a Sliding Mode Observer

The ability of current-derivative based speed and position estimation of IPMSMs over a full speed range has recently been demonstrated. However, at high-speeds, the modulation index becomes limited because the extension of the zero-voltage vectors and current waveforms become distorted. This article proposes a hybrid position and speed estimation technique which uses current derivatives at the first active-voltage vector during each pulsewidth modulation (PWM) switching period for enhancing the performance of a sliding mode observer at low and very low speeds. This article presents the theoretical analysis and experimental evaluation of the proposed sensorless method for an IPMSM over a full speed range from zero to rated speed. The experimental results have shown a significant improvement in speed and position estimation accuracy at low speeds and a considerable reduction of the current distortion over the full speed range, compared to the existing fundamental PWM excitation sensorless control methods.

Current derivative measurement using closed‐loop hall‐effect current sensor

This paper discusses a method of the current derivative measurement using a standard closed-loop Hall-effect current sensor. The proposed method can operate with PWM-driven inverters and provides the estimation of motor-phase inductances required for an encoderless or self-sensing control. The method is based on the current transformation feature of the closed-loop sensor where a sensing inductor is connected in series with the measuring resistor. The voltage drop across the inductor is proportional to the current derivative. The experimental results are demonstrated that the measurement of the current derivative can be performed under a good accuracy, though the measurement should be executed while inverter is in the steady-state condition.

A Modified Sensorless Control Scheme for Interior Permanent Magnet Synchronous Motor Over Zero to Rated Speed Range Using Current Derivative Measurements

This paper proposes a modified sensorless control technique for an interior permanent magnet synchronous motor over its full-speed range based on current derivative measurements and fundamental pulsewidth modulation excitation (FPE). The proposed method employs measurement of the current derivative at only one active-voltage vector at low speeds, and at one active-voltage vector and one zero-voltage vector at medium and high speeds during each pulsewidth modulation (PWM) cycle, in contrast to two active- and two zero-voltage vectors in the conventional FPE method. The theoretical analysis is developed based on the three-phase model of the machine. The rotor position and speed are estimated at PWM frequency. In addition, the selection voltage vectors for current derivative measurement as well as the pulse stretching scheme for extending and compensating the selected voltage vectors is proposed in order to improve the accuracy of the current derivative measurement and to minimize the current distortion. The experimental results show that the proposed method results in a considerable improvement of the estimation accuracy at low speeds, a significant reduction of current distortion compared to the conventional FPE method and a full-speed range operation from no load to full load.

Characteristics of the most intense lightning storm ever recorded at the CN Tower

Lightning strikes to the CN Tower have been optically observed since 1978. In 1990, five independent systems started to operate to simultaneously record parameters of lightning strikes to the tower, including the time derivative of the current, the associated electric and magnetic fields, and the channel optical characteristics. On August 24, 2011, during an unusually severe lightning storm, video records showed that the CN Tower was struck with 52 lightning flashes within 84min and 6.9s. Thus, this storm produced, on average, a flash to the tower every 99s. However, the CN Tower lightning current derivative measurement system only recorded 32 flashes, which were perfectly time-matched with 32 of the 52 video-recorded flashes. It is found that the current derivative measurement system recorded every video-recorded flash that contained at least one return stroke. Based on the analysis of video records, it is noted that each of the storm's 52 flashes contains an initial-stage current, proving that all flashes were upward initiated. This unique CN Tower storm – the most intense ever recorded at the tower – is here thoroughly analyzed, based on video and current records. The inter-flash time within the storm is found to vary between 10.6s and 274s, with an overall average of 98s. It is also found that the inter-flash time between successive non-return-stroke flashes is on average 64% longer than that for successive flashes containing return strokes. Statistical analysis of video and current data clearly reveals that the time duration of flashes containing initial-stage currents and return strokes is on average 27% longer than that of flashes that only have initial-stage currents. Furthermore, it is important to note that the time duration of the initial-stage current in flashes containing no return strokes is on average 76% longer than that in flashes containing return strokes. Therefore, it is possible to conclude that if the time duration of the initial-stage current in a flash is long enough, resulting in large charge transfer, then there is less probability of having return strokes following it. The 32 current-recorded flashes contain a total of 156 return strokes, with an average multiplicity of 4.875. It is worth mentioning that during one decade, 1992–2001, the CN Tower current derivative measurement system only recorded 478 return strokes, demonstrating that the number of return strokes recorded at the tower within about 84min is close to one third of those recorded at the tower during one decade. This finding clearly shows the great value and rarity of the presented extensive lightning current derivative data. Only one of the 32 current-recorded flashes is proved to be positive with a single return stroke. Based on current records, out of a total of 124 inter-stroke time intervals, 94% are found to be within 200ms, with an overall inter-stroke time average of 68.1ms. The maximum inter-stroke time recorded during this storm is 726.3ms, the longest ever recorded at the CN Tower.

Indirect Measurement of Motor Current Derivatives in PMSM Sensorless Drives

Motor current derivatives contain useful information for control algorithms, especially in sensorless electric drives. The measurement of motor current derivatives in electric motors supplied by voltage source inverter can be performed using di/dt transducers. However, in such a solution additional sensors have to be installed, e.g. Rogowski coils. Another approach is to measure current derivatives indirectly – by oversampling the motor currents. In such a method special attention must be paid to determination of current sampling instants. Measurement triggering times must be recalculated in each voltage modulation period with regard to transistors switching. The paper presents different current sampling approaches. Considered oversampling algorithms were experimentally tested in sensorless PMSM drive. The impact of different sampling approaches on the accuracy of rotor position estimation has been discussed. DOI: http://dx.doi.org/10.5755/j01.eee.20.7.8019

Determination of reflection coefficients at the top and bottom of elevated strike objects struck by lightning

In this paper, we present an analysis of lightning return stroke currents along an elevated strike object. We derive closed form expressions, both in the frequency domain and in the time domain, to calculate the lightning current at any height along a strike object taking into account reflections at the top and at the bottom. The frequency dependence of reflection coefficients is taken into account. We also derive an expression to calculate the reflection coefficient as a function of frequency at the bottom of the lightning strike object from two currents measured at different heights along the strike object. We show that, if the current and its time derivative overlap with reflections at the top or bottom of the strike object, it is impossible to derive the reflection coefficient at the top of the strike object exactly from any number of simultaneous current measurements. We propose an extrapolation method to estimate this reflection coefficient. We propose a second method to calculate the top reflection coefficient from just one current derivative measurement if the current derivative and its reflections do not overlap significantly. We apply the proposed methodology to experimental data obtained on Peissenberg Tower (Germany) consisting of lightning currents measured at two heights. The results suggest that the reflection coefficient at ground level can be considered as practically constant in the frequency range 100 kHz to 800 kHz. Although the estimated ground and top reflection coefficients are in good overall agreement with values found in the literature, the estimated values for the top reflection coefficient from the extrapolation method are somewhat lower than those found employing the current derivative method; the differences are discussed.