High-frequency Square-wave Voltage Injection Research Articles

A Square-Wave Voltage Injection Sensorless Control for Dual Three-Phase IPMs Robust to Open-Circuit Faults

Conventional sensorless control methods fail to estimate the accurate rotor position in case of open circuit faults (OCFs) in dual three-phase interior permanent-magnet machine (DT-IPM) drives, resulting in poor stability of the system. OCFs regularly contain open-phase faults (OPFs) and open-switch faults (OSFs). However, the current under OSFs can be considered as a combination of a one-half period of health status with a normal current and the other half period of OPF with zero current. Consequently, OSF is regarded as a generalized OPF. Based on the general solution to OCFs, a novel high-frequency (HF) square-wave voltage injection (HFSVI) sensorless control method is proposed for DT-IPMs at low speed to improve the fault-tolerance ability, which is robust to both OPFs and OSFs. With the help of vector space decomposition, the HFSVI is implemented in the decoupling space, where the effects of OCFs, e.g., varying amplitude and extra negative-sequence component of responded HF currents, can be compensated by HF currents in both αβ- and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</i> -subspaces in the rotor position estimation module. Compared with the non-compensation method, the proposed one is robust to parameter mismatches and only increases the computation burden slightly. Finally, experiments on a prototyped DT-IPM verify the proposed method.

Position Sensorless Control of Dual Three-Phase IPMSM Drives With High-Frequency Square-Wave Voltage Injection

Dual three-phase interior permanent-magnet synchronous motor (IPMSM) drives have received more attention by the merits of better fault-tolerant capability and lower torque ripples. To improve the reliability of the system against failures in position sensor, it is necessary to investigate the position estimation method for dual three-phase IPMSM drives. The high-frequency (HF) signals injection is utilized for position estimation in three-phase IPMSM drives during low-speed operation region. However, the torque ripples are inevitable owing to the mixing of fundamental and HF components in the same control space for three-phase IPMSM drives. In this paper, the position sensorless control method has been proposed by injecting HF square-wave voltage in the harmonic subspace for the dual three-phase IPMSM drives. Since the harmonic subspace is decoupled from the torque subspace, the torque disturbance can be mitigated well with the proposed HF signal injection based position sensorless method. Moreover, the digital filters in signal extraction and current feedback can be avoided and the signal separation process becomes easy with the proposed method. The experiments have been conducted to validate the performance of the proposed method.

Novel Random High-Frequency Square-Wave and Pulse Voltage Injection Scheme-Based Sensorless Control of IPMSM Drives

Signal injection-based sensorless control schemes for interior permanent magnet synchronous machine (IPMSM) drives at zero and low speed are generally troubled by the audible noise induced by the fixed-frequency injected signals and the control performance sensitive to voltage distortions. Aiming at that, a novel random high-frequency square-wave and pulse voltage injection (RHFSPVI) with novel signal demodulation method-based sensorless control of IPMSM drives is proposed. First, the power spectra density (PSD) analyses of conventional high-frequency square-wave voltage injection (HFSVI) and high-frequency pulse voltage injection (HFPVI) methods are carried out. On the basis of the analysis results, the simple form of random square-wave and pulse voltage injection is analyzed and designed to eliminate discrete harmonics in the current PSD spectrum for the audible noise reduction. Moreover, a signal demodulation scheme matched with the proposed injected form is designed to prevent the impact of voltage distortions on the position estimation accuracy. The capability of the proposed sensorless control scheme is verified on a 750-W IPMSM drive platform.

Analysis on Position Estimation Error of Sensorless Control Based on Square-Wave Injection for SynRM Caused by Dead-Time Harmonic Current

Sensorless control based on high-frequency square-wave voltage injection (HFSVI) is one of the most common sensorless control methods for synchronous reluctance motors (SynRMs). However, the injection frequency for SynRMs cannot be too high due to various factors. As the injection frequency decreases, the dead-time harmonic current will greatly affect the separation of high frequency signals. This paper analyzes the effect of dead-time harmonic current on the HFSVI-based sensorless control performance of SynRMs and proposes a source of position estimation error. Then, a dead-time compensation method suitable for filter-free HFSVI is proposed. It can estimate current vector spatial orientation without any low-pass filters (LPFs) and effectively compensate the impact of dead-time setting. The correctness of the theoretical analysis and the feasibility of the proposed methods in this paper are verified by experiments.

Sensorless Control for SynRM Drives Using a Pseudo-Random High-Frequency Triangular-Wave Current Signal Injection Scheme

This article proposes a pseudo-random high-frequency triangular-wave current signal injection (PR-HFTCI) based sensorless control scheme for synchronous reluctance motor (SynRM) drives at zero-low speed domain to suppress the high-frequency (HF) loss and the HF audible noise which are introduced by the significant nonlinearities of SynRMs and the traditional constant amplitude HF square-wave voltage injection method. The pseudo-random HF triangular-wave current signal with random frequency and random phase is injected to eliminate the discrete spectrum of the current power spectra density (PSD) and the corresponding current PSD analysis is performed to evaluate it. In addition, the HF component amplitude of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis voltage reference can be adjusted adaptively with the variation of load to maintain the HF current amplitude constant, it is easy to implement and does not require any extra regulator and signal processing. Hence, the HF loss and the HF torque ripple can be effectively reduced under the heavy load. Finally, the effectiveness and the correctness of the proposed PR-HFTCI based sensorless control scheme are validated with experiments on a 1.5-kW SynRM drive platform.

Minimization of Additional High-Frequency Torque Ripple for Square-Wave Voltage Injection IPMSM Sensorless Drives

The high-frequency (HF) square-wave voltage injection sensorless control method will bring additional HF torque ripple to interior permanent magnet synchronous motor (IPMSM). Focused on this problem, this article analyzes the relationship between the HF response current and the HF torque ripple resulting from HF square-wave voltage injection. It is concluded that when the fluctuation direction of HF response current is vertical to the stator current vector direction at the maximum torque per ampere (MTPA) operating point, the resulting HF torque ripple reaches its minimum. Based on this conclusion, a novel HF square-wave voltage injection sensorless control method is proposed in this article, which can realize the sensorless control and minimize the HF torque ripple at the same time. The injection angle of HF square-wave voltage in the estimated synchronous rotating reference frame is adjusted in real time according to the operating conditions, so that the HF response current always fluctuates along the vertical direction of the stator current vector at the MTPA operating point. Besides, the corresponding demodulation method of the rotor position estimation error is illustrated. Finally, the experiments are performed on a 20-kW IPMSM platform and the results verify the effectiveness of the proposed method.

Design of a Low-Order FIR Filter for a High-Frequency Square-Wave Voltage Injection Method of the PMLSM Used in Maglev Train

In position sensorless control based on a high-frequency pulsating voltage injection method, filters are used to complete the extraction of high-frequency response signals for position observation. A finite impulse response (FIR) filter has the advantages of good stability and linear phase. However, the FIR filter designed by using traditional methods has a high order which will cause a large time delay. This paper proposes a low-order FIR filter design method for a high-frequency signal injection method in the permanent magnet linear synchronous motor. Based on the frequency characteristics of the current signal, the requirement that the FIR filter needs to meet were analyzed. According to the amplitude–frequency characteristic of the FIR filter, these requirements were converted into constraint equations. By solving these equations, the coefficient of the FIR filter could be obtained. The simulation and experiment results showed the effectiveness of this low-order FIR filter.

High Frequency Square-Wave Voltage Injection Scheme-Based Position Sensorless Control of IPMSM in the Low- and Zero- Speed Range

In this paper, a new sensorless control scheme with the injection of a high-frequency square-wave voltage of an interior permanent-magnet synchronous motor (IPMSM) at low- and zero-speed operation is proposed. Conventional schemes may face the problems of obvious current sampling noise and slow identification in the process of magnetic polarity detection at zero speed operation, and the effects of inverter voltage error on the rotor position estimation accuracy at low speed operation. Based on the principle analysis of d-axis magnetic circuit characteristics, a method for determining the direction of magnetic polarity of d-axis two-opposite DC voltage offset by uninterruptible square-wave injection is proposed, which is fast in convergence rate of magnetic polarity detection and more distinct. In addition, the strategy injects a two-opposite high-frequency square-wave voltage vectors other than the one voltage vector into the estimated synchronous reference frame (SRF), which can reduce the effects of inverter voltage error on the rotor position estimation accuracy. With this approach, low-pass filter (LPF) and band-pass filter (BPF), which are used to obtain the fundamental current component and high-frequency current response with rotor position information respectively in the conventional sensorless control, are removed to simplify the signal process for estimating the rotor position and further improve control bandwidth. Finally, the experimental results on an IPMSM drive platform indicate that the rotor position with good steady state and dynamic performance can be obtained accurately at low-and zero-speed operation with the sensorless control strategy.

Noise Spectrum Shaping of Random High-Frequency-Voltage Injection Based on Markov Chain for IPMSM Sensorless Control

The high-frequency (HF) voltage injection method can accurately estimate the rotor position of an interior permanent magnet synchronous motor (IPMSM) at low speed and zero speed. However, the fixed injection frequency for the traditional HF-voltage injection method will produce loud audible noise. The random HF-voltage injection method has a spread spectrum, which can reduce the audible noise. However, random HF voltages are controlled by constant probability rules, and it is inevitable that continuous multiple random numbers are larger or smaller than the mathematical expectation in the digital implementation, which will lead to spectrum concentration of the HF current. Thus, the random HF-voltage injection method cannot reduce the audible noise effectively. A novel random HF square-wave voltage injection method for an IPMSM based on the Markov chain (MC) is proposed to reduce the audible noise. The transition of the injected HF square-wave voltages obeys the MC instead of constant probability rules, which not only can shape the power spectrum of the HF current but also enable the explicit control of the HF current time-domain performance to reduce the audible noise. In order to reduce the position error caused by the phase mismatch between the HF current and the demodulation signal, an enhanced signal processing method is presented. Then, the power spectra density of the proposed method is analyzed to verify the effectiveness. Finally, the correctness and the effectiveness of the proposed method are verified by experiment on a 2.0-kW IPMSM drive platform.

IPMSM Sensorless Control Using High-Frequency Voltage Injection Method With Random Switching Frequency for Audible Noise Improvement

A high-frequency (HF) voltage injection method can accurately estimate the rotor position of an interior permanent magnet synchronous motor at low speed. However, the fixed injection frequency for the traditional HF voltage injection method will produce a loud audible noise that limits the actual application of HF voltage injection method. In order to reduce the audible noise, a novel HF square-wave voltage injection method with the random switching frequency is proposed in this article. The frequency of the injected HF voltage varies with the random switching frequency, so it can effectively spread power spectrum caused by HF current and pulsewidth modulation (PWM), which will effectively reduce the audible noise caused by the HF current and PWM. Additionally, the power spectral density of the HF current based on the proposed method is analyzed to verify the effectiveness in reducing audible noise. Then, a corresponding demodulation method for induced HF current is presented. Finally, the experimental results show that the proposed method has continuous spectra and the audible noises can be suppressed significantly.

A Novel Sensorless Rotor Position Estimation Method for PMSM Based on High-Frequency Square-Wave Voltage Injection with Less Iron Loss

A novel sensorless rotor position estimation method for permanent magnet synchronous machine (PMSM) based on high-frequency square-wave (HFSW) voltage injection has been proposed in the article. Comparing with the existing HFSW voltage injection schemes, the proposed method features a unipolar injection into the estimated synchronous reference frame which can decrease the energy loss resulting from HFSW injection and hence improve the system efficiency. A practical calculation method based on the co-simulation platform integrating Matlab and finite-element analysis (FEA) tools are also proposed in the article to study and compare the energy loss resulting from different HF injection schemes. Both simulation and experimental verification are conducted in the article to verify the feasibility of the proposed strategy.

Square-Wave Voltage Injection Algorithm for PMSM Position Sensorless Control With High Robustness to Voltage Errors

Rotor position estimated with high-frequency (HF) voltage injection methods can be distorted by voltage errors due to inverter nonlinearities, motor resistance, and rotational voltage drops, etc. This paper proposes an improved HF square-wave voltage injection algorithm, which is robust to voltage errors without any compensations meanwhile has less fluctuation in the position estimation error. The average position estimation error is investigated based on the analysis of phase harmonic inductances, and deduced in the form of the phase shift of the second-order harmonic inductances to derive its relationship with the magnetic field distortion. Position estimation errors caused by higher order harmonic inductances and voltage harmonics generated by the SVPWM are also discussed. Both simulations and experiments are carried out based on a commercial PMSM to verify the superiority of the proposed method and the investigations in this paper.

Pseudo-Random High-Frequency Square-Wave Voltage Injection Based Sensorless Control of IPMSM Drives for Audible Noise Reduction

High frequency (HF) signal injection is an effective sensorless control scheme for interior permanent-magnet synchronous motor (IPMSM) drives to achieve low and zero speed operation. However, the audible noise produced by the injected HF signal is often very shrill and harsh to hear, which restricts the actual application. In order to reduce the audible noise, a novel pseudo-random HF square-wave voltage injection scheme is proposed in this paper. The HF voltages with two different frequencies are randomly injected into the estimated rotor reference frame cycle by cycle, and a corresponding signal demodulation method for extracting the rotor position information is presented. Based on the principle analysis of this random frequency injection scheme, the digital time-delay effect in HF signal is considered and a compensation method for signal demodulation is proposed, which is effective in reducing position estimation error. Then, the power spectra density (PSD) in fixed frequency and pseudo-random frequency injection schemes are compared both theoretically and experimentally. The distribution of HF voltage and current PSD is extended by using the proposed injection scheme. Finally, this sensorless control method is verified by simulation and experiment on a 2.2-kW IPMSM drive platform.