Low-harmonic trajectory synthesis using trajectory pattern method (TPM) for high-speed and high-precision machinery

In high-speed and high-precision machinery, trajectories with high-frequency harmonic content are one of the main sources of reduction of operational precision. Trajectories with high-frequency harmonic content generally demand even higher-harmonic actuating forces/torques due to the nonlinear dynamics of such systems, which may excite natural modes of vibration of the system and/or be beyond the dynamic response limitation of the actuation devices. In this paper, a global interpolation algorithm that uses the trajectory pattern method (TPM) for synthesizing low-harmonic trajectories is presented. The trajectory synthesis with the TPM is performed with a prescribed fundamental frequency and continuous jounce boundary condition, which would minimize the number of high-harmonic components in the required actuation forces/torques and avoid excitation of the system modes of vibration. The minimal curvature variation energy method, Lagrange multiplier method, and contour error control are used to obtain smooth kinematic profiles and satisfy the trajectory accuracy requirements. As an example, trajectory patterns that consist of a fundamental frequency sinusoidal time function and its first three harmonics are used to synthesize the desired trajectories for a selected dynamic system. The synthesized trajectories are shown to cause minimal system vibration during its operation. A comparison with a commonly used trajectory synthesis method clearly shows the superiority of the developed TPM-based approach in reducing vibration and demand on the actuator dynamic response, thereby allowing the system to operate at higher speeds and precision.

DC-link Current Harmonic Mitigation via Phase-shifting of Carrier Waves in Paralleled Inverter Systems

DC-connected parallel inverter systems are gaining popularity in industrial applications. However, such parallel systems generate excess current ripple (harmonics) at the DC-link due to harmonic interactions between the inverters in addition to the harmonics from the PWM switching. These DC-link harmonics cause the failure of fragile components such as DC-link capacitors. This paper proposes an interleaving scheme to minimize the current harmonics induced in the DC-link of such a system. The results show that when the carrier waves of the two inverters are phase-shifted by 90° angle, the maximum high-frequency harmonic ripple cancellation occurs, which reduces the overall RMS value of the DC-capacitor current.The outcome of this proposed solution is a cost-effective DC-harmonics mitigating strategy for the industrial designers to practically configuring multi-inverter systems, even when most of the drives are not operating at rated power levels. Experimental and simulation results presented in this paper verify the effectiveness of the proposed carrier-based phase-shifting scheme for two different configurations of common DC connected multi-converter systems.

Effect of high frequency harmonic voltage on the performance of line start permanent magnet synchronous motor

Purpose A large number of high-frequency harmonic voltages exist in the output voltage of the inverter, which will affect the performance of the motor. The purpose of this paper is to obtain the influence of high frequency harmonic voltage on the performance of the line start permanent magnet synchronous motor (LSPMSM) and reveal the mechanism of influence. The research results can provide help for the design of LSPMSM driven by inverter drives. Design/methodology/approach First, the actual output voltage data of the inverter is collected, and then the fundamental voltage and high frequency harmonic voltage data can be obtained by performing the fast Fourier transformation method on the voltage data. Second, the finite element model is established. During the finite element calculation, the obtained fundamental voltage and the main harmonic voltage components are used as the voltage source. To research the effect of high frequency harmonic voltage on the performance of motor, a reference group without high frequency harmonic voltage is set up, which is used to compare and analyze the effect of high-frequency harmonics on the performance of the motor. To verify the correctness of the model, a prototype based on the model parameters is manufactured, and then the back EMF experiment and load experiment are performed. The test data and calculation results are compared and analyzed. Findings The coupling relationship between high frequency time harmonic magnetic field and low frequency space harmonic magnetic field is obtained. The stator copper loss and rotor eddy-current loss are calculated and analyzed under normal supply voltage and abnormal supply voltage, and the influence mechanism is revealed Originality/value The coupling relationship between high frequency time harmonic magnetic field and low frequency space harmonic magnetic field is obtained. The sensitivity of the high frequency harmonic voltage to the stator copper loss and rotor eddy-current loss is obtained, and the mechanism of losses change is revealed.

Early Fault Detection Method for Rotating Machinery Based on Harmonic-Assisted Multivariate Empirical Mode Decomposition and Transfer Entropy

It is a difficult task to analyze the coupling characteristics of rotating machinery fault signals under the influence of complex and nonlinear interference signals. This difficulty is due to the strong noise background of rotating machinery fault feature extraction and weaknesses, such as modal mixing problems, in the existing Ensemble Empirical Mode Decomposition (EEMD) time–frequency analysis methods. To quantitatively study the nonlinear synchronous coupling characteristics and information transfer characteristics of rotating machinery fault signals between different frequency scales under the influence of complex and nonlinear interference signals, a new nonlinear signal processing method—the harmonic assisted multivariate empirical mode decomposition method (HA-MEMD)—is proposed in this paper. By adding additional high-frequency harmonic-assisted channels and reducing them, the decomposing precision of the Intrinsic Mode Function (IMF) can be effectively improved, and the phenomenon of mode aliasing can be mitigated. Analysis results of the simulated signals prove the effectiveness of this method. By combining HA-MEMD with the transfer entropy algorithm and introducing signal processing of the rotating machinery, a fault detection method of rotating machinery based on high-frequency harmonic-assisted multivariate empirical mode decomposition-transfer entropy (HA-MEMD-TE) was established. The main features of the mechanical transmission system were extracted by the high-frequency harmonic-assisted multivariate empirical mode decomposition method, and the signal, after noise reduction, was used for the transfer entropy calculation. The evaluation index of the rotating machinery state based on HA-MEMD-TE was established to quantitatively describe the degree of nonlinear coupling between signals to effectively evaluate and diagnose the operating state of the mechanical system. By adding noise to different signal-to-noise ratios, the fault detection ability of HA-MEMD-TE method in the background of strong noise is investigated, which proves that the method has strong reliability and robustness. In this paper, transfer entropy is applied to the fault diagnosis field of rotating machinery, which provides a new effective method for early fault diagnosis and performance degradation-state recognition of rotating machinery, and leads to relevant research conclusions.

Modeling Dynamic Response of Hydraulic Fluid Within Tapered Transmission Lines

This paper examines modeling of the laminar dynamic fluid responses within hydraulic transmission lines that have a tapered shape between the inlet and the outlet. There are excellent models available for fast simulation of pressure and flow dynamics within uniform lines; however, the established models for tapered lines either cannot be implemented in the time domain, are complex to implement, or have long simulation times. The enhanced transmission line method (TLM) structure is applied in this paper since it can be computed quickly in the time domain and has shown to accurately model the effects of frequency-dependent friction. This paper presents a method of optimizing the TLM weighting functions, minimizing the error between the TLM transmission matrix terms and a numerical ordinary differential equation (ODE) solution calculated using a boundary value solver. Optimizations have shown that using the TLM to model tapered lines can provide a fair approximation when compared in the frequency domain. Two-dimensional (2D) interpolation of a look-up table is possible allowing for quick selection of the optimized parameters. Further investigation into the effects of pipe wall elasticity and its inclusion into the TLM is also performed. Also, an experiment was performed to validate high frequency harmonic peaks present in the frequency response, which yielded acceptable results when compared to the theory, and the proposed tapered TLM. This model can be used in numerous applications where line dynamic effects must be accounted for, especially with digital hydraulic switched inertance converters where high frequencies are present.