Low Carrier Ratio Research Articles

Discrete-Time Model Based Dynamic Decoupling Active Damping Current Control for CSI-Fed High-Speed PMSM with Low Carrier Ratio

Discrete-Time Model Based Dynamic Decoupling Active Damping Current Control for CSI-Fed High-Speed PMSM with Low Carrier Ratio

Proportional Resonant Control With Phase Correction for Stability and Dynamics Enhancement Under Low Carrier Ratio Conditions

Phase-corrected proportional resonant (PCPR) current controllers are mainly studied under high carrier ratio conditions. When applied to high-power converters with low carrier ratios (LCR), the system could be unstable or have poor dynamics without a proper parameter design. In order to illustrate both stability and dynamics to guide parameter design, bilateral Bode plots are tailored in this paper that considers the correct negative jump direction at resonant frequencies. Then, this analysis tool verifies the feasibility of the phase correction angle set over 90°, especially under a carrier ratio below six. With the designed phase correction, the stability region of the carrier ratios is characterized as extending to the theoretical limit of one. Moreover, the resonant gain of PCPR is quantitatively designed considering the variation of carrier ratios by maximizing the bandwidth under guaranteed stability and margins. Finally, the simulations and experiments verify the enlarged stability region with the phase correction and improved dynamic performance with the proposed resonant gain design method.

Sensorless Control Method of High-Speed Permanent Magnet Synchronous Motor Based on Discrete Current Error

When the Surface-Mounted Permanent Magnet Synchronous Motor (SPMSM) is in the condition of high-speed and low carrier-wave ratio, the performance of sensorless control is more affected by digital control delay, parameter inaccuracy, and other factors. This paper presents a sensorless control method based on the static error between the discrete d-axis current and the corresponding reference value. If there is no error in position angle, the discrete d-axis current should have no static error approximately. In addition, the static error of the d-axis current is related to the speed, so the PI controller with a variable proportional integral coefficient is used to ensure a stable error compensation performance in a wide speed range. The proposed method can accurately compensate the estimated rotor position of the motor under high-speed and low carrier ratio conditions and improve the accuracy of sensorless control. It provides an effective measure for the stable and reliable acceleration of electric vehicles and has specific practical significance for the development of electric vehicle control.

Variable Switching Frequency Deadbeat Predictive Current Control for PMSM with High-Speed and Low-Carrier Ratio

The predictive current control method of permanent magnet synchronous motor has the advantages of fast dynamic response and easy digital implementation, so more attention has been paid to it. When the motor operates in a high-speed condition, the switching frequency is relatively low, the carrier ratio is low, and the rotor angle varies greatly within a control cycle, resulting in a large error in the traditional liner approximation prediction model and inaccuracy of the voltage control quantity calculation, which leads to the deterioration of the predictive current control effect. At the same time, the output harmonic of the three-phase current increases, which affects the stable operation of the motor. In this paper, we study the causes of the large errors in the prediction model based on the traditional linear approximation and phase current fluctuation of the permanent magnet synchronous motor under high speed and low carrier-ratio conditions. Based on the improvement of the prediction model and modulation, a new control strategy of variable switching frequency deadbeat predictive current control is proposed. The control method proposed in this paper improves the dynamic and steady-state performance of the motor, under the condition that the carrier ratio does not increase and reduces the fluctuation of the output current of the motor. Finally, the effectiveness and superiority of the proposed method are verified by an experiment.

Research on Master–Slave Windings Motor Drive System and Control Strategy

To improve the torque performance limited by the low carrier ratio operation in motor drive system, a master–slave motor drive system based on dual stator winding structure is researched in this article. A high-frequency harmonic current is injected through the auxiliary windings to compensate the torque ripple and dynamic issue caused by the low carrier ratio. The basic operation principle in master–slave motor drive system is presented and then the turn ratio, mutual inductance, and carrier ratio in both windings are studied to achieve the optimization for the torque performance and power loss. The control method aiming at depression on toque ripple and load disturbance is proposed and gets merged with the vector control strategy. The loss analysis considering the injected high-frequency current is presented to compare with the three-phase system in high carrier ratio operation. It is found that a 30% total loss reduction can be achieved under the same torque ripple. Both simulation and experiments show the effectiveness of proposed master–slave windings system and the control strategy.

PMSM Torque Ripple Minimization Based on Novel Low Carrier Ratio PWM Technique

Harmonic injection is commonly used in permanent magnet synchronous motor torque ripple minimization (TRM) of electric vehicle. Traditional inverter switching frequency limits TRM application at high speed due to harmonic modulation accuracy and inverter loss. To achieve TRM in the whole speed range and reduce inverter loss, a novel online calculated low carrier ratio pulsewidth modulation (LCRPWM) is proposed in this article. The carrier ratio determining regular according to the injected harmonics is established first. The relationship between injected harmonics and LCRPWM switching angle is revealed and a set of nonlinear equations is established. Thus, the problem is transformed from solving nonlinear equations into optimization by establishing a cost function. The analytical solutions of nonlinear equations are obtained, which avoids iterative operation and plunging into local minimum. Therefore, the switch angle solution method is suitable for online calculation. The LCRPWM is verified in simulation compared with the traditional regularly sampled space vector PWM, which achieves better results in voltage harmonic injection and flux tracking at a much lower switching frequency. At last, the LCRPWM is used in a test bench experiment that shows good TRM effects. The influence of sideband harmonics on torque ripple is analyzed.

An Optimized Pulsewidth Modulation for Dual Three-Phase PMSM Under Low Carrier Ratio

In a high-power traction system, the stator current of the dual three-phase permanent magnet synchronous motor (DTP-PMSM) suffers from a large number of current harmonics due to the limitation of the switching frequency of the inverter. Thus, this article proposes a novel current harmonic distortion minimization pulsewidth modulation (PWM) method under a low carrier ratio to suppress current harmonics for the DTP-PMSM, which takes the salient pole ratio, the leakage inductance, and the load angle of DTP-PMSM into consideration. The mathematical model of current harmonics of DTP-PMSM using synchronous PWM is established under a low carrier ratio. The established model demonstrates that the current harmonics of the DTP-PMSM are not only affected by the inverter output voltage but also affected by the salient pole ratio, the leakage inductance, and the load angle of DTP-PMSM. To achieve better control performance on harmonics suppression of the DTP-PMSM, an optimization problem considered characteristics of the DTP-PMSM is formulated to minimize the current harmonics by regulating the switching angles of each phase. The total harmonic distortion of stator current can be reduced effectively by solving the optimization problem. The effectiveness and robustness of the proposed method are verified and compared with three other methods under the same switching frequency.

New PWM predictive control suitable for low carrier ratio of permanent magnet synchronous motor drive systems

The drive inverters for high-power motors often need to reduce the carrier ratio (usually by reducing the lower switching frequency) to increase its capacity. However, the low carrier ratio results in motor control performance degradation. In this paper, an inverter and a permanent magnet synchronous motor (PMSM) are integrated to establish a unified prediction model with the delay caused by sampling and modulation that cannot be ignored under a low carrier ratio. Based on this model, a new PWM predictive control suitable for low carrier ratio (PPC-LCR) is proposed, which has better stability, dynamic performance, model accuracy and robustness under a low carrier ratio. To further enhance the control accuracy of the proposed strategy, prediction errors by parameter mismatch are analyzed, and a correction method of feedbacking the last beat prediction error is proposed to compensate for model error and parameter mismatch. Finally, experimental results are presented to support theoretical analysis and the proposed strategy.

Model Predictive Current Control of Multiphase Motor at Low Carrier Ratio

Multiphase motors have multiple control planes, and harmonics are decoupled in different planes. Multiphase motors can improve magnetic field distribution, power density and core utilization by injecting certain harmonic currents into the harmonic planes. In the harmonic plane control process, due to the switching frequency of the inverter being limited, the ratio of the switching frequency to the current frequency (the carrier ratio) of the harmonic plane is low, the digital control delay increases, and the inverter output current contains more harmonics, which makes it difficult for the proportional-integral (PI) current controller to effectively control the d-axis and q-axis currents of the harmonic plane and thus unable to track the given values stably. Moreover, the PI current controller is relatively dependent on the motor parameters. For these reasons, a model predictive current control method with predictive error compensation is proposed. Taking a nine-phase induction motor as an example, the control voltage is calculated by the cost function and corrected by the current predictive error, which realizes the current control method at a low carrier ratio. Additionally, the robustness of the control method is analyzed after the parameters of the multiphase motor have large errors. The experimental results show that the proposed method can control the current of the harmonic plane at low carrier ratio, accurately track the harmonic current commands and attain strong robustness for the motor parameters.

Review of low carrier ratio converter system

With the rapid development of new energy power generation and high-power traction technology, the voltage and power levels of converter devices have been continuously improved, and the application of high-power converters is becoming increasingly widespread. However, high-power converters are affected by switching losses and heat dissipation, meaning they are not suitable for high carrier conditions. Therefore, research of low carrier ratio converter systems has received increased attention. Based on existing research, the problems of large current harmonics, low observation accuracy, and poor stability that may occur at low carrier ratios are explained. In addition, the topologies, modulation strategies, and control methods of the low carrier ratio converter system are analyzed and classified. Finally, future research directions of low carrier ratio converter systems are proposed.

A Deadbeat PI Controller With Modified Feedforward for PMSM Under Low Carrier Ratio

When the permanent magnet synchronous motor (PMSM) operates at low carrier ratio, the decoupling capability and dynamic performance of the proportional-integral (PI) controller are limited by the digitization delay. In this paper, a deadbeat PI controller is proposed by modified the feedforward. With the modified feedforward, the open-loop transfer function can eliminate imaginary components. Thereby the full decoupling of $d$ and $q$ is realized. At the same time, the controller also has full control over the location of the closed-loop poles, indicating that it can have a deadbeat response for the command tracking. For the disturbance rejection, the controller allows us to select the speed with which the controller can cancel the effect of a disturbance. Further considering that the motor parameters are inaccurate, by designing the controller coefficients with the maximum value of the closed-loop poles, the current-loop can ensure the dynamic performance and harmonic suppression ability. Finally, the effectiveness of the proposed controller is verified by the simulations and experiments.

Hybrid Improved Carrier-Based PWM Strategy for Three-Level Neutral-Point-Clamped Inverter With Wide Frequency Range

The three-level neutral-point-clamped inverter used in the variable frequency system has the characteristics of a wide frequency range, and the pulsewidth modulation (PWM) strategy needs to be designed for the low-frequency region with low modulation index and the high-frequency region with low carrier ratio, respectively. The traditional carrier-based PWM (CBPWM) is simple to implement, but in the low-frequency region, CBPWM will cause narrow pulse and output voltage distortion; while in the high-frequency region, CBPWM can only achieve the synchronized modulation with half-wave symmetrical (HWS) and three-phase symmetrical (TPS) waveforms when the carrier ratio is an odd integer multiple of three, and it cannot realize the square-wave modulation. To solve the defects of CBPWM, this article proposes improved CBPWM (ICBPWM) I, which can avoid narrow pulse and generate line voltage accurately at any low modulation index, ICBPWM II, which can ensure the voltage to meet TPS and HWS when the carrier ratio is an arbitrary integer multiple of three, and ICBPWM III, which can achieve square-wave modulation, separately. On this basis, by using ICBPWM I, ICBPWM II, and ICBPWM III in combination, a hybrid ICBPWM strategy with wide frequency range is further proposed. Finally, the proposed strategy is verified by simulation and experiment.

Closed-Loop Dynamic Control for Dual-Stator Winding Induction Generator at Low Carrier Ratio With Selective Harmonic Elimination Pulsewidth Modulation

In this article, we present a closed-loop dynamic control scheme for a dual-stator winding induction generator (DWIG) with selective harmonic elimination pulsewidth modulation (SHEPWM). This control scheme can be applied in a variable-frequency ac power system based on the DWIG, which is able to operate in low-carrier-ratio conditions, especially in high-power aeroapplications. Common closed-loop induction machine control schemes, such as vector control strategy, generally lead to control failure with SHEPWM implemented. This proposed closed-loop dynamic control scheme makes the dynamic operation of the DWIG power system feasible with SHEPWM. The scheme consists of three main parts: the complex-signal observer for DWIG, outer loop controller for DWIG, and stator flux-linkage trajectory tracking controller. The complex-signal observer provides the extra steady-state components of control signals by using the complex coefficient filter. The outer loop controller provides the dynamic commands for control signals. Finally, the flux-linkage trajectory tracking control (FTTC) synthesizes these signals and serves as the inner loop. The simulation and experimental results verify the validity and effectiveness of the proposed scheme.

Comparative Study on Single Pulse and Dual Pulses Variable Width Control Strategies for High-Speed PM BLDC Motor Drive

Pulse width modulation (PWM) of voltage source inverter (VSI) is common for speed regulation of permanent magnet (PM) brushless direct-current (BLDC) motor drives. However, when the motor runs at high speed, the conventional PWM technique may become unfeasible due to the low carrier ratio of inverter, which makes the motor current distorted and the motor core loss increased significantly. In this paper, two control strategies, namely single pulse variable width (SPVW) and dual pulses variable width (DPVW), are introduced for the high-speed PM BLDC motor drives, and are comprehensively investigated. Finite element method (FEM) is employed to evaluate and compare the drive system performance when using the conventional PWM, and the proposed SPVW and DPVW, respectively. Influence of the control techniques, especially on the loss distribution, is revealed.

Quasi-Proportional-Resonant Controller Based Adaptive Position Observer for Sensorless Control of PMSM Drives Under Low Carrier Ratio

The position and speed estimation performance of the sliding mode observer (SMO) for permanent magnet synchronous motor (PMSM) drives under low carrier ratio degrades, due to the inherent chattering and enlarged control delay. To improve estimation performance, this paper proposes a quasi-proportional-resonant (QPR) based adaptive observer to obtain back electromotive force with adaptive harmonics cancellation. In this observer, the QPR controller is employed to eliminate errors between the observed currents and the actual ones in the αβ reference frame, replacing sign function and low pass filter (LPF) of the SMO to cancel the chattering, and harmonics immune performance can also be achieved thanks to frequency selection characteristic of the QPR controller. Besides cancelling the chattering, the proposed observer can also eliminate phase shift produced by the LPF, since the QPR controller is a zero phase-shift amplifier at the resonant frequency. Comparative experiments are carried out in a 3-kW PMSM drive, and the results validate the effectiveness of the proposed adaptive position observer.

Dahlin-Based Fast and Robust Current Control of a PMSM in Case of Low Carrier Ratio

The low ratio of sampling frequency to electrical frequency (carrier ratio) is a challenging issue for applications, such as high-speed or high-power drives. In fact, high-speed drives have high fundamental frequency and high-power drives have low switching (sampling) frequency, leading to the same control challenges of having high dynamic and stability with a limited number of control actions in one period. Parameters mismatch occurs due to the converter non-linearities, deadtimes, temperature change, and saturation; hence, providing robust control is a key challenge. This paper starts reviewing the problems of controlling machines with a few switching instances per fundamental period and an analysis of the state-of-the-art current control strategies for permanent magnet synchronous motors (PMSMs). Three different control schemes are analyzed. The discrete-time PI current controller is providing good robustness, while the dynamic performance may not be sufficient for some applications. Second, the deadbeat control offers very fast dynamic performance but is weak under parameter mismatch. The novel application of the Dahlin controller offers a tradeoff between performance and stability. The control algorithms are evaluated based on the stability, robustness, and dynamic and steady-state performances. Their performance and sensitivity to parameter variation are analyzed through simulations, and the experimental measurements are proving the results.

Composite differential evolution algorithm for SHM with low carrier ratio

This study presents a new method of switching angle solution based on composite differential evolutions (CoDE) in selective harmonic mitigation pulse width modulation (SHMPWM). The method can effectively improve the global searching ability and convergence rate of the solution by the combination of multiple composite trial vectors and control parameter settings. Its great generality makes itself applicable to selective harmonic elimination PWM and synchronous harmonic optimum PWM as well. This study introduces the basic principles of SHMPWM and CoDE, constructs the constraint and objective functions by means of penalty, and gives detailed solution steps. After getting the switching angle solutions from comparative studies including different switching angle numbers, different modulation degrees, or different optimised PWM methods, the experimental platform finally has been designed and carried out to verify the accuracy and generality of the proposed method.

Improved Asymmetric Space Vector Modulation for Voltage Source Converters with Low Carrier Ratio

This paper presents an improved asymmetric space vector modulation (ASVM) for two-level voltage source converters (VSCs) when the switching frequency is as low as nine times of line frequency. By adding two pulses in each line cycle when the fundamental voltage crosses zero, the total harmonic distortion (THD) of output current can be reduced significantly. The penalty of additional switching loss is very limited for high power factor operation. The applications of the improved ASVM in a single VSC or in two interleaved VSCs are shown, respectively. With the optimization of the duration and position of the additional pulses, the ac current THD can be reduced to as low as 50% for single VSC and even lower to less than 25% for interleaved VSCs systems. Such THD reduction has close relationship with space vectors' position, modulation index, and interleaving angle. Improved ASVM can also reduce the amplitude of circulating current in the interleaved VSCs, leading to smaller interphase inductors. Finally, the weights of total inductors needed to meet the same THD requirement are compared to demonstrate the benefits of improved ASVM when different pulsewidth modulation schemes are used. The analysis results are verified by experiments on a demo system.