In bipolar DC-bus systems, the extreme-value constraint on the neutral point (NP) current limits the unbalanced power operating range and degrades grid-side power quality in electrolytic capacitorless Vienna rectifiers. To address these challenges, this article proposes a coordinated control strategy for unbalanced power and bipolar voltage. A prediction-based clamping selection mechanism is proposed by computing a one-step-ahead NP voltage estimate at each sampling instant, effectively suppressing bipolar voltage fluctuations. Furthermore, the mapping between the power imbalance degree and the bipolar voltage is exploited to derive the optimal voltage imbalance degree, through which the unbalanced power operating range under NP current constraints is expanded. Additionally, a voltage vector trajectory optimization based on vertical projection minimizes the voltage vector synthesis errors within infeasible regions. Experimental results demonstrate that the proposed strategy extends the unbalanced power operating range, improves grid-side power quality, and enhances the stability of the bipolar DC-bus voltage in an electrolytic capacitorless Vienna rectifier.

Active damping strategies in electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives are prone to failure under wide variations of grid impedance. Thus, a robust grid current harmonics suppression strategy based on online virtual impedance optimization is proposed. Firstly, evaluation metrics are constructed to quantify the quality of grid currents and the system stability. An entropy-weighted technique for order of preference by similarity to ideal solution (TOPSIS) is employed to obtain an optimal impedance reshaping factor (IRF) subject to stability constraints. To derive the model parameters of the transfer function between the IRF and the DC-link voltage, an online gradient descent algorithm is presented incorporating real-time motor operating conditions. Based on the parameters and discrete vector synthesis, the IRF satisfying preset amplitude and phase constraints is obtained and utilized to reconstruct the DC-link voltage reference for space vector pulse width modulation (SVPWM). The proposed strategy can improve the resonance suppression capability under wide variations of grid impedance and motor operating conditions. Finally, the proposed strategy is verified on a platform of electrolytic capacitorless PMSM drive.

The existing adaptive linear neuron (ADALINE) based speed ripple suppression method is affected by the permanent magnet synchronous motor (PMSM) control system delay and limited by the speed controller cutoff frequency, resulting in system instability. This article proposes a speed ripple suppression based on stability-enhanced ADALINE for PMSM drives. Under unknown system delay conditions, the integral saturation characteristics in the ADALINE network are extracted to obtain system instability information. An anti-instability disturbance sliding mode tracking controller is constructed to extract the phase delay of the speed ripple suppression system and optimize the phase convergence trajectory. Besides, according to the desaturation mapping relationship of the speed ripple sine-cosine components, a phase delay adaptive selection strategy is proposed to achieve adaptive regulation for phase delay, enhancing the speed ripple suppression system stability when the ripple frequency exceeds the speed controller cutoff frequency. The stability and convergence are analyzed in detail. The effectiveness of the proposed method is verified on a 2.2 kW PMSM drive platform.

The beat phenomenon in electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives is serious within field-weakening (FW) region. This article proposes an adaptive beat suppression strategy through regulating the voltage angle harmonics. By dividing the admittance in FW region into voltage sampling time-delay admittance and FW characteristic admittance, the relationship between beat envelope and the admittances is quantitatively analyzed. It is revealed that the conventional method can only reduce the influence of voltage sampling time-delay admittance. The proposed strategy constructs a closed-loop harmonic control of the dc-link voltage and the voltage angle to minimize the amplitude of beat envelope. By reshaping the impedance relationships between dc-link voltage and motor currents at inherent frequency, the FW characteristic admittance is reduced and the beat phenomenon in this region is suppressed effectively. Based on the reshaped impedance model, the control parameters are adaptively regulated with the motor speed and dq-axis currents. Experimental results show the effectiveness of the proposed method in a PMSM system with small dc-link capacitors.

In electrolytic capacitorless motor drives, the drastic variation of system impedance from the constant torque (CT) region to the flux-weakening (FW) region is the root cause of the degraded performance of harmonic suppression. In this letter, a new voltage amplitude-phase decoupling control method is proposed. By reconstructing the dq-axis current control loops, the modulation index and voltage angle can be controlled in a decoupled manner. Then the loop gains are adaptively adjusted according to operating conditions to ensure the loop bandwidth. No additional control loops are introduced in the FW control, which enables the continuous variation of impedance characteristics. A voltage angle harmonic regulation mechanism based on the DC-link voltage is established. The control parameters are optimized according to the continuous impedance model and steady-state operating point information to realize specific-order harmonic suppression. Experimental results demonstrate that the proposed method can effectively reduce grid-side current harmonics across different operation regions.

Fixed damping strategies are inadequate for suppressing the dc-link capacitor ripple current in permanent magnet synchronous motor (PMSM) drives across a wide power range. Therefore, a ripple current suppression strategy based on adaptive active damping with iterative learning is proposed. The strategy indirectly characterizes the ripple current by the dc-link voltage, avoiding the need for additional sensors or current reconstruction algorithms. First, the limitation of fixed damping in suppressing the ripple current is revealed using the equivalent admittance model. Then, an adaptive suppression mechanism based on P-type iterative learning is constructed. The balance between the convergence speed and the disturbance rejection capability is achieved by introducing a forgetting factor. On this basis, the initial admittance parameters are dynamically matched to improve the iterative efficiency under variable-speed conditions. The analysis of convergence and parameter sensitivity demonstrates that the proposed strategy exhibits rapid convergence, high accuracy, and strong robustness. Finally, the effectiveness of the proposed strategy is verified on the experimental platform.

The virtual admittance reshaping strategy based on specific harmonic suppression can effectively suppress LC resonance for electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives, yet its performance relies on the periodic characteristics of the DC-link voltage under ideal grid conditions. In this article, a DC-link voltage fluctuation suppression strategy based on rectified voltage harmonic disturbance decoupling is proposed. An analytical model describing the harmonic suppression capability of the traditional strategy under grid background harmonics is established, which can reveal the nonlinear disturbance mechanism of damping performance caused by the variations of grid harmonics. Different from the conventional methods, the proposed modeling method models the small signal of rectified voltage as a disturbance term. Therefore, a harmonic decoupling mechanism between the disturbance term and the closed-loop vector control system is constructed, which can enhance the capability to mitigate DC-link voltage fluctuations under grid background harmonics. Considering the incomplete decoupling problem caused by digital control delay, the decoupling branch is optimized as a virtual admittance. Meanwhile, the DC-link voltage harmonic factor is constructed to provide theoretical guidance for the parameter design of virtual admittance. Experimental results validate the effectiveness of the proposed scheme.

In electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives, when the harmonic component of the position fluctuation is in a canceling relationship with the corresponding harmonic introduced by the DC-link voltage fluctuation, simply suppressing the position fluctuation aggravates the beat phenomenon. This article proposes a beat suppression strategy based on extended back electromotive force (EEMF) harmonic reconstruction. Small signal analysis reveals the impedance relationship between position compensation and beat current, quantitatively clarifying the nonlinear increment of beat currents. Specifically, multiple complex filtering is utilized to extract EEMF harmonics induced by DC-link voltage fluctuations. By feeding back the electrical angular frequency as the center frequency, the right sideband harmonic component is reconstructed for position estimation based on established current and EEMF frequency characteristics. Finally, the effectiveness of the proposed strategy is validated on an experimental platform, verifying beat suppression under various speed and torque conditions.

High-frequency (HF) noise is unavoidable with HF injection methods in sensorless permanent magnet synchronous motor (PMSM) drives, limiting its application scenarios. To reduce acoustic noise, a positive-negative sequence current (PNSC) decoupling and reconstruction-based position estimation method using low-frequency (LF) injection is proposed. Based on the positive-negative frequency characteristics of the excited currents, a cross-decoupled complex coefficient filter is used to overcome the phase shift of conventional filters under LF injection. Stability analysis and parameter design demonstrate that the proposed method achieves a phase-shift-free separation between the fundamental and the LF excited currents. Furthermore, to compensate for errors originating from the stator resistance and mutual inductance, a position error suppression method based on the reconstruction of the PNSC is proposed. A unified mapping model between the injection frequency and the estimation error is established to optimize the injection method for increasing estimation accuracy. Analysis of the current power spectral density and A-weighted curve demonstrates that the proposed method can reduce acoustic noise. Finally, the effectiveness of the proposed method is verified on a 2.2-kW interior PMSM drive platform.

In electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives, the output voltage vector in the flux-weakening (FW) region exhibits significant fluctuation due to the periodic oscillations of DC-link voltage and reference voltage vector, leading to increased motor current harmonics. To suppress the current distortion, a harmonic impedance reshaping based flux-weakening control strategy is proposed which is effective only when the machine operates in the motor mode. By analyzing the impact of inherent periodic fluctuation on output voltage, the influence mechanism of reference voltage vector oscillation on motor current harmonics is revealed. Multi harmonic digital filters are employed to extract inherent frequency components from the reference modulation index, and a flux-weakening coefficient adjustment component is generated. In this way, the flux-weakening depth can be regulated in real-time, optimizing the trajectory of the output voltage vector and achieving effective suppression of motor current harmonics. The proposed method extracts harmonics from the reference modulation index, enabling feedforward-based decoupling of modulation output harmonics and suppression of motor current harmonics. Compared to feedback control methods, the proposed strategy directly controls the modulation command, avoiding complex angle observation and parameter dependency issues. This not only simplifies the control loop but also enhances the system's adaptability to varying operating conditions. Experimental results validate the effectiveness of the proposed method.

In permanent magnet synchronous motor (PMSM) drives without electrolytic capacitors, modulation index (MI) fluctuation leads to a lower dc-link voltage utilization under flux-weakening (FW) control. In this article, an adaptive MI fluctuation suppression strategy is proposed to enhance the voltage output capability of the inverter. The mechanism of MI fluctuation is analyzed through impedance modeling of the drive system. Furthermore, the influence of dc-link voltage utilization is analyzed based on the impedance relationship between MI and rectified voltage. To suppress the MI fluctuation, harmonics of the dc-link voltage and motor voltage vector reference are extracted to generate compensation voltage angle by considering the average of MI. Through a closed-loop regulation of the voltage vector reference with angle compensation, adaptive suppression of MI fluctuation can be achieved. Furthermore, the coefficient of the FW controller is adaptively regulated according to the peak value of MI. Finally, the effectiveness of the proposed control strategy is verified on an electrolytic capacitorless PMSM platform.

The voltage-source inverter (VSI)-based AC-DC-AC drive employing pulse width modulation (PWM) is extensively applied in permanent magnet synchronous motor (PMSM) systems due to its superior speed regulation capabilities and ease of digital control implementation. Nevertheless, the high-frequency switching operations of inverter semiconductor devices introduce large-amplitude, high-frequency common-mode voltages (CMV) within the drive system. These voltages can lead to motor insulation degradation, common-mode electromagnetic interference (EMI), and bearing damage, thereby significantly reducing the operational lifespan of the motor. To address these issues, this study proposes a CMV suppression modulation strategy based on the use of equivalent zero vectors. By applying the equivalent zero vector approach, the proposed method effectively reduces the CMV associated with the extended double carrier PWM strategy, particularly in low modulation regions.

-The fluctuation of DC-link voltage can cause fluctuations in the motor current and voltage at corresponding frequencies, affecting the output power of the motor. This article proposes a power fluctuation suppression strategy based on the harmonic injection, which adapts to the DC-link voltage fluctuations under maximum torque per ampere (MTPA) control. By injecting harmonics that characterize power fluctuation characteristics into the d-axis current, the harmonics caused by the DC-link voltage ripples in the input power can be reduced. This method can reduce motor power fluctuations and improve the motor output characteristics.

Addressing the coupling effect between speed and voltage controllers in the traditional antiovervoltage control strategy for electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives, a novel antiovervoltage control strategy based on power balance state regulation is proposed. The active-reactive power coordinate frame based on synthesized voltage vector orientation is constructed in the proposed scheme. Subsequently, the power balance current for maintaining dc-link voltage constant can be extracted independently of inverter and motor parameters. To achieve the decoupling between controllers, the power balance current is set as a threshold to switch the designed operating mode. Thus, the coupling issue can be solved between the speed and voltage controllers in the case of reduced dc-link capacitance values. To control the dc-link voltage following the designed voltage trajectory in braking mode, the active and reactive currents are allocated based on the power balance current. Furthermore, controller coefficients are designed from frequency domain to ensure a sufficient phase margin. While ensuring maximum copper loss, the dc-link voltage overshoot can be significantly reduced by the proposed scheme. Experimental results validate the effectiveness of the proposed scheme in 2.2-kW reduced dc-link capacitance PMSM drives. Compared with the traditional antiovervoltage control scheme, the proposed scheme can suppress dc-link voltage overshoot to 2%.

For the electrolytic capacitorless permanent magnet synchronous motor drives with low dc-link inductance, the increase of the resonant frequency and the complex coupling between the grid- and dc-side currents result in the performance reduction of the active damping method. This article proposes a suppression strategy based on the feature extraction of the grid current harmonics from frequency mapping. With the high-to-low frequency mapping, the low-frequency feature signals of grid current harmonics are applied to characterize the high-frequency resonance, which reduce the sampling and update errors caused by the higher resonant frequency. On the basis, the closed-loop control of the low-frequency feature signal is adopted to reshape the impedance relationship between the grid current and rectified voltage. Therefore, the harmonics of the grid current can be decoupled from the dc-side current, and the high-frequency resonance of the grid current can be directly controlled, which realizes resonance suppression in the low dc-link inductance drives. Experimental results verify the effectiveness of the proposed suppression strategy.

In the permanent magnet synchronous motor (PMSM) drives with small dc-link capacitors, conventional beatless methods cannot characterize the harmonic internal model, which causes the phase current harmonics to still exist. Besides, the coupling of the beat envelope and current harmonics further the application range of the conventional methods, like in flux-weakening (FW) region. This article proposes a coordinated astatic suppression strategy based on positive-negative sequence regulation, which can solve the beat envelope and the current harmonics at the same time. The feature signals of phase current harmonics are generated with the multiple synchronous rotating frame transformations (MSRFTs), and the positive and negative sequence components can be separated. The influence of the fluctuated position error is eliminated, and the amplitudes of different sequence harmonic can be extracted with the feature signals, which improves the adaptability to the current coupling and operating conditions. The compensation voltages generated from the inverse MSRFTs are used to reshape the impedance relationship between beat current and rectified voltage. The equivalent harmonic controller contains the internal model of the motor current, which can realize the coordinated suppression of the harmonics and the beat envelope without static error. The experimental results show that the strategy can suppress both the beat envelope and the phase current harmonics effectively.

Due to the periodic dc-link voltage and the fluctuation of the reference voltage vector, which is caused by the incomplete voltage compensation, the electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives have obvious harmonics in overmodulation (OVM) regions. To address this issue, a novel OVM strategy based on dynamic voltage boundary (DVB) regulation is proposed. By analyzing the trajectories of output voltage vectors with the consideration of periodic fluctuation, the harmonics of stator voltage caused by switching aliasing in OVM regions are revealed. The OVM regions are divided by a dynamic voltage which contains the characteristics of reference voltage vectors. Then the action time of fundamental vectors can be obtained by using the dc-link voltage and the dynamic voltage. Based on the fluctuating information of dynamic voltage, OVM regions can be smoothly switched with the dc component of the amplitude of reference voltage vectors. The proposed method can reduce the fluctuation of reference modulation index (RMI), thus decreasing the total harmonic distortion (THD) of stator voltage and current. Experimental results on a 2.2 kW electrolytic capacitorless PMSM platform validate the effectiveness of the proposed method.

The energy buffering ability of the DC-link capacitor is weak in the electrolytic capacitorless system, so that the control of antiovervoltage and the voltage sag ride-through is difficult. In this paper, a DC-link voltage control strategy based on energy regulation is proposed. In the case of overvoltage, the DC-link voltage is stably controlled by regulating the q-axis current to prevent energy flow on the DC-link capacitor, and the braking rate is accelerated by the loss controller. When the grid voltage sags, the q-axis current is regulated to recover the kinetic energy of the motor to extend the time of the DC-link voltage at the preset value. The effectiveness of the proposed method in the grid voltage sag and different load conditions is verified in the simulation model of the electrolytic capacitorless system.

Interior permanent magnet synchronous motor (IPMSM) drives with single-phase input diode rectifiers using small-volume film capacitors offer many advantages, such as high reliability, low cost, and high power density. However, the position observation error in position sensorless control fluctuates more compared to conventional topologies due to the use of slim film capacitors. In this paper, a position observation error suppression strategy using multiple second-order generalized integrators is proposed. Cross-pair harmonic cancellation is performed using parallel multiplexed filter modules. The method proposed in this paper improves the frequency-specific harmonic suppression compared to conventional harmonic suppression methods.

Active damping strategies are commonly used for grid current harmonic suppression in electrolytic capacitorless motor drives. However, they lead to the increase of motor harmonics. In this letter, a multiport-impedance-optimization-based harmonic suppression strategy is proposed, which considers both grid current and motor current harmonics. A multiport impedance model is constructed, in which the rectifier voltage is served as the input, while motor current and dc-link current serve as outputs. Moreover, the impedance optimization index that quantifies harmonic content on the motor and grid sides is constructed. The voltage for regulating the port impedance is derived from the harmonic information of the system, which contains the motor torque and the dc-link voltage. An analysis is conducted on the effect of the angle of impedance regulation voltage on the impedance optimization index. The ideal angle can be determined using entropy-weighted technique for order of preference by similarity to ideal solution (TOPSIS). This enables vector synthesis of the port impedance regulation voltage under the co-optimization of port impedance, which improves the coordination between the quality of the grid current and the harmonics of the motor torque.