Electrolytic Capacitor-Less Research Articles

Active damping control based bus voltage resonance suppression in electrolytic capacitorless PMSM application

Abstract The structure of electrolytic capacitorless in automotive electronic applications has the advantages of lower cost and better reliability. However, motor drive systems using this structure may experience unstable bus voltage. To this end, this paper proposes an active damping control strategy based on virtual impedance. By modelling the electric drive system and conducting stability analysis, the cause of bus voltage resonance due to the use of small capacitors is revealed. Based on the extracted DC bus voltage harmonic signal, additional voltage vectors are added in the d-axis and q-axis voltage vectors, eliminating the impedance mismatch problem in the drive system caused by the reduction of bus capacitance, effectively suppressing the voltage oscillation on the machine side of the drive system. Simulation data shows that under the condition of using small-capacity ceramic capacitors, the method proposed in this paper achieves a harmonic suppression capability similar to that of large-capacity electrolytic capacitors, effectively ensuring the application safety of automotive drivers with electrolytic capacitorless architecture.

Current Control of Electrolytic Capacitor-Less Variable Frequency Drive System for Synchronous Reluctance Motors Based on Power Balancing and Compensation

Current Control of Electrolytic Capacitor-Less Variable Frequency Drive System for Synchronous Reluctance Motors Based on Power Balancing and Compensation

Linearized Minimum Current Stress Modulation Scheme of Single-Phase Bidirectional DAB AC–DC Converters

In this paper, the detailed steps for the derivation of linearized minimum current stress (LMCS) modulation scheme for single-phase bidirectional and isolated dual active bridge (DAB) ac-dc converters is presented. In order to reduce the current stress of the converter, a Lagrange multiplier method (LMM) scheme is designed to obtain the control coordinates constraint on the minimum value of the current stress. Compared with the conventional minimum current stress (MCS) control scheme, the proposed scheme realizes the linearization of power control, which significantly reduces the complexity of the controller algorithm. Moreover, the synchronous inverter control applied to the back-stage full-bridge is designed. Thus, the single stage power conversion is realized and the converter topology is electrolytic capacitorless, which promote the improvement of system reliability and power density. The impact of the ZVS scheme is analyzed in detail, and the adaptive-ZVS scheme for less system loss is selected. Finally, experimental results confirm the validity and feasibility of the proposed control scheme.

Electrolytic capacitorless STATCOM with both inductive and capacitive VAR compensation modes

Electrolytic capacitorless STATCOM with both inductive and capacitive VAR compensation modes

Power Decoupling Rectifier With Common-Ground Concept for Lighting Applications

The lightweight and the electrolytic capacitor-less are the development trends of microconverters for transportation lighting applications. Some solutions available to address the power fluctuations are caused by electrolytic capacitor-less. However, the leakage currents caused by nonisolated converters have been little studied. Given this, an improved transformerless single-phase rectifier based on the virtual dc-bus concept is proposed in this letter. This solution connects the negative of the LED array directly to the grid neutral, thus shorting the stray capacitance to the ground, suppressing leakage currents, and improving system reliability. In addition, the active pulsating power buffering solution is introduced with only one additional power switch due to the sharing of cells. Finally, the experimental results verify the correctness and superior performance of the proposed solution.

Impedance Reshaping for Inherent Harmonics in PMSM Drives With Small DC-Link Capacitor

Sharp <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance peak may enlarge inherent harmonics, dominant harmonics of the supply voltage generated by a three-phase diode rectifier, around the resonance frequency, which will intensify fluctuations of the dc-link voltage, and grid currents in motor drives with small dc-link capacitor. In this article, a novel resonance suppression strategy based on inherent harmonics impedance shaping is proposed specially for three-phase input permanent magnet synchronous motor (PMSM) drives with small dc-link capacitor. Instead of increasing the damping of the whole system for resonance suppression, the motor side power disturbance can be reduced by designing the impedance for inherent harmonics around <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> resonance frequency based on the new model with the consideration of motor side characteristic. For damping current generation, the angle of the virtual admittance is modified to eliminate the influence of the dc-link voltage sampling delay. Experimental results show the effectiveness of the method on a prototype of electrolytic capacitorless PMSM drive.

A Hybrid Modulation Strategy With Neutral Point Voltage Balance Capability for Electrolytic Capacitorless Vienna Rectifiers

Electrolytic capacitorless Vienna rectifiers have many advantages, such as longer lifetime and higher power density. However, the reduced dc-link capacitance aggravates the voltage stress due to the neutral point (NP) fluctuation. In this article, a hybrid modulation strategy combining the modulations of redundant vector and compression vector is proposed, which can realize the NP voltage balance for electrolytic capacitorless Vienna rectifiers. On the basis of analyzing the limitation of NP-balance capability of conventional space vector pulsewidth modulation (PWM) strategy in the region of high modulation index, the negative influence of reduced capacitance on the NP fluctuation and the input current harmonics is revealed. To suppress the NP fluctuation, the compression coefficient is introduced to redistribute the duty cycles of voltage vector, which can reduce the negative effect of medium vector on the NP voltage. In addition, the phase voltage error is modeled to reduce the input current harmonics with the appropriate adjustment factor. The implementation of the proposed strategy is realized by the equivalent carrier-based PWM, which can avoid the sector judgment and angle calculation. By using the proposed strategy, the NP voltage balance and the input current harmonics reduction can be realized simultaneously. The effectiveness of the proposed strategy is verified on an electrolytic capacitorless Vienna rectifier platform.

Torque Ripple Compensation With Anti-Overvoltage for Electrolytic Capacitorless PMSM Compressor Drives

As the dc-link capacitance decreases obviously, the dc-link voltage fluctuates severely in the electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives for compressor applications. The control performance of the compressor deteriorates, and the dc-link may suffer from the fault of overvoltage. In this article, an acceleration extraction-based torque ripple compensation method considering safe operation with dc-link anti-overvoltage is proposed for electrolytic capacitorless PMSM compressor drives. The fluctuation characteristics of the compressor torque and the speed caused by the interaction of the dc-link voltage and the load are analyzed. The load torque is estimated online using the orthogonality theory to suppress the torque ripple. Based on the hybrid proportional–integral–resonant regulator, an anti-overvoltage control strategy is proposed for the safe operation of the regenerating state. Experimental results are performed in the air-conditioner compressor drive system to verify the effectiveness of the proposed method.

Predictive Direct DC-Link Control for 7.2 kV Three-Port Low-Inertia Solid-State Transformer With Active Power Decoupling

Promising for applications including renewable energy and electric vehicle fast charging, a medium-voltage (MV) solid-state transformer (SST) typically has multiple modules series stacked, which requires the modules to be single phase. One critical issue of the single-phase SST is the double-line-frequency power ripple. Traditionally, large passives are used to buffer the ripple, resulting in significantly increased volume and cost. This article for the first time proposes active power decoupling (APD) for the SST and a predictive direct dc-link control method, using a current-source (CS) single-stage SST as an example. An electrolytic capacitorless buffer port is used to absorb the ripple, which tolerates up to a 30% voltage ripple for small capacitance. The APD SST control is challenging. First, the CS SST realizes isolation, dc-link, and multiport in a single stage. Second, different from conventional SSTs or APD converters, the low-inertia dc-link in this SST has a 40% switching ripple, which is difficult to stabilize. To address the control challenge, a direct dc-link control architecture and a predictive control method are proposed. Simulation and experimental results verify the proposed control method on an MV SiC modular soft-switching solid-state transformer (M-S4T) prototype. The proposed APD reduces the SST volume by 53.8%. Importantly, the proposed concept is not limited to the M-S4T, but is generic to other SSTs or APD converters.

A Simple Modulation Strategy for Full ZVS of Single-Stage Electrolytic Capacitor-Less EV Charger With Universal Input

The single-stage electrolytic capacitor-less on-board charger (OBC) is attracting attention with the possibility of achieving high efficiency, high power density, and low component count. However, under universal input and wide battery voltage, the single-stage OBC has a difficulty in achieving ZVS turn- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> while maintaining unity power factor. In order to achieve ZVS under wide voltage range, the conventional single-stage OBC uses multiple control variables including switching frequency where the switching frequency usually varies widely, which complicates the converter design and optimization. In this regard, a totem-pole based single-stage electrolytic capacitor-less OBC was introduced in [36]. It uses one control variable and fixed switching frequency. However, this topology is not able to achieve full ZVS under wide voltage range and has high grid current total harmonic distortion (THD). This article proposes a simple modulation strategy that uses an adaptive duty-cycle and phase-shift modulation to achieve full ZVS under universal input and wide battery voltage. In addition, the fourth-harmonic injection method greatly reduces the grid current THD. The effectiveness of the proposed modulation was validated on a 3.84-kW prototype with 100–240 V ac input and 460–800 V battery voltage. The efficiency is also increased up to 2.3%p under low-voltage grid compared to the previous work.

A Novel Flux-weakening Control Method with Quadrature Voltage Constrain for Electrolytic Capacitorless PMSM Drives

In electrolytic capacitorless permanent magnet synchronous motor (PMSM) drives, the DC-link voltage will fluctuate in a wide range due to the use of slim film capacitor. When the flux-weakening current is lower than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$-\psi_{\mathrm{f}}/L_{\mathrm{d}}$</tex> during the high speed operation, the flux-weakening control loop will transform to a positive feedback mode, which means the reduction of flux-weakening current will lead to the acceleration of the voltage saturation, thus the whole system will be unstable. In order to solve this issue, this paper proposes a novel flux-weakening method for electrolytic capacitorless motor drives to maintain a negative feedback characteristic of the control loop during high speed operation. Based on the analysis of the instability mechanism in flux-weakening region, a quadrature voltage constrain mechanism is constructed to stabilize the system. Meanwhile, the parameters of the controller are theoretically designed for easier industrial application. The proposed algorithm is implemented on a 1.5kW electrolytic capacitorless PMSM drive to verify the effectiveness of the flux-weakening performance.

A Single-Stage Electrolytic Capacitor-Less EV Charger With Single- and Three-Phase Compatibility

This article proposes a modular single-stage electrolytic capacitor-less electric vehicles charger with single and three-phase grid compatibility. The proposed single-stage structure inherently maintains dc charging current for three-phase grid. For single-phase grid, a phase module is reconfigured to operate as a power decoupling circuit, making battery current to be dc. Furthermore, the proposed single-stage on-board charger is able to achieve zero voltage switching under wide grid and battery voltage ranges with only one control variable of phase shift angle. A balancing control method is proposed to ensure pure dc battery charging under unbalanced grid conditions. An optimized design of the planar core with Litz wire for achieving low profile is presented. Finally, a 11-kW prototype of the proposed charger achieved a power density of 5.25 kW/L and demonstrated 97.01% peak efficiency.

Suppression of Beat Phenomenon for Electrolytic Capacitorless Motor Drives Accounting for Sampling Delay of DC-Link Voltage

Beat phenomenon is an important issue for the practical application of electrolytic capacitorless motor drives. In this study, the characteristics of stator current harmonics caused by the voltage sampling delay are analyzed. Further, the beat phenomenon generated from the interaction between the harmonics and the fundamental currents is investigated, and the envelope feature of the stator current is derived mathematically. For the purpose of suppressing the beat phenomenon, a voltage reconstruction strategy is proposed to reduce the influence of dc-link voltage sampling delay at the six times of grid frequency. By utilizing the reconstructed dc-link voltage for calculation of PWM duty ratio, the beat phenomenon can be attenuated significantly. The proposed method can be integrated into motor control system easily. Experimental results show the effectiveness of the proposed strategy in a prototype of electrolytic capacitorless permanent magnet synchronous motor drive.

Control Method of Electrolytic Capacitorless Dual Inverter for Harmonic Compensation Under Distorted Grid Voltage

This article proposes a harmonic compensation method using an open-end winding interior permanent magnet synchronous motor driven by an electrolytic capacitorless dual inverter under grid disturbances. In a conventional electrolytic capacitorless single inverter, harmonic currents are superimposed on the output current of the inverter owing to the increase in the dc-link voltage ripple caused by grid disturbances. Consequently, the reliability of the motor drive system is reduced, and the torque ripple causes mechanical vibrations. The proposed harmonic compensation method estimates the harmonic voltage and outputs it using a compensating inverter. The experimental results show that peak-to-peak of the motor current and the 150 Hz component of the shaft torque are reduced by 10.3 and 92.4%, respectively, compared to the conventional system under unbalanced input voltage. Therefore, the improvement of reliability of a motor drive system and reduction of the torque ripple are achieved without an energy buffer under grid disturbances.

Stability Analysis of Two-Stage Single-Phase Converter System Adopting Electrolytic Capacitor-Less Second Harmonic Current Compensator

For the two-stage single-phase converter, including the power factor correction (PFC) ac-dc converter and dc-ac inverter, a second harmonic current compensator (SHCC) can be introduced to handle the second harmonic current (SHC) for removing the undesired electrolytic capacitor. Consequently, the two-stage single-phase converter becomes a multi-converter system. In this paper, the ac-dc stage or dc-ac stage in the system is categorized into two types in terms of the control objectives, i.e., the bus-voltage-controlled converter (BVCC) and the bus-current controlled converter (BCCC). The SHCC is a BCCC since its bus-port current is directly controlled, and the bus-port impedance of the SHCC is derived, which is affected by the ac-dc stage or dc-ac stage since the SHC reference is extracted from them. The system stability is investigated with the impedance-based stability criterion, and it is found that the system stability is different when the ac-dc stage or dc-ac stage is operated as a BVCC or a BCCC. Specifically, only when the ac-dc stage is operated as a BVCC, the system is unstable; while for other cases, the system is certainly stable. For the applications where the ac-dc stage is operated as a BVCC, a virtual resistor is introduced and realized by the control scheme of the SHCC to ensure the system stability. Finally, a two-stage single-phase PFC ac-dc converter is fabricated and tested to verify the theoretical analysis.

Elimination of DC-Link Voltage Ripple in PMSM Drives With a DC-Split-Capacitor Converter

This article presents an electrolytic capacitorless (ECL) motor drive based on a dc-split-capacitor converter. In order to decrease the dc-link voltage ripple of ECL motor drive, an active power decoupling circuit (APDC) with a dc-split-capacitor is proposed. The APDC is composed of two converters, among which the boost converter is named the main converter and the buck-boost converter is named the auxiliary converter. The output capacitors of the two converters are connected in series to increase the dc-link voltage, which expands the speed range of the internal permanent magnet synchronous motor. When there is voltage ripple on the capacitor of the main converter, the auxiliary converter will produce complementary voltage on another capacitor. In addition, an instantaneous current control strategy is proposed in the auxiliary converter to reduce the voltage ripple, while the conventional control strategy is applied in the main converter. The main converter can achieve unity power factor, and the auxiliary converter is used to suppress the dc-link voltage ripple. Experiments are conducted, and the results verify the feasibility and effectiveness of the APDC.

Control of Single-Phase Electrolytic Capacitor-Less Isolated Converter for DC Low Voltage Residential Networks

In recent years, there has been a desire to improve electricity generation and consumption, to reach sustainability. Technological solutions today allow a rational use of electricity with good overall performance. Traditionally, from production to distribution, electrical energy is AC-supported for compatibility reasons and easy voltage level transformation. However, nowadays most electric loads need DC power to work properly. A single high-efficiency central AC-DC power converter may be advantageous in eliminating several less efficient AC-DC embedded converters, distributed all over a residential area. This paper presents a new single-phase AC-DC converter using one active bridge (most isolated topologies are based on the dual active bridge concept) and a high-frequency isolation transformer with low-value non-electrolytic capacitors, together with its control system design. The converter can be introduced into future low-voltage DC microgrids for residential buildings, as an alternative to several embedded AC-DC converters. Non-linear control techniques (sliding mode control and the Lyapunov direct method) are employed to guarantee stability in the output DC low voltage with near unity power factor compensation in the AC grid. The designed converter and controllers were simulated using Matlab/Simulink and tested in a lab experimental prototype using digital signal processing (DSP) to evaluate system performance.

Interleaved Totem-Pole ZVS Converter Operating in CCM for Single-Stage Bidirectional AC–DC Conversion With High-Frequency Isolation

In this article, a new bidirectional single-stage interleaved totem-pole electrolytic capacitorless ac-dc converter with high-frequency isolation and low components count is proposed. The proposed converter is constructed using nonregulating two-phase interleaved totem-pole converter switched with a fixed 50% duty on the grid side and a full-bridge on the dc-side for active power and dc output regulation. This switching method results in a ripple-free grid current regardless of the magnitude of the input inductances. Consequently, a proper design of input inductance secures soft switching for all switches under wide voltage and load ranges without an auxiliary circuit or resonant tank. Hence, the proposed topology overcomes the reverse recovery issue, thereby enabling the use of Si devices in CCM. Moreover, the current spike around the ac main zero-crossing is avoided in the CCM operation due to small rectified voltage around zero-crossing. Furthermore, the instantaneous powers at the grid side and dc-side are identical since the proposed topology is electrolytic capacitorless with inherent second harmonic ripple current at the dc-side. PFC is inherently performed in the proposed converter without a current shaping control loop, and the phase-shift angle is the only control variable. Hence, the control system is simple and reliable. A 3.3 kW prototype of the proposed converter is built and tested in order to verify the performance and the theoretical claims.

Direct Load Voltage Control for Electrolytic Capacitorless Wireless Power Transfer System Without DC/DC Converter

This article presents a new direct load voltage control method for electrolytic capacitorless wireless power transfer (WPT) system without dc/dc converter. In specific, the three-phase low-frequency ac to the high-frequency ac (HFac) converter is employed into the electrolytic capacitorless WPT system by using the bidirectional power switches. The HFac voltage is directly generated on the transmitting tank without using the electrolytic capacitor. Furthermore, in order to realize the discretionary and accurate load voltage control without dc/dc converter, the nine voltage vectors, including six effective voltage vectors and three zero voltage vectors, are selectively exported for the transmitting tank with different duty cycles. In addition, the unity power factor correction and direct load voltage control are both achieved only by transmitting side control. Meanwhile, theoretical analysis of double series-compensated transmitting network and duty cycles under resonant frequency calculation in microchip are demonstrated in detail. Finally, both simulation and experimental results are provided to verify the feasibility and correctness of the proposed system, which operates at 85 kHz with 90% efficiency and about 9% total harmonic distortion.

An Electrolytic Capacitorless Modular Three-Phase AC–DC LED Driver Based on Summing the Light Output of Each Phase

The proposal of this paper is a modular three-phase ac–dc light-emitting diode (LED) driver for high-power luminaires based on LEDs that uses each phase to control an independent LED load removing in the process both the electrolytic capacitor and the second stage to increase both the lifetime and the efficiency. The driving of each LED load is done by means of a dc–dc converter operating as a loss-free resistor responsible for controlling the current across it. Furthermore, each dc–dc converter needs to achieve power factor correction (PFC) to comply with the restrictive IEC 61000-3-2 class C requirements, hence, achieving unity power factor and low total harmonic distortion. Taking advantage of the light properties, the output of the LED driver will be the sum of the light of each of the phases. Therefore, a theoretical study will be carried out to observe the feasibility of removing the electrolytic capacitor while guaranteeing a flicker-free behavior of the LED luminaire, even if the current of each string is pulsating at twice the mains frequency. This particular performance under high output current and voltage ripples requires reevaluating the well-known limits between the conduction modes in PFC converters. In addition, the theoretical analysis also discusses and proposes control methods for the LED driver, which thanks to its modularity can easily scale in power to drive high-power luminaires. In order to validate the theoretical analysis, a prototype has been built comprised three PFC boost converters disposing of their electrolytic capacitors. The designed prototype operates in the full range of the European three-phase line voltage, which varies between 380 and 420 V, and supplies an output light of 42.000 lm at a maximum power of 300 W while achieving an electrical efficiency of 97.5%.