Carrier Phase-shifted Modulation Research Articles

Topology, Analysis, and Modulation Strategy of a Fully Controlled Modular Reconfigurable DC Battery Pack With Interconnected Output Ports for Electric Vehicles

Modular battery-integrated converters or so-called dynamically reconfigurable battery packs are expanding into emerging applications. Although they offer many degrees of freedom (DoF), the state of the art focuses on single-output systems and neglects the potential of such systems to generate multiple outputs with minimum added components. This paper investigates the feasibility of a multiport system for various independent loads. The proposed techniques can achieve higher functionality and reduce power conversion stages. Interleaved ports with shared modules can also increase modules’ utilization, avoid redundant power electronics, and reach a better cost-weight trade-off. However, using conventional modulation techniques in particular phase-shifted carrier modulation can be challenging with shared modules among multiple ports, and different control objectives can adversely impact the overall performance. Therefore, this paper analyzes the inherent dynamics of modular batteries and proposes a strategy to decouple the control of multiple ports to simplify power electronics’ complexity and size while improving performance. In addition to the distinct advantages of modular reconfigurable batteries, the proposed concept would not require additional active switches, can operate with a wide range of output voltages, can reduce the size of the filters and transformers, and is extendable to larger setups. Simulation and experiments verify the developed concept.

DC Cascaded Energy Storage System Based on DC Collector With Gradient Descent Method

With the continuous development of distributed energy, the energy storage system (ESS) is indispensable in improving power quality. Aiming at the application of large-capacity storage battery access to medium voltage dc power grid, a dc cascaded energy storage system based on the dc collector is proposed, and the characteristic, topology and control are presented in detail. In this scheme, the low-voltage storage batteries are accessed to medium voltage dc bus directly with dc collectors, which not only has higher efficiency, but also improves power density. Especially, the diversity of state of charge (SOC) is only reflected in the duty cycle of submodules (SMs), rather than the voltage deviation. Further, a variable angle carrier phase-shifted modulation with gradient descent method is discussed to eliminate the dominant current harmonics. By calculating the harmonic amplitude and solving the Jacobian matrix, the gradient that reduces harmonic current is obtained, and the optimal combination of the carrier phases is deduced by iterative calculation. Meanwhile, the method can be extended in the dc collector with any number of SMs to eliminate the dominant harmonics. Finally, the experimental prototype is built and the benefit of proposed solution is verified.

Improved carrier phase shift modulation and voltage equalization control strategy in modular multilevel converter

Improved carrier phase shift modulation and voltage equalization control strategy in modular multilevel converter

Sensorless Capacitor Voltage Detection Method of Cascaded H-Bridge STATCOM Based on Special Switching Mode Identification

The cascaded H-bridge (CHB) static synchronous compensator (STATCOM) has been widely used in wind farm and conflux station. As the grid-connected voltage increases, the number of cascaded CHB proportionately increases. In order to achieve the capacitor voltage balance, it is necessary to independently detect the capacitor voltage of all H-bridge cells, which raises the cost of capacitor voltage detection. To solve this problem, the mapping relationship is studied between the converter output voltage and capacitor voltages by analyzing carrier phase-shifted sinusoidal pulse width modulation technique (CPS-SPWM), and special switching mode is firstly found. Based on the above finding, without changing the conventional CHB topology, an improved sensorless detection method is proposed to solve the problems of detection error, large computation burden and the application limitation in existing sensorless detection methods. Compared with conventional sensor detection, this method not only saves DC voltage sensors and data transmission channels but also suppress the third harmonics in the converter current. Finally, the effectiveness of the detection method applied on CHB STATCOM is proved by simulation and experiment.

Fault detection and localization method for modular multilevel converters in offshore DC wind turbines

The offshore DC wind turbine, consisting of direct-drive permanent magnet synchronous generator (PMSG) and modular multilevel converter (MMC), has become a promising candidate for the large-capacity wind energy conversion system. Submodule (SM) failure detection and localization are crucial for reliable operation of the MMC. However, existing techniques mainly focus on the rated operation condition, which may not be suitable for the MMC in wind turbine due to varying wind speed. Moreover, proper injection of second-order harmonic circulating current (SHCC) is desirable to reduce capacitor voltage ripple and power loss, which may also affect the accuracy of fault detection. This paper proposes a fault-tolerant strategy immune to variable operation conditions, as well as SHCC injection, for the MMC with phase-shifted carrier modulation. Firstly, the inherent switching harmonics of circulating current with SM failure are analyzed, based on which the fault detection method is developed. Then, the localization approach is presented by measuring the difference of SM capacitor voltages. Compared with existing techniques, the proposed strategy requires neither estimator nor additional sensor, which is robust, simple, and economical. Finally, both simulation and experimental results demonstrate the effectiveness of the proposed method, which is not influenced by SHCC and varying wind speed.

Discrete-Time Sliding Mode Current Control for a Seven-Level Cascade H-Bridge Converter

This paper deals with the implementation and performance analysis of discrete-time sliding mode (DTSM) current control applied to a seven-level cascade H-bridge converter to track three-phase reference currents for a reactive load. The converter output voltages are synthesized using a modulation scheme based on phase-shifted carrier modulation. Simulation and experimental tests have been added to demonstrate the performance of the proposed controller. At the same time, the effectiveness of the DTSM is verified under transient and steady-state conditions, respectively, by measuring the total harmonic distortion and the mean square error.

Selective Virtual Synthetic Vector Embedding for Full-Range Current Harmonic Suppression of the DC Collector

With the rapid development of rene wable energy (e.g., wind and photovoltaic energy) and energy storage, the dc collector has become an effective conversion link of distributed energy access to medium-voltage power distribution grids. However, considering the inconsistency of dc voltage and the duty cycle of each submodule, the traditional carrier phase-shifting modulation is difficult to achieve the excellent harmonic characteristic in the dc collector, thereby introducing difficulties in the design of passive filters. To solve this problem, this article proposes a selective virtual synthetic vector embedding algorithm to realize full-range current harmonic suppression in the dc collector system. In this scheme, the switching voltage vectors outputted by each submodule are sorted, and the voltage vectors are selectively extracted and synthesized to calculate the embedded virtual voltage vector. Afterward, the voltage vector of each submodule is rotated and calculated online from the perspective of space geometry, and the optimal carrier phase combination in variable-angle carrier phase-shift modulation is obtained. Finally, the experimental results show that the proposed control algorithm can not only be used in the dc collector with any number of modules but also achieve fast and effective harmonic suppression in the whole operating range.

A New Carrier Phase-Shift Modulation Based on Switching the Displacement Angle

In this paper, a new carrier phase-shift (CPS) modulation method based on switching the displacement angle (SDA) is proposed to compromise the harmonic content of the output voltage and the circulating current. It can be used in medium- and low-voltage applications where the AC-side voltage and DC-side current of the modular multilevel converter (MMC) are required to have low harmonic content simultaneously. In this proposed SDA-based CPS modulation, the carrier displacement angle of the MMC with N submodules in each arm is periodically switched between the values of 0 and π/N degrees, so that the harmonic content of the output voltage and the harmonic content of the circulating current will not be in extreme conditions, which occurs when the displacement angle is set to 0 or π/N degrees. The effectiveness of this method has been verified by simulation and experimental results.

A Three-Level Output Modulation Strategy for Conventional 3 × N Direct Matrix Converters

To utilize the full potential of the direct matrix converter (DMC) and improve the output waveform quality, a three-level output strategy for conventional 3N (N3) DMCs is presented, where three-level output voltages are achieved without any changes in the topology. In this developed strategy, the DMC is treated as a two-stage converter that consists of a fictitious rectifier and a neutral-point clamped (NPC) three-level inverter. By applying a phase-shifted carrier modulation strategy to the rectifier and a modified carrier-based double-signal pulse width modulation strategy to the NPC inverter, sinusoidal input and output, reduced switching losses, and controllable input power factors are achieved in conventional 3N DMCs. The developed three-level output strategy improves output waveform quality while sacrificing input performance to some extent. Finally, the effectiveness of the developed strategy is verified by both simulations and experimental results.

Precise Mathematical Model of PSCM Class-D Amplifiers

A mathematical analysis of four-level (three-phase) phase-shifted carrier modulation class-D amplifiers with analog feedback is proposed. The nonlinear difference equations are extracted and solved using the perturbation theorem. In this way, a closed-form function describes the low-frequency part of the output for an arbitrary input signal. The results are generalized for an arbitrary number of levels by analogy, well matched with the previous model of two-, three-, and the proposed four-level ones. The analytical results confirm that, apart from switching frequency, the multilevel class-D amplifiers converge to linear amplifiers as the number of output levels increases. An analytical equation expresses the harmonic distortion of practically interesting five-level amplifiers with bridge-tied load. The model is verified by system-level simulations and circuit-level implementation. In this way, a prototype fully differential five-level circuit is implemented on the printed circuit board to confirm the model.

Circulating Current Control of Phase-Shifted Carrier-Based Modular Multilevel Converter Fed by Fuel Cell Employing Fuzzy Logic Control Technique

The contribution of the modular multilevel converter (MMC) in integrating non-conventional energy sources into the grid is significant; the integration of fuel cells with distributed energy sources is especially prominent as they provide a constant voltage and current for constant load applications. Still, there is a high demand for a high-quality power conditioning unit since there is an occurrence of frequent power spikes. Further, the circulating current (CC) in phase legs is an inherent phenomenon of MMC that must be mitigated. Hence, this article proposed an MMC incorporating a fuzzy logic controller (FLC)-based technique to control the circulating currents. The fuzzy controller effectively reduced the harmonics of the CC in the dc-link system. In addition, phase-shifted carrier (PSC) modulation was employed for the MMC to improve the capacitor voltage balancing to maintain the constant input voltage. Moreover, a mathematical analysis of PSC modulation for MMC was performed to identify the PWM harmonic characteristics of the output voltage and the CC. The performance analysis of the proposed system was tested using the hardware in loop (HIL) simulation with the help of the real-time simulator OP-5700 to verify the feasibility.

High‐frequency harmonic suppression method for interleaved traction converters based on synchronous sampling

High-frequency resonance in traction power supply systems (TPSSs) is of great concern because of its potential to cause great damage to the safety and stable operation of railroad systems; it has been demonstrated that when a locomotive generates a harmonic current with the resonant frequency of the series impedance on the traction network, a large amount of high-frequency harmonic voltage is generated. This paper proposes a high-frequency harmonic suppression method based on synchronous sampled carrier phase-shift PWM modulation strategy (SSCPS-PWM), which has the advantage of not only considering the consistency of sampling the analogue signal by multiple controllers, but also further optimising the precise synchronization between multiple converter pulses. This method generates lower high-frequency harmonic content and is particularly suitable for the field of high-power, low switching frequency, multi-controller locomotive traction converters. The proposed method was simulated and compared with the traditional method for the harmonics injected by the locomotive, and a real railway line with a harsh power supply condition was selected and field tests were conducted in four sections by a 7200kW 6-axle electric locomotive. The test results showed that the proposed method effectively reduced the high-frequency harmonic current of the locomotive and reduced the high-frequency resonant overvoltage in the TPSS.

A Novel Multiport DC-DC Converter for Enhancing the Design and Performance of Battery–Supercapacitor Hybrid Energy Storage Systems for Unmanned Aerial Vehicles

This paper proposes an integrated multiport non-isolated DC–DC converter system for integrating battery–supercapacitor hybrid energy storage with photovoltaics for solar-powered unmanned aerial vehicles applications. Compared to the traditional topologies used, the proposed converter allows a size reduction of at least 20% of the supercapacitor by maximizing the utilization of the rated energy capacity. In addition, by proposing to use a phase-shifted carrier modulation technique, the inductors’ current ripple is reduced, which enables a further reduction in the inductor size. These improvements in capability and performance of the proposed topology are experimentally validated on a 500 W PV/battery–supercapacitor integrated power system prototype.

Photovoltaic grid-connected inverter based on super capacitor energy storage MMC

In order to improve the reliability of grid-connected operation of photovoltaic power generation systems, this paper proposes a photovoltaic grid-connected inverter based on supercapacitor energy storage MMC. Compared with traditional battery energy storage devices, the converter has the advantages of environmental friendliness, high energy storage efficiency, and long service life. The control strategy of the system is divided into three parts: carrier phase shift modulation strategy (CPS-SPWM), voltage balance control strategy and super capacitor charging control strategy. Finally, the feasibility of the proposed photovoltaic grid-connected inverter and its control strategy is verified in MATLAB/Simulink. The results show that the system can realize the photovoltaic grid-connected inverter process, realizes soft switching, and has high Energy storage efficiency.

A double input-parallel-output-series hybrid switched-capacitor boost converter

A double input-parallel-output-series hybrid switched-capacitor boost (DIPOS-HSCB) converter is proposed which consists of two different kinds of input-parallel-output-series (IPOS) circuits, i.e., inner IPOS circuit and outer IPOS circuit. Two boost modules and one switched-capacitor network build an inner IPOS circuit based IPOS-HSCB converter and two IPOS-HSCB converters develop the outer IPOS circuit based DIPOS-HSCB converter. With the proposed DIPOS-HSCB converter, a high voltage-gain with low component stress and small input current ripple are achieved. Furthermore, an automatic current balancing function for all input inductor currents can be also achieved using a special carrier phase-shifted modulation scheme. A prototype rated at 200 V/120 W has been developed and the maximum efficiency of the proposed DIPOS-HSCB converter is 95% at 120 W. Both steady and dynamic results are presented to validate the effectiveness of the proposed DIPOS-HSCB converter.

DC-side modeling of the modular multilevel battery energy storage system based on carrier phase shift modulation

DC-side modeling of the modular multilevel battery energy storage system based on carrier phase shift modulation

Analysis on harmonic characteristics of interleaving paralleled static inverters under asymmetric conditions

With the large number of applications for multi electric aircraft (MEA), the power capacity of the aviation static inverter (ASI) has been continuously improved. Therefore, more and more modular parallel-based topologies are being used in the ASI to achieve power expansion. Combined with carrier phase-shift modulation, the harmonic components of a system can be further reduced. However, due to the parameter asymmetry between paralleled modules and power system disturbances, additional low frequency and DC bias components are superimposed on the control signal. This paper uses exponential function analysis to analyze the harmonic distribution of a modular ASI based on carrier phase-shift modulation under non-ideal conditions. In addition, the distribution characteristics of different paralleled topologies are compared. Finally, the correctness of the theoretical analysis is verified by simulation and experimental results.

A Generic Scheduling Algorithm for Low-Frequency Switching in Modular Multilevel Converters With Parallel Functionality

Since the introduction of modular multilevel converters (MMC), various additional features have been introduced for MMCs, among them parallel inter-module connectivity. However, such a parallel mode requires appropriate modulation and switching strategies to exploit its full potential. Low-frequency switching modulation is widely used with half-bridge modules and a large body of research focusses on the optimum control and scheduling of these methods. However, so far, a suitable adaptation for MMCs with parallel mode is missing, and existing methods perform suboptimum. This article proposes a generic scheduling algorithm for simple and low-cost integration with low-frequency switching modulation. The proposed method reduces control complexity, minimizes power loss, and can be combined with most modulation techniques, including nearest-level modulation (NLM) and selective harmonic elimination. The text in this article provides a general algorithm for integrating this method with other control levels and analyzes its effect on MMCs with parallel functionality. Moreover, it examines the performance of the system with NLM combined with the proposed scheduler and compares it to other alternatives. Results show up to a 50% reduction in power loss with a similar modulation technique as well as significantly lower THD and power loss compared to optimized phase-shifted carrier modulation as another sensorless alternative method.

Novel Submodule Topology With Large Current Operation and DC-Fault Blocking Capability for MMC-HVDC

High-voltage direct-current system based on modular multilevel converter (MMC-HVDC) is widely expected to plays a significant role in promoting the development of large-scale offshore wind power. The maximum current limit of insulated-gate bipolar transistor (IGBT) is the main constrain for MMC-HVDC to operate in large current operation, while DC-fault blocking ability and economy are the two important concerns of MMC-HVDC. This paper proposes a novel parallel multiple submodule (PM-SM) topology to realize parallel output of submodule currents, which make MMC capable of large current operation and have filtering effect on high frequency harmonics. Combining with carrier phase-shift modulation or nearest level modulation, the frequency multiplication of bridge arm current of MMC can be realized to further improve the power quality of the system. Considering the demand of DC-fault blocking ability, simplified full-bridge double submodule (S-FBDSM) is also proposed as an economical option to compose PM-SM. It can provide double the reverse capacitance voltages in the arm current path regardless of a positive or negative arm fault current. The economic analysis is conducted to demonstrate the advantage of S-FBDSM. Simulation results and experiment results verify the feasibility and superiority of PM-SM composed of S-FBDSM.

Symmetrical DC-Link Capacitor Voltage for Multi Solar PV Array Fed CHBMLI in Standalone Application

In this paper, a generalized algorithm is proposed to balance the DC-link (DCL) voltage across each power cell of n number of cascaded H-bridge multilevel inverter (CHBMLI), using dc-dc converter, fed from multi solar photovoltaic (SPV) array for standalone application under varying environmental conditions, i.e. variation in radiation and temperature. Due to variation in the environmental conditions, the power flow through each H-bridge modules changes and subsequently the DCL voltage might change. This leads to unequal DC levels in the pole voltage of the CHBMLI, which results in different switching stress of the power modules. Therefore, the life span of the switches will get reduced. To maintain equal switching stress on each H-bridge module, duty cycle of the boost DC to DC converters is varied according to the proposed algorithm. It maintains equal voltage at the output of the boost converter under uniform/non-uniform environmental conditions. To operate the CHBMLI, the triangular carrier phase-shifted modulation has been used. The proposed algorithm as well as performance of the multi-SPV fed CHBMLI is simulated using PSCAD/EMTDC software for three-bridge seven-level CHBMLI. The experimental results are obtained using E4360 Modular Solar Array Simulator and Spartan 3AN FPGA controller for two-bridge five-level CHBMLI.