Current Balance Control Research Articles

An On-Board Two-Stage Integrated Fast Battery Charger for EVs Based on a Five-Phase Hybrid-Excitation Flux-Switching Machine

In this article, to solve the existing problems in general on-board integrated chargers, a novel three-phase on-board two-stage integrated charger is proposed by taking the unique advantages of a five-phase hybrid-excitation flux-switching (HEFS) motor. The general topologies and newly presented integrated chargers are reviewed first, and existing problems are concluded. Then, a two-stage integrated charger is proposed, and all winding selections are thoroughly investigated by theoretical analysis, finite-element analysis (FEA), and experiments. In the proposed topology, the existing problems are all solved by employing this multiphase system, reasonable winding selection, and reconfiguring the field winding. After that, a current balance control method for charge mode without a phase-locked loop circuit is presented. The simulation results verify the effectiveness of the proposed control methods. Finally, based on a 5-kW five-phase HEFS prototype machine and two sets of the three-phase generic motor controller, an experiment platform is built. The experiment results agree well with the simulation results. Therefore, the feasibility of a two-stage integrated on-board charger that can operate at any voltage level is confirmed, where only the hybrid-exciting machine and its driving system are used without any additional power devices.

A Single-Phase On-Board Two-Stage Integrated Battery Charger for EVs Based on a Five-Phase Hybrid-Excitation Flux-Switching Machine

In this paper, to solve the existing problems in general on-board integrated chargers (IC), a novel single-phase on-board two-stage integrated charger is proposed by taking the unique advantages of the five-phase hybrid-excitation flux-switching (HEFS) motors. The general topologies and newly presented ICs are reviewed firstly, and three main problems are concluded. Then, the proposed two-stage IC is presented, and all winding selections are thoroughly investigated by theoretical analysis, finite-element analysis (FEA) and experiments. In the proposed topology, the existing problems are all solved by employing this multi-phase system, making the reasonable winding selection, and reconfiguring the field winding. After that, a control method for charge mode and two current balance control methods are developed. The simulation results verify the effectiveness of the proposed control methods. Finally, based on a 5-kW five-phase HEFS prototype machine and two sets of the 3-phase generic motor controller, an experiment platform is built. The experiment results agree well with the simulation results. Therefore, the feasibility of a two-stage integrated on-board charger that can operate at any voltage level is confirmed, where only the hybrid-exciting machine and its own driving system are used without any additional power devices.

Current Balancing Control Methods Using Advanced Carrier-Based Modulation for Five-Level Current Source Rectifiers

In an ideal ac–dc five-level current source multilevel converter, the dc current is equally divided between the two converters connected in parallel. However, current imbalances occur due to the nonidealities of the system, making the current balancing control to improve the multilevel converter performance. This article proposes two different methods for dc current balancing control for a five-level current source rectifier using an advanced carrier-based modulation strategy implemented through three different modulation patterns. A 6-kW prototype is constructed to demonstrate the current balancing control and a comparison among the methods is presented.

Research on Control Method of Multi-terminal Flexible DC Transmission System Based on Voltage Droop Control

Flexible DC transmission system has the advantages of small line loss, high reliability and strong controllability, and can reduce the frequency of system inactivity. In this paper, the voltage droop control method of flexible DC transmission system is studied in detail. Firstly, the principle and characteristics of the series structure, parallel structure and hybrid structure of multi-terminal flexible DC transmission system are introduced in detail. Based on this, the principle and characteristics of the control strategy of DC voltage droop control of the system are analyzed, and an improved voltage droop control strategy is proposed. Finally, a three-terminal flexible DC transmission system model is built on the Matlab/Simulink platform. The simulation results show that the control strategy plays a certain role in stabilizing DC, AC voltage, AC current and power balance control.

Non-isolated input-series–output-parallel three-level buck converter

This paper proposes a non-isolated input-series–output-parallel (ISOP) three-level buck converter. A theoretical analysis indicates that it has a large step-down ratio and low component voltage stress with the input and output terminals sharing the same ground. An automatic current-balancing mechanism is revealed, and it indicates that the parasitic parameters and inductance variations influence the automatic current-balancing effect. Thus, current-balance control is necessary. Considering that the proposed topology has an ISOP configuration, two voltage-balance control strategies are proposed to realize input capacitor voltage balancing and output inductor current balancing. One is implemented based on a two-loop configuration with an output voltage loop and a voltage-balance loop. The other is developed based on a three-loop configuration by adding one inner current loop on the two-loop configuration. Finally, experimental results have been given to verify both the proposed converter and voltage-balance control.

A Simple Control Strategy Extending Intrinsic Current Balancing Characteristics to Achieve a Full Operating Range for Interleaved Voltage-Doubler Boost DC-DC Converters

The interleaved voltage-doubler boost converter strategy exhibits a very good performance, namely, in a low conduction loss, an acceptable switch stress, a fast transient response, and a very high power density. However, the bottleneck for application in the interleaved topology lies in the limit of operating duty ratio. In this article, an intrinsic current-balancing control method to achieve full operating range in duty ratio is proposed, and it can be easily implemented by including a voltage limiter to the conventional control configuration. With this novel design, both voltage-doubler and the current-balancing characteristics can be achieved within full range in duty cycle without any current sensor. The proposed method is implemented in a field programmable gate array chip. The provided simulations and experimental results validate the proposed method.

Adaptive electronic differential control of vehicle by torque balance

Current adaptive torque balancing control of electric wheel-driven vehicle has shortcomings in electronic differential control of drive motor by using rotation speed mode. In order to solve this problem, an adaptive electronic differential control method of electric wheel-driven vehicle is proposed in this paper by torque balance. Firstly, by starting from the kinematics and dynamics of vehicle steering, the speed and force of each drived wheel in the steering are analyzed to explain the auxiliary role of electronic differential control to adaptive torque balancing, as well as influence of steering radius in vehicle. Then, electronic differential distribution by torque of wheel is used to control the abnormal jump interference and calculate the optimal combination of parameters in electronic differential control system. Finally, based on the optimal combination of these parameters, an adaptive electronic differential control of electric wheel-driven vehicle by torque balance is realized with fuzzy control in active and the reactive power. Experimental results show that the proposed method suppresses the abnormal jump interference factors of electronic differential control, as well as realizes the differential functions in control system. It has far-reaching significance by provideing a basic guarantee to realize adaptive electronic differential control system in electronic wheel-driven vehicle.

Decoupling of Current Balancing and Reference Tracking Control in Parallel Interleaved Converters

An attractive approach to increasing the output power and bandwidth of converters is through the parallel connection of multiple, subrated converter cells via mutually coupled inductors. Achieving a balanced contribution to the output current by all paralleled converter cells is critical; good reference tracking performance, however, should also be maintained. Since these two control tasks are coupled, tuning of the controller parameters is challenging. This article demonstrates a methodology for decoupling the output current reference tracking control task from the current balancing control. We show that once balancing and tracking controllers are decoupled, the controller parameter tuning can be conducted independently, simplifying design and analysis of controller performance. Experimental results are presented, which validate the proposed methodology, applied to a three-cell, parallel interleaved converter with cyclic cascade coupled inductor filter network, operating at 100 ${\rm V}_{\rm RMS}$ and 9 ${\rm A}_{\rm RMS}$ .

Arm Current Balancing Control for Modular Multilevel Converters Under Unbalanced Grid Conditions

Symmetrical ac-side current control is widely used for grid-connected modular multilevel converters (MMCs) under grid fault conditions. However, it is revealed that this control method can lead to unbalanced arm currents and consequently asymmetrical electrical stresses and nonuniform temperature distributions. This paper aims to analyze the mechanism of the unbalanced arm currents and propose an effective method to solve this problem. First, the electrical quantities inside MMCs are analyzed under unbalanced grid fault conditions. The analytical expressions of the unbalanced arm currents are derived considering different fault severities and operating conditions to reveal the “side-effects” of the symmetrical ac-side current control. After that, a zero-sequence ac voltage injection method is proposed. The injected voltage is directly derived from negative-sequence ac current controller and ac-side current with pure mathematical manipulations, which can be easily obtained without extra controllers. The effect of the injected voltage on the original modulation index is very limited according to an accurate quantitative analyzation. Moreover, the proposed method does not affect the already achieved symmetrical ac-side current control and the circulating current suppression. The effectiveness and performance of the proposed analysis and control method are verified by both simulation and experimental results.

Optimal Current Balance Control of Three-Level Inverter under Grid Voltage Unbalance: An Adaptive Dynamic Programming Approach

When the grid voltage is unbalanced, the positive and negative sequence components in the grid voltage cause grid current to be disordered. Under current balance control, proportional integral (PI) closed-loop control will increase the grid currents instantaneously, which affects the safety and reliability of the inverter operation, and PI parameters are difficult to select without the complete system mathematical model. This paper introduces an adaptive dynamic programming (ADP) approach to solve this problem. The best state feedback controller for the system is obtained by driving the ADP by the value iteration ( V I ) algorithm without the need for an accurate mathematical model. In the simulations, the ADP approach can improve the dynamic performance of the system, the current increase can be suppressed when the grid voltage is unbalanced, and the harmonic rate of output currents is reduced.

Final Design and Analysis of Control Strategies on ITER PF Converter

The ITER poloidal field (PF) coil power supply system consists of 14 basic converter units that feed six superconducting coils. The converter unit is the complicated, challenging, and unique system to realize four-quadrant operation compatible with the superconductive load and the demand for plasma control. This paper describes the final design of the control strategies, which are implemented in the local controller of the PF converter system. They are zero crossing current control strategy in circulating operation mode, current balance control strategy in parallel operation mode, and hysteresis band control strategy in mode transition. In addition, the performance of the control system is demonstrated by the analysis, and the control strategies are validated by the simulations and corresponding tests.

Current balancing control for an interleaved boost power converter

ABSTRACTThe interleaved boost power converter has the advantages of ripple cancellation and better efficiency. The major problem of the interleaved boost power converter is the current balancing among different phases of the boost power converters. In this paper, a current balancing control method for equalizing the currents of two-phase interleaved boost power converter is proposed. The output current can effectively detect the mismatch between the boost power converters for the interleaved boost power converter. The output current is used to perform both the current balance and the current-mode control. The salient feature is that only one current sensor is used in the proposed current balancing control method. A hardware prototype is developed, and the experimental results verify the performance of the proposed current balancing control method is as expected.

A Novel Model Predictive Control Strategy to Eliminate Zero-Sequence Circulating Current in Paralleled Three-Level Inverters

The main contribution of this paper is the proposal of a novel finite control set model predictive control (MPC)-based zero-sequence circulating current (ZSCC) elimination strategy for parallel operating three-level inverters without any modification or extra hardware on the three-level inverters. An equivalent model of the ZSCC is first developed, and the voltage differences of common-mode voltages (CMVs) among paralleled inverters as well as those of the neutral point potentials (NPPs) are proved to be the exciting sources of the ZSCC. With the analysis, an MPC-based zero CMV method (ZCMV-MPC) is presented to reduce the difference of CMVs among the paralleled inverters, meanwhile, an active NPP perturbation-based ZSCC feedback control method is proposed to further eliminate the ZSCC, that may be caused by dead-time effects and the asymmetries of both hardware and control parameters. With the proposed method, the ZSCC between paralleled inverters can be eliminated effectively, and both grid current tracking and NPP balance control can also achieve satisfactory performances. Simulation and experimental results supported the theoretical study and verified the effectiveness of the proposed scheme.

A Current Balance Control Strategy Applied in Inductively Coupled Power Transfer System With Multiple Parallel Pickup Modules

For large power application of inductively coupled power transfer (ICPT) system, such as traffic railway, multiple pickups have to be adopted. The condition exists that current unbalance of ICPT system with multiple parallel pickup modules, which will cause instability and low reliability. Aimed to solve the issue, the paper analyses the uncoupled module of ICPT system, assesses the impact of the mutual inductance, compensated state, and coil resistance on current unbalance, and put forward a novel current-balance strategy to balance the parallel currents by introducing the circuit of impedance transformation including semi-controlled rectifier, and BUCK, and BOOST circuits. Experiments have been done on the platform of ICPT prototype, and the experimental results are presented to show the correctness of the theoretical analysis and the effectiveness of the control strategy. When the output voltage is 220 V and load is 6 Ω, the output power is 8 kW. The amplitude ratio of the two parallel currents is 2.04 without control, and the amplitude of the two current is almost equal when adopting the strategy. System efficiency stays constant or increases slightly after adopting the proposed control strategy.

Coordinate Control of Power/Current for Grid‐Connected Inverter Based on PCI Controller under Unbalanced Grid Conditions

The oscillations on output power and distortion of the inverter currents will occur in the case of unbalanced grid voltage faults. Constant output power and good current quality cannot be achieved simultaneously. Aiming at these problems, a coordinate control strategy for suppressing power fluctuations and current harmonics is proposed by analyzing instantaneous power control and current balance control. The proposed control is achieved by adjusting the weight coefficient of current reference values to change the current harmonic contents based on proportional complex integral (PCI) controller and proportional multiple complex integral (PMCI) controller. The control strategy with a simple control structure neither needs to detect harmonic components of the inverter currents, nor needs to separate the positive and negative components of voltage and current, which is easy to be realized. The feasibility and effectiveness of the proposed control are verified by the comparison and analysis of simulation.

Elimination of zero sequence circulating currents in paralleled three‐level T‐type inverters with a model predictive control strategy

The configuration of modular paralleled three-level T-type inverters (3LT2Is) has been widely utilised to extend the system power rating. However, zero sequence circulating currents (ZSCCs) are generated when sharing the common DC-link and the AC side without isolated transformers. This study presents a novel model predictive control (MPC) based strategy to eliminate the ZSCC in parallel operating 3LT2Is. Both the differences of common-mode voltages (CMVs) and neutral point potentials (NPPs) between paralleled 3LT2Is are investigated to be the potential exciting sources of the ZSCC based on the developed model of the ZSCC. According to this conclusion, an MPC-based zero CMV method which adds an additional term to the cost function is used to reduce the differences of CMVs between paralleled 3LT2Is. Besides, a closed-loop ZSCC feedback control method is further introduced to compensate the ZSCC by modifying the cost function. With the proposed MPC-based ZSCC elimination strategy, the ZSCC between the paralleled 3LT2Is can be effectively eliminated in both steady and dynamic states. Besides, good performances can be achieved for both load current tracking and NPP balance control. Simulation and experimental results validate the effectiveness of the proposed ZSCC elimination strategy.

Simultaneous DC Current Balance and Common-Mode Voltage Control With Multilevel Current Source Inverters

The current source converter (CSC) has been popular in high-power medium-voltage applications. To increase the system power capacity and reduce the output harmonics, parallel connection of CSCs with multilevel current output is a practical approach. There are mainly two types of parallel based configurations. The structure with an independent dc link for each paralleled CSC can be regarded as the first configuration, where the dc current flowing into each CSC can be controlled from the rectifier side independently. The second type is constructed with only one current source rectifier (CSR) on the grid side and paralleled current source inverters (CSIs) on the load side, which could potentially reduce the cost and size of the system. However, with a common dc source, the dc current for each CSC should be carefully controlled with proper modulation design. At the same time, the common-mode voltage (CMV), which increases the motor line-to-ground voltage and causes additional stress to the insulation system, should also be suppressed. In this paper, with a focus on the shared dc-link structure, we thoroughly analyze the dc-link current flow and common-mode loop circuit. We propose a multilevel modulation strategy of the parallel CSI system considering the requirement of dc current balancing and CMV reduction to improve the overall system performance. The effectiveness of the proposed method is verified by both simulation and experiment in a transformerless parallel CSC system.

A New Configuration Using PWM Current Source Converters in Low-Voltage Turbine-Based Wind Energy Conversion Systems

Current source converter (CSC)-based wind energy conversion systems (WECSs) are recently gaining increasingly attention due to its reliable short-circuit protection. However, all existing CSC-based configurations are proposed for medium-voltage (MV) (3–4 kV) wind turbine systems, but not for low-voltage (LV) (690 V) systems which are dominating the market of WECS. The biggest challenge for using CSCs in LV systems is no proper switching devices in the market. This paper proposes a new configuration, where a proven modular LV voltage source converter is used as the generator-side converter to be compatible with an MV CSC. By such a design, MV CSCs are successfully used in LV systems with all advantages being inherited. In addition, this configuration features high reliability and reduced size and weight, thanks to the adoption of the modular converter. The performance of the configuration under normal and fault conditions are investigated. Apart from fulfilling traditional control objectives in WECS, a current balancing control is added to ensure safe operation. Additionally, limits and constraints of the configuration using in practice are discussed. Finally, simulation and down-scaled experimental results are presented.

Model predictive control methods of leakage current elimination for a three‐level T‐type transformerless PV inverter

This study presents finite control set model predictive control (FCS-MPC) methods to eliminate leakage current for a three-level T-type transformerless photovoltaic (PV) inverter without any modification on topology or any hardware changes. The proposed FCS-MPC methods are capable of eliminating the leakage current in the transformerless PV system by applying the defined candidate voltage vector (VV) combinations with only six medium and one zero VVs (6MV1Z) or three large and three small VVs, which generate constant common-mode voltage to perform the optimisation in every control period. With fewer VVs used for the optimisation, the computational burden can be significantly reduced. Furthermore, comparative analysis is performed to show that among these proposed methods, the 6MV1Z method can achieve satisfactory performances in both grid current tracking and neutral point potentials balance control even with less number of candidate VVs, which exhibits the FCS-MPC as an alternative control strategy to be used in the grid-connected transformerless PV system. Finally, experiments are performed to validate the analysis and the effectiveness of the proposed methods.

Independent Control of Multicolor-Multistring LED Lighting Systems With Fully Switched-Capacitor-Controlled $LCC$ Resonant Network

Current imbalance is a major problem in multistring LED lighting systems. Significant research efforts have been directed to solve the problem by either an active or passive approach. However, in view of some system requirements or other emerging lighting applications, independent control of different LED strings is getting more important to obtain different desirable brightness and/or color spectrums. The existing active and passive approaches have their limitations to perform current balancing and independent control simultaneously, thus posing another great challenge for the design of LED drivers. In this paper, a fully switched-capacitor-controlled $LCC$ resonant converter is designed to address this challenge. With the replacement of all fixed capacitors in the resonant tank of the $LCC$ converter with switch-controlled capacitors (SCCs), the regulation of the common ac bus voltage, current balancing, and individual current control of LED strings can be readily achieved with a single LED driver by varying the effective capacitances of the SCCs under constant switching frequency. In this way, the circuit complexity can be greatly reduced while the circuit performances can be significantly improved. An experimental prototype of driving LED growth light for indoor farming applications is designed and constructed to verify the idea.