Liping Zhong’s research while affiliated with Changshu Institute of Technology and other places


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Publications (12)


A CLCLC-Type Immittance Resonant DAB Converter with Dual Unbalanced Modulation for Electric Vehicle Charger
  • Article
  • Full-text available

January 2024

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28 Reads

IEEE Transactions on Transportation Electrification

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The DC-DC converter is a crucial component of an electric vehicle (EV) charger, and its performance is essential for the charging speed and driving range of EVs. Despite recent advancements in converter topology and modulation techniques, enhancing both switching and conduction losses in dual active bridge (DAB) converters continues to be challenging. This paper introduces a novel dual unbalanced modulation (DUM) for EV chargers. The DUM strategy, when combined with a CLCLC-type immittance resonant DAB (IRDAB) converter, can simultaneously reduce the switching and conduction losses. When the rated output power exceeds 25%, the DUM strategy operates in full-bridge mode, achieving zero-voltage switching (ZVS) operation of all switches, minimizing backflow power on both sides, and maintaining near-minimum root mean square (RMS) currents. For output power rated below 25%, the DUM strategy shifts to half-bridge mode. This mode slightly increases the RMS currents, yet it still ensures ZVS operation of all switches and minimum backflow power on both sides. Theoretical analysis and experimental results demonstrate that, when compared to conventional modulation strategies, DUM strategy maintains the highest efficiency across the entire load range.

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Zero-Sequence-Current Suppression of Open-End Winding PMSM with Common DC Bus Based on Virtual Vector Control

January 2023

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18 Reads

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2 Citations

IEEE Transactions on Industrial Electronics

This paper presents a novel zero-sequence-current suppression method for open-end winding permanent magnet synchronous motor. Firstly, a pair of orthogonal DC signals proportional to the amplitude of the zero-sequence-current are detected through the orthogonal gate-integral circuit, which will be regarded as the projection of the zero-sequence-current on the three times synchronous rotating coordinate system. Secondly, by imitating the idea of vector control, the two projections are tracked respectively, and two orthogonal voltage components are obtained. Finally, the zero-sequence-voltage for compensating the zero-sequence-current is obtained by performing synchronous rotation inverse transformation on the two voltage components. The algorithm is simple and can realize the error-free tracking of the zero-sequence-current by common PI regulator. It can not only significantly improve the suppression accuracy of zero-sequence-current, but also reduce the design difficulty of the controller. The experimental results verify the effectiveness and feasibility of this strategy.



Figure 1. The topology of the Dual-Transformer DC-DC Resonant Converter.
Figure 2. The steady-state operation waveforms of the DTRC. Interval 1 (t 0 -t 1 ) (Figure 3a): Before t 0 , switches M B and M D were conducted. At t = t 0 , M B is turned off and M A is turned on. The current flows through d A . The resonant current i r is negative and increases gradually. On the secondary side, the resonant current flows through diodes d 2 and d 3 ; therefore, the voltages v xz = +V H /2, v yz = −V H /2, v mn = −V L . This interval ends when M D is turned off and M C is turned on. Interval 2 (t 1 -t 2 ) (Figure 3b): In this interval, M D is turned off and M C is turned on. The resonant current i r is constantly negative and gradually increasing. Meanwhile, it flows through diodes d 2 and d 3 . Therefore the voltage v mn = −V L . The currents flow through d A and d C on the primary side. The mid-point voltages v xz = +V H /2, v yz = +V H /2. This interval ends when i r reaches 0. Interval 3 (t 2 -t 3 ) (Figure 3c): Compared with Interval 2, the resonant current changes the polarity in this interval. It increases from 0 to positive and flows through diodes d 1 and d 4 . The switch currents become positive and flow through M A and M C , so the voltages v xz = +V H /2, v yz = +V H /2, v mn = +V L . This interval ends when M A is turned off and M B is turned on. Interval 4 (t 3 -t 4 ) (Figure 3d): This interval begins when M A is turned off and M B is turned on forcibly. The current is shifted from M C to d B , which enables the zero-voltage turn-on of M B . There is no change on the secondary side except for a gradual decrease in the resonant current. The voltages v xz = −V H /2, v yz = +V H /2, v mn = +V L . This interval lasts until M C is turned off and M D is turned on.
Figure 3. The equivalent circuits during different intervals of DTRC.
Figure 4. The FHA equivalent circuit of the DTRC.
Figure 5. The ZVS operation regions for the trajectory of the power transfer.

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Analysis and Design of a High-Frequency Isolated Dual-Transformer DC-DC Resonant Converter

December 2022

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731 Reads

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2 Citations

Electronics

This paper presents the operation, analysis, design, simulation, and experimental results for a proposed Dual-Transformer DC-DC Resonant Converter (DTRC). A three-arm bridge is employed on the input side and an H-type bridge is employed on the output side of the DTRC, and the two bridges are connected with two high-frequency (HF) transformers. By optimizing the ratio k of the two HF transformers, the proposed DTRC has a lower boundary power for losing zero-voltage switching (ZVS). That means the DTRC has a wider ZVS operation range and lower switching loss when compared with a traditional soft-switching pulse width modulation (PWM) resonant converter. The operation principle, power transfer, ZVS characteristics, and design procedures are analyzed in detail. Both simulation and experimental results prove the feasibility and superiority of the proposed Dual-Transformer DC-DC Resonant Converter.


Three-phase Reference Voltage Independent Control Based Discontinuous Modulation Algorithm for Open-End Winding PMSM Fed by Dual 3-Level inverters with Common DC Bus

July 2022

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21 Reads

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8 Citations

IEEE Transactions on Power Electronics

This article proposes a novel modulation strategy forthe open-end winding permanent magnet synchronous motor (OEW-PMSM) fed by dual three-level inverters with common dc bus. First, by constructing a virtual orthogonal zero-sequence current, the tracking of the sinusoidal signal is transformed into the tracking of the dc signal, which improves the performance of suppressing the zero-sequence current. Second, making use of the characteristic that the phase voltage of the OEW-PMSM can be controlled independently, the neutral point voltage is balanced by synchronously adjusting the reference voltages of the dual inverters in each phase, which does not need to inject zero-sequence voltage like in the traditional method and will not conflict with the suppression of the zero-sequence current. Finally, by carefully setting the adjustment direction and amplitude of the reference voltages of dual inverters, the switching times are reduced to the same level as that of the single inverter, and the switching loss of the two inverters is equalized. The experimental results verify the effectiveness and feasibility of this strategy.


60 ° phase difference current control‐based open‐phase fault‐tolerant operation strategy for open‐end winding permanent synchronous motor

June 2022

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14 Reads

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1 Citation

International Journal of Circuit Theory and Applications

As the most favorable candidate of electric vehicle drive system, the fault tolerance of open‐end winding permanent synchronous motor (OEW‐PMSM) fed by dual inverter with common DC bus is of great significance because it is related to the reliability and safety of the system. Aiming at the most common fault of open‐phase, a fault‐tolerant operation strategy based on 60° phase difference current control is proposed by making full use of the characteristics that each phase of OEW‐PMSM can be controlled independently. Through this method, the same stator rotating magnetic field can be generated before and after the open‐phase fault without reconfiguring the controller, so as to reduce the torque ripple after the fault and ensure the continuous and stable fault‐tolerant operation of the motor. In addition, this method can reduce the switching times by 50%. The proposed method can reduce the switching loss by 50% compared with the ordinary modulation method, reduce the switching loss, and will not produce large zero sequence current. Experimental results show that the fault‐tolerant performance of this strategy is significantly improved compared with the traditional methods. The general control method proposed in this paper can realize fault‐tolerant operation without reconfiguring the controller. The same stator rotating magnetic field can be generated before and after the fault, which reduces the torque ripple after the fault, ensures the stability of open‐phase fault operation, and reduces the current after the fault. The discontinuous PWM of dual inverters is realized by a very simple method, which reduces the switching times to the level of single inverter and greatly reduces the switching loss.


Model Predictive Control based Discontinuous PWM Algorithm for 3L-NPC Inverter

September 2021

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14 Reads

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8 Citations

Journal of Electrical Engineering and Technology

This paper proposes a novel model predictive control based discontinuous PWM strategy for 3L-NPC inverter. Through the model predictive control principle and special output level sequence arrangement, the optimal voltage vector and zero sequence voltage are selected, so that the neutral point voltage can be controlled on the basis of discontinuous modulation strategy, thus achieve the purpose of balancing the neutral point voltage and reducing the switching loss. Because there are most three elements in the control set, the calculation of this method is quite simple. Compared with carrier based PWM and space vector PWM, it does not need vector synthesis and complex zero sequence voltage calculation, so it is easy to implement. Experimental results verify the validity of the method.


A hybrid discontinuous PWM algorithm of balancing neutral point voltage for 3L‐NPC inverter

July 2021

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11 Reads

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3 Citations

International Journal of Circuit Theory and Applications

Wider linear modulation range, less switching loss, and simplicity are the goals pursued by various modulation methods of multilevel inverters. This paper proposes a new hybrid discontinuous pulsewidth modulation (HDPWM) strategy for three‐level neutral‐point‐clamped (3L‐NPC) inverter that can achieve the above goals to a certain extent. According to the position of the reference voltage vector and the actual situation of the neutral point voltage, different control modes and clamping types are selected. The neutral point voltage is controlled by DPWM strategy, which can not only greatly reduce the switch loss but also maintain the balance of the neutral point voltage and expand the linear modulation range. The implementation of the algorithm combines the advantages of carrier‐based PWM (CBPWM) and space vector PWM (SVPWM). There is no need to select the nearest three vectors (NTVs) and calculate their dwell time. Only the reference voltage needs to be modified according to the control requirements, and then by comparing the modified reference voltage with the carrier, the driver pulse required by the switching devices can be generated. Compared with the existing PWM methods, it is more simple and easy to implement. Experimental results verify the validity of the method. (1) The NP voltage is balanced by selecting different clamping types in real time. (2) The idea of discontinuous PWM (DPWM) is adopted, and through a special carrier comparison method, the switching times can be reduced by 1/3. (3) The advantages of SVPWM and CBPWM are combined to generate driving pulse, which saves the complex process of voltage vector synthesis and makes the algorithm easy to implement.


Vector Decomposition and Model Predictive Control based Hybrid PWM Algorithm for 5L-ANPC Inverter

June 2021

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11 Reads

International Journal of Electronics

This paper proposes a novel modulation algorithm based on vector decomposition and model predictive control for 5-level active neutral-point-clamped (5L-ANPC) inverter. Firstly, the control of 5-level inverter is transformed into that of 3-level inverter by vector decomposition, which reduces the control complexity. Secondly, based on the framework of 3-level inverter, the optimal zero sequence voltage and switch state sequence are selected by multi-objective optimization of model predictive control to balance the neutral point voltage and floating capacitors voltages simultaneously. Finally, according to the optimal choice, single-carrier comparison is used to generate the drive signal, which does not require traditional dual-carrier or vector synthesis, and is relatively easy to implement. Experimental results verify the validity of the method.


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Citations (5)


... The obtained results of calculations and simulation tests were verified by tests of a laboratory model of the converter, conducted using the topology shown in Fig. 10. Figure 11 shows a photos of the experimental setup capable of investigating voltage and current waveforms (Fig. 12) of the primary winding and the determining the total power losses occurring in the converter. Total transformer losses ∆P TR can be expressed using two alternative Formulas: (4) and (5). ...

Reference:

Analysis and estimation of power losses in high-power, high-frequency transformers for isolated DC/DC converters
Analysis and Design of a High-Frequency Isolated Dual-Transformer DC-DC Resonant Converter

Electronics

... Another study explores a carrier-based DPWM for single and parallel 3L T-Type converters, focusing on neutral point potential balancing, which is extendable to FLNPCHC [19]. A novel low-frequency virtual space vector PWM (SVPWM) for a single-phase NPC 3L inverter, which improves output average voltage and bus voltage utilization [20]. Adapting PS-PWM techniques to FLNPCHC can significantly improve voltage regulation, performance, and efficiency. ...

Three-phase Reference Voltage Independent Control Based Discontinuous Modulation Algorithm for Open-End Winding PMSM Fed by Dual 3-Level inverters with Common DC Bus
  • Citing Article
  • July 2022

IEEE Transactions on Power Electronics

... This includes conflicts such as balancing performance in steady-state with low switching frequency operation. Regarding MPC methods applied to PWM rectifiers, they can be classified according to VOC and DPC techniques, including model predictive current control (MPCC) [9], model predictive virtual flux control (MPVFC) [8,10], model predictive direct power control (MPDPC) [9,11], and model predictive virtual flux direct power control (MPVFDPC) [7,12]. Despite sharing the prediction concept, these approaches utilize proper cost functions to obtain diverse performances, especially under conditions of distorted source voltage states. ...

Model Predictive Control based Discontinuous PWM Algorithm for 3L-NPC Inverter
  • Citing Article
  • September 2021

Journal of Electrical Engineering and Technology

... In higher number of levels, both of neutral-point clamped (NPC) and flying capacitor converters have the problem of balancing the capacitors (dc-link capacitors for NPC and flying capacitors for flying capacitor converters). Recently, several works have been done on balancing the capacitors in NPC [7][8][9][10], flying capacitor [11][12] and modular multilevel [13][14][15] topologies. ...

A hybrid discontinuous PWM algorithm of balancing neutral point voltage for 3L‐NPC inverter
  • Citing Article
  • July 2021

International Journal of Circuit Theory and Applications

... 16 To increase the electric power assist torque and further improve the performance of the booster motor, permanent magnet synchronous motors (PMSM) and AC induction motors are also widely used in EPS systems. [17][18][19][20] Especially open-end winding PMSM motor driven by two different inverters as illustrated in Refs., [21][22][23] where the dual inverter composed of double two-level inverters can produce space vector locations identical to that of a three-level inverter. So, an increase of dc-link voltage utilization in the open-end winding topology is achieved comparing with the two-level inverter fed star-connected winding topology. ...

Reference Voltage Self-Equalization based Modulation Strategy for Open-End Winding PMSM Fed by Dual 3-Level inverters with Common DC Bus
  • Citing Article
  • March 2021

IEEE Journal of Emerging and Selected Topics in Power Electronics