Abstract: The present disclosure provides a positive and negative bipolar modular multilevel alternating current (AC)-AC frequency converter, including a modular multilevel frequency converter and a three-phase three-winding bipolar transformer. The modular multilevel frequency converter has an ABC three-phase structure, each phase includes the same upper bridge arm and lower bridge arm, and the upper and lower bridge arms include n full-bridge sub-modules (FBSMs) and a bridge arm inductor connected in series. The positive and negative bipolar modular multilevel AC-AC frequency converter can be further expanded and enable bidirectional energy flow. In the present disclosure, by introducing a positive and negative bipolar three-winding transformer, an AC-AC frequency converter topology with simple structure, high efficiency, flexibility and reliability is realized, which has high practical value.

Abstract: The present disclosure provides a positive and negative bipolar modular multilevel alternating current (AC)-AC frequency converter, including a modular multilevel frequency converter and a three-phase three-winding bipolar transformer. The modular multilevel frequency converter has an ABC three-phase structure, each phase includes the same upper bridge arm and lower bridge arm, and the upper and lower bridge arms include n full-bridge sub-modules (FBSMs) and a bridge arm inductor connected in series. The positive and negative bipolar modular multilevel AC-AC frequency converter can be further expanded and enable bidirectional energy flow. In the present disclosure, by introducing a positive and negative bipolar three-winding transformer, an AC-AC frequency converter topology with simple structure, high efficiency, flexibility and reliability is realized, which has high practical value.

Abstract: The present invention discloses an isolation forest (IF)-based modular multilevel converter (MMC) open-circuit (OC) fault diagnosis method, including the following steps: sampling capacitor voltages of submodules (SM), constructing an isolation tree (IT) according to capacitor voltage data, and calculating a depth of each SM in the IT; and forming an IF based on the ITs, calculating average depths of the SMs in the IF, taking an SM with the minimum average depth as an output of the IT, and finally locating a faulty SM by an output buffer to realize accurate location of the faulty SM. Only capacitor voltages of SMs are involved, and no extra hardware resources are required. System parameters are not involved, construction of a system mathematical model and manual setting of an empirical threshold are not required, and the robustness is high.

Abstract: Disclosed are a multi-port magnetic network energy router and a control method. A magnetic network energy router includes a dual magnetic plate crimped N-winding transformer containing distributed magnetic core columns, and N full-bridge converters. The control method includes: S1. calculating equivalent connection inductance between different converters; S2. calculating steady-state control phase shift angles on the basis of reference powers of all converters; S3. calculating a power decoupling control matrix; S4. calculating control phase shift angle micro-increments of second to Nth converters by the power closed-loop control; and S5. controlling the converters to output square-wave voltages of 50% duty with different phase shift angles, and realizing given-power control.

Abstract: Disclosed are a multi-port magnetic network energy router and a control method. A magnetic network energy router includes a dual magnetic plate crimped N-winding transformer containing distributed magnetic core columns, and N full-bridge converters. The control method includes: S1. calculating equivalent connection inductance between different converters; S2. calculating steady-state control phase shift angles on the basis of reference powers of all converters; S3. calculating a power decoupling control matrix; S4. calculating control phase shift angle micro-increments of second to Nth converters by the power closed-loop control; and S5. controlling the converters to output square-wave voltages of 50% duty with different phase shift angles, and realizing given-power control.

Abstract: The present invention discloses an isolation forest (IF)-based modular multilevel converter (MMC) open-circuit (OC) fault diagnosis method, including the following steps: sampling capacitor voltages of submodules (SM), constructing an isolation tree (IT) according to capacitor voltage data, and calculating a depth of each SM in the IT; and forming an IF based on the ITs, calculating average depths of the SMs in the IF, taking an SM with the minimum average depth as an output of the IT, and finally locating a faulty SM by an output buffer to realize accurate location of the faulty SM. Only capacitor voltages of SMs are involved, and no extra hardware resources are required. System parameters are not involved, construction of a system mathematical model and manual setting of an empirical threshold are not required, and the robustness is high.

Abstract: A loss optimization control method for modular multilevel converters (MMCs) under fault-tolerant control is disclosed. The method includes the following steps: when a fault of a SM in a MMC occurs, bypassing the faulty SM to achieve fault-tolerant control; suppressing the fundamental circulating current using a fundamental circulating current controller; respectively calculating the loss of each SM in faulty arms and healthy arms by using loss expressions of different switching tubes in SMs of the MMC; aiming at the loss imbalance between the arms of the MMC, taking the loss of a healthy SM as the reference, adjusting the period of capacitor voltage sorting control in the faulty SMs, achieving the loss control over the working SMs in the faulty SMs, and finally achieving the loss balance of each SM in the faulty arms and the healthy arms. Compared with the conventional methods, the proposed method is easier to implement and does not increase the construction cost of MMCs.

Abstract: The present invention discloses a method for modeling sequence impedance of a modular multilevel converter (MMC) under phase locked loop (PLL) coupling. The method includes the following steps: S1, establishing a circuit topology model; S2, establishing a PLL output characteristic model; S3, establishing a PI controller output control small signal model under a dq axis; S4, deducing a modulation small signal; and S5, calculating MMC port impedance. According to the method, a precise MMC port impedance model is established by analyzing a double mirror frequency coupling effect in the output of a modulation signal in a control link caused by a phase angle disturbance and comprehensively considering the combination of the multi-harmonic coupling effect of an MMC.

Abstract: A loss optimization control method for modular multilevel converters (MMCs) under fault-tolerant control is disclosed. The method includes the following steps: when a fault of a SM in a MMC occurs, bypassing the faulty SM to achieve fault-tolerant control; suppressing the fundamental circulating current using a fundamental circulating current controller; respectively calculating the loss of each SM in faulty arms and healthy arms by using loss expressions of different switching tubes in SMs of the MMC; aiming at the loss imbalance between the arms of the MMC, taking the loss of a healthy SM as the reference, adjusting the period of capacitor voltage sorting control in the faulty SMs, achieving the loss control over the working SMs in the faulty SMs, and finally achieving the loss balance of each SM in the faulty arms and the healthy arms. Compared with the conventional methods, the proposed method is easier to implement and does not increase the construction cost of MMCs.

Abstract: The present invention discloses a method for modeling sequence impedance of a modular multilevel converter (MMC) under phase locked loop (PLL) coupling. The method includes the following steps: S1, establishing a circuit topology model; S2, establishing a PLL output characteristic model; S3, establishing a PI controller output control small signal model under a dq axis; S4, deducing a modulation small signal; and S5, calculating MMC port impedance. According to the method, a precise MMC port impedance model is established by analyzing a double mirror frequency coupling effect in the output of a modulation signal in a control link caused by a phase angle disturbance and comprehensively considering the combination of the multi-harmonic coupling effect of an MMC.

Abstract: A hybrid modular multilevel converter having fault blocking capability, and a control method thereof are disclosed. The hybrid modular multilevel converter has an ABC three-phase structure, each phase includes an identical upper arm and lower arm, and the upper arm and the lower arm are each composed of N submodules, including M unipolar full bridge submodules and N-M half bridge submodules, which are connected in series; two identical arm inductors are connected in series between a lower end of the upper arm and an upper end of the lower arm in a same phase; and upper arms and lower arms of three phases are connected in a staggered manner through six thyristor branches, the upper ends of the upper arms of the three phases are short-circuited and are connected to a DC side via a first isolating switch.

Abstract: A hybrid modular multilevel converter having fault blocking capability, and a control method thereof are disclosed. The hybrid modular multilevel converter has an ABC three-phase structure, each phase includes an identical upper arm and lower arm, and the upper arm and the lower arm are each composed of N submodules, including M unipolar full bridge submodules and N-M half bridge submodules, which are connected in series; two identical arm inductors are connected in series between a lower end of the upper arm and an upper end of the lower arm in a same phase; and upper arms and lower arms of three phases are connected in a staggered manner through six thyristor branches, the upper ends of the upper arms of the three phases are short-circuited and are connected to a DC side via a first isolating switch.

Abstract: The present invention discloses a high-power machine drive system based on a modular multilevel converter (MMC), which belongs to the technical field of power generation, power transformation, or power distribution. The high-power machine drive system consists of a modular multilevel converter and a multi-pulse cycloconverter. The MMC outputs k phases of high-frequency AC voltages with a phase difference of 2?/k, and the multi-pulse cycloconverter outputs a low-frequency voltage to drive a corresponding machine. According to the present invention, the MMC is combined with the multi-pulse cycloconverter, and by adopting the MMC that operates at a high frequency, the capacity, the volume, and the weight of the energy storage capacitor of the MMC are reduced, the voltage level at the DC side of the MMC is increased, and the capacity of the drive system is increased.

Abstract: The present invention discloses a high-power machine drive system based on a modular multilevel converter (MMC), which belongs to the technical field of power generation, power transformation, or power distribution. The high-power machine drive system consists of a modular multilevel converter and a multi-pulse cycloconverter. The MMC outputs k phases of high-frequency AC voltages with a phase difference of 2?/k, and the multi-pulse cycloconverter outputs a low-frequency voltage to drive a corresponding machine. According to the present invention, the MMC is combined with the multi-pulse cycloconverter, and by adopting the MMC that operates at a high frequency, the capacity, the volume, and the weight of the energy storage capacitor of the MMC are reduced, the voltage level at the DC side of the MMC is increased, and the capacity of the drive system is increased.