With the increasing penetration rate of distributed photovoltaics in distribution network, the problems of photovoltaic power backflow and voltage overrun are becoming more and more serious. Meanwhile, the distribution network is faced with different control methods and regulation potentials of photovoltaic, which makes the heterogeneous photovoltaics difficult to coordinate and further affects the regulation and operation of distribution network. Therefore, an optimal regulation method for distribution network clustering (DNC) considering the voltage governance potential of heterogeneous distributed photovoltaics (HDPV) is proposed. First, to solve the problem of node voltage overrun under a scenario of the integration of high-penetration distributed photovoltaics, a DNC partitioning method considering voltage deviation sensitivity is proposed by combining the voltage deviation, power balance and node coupling degree. Second, the active and reactive power regulation characteristics of HDPV are analyzed, and a regulation model in different operation modes is established. Furthermore, based on the synchronous alternating direction method of multipliers, an optimal regulation method for DNC considering the voltage governance potential of HDPV is developed with an objective of minimizing the comprehensive operating cost and voltage deviation. Finally, an improved IEEE 33-node distribution network is used as an example to verify the effectiveness of the proposed optimization model, and results show that the proposed strategy realizes an efficient control of HDPV, and it can guarantee an economic operation of distribution network while improving its voltage level.

Aimed at the issue of self-healing and coregulation of distributed energy storage in multi-energy distribution networks under fault, three key aspects are studied, i.e., improving the state estimation accuracy of energy storage batteries, fully utilizing the potential of demand-side load response, and reducing the lifetime losses of energy storage and the system’s operation costs. On this basis, an optimal configuration method for energy storage taking into account lifetime losses and demand response is proposed, which can reduce the lifetime losses of energy storage and the system’s operation costs while realizing the adaptive regulation of states of the energy storage system. First, a recalibration step is added to improve the extended Kalman filter algorithm, and the estimator is allowed to bypass ineffective updates in the meantime, so as to ensure a precise state estimation of energy storage batteries. Second, a demand response model based on price elasticity and behavioral correlation is constructed to optimize the load curves through a dual-effect of price signals and incentive fees. Finally, a mixed-integer linear programming model for energy storage configuration is developed to incorporate the costs of battery lifetime losses, and a demand response model is used to adjust load while integrating the incentive fees into the daily operation cost. Based on the real-time, dynamic and high-precision estimation results, the approach adaptively refines parameters such as the battery lifetime losses and the depth of discharge, as well as the lower and upper bounds of state-of-charge constraints. The analysis results of a case study demonstrate that compared with other models, the proposed model can significantly reduce the lifetime losses of energy storage and the system’s daily operation costs.

With the access of power electronic equipment to distribution networks, the harmonic problem therein is becoming increasingly serious. Photovoltaic (PV) inverters are topologically homologous with active filters, which have the capability of controllable harmonic management. However, the application of PV inverters for harmonic management involves multiple entities of interest, more independence is granted to PV users in terms of pricing, and there is still a lack of trading models that account for harmonic management. First, the concept of a harmonic management aggregator is proposed, which is involved in harmonic management trading as a third party and thus realizes a unified constraint on the random pricing behaviors of multiple PV user. Second, a two-layer master-slave game harmonic management trading model with the participation of three parties is formulated, in which a price game between the harmonic management aggregator and harmonic source users is realized in the upper layer and a price game between the aggregator and PV users is performed in the lower layer. Finally, the proposed method is verified by an IEEE 13-node system, and simulation results show that the established model has an obvious harmonic management effect and different parties have significant benefits, which can effectively incentivize the three parties to participate in the management.

Resonant converters with a wide input range are much in demand in energy storage and new energy systems. When the voltage gain characteristics of an LLC resonant converter are calculated using the operation mode analysis (OMA) method, it is often assumed in previous studies that the circuit under phase shift control is in discontinuous conduction mode, resulting in significant errors in the gain analysis result of a converter which is in continuous conduction mode. On the basis, an OMA calculation method for an LLC resonant converter with a voltage doubling rectifier is proposed to identify the two modes. First, the criterion for determining whether the converter operates in continuous or discontinuous conduction mode is obtained through the modal analysis. Then, the normalized calculation models of these two modes are derived by OMA, and the calculation results and the criterion are used to verify the actual mode. Finally, a comparison among the calculated, simulated and experimental voltage gain curves under different conditions indicates the effectiveness of the proposed method. This method is more applicable to LLC converters in possible continuous mode, improves the accuracy of the gain analysis and is helpful for parameter design.

When a three-level bidirectional DC converter is under carrier modulation, the switching between its forward and reverse operations is not smooth and the dynamic response is slow, which will easily cause harmonics in the resonant circuit. To solve these problems, a carrier modulation method for the three-level bidirectional DC converter based on neutral point shift is proposed. The working principle for the bidirectional DC converter is analyzed. Based on the principle of neutral point shift, the phase angle mode of three-phase output voltage from the converter is adjusted. On the basis of constant switching frequency, the neutral point shift voltage with different amplitude modulation ratios is calculated. According to the actual fault state, the shift between adjacent carriers in the same phase unit is rectified, and the carrier phase shift pulse width modulation is used to modulate the carrier of the three-level bidirectional DC converter. Simulation results show that the proposed modulation method can effectively control the output waveform of the three-level bidirectional DC converter. When the converter operates normally, the amplitude modulation ratio is greater than 1.0, the phase voltage is saturated, and the modulation signal is overshoot.

DC-DC converters are key devices for realizing the interconnection of high voltage direct current (HVDC) networks with different voltage levels and line topologies. Owing to their advantages such as increasing the controllability of power grid and enhancing the power flow control, voltage regulation and fault blocking capabilities of power grid, DC-DC converters have become one of the research hotspots with the gradual construction of novel power systems, among which the DC modular multilevel converter (DC-MMC) is an effective and non-isolated method for interconnecting HVDC systems with the same line topology. However, DC systems in practice often have large differences in voltage levels and line topologies. In this paper, a novel control strategy for a flexible DC-MMC is proposed, which can realize the interconnection of HVDC systems with different line topologies, such as bipolar and symmetric monopolar interconnection. First, the characteristics of different line topologies in a HVDC transmission system are introduced in detail. Then, a mathematical model including variable transformation is established for the novel DC-MMC, and a control method based on an average bridge arm model and simplified DC grid is put forward. Finally, the simulation results in MATLAB/Simulink show that the proposed method can guarantee the normal operation of DC-MMC in both the normal and degraded modes.

A soft-switching high step-up converter based on switched-coupled-inductor is proposed to improve its voltage gain and efficiency for the applications of fuel cell. The switched-coupled-inductor and switched capacitor are utilized to achieve a high voltage gain under an appropriate duty cycle, and an active clamp circuit is used to reduce the voltage stress of power switches and recycle the energy of leakage inductor. All the power switches achieve zero voltage switching. In addition, the number of components is less, the power loss is reduced, and the efficiency and power density are improved. The operation principle and steady-state analysis are also introduced in detail. Finally, a 250 W experimental prototype was fabricated to verify the performance. Results show that the measured maximum and full-load efficiencies were 97.4% and 96.1%, respectively.

As the interface between a new energy power generation system and power grid, inverters play an important role. However, the stable operation of the system may be threatened by the changes in grid impedance in a weak grid environment, interaction between parallel inverters and delay in the control system. Under this background, a novel virtual impedance remodeling strategy based on the passivity theory and traditional proportional voltage feedforward is proposed, which can eliminate the non-passive region below the Nyquist frequency and keep the inverter output impedance phase within [-90°, 90°]. The results of numerical examples show that the proposed scheme can keep a good stability of the inverter parallel system under changes in grid impedance, number of inverters and parameters.

In an LCL grid-connected inverter system under digital control, the control delay reduces the performance of a capacitive current feedback active damping method for suppressing resonance peaks, i.e., the effective damping zone is only 0–f_s/6 (where f_s is the sampling frequency), which seriously affects the system stability. Aimed at this problem, a delay compensation strategy is proposed. First, a delay compensation link is added to the forward path to increase the system boundary frequency. Then, the stable conditions for the system after compensation are deduced according to the stability criterion. Finally, the capacitive current feedback coefficient is designed under the new stable conditions. The analysis results show that the proposed strategy can widen the effective damping zone to 0–0.4f_s, thereby expanding the selection range of the filter resonant frequency f_r, reducing the inverter’s design cost and improving the system’s adaptability to a wide range of grid impedance changes. Simulation and experimental results show that the proposed strategy widens the stable operation zone of the system and improves its poor stability when the resonant frequency f_r is equal to or more than f_s/6 under the weak grid.

Since the traditional algorithm for the space vector modulation (SVM) of a VIENNA rectifier is computationally intensive, complicated and difficult to implement digitally, a fast algorithm for implementing the SVM of the VIENNA rectifier is proposed in this paper. This algorithm does not require coordinate transformation, avoids a large number of root square and trigonometric operations, and only requires simple logic judgment and addition and subtraction operations to quickly determine the duty cycle of a three-phase drive signal, which is easy to implement digitally and saves the time resources of DSP. In addition, a neutral point voltage control strategy is redesigned accordingly. Finally, the effectiveness of the proposed fast algorithm was verified by MATLAB simulations and experiments conducted on a hardware platform.