Low-cost charging pile topology oriented to'fast charging-slow discharging 'scene of electric vehicle and modulation strategy of low-cost charging pile topology

Abstract

The invention discloses a low-cost charging pile topology for a fast charging-slow discharging scene of an electric vehicle and a modulation strategy of the low-cost charging pile topology. According to the low-cost charging pile topology, a group of half-bridge type shunt diodes are connected in parallel to each phase of main bridge arm of a traditional T-shaped three-level converter. In the discharging mode, the charging pile is consistent with a traditional T-type three-level operation state, and works in a slow-release scene with rated power and below. In the charging mode, the charging pile continuously shunts the main bridge arm power device by using the additionally arranged shunting diode, so that the current stress and thermal stress of the main bridge arm power device are reduced; and through a self-adaptive modulation strategy of three-level / two-level modulation mode switching, the loss distribution of a power device is optimized, the active power output capability of the charging pile in a charging mode is improved, the fast charging operation of the charging pile with over-rated power is realized, the equipment capacity utilization rate of the charging pile is fully excavated, and the method has remarkable engineering application value.

Description

Technical Field

[0001] The present invention relates to the field of AC-DC power conversion technology, and in particular to a low-cost charging pile topology and modulation strategy for the "fast charge-slow discharge" scenario of electric vehicles. Background Art

[0002] Against the backdrop of the global low-carbon transformation of the energy structure, the new energy vehicle industry has become the core carrier for achieving the "dual carbon" strategy, which has promoted the construction and development of fast charging piles.

[0003] However, existing V2G charging stations focus on providing fast-charging power during charging mode. When electric vehicles are connected to the grid as distributed power sources for discharge, owners often prefer not to discharge at high power levels due to concerns about battery life. This bidirectional power asymmetry results in low equipment utilization. Due to the "fast charging and slow discharge" requirements of electric vehicles, charging stations in current fast-charging stations face severe technical challenges. To improve equipment utilization, a high-overload solution can leverage the high-overload characteristics of the equipment to provide fast-charging power during charging, while also ensuring the rated power of the equipment meets the "slow discharge" requirements of electric vehicles. However, in engineering, most high-overload solutions employ over-capacity, significantly increasing system costs while failing to fundamentally address the equipment utilization issue.

[0004] There are also related studies on achieving high overload in converters, mainly focusing on modulation strategies and heat dissipation structures: 1. Reducing the temperature rise of power devices by adjusting the switching frequency or changing the modulation strategy, but this method is not very effective and will lead to a decrease in the quality of the converter's output power; 2. Improving the heat dissipation structure and improving the heat dissipation performance can suppress the temperature rise of power devices, but this solution has little effect on instantaneous temperature changes.

[0005] In summary, existing high overload solutions for converters have many drawbacks, such as excessive costs and poor power quality. Therefore, a new solution is urgently needed to address these issues. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to propose a low-cost charging pile topology and its modulation strategy for the "fast charging-slow discharging" scenario of electric vehicles in response to the shortcomings of the existing technology. While ensuring the utilization rate of the equipment, the active output capacity of the charging pile is improved, thereby realizing the "fast charging" operation of the charging pile exceeding the rated power without significantly increasing the hardware cost.

[0007] In order to solve the above technical problems, the technical solutions of the present invention are as follows:

[0008] A low-cost charging pile topology for the "fast charge and slow discharge" scenario of electric vehicles, including: DC side capacitors, three-phase TNPC bridge arms, shunt diodes, and AC filter inductors;

[0009] The DC link capacitor includes a first capacitor C electrically connected in series dc1 and the second capacitor C dc2 connected in series to form a series circuit; the first capacitor C dc1 and the second capacitor C dc2 The series connection point is the neutral point O;

[0010] The three-phase TNPC bridge arm includes three TNPC bridge arms, each of which is an EasyPack TM Module; the EasyPack TM The module includes four switch tubes connected in reverse parallel with diodes, the switch tubes including a first switch tube T x1 , the second switch tube T x2 , the third switch tube T x3 and the fourth switch tube T x4 ; The first switch tube T x1 The collector is electrically connected to one end of the series circuit and the third switch tube T x3 The emitter of the first switch tube T x1 The emitter is electrically connected to the second switch tube T x2 The collector and charging pile input end, the second switch tube T x2 The emitter of the third switch tube T is electrically connected to the other end of the series circuit; x3 The collector is electrically connected to the fourth switch tube T x4 The collector of the fourth switch tube T x4 The emitter of the third switch tube T is electrically connected to the neutral point O; x3 and the fourth switch tube T x4 As a neutral point clamping power device; the first switch tube T x1 And the second switch tube T x2 As the main bridge arm power device;

[0011] Each phase TNPC bridge arm is electrically connected to a group of shunt diodes; each group of shunt diodes includes a first shunt diode D x1_div and the second shunt diode D x2_div ; The first shunt diode D x1_div The negative electrode is electrically connected to the first switch tube T x1 The collector of the first switch tube T x1 The emitter of the second shunt diode D x2_div The negative electrode is electrically connected to the second switch tube T x2 The collector of the second switch tube T x2 The emitter;

[0012] The charging pile input terminal passes through the AC filter inductor L fElectrical connection to the grid.

[0013] Furthermore, the switch tube and the diode are connected in reverse parallel in such a way that the collector of the switch tube is electrically connected to the cathode of the diode, and the emitter is electrically connected to the anode of the diode; the switch tube is an IGBT; the first shunt diode D x1_div and the second shunt diode D x2_div All are fast recovery diodes; each EasyPack TM The module is placed separately on a heat dissipation module, and all the first shunt diodes D x1_div and the second shunt diode D x2_div Installed on the same heat sink module.

[0014] Further improvements include a communication unit, a sampling unit, a calculation unit and a drive signal generation unit. The real-time maximum power tolerance of the electric vehicle is transmitted to the charging pile through the communication unit for real-time adjustment of the power instruction; the sampling unit collects the voltage and current data of the main circuit and sends them to the STM32F28335, and then generates a modulation wave through the calculation unit; the drive signal generation unit converts the signal generated after comparing the modulation wave with the carrier into a drive level to realize the IGBT action.

[0015] A modulation strategy for a low-cost charging pile topology for a "fast charge-slow discharge" scenario for electric vehicles, the low-cost charging pile topology for the "fast charge-slow discharge" scenario for electric vehicles being as described above, comprising the following steps: switching between three-level and two-level modulation modes within a modulation cycle, wherein the two-level modulation mode is used in the interval θ∈([1-k]π,[1+k]π) and the three-level modulation mode is used in the remaining intervals, to balance the junction temperature of the neutral point clamp power device and the main bridge arm power device;

[0016] Wherein, θ is the phase of the modulation wave, and k is the duty cycle of the two-level modulation mode;

[0017] When working in three-level modulation mode:

[0018] When the modulation wave is greater than 0, if the modulation wave is greater than the carrier, the output is P state; if the modulation wave is less than the carrier, the output is O state; when the modulation wave is less than 0, if the modulation wave is greater than the carrier, the output is O state; if the modulation wave is less than the carrier, the output is N state;

[0019] Among them, when the output is in P state, the first switch tube T x1 And the third switch tube T x3 The second switch tube T x2 and the fourth switch tube T x4 closure;

[0020] When the output is in O state, the third switch tube T x3 and the fourth switch tube T x4The first switch tube T is turned on. x1 And the second switch tube T x2 closure;

[0021] When the output is in N state, the second switch tube T x2 and the fourth switch tube T x4 The first switch tube T is turned on. x1 And the third switch tube T x3 closure;

[0022] When working in two-level modulation mode:

[0023] If the modulated wave is larger than the carrier wave, the output is P state; if the modulated wave is smaller than the carrier wave, the output is N state;

[0024] Among them, when the output is in P state, the first switch tube T x1 The second switch tube T x2 , the third switch tube T x3 and the fourth switch tube T x4 closure;

[0025] When the output is in N state, the second switch tube T x2 The first switch tube T is turned on. x1 , the third switch tube T x3 and the fourth switch tube T x4 closure.

[0026] Furthermore, the value ΔT obtained by subtracting the junction temperature of the neutral point clamped power device from the junction temperature of the main bridge arm power device is obtained. k is inversely proportional to ΔT. In steady state, when |ΔT| exceeds the set temperature difference threshold, if ΔT>0, the k value is reduced, and if ΔT<0, the k value is increased.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) This paper proposes a novel, low-cost charging pile topology for the "fast charge, slow discharge" scenario of electric vehicles. By adding shunt diodes to the main bridge arm, the thermal stress on the main bridge arm's power components is significantly reduced during charging mode, thereby improving the active power output of the charging pile while ensuring device utilization.

[0029] 2) This invention also proposes an adaptive modulation strategy applicable to the above topology. By switching between three-level and two-level modulation modes, the thermal stress of the main bridge arm power devices and the neutral point clamp power devices is balanced, further improving the active power output capacity of the charging pile in charging mode.

[0030] 3) The new solution proposed in this invention for the "fast charging and slow discharging" demand of electric vehicles, namely the coordinated optimization solution of topology structure and modulation strategy, improves the active output capacity of charging piles in charging mode without significantly increasing costs, while ensuring equipment utilization compared to existing high overload technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a charging pile topology structure according to an embodiment of the present invention;

[0032] Figure 2 A control structure diagram of an embodiment of the present invention;

[0033] Figure 3 The driving signal of each IGBT in one cycle in a three-level modulation mode according to an embodiment of the present invention;

[0034] Figure 4 The driving signal of each IGBT in one cycle in a two-level modulation mode according to an embodiment of the present invention;

[0035] Figure 5 The driving signal of each IGBT in a steady state under the adaptive modulation strategy according to an embodiment of the present invention is:

[0036] Figure 6 The junction temperature of the power devices when the traditional TNPC topology adopts three-level modulation mode and outputs 100kW active power;

[0037] Figure 7 The junction temperature of the power device when outputting 100 kW active power in a three-level modulation mode according to an embodiment of the present invention;

[0038] Figure 8 The junction temperature of the power device when outputting 100kW active power under the adaptive modulation strategy according to an embodiment of the present invention;

[0039] Figure 9 This is the junction temperature of the power device when outputting 165 kW active power under the adaptive modulation strategy according to an embodiment of the present invention. DETAILED DESCRIPTION

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0041] In order to ensure equipment utilization, a high overload solution can be adopted to meet the needs of "fast charging and slow discharge" of electric vehicles. The existing high overload solution mainly improves the thermal characteristics of the power module by optimizing the modulation strategy and thermal management design. However, due to the many limitations of the existing high overload solution, this patent proposes a collaborative optimization solution of topology structure and modulation strategy, including a new low-cost charging pile topology and its modulation strategy for the "fast charging and slow discharge" scenario of electric vehicles, aiming to ensure equipment utilization while improving the active power output capacity of the charging pile in charging mode, and realizing the "fast charging" operation of the charging pile exceeding the rated power. From a thermodynamic point of view, the "fast charging" operation of the charging pile exceeding the rated power can be characterized as follows: when the junction temperature of any power device in the power module reaches a preset threshold (set to 125°C in this article), the charging pile has the ability to output active power exceeding the rated power in charging mode.

[0042] When the TNPC topology converter operates in rectification mode, when the main bridge arm power device is turned on, the current only flows through its anti-parallel diode; when the neutral point clamped power device is turned on, the current flows through the turned-on IGBT and the diode connected in series with it. Based on this, if the power loss of the diode in the main bridge arm can be reduced, and at the same time, the power loss of the power module can be balanced by changing the conduction time of the neutral point clamped power device, the thermal stress of the power device when the converter outputs active power will be reduced, thereby effectively improving the active output capacity of the charging pile in the charging mode. Therefore, an embodiment of the present application provides a low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles, including: a DC side capacitor, a three-phase TNPC bridge arm, a shunt diode, an AC filter inductor, a communication unit, a sampling and calculation unit, and a drive signal generation unit;

[0043] like Figure 1 As shown, the DC side capacitor consists of two capacitors C dc1 with C dc2 The three-phase TNPC bridge arm is composed of IGBTs with anti-parallel diodes. Each phase bridge arm adopts EasyPack TM Module, each module is placed on a heat sink. There are 4 groups of IGBT in the module, denoted as T x1 -T x4 (x=a,b,c), where T x3 and T x4 Reverse series connection, one end is connected to the neutral point O, the other end is connected to the charging pile input terminal, T x1 and T x2 The midpoint of the series connection is connected to the charging pile input. The three-phase shunt diodes are placed on the same heat sink and are connected in parallel to T x1 and T x2 Both ends, denoted as D x1_div and D x2_divIts direction is consistent with the direction of the anti-parallel diode in the IGBT module, which is used to provide a shunt channel. The sampling unit collects the relevant data of the main circuit and sends it to the STM32F28335, and then generates the modulation wave through the calculation unit. The control block diagram is as follows Figure 2 The drive signal generation unit converts the signal generated by comparing the modulated wave with the carrier wave into a drive level to realize the IGBT operation.

[0044] The working principle of the proposed low-cost charging pile topology and its modulation strategy for the "fast charging and slow discharging" scenario of electric vehicles is described in detail as follows:

[0045] Considering the operating condition of a charging pile outputting active power in charging mode, the three-level modulation mode and the two-level modulation mode can be applied to the TNPC topology.

[0046] When the three-level modulation mode is applied, the charging pile has three switching states, as shown in Table 1.

[0047] Table 1 Switch status in three-level mode

[0048]

[0049] When the modulation wave is in the positive half cycle, the circuit switch state switches between P and O. When the switch state is P state, T x1 、T x3 is turned on, and current will flow through D x1 and D x1_div ; When the switch state is O state, T x3 、T x4 is turned on, and the current will flow through T x4 and D x3 Therefore, when the modulation wave is in the positive half cycle, due to the presence of the shunt diode, the current flowing through D x1 The current is small, and the EasyPack TM The device with the highest thermal stress in the module is T x4 and D x3 .

[0050] Similarly, when the modulation wave is in the negative half cycle, the circuit switch state switches between N and O. When the switch state is N, T x2 、T x4 is turned on, and current will flow through D x2 and D x2 div ; When the switch state is O state, T x3 、T x4 is turned on, and the current will flow through T x3 and D x4 Therefore, when the modulation wave is in the negative half cycle, due to the presence of the shunt diode, the current flowing through Dx2 The current is small, and the EasyPack TM The device with the highest thermal stress in the module is T x3 and D x4 .

[0051] It can be concluded that when applied in the three-level modulation mode, the device with the highest thermal stress in the proposed charging pile topology is the neutral point clamped power device. The driving signals of each IGBT in one cycle in the three-level modulation mode are as follows: Figure 3 shown.

[0052] When the two-level modulation mode is applied, the charging pile has two switching states, as shown in Table 2.

[0053] Table 2 Switch status in two-level mode

[0054]

[0055] At this time, since the neutral point clamped power device is not conducting, when applied in the two-level modulation mode, the device with the highest thermal stress in the proposed charging pile topology is the main bridge arm power device. In the two-level modulation mode, the driving signals of each IGBT in one cycle are as follows: Figure 4 shown

[0056] In summary, an adaptive modulation strategy for switching between three-level and two-level modulation modes is proposed to balance the losses of the main bridge arm and the neutral point clamped power devices and reduce the EasyPack TM The thermal stress of the entire module is reduced, thereby further improving the active output capacity of the charging pile in charging mode while ensuring equipment utilization. The specific implementation process is as follows:

[0057] In order to ensure T x1 and T x2 、T x3 and T x4 To balance the losses, it is necessary to ensure the symmetry of its conduction. Therefore, consider switching to two levels in the interval θ∈([1-k]π,[1+k]π), where θ is the phase of the modulation wave and k is the duty cycle of the two-level modulation mode. The temperature difference between the main bridge arm power device and the neutral point clamped power device is controlled within a certain range (the temperature difference threshold is taken as 35°C in this article) through the proportional link to obtain a duty cycle k, which is loaded at the beginning of each cycle to ensure the symmetry of the power device conduction and balance the thermal stress of the main bridge arm power device and the neutral point clamped power device. Under the adaptive modulation strategy, the driving signals of each IGBT in one cycle in steady state are as follows: Figure 5 As shown, k=0.77 at this time.

[0058] The simulation model of the proposed low-cost charging pile for the “fast charge-slow discharge” scenario of electric vehicles was built for verification on the Plecs simulation platform. The specific simulation parameters and device parameters are shown in Table 3.

[0059] Table 3 Simulation parameters

[0060]

[0061] In the simulation, the charging pile is considered to work in charging mode. Figure 6 The junction temperature of the power devices when the traditional TNPC topology adopts three-level modulation mode and outputs 100kW active power; Figure 7 The junction temperature of the power devices when the proposed charging pile topology adopts a three-level modulation mode and outputs 100kW of active power; Figure 8 The junction temperature of the power devices when the proposed charging pile topology adopts an adaptive modulation strategy and outputs 100kW of active power; Figure 9 The junction temperature of the power device when the proposed charging pile topology adopts an adaptive modulation strategy and outputs 165kW active power. x1 With T x2 、T x3 With T x4 The conduction conditions of the corresponding anti-parallel diodes are symmetrical, so only T is recorded here. x1 、D x1 、T x3 and D x3 Temperature data.

[0062] It can be seen that the proposed low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles adds a shunt diode to the traditional TNPC topology, so that when the output active power is 100kW, D x1 The thermal stress of the main bridge arm power devices and the neutral point clamped power devices is greatly reduced, but the junction temperature of the neutral point clamped power devices is not suppressed. After the adaptive modulation strategy is adopted, the thermal stress of the main bridge arm power devices and the neutral point clamped power devices is balanced, reducing the thermal stress of the entire EasyPack. TM The thermal stress of the module is reduced, enabling the charging pile to operate at a "fast charge" of 65% over the rated power.

[0063] The embodiment of the present invention does not significantly increase the cost of the charging pile. The traditional TNPC topology power circuit part includes 3 EasyPack TMThe cost of the modules, DC capacitors, filter inductors, etc., is approximately 10,000 yuan; the control system includes DSP chips, sampling chips, power supply chips, etc., costing approximately 1,000 yuan; the protection system includes AC circuit breakers, DC circuit breakers, etc., costing approximately 3,000 yuan; the heat dissipation system includes radiators, fans, etc., costing approximately 1,000 yuan; and the cabinet costs approximately 4,000 yuan. Considering only the above costs, the total cost is approximately 19,000 yuan. The charging pile topology proposed in this patent adds three shunt diodes, costing approximately 1,000 yuan, for a total cost of approximately 20,000 yuan. With the cost only increasing by 5.3%, the active output capacity of the charging pile in charging mode increases by 65%.

[0064] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0065] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles, characterized by: include: DC side capacitors, three-phase TNPC bridge arms, shunt diodes, and AC filter inductors; The DC link capacitor includes a first capacitor (C dc1 ) and the second capacitor (C dc2 ) are connected in series to form a series circuit; the first capacitor (C dc1 ) and the second capacitor (C dc2 ) is the neutral point (O); The three-phase TNPC bridge arm includes three TNPC bridge arms, each of which is an EasyPack TM Module; the EasyPack TM The module includes four switch tubes connected in reverse parallel with diodes, and the switch tubes include a first switch tube (T x1 ), the second switch tube (T x2 ), the third switch tube (T x3 ) and the fourth switch tube (T x4 ); the first switch tube (T x1 ) is electrically connected to one end of the series circuit and the third switch tube (T x3 ) emitter, the first switch tube (T x1 ) is electrically connected to the emitter of the second switch tube (T x2 ) collector and charging pile input terminal, the second switch tube (T x2 ) is electrically connected to the other end of the series circuit; the third switch tube (T x3 ) is electrically connected to the collector of the fourth switch tube (T x4 ) collector, the fourth switch tube (T x4 ) is electrically connected to the neutral point (O); the third switch tube (T x3 ) and the fourth switch tube (T x4 ) as a neutral point clamping power device; the first switch tube (T x1 ) and the second switch tube (T x2 ) as the main bridge arm power device; Each phase TNPC bridge arm is electrically connected to a group of shunt diodes; each group of shunt diodes includes a first shunt diode (D x1_div ) and the second shunt diode (D x2_div ); the first shunt diode (D x1_div ) is electrically connected to the negative electrode of the first switch tube (T x1 ) collector, the positive electrode is electrically connected to the first switch tube (T x1 ) emitter; the second shunt diode (D x2_div ) is electrically connected to the negative electrode of the second switch tube (T x2 ) collector, the positive electrode is electrically connected to the second switch tube (T x2 )'s emitter; The charging pile input terminal passes through the AC filter inductor (L f )Electrically connected to the grid.

2. The low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles as claimed in claim 1 is characterized in that: The switch tube and the diode are connected in reverse parallel in such a way that the collector of the switch tube is electrically connected to the cathode of the diode, and the emitter is electrically connected to the anode of the diode; the switch tube is an IGBT; the first shunt diode (D x1_div ) and the second shunt diode (D x2_div ) are fast recovery diodes; each EasyPack TM The module is placed separately on a heat sink module, and all the first shunt diodes (D x1_div ) and the second shunt diode (D x2_div ) are installed on the same heat dissipation module.

3. The low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles as claimed in claim 1 is characterized in that: It also includes a communication unit, a sampling unit, a calculation unit, and a drive signal generation unit. The real-time maximum power of the electric vehicle is transmitted to the charging pile through the communication unit for real-time adjustment of the power instruction; the sampling unit collects the voltage and current data of the main circuit and sends them to the STM32F28335, and then generates a modulation wave through the calculation unit; The drive signal generation unit converts the signal generated by comparing the modulated wave with the carrier wave into a drive level to realize the IGBT operation.

4. A modulation strategy for a low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles, characterized by: The low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles is as described in any one of claims 1-5; comprising the following steps: within a modulation cycle, switching between three-level and two-level modulation modes, wherein the two-level modulation mode is used in the interval θ∈([1-k]π,[1+k]π) and the three-level modulation mode is used in the remaining intervals, so as to balance the junction temperature of the neutral point clamp power device and the main bridge arm power device; Wherein, θ is the phase of the modulation wave, and k is the duty cycle of the two-level modulation mode; When working in three-level modulation mode: When the modulation wave is greater than 0, if the modulation wave is greater than the carrier, the output is P state; if the modulation wave is less than the carrier, the output is O state; when the modulation wave is less than 0, if the modulation wave is greater than the carrier, the output is O state; if the modulation wave is less than the carrier, the output is N state; Among them, when the output is in P state, the first switch tube (T x1 ) and the third switch tube (T x3 ) is turned on, the second switch tube (T x2 ) and the fourth switch tube (T x4 )closure; When the output is in the O state, the third switch tube (T x3 ) and the fourth switch tube (T x4 ) is turned on, the first switch tube (T x1 ) and the second switch tube (T x2 )closure; When the output is in N state, the second switch tube (T x2 ) and the fourth switch tube (T x4 ) is turned on, the first switch tube (T x1 ) and the third switch tube (T x3 )closure; When working in two-level modulation mode: If the modulated wave is larger than the carrier wave, the output is P state; if the modulated wave is smaller than the carrier wave, the output is N state; Among them, when the output is in P state, the first switch tube (T x1 ) is turned on, the second switch tube (T x2 ), the third switch tube (T x3 ) and the fourth switch tube (T x4 )closure; When the output is in N state, the second switch tube (T x2 ) is turned on, the first switch tube (T x1 ), the third switch tube (T x3 ) and the fourth switch tube (T x4 )closure.

5. The modulation strategy for the low-cost charging pile topology for the "fast charge-slow discharge" scenario of electric vehicles as claimed in claim 4 is characterized in that: Obtain the value ΔT obtained by subtracting the junction temperature of the neutral point clamped power device from the junction temperature of the main bridge arm power device. k is inversely proportional to ΔT. In steady state, when |ΔT| exceeds the set temperature difference threshold, if ΔT>0, reduce the k value; if ΔT<0, increase the k value.

Images