A low-cost charging pile topology and its modulation strategy for electric vehicle "fast charging-slow discharging" scenarios

Abstract

This invention discloses a low-cost charging pile topology and its modulation strategy for the "fast charging-slow discharging" scenario of electric vehicles. The low-cost charging pile topology connects a set of half-bridge shunt diodes in parallel on each phase of the main bridge arm of a traditional T-type three-level converter. In discharge mode, the charging pile operates in the same manner as the traditional T-type three-level converter, working in a "slow discharging" scenario at or below the rated power. In charging mode, the charging pile utilizes the added shunt diodes to continuously shunt current to the main bridge arm power devices, reducing the current and thermal stress on the main bridge arm power devices. Furthermore, through an adaptive modulation strategy that switches between three-level and two-level modulation modes, the loss distribution of the power devices is optimized, improving the active power output capability of the charging pile in charging mode and enabling "fast charging" operation exceeding the rated power. This fully utilizes the equipment capacity of the charging pile and has significant engineering application value.

Description

Technical Field

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

[0002] Against the backdrop of the global energy structure's transition to low-carbon development, the new energy vehicle industry has become a core vehicle for realizing the "dual-carbon" strategy, which has promoted the construction and development of fast charging stations.

[0003] However, existing V2G charging piles focus on providing fast charging power in charging mode. When electric vehicles are connected to the grid as distributed power sources for discharge, owners often do not want to discharge at high power due to concerns about battery life. This bidirectional power asymmetry leads to low equipment utilization. Due to the "fast charging-slow discharging" requirements of electric vehicles, charging piles in current fast charging stations face severe technical challenges. To improve equipment utilization, high overload solutions can utilize the high overload characteristics of the equipment to provide fast charging power during charging, while the rated power of the equipment can meet the "slow discharging" requirements of electric vehicles. However, in engineering practice, most high overload solutions adopt an over-configuration approach, which significantly increases system costs without fundamentally solving the equipment utilization problem.

[0004] There is also research 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 power quality of the converter output; ② Improving the heat dissipation structure to enhance heat dissipation performance, thereby suppressing the temperature rise of power devices, but this approach has little effect on instantaneous temperature changes.

[0005] In summary, existing high overload converter solutions suffer from numerous drawbacks, including excessive costs and poor power quality. Therefore, a novel solution is urgently needed to address these issues. Summary of the Invention

[0006] The technical problem to be solved by this invention is to address the shortcomings of existing technologies by proposing a low-cost charging pile topology and its modulation strategy for the "fast charging-slow discharging" scenario of electric vehicles. This approach improves the active power output capability of the charging pile while ensuring equipment utilization, thereby enabling "fast charging" operation of the charging pile at over-rated power without significantly increasing hardware costs.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] A low-cost charging pile topology for electric vehicle "fast charging-slow discharging" scenarios includes: DC-side capacitor, three-phase TNPC bridge arm, shunt diode, and AC filter inductor;

[0009] The DC-side capacitor includes a first capacitor C connected in series. dc1 Second capacitor C dc2 The capacitors are connected in series to form a series circuit; the first capacitor C dc1 Second capacitor C dc2 The series connection point is the neutral point O;

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

[0011] Each phase TNPC bridge arm is electrically connected to a set of shunt diodes; each set of shunt diodes includes a first shunt diode D. x1_div Second shunt diode D x2_div First shunt diode D x1_div The negative terminal is electrically connected to the first switching transistor T. x1 The collector of the transistor is positively connected to the first switching transistor T. x1 The emitter of the second shunt diode D; x2_div The negative terminal is electrically connected to the second switching transistor T. x2 The collector of the transistor is positively connected to the second switching transistor T. x2 The emitter;

[0012] The charging pile input terminal is connected to the AC filter inductor L. fElectrically connected to the power grid.

[0013] Furthermore, the switching transistor and diode are connected in reverse parallel such that the collector of the switching transistor is electrically connected to the negative terminal of the diode, and the emitter is electrically connected to the positive terminal of the diode; the switching transistor is an IGBT; the first shunt diode D... x1_div Second shunt diode D x2_div All are fast recovery diodes; each EasyPack TM The module is placed on a separate heat dissipation module, and all the first shunt diodes D x1_div Second shunt diode D x2_div They are installed on the same heat dissipation module.

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

[0015] A modulation strategy for a low-cost charging pile topology for electric vehicles in the "fast charging-slow discharging" scenario, the low-cost charging pile topology for electric vehicles in the "fast charging-slow discharging" scenario is as described above; including the following steps: within a modulation cycle, switching between three-level and two-level modulation modes is implemented, 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 interval, so as to balance the junction temperature of the neutral point clamping power device and the main bridge arm power device;

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

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

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

[0019] When the output is in state P, the first switch T x1 and the third switch T x3 The second switch T is turned on. x2 and the fourth switch T x4 closure;

[0020] When the output is in state 0, the third switch T x3 and the fourth switch T x4The first switching transistor T is turned on. x1 Second switch T x2 closure;

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

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

[0023] If the modulating wave is greater than the carrier wave, output state P; if the modulating wave is less than the carrier wave, output state N.

[0024] When the output is in state P, the first switch T x1 The second switch T is turned on. x2 Third switch T x3 and the fourth switch T x4 closure;

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

[0026] Furthermore, the junction temperature of the main bridge arm power device is subtracted from the junction temperature of the neutral point clamping power device to obtain the value ΔT. k is inversely proportional to ΔT. In steady state, when |ΔT| exceeds the set temperature difference threshold, if ΔT>0, the value of k is decreased; if ΔT<0, the value of k is increased.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1) This invention proposes a novel low-cost charging pile topology for the "fast charging-slow discharging" scenario of electric vehicles. By adding shunt diodes to the main bridge arm, the thermal stress of the power devices in the main bridge arm is greatly reduced in charging mode, thereby improving the active power output capability of the charging pile in charging mode while ensuring equipment utilization.

[0029] 2) This invention also proposes an adaptive modulation strategy suitable for 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 clamping power devices is balanced, further improving the active power output capability of the charging pile in charging mode.

[0030] 3) The novel solution proposed in this invention for the "fast charging-slow discharging" requirements of electric vehicles, namely the synergistic optimization scheme of topology and modulation strategy, improves the active power output capability of charging piles in charging mode without significantly increasing costs, compared with existing high overload technologies, while ensuring equipment utilization. Attached Figure Description

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

[0032] Figure 2 This is a control structure diagram of an embodiment of the present invention;

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

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

[0035] Figure 5 This is the driving signal of each IGBT in one cycle under steady state in an embodiment of the present invention under an adaptive modulation strategy;

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

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

[0038] Figure 8 This is an embodiment of the present invention showing the junction temperature of a power device when outputting 100kW active power under an adaptive modulation strategy;

[0039] Figure 9 This is an embodiment of the present invention showing the junction temperature of the power device when outputting 165kW active power under an adaptive modulation strategy. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] To ensure equipment utilization, a high overload solution can be adopted to meet the "fast charging-slow discharging" requirements of electric vehicles. Existing high overload solutions mainly improve the thermal characteristics of power modules by optimizing modulation strategies and thermal management design. However, due to the many limitations of existing high overload solutions, this patent proposes a synergistic optimization scheme of topology and modulation strategy, including a novel low-cost charging pile topology and its modulation strategy for the "fast charging-slow discharging" scenario of electric vehicles. This aims to improve the active power output capability of the charging pile in charging mode while ensuring equipment utilization, achieving "fast charging" operation of the charging pile exceeding its rated power. From a thermodynamic perspective, the "fast charging" operation of the charging pile exceeding its rated power can be characterized as follows: when the junction temperature of any power device in the power module reaches a preset threshold (set as 125℃ in this paper), the charging pile has the ability to output active power exceeding its rated power in charging mode.

[0042] When the TNPC topology converter operates in rectification mode, when the main bridge arm power devices are turned on, current flows only through their anti-parallel diodes; when the neutral point clamping power devices are turned on, current flows through the conducting IGBT and the diode connected in series with it. Based on this, if the power loss of the diodes in the main bridge arm can be reduced, and the power loss of the power modules can be balanced by changing the conduction time of the neutral point clamping power devices, the thermal stress of the power devices when the converter outputs active power will be reduced, thereby effectively improving the active power output capability of the charging pile in charging mode. Therefore, this application provides a low-cost charging pile topology for the "fast charging-slow discharging" scenario of electric vehicles, including: a DC-side capacitor, a three-phase TNPC bridge arm, shunt diodes, 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 series connection serves to stabilize voltage and provide a zero-level signal; the series connection point is designated as neutral point O. The three-phase TNPC bridge arms are composed of IGBTs with anti-parallel diodes, and each phase arm utilizes EasyPack. TM Each module is placed on a separate heatsink. Each module contains four IGBTs, denoted as T. x1 -T x4 (x = a, b, c), where T x3 and T x4 The circuit is connected in reverse series, with one end connected to the neutral point O and the other end connected to the input terminal of the charging station. T x1 and T x2 After series connection, the midpoint is connected to the charging pile input terminal. The three-phase shunt diodes are placed on the same heatsink and connected in parallel to T. x1 and T x2 The two ends are denoted as D. x1_div and D x2_divIts direction is consistent with that of the anti-parallel diode in the IGBT module, used to provide a shunt channel. After the sampling unit collects relevant data from the main circuit, it sends it to the STM32F28335, and then the calculation unit generates a modulation wave. 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, thereby enabling the IGBT to operate.

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

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

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

[0047] Table 1 Switching status under three-level mode

[0048]

[0049] When the modulated wave is in the positive half-cycle, the circuit switching state switches between P and O. When the switching state is P, T x1 T x3 When the circuit is turned on, current will flow through D. x1 and D x1_div When the switch is in state 0, T x3 T x4 When the circuit is turned on, current will flow through T. x4 and D x3 Therefore, when the modulated wave is in the positive half-cycle, due to the presence of the shunt diode, current flows through D. x1 The current is relatively small at this time, EasyPack TM The component with the highest thermal stress in the module is T. x4 and D x3 .

[0050] Similarly, when the modulated wave is in the negative half-cycle, the circuit switching state switches between N and O. When the switching state is N, T x2 T x4 When the circuit is turned on, current will flow through D. x2 and D x2 div When the switch is in state 0, T x3 T x4 When the circuit is turned on, current will flow through T. x3 and D x4 Therefore, when the modulated wave is in the negative half-cycle, due to the presence of the shunt diode, current flows through D.x2 The current is relatively small at this time, EasyPack TM The component with the highest thermal stress in the module is T. x3 and D x4 .

[0051] Therefore, 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 clamping power device. The IGBT drive signals within one cycle in the three-level modulation mode are as follows: Figure 3 As 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 Switching Status under Two-Level Mode

[0054]

[0055] Since the neutral point clamping power device is not conducting at this time, when applied in two-level modulation mode, the device with the highest thermal stress in the proposed charging pile topology is the main bridge arm power device. The IGBT drive signals in one cycle under two-level modulation mode are as follows: Figure 4 As 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 neutral point clamping power devices, thereby reducing the EasyPack's losses. TM The overall thermal stress of the module is reduced, thereby further improving the active power output capability of the charging pile in charging mode while ensuring equipment utilization. The specific implementation process is as follows:

[0057] To ensure T x1 and T x2 T x3 and T x4 Loss balancing requires ensuring the symmetry of conduction. Therefore, a two-level switching is considered 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. A duty cycle k is obtained by controlling the temperature difference between the main bridge arm power device and the neutral point clamping power device within a certain range (the temperature difference threshold is taken as 35℃ in this paper) through a proportional element. Loading is performed at the beginning of each cycle to ensure the symmetry of power device conduction and balance the thermal stress of the main bridge arm power device and the neutral point clamping power device. Under the adaptive modulation strategy, the steady-state driving signals of each IGBT within one cycle 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 charging-slow discharging" scenario of electric vehicles was built on the Plecs simulation platform. The specific simulation parameters and device parameters are shown in Table 3.

[0059] Table 3 Simulation Parameter Table

[0060]

[0061] The simulation assumes that the charging station is operating in charging mode. Figure 6 The junction temperature of the power device when the traditional TNPC topology adopts a 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 active power is measured. Figure 8 An adaptive modulation strategy is adopted for the proposed charging pile topology to determine the junction temperature of the power devices when outputting 100kW active power. Figure 9 An adaptive modulation strategy is adopted for the proposed charging pile topology, and the junction temperature of the power devices is determined when outputting 165kW active power. Due to T x1 With T x2 T x3 With T x4 And since the conduction status of its corresponding anti-parallel diode is symmetrical, only T is recorded here. x1 D x1 T x3 and D x3 Temperature data.

[0062] It is evident that the proposed low-cost charging pile topology for the "fast charging-slow discharging" scenario of electric vehicles adds a shunt diode to the traditional TNPC topology, enabling D to achieve the same output of 100kW active power. x1 The thermal stress is significantly reduced, but the junction temperature of the neutral-point clamped power devices is not suppressed. By adopting an adaptive modulation strategy, the thermal stress of the main bridge arm power devices and the neutral-point clamped power devices is balanced, reducing the overall thermal stress of the EasyPack. TM The module's thermal stress enables the charging pile to operate at 65% above its rated power for "fast charging".

[0063] The embodiments of the present invention do not significantly increase the cost of charging piles. The power circuit section of the traditional TNPC topology includes 3 EasyPacks. TMThe cost of the modules, DC capacitors, and filter inductors is approximately 10,000 yuan; the control system, including DSP chips, sampling chips, and power supply chips, costs approximately 1,000 yuan; the protection system, including AC circuit breakers and DC circuit breakers, costs approximately 3,000 yuan; the heat dissipation system, including heat sinks and fans, costs approximately 1,000 yuan; and the enclosure costs approximately 4,000 yuan. Considering only these components, the total cost is approximately 19,000 yuan. The charging pile topology proposed in this patent incorporates three shunt diodes, costing approximately 1,000 yuan, bringing the total cost to approximately 20,000 yuan. With only a 5.3% increase in cost, the active power output capability of the charging pile in charging mode is increased by 65%.

[0064] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0065] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A modulation strategy for low-cost charging station topology oriented to the "fast-charge-slow-discharge" scenario of electric vehicles, characterized by, The low-cost charging pile topology for the "fast charging-slow discharging" scenario of electric vehicles includes a DC side capacitor, a three-phase TNPC bridge arm, a shunt diode, and an AC filter inductor. The direct current side capacitor comprises a series circuit composed of a first capacitor (C dc1 ) and a second capacitor (C dc2 ); the series connection of the first capacitor (C dc1 ) and the second capacitor (C dc2 ) is a neutral point (O); The three-phase TNPC bridge arm comprises three TNPC bridge arms, each TNPC bridge arm being an EasyPack. TM Module; the EasyPack TM The module includes four switching transistors with diodes connected in reverse parallel, the switching transistors including a first switching transistor (T). x1 ), second switching transistor (T) x2 ), third switching transistor (T) x3 ) and the fourth switch (T) x4 ); First switching transistor (T) x1 The collector of the transistor is electrically connected to one end of the series circuit and the third switch (T). x3 The emitter of ) and the first switch (T) x1 The emitter of ) is electrically connected to the second switching transistor (T) x2 The collector of the second switching transistor (T) and the input terminal of the charging pile are connected. x2 The emitter of the third switch (T) is electrically connected to the other end of the series circuit; x3 The collector of ) is electrically connected to the fourth switching transistor (T) x4 The collector of the fourth switching transistor (T) x4 The emitter of the third switch (T) is electrically connected to the neutral point (O); x3 ) and the fourth switch (T) x4 ) as a neutral point clamping power device; the first switching transistor (T) x1 ) and the second switching transistor (T) x2 ) as the main bridge arm power device; Each phase TNPC bridge arm is electrically connected with a group of shunt diodes; each group of shunt diodes comprises a first shunt diode (D x1_div ) and a second shunt diode (D x2_div ); the negative electrode of the first shunt diode (D x1_div ) is electrically connected with the collector of the first switch tube (T x1 ), and the positive electrode is electrically connected with the emitter of the first switch tube (T x1 ); the negative electrode of the second shunt diode (D x2_div ) is electrically connected with the collector of the second switch tube (T x2 ), and the positive electrode is electrically connected with the emitter of the second switch tube (T x2 ); The charging pile input end is electrically connected to the power grid through the AC filter inductor (L f ) The modulation strategy comprises the following steps: in a modulation period, switching between three-level and two-level modulation modes is implemented, wherein The interval is a two-level modulation mode, and the remaining intervals are three-level modulation modes, so as to balance the junction temperature of the neutral point clamped power device and the main bridge arm power device. wherein, k is the duty cycle of the two-level modulation scheme for the modulation wave phase. When working in a three-level modulation mode: When the modulation wave is greater than 0, if the modulation wave is greater than the carrier wave, the P state is output; if the modulation wave is less than the carrier wave, the O state is output; when the modulation wave is less than 0, if the modulation wave is greater than the carrier wave, the O state is output; if the modulation wave is less than the carrier wave, the N state is output. Wherein, the first switch tube (T x1 ) and the third switch tube (T x3 ) are turned on, and the second switch tube (T x2 ) and the fourth switch tube (T x4 ) are turned off when the output P state is outputted. The third switch tube (T x3 ) and the fourth switch tube (T x4 ) are turned on, and the first switch tube (T x1 ) and the second switch tube (T x2 ) are turned off when the output O state is reached. The second switch tube (T x2 ) and the fourth switch tube (T x4 ) are turned on, and the first switch tube (T x1 ) and the third switch tube (T x3 ) are turned off when the output N state is output. When working in a two-level modulation mode: If the modulation wave is greater than the carrier wave, the P state is output; if the modulation wave is less than the carrier wave, the N state is output. Wherein, the first switch tube (T x1 ) is turned on and the second switch tube (T x2 ), the third switch tube (T x3 ) and the fourth switch tube (T x4 ) are turned off when the output P state is outputted. The second switch tube (T x2 ) is turned on when the output N state is output, and the first switch tube (T x1 ), the third switch tube (T x3 ) and the fourth switch tube (T x4 ) are turned off.

2. The modulation strategy for low-cost charging station topology for electric vehicle "fast-charge-slow-discharge" scenario of claim 1, wherein, The switch tube and the diode are reversely connected in parallel, the collector of the switch tube is electrically connected to the negative pole of the diode, and the emitter is electrically connected to the positive pole 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 both fast recovery diodes; each EasyPack TM module is separately placed on a heat dissipation module, and all the first shunt diodes (D x1_div ) and the second shunt diodes (D x2_div ) are installed on the same heat dissipation module.

3. The modulation strategy for low-cost charging station topology for electric vehicle "fast-charge-slow-discharge" scenario as claimed in claim 1, wherein, It also includes a communication unit, a sampling unit, a calculation unit, and a drive signal generation unit. The real-time maximum bearing 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 calculation unit, which is an STM32F28335. Then, the modulation wave is generated through the calculation unit. The drive signal generation unit converts the signal generated by comparing the modulation wave with the carrier wave into a drive level to realize the action of the IGBT.

4. The modulation strategy for low-cost charging station topology for electric vehicle "fast-charge-slow-discharge" scenario of claim 1, wherein, The value obtained by subtracting the neutral point clamped power device junction temperature from the main bridge arm power device junction temperature , k is inversely proportional to , at steady state, when exceeds the set temperature difference threshold, if , the value of k is reduced, and if , the value of k is increased.

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