Low-cost high-reactive overload energy storage converter topology and modulation strategy thereof

Abstract

The invention discloses a low-cost high reactive overload energy storage converter topology and a modulation strategy thereof, is used for improving the reactive overload capacity of an energy storage converter, and belongs to the technical field of alternating current-direct current converters. According to the invention, the auxiliary diode is additionally arranged on the traditional ANPC bridge arm, so that the reverse current of the IGBT module is shared during high-proportion reactive output of the converter, and the reactive overload capacity of the converter can be efficiently improved with low cost on the basis of fully utilizing the existing equipment. Besides, a reactive overload capacity enhancement modulation strategy based on third harmonic injection is provided for the topology, and third harmonics are injected into modulation waves, so that the utilization rate of an auxiliary diode is improved, and the output capacity of reactive current is further enhanced. According to the method, a 100kVA prototype is tested and verified in Simulink / Plecs, the device cost of the proposed topology is only increased by 5.45% on the basis of a traditional ANPC, the reactive overload capacity is increased by 22%, and the power grid voltage supporting capacity of the energy storage converter can be effectively enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a low-cost high-reactive overload energy storage converter topology and a modulation strategy thereof. Background Art

[0002] Renewable energy power generation bases are usually far away from the load center, lack synchronous power support, and have relatively weak system grid structures, showing low anti-interference and weak support. This makes the voltage stability margin and dynamic voltage support capacity of the renewable energy power generation bases significantly lower than those of the traditional thermal power-dominated system. In addition, renewable energy output is often volatile, intermittent, and uncertain, further exacerbating the complexity of the voltage fluctuation problem.

[0003] To this end, some scholars have proposed using the power flexible regulation capability of grid-type energy storage to improve the voltage safety and stability level of new energy bases. Grid-type energy storage acts as a stable and reliable reactive power source when the grid is in a steady state, providing steady-state reactive power support for the grid; when the grid voltage drops, energy storage can generate reactive power, provide instantaneous voltage support for the grid, and quickly restore the system voltage.

[0004] In the selection of topology for energy storage converters, the Active Neutral Point Clamped (ANPC) topology introduces active switches at the midpoint to reconstruct the current loop, optimizes the device loss distribution, significantly reduces the switching loss of the equipment and improves the voltage balancing capability, and has been widely used in the field of medium-voltage energy storage converters. However, in scenarios where overload voltage support is required, the junction temperature may exceed the limit, which in turn triggers the over-temperature protection to disconnect from the grid, making it difficult to fully realize the application potential of grid-type energy storage.

[0005] In order to improve the overload capacity of grid-type energy storage converters, domestic and foreign research mainly focuses on the following aspects: 1. Adjust the control strategy: Reduce the junction temperature of the device by changing parameters such as switching frequency and duty cycle. This method is low-cost, but the effect is limited, and changes in control parameters during operation may lead to unstable control.

[0006] 2. Optimize heat dissipation structure: Use phase change thermal conductive materials to absorb device power loss and improve instantaneous overcurrent capacity, but do not consider long-term reactive power support scenarios. Other studies use liquid cooling to reduce device junction temperature, but this method is difficult to cope with instantaneous temperature changes.

[0007] 3. Hardware over-provisioning: Improve system overload capacity by increasing device rated capacity, but this will lead to increased costs and volume.

[0008] In summary, the existing solutions have problems such as significantly increased costs, increased system complexity or limited effects in improving the reactive overload capacity of energy storage converters. A new technical solution is urgently needed to overcome the above shortcomings.

[0009] Glossary: IPM: Intelligent Power Module.

[0010] Modulation: It is an important parameter of the modulated wave, reflecting the degree to which the amplitude, frequency or phase of the carrier is controlled by the low-frequency modulation signal. Modulation = modulation wave amplitude / carrier amplitude; in general SPWM, modulation wave = sine wave, carrier = triangle wave; the output amplitude is proportional to the modulation. Summary of the invention

[0011] The technical problem to be solved by the present invention is to propose a low-cost high reactive overload energy storage converter topology and its modulation strategy in view of the deficiencies in the prior art, so as to enhance the reactive output capacity of the converter, thereby improving the voltage support capability of the converter without significantly increasing the hardware cost.

[0012] In order to solve the above technical problems, the technical solution of the present invention is as follows: A low-cost high reactive overload energy storage converter topology, comprising: a three-phase output line, a three-phase converter bridge arm, a three-phase auxiliary diode, a data acquisition and calculation unit and a drive signal generation unit; The three-phase output circuit includes an A-phase circuit, a B-phase circuit and a C-phase circuit, and its input end is electrically connected to the auxiliary diode group and the output end of the converter bridge arm; Each phase of the three-phase auxiliary diode group includes an upper diode and the lower diode , upper two-stage tube The positive electrode and the lower diode The negative electrodes of the upper diodes are connected to the output end of the bridge arm circuit of the converter. The negative pole is connected to the positive pole of the DC bus , lower diode The positive pole is connected to the negative pole of the DC bus ; , corresponding to the A phase line, the B phase line and the C phase line respectively; The A-phase line, the B-phase line and the C-phase line are also electrically connected to a data acquisition and calculation unit, which is communicatively connected to a control system; the control system generates a modulation signal according to the current and voltage signals of the A-phase line, the B-phase line and the C-phase line and according to a control algorithm, and the drive signal generation unit generates a drive signal according to the modulation signal to control the on and off of the switching device in the bridge arm of the converter.

[0013] Optionally, the converter bridge arm is an ANPC bridge arm, an NPC bridge arm or a two-level bridge arm.

[0014] Optionally, the converter bridge arm circuit is an ANPC bridge arm, and the ANPC bridge arm includes six switch devices, and the switch devices are represented by letters S Indicates that each switching device contains a switch tube and an anti-parallel diode, where the switch tube is represented by the letter T Indicates that the corresponding anti-parallel diode is represented by the letter D Indicates; Taking phase A as an example, the six switching devices are the first switching device , the second switching device , the third switching device , the fourth switching device , the fifth switching device and the sixth switching device , the first switching device The collector is connected to the positive pole of the DC bus , the emitter is electrically connected to the second switching device The collector and fifth switching device The collector of the second switching device The emitter of the third switching device is electrically connected to The collector and the converter output terminal; the fifth switching device The emitter of the sixth switching device is electrically connected to The collector and neutral point O ; The third switching device The emitter and the sixth switching device The emitter of the fourth switching device is electrically connected to The collector of the fourth switching device The emitter is electrically connected to the negative pole of the DC bus ; Neutral point O Electrical connection capacitor One end and the lower capacitor One end of the upper capacitor The other end is connected to the positive pole of the DC bus , lower capacitor The other end is connected to the negative pole of the DC bus .

[0015] Optionally, in the ANPC bridge arm, the first switch device and the fifth switching device Placed in the same IPM, the second switch device and the third switching device In the same IPM, the fourth switch device and the sixth switching device Placed in the same IPM, the two switching devices in each IPM are turned on and off complementarily.

[0016] Optionally, the switch tube is an IGBT or a MOS tube; the switch tube is anti-parallel connected to the diode in such a way that the positive electrode of the diode is electrically connected to the emitter of the switch tube, and the negative electrode of the diode is electrically connected to the collector of the switch tube.

[0017] Optionally, three IPMs of the same ANPC bridge arm are placed on the same heat dissipation module.

[0018] Optionally, the upper diode and the lower diode All are Schottky diodes or fast recovery diodes; three auxiliary diode groups are placed together on the same heat dissipation module.

[0019] A modulation strategy for a low-cost high reactive overload energy storage converter topology. The low-cost high reactive overload energy storage converter topology is as described above. The modulation strategy for the ANPC bridge arm corresponding to each phase output line includes the following steps: Step 1: Generate a modulation signal, the modulation signal is a modulation wave ; Step 2: Modulation Wave When greater than 0, if the modulation wave If the modulated wave is smaller than the carrier wave, the output is P state. State; Modulation wave When it is less than 0, if the modulated wave is greater than the triangular carrier wave, the output 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 , and Conductivity; Output O+ state , and Conductivity; Output O-state , and Conductivity; When outputting N state , and Conductivity.

[0020] Optionally, a third harmonic injection SPWM modulation method is used to generate a modulation signal, and the modulation signal is:

[0021] is the modulated wave, To adjust the system, is the angular frequency, For time.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1) This invention improves the topology and modulation method of the traditional ANPC converter, concentrates the reactive current loss in the auxiliary diode as much as possible, thereby reducing the junction temperature of the ANPC bridge arm and effectively improving the reactive overload capacity of the three-level topology converter. Through reactive overload, the converter can better provide voltage support when a transient fault occurs in the power grid; a large amount of reactive power also helps the grid voltage to recover during the fault process, ensuring the safe and stable operation of the power grid.

[0023] 2) Compared with the use of over-matched converters to achieve overload capacity in engineering applications, the topology proposed in the present invention only needs to add diodes to the traditional ANPC topology, which can greatly reduce the device cost of the converter while achieving the same overload capacity. It is one of the best topology choices for grid-type energy storage.

[0024] 3) The present invention verifies the reactive overload capacity of the proposed topology and modulation method by analyzing the junction temperature of the converter device, and at the same time provides a basis for quantifying the converter overload capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A low-cost high reactive overload energy storage converter topology structure according to an embodiment of the present invention.

[0026] Figure 2 The figure is a schematic diagram of a heat dissipation structure according to an embodiment of the present invention.

[0027] Figure 3 This is a main circuit structure of an embodiment of the present invention.

[0028] Figure 4 The driving signals of different devices in one modulation period according to an embodiment of the present invention.

[0029] Figure 5 This is a voltage and current waveform diagram when only reactive power is output according to an embodiment of the present invention.

[0030] Figure 6 Schematic diagram of the current loop in different output states of an embodiment of the present invention, wherein (a) is the circuit diagram when the output is in P state; (b) is the circuit diagram when the output is in O+ state; (c) is the circuit diagram when the output is in O- state; and (d) is the circuit diagram when the output is in N state.

[0031] Figure 7 1 is a comparison diagram of device power losses of an embodiment of the present invention, wherein (a) is a power loss diagram of a traditional ANPC topology; and (b) is a power loss diagram of a low-cost, high reactive overload energy storage converter of the present invention.

[0032] Figure 8 This is a diagram showing the distribution of current in different devices when only reactive power is output according to an embodiment of the present invention.

[0033] Fig. 9 This is a comparison diagram of junction temperatures of ANPC bridge arm devices when only reactive power is output according to an embodiment of the present invention.

[0034] Fig.10 This is a comparison diagram of junction temperature before and after overload according to an embodiment of the present invention.

[0035] Fig.11 The circuit diagram of the converter bridge arm circuit according to an embodiment of the present invention is an NPC bridge arm.

[0036] Fig.12 The circuit diagram of the converter bridge arm circuit as a two-level bridge arm according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 creative work are within the scope of protection of the present invention.

[0038] The output capacity of the converter depends on the device operating rating, which is actually the thermal constraint of the device. Therefore, if the converter outputs more power at a certain junction temperature, it can be considered that the converter has overload capacity.

[0039] For the ANPC topology converter, when its output power factor is not 1, a phase difference occurs between the output voltage and current. At this time, part of the current will flow through the anti-parallel diode, generating power loss on the diode. If this part of the loss can be reduced, the junction temperature of the device in the ANPC bridge arm can be effectively reduced when outputting reactive power, thereby increasing its reactive overload capacity. Based on this idea, the present invention provides a low-cost high reactive overload energy storage converter topology, the structure of which includes a three-phase output line, a three-phase converter bridge arm, a three-phase auxiliary diode, a data acquisition and calculation unit, and a drive signal generation unit; See attached Figure 1 , low-cost high reactive overload energy storage converter DC side bus capacitor including upper capacitor With the lower capacitor , used to provide midpoint potential and stabilize DC voltage. The two capacitors are connected in series and then connected in parallel to the positive pole of the DC bus. and negative electrode Both ends, the middle series connection is the neutral pointO .

[0040] Each phase ANPC bridge arm consists of 6 IGBTs with anti-parallel diodes. The anti-parallel structures formed by anti-parallel connection of IGBTs and diodes are recorded as Corresponding to the A phase line, B phase line and C phase line respectively), The IGBTs in the modules are used for complementary switching of intelligent power modules (IPM). T Indicates that the diode is used D The IPMs in one phase are placed on the same heat sink module. Figure 1 . and Midpoint connected to neutral O , and The midpoint is brought out as the output terminal of the converter.

[0041] The auxiliary diode of each phase includes the upper tube and down tube , which uses Schottky diodes or fast recovery diodes, has a smaller on-resistance and better switching performance. The auxiliary diodes of the three phases A, B, and C are placed together on the same heat dissipation module, and the two ends are connected in parallel to the output end of the converter and the positive and negative stages of the DC bus, respectively, to provide an additional reactive current channel for the converter; The three-phase voltage and current data are sent to the STM32F28335 for calculation after passing through the acquisition unit to generate a modulation wave; the input end of the drive signal generation unit is connected to the EPWM pin of the STM32F28335 to receive the PWM drive signal, and the output end is connected to the IPM drive pin in the ANPC bridge arm to control the IGBT action and realize the converter power transmission.

[0042] For the three-phase main circuit structure, please refer to the attached Figure 3 , the DC side of the converter is directly connected in parallel with the energy storage battery, and the voltage of the energy storage battery is The AC side passes through the filter inductor It is connected to the public connection point (PCC) and then connected to the grid through line impedance. is the grid voltage, and its phase voltage effective value is recorded as is the voltage at the converter outlet, and its phase voltage effective value is recorded as is the voltage at the PCC point, and its phase voltage effective value is recorded as is the inverter output current, and its effective value is recorded as I By changing the output voltage of the converter port The amplitude and phase of the inverter can control the active power and reactive power delivered to the grid. Ignoring the line resistance, the inverter delivers active power to the grid. and reactive power The expression is as follows: (1); In the topology proposed in the present invention, the auxiliary diode provides an additional current path for the ANPC bridge arm when the converter outputs reactive current. As a passive device, no driving signal needs to be applied. Therefore, the modulation method of the ANPC topology is also suitable for low-cost high reactive overload energy storage converters, and different modulation methods will not affect the shunt characteristics of the auxiliary diode.

[0043] From formula (1), we can see that when the grid voltage is constant, the reactive power transmitted by the converter is subject to and If sine wave modulation is used, the modulation index When the maximum value is 1 In order to further improve the output reactive power capability of the converter, this paper adopts the SPWM modulation method of third harmonic injection. After injecting the third harmonic, the modulation index The maximum value is 1.15. The modulation function expression is as follows.

[0044] (2); At the same time, due to By using IGBT modules with complementary on-off functions and different combinations of driving signals, the four switching states (P, O+, O-, and N) shown in Table 1 can be generated.

[0045]

[0046] Taking phase A as an example, the IGBT drive signals in one modulation cycle after the third harmonic is injected are shown in the attached Figure 4 .

[0047] Specifically, the working principle of the low-cost high reactive overload energy storage converter topology converter and modulation strategy is described: Taking the inverter outputting reactive power as an example, the power factor angle , see attached Figure 5 At this time, the converter output modes can be divided into four types: (1) positive voltage and negative current; (2) positive voltage and positive current; (3) negative voltage and positive current; (4) negative voltage and negative current.

[0048] When in mode 1, the circuit's switch state switches between P and O+; Figure 6 As shown in (a) and (b), for the P state, due to the auxiliary diode conduction voltage drop Less than the threshold voltage of two IGBT anti-parallel diodes , the current will flow only through the auxiliary diode; for the O+ state, the current flows through and . Therefore, during Mode 1, There are switching losses and conduction losses. Compared with the traditional ANPC topology, part of the ANPC bridge arm loss in mode 1 is transferred to the auxiliary diode, thereby optimizing the loss distribution.

[0049] When in mode 2, the circuit's switching state still switches between P and O+; but because the current flows in the forward direction, its commutation circuit has changed. Figure 6 As shown in (c) and (d), for the P state, the current flows through and ; For the O+ state, the current flows through and . Therefore, during Mode 2, There are switching losses and conduction losses. Only conduction loss, Conduction loss and recovery loss are generated, and all losses are generated in the ANPC bridge arm. Before and after the injection of the third harmonic, the auxiliary diode action time in one modulation cycle is As shown in formula (3): (3) in, To adjust the system, is the switching cycle, is the carrier ratio, Indicates It can be seen from formula (3) that the third harmonic injection can not only improve the reactive power output capability of the converter, but also effectively increase the action time of the auxiliary diode and improve the shunting effect.

[0050] The effectiveness and advancement of the control method proposed in the embodiment of the present invention are verified by Simulink / Plecs software.

[0051] See attached Figure 1-3 In the circuit structure, a circuit model is built in the simulation software. The device selection and parameters are shown in Table 2.

[0052]

[0053] See attached Figure 7 In (a) and (b), still taking phase A as an example, the figure shows the power loss of each device when the traditional ANPC topology and the low-cost high reactive overload energy storage converter topology output 100kVar reactive power at the same time. It can be seen that the auxiliary diode in the low-cost high reactive overload energy storage converter topology effectively bears the reactive current, reducing the ANPC bridge arm. Tube power loss, and The current waveform in one cycle is shown in the attached Figure 8 .

[0054] See attached Fig. 9 Compared with the traditional ANPC topology, due to the low-cost high reactive overload energy storage converter, the overall power loss is reduced, and the average junction temperature is reduced by 9.35℃ when emitting 100kW reactive power, and the maximum junction temperature is reduced by Transfer to .

[0055] To improve the reactive power output of low-cost high reactive overload energy storage converter, in order to keep the maximum junction temperature unchanged, it is considered that the ANPC bridge arm in the low-cost high reactive overload energy storage converter Junction temperature and traditional ANPC topology The maximum reactive power output is achieved when the junction temperatures are the same. See the attached temperature curve for the two tubes. Fig.10 At this time, the output reactive power of the traditional ANPC topology is 100kVar, and the output reactive power of the low-cost high reactive overload energy storage converter is 122kVar, that is, the low-cost high reactive overload energy storage converter can improve the reactive power overload capacity by 22% compared with the traditional ANPC topology converter. The simulation waveform verifies the effectiveness of the low-cost high reactive overload energy storage converter topology and the proposed modulation method.

[0056] The embodiment of the present invention improves the reactive power overload capacity by 22% without significantly increasing the cost of converter components. Taking the component prices on the website of LiChuang Mall (www.szlcsc.com) as an example, the parameters and prices of each component are shown in Table 3.

[0057]

[0058] IGBT drive is part of the cost of the switching device, so it is taken into account in the table. The traditional ANPC topology requires 9 IPMs, with a total device cost of 9323.73 yuan. After adding three auxiliary diodes to the low-cost high reactive overload energy storage converter topology proposed by the present invention, the total device cost is 9831.96 yuan, and the device cost is only increased by 5.45%, and the reactive power overload capacity is increased by 22%.

[0059] 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 falling within the scope of the present application.

[0060] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A low-cost high reactive overload energy storage converter topology, characterized in that: include: Three-phase output circuit, three-phase converter bridge arm, three-phase auxiliary diode, data acquisition and calculation unit and drive signal generation unit; The three-phase output circuit includes an A-phase circuit, a B-phase circuit and a C-phase circuit, and the input ends of the A-phase circuit, the B-phase circuit and the C-phase circuit are respectively electrically connected to the output end of the auxiliary diode group and the converter bridge arm; Each phase of the three-phase auxiliary diode group includes an upper diode and the lower diode , upper two-stage tube The positive electrode and the lower diode The negative electrodes of the upper diodes are connected to the output end of the bridge arm circuit of the converter. The negative pole is connected to the positive pole of the DC bus , lower diode The positive pole is connected to the negative pole of the DC bus ; The A-phase line, the B-phase line and the C-phase line are also electrically connected to a data acquisition and calculation unit, which is communicatively connected to a control system; the control system generates a modulation signal according to the current and voltage signals of the A-phase line, the B-phase line and the C-phase line, and the drive signal generation unit generates a drive signal according to the modulation signal to control the on and off of the switching device in the bridge arm of the converter.

2. The low-cost high reactive overload energy storage converter topology according to claim 1, characterized in that: The converter bridge arm is an ANPC bridge arm, an NPC bridge arm or a two-level bridge arm.

3. The low-cost high reactive overload energy storage converter topology as claimed in claim 2, characterized in that: The converter bridge arm circuit is an ANPC bridge arm, and the ANPC bridge arm includes six switch devices, each of which includes a switch tube, and the switch tube is anti-parallel connected with a diode. The six switch devices are respectively the first switch device , the second switching device , the third switching device , the fourth switching device , the fifth switching device and the sixth switching device , the first switching device The collector is connected to the positive pole of the DC bus , the emitter is electrically connected to the second switching device The collector and fifth switching device The collector of the second switching device The emitter of the third switching device is electrically connected to The collector and the converter output terminal; the fifth switching device The emitter of the sixth switching device is electrically connected to The collector and neutral point ; The third switching device The emitter and the sixth switching device The emitter of the fourth switching device is electrically connected to The collector of the fourth switching device The emitter is electrically connected to the negative pole of the DC bus ; Neutral point Electrical connection capacitor One end and the lower capacitor One end of the upper capacitor The other end is connected to the positive pole of the DC bus , lower capacitor The other end is connected to the negative pole of the DC bus .

4. The low-cost high reactive overload energy storage converter topology as claimed in claim 3, characterized in that: In the ANPC bridge arm, the first switch device and the fifth switching device Placed in the same IPM, the second switch device and the third switching device In the same IPM, the fourth switch device and the sixth switching device Placed in the same IPM, the two switching devices in each IPM are turned on and off complementarily.

5. The low-cost high reactive overload energy storage converter topology as claimed in claim 3, characterized in that: The switch tube is an IGBT or a MOS tube; the switch tube is anti-parallel connected to the diode in such a way that the positive electrode of the diode is electrically connected to the emitter of the switch tube, and the negative electrode of the diode is electrically connected to the collector of the switch tube.

6. The low-cost high reactive overload energy storage converter topology according to claim 4, characterized in that: The three IPMs of the same ANPC bridge arm are placed on the same heat dissipation module.

7. The low-cost high reactive overload energy storage converter topology according to claim 1, characterized in that: The upper diode and the lower diode All are Schottky diodes or fast recovery diodes; the three-phase auxiliary diode groups are placed together on the same heat dissipation module.

8. A modulation strategy for a low-cost high reactive overload energy storage converter topology, characterized in that: The low-cost high reactive overload energy storage converter topology is as described in any one of claims 3-6, and the modulation strategy of the ANPC bridge arm corresponding to each three-phase output line includes the following steps: Step 1: Generate a modulation signal, the modulation signal is a modulation wave ; Step 2: Modulation Wave When greater than 0, if the modulation wave Greater than the triangular carrier, output P state; If the modulated wave is smaller than the carrier wave, the output State; Modulation wave When it is less than 0, if the modulated wave is greater than the triangular carrier wave, the output state; If the modulated wave is smaller than the carrier wave, the output is in N state; Among them, when the output is in P state , and Conductivity; Output O+ state , and Conductivity; Output O-state , , Conductivity; When outputting N state , and Conductivity.

9. The modulation strategy of the low-cost high reactive overload energy storage converter topology as claimed in claim 8, characterized in that: The SPWM modulation method with third harmonic injection is used to generate the modulation signal, and the modulation signal is: ； is the modulated wave, To adjust the system, is the angular frequency, For time.

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