Multi-inverter series-parallel connection unified control method

Abstract

The invention discloses a multi-inverter series-parallel connection unified control method, which comprises the following steps: S1, the direct current side of each inverter module is connected in parallel to the same direct current source, and the alternating current side is switched to a parallel connection or series connection output mode through a relay; s2, adopting a voltage loop and current loop double-closed-loop control strategy; s3, the relay is a single-pole double-throw switch, and the control logic is switched through the single-pole double-throw switch; the invention belongs to the technical field of power electronics, aims to solve the problems of limited output voltage range and high implementation difficulty caused by fixed or complex switching or control of series-parallel connection modes in the prior art, and achieves the technical effects that the series-parallel connection modes are flexibly switched through a relay, and a double-closed-loop control strategy is combined, so that the series-parallel connection modes are flexibly switched; dynamic adjustment of output voltage, reference value sharing in a parallel connection mode or independent voltage sharing in a series connection mode are realized, multi-module competition is avoided, flexible switching of series-parallel connection modes of output of each stage is realized, and the converter can be applied to occasions with high power and wide voltage range.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and particularly to a unified control method for multi-inverter series-parallel connection. Background Art

[0002] DC-AC inverters are widely used in energy storage systems, distributed generation, and new energy fields. Traditional wide-voltage-range inverters have problems such as large voltage / current stress and low power density. Although the multi-inverter series-parallel structure can alleviate this problem, its independent control strategy has a significantly increased complexity when the number of modules increases. In the prior art, the series-parallel mode switching is fixed or the control is complex, resulting in a limited output voltage range and high implementation difficulty. Therefore, it does not meet the existing requirements, and for this reason, we propose a unified control method for multi-inverter series-parallel connection. Summary of the Invention

[0003] For this purpose, the present invention provides a unified control method for multi-inverter series-parallel connection to solve the above problems in the prior art.

[0004] To achieve the above object, the present invention provides the following technical solutions: According to the first aspect of the present invention, a unified control method for multi-inverter series-parallel connection, the control method includes: S1. The DC sides of each inverter module are connected in parallel to the same DC power source, and the AC sides are switched to a parallel or series output mode through a relay. S2. Adopt a double closed-loop control strategy of voltage loop and current loop. S3. The relay is a single-pole double-throw switch, and the control logic is switched through the single-pole double-throw switch.

[0005] The output parallel or series mode conversion is switched through the relay.

[0006] Further, the double closed-loop control strategy includes: Voltage loop: Generate a current reference value (i ref ) according to the error between the output voltage reference value (v ref ) and the sampled output voltage. Current loop: Generate a drive signal for each inverter switch according to the error between the current reference value and the sampled output current.

[0007] Further, the switch switching control logic includes: In the parallel mode, each inverter module shares the same current reference value. In the series mode, each inverter module independently generates a current reference value.

[0008] Further, the switch switching control logic further includes: In the parallel mode, closing the relay shorts the output terminals of each inverter module with the same polarity; In the series mode, closing the relay cascades the output terminals between each inverter module.

[0009] Furthermore, in the parallel mode, the output voltages of each inverter module are equal, and the current loop reference value is the shared i ref1 ; in the series mode, the output currents of each inverter module are equal, and the voltage loop reference value is the same v ref .

[0010] Furthermore, it also includes an overload protection mechanism, namely overcurrent / overvoltage protection. When the DC voltage or output current exceeds the threshold, all switching tubes are immediately turned off.

[0011] Furthermore, it also includes the ability to expand multiple inverter modules. By adding relays and control logic, parallel or series output of N inverter modules can be achieved.

[0012] Furthermore, the inverter module has a full-bridge topology structure, including four switching tubes (Q1~Q4) and a series inductor (Lr), where: Q1 and Q2 form the first bridge arm. The drain of Q1 is connected to the DC positive pole, and the source of Q2 is connected to the DC negative pole; Q3 and Q4 form the second bridge arm. The drain of Q3 is connected to the DC positive pole, and the source of Q4 is connected to the DC negative pole; The series inductor (Lr) is connected between the source of Q1 and the source of Q3 and serves as the AC output terminal.

[0013] The present invention has the following advantages: This unified control method for series-parallel connection of multiple inverters flexibly switches between series and parallel modes through relays, combines a double closed-loop control strategy, realizes dynamic adjustment of the output voltage, shares the reference value in the parallel mode or achieves independent voltage equalization in the series mode, avoids competition among multiple modules, realizes flexible switching between series and parallel output modes at all levels, and enables the converter to be applied to high-power and wide-voltage-range occasions. Description of the Drawings

[0014] Figure 1 is the unified closed-loop control block diagram of series-parallel connection of multiple inverters for the unified control method of series-parallel connection of multiple inverters proposed by the present invention; Figure 2 is the full-bridge inverter topology diagram of a single inverter module for the unified control method of series-parallel connection of multiple inverters proposed by the present invention; Figure 3 is the output parallel mode diagram of two inverter modules for the unified control method of series-parallel connection of multiple inverters proposed by the present invention; Figure 4 is the output series mode diagram of two inverter modules for the unified control method of series-parallel connection of multiple inverters proposed by the present invention; Figure 5 This is the unified closed-loop control block diagram of the series-parallel connection of two inverter modules for the multi-inverter series-parallel unified control method proposed by the present invention. Specific implementation mode

[0015] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0016] Embodiment 1 Refer to Figures 1-5 , the multi-inverter series-parallel unified control method includes: Inverter module: It is composed of a full-bridge inverter circuit and a series inductor Lr. The full-bridge inverter circuit includes 4 switching tubes (Q1~Q4), and switching tubes Q1 and Q2 form a bridge arm, the source of Q1 is connected to the drain of Q2; switching tubes Q3 and Q4 form a bridge arm, the source of Q3 is connected to the drain of Q4. The drains of switching tube Q1 and switching tube Q3 are connected together as the positive pole of the DC input of the inverter; the sources of switching tubes Q2 and Q4 are connected together as the negative pole of the DC input of the inverter. The switching tube type selection: IGBT or SiC MOSFET is adopted, and the withstand voltage level is determined according to the DC input voltage and output power. One end of the series inductor Lr is connected to the source of Q1, that is, the drain of Q2, and the other end and the source of Q3, that is, the drain of Q4, are used as the AC output of the inverter; The DC sides of each inverter are connected in parallel to the same DC source, and the AC sides are switched to parallel or series output modes through relays, as Figure 1 and Figure 5 shown; The relay adopts a single-pole double-throw switch to switch the output to parallel or series modes, and voltage-current double closed-loop control is adopted. When the mode is switched, the reference value distribution logic is adjusted. The voltage loop is shared in parallel mode, and the independent voltage loop is used in series mode. The current loop generates a drive signal according to the reference value; Parallel mode: The relay is closed, and the single-pole double-throw switch S is set to 1, so that the output ends of the inverter modules are connected in parallel; the voltage loop outputs iare1 as the current reference of the two modules; the current loop adjusts the drive signal according to iare1 to ensure even current output; Series mode: The single-pole double-throw switch S of the relay is set to 2, and the output ends of the inverter modules are switched to be connected in series; each inverter module has an independent voltage loop to output iare1 and iare2; the current loop adjusts the drive signal according to the independent reference value to ensure even voltage output; The adjustment strategy adopts SPWM (Sinusoidal Pulse Width Modulation). The current loop controller generates the driving signal of the switching tube according to the current error to ensure the quality of the AC output waveform; The function of the voltage loop (outer loop) is to ensure that the output voltage V0 accurately tracks the reference voltage V ref value. By comparing the error between the output voltage and the reference voltage (eu = V ref - V0), after being processed by the voltage controller, the current reference value is output; the meaning is that i ref1 represents the adjustment amount of the output current required to compensate for the voltage error. For example, if V0 < V ref , the voltage loop will increase i ref1 to increase the output current, and then increase the voltage through inductive energy storage and switching tube modulation; The function of the current loop (inner loop) is to ensure that the actual output current i0 quickly tracks the current reference value i provided by the voltage loop ref1 ; by comparing the current error (e i = i ref1 - i0), after being processed by the current controller, a driving signal of the switching tube (such as the SPWM duty cycle) is generated. The meaning is that the current loop directly controls the switching action of the inverter and adjusts the current to dynamically respond to the requirements of the voltage loop; For example: in the parallel mode; Voltage loop control: Sample the output voltages V of the two inverter modules 01 = V 02 = V0. In the parallel mode, the output voltages are equal. Each inverter module shares a voltage loop, compares with the reference value V ref to generate a unified current reference value i ref1 ; Current loop control: Each inverter module independently samples the output current i 01 , i 02 , compares with i ref1 to generate a driving signal through the PR controller. The driving signal is modulated by SPWM, and the duty cycle calculation formula is: D = v control / V tri , where v control is the output of the controller, and V tri is the amplitude of the triangular carrier wave; In the series mode: Voltage loop control: Each inverter module independently samples the output voltages V 01 , V 02 , both compare with V ref to generate independent current reference values i ref1 , i ref2 ; Current loop control: Sample the total output current i0 (i01 = i 02 = i0), are respectively compared with i ref1 and i ref2 to generate independent drive signals; Working principle: Step 1: Output voltage reference v ref and the voltage errors between the sampled output voltages v o1 and v o2 of each inverter module are used as the inputs of the voltage loop controllers of each inverter module. In different output series - parallel modes, the current loop references of each inverter module are different; Step 2: When the outputs of each inverter module are in parallel mode, the single - pole double - throw switch S is set to 1. At this time, the sampled output voltages of each inverter module are equal, v o1 = v o2 , and each inverter module shares a voltage loop. The output of the voltage loop is i ref1 , which is used as the current loop reference of each inverter module; when the output is in series mode, the single - pole double - throw switch S is set to 2. At this time, the sampled output currents of each inverter module are equal, i o1 = i o2 , the voltage loop reference value is v ref , and the voltage loop outputs of each inverter module are i ref1 and i ref2 , which are used as the current loop references of each inverter module.

[0017] Step 3: The current loop references i ref1 or i ref1 , i ref2 and the current errors between the sampled output currents i o1 and i o2 of each inverter module are used as the inputs of the current loop controllers of each level of modules. The output of the current loop controller is the control quantity for generating the inverter drive signals of each inverter module. Finally, modulation strategies such as SPWM are used to generate the drive signals of the inverter switching tubes of each inverter module through the obtained control quantity; Embodiment

[0018] Is basically the same as Embodiment 1. Further, the unified control method for multi - inverter series - parallel connection also includes an overload protection mechanism, that is, over - current / over - voltage protection. A fuse is configured on the DC side, and a transient voltage suppressor is configured on the AC side. When the DC voltage or output current exceeds the threshold, all switch tubes are immediately turned off.

Claims

1. Unified control method for multi-inverter series and parallel connection, characterized in that: The control method includes: S1. The DC sides of each inverter module are connected in parallel to the same DC power source, and the AC sides are switched to a parallel or series output mode through a relay; S2. Adopt a double closed-loop control strategy of voltage loop and current loop; S3. The relay is a single-pole double-throw switch, and the control logic is switched through the single-pole double-throw switch.

2. The multi-inverter series-parallel unified control method according to claim 1, wherein The double closed-loop control strategy includes: Voltage loop: Generates a current reference value (i ref ), based on the error between the output voltage reference value (v ref ) and the sampled output voltage; Current loop: Generate drive signals for each inverter switch according to the error between the current reference value and the sampled output current.

3. The multi-inverter series-parallel unified control method according to claim 2, wherein, The switch switching control logic includes: In parallel mode, each inverter module shares the same current reference value; In series mode, each inverter module independently generates a current reference value.

4. The multi-inverter series-parallel unified control method according to claim 3, characterized in that The switch switching control logic also includes: In parallel mode, close the relay to short-circuit the output terminals of each inverter module with the same polarity; In series mode, close the relay to cascade the output terminals between each inverter module.

5. The multi-inverter series-parallel unified control method according to claim 4, characterized in that, In the parallel mode, the output voltages of all inverter modules are equal, and the reference value of the current loop is the shared i ref1 ; In the series mode, the output currents of all inverter modules are equal, and the reference value of the voltage loop is the same v ref .

6. The multi-inverter series-parallel unified control method according to claim 1, characterized in that, It also includes an overload protection mechanism, namely overcurrent / overvoltage protection. When the DC voltage or output current exceeds the threshold, all switch tubes are immediately turned off.

7. The multi-inverter series-parallel unified control method according to claim 1, wherein It also includes that multiple inverter modules can be expanded. By adding relays and control logic, parallel or series output of N inverter modules can be realized.

8. The multi-inverter series-parallel unified control method according to claim 1, wherein The inverter module is a full-bridge topology structure, including four switch tubes (Q1~Q4) and a series inductor (Lr), where: Q1 and Q2 form the first bridge arm, the drain of Q1 is connected to the DC positive pole, and the source of Q2 is connected to the DC negative pole; Q3 and Q4 form the second bridge arm, the drain of Q3 is connected to the DC positive pole, and the source of Q4 is connected to the DC negative pole; The series inductor (Lr) is connected between the source of Q1 and the source of Q3 as the AC output terminal.

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