Multi-inverter parallel and series connection unified control method

Abstract

The application discloses a multi-inverter series-parallel connection unified control method, which comprises the following steps: S1, DC sides of each inverter module are connected in parallel to the same DC source, and AC sides are switched to parallel or series output modes through relays; S2, a voltage loop and a current loop double closed loop control strategy are adopted; and S3, the relays are single-pole double-throw switches, and switching control logic is switched through the single-pole double-throw switches; the application belongs to the technical field of power electronics, and aims to solve the problems that the series-parallel connection mode switching is fixed or complicated in the prior art, the output voltage range is limited, and the realization is difficult, and achieves the technical effects that the series-parallel connection mode is flexibly switched through the relays, the double closed loop control strategy is combined, the dynamic adjustment of the output voltage is realized, the reference value is shared under the parallel mode or the independent voltage sharing is realized under the series mode, the multi-module competition is avoided, the flexible switching of the series-parallel connection mode of each level output is realized, and the converter can be applied to high-power and wide voltage range occasions.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to a unified control method for multiple inverters connected in series and parallel. Background Technology

[0002] DC-AC inverters are widely used in energy storage systems, distributed generation, and new energy fields. Traditional wide-voltage-range inverters suffer from problems such as high voltage / current stress and low power density. While multi-inverter series-parallel structures can alleviate this problem, their independent control strategies become significantly more complex as the number of modules increases. In existing technologies, the switching between series and parallel modes is fixed or complex, resulting in a limited output voltage range and high implementation difficulty.

[0003] Therefore, this method does not meet the existing requirements, and we propose a unified control method for multiple inverters connected in series and parallel. Summary of the Invention

[0004] To address these issues, the present invention provides a unified control method for multiple inverters connected in series and parallel, thereby resolving the aforementioned problems in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] According to a first aspect of the present invention, a unified control method for multiple inverters connected in series and parallel, the control method comprising:

[0007] S1. The DC side of each inverter module is connected in parallel to the same DC source, and the AC side is switched to parallel or series output mode through relays.

[0008] S2. A dual closed-loop control strategy, consisting of voltage loop and current loop, is adopted.

[0009] S3, the relay is a single-pole double-throw switch, which switches the control logic.

[0010] The output can be switched between parallel and series modes via relays.

[0011] Furthermore, the dual closed-loop control strategy includes:

[0012] Voltage loop: Based on the output voltage reference value (V) ref The error between the sampled output voltage and the actual voltage is used to generate a current reference value (i). ref );

[0013] Current loop: Based on the error between the current reference value and the sampled output current, drive signals for each inverter switch are generated.

[0014] Furthermore, the switch switching control logic includes:

[0015] In parallel mode, each inverter module shares the same current reference value;

[0016] In series mode, each inverter module generates its own current reference value.

[0017] Furthermore, the switch switching control logic also includes:

[0018] In parallel mode, closing the relay shorts the output terminals of each inverter module with the same polarity.

[0019] In series mode, closing the relay cascades the output terminals of each inverter module.

[0020] Furthermore, in the parallel mode, the output voltage of each inverter module is equal, and the current loop reference value is shared by i. ref1 In the series mode, the output current of each inverter module is equal, and the voltage loop reference value is the same (v). ref .

[0021] Furthermore, it also includes an overload protection mechanism, namely overcurrent / overvoltage protection, which immediately shuts down all switching transistors when the DC voltage or output current exceeds the threshold.

[0022] Furthermore, it also includes the ability to expand to multiple inverter modules, and to achieve parallel or series output of N inverter modules by adding relays and control logic.

[0023] Furthermore, the inverter module has a full-bridge topology, comprising four switching transistors (Q1~Q4) and a series inductor (Lr), wherein:

[0024] Q1 and Q2 form the first bridge arm, with the drain of Q1 connected to the positive DC terminal and the source of Q2 connected to the negative DC terminal.

[0025] Q3 and Q4 form the second bridge arm, with the drain of Q3 connected to the positive DC terminal and the source of Q4 connected to the negative DC terminal.

[0026] A series inductor (Lr) is connected between the sources of Q1 and Q3 as the AC output terminal.

[0027] The present invention has the following advantages:

[0028] This multi-inverter series-parallel unified control method uses relays to flexibly switch between series and parallel modes, combined with a dual closed-loop control strategy, to achieve dynamic adjustment of the output voltage. In parallel mode, it shares a reference value, or in series mode, it independently equalizes voltage, avoiding competition among multiple modules. It enables flexible switching between series and parallel modes of each output stage, allowing the converter to be applied to high-power, wide-voltage-range applications. Attached Figure Description

[0029] Figure 1 This is a block diagram of the unified closed-loop control of the multi-inverter series-parallel unified control method proposed in this invention.

[0030] Figure 2 This is a full-bridge inverter topology diagram of a single inverter module for the multi-inverter series-parallel unified control method proposed in this invention.

[0031] Figure 3 The diagram shows the parallel output mode of two inverter modules in the multi-inverter series-parallel unified control method proposed in this invention.

[0032] Figure 4 The diagram shows the series output mode of two inverter modules in the multi-inverter series-parallel unified control method proposed in this invention.

[0033] Figure 5 The diagram shows the unified closed-loop control block diagram of two inverter modules connected in series and parallel, which is the multi-inverter series-parallel unified control method proposed in this invention. Detailed Implementation

[0034] The following specific embodiments illustrate the implementation 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 only some, not all, of the embodiments of the present invention. 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.

[0035] Example 1

[0036] Reference Figure 1-5 A unified control method for multiple inverters connected in series and parallel includes:

[0037] The inverter module consists of a full-bridge inverter circuit and a series inductor Lr. The full-bridge inverter circuit includes four switching transistors (Q1~Q4). Transistors Q1 and Q2 form one arm, with the source of Q1 connected to the drain of Q2; transistors Q3 and Q4 form another arm, with the source of Q3 connected to the drain of Q4. The drains of transistors Q1 and Q3 are connected together, serving as the positive terminal of the inverter's DC input; the sources of transistors Q2 and Q4 are connected together, serving as the negative terminal of the inverter's DC input. The transistors are selected using IGBTs or SiC MOSFETs, with their voltage ratings determined based on the DC input voltage and output power. One end of the series inductor Lr is connected to the source of Q1 (i.e., the drain of Q2), and the other end is connected to the source of Q3 (i.e., the drain of Q4), serving as the inverter's AC output.

[0038] 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 mode via relays, such as... Figure 1 and Figure 5 As shown;

[0039] The relay uses a single-pole double-throw switch to switch between parallel and series output modes. It employs dual closed-loop control of voltage and current. When switching modes, the reference value allocation logic is adjusted. In parallel mode, the voltage loop is shared, while in series mode, the voltage loop is independent. The current loop generates drive signals based on the reference value.

[0040] Parallel mode: The relay is closed, and the single-pole double-throw switch S is set to 1, so that the output terminals of the inverter modules are connected in parallel; the voltage loop output iare1 serves as the current reference for the two modules; the current loop adjusts the drive signal according to iare1 to ensure current sharing.

[0041] Series mode: The single-pole double-throw switch S of the relay is set to 2, switching to connect the inverter module outputs in series; each inverter module has an independent voltage loop outputting iare1 and iare2; the current loop adjusts the drive signal according to an independent reference value to ensure equal voltage output.

[0042] The adjustment strategy adopts SPWM (sinusoidal pulse width modulation). The current loop controller generates the drive signal for the switching transistor based on the current error to ensure the quality of the AC output waveform.

[0043] The function of the voltage loop (outer loop) is to ensure that the output voltage V0 accurately tracks the reference voltage V. ref The value is determined by comparing the error between the output voltage and the reference voltage (eu = V). ref -V0), after being processed by the voltage controller, is the output current reference value; its meaning is i ref1 This represents the amount of output current adjustment required to compensate for voltage errors. For example, if V0 < V ref The voltage loop will increase i ref1 To increase the output current, and then increase the voltage through inductor energy storage and switching transistor modulation;

[0044] 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 current error (e) i =i ref1 -i0), after being processed by the current controller, generates the drive signal for the switching transistor (such as SPWM duty cycle). The significance is that the current loop directly controls the switching action of the inverter, and dynamically responds to the needs of the voltage loop by adjusting the current.

[0045] For example: in parallel mode;

[0046] Voltage loop control: Samples the output voltage V of the two inverter modules 01 =V 02 =V0, in parallel mode the output voltages are equal, all inverter modules share a voltage loop, and the voltage is equal to the reference value V. ref Comparison to generate a unified current reference value i ref1 ;

[0047] Current loop control: Each inverter module independently samples the output current i 01 i 02 , with i ref1 In comparison, the drive signal is generated by the PR controller, and the drive signal is modulated by SPWM. The duty cycle is calculated using the following formula:

[0048] D = v control / V tri , where v control For controller output, V tri The amplitude of the triangular carrier wave;

[0049] In series mode:

[0050] Voltage loop control: Each inverter module independently samples the output voltage V 01 V 02 All at V ref Compare and generate independent current reference values ​​i ref1 i ref2 ;

[0051] Current loop control: Sampling total output current i0 (i 01 =i 02 =i0), respectively with i ref1 i ref2 Compare and generate independent drive signals;

[0052] Working principle: Step 1: Output voltage reference v ref Sample the output voltage v of each inverter module o1 v o2 The voltage error is used as the input of the voltage loop controller of each inverter module. Under different output series-parallel modes, the current loop reference of each inverter module is different.

[0053] 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. o1 =v o2 Each inverter module shares a voltage loop, and the voltage loop output is i. ref1 This serves as the current loop reference for each inverter module; when the output is in series mode, the single-pole double-throw switch S is set to 2, at which point the sampled output current of each inverter module is equal. o1 =i o2 The voltage loop reference value is v ref The voltage loop output of each inverter module is i ref1 i ref2 This serves as a reference for the current loop of each inverter module.

[0054] Step 3: Current loop reference i for each inverter moduleref1 or i ref1 i ref2 The output current i of each inverter module is sampled. o1 with i o2 The current error is used as the input of the current loop controller of each module. The output of the current loop controller is the control quantity that generates the inverter drive signal of each inverter module. Finally, a modulation strategy such as SPWM is used to generate the drive signal of the inverter switching transistor of each inverter module through the obtained control quantity. Example

[0055] Similar to Example 1, but further: the multi-inverter series-parallel unified control method also includes an overload protection mechanism, namely overcurrent / overvoltage protection, with a fuse configured on the DC side and a transient voltage suppressor configured on the AC side. When the DC voltage or output current exceeds the threshold, all switching transistors are immediately shut off.

Claims

1. A unified control method for multiple inverters connected in series and parallel, characterized in that: The control method includes: S1. The DC side of each inverter module is connected in parallel to the same DC source, and the AC side is switched to parallel or series output mode through relays. S2. A dual closed-loop control strategy, consisting of voltage loop and current loop, is adopted. S3, The relay is a single-pole double-throw switch, and the control logic is switched by the single-pole double-throw switch; The dual closed-loop control strategy includes: Voltage loop: Based on the output voltage reference value (V) ref The error between the sampled output voltage and the actual voltage is used to generate a current reference value (i). ref ); Current loop: Based on the error between the current reference value and the sampled output current, drive signals for each inverter switch are generated; The switch switching control logic includes: In parallel mode, each inverter module shares the same current reference value; In series mode, each inverter module generates its own current reference value. The switch switching control logic also includes: In parallel mode, closing the relay shorts the output terminals of each inverter module with the same polarity. In series mode, closing the relay cascades the output terminals of each inverter module.

2. The multi-inverter series-parallel unified control method according to claim 1, characterized in that, In the parallel mode, the output voltage of each inverter module is equal, and the current loop reference value is shared by i. ref1 In the series mode, the output current of each inverter module is equal, and the voltage loop reference value is the same (v). ref .

3. 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, which immediately shuts down all switching transistors when the DC voltage or output current exceeds the threshold.

4. The multi-inverter series-parallel unified control method according to claim 1, characterized in that, It also includes the ability to expand to multiple inverter modules, and to achieve parallel or series output of N inverter modules by adding relays and control logic.

5. The unified control method for multiple inverters in series and parallel operation according to claim 1, characterized in that, The inverter module has a full-bridge topology and includes four switching transistors (Q1~Q4) and a series inductor (Lr), wherein: Q1 and Q2 form the first bridge arm, with the drain of Q1 connected to the positive DC terminal and the source of Q2 connected to the negative DC terminal. Q3 and Q4 form the second bridge arm, with the drain of Q3 connected to the positive DC terminal and the source of Q4 connected to the negative DC terminal. A series inductor (Lr) is connected between the sources of Q1 and Q3 as the AC output terminal.

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