A single-phase low-dc-voltage pulsating multi-port ac power conversion circuit

Abstract

The application is a single-phase low DC voltage pulsation multi-port AC power conversion circuit, comprising a filter inductor, a filter capacitor, a 1:2 multi-port AC bidirectional power conversion circuit, an AC grid-connected port and an AC load port, the 1:2 multi-port AC bidirectional power conversion circuit has three output ends, each output end is connected with a filter inductor, and the filter inductor is connected with a firewire of each AC port, the firewire and the zero line of the AC port are connected through the filter capacitor, the number of power switches in the multi-port converter is reduced by using switch multiplexing and shared zero line structure, the system capacity is not changed, the topology structure is simplified, and the system cost is reduced.

Description

Technical Field

[0001] This invention relates to a multi-port AC power converter, and more particularly to a single-phase low DC voltage pulsation multi-port AC power conversion circuit, belonging to the field of power equipment technology. Background Technology

[0002] With the continuous development of internet technology, the development speed of electronic power technology has also accelerated. In contemporary society, where energy resources and environmental issues are becoming increasingly prominent, the development of power resources is being intensified. Power routers, as a bridge connecting the power grid and users, have high research value and promising development prospects.

[0003] Current distribution network structures are fragile and cannot support the integration of robust renewable energy sources. Forcing such integration would have irreversible consequences for the overall power grid. Therefore, power converter ports need to be added between the distribution network and distributed generation. Microgrids connect multiple power inputs and load outputs, breaking away from the traditional single-input-single-output power conversion structure. Traditional two-port converters, with their limited functionality, are no longer sufficient for microgrid systems containing distributed generation. Multi-port converters, capable of multi-directional energy flow and offering various conversion functions, are crucial for the stable and efficient integration of distributed generation into microgrids and are currently a hot research topic.

[0004] In distributed photovoltaic energy storage grid-connected and power supply systems, the most common method currently used is to implement AC-DC-AC conversion using a relatively traditional full-bridge inverter and rectifier circuit. Single-phase circuits exhibit significant DC voltage second-harmonic fluctuations, which affect the AC voltage output and result in large DC bus capacitors with high costs. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a single-phase low DC voltage ripple multi-port AC power conversion circuit, which features low power loss, low switching ripple current, and simple structure.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A single-phase low DC voltage pulsation multi-port AC power conversion circuit includes a filter inductor, a filter capacitor, a 1:2 multi-port AC bidirectional power conversion circuit, an AC grid-connected port, and an AC load port. The 1:2 multi-port AC bidirectional power conversion circuit has three output terminals, each connected to a filter inductor, and each filter inductor connected to the live wire of each AC port. The live and neutral wires of the AC ports are connected through a filter capacitor.

[0008] The 1:2 multi-port AC bidirectional power conversion circuit includes eight power switches. Every two power switches are connected in series to form a bridge arm. The eight power switches are divided into four bridge arms connected in parallel. The four bridge arms are connected in parallel with a DC capacitor to form a multi-port AC bidirectional power conversion circuit.

[0009] The four bridge arms are divided into one left bridge arm, one middle bridge arm, and two right bridge arms. The midpoint of the left bridge arm serves as an output terminal connected to a filter inductor, with the other end of the filter inductor connected to the live wire of an AC grid-connected port. The two right bridge arms are divided into upper and lower groups. The midpoint of the upper right bridge arm serves as an output terminal connected to a filter inductor, with the other end of the filter inductor connected to the live wire of an AC load port; the midpoint of the lower right bridge arm serves as an output terminal connected to a filter inductor, with the other end of the filter inductor connected to the live wire of another AC load port. The midpoint of the middle bridge arm serves as the neutral point and is connected to the neutral wires of the three AC ports, forming a shared neutral wire structure.

[0010] The live and neutral wires of each AC port are connected by a filter capacitor.

[0011] The power switch is an IGBT, GTO, or IGCT power semiconductor switch.

[0012] The up and down switch drive signals of each bridge arm are interlocked.

[0013] Beneficial effects

[0014] The present invention has the following advantages due to the adoption of the above technical solutions:

[0015] 1. This invention utilizes switch multiplexing and a shared neutral wire structure to reduce the number of power switches in a multi-port converter without changing the system capacity, simplifying the topology and reducing system costs.

[0016] 2. This invention switches the circuit state by switching the intermediate multiplexed bridge arm according to the line frequency, thereby reducing the bridge arm current and enabling bidirectional AC / DC / AC power control with low power loss.

[0017] 3. This invention employs user port phase-shifting splitting, utilizing the quadrature phase-shifting control of each bridge arm of the two load ports to track port power changes and achieve the cancellation of second harmonic power fluctuations on the DC side of a single-phase AC system. Attached Figure Description

[0018] Figure 1 This is a topology diagram of a single-phase low DC voltage pulsating multi-port AC power conversion circuit according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the principle of reducing DC-side double-frequency power fluctuation control in a multi-port AC power conversion circuit according to an embodiment of the present invention. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. The technical problems solved by the present invention and its beneficial effects will also be described. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention and do not limit it in any way.

[0021] The circuit of this invention is a single-phase AC / DC / AC bidirectional power conversion circuit that can be applied to distributed power routers, photovoltaic energy storage, distributed power sources and other applications.

[0022] The idea behind this invention is to add a parallel bridge arm to a single-phase three-bridge bidirectional AC / DC topology, and to draw an output port from the midpoint of this bridge arm, thus forming a 1:2 multi-port AC power conversion circuit. Each AC port is connected to the output terminal of the 1:2 multi-port AC power conversion circuit through a filter inductor, and the live wire and neutral wire of the AC port are connected through a filter capacitor, forming the final topology of this invention.

[0023] Implementation, for example Figure 1 As shown, the circuit proposed in this invention is mainly a 1:2 multi-port AC power conversion circuit that connects three single-phase AC output ports through filter inductors and capacitors. One port is an AC grid-connected port, and the other two ports are AC load ports. The single-phase AC output ports of the converter are divided into live wires and neutral wires. The neutral wires of the two AC ports are connected together to form a common neutral wire structure.

[0024] The 1:2 multiport AC power converter circuit has a four-bridge arm structure, with S1 and S2 forming the left bridge arm. N1 and S N2 Forming the intermediate multiplex bridge arm, S LH1 and S LL1 Forming right bridge arm 1, S LH2 and S LL2 The right bridge arm 2 consists of the energy storage battery E and the DC capacitor C. dc This forms the DC power supply section. The midpoint of the S1 and S2 bridge arms serves as one output terminal of the multi-port AC power converter circuit, connected to the filter inductor L. g Connected, filter inductor L g The other end is connected to the AC grid port u gac The live wire connection. S N1 and S N2 The midpoint of the bridge arm serves as the common neutral wire connection point, connecting to the AC grid port u. gac AC load port u Lac1 and u Lac2 Neutral wire connection. S LH1 and S LL1 The midpoint of the bridge arm serves as a load output terminal of the multi-port AC power converter circuit, connected to the filter inductor L.Lac1 Connected, filter inductor L Lac1 The other end is connected to the AC load port u Lac1 The live wire connection. S LH2 and S LL2 The midpoint of the bridge arm serves as another load output terminal of the multi-port AC power converter circuit, connected to the filter inductor L. Lac2 Connected, filter inductor L Lac2 The other end is connected to the AC load port u Lac2 The live wire connection.

[0025] A filter capacitor is connected between the live wire and the neutral wire of each AC port. AC grid-connected port u gac A filter capacitor C is connected between the live wire and the neutral wire. go AC load port u Lac1 A filter capacitor C is connected between the live wire and the neutral wire. Lac1 AC load port u Lac2 A filter capacitor C is connected between the live wire and the neutral wire. Lac2 .

[0026] In this single-phase low DC voltage pulsating multi-port AC power conversion circuit, each power switch can operate in pulse width modulation (PWM) mode, and the modulation method for the power switches can be PWM chopper modulation. N1 and S N2 The intermediate multiplexed bridge arm switches according to the line frequency and is synchronized with the AC voltage to achieve low switching losses and high efficiency. The left bridge arm, composed of S1 and S2, and S... N1 and S N2 The intermediate multiplexed bridge arms form a pulse width modulation (PWM) converter to convert AC voltage to DC voltage; S LH1 and S LL1 S LH2 and S LL2 The two right-side bridge arms, respectively, are connected to S. N1 and S N2 The intermediate multiplexed bridge arms form two pulse width modulation (PWM) converters to convert AC voltage to DC voltage. Simultaneously, it is necessary to ensure that the upper and lower switch drive signals of each bridge arm are complementary.

[0027] The single-phase low DC voltage ripple multi-port AC power conversion circuit proposed in this invention can reduce DC-side second harmonic power fluctuations. Because the multi-port AC power conversion circuit uses a simple splitting mechanism at the user port, it has two load ports. By performing quadrature phase-shift modulation of the voltage vectors at the two user ports, the phase of the second harmonic power fluctuation at the AC output port is made opposite or nearly opposite, ultimately achieving cancellation of the DC-side second harmonic power fluctuation. Figure 2 As shown, the specific control method is as follows:

[0028] The single-phase low DC voltage pulsation multi-port AC power conversion circuit proposed in this invention has three ports, each independently controlled. The AC grid-connected port adopts a current closed-loop grid-connected control method. Firstly, the grid voltage u collected at the grid-connected AC port... gac The phase angle θ and angular frequency ω are given through a phase-locked loop. The active current is specified as i. p_ref and the specified value of reactive current i q_ref For DC current, the specified current value i is given by the phase angle θ and angular frequency ω. p_ref i q_ref Multiplying by sinθ and cosθ respectively and adding them together gives the given value of the single-phase AC current. The given value of the single-phase AC current and the actual value i gac The difference is used as the output value of the PR controller (proportional resonant controller). After PR control and output limiting, the modulated wave x is obtained, where the value of x is between positive and negative 1. The comparison carrier is a triangular wave with an amplitude of ±1. The modulated wave and the carrier are passed through a comparator to obtain the drive signal of the power switching device S1. At the same time, the inversion is used to obtain the drive signal of the power switching device S2.

[0029] For intermediate multiplexed bridge arm power switching device S N1 S N2 A fixed-phase control method is adopted, with the phase control of each switching device ranging from 0 to 90°. sin(θ-180°) is used as the modulation wave and compared with a triangular carrier wave with an amplitude of ±1 to obtain the power switching device S. N1 The drive signal is simultaneously inverted to obtain the power switching device S. N2 The drive signal controls the phase of the voltage at the midpoint of the bridge arm at 180°.

[0030] The control method for the two load ports employs a dual closed-loop control approach, utilizing both voltage and current. The voltage closed-loop control is a voltage vector quadrature phase-shift control, u Ms For grid voltage u gac The amplitude of u Ms respectively with sin(θ) L1 ) and sin(θ L2 The product is used as the voltage control setpoint for the two load ports, where θ L1 and θ L2 This is the phase angle of the load voltage vector. The phase angle is obtained through fuzzy control algorithm based on load power and energy management strategy. This control method can achieve a 90° lead and a 90° lag in power at one load port. The 180° phase difference between the two load ports can cancel out the second harmonic power fluctuation. The specific implementation is as follows:

[0031] First, consider the economics of the energy management strategy for the energy storage regulation system, and set the DC bus voltage u dcThe control is combined with the battery's SOC, and the control parameters of the DC bus voltage are dynamically changed according to the real-time changes in the SOC. Then, based on the battery's SOC and the grid voltage u... gac and load power P load The fuzzy set and weights for fuzzy control are designed, and the energy management strategy for the 1:2 multiport AC power conversion circuit is obtained based on the fuzzy control algorithm. The given values ​​P of the active and reactive power required for grid connection are obtained from the energy management strategy. ref Q ref Because single-phase AC systems exhibit DC-side second-harmonic power fluctuations, the power setpoint P is used as a reference. ref Q ref The second harmonic power vector S on the grid-connected side is calculated in the second harmonic vector plane. g The phase angle θ is obtained. g2 And the amplitude |S|. By utilizing the controllable phase angle of the load power vector, the phase angle of the total load power is controlled to be aligned with the power vector S on the grid-connected side. g The directions with a phase difference of 180° allow us to deduce the amplitude and phase angle of the total load power. The total load power can be divided into two load power vectors S. L1 and S L2 The vector sum, due to the load power S L1 and S L2 The magnitude is determined by the nature of the load, therefore the load power S at this time can be calculated. L1 S L2 The phase angle. The required load power vector S for each load port is obtained through the above control method. L1 S L2 Based on the current value i collected at each load port Lac1 i Lac2 The phase angle θ of the voltage vector can be calculated. L1 and θ L2 This enables directional control of the load voltage vector.

[0032] The voltage control of the two AC load ports is achieved using the voltage vector quadrature phase-shifting control method described above. The current control of the two AC load ports is independent yet consistent. For AC load port 1, the load voltage setpoint and the actual load voltage u will be obtained. Lac1 The difference is used as the input value of the PI controller, and the output of the PI controller is used as the load current setpoint, which is compared with the actual load current value i. Lac1 The difference is used as the input value of the PR controller. After PR control and output limiting, the modulated wave x is obtained, where the value of x is between ±1. The comparison carrier is a triangular wave with an amplitude of ±1. The modulated wave and the carrier are passed through a comparator to obtain the power switching device S. LH1 The drive signals are inverted to obtain the power switching device S.LL1 The drive signal. For AC load port 2, the load voltage setpoint and the actual load voltage u will be obtained. Lac2 The difference is used as the input value of the PI controller, and the output of the PI controller is used as the load current setpoint, which is compared with the actual load current value i. Lac2 The difference is used as the input value of the PR controller. After PR control and output limiting, the modulated wave x is obtained, where the value of x is between ±1. The comparison carrier is a triangular wave with an amplitude of ±1. The modulated wave and the carrier are passed through a comparator to obtain the power switching device S. LH2 The drive signals are inverted to obtain the power switching device S. LL2 The driving signal.

[0033] The single-phase low DC voltage pulsation multi-port AC power conversion circuit proposed in this invention is equipped with an energy storage battery and can be used as an energy storage regulation system in practical applications. Since the second harmonic fluctuation of the DC bus voltage affects battery life, the single-phase low DC voltage pulsation multi-port AC power conversion circuit proposed in this invention can offset the second harmonic power fluctuation on the DC side, reducing its impact on battery life.

[0034] In summary, the single-phase low DC voltage pulsation multi-port AC power converter circuit provided by this invention achieves low-power-loss bidirectional AC / DC / AC conversion by switching the circuit state according to the line frequency through the intermediate multiplexed bridge arm. Furthermore, this invention constructs two output AC load ports, utilizing phase interleaving of each bridge arm for optimized modulation to track port power changes and cancel out DC-side second-harmonic power fluctuations—this is the most significant feature of this invention. This multi-port bidirectional power converter circuit has a simple structure, low cost, and convenient modulation and control, showing promising application prospects.

[0035] The above detailed description further illustrates the purpose, technical solution, and beneficial effects of the invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A single-phase low DC voltage pulsation multi-port AC power conversion circuit, comprising a filter inductor, a filter capacitor, a 1:2 multi-port AC bidirectional power conversion circuit, an AC grid connection port, and an AC load port. The 1:2 multi-port AC bidirectional power conversion circuit has three output terminals, each output terminal being connected to a filter inductor, each filter inductor being connected to the live wire of each AC port, and the live wire and neutral wire of the AC port being connected through a filter capacitor. The 1:2 multi-port AC bidirectional power conversion circuit includes eight power switches. Every two power switches are connected in series to form a bridge arm. The eight power switches are divided into four bridge arms connected in parallel. The four bridge arms are connected in parallel with a DC capacitor to form a multi-port AC bidirectional power conversion circuit. The four bridge arms are divided into a left bridge arm, a middle bridge arm, and two right bridge arms. Switch S1 and switch S2 are connected in series on the left bridge arm. The midpoint of switch S1 and switch S2 serves as an output terminal connected to the first filter inductor L. g Connected, the other end of the filter inductor is connected to the live wire of the AC grid-connected port. The two right-side bridge arms are divided into upper and lower groups, with the upper right bridge arm connected in series with switch S. LH1 and switch S LL1 Switch S LH1 and switch S LL1 The midpoint is used as an output terminal and connected to the second filter inductor L. Lac1 Connected, the second filter inductor L Lac1 The other end is connected to the live wire of an AC load port; a switch S is connected in series on the lower right bridge arm. LH2 and switch S LL2 Switch S LH2 and switch S LL2 The midpoint is used as an output terminal and connected to the third filter inductor L. Lac2 Connected, third filter inductor L Lac2 The other end is connected to the live wire of another AC load port, and a switch S is connected in series on the middle bridge arm. N1 and switch S N2 Switch S N1 and switch S N2 The midpoint of the line is used as the neutral point and connected to the neutral wires of the three AC ports to form a shared neutral wire structure. And switches S1 and S N1 Switch S LH1 and switch S LH2 The upper ends of the bridge arms are connected, with switches S2 and S... N2 Switch S LL1 and switch S LL2 The lower ends of the bridge arms are connected.

2. The single-phase low DC voltage pulsation multi-port AC power conversion circuit as described in claim 1, characterized in that, The live wire and neutral wire of each AC port are connected by a filter capacitor.

3. The single-phase low DC voltage pulsation multi-port AC power conversion circuit as described in claim 2, characterized in that, The power switch is an IGBT, GTO, or IGCT power semiconductor switch.

4. The single-phase low DC voltage pulsation multi-port AC power conversion circuit as described in claim 3, characterized in that, The up and down switch drive signals of each bridge arm are interlocked.

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